Design and characterization of a compliant six axis force/torque sensor with low cross-axis sensitivity

Abstract

A compliant six-axis force/torque sensor (FTS) with low cross axis sensitivity is developed. The FTS has a central cross beam suspended by four compliant mechanisms. The compliant mechanism is a series connection of cantilever beams and folded beams. The low in-plane and out-of-plane stiffness of the compliant mechanism can boost the sensitivity of the sensor. The compliant interaction between the sensor and the sensing target may mitigate the harmful effects at the event of high impact forces. Strain gauges for sensing the forces and torques are attached to the four surfaces of the beams of the sensing structure to form Wheatstone bridges for sensing. Decoupling of the force and torque measurements is achieved by configuring the bridges to obtain the voltage outputs of the forces and torques with low crosstalk. Finite element models are developed to assist the design of the sensor. The experimental nonlinearity and crosstalk of the sensor are lower than 1.3%FS and 2.4%FS, respectively. Sensitivities of the force measurements are 0.040 $\frac{\mathrm{mV}}{V_{\mathrm{exc}}N}$ and 0.041 $\frac{\mathrm{mV}}{V_{\mathrm{exc}}N}$ in the two in-plane directions, and 0.094 $\frac{\mathrm{mV}}{V_{\mathrm{exc}}N}$ in the out-of-plane direction. Sensitivities of the torque measurements are 5.918 $\frac{\mathrm{mV}}{V_{\mathrm{exc}}N\bullet m}$ and 5.871 $\frac{\mathrm{mV}}{V_{\mathrm{exc}}N\bullet m}$ with respect to the two in-plane axes and 1.480 $\frac{\mathrm{mV}}{V_{\mathrm{exc}}N\bullet m}$ with respect to the out-of-plane axis. The novelty of this work lies in the introduction of a sensing structure design that combines straight and folded compliant beams, resulting in high sensitivity and low cross-talk.