Optimization of Postural Transition Scheme for Quadruped Robots Trotting on Various Surfaces

Achieving stable trotting of quadruped robots on various surfaces is challenging because they lose balance due to the displacement of their center of gravity (COG) and undesirable impulse forces. This paper proposes schemes for postural transition and robust posture control, thus enabling quadruped robots to trot on horizontal and slanted surfaces. For a region connected by surfaces with different angles, the postural transition scheme (PTS) is implemented by the movement values optimized by a real-coded genetic algorithm (RCGA), which regulates the location of the center of gravity (COG) projection point of robots. In addition, the movement values are applied to the center points of the desired foot trajectories by using cubic polynomial, which is able to generate adaptive foot motion continuously and gradually. For robust posture control, admittance control with impedance modulation (IM) is applied to the foot trajectories, which changes the impedance parameters in real-time depending on the magnitude of the disturbances, such as the excessive swaying of the robot body that cause instabilities in the robot posture during locomotion. Control thresholds regulated by the angular speed of the robot body are proposed as a criterion for controlling the excessive swaying by IM. Computer simulations and hardware experiments were carried out to verify the performance of the proposed schemes.