Kinematics and compliance analyses of a 3T1R parallel manipulator with rotational symmetry

Abstract

Pick-and-place automation requires manipulators to have at least three translational (3T) and one rotational (1R) degrees of freedom. Parallel manipulators usually include four limbs connected to a traveling plate to generate 3T1R motion. For the four limbs to be arranged with rotational symmetry, complicated types of passive joints and traveling plates are required, which make 3T1R manipulators structurally weaker and prone to wear and clearance issues. This paper presents a new 3T1R parallel manipulator that uses only revolute joints as the active and passive joints. Compared with other joint types, revolute joints are structurally simpler and stronger. They have an unlimited range of motion and can be preloaded to eliminate clearance. The proposed manipulator allows the four limbs to be connected to a simple H-shaped traveling plate with rotational symmetry. Kinematic analysis shows that the new 3T1R manipulator has a homogenous workspace with a high workspace-to-footprint ratio. Compliance analysis and experiments are given to verify that the manipulator can achieve low and homogenous compliance. The proposed manipulator is expected to provide an alternative in pick-and-place applications.