[Br...] Posted January 10, 2020 Share Posted January 10, 2020 Hello Zeiss forum. This is my first post and first day on this forum. Thank you in advance for any information you can provide. I am a Calibration Technician not a CMM technician or Operator so please forgive my lack of knowledge of CMM's in general and Zeiss CMM's specifically. I need a lesson in how to determine the accuracy of a Zeiss Prismo CMM with Calypso software from a calibration cert from Zeiss. I am going on a job interview for a calibration technician position at a different company and need to show i have some knowledge of Zeiss CMM accuracy. This position availability has come up suddenly and needs to be filled quickly so this is the start of my quest for additional knowledge in this area. I have previously reviewed Hexagon CMM certs for accuracy which seem to be more straight forward from what i remember (its been a few years since I dealt with them) The parts being inspected are metal disks of different size and shape with tall hubs, short hubs, landings and troughs so the measurements will be dimensions such as diameter, thickness, flatness, parallelism and concentricity. I am guessing this wont be a quick lesson but if someone can provide links to posts or other documentation that can help me gain some basic knowledge or to at least be able to tell the interviewer halfway intelligently what I am in the process of learning it will be much appreciated. I'm not trying to fool anyone just want to show i have made a honest effort to gain more knowledge. Thanks again. Brandon Link to comment Share on other sites More sharing options...
[SH...] Posted January 10, 2020 Share Posted January 10, 2020 First up all we don't use to word accuracy in cmm,we call it as error ,MPE maximum permissible error. It is usually stated in the form MPE=A+L/B in micron meter. Where L is the measuring length,A and B are constant dependent upon the machine size and the technology used in the machine. We have lot of international standards available for calculating the uncertainty of cmm such as ISO 103600. A cmm machine can have errors along 21 different measuring axis,so we should use accurate calibration data to make sure any misalignment is determined. During calibration we calculate the volumetric accuracy of the machine.For calibrating cmm artefacts are being used, different artefacts are using dependent upon the type of probe and machine ,common names are step gauge, length block etc. Link to comment Share on other sites More sharing options...
[Er...] Posted January 10, 2020 Share Posted January 10, 2020 😱? Sure we use the term accuracy as well as repetabillity and a bunch of other terms. How would you otherwise explain the errors? Lets say we have 5 points. Then accuracy describes how close our 5 points are to the true value. Repetabillity describes how close those 5 points are to each other. Link to comment Share on other sites More sharing options...
[SH...] Posted January 10, 2020 Share Posted January 10, 2020 Please sign in to view this quote. Accuracy is the used in manufacturing,especially VMC HMC machines. In measuring we using the time uncertainty... Link to comment Share on other sites More sharing options...
[Er...] Posted January 10, 2020 Share Posted January 10, 2020 And how do we find uncertainty? In a very simplified equation: a_ _ _ _ _ _ _ + _ _ _ _ _ _ _ _illity, feel free to fill in the blanks... Link to comment Share on other sites More sharing options...
[SH...] Posted January 10, 2020 Share Posted January 10, 2020 Please sign in to view this quote. For a new machine it defined by manufacturer,for old machine through experience we can predict it. Link to comment Share on other sites More sharing options...
[Er...] Posted January 10, 2020 Share Posted January 10, 2020 And how do you think the manufactures determines it? What would you say is the issue here? Link to comment Share on other sites More sharing options...
[De...] Posted January 10, 2020 Share Posted January 10, 2020 When Zeiss determines if a machine is within manufacturers specifications, they use the ISO 10360 standard. ISO 10360-2 is used for 1D Linear and 3D Spatial runs to check maximum permissible error in length measurement MPE. (E0) ISO 10360-4 is used to check scanning (THP and T) ISO 10360-5 is used to check single stylus form error (PFTU) Depending on the machine and the spec for the machine, additional checks may be made for roundness (RONt) These checks would use ISO12181 or VDI/VDE 2627 I have based this off the checks they perform on our various machines. If the machines includes optical or other sensors, then they would likely have other checks made to test that functionality. We do not have any machines with those additional functionality so I do not have any information on what those checks might be. Link to comment Share on other sites More sharing options...
