Low-Level Force-Control of MR-Hydrostatic Actuators

Precise and high-fidelity force control is critical for new generations of robots that interact with humans unknown environments. Mobile robots, such as wearable devices legged must also be lightweight to accomplish their function. Hydrostatic transmissions have been proposed a promising strategy meeting these two challenging requirements. In previous publications, it was shown using magnetorheological (MR) actuators coupled hydrostatic provides high power density great open-loop human-robot interactions. Still, the fidelity at low frequencies are decreased by transmission's dynamics nonlinear friction. This letter compares strategies MR-hydrostatic actuator systems increase its torque fidelity, defined bandwidth (measured vs desired reference) transparency (minimizing undesired forces reflected end effector when backdriving robot). Four approaches developed compared experimentally: (1) Open-loop friction compensation; (2) non-collocated pressure feedback; (3) collocated (4) LQGI state feedback. A dither implemented smoothen ball screw Results show (1), can performances but facing compromises, while approach simultaneously improve all metrics. These results potential schemes improving performance tethered architectures, addressing issues transmission