Bell GettingStarted

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Simpl I Q f or St eppers Simpl I Q f or St eppers Simpl I Q f or St eppers Simpl I Q f or St eppers

Get t i ng St a r t ed &Tun ing and Com m ission ing

Guide

Ver 1 .1 - June 200 9



The SimplI Q for Steppers Gett ing Start ed & Tuning and Comm issioning Guide MAN-BELGS (Ver. 1.1) 2

Not ice This guide is delivered su bject to the following conditions and restrictions:

This guide contains prop rietary information belonging to Elmo Motion

Control Ltd. Such information is supp lied solely for the pu rpose of assisting

user s of the Bell servo d rive in its installation.

The text and grap hics includ ed in this manu al are for the pu rpose of

illustration and reference only. The specifications on wh ich they are based

are subject to change w ithout notice.

Elmo Motion Cont rol and th e Elmo Motion Control logo are trademarks of

Elmo Motion Control Ltd.

Information in this docum ent is subject to change w ithout n otice.

Docum ent N o. MAN-BELGS

Copyright 2009

Elmo Motion Control Ltd.

All rights reserved

The mod el that is currently available is the

BEL-5/ 100.

Rev i s i on H i sto ry : Ver . 1.0 January 2008 (MAN -BELIG.PDF)

Ver 1.1 June 2009

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Israel

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Fax: +972 (3) 929-2322

info-il@elmom c.com

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USA

Tel: +1 (603) 821-9979

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info-us@elmom c.com

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info-de@elmom c.com w w w . e l m o m c . c o m

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mailto:[email protected]






Con ten ts

Ch ap ter 1:Introd uction ...............................................................................................................5

1.1 Qu alified Person nel ....................................................................................................7

1.2 Wor king with th is Docu m ent ....................................................................................7

Ch ap ter 2:Elemen ts ...................................................................................................................8

2.1 Estab lishing Com municat ion with a Drive ..............................................................8

2.1.1 Changin g the Com munication Param eters ....................................................................... 11

2.2 Ap plication Parameters and Program ming ........................................................... 13

2.2.1 Flash , RAM and Tables......................................................................................................... 13

2.2.2 Creat ing an Ap plication File................................................................................................ 14

2.2.3 Dow nload ing an Ap plication File....................................................................................... 14

2.2.4 Observing the Con tent s and Editing an Application File................................................ 15

2.3 Firm ware....................................................................................................................15

2.3.1 Version Verificat ion .............................................................................................................. 15

2.3.2 Normal Firm ware Dow nload ..............................................................................................16

2.3.3 Abn orm al (from Boot) Firmware Down load .................................................................... 16

2.4 The Conductor Wiza rd .............................................................................................17

2.4.1 The Conductor Tabs .............................................................................................................. 17

2.4.2 The Expert List ....................................................... ........................................................... ..... 18

2.4.3 Accep ting a Chan ge of Parameters .....................................................................................20

Ch ap ter 3:Gettin g Started w ith Sen sors an d M otion Con trol Setu p ................................21

3.1 Int roduction ............................................................................................................... 21 3.1.1 Tune the Drive to the Motor ................................................................................................ 21

3.1.2 Tune the Mot ion Con troller ................................................................................................. 21

3.1.3 Database Maintenance.......................................................................................................... 21

3.2 Abort and Enab le Switches ...................................................................................... 21

3.2.1 Brakes..................................................... ........................................................ ......................... 22

3.2.2 Ap plication Limits ................................................................................................................23

3.3 Set up the Sensor s ..................................................................................................... 25

3.3.1 Settin g up Sensor #1 ............................................................................................................. 26

3.4 Tunin g the Driv e to the Motor ................................................................................. 27

3.4.1 Selecting the Motor Typ e ..................................................................................................... 28 3.4.2 Tuning or Checking th e Cu rrent Con trol .......................................................................... 29

3.5 Commuta tion.............................................................................................................30

3.6 Motion Tuning...........................................................................................................32

3.6.1 Torqu e Drive .......................................................................................................................... 32

3.6.2 Stepper Drives with no Com mutation Sensor................................................................... 33

3.6.3 Speed and Position Con trol ................................................................................................. 35

3.7 Fine Tuning ................................................................................................................45

3.7.1 Coggin g Com pensat ion ........................................................................................................ 45

3.7.2 Fine Tunin g an Analog Encoder ......................................................................................... 49

3.8 Database Maintenance.............................................................................................. 51




Chapter 4:Advanced Control Tuning.....................................................................................52

4.1 Star t Step Contro l ...................................................................................................... 52

4.2 Identifica tion ............................................................................................................. 52

4.2.1 Identificat ion and Uncertain ty ............................................................................................ 53

4.2.2 Identificat ion Resu lts Managem ent .................................................................................... 53 4.2.3 Identificat ion Wor k Poin t..................................................................................................... 54

4.2.4 Selecting the Identificat ion Frequencies............................................................................. 55

Append ix A: Man ua l Tu n ing of Sp eed and Posit ion Con trol ....................................60

A.1 Scope...........................................................................................................................60

A.2 Safety ..........................................................................................................................60

A.3 Make it Simple........................................................................................................... 61

A.4 Keep Margins ............................................................................................................62

A.5 The Basic Concep ts ...................................................................................................62 A.5.1 Fixed- vs. Gain -scheduled Con trollers ...............................................................................62

A.5.2 Resonance and Notch Filter s ............................................................................................... 63

A.5.3 High Frequency Noise and Low-pass Filter s .................................................................... 63

A.5.4 Evalu ating a Step Respon se – Rise Time, Settling Time, and Oversh oot. ..................... 64

A.6 The Exam ple System ................................................................................................. 65

A.7 Testin g th e Response of a Con troller ......................................................................66

A.7.1 Cu rrent Limits ....................................................................................................................... 66

A.7.2 Record ing th e Experiment Results ......................................................................................66

A.8 Fixed Gain Manual Tunin g for a Speed Loop ........................................................67

A.8.1 Manu al Tunin g of a PI Con troller .......................................................................................67 A.8.2 Man ual Tun ing of a PI Con troller and a Low Pass Filter ................................................ 72

A.8.3 Manual Tuning of a PI Con troller and a Notch Filter ...................................................... 74

A.9 Executing Man ua l Tuning for a Cascad ed Position Controller ............................ 78

A.10 Manual Tun ing of Gain Sched uling ........................................................................79

A.10.1 Manu al Gain Sched uling...................................................................................................... 79

A.10.2 Au tom atic Gain Sched u ling ................................................................................................. 80

App end ix B: A Sh ort Cou rse in Linear Con tro l ............................................................82

B.1 Linear Syst em s and Tran sfer Fun ctions.................................................................. 82

B.2 Mathem atical Mod els for LTI Syst em s ...................................................................83

B.3 Motor System s Mod els .............................................................................................85

B.3.1 A Simple Model ...................................................... .......................................................... ..... 85

B.3.2 Mod el with Flexible Transmission (resonance) ................................................................ 86

B.4 Feed back Con trol ...................................................................................................... 90

B.4.1 Why Feed back is Requ ired .................................................................................................. 90

B.4.2 Open Loop, Gain Margin and Phase Margin, Band wid th and Stability ....................... 91 B.4.3 P, PD, PI and PID Con troller s.............................................................................................. 92




Chap t e r 1 : I n t r oduc t i on The Simp lIQ docum entation and sup port software is divid ed into the following

areas:

Usage Phase Documen t Tool

Exploratory Sales docum ents for Simp lIQ and Bell

Planning/ configuration Simp lIQ for Stepp ers Sizer configuration

tool

Decision/ ord ering Elmo Catalog and website

Installation/ assembly Device specific installation guid e, e.g.

Bell Installation Guid e

Comm issioning and Getting Started This guid eComposer Guide

Usage/ operation Simp lIQ for Stepp ers Comm and Reference

Manual

SimplIQ Programm ing and Language Guid e

Simp lIQ for Stepp ers App lication N ote

DS301 docum ent

DS402 docum ent

The diagram below sh ows the Simp lIQ for Stepp ers docum entation set:

As dep icted in th e previous figure, this Getting Started & Tun ing gu ide is an

integral part of the Bell documen tation set, comp rising:




The SimplIQ for Steppers Command Reference and the SimplIQ for Steppers

Application Note, wh ich d escribe in d etail each software comm and used to

man ipu late the Bell motion controller.

The SimplIQ Programming and Language Manual, wh ich includes explanations of

all the software tools that are part of Elmo’s Comp oser software environm ent.

The Bell Stepper Drive Installation Guide, w hich describes, in d etail, the differences

that h ave been introdu ced by the Bell to SimplIQ to cover 2-phase motors an d

steppers.

The SimplIQ for Steppers Getting Started Guide, which describes how to set up an d

tune the stepper d rive.

Note that th is documen tation does not contain all the information for all prod uct

types an d cannot take into account every p ossible aspect of installation, operation,

or maintenan ce.

Su p p o r t So f tw a re

This Getting Started m anu al relies heavily on the Comp oser and Cond uctor tools.

The Composer is a supp ort progr am by Elmo for Simp lIQ.

The Composer su pp lies the basic services for comm un icating w ith d rives and

collecting d ata from th em.

The Condu ctor is a tun ing tool d eveloped b y Digital Feedback Technologies. The

Cond uctor enables the Simp lIQ param eters to be tuned .

The Condu ctor is norm ally called from th e Comp oser environment.

Aud ience and Ob j ect i v eThis document is intend ed for machine man ufacturers, commissioning engineers,

and service personnel wh o use the Simp lIQ d rive system.

It is intended to m ake you familiar with the software environment p rovided for

Simp lIQ. With this environment, you will be able to set up your dr ive with relative

ease.

This man ual is intend ed to give you a solid starting point. Once you u nd erstand th e

environm ent's core logic, you can wor k efficiently by referring to th e online help. In

add ition, there is a lot of relevant information in other the m anu als of the

documentation set.

Pre requ is i te

This manu al assum es that you installed th e drive correctly according to the Bell

Stepp er Drive Installation Gu ide.

D a n g e r a n d Wa rn i n g Sy m b o l s

The following d anger and warn ing notices are used in th is document:

Danger:

This symbol indicates that death , severe personal injury, or

substantial prop erty dam age may result if prop er precautions are not

taken.




Caution (With or w ithout a w arning tr iangle, accord ing to severity):

This symbol indicates that m inor personal injury or p roperty d amage

may resu lt if proper precautions are not taken.

Note:

This symbol highlights sup plementar y information

This symb ol indicates that the top ic is normally han dledautom atically by supp ort software, and the m aterial is only given for

enhanced u nderstanding.

1.1 Qual i f i ed Personn e l

For this docum ent, Qualified Personnel means:

For devices that ar e 60 V or less: som eone familiar w ith the dr ive, following a

training course, after reading m aterial, and w ith ad equate technical education.

For higher voltage drives it has the ad ditional meaning of someone licensed to

deal w ith electricity of the relevant voltage an d pow er, according to local

regulations.

Up-to-date information about ou r prod ucts can be foun d on th e Internet at the

following ad dr ess: www.elmomc.com ESD Not ices

Caution:

The SimplIQ drives are Electrostatic-Sensitive Devices (ESD). This

means th at hand ling them incorrectly may d amage them . Please

carefully read the ESD p recautions in the Installation Gu ide.

Danger:

All the devices mu st be installed accord ing to the d evice-specific

Installation Gu ide. Special attention m ust be given to earth

groun ding an d for high voltage connections and insulations.

Before d ealing with a d evice, verify it is in the p roper condition, and

that it is not d amag ed mechanically or electrically.

1 . 2 W or k i ng w i t h t h i s Docum en t

We recommend new u sers to:

Thorough ly read Chapter 2: Elements.

Go through Chap ter 3: Getting Started .

Chapter 4: Ad vanced Control Tuning is for experienced control practitioners, who

can exploit the extra flexibility of the Sim plIQ environm ent beyon d th e "Getting

Start ed" level.

The append ices give more general data on the linear system and on m anu al tuning.







Chapt e r 2 : Elem ent s This section d eals with th e m ost basic concepts of drive comm issioning:

Communication

Application programm ing

Firmware

The Condu ctor Wizard

2 .1 Es tab l i sh ing Com m un ica t i on w i th a Dr i ve

When you op en the Comp oser it tries to comm un icate with the drive. The

commu nication m ay be one of the following:

RS-232

CANopen

The Composer app lication can be connected simu ltaneously to more than on e

dr ive. In this m anu al we focus on single drive connections.

The Comp oser can comm un icate with mu ltiple drives and d efine a network

setup . For further details, refer to the Comp oser online help.

