Position error is associated with actual amount factors on changes of the elements being measured. As the benchmark of the actual parts also has shape error, thus it need to simulate benchmark elements in conventional measurement, which usually use the surface with enough shape.
When using three coordinate measuring machine, we only need to measure several coordinate points on the work-piece, then parallel error can be calculated by computer. Measuring precision depends on the CMM accuracy, it has nothing to do with artifacts of place, so it more close to the actual situation of parts being tested.
Surface measurement can be divided into two kinds: one is the theory of the measured surface shape has been known, then assess the actual surface, in fact it often requires measuring curved surface profile error; The other is the theory of curved surface shape is unknown, according to the actual measured data, fitting theory surface. The conventional method is mainly used for the first kind of measurement.
During the measurement process by using CMM, we only need to place the parts to be tested on the workbench, correct positioning and alignment, measure several points in manual measurement mode, and compare the measured results with theoretical contour.
Conventional measuring method has not only poor repeatability but low measuring efficiency. Three coordinate measuring machine is more difficult to master than conventional measuring instruments, but it can measure the geometry size and shape at the same time. In the position error of measurement, we don’t need to use auxiliary device to simulation benchmark. Moreover CMM is with high measuring accuracy and measuring efficiency, which is a must in manufacturing quality test.
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