proper way to adjust Kinetix 6500

Hi:

1st post but I have been lurking for a while so I will try to give all the pertinent information:

Maintenance tech, 7 years, mostly working the mechanical side,
trying to learn more of the controls side

The machine with the Kinetix 6500 is a tube cutting machine, it is currently cutting 3/16 tubing with .028 wall thickness within +/- 1mm length tolerance in lengths between 300mm and 4 meters.

The main parts of the drive system consist of:

CompactLogix L33ERM
RSlogix5000 mini edition v24
Kinetix 6500 (connected by Ethernet)
MPL-B520K-MK72AA motor with a UltraTrue 5:1 reduction connected through a coupling directly to a feed roller with timing belts and pulleys from the this feed roller to drive 3 more rollers.
Directly after the tube passes through the feed rollers it goes through a pre straightener consisting of 14 rollers before it gets to the cut head. After cut head it to goes to a final straightener

The problem I keep running into is that every month I have to change this machine from running 3/16 tubing to running 5/16 tubing for about 2 days then switch it back. When I changed it to 5/16, the feed rollers will not feed the tube through like they should. The pre straightener is suppose to do 90% of the straightening with the final straightener doing the last 10% but I cannot apply hardly any pressure to the pre straightener rollers or the servo will error out with FLT S54 position error. Because of this, I end up backing off on the pre straightener and running the final straightener way too tight to make the machine run. This is really hard on the final straightener.

I am assuming the servo is faulting because the 5/16 is much harder to push through the pre straightener then the 3/16. I had been considering manually adjust the Load Inertia or Peak Torque values in the parameters to compensate but I realize that is not the proper way to address this problem.

What would be the proper way to address this problem? Please keep in mind I am more or less a beginner.

My first question would be, is the servo that is pushing the pipe through the straighteners also being used to determine the cutoff length? If it is not, then you could play around a little with the position tolerance a little and see if that helps, but the position error is really just the symptom of the real problem.

Question #2 would be, does the pipe get fed completely through the straightener before getting cut, or does it motor have to get it moving again from a stop while it is in the straightener? If it has to get it moving again while in the straighter, I would slow down the acceleration rate. It may well be possible that you will need to slow the acceleration rate down regardless.

My suggestion would be to slow the feed rate down (commanded speed on the servo) when you are running the 5/16 pipe. That will likely give you the best result. I have on rare occasions had to adjust the torque values, but this was usually a stop gap measure to compensate for a mechanical issue.


Hope this helps,
Will.

Thanks for the reply.

In response to your first question, cut length is determined by an external encoder positioned right before the cut head.Slippage at the feed rollers would account for the S54 fault.
Secondly, the pre straightener is between the feed rollers and cut head so the machine does have to push the tube through the pre straighteners from a dead stop each cycle.
I do adjust the speed down somewhat for the 5/16, I run 3/16 at 40 and 5/16 at 30.I adjust this speed in the receipt table of the HMI.
It may well be that I need to adjust the velocity loop instead of the torque loop, which parameter would you suggest to adjust?

The S54 error is a position error. This normally occurs when there is not enough torque for the axis to follow the position plan. I have not used an external encoder with an axis before but I am pretty sure you won't get position error because of slip at the drive rollers because the error is measured at the motor feedback. The external encoder is used to compensate for the probability of slip at the drive.

You may not have enough grunt to do the job. You can cheat by adjusting the position error window when feeding length then slow down to a crawl near the final position and adjust the position window down again.

The position window can be adjusted using SSV commands.

Geoff White said:

The S54 error is a position error. This normally occurs when there is not enough torque for the axis to follow the position plan. I have not used an external encoder with an axis before but I am pretty sure you won't get position error because of slip at the drive rollers because the error is measured at the motor feedback. The external encoder is used to compensate for the probability of slip at the drive.

Click to expand...

Thanks for the info,I had that wrong,I was thinking the error was generated when the difference between the encoders became too large.

[/QUOTE]You may not have enough grunt to do the job. You can cheat by adjusting the position error window when feeding length then slow down to a crawl near the final position and adjust the position window down again.

The position window can be adjusted using SSV commands.[/QUOTE]

This sounds interesting, could you direct me to where I could read up on on this.I tried the help files in studio 5000 but I didn't get enough out of them to fully understand,some examples would be really helpful.

To modify the axis properties dynamically you can use a SSV command
SSV(Class Name, Instance Name, Attribute Name, Source)

eg
SSV(Axis,Collator_Axis,PositionErrorTolerance,HMIrLagErrorEstop)

Create a SSV and have a look at the available Attribute Names available.

IF you want to try and change the motion dynamics make sure you don't change the speed/ramp such that the target position cannot be reached without overshooting! The MCD command can be used to change all the parameters of the current motion. It you do something like setting the speed to zero any moves will not complete.

There is a stupendous amount of information available about motion in the start page and resource center.

If you can live with the larger position error tolerance I would just set it to a large value and leave it alone. The position error tolerance is a protection mechanism to make sure an axis doesn't come completely off the rails and damage something. It is the in position window size that determines when an axis is close enough to the position setpoint to consider the motion complete.

I do agree with Geoff White that you don't have enough driving capability to straighten the larger diameter tube. The 5/16" tube is probably something along the lines of 4 times stiffer that the 3/16" tube. That is a big difference. You may be slipping or you may be stalling the motor but either way you don't have enough driving force to bend the bigger tube.

Keith

kameges makes a valid point. The position window may be stupidly small. When you create an axis the position error window is usually miniscule in engineering terms and normally it can be increased significantly without any noticeable effect.