CLX Servo App Help

johnfarrugi · Jul 9, 2008

I have a press steel feeder application which I need some help with. Currently there are three servos being controller through a CLX PLC, sercos system. There is a cradle servo which rotates the large steel roll and two "pulling" servos which help feed the steel into the press. Right now all servos are controlled by independent MAM commands. The problem I have is slippage. If one or more of the servos slip on the steel, a 10" feed length may only be 9.5" in the press. To help this issue, I've installed an external encoded which is mounted on a set of "free wheeling" rolls which will read the actual steel feed length. I would like to use this external feed encoder to adjust the three feeder servos to conpensate for slipage. I'm a little unsure how to do this. I want to tell the three servos to move 10" and and then use the external encoder for reference.

bkottaras · Jul 9, 2008

johnfarrugi said:
I have a press steel feeder application which I need some help with. Currently there are three servos being controller through a CLX PLC, sercos system. There is a cradle servo which rotates the large steel roll and two "pulling" servos which help feed the steel into the press. Right now all servos are controlled by independent MAM commands. The problem I have is slippage. If one or more of the servos slip on the steel, a 10" feed length may only be 9.5" in the press. To help this issue, I've installed an external encoded which is mounted on a set of "free wheeling" rolls which will read the actual steel feed length. I would like to use this external feed encoder to adjust the three feeder servos to conpensate for slipage. I'm a little unsure how to do this. I want to tell the three servos to move 10" and and then use the external encoder for reference.

I assume you use Kinetix so this can be easy to set up.
Use the IAM's AUX Encoder and plug in your external emcoder.
Set it up in the IAMs configuration as node 129 (I think).
Then use the feedback to send all your axis to their position(s).
You will not be able to do an absolute MOV since you will have to initiate a MOV and don't stop until you get to the point (10" distance) and your external encoder will provide the "marker" for in position.
A bit of math is involved, nothing major a couple of compares, to know when to generate the "marker"
Once the "marker" is generated, issue a sTOP command for all of your axis.
Good luck

johnfarrugi · Jul 9, 2008

If I use the stop command when it reaches 10" then I will have to use immidiate stop or if I decel then the position will be out. I need to be able to decel the servos and still maintain an exact position.

johnfarrugi · Jul 9, 2008

After thinking about this for a bit, it might be better for me to command the servos 2 or 3 inchs past the disired position and then when the steel is fed to within 1 inch of the final position, I would dynamically change the velocity in relation to the final position error taken from the external encoder. Once the encoder is within my final positional window, I would send and imidiate stop to the servos. The servos should be pretty much stopped by then.

kolyur · Jul 9, 2008

If I use the stop command when it reaches 10" then I will have to use immidiate stop or if I decel then the position will be out.

I'm not familiar with Kinetix servos but you should be able to calculate the ramp-down (deceleration) distance based on the nominal velocity. For example, knowing that:

(final velocity)^2 = (initial velocity)^2 + (2 * distance * accel)

and if your external encoder triggers at say 9.5 inches, you can calculate what your deceleration rate should be so that you stop right at 10 inches.

Peter Nachtwey · Jul 9, 2008

Do you know when the slippage occurs? If it occurs at the beginning while accelerating then this problem can be easily solved. You should also be able to re-issue the move command with a new position after computing the slippage and adjusting the final positions. It would be best if the calculation and adjustment is done just before deceleration. If the slippage occurs while decelerating this will be MUCH more difficult to solve. To avoid this the deceleration shouldn't be so high that the motors slip.

CLX Servo App Help

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Peter Nachtwey

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