Variable stiffness probing systems for micro-coordinate measuring machines

Micro-scale probing systems are used on specialist micro-coordinate measuring machines to measure small, intricate and fragile components. Probe stiffness is a critical property of micro-scale probing systems; it influences contact force, robustness, ease of manufacture, accuracy and dynamic response. Selecting the optimum stiffness, therefore, represents a significant design challenge, and often leads to undesirable compromises. For example, when contacting fragile surfaces the probe stiffness should be low to prevent damage; however, for a more robust probing system the stiffness should be increased. This paper presents a novel concept for micro-scale probing systems with the ability to quickly and easily change and control probe stiffness during use. The intended strategy for using the proposed probe is first explained. Then the new concept is fully defined and explored through a combination of finite element analysis and experimental results. Two possible configurations of probe are described, and models for predicted performance for each are presented and compared. The models demonstrate significant stiffness reduction is possible with the proposed concept, and show it is theoretically possible to achieve a probing system with perfectly isotopic stiffness.