Touch trigger probes are devices through which coordinate measuring machines (CMMs) collect dimensional measurement data in modern manufacturing environments. The vast majority of probes used on CMMs are touch triger probes, and most of these probes employ a kinematic seating mechanism for the probe stylus (Reid, 1993). Point-to-point probing test is typically used to evaluate touch trigger probe performance. The test method secpified in the ANSI (American National Standards Institute) B89 standard consists of measuring 49 points on a highly spherical reference ball and the 49 points are distributed by following a sampling plan or test pattern (ANSI, 1991). the user is allowed to specify desired sampling plan which contains 49 points. Standards of other countries usually require that a number of points are taken over one hemisphere of a reference ball roughly uniformly distributed. (For example, fifty points are used in VDI/VDE 2617 standard.) A best-fit sphere is then computed using the manufacturer's recommended algorithms (usually least squares) and the set of radii to each probing point (from the best-fit center) is calculated. The range of the 49 radii is defined as the point-to-point perfomrance index.
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