A brief review of the developments in the design and performance of electric d.c. motors suitable for servo systems is given, and graphs of power rate against angular velocity times the square root of the rotation inertia show how the designs have advanced rapidly in recent years. A comparison is made with the power rates of hydraulic motors, showing the latter to still have significant advantage. A basic, approximate mathematical analysis of the servo-loop for each case is presented, showing the similarities of the block diagram and transfer function for the case of velocity control. Obervations are made about the sensitivity to load disturbance and speed of response. The conclusion is that the hydraulic servo could still be a strong competitor, providing that care is taken with the shaping of the control loop. Overall cost is likely to be in favour of the electric drives.

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The development in the cartridge and proportional techniques may be one of the most important affairs in hydraulic control fi eld within last 20 years. The background of it is demonstrated in the paper, especially the combination of proportional technique with cartridge technique in recent years. An analysis and synthesis of their constructional principles are given. The trend of development of them are also forecasted in the paper.

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This paper attempts to bring together a number of issues relating to the use of microcomputers in three distinct areas: CAD, real-time control and condition monitoring. Some comments and suggestions that might be of value when considering future developments are included.

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A brief survey is given of the scope of the design of displacement pumps and hydromotors which are used in the realisation of hydrostatic power transmissions.
During the recent 25 years the computer is playing a role of ever increasing importance in the design and the development of these hydraulic energy converters.
This role has been started on the testbench for pumps and hydromotors. The data aquisition and data processing by computer has led to a much better guidance of the design process. The testing developed from a simple and sometimes very inaccurate determination of efficiencies, based on sometimes very doubtful definitions, into an accurate tool for the designer, with a quite good resolution for detailed analysis of the losses within the prototype. The introduction of the computer to testing had a very upgrading effect on the quality of the testresults.
The disadvantages were the higher costs of testing equipment, the need for higher qualified operators and the generation of a flux of information, demanding qualified engineers that understand the meaning of this information.
The use of the computer also penetrated into the design of pumps and hydromotors. Not only into the design of details of these energy converters but also into optimising the design. The design of controls for pumps and hydromotors, with variable displacement, also has become ‘computer aided’. In this publication some examples are given of the use of computers to enhance the design of details of hydraulic energy converters.
Also the computer can be applied to ‘integrate’ the different procedures which we usually have to execute during a design process, into one coherent package of software.
The computer can perform the design cycle much faster and much more often than a human designer. Once such a package has been realised, it can be used to produce an optimised design. A hydromotor designed by such an integrated design software package is shown. Here again one can mention disadvantages of the introduction of computers into the design process. The designer should have adequate knowledge of the use of computers, in order to be able to use the sometimes expensive computer hardware as a tool for design. The creation of an integrated software package has a long leadtime. Many times one finds ‘blank spots’ or even ‘blank fields’ in the available knowledge about the object to be designed. Without filling these ‘blanks’ with information, the integration of the design package can not be completed. Sometimes tests have to be run, in order to fill in these blanks with information of acceptable quality.
The advantages of the introduction of computer aided design for pumps and hydromotors have become clearly noticable. The improvement of the quality of design is undeniable. The attention of the designer is focussed on the optimization of the design, both in detail and integrally. His understanding of what is going on inside the pump or hydromotor is improved considerably.

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Fluid power systems and components become more complex and sophisticated. Although great efforts have been made to make hydraulic components quieter, noise and vibration problems are major and growing drawbacks of fluid power systems.
A variety of methods to measure the oscillary flow from a fluid power pump have been proposed during the last decades. This paper is concerned with the “anechoic termination” method. A mathematical model is proposed in order to control the errors introduced by the actual device used to achieve anechoic conditions. Results from measurements on pump flow ripple using this method are presented.
The noise and vibration problems can be considerably reduced by means of a fluid power attenuator. A very simple one, the one-chamber expansion chamber attenuator, is studied in this paper.
Standing wave phenomena due to the chamber itself are carefully penetrated. It is also shown how to improve the attenuation by means of a mode cancellation pipe. In both cases simulations and measurements are carried out and the agreement is generally fairly good.

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In mobile machinery powered by hydraulics, such as cranes and excavators there is much oscillation in the mechanical structure of the machine if the controls are not handled very gentle by the operator.
Reducing the oscillations reduces the dynamic loads on the machine, which means that a crane can be rated for higher loads. In an excavator the operator will be exposed to less vibrations and since the operator will not have to be so careful with the controls, productivity will increase.
This paper explores two different methods to introduce damping in mobile systems. First, the very simple yet very powerful method of pressure feed back with guide function is discussed. Second, the method of, identification on-line and pressure feedback from an observer is discussed.

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A method for simulating transient flow in a hose is proposed. The method makes it possible to account for both linear and nonlinear hose damping properties and has been used to investigate how different types of hysteresis can be recognized from measurements. It is shown that the proposed model is an adequate basis for investigating which properties one should promote in order to improve a hose's damping characteristics.

