Motion control use torque loop in Rockwell Studio 5000

[hugheydarryl]

I have always controlled servos in Rockwell motion using position loop. I have an application where one process will push against a servo controlled motor and cause the servo to fight against the push and cause the torque to spike and possibly fault the servo due to position error tolerance from being pushed. I have temporarily countered this by issuing a MSF to the servo ... allowing it to be pushed and then issuing a MSO after it has been pushed. This is working as intended ... but I figure turning off the servo and turning it back on once a minute will not be ideal for the servo drive. I have found a Rockwell document that shows home to torque and this would probably be ideal for part of my application ... but I was wondering if there may be a better way to allow a servo to be pushed a small amount with out turning it off every time.

 

[robertmee]

Open up the position error limit in the axis properties, and monitor the position error yourself and do something accordingly. I do torque to home often. The Rockwell AOI they provide is buggy and doesn't account for velocity error, but it is a good starting point for understanding. What I do is use SSVs to open up position and velocity error, limit the torque and monitor the position error. Once it exceeds a limit for time, I home the axis and reset the PE and VE back to operating limits.

In your case, use a redefine position after the push to reset the axis to the current position, so it doesn't try to reduce the position error you've created. I would also reduce the torque limit on the axis that's being pushed so it is not fighting so hard.

 

[hugheydarryl]

Open up the position error limit in the axis properties, and monitor the position error yourself and do something accordingly. I do torque to home often. The Rockwell AOI they provide is buggy and doesn't account for velocity error, but it is a good starting point for understanding. What I do is use SSVs to open up position and velocity error, limit the torque and monitor the position error. Once it exceeds a limit for time, I home the axis and reset the PE and VE back to operating limits.

In your case, use a redefine position after the push to reset the axis to the current position, so it doesn't try to reduce the position error you've created. I would also reduce the torque limit on the axis that's being pushed so it is not fighting so hard.

Thank you for your reply. I am considering doing a torque to home each time I was to grab my package and then when I transport that object ... the next process will push against the servo that is holding the package. The position error limits are high enough that the servo will not fault from being pushed ... however the torque will greatly increase trying to hold position and slightly misshape the package being held. I take it that you are telling me to lower the torque limit and this should let the servo relax easier as long as the position error limit is not reached?

 

[robertmee]

Thank you for your reply. I am considering doing a torque to home each time I was to grab my package and then when I transport that object ... the next process will push against the servo that is holding the package. The position error limits are high enough that the servo will not fault from being pushed ... however the torque will greatly increase trying to hold position and slightly misshape the package being held. I take it that you are telling me to lower the torque limit and this should let the servo relax easier as long as the position error limit is not reached?

Yes....you can SSV a torque limit if you know when you're pushing against it, then put it back when done.