System and method for positioning a tool relative to an anatomical structure using force control

A method of positioning a tool relative to an anatomical structure, wherein the tool is attached to an end-effector of a robotic arm, the method comprising:

• receiving data indicating the position of a target tracker and a position of the tool;
• receiving data indicating a force applied by the tool to the anatomical structure, wherein the data indicates a force vector representing a magnitude and a direction of a force applied by the tool to the anatomical structure;
• determining, from the received data, whether the tool contacts the anatomical structure;
• and
• controlling a movement of the robotic arm based on the received data and the determination of a contact or no contact with the anatomical structure by:
• when it is determined that the tool is not in contact with the anatomical structure, moving the tool along a predefined trajectory relative to the position of the target tracker until it is determined that the tool is in contact with the anatomical structure, and
• after determining that the tool is in contact with the anatomical structure, adjusting a force applied to the tool such that the magnitude of the force is within a predefined force range and the direction of the applied force is within a predefined range of directions,
• wherein adjusting the force applied to the tool comprises adjusting the position of the tool and following the anatomical structure when the anatomical structure moves in any direction.

A method of determining control instructions for a robotic arm, the robotic arm comprising a plurality of segments connected by joints and driven by motors, and the control instructions comprising computer-readable commands for the robotic arm to adjust a pose of the robotic arm or a torque generated by at least one of the motors acting in at least one of the joints, the method comprising:

• receiving data indicating the position of a target tracker and a position of a tool held by the robotic arm;
• receiving data indicating a force, wherein the data indicates a force vector representing a magnitude and a direction of a force acting on the tool;
• determining, from the received data, whether the tool is in contact with an object;
• determining control instructions for the robotic arm based on the received data and the determination of a contact or no contact with the object by:
• when it is determined that the tool is not in contact with the object, generating control instructions to adjust the pose of the robotic arm to move the tool along a predefined trajectory relative to the position of the target tracker until it is determined that the tool is in contact with the object, and
• after determining that the tool is in contact with the object, generating control instructions to adjust the torque by at least one of the motors acting in at least one of the joints such that the magnitude of the force is within a predefined force range and the direction of the force is within a predefined range of directions and such that the tool follows the object when the object moves in any direction.

A robotic arm for positioning a tool relative to an anatomical structure, the robotic arm comprising:

• a plurality of segments driven by motors;
• an end-effector attached to the robotic arm and configured to hold the tool, wherein the robotic arm is configured to position the tool and to adjust a force applied to the tool by driving the motors;
• at least one force determination means configured to determine a force vector representing a magnitude and a direction of a force applied by the tool to the anatomical structure;
• and
• a controller configured to:
• receive data indicating the positions of a target tracker and the tool and data indicating the force applied by the tool to the anatomical structure,
• determine, from the received data, whether the tool is in contact with the anatomical structure, and
• control the robotic arm in accordance with the received data and the determination of a contact or no contact with the anatomical structure;
• wherein the controller is configured to control the robotic arm to:
• when it is determined that the tool is not in contact with the anatomical structure, moving the tool along a predefined trajectory relative to the position of the target tracker until it is determined that the tool is in contact with the anatomical structure, and
• after determining that the tool is in contact with the anatomical structure, adjusting the force applied to the tool such that the magnitude of the force is within a predefined force range and the direction of the applied force is within a predefined range of directions,
• wherein adjusting the force applied to the tool comprises adjusting the position of the tool and following the anatomical structure when the anatomical structure moves in any direction.