Structural Compliance Analysis and Experiment of a 4-DoF Parallel Robot

Pick-and-place automation requires robots to have at least three translational (3T) and one rotational (1R) degrees of freedom. Parallel robots 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 robots structurally weaker and prone to wear and clearance issues. This paper presents a new 3T1R parallel robot 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 robot allows the four limbs to be connected with rotational symmetry. Compliance analysis shows that the 4-DoF robot has a homogenous compliance distribution. Experiments are given to verify that the robot can achieve low structural compliance when compared with existing counterparts. The robot is expected to provide an alternative solution in pick-and-place applications.