R&P problems

Hey guys,

I've got a problem with my DIY cnc router.

The machine is a dual-x AC servo driven machine on module 1 R&P with 8:1 reduction gearboxes, on a 50mm PCD pinion.
This corresponds to ~157mm of linear travel per output revolution.

However, with the X axis I am having a problem.
The motion when the gears are not engaged, i.e. the pinion is disengaged from the rack is extremely smooth.
When the gear and rack ARE engaged, the motion is choppy and vibrates quite significantly, even when moving very slow. This translates to odd artefacts appearing on the work piece.

The problem does not exist with the motors or gearbox, as the Y axis uses an identical system (albeit only a single motor), and the motion is very smooth.

The X does make some odd noises. The only way to describe it is that it sounds like car wheels that have a very high rolling resistance - this constant frictional noise.


Has anyone encountered this before? or know of solutions/causes?


Please see attached pictures to get a clearer idea of the situation (and ignore the junk in the background too :P).

I'll bet the servos are fighting each other a little bit when both are trying to keep closed loop position against each other. Maybe try loosening one of the pinion gears, and tighten it while the servos are powered up and the gantry is square?

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Good suggestion, but the problem exists even when the motors are off. Just pushing the gantry by hand with everything off exhibits the same problem. I know it's something mechanical with the R&P, but I have no idea what it is.

Problem with one of the gearboxes perhaps?

I wonder if they didnt send you the wrong gears for that rack it just does not look right hard to tell

Problem with your LM bearings? Servos sized right for the gantry axis?

Quote:

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Originally Posted by kevin swan

I wonder if they didnt send you the wrong gears for that rack it just does not look right hard to tell

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This is worth checking on, also might be worth checking are the gears squared to the rack correctly?

Great suggestion robe_uk, the rack was at a slight angle across it's length. the gear and rack are now squared and the noise has gone away. Still getting the strange jittery movement, although it has lessened since squaring the two.

The gearboxes are fine. To my knowledge the LM bearings are ok, but I'm not aware of ways to identify the condition.

Does anyone have suggestions on how to check the condition of the bearings? upon opening them up, nothing looked irregular.