A new family of hybrid 4-DOF parallel mechanisms with two platforms and its application to a footpad device

This paper proposes a new family of four degrees-of-freedom (dof) parallel mechanisms with two platforms and its application to a footpad device that can simulate the spatial motions of the human foot. The new mechanism consists of front and rear platforms, and three limbs. Two limbs with 6-dof serial joints (P-S-P-P) are attached to each platform and are perpendicular to the base plate, while the middle limb is attached to the revolute joint that connects the front and rear platforms. The middle limb is driven by the 2-dof driving mechanism that is equivalent active serial prismatic and revolute joints (Pe-Re), or prismatic and prismatic joints (Pe-Pe) with two base-fixed prismatic actuators. Since the middle limb perpendicular to the base plate has 3-dof serial joints (Pe-Re-R or Pe-Pe-R), two new 4-dof parallel mechanisms with two platforms can generate pitch motion of each platform, and roll and heave motions (1T-3R) or pitch motion of each platform and two translational motions (2T-2R) at both platforms, according to the type of the 2-dof driving mechanism. Kinematic 2 analyses of the 1T-3R mechanism were performed, including inverse and forward kinematics, and velocity analysis. Based on the 1T-3R mechanism, a footpad device was designed to generate foot trajectories for natural walking.