Quick response solenoid valves acting as simple on-off hydraulic control devices are inexpensive and easy to operate. There are several hydraulic cylinder control methods using the quick response solenoid valves, which control the flow rate by varying the number of opened valves. Based on these methods, multiple valves open and close simultaneously so that the flow rate and the corresponding cylinder motion become stepwise. This might cause noise and/or vibration on the hydraulic system or the machinery moved by the cylinder. We have developed a new hydraulic cylinder control method to cope with this problem. Based on the method, in addition to the number of the opened valves, the period of the open time of each valve is appropriately controlled, while shifting the timing of the opening action. This improves the continuity of the cylinder motion in a wide range of flow rate. This paper presents the specification of the method and the result of application to the servo control of heavy machinery.

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In manufacturing technology, it is a dominant tendency in recent years that machine tools for machining, grinding and so on, employ electric operated actuators such as a servo-motor equipped with a ball screw. Some problems of these electric driving systems are, they are excessively large-sized with complex machinery and expensive, as seen in their application to, for example, NC-machine. In order to solve these problems, this study aims to develop a precision driving system actuated by a hydraulic cylinder. The hydraulic driving system consists of a cylinder and four ON/OFF solenoid valves. The valves are the same as those used in a fuel injector of an automobile and thus are capable of high speed switching such as 1.5 ms. It was confirmed in experiments that the developed system had a moving resolution of 1.2 μm and, as a result, was applicable to a precision driving table for micro processing.

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This paper proposes a PWM (pulse-width-modulation) control of a pneumatic single-rod cylinder positioning system. In the system, the rod chamber pressure of the cylinder remains constant, and the head chamber pressure is controlled by two solenoid valves. The valves are under PWM mode control. In synthesizing the PWM servomechanism, the solenoid valves are characterized by a static characteristic equation incorporating the nonlinear elements caused by the switching time of the valve. The proposed PWM method can assign the steady-state duty ratios of the valves to the desired locations of their flow characteristics, which makes it possible for the system to avoid the dead-zone or the nonlinear region caused by the PWM solenoid valves. Also, a threshold near the desired position is set up so that the valves are closed at steady state. An experimental study of the proposed system is performed. These experiments verify the theoretical design work, and indicate that the proposed control system is feasible for pneumatic positioning.

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The flow characteristics of valves and restrictions are often represented by the effective area. The effective area is often measured using a method defined in the ISO standards. The method is to measure the flow rate and differential pressure between the tested valve. Therefore, the accuracy of the method depends to a great extent on the accuracy of the flow meter.
On the other hand, a more simplified method to measure the effective area is defined in the JIS standards. This method discharges air from the chamber through the tested valve, and the effective area is measured indirectly from the pressure response of the air in th chamber. The method calculates the effective area, assuming the adiabatic conditions during discharge. Though, even in-a sudden discharge, the heat is transferred into the chamber. Therefore, this causes a measurement error.
In this study, the relation between the temperature change of the air and the measurement error of the JIS method owing to the chamber volume and the length of the pipeline are examined. Then, it became clear that by stuffing the steel wool into the chamber, the transfer area and heat transfer coefficient could be made larger and an isothermal condition could almost be realized. This chamber is called an “Isothermal chamber”. The method to measure the effective area has been proposed using an isothermal chamber. The proposed method can lessen the measurement error as a result of the chamber volume and length of the pipeline compared with the JIS method.

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In this study, the force and velocity control of hydraulic cylinders was performed using a single proportional-type valve with a built-in overlap-type 4-way spool valve. In the case of the velocity control, the valve opening value of a proportional-type valve was calculated by mean of a personal computer to the desired flow rate flowing into the hydraulic cylinder. For the purpose of determining the valve opening, the pressure value in the hydraulic circuit was detected using pressure sensors and a characteristic restrictor equation was employed. Thus, the control method to keep the constant flow rate, which is not affected by a load, was considered.
In the force control of hydraulic cylinders, the pressure control of a cylinder chamber was carried out when the flow rate running into the cylinder was nearly equal to zero for such cases as a fastening body and a loading one. For pressure control on-off operation to a proportional-type valve method was adopted, and the desired force of the cylinder was controlled by taking a little flow in and out of the cylinder.
In this paper, the above-mentioned control methods are proposed and the control characteristics are reported.

