Biped locomotion by reduced ankle power

Power reduction in the ankle joints of a biped robot is considered in this paper. Ankles of human beings have small torque and are very flexible within a certain range of motion (very stiff near and beyond this range). This characteristic makes foot landing soft and gives a good contact between its sole and the ground. This feature can be implemented in a biped robot by using a small actuator for the ankle joints. A small actuator consumes less energy and reduces the weight of the leg. With less power in the ankle joints, robot walking becomes more difficult to control. This problem can be solved by providing a feedback control mechanism as presented in this paper. The control mechanism uses the motion of the body and the swinging leg to eliminate instability caused by the weak ankle. Two locomotion examples, standing and walking, were investigated respectively to show the validity of the proposed control scheme. In standing, the control input is the displacement of the ankle joint of the supporting leg. The control mechanism decides the bending angle of the body and the position of the swinging leg. For walking, only the bending angle of the body is used to avoid the discontinuity of the control input. Experimental results are presented to show the effectiveness of the control mechanism.