Ashu Trng Rport

8/13/2019 Ashu Trng Rport

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CNC SYSTEMS chapter1

1. INTRODUCTION

Numerical control (NC) is a method employed for controlling the motions of a machine tool slide and

auxiliary functions with input in the form of numerical data. A computer numerical control (CNC) i

microprocessor-based system to store and process the data for the control of slide motions and auxili

functions of the machine tools. The CNC system is the heart and brain of a CNC machine which enables

operation of various machine members such as slides spindles etc. as per the se!uence programmed into

depending on the machining operations.

The main advantage of a CNC system lies in the fact that the s"ills of the operator hitherto re!uired in

operation of a conventional machine is removed and the part production is made automatic.

The CNC systems are constructed with a NC unit integrated with a programmable logic controller (#$C)

some times with an additional external #$C (non-integrated). The NC controls the spindle movement and

speeds and feeds in machining. %t calculates the traversing path of the axes as defined by the inputs. The #

controls the peripheral actuating elements of the machine such as solenoids relay coils etc. &or"ing togeth

the NC and #$C enable the machine tool to operate automatically. #ositioning and part accuracy depend on

CNC system's computer control algorithms the system resolution and the basic mechanical machine accura

Control algorithm may cause errors while computing which will reflect during contouring but they are v

negligible. Though this does not cause point to point positioning error but when mechanical mach

inaccuracy is present it will result in poorer part accuracy.

Computer Numerical Control (CNC) is a specialied and versatile form of oft Automation and

applications cover many "inds although it was initially developed to control the motion and operation

machine tools.

Computer Numerical Control may be considered to be a means of operating a machine through the use

discrete numerical values fed into the machine where the re!uired 'input' technical information is stored o

"ind of input media such as floppy dis" hard dis" C* +, ** /0 flash drive or +A card etc. T


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machine follows a predetermined se!uence of machining operations at the predetermined spe

necessary to produce a wor" piece of the right shape and sie and thus according to completely predicta

results. A different product can be produced through reprogramming and a low-!uantity production run

different products is 2ustified.


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1.2 CONI!UR"TION O T#E CNC SYSTEM

$%.1shows a schematic diagram of the wor"ing principle of a NC axis of a CNC machine and the interface o

CNC control.

CNC system

$%.1.2chematic diagram of a CNC machine tool

A CNC system consists of the following 7 ma2or elements5

a. %nput *evice

b. achine Control /nitc. achine Tool

d. *riving ystem

e. 4eedbac" *evicesf. *isplay /nit

1.2.1 Inp&t De'$ces

a. 4loppy *is" *rive

4loppy dis" is a small magnetic storage device for CNC data input. %t has been the most

common storage media up to the 189:s in terms of data transfer speed reliability storage

sie data handling and the ability to read and write. 4urthermore the data within a

NC(L

C

Ser'oDr$'e Ser'o Motor

Sp$n)le #ea)

*or+ p$ece

Ta,le

Enco)er

(os$t$on ee),ac+

Tacho

!enerator-eloc$ty

ee),ac+

Tape Rea)er

Tape (&nch

Other De'$ces

Mach$ne

Elements

Inp&ts

O&tp&ts

Lea)

Scre

Command

value

#roximity switches

$imit switches

+elay coils

#ressure switches

4loat switches


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floppy could be easily edited at any point as long as you have the proper program to read it.


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*irect Numerical Control is referred to a system connecting a set of numerically

controlled machines to a common memory for part program or machine program

storage with provision for on-demand distribution of data to the machines. (%),

3?:7518?:) The NC part program is downloaded a bloc" or a section at a time into the

controller. ,nce the downloaded section is executed the section will be discarded to

leave room for other sections. This method is commonly used for machine tools that do not

have enough memory or storage buffer for large NCpart programs.

*istributed Numerical Control is a hierarchical system for distributing data between a

production management computer and NC systems. (%, 3?:75188;) The host computer is

lin"ed with a number of CNC machines or computers connecting to the CNC

machines for downloading part programs. The communication program in the host

computer can utilie two-way data transfer features for production data communication

including5 production schedule parts produced and machine utiliation etc.


