Despite the maturity of classical industrial actuators with high reduction gearing, the new trend of more dynamic robots that require smaller weight has promoted the development of high torque electrical motors utilizing lower gear ratios - quasi-direct-drive actuation. The result has been actuators with reduced reflected inertia, higher speeds, and generally reduced output impedance with better interaction capabilities. For example, in recent years many small quadrupedal robots have been introduced with excellent physical capabilities.
However, this trend also poses significant challenges. First, the lower gearing ratio results in larger currents, and associated heating. Secondly, torque capacity and density suffer, which is why most applications of quasi-direct-drive actuation have been limited to smaller robots, and a clear gap exists towards application on larger, more powerful robots.
A popular alternative, series-elastic actuation, does not suffer from these limitations but poses different challenges. In series-elastic actuators, an elastic element is placed between the motor+gearbox and actuator output. This allows for regulation of the actuator's output force, giving it some of the same benefits as quasi-direct-drive, while also achieving high torque capacity and density. However, design and mechanical complexity increases and output impedance tends to be not as good as quasi-direct-drive actuators.
This assignment focuses on seeing how the benefits of both of these concepts can be combined, specifically in bridging the technological gap towards larger robots like humanoids. The focus will be on modelling, analysis and parametric design of the actuation system, as well as torque/impedance control.