Motion Control

[houndss]

I have a system that uses Kinetix 6000 drives to control servo motors for positioning. I was wanting to know if there is a way to use a continous move command that will follow a setpoint from a feedback device. So if the signal goes positive the servos will go forward and if the signal goes negative the servos reverse.

I can only see motion commands that exucute once, not one that is continous. Is there a way to do this?

[NorwichUK]

Others have asked similar questions. Some options you can consider:-

1.

Set the absolute posiiton of the servo to zero at its mid so that it can swing positive and negative (a home routine would be required on power up)

Scale your PID output to correspond to absolute position.

Every time your PID block is done - just execute an absolute MAM (just ensure you are't doing this too quick an update).

Note - it doesn't matter if there's no new position to go to - if the servo is alreadt at the destination - it will go no where with a new absolute MAM to the same place.

2. If you want to do something with incremental moves instead, just periodically refresh an MAM instruction at a chosen rate again.

[houndss]

Well unfortunately this application has to be continous. Refreshing the MAM instruction doesn't work because the updates are too fast.

Right now we have to use MAJ to get it to work with a routine that looks for error  and  then corrects it when it gets out of the tolerance. 

Neither of your suggestions will work, we have tried them.

[NorwichUK]

There's no continuous move instruction that I know of, but if there was you would have to :-

 Refresh the instruction (or some buffer register) with the required new position.

 Wait for the next Sercos refresh to load the new position to the motion planner.

 Allow the servo closed loop control to move the servo.

If you programmed your motion in structured text, there are advantages in that your motion instructions can execute every scan of your code (as long as what you are doing doesn't generate Instruction Collision erros).

Without going into detail of the cascaded loops of a PID process, tuning dynamics, loop refresh rates and positive feedback etc that can cause response issues, and going back to the question of is there a means of implementing a continuous move - yes there is. An MAM operating every scan in structured text would do exactly the same thing as a continuous move instruction would, considering you would have to pass the new position in your code to it somehow, and it then wait for that to go over the Sercos network.

The only way you could improve on a free running MAM is to somehow have a 'gear' of the servo locked to an analog signal going straight into the Kinetix such that the operation totally bypasses your PLC code - sort of thing like 10V = a position, 0v = another position etc. I don't think this can be done - but firmware and software changes all the time - so it might be available now?

Good luck with your process, if an MAM hasn't proved satisfactory for you then others reading here may be able to help. 

Message Edited by NorwichUK on 09-03-2009 08:42 PM

Message Edited by NorwichUK on 09-04-2009 07:26 AM

[houndss]

Thanks for the reply Norwich. This application uses a contact roll to put continuous pressure against a roll that is being wound. Continuous movement keeps the density of the roll from changing.

We tried the MAM in ladder and it would only execute one move, then lock up. Perhaps it had something to do with update rates, motion planner, etc... I do not have access to the structured text programming features.

I think you answered my question in yes there is continuous movement in a very roundabout way. We have other motion controllers that will follow a position. Hopefully AB will be able to come up with this sometime in the near future.

[deekster]

What type of feedback is coming from this external device, actual feedback counts or a variable voltage?  If feedback type and it is compatible with our auxiliary port, then you could configure this input as a feedback only axis and then use either MAG (gearing) or MAPC (position cam) to have the controlled axis follow it.

Hope I'm not too far off base.

[NorwichUK]

example attached as per our messages

[houndss]

Thanks for the example NorwichUK, I will check it out and see if it fits our application.

The feedback is a calculated diameter in the PLC. So it is not an exernal device. It would be in the program.

[flashbif]

I am doing something similar with CLX, M08SE, and Kinetics 6K. Our input is an aux feedback encoder that I MAG a Virtual Axis to, then use in a MAPC. However, if you CPT the diameter to a contact roll position value, then MRP the position value to the Contact Roll Virtual Axis.ActualPosition, you can MAG your Contact Roll Servo axis to the Virtual Axis. Additionally you can make the Ratio parameter a variable if the diameter on your roll varies with width.

[synrobot]

I am not sure that I completely understand your application, but it seems like Electronic Camming or Gearing would be the way to go.  You can have your feedback device be the Master and the positioning servos be the Slave.  You can set this up for continuous operation.