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Fig.1.2.1 Serial communication in a Distributed Numerical Control system

1.2.2 Mach$ne Control Un$t /MCU0

The machine control unit is the heart of the CNC system. There are two sub-units in the machine control u

the *ata #rocessing /nit (*#/) and the Control $oop /nit (C$/).

a.Data Processing Unit

,n receiving a part programme the *#/ firstly interprets and encodes the part programme into inter

machine codes. The interpolator of the *#/ then calculate the intermediate positions of the motion in ter

of 0$/ (basic length unit) which is the smallest unit length that can be handled by the controller. The calcula

data are passed to C$/ for further action.

,. Control Loop Unit

The data from the *#/ are converted into electrical signals in the C$/ to control the driving system

perform the re!uired motions. ,ther functions such as machine spindle ,N@,44 coolant ,N@,44 t

clamp ,N@,44 are also controlled by this unit according to the internal machine codes.


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1.2. Mach$ne Tool

This can be any type of machine tool or e!uipment. %n order to obtain high accuracy and repeatability

design and ma"e of the machine slide and the driving lead screw of a CNC machine is of vital importance. T

slides are usually machined to high accuracy and coated with anti-friction material such as #T4= and Turcite

order to reduce the stic" and slip phenomenon. $arge diameter recirculating ball screws are employed

eliminate the bac"lash and lost motion. ,ther design features such as rigid and heavy machine structure sh

machine table overhang !uic" change tooling system etc also contribute to the high accuracy and h

repeatability of CNC machines.

4ig.1.3.6.1 Ball Screw in a CNC machine 4ig.1.3.6.3 Ball screw structure


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1.2. Dr$'$n% System

The driving system is an important component of a CNC machine as the accuracy and repeatability depend v

much on the characteristics and performance of the driving system. The re!uirement is that the driving syst

has to response accurately according to the programmed instructions. This system usually uses electric mot

although hydraulic motors are sometimes used for large machine tools. The motor is coupled either directly

through a gear box to the machine lead screw to moves the machine slide or the spindle. Three types

electrical motors are commonly used.

a. DC Servo Motor

This is the most common type of feed motors used in CNC machines. The principle of operation is based on

rotation of an armature winding in a permanently energied magnetic field. The armature winding

connected to a commutator which is a cylinder of insulated copper segments mounted on the shaft. *C curr

is passed to the commutator through carbon brushes which are connected to the

machine terminals. The change of the motor speed is by varying the armature voltage and the contro

motor tor!ue is achieved by controlling the motor's armature current. %n order to achieve the necess

dynamic behaviour it is operated in a closed loop system e!uipped with sensors to obtain the velocity

position feedbac" signals.


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DC Ser'o Motor

,. "C Ser'o Motor

%n an AC servomotor the rotor is a permanent magnet while the stator is e!uipped with 6-phase

windings. The speed of the rotor is e!ual to the rotational fre!uency of the magnetic field of the stator which

regulated by the fre!uency converter. AC motors are gradually replacing *C servomotors. The main reason i

that there is no commutator or brushes in AC servomotor so that maintenance is virtually not re!uired.

4urthermore AC servos have a smaller power-to-weight ratio and faster response.

4ig.1.3.;.b AC ervo otor


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c. Stepp$n% Motor

A stepping motor is a device that converts the electrical pulses into discrete mechanical rotatio

motions of the motor shaft. This is the simplest device that can be applied to CNC machines since it

convert digital data into actual mechanical displacement. %t is not necessary to have any analog-

digital converter nor feedbac" device for the control system. They are ideally suited to open loop systems.


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1.2.3 ee),ac+ De'$ce

%n order to have a CNC machine operating accurately the positional values and speed of the axes need to be

constantly updated. Two types of feedbac" devices are normally used positional feedbac" device and veloci

feedbac" device.

a.Positional Feed Back Devices

There are two types of positional feedbac" devices5 linear transducer for direct positional measurement and

rotary encoder for angular or indirect linear measurement.

a.1 L$near Trans)&cers 4

A linear transducer is a device mounted on the machine table to measure the actual displacement of the

slide in such a way that bac"lash of screws motors etc would not cause any error in the feedbac" data. This

device is considered to be of the highest accuracy and also more expensive in comparison with other measuri

devices mounted on screws or motors.

$%.1.2.3.a.1 L$near Trans)&cer


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a.2 Rotary Enco)ers 4

A rotary encoder is a device mounted at the end of the motor shaft or screw to measure the angular

displacement. This device cannot measure linear displacement directly so that error may occur due to the

bac"lash of screw and motor etc. Denerally this error can be compensated for by the machine

builder in the machine calibrationprocess.

