Investigation on Adding Passive Toe Joints to the Feet Structure of 2D Humanoid Robot

The main objective of this paper is to design a passive toe for Surena ||| humanoid robot which is designed and fabricated at the center of advanced systems and technologies of the University of Tehran (CAST). To this end, a 2D model of robot has been adopted. The first step is to design the trajectory of joints neglecting the toe joints. The second step is to investigate the motion stability of the humanoid robot which has equipped with a passive toe using zero moment point criteria. For this purpose, angles of the passive toe during motion is needed which is obtained using vibrational equations. Afterward, the dynamic model of the robot is derived. Constraint-relaxation method is used to determine the reaction forces on the robot, then calculating generalized force vector which contains all joint torques and reaction forces for different phases of motion. To validate the derived dynamic model, the position of the zero moment point is calculated again using reaction forces. Therefore, the position of the zero moment point has been calculated using two different methods. The first one is according to the kinematic of the robot and the second is based on the dynamic of the robot. Finally, the spring constant and the damping coefficient parameters have been changed to investigate how these parameters affect on the angle of passive toe and a parametric analysis has been adopted to inspect the effects of the aforementioned parameters on joint powers and joint torques.