My microstepping problem

We have a stepper motor and microstep stepper motor controller. The microstep controller provides 128 microsteps. We need as many as possible.

We have a problem. When we study the movement of the motor closely we can see that the velocity seems to change momentarily on the 128th microstep i.e. at the step change. We believe that this is not an uncommon problem. Can you explain what the problem is and why it occurs?

The way we are measuring the problem is we have a mirror on the motor and a laser pointer reflecting off the mirror onto a target. As the mirror rotates we are imaging the target with an ultrafast camera (1000’s of frame per second). We then measure the position of the laser point on the target in every image and plot it. This clearly shows a variation every 128th microstep. We assume this means it is happening on every step change.

The microstep controller that has been used (by our contractor who designed the system) is a cheap one. Can you provide a microstep controller with at least 128 microsteps (more is better) that does not have this problem.

The motor is a 14HS13-0804S-PG5
https://www.oyostepper.it/goods-283-Motore-passo-passo-Nema-14-Bipolare-L%3D33mm-18Ncm-035-Gradi-08A-54V-con-riduttore-epicicloidale-5-1.html

The motor is already mechanically designed in and changing the motor model at this point in time will be a significant problem unless the replacement is a perfect match.

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