Null space control for end effector joints of a robotic instrument

A robotic method comprising:

• providing a redundant degree of freedom (DoF) for an end effector joint of one DoF by driving the joint with two actuators;
• calculating a position displacement of the joint to effect a desired end effector movement in response to an input command;
• calculating a first movement of the two actuators based on the position displacement of the joint and a second movement of the two actuators based on a second control objective in a null space corresponding to the redundant DoF;
• driving the joint according to the first movement and the second movement to effect the desired end effector movement while accomplishing the second control objective in the null space,
• wherein the joint is a closure jaw joint of the end effector, wherein the second control objective is providing a certain torque at the closure jaw joint, wherein the certain torque is maintained by a control system having an error signal based on a first torque of one of the two actuators and a second torque of the other of the two actuators.

An apparatus to provide a control objective using a null space of a redundant degree of freedom of a surgical tool, the apparatus comprising:

• a tool driver including a plurality of actuators providing a redundant degree of freedom (DoF) for an end effector joint of one DoF;
• and
• one or more processors configured to:
• provide a redundant degree of freedom (DoF) for an end effector joint of one DoF by driving the joint with two actuators;
• calculate a position displacement of the joint to effect a desired end effector movement in response to an input command;
• calculate a first movement of the two actuators based on the position displacement of the joint and a second movement of the two actuators based on a second control objective in a null space corresponding to the redundant DoF;
• and
• generate a joint command for the joint according to the first movement and the second movement to effect the desired end effector movement while accomplishing the second control objective in the null space,
• wherein the joint is an articulation wrist coupled to two actuators through cables,
• wherein the second control objective is maintaining a minimum tension on the cables, and
• wherein the minimum tension is maintained by a control system having an error signal based on a first torque of one of the two actuators and a second torque of the other of the two actuators.

A non-transitory computer readable medium including instructions to cause one or more processors to perform:

• identifying a redundant degree of freedom (DoF) for an end effector joint of one DoF by driving the joint with a plurality of actuators;
• calculating a position displacement of the joint to effect a desired end effector movement in response to an input command;
• calculating a first movement of the plurality of actuators based on the position displacement of the joint and a second movement of the plurality of actuators based on a second control objective in a null space corresponding to the redundant DoF;
• and
• driving the joint according to the first movement and the second movement to effect the desired end effector movement while accomplishing the second control objective in the null space,
• wherein the joint is a closure jaw joint of the end effector, wherein the second control objective is providing a certain torque at the closure jaw joint, wherein the certain torque is maintained by a control system having an error signal based on a first torque of one of the plurality of actuators and a second torque of another of the plurality of actuators.