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 moir & eacute; (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.

Terrestrial insects, such as ants, are known for their agile locomotion on six legs. However, the ground reaction force (GRF) of each leg has not been well characterized due to its difficulty in measurement. In this report, a micro force plate array is presented that uses the sampling Moire (SM) method, a prism, and a single camera to simultaneously measure the triaxial GRFs of multiple legs of an ant during its locomotion. The SM method is a high-resolution measurement method that measures the amount of displacement based on the shift of a captured grid pattern. The proposed micro force plate array consists of a 3 x 3 array of 2900 x 2900 x 70 mu m plate bases with a gap of 100 mu m as the contact surface of the ant legs. The plate base is supported by a spring structure with a grid pattern. By capturing this grid pattern from the backside via a prism, a camera can capture images from two different directions, allowing the triaxial displacement to be measured. By dividing the plate surface into nine sections and evaluating the error based on the position of the force application in the z-direction force, a maximum measurement error of 6% was found. The average force resolution in the x-, y-, and z-directions for the nine plates was 3.34, 2.47, and 1.20 mu N, respectively. With the developed force plate array, it was possible to measure the GRF of each leg simultaneously while the ant was walking.

Continuous measurement of the body mass of seabird chicks during the nestling period is valuable for investigating their growth ecology. To periodically measure their body mass without excessive disturbance, weight scales have been installed inside nests that have been constructed previously. Conventional weight scales had difficulty with low output drift and maintaining low power consumption. A force plate utilizing the sampling Moiré (SM) method, achieving high resolution and drift robustness in human use, was proposed. An applied force was calculated from a displacement detected by analyzing the stripe pattern captured by a camera. However, if there is a change of more than half the pattern pitch between frames, it cannot be measured correctly. Then, we propose an SM method-based weight scale that can be installed in nests and is suitable for time-lapse measurements, reducing power consumption. The proposed weight scale comprises a top plate supported with springs, an optical prism, and a microcontroller-based camera board. A dual-pitch stripe pattern, incorporating both short- and wide-pitch components, is attached to the backside of the top plate. Plate displacement is measured by analyzing images of the stripe pattern captured through the prism. Correction of the short-pitch results using the long-pitch results resolves phase wrapping and enables both high resolution and a wide measurement range. Calibration experiments of the developed weight scale demonstrated that the dual-pitch approach measured weights up to 2 kg while maintaining a high resolution of 45 mN, which corresponds to 4.6 g. The proposed weight scale is suitable for time-lapse monitoring of body mass in seabird chicks. [Figure presented] © 2025 IEEE.