Prospects for Improved Thermodynamic Efficiency in Hydraulically Driven Robots

This paper considers several control strategies for reducing the power consumption of fluid power servo-systems. It is assumed that this reduction must be accomplished without sacrificing the dynamic response of the system or altering the desired time history of the output motion. The results are obtained through computer simulation. They are expressed in terms of a performance ratio, ¿. The performance ratio compares the hydraulic power input to a reference system (or conventional system) with the power input to a controlled system. Both systems operate under the same load conditions and achieve the same motion. Thus, the effect of the control strategy on reducing power consumption with respect to the reference fluid power system can be determined. The reference system has a constant supply pressure with flow controlled by a 4-way line-to-line servo-valve. The control strategies considered utilize modified servo-valves and/or variable supply pressures to reduce power consumption. The first of these strategies consists of maintaining a constant supply pressure with a valve with independently controlled orifices. The second strategy maintains a constant supply pressure but replaces two of the valve orifices with variable jet pumps. The third and fourth strategies vary the supply pressure of the system and use a conventional servo-valve or one with independently controlled orifices. The results show that significant reduction of power consumption is possible. The greatest savings shown is 75%.