A new virtual-real gravity compensated inverted pendulum model and ADAMS simulation for biped robot with heterogeneous legs

Our research team combined humanoid robots with intelligent lower limb prostheses to study the dynamic characteristics of intelligent lower extremity prostheses for disabled people in the walking process, and proposed a biped robot with heterogeneous legs (BRHL). This paper proposes a new virtual-real inverted pendulum system model to unify the models for both single support phase and double support phase in walking process and builds a special simulation platform which can acquire the real-time center of mass (COM) trajectory. Initially, a gravity-compensated inverted pendulum model was built and improved the stability of gait, a natural ZMP trajectory improved the anthropomorphism of the gait. Furthermore, in double support phase, a virtual inverted pendulum model was established and a virtual-real inverted pendulum model was proposed and used to plan the gait of both single support phase and double support phase in the walking process. Additionally, the joint angles were obtained by inverse kinematics; the stability of the system was analyzed to be feasible and effective by phase trajectories. A special ADAMS simulation platform was built to simulate the walking process and acquire real-time COM trajectory. The feasibility of the gait planning was also verified. Finally, the trajectory of COM was optimized based on the minimum energy criterion according to the geodesic equation.