Philosophy of CMM Software and CMM

Z

zancky

I would like to start a thread about CMM.
I'm using a small Mitutoyo's one with Renishaw's touch probe and camera system
the handbook with the machine it is not enough for good performance, training from dealers not to be mentioned, help from Mitutoyo most of the time lacking. therefore I learned by myself how to use it, writing scripts, testing (some failures), asking help to some friends and so on. Now I have found this forum and a lot of very good technicians so I suppose it is time to to share my experience and find some suggestions and help
some the topics I would like to discuss with You:

-1) writing programs or use "learn mode"?
Personally I have promised to cut one finger to anybody in my lab. each time they try to use "learn mode" (so they have max 10 trials:mad:)
Once a techician from Mitutoyo asked me the reason why I was so against "learn mode"
My answer was: "First are You able to elaborate a program in "learn mode" to measure a part with an accuracy about 2 microm wherever is the part, whichever is the operator?.
Second how You can optimize the program (approcing distances, speed, movements) in "learn mode"?
Third how you can compensate the algorithm bugs of Your system in "learn mode"? (I will explain after that topic)
Forth I know trigonometry,some basic other languages and programming tecnique, I can read a drawing, why I can not apply my knowledge?
Which are Your point of view and Your experiences?

-2)How You start your program, i.e. alignement of the axis and origin to the part.
Normally I spend from a third to half of the working time for alignments looking for part simmetry (luckly we are measuring deep drawing parts so there should be a revolution axis)


-3)CMM touch probe, European point of view on measuring (mean value) and Taylor principle (every point inside tolerances).
let's consider just a bore with diameter Ø12±0.1mm for a length of 20 mm. Standard CMM results will give You the mean value and the roundness of the cylinder (mean value is the way used to calibrate the machine). Asking for inner material or outer material diameter will sometime give You strange results (see how roundness changes respect to mean value one). therefore CMM touch probe seems to fit european point of view about measurements and have some problems with Taylor principle. Which are Your point of view and Your experiences?

-4)Touch proble single point bug. Try to measure a inner diameter of a known calibrated ring. if You use the circle or cylinder feature the discrepancy may be 2 microns. Now try to measure the same ring using point (edgepoint). Well if you plot the data on XY diagram You will find that at 45°, 135°, 225° and -45° the points are closer to the center of the circle while they perfecly on the circle every 90°. It seems it comes from a bug into the system. When the touch probe touches the surface it allocates the point coordinates like touching moving along X or Y whatever it is the actual direction vs surface normal. If You change the refence axis according the the direction of approcing to the surface the mistake vanishes. How many other bugs do You know?

-5)I have used CMM to measure wall thinckess on a cylinder like part. Well it took one month to establish the best fixture and the related program but at the end the correlation with the customer laboratory was better then 2 microns. Have you any strange application of CMM?

-6)I have taken the choice to ask to Mitutoyo to perform calibration so my customers are happy (traceability etc..) but I think that 95% of accuracy, while measuring a real part, depends on how I have written the program. the influence on temperature, humidity, etc is a secondary problem. Just to give an idea. Some years ago a customer asked me to measure the minimum and maximum inner diameter point to point on a cylinder like part with nominal diameter of 6.04 mm and wall thickness of 0.15mm. First I said "Sorry but at the moment I'm not able to do it". He said "ok we know a certified/accreditated external laboratory that can perform the task, they are actually calibrating our gauges". After one month we have the results: the certified laboratory declared that the minimum inner diameter was on 5 samples between 5,98 and 6.00 mm. I called them and I asked "how can you explain me that You have found 5.98-6.00 but a Ø6.01 mm plug gauge passes frely through the parts?". "May be there is a mistake somewhere" was the answer.:(
Do you know something similar?

-7)I would like to know how the machine calculates the features (interpolation algorithms) as asking for microns even the philosophy behing the machine software may have an influnce. What do you think?


sorry for my english and typing mistakes, but let me know if you are interested on it and your opinion:thanx:
 
T

True Position

For those of us who don't run Mitutoyo CMMs, what is 'Learn Mode'? Automatic feature generation? Zeiss's use that and I love it. It prevents me from going back to the machine as often when trying to write a program.

Also, this thread would make more sense in the Inspection and Test forum.
 
