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Lab2A:RobotDCMotor

ECEN2270 ElectronicsDesignLaboratory 1

Characterization,modeling,

and

simulation

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ECEN2830 ElectronicsDesignLaboratory 2

DiscussionItems

Labreports:

must

be

uploaded

via

D2L

dropbox by

the

deadline

Onereportpergroup,includebothnamesonthefrontpage

Attendanceisrequired!!!!!!!

TakeawayfromLab1demos

Donotrushthroughthelab;takethetimetounderstandwhatyouaredoingandwhy

Makesure

both

partners

know

and

understand

all

aspects

of

the

lab;donotsplitportionsofthelabbetweenpartnerstorushthrough

ReviewcarefullytheLectureslidesandtheLabTasks,includingthestatementsonwhattoincludeinthefinalreport

DosotodaybeforestartofLab2tomorrow!

ElectronicsDesignLaboratory 2ECEN2830

7/29/2019 Lecture Lab2 PartA

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ECEN2830 ElectronicsDesignLaboratory 3

Lab2,PartA

Broaderobjectives:

working

with

aload

Understandthephysicalbehavioroftheload:DCmotor

DevelopinganelectricalmodelfortheDCmotorasaload

Experimentallyfinding

model

parameters

Performingdesignandsimulationusingmodels

Hardwareimplementation,verification,andtesting

ElectronicsDesignLaboratory 3ECEN2830

7/29/2019 Lecture Lab2 PartA

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ECEN2830 ElectronicsDesignLaboratory 4

Robotplatform

TwoDCmotors,eachdrivingawheel

+

_

VDC

IDC

wheel

64:1

gearOptical

encoder:

12 pulses

permotor

shaft

rotation

DCmotor

1 2 3 4

1EncoderpowersupplyVCC=+710V

2Encoderground

3EncoderoutputpulsesA,frequencyfenc4EncoderoutputpulsesB,frequencyfenc

DCsupply

10

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ECEN2830 ElectronicsDesignLaboratory 5

DCMotorbasics:TorqueT

Diagramfrom:http://www.animations.physics.unsw.edu.au/jw/electricmotors.html

+

_

VDC

righthandrule

IDC

IDC

Armature

winding

BlIF DC

Force[N] Current[A]

Vectoralignedwith

theconductorof

lengthl,direction

alignedwith

currentdirection

Magnetic

fluxdensity

vector[T]

Torque[Nm]DCkIT

k=motorconstant[Nm/A]

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ECEN2830 ElectronicsDesignLaboratory 6

DCMotorbasics:ElectromotiveForce(EMF)

Diagramfrom:http://www.animations.physics.unsw.edu.au/jw/electricmotors.html

+

_

VDC

righthandrule

IDC

IDC dt

dVEMF

InducedEMF[V]

Rateofchangeof

magneticflux

throughthe

armaturewinding

kVEMF

Faradayslaw

of

induction

Armature

winding

k=motorconstant[Nm/A],[V/(rad/s)]

InducedEMF

[V] Speed

[rad/s]

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ECEN2830 ElectronicsDesignLaboratory 7

DCmotorequations

kVEMF

Electricalmodel(armaturecircuit)

EMFDC

MDCMDC V

dt

dILIRV

Mechanicalmodel

loadTBdtdJT

DCkIT

J =momentofinertia

B =frictioncoefficient

extintload TTT Loadtorqueisacombinationofinternal

gearboxloadandexternalload

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ECEN2830 ElectronicsDesignLaboratory 8

DCmotorequivalentcircuitmodel

+

+

VDC

_

IDCLM RM

VEMF= k T = kIDC

Tload1/BJ

EMFDC

MDCMDC V

dt

dILIRV

loadTB

dt

dJT

kVEMF DCkIT

Considerhowtomeasureallcircuitparametersfromthemodel

Requiresmeasurement

of

inputterminals,VDCandIDC

frequency inrad/s useopticalencoder

extintload TTT

Combinedinternal

gearandloadtorque

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ECEN2830 ElectronicsDesignLaboratory 9

