The factors that affect the accuracy of image measuring instruments mainly include accuracy instructions, structural principles, measurement methods, and routine careless maintenance. In 1994, China implemented the international "Acceptance Testing and Retest Measurement of Coordinate Surveying". The specific content is as follows:
Part 1: Coordinate measuring machine for measuring linear dimensions;
Part 2: Coordinate measuring machine with the turntable axis as the fourth axis;
Part 3: Scanning measurement type coordinate measuring machine;
Part 4: Coordinate measuring machine for multi-probe detection system;
Part 5: Calculation of Gaussian auxiliary elements error assessment. Measure a set of gauge blocks of five sizes at any seven different orientations in the measurement space. Each gauge block length is measured three times. All measurement results must be within the specified MPEE value range.
Maximum allowable detection error (MPEP): 25-point measurement precision standard ball, evenly distributed detection points. The maximum allowable detection error MPEP value is the maximum value of all measurement radii.
ISO 10360-3 (2000) "Coordinate measuring machine equipped with a turntable axis as the fourth axis": For measuring machines equipped with a turntable, the measurement error of the measuring machine is defined in this part. It mainly includes three indicators: radial four-axis error (FR), tangential four-axis error (FT), and axial four-axis error (FA).
ISO 10360-4 (2003) "Scanning measurement type coordinate measuring machines": This part applies to coordinate measuring machines with continuous scanning function. It describes the measurement error in scan mode.
Most measuring machine manufacturers define spatial scan detection errors in the case of THP. In addition to THP, the standard also defines scan detection errors in the cases of THN, TLP and TLN. Scan along 4 determined paths on the standard sphere. The maximum allowable scan detection error MPETHP value is the maximum difference between all scan radii. THP describes the scanning characteristics along a known path at the point of greatest density. Note: The description of THP must include the total measurement time, for example: THP = 1.5um (scan time is 72 seconds).
ISO 10360-4 further explains the following definitions:
TLP: Scanning at a low density of points along a known path.
THN: Scan with a high density of points along an unknown path.
TLN: Scan with low-density points along an unknown path.