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Constant Current Control of Stepper Motor inMicrostepping Mode using PIC16F877A

B. S. Somesh 1 A. Mu!her"ee # S. Sen$ P. %arma!ar &

1AcSI'(CM)'I Ph * Scholar+ # $ &)lectronics and Instrumentation ,a-CSI'(Central Mechanical )ngineering 'esearch Institute

*urgapur India

Abstract This paper presents a microstepping steppermotor with constant current control algorithm for a precisionpositioning system. An open loop microstepping controller hasbeen developed without position feedback. A constant currentcontrol algorithm has been designed with the feedback current tomaintain the phase currents constant at any desired level. Thecurrent regulation of PMSM results in improvement ofpositioning accuracy of the system. The system has beensimulated using MATLA !S"M#L"$% and the controller hasbeen implemented using low cost P"&'()*++A microcontroller.The simulation and e,perimental results depict the effectivenessof the controller.

Keywordsmicrostepping; stepper motor; current control;

I. I /'0* C/I0

Permanent magnet stepper motor 2PMSM3 has -ecome popular in positioning applications -ecause of their dura-ilit4high efficienc4 simplicit4 and relia-ilit4 as 5ell as high tor ueto inertia ratio and a-sence of rotor 5inding 1 # . It 5or!sconsidera-l4 5ell in open loop control. 9o5e:er in precise

positioning application the standard PMSM has some pro-lems$ . Standard PMSM usuall4 ha:e large 21;#< o. /he microstepping control of stepper motoris useful in precision positioning control s4stem. It has -eenimplemented in PIC microcontroller and also in MA/,AB(SIM ,I %. /he stepper motor has -een simulated using themathematical model as discussed -elo5.

B. Mathematical Model of the Stepper Motor

/he follo5ing parameters are used for the purpose of definingthe mathematical modelE

1 # and i 1 i# are the :oltages and currents in phases A and B.

is the rotor speed is the rotor position

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B is the friction coefficientG is the inertia of the motor % is the motor to ue constant' is the resistance of the phase 5indingL is the inductance of the phase 5indingN is the num-er of the rotor teeth.

/he inductance change detent tor ue and slightmagnetic coupling -et5een the phases are neglected in thismodel. Ideal sinusoidal flu distri-ution is assumed 11 . /hestate space representation of the d4namical e uation is

H f(x,u) 11 16 5here

x H is state :ector and u H is the input.

/he d4namical e uation is gi:en -4E

H

213

H

2#3

H

2$3

H

2&3/he mathematical model discussed a-o:e along 5ith the

current control algorithm has -een implemented in theMA/,AB(SIM ,I %

III. C '') / C0 /'0, A ,D0'I/9M

/he current has -een controlled -4 controlling the 5idth of thedut4 c4cle of the sinusoidal pulse 5idth modulated signal2SPJM3 signal. A sine loo! up ta-le 2S, /3 has -eengenerated 5here the dut4 c4cle :aries sinusoidall4. Currenthas -een controlled -4 controlling the 5idth of the dut4 c4cleof the S, /. /he feed-ac! current has -een compared 5iththe desire current limit 2I min K Id K Ima 3. If the feed-ac! current2If 3 is greater than the ma imum current limit 2I ma 3 then the5idth of the dut4 c4cles of SPJM has -een decreased -4 a

fraction. In case of the feed-ac! current is smaller than theminimum current 2I min3 limit then the 5idth of the same has

-een increased -4 a fraction. /he flo5 diagram of the currentcontrol algorithm has -een sho5n in fig #.

Fig 1. Stepper motor current control -loc! diagram

Fig 1. Bloc! diagram of microstepping stepper motor precision positionings4stem

Yes

Yes

No

No

Start

Select duty cycle ofSPWM from SLUT

Check phaseangle=1 ! ! orphase angle=! !

Check " f#"m$n

Check " f%"ma&

Changephase

"ncreaseduty '$dth

(ecrease

duty '$dth

Yes

Fig #. Current control algorithm

I . S IM ,A/I0 A * ) LP)'IM) /A, ' )S ,/S

/he stepper motor and the current control algorithm ha:e -eenmodeled using MA/,AB(SIM ,I % as sho5n in fig $. /he

parameters of the stepper motor that is used fore perimentation and simulation are gi:en in /a-le 1. 9ere $#steps for 1.8 o has -een ta!en 2i.e. 6&. /he magnitude of the currentcan -e controlled -4 selecting the :alue of I ma and I min .

/AB,) I Parameters Value

9olding tor ue

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Fig $. SIM ,I % model of the current controlled stepper motor

Fig &. Speed profile and desired phase angle

Fig ?. *esired input phase currents

Fig 6. 0utput phase currents 5ithout current feed-ac! loop

Fig 7. 0utput phase currents 5ith current feed-ac! loop

Fig 8. /rac!ing position error

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Fig 8. ) perimental setup of current controlled stepper motor

Fig >. ) perimental output of phase currents

C0 C, /I0

Among the :arious reasons for the popularit4 of the steppermotor one of the :ital reason is that it performs considera-l45ell in the open loop. 9ere 5e ha:e implemented an open loopmicrostepping control algorithm using PIC microcontroller16F877A. /5o sinusoidal pulse 5idth modulated 2SPJM3signals ha:e -een generated 5ith >< o phase difference using thePIC microcontroller. Current feed-ac! is gi:en to the controllerto control the phase current constant 5ithin a prescri-ed limitto increase the positioning accurac4. /his has -een achie:ed -4

controlling the 5idth of the dut4 c4cle of the SPJM signal./he stepper motor and control algorithm has -een simulatedusing MA/,AB(SIM ,I % and also e perimentall4:alidated. /his 5or! is important for de:eloping a lo5 cost

precision positioning control s4stem.

' )F)') C)S1 B. C. %uo /heor4 and Applications of the Step Motors. e5 Oor!E

Jest Pu-lishing Co. 1>7&.# P. P. Acarnle4 Stepping MotorsE A Duide to Modern /heor4 and

Practice. e5 Oor!E Peregrinus 1>8#.$ Microstepping

httpE;;machinedesign.com;Basics0f*esign)ngineeringItem;71&;6?78>;Microstepping.asp .

& *ouglas J. Gones ?. Microstepping of Stepping MotorshttpE;;555.cs.uio5a.edu; "ones;step;micro.html.

? M. F. 'ahman and A. Poo An application oriented test procedure fordesigning microstepping step motor controllers Q I))) /rans. Ind.)lectron. :ol. $? no. & pp. ?@?&6 o:. 1>88.

6 A. Bellini C. Concari D. Franceschini and A. /oscani Mi ed(modePJM for high(performance stepping motors Q I))) /rans. Ind.)lectron. :ol. ?& no. 6 pp. $167@$177 *ec. #