Use of Force and Attitude Sensors for Locomotion of a Legged Vehicle over Irregular Terrain

A number of legged vehicles are being developed for their mobility characteristics over irregular terrain. One such vehicle is The Ohio State University Hexapod vehicle ( OSU Hexapod) . Recently, the vehicle has been modified so that it can successfully walk over uneven terrain. Each of the feet has been equipped with two semiconductor strain gauges to measure lateral forces and a piezoelectric load cell to measure vertical forces. A vertical gyroscope and pendulums for orientation sensing have also been added. The control of locomotion over rough terrain can be decomposed into two complementary control processes, attitude control and active compliance. Attitude control is used to maintain the body tilt in a desired orientation, and active compliance is used to provide a suspension system by distributing force loading among the legs. It has been found that optimal force setpoints for the active-compliance algorithm can be calculated in closed form. This paper discusses the sensing hardware and the control system needed for legged locomotion over irregular terrain. Experimental results are provided for both statically determinate and indeterminate hexapod gaits.