Qualification after drives off

[[Pa...]]

Accura and Accura2, VAST Gold in each

My company requires qualification of all styli after drives off, whether it happened due to a collision or a holiday weekend shutdown.  I've felt for a long time that this is unnecessary, particularly in the intentional shutdown scenario. What would change about a stylus or a stylus system (relative to the Master Stylus) during a shutdown?  I've got a couple machines; each has a rack with 21 systems.  They're all very different from one another, meaning I need to use 3 different sphere sizes in a total of 7 positions.  A full qualification of both machines takes just under 3 hours.  This past holiday the pain of lost hours was great enough I think I'm poised to make a change here.

I'd happily verify a couple and get back to work in 15 minutes if there were no findings.

Google's AI bot says there's no reason.  I believe him, but I don't trust him 😉

What do you guys think?

[[Ma...]]

I would calibrate right after crash just that probe system and then regularly, depending on your usage.

You can get into situation, where you have a collision which is not a collision, just a probe which ran into a void.
There is no need to do such calibration after drives are off - they can shut down to conserve air consumption every 15 minutes of inactivity - that would be hilarious to do calibration in this case.

I am running calibration program, which measure before calibration and then after calibration - this can tell you if you have a problem with specific probe ( lose screw and so on )

[[Da...]]

I'm using quite a number of different probe systems. If I did a complete re-qualification every day, I wouldn't do much else. So, I have to be smart about it.

I want to make sure of two things:

1. The probe systems measures the correct diameter. Instead of a whole calibration routine, I run a small routine that measures the reference sphere. That way I can make sure the measured diameter is within limits.
2. If I use multiple probes in one program, I re-calibrate those (and only those) ahead of my first run of the day.

Usually, I check the probes more often than I calibrate them. It's faster and gives you a feeling of security, because I had calibrations that I had to repeat, because the positions among the probe systems were not satisfyingly precise.

Edited Monday at 06:36 AM

[[Pa...]]

So far, just as I thought, except I didn't know about the drives shut down after 15 minutes.  That's a new one on me.  Is there a way I can validate this and show it to the people requiring this needless exercise?

Yes, qualification after collision is certainly necessary.

[[No...]]

They only shut down if the CMM is equipped with AirSaver. Then you have a small application on the PC where you can set the timeout and also shut them off manually. The default is 15 minutes.

This thread has a screenshot of the app:

https://qualityforum.zeiss.com/topic/18466-air-saver-help/

[[Je...]]

I would recommend you ask for proof of the claim that verification is needed after CMM shutdown.  In most situations, it is not risk-mitigating or necessary to requalify all styli after a power shutdown.

[[Ze...]]

I think a circumstance you might need to recalibrate after a shutdown is if you use the machine origin/coordinates for something in your inspection process. When the machine homes I think it resets the machine origin. It might be an inconsequential amount, but I suppose it could have an effect on accuracy. I don't know this for a fact. Just basing this on other machines that I've used. 

[[Ch...]]

not needed but probably recommended by Zeiss due to : when the machine loses air, the brakes stop the RAM, and this could result in very small positioning error such as loss of position < or = to 1 micron. Also for example when machine is homed it never goes to exact exact exact same spot, so positions will be extremely minor differences. That said, this minor position will not affect typical use, you usually have plenty of clearance to navigate to your part, also active scanning and feature measurement are based on the found datum base alignment, so standard clearances apply here as well.

My suggestion :

Daily: home machine calibrate all probes if possible.

soft to medium collision of stylus components : calibrate master probe and stylus system affected.

hard collision to the ram or the probe head that holds the stylus : home machine calibrate all probes as soon as possible.

Good luck, happy measuring !!

Edited 13 hours ago