"Hydraulic Stepper Drive : Conceptual Study, Design and Experiments"
Hydraulic Stepper Drive : Conceptual Study, Design and Experiments
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Position control by hydraulic drives is recommendable if high forces, very fast response or a very compact solution are required. The convenient technology is closed loop servo or proportional control which provides excellent dynamics and precision if all components, i.e. the hydraulic cylinder, the proportional or servo valve and the position sensor have adequate accuracy and dynamical performance characteristics. But this technology has its downsides, namely, high component costs, high oil cleanliness requirements and bad efficiency. Even though efficiency is not always a critical issue from the energy cost perspective, particularly if that drive consumes low portions of the overall used energy, the cost and installation effort of the hydraulic power supply unit may be critical factors. This thesis presents the development and test of a linear, compact hydraulic stepper drive consisting of few, cheap components to avoid expensive position sensors. The basic idea is to transmit very precise quantities of fluid to a hydraulic cylinder in a stepwise fashion and to create in this way well defined motion steps. The first part deals with the practicability of the sensorless concept based on a 220 kN cylinder drive. Based on this concept a hydraulic stepper converter for an energy efficient control and the capability to recuperate energy was developed. Simulations and experiments showed the improvement potential of the prototype. The weak points are the commercially available check valves and the used guidance system for the pistons. The second part of the thesis is dedicated to the development of a fast check valve and the development 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 of the prototype.