Optimal locomotion trajectory for biped robot 'D2' with knees stretched, heel-contact landings, and toe-off liftoffs

Most of the current biped robots with active revolute joints walk with their knees bent while a human walks without bending his or her knees in natural gaits. This paper proposes a method to generate natural locomotion trajectory for biped robots without bending knees based on a 2-DOF model of an inverted pendulum. In addition to the natural leg motion, this paper proposes a foot trajectory that has heel-contact landing and toe-off liftoff phases similar to the human foot. The trajectory is parameterized and optimized with a genetic algorithm based on energy consumption. In simulation of locomotion of biped robot, D-2, which has a double deck structure of parallel mechanisms, the resulting trajectory looks natural and requires approximately 28% less energy than the one generated by the LIPM method. In addition to proposing the method to generate trajectory for a biped robot, this paper introduces the mechanism of serially linked parallel-mechanism for a biped robot with knees.