unevent motion with microstepping

[marcalap]

HI,

I have some trouble for microstepping of a Portescap bipolar stepper linear actuator (20DAM20D1B-K) (24 step/rev). For a 1/2 microstep, the first microstep is small but the next one is much bigger. For exemple, at 1/16 microstep, there is a couple of small motions but one of the microstep will produce a lot bigger motion (~30um) . I'm using a leadshine M415B microstepper driver.

The motor pitch is 42um/step. Thus it should definitly not move more than 21 um at 1/2. A stepper with this screw pitch should be able to do below 5um per microstep. What is wrong?


Thanks

[Mariss Freimanis]

Your problem is motor linearity. One expects a motor to divide a full-step evenly into equally spaced microsteps when it's driven by a microstepping drive. This evenness depends on the motor having good linearity. What you have is a "tin can" motor meaning it is constructed from stamped metal parts. These motors have terrible linearity; the ratio between the biggest microstep and the smallest microstep can be as bad as 5:1.

Machined motors (NEMA-17 and larger) have much better linearity. It can be under 1.1:1 for the best motors.

Mariss

[marcalap]

Thanks,

This is definitly a good explaination.