When you open the Comp oser, the following w indow opens:

Figure 1: Starting the Composer

Click Open Communication Directly. The following w indow opens:




Figure 2: Compos er connecti ng w indow

Ignore the Application Name field.

Look at Last Su ccessful Comm un ication Prop erties. If the p roperties listed th ere

are as required , click Finish . Oth erw ise, click Properties:

For RS-232 you n eed to set the nu mber of the COM p ort in u se, the bau d rateand the p arity. The comm un ication is always 8 bits in a by te, and it has on e stop

bit.

For CAN you need to set the ID and the bau d rate. In ad dition, you will have to

select the CAN ad apter from the supp orted typ es.

Then click Finish . The Composer opens to the m ain window :

Figure 3: The main Composer w indow




The Smart Terminal lets you en ter comman ds m anu ally – please refer to the

Simp lIQ for Stepp ers Comm and Reference Manual. To send a comman d, typ e it

in the Enter Comman d field a nd click Send .

Notes:

At the connection step you need to know the drive commu nication param eters.

It is possible to change th e dr ive comm un ication p arameters only later, after

commu nication is established .

If you d o not know the CAN ID, you may either:

o Connect first with RS-232, then ask for PP[13] (can ID) and PP[14] (CAN

baud rate).

o Use the DSP 305 protocol to find ou t the drive p aram eters (you will need

your ow n CAN ap plication for that).

The drive stores a lot of information about itself internally and this enablesthe Comp oser to interact with a m ultitud e of drive typ es. When a Com poser first

meets a d rive version it upload s this internal information. You w ill see the

following window :

Figure 4: Uploading personality dat a

The next time you contact the sam e drive version, the Comp oser already has all

its personality data stored an d w ill not ask you to w ait again.

If the dr ive lost its software, for examp le by a power-dow n d uring firmw are

dow nloading, it w ill withd raw to a very limited d efault, or "boot" software. With

this boot, it is only possible to d own load the n ew firmw are version. The

commu nication p arameters in the "boot" state are fixed (not affected by an y u ser

setting):

Baud rate of 57600 and no pa rity for RS-232.

Baud rate of 500000 and CAN ID of 127 for CAN .

After you set the correct comm un ication p aram eters, you will see the following

message:




Figure 5: Bo ot sof tw are m essage

Click Yes to open the wind ows related to d ownloading the firmware.

2.1 .1 Chang in g th e Com m un ica t ion Param eters

2.1 .1 .1 Chang ing t he RS-23 2 Com m unica t ion Rate and

Par i t y

First set the desired param eters in the Com poser smart t erminal:

PP[2] RS-232 baud ra te. 5: 115,200;

4: 57,600

3: 38,400

2: 19,200

1: 9,600

0: 4,800

PP[4] RS-232 parity. 0: None

1: Even

2: Od d

Setting PP[2] and PP[4] alone d oes not change the comm un ication setting , so the

Comp oser can continue comm un ication with the drive.

Write, for exam ple, PP[2]=5. This is a requ iremen t for a bau d rate of 115200/ sec.

Next w rite PP[2]=1. This is a comman d to accept th e new setting. Almost

imm ediately, you w ill see:

Figure 6: Communication disconnect m essage

This is because you changed th e baud rate so the comm un ications from th e

Com poser fail. Click Yes to d isconnect, than re-open commu nication by clicking

Connect.






Figure 9: The Connect but t on, circled in red

Next select the new bau d-rate using th e Properties button (see Figure 2).

When th e Composer Smart Term inal re-opens, you m ay use the SV comman d to

make the new baud setting permanent.

2 .2 App l i ca t i on Param ete rs and Progr am m ing

When you commission a dr ive, you create an Ap plication. An App lication refers

to the entire data set you d own load and store into the drive. The app lication

includes:

Parameters to store perm anently in the d rive, such as controller coefficients.

User program s: please refer to the Simp lIQ Programm ing and Language Guid e.

The Composer packs all the non -volatile param eters and the User Program in a

single file, w ith the .dat extension.

The Composer can later use this .dat file to prog ram m any am plifiers to the same

parameters and User Program.

2.2 .1 Flash, RAM and Tables

The drive contains the following m emory typ es:

Memory Type Used for

Serial Flash N on-volatile This flash stores all the non -volatile

param eters, as well as the User Program

Table Flash Non-Volatile This high speed flash stores the m otion

correction tables for real-tim e use.

The data in th e Table Flash mu st be an

iden tical copy of the da ta in the serial flash.

RAM Volatile Stores a volatile copy of the serial-flash

param eters for real-time high-speed use.

When th e drive p owers-on, it loads th e RAM as a copy of the table flash.

It also com pares the Table Flash w ith the Serial Flash. If the conten ts are not -

equal, you w ill not be able to start the m otor un til the situation is corrected.

When you comm unicate with the d rive the parameters you mod ify are in the

RAM. When you w rite, for exam ple, KI[1]=1, you u pd ate the copy of KI[1] in the

RAM. The p aram eter KI[1] has a copy in the serial flash w hich rem ains as is.

When you wan t to synchronize the RAM and the serial flash, you can:

Use the SV comm and to copy th e entire RAM conten ts into the serial flash (forexample, after you tu ned som e param eters).




Use the LD comm and to copy th e entire Serial Flash contents into the RAM.

When you wan t to syn chronize the Table Flash and the Serial Flash, use th e SI=1

command.

Notes:

The SV, LD, and SI comm and s w ork on an entire d ata set. There is no w ay to

save some of the param eters and not save others.

SV does not au tom atically synchronize th e Table Flash because Table Flash

synchronizations take a long time. Table Flash syn chronizations are carried out

very rarely.

2.2.2 Creat ing an Appl ica t io n Fi le

In this Section we will create an ap plication file in the PC com puter.

From the m enu select File>Save App lication .

The Composer will prepare to pa ck all the param eters and the User Program into

an application file. It displays the following message:

Figure 10: Save application m essage

The Comp oser up loads the p arameters d irectly from the serial flash. It enables

you to synchronize the p arameters in th e Serial Flash to the copy in the RAM

<Yes>, or to skip synchronization <N o>.

After this enter a file nam e.

2.2 .3 Dow n load ing an App l i cat ion Fi le

In order to distribute an app lication from a d ata file to a driver, do the following:

From the m enu select File>Open App lication . The following w indow opens:




Figure 11: Open Application w indow

Upon selection, look at th e Commun ication Info data box. Verify th at the

commu nication param eters there are correct, or click Change to edit them.

Then click Download to complete the downloading.

After d own loading, the Serial Flash and the Table Flash may become n on-

synchronized, and in this case you n eed to enter SI=1 at the smart term inal in

ord er to comp lete the synchronization.

2.2 .4 Observ ing th e Cont en ts and Ed i t in g an App l i ca t ionFi le

The Comp oser has a tool called th e App lication Editor.

2 . 3 F i r m w a r e

This section deals with keeping the d rive softwar e version u p-to-date.

The drive m ust be load ed w ith the correct software to operate. You w ill norm ally

receive the drive loaded with t he correct software from the d ealer. Firmw are

up grad es are, how ever, available from time to time. You can d own load the latest

firmw are from th e Elmo w eb site. It is a text file with th e .abs extension .

2.3.1 Vers ion Ver i f ica t ion

For version v erification, use the VR comm and . It shou ld retu rn som ething like

Bell 2.02.07.21 10Dec2007. You can compare this string with the latest available

firmw are at the Elmo w eb site.




2 . 3 .2 No rm a l Fi rm w are Dow n load

In the Composer Smart Terminal, select Tools>Firmware D own load . The

following w indow opens:

Figure 12: Do w nl oa d fi rmw are w in do w

Use the Browse bu tton to select the firmw are .abs file, and then click OK.

The firmw are starts to load, and you can w atch the progress bar:

Figure 13: The Firmw are progress bar

The firmw are is internally divid ed into a few sections, and you can observe the

part that is currently being loaded. The first part is "Firmw are dow nloading" and

the last part is "Extended firm ware d own loading".

When it has finished loading, a m essage asks you to reboot the d rive by

d isconnecting it from the electricity.

2 . 3 .3 A bno rm a l ( f r om Boo t ) Fi rm w are Dow n load

If the dr ive lost its software, for example by a pow er-dow n d uring firmw are

dow nloading, it w ill withd raw to a very limited d efault, or "boot" software. With

this boot, it is only possible to d own load the n ew firmw are version. The

commu nication p arameters in the "boot" state are fixed (not affected by an y u ser

setting):

Baud rate of 57600 and no pa rity for RS-232.

Baud rate of 500000 and CAN ID of 127 for CAN .

After you set the correct comm un ication p aram eters, you will see the following

message:




Figure 14: Firmw are message

2.4 The Cond uc to r W izard

2.4.1 The Cond ucto r Tabs

The Condu ctor is the main t ool for tu ning th e Simp lIQ control functions.

Figure 15: The Conductor w indow

The Cond uctor manages some experimen ts for the tuning current and motion

controls. You have a lot of flexibility in m anaging th e experiment, but y ou d o not

need to be an expert.

A color code d efines which param eter fields you may leave as is, and w hich require

your attent ion and u nd erstanding – refer to the figure below.




Figure 16: User edit able fields in a t uning experim ent

2.4.2 The Exp er t Lis t

The Expert list is a tool for observing an d editing th e drive p aram eters. It gives

extra flexibility for the experienced u ser, and it lets you tr ack wh ich drive

parameters you changed and h ow.

Expert lists and the Condu ctor wizards work w ith the param eters in RAM

only. Your work is volatile (will disapp ear at th e next pow er-on or LD

comman d), until you click Save in Flash in the Database tab.

When you open th e Expert List using the Expert list button , you see the

following:




Figure 17: Expert li st w in dow

Here you see, and may edit (simply by clicking the valu e), each of the p arametersthat this wizard pad controls.

The Expert List find s wh ich p aram eters relate to a given Cond uctor tab u sing a

keyword ; Cond uctor tabs use keyword s that are delimited by $ signs at both

ends.

You can, how ever, select anoth er keyword from the list, or type a k eyword

m anu ally. Then click Search .

If the Expert List detects a chan ge wh en you exit, it will display :

Figure 18: Expert Li st exi t com pariso n




2.4.3 Accept ing a Chang e of Param eter s

When you change drive param eters with the Condu ctor, and you exit a tab, the

condu ctor displays an exit comp arison, as in Figure 18.

After confirmation, the p arameters are accepted and cannot be restored by th e

Conductor.

Expert lists and the Condu ctor wizards work w ith the param eters in RAM only.

Your w ork is volatile (will disapp ear at the next pow er-on or LD comman d),

until you click Save in Flash in the Database tab.




Chap t e r 3 : Ge t t i ng St a r t ed w i t h

Sensors and Mot ion Con t ro l Se tu p

3 . 1 I n t r o d u c t i o nTuning a SimplIQ drive to a m otor is an ord ered, step-by-step p rocess. In this

"Getting Started" chap ter, we go throu gh th e setup p rocess step by step.

Note th at this chap ter does not contain all the detailed information for all prod uct

types and cannot take into accoun t every possible aspect of the drive setup .

3.1 .1 Tune the Dr ive to the Moto r

All motor an d ap plication types:

Set the sw itch functions for limits; enable functions, br akes, etc. This will create

the initial cond itions for the m otor to w ork.

Set the ap plication limits for current, speed, an d position. This will prevent

system constraints being violated later on.

Defining th e sensors.

Selecting th e motor typ e (DC, Stepper , Bru shless).

Tuning th e curr ent controller.

Brush less motors only:

Commu tation tu ning (finding how to pow er the stator so that the m otor will

develop m aximu m torqu e in the desired direction).

3.1 .2 Tune th e Mot ion Cont ro l le r

For open loop stepp ing app lications, you on ly need to set few p arameters.

If you h ave a motion sensor, you m ay wan t the following:

Tune speed and position controls.

Set corrections for motor cogging and define the speed -depend ent corrections

to the curren t loop.

3.1.3 Database Main t enance

All the steps un til now have m anipu lated variables in the d rive's datab ase. The

last step is to check datab ase validity, and to save the outcome in a perm anent

(flash) memory.

3 .2 Abor t and Enab le Sw i t ches

First, set the enabling sw itches.

The drive has several digital inpu ts (dep ending on the d rive type). There are

several automatic fun ctions that m ay be assigned to dr ive digital inpu ts.

It is imp ortant th at at this stage you d efine which switches are used to abort or tostop m otion, as well as limit sw itches w hen app licable.




For this pu rpose, use the Inp ut Logic tab in the Smart Terminal.

