Gear backlash on stepper motor

[htngwilliam]

I purchase a stepper motor with a coupled gearbox. The gearbox have a backlash of 1 degree. I wonder how I can reduce the backlash.

If I run the motor only on 1 direction, will the backlash be eliminated?

 

[MikeHalloran]

Steppers are usually used where backlash is not terribly important, or is accounted for in the system design somehow, e.g. by seeking for the center of an interrupter slot that may be a few steps wide at the motor, or by using a bull gear or timing belt as the last pass, or by using a high gear ratio so that the stepper has to really scream to drive the system at max speed so backlash upstream of the last pass is reduced at the output shaft.

Running the motor in only one direction might help if your system has enough damping to minimize the stepper's natural ringing. Electronic damping in the drivers is sometimes used instead of or in addition to friction damping.

But the general answer to your question is 'no'.





Mike Halloran
Pembroke Pines, FL, USA

 

[htngwilliam]

Hi Mike

Thanks for the comments. I am planning to put a rotary encoder at the end so as to provide a closed loop feedback to the stepper motor to do some adjustment. I wonder whether this eliminates the backlash problem?

 

[israelkk]

How did you conclude that the backlash is a problem at all?

 

[htngwilliam]

The positioning accuracy of the system is +/-0.1deg. The current backlash of my motor is +/-1 deg. I have a 2:1 pulley system which will further reduce this backlash to +/-0.5deg. However, I am planning in advance in case there is really a problem.

Based on my understanding, if we run the motor at uni-direction, the backlash can be eliminated unless we drive it at bi-direction. However, seems that this is not the case

 

[israelkk]

One direction will not solve the problem because every time you stop the power to the motor the backlash will appear unless you have a counter load and a brake that will assure keeping the backlash zero even when the power is off. However, adding these features may require stronger motor. You may find a lower backlash gear than can be coupled with the motor or even claimed "zero backlash" gearbox but it will cost much more and again may require stronger motor to covecome reduced gear efficiency.

 

[tbuelna]

htngwilliam,

Most gear meshes must have a small amount of backlash in order to transfer power with a minimum of loss. If a gear mesh has no backlash at assembly, the tooth-to-tooth interference due to index and profile errors during running will result in high friction losses.

If you're only driving in one direction, then backlash should not be an issue. The only time backlash is an issue is when the gear train experiences reversing loads. The only way I know of to eliminate backlash in a gear train driving in both directions is to use dual gear paths, with each one preloaded in opposite directions. The drawback is that this doubles the number of gears in the system.

Regards,
Terry