A supernumerary robotic limb (SRL) system can include a plurality of rigid links, a joint that connects one rigid link to another rigid link in the plurality of rigid arms, and two variable stiffness actuators (VSAs) configured to drive the plurality of rigid links in order to complete at least one task. The VSAs can exhibit infinite rotation and infinite stiffness. The VSAs can include an output link. Additionally, the VSAs can include a set of elastic elements mounted on the output link. The VSAs can include an input link configured to provide kinetic energy for the output link. The VSAs can include a dynamic chassis configured to connect with the input link. Additionally, the VSAs can include a stiffness adjustor included in the dynamic chassis and configured to adjust an elastic transmission between at least one elastic element of the set of elastic elements and the output link.

A torque coupler includes a first torque plate having a first slot extending in a radial direction, and a second torque plate having a second slot extending in the radial direction. The second slot has a side formed of a flexible beam. A cam plate is pivotable about an axis, and has a cam slot having a first portion at a first radial distance from the axis and a second portion at a second radial distance, where the second distance is greater than the first distance. A torque transfer member is slidably received within the first slot, the second slot, and the cam slot. The transfer member transferring torque between the first and second torque plates. A drive device rotates the cam plate about the axis, which causes the first cam slot to radially slide the transfer member along the flexible beam.

A stiffness control apparatus includes a base member, an output link configured to move along a plane parallel to a surface of the base member, and at least one stiffness control unit configured to control stiffness of the output link. The at least one stiffness control unit includes a shaft including a first end and a second end, the first end being rotatably coupled to the base member, a rotating member including an elongated hole into which the second end of the shaft is movably inserted, and rotatably arranged by the shaft at a position having contact with the output link on an outer side or an inner side the output link, and an elastic member between the second end of the shaft and at least one inner wall of the elongated hole in a longitudinal direction thereof.

According to one embodiment, a transporter includes a holder, a joint, an actuator, and a controller. The holder is configured to hold an object. The joint is configured to support the holder and to allow a change in posture of the holder. The actuator is configured to output a force suppressing a movement of the joint. The controller is configured to change stiffness of the joint by controlling an amount of the force.

A surgical tool includes a handle having opposing first and second ends, a lead screw and a spline are rotatably coupled to and extend between the opposing ends. The spline is arranged a distance from the lead screw such that the lead screw assumes torsional loading generated by the spline. Another surgical tool includes first and second splines with a first activating mechanism coupled to the first spline and a second activating mechanism coupled to the second spline. Torsional loading generated by the first and second splines to operate the first and second activating mechanisms are balanced by rotating the first and second splines in opposite directions. A method of minimizing torsional loads on components of a robotic surgical tool includes actuating the surgical tool and assuming a torsional force acting on a carriage of the surgical tool with a load balancing member included in the surgical tool.

A supernumerary robotic limb (SRL) system can include a plurality of rigid links, a joint that connects one rigid link to another rigid link in the plurality of rigid arms, and two variable stiffness actuators (VSAs) configured to drive the plurality of rigid links in order to complete at least one task. The VSAs can exhibit infinite rotation and infinite stiffness. The VSAs can include an output link. Additionally, the VSAs can include a set of elastic elements mounted on the output link. The VSAs can include an input link configured to provide kinetic energy for the output link. The VSAs can include a dynamic chassis configured to connect with the input link. Additionally, the VSAs can include a stiffness adjustor included in the dynamic chassis and configured to adjust an elastic transmission between at least one elastic element of the set of elastic elements and the output link.