Figure 19: Defi ni ng in pu t lo gic

For a detailed description of the fun ctions that may be assigned to d igital inpu ts,

refer to th e IL[N] comm and in the SimplIQ for Stepp ers Comm and Reference

Manual.

Correct digital inpu t definitions help to gu arantee that the d rive

generates only safe motions in the course of the tun ing p rocess.

Incorrect digital inp ut settings may p revent dr ive motion or tuning.

3.2 .1 B rakes

If a brake is installed an d you wan t to operate it autom atically wh en the m otor

starts, set it up now .

First select the brake engage an d release delays. For this p urp ose select th e

Protections>Brake tab in th e Comp oser’s Smart Terminal:

Figure 20: The Brake tab






Notes:

The MC comman d retu rns the current limit of the drive peak.

You m ay set the curr ent limits in the Cond uctor wizard as well.

Refer to t he CL[1],PL[1], and PL[2] com m and s in th e Simp lIQ for Stepp ersComm and Reference Manual.

3.2 .2 .1 Speed L imi t s

Use the Limits>Velocity tab in the smart term inal:

Figure 23: Setting the speed limit s

In the Speed Limits tab , you can select RPM as the speed un its. For correct

translation between RPM and sensor counts, you n eed to set th e CA[18]

param eter (sensor counts p er motor revolution) prop erly. Take care before you

change CA[18] because if you enter an incorrect value, brushless and stepper

motors cannot work.

3 .2 .2 .2 Pos it i on L im i t s

Open the Protections>Position tab in the smart terminal:

The position comm and limits apply for open loop stepp er app lications as well asfor position feedback applications. They d o not ap ply to sp eed-only or curren t-

only ap plications.




Figure 24: Position command limit s

Notes: This tab does not set the counting r ange (mod ulo limits). You can define the

mod ulo limits in the setup w indow of the feedback sensor in the Condu ctor

Wizard. In an op en loop stepping ap plication the relevant m odu lo limits are

XM[1],XM[2].

The comm and limits m ust alw ays be stricter than the feedb ack limit.

If the comman d limits are beyond the m odu lo limits they will be ignored .

3.3 Set up t he SensorsThe drive m ay accept tw o sensors. Sensor # 1 is for speed feedback and possibly

position feedback. The second feedback serves for position feedback, or as a

sou rce for ECAM.

To set up the sensor, open th e Condu ctor tool:

From the Com poser, select the Wizard from the tools menu , or use the Wizard

button:

Figure 25: The W iz ard butt on, encircled in red

This will open the Cond uctor wind ow.




3.3 .1 Se t t ing up Sensor # 1

Skip th is section for open loop stepp er app lications.

Figure 26: Sensor #1 tuning w indow

Select the typ e of mo tion sensor # 1.

For a d etailed explanation of each of th e fields in th e tab, click th e H elp bu tton.

If the motor is small and you can m ove it by hand , you can observe that the

position read out behaves correctly – either by observing the online p osition

disp lay, or by taking a record.

Setting up Sensor #2

You n eed to set u p sensor #2 if you are going to u se it for load feedback, ECAM,

or as PWM inpu t.




Figure 27: Sensor #2 setup

Sensor #2 can also be configured as a PWM inp ut, or as a PWM ou tpu t – refer to

the online help.

3 . 4 Tun i ng t he D r i v e t o t he Mo t o r

The next step is to d efine the m otor typ e. After this step, the d igital curr ent

control of the m otor w ill work, at least at the basic level.

The motor tu ning w ill not be comp lete after this stage. Additional stages are

required, as will be explained, before going to the final fine tun ing.




3.4 .1 Se lect in g th e Moto r Type

The Simp lIQ d rive can drive DC, 2-ph ase steppers, or bru shless motors.

Notes:

Check that th e m otor leads ar e connected correctly. DC motors connect between

M1 and M2. Bru shless 3-ph ase motors connect betw een M1, M2, and M3, the

ph ase order d oes not matter. Stepp ers connect one phase between M1 and M2,

and the other phase between M3 and M4.

You d o not need to kn ow an y of the motor param eters (resistance, indu ctance,

torqu e sensitivity, etc.) in ad van ce.

You p robably do n ot need to ed it the curr ent limiting values, as this was don e

at the p rotections stage.

Figure 28: Selecting the motor type




3.4 .2 Tun ing o r Check ing the Cur r en t Con t ro l

In the same w indow , select the au tomatic curren t control tool.

Figure 29: Entering the current cont rol tun er

The following w indow opens:

Figure 30: Current tuning w indow

In general, you d o not h ave to change anyth ing in this w indow , just click Start.

When tu ning is over, you w ill see a graph of the resulting current controller

response.




By clicking t he frequency grap h b utton , you can also see the frequency response

of both the open and closed current controller.

Notes:

Setting greater phase m argins redu ces overshoot, but it also reduces theband wid th of the resulting curr ent loop.

App ly the low -pass filter only if the current control is very noisy (this is very

rare).

Use greater curr ent levels if you su spect the motor is w orking near m agnetic

saturation.

Un-checking Measure all phases will result in shorter, bu t less accurate current

control tun ing.

3 . 5 Commut a t i on

Comm utation tu ning mean s the process of:

Defining wh ich rotation d irection is positive (this is a subjective user d ecision).

Learning the ord er and th e polarity at wh ich the m otor phases were connected.

Learning th e order an d the p olarity of the H all sensors (if present).

Adjusting the p arameters of the initial rotor position find ing – this is essential

for a brushless motor to rotate.

Click th e Commutation tab:






Check Reset Commu tation Every Hall Edge if your p osition sensor is n ot

mou nted d irectly on the motor, but throu gh a gear train or a backlash.

3 .6 Mot i on Tun in g

This step d epends up on the drive method you choose.

3.6 .1 Torqu e Dr ive

If you w ant to enh ance the torque control smoothn ess and performan ce, you m ay

wan t cogging and speed corrections. For that you will need to tu ne a speed

controller (even th ough you will disable it later). After tun ing the sp eed

controller, go to the Fine Tun e tab, finish the fine tun ing, and th en back to the

Motion tab to select Torqu e control .

If you d o not need to enhance the torque control, go to the Database tab and save

your w ork. Then exit the Condu ctor.

Figure 33: Mot io n t ab fo r t orque drives




3.6 .2 Stepper Dr i ves w i th no Com m ut a t ion Sensor

For stepp er dr ives, click the Motion tab and select either Op en loop stepper or

Closed loop stepp er with sensor #1.

Figure 34: Mot ion tab

Here you need to enter the hold ing torque comp onent (static torque, speed

dep endent torqu e, and accelerating torque).

The Motor Calculator button helps you to find the required parameters.




Motor calculator tool

Figure 35: Mot ion tab for stepper

After opening t he Motor Calculator tool the following w indow app ears:




Figure 36: Mot or calculation w indow

Complete the Inputs section of the form from the motor data sheet; then click

Calculate . This will give the hold ing torqu e fixed, speed d epend ent, and

acceleration d epend ent comp onents, and also the maximu m deceleration SD – for

further explanations click the H elp butt on.

For closed loop position control, this calculator also obtains th e d ynam ic torque

limit PF[29].

You can d own load the calculated p arameters to the d rive by clicking Download .

3.6.3 Speed and Pos i t io n Cont ro l

This section d escribes the speed and position control loop closure w ide view. The

details are also d escribed.

There are three options that lead to ap proximately the same setup actions:

Speed control with sensor #1.

Position and speed control with sensor # 1.

Speed control on sensor #1 and position control with sensor #2.

Select one and the Motion tab app ears as follows:




Figure 37: Mot ion tab fo r clos ed lo op con t rol

The Cond uctor presents an adv anced set of motion tu ning tools.

The usage level for the tools can be any thing from novice to control expert.

Before using the Motion tab read the following sections.

The process is d ivided into several steps:

Prepare for identification.

Identification.

Design.

Verification.

This division is because the pr ocess may be iterative in w hich case you m ay need

to repeat som e of the steps.




Notes:

This step assum es that you have pr operly set the curren t control and th e

commu tation in adva nce. If the current control or comm utation are not

optim um , the controller tuning w ill yield p oor results. If you use an alog sensor s (Analog encod er, Resolver, Potentiom eter, LVDT, etc.)

take extra care to ensu re you r p osition signals are clean before you start motion.

The sensor quality mu st be tested w ith the m otor fully powered , since RFI from

the m otor occasionally d isturbs the sensor quality. To find th e sensor qu ality,

open the Com poser, set UM=3 (Open loop ), set HT[1]=CL[1] (maxim um

holding torq ue), and record th e motion sensor Position and Speed. (The

distu rbance display on the speed record is m uch clearer than on the position

record).

3 .6 .3 .1 Prepa re fo r I den t i f i ca t i on

The control tun ing environm ent needs a w orking closed loop to start from. The

initial closed loop d oes not need h igh p erforman ce.

Allow the Cond uctor to find a controller au tomatically. The Condu ctor tries to

follow th e guid elines of the Append ix on manu al tuning automatically. It concludes

with a controller that has quite low performan ce – only enoug h to continue

autom atic tun ing from h ere.

On starting th e Controller tool, the following w indow opens:




Figure 38: Start step designer w indow

Click Start and wait for the Cond uctor. Usually it succeeds and y ou hav e

completed th e process.

If it failed, u se the controls and read th e online help in ord er to obtain a w orking

starting controller.

The starting controller replaces the motion controller with a low-performan ce fixed controller. If you h ad a good controller in th e d rive before

starting the p rocess of finding a controller, save your w ork (using th e Database

tab) before opening th is window .

3 .6 .3 .2 I den t i f i ca t i on

Iden tification is the process of finding the tran sfer function of the controlled

plant. The transfer function will serve you later when y ou d esign a controller to

match it.




The meth od for findin g the tran sfer fun ction is simp le: inject sine signals of

varying frequency to the plant and m easure the resulting m otion. The

imp lementation of this method by the Cond uctor, however, is quite complex.

The transfer fun ction of motion systems d epend s on the signal amplitud e and the

work ing cond itions. You can log d iffering tr ansfer fun ctions, identified withdifferent working conditions, and then u se them all in a combined design p rocess

to generate a controller that fits them all.

For qu ick identification, select the Identify tool.


Figure 39: Id ent if ica t io n w in dow

Click Ru n , answer Yes to confirm the change of control param eters, and wait

un til completion. The noises you hear are the frequen cies that run throu gh you r

plant.

You will receive an id entification result w ith a frequency respon se plot:




Figure 40: Exam pl e of a frequ ency respo ns e

Click OK to return t o the main id entification screen, then save your wor k using

the File>Save men u. Nam e it MyFirstIden.idn .

3.6 .3 .3 Des ign

With th e identification r esults you can design a controller. The controller h as to

meet th e following goals:

The robustness figures of merit: acceptable gain and ph ase margins.

Maximize crossover frequency and low frequency gain for agile and accurate

control.

Minimize high frequency respon se, in order to attenu ate noises and in order to

de-sensitize the controller to th e large u ncertainties of high frequen cyidentification.

These is a conflict betw een these goals so there is a tra de off. The design

environm ent of the cond uctor is built to optim ize this trade off.

Examp le: a comp letely autom atic design: Select the Design tool.

Select th e Plant tab an d click Ad d . Select MyFirstIden .idn as the iden tification

file. The following w indow opens:




Figure 41: Add id ent ifi ed pl an t to the designer

Select Tools>Automatic d esign .





Figure 42: A ut om at ic design w in dow

Click Ru n . The results app ear in the following w indow :

Figure 43: Compl ete design




You h ave now comp leted you r first successful design . You can sav e it to a file.

Select Tools>Download Design , and in the following wind ow:

select the “Position” un it mod e.

3.6 .3 .4 Ver i f i ca t ion

In the verification stage simp ly run step responses and jud ge them accord ing to

your needs.

Click the Verification tool.





Figure 44: Verification w indow

Click Start, and th e results appear in the following w indow :




Figure 45: Controller verification results

3.7 Fine Tun ing

The Fine Tuning tab enables special enhancements to be tu ned . This is not

required for all applications.

The following fine tunings are available:

Cogging compensation

Analog encoder ind ex tun ing

3.7.1 Coggi ng Com pensat ion

The first comp ensation is for cogging . It becom es available when y ou check

Enable Cogging Comp ensation .

The cogging comp ensation add s a comp ensation torque )(T θ where θ is the

m otor’s electrical ang le; The aim of this wind ow is to m ap )(T θ .

This map ping can be saved in the d rive, saved to a file, or retrieved from a file.




Figure 46: The Fine Tunin g Tab

On op ening the cogging compen sation tool, the following w indow opens:




Figure 47: Cogging com pensati on tuner w indow

The following options are available:

Set the cogging com pen sation to d efault, i.e., there w ill be no coggingcompensation.

