An End-Effector Wrist Module for the Kinematically Redundant Manipulation of Arm-Type Robots

Industrial arm-type robots have multiple degrees-of-freedom (DoFs) and high dexterity but the use of the roll-pitch-roll wrist configuration yields singularities inside the reachable workspace. Excessive joint velocities will occur when encountering these singularities. Arm-type robots currently don't have enough dexterity to move the end-effector path away from the wrist singularities. Robots with redundant DoFs can be used to provide additional dexterity to avoid the singularities and reduce the excessive joint velocity. An end-effector wrist module is proposed to provide two redundant DoFs when interfaced with an existing 6-DoF robot. The new 8-DoF robot has a compact roll-pitch-yaw wrist that has no singularities inside the reachable workspace. The highly redundant robot can also be used to avoid collisions in various directions. Path tracking simulation examples are provided to show the advantages of the proposed design when compared with existing redundant or nonredundant robots. We expect that this module can serve as a cost-effective solution in applications where singularity-free motion or collision-free motion is required.