Design and adaptive balance control of a biped robot with fewer actuators for slope walking

Although reducing the number of actuators in mobile robots contributes to weight saving and results in high efficiency or damage reduction in the event of an accident such as falling over, ideally it should not degrade the robot's performance and functionality. In this study, we propose a new biped mechanism that reduces the number of actuators in a robot without sacrificing its ability to walk adaptively on slopes. We address two issues from both the mechanical and the control viewpoints that are required to achieve straight walking on slopes. For the biped mechanism, we studied the required degrees of freedom of the biped robot and then proposed an actuation mechanism for the hip joint structure. Subsequently, we designed and constructed a biped robot with six actuators, including two actuators for each ankle, no knees, and two actuators for the hip joint structure. For control, we applied feedback from the center of pressure (CoP) of the ground reaction forces in addition to gravity compensation and discussed the stability of CoP movement. Experiments conducted using the constructed biped robot with fewer actuators demonstrated the viability of the proposed mechanism in terms of walking on slopes and the effectiveness of the proposed control concept, which introduces adaptability to the biped robot.