# Thread: Effect of a single electrical pulse to stepper/servo

1. ## Effect of a single electrical pulse to stepper/servo

The result is some displacement in slide position.
I want to know a typical order of magnitude of this displacement.
Specifically, how many pulses are typically needed for least slide movement in IS-C (i.e., 0.0001 mm / 0.00001 inch)? 1, 10, 100 or something else?

Al the man is requested to respond, since most of us do not understand the behavior of the control at hardware-design level.

I have heard that one pulse typically causes a rotation of 1.8 degree in stepper motor.
That is, 200 pulses for a complete rotation. If gear ratio is R, and pitch of the lead screw is 10 mm, this will cause a displacement of 10/(200R) per pulse, which is equal to 0.05/R mm. To ensure an accuracy of 0.001 mm, R should be minimum 50. On a servo, similar thing might be happening.
How accurate is my information? I would appreciate correct / more detailed information.

3. Your self answer is correct on a stepper the smallest increment is based on the mechanical resolution at 1.8° degree movement of the stepper.
On a servo it is based on the resolution of one encoder pulse count after any x4 increase in pulse resolution.
Al.

In case of a servo, typically how many pulses cause one complete rotation?

• For Fanuc they go from 2000 ~2500 x4 to the serial Hi-res type that are 300,000 pulses/rev.
Al.

• Thanks again for the information.
I was expecting that total number of pulses associated with one revolution must be in thousands. You gave a typical value of 300000.

I guess steppers also might have become more accurate than just 200 pulses/rev. What is the typical max value these days?

• It depends, if you use built-in electronic gearings in the servo systems, you can reduce the no. of steps for one rotation

• Electronic gearing!
Thanks for new information.
Reducing the number of steps might affect the accuracy.

• I got the following information (http://www.omega.com/prodinfo/stepper_motors.html):

"Microstepping is a relatively new stepper motor technology that controls the current in the motor winding to a degree that further subdivides the number of positions between poles. Omegamation microstepping drives are capable of dividing a full step (1.8º) into 256 microsteps, resulting in 51,200 steps per revolution (.007º/step). Microstepping is typically used in applications that require accurate positioning and smoother motion over a wide range of speeds. Like the half-step mode, microstepping provides approximately 30% less torque than full-step mode".

But, I have also read that reducing step angle deteriorates repeatibility.