REFERENCE MANUAL

STEPPER MOTOR A stepper motor is a low speeed , high torque motor which characterises itself with a number of unusual features such as mentioned below:1) It moves in 200 discret steps in one revolution.2) It is a bi-directional motor, can rotate in either direction.3) It is a self-starting motor, no external means are required for starting it.4) Its affective inertia is very low. It starts, stops

and reverses practically instantaneously.5) Its starting, running and stalling currents are of the same order. There is no heavy inrush current at start. Its motor can be stalled forcibly without any fear of damage to windings.

6) Its low basic shaft speed eliminate the complex gear trains in many applications

When driven through a translator a stepper motor acts as a Transducer having a high gain. It generate large torques with micro watts of input control power.

Its torque output is manyfold on comparison

with the conventional motor of the same size

and weight.

A stepping motor can also be used in integrator by feeding a continuously variable

signal to an anlogue to digital convertor giving a pulse frequency proportional to

the amplitude of the input signal. A stepping motor when supplied with these pulses

will move the load attached to its shafts through a distance proportional to the time

integral of the signal.

-STATOR WINDINGS .

7ZZZZZZ

p ARMAMENT MAGNCT

ROTOR DISC

/ /♦ si r

FIG. 21 PERMANENT MAGNET MOTOR

Some of the common applications of stepper

motor are -

1) Remote control of Dimmerstats,

potentiometers, camera focusing process

timing etc,

2) Numerically controlled machine tools and

robots.

3) Punched tape drives.

4) As variable speed drives.

5) Paper feed drive in recorder.

6) Drives for electronic sweep generators.

7) Curve tracers.

TYPES OF STEPPER MOTOR CONSTRUCTION

Three basic type of stepper motor are there in

use . They are permanent magnet, variable

reluctance and hybrid .Each type may vary

widely in constructional details but all have a

cylindrical stator with salient poles or teeth each

of which carries a coil to which the pulses are

sucessively applied.

1) PERMANENT MAGNET MOTOR

As name suggests this type of motor has a

permanent megnet rotor. Rotor has two identical

discs withs a permanent megnet between them.

It has teeth, the number of which decides the degree

of angular movement of the shaft per switching

pulse. Stator has two phase winding ; the coils of

which produce mmf fields displaced by 90°

electrical in space from each other.

When supplied with two phase A.C. supply; a rotating magnetic field is produced

which make the permanent magnet rotor to rotate. In D.G. operation, pulses are

applied to each of stator winding, sucessively creating a series of magnetic fields.

The rotor with this magnetic field experiences torque. By changing the excitation

sequence, the motor can be made to rotate in the clockwise or anticlockwise

direction. Hence It Is a blrectional motor.

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2) VARIABLE RELUCTANCE MOTOR :

In this type of motors, It is made up of soft iron with

negligible residual magnetism and has number of

poles teeth differing from that for the stator. When a

pulse is . applied to coils on stator, the rotor tries to

seek a position of minimum reluctance and moves by

a step of angle which depends on stator and rotor

pole numbers.

Torque is produced by electromagnetic flux as it

establishes paths of least reluctance through what

amounts to a variable air gap between a

multipole,multi phase stator and a toothed,

nonretentive rotor.

HYBRID MOTOR >

These combines the above two types of motors. It has a rotor comprising or axially

magnetized permanent magnet with two cup shape end pieces with axial teeth . The

number of rotor and stator teeth governs the stepping angle.

Depending on the characteristics, these motors can be compared as below. 4-LEAD

TYPE : The 4 Leads Stepper Motors are useful when the isolation between the two

Permanent magnet Stepper motor can have either single winding (coil) per phase 1

or two windings per phase (bifilar wound motor). Formar is a 3-lead motor requiring two power supplies, while the

later is a 5 lead motor requiring only single power supply . In bifilar wound motor , to reverse the magnetie polarity ,

instead of reversing current in winding , current of same polarity is switched to an indentical winding wound in

opposite direction.

Because of rotor reaction and relatively large step angles, there is little tendency to overshoot. So damping is rarely

used in this type of motors. These type of motors have therefore lower stepping rates.

windings is required .4 Leads Stepper Motor can be easily converted into 3 leads type

by shorting terminals 2 and 4 . These require single ended power supply and double

pole double through switchings.

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REFERENCE MANUAL

5-LEADS. (BIFILAR TYPE): This type of stepper

Motor is useful where application of push-pull

circuitory and centre tap power supply is not

possible and also more where more torque

output is required at higher stepping rates. In

bifilar motor each stator coil is wound in

opposite directions and these are stepped by

switching from one half of the winding to the

other half.

TERMINOLOGY USED IN STEPPER MOTORS :-

1) STEP ANGLE The motor shaft rotateis its specific

angular increment each time the winding polarity

is changed . This specific degree of rotation on

increment is called the step angle . It is specified

in degrees . Now a days motors with step angle

PermanentMagnet

VariableReluctance

Hybrid

1)Maximum pulserate per second 400 1000 20,000

2)Stepping angle 40-120 1.8-30 0.9 -15

3)Maximum torque N-m . 0.3 -20 30 -40 0.15-8

4)lnertia Kg-m2101-20 2-200 - 3 -4000

as small as 0.9° are available .

