A tri-axial force sensor based on light intensity modulation for detecting ground reaction force

In this paper, we proposed a compact and light tri-axial force sensor with four miniaturized photo-interrupters and an elastic component. Compared to previous F/T sensors, the proposed sensor provides a compact size of multi-axial sensing system taking the advantages of optic-based sensor (i.e., low noise of output signal, high cost-performance). Since we determined the design variables with consideration of ground reaction force (GRF) sensing application, the proposed sensor meets our performance requirements, having three-axial forces capability with 600N for z-axis, ±250N for x- and y-axis, respectively, a light mass of 11g, and a thin size of 7mm thickness. The RMS errors are 4.3±0.25% and 4.4±1.5% of the maximum horizontal force in x- and y-axis, respectably, and 2.8±0.8% of the maximum vertical force in z-axis. The sensor operates without the use of an external amplifier, which can be advantageous in applications where space is limited, as with the case in the GRF application.