Eva Holl, Rudolf Scheidl,
"Experimental Analysis of an electro-hydraulic drive for an elbow support exoskeleton"
, in Kalevi Huthala: Proceedings of the The 16th Scandinavian International Conference on Fluid PowerMay 22-24, 2019, Tampere, Finland, 5-2019
Experimental Analysis of an electro-hydraulic drive for an elbow support exoskeleton
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Proceedings of the The 16th Scandinavian International Conference on Fluid PowerMay 22-24, 2019, Tampere, Finland
This paper reports about performance characteristics of a special hydraulic drive for exoskeleton applications. An arm exoskeleton is taken as reference case. The envisaged final control concept is force support for the wearer in load lifting by measuring the active force at the human hand and deriving requested support as desired value for the hydraulic drive operating in in force control mode.
The hydraulic drive combines a speed variable electric motor with a fixed displacement pump to drive a hydraulic cylinder which transmits its force to the elbow joint of the exoskeleton. The investigation of this drive concept serves as a benchmark for other, primarily digital hydraulic concepts which were already started and shall be continued in the future. The essential performance criteria of drives for exoskeletons are low weight and high compactness. Drive efficiency is relevant as far as it serves these criteria by keeping battery and motor lightweight and small. Dynamic response has to be judged with respect to the wearer?s expectations for a convenient arm motion.
As simple test rig represents upper and lower arm of an exoskeleton and the flexional degree of freedom of the elbow joint. Of the shelve components are used to form a closed hydraulic system with a low pressure accumulator as hydraulic tank. The performance of the drive system is measured for different loads. Weight of the components and efficiency values are evaluated as performance indicators. The weight of this drive exceeds acceptable limits, is dominated by motor weight but is also raised by the bulky design of several hydraulic components. Measured efficiencies were in the range 24% to 54 %. Recuperated energy is a negligible quantity for the tested loads.