[To...] Posted January 10, 2020 Share Posted January 10, 2020 Semantics? Machine tool people speak in "accuracy and repeatability" and cmm metrologists speak in "allowable error" but it all still comes down to the accuracy and the repeatability of the results. Link to comment Share on other sites More sharing options...
[Er...] Posted January 10, 2020 Share Posted January 10, 2020 Please sign in to view this quote. Semantics, nah, a plain wrong statement. We do use accuracy. MPE, maximum permissable error is used to "Grade" the machine. To find out if it is up for the task. Uncertanity, then a part is most likely involved. And is determined with either a rigorous study or vcmm or ovcmm module. As I posted previously, what would you say about the issue in the picture, repetabillity? Uncertanity? Accuracy? Out of beer? Link to comment Share on other sites More sharing options...
[De...] Posted January 10, 2020 Share Posted January 10, 2020 I would wonder how that axis was finding all measurements to be long by the same amount. Did someone stretch this machine out, is it made from rubber? 😃 In the real world, you would need to see all the other axes in order to make a determination as to what was going on with the machine. I am guessing the answer you are trying for is accuracy though, although I think a better example graphic to use is a target with a bullseye since there is less interpretation with that than with a trumpet chart of a linear axis. Link to comment Share on other sites More sharing options...
[SH...] Posted January 10, 2020 Share Posted January 10, 2020 Please sign in to view this quote. I have no intention to argu with you, you might be correct. I told what I know... That picture is a different scenario, that is related to SPC. In SPC we would use the word repeatability, reproducibility etc... Link to comment Share on other sites More sharing options...
[Er...] Posted January 10, 2020 Share Posted January 10, 2020 Haha, yes, I agree a that a "bulls eye" or a circle would make a better example, but I had that picture on my desktop, call me lazy. How ever, it have a near constant issue with accurcy regardless of lenght. And neglible disspersion in relation to the accuracy. My point is that the word accuracy it very relevant. How ever, Im not sure what the OPs problem is, if he cant interpret the calibration reports or.. Since he have previous experience Im pretty sure he knows about 10360 since they arn't Zeiss specific. Link to comment Share on other sites More sharing options...
[To...] Posted January 10, 2020 Share Posted January 10, 2020 Please sign in to view this quote. It appears that "out of beer" is not the problem 🤣 Link to comment Share on other sites More sharing options...
[To...] Posted January 10, 2020 Share Posted January 10, 2020 Eric, If someone asks "how accurate and repeatable is the (fill in the model)", how do you answer that question? Link to comment Share on other sites More sharing options...
[Er...] Posted January 10, 2020 Share Posted January 10, 2020 ...prismo? Then I say "it has a guranteed mpe-thp of 0.9 in 40 seconds before you entered my room and Messing up the environment, without bringing me danish wiener. (thp is the most important parameter for us.) Accuracy and repetabillity depends on what part you bring me, and I can only give you an estimation before Im done." or something like that. Or "sorry, no swedish, no no, russki?" if its someone from the burner crew, hate those parts. Really tricky get good measurements on. Shabu "That picture is a different scenario" - how? Im not sure I understand what you are saying. Link to comment Share on other sites More sharing options...
[Is...] Posted January 13, 2020 Share Posted January 13, 2020 The maximum permissible error is the tolerance for the accuracy and precision (repeatability). in the Eric's MPE graphic is evident the high precision and the accuracy deviation. Link to comment Share on other sites More sharing options...
[Gr...] Posted January 15, 2020 Share Posted January 15, 2020 Here is a CMM Accuracy Statement.pps I got a conference a couple of years back. Shows how how Zeiss certifies their CMMs Hope it is helpful. Had to zip the file because the forum does not let me attach a power point file. Greg K Link to comment Share on other sites More sharing options...
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