Load a cogging table from a file, withou t m easuring any thing.

Measure th e actual m otor cogging by clicking Start.

When starting a cogging measurem ent, the following wind ow op ens:

When you click Yes , the experimen t starts and th e progress is displayed at the

bottom of the window .







3.7.2 Fine Tun ing an Analog Encoder

If sensor # 1 is set to "Analog incremen tal encoder " in the "Sensor # 1" w ind ow ,

then t he "Analog ind ex tuning" button is visible. This tuning d efines the signal

level and position wh ere analog index capture occurs.

Please note that for analog encoder, the index app ears at d ifferent p ositions for

forward travel and for reverse travel; both cases are measured.

Figure 48: The Fine Tuning w indow w hem sensor #1 is an analog encoder

When you click Analog Ind ex Tunin g, you need to d efine the experiment motion

in the following w indow . The motion h as to traverse the analog encoder ind ex.




Figure 49: Ana lo g ind ex t un in g

After you set the p aram eters for th e experiment, click Start to begin; progr ess is

displayed in the progress bar at the bottom of the window .




3.8 Database Main t enance

Finally, save the resu lts. Click the Database tab:

Figure 50: Da tabas e m ai nt ena nce t ab

Check the d ataba se integrity. This checks for certain conflicts that can p reven t

the m otor from starting. For examp le, if you selected a comm utation finding

method by CA[17] that d oes not m atch the installed sensors, the motor w ill not

start and it will report "Bad Database". Checking th e datab ase here will prevent

this error.

Save your p arameters in flash mem ory.

Restore your previously stored par ameters from flash memor y if you w ant to

pu rge your Condu ctor session.

The Expert List of this window brings up the entire Simp lIQ d atabase.




Chapt e r 4 : Advanced Cont r o l Tun ing This chap ter is intend ed for users w ishing to u se the extra flexibility of the

motion control tu ning system beyon d the "getting started" level.

This chap ter assum es you are familiar w ith Section 3.6.3.

Feedback d esign is a four-step p rocedu re.

The first step is to generate a low p erform ance controller that is called the

"starting step con troller".

This minimal controller only has to stabilize the m otor w hile the plant d ynam ics

are identified. The Getting Started chapter, together with th e Manual Tuning

App end ix, covers this step.

The second step is to identify the plant mod el, that is, to find its transfer

function; amplitud e-ph ase versus frequency. Several frequen cy responsemeasu rements can d escribe the same plant in ord er to reflect plant u ncertainty.

The third step is to design a controller to match th e plant's frequency response.

The user orients the design optimization by emp hasizing design margins,

bandw idth, or noise attenuation.

The fourth step is verification – run ning a 'field' evalua tion test.

Notes:

The "Getting Started" chapter h as taken you throu gh all these stages, choosing

full automation. This chap ter goes over the tun er options in greater d etail.

The feedback design p rocess may be iterative – you can return to the d esignstage to impr ove on th e test results, or you can return to the identification stage

to add the results of new w orking points.

The auto-tuner is very flexible regarding th ese steps, as explained in t he

follow ing sections.

4.1 Star t Step Cont ro l

4 . 2 I den t i f i ca t i on

This chap ter deals with id entifying the p lant includ ing, its uncertainty.

Notes:

This Chapter focuses on und erstanding w hat you d o rather than on detailed

explanations of the w indow controls.

Detailed explanations of the wind ow controls are in the online help.

The wind ow controls may d iffer between Cond uctor versions, so the

explanations given here m ay also vary slightly.




4 . 2 .1 I den t i f i ca t i on and Unce r t a i n t y

The identification p rodu ces a frequency respon se. A frequency respon se is a

characteristic of a linear, time invariant plant. We take frequency respon se not

because the plant is really linear and time invariant; but because all the

established control design theory d eals with p lants having frequency responses.

Knowing very w ell the limitations of frequency responses, the DFT tuner

identifies man y frequency responses instead of one. Each frequency response

describes the plant linearized about a d ifferent w orking point.

After this process, you w ill have many m easured values for the amp litud e/ phase

of the plant at any given frequency. This set of values forms an "un certainty set"

for the frequency.

Later, the Cond uctor w ill design a controller that op timizes the response to the

entire uncertainty set. This is much better than trad itional m ethods th at can only

consider one p lant mod el at a time.

When the Cond uctor presents the identification result it normally shows one

nom inal transfer function. This is because han dling a mu ltitude of transfer

functions is very comp lex.

Identification is an involved process, as it is nonlinear an d noisy.

The Condu ctor is based on man y years of trials and collecting d ata from actual

motion systems.

4.2 .2 I den t i f i cat ion Resu l t s ManagementThe Condu ctor stores the identification results in files with th e .idn extension.

An identification file stores a list of frequencies and the associated amp litud e and

ph ase values of the p lant transfer fun ction.

You can keep several .idn files, each d escribing the p lant w ith d ifferent w orking

conditions.

Identification file maintenance is from the w indow that opens b y clicking

Identify in the Motion tab of the Cond uctor.




New

OpenSave

Cleanup

Figure 51: Iden t if icat io n fi le mai nt enan ce opt io ns

You can r eset the iden tification p rocess (New ) and store results (Save).

You can also ed it existing id entification resu lts.

You can ad d frequency points to an existing identification. Op en an existing

file, then ad d the frequencies you w ant (furth er details app ear later in this

man ual). This mean s that if you w ant to ad d d ata in a certain frequency region

you d o not need t o go throu gh th e entire identification p rocess.

You can clean outliers from frequency respon ses (Cleanup) – deleting an

identified frequency w hich you consider un reliable

4 . 2 .3 I den t i f i ca t i on Work Po in t

Identification is th e art of exciting the p lant w ith signals, so that its respon se will

reveal the most about its nature.

The Condu ctor identifies frequency respon ses, thu s it natu rally selects sinusoidal

excitation. App lying pu re sinusoidal excitation in an op en loop m ay not be su cha good idea – the motor may d rift away and high frequency data m ay be

completely obscured by frictions.

The Condu ctor uses the "Starting Step" controller to set the p lant w orking p oint;

at this w orking p oint it app lies the sinu soidal exciting signals.

You need to help th e Cond uctor in selecting the id entification w ork-point, from

the following options:

Stay in p lace: The start step controllers hold the m otor m ore or less in a fixed

position. The m otor w ill har d ly dr ift; the id entification w ill suffer from

frictions.




Free: For non-restricted displacement arou nd the initial position. The starting

step controller w ill keep the m otor w ith constant speed , so that the frictions w ill

m inim ally affect identification. This mod e gives the best linear id entification.

Bounded: For restricted d isplacement arou nd the initial position w ith given

position limits aroun d the initial position. This mod e gives most of the Free

mod e advantag es when you cannot allow free rotation of the motor.

You can id entify in each of the "Stay in p lace", "Free" or "Bound ed" m odes.

The comp arison will inform you how frictions affect you r system; and the later

control design m ay consider all the cases.

The following figure show s you r selection. The w indow opens by clicking

Identify in the Motion tab of the Cond uctor.

Figure 52: Selecting the identification method

Check Iden tify Aux. Sensor if you intend to use sensor # 2 for position control.

4.2 .4 Se lect in g th e I den t i f i cat ion Frequenc ies

The Condu ctor applies sine signals to the plant. Each sine signal mu st be

maintained long enough for the transients to disappear, then the Condu ctor can

extract th e frequency response for th at single frequency.

Putting so mu ch energy in a single frequency gives the best results which are also

the m ost noise imm un e. However, the identification is slow.

The Condu ctor mu st select the identification frequency with care, so that:

It will find all the critical plant d ata, withou t m issing imp ortant p oints.

It can com plete the identification in a reason able time.

The Condu ctor applies an iterative search w hich first spans a broad set of

frequencies. Where th e frequ ency respon se looks locally sm ooth , it accepts it.

Where it finds large am plitud e or ph ase gradients, it applies denser frequencies.




Although the autom ated frequency search w orks well in m ost cases, the

Cond uctor may miss very narrow resonance/ anti-resonance pairs.

We recomm end th at you first let the Condu ctor ident ify with au tomated

frequency search.

Check Automatic Refinemen t to allow intensified resolution wh ere the

frequency respon se changes rap idly, e.g. near resonant m odes.

Make manual adjustments when:

The identification results do not look continu ous and smooth enou gh.

You su spect, based on th e evaluation results, that th e Condu ctor missed a

resonance.

For this purp ose, use the Frequency Editor.

Figure 53: Selecti ng the frequency edit or

If you open the Frequency Editor before you have an identification resu lt, the

wind ow looks like this:




Figure 54: Frequency Edit or, w hen no identif ication is av ailable

The red p oints, and t he list in the Frequency area, show th e frequen cies for p lantexcitation. For every frequ ency there is also an associated excitemen t curren t

amplitude.

Before the ident ification you can see the defau lt set of frequen cies that th e

Cond uctor sets before learning the plant.

Bigger curr ent am plitud es generate a better signal to noise ratio, and are thu s

better for identification. There are other considerations, however:

o Large curren ts at high frequencies tend to saturate th e amp lifier voltage

du e to m otor ind uctance. This saturat ion is reflected in the id entified

transfer function by decreased amp litude and increased d elay.

o Large curren t near resonant m odes lead to u np leasant noises, or even

mechanical damage.

After clicking Run Iden tification the wind ow ap pears as follows:




Figure 55: Frequency editor w indow after identification

The blue points sh ow identification resu lts.

There are no red points an d no p oint listing in the selection box since all the

frequen cy points have been run and there has not yet been a new requ est.

You can add and edit new frequency points and r un th em; their identification

result will be app ended to the existing frequency respon se results.

For the above identification, the resolution seems poor near th e anti resonance

and near th e 2-3-4 resonances. We wou ld like to increase the resolution there, and

use the Add>Graphics tool.

Add the red frequency p oints to the grap h; on the next "Run Identification" onlythe frequencies you ad ded will be iden tified, and ap pend ed to the existing

identification record.

Notes:

Poor resolution u sually reflects in the p hase wind ow being clearer than in the

amplitude window.

Do not confuse 360° ph ase jum ps with p hase resolution problems. Phase jum ps

of 360° (see the right end of the above p hase p lot) come from angle d isplay

folding.




Figure 56: The Frequency Editor




Append ix A : Manua l Tun ing o f Speed

and Posi t i on Con t ro l

A.1 ScopeThis Append ix explains how to man ually tun e controllers of the following t ypes:

1. A PI speed controller.

2. Cascaded position controller: The inner loop is a PI speed controller and the ou ter

loop is a p osition sim ple gain controller.

3. A PI speed controller w ith a single notch filter, a low-pass filter or both .

4. Cascaded position: The inner loop is a PI speed controller w ith a single notch filter,

a low-pass filter or both; and the ou ter loop is a simple gain.

The notch filter and / or low-pass filter are termed in th is documen t as "High

ord er filters". High order filters are expected to im prove closed loop p erforman ce

if the sensors are noisy with systems th at exhibit resonance, and wh en it isessential to d ecrease high frequency m otor currents. The H igh ord er filter can

imp rove the controller p erforman ce dram atically when used correctly. Incorrect

usage of the H igh ord er filter can lead to a poor or even un stable controller.

Use the manu al tuning as a starting point for autom atic tun ing: Autom atic tun ing

brings better results than hu man tun ing in most cases.

Notes:

This app endix concentrates on man ual tun ing tips and theory, and it does not

prov ide an accurate description of controller p aram eterization. For that, refer tothe KP[N], KI[N] comm and s etc in the SimplIQ for Stepp ers Comm and

Reference Manual. All the relevant comm and s hav e links to the full control

structure description.

This appen dix d oes not d escribe the tu ning int erfaces – see the sections on

motion tun ing for that.

We strongly recomm end familiarizing yourself with the controller structur e and

param eterization before attemp ting to tune it.

A.2 Safety

Servo systems mu st be treated w ith care. In the tu ning p rocess, they mu st be

treated w ith extreme care. Although we hav e mad e our best efforts to generate

safe tun ing conditions:

In the tu ning p rocess, the motion controller m ay become un stable, leading to an

abrupt, unexpected response.

In the tun ing p rocess, the m otion controller may become very w eak, letting

distur bances and external loads d rive the shaft.

Read this app end ix carefully before launching an experiment, and evaluate the

experiment p aram eters carefully before laun ching it. The Cond uctor sug gests

some experiment par ameters, but it may mislead you, being u naw are of yourspecific limitations.




Treat un balanced1

systems w ith extreme care.

