Servo Gearhead with Encoder Question

[Gene-Yo]

I plan to add either a set of the mini Pittman or Faulhaber servo gearhead motors with encoders to drive a small 3 axis closed loop CNC setup. So the servo drivers will be connected to the encoder. I need some help or advice if these types of motors are a good choice for CNC work or not.

The small servo motors which I'd like to use have gearheads which gives them needed torque to drive a CNC axis. The problem I noted is these gearheads do have a small amount of backlash <1 degree according to the product specifications.

Since the servo motors also have very accurate encoders, will these encoders correct for this small amount of backlash or will it be accumulative which means these small motor gearhead setups are not good for using with CNC equipment?

[Al_The_Man]

Backlash is not cumulative, it only occurs once in one direction.
Your software may have backlash compensation, usually this works in one direction and will automatically take up the amount of backlash when reversing.
1° of backlash is considered high, usually planetary G.B.'s have a lot less B.L.
Al.

[Gene-Yo]

Thanks for the reply. I am familiar with the backlash controls in Mach3 but what I want to figure out is if the Servo Encoder feedback compensates for this backlash within a closed loop system?

These encoders are super accurate and they will be able to measure all backlash down to something like 0.001 degrees. So I'm not sure if the encoder measures this small amount of planetary gear (gearhead) backlash and then compensates or if I'm left guessing and correcting within the software in a servo closed loop system.

[Al_The_Man]

If the encoder is on the motor, the encoder cannot measure the BL itself, it has no way of knowing what the final motion is doing, BL has to be calculated or detected and the value fed into some kind of controller comp.
If the encoder is on the final motion, then the BL is automatically compensated or ignored.
Al.

[Gene-Yo]

Thanks for clarifying everything Al. You just saved me a headache!!