BASICS OF STEPPER MOTOR
Of all motors, st
ep motor is the easiest to control. It's handling simplicity is really hard to deny - all there is to do is to bring the sequence of rectangle impulses to one input of step controller and direction information to another input. Direction information is very simple and comes down to "left" for logical one on that pin and "right" for logical zero. Motor control is also very simple - every impulse makes the motor operating for one step and if there is no impulse the motor won't start. Pause between impulses can be shorter or longer and it defines revolution rate. This rate cannot be infinite because the motor won't be able to "catch up" with all the impulses (documentation on specific motor should contain such information). The picture below represents the scheme for connecting the step motor to microcontroller and appropriate program code follows.
ep motor is the easiest to control. It's handling simplicity is really hard to deny - all there is to do is to bring the sequence of rectangle impulses to one input of step controller and direction information to another input. Direction information is very simple and comes down to "left" for logical one on that pin and "right" for logical zero. Motor control is also very simple - every impulse makes the motor operating for one step and if there is no impulse the motor won't start. Pause between impulses can be shorter or longer and it defines revolution rate. This rate cannot be infinite because the motor won't be able to "catch up" with all the impulses (documentation on specific motor should contain such information). The picture below represents the scheme for connecting the step motor to microcontroller and appropriate program code follows.The key to driving a stepper is realizing how the motor is constructed. A diagram shows the representation of a 4 coil motor, so named because 4 coils are used to cause the revolution of the drive shaft. Each coil must be energized in the correct order for the motor to spin.
Step angle
It is angle through which motor shaft rotates in one step. step angle is different for different motor . selection of motor according to step angle depends on the application , simply if you require small increments in rottion choose motor having smaller step angle.
No of steps require to rotate one complete rotation = 360 deg. / step angle in deg.
Steps/second
The relation between RPM and steps per sec. is given by ,
steps or impulses /sec. =(RPM X Steps /revolution ) /60
Pause between impulses can be shorter or longer and it defines revolution rate. This rate cannot be infinite because the motor won't be able to "catch up" with all the impulses (documentation on specific motor should contain such information). So referring to RPM value in datasheet you can calculate steps/sec and from it delay or pause between impulses.
INTERFACING TO 8051.
To cause the stepper to rotate, we have to send a pulse to each coil in turn. The 8051 does not have sufficient drive capability on its output to drive each coil, so there are a number of ways to drive a stepper,
Stepper motors are usually controlled by transistor or driver IC like LM293D.
Driving current for each coil is then needed about 60mA at +5V supply. A Darlington transistor array, ULN2003 is used to increase driving capacity of the 2051 chip. Four 4.7k resistors help the 2051 to provide more sourcing current from the +5V supply.
Stepper motors are usually controlled by transistor or driver IC like LM293D.
Driving current for each coil is then needed about 60mA at +5V supply. A Darlington transistor array, ULN2003 is used to increase driving capacity of the 2051 chip. Four 4.7k resistors help the 2051 to provide more sourcing current from the +5V supply.
Coil AA’ | Coil BB’ | Coil CC’ | Coil DD’ | Step |
1 | 0 | 0 | 0 | 1 |
0 | 1 | 0 | 0 | 2 |
0 | 0 | 1 | 0 | 3 |
0 | 0 | 0 | 1 | 4 |
Programming
MOV B,#data \\Number of Rotation
MOV A,#11
L: MOV P2,A
RR A
DEC B
JNZ L