Z

zancky

For those of us who don't run Mitutoyo CMMs, what is 'Learn Mode'? Automatic feature generation? Zeiss's use that and I love it. It prevents me from going back to the machine as often when trying to write a program.

Also, this thread would make more sense in the Inspection and Test forum.

Hi Hawat,
I don't like Mitutoyo learn mode, I suppose it is something like your "Automatic feature generation". To me it sounds like using the machine at 50% of its capability. I find the typing the program is faster with a better accuracy. Some task can not be performed in "Automatic feature generation" for sure (e.g. I have been requested to measure a runout error on 90 points on a inside diameter).
For us how long it takes to measure a part is very important as we have so many parts to be measured by hour (one minute quicker is appreciable). Therefore even if I use "Automatic feature generation", I would have to go into the script to minimize/optimize touch probe travels.
Anyway I would like to know Your experience, may I ask You your repeatibility with "Automatic feature generation"?

thanks
 
T

True Position

I run a Zeiss with Calypso and have a scanning head so taking lots of points (I'll usually take 360 per rotation) isn't a large deal. For something like a deep cylinder I might take a helical path with 2000+ points and something like that might only take a minute or so to scan.

As for moving around the part, instead of stringing together goto points and measure points like a CNC program, with Calypso you generally just define a safety cube around the part and fixture then the CMM will guess the closest retract plane. If you prefer another you can manually edit it. Increasing speeds with sub-clearance planes can be done if time is super critical.

The programming between like Geomeasure and Calypso is pretty different. Geomeasure used to always feel like programming a milling machine, 'rapid to here' 'measure speed move this direction' 'rapid to here' 'measure speed move this direction' etc. There is none of that to Calypso, you can select only certain features in a measurement plan and it can align and only measure those few dimensions.
 
J

John Nabors - 2009

I've run many different makes of CMM's using a lot of different software packages. Right now I'm early in the process of learning Calypso sort of the same way the cat learned how to swim (no real training, just 'poking and hoping' and I'm still struggling a bit with it), but I can already see that Calypso is utterly superior to any software I have used before. The shame is that the last time I was on a Zeiss (10 to 13 years ago) we bought our Eclipse something like 6 months before Calypso first came out and I learned the Zeiss using the old UMESS software. If we'd just waited a little longer to buy the machine I wouldn't be having to unlearn everything I ever learned using Zeiss UMESS, Geomeasure, DMIS, and the rest.

Yesterday I programmed a fairly complex aerospace part by extracting the features to Calypso from a Catia V solid model. Took about 3 hours programming a part that probably would have required 2 days on any other software I have used. That was COOL!! :)

Hawat- One thing though- for whatever reason I can't get the X axis clearance planes to work properly. Even Zeiss IMT in Michigan couldn't figure it out and referred the problem to Germany. Still waiting to hear back on that but it's an easy workaraound, I just retract to the Z axis clearance plane where I would normally use X. Programs take marginally longer to run, but it works.

(I am not affiliated with Zeiss or any other CMM manufacturer)
 
T

True Position

About your X axis retract, did you try setting a sub-clearance plane in X and retracting to that? I rarely have issues with retract planes, and most of the time it's my own fault for not noticing I'm about to retract into my part.

As to your CAD models, I wish I would get them from my customers. I still work almost entirely from paper drawings, I've tried to do some samples from cad data and it seems a lot faster except for the 'Why is my part rotated 90 degrees and backwards when I import it into Calypso?' issues.

I've had a lot of good luck with IMT support the couple of times I've called, hopefully they'll come through for you.
 
P

prototyper

I would like to start a thread about CMM.
I'm using a small Mitutoyo's one with Renishaw's touch probe and camera system
the handbook with the machine it is not enough for good performance, training from dealers not to be mentioned, help from Mitutoyo most of the time lacking. therefore I learned by myself how to use it, writing scripts, testing (some failures), asking help to some friends and so on. Now I have found this forum and a lot of very good technicians so I suppose it is time to to share my experience and find some suggestions and help
some the topics I would like to discuss with You:

-1) writing programs or use "learn mode"?
Personally I have promised to cut one finger to anybody in my lab. each time they try to use "learn mode" (so they have max 10 trials:mad:)
Once a techician from Mitutoyo asked me the reason why I was so against "learn mode"
My answer was: "First are You able to elaborate a program in "learn mode" to measure a part with an accuracy about 2 microm wherever is the part, whichever is the operator?.
Second how You can optimize the program (approcing distances, speed, movements) in "learn mode"?
Third how you can compensate the algorithm bugs of Your system in "learn mode"? (I will explain after that topic)
Forth I know trigonometry,some basic other languages and programming tecnique, I can read a drawing, why I can not apply my knowledge?
Which are Your point of view and Your experiences?