A.3 Make i t Sim p le

This Append ix gives some simp le guidelines for m anu al controller tuning. In

ord er to simp lify the tu ning p rocess we d ivide it into a series of steps.

The ru les of simp lification are:

Never tu ne your controller to perform better than you need. A controller of

lower band wid th d ecreases stresses and is more robu st to changes and ageing.

In this Append ix you w ill learn how th e High ord er filter may decrease control

stresses.

Tuning a speed controller is simpler than tun ing a p osition controller. If you

need to tu ne a position controller, try to tu ne first its emb edd ed speed

controller. The Condu ctor program lets you tu ne a speed controller withou t the

risk that the m otor w ill drift away from its starting shaft position.

If your m echanics are simp le and good enough to avoid the H igh order filter,

adh ere to the simp le PI speed controller. The High ord er filter requires more

skill to u se. The H igh ord er filter always introdu ces a filtering d elay, which

usu ally limits the achievable band wid th compar ed to a simple PI.

Use the High ord er filter when en countering oscillations and high frequency

noise. The sm all extra effort of tun ing the High or der filter can be very

beneficial.

If your en coder has good enou gh resolution and the friction is low enough , use

a fixed cont roller.

Use controller sched uling (dynam ic adap tation of the controller param eters tothe situation) if you h ave a low -resolution encoder or high friction. The extra

effort of tun ing th e High ord er filter can be very ben eficial.

Work linearly. With high controller gains the curren t comm and saturates for

very sm all tracking errors. The saturation m akes the evaluation of control

quality very d ifficult. Keep th e motions sm all enou gh an d verify by th e current

wav eforms that th e curr ent comman d d oes not saturate2. Verify how th e

controller w orks w ith large signals only after it is satisfactory with small

signals.

Work w ith steps. When y ou test a controller with limited acceleration or even

smooth ed reference w aveforms, d on't excite high frequencies. The resu lts willnot reveal oscillations and high frequency p roblems that may exist.

Do not fear oversh oots. Overshoots are necessary if the controller is to track

withou t a time d elay. Redu cing th e height of the overshoots lengthen s their

du ration. Evaluate the overshoot that y ou can tolerate by experimen ting with

acceleration limited test waveforms, without exceeding the acceleration you

actually u se.

1Systems that do not stay in place when the motor is shut down.

2 Note that the rate of change of the current command is also limited. This is because

LVdtdImax B= where I is the motor current, BV is the supply voltage and L is the motor

inductance.




A.4 Keep Marg in s

It is very temp ting to increase the controller gains and enjoy the m aximal

performan ce of your system. You m ust bear in m ind th at the price of maximu m

performan ce is decreased robustn ess to system variations. The higher the gains, the

greater the chance that the system w ill become n oisy or even unstable d ue tochanging w ork conditions, or du e to ageing. The following tips w ill help you create

a stable, long-lasting m otion system:

Tune for m inimu m inertia. If the inertia of the system varies, e.g. for a rotary

robot arm , tune for minimal inertia3. Positions or loading conditions with

higher inertia w ill have a slow er response time, but are likely to remain stable.

The controller must rem ain stable (it does not h ave to maintain an op timu m

response) when you dou ble the selected gains, and also when th e selected gains

are redu ced by half4.

Acceleration limits. For a position controller, the maximum motor acceleration

(parameter GS[9]) mu st be set high enou gh so that it does not d isturb norm aloperation, but also low en ough so that it prevents p osition d isturbances from

creating large overshoots.

A.5 The Bas ic Con cept s

This section concisely and inform ally explain s the entities you w ill come across

when tuning.

A.5.1 Fixed - vs . Gain-schedu led Cont ro l l e rs

The drive can ru n either a fixed - or a gain-sched uled con troller. A fixed contr ollerrun s a fixed set of control param eters

5.

Gain scheduling is the p rocess of adap ting the controller param eters "on th e fly"

to a given situ ation. The Drive stores 16 sets of contr oller param eter sets. The

active controller p aram eters set is chosen by the gain sched uling p rocess.

The drive supp orts two typ es of gain sched uling.

Autom atic gain scheduling: the Drive adap ts the controller to the speed

controller comm and , in real-time. The reasons for au tomatic gain schedu ling

are:

o When th e speed becomes low, there is a large delay between consecutive

encoder position u pd ates. This delay requires a decreased controller

bandwidth.

o At low sp eeds friction becomes a dom inant control pr oblem. Increasing

the integrator gain at low speeds m ay improve low speed behavior.

3 Tuning for the least inertia may have a high price with high inertia postures or load conditions. You

can tune instead for several postures or loads and apply manual gain scheduling.4

If you tune a speed controller you don't have to test with halved gains. Position controllers are,however, conditionally stable. This means that a position controller will loose stability with gains that

are small enough.5The fixed/scheduled option refers to the proportional and the integral speed gains, position gain, and

some parameters of the Advanced filter.




Manu al gain schedu ling: The controller param eters may adap t du e to a user

program or an external comman d . For example, the controller gains of a wind er

may be increased as it rolls and gains w eight.

For convenience, wh en you p rogram a fixed controller you d on't overwr ite the

schedulable param eters, and vice versa.

The Au to-tun er always programs an au tomatically gain-sched uled controller.

A.5.2 Resonance and Notch Fi l t e rs

Resonance is a very comm on m echanical phen omenon , in w hich a flexible system

vibrates in its natu ral frequencies. In man y ap plications, the natu ral frequencies

are too h igh for the m otion controller to control. The best policy for the m otion

controller is then to a void exciting the oscillations. You chain a ba nd -stop (notch)

filter to the controller to p revent th e controller from d riving the oscillatory

frequency.

If you d on't u se a notch filter wh ere necessary, either:

Severely limit th e possible controller band wid th.

Risk instability an d extreme stresses to th e controlled system.

Tips:

Norm ally there is m ore than one resonance frequen cy. It may be n ecessary to

set more than a single notch.

In some systems th e resonance frequency changes significantly d ue to load or

postu re changes. Verify that you r d esigned notch covers the entire operational

envelope.

A.5 .3 H igh Frequency No ise and Low -pass Fi l t e rs

High frequen cy noise mean s vibration, acoustically un acceptable noise, and

mu ch greater pow er consum ption than is necessary just to d rive the motor to its

desired sh aft position. The main r easons for high frequency noises are:

Sensor in accur acy.

Plays or backlash in the mechanics.

High frequency, unid entified resonance, possibly du e to aliasing6.

The best policy for the m otion controller is to avoid exciting the m otor at a high

frequency because th e system v ibrates there or because the feedback is not

reliable. For this pu rp ose chain a low -pass filter to the controller.

The pr ice of a low-pass filter is an equivalent d elay. For a d ouble pole filter w ith

a d amp ing factor of 0.7, the insertion d elay is about 0.23/ f, wh ere f is the corner

frequency.

6

We deal with a sampled system. High frequency signals may appear to sampled systems in changed,low frequencies. For example, if the Drive samples at 300 usec (TS=75), then an oscillation with a

period of 300 usec (3333 Hz) appears to the Drive as a constant value (frequency=0).




A.5.4 Eva luat ing a Step Respon se – R ise Tim e, Set t l ing

T im e, and Overshoo t .

A step respon se is the w aveform (position or sp eed) the motor exhibits when its

reference comm and (position or speed) changes abru ptly. Step resp onses are not

very p ractical in real-life m otoring ap plications, as the reference comm and s arenearly always acceleration limited and man y times smoothed .

A step respon se is, however, good to r eveal the detailed dyn amic behavior of the

controller. The m ost pop ular step -respon se figures of m erit are:

Rise time: The tim e since the reference has been chan ged u ntil the valu e

(position or sp eed) covers 90% of the step .

Settling tim e: The tim e since the reference has b een changed un til the value

(position or sp eed) remains perm anently w ithin 3% of the step.

Overshoot: The percentage of the deviation to the oth er side w hile stabilizing

the step.

These figures of merit are show n in Figure 57.

0.011 0.012 0.046 0.050 0.0740

200

400

600

800

1000

1200

1400

Target

Time

Figure 57: A st ep respo ns e: The rise t im e is abou t 0.01, t he set t li ng t im e is 0.074, an d the

overshoot is about 30%.

The overshoot level, as well as the ratio between th e rise time an d the settling tim e,

reflect the gain and the ph ase margins7. Gain or p hase margin resu lts that are too

low m ay result in a high step response overshoot (more th an 40%) followed by an

un dershoot and a long settling tim e. If the phase m argin is too high, the settling time

is too long. These prop erties are d epicted in Figure 58 below w hich is a simu lation

of three design examp les: One w ith reasonable margins, one w ith margins that ar e

too low and one with ph ase margins that are too high.

7The gain margin is the factor in which the controller gain can be increased until loosing stability. The

phase margin is the difference of the open-loop phase from -180 degrees at the point where the open-




0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

2000

4000

6000

8000

10000

12000

14000

16000

Time (sec.)

S t e p r e s p o n s e

Accep table margins: Nice response

Too low margins: large overshoot and oscillations

Too much margins: long settling time

Reference

Figure 58: Comparison bet w een st ep responses of acceptable controllers and non-

acceptable controllers. Details on t he plot.

A.6 The Exam ple Sys tem

Manu al tun ing is not a true science with closed formulas. It is heur istic, and theheu ristics fit only a (relatively w ide) selection of systems. All the explanat ions in

the rest of this Append ix refer to the tw o laboratory systems, shown b elow.

Both the systems hav e the same motor and amp lifier:

Characteristic Value

Motor type Brush less, three pole pairs, 4 Amp continu ous.

Encoder resolut ion 4000 coun ts/ rev (1000 lines)

Am plifier Bell 5/ 100

In system # 1, the m otor is loaded by a simp le inertia. This simp le inertia loadenables high band wid th control. In system #2, the load inertia is coup led to the

motor throu gh flexible coup ling. The coupling introd uces a mechanical

resonance.

loop gain is 0 db. For further explanation, see the Auto-tuning manual, or any basic textbook in control

theory.

Acceptable margins: good responseMargins too low: large overshoot and oscillationsMargins too high: long settling timeReference




A.7 Tes t ing t he Respon se o f a Cont ro l le r

Manu al tuning is an iterative process in w hich you select param eters for the

controller, and then test them .

A.7 .1 Cur r en t L im i t s

Beware that th e peak current limit and the continuou s curren t limit of the dr ive

may differ. If you u se excessive current levels in the experiment, the d rive may

switch autom atically to the continu ous limit, and exhibit saturation b ehavior.

A.7 .2 Record in g the Exper im ent Resu l t s

The Condu ctor's Wizard records the resu lts of the tu ning experiment. The

recorder is autom atically triggered wh en the motion comm and (speed or target

position) changes.

The record er records th e reference and the actual speed an d position waveforms,

and also the motor's current d emand . The current dem and is very useful for:

Detecting saturation. If the current d emand is saturated th en the system

reached ph ysical limitations, and you cannot distinguish th e small signal

response from the experiment result.

Current comm and wav eforms easily reveal ph enomena like friction (curr ent

increases for a wh ile before the motor starts to m ove), cogging (period ic-in-

position torqu e distur bance), dyn amic un balance (periodic-in-position torqu e

distur bance, prop ortional to the squared speed), play (the ratio between current

and acceleration jumps wildly), resonant limit cycle (constant frequencysinusoidal disturban ce) and m uch more.

Large high frequency current d eman ds reveal the need for high frequency

filtering in a m ore vivid way th an p osition or sp eed error.

Check that the currents are near th e expected v alues for the accelerations used .

This gives you extra assuran ce that the system is prop erly assembled an d w ell

calculated.

You can set the recorder time as long as you wan t, but for large recording times

you w ill lose resolution, as the num ber of the record ed d ata points is limited .

Notes:

The recorder can export th e experiment r esults to Matlab8 for further analysis.

When d ecreasing the recorder resolution, you become m ore susceptible to

aliasing. In other w ord s, high frequency d isturbances may be totally mis-

presented, and they may look as phenom ena of a mu ch lower frequency.

8 Popular, excellent technical calculations software by MathWorks.




A.8 Fixed Gain Manua l Tun ing fo r a Speed Loop

This section d eals with choosing th e KI and KP par am eters of the PI contr oller

and the p aram eters of the High ord er filter. We first d escribe how to select the KI

and KP parameters. Then w e explain h ow to add a low-pass filter. Finally we

explain how to decide if a notch filter is needed and how to add it.

A.8 .1 Manua l Tun in g o f a PI Con t ro l le r

We present an iterative pr ocess of choosing KI and KP and testing the closed loop

step respon se. We evaluate the step respon se in order to iterate the KI and KP

param eters for impr oved closed loop p erforman ce. The steps are:

1. Start w ith th e very low gains of the PI controller: KI=3 and KP=1 for examp le,

then set the following step reference comm and param eters:

(a) Set a long recorder tim e, as with low gains the respon se is going to be slow.

