# Noncircular gear CMM measurement

Noncircular gear will produce machining error in the process of machining. The size of machining error reflects the level of machining accuracy. In the process of machining, manufacturing error and wear of machine tool, fixture and workpiece clamping error will cause machining error of workpiece.

When using CMM to measure non-circular gear, it is necessary to measure the non-circular gear point. The error value of the non-circular gear error item is obtained by calculating, and then the accuracy grade of the error item of the non-circular gear is obtained by looking up the table. The measuring method is that the non-circular gear is clamped on the workbench, and the three-dimensional probe is used for tooth by tooth contact scanning measurement

1) There are sensors in the three-dimensional probe, which can aim signal and micro displacement in three directions of X, y and Z in the three-dimensional coordinate system, and trigger aiming can be realized to measure the deviation from the given standard value. Therefore, tp200 contact electric probe is selected for measurement It has the advantages of ultra micro trigger technology, precise spatial shape measurement accuracy and excellent repeatability

2) If the measurement path is not reasonable, it may lead to collision between the probe and the workpiece to be measured, damage the probe, and the measurement data is not accurate. Therefore, when planning the measurement path, the movement path of the probe should be reasonably arranged.

3) The measured data are fitted by curve fitting. There are three methods of curve fitting: cubic spline interpolation fitting, least square fitting and polynomial fitting. The above three methods are used to fit the measured data. By comparing the expression of fitting curve and residual value, the quintic polynomial is selected as the fitting curve of tooth profile.

4) The error of non-circular gear measurement items is obtained by calculation. The calculation method of each error item of non-circular gear is studied, and the mathematical model of each error item is deduced. The tooth pitch error, tooth profile error and tooth thickness error of non-circular gear are obtained by calculation.

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