A Study of the Accuracy of Touch-Trigger Probe.

A touch-trigger probe is widely used as a position-detecting device for coordinate measuring machines. There are a few problems to be solved concerning the accuracy of the probe. One is that the sensitivity periodically changes because of the directional quality of the measuring force ; also, the detected position fluctuates corresponding to the contact speed and the moving direction of the probe. These are considered to be systematic error components. As for measurements performed in the XY-plane, these errors can be conveniently compensated by probe ball diameter correction. The correction value and its direction, however, must be estimated taking the contact direction angle into consideration. Therefore, errors due to the touch-trigger probe are hardly compensated in the case of accurate measurement that involves various directional approaches of the probe, for example, complicated curved surface. In this study, the directional quality of measuring force is investigated. It is indicated that the sensitivity of the probe is caused mainly by the deformation of the probe stylus due to measuring force. The relationship between the deformation and the contact direction angle is obtained. The experiments show that the effects of the directional quality can be nearly eliminated by the correction proposed.