An active piezoelectric probe for precision measurement on a CMM

Abstract

The use of coordinate measuring machines (CMMs) for post-process inspection has increased as their speed and accuracy of measurement have improved; however, current passive CMM probes are still limited with respect to these criteria. The implementation of a piezoelectric (PZT) actuator as an active probe for use on CMMs is investigated. PZT actuators provide machines with a higher bandwidth response, enabling a CMM to measure more accurately at faster speeds. The development and control of the PZT probe are detailed. Upon development of the probe's experimental setup, validation of its performance is achieved by the implementation of a basic (proportional) control scheme. The goal of the probe's controller is to maintain a constant contact force between the probe and workpiece, following (while measuring) the profile of the workpiece at highly precise levels. Experimental results of the PZT based active probe are compared with results from a passive probe to quantify its relative advantages. The PZT based probe performs better than the passive probe in two areas. First, it is more effective at maintaining a constant contact force. Secondly, it more accurately measures the size of the workpiece.