Abstract
This paper presents the development of an energy efficient low power stepper converter. A prototype with a hydraulic output power of ≈600 W was designed, manufactured, investigated and improved. The converter consists of a hydraulic cylinder piston unit controlled by a fast switching valve to displace a defined fluid quantum by the limited forward stroke of the piston in its cylinder. The displaced fluid generates a precise, incremental motion of a load cylinder which should be controlled. Energy saving is achieved by storing the pressure surplus intermediately in the kinetic energy of the piston to displace a part of the fluid quantum without hydraulic energy from the supply line. Energy recuperation can be done in a similar way. Simulations and experiments showed two main efficiency improvement measures of the first converter prototype. The weak points were the commercially available check valves and the used guidance system for the pistons. The second part of the paper reports about the development of a fast check valve and of a combined hydrostatic hydrodynamic bearing system based on the elastic deformation of plastics. The theoretical and experimental results show a significant improvement of the energy efficiency, the potential of this drive technology and further improvement potential. Expressed in terms of numbers an energy efficiency increase compared to a resistance control up to 30% and a maximum recuperation energy efficiency over 60% were measured.
Highlights
Reduction of energy consumption is an important topic for many modern machine systems.the saving of energy is often traded-off by several other requirements, like robustness, low investment costs, higher precision, e.g., to improve product quality, and higher productivity.Fluid power drives, in particular hydraulic drives, are often not the main drives of a machine, but provide auxiliary actuation, e.g., for tool positioning
A prototype with a hydraulic output power of ≈600 W was manufactured and investigated. With this converter an energy efficiency increase compared to a resistance control up to 30% was measured
The maximum recuperation energy efficiency is over 60%
Summary
Reduction of energy consumption is an important topic for many modern machine systems. Stepper drives create defined motion steps which can potentially save costly position sensors with all the necessary cabling and connectors, if the steps are done with sufficient accuracy If this simple control functionality can be combined with low average energy consumption in a specific application, a contribution to energy saving in general is made. An obvious idea in terms of sensorless position control of hydraulic actuators is to use a speed variable motor which drives a constant displacement pump [7,8] This approach has a quite limited position accuracy because of the pump leakage and the fluid compressibility. For this a fast switching plate type check valve and a combined hydrostatic hydrodynamic bearing based on elastic deformations were developed and investigated.
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