Optimizing resolution in force plate using the sampling moiré method

Abstract Ground reaction force is an important parameter for evaluating terrestrial animal locomotion, and force plates (FPs) are widely used. Unlike conventional FPs employing strain sensors, high-resolution optical FPs based on the sampling moiré (SM) method have been developed. However, no quantitative experimental evaluation of the system-level resolution of FPs utilizing the SM method has yet been conducted. In this study, the relationship between brightness amplitude and image noise was evaluated through simulations and experiments, demonstrating that the phase analysis error is inversely proportional to the signal-to-noise ratio of the pattern images. We developed a 250 mm square SM-based FP with a force resolution better than 20 mN by adjusting the optical components. Walking experiments showed good agreement with a commercial FP, demonstrating the high-resolution and reliability of the proposed FP. Thus, our quantitative evaluation of the resolution using the SM method provides a basis for optimizing the performance of FPs.