Robotic system and method for backdriving the same

A method of operating a robotic surgical system comprising a surgical tool, a manipulator supporting the surgical tool and comprising a plurality of joints, and a plurality of joint actuators, and a controller being in communication with the manipulator, and a virtual simulation representing the surgical tool as a virtual rigid body having a virtual mass with the virtual mass having an inertia about at least one of the joints, the method comprising the controller:

• determining an expected joint torque for the at least one joint;
• comparing the expected joint torque to an actual joint torque of the at least one joint to determine a joint torque difference;
• determining the inertia of the virtual mass about the at least one joint;
• computing an angular acceleration about the at least one joint using the joint torque difference and the inertia;
• projecting the angular acceleration to the virtual mass to determine an external force by combining the angular accelerations of the plurality of joints to obtain an acceleration of the virtual mass in six-degrees of freedom (6DOF);
• simulating dynamics of the surgical tool the virtual simulation in response to the external force;
• and
• commanding action of the joint actuators in accordance with the virtual simulation.

A method of backdriving a robotic system comprising a tool, a manipulator supporting the tool and comprising a plurality of joints, a plurality of joint actuators, and a controller being in communication with the manipulator, and a virtual simulation representing the tool as a virtual rigid body having a virtual mass with the virtual mass having an inertia about each of the joints, the method comprising the controller:

• determining an expected joint torque for each joint individually;
• comparing the expected joint torque to an actual joint torque to determine a joint torque difference for each joint individually;
• determining the inertia of the virtual mass about each joint individually;
• computing an angular acceleration about each joint individually using the joint torque difference and the inertia;
• obtaining an acceleration of the virtual mass in more than one degree of freedom using the angular accelerations of the plurality of joints in combination;
• projecting the angular acceleration to the virtual mass in more than one degree of freedom to determine an external force;
• simulating dynamics of the tool in the virtual simulation in response to the external force;
• and
• commanding action of the joint actuators in accordance with the virtual simulation.