The Design of A Gearless Pitch-Roll Wrist

Robotic wrists are commonly used in manipulators for applications that require a large dexterous workspace. Although bevel-gear wrists are widely used in industrial manipulators due to their simple kinematics and low manufacturing cost, their gear trains function under rolling and sliding, the latter bringing about noise and vibration. Sliding is inherent to the straight teeth of the bevel gears of these trains. To alleviate these drawbacks, a wrist with cam-roller pairs under pure rolling is proposed here. This paper reports the design of an innovative robotic pitch-roll wrist using multi-lobe cams. The wrist has two degrees of freedom and consists of two roller-carriers (RCs) driving a multi-lobe cam to produce roll and pitch motions. The pure rolling between cam and rollers helps reduce the friction. Moreover, the cam transmission works with low backlash and high stiffness. In view of the kinematic performance, the wrist exhibits favorable features, including a singularity-free unlimited workspace.