H ere the M ax. Record Tim e is 0.48 seconds.

(b) Velocity: 12000 counts/ second (fits 180 RPM for encoder of 4000 counts per

revolution). This ma y be too slow a velocity for optim al tun ing. We will increase

the reference speed later, wh en w e are more confiden t of the motor's response.

(c) Displacem ent: Displacement o f at least Max. Record Time m ultip lied by

Velocity (about 5000 in th is examp le), un less it violates the m echanical lim its.

The test data is sum marized in the following table.

KP KI Velocity +Disp l. -Displ. Rec. T. Rec. Res Profile

1 3 12000 5000 -5000 0.48 sec 400 musec off

Let us observe two plots, the measu red sp eed and the motor current . With the

low gains the m otor's response is very sluggish, as in Figure 59.

0 0.1 0.2 0.3 0.4 0.5

-3

-2.1

-1.2

-0.3

0.6

1.5x 10

4

Time (sec.)

C o u n t s / s e c .

Speed

Reference

0 0.1 0.2 0.3 0.4 0.5-0.15

-0.12

-0.09

-0.06

-0.03

0

A m p e r e

Time (sec.)

Figure 59: First t est w ith low KI and KP




Figure 59 reveals the following:

1. The measured outpu t d oes not reach the comm anded step.

2. Current comman d is far from satu ration, therefore you can increase the

velocity comm and .

Figure 60 repeats the sam e test with increased velocity and test du ration as given

in the table below. Note th at there is a long tim e du ration (from 0.7 to 1.3 sec.)

tha t the velocity is almost fixed w hile the curr ent increases, this is a result of high

friction.


1 3 48000 20000 20000 2.4 sec 2 msec Off

0 0.1 0.2 0.3 0.4 0.5-3

-2.1

-1.2

-0.3

0.6

1.5x 10

4

Time (sec.)

C o u n t s / s e

c .

Speed

Reference

0 0.5 1 1.5 2 2.5-0.3

-0.2

-0.1

0

0.1

0.2

A m p

e r e

Time (sec.)

Figure 60: A t est w it h the sam e cont roll er as the t est of Figure 59 w ith a higher velocity

comm and an d a l onger recording tim e (Speed2)

1. Repeat step 1, increasing KI and KP simu ltaneously by 50% at a time u ntil one

of the following occur s:

The step respon se exhibits an overshoot of about 20%.

The step response is u nacceptable for any reason, for examp le any sign of

resonant oscillation.

The system exhibits large overshoot and un dershoot w hich is a sign of being

close to instability. In th is case decrease KP by at least a factor o f 2.0.

The final respon se is in Figu re 61, wh ich includ es several tests based on increasing

KI and KP with the values given in th e following table


10,20,30,40 6 KPπ 12000 5000 5000 0.48 sec 400 usec Off




Figure 61: Test results for maxim um KP for KI/KP=3

Adjust the speed comm and for optimal tuning. The speed command should be as

large as possible to minim ize friction effects and inform ation d elay effects9.

When th e gains increase, the friction is less app arent, but the current

consump tion for the same r eference speed increases. You will have to red uce thespeed comm and u ntil the current wav eform d oes not saturate. Let us denote the

final KI and KP by KI0 and KP0, here KP0=40 and KI0=120.

Remark : The speed comman d sh ould be large enoug h to m inimize friction

effects, w hich decreases ou r ability to evalu ate the test resu lts. Friction is

considered high if the speed response d epend s significantly on the reference

mag nitud e. In extreme cases we observe the current increasing w hile the motor

speed stays fixed below its destination. See an examp le in Figure 59. Increasing

the velocity comm and helps to minim ize the friction effect. The steady state

current (0.1 Amp ere in one d irection and 0.1 Amp ere in the other direction) is a

measu re of the amou nt of friction.

2. Fix KP=KP0 / 1.3, w hich in ou r exa m ple gives 40/ 1.3=30, then per for m step

response tests w hile increasing KI by a factor of 1.3 at a time, from the initial

valu e of KI0. Continue increasing KI until the system exhibits overshoot of abou t

30%. In ou r exam ple th e final valu es are KP=30 and KI=8000, see the results in

Figure 62, wh ich includ es several tests of increasing KI in th e range given in th e

following table and m arked on th e plot.

9Friction will cause the response to behave differently as a function of speed. Information delay is

explained in the "Fixed vs. Gain Scheduled Controllers" section above.

0.1 0.12 0.14 0.16 0.18 0.2-1.5

-0.9

-0.3

0.3

0.9

1.5x 10

4


Time (sec.)

KI=120,KP=40

KI=90,KP=30

KI=60,KP=20

KI=30,KP=10

Reference

0.1 0.12 0.14 0.16 0.18 0.2-0.5

-0.10.3

0.7

1.1

1.5

A m

p e r e

Time (sec.)

KI=120,KP=40

KI=90,KP=30

KI=60,KP=20

KI=30,KP=10




KP KI Velocity +Displ. -Displ. Rec. T. Rec. Res Profile

30 Marked

On Plot

12000 5000 5000 0.48 sec 400 musec off

Figure 62: Test result s for several KI and fixed KP. The test w it h KI=8000 has an

ov ershoot of 30% w it h negligible undershoot a nd can be considered a good choice

3. The final step is perform ing sm all iterations on KI and KP (a 10% param eter

change in each test) and testing in order come up with th e best solution d efined

by the u ser. How ever, the user m ust be careful to pr eserve the gain m argin as

explained in Section A.4

We are now ready to give the first guid elines for what to look for when searching

for a good controller:

Guid eline 1: When sear ching for good cont rollers try to increase KI in ord er to

imp rove the closed loop p erform ance of the system. H owever, increasing KI too

mu ch creates unacceptable oscillations as shown in Figu re 63.

Guid eline 2: Never allow an overshoot of m ore than 40%. A typical overshoot

selection is 25%. The example in Figure 63 reflects a non-robust controller with

poor p roperties such as a large settling time.

0.1 0.12 0.14 0.16 0.18 0.2-1.5

-0.7

0.1

0.9

1.7

2.5 x 104


Time (sec.)

KI=8000

KI=6000

KI=4000

KI=2000

KI=1000

KI=500

Reference

0.1 0.12 0.14 0.16 0.18 0.2-0.5

-0.1

0.3

0.7

1.1

1.5

A m p e r e

Time (sec.)

KI=8000

KI=6000

KI=4000

KI=2000

KI=1000

KI=500




Figure 63: A n exa mpl e of un accept ab le cont roll er – KI is too la rge

Guid eline 3: The final response shou ld h ave an overshoot of about 25%, no

und ershoot and n on-saturating current demand .

0 0.01 0.02 0.03 0.04 0.05-2

-1.2

-0.4

0.4

1.2

2x 10

4

Time (sec.)


Speed

Reference

0 0.01 0.02 0.03 0.04 0.05-4

-2.4

-0.8

0.8

2.4

4

A m p e r e

Time (sec.)

Figure 64: A smal l si gnal st ep respo ns e charact eriz at ion of a good PI con t roller. I t

should hav e an overshoot of about 20-30% and a v ery small or zero undershoot

0.1 0.12 0.14 0.16 0.18 0.2-1.5

-0.6

0.3

1.2

2.1

3x 10

4

C o u n t s

/ s e c .

Time (sec.)

KI=20000,KP=30

KI=16000,KP=30

Reference

0.1 0.12 0.14 0.16 0.18 0.2-2

-1.2

-0.4

0.4

1.2

2

A m p

e r e

Time (sec.)

KI=20000,KP=30

KI=16000,KP=30




Theoretical Tip: We suggest to start the manual tuning w ith KI/ KP= 6π ,

assum ing you can achieve a bandw idth greater than 3 Hz. Then find the

maximu m KP where KI/ KP=3. Above the bandw idth of 3 Hz, the value of KP

w ill be respon sible for stability rath er tha n KI. The next step is to d ecrease KP by

abou t 30% to leave sp ace for increasing KI and leave it fixed w hile increasing KI.

This procedu re converges, except for rare systems for wh ich th e band wid th of 3

Hz cannot be achieved10

.

A.8 .2 Manua l Tun in g o f a PI Con t ro l le r and a Low Pass

Fi l te r

A low-pass filter enables decreasing and smooth ing the curren t injected to the m otor

du e to the sensor’s noise and/ or du e to plant resonance appearing at very high

frequencies. Moreover, it can avoid un expected mechanical phenom ena, as d etailed

in section A.5.3. Most likely, using a PI controller with a low -pass filter decreases the

closed loop agility p erforma nce comp ared to a PI controller. However if agility can

be sacrificed it is highly recomm end ed to u se a low -pass filter. The follow ing

procedu re for incorporating a low -pass filter is recomm ended :

1. Start w ith d esigning a PI controller w ithout a low-pass filter as d escribed abov e.

Denote the PI param eters by KI0 and KP0.

2. Add a low-pass filter at the frequency of 0.2/ [Speed Samp ling Time] with a

dam pin g factor of 0.6.

Design a PI cont roller as described below . First find the largest KP where

KI/ KP= 6π . Figu re 63 describes tw o tests, the v alue KP=50 is too high, KP=40 is

satisfactory. Then choose KP=40/ 1.3=30 and increase KI until a satisfactory

response is achieved. Figu re 66 show s tests w ith severa l KI valu es, KI=5000 is the

recomm ended value because larger values exhibit un dershoot and lower values

exhibit overshoo t less than 10%. Repeat this step w hile decreasing the corner

frequen cy of the low -pass filter 20% at a time u ntil a satisfactory r esult is

achieved (see Guideline 4), or follow th e instructions in the next step.

10We don’t recommend implementing closed loop responses slower then 1 Hz, as the numerical

controller of the Drive is not optimized for such low frequencies.




0.1 0.12 0.14 0.16 0.18 0.2-1.5

-0.8

-0.1

0.6

1.3

2x 10

4

C o u n t s

/ s e c .

Time (sec.)

KI=150,KP=50

KI=120,KP=40

Reference

0.1 0.12 0.14 0.16 0.18 0.2-1

-0.4

0.2

0.8

1.4

2

A m p

e r e

Time (sec.)

KI=150,KP=50

KI=120,KP=40

Figure 65: Tests f or finding the m axim um KP f or KI/KP=3. KP=40 is accept able, w hile

KP=50 is too large

0.1 0.12 0.14 0.16 0.18 0.2-1.5

-0.7

0.1

0.9

1.72.5

x 104


Time (sec.)

KI=10000

KI=7000

KI=5000

KI=3000

Reference

0.1 0.12 0.14 0.16 0.18 0.2-0.5

0

0.5

1

1.52

A m p e r e

Time (sec.)

KI=10000

KI=7000

KI=5000

KI=3000

Figure 66: Test result s for searching for the m axim um KI. The candida te for KI is K I=5000,w here the overshoot is about 20%




If a settling tim e of 25 msec at least is satisfactory, try to in sert a second ord er

low-p ass filter. The starting corner frequency is (10/ Settling tim e) H z. Iterate step

2 for low -pass filters decreasing by 25% each test. Repeat, decreasing the low -

pass frequ ency un til a satisfactory controller is achieved ; see Guideline 4 below.

Guid eline 4: A satisfactory resu lt is the low -pass filter with the low est cornerfrequen cy that satisfies the required performance. The low-pass m inimizes the

expected current consum ption an d curr ent noise level.

A.8 .3 Manua l Tun in g o f a PI Con t ro l le r and a Notch Fi l t e r

During the d esign of a PI controller, the designer can conclud e from the test

results if a notch filter is required and in wh ich frequency it shou ld be ad ded .

Below is a char acteristic examp le, using the second (resonant) test system .

Let us start d esigning a PI controller. After several iterations increasing KI and

KP (KI/ KP= 2π ), we have th e test results given in Figure 67. The measured

curren t exhibits oscillations, wh ich indicates the existence of resonan ce.

Remar k: In this example th e m easured speed also exhibits oscillations. In m ost

cases, however, the resonance phenom enon is m ore clearly identified from the

current response than from the speed response.

0 0.1 0.2 0.3 0.4 0.5-3

-1.8

-0.6

0.6

1.8

3x 10

4

Time (sec.)

C o u n t s

/ s e c .

SpeedReference

0 0.1 0.2 0.3 0.4 0.5-0.8

-0.16

0.48

1.12

1.76

2.4

A m p

e r e

Time (sec.)

