Resonance-based vector touch sensors

Abstract The objective of this paper is to highlight some of the numerous issues that occurred during the assessment of four different resonance-based vector touch sensor (VTS) designs. As well as being inexpensive to manufacture, the novel feature of this probe is that it monitors the change in three responses of mechanical resonances of the probe, each resonant vibration mode being in orthogonal planes. Effectively, a VTS probe would detect the magnitude and direction of contact between the probe tip and a specimen. Potentially, because this can discern point of contact and contact slope this approach can increase the sampling rate compared to current touch trigger probes. Additionally, this eliminates problems associated with deconvolution of the probe–specimen interaction necessary with simple touch sensors. This paper presents a method for contact force operation, apparatus and method for experimental probe evaluation in three dimensions, and performance characteristics and operational issues of four different probe designs. Typically these probes have been characterized for loads ranging from 10 to 100 mN with contact points covering the outer hemisphere of the spherical probe tips. While, in principle, it should be possible to determine vectored contact as the superposition of three independent orthogonal resonant responses, in practice, there are considerable complexities that lead to cross-coupling and other inherent characteristics such as non-linearities, hysteresis and lack of repeatability. Possible sources and some design solutions to reduce these deviations from the ideal probe are discussed.