Adapter for contact force sensing of the da Vinci robot

At present, the da Vinci surgical robot system does not provide haptic feedback. One of the authors has proposed a contact-force sensing method called the 'overcoat method', in which the instrument/driver is supported by force sensors. In the da Vinci robot, the instrument jaws are powered by a wire-pulley mechanism; thus, in order to apply the overcoat method to the da Vinci system, we must transfer the power through a frame that is supported by force sensors.

The authors have attempted to add a force-sensor function to the Sterile Adapter of the da Vinci system. In developing a sensorized adapter, a new configuration of force sensors and a new axial-force-free (AFF) joint have been devised in order to obtain an independent 'axial force effect' from the drive torque fed from the da Vinci robot arm.

The force-sensing errors of the present system have been measured to have a maximum value of approximately 0.2 N while driving the jaws, and a maximum value of approximately 0.2 N when the robot arm is inclined with some excitation. Some impact reference forces applied on to the ends of the jaws agree with the outputs of the sensorized adapter to within <0.05 N.

It is shown that the new adapter can be sterilized. One apprehension is that the total weight of the new adapter-approximately 1.2 kg-might unbalance the robot arm. In the case of the new adapter, the centre-line of the instrument shaft is shifted externally through approximately 3.5 mm from its original position. However, a new cannula for the da Vinci robot might solve this problem.

The new configuration of force sensors and the new AFF joint work well in their basic functions. The total force-sensing error is estimated as approximately 0.5 N. One of the main reasons for the error appears to be the deformation of the adapter frame.