Study on Water hydraulic System

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Two kinds of driving and control methods for a water hydraulic system are investigated in this study. The first is a method using a water hydraulic servovalve, which aims high speed and high performance control. The second is a method using ON/OFF solenoid valves, which aims to avoid failures of water hydraulic-system caused by contaminants such as microorganisms.A position control system using a servovalve shows good performance due to large bulk modulus of water. But force control is more difficult than position control because of the property of water. Derivative feedback of load pressure is effective to compensate the force control. Usage of a disturbance torque observer is effective to motion control and is expected as a control approach to compensate large friction force caused by low lubrication of water.The PWM and differential PWM control method using ON/OFF solenoid valves show good performances in stepwise responses by using PID controllers with suitably adjusted parameters. … More In the step responses pressure variations and noises do not cause serious problems, because the switching of valves occurs, at most, several times in settling time. On the other hand, continuous position control shows good following characteristic by the PWM and differential PWM control method. But in this case, switching of valves always occurs and it causes noisy behaviors. The differential PWM control gives slightly lower pressure variations and smoother positional responses than the PWM control. Remarkable shortening of PWM carrying wave period provides smoother position control and enables stable force control.We made a 3 D-O-F water hydraulic manipulator as one concrete example of water hydraulic system required high performance control. Preliminary control experiments have been made so far. The driving and control methods described above and some other methods will be applied to realize a water hydraulic manipulator with high performance, robustness against contamination of water, and lower level noises. Less