Design and Control of Efficient and Powerful Robot Joints

Despite several advantages such as simplicity, controllability and back drivability, one drawback that direct-drive actuator has is the power loss caused mainly by Joule heating. This results in poor energy efficiency and limits the maximum forces(torques) of the motors. Among all the actuator designs proposed to overcome the limitation of single direct-drive(DD) motors, two types of actuators have been widely used; quasi-direct drive(QDD) and series-elastic actuator(SEA). However, neither can perfectly resolve the issue due to their intrinsic disadvantages; low torque capacity or density for QDD and low control bandwidth of SEA.

In the first part, this paper introduces a method of designing both types of actuators with optimally selected parameters, as well as a straightforward and effective procedure of controller design for nonlinear robot dynamics.

To take advantage of the possible strong points as well as get rid of the disadvantages of both two types of actuators, a novel way to combine two concepts will be introduced in the second part of this paper.

Through simulations using 1-DOF and 3-DOF robot models, it is shown that a redundant actuator model having the same weight of that of DD, similar tracking performance, better energy efficiency, and bigger forces(torques) can be designed.