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A significant development goal in the field of hydraulics is economizing energy. The higher the efficiency of a system, the lower the required installed input power is. Because less heat is lost, the effort required to cool the pressure medium is reduced. Aside from the reduced operation costs due to the lower energy consumption, one also saves investment costs by utilizing power in better ways. Displacement units in pumps and motors can provide energy economizing features.
Variable displacement pumps for open circuits are equipped with separate controllers for pressure, piston stroke, volume flow and power, in each case providing only as much power as the consumer requires.The controllers which are available on the market today are nearly exclusively mechanic-hydraulic systems. At the IHP, a systematic investigation of the possibilities which electrical circuits provide for pump control is being carried out.

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The presence of high performance components in modern hydraulic systems has improved system performance significantly compared to equivalent circuits of only a few years ago. However, problems associated with interactions between components are not uncommon; these interactions appear in some instances to be highly unpredictable and therefore difficult to compensate for. The use of modelling techniques, combined with modern computers and software simulation packages, has provided a means of investigating interactions under controlled situations.
This paper will consider the interaction between a pressure compensated pump and a pressure limiting device such as a two stage relief valve or a sequence valve. The combination of a pressure compensated pump and relief valve might appear to be an unlikely pair, but the use of the relief valve as a safety device is quite common. Problems have been reported when the setting of the relief valve or sequence valve approaches that of the pump compensator.
This paper, then, presents a model of a pump and relief (sequence) valve using a lumped parameter approach and the Bond Graph representation of the hydraulic components. Experimental verifications of each component model, along with a verification of a more complex circuit configuration, are presented in the form of transient response comparisons. Using the models, conditions under which adverse interactions can occur are investigated. Suggestions are presented for eliminating or minimizing such interactions.

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From a view point of saving energy, power losses in hydraulic systems including power sources should be minimized as small as possible. In conventional hydraulic power units, the output power is adjusted by controlling a displacement of variable displacement pump to avoid a waste of excess power. In this study, it is proposed for adjustment of the output power that rotating speeds of a fixed displacement pump is controlled by making use of a inverter-motor drive. We apply a digital control scheme to the energy-saving hydraulic system. A pressure feedback control system and an estimated pressure feedback control system are discussed and the results are experimentally verified. Experimental results demonstrate that the studied systems are effective to save energy for constant pressure power sources.

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A new type of electrohydraulic proportional constant pressure and flow pump with electric feedback and compensation is introduced in this paper. The pump control system has be designed to realize constant pressure control by load pressure electric feedback and constant flow control by leakage flow compensation. A new principle of leakage flow electric compensation to pump constant flow control is proposed in this paper. Unlike conventional constant flow pump, which directly detects the load flow on the main oil-road, the additive main flow throttle loss may be avoided completely. The structure characteristics of the pump control system and experimental research results also are introduced in this paper.

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For a medium pressure axial piston unit installed in a test circuit where two variable restrictors excite the system transients, a dynamic model explores the performances of individual controls. For two case-studies (“pressure compensator” and “flow compensator”) a reference configuration is treated in some detail and checked for sensitivity. Multiple controls are then introduced by giving two examples of “free” structures, identifying the general class of “modular” structures and outlining few interaction problems.

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This paper describes the reliability of 25 SCY hydraulic axial piston pumps. On the basis of investigations, experiments and theoretical analyses, the pump failure mode and failure mechanism were found. The statistical study of test data was done, the failure distribution function and the distribution parameters were determined, and the pump life was estimated.
In order to save testing time and money, an accelerated life test has been conducted. The acceleration equation has been formulated successfully.
After making an improved design, the pump life has been prolonged greatly. At the end of this paper, a life acceptance testing plan of censored small samples is put forward.

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One major factor which decides the performance of hydraulic continuously variable transmission, is a pair of pump/motor. We have developed a compact, light, and very efficient pump/motor unit, the structure of which bases on a new concept and is completely different from the conventional ones.
And as its application, the hydro-mechanical transmission is also developed.
The transmission is compact, light and fuel-saving. This thesis describes outline of their construction and operation.

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The present report deals with an analysis of a pressure-compensated variable displacement vane pump regarded as a load-compensating control system. On the basis of experimental data of an article on the market, the effective transfer function of he mechanical system can be reduced to a form of 1st order lag system. Furthermore including the pressure surge in actual circuits due to the sudden change of the oad flow into the analysis, it becomes clear that the entire transfer function of the mechanical and hydraulic system has a form of phase lead system. The theoretical solution of the step response of the output pressure is similar to the experimental data. After the consideration of effective parameters in the entire system based on he above results, several guides for parameter design are to improve the load-sensing function and to optimize its step response.

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Pressure and flow ripples of a variable-displacement vane-pump with a pressure compensator were analyzed by numerical calculations, and their results were compared with experiments. The behavior of the leakages and the other factors affecting pressure ripples were examined in detail. It was proved that the apparent leakages due to a fluid compressibility in both compression and expansion processes of a confined pumping chamber influence definitely the ripples of pressure and flow, and that a transient pressure curve of the chamber and its bulk modulus are important. Furthermore, it was shown that the pressure ripples in the regulating region (the pressure-compensated state) become extremely larger than those in the non-regulating region according to the vibration of a cam-ring excited by the fluctuating internal force induced by a variation of the numbers of chamber exposed to the delivery port.

