Help with Y axis jumping <Resolved, bad encoder coupler>

[dlenardu]

I converted a milltronics partner 1e a couple of years ago to the Allin1dc. Recently I started having problems with the Y axis jumping. I thought it was something mechanical but I have disconnected the drive and I have turned the ballscrew by hand throughout the full range of travel. Tried to find some play in the linear Rails but everything seems to be tight and smooth. When I homed the machine today it acting like the servo stalled out and it just sat there and hummed at the home position. Not sure if maybe the servo is going bad. I was running a program today and it kept doing it almost in the same place when cutting in Y but it would also cause the whole table to jump when cutting in X. Almost like the motor wasn't holding, the encoder is not reading correctly or there is alot of play in the ballscrew which I can't find. Here are 2 videos. 1 of the y axis jumping and the other of the screen showing the servo power bar going red

https://youtube.com/shorts/QTz4H2VL0Jc? ... Jhz9pUnOr1

https://youtube.com/shorts/WQ5Ea_6PaVM? ... ishTvx2Kha

[cncsnw]

Do you have limit switches wired to INP3 and INP4?

If so, do you have their input numbers entered in the "Limit" columns of the Machine Configuration -> Motor Parameters table?

If the answers were "yes" and "no", then it is possible that an intermittent limit switch circuit could cause exactly that kind of shuddering.

Does it ever happen during conventional milling (feeding against cutter rotation)? Or does it only happen during climb milling (feeding with cutter rotation, as in your video)?

What are your Kp, Ki and Kd values for the Y axis? Excessive Ki can sometimes cause that type of behavior.

You said that it would also happen "while cutting in X". When that happens, is it the X axis jumping, or still the Y axis jumping?

If you were to post a Report from your control, then we would be able to see your limit switch configuration, PID gains, turns ratios, error messages, and other useful information.

[dlenardu]

cncsnw,

Attached is the report. I just realized the date is not correct on the computer but this is the current report. Also, yes, when cutting in X the Y jumps.

It doesn't seem to matter whether conventional or climb milling. It will do it driving the Y axis back and forth with the wireless pendant.

I tried running autotune again but it didn't seem to make a difference, might even be a little worse. Which would lead you to the pid correct?

Today just trying to home the machine when it was homing Y it started bouncing and then the motor just hummed until I drove it in Y a little. So it has to be something in the tune right, or I guess it still could be a limit switch issue too?
Also I'm a attaching a pic of what the PID was before this last autotune

[Centroid188]

You maybe looking for a bad motor power cable, bad connection, or a bad motor, however if it primary happens in the same area, not thru entire travel, I would be looking for a cable that has a bad spot and a certain flex causes the problem. You do not have encoder errors in your report, so the encoder are being seen and working.

[dlenardu]

Centroid188,

The Y axis motor and cables are fixed and do not move. I installed new power cables (order the cables from centroid) when I did the conversion. Now that doesn't mean that something could have gone wrong with the install. I removed the covers and tried wiggling the wires to see if It would do anything while it was moving back and forth but that didn't seem to change anything. I will try to remove the motor and double check the connections inside. I will say that I did change the PID settings back to what the were before this last autotune and it seems to be better. I haven't gotten it to hum/stall when homing and I have tried it multiple times. I am still getting the jumping though. Unfortunately, I do not know enough about the PID tuning to fully understand what changes I should try. Maybe the brushes are going bad in the motor, could that cause this? I do know that I looked at the graph in the PID page and the Y axis is up and down a lot where the X and Z seem pretty steady

[dlenardu]

Now when I try to home the machine, I get a warning saying the Y count is off and asks if I want to change the value. I have had this happen before on the Z axis and I would just say "no" and then home it again and it would be fine, but this time the Y continues to be off. Should I accept the new values? What are some of the things that cause this?

[tblough]

If you are sure the motor and electrical connections are good, i would look for mechanical slippage between the motor and ball screw. Check the setscrews and keys on all drivetrain components.

[cncsnw]

Perhaps the rotary position encoder is slipping on the motor back shaft.

That would explain both the occasional instability ("jumping"), and also the change in the homed position.

[dlenardu]

@tblough. I have checked all of the connections from the belt drive through the ball screw and everything seems tight

@cncsnw. My plan is to remove the servo motor to double check the wire connections to make sure nothing has come loose. I will also check the encoder coupler at the same time

[tblough]

seems tight

I suggest using a marker and making match marks at each joint, and checking if they all still line up after you experience this phenomenon again. What may feel tight when testing by hand may not be tight enough to transmit the actual torque required to move the machine.