Ultra-miniature force plate for measuring triaxial forces in the micronewton range.

Measuring the ground reaction forces of a single leg is indispensable to understanding the dynamics of legged locomotion. Because of the technical state of the art, investigations are limited to animals with a body mass above 1 g. Here we present the design, fabrication, calibration and performance of a novel ultra-miniature force platform at the micronewton level. The sensor was built using the stereolithography technology and is equipped with semiconductor strain gauges. We found a highly linear signal response in the calibrated force range to ±1300 μN. Individual tests revealed that our force plate still shows a linear response at forces as great as 4 mN, confirming a large measuring range and particular robustness. The sensitivity was above 50 V N(-1) in all directions, which makes it possible to resolve forces of 10 μN. We demonstrated the suitability of the device on the basis of a typical ground reaction force measurement of an ant, Formica polyctena.