Figure 67: Exam pl e of a t est , w hi ch call s fo r usi ng a no tch – t he current exhi bi t s period ic

noise wav eform

Measure the r esonance frequency, that is, how m any oscillations app ear in a

second . By enlarging an interval of the measured current, one can m easure 30

cycles in 0.0837 second s w hich fits to a reson ance frequen cy of 10/ 0.0387=359 Hz.




0.3 0.32 0.34 0.36 0.38 0.40.2

0.24

0.28

0.32

0.36

0.4

A m p e r e

Time (sec.)

Figure 68: Zoo m of current t est meas urement fo r m eas urin g t he pl an t ’s expected

resonance. (RSpeed2)

Add a notch at frequen cy 359 Hz with dam ping factor of 0.07. Click the H igh-

ord er Filter Design but ton, choose a notch filter, type its corner frequency anduse th e slider to choose the dam ping factor. The screen is show n in Figu re 69.

Click OK to retu rn t o the Tuning Velocity Loop screen, and then click Ru n to

perform a test. The outcome is shown in Figure 70. Note that the resonance

phenom enon disappeared (compare Figu re 67 an d Figure 70). The improvem ent

is apparent in Figure 71, wh ich is zoomed to the scale of Figure 68.




Figure 69: Not ch fi lt er at the corner frequ ency 359 Hz an d a da mpi ng fa ct or of 0.07

0 0.1 0.2 0.3 0.4 0.5-3

-1.8

-0.6

0.6

1.8

3x 10

4

Time (sec.)

C o u n t s / s

e c .

Speed

Reference

0 0.1 0.2 0.3 0.4 0.5-0.8

-0.16

0.48

1.12

1.76

2.4

A m p e r

e

Time (sec.)

Figure 70: Test result show ing how a notch filter eliminat es current oscillations due to

mechanical resonance






A.9 Execut ing Manua l Tun ing fo r a Cascaded

Pos i t i on Cont ro l le r

Design of a position cont roller is a two-stage sequence. The first is to tun e a

speed controller and the second is to tune the simp le gain ou ter controller.

Assum e the speed controller was designed and tested as shown in Figu re 62 forw hich KI=8000, KP=30. The r ise time is d T=0.0034 second s. The suggested dua l

loop contr oller is:

1. Inner loop p arameters: KI is half that of the speed loop d esigned in th e first

stage and KP remains the sam e.

2. Outer loop p aram eters are: KP=0.5/ dT=16.

Explanation:

(a) The KP of the outer loop w ill decrease the phase mar gin. The KI of the inner

loop w as designed to achieve the minimal ph ase margin allowed. It is thereforerequired to increase the ph ase margin of the inner loop by d ecreasing KI in ord er

to leave some extra p hase marg in for KP of the outer loop.

(b) The outer loop formu la for KP is based on th e estimate of the system’s

bandwidth.

(c) KP of the inner loop mainly d ictates the gain m argin; as such it remains

unchanged.

The tested results are shown in Figure 72 for the param eters in th e table below.

KP KI KP -outer

Velocity Step Rec. T. Rec. Res Acc/ Dec

30 4000 150 100000 2000 0.48 sec 400 musec 60 M




0 0.02 0.04 0.06 0.08 0.10

500

1000

1500

2000

2500

Time (sec.)

C o u

n t s

Speed

Reference

0 0.02 0.04 0.06 0.08 0.1-2

-0.8

0.4

1.6

2.8

4

A m p

e r e

Time (sec.)

Figure 72: Tests of posit ion design

3. The third step is to iterate on the KI param eter of the inner loop and on th e

outer loop KP param eter. The iteration range for the KI of the inner loop shou ld

not exceed 50% of its original value, and the iteration on th e outer loop shouldnot exceed 100% of its original valu e.

A.10 Manua l Tun ing o f Ga in Schedu l in g

The previous sections dealt with the m anu al tuning of a fixed controller. In th is

section w e extend our ability to tu ne a gain-schedu led controller.

Controller gains can be schedu led either m anu ally or by reference to the speed

controller.

A.10.1 Manual Gain Schedul in gManu al gain schedu ling is useful w hen on e can learn of the changing conditions:

Using position data - for example in a w inder ap plication.

Using external data, by analog inpu t or commu nication. For example, a winder

may learn the w heel weight by feeding the ou tpu t of a load-cell to the analog

inpu t, or a robot arm d river may receive a gain-sched uling comman d from a

central controller, that is aware of the en tire robot postu re.




For manu al gain schedu ling, tun e a series of fixed controllers and log their

param eters. Keep in m ind th at the H igh-order filter must be similar for all the

param eter sets. Then p rogram them to the controllers’ array u sing the KG[N]

comm and , and set GS[2] for the selection of the app rop riate controller. Refer to

the chapter on th e Speed an d th e Position Controller in the App lication Manu al

for more d etails.

A.10 .2 Au tom at ic Ga in Schedu l ing

In man y app lications there is a good reason to schedu le the controller gains by

the speed comm and . The two m ain reasons are:

At low speeds th e information comes from the encoder at a redu ced rate. The

resulting d elay destabilizes the controller. The motion controller starts to

develop oscillations until the instantaneou s speed is enou gh to stabilize the

motor. The only way to rend er the information d elay insignificant is to redu ce

the controller’s ban dw idth, sacrificing h igh-speed p erforman ce. The autom atic

gain-scheduling process enables switching to slower controllers when the sp eed

is slow, and recovering full performan ce wh en the speed d emand or the

position error12 are high again.

At low sp eeds the p lant behavior m ay change significantly, du e to frictions and

plays. Frictions app ear at h igher speeds as constant d isturbance, easily taken by

the integrator of the controller. Plays may be less disturbing at high speeds,

wh ere the sign of the torqu e is fixed.

A.10 .2 .1 Tun ing a Speed Cont ro l le r

The highest speed for tuning is about tw o encoder pu lses per controller sampling

time, since for h igher speed s the inform ation d elay is insignificant.

The tuning speeds are calculated t o generate equally distributed information

delays. For this reason, at high speed s there is a larger gap between the sp eed

options, whereas at slower speeds the gap is smaller.

You can select any su bset of the op tion speeds an d tun e the controller for them.

The following algorithm calculates the m aximu m recomm end ed closed loop

bandw idth for a given speed:

Delay = Speed contro ller samp ling time + 1 / (2 Speed reference). The first term

in the formu la includ es the comp utation d elay, the zero-ord er-hold d elay, th espeed calculation d elay, and other m inor d elay contribut ors. The second term is

the information delay.

Minimal recommen ded speed settling tim e = (20 to 25) times the d elay.

For examp le, for a speed of 500 coun t/ sec, the information d elay is 1 msec. With

TS=75, the sp eed cont roller sam pling time is 300 usec, totaling 1.3 m sec of delay.

The best speed settling time for the sp eed of 500 coun t/ sec is about 30 msec.

Speed settling times d own to 20 msec can be achieved for the sp eed of 500

count/ sec with reduced phase margins.

12 In position control, a position error translates into a speed demand.




0 10 20 30 40 50 60 700

2000

4000

6000

8000

10000

12000

c o u n t s / s e c

Index

Figure 73: An exam pl e of op t io n speed s

Position gain schedu ling is similar to speed gain schedu ling.

The minimal recommen ded position settling time = twice the speed settling time.






B.2 Mathem at i cal Mode l s f o r LTI Sys tem s

LTI systems, like any other system , are mod eled by d ifferential or algebraic

equations. The basic one is the differential equation, which m eans that t he

relation between the outpu t, y , and inpu t, u , should obey the d ifferential

equation( ) ( ) ( ) ( ) ( ) ( )

ubububu ya ya ya ya m

n

mn

n

n

n 0

1

1

1

10

1

1

1

1 ++++=++++−

−

−

−

ΛΛ (2)

A simp le examp le is a DC motor in current m ode, described by the d ifferential

equation

ku y =&& (3)

where u is the curren t and y the shaft angle. Let us now assu me that th e inp ut

to th e system (2) is ( )t u ω sin= . It can be confirmed by substitution th at

( ) ( )( )ωϕ+ω⋅ω= t sina y (4)

solves (2), that is it is the system ou tpu t, where ( )ω a an d ( )ω ϕ are the absolute

value an d ph ase, respectively. The depend ence of α an d ϕ on th e frequencyω is

called a Transfer fun ction . For the system of (2), the tran sfer fun ction is:

( ) ( ) ( )

( ) ( ) 01

01

1

1

a ja j

b jb jb jbm

n

n

n

n

+⋅++

+⋅++⋅+⋅−

−

ω ω

ω ω ω

Λ

Λ (5)

Note th at the expression in (5) yields a complex num ber. The m agnitud e of this

num ber is )(ω α and its phase is )(ω ϕ .

A m ajor p roperty of an LTI system is that its outp ut, )(t y , for an inp ut of the

form ( )t u ω sin= is ( ) ( )( )ωϕ+ω⋅ω= t sina y , hence, the outp ut is the sam e as

the inpu t apart from an amp lification factor ( )ω a and time delay ( ) ωωϕ− / . The

parameter ω is called th e frequ ency of the signal u (and y ), ( )ω a th e

amp litud e of y an d ( )ω ϕ its phase.

The transfer function is the basic engineering d escription of a linear system . It

directly describes the frequency response - the way the system respon ds to a

sinu soida l signa l of any frequ ency. The tran sfer fun ction is closely related to theLaplace transform of the system . In fact, the Laplace transform of the system is

obtained by r eplacing in (2) the expr ession ω j with the Laplace variable s . The

Laplace transform o f the system described by the d ifferential equ ation (2) is:

01

01

1

1

asas

bsbsbsbm

n

n

n

n

+++

++++−

−

Λ

Λ (6)




Comp aring (6) and (2), we find that th e Laplace variable s is equivalent to th e

derivative operator, dt

d s⇔

and its inverse to an integrator,∫ ⇔

t

d s

τ

1

. The

transfer fun ction that relates the torqu e of a motor to its position is roughly a

dou ble integral (the torqu e is rough ly prop ortional to acceleration), so that th e

transfer fun ction from th e motor tor que to its position is rough ly2

1

s J m where

m J is the motor inertia.

Please note th at the transfer function is a full description of the response of its

related system to any inp ut, not just to sinu soids.

It is custom ary to describe the frequen cy response of a system pictorially by a

plot of the amp litude an d ph ase of (6) versus the frequency ω where ω= js , this

plot is know n as its Bode p lot. A Bode p lot examp le for the fun ction

( )( )( )3360

32000102

++

+⋅

ss

s

s is given in Figu re 75.

10 0

101

10 2 -30

-20 -10

0 10 20 30

dB

10 0

101

10 2 -200

-180

-160

-140

-120

-100

deg

log(ω)

Figure 75: Bode plot of a fu nct ion

Anot her efficient p ictorial rep resentat ion of a linear system is the Nichols plot.

The Nichols plot is a plot of the am plitud e of (6) versus its ph ase along the real

parameter,ω

, whereω js =

. The N ichols plot of the same tra nsfer function isshown in Figure 76. As will be show n in th e next plot, the Nichols plot is a very

attra ctive description of an LTI system for feedback control d esign. An examp le

N ichols char t of the tran sfer function

( )( )( )3360

32000102

++

+⋅

ss

s

s is in the figure below.




-360 -315 -270 -225 -180 -135 -90 -45 0-40

-30

-20

-10

0

10

20

30

dB

deg

ω=1.5

ω=2

ω=3

ω=5

ω=10

ω=20

ω=40

ω=60

ω=80

L(jω)

Figure 76: A n exa mpl e N icho ls cha rt

B.3 Moto r Sys tem s Models

B.3.1 A Sim ple Model

A m otor is a d evice that translates electrical energy into mechanical energy.

Figure 77 is a simp lified schem atic rep resenta tion of a fixed ma gnet electrical

motor.

E

L

B,J,T,θ

v ConstantField

i

R

M

Figure 77: Schemat ic model of a DC motor

Mathem atically it can be d escribed by the set of equations

C T

E E

T B J iK T

K K E

dt

di L E iRv

++==

==

++=

θ θ

θ ω

&&&

&

(7)

where v is the applied voltage, i motor current, R resistance, L inductance, E

back e.m.f., E K motor e.m.f. constant, θ=ω shaft speed an gle, θ shaft angle,

T motor torque, J shaft inertia, B shaft viscous friction, and C T shaft coulom b

friction.

For linear control systems d esign, Equation 7 applies for both br ush and brush less

DC motors.

Equations (7) where C T is neglected is schem atically described in Figur e 78.




