define comp error

Dear All,

 

I'm new to PMAC and currently I'm in the process of building a new precision machine using UMAC. We have 2 identical stages and I'm facing problem with one of the axis while the other axis is working fine all the time. The following are the problem with the axis:

1) There are run-away and jerky motion of the stage which eventually ends up in tripping of the amplifier and fault error flag in PMAC.

2)After entering the compensation value in descending order of the motors, the second motor which has the above mentioned problems, continues to have the same amount of Following error.

But the comp tables are save for both the motor which is seen from the List comp option.

 

Kindly help me in setting up the motor to work fine. Thanks in advance.

 

Regards,

Raghav

Hi Raghav, it sounds like this might be a tuning problem. Have you tuned your axes to have tight following error? If your axes are not tuned well, they will have too much following error, regardless of your compensation table effects. Please refer to this brief tutorial on tuning (attached).

Servo Loop Tuning.pdf

Dear Charles,

Thanks for your reply. I had tried to tune the machine and maintain a tight F.E. I had attached the F.E. graph for the axis in which we face the most of the problem. Instead of a 5 point compensation, we gave a 9 point compensation for the 2 motors and it seems the compensation table is working fine. I still have doubt in whether the value which i gave is correct. Following the calculation which we did and input into the compensation table.

Eg:-

Error value from Laser Interferometer: 2.5 micron = 2500nm

Encoder 1 counts = 10nm

So, 2500/10 = 250 -> 250*16 = 4000 counts

 

So is this the correct procedure to take the encoder resolution as the base and form the comp. table? And when I try to do a step motion, the actual position seems to be consisting of vibrations which is about 5 cts which is almost 50nm. So what should I do to eliminate it.

 

Thank you once again for your valuable response.

 

Regards,

Raghav

 

Hi Raghav,

 

Can you please post a screenshot of your step move from tuning (actual and commanded position vs. time), one parabolic move (velocity and following error vs. time), and another parabolic move (acceleration and following error vs. time)? Thanks.