Positive Utilization of Nonlinearity of Fluid Control Systems

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This research deals with fundamental research on positive utilization of the nonlinear characteristics of fluid control systems. Hydraulic control systems have advantages of high power and quick response but also have strong nonlinearity which prevents application of the modern linear control theory. Most hydraulic control systems have been designed through traditional PID control approach in which the nonlinearity of the system is ignored or the operation is restricted within a small linear range. However recent development of nonlinear control theory has enabled us to treat the nonlinear systems directly. As the typical example of such kind of problem, positioning of a hydraulic manipulator is investigated here using a specially designed hydraulic control system with strong nonlinear characteristics. A hydraulic motor is driven by a bridge circuit of four rotary valves each of which is controlled by a pulse motor. Based on a mathematical model of the system feedback linearization and … More conventional pole placement is applied to design the servo system. Numerical simulation and experiment were performed to confirm the validity of the present nonlinear hydraulic system in comparison with a traditional linear hydraulic control system.The present hydraulic manipulator has two degrees of freedom in its input. This provides the flexibility in control performance of the manipulator. Compliance control of the manipulator, which is essential in the man-machine interface environment, is easily realized.Optimization of the control valves applicable to the purpose of nonlinearity utilized hydraulic control systems is necessary based on the simulation of the 3-dimensional unsteady flow structure in the valves. As the fundamental consideration of this problem, unsteady calculation has been performed for the flow through the spool valve and its dynamic characteristics was investigated.Self-excited vibration due to nonlinearity is closely related to the control perfornance of the system. Experiment and numerical simulation has been performed for the fundamental hydraulic servo system and investigated on several types of the stick-slip vibrations which are generic to hydraulic control systems. Less