SUMMARYA disturbance rejection controller is proposed based on the general dynamic model of 3D biped robots. For the first time, with this proposed approach, not only the Zero Moment Point (ZMP) location remains unchanged in presence of disturbances but also the longitudinal and lateral ground reaction forces and the vertical twist moment remain unchanged. This way, slipping as well as tipping is prevented by the controller. The swing phase of the robot's walking gait is considered. An integral sliding mode architecture is chosen for the disturbance rejection. The support forces and moments of the stance foot are the control outputs. The acceleration of the arm/body joints are chosen as the inputs. During the disturbance rejection, the leg joints remain at their desired trajectory. Since the leg joint trajectories are unaffected, the robot is still able to complete its step as planned, even when bounded disturbances are experienced. For simulations, the general method is applied to an 18-degree of freedom biped humanoid robot. Simulations show that the controller successfully mitigates bounded disturbances and maintains all of the support reactions extremely close to their desired values. Consequently, the shift in the position of the ZMP is negligible, and the robot foot does not slip.
A control system for the walking of a redundant biped robot in the swing phase is considered. The biped is a humanoid with 6DOF per leg and 3DOF per arm. The controller will be based on a full kinematic model of the robot to depict a more accurate behavior of the robot. The arms of the robot are used to compensate for disturbances the robot may experience during walking. Instead of controlling the robots ZMP, keeping it within the support polygon, all six foot support reaction components are controlled. First, a “shoe” with force sensors detect the forces and moments on the foot for feedback. The feedback from the joint servos provide position and velocity information. The support reaction and the joint position/velocities are fedback to a sliding mode controller, which makes adjustments to the arm links’ acceleration to compensate the shift in the reaction components. Simulations show the comparison of the ZMP shift when disturbances are applied with and without controlling the reaction forces to prove the effectiveness of the approach.
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