$%.1.2.3.a.2 Incremental an) ",sol&te Rotary Enco)er


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,. -eloc$ty ee),ac+ De'$ce

The actual speed of the motor can be measured in terms of voltage generated from a tachometer mounted at

end of the motor shaft.*C tachometer is essentially a small generator that produces an output volt

proportional to the speed. The voltage generated is compared with the command voltage corresponding to

desired speed. The difference of the voltages can is then used to actuate the motor to eliminate the error.

4ig.1.3.>.b Tachogenerator


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1.2.5 D$splay Un$t

The *isplay /nit serves as an interactive device between the machine and the operator. &hen the machine

running the *isplay /nit displays the present status such as the position of the machine slide the spindle

+# the feed rate the part programmes etc. %n an advanced CNC machine the *isplay /nit can show the

graphics simulation of the tool path so that part programmes can be verified before the actually

machining. uch other important information about the CNC system can also displayed for maintenance an

installation wor" such as machine parameters logic diagram of the programmer controller error massages an

diagnostic data.

Ser'o Dr$'e chapter 2

A servo drive consists of a servo amplifier and a servo motor. The main tas" of a servo amplifier (also cal

amplifier servo controller or 2ust controller) is the control of the motor current. %n addition =+ se

amplifiers offer a broad spectrum of functionality

&hile most of the electrical drives are operated at constant speed a servo drive has a rather EhecticE life. ,f

it has to accelerate to the rated speed within a few milliseconds only to decelerate a short time later 2ust

!uic". And of course the target position is to be reached exactly with an error of a few hundredths of a m

-meter.

Compared to other controlled drives servo drives have the advantage of high dynamics and accuracy full s

tor!ue and compact motors with high power density.

ervo drives are used where high dynamics (i. e. fast acceleration and deceleration) and good accuracy

reaching target positions are important. The good control behaviour allows the optimal adaptation to

application (e. g. positioning without overshoot). 0ut also the smooth run (due to sinusoidal commutation)


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the possibility of exact synchronisation of two or more drives open a wide field. 0ecause of their wide sp

range servo drives can be used in a huge number of applications.

ervo drives run in large highly automated installations with several doens of axes as well as in machines w

only a few axes which perhaps operate independently.

2.1 Ser'o motor

ervo motors are electric motors that are designed specially for high dynamics. ervo motors by =

distinguish themselves by a compact design with high power density and a high degree of protection (up to

7>). They come as AC servo motors (brush less) or *C servo motors (with brushes for the commutation). T

high power density is achieved by permanent magnets made of neodymium-iron-boron (Nd4e0) samariu

cobalt (mCo) or ferrite material. The servo motor is e!uipped with a position sensor which provides

controller with position and speed information.

As a standard the AC servo motors are e!uipped with resolvers. %n combination with the digital se

amplifiers sincos encoders (absolute encoder single-turn or multi-turn) and high-resolution incremen

encoders may be used as well in case higher accuracy or dynamics is re!uired. The *C servo motors can

e!uipped with tacho generators and@or incremental encoders. 4or dimensioning the motor the following d

are important5 the mass of the parts to be moved the cycle time of the application and the friction tor!ue. &

these data the rated and pea" tor!ue (maximum acceleration or deceleration) and the rated speed can

calculated. %f re!uired gears are used to match the moment of inertia of the motor to the moment of inertia

the application.

2.2 Ser'o ampl$6$er

The servo amplifier (also called amplifier servo controller or 2ust controller) controls the current of the mo

phases in order to supply the servo motor with exactly the current re!uired for the desired tor!ue and the desi

speed. The essential parts of a servo amplifier are the power section and the control loops.


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The power section consists of a mains rectifier a *C-bus and a power circuit which supplies the individ

motor phases with current.

The control loops (analogue or digital) drive the power circuit and by constantly comparing setpoint with act

values ensure that the motor "eeps exactly to the desired motions even under varying load.

