Disturbance-observer-based user force estimation for bilateral teleoperated needle insertion

The work reported in this paper is part of a project aiming at designing a teleoperated tool to perform a needle insertion task through an endoscope. The focus is on the design of the master interface. The proposed mechanical design ensures that the gesture performed by the operator is as close as possible to the original clinical gesture. As this design does not allow for an easy measurement of the interaction force with the operator, a software sensor is used to estimate this force from an encoder measurement. It relies on a disturbance observer (DOB), for which a systematic design approach is presented. The DOB requires the velocity of the one dof master device as input. A comparative study between four possible approaches is performed in order to determine the most appropriate method to estimate this velocity. A method relying directly on the encoder pulses appears to surpass the classical velocity estimators.