[baja_10]

Hello,
I'm nearing the end of a very long rebuild on a large 4'x8' Vytek monument laser system that attempted to destroy itself. It started with the linear bearings going out and the gantry rails warping, proceeded to eat the acme rod and finally lock up.

It now has new linear bearings, a new ball screw and the gantry rails are all aligned to withing about 5 thousands of each other. My last remaining problem is a repeating pattern at full speed raster engraving (20 to 30 inches per second) and a pretty pronounced machine shudder when vector cutting small objects at anything over ~2 inches per second. It really has issues with circles smaller than half an inch.

I've measured everything I can and it looks good. Nice sinusoidal waveform when I back drive the motor, no shorts to ground, similar ohm reading on each of the poles, good diode readings on the drivers, etc. However the motor that drives the laser head back and forth on the gantry, the Y motor, (ya, the whole 40 lbs of it, great design lol) cogs when i have it connected to the servo driver. The X motor that moves the gantry does not cog at all.

It seems to me that there is something wrong internally that I can/don't know how to measure. If I do the raster engraving with an exaggerated acceleration mode it will cooperate and produce with little repeating pattern but this nearly doubles the work time on small projects. A loose or tight backlash nut does not seem to affect the pattern. It strikes me as something off in the torque of the motor that matches up with the cogging I'm feeling, that when ran slow enough it can compensate for. I have tried running the sigmawin program but the output plots don't seem to show anything obvious enough for me.

Does anyone have any have any recommendations? At this point I'm ready to ship the motors off to be rebuilt even though the hours are probably not over 5,000.

Y Motor:
SGMG-08K3A-YA11
Y Driver:
SGDA-08AP, Y195

X Motor:
SGMG-03K3A-YA11
X Driver:
SGDA-04AP, Y195

[mactec54]

Hello,
I'm nearing the end of a very long rebuild on a large 4'x8' Vytek monument laser system that attempted to destroy itself. It started with the linear bearings going out and the gantry rails warping, proceeded to eat the acme rod and finally lock up.

It now has new linear bearings, a new ball screw and the gantry rails are all aligned to withing about 5 thousands of each other. My last remaining problem is a repeating pattern at full speed raster engraving (20 to 30 inches per second) and a pretty pronounced machine shudder when vector cutting small objects at anything over ~2 inches per second. It really has issues with circles smaller than half an inch.

I've measured everything I can and it looks good. Nice sinusoidal waveform when I back drive the motor, no shorts to ground, similar ohm reading on each of the poles, good diode readings on the drivers, etc. However the motor that drives the laser head back and forth on the gantry, the Y motor, (ya, the whole 40 lbs of it, great design lol) cogs when i have it connected to the servo driver. The X motor that moves the gantry does not cog at all.

It seems to me that there is something wrong internally that I can/don't know how to measure. If I do the raster engraving with an exaggerated acceleration mode it will cooperate and produce with little repeating pattern but this nearly doubles the work time on small projects. A loose or tight backlash nut does not seem to affect the pattern. It strikes me as something off in the torque of the motor that matches up with the cogging I'm feeling, that when ran slow enough it can compensate for. I have tried running the sigmawin program but the output plots don't seem to show anything obvious enough for me.

Does anyone have any have any recommendations? At this point I'm ready to ship the motors off to be rebuilt even though the hours are probably not over 5,000.

Y Motor:
SGMG-08K3A-YA11
Y Driver:
SGDA-08AP, Y195

X Motor:
SGMG-03K3A-YA11
X Driver:
SGDA-04AP, Y195

Your linear rails would have to be setup better than .001 to have no binding, .005 is way to much

What encoder resolution are you using

[Bdrangdo]

You can test the motor windings just by measuring the three resistances across the windings and ensuring that they are exactly the same. They will typically have very low resistances which can be hard to measure and compare at times if the motors are large. You need good test leads and probes. If one of the windings has a partial short circuit often it can be sensed just by disconnecting the coupling or drive belt and turning the shaft by hand. The shorted winding will try and lock the shaft in two places at every revolution. Even a partial short will cause the motor to turn unevenly at low speeds and this can show up on the finish sometimes. Usually the motor will tend to run hot even under light loading.

[mactec54]

You can test the motor windings just by measuring the three resistances across the windings and ensuring that they are exactly the same. They will typically have very low resistances which can be hard to measure and compare at times if the motors are large. You need good test leads and probes. If one of the windings has a partial short circuit often it can be sensed just by disconnecting the coupling or drive belt and turning the shaft by hand. The shorted winding will try and lock the shaft in two places at every revolution. Even a partial short will cause the motor to turn unevenly at low speeds and this can show up on the finish sometimes. Usually the motor will tend to run hot even under light loading.

This would be a total waste of time to check the motor windings, he does not have a motor winding problem, the motor with these drives would not run at all, if it had any kind of electrical winding problem, they have built in safe guards that would not allow the motor to run

There are other things that could be at play as well, Motor / Drive could be to small for the speeds he is trying to achieve

His machine could be binding which if his rails are only within .005 it would be facing extra loading

Encoder resolution set to low in the Servo Drive

Motor Drive rating to small for the job he is doing

Tuning

Another problem I see is 8' x 4' travel with a single ballscrew in the middle is not going to work very well, this will be raking and could be the cause of the problem also

[baja_10]

Thanks for the posts so far, I'll try and answer all the questions. I did not have time to pull the settings from the drivers today so some will have to wait until tomorrow.

I just want to confirm that the "Y" axis motor, the Yaskawa SGMG-08K3A-YA11, is fine with the cogging effect. It does not cog when disconnected but as soon as you connect it to the unpowered driver it cogs about every 20-40 degrees. I can get a specific measurement/number tomorrow if it would help. Everything I had read said that AC servo motors do not have much of if any cogging but maybe this is normal for this motor.


At this point I would be happy just getting the machine to near like new. It was capable of doing good quality raster engravings when it was purchased, I just hope I did not make a poor design choice in changing to a ball screw.