-2)How You start your program, i.e. alignement of the axis and origin to the part.
Normally I spend from a third to half of the working time for alignments looking for part simmetry (luckly we are measuring deep drawing parts so there should be a revolution axis)


-3)CMM touch probe, European point of view on measuring (mean value) and Taylor principle (every point inside tolerances).
let's consider just a bore with diameter Ø12±0.1mm for a length of 20 mm. Standard CMM results will give You the mean value and the roundness of the cylinder (mean value is the way used to calibrate the machine). Asking for inner material or outer material diameter will sometime give You strange results (see how roundness changes respect to mean value one). therefore CMM touch probe seems to fit european point of view about measurements and have some problems with Taylor principle. Which are Your point of view and Your experiences?

-4)Touch proble single point bug. Try to measure a inner diameter of a known calibrated ring. if You use the circle or cylinder feature the discrepancy may be 2 microns. Now try to measure the same ring using point (edgepoint). Well if you plot the data on XY diagram You will find that at 45°, 135°, 225° and -45° the points are closer to the center of the circle while they perfecly on the circle every 90°. It seems it comes from a bug into the system. When the touch probe touches the surface it allocates the point coordinates like touching moving along X or Y whatever it is the actual direction vs surface normal. If You change the refence axis according the the direction of approcing to the surface the mistake vanishes. How many other bugs do You know?

-5)I have used CMM to measure wall thinckess on a cylinder like part. Well it took one month to establish the best fixture and the related program but at the end the correlation with the customer laboratory was better then 2 microns. Have you any strange application of CMM?

-6)I have taken the choice to ask to Mitutoyo to perform calibration so my customers are happy (traceability etc..) but I think that 95% of accuracy, while measuring a real part, depends on how I have written the program. the influence on temperature, humidity, etc is a secondary problem. Just to give an idea. Some years ago a customer asked me to measure the minimum and maximum inner diameter point to point on a cylinder like part with nominal diameter of 6.04 mm and wall thickness of 0.15mm. First I said "Sorry but at the moment I'm not able to do it". He said "ok we know a certified/accreditated external laboratory that can perform the task, they are actually calibrating our gauges". After one month we have the results: the certified laboratory declared that the minimum inner diameter was on 5 samples between 5,98 and 6.00 mm. I called them and I asked "how can you explain me that You have found 5.98-6.00 but a Ø6.01 mm plug gauge passes frely through the parts?". "May be there is a mistake somewhere" was the answer.:(
Do you know something similar?

-7)I would like to know how the machine calculates the features (interpolation algorithms) as asking for microns even the philosophy behing the machine software may have an influnce. What do you think?


sorry for my english and typing mistakes, but let me know if you are interested on it and your opinion:thanx:

The UK's National Physical Laboratory (NPL) have produced a very good guide on probing strategies, which covers many of your issues in detail.

I have attached a link to their e-store. I would recommend guide number GPG No.41. GPG No's 42 and 43 are also a good source of reference on other CMM issues.
https://e-store.npl.co.uk/e-store/p...tall&numrows=59&offset=30&subproducttype_id=9

(I have no connection with NPL)
 
J

John Nabors - 2009

. I've had a lot of good luck with IMT support the couple of times I've called, hopefully they'll come through for you.

Believe me, the tech support folks in Michigan are fantastic.. I recently sent them an email praising them and cc'd it to their VP for customer service in Minneapolis. This particular issue had to be referred to Germany and I haven't heard back yet.

Actually, I'll be calling Zeiss tech support this morning, have an issue I can't figure out. I'm pulling a program off another solid model. I have almost all of the features for this part running fine, but when I extract one stupid little bolt hole from the model into Calypso the probe wants to miss by about .100". There's either something wrong with the way Calypso is extracting the feature or something wrong with my teeny little brain. :bonk:
 
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