In this study, a new sliding mode control with varying boundary layers is proposed to improve the tracking performance of a nonlinear electro-hydraulic position servo system, which can be found in many manufacturing devices. The key feature of the proposed control scheme is the use of varying boundary layers instead of fixed boundary layers, which are usually employed in conventional sliding mode control. The validity of the proposed control scheme is verified through practical testing on an experimental electro-hydraulic positioning device. In the cases of step and sinusoidal command inputs, the experimental results strongly suggest that the proposed control scheme is capable of improving the tracking precision without causing any chattering. In addition, the new control scheme seems to be very robust against various set point conditions.
In this study, an unconventional electro-hydraulic proportional flow control valve based on a switching solenoid and a fuzzy-logic controller is proposed for application to hydraulic presses. The main purpose of this study is the attempt to develop an electro-hydraulic proportional flow control valve with lowest cost. Since the switching solenoid possesses quite nonlinear force/stroke characteristics, it is basically not suitable for the development of hydraulic proportional valves. Therefore, the fuzzy-logic controller is employed to linearize the force/stroke characteristics. The basic idea is the utilization of the numerically estimated pseudo-force as the feedback signal. Finally, this newly developed electro-hydraulic proportional flow control valve is installed in a hydraulic press. Experimental results show that the control of the ram velocity of the press cylinder using the proposed electro-hydraulic proportional flow control valve is quite successful.
In this study, the performance of the rotational speed control of a proportional-valve-controlled pneumatic motor is investigated. The main application field of the proposed prototype is the pneumatic tools, which are currently very important manufacturing devices. Generally speaking, it is usually quite difficult to obtain a satisfactory and precise speed control of a servo-pneumatic motor at a low rotational speed because of the nonlinear deadband and stick-slip friction inside the proportional valve. Therefore, the fuzzy-sliding mode controller is proposed. Experiment results show that the fuzzy-sliding mode controller is superior to the traditional PID controller, especially when the command input is set at a low rotational speed. This newly designed prototype may be utilised to develop advanced pneumatic tools.
In this study, the sensorless control algorithm is applied to improve the position control accuracy of the output plunger of a switching solenoid. The main purpose of this study is the attempt to develop a fluid-technical proportional valve with simplest construction and lowest cost. Since the switching solenoid is not equipped with a position sensor and consequently no closed-loop control theory can be applied, the accuracy of the position control of the output plunger becomes a most critical question. Therefore, a modified open-loop controller using the sensorless control algorithm is proposed. The basic idea is the utilization of the sensorless control algorithm to estimate the steady-state position of the plunger. Then, this estimated position is fedback to the controller and the input current during the steady-state response is real-time adjusted according to the error signal. Finally, a series of experiments are carried out and the results show that the proposed modified open-loop controller improves significantly the steady-state accuracy of the plunger position and provides an alternative approach to design unconventional proportional valves.
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