SYSTEM

SINUMERI7 SIEMENS

8 9

9

8;

;

(O*ERON

=mergency top

Cycle

$%.2.2Typical numerical control configuration of


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2. Operator Control (anel

$%. shows a typical


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3. Color displays

Operator>s an) mach$ne panel

SYSTEM

SINUMERI7 SIEMENS

8 9

9

8;

;

(O*ER

ON

=mergency top

Cycle

Control elements an) $n)$cators o6 the operator>s panel

#rogram in progress

4eed hold

#osition not yet reached

(achine in motion)

Alarm

0asic display

Tool compensation

Gero offset

Test

#art program

CRT

$=*-indicator

4or assignment,f "eys

Change to actual

value display

Change of display

$eaf forwards

$eaf bac"wards

+ight-$eft Cursor

+eset changeover

Assignment of "eCancel word

Alter word

=nter word

Change over to

customer display

,perator guidanc

esNo

*elete input

tart$%.2..1,perator control panel of


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2..2#ey$oard

A "eyboard is provided for the following purposes5

=diting of part programs tool data and machine parameters.

election of different pages for viewing.

election of operating modes e.g. manual data input.

election of feed rate override and spindles speed override.

=xecution of part programs.

=xecution of other toll functions.

2. Mach$ne Control (anel /MC(0

%t is the direct interface between operator and the NC system enabling the operation of the machine through

CNC system. $%.3shows the C# of


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Control elements o6 the mach$ne control panel

2.%.1 Modes o& operation

Denerally the CNC system can be operated in the following modes5

anual mode

anual data input (*%) mode

Automatic mode

+eference mode

%nput mode

,utput mode etc.

8 9

9

8;

;

(O*ERON

=mergency top

Cycle

ode selectorwitch

pindle speedoverride

4eedrate@rapid traverseoverride

+apid traverse activate

*irection "eys

pindleO ON

4eed


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2.%.1.1 Man'al mode(

%n this mode movement of a machine slide can carried out manually by pressing the particular 2og button

or -). The slide (axis) is selected through an axis selector switch or through individual switches (e.g. BH

H - GH G- etc.). The feed rate of the slide movement is prefixed. CNC system allows the axis to be 2ogg

at high feed rate also. The axis movement can also be achieved manually using a hand wheel interface inst

of 2og buttons. %n this mode slides can be moved in two ways5

Continuous

%ncremental

2..1.1.1 Cont$n&o&s mo)e: %n This mode the slide will move as long as the 2og button is pressed.

2..1.1.2 Incremental mo)e:


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------ Gero offsets (G,)

------ Test data etc.

*eac+,in

ome system allows direct manual input of a program bloc" and execution of the same. The bloc"s th

executed can be chec"ed for correctness of dimensions and conse!uently transferred into the program mem

as part program.

Play$ack

%n setting up modes li"e 2og or incremental the axis can be traversed either through the direction "eys or via

hand wheel and the end position can be transferred into the system memory as command values. 0ut

re!uired feed rates switching functions and other auxiliary functions have to be added to the part program

program editing mode.

Thus teach-in and playbac" operating method allows a program to created during the first component pr

out.

2.%.1.3 -'tomatic Mode !-'to and Single Block"

%n this mode the system allows the execution of a part program continuously. The part program is execu

bloc" by bloc". &hile one bloc" is being executed the next bloc" is read by the system analyed and "

ready for execution. =xecution of the program can be one bloc" after another automatically or the system w

execute a bloc" stop the execution of the next bloc" till it is initiated to do so (by pressing the start butto

election of part program execution continuously (-'to) or one bloc" at a time (Single Block) is done throu

the machine control panel.

any systems allow bloc"s (single or multiple) to be retraced in the opposite direction. 0loc" retrace is allow

only when a cycle stop state is established. #art program execution can resume and its execution begins with


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retraced bloc". This is useful for tool inspection or in case of tool brea"age. #rogram start can be effected at a

bloc" in the program through the 0$,CF =A+C< facility.

2.%.1.% e&erence Mode

/nder this mode the machine can be referenced to its home position so that all the compensations (e.g. pi

error compensation) can be properly applied. #art programs are generally prepared in absolute mode w

respect to machine ero. any CNC systems ma"e it compulsory to reference the slides of the machine to th

home positions before a program is executed while others ma"e it optional.

2.%.1./ )np't Mode and 0'tp't Mode !)0 Mode"

%n this mode the part programs machine setup data tool offsets etc. can be loaded@unloaded into@from

memory of the system from external devices li"e programming units magnetic cassettes or floppy discs e

*uring data input some systems chec" for simple errors (li"e parity tape format bloc" length un"no

characters program already present in the memory etc.). Transfer of data is done through a +363C

+;33C port.

Other (er$pherals

These include sensor interface provision for communication e!uipment programming units printer t

reader@puncher interface etc.


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INTER"CIN! chapter

%nterconnecting the individual elements of both the machine and the CNC system using cables and connector

called interfacing.

