Hydraulic Transmissions for "High Force Haptic" Device Actuation

Robots for neurological rehabilitation and similar "high force haptic" devices require actuators with high force/weight ratio and the ability to render virtual objects, which requires low mechanical impedance. Conventional actuators are generally inadequate when the device kinematics are complicated. In this actuator development project, a low-impedance electromagnetic source actuator is used with a purely passive hydraulic transmission contained in a flexible hose. The source actuator has poor force density but can remain stationary while the hydraulic system can be designed with low intrinsic impedance because unlike conventional servovalves, this system requires no small orifices for pressure or flow control. A feedback control loop can be closed locally around the actuator, leaving the transmission dynamics outside the loop. Dynamic features of the transmission can shape the port impedance advantageously. The transmission can provide gear reduction without backlash and with minimal friction. The photo shows a prototype for linear actuation that reduces the endpoint package weight by more than 70%.