Pneumatic solenoid valves represent the link between digital controls and fluid flow. The pneumatic valves used to proportionally control the fluid flow of a pneumatic servomotor are divided into two ...categories: continuous-acting (analog proportional valves) and discrete-acting valves (proportional valves working in switching). The paper proposes constructive-functional solutions alternative to company products, with close / similar static and dynamic performances, which allow a simple technological realization. The proposed variants on a two-position pressure regulation scheme in a tank with variable losses are analyzed, and the obtained performances are compared with reference versions. Notable results can be mentioned: confirmation of theoretical hypotheses by experimental data obtained, increasing the performance of digital solenoid valves with the frequency of control pulses, the constructive simplicity of the proposed digital solenoid valves into analog ones.
Robust Optimal Design of Unstable Valves QingHui Yuan; Li, P.Y.
IEEE transactions on control systems technology,
11/2007, Letnik:
15, Številka:
6
Journal Article
Recenzirano
This paper is concerned with the application of robust control design concepts for the physical geometric design of electrohydraulic valves. Limitations of solenoid actuators have prevented single ...stage electrohydraulic valves which are simpler and more cost effective from being utilized in high flow rate and high bandwidth applications. Fluid flow force induced instability has been proposed as a means to alleviate the demand on the solenoid actuators. Previous research has demonstrated that simple changes in the valve geometry can be used to manipulate both the transient flow force as well as the steady flow force for this purpose. This paper considers the dimensional design of such ldquounstablerdquo valves to minimize the net steady flow force. The robust optimal design method, in which the design must be robust to uncertainties such as variations in operating pressure ranges and dynamic viscosity, etc., is proposed. By representing the original problem as a linear fractional transformation interconnection, the robust design problem is formulated into one of synthesizing an optimal controller for an appropriate static plant with a structured uncertainty. An algorithm for solving this design synthesis problem is proposed. A case study is conducted to compare the nominal optimal (without considering uncertainty) and the robust optimal designs. It is shown that viscosity effect is exclusively utilized in the nominal optimal design, whereas both the viscosity effect and the nonorifice flux effect are needed in the robust optimal design. The robust optimal design imposes smaller steady flow force on the spool than the nominal optimal design under perturbed situations. Based on the robust design method, an actual prototype design of the unstable valve has been developed.
Injection velocity to a large degree determines the melt injection rate during the injection phase, and it has critical impact on the molded part quality, such as shrinkage, warpage, and impact ...strength. An injection molding machine operates with different injection velocity profiles, barrel temperatures, molds, and materials. These strongly different molding conditions cause the injection velocity dynamics to very significantly and to make the control performance of the injection velocity poor with a typical PID controller. A real‐time, closed‐loop feedback and feedforward control system based on fuzzy logic has been designed, developed, and implemented to control the injection velocity. The fuzzy logic rules of the controller are optimized by analyzing phase plane characteristics. The controller output membership functions are optimized based on a 2k factorial design technique. The experimental results reveal that the fuzzy logic‐based controller works well with different molds, materials, barrel temperatures, and injection velocity profiles, indicating that the fuzzy logic controller has superior performance over the conventional PID controller in response speed, set‐point tracking ability, noise rejection, and robustness.
Water hydraulics is both old and new technology area. The first fluid power applications were using water as pressure medium already in 18th-century, but the modern water hydraulics has been rapidly ...growing just recently in 1980's and 1990's. The main reasons for the comeback are environmental and safety aspects. Water hydraulics offers a significant alternative to establish motion control systems in environments, where possible oil leakage can cause serious problems.
One of the major tasks to solve in modern water hydraulics is to achieve more accurate control systems than today`s technology provides. The present water hydraulic control valves are not yet at the same technology level as that of oil hydraulics. This means that a lot of effort has to be put to develop better and more accurate valve constructions and on the other hand more intelligent control methods has to be developed to achieve reasonable valve characteristics.
This paper concentrates on a study of water hydraulic proportional valves, which are still very new developments in water hydraulics. The steady state and dynamic charateristics of water hydraulic proportional ceramic spool valve is studied both by computer simulation and laboratory tests. Some constructional improvements for the valves are studied and also different control methods are discussed and proposed.
Starting from previous papers 1, where hydrostatic transmissions automotive controls functionalities were investigated, an embedded electronic control system was designed. It is based on a low cost ...electronic control unit, controlling a hydrostatic transmission with a variable displacement axial piston pump and an axial piston dual displacement motor. The pump displacement control strategy, which depends on diesel engine working point and delivery pressure, is based on a fully customisable engine performance map. Special control strategies superimposed on this strategy and depending on autorecognized working mode, that allowed excellent performance in the vehicle field test phase to be reached. Special diagnostic strategies were introduced, based on functional and congruence controls, relying on fault recovery systems, to maintain the system in a high safety condition and to modify automatically the system working mode in case of fault occurrence. This approach allows reductionof overall risks for the operator and the environment.
Optimal control of a pneumatic cylinder YAMAFUJI, Kazuo; KOBAYASHI, Yoshitake; ISHIBASHI, Masahiro
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series C,
1987, Letnik:
53, Številka:
487
Journal Article
OPTIMAL CONTROL OF A PNEUMATIC CYLINDER YAMAFUJI, Kazuo; KOBAYASHI, Yoshitake; ISHIBASHI, Masahiro
Transactions of the Japan Society of Mechanical Engineers Series C,
1987/03/25, Letnik:
53, Številka:
487
Journal Article
Odprti dostop
In order to achieve high speed driving and accurate positioning of a pneumatic cylinder, the optimal control method has been applied to a pneumatic servo-system composed of a cylinder, ...electro-pneumatic proportional valves of pressure type and feedback equipment. State and output equations for the control system were formulated and a quadratic performance function was introduced to obtain optimal feedback coefficients. Optimal regulators, namely control inputs have been computed by a microcomputer without any hardware controller using optimal feedback coefficients which are determined from Riccati's equation so as to minimize settling time of step response in positioning the cylinder. Experimental results show that positioning accuracy is about ±0.2 mm for optimal control and about ±0.1 mm for optimal control with integral compensation at a mean velocity of about 200--300mm/s. These results are compared with those of classical RI control. As a result, the optimal control method, especially optimal control with an integral compensator, is much better in controlled deviation and stability than the PI control method.
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