=xtreme care should be ta"en during interfacing. #roper grounding in electrical installation is most essent

This reduces the effects of interference and guards against electronic shoc" to personnel. %t is also essential

properly protect the electronic e!uipment.

Cable wires of sufficiently large cross-sectional area must be used. =ven though proper grounding reduces

effect of electrical interference signal cable re!uires additional protection. This is generally achieved by us

shielded cables. All the cable shields must be grounded at control only leaving other end free. ,ther no

reduction techni!ues include using suppression devices proper cable separation ferrous metal wire ways

=lectrical enclosures should be designed to provide proper ambient conditions for the controller.

MONITORIN! chapter

%n addition to the care ta"en by the machine tool builder during design and interfacing basic control a

includes constantly active monitoring functions. This is in order to identify faults in the NC the interf

control and the machine at an large stage to prevent damages occurring to the wor" piece tool or machine.

fault occurs first the machining se!uence is interrupted the drives are stopped the cause of the fault is sto

and then displayed as an alarm. At the same time the #$C is informed that an NC alarm exits. %n


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#osition encoders and drives

Contour

pindle speed

=nable signals

oltage

Temperature

icroprocessors

*ata transfer between operator control panel and logic unit

Transfer between NC and #$C

Change of status of buffer battery

ystem program memory

/ser program memory

erial interfaces

DI"!NOSTICS chapter 3

The control will generally be provided with test assistance for service purposes in order to display some sta

on the C+T such as5

%nterface signals between NC and #$C as well as between #$C and machine

4lags of the #$C

Timers of the #$C

Counters of the #$C

%nput@output of the #$C


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4or the output signals it is also possible to set and generate signal combinations for test purposes in order

observe how the machine react to a changed signal. This simplifies trouble shooting considerably.

M"C#INE D"T" chapter 5

Denerally a CNC system is designed as a general-purpose control unit which has to be matched with

particular machine to which the system is interfaced. The CNC is interfaced to the machine by means of da

which is machine specific. The NC and #$C machine data can be entered and changed by means of exter

e!uipment or manually by the "eyboard. These data are fixed and entered during commissioning of the mach

and generally left unaltered during machine operations.

achine data entered is usually relevant to the axis travel limits feed rates rapid traverse speeds and spin

speeds position control multiplication factor Fv factor acceleration drift compensation ad2ustment

reference point bac"lash compensation pitch error compensation etc. Also the optional features of the con

system are made available to the machine tool builder by enabling some of the bits of machine data.

"ppl$cat$ons o6 CNC Mach$nes

CNC machines are widely used in the metal cutting industry and are best used to produce

the following types of product5

I #arts with complicated contours

I #arts re!uiring close tolerance and@or good repeatability

I #arts re!uiring expensive 2igs and fixtures if produced on conventional

machines


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I #arts that may have several engineering changes such as during

the development stage of a prototype

I %n cases where human errors could be extremely costly

I #arts that are needed in a hurry

I mall batch lots or short production runs

)ome common types of CNC machines and instruments used in industry are as

following5

I *rilling achine

I $athe @ Turning Centre

I illing @ achining Centre

I Turret #ress and #unching achine

I &irecut =lectro *ischarge achine (=*)

I Drinding achine

I $aser Cutting achine

I &ater Jet Cutting achine

I =lectro *ischarge achine

I Coordinate easuring achine

I %ndustrial +obot


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(LC (RO!R"MMIN! chapter ?

?.1 (ro%ramma,le Lo%$c Controller /(LC0

A #$C matches the NC to the machine. #$Cs were basically introduced as replacement for hard wired re

control panels. They were developed to be reprogrammed without hardware changes when re!uirements w

altered and thus are reusable. #$Cs are now available with increased functions more memory and la

input@output capabilities. $%.?gives the generalied #$C bloc" diagram.

%n the C#/ all the decisions are made relative to controlling a machine or a process. The C#/ receives in

data performs logical decisions based upon stored programs and drives the outputs. Connections to a compu

for hierarchical control are done via the C#/.

The %@, structure of the #$Cs is one of their ma2or strengths. The inputs can be push buttons limit switch

relay contacts analog sensor selector switches proximity switches float switches etc. The outputs can

motor starters solenoid valves position valves relay coils indicator lights $=* displays etc.