R

1T

K

i

Ls−

J

1

s

1

B−

EK

+ θ⋅

_

v T

Figure 78: Bl ock di agram of the sim pl if ied DC mot or model

The transfer function from voltage inpu t, v , to motor shaft angle, θ , is

( ) R

L ,

K K

JR;

sss

K /

v

e

E T

m

mem

E =τ=τ

ττ+τ+

=θ

2

1

1& (8)

Usually, eτ is much sm aller then m

τ . The electrical time constan t eτ is normally

in the ord er of magnitud e of 1 msec, wh ereas in low friction systems mτ may be

in th e ord er of 1 sec. If meτ τ << , we can replace m

sτ in the d enominator of (8)

by ( )em

s τ+τ to get the approximation

( )( )sss

K

v em

E

τ τ

θ

++=

11

/ 1& (9)

Equation (9) is a comm on expression found in the literature and suits feedback

design w here resona nce effects can be neglected . We will now describe and

analyze motors w ith resonance.

B.3 .2 Mode l w i th Flex ib le Transmiss ion ( resonance)

Figure 79 is a schem atic representa tion of a ‘constan t field’ m otor w ith the load

connected to the m otor shaft by a flexible axis.

LB

M otor L oad

1M2M

MLd

MLc

Mθ

MB

Lθ

Figure 79: Schematic connection of load via flexible coupling




Sup pose that in the system of Figu re 79 the motor is brought abru ptly to some

constant torqu e. Initially the load will not react. This is because th e axis mu st be

deformed in order to convey torqu e to the load. When the load finally moves, its

acceleration w ill oscillate. The oscillations in the load w ill ind uce oscillations in

the motor, as shown in Figure 80 for a step comm and . This oscillation

ph enomenon is called Resonance.

0 2 4 6 8 10 0

0.3

0.6

0.9

1.2

1.5

1.8

time

Figure 80: Typical response of an oscillating syst em t o t orque step

Mathem atically, the following equations d escribe the system:

( ) ( )ML L M ML L M L

T M

L M M M M M

DL L L L L L

d ncnT

iK T

nT BT J

T BT J

θ−θ+θ−θ=

=

−θ−=θ

+θ−=θ

&&

&&&

&&& (10)

where, L J is the load inertia, Lθ load angle, L

T load torque, L B load viscous

friction, DLT disturbance mom ent on the load, M

J motor inertia, M θ motor shaft

angle, M T motor torque, M B motor shaft viscous friction, n gear ratio, i motor

current, T K motor e.m.f. constant, MLc transm ission sp ring factor and MLd th e

transm ission d amp ing factor. Equations (10) where B is neglected, is

schematically described in Figure 81.




mTi

TKsJ

1

M s

1

n

1

n

1MLc

MLd

s

1

+

+

_

_

_

DLT

Lθ

sJ

1

L

n

1

mθ + +

+

+

Figure 81: Bl ock di agram of a DC mot or w ith f lexi bl e loa d

The transfer functions of (10) from curr ent inp ut , i , to motor an d load an gles,

M θ an d Lθ , respectively, are

++

++

++

=

M

ML

L

ML

m

ML

L

ML L M

L

ML

L

ML LT

M

J n

c

J

cs

J n

d

J

d ss J J

J

cs

J

d s J K

i

22

22

2

θ

(11)

( )

++

++

+=

M

ML

L

ML

m

ML

L

ML L M

ML ML LT L

J n

c

J

cs

J n

d

J

d ss J J

sd c J K

i

22

22

θ (12)

An exam ple of the Bode and Nichols p lots of the tra nsfer function (11) and (12) are

given in Figure 82 an d Figure 83 respectively.




3 4 5 6 7 8 9 10 15 20 30-70-60

-50

-40

-30

-20

dB

3 4 5 6 7 8 9 10 20 30-180-160-140-120-100

-80-60-40

Figure 82: Bo de pl ot of a m ot or w it h flexi ble loa d (resonan ce m od el)

At low frequ encies, w ell below th e oscillations, the transfer function rolls dow n

with a fixed slope and fixed ph ase angle. This behavior is du e to the d ouble

integration that relates the system p osition to its torque inpu t. At the higher

frequen cy axis, Figu re 82 presents tw o well-know n p henom ena. The first, at the

frequen cy of 10, is called an ti-resonance. At this frequency torq ue is pa ssed from

the motor to the load an d th e load oscillates wildly, but hard ly any motion is

seen on the m otor shaft. This is the frequency in w hich the load w ould freely

oscillate if the iner tia of the m otor w ere infinite. The second , at frequency 11, is

the resonance. In the resonant frequency the motor and the load oscillate abouteach oth er, in opp osing d irections.

The anti-resonance and the resonance are w ell seen also in the Nichols chart

below. At the anti resonance frequency, about 10=ω , the plot has a minimu m

on th e dB scale and the p hase increases. At the resonan t frequency of 11=ω , the

plot attains a maximum on the d B scale, and the ph ase drops again.

-360 -315 -270 -225 -180 -135 -90 -45 0-80

-70

-60

-50

-40

-30

-20

-10

0

dB

deg

ω=1

ω=2

ω=4

ω=6

ω=8

ω=10

ω=10.5

ω=11

ω=16

ω=30

ω=60

L(jω)

Figure 83: N ich ol s pl ot of a mot or w it h flex ib le lo ad (resonan ce m od el)




B.4 Feedb ack Con t ro l

The system we consider here is shown in block diagram form in Figu re 84, where

P den otes the controlled transfer fun ction (the p lant).

C(s) P(s)

u yr

Sensor

-

Figure 84: Bl ock di agram of a si mpl e feedback sy stem

The inp ut to the p lant in Figure 84, is the outp ut of the controller ( )sC , whose

inpu t is the d ifference of two signals:

The comm and inpu t, r , which is an external inpu t to the system. The externalcomm and does not depend on the system’s outpu t and the user has complete

control over it.

The feedback inp ut, wh ich is the measured ou tpu t of the plant.

A system as in Figure 74, that is, without the feedback, is called an open-loop

system. A system w hose inpu t dep end s on its outpu t is called a closed-loop

system or a feedback system – for examp le the feedback system d escribed in

Figure 84.

B.4.1 Wh y Feedback is Requi r ed

Given a plant, P , its outpu t, y is generated by its inpu t, u and disturbance, d .

d Pu y += (13)

Our goal is to achieve a desired outp ut u sing the inpu t. A desired outp ut, r y , can

be achieved using the inpu t

( )d yPur r −=

−1 (14)

The synthesis of (14) does not use the measu red p lant outp ut, y . This op en-loop

solution m ay not be app licable because of the following reasons: The plant mod el is not know n exactly.

The plant, even if known , may n ot be stably invertible.

The disturban ce, d , is not know n or p artially know n, thus as before, r u which

depend s on d may n ot be accurate enough.

By embed ding the p lant in a feedback stru cture, it is possible to byp ass these

difficulties and th us achieve desired outp uts to a very high d egree of accuracy.

How ever, use of feedback has tw o m ajor d rawb acks:




The sensor, wh ich measu res the plant outp ut, add s noise to the measuremen t.

The controller amp lifies the measu rement noise. A highly am plified

measu rement noise may even saturate the plant inpu t, wh ich migh t destabilize

the system, or prod uce an unacceptable outpu t.

Feedback should be carefully designed in ord er to avoid loss of stability due to

plant un certainty and plant inpu t saturation.

B.4.2 Open Loop, Gain Marg in and Phase Marg in ,

B andw id t h and St ab i l i t y

A feedback-controlled system sh ould be carefully d esigned so that it will not

loose stability, will not oscillate too mu ch and will have good performan ce in its

entire operating envelope. Stability, bandw idth an d gain an d p hase margins are

the key p arameters u sed to d escribe a feedback design. These param eters are

now explained, bu t first we d efine the open loop of a feedback system.

Open loop – The open loop of the system is the transfer fun ction:

( ) ( ) ( ) ( )sSensor sC sPs L ⋅⋅= (15)

where )s(P , )s(C and ( )sSensor are the transfer functions of the plant controller

and sensor, respectively.

The design criterion to gu aran tee stability of an LTI feedback system is the

Nyq uist stability criterion, which is a frequency d omain criterion app lied on the

open loop tran sfer function. A simplification of th e Ny quist criterion, ad equate

for most m otion app lications, simp ly requires that the Bode plot of ( )ω j L will

have a ph ase larger than ο180−

at the frequency 0ω where ( ) 10 =ω j L . Clearly,

the N yqu ist criterion gu arantees that there exists no frequency such that

( ) 1−=ω j L . A feedback design for w hich ( )ω j L is far from th e ‘dan gerous’

value -1 at all frequencies guarantees th e following tw o very imp ortant closed

loop prop erties:

The plant outp ut w ill not oscillate du ring operation.

If the p lant tr ansfer function (char acteristic), )s(P , slightly changes du ring

operation, the changed open loop, ) j( L ω , will also satisfy the Ny qu ist stability

criterion, which means th at stability remains u nd er slight m odel changes.

How mu ch the open loop, ) j( L ω , is far from the 1− value is, therefore, a critical

design criterion, and is measur ed by the open loop gain and p hase margins.

Gain margin - The gain m argin of the tran sfer function )(s L is k , if k is the

smallest positive value such that th e plant )(sPk ⋅ becomes u nstable. For sim ple

plants, k is the sm allest p ositive value for wh ich th ere exists a frequency, GM ω ,

so that

( ) ( ) ο18020 −=ω−=ω⋅GM GM j Larg ,k j Llog and (16)




Phase margin – We will say that the p hase m argin of the tran sfer function )(s L

isο

ϕ (degree u nits), if ο

ϕ is the smallest positive value such that at any

frequency, PM ω , for wh ich ( ) 1=ωPM j L , the phase of ( )PM j L ω is

ο

ϕ+−180 .

The third design criterion is the system’s bandwidth . The band wid th is a figure

of merit for the performan ce of the closed loop system d uring operation. Several

definitions of the term band wid th app ear in the literature. The band wid th

definition w e use here is the following:

The bandwidth of )(s L is Bω rad / sec, if it is the lowest frequency such that

1)( = B j L ω .

Figure 85 is a pictorial description of gain and p hase margins and band wid th for

the op en loop tran sfer function built from:

1. A m otor w hose transfer fun ction is2sk ;

2. A controller tra nsfer function ) /()( bsas ++ ;

3. An accurate, static sensor (sensor tran sfer function =1 ).

-360 -270 -180 -90 0-30

-20

-10

0

10

20

30

Open-Loop

Gain(dB)

Open-Loop Phase (deg)

Nichols Chart

6 dB

3 dB

1 dB

0.5 dB

0.25 dB

-1 dB

-3 dB

-6 dB

-12 dB

-20 dB

φ

M

L(jω)

ωB,ω

PM

ωGM

Figure 85: Defi ni t io n o f gai n m argin M , phase m argin φ and bandw idth frequency Bω of

t he open loop ( )s L

B.4.3 P, PD, PI and PI D Cont ro l l e rs

A P ty pe controller is a simp le gain controller, that is, PK sC =)( . P type

controllers cannot stab ilize a position ing m otion system . It is, therefore, lim ited

to systems that are not relevant an d will not be discussed further. A PD controller

includ es a simp le gain and a derivative, sK K )s(C DP ⋅+= . It mean s that the

signals used to d rive the system are, except for the comm and inpu t, the plant

outp ut an d its derivative. For examp le, the inpu t, u , to a motor with command

angle, θ , and m easured ou tput angle, M θ , will be

( ) ) M D M P K K uθ θ θ θ &&−⋅+−⋅= (17)






For speed control, the derivative term represents acceleration. Acceleration is

hard to estimate w ith acceptable noise, so that th e inclusion of the D term in

speed controllers is im pr actical. We therefore use the PI (PID with out t he D) form

for speed cont rollers. To sum m arize, for PI contr ollers we use

P I K

s

K sC +=)(

(20)

that is

( ) ( )( ) ( ) ( )( )t t K d K )t (u M P

t

M I θ−θ⋅+ττθ−τθ⋅= ∫ ∞−

&&&&(21)

and for PID cont rollers we u se (19).

B.4 .3 .2 The H igh Order Fi l t e r

The PI/ PID controllers by themselves are fine for m any ap plications, but they

have th e following limitations:

They cannot notch ou t resonance.

They have poor high frequency measurement n oise attenuation.

They have limited a bility to add extra phase comp ensation, as required by

plants w ith a large mism atch between the inertias of the motor an d th e load.

The Simp lIQ controller stru cture includ es, in ad dition to the PI/ PID controller, a

freely param eterized high-order (up to 8th ord er) linear filter to overcome the

PI/ PID limitations. The resulting structur e is:

KP[2]+KI[2]/s P(s)

s

-

Position

Speed

KP[3]

Ref

-

High

orderfilter

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