Intrinsically backdrivable hydraulic servovalve for interactive robot control

There has been consistent trials to make a hydraulic actuator to be effective in interactive robot applications that require high power and durability. However, conventional strategies to obtain this goal, such as force/torque servo control or adding elastic components, suffer from complexity, sensor problems, and reduced system robustness. In this paper, we show that introducing backdrivability to hydraulic system may be an ultimate solution to constructing interactive hydraulic robot systems, by analyzing the advantages of backdrivability for this application. Moreover, we show that the backdrivability of valve-controlled hydraulic system can be achieved by adding a load pressure feedback mechanism on the spool of the servovalve, using the similarity of its dynamics structure to that of a flexible joint robot. Finally, we show that the derived backdrivable servovalve dynamics is actually the dynamics of the pressure control valve, and we report experiments that verify the analyzed advantages of backdrivability.