A Compliance Model to Improve the Accuracy of the da Vinci Research Kit (dVRK)

Abstract

The da Vinci surgical robot is widely used for minimally-invasive surgery. It inserts multiple articulated instruments through small incisions into the patient. The robot system contains encoders to measure joint displacements which, when combined with the kinematic model of the robot, measures the instrument position and orientation. But, the accuracy of these measurements is affected by non-kinematic errors, such as bending of the instruments due to applied loads. We develop a compliance model that relates displacement of the first two joints of the da Vinci Patient Side Manipulator (PSM) to lateral forces applied to the instrument shaft. This model enables us to compensate for these errors based on the measured joint efforts, which are derived from the measured motor currents. We perform experiments with the open-source da Vinci Research Kit (dVRK) to estimate the model parameters and to evaluate the accuracy improvement that results from application of this model. Preliminary results indicate that the model-based correction can reduce instrument position error due to externally-applied forces.