Performance of Coordinate Measuring Machines

Article

Elshennawy, Ahmad K.; Cohen, Paul H.   (1987, ASQC)   University of Central Florida, Orlando, FL; The Pennsylvania State University, University Park, PA

41st Annual Quality Congress, May 1987, Minneapolis, MN    Vol. 41    No. 0
QICID: 3354    May 1987    pp. 595-604
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Article Abstract

Coordinate measuring machines (CMMs) are now representing the most efficient universal type of measuring equipment for the purpose of controlling the Quality of products. Assessing the performance of coordinate measuring machines is, therefore, an important issue that has led to a large number of papers dealing with calibration methods for coordinate measuring machines and improving their accuracy of measurement.

The geometric accuracy of coordinate measuring machines is affected by errors in the coordinate measuring system which can be mechanical, thermal, or electrical in nature, thermally induced errors which causes structure changes due to variation in the operating environment, deformations caused by the weight of the structure and the part under inspection, and by kinematic errors of the machine structure which introduce unfavorable form and motion errors. Testing the performance of coordinate measuring machines can be divided into three major areas; repeatability, linear displacement accuracy, and volumetric testing using a socketed ball bar. There are different methods that can be used to assess the accuracy of CMMs. These methods include: parametric testing of the machine, using stnadard artifact, or using the ball bar. Parametric testing of coordinate measuring machines with complete motion equations can be used to draw the error map of the machine. This is usually done using a laser interferometer system or another standard in direct comparison with the measuring and straightness and squareness errors. The use of volumetric standard or artifact is a direct method for assessing the machine performance that includes the overall geometric errors at the measuring point. The ball bar can be used as a rapid and easy check of machine performance and an estimation of its volumetric accuracy. The B89.1.12 standard on coordinate measuring machines defines a procedure for testing CMMs and clarifies their performance evaluation. In this paper, this procedure is applied to a moving-bridge coordinate measuring machine and typical results are presented.

Keywords

Inspection division,Coordinate measuring machine (CMM)


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