Many kinds of nozzle-flapper type pneumatic pressure control proportional valves are in use. This paper describes the results of experiments and theoretical analyses regarding the characteristics of ...the valve pneumatic circuit. It was found that the characteristics of the output pressure versus the nozzle flapper clearance has a switching point as a relay. As it has a direct relation with valve linearity, this phenomenon has been studied experimentally and theoretically for various valve parameters. A way for choosing the optimum nozzle-flapper clearance is suggested from the results presented in this paper.
The use of hydraulic proportional valves in industry is becoming increasingly popular as they have better performance than conventional on-off valves and lower cost than servovalves. However, due to ...significant time delay in valve dynamics, they are currently used for low-accuracy and low-dynamics applications. In this study, an adaptive self-tuning controller is proposed to enable a hydraulic proportional valve to achieve accurate set-point flow rate control. A moving model which reduces the system order and hence reduces the identification effort was used for the controller design. The controller is based on the pole-placement technique which shifts the dominant pole to the desired location. In addition, a predictor has been proposed to overcome the effect of the time delay. Experimental results have shown that the proposed self-tuning controller is better than the conventional PI controller as both transient oscillation and steady-state error shown in the PI control have been significantly reduced. Also, the performance of the closed-loop system is very robust as the system response remains the same under Various operating conditions.
We tried to control pressure of a chamber at some constant uniform pressure by using the electro-pneumatic pressure proportional valve. If compressed air of the chamber which is closed, is bled by ...disturbance, or if compressed air of the chamber which is open, is closed by disturbance, both cases we can control it at some constant uniform pressure by using method of feedback control system and learning control. Next we provide several step inputs of pressure to the chamber. Fluctuation of pressure servo can be made smaller and faster by control based on hysteresis of the elctro-pneumatic pressure proportional valve.
The new type three-way pilot proportional pressure reducing valve can be used for stable and accurate control of pressure under conditions of positive, zero or negative steady load flow, step or ...dynamic flow from or into the load volume because of the application of the A-type halfbridge of resistors with double variable orifices to the main valve. Because of the restriction of struture of the two-way pilot pressure reducing valve, in which asingle variable orifice is used, it can hardly or even not be used for accurate and stable control of pressure under conditions of zero or negative steady load flow and the step load flow inputted into the load volume. Two new concepts are still applied in the three-way valve. They are “direct detecting and feeding back the output pressure” and “feeding back the dynamic pressure interacted between the pilot and main stages”, with which the valve showes almost horizontal “constant-pressare” characteristics and superior stability. Moreover, by use of the pilot sliding spool with double variable orifices, the response speed of the three-way valve has been increased to a great extent and its stability improved further more. Another three-way pressure reducing valve has been refered in the paper in which the pilot valve is alternated to be supplied with the inlet or supply pressur but not the output pressure as generally used. This can lower the minimun output pressure and highten the response speed.
Desenvolvimento e avaliação de uma servoválvula de baixo custo para a aplicação de insumos líquidos Johann, André L.(Universidade Estadual de Campinas FEAGRI Laboratório de Instrumentação e Controle); Russo, Edison(Universidade Estadual de Campinas FEAGRI Laboratório de Instrumentação e Controle); Cappelli, Nelson L.(Universidade Estadual de Campinas FEAGRI Laboratório de Instrumentação e Controle) ...
Engenharia Agrícola,
2006, Letnik:
26, Številka:
1
Journal Article
Recenzirano
Odprti dostop
O presente trabalho teve o objetivo de desenvolver uma servoválvula de baixo custo, que respondesse a um sinal eletrônico de controle, para a aplicação de insumos líquidos a taxas variáveis. Depois ...de realizada pesquisa na literatura das opções de válvulas existentes para a dosagem de líquidos a baixas pressões, partiu-se para o desenvolvimento de uma válvula proporcional com acionamento mecânico por intermédio de um servomotor controlado eletronicamente. Uma vez desenvolvida a servoválvula, o sistema foi submetido a um conjunto de testes, realizados em bancada desenvolvida especificamente para esse fim, onde se procurou avaliar seu comportamento em termos de repetitividade, histerese e linearidade. Como resultados, obtiveram-se três curvas de vazão em função do percentual de abertura, descrevendo três incrementos de abertura e fechamento em duas pressões diferentes de trabalho. A servoválvula apresentou boa repetitividade, razoável histerese e curva tipicamente quadrática, bem como manteve a proposta de baixo custo. Esses resultados apresentaram-se bastante satisfatórios, uma vez que a não-linearidade e a histerese podem ser facilmente corrigidas por meio de software.
The present work aimed the development of a low cost servo-valve that answers to an electronic control signal, for variable rates liquid inputs application. A literature research to define which valve type should be used was made. A mechanically activated proportional valve with an electronically controlled servo-engine was designed and evaluated. Since developed the servo-valve, the system was submited to a number of tests .The evaluation of its behavior was obtained in terms of repeatability, hystheresis and linearity. The test was accomplished in a bench, specially developed for this aim. As a result, were obtained three curves of opening percentage as function of flow rate, describing three opening and closing increments in two different work pressures. The servo-valve presented a good repeatability, reasonable hysteresis and a typically quadratic curve. This one maintained the low cost target. These results were very satisfied because the non-linearity and the hysteresis could be easily corrected by software.
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