Miniaturized three-dimensional touch trigger probe using optical fibre bundle

Abstract

This paper presents a miniaturized touch trigger probe system using optical fibres. In this probe, a 1.2 mm diameter tip ball is attached to the end surface of a 0.8 mm diameter stylus stem by an elastic body that enables the ball to be displaced in three directions. One illuminating fibre and three bundles of receiving fibres are incorporated into the stem. Light reflected on the tip ball surface is detected by three photodetectors, one for each fibre bundle. Consequently, the probe system measures directly the ball's displacement and direction when the tip ball touches the workpiece. Because the offset between the fibre bundle and the measuring point or the ball is very small, this probe complies with the Abbe principle, which is a basis of precision measurement. Various performance tests have been performed using a one-dimensional stage. In those experiments, the measurement resolution of the tip ball displacement was less than 0.5 µm. Thus, the probe triggering level was set safely to 0.6 µm, taking into account the associated noise levels. The pretravel variation was less than 0.65 µm in all measurement directions. The measurement force was less than 0.9 mN in all directions.