Y-Axis Drifting Out of Position

[schmittys]

Recently our Hypertherm HPR130 system has started to have a mind of its own. It is a 3-axis system, 144" x 96", running with 3 servo motors. The controller is a Hypertherm EDGE.

During the last week, the plasma torch has begun to drift to the far side of the Y-Axis as cutting progresses through a nest. For example, we cut a series of 3 rows of 10 holes in a part that are in a straight line going up the X-Axis. The center to center distance from the first hole cut to the last hole cut should have been 75" on the X-Axis and 46" on the Y-Axis. When measuring the hole, the X-Axis reads 75", but the Y-Axis measurement is 46.3125"! The hole pattern was off by 5/16" to the far side of the Y-Axis, which is completely unacceptable.

When we slow the traverse speed down to half of the original settings, the results are mildly better, but the Y-Axis is still out of position on almost any part.

We have been digging into our parameters and looking at the torch head, as well as the gears and rollers, but have found nothing. After some thinking and some research, we believe that this is a mechanical problem with the DC servo motor on the gantry, but want to make sure before we replace expensive parts. We have retained all of the settings that have been working for 2+ years.

Has this ever happened to anyone or anything similar? Is there a parameter to set within the machine that would change how this happens? Are we doomed?

I hope that I am posting within the regulations of this great site. If not, please let me know and I will shape up. Thank you for looking!

Joey

[WSS]

Loose pinion gear? Maybe the tensioner is not tight enough. Is the pinion worn excessively? Two years of running, something is bound to change, sometimes all of the sudden. A loose pinion will show up on accel like a rapid move to next pierce, so it might not show up on the actual cut ie. oblong or oval instead of circle. Does the shaft-to-servo have a keyway or is it a flatted shaft? Keys work better but when or if they shear things can get way out there. I would pull the pinion first to take a look before moving to a servo or encoder. Encoders can be finicky too.

Good luck,
Welcome to PlasmaSpider!
WSS

[srp]

If you have a servo system you should have a feed back loop from encoders. This relates to the position of the torch to the controller. On your EDGE controller you should be able to see what the following error is. I think you are about to enter a learning curve about motion control. This will be an opportunity to learn what you can do with that controller to obtain the best performance with your setup. Good luck. - John

[schmittys]

Thank you both for the responses.

We have checked the tensioner, but that is tight. We have also looked at the pinion mount, but that also looks like it is performing up to standards -- it has been updated through the years and does not appear worn or loose. The shaft-to-servo has a keyway, but the group of people looking at the system believe it to be of acceptable quality for standard performance. We will re-check these elements today just to make sure.

Next we will give the system a feedback loop to see what happens. I will update this as it goes if I find anything. Signs are pointing in the encoder/motor direction, which is unfortunate. Thank you for all the suggestions.