Sampling Moiré Method-Based Weight Scale Utilizing Dual-Pitch Stripe Pattern for High Resolution and Wide Range

Abstract

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.