Opticalencoder

Encoderoutputpulses,frequencyfenc

[Hz]is

proportionalto speed

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ECEN2830 ElectronicsDesignLaboratory 10

Speedconversions

n =wheelspeed,rotationsperminute[rpm]

n/60=wheelspeed,rotationspersecond[rps]

=wheelrotationalspeed[rad/s]=2n/60 Usedinmodelequationsnm =motorshaftspeed,nm =(gearratio)*n =64n[rpm]fenc =frequencyofencoderpulses[Hz]=12*nm/60=12*64*n/60[Hz]

Example:wheelspeedis1

rotationpersecond:1rps

n =60rpm

=2 rad/s=6.28rad/s

nm =64*60rpm=3840rpm

fenc =12*nm/60=768Hz

6412

2

encf

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ECEN2830 ElectronicsDesignLaboratory 11

Opticalencoder:direction

counterclockwise

clockwise

Encoderpulse

outputA

Encoderpulse

outputB

Encoderpulse

outputA

Encoderpulse

outputB

InLab

2,

only

one

encoder

pulse

output

is

needed

Optionalextracreditusesbothpulsestodeterminedirection

A B

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ECEN2830 ElectronicsDesignLaboratory 12

Encodercircuit

+VCC=+5V

GND

PulseoutA

Pulseout

B

LEDsPhoto

transistors Logicinverters(shape

thesensedsignalsinto

squarewaveoutput

pulses)

Encoderconnector

(encoderinternallyuses

a+5Vpowersupply;

externally,wecan

supplyany

supply

voltagebetween7Vand

10V)

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ECEN2830 ElectronicsDesignLaboratory 13

DCMotorSpicemodel

Modelparameters

tobedetermined

byexperiments:

RM,k,J,B,Tint

Internaltorqueload

fromgearbox,Tint

Encodermodel:

correct

speed

to

fenc frequencyconversionhasalready

beendone,noneedtochangeanythinginthispartofthemodel

Inputandoutput

portsdefined

DownloadthemodelfromtheLab2website

Onlyeditthemodeldesignatedparameters

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ECEN2830 ElectronicsDesignLaboratory 14

TestingSpicemodel

ElectronicsDesignLaboratory 14

Externalload

torque

Textattachedhere

Externalload

mustsinkto

ground Simulationsetupto

1. Startmotor:

bring

up

VDC,

over

first

1ms

2. Pulseloadtorque:0A(noload)forfirst50ms,1Afornext50ms

3. Stopmotor:bringdownVDCfrom100msto101ms,10Vto0V

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ECEN2830 ElectronicsDesignLaboratory 15

MotorSimulationResults

ElectronicsDesignLaboratory 15

+

+

VDC

_

IDCLM RM

VEMF= k T = kIDC

Tload1/BJ

EMFDC

MDCMDC Vdt

dILIRV loadTB

dt

dJT

kVEMF DCkIT

Considerwaveforms

and

model

in

each

mode:

motor

start,

load

change,

motor

stop

extintload TTT

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ECEN2830 ElectronicsDesignLaboratory 16

Findingmodelparametersfromexperiments

RM fromlockedmotortest

kfromspeedasafunctionofvoltage,unloadedmotor

B and

Tint from

internal

losses,

unloaded

motor J fromatransient:considerpoweronorofftransient

+

+

VDC

_

IDCLM RM

VEMF= k T = kIDC

Tload1/BJ

EMFDC

MDCMDC Vdt

dILIRV loadTBdtdJT

kVEMF DCkIT extintload TTT

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ECEN2830 ElectronicsDesignLaboratory 17

Lab2objectives

PartA

MeasureDCmotorcharacteristics

DevelopaSpicecircuitmodelfortheDCmotoranddetermine

modelparameters

based

on

experiments

Validatethemodel:compareexperimentalandsimulationresults

PartB

UseDC

motor

Spice

model

to

design

aspeed

sensor

(tachometer)

circuitthatoutputsvoltageproportionaltowheelspeed

Build,testanddemothespeedsensorcircuit