Prospects for improved thermodynamic efficiency in hydraulically driven robots

Several control strategies for reducing the power consumption of fluid power servo-systems are tested by computer simulation. Results are expressed in terms of a performance ratio, which compares the power input to a controlled system with the hydraulic power input to a reference (or conventional) system. Control strategies examined use modified servo-valves and/or variable supply pressures (e.g., one that maintains a constant supply pressure with a valve that has independently controlled orifices). Real savings are 65 percent for the modulated pressure strategies, 60 percent for the variable jet pump valve, and 50 percent for the independent orifice valve. Control strategies show the greatest effectiveness with an inertial load or with a large static pressure term which are the case in most robotic applications.