Ultra 3000 Jumping while stopped

[ckaffer85]

Hello All,

I am having an issue with a Ultra 3000 jumping while stopped. It seem to be intermittent. I am using RS5K to control the servo. It does have an external encoder to measure the length of product it moves. Sometime when using the MAS command the servo will begin to jump forwards and backwards. Any help or ideas to prevent this would be appreciated. If you need any other details please let me know.

Thanks

 

[ckaffer85]

Will the MAS command prevent any movement until a MAM command is given? When I issue the drive a MSF command the jumping goes away.

 

[MATT116]

Is the MAS told to stop the current motion instruction?

 

[ckaffer85]

I have the MAS set up to stop all motion, once the MAM is complete

 

[kamenges]

How far is it "jumping". 1/10 rev, 1 rev, 10 revs? An order of magnitude is fine. How quickly is it jumping? Is it extremely aggressive or is it more of a drift?

Keith

 

[ckaffer85]

I would say it is around 1/10 of a rev (give or take) and aggressive at times going back and forth. The problem is that the material is copper tubing that is clamped for cutting once the servo has "stopped". When the servo jumps it bends the tubing causing material damage and feed issues.

 

[kamenges]

An MAS (Motion Axis Stop) will in effect terminate an active motion using the stop parameters defined by the MAS. However, it leaves the servo loop enabled. The MSF (Motion Servo Off) instruction disables the servo loop and the amplifier.

It sounds like you are going into oscillation when you are stopped. There are probably tuning issues with either the position or velocity loop of the axis.

Keith

 

[ckaffer85]

Thanks Keith, any luck that an auto tune would resolve the issue? If not, what parameters do you suggest looking at first?

 

[keithkyll]

Noise on the encoder feedback will cause this. Hook up laptop with Ultraware and monitor encoder feedback.

 

[ckaffer85]

Can I monitor it with RSLogix 5000? Or is this specific to Ultraware?

 

[keithkyll]

I don't have RSlogix 5000, so I couldn't say. Ultraware should be a free download.
We had a machine that would be fine at startup, then drift during the day. Homing would correct it.
The software was designed for stepper motors - open loop. Our encoders fed back to the Ultra. When I connected Ultraware, I could see the position slowly changing. Someone built a lousy circuit to convert the signals from differential to TTL. They were picking up noise. I was surprised how little noise it took to "fool" the Ultra drives.
Had to do another circuit inside a metal box, and get religious about shielding and grounding. Noise from the drive's motor cables can feed back into the inputs.
Make sure motor lead cable is grounded, and power supply leads are routed far away from control signals.

 

[ckaffer85]

Sorry this is such a late response. I wanted to check back in to tell you all what the solutions were.

After a lot of digging I was able to find the original program for the the machine. I did a quick compare of the drive's parameters and noticed that there were major differences.(These changes were before I started here. I guess they have been fighting this issue for years) I made the current program with all of the current "recipes" on it match what the original program was for the drive. This solved most of the issues.

I then took a look in the cabinet and noticed that the auxiliary feedback cable was ran with the 480. I rerouted the cable to reduce the noise on the line.

Thanks for the inputs!