Surgical robotic system and method for calibration of jawed instruments

A surgical robotic system comprising:

• a robotic arm including an instrument drive unit having a motor, a torque sensor, and a position sensor;
• an instrument including:
• a coupler configured to engage the motor;
• a drive rod longitudinally movable by the coupler;
• a spring compressed by the coupler during movement of the drive rod;
• and
• a pair of opposing jaws movable by the drive rod to a closed position;
• and
• a controller configured to:
• actuate the motor to approximate the at least one jaw of the pair of opposing jaws to the closed position;
• receive torque imparted by the motor from the torque sensor and rotational position of the coupler from the position sensor;
• determine a change in slope point from a plot of the torque and the rotational position;
• identify a coupler position corresponding to the change in slope point as a calibrated coupler position;
• and
• control movement of the at least one jaw based on the calibrated coupler position.

A method for calibrating a surgical robotic instrument, the method comprising:

• actuating a motor to rotate a coupler of a surgical robotic instrument, wherein rotation of the coupler moves a drive rod disposed within the instrument in a longitudinal direction to approximate at least one jaw of a pair of opposing jaws of the instrument until the pair of opposing jaws contact each other;
• measuring torque imparted by the motor during actuation of the motor approximating the at least one jaw of the pair of opposing jaws of the instrument to the closed position;
• determining the pair of opposing jaws contact each other based on measured torque;
• actuating the motor to rotate the coupler of the surgical robotic instrument, wherein rotation of the coupler moves the drive rod to compress a spring and approximate the at least one jaw of the pair of opposing jaws of the instrument to a closed position;
• measuring torque imparted by the motor and rotational position of the coupler during actuation of the motor approximating the at least one jaw of the pair of opposing jaws of the instrument to the closed position and compressing the spring;
• determining a change in slope point from a plot of the torque and the rotational position;
• identifying a coupler position corresponding to the change in slope point as a calibrated coupler position;
• and
• controlling movement of the at least one jaw based on the calibrated coupler position.