Triaxial Force Plate With Prism Imaging and Sampling Moiré Method

Many studies have been conducted on the locomotion of terrestrial animals to evaluate ground reaction forces (GRFs) using a force plate. Conventional force plates typically utilize strain gauges, but there are challenges in developing small force plates. While force plates with noncontact type sensors have been developed, these are not suitable for multiaxial measurement. On the other hand, the sampling moiré (SM) method has garnered attention as a high-resolution in-plane measurement technique. This study proposes a force plate capable of triaxial force measurement with a single camera using the SM method. The proposed force plate comprises a plate, spring structure, 2-D grating, prism, and camera. Three directional displacements are measured from images that have two inclined grating images (GIs) before and after displacement by the SM method. In this study, we designed and fabricated a
$25\times25$
mm force plate element with a resonant frequency of approximately 100 Hz. The fabricated force plate independently enabled three-axis measurements, with each axial force resolution < 1 mN, and the positional error for vertical forces remaining within ±3%. Therefore, the proposed sensor can be utilized for evaluating GRFs of small animals.