Design and experimental characterization of a high performance hydrostatic transmission for robot actuation

This paper introduces a hydrostatic torque-transmission for robotic applications based on rolling diaphragm cylinders. The proposed design solution, that relies on a novel floating-cylinder architecture, can be effectively employed for the implementation of robots with actuators that are remotely located with respect to their kinematic structure, without sacrificing performance and controllability. A prototype of proposed system is designed and implemented to comply with requirements for the actuation of a robotic arm exoskeleton. Such a system brings together a set of interesting attributes such as an extremely low level of friction (<0:8% of rated torque), transparent torque transmission (with average errors in open-loop sinusoidal torque-tracking in the range of 0.2-0.4 Nm), high torque (in the range of 30 Nm), large force bandwidth (20-30 Hz), large range of motion (>140 degrees), simple design, ease in assembling, low-cost, reduced encumbrance (compatible with the integration with robotic links) and lightweight. Additionally, we demonstrate that the presented system allows to integrate a very accurate pressure-based output torque estimation which can be employed to further improve the system performance without the use of strain-based load-cells.