Variable stiffness probing systems for micro-coordinate measuring machines

Abstract

Abstract: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.

Performance Assessment of a New Variable Stiffness Probing System for Micro-CMMs

“…As well as determining the effect that switching from stiff to flexible mode has on sensitivity, it was also necessary to determine any unwanted stylus tip position offset error. This was determined with the knowledge that the load applied to the beams will result in a deflection of the stylus tip, which is most dominant in the z direction [ 12 ]. If the probing system was not able to return to the same initial zero offset when switched to flexible mode, it would directly impact the probing system error.…”

“…Controlling the magnitude of the compressive force, therefore, allows the probe stiffness to be controlled. A full description of the design and working principle behind the variable stiffness probing system is presented elsewhere [ 11 , 12 ].…”

Investigating Characteristics of the Static Tri-Switches Tactile Probing Structure for Micro-Coordinate Measuring Machine (CMM)

“…To prevent the undesirable elastic deformation of the bending stylus impeding the triggering accuracy, the stylus of 5 mm was used. Although using a finite element model (FEM) to study the relationship between applied sensing load and probe stiffness is not within the scope of the study, a trend of using FEM facilities has led to a similar development approach [15]. …”

“…Subsequently, our other previous work enhanced both fabrication of micro-styli and multi-directional tactile triggering structure, facilitating the exploration of diverse measurement strategy [13]. Through system advancements, Alblalaihid et al defined an associated measurement strategy for a specific probe [14,15] with stiff and flexible modes. It is observed that such an integral strategy is customized to a developed micro-CMM system while some benchmark parameters associated with the triggering scenarios are affected by the stiffness of a micro-probe, and are transferrable among micro-CMMs.…”

3D piezoresistive silicon microprobes with stacked suspensions for tailored mechanical anisotropies

“…However, the inertial mass of this microprobe combined with its low stiffness prohibits its integration in a conventional CMM because the low resonance frequency renders movements of the probing system impossible. Previous works include a probing system with a variable stiffness [10], which is able to achieve close to isotropic mechanical behavior (1.3) by using a special suspension structure and applying piezo-electric compressive loads. Furthermore, three-legged suspension structures for low-probing forces have been also investigated [11].…”