Three-dimensional touch probe using three fibre optic displacement sensors

This paper presents a touch probe system with improved sensitivity and repeatability. In this probe, a tip ball is attached to the probe stylus through elastic bodies that enable the ball to be displaced in three directions. When the tip ball touches the workpiece, three fibre optic lever displacement sensors measure directly the ball's displacement and direction. Because the ball is located in sensitive directions of all of the sensors, this probe complies with Abbe's principle, which is a basis of precision measurement. Various performance tests have been performed using one-dimensional stages. The measurement resolution of the tip ball displacement was less than 12 nm in these experiments. Thus, the probe triggering level was set safely to 50 nm, taking into account the associated noise levels. The variation of the pretravel was less than 25 nm in all directions. The measurement force was approximately 0.6 mN in the horizontal direction and 4.5 mN in the vertical direction.