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Design and analysis of electrohydraulic pressure systems for variable recruitment in fluidic artificial muscles

This paper investigates the energetics and performance of an electrohydraulic power system with variable recruitment fluidic artificial muscle (FAM) actuators. A coupled dynamic model of the system is developed and applied to study the implications of hydraulic power system architecture for both variable recruitment actuator bundles and equivalent single-muscle actuators. This analysis extends previous FAM literature by considering both actuator recruitment methodology as well as the complete electromechanical circuit and the interactions of these two subsystems. Specifically, for both single-muscle actuators and variable recruitment muscle bundles, hydraulic architectures with a continuously-operating motor and pump are compared with a system in which the motor is intermittently shut down and restarted based on accumulator pressure. The results reveal that variable recruitment offers bandwidth advantages over the single equivalent actuator regardless of the hydraulic power architecture that is selected. However, use of the intermittently-operating motor and pump system allowed the variable recruitment system to achieve efficiency advantages over the other configurations considered. A steady-state analytic solution for the operating envelopes of the variable recruitment and single-muscle systems, including force limits and flow rate limits, was also developed and used to investigate effects of pump displacement on system bandwidth and stroke. The results of these analyses provide tools for the selection of actuator configuration, system architecture, and component design in FAM-actuated electrohydraulic robots.