Indirect foot force measurement for obstacle detection in legged locomotion

Foot/ground detection is crucial in legged locomotion because it determines which leg can be swung to reach its new footprint in such a way that the robot moves properly while keeping stability. Generally, contact is detected with sensors located on the feet: however, they are likely to meet hazardous environments in legged locomotion. For this reason, another method to detect ground, or more generally obstacles, is desirable with the aim of improving the robot's robustness. This article assesses an indirect foot force measurement: on the one hand, a dynamic model computes in real-time the joint forces as if there were no obstacles. On the other hand, the real joint forces are measured through a motor current transducer. Comparison between real and estimated forces shows if an obstacle is present. The principle is developed for obstacle detection in 3D, and is implemented on the hexapod robot AMRU5 for ground detection. A discussion establishes the potential interests of the developed method.

► We develop a method for ground detection and apply it successfully to a real hexapod robot.
► The method is a complement to the classical use of force sensors located at foot.
► The method has the advantage of improving, at low cost, the overall robustness of the machine.