The field devices are typically selected supplied and installed by the machine tool builder or the end user. T

voltage level of the field devices thus normally determines the type of %@,. o power to actuate these devi

must also be supplied external to the #$C. The #$C power supply is designated and rated only to operate the

internal portions of the %@, structures and not the field devices. A wide variety of voltages current capaci

and types of %@, modules are available.


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The principle of operation of a #$C is determined essentially by the #$C program memory processor inp

and outputs.

The program that determines #$C operation is stored in the internal #$C program memory. The #$C opera

cyclically i.e. when a complete program has been scanned it starts again at the beginning of the program.

the beginning of each cycle the processor examines the signal status at all inputs as well as the external tim

and counters and are stored in a process image input (#%%). *uring subse!uent program scanning the proces

the accesses this process image.

To execute the program the processor fetches one statement after another from the programming memory

executes it. The results are constantly stored in the process image output (#%,) during the cycle. At the end o

scanning cycle i.e. program completion the processor transfers the contents of the process image output to

output modules and to the external timers and counters. The processor then begins a new program scan.

(ro%ramm$n%

Un$ts

Tape

Rea)er

(r$ntersTape

(&ncher


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$%.?.1.1 ystem with peripheral devices

$%.?.1.2 Deneralied #$C bloc" diagram

*hat )oes @(LCA meanB

A #$C (#rogrammable $ogic Controllers) is an industrial computer used to monitor inputs and depending

upon their state ma"e decisions based on its program or logic to control (turn on@off) its outputs to automate

machine or a process.

(RO!R"MM"LE LO!IC CONTROLLER

A digitally operating electronic apparatus which uses a programmable memory for the internal

storage of instructions by implementing specific functions such as logic sequencing, timing, countin

and arithmetic to control, through digital or analog input/output modules, various types of machines

processes.

Tra)$t$onal (LC "ppl$cat$ons

%n automated system #$C controller is usually the central part of a process control system.

KTo run more complex processes it is possible to connect more #$C controllers to a central computer.

Disadvantages o& PLC control

- Too much wor" re!uired in connecting wires.

- *ifficulty with changes or replacements.

(rocessor Lo%$c

memory

Stora%e

memory

(oer

S& l

Inp&ts

O&tp&ts

(oer

S&pply

(ro%rammer $el)

De'$ces


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- *ifficulty in finding errors re!uiring s"illful wor" force.

- &hen a problem occurs hold-up time is indefinite usually long.

-dvantages o& PLC control

K +ugged and designed to withstand vibrations temperature humidity and noise.

K


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subsystems li"e +emote Telemetry /nits


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- The control bus for signals relating to internal control actions

- The system bus is used for communications between the %@, ports and the %@, unit.

?.. Memory

ystem (+,) to give permanent storage for the operating system and the fixed data used by the C#/.

+A for data. This is where information is stored on the status of input and output devices and the values of

timers and counters and other internal devices. =#+, for +,Ms that can be programmed and then the

program made permanent.

?.. IFO Sect$ons

%nputs monitor field devices such as switches and sensors.

,utputs control other devices such as motors pumps solenoid valves and lights.

?..3(oer S&pply

ost #$C controllers wor" either at 3; *C or 33: AC. ome #$C controllers have electrical supply as a

separate module while small and medium series already contain the supply module.

?..5 (ro%ramm$n% De'$ce

The programming device is used to enter the re!uired program into the memory of the processor.

The program is developed in the programming device and then transferred to the memory unit of the #$C.

?. (LC O(ER"TIONS:

?..1 Inp&t Relays

These are connected to the outside world. They physically exist and receive signals from switches sensors e

Typically they are not relays but rather they are transistors.

?..2 Internal Ut$l$ty Relays

These do not receive signals from the outside world nor do they physically exist. They are simulated relays an

are what enables a #$C to eliminate external relays.


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There are also some special relays that are dedicated to performing only

one tas".

?.. Co&nters

These do not physically exist. They are simulated counters and they can be programmed to count pulses.

Typically these counters can count up down or both up and down. ince they are simulated they are limited i

their counting speed.

ome manufacturers also include highspeed counters that are hardware based.

?.. T$mers

These also do not physically exist. They come in many varieties and increments.

The most common type is an on-delay type.

,thers include off-delay and both retentive and non-retentive types. %ncrements vary from 1ms through 1s.

?..3 O&tp&t Relays

These are connected to the outside world. They physically exist and send on@off signals to solenoids lights e

They can be transistors relays or triacs depending upon the model chosen.

