First i apologise for asking this basic question. i am totally confused with concept of normal dc motor.
In DC motor speed control could be achieved by varying the duty cycle of pulses.
In stepper each pulse would cause the motor to rotate a single step(approx 1.8 deg).
There is any minimum and maximum pulse width required for each pulse or they must be constant.
I read increasing the frequency of applying pulses (i.e) reducing time between two adjacent pulses would cause the motor to run faster.
Now let T1 be the pulse width required to move single step 1.8deg. to increase rpm i need to reduce the offtime of pulse i.e, T2(Ton + Toff = T)
while T1+T2 decides the frequency of the pulse signal T1 remains constant , T2 is also must be a constant. then only frequency would be maintained constant.So without reducing time t2 how can i maintain the same frequency for various speed as like in DC motor.
If anyone tell me about how to control(RPM) stepper by PWM as like DC motor
If you are using a stepping motor controller, the motor takes one step each time you pulse the step input. Therefore, you control the RPMs of the stepper motor by varying the time between the step pulses.
Alternatively, a microprocessor can control of the direction of the current in the motor windings. However, you still take one step at a time, by changing the direction that the currents flow.
For a DC motor, pulse width modulation (PWM) varies the average voltage across the motor windings, controlling the speed of rotation.
Is there any minimum or maximum pulse duration for each pulse applied to stepper
There's a minimum that is dependent on the motor, and can probably be found in the datasheet for the motor. (Unfortunately, most hobbyist motors don't come with any datasheet.) Then it might also vary depending on the type of driver you are using (eg, you can microstep or half-step a stepper motor, which might change behavior. you are essentially fighting the physical limitations in the motor - inertia, friction, and so on.)
There isn't any maximum. If you leave the windings in a particular state, the motor just stops.
westfw:
There isn't any maximum. If you leave the windings in a particular state, the motor just stops.
Now when talking in terms of "pulses", the question is what happens when you actually switch off the current - whether the stepper will hold its position with no current applied.
In general, you keep the last position current going to hold the position reliably.