Controlling a surgical instrument

CONTROLLING A SURGICAL INSTRUMENT A control system for controlling manipulation of a surgical instrument in response to manipulation of a remote surgeon input device, the surgical instrument comprising opposable first and second end effector elements connected to a shaft by an articulated coupling, the articulated coupling comprising a first joint driveable by a first pair of driving elements so as to permit the first end effector element to rotate, and a second joint driveable by a second pair of driving elements so as to permit the second end effector element to rotate, the control system configured to: respond to a closing motion of the surgeon input device by: comparing a demanded first yaw torque forthe first end effector element to a first maximum yaw torque, and comparing a demanded second yaw torque for the second end effector element to a second maximum yaw torque, and only if the demanded first yaw torque is less than the first maximum yaw torque, and the demanded second yaw torque is less than the second maximum yaw torque, commanding the demanded first yaw torque to be applied to the first end effector element and the demanded second yaw torque to be applied to the second end effector element, so as to cause the first and second end effector elements to rotate in opposing rotational directions towards each other with a closing force; and on detecting a yawing motion of the surgeon input device, command co-directional forces to be applied to the first and second pairs of driving elements, thereby causing both the first and second end effector elements to be rotated in the same rotational direction. Figure 6 Is closing No motion of the Yes surgeon input device detected? Is Is No demandedyaw Yes No demandedyaw Yes torque > rcap or torque > rcap or 4 cap 4 cap Apply Apply max Apply Apply max demanded (or min) demanded (or min) torque torque torque torque --- - --- --- --- (604 605 606 607 Is yawing No motion of the Yes surgeon input device detected? Apply co-directional -610 forces to driving elements to cause end effector elements to rotate in same direction