?..5 Data Stora%e

Typically there are registers assigned to simply store data. /sually used as temporary storage for math or data

manipulation.

They can also typically be used to store data when power is removed from the

#$C.

The S$mat$c S3 (LCis an automation system based on #$C. %t was manufactured and sold by iemens.

automation systems control process e!uipment and machinery used in manufacturing.

T=# > programming language is used for writing user programs for %AT%C > programmable controlle

The program can be written and entered into the programmable controller as in5


36/43

tatement list (T$) $%.?..5(a)

Control system flowchart (C4) $%.?..5(b)

$adder diagram ($A*) $%.?..5(c)

/a0

$%.?..5#rogrammable controller

Thestatement listdescribes the automation tas" by means of mnemonic function designations.

The control system flowchart is a graphic representation of the automation tas".

The ladder diagram uses relay ladder logic symbols to represent the automation tas".

The statement is the smallest T=# > program component. %t consists of the following5

,peration i.e. what is to be done?

=.g. A AN* operation (series connection), ,+ operation (parallel connection)

=T operation (actuation)

tatement list

T$

A % 3.6

A % ;.1

, % 6.3 1.7

A % 3.6

A % 3.6

% 3.6

AN

*

,

+

% 3.6

% ;.1

% 6.3 O 1.7

tatement

,perand,peration

,perand identifier

#arameter

/,0Control system flow

chart C4

/c0$adder diagram $A*

% 3.6 % ;.1

% 6.3


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,perand i.e. what is to be done withP

=.g. % ;.> i.e. with the signal of input ;.>

The operand consists of5

,perand identifier (% input O output 4 flag etc.)

#arameter i.e. the number of operand identifiers addressed by the statement. 4or inputs outputs a

flags (internal relay e!uivalents) the parameter consists of the byte and bit addresses and for timers a

counter byte address only.

The statement may include absolute operands e.g. % >.1 or symbolic operand e.g. % $1. #rogramming

considerably simplified in the later case as the actual plant designation is directly used to describe the dev

connected to the input or output.

Typically a statement ta"es up one word (two bytes) in the program memory.

STRUCTURED (RO!R"MMIN! chapter G

The user program can be made more manageable and straightforward if it is bro"en down into relative sectio

arious software bloc" types are available for constructing the user program.

8. !rogram bloc"s !PB"contain the user program bro"en down into technologically or functionally rela

sections (e.g. program bloc" for transportation monitoring etc.). 4urther bloc"s such as program bloc"s

function bloc"s can be called from a #0.

8.# $rgani%ation bloc"s !0B0 contain bloc" calls determining the se!uence in which the #0s are to

processed. %t is therefore possible to call #0s conditionally (depending on certain conditions).

%n addition special ,0s can be programmed by the user to react to interruptions during cyclic programm

processing. uch an interrupt can be triggered by a monitoring function if one or several monitored eve

occur.


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8.& 'unction bloc" !FB0 is bloc" with programs for recurrent and usually complex function. %n addition to

basic operations the user has a extended operation at his disposal for developing function bloc"s. The progr

in a function bloc" is usually not written with absolute operands (e.g. % 1.>) but with symbolic operands. T

enables a function bloc" to be used several times over with different absolute operands.

4or even more complex functions standard function bloc"s are available from a program library. uch 40s

available e.g. for individual controls se!uence controls messages arithmetic operations two step cont

loops operator communications listing etc. These standard 40s for complex functions can be lin"ed it the u

program 2ust li"e user written 40s simply by means of a call along with the relevant parameters.

8.( )he *equence bloc" !SB0contain the step enabling conditions monitoring times and conditions for

current step in se!uence cascade. e!uence bloc"s are employed for example to organise the se!uence casc

in communication with a standard 40.

8.+ )he data bloc"s !DB0 contain all fixed or variable data of the user program.

CYCLIC (RO!R"M (ROCESSIN! chapter H

The bloc"s of the user program are executed in the se!uence in which they specified in the organisation bloc"

INTERRU(T DRI-EN (RO!R"M (ROCESSIN! chapter 1

&hen certain input signal changes occur cyclic processing is interrupted at the next bloc" boundary and an ,

assigned to this event is started. The user can formulate his response program to this interrupt in the ,0. T

cyclic program execution is the resumed from the point at which it was interrupted.

