Homing of a cable-driven surgical tool in a surgical robotic system

1 . A method for homing a cable-driven instrument of a surgical robotic system, the method comprising:

engaging the cable-driven instrument with a tool driver of a surgical robotic arm;

positioning, after the engaging, motors of the tool driver to first calibrated positions for a home configuration of the cable-driven instrument, the home configuration being a first pose of the cable-driven instrument;

applying tensions to cables of the cable-driven instrument by the motors, the applying removing any slack in the cables at the home configuration of the cable-driven instrument;

articulating the cable-driven instrument to one or more pre-determined positions from the home configuration, wherein articulating to the one or more pre-determined positions comprises articulating to a jaws-closed position with a predetermined non-zero grip force;

updating the first calibrated positions of the motors based on positions of the motors after applying the tensions to the cables, the first calibrated positions as updated designating the home configuration of the cable-driven instrument in the first pose as distinguished from other possible poses, wherein updating comprises:

updating based on positions of the motors with the cable-driven instrument at the one or more pre-determined positions, and

determining changes in lengths of cables of the cable-driven instrument from forces on the cables at the jaws-closed position with the predetermined non-zero grip force and based on a relationship given by Hooke's law; and

controlling the cable-driven instrument in surgery based on the updated first calibrated positions.

2 . The method of claim 1 wherein articulating to the one or more pre-determined positions comprises articulating to a jaws-closed position and a jaws-colliding-with-a-trocar position, and wherein updating comprises updating based on the positions of the motors with the cable-driven instrument at the jaws-closed position and the jaws-colliding-with-a-trocar position.

3 . The method of claim 1 wherein updating comprises updating based on an angle of a first jaw being equal to an angle of a second jaw in the jaws-closed position and based on a movement of the first jaw being of equal magnitude and opposite direction to a movement of the second jaw.

4 . The method of claim 1 wherein updating comprises updating based on assumptions that the changes in the lengths of the cables for closing first and second jaws are equal and the changes in the lengths of the cables for opening the first and second jaws are equal.

5 . The method of claim 1 wherein updating comprises changing the first calibrated positions to account for elongation of cables of the cable-driven instrument.

6 . The method of claim 1 wherein positioning comprises positioning the motors using position mode control based on absolute position sensors, where the first calibrated positions are from a factory calibration.

7 . The method of claim 1 wherein applying comprises applying with the motors in a force mode and control by an outside impedance loop for position or with the motors in a position mode and control by admittance control for force.

8 . The method of claim 1 wherein four cables control three degrees of freedom of the cable-driven instrument, and wherein applying comprises applying a threshold tension by driving the motors in a null space.

9 . The method of claim 1 wherein applying comprises applying a threshold tension to all the cables such that the cable-driven instrument is maintained in the home configuration.

10 . The method of claim 1 wherein controlling comprises (1) changing an angle of a joint of the cable-driven instrument and/or (2) opening or closing jaws of the cable-driven instrument, with an amount of change in the changing or the opening or the closing controlled by a difference from the updated first calibrated positions.

11 . A method for homing a cable-driven instrument of a surgical robotic system, the method comprising:

positioning the cable-driven instrument at a home position at a first pose;

applying tension to cables of the cable-driven instrument while at the home position;

articulating the cable-driven instrument to one or more pre-determined positions from the home configuration, wherein articulating to the one or more pre-determined positions comprises articulating to a jaws-closed position with a predetermined non-zero grip force;

updating the first calibrated positions of actuators based on positions of the actuators after applying the tensions to the cables, the first calibrated positions as updated designating the home configuration of the cable-driven instrument in the first pose as distinguished from other possible poses, wherein updating comprises:

updating based on positions of the actuators with the cable-driven instrument at the one or more pre-determined positions, and

determining changes in lengths of cables of the cable-driven instrument from forces on the cables at the jaws-closed position with the predetermined non-zero grip force and based on a relationship given by Hooke's law;

operating the cable-driven instrument in surgery with control of the actuators accounting for the elongations.

12 . The method of claim 11 wherein determining the elongations comprises determining from differences in the positions of the actuators from pre-determined positions and the forces.