Sampling Moiré Method Force Plate Utilizing Smartphone Camera

Ground reaction force (GRF) is a significant factor for evaluating foot biomechanics, and force plates (FPs) are commonly employed for assessment. Conventional FPs feature an integrated design of a supporting structure and sensor elements but face the challenges of high cost and limited customizability. Recently, high-resolution triaxial force measurements have been conducted using a prism and sampling moiré (SM) method within an optical experimental setup. Herein, we propose an FP that utilizes a commercial smartphone and the SM method. The proposed design simplifies the FP configuration, which comprises mechanical spring structures, a simple optical setup, smartphone, and smartwatch. We constructed a prototype FP of 200 mm × 400 mm capable of force resolution under 1 N. Camera images from the smartphone displayed two inclined grating images (GIs) via the prism, accurately reflecting vertical force applications. In the experiment, the developed FP measured the GRF in a manner similar to that of a commercial FP during human walking. The proposed method is practical for developing high-performance FPs.