TIME CONTROLLED (RO!R"M EECUTION chapter 11

Certain ,bs are executed at the predetermined time intervals (e.g. every 1::ms 3::ms >::ms 1s 3s and >

4or this purpose cyclic program execution is interrupted at the bloc" boundary and resumed again at this po

once the relevant ,0 has been executed. $%.1 gives the organisation and execution of a structured u

program.


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#01

#03 406

403,01

tructured programming

#0 40

#0 40

,rganisation bloc" (,0)#rogram bloc" (#0) 4unction bloc" (#0)

Cycle execution

,0

#0 40,0

%nterrupt-driven execution


40/43

$%.11 ,rganisation and execution of a structured user program

E"M(LES O (LC (RO!R"M chapter 12

0efore attempting to write a #$C program first go through the instruction set of the particular language u

for the e!uipment and understand the meaning of each instruction. Then study how to use these instruction

the program (through illustration examples given in the manual). ,nce the familiariation tas" is over then s

writing the program.

4ollow the following steps to write a #$C program.

$ist down each individual element (field device) on the machine as %nput@,utput.

%ndicate against each element the respective address as identifier during electrical interfacing of th

elements with the #$C.

0rea" down the complete machine auxiliary functions that are controlled by the #$C into individual s

contained functions.

%dentify each individual function as separate bloc" (#0xx@40xx)

,nce the #0s and 40s for each function are identified ta"e them one by one for writing the program.

$ist down the preconditions re!uired for the particular function separately.

Note down the address of the listed elements.

#oints at which interrupt-driven program can be inserted

tart and finish of interrupt-driven program execution


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&rite down the flow chart for the function.

Translate the flow chart into #$C program using the instructions already familiaried.

Complete the program translation of all individual functions in similar lines.

Chec" the individual bloc"s independently and correct the program to get the re!uired results.

,rganie all the program bloc"s in the organiation bloc" depending upon the se!uence in which they

supposed to be executed as per the main machine function flow chart.

Chec" the complete program with all the bloc"s incorporated in the final program.

4ample 12.1( Spindle 05

(recon)$t$ons ee),ac+ elements "))ressa&lt $n)$cat$on "))ressRemar+

Tool clamp #ressure switch % 3.; $amp O 3.1

Job clamp #roximity switch % 6.3 $amp O 1.9*oor close $imit switch % >.9 $amp O ;.:

$ubrication ,N #$C output bit O 1.: $amp O 9.9

*rive ready %nput signal from % ;.7 $amp O :.;*rive unit

#0 13 written is the individual function module for spindle ,N for all the preconditions chec"ed and fou

satisfactory. This function is re!uired to be executed only when the spindle rotation is re!uested by the NC

the form of a bloc" in the part program.

&henever NC decodes the part program bloc" it in turn informs the #$C through a fixed buffer location t

spindle rotation is re!uested. ay 4lag bit 4 1::.: is identified for this information communication. &ith t

data spindle ,N function module can be recalled in the organisation bloc" ,01 as follows.

,0 1

QQ


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A 4 1::.:

JC #013

QQ

0=

Now spindle ,N function module #013 will be executed only when 4 1::.: is set. ,therwise the funct

execution will be bypassed.

LO* C#"RT chapter 1

TA+T

T,,$ C$A#

J,0 C$A#

*,,+ C$,=*

$/0+%CAT%,N

,N

*+%= +=A*

%N*%CAT=

4A/$T

%N*%CAT=

4A/$T

%N*%CAT=4A/$T

%N*%CAT=

4A/$T

%N*%CAT=

4A/$T

#013

AN % 3.; Tool not clamped

O 3.1 *isplay fault lamp

AN % 6.3 Job not clamped


AN % >.9 *oor not closed

O ;.: *isplay fault lamp

AN O 1.: $ubrication not on


AN % ;.7 *rive not ready

O :.; *isplay fault lamp

Comments

=

=

=

=

=

N,

N,

N,

N,

N,

=


43/43

AN 4A/$T

*, #%N*$=,N

=N*

T,#

#%N*$=,N % 3.; Tool not clamped

,N % 6.3 Job not clamped

,N % >.9 *oor not closed

,N O 1.: $ubrication not on

,N % ;.7 *rive not ready

+ O 79.6 +eset spindle enable bit0=C 0loc" end conditionally

A % 3.; Tool clamped

A % 6.3 Job clamped

A % >.9 *oor closed

A O 1.: $ubrication ,N

A % ;.7 *rive ready

O 79.6 et spindle enable bit

0= 0loc" end

=xit

N,

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