Triaxial Micro Force Plate Array for Measuring Ground Reaction Force in Ant Locomotion

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 Moiré (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 $3 \times 3$ array of $2900 \times 2900 \times 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.