2) STEPS PER REVOLUTION : This term describes the

total number of steps required for the output

shaft to rotate through 360° or one complete

revolution . Steps per revolution are calculated

by dividing 360° by step angle.

3) STEPS PER SECOND :-The number of angular moments (steps) accomplished by

the motor in one second of time . It corresponds to pulse rate.

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04)3TEP ACCURANCY : It is defined as a positionai accurancy tolerance . This

figure is generally expressed in percent and indicate the total error Introduced by

the stepping motor in a single step movement . The error is non cumulative l.e. , it

does not increase as additional steps are taken.

05)HOLDING TORQUE : With the motor shaft at standtUt or zero r.p.m. condition

, the amount of torque from an external source , required to break away the

shaft from its holding position . This is measured with rated voltage and

current applied to the motor and is the basic characteristic of stepping

motor.

Q6)RESIDUAL TORQUE: The torque present at standstill under power -off condition is a result of the

permanent magnetic flux acting on the stator poles. Residual torque is present under power off

condition only with a motor of permanent magnet rotor design.

7) TORQUE TO INERTIA RATIO :Thts ratio is determined try dividing the rased holding

torque of the motor by its inertia. The better the torque to inertia ratio, the better

the response. When dealing with step response problems, it is

important to know the torque to inertia ratio of the motor.

8) ST£P RESPONSE >When given a command to move a step, the mater will respond within a specific

time period . This “time for a single stepper step response is a fuction of the torque to inertia ratio of

the motor and the characteristics of electronics drive system. Ratings are given for ncload ccrrti-

tions with time generally expressed in miViseconds.

Q9)RESONANCE .-Stepper motors cart be simulated as a spring mass

system, and 33 3:UCn have certain ‘natural * frequency chractenstics

.When motor's natural frequency or‘resGoance* is reached, an

increase in toe audible \evei of toe

REFERENCE MANUAL m

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motors operation can be detected . In case

of severe resonant condition ffi may loose

steps and or oscillate about a point. The

frequency at which this resonance occurs

varies, depending on the motor and the

load.

10)DRIVES > This is a broad term used to

describe the circuitary which controls the

stepping motors and usually consist of a

power supply, sequencing logic and power

output switching components.

11)RAMPING The process of controlling pulse

frequency to acceleate the rotor from zero

speed to maximum speed as well as to

deaccelerate the rotor from maximum speed

to zero speed . Ramping increases the

capability of driving motor and load to higher

speed levels, particularly with large intertial

loads.

12) START / STOP ERROR :-An additional curve found

on some speed torque curves which indicates the

maximum step rate to which the particular

motor can start and stop without loosing steps or

falling out of synchronism. This condition

assumes no acceleration /deceleration time.

These are usually the result of actual testing

with negligible external load inertia.

13) SLEW RATE An area of high speed operation

where the motor can run

unidirectionaly in synchronism. However, it

cannot instantaneously start, stop or reverse. A

stepper motor is brought up to slewing rate

using acceleration and is then decelerated to

stop under conditions where no step loss can be

tolerated . Now a days motors with slewing

speeds of from 10,000 steps/sec to 20,000

steps/sec are available . The secret lies in the

electronics control.

14) DAMPING :-The reduction or elimination of step

overshoot is defined as damping It is used in

applications where settling down time is

important. Damping methods used include

mechanical, electronic and viscous (fluid).

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TRANSLATOR. '.-Stepper Motor translator Is a versatile electronic

control,capable of producing the proper pulse trains for driving the stepper

motor . It is designed for controlling 5-lead type i.e. bifilar motor only . The

complete circuit diagram Is shown in figure . It basically consists of a CMOS

dual D-type Flip-Flop CD 4013.

The Q and Q outputs of 1st D-flip-flop are directly connected to windings Aland A2

of stepper motor through power Amplifiers . Whereas other two inputs to B1 &

B2 are controlled by 2nd D-FLIP-FLOP and a CMOS DEMULT\RLEXER CD 4053 The

functionn of DEMULTIPLEXER is to change the direction of stepper motor .

This is done by either grounding pin 10 and 11 or connecting them to +Vcc .The truth table

for logic signals for forward and reverse direction is given along with timing diagram.

CLOCK GENERATOR Thie clock pulses are generated by

using 555 Timer \C.

The clock frequency can be selected in two modes,

High or Low . This is done by selecting different

values of capacitors . Fine adjustments of the ciock

frequency can be done by varying the potentiometer

provided on the front pannei.

POWER AMPLIFIERS Since the output of the translator

cannot drive the stepper Motors windings directly hence

the use of power Ampiifiers. \t consists of a driver

stages SL100 and power transistors 2N3055 . The

Stepper Motor windings are connected in series with the

power transistor. Four such stages of power Amplifiers

are used .

