Fabrication and characterisation of a novel smart suspension for micro-CMM probes

In tactile micro coordinate metrology, miniature probing systems are required to allow geometric measurements of miniature, delicate, high precision components. These probing systems typically comprise of a small stylus of only a few mm in length, with a spherical tip of around 100 μm in diameter or less. The stylus is mounted to a flexible suspension structure which is designed to deflect during measurement, and defines the stiffness of the probing system. Stiffness is of critical importance for optimum measurement performance, and selection of the correct stiffness involves a difficult trade-off. Stiff probes are needed to overcome surface attraction forces which are significant for the small stylus tips, while flexible probes are needed for contact with delicate parts to reduce contact stress and ensure no damage is caused. To eliminate the need for compromise a novel micro tactile probing system with active stiffness control using a novel suspension structure has been designed. This paper presents the initial fabrication and the test of the suspension structure. The stiffness of the structure is assessed by measuring the modal frequencies of the suspension structure that correspond to vertical and lateral probe motion. Using this method results show it is possible to reduce the vertical and torsional frequency by 69% and 33 %, respectively. Using finite element analysis it is shown that this equates to vertical and lateral stiffness reductions to 12% and 46% of their initial value respectively.