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 January 19

[[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 January 22

[[Pa...]]

Thanks everyone.  There is no way we can qualify 75+ styli every day.  Our machines are shut down and homed at most 5 times per year; we do not home for any other reason.  We constantly check parts 30+ inches long with .0005" positions and ± .0001" diameters and have been doing so with one of these machines for almost 30 years, so...

We have 78 "standard" styli in the MSR rack at all times; these are all qualified weekly or Calypso won't run them.  We have probably 100 more in various configurations that are used occasionally and qualified prior to use.  Some of these are qualified only once or twice per year.  I almost always have some systems that haven't been used in over a year and I consider breaking them down to free up storage of other systems.

As far as loss of position, I feel the base alignment resolves this loss.  We use manual start alignments to locate at first piece setup. At the time of inspection, all points are relative to one another.  They have a reference in MCS, but the nominal locations of every point in the inspection are relative to a base or subsequent alignment.    Qualification simply measures the subject stylus using the Master Stylus as reference.  MCS location becomes inconsequential.

I do have a routine that moves the machine to the back top RIGHT corner of both machines in one room.  They share a hoist and it approaches from the outboard side of each.  It isn't high enough to clear the towers of my big (16 42 15) CMMs.  We have an interlock that sees the machine in the correct "interlock" position (using MCS) and will not allow the hoist over the machine unless that interlock position is satisfied.  In 12 years I've not seen it fail regardless of what kind of mayhem an operator has put the machine through.

If the machine comes down somewhere other than it's expected, we depend on (require) operators to be watching for those first couple of features.  It's very rare and so far ALWAYS to do with an operator setup error, incorrect stylus qualification, or incorrect program run.

Imagine I have 5 styli.  One is the Master, 2 other systems have two styli each.  I have a major crash using stylus number 1 on system 1.  It breaks both styli on the system, drives off.  It's a good one.  Why would I think there's been a change to the relationship between the Master and stylus 5 on system 2, both of which sat safely in the MSR for the entire event?  Why would I think anything at all has changed about #5 that couldn't occur in another scenario that does not include a collision to some other system or even the sensor (VAST Gold?  Calypso, if I haven't broken anything, has reliably confirmed this many times for me.

I'd restart drives, home the machine, rebuild the system, locate the reference sphere using Master, and qualify my new styli only.  I'd make a quick check of something I picked up just prior to the crash with the new system.  Re-run the base alignment and begin the inspection again.  Keep going.

FWIW, I've been qualifying the 52 standards immediately after drives on for 12 years.  I've never seen any tangible change to any stylus except for the one that crashed.

I've made my decision.  We'll use that 3 hour qualification period to add value to workpieces.

[[Ch...]]

Pat,

 

 You can also add stylus qualification inside the programs for just the tips needed and run that before inspecting a lot of parts.(not for every part in the lot of course.)

Also if you search in calypso help file I believe it states you can use a 6 point qualification for a quick probe check and it may actually recommend this to save time for normal probe qualifications. This should reduce your time significantly.

 

 

[[Ch...]]

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**This. This could mean a few things, but if it's major it could have moved position slightly or affected torque/components of the sensor. If it did not involved the RAM or outside of the probe hitting something hard ( I think Zeiss has limits for hard/soft hard may be over 200mm/s ), then re-qualifying only the stylus system is generally fine.

 

 

[[Pa...]]

Yeah the CMM folks are always at odds with management about what is a major / minor / moderate collision.  I do like our existing policy which states a "Major" collision (a pretty comprehensive definition exists in the procedure) is to be followed by (many things including) a very thorough artifact check in multiple positions. A tech is called if I see anything and the machine does not move until the tech moves it.  Ring scans can tell a lot more than a qualification failure.  You're right though, context is everything.

I've not looked at 6 point qualification.  I can see this being helpful, and perhaps a nice compromise.  

I'm aware that I can put qualification routines in the program.  In many cases there (may or may not) be clearance issues.  Huge parts, styli that reach 35+" from the head in two directions, etc.  While this is a super useful tool I don't see implementing it here.  I create a setup instruction in Pptx that address qualification before loading the piece, MSR pocket choice for the unusual systems, part location, cleaning instructions, and expected run time. 

As always, I appreciate the time everyone takes here.