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In recent years, two types of variable valve actuators, electromagnetic and electro-hydraulic, have been developed for cam-less engines. The issue of these actuators is how to attain reliable control of the valve landing-velocity deceleration without any electronic position sensor. With this in mind, the former type of actuator is not so resistant to gas-pressure change, while the latter has issues of power waste and limited speed for quick motion control. The authors developed a sensor-less electro-hydraulic valve actuator (EHVA), with a hydro-mechanical position feedback mechanism in 2002 by using a 2-port switching valve. It operated in 24ms for positioning 12mm in stroke. This paper presents acceleration technology for working at an engine speed of 2100rpm and total valve opening time of 19ms, by applying a 3-port switching valve to the EHVA. The parameters of the EHVA were optimized using the bond graphs simulation program, and it succeeded in completing the valve lift motion within 19ms in a full stroke.

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If the airflow from source is controlled directly with a high-speed switching valve, and the pressure in the downstream can be operated as desired. The pressure regulator, using the high-speed switching valves, is shown in this paper. The dynamic characteristics of the regulator depend on the response of the high-speed valve, then it exceeds that of a conventional diaphragm type pressure regulator. To control the pressure, the valve turns on or off the airflow very frequently according to the load conditions. In this operation, both the load flow rate and the load volume are estimated by measuring the pressure in load and the turning on/off durations are decided to keep the minimum fluctuating condition of the output pressure. Then, output pressure precision of regulator is tuned to the optimal condition at various loads, automatically. The effect of automatically tuning is shown theoretically and experimentally in this paper.

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In the preceding papers, the authors proposed a new method of differential PWM for a hydraulic actuator operated by two 3-way solenoid valves. An arbitary pulse width of the pressure difference across both sides of the actuator piston was realized by adjusting the switching time of each valve. The actuator operated by differential PWM shows good linearity as a control element, achieving accurate positioning. This study, as the application, deals with a hydraulic servosystem composed of a 4-way spool valve and a load cylinder, where the spool valve is driven directly by the differential PWM actuator. The servosystem is designed by the optimal regulator method of the state variable model. The system performance is investigated by simulations and experiments. Consequently, it proves that the actuator, operated by differential PWM, plays the role of a linear control element, and the servosystem is well designed by the optimal regulator.

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A pneumatic regulator using a solenoid valve is more useful than a conventional diaphragm-type regulator, in view of output accuracy and response against the changes in the load. However, if solenoid valve is controlled using an ordinary control method such as the Bang·Bang control, the fluctuation of output pressure is inevitable due to the switching action of the solenoid valve.
In this paper, we propose a method capable of a continuous flow rate and pressure. It can be shown that the providing a high-speed operation pulse to a solenoid valve makes the plunger of the valve to be wafted in the middle of the stroke.

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A logic valve is a controllable check valve consisting of a poppet, a sleeve and a return spring. This type of valve is mostly used as an on/off valve. Since the demands for proportional control of flow rate have been increased, these valves have been used for the proportional control. However, a seat valve is not suitable for flow control.In this paper, to make the logic valve controllable for flow, a new poppet structure is proposed.
The new poppet has been designed based on balance of forces by rearranging area ratio of the poppet. Determining areas so that unbalance force caused by supply pressure and pilot pressure is canceled by spring force, the valve lift can be proportionally controlled by the pilot pressure.
PWM control of the pilot pressure is also investigated. An attenuator is used to reduce pressure fluctuation caused by PWM drive of a pilot valve. Combination of the new type poppet and the attenuator is the PWM-controlled logic valve. Using the simulation model of the attenuator circuit, flow characteristics of the PWM-controlled logic valve can be calculated.

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Regarding electrical power sources, the switching regulator is widely used because the efficiency exceeds that of other types such as the regulator using an analog circuit. A pneumatic pressure servo system directly operated by switching valves is expected to have a higher efficient and compact pressure regulator, instead of the diaphragm type pressure regulator, though there is a ripple in the output pressure fundamentally. The ripple is not improved sufficiently because when the operating threshold level of switching valves is set to its extreme to reduce the ripple, unexpected switching occurs caused by noise which is included in the output pressure.
In this report, the mechanism of the appearance of the unexpected switching action is analyzed, and as a result, it is shown that the principal cause of this problem is the resonance occurring in the pressure vessel and the detected pressure crosses the threshold level incorrectly having a detrimental influence on the resonance. The frequency of resonance can be supposed easily and it is convenient in designing a noise filter to its reduction. From this viewpoint, the digital FIR or IIR filter is introduced to overcome this problem and the effect on the reduction of ripple and the performance are determined by the use of experiments. Furthermore, the proper design of the filter for this system is discussed and shown.

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Switching valves are used in the pulse flow control systems of automotive power transmissions and construction machines. These systems require rapid switching speed for improving precision in control. A combination of overexcitation and demagnetization of the solenoid shortens the switching lag time, while it increases the eddy current in the magnetic circuit. This paper clarifies the nonlinear transient characteristics of magnetic flux flow and electric current by both FEM magnetic analysis and measurement of the solenoid. Newly developed magnetic stainless steel material with a quarter of the electrical conductivity of usual low carbon steel reduces the eddy current and shortens the lag time of magnetic flux flow. The valve switches the flow rate of 7L/min at 14 MPa within 0.8ms.