TRANSIENT VOLTAGE SUPPERESSION:- During D.C. stepping transient voltages are

generated as the voltage is swithced across the windings . if these voltages are not

removed or limited to a safe value, they can cause fauity operation or damage to Motor and

other circuit components. Hence Shunt diodes anconnected across each windings as shown in circuit digram.

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STEPPER MOTOR CONTROLLER

Stepper motor requires an electronic controller to energise its windings in the proper sequence, there by causing It to step. Block diagram of stepper motor controller Is as under

Stator windings of the PM stepper motor must

be excited in a pedicular sequence to cause

the motor to move from the exciting step to the next

step.

Logic circuit is to be designed OR tn case of Microprocessor based

system , program is to be prepared to provide the proper sequential

output to power driver. Excitation sequence for bifilar wound PM

motor is shown in Table,.

REFERENCE MANUAL

The signal from the 8256 PR of Mtcroprcces&er kit provide proper sequential output.

To increase fie power level of these signal sufficiently, to energies the motor wmdfcig 'power drivers vsmgpomer transistor or

fiyrators are used

REFERENCE MANUAL

PROCEDURE :

Stepper motor with dial & pointerls provided on main unit.Operating voltage : 12 volt DC Torque: 3.5 Kg-cmStep Angle : 1.8°

Motor driver and controller is provided in control

unit. .

Variable Clock Generator is provided with

potmeter (Speed Adjust) for applying clock to the

controller.Mode Input sets the direction of motor.( Mode = 1 - FW & Mode = 0 - REV).

A) AUTO OPERATION

1) Connect clock CLK from Clock Generator to the clock input (CLK) of synchronous up/down counter.

2) Connect MODE input to synchronous up/down counter.Keep FW/REV switch for FW position.

3) Connect output from code converter and driver stage A11 to base of Q1,B11 to base of Q2 , A21 to base of Q3 , and B21

to base of Q4.

4) Make powe on to the unit.

5) Keep Speed Adjust potmeter for minimum

clock speed).

6) Note the output pulse pattern as observed on

LED D1 D2 D3 D4.

REFERENCE MANUAL

7) Change the MODE switch to REV position.

Note the output pulse pattern as observed on

LED D1 D2 D3 D4.

8) Count total number of steps for one complete

rotation.

No. of Steps for one rotation =

360°Step Angle = ------------------

No. of Steps for one rotation .

AUTO OPERATION:

Connect output from code converter and driver stage A11 to base of Q1,B11 to base of Q2 ,A21 to base of Q3 , and B21 to base of Q4.Connect CLK and MODE input to synchronous up/down counter.

STEPPER MOTOR CONTROL USING MICROPROCESSOR

ftcmumcc mmm

1) Connect 8255 from Benlx 8085 Microprocessor kH to stepper mM$f unit using fiat cable cord provided with system,(28 pin FRC connector to 8255 port of Microproc**$6f tot and 9 pin D-connector(male) to 9 pin Oconnector(fermie) on stopper ewtor control unit.)

Connect output from BUFFER At to base of Q1f

B1 to base of 02,A2 to base of 03, and B2 to base of 04.

2) Connect power supply to Microprocessor kit.Make power ON to both Microprocessor kit and Stepper motor confrof unit

3)Hard copy of the program is provided on EPROM at location 4300W Execute the program stored at location 4300H.

GO 4 3 0 0 EXEC

4) Direction of motoris controlfed by FW/REV switch on Stepper motor control unit

*12 VOLTSTEPPER MOTOR

REV

asTORFA -OilTWJT ant FOPTH-.NFUT PLC APPUCATICN TRACER.

STEPPER MOTOR CONTROL PROGRAM

RFFERENCE MANUAL

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82S5a* PORT

NPur

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FORWARD SEQUENCE REVERSE SEQUENCE

Enter the above programme in RAM from location 1000H. Execute: 00 1 0 0 0 EXEC

Define

$ PVT im

ADDRESS

OPCODE MNEMONIC

COMMENT

1000 3E 82 IVM 82SET 82?5 CONTROL REGISTOR

1002 D3 03 OUT 03 PORTA-O/P PORT B -I

1004L1 06 04 MVI 6 04 SET COUNTER

1006 DB 01 IN B CHECK FW/REV MOTOR DIRECTION

1008 E6 01 ANI 01

100 A

CA 13 10 JZ L2

100D

21 50 10 LX I H 1050 LOAD HL POINTER (FW)

1010 C3 16 10 JMP L3

1013L2 21 60 10 LXI H 1060 LOAD HL POINTER (REV)

1016L3 23 INX H

1017 7E MOV A , M GET DATA VALUE

1018 D3 00 OUT A OUT DATA ON PORT A

101A 11 FF 3F LXI D 3FFF LOAD DELAY COUNT

101D CD 98 09 CALL DELAY

1020 05 DCR B DECREMENT COUNTER

1021 C2 16 10 JNZ L3 IF COUNTER NOT ZERO GO TO L3

1024 C3 04 10 JMP L1

1051 5 1061 6

1062 9 1062 A

1053 A 1063 9

1054 6 1064 5