Pin-jointed wrist mechanisms provide compact articulation for surgical robotic applications, but are difficult to miniaturize at scales suitable for small body cavity surgery. Solid surface cable guide channels, which eliminate the need for pulleys and reduce overall length to facilitate miniaturization, were developed within a three-degree-of-freedom cable-driven pin-jointed wrist mechanism. A prototype was 3D printed in steel at 5 mm diameter.

Friction generated by the guide channels was experimentally tested to determine increases in cable tension during constant cable velocity conditions. Cable tension increased exponentially from 0 to 37% when the wrist pitched from 0 deg to 90 deg. The shape of the guide channel groove and angle, where the cable exits the channel impacts the magnitude of cable tension. A spring tensioning and cam actuation mechanism were developed to account for changing cable circuit path lengths during wrist pitch.

This work shows that pulley-free cable wrist mechanisms can facilitate miniaturization below current feasible sizes while retaining compact articulation at the expense of increases in friction under constant cable velocity conditions.