Abstract

Realizing quadrupedal robots, inspired by the biology of quadrupeds, is very challenging due to fulfilling high speed locomotion with relatively low cost of transport (CoT) at the same time. To accomplish the low CoT for given speed, a semi-active pneumatic actuator is proposed in the leg of Cheetaroid, an inhouse developed quadrupedal robot. This semi-active pneumatic actuator provides a switchable stiffness. During stance, it relieves the load of an actuation module that consists of gears and motors, leaving dynamics of the actuation module nearly intact. During swing, just with an infinitesimal power input, the stiffness changes to a minimum, such that the actuation module can control the leg with no resistance. Based on motion and torque data obtained through a 2-D whole body dynamic simulation of Cheetaroid for bounding, the semi-active pneumatic actuator was efficiently designed by optimization. As a result, the robot's CoT was reduced by more than 50% compared to that without semi-active pneumatic actuators in simulation. The low CoT is expected to improve operation time without losing high speed capability.