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A medical robotic system has a robot arm holding an instrument for performing a medical procedure, and a control system for controlling movement of the arm and its instrument according to user manipulation of a master manipulator. The control system includes at least one joint controller that includ

A medical robotic system has a robot arm holding an instrument for performing a medical procedure, and a control system for controlling movement of the arm and its instrument according to user manipulation of a master manipulator. The control system includes at least one joint controller that includes a controller having programmable parameters for setting a steady-state velocity error and a maximum acceleration error for the joint's movement relative to a set point in response to an externally applied and released force.

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We claim: 1. A medical robotic system comprising: a manipulator having a motor driven joint for moving the manipulator; and a processor configured to control movement of the joint from a current position to a target position according to a control law from which a motor joint command may be determi

We claim: 1. A medical robotic system comprising: a manipulator having a motor driven joint for moving the manipulator; and a processor configured to control movement of the joint from a current position to a target position according to a control law from which a motor joint command may be determined using joint feedback and feedforward motor torque terms and a gravity compensation joint motor torque term, wherein the joint feedback motor torque term is computed as a function of at least a position error computed as a difference of the current and target positions, the feedforward joint motor torque term is computed as a function of the joint target position, the feedback motor torque term is limited to a first programmable limit value, the feedforward motor torque term is limited to a maximum motor torque value, and the gravity compensation joint motor torque term is computed as a function of at least the current position. 2. The medical robotic system according to claim 1, wherein the joint feedback motor torque term is computed as a function of the position error and a velocity error equal to a derivative of the position error. 3. The medical robotic system according to claim 1, wherein the feedforward joint motor torque term is computed as a function of the target position and a target velocity equal to a derivative of the target position. 4. The medical robotic system according to claim 1, wherein the feedforward joint motor torque term is computed as a function of the target position, a target velocity equal to a derivative of the target position, and a target acceleration equal to a derivative of the target velocity. 5. A medical robotic system comprising: a manipulator having a motor driven joint for moving the manipulator; and a processor configured to control movement of the joint from a current position to a target position according to a control law from which a motor joint command may be determined using joint feedback and feedforward motor torque terms, wherein the joint feedback motor torque term is computed as a function of at least a position error computed as a difference of the current and target positions and a velocity error computed as a derivative of the position error, the feedforward joint motor torque term is computed as a function of the target position, the feedback motor torque term is limited to a first programmable limit value the feedforward motor torque term is limited to a maximum motor torque value, the function used to compute the joint feedback motor torque term including first and second contributions respectively from first and second processing paths in response to at least the position error and velocity error, the first contribution limited to a programmable limit value, the second contribution generated by multiplying the velocity error by a programmable gain, and wherein the joint feedback motor torque term serves to prevent the current velocity error of the joint movement to exceed in absolute value a programmable maximum velocity error value that is determined by the ratio of the programmable limit value to the programmable gain. 6. The medical robotic system according to claim 5, wherein the joint feedback motor torque term is computed as a function of the position error and the velocity error, and serves to constrain the absolute value of the acceleration/deceleration error to a programmable maximum acceleration error value as long as the absolute value of the velocity error is not being limited to the programmable maximum velocity error value. 7. The medical robotic system according to claim 6, wherein the joint feedback motor torque term is computed as a function including a contribution calculated by summing first and second products, the first product calculated by multiplying the position error by a first programmable constant, the second product calculated by multiplying a square of the velocity error by a second programmable constant, and the programmable maximum acceleration error value is determined by half of the ratio of the first programmable constant to the second programmable constant. 8. A medical robotic system comprising: a manipulator having a motor driven joint for moving the manipulator; and a processor configured to control movement of the joint from a current position to a target position according to a feedback control law that computes the motor joint command as a function of the difference between the position and the target position and as a function of the difference between a current velocity and target velocity while preventing the current velocity error of the joint movement to exceed in absolute value a programmable maximum velocity error value, wherein the joint torque command is generated so as to include first and second contributions respectively from first and second processing paths in response to a difference of the current and target positions, the first contribution limited to a programmable limit value, the second contribution generated by multiplying a derivative of the difference by a programmable gain, and the programmable maximum velocity error value is determined by the ratio of the programmable limit value to the programmable gain. 9. A medical robotic system comprising: a manipulator having a motor driven joint for moving the manipulator; and a processor configured to control movement of the joint from a current position to a target position according to a feedback control law that computes the motor joint command as a function of the difference between the current position and the target position and as a function of the difference between a current velocity and target velocity while preventing the current velocity error of the joint movement to exceed in absolute value a programmable maximum velocity error value, wherein the processor is further configured to control movement of the joint by constraining the absolute value of an acceleration/deceleration error of the joint movement to a programmable maximum acceleration error value as long as the joint movement is not being limited to the programmable maximum velocity error value. 10. The medical robotic system according to claim 9, wherein the processor generates a joint torque command including a contribution calculated by summing first and second products, the first product calculated by a difference of the current and target positions multiplied by a first programmable constant, the second product calculated by a square of a first derivative of the difference multiplied by a second programmable constant, and the programmable maximum acceleration error value is equal to one-half of a quotient calculated by dividing the first programmable constant by the second programmable constant. 11. A method for controlling movement of a motor driven joint of a manipulator, comprising; controlling movement of the joint from a current position to a target position according to a feedback control law that computes the motor joint command as a function of the difference between the current position and the target position and as a function of the difference between a current velocity and target velocity while preventing the current velocity error of the joint movement to exceed in absolute value a programmable maximum velocity error value. wherein the controlling movement of the joint comprises: generating a joint torque command including first and second contributions respectively from first and second processing paths in response to a difference of the current and target positions, wherein the first contribution is limited to a programmable limit value, the second contribution is generated by multiplying a derivative of the difference by a programmable gain, and the programmable maximum velocity error value is determined by the ratio of the programmable limit value to the programmable gain. 12. A method for controlling movement of a motor driven joint of a manipulator, comprising: controlling movement of the joint from a current position to a target position according to a feedback control law that computes the motor joint command as a function of the difference between the current position and the target position and as a function of the difference between a current velocity and target velocity while preventing the current velocity error of the joint movement to exceed in absolute value a programmable maximum velocity error value; and constraining the absolute value of an acceleration/deceleration error of the joint movement to a programmable maximum acceleration error value as long as the joint movement is not being limited to the programmable maximum velocity error value. 13. The method according to claim 12, wherein the constraining of the acceleration of the joint movement comprises: generating a joint torque command including a contribution calculated by summing first and second products, the first product calculated by a difference of the current and target positions multiplied by a first programmable constant, and the second product calculated by a square of a first derivative of the difference multiplied by a second programmable constant; and calculating the programmable maximum acceleration error value by calculating a quotient by dividing the first programmable constant by the second programmable constant, and multiplying the quotient by one half.