Walking of a piped robot with passive ankle joints

This paper deals with a walking of a biped robot which has ankle joints without motor. Ankle joints have been built using springs and mechanical constraints, which gives a flexibility of joint within a certain range and a stiffness beyond the range. The biped with the passive ankles proposed gives a good contact between its sole and the ground and makes soft foot landing. As a result, installing force sensors for measuring the center of gravity of the biped becomes easier, and the weight/cost of legs are also reduced. However, the control problem becomes more difficult because the torque of the ankle joint to put the biped in a desired walking gait cannot be provided from the passive ankle joint. To solve this problem, we proposed a dynamic gait modification method by adjusting the position of a hip joint. Experimental results with the minor modification of the SD-2 robot in the Ohio State University are given to show the validity of the proposed controller.