An end-effector wrist module for the kinematically redundant manipulation of arm-type robots

Industrial arm-type robots have multiple degrees-of-freedom (DoFs), but the use of the roll-pitch-roll wrist configuration yields singularities inside the reachable workspace. Excessive joint velocities will occur and result in a poor path tracking response when encountering the wrist singularities. Arm-type robots currently do not 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 required to avoid the singularities and reduce the excessive joint velocities. 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. Hence excessive joint velocities can be avoided. The highly redundant robot can also be used to avoid collisions in various directions. Three path tracking examples with experiments are provided to show the advantages of the proposed design when compared with existing redundant or non-redundant robots.