Bi-Axial Micro Force Plate Utilizing Dual Laser Displacement Meters for Ground Reaction Force Measurement in Fruit Flies

The measurement of ground reaction forces is crucial for evaluating the gait mechanics of small insects, which can contribute to advancements in microrobots. Although a micro force plate capable of multi-axis measurement at the μN scale is desired to fully understand this mechanism, fabrication remains challenging. This study proposes a force plate capable of measuring both vertical and shear forces for a fruit fly, which can be constructed with relative ease. The proposed force plate is fabricated by laser processing, simultaneously producing a plate and its supporting spring structure, which facilitates displacement in the bi-axial directions. The plate displacement is measured using two laser displacement meters inclined at ±45°, directed toward a right isosceles triangular bump located at the plate center. Subsequently, the bi-axial forces are calculated based on Hooke's law. The fabricated force plate realized force resolutions of approximately 0.3 μN in both directions, equivalent to 1/30 of a fruit fly’s body weight. Finally, ground reaction force measurements during fruit fly walking were successfully demonstrated using the fabricated force plate.