Prehit detour

[pernilla]

Hi.

I've got this old CMM (Mistral) that's started acting in a way it didn't use to before... We recently had it served and calibrated by Hexagon but I can't say when (other than recently) this started.

When it's taking a point on a plane (Z+ or X+/-), in the prehit distance it takes a small detour. I had to snap a video in slow motion to properly see what it was doing, but I couldn't upload it, so I tried to draw the path that it takes before the hit, on a photo (borrowed from an NPL good practice guide pdf).

This happens to at least two different probes and it seems to happen mostly when moving between two points in Y-axis.

Measurements don't seem to be affected by this, and the calibration results were fine. But I'd like to know why this has happened, has anyone seen this before? Is there an explanation to this odd behavior?

123.png

[AndersI]

Different acceleration in different axes?

[pernilla]

I don't think so, I haven't changed any acceleration settings. But where do I check this?

[pernilla]

Found it. Machine acceleration 175 in each axis.

[Sora5]

Is it some kind of oscillation? Does this still happen when you slow the machine down?

I had a 20yr PFX that had some oil in the line and caused it to oscillate back and forth when traveling at high speed.

[Matthew D. Hoedeman]

what hardware (TP20, SM25)?

WAY back in the day, a Pcdmis upgrade screwed up the way my Validator moved. It no longer would move correct vectors in the Z plane (moving in X & Y at the same time, not sure if it also did it in any other plane, but I could SEE it when working on a flat part, checking the side), it would sort of 'curve' as it moved to take a touch. The servo's needed to get re-tuned for it to move correctly again.

Also, is your positioning tolerance set too tight?

[A_Shomshor]

This ^^^^^^^

[pernilla]

I'll see what happens when I slow the machine down, but it'll have to wait to tomorrow.

And I use a TP200, which is only a few months old. I haven't upgraded recently.

How do I check positioning tolerance?

[RandomJerk]

Positioning tolerance is under Edit...Preferences...Parameters (F10). There's a tab for either Opt. Probing or Probing Options, on the left is a positioning accuracy box.

Take a vid, upload it to YouTube with the unlisted option, then you can post the YouTube link here.

[Peter Fuller]

My bet is a failing drive screw.

[louisd]

Yes our mitutoyo bright apex did this to us along a certain worn-out (damaged) spot in Y axis.

[pernilla]

So here's a video:

https://youtu.be/cAnQ-vc9tB4

And here's the positioning accuracy box:

positioning accuracy.png


Can I check if it's a failing drive screw?

[pernilla]

Also, I slowed the machine down and the more I slowed it down, the better it got.

[Peter Fuller]

Option probe statements have nothing to do with touch trigger probes. It looks like a service issue, I wouldn't suggest tinkering with it.