Bipedal robot walking control on inclined planes by fuzzy reference trajectory modification

The two-legged humanoid structure has advantages for an assistive robot in the human living and working environment. However, the control of bipedal walk is a challenge. Walking performance on solely even floor is not satisfactory. This paper presents a study on bipedal walk on inclined planes with changing slopes. A Zero Moment Point (ZMP) based gait synthesis technique is employed. The pitch angle reference for the foot sole plane-as expressed in a coordinate frame attached at the robot body-is adjusted online by a fuzzy logic system to adapt to different walking surface slopes. Ankle pitch torques and the average value of the body pitch angle, computed over a history of a predetermined number of sampling instants, are used as the inputs to this system. The proposed control method is tested via walking experiments with the 29 degrees-of-freedom human-sized full-body humanoid robot SURALP (Sabanci University Robotics Research Laboratory Platform) on even floor and inclined planes with different slopes. The results indicate that the approach presented is successful in enabling the robot to stably enter, ascend and leave inclined planes with 15 % (8.5A degrees) grade. This, to the best knowledge of the authors, constitutes the steepest ascend reported to date, with a transition from even floor, by a blind walking biped robot.