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In this study, a new PWM method using high speed sampling strategy based on the presupposition of using a quick driving circuit which can rapidly switching the high speed solenoid valve as quickly as possible is proposed to improve the response precision and to reduce undesirable on-off characteristic in steady state of electro hydraulic servo system controlled by high speed solenoid valve. In addition, the decision method for PWM parameters such as gain, basic period of PWM and sampling time is cleared up. The experimental result shows that it is possible to achieve precise and quiet control without occurrence of limit cycle and without necessary of designing wide range dead band.

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The method referring to the ISO standard concerned with the purpose of measuring effective area is frequently used to determine the flow rate characteristics of a test valve. This method is to measure the flow rate through a valve and differential pressure across the test valve. However, the experiment and calculation is complex and the accuracy of the method depends to a great extent on the precision of the flow meter. On the other hand, a simple method to measure the effective area is defined by JIS B 8373. In this method, compressed air is discharged from chamber through the test valve without using flow meter. The effective area is measured indirectly from the pressure response of air in the chamber. Due to discharging, the chamber air temperature drops about 40 [K], and the cool air enters the pipe but recovers because of the heat transfer between air and the pipe. This study shows the effect of connecting pipe air temperature recovery on the measurement of effective area. In this research, experiments and simulation were carried out to estimate the air temperature recovery effect. Generally, the connecting pipe effect caused by air temperature recovery is about 2% to 3%.

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When tap water is used as a pressure medium, the structure and material of an oil hydraulic high-speed solenoid valve can not be used because internal leakage and rust can occur. Accordingly, the authors have proposed a novel water hydraulic high-speed solenoid valve. This study is mainly concerned with the development of direct-driven water hydraulic high-speed solenoid valve. Through the investigation of soft magnetic material which has anti-corrosion and low eddy current characteristic, a solenoid design method using soft magnetic stainless steel instead of soft magnetic iron was established. Furthermore, a high-speed driving circuit, which compulsively imprints over-excitation voltage and demagnetization voltage onto the solenoid, is used in order to reduce the switching time of the water hydraulic high-speed solenoid valve. From the linear characteristics of Duty and mean flow, as well as fast switching time within 1.5ms, the validity of solenoid and direct driven valve design method for water hydraulics is verified.

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The on-off controlled pneumatic servo system using the high speed solenoid valves instead of a servo proportional valve is very compact in form and has very high operating accuracy. In this system, the opening and closing periods of valves must be modulated according to system state values. Design for optimal control is quite difficult, since the system parameters vary with sampling time.
System parameters are not required for the Model Reference Adapting Control (MRAC) law. MRAC is induced to lessen the number of calculation of system parameters. MRAC design is shown and the effects of varying sampling time are discussed. A comparison is made of the performance of indirect law and direct law MRACs.

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In the preceding papers, the authors proposed a method of the differential PWM for a hydraulic actuator operated by two 3-way high-speed solenoid valves. The actuator operated by this method shows good linear characteristics as a controller which achieves accurate positioning. However, when the actuator is connected to a load with large force over Coulomb friction, an oscillatory motion appears in the steady state. Therefore, the actuator control system becomes considerably inaccurate. To solve this problem, a new type of actuator, which has 4 check valves, is designed in this study. The dynamic characteristics of the actuator, which has a spring as a load, are investigated by simulations and experiments. Consequently, it is clarified that the actuator can be controlled with high accuracy, retaining a merit of the differential PWM method, and moreover, that the permanence of the proposed actuator can be improved by adopting a locking mechanism.

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A precise force control system is designed by using a pneumatic piston-cylinder, membrane type electro-pneumatic converter and microprocessor, and a favorable result is obtained. The pneumatic piston-cylinder has relatively large frictional force and its irregularity even if the stroke is short. Then a closed loop control circuit with microprocessor so called software servo-system are employed to eliminate the affection. To obtain a higher accuracy in operating force, the effect of PD and PI controls are examined with a simple feedback system.
A favorable result is obtained by changing the sensitivity of integral action with the change of error. The level of reproducibility in controlled force is obtainable better than 0.095% of desired value 20.3N in standard deviation. The settling time can be reduced by changing control mode. At the start, derivative action is added to proportional action, but PI combination is supposed to be best for the settling and to reduce the difference between desired value and set value. The stability of the control system is assured by Hurwitz's criterion and experiment.

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