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A detailed simulation program is presented for investigating the performances of an external gear pump. The geometrical aspects and the differential equations representing the quasi-steady state mathematical model of the pump are accounted for and discussed. Initial conditions are determined accordingly to a new proposed method and numerical aspects bound to the solution of the stiff ODE system are addressed. Experimental data generated on a commercially available medium size external gear pump were used to validate the model predictions. Agreement between experimental and predicted values of pump performances was satisfactory. Being the model unable to simulate pressure ripples generated by the unsteady nature of the flow within volumes and along the lines, several experimental results of inlet pressure fluctuations are reported. Predicted and unpredicted fluid borne noise sources are hence accounted. Finally, the influence exerted on the operation of the pump by pressure forces and forces exchanged between meshing teeth is investigated and a predictive method foreseen (useful in condition monitoring) based on the observation of outlet pressure waveforms.

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The rapid advances in computer, microcomputer and microprocessor technology has opened many new application possibilities for the fluid power industry. Smart controllers integral to the hydraulic component are now commercially available using concepts which as much as five years ago were considered strictly academic.
Associated with this growth has been the development of computer software for purposes of control, data collection and manipulation, circuit simulation and design. The combination of the microcomputer with relevant software can produce a very powerful design and control tool specifically oriented towards fluid power applications. One such approach uses a microcomputer and the reasoning capabilities of an artificial intelligence based high-level language programming technique known as “expert systems”.
An expert system allows the programmer to develop both mathematical and symbolic logic in terms of defined words and phrases called rules. These rules can tell the computer to monitor a certain device, to switch on or off a specified valve, or to do a complex mathe matical evaluation if acertain set of conditions are satisfied. Use, then, of an expert system in controland condition monitoring is greatly facilitated using this approach. If theserules are coded to relfect verbalstatements rather than analyticin for mation, then the expert system can beapplied as an example to the process of design.
This paper will consider the application of an expert system to the control, monitoring, and self-diagnosis ofa hydraulic circuit. The philosophy behind the expert system approach will be briefly examined and its application to diagnosis and control of a hydraulic circuit presented through very basic examples.

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In recent years microcomputers have become very powerful in terms of communication capabilities and computing power. All that at a lower cost. As a result of the availability of these powerful, low cost microcomputers, it is now possible to integrate them into hydraulic products to form an Xpert family. In this paper the theory, design and application of these products will be discussed. These products include servovalves for industrial applications and mobile valves for off highway vehicles.
These Xpert valves are used to control position velocity, acceleration and force in different applications.

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In this work, a control method to reproduce input waverorm is discussed. The acceleration waverorm of an electrohydraulic servo system is controlled by means or Linear Model Following Control (1MUC) with a timedelay reference model. This control system makes the signal transfer characteristics or forward path equivalent to that of the 2nd order Pade approximation or the timedelay characteristics. The difference signal between the output signal or the timedelay model and the output acceleration signal of the hydraulic servomotor, which is called acceleration error signal, is red back. Then, the acceleration error signal reedback makes the signal transfer characteristics or the servomotor more exact to that of the timedelay reference model. The performance or this control system is confirmed by experiments.

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Electrohydraulicservos exhibit nonlinear behavior whenever subjected to dynamic inputs due to the presence of several significant nonlinearities in the servovalve and hydraulic motor. Some mechanical nonlinearities are often responsible for performance limitations as expressed by speed of response, accuracy and stability. This paper deal with the dynamic characteristics of electrohydraulic velocity servos in order to throw more light on the complicated role played by stick-slip friction of the actuator.

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The paper is concerned with examining the performance potentials of electric, hydraulic and air motor drive technologies when applied to control the position of the same load. The work is referenced loosely to a 20 kg payload situation. It is recognized that the amplification between servoactuator output displacement and payload displacement for a particular drive axis can be anything from zero to perhaps 20 to 1. For this reason, the load to be directdriven by the proposed servodrives was taken as 0 to 200 kg; i.e. a 10: 1 mechanical amplification of motion was assumed. The work was pursued via digital simulation of dynamic models which were derived using power flow (bond graphs) techniques. The simulations were authenticated via measurements of the responses of hardware systems assembled for the purpose. The servodrives are described briefly and their responses to step input position change commands are presented and compared.

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The dynamic characteristics of the hydraulic system made of the four cylinders, all of which were connected tandem and able to move on a linear guide rail, was investigated in this research.
In this system, four directional control valves controlled the ON-OFF motions of the cylinders of the same number respectively and separately. A valve was connected to a cylinder by a pair of flexible pipes. One micro-computer drove all the valves by its ON-OFF electric signals. One end of the system was fixed to the rail and the other was free. Displacements of the free end were the outputs of the system. The strokes of the cylinders were chosen as 1cm, 2 cm, 4 cm and 8 cm from the free end, for the free end of the system could stop anywhere in the 16 positions from 0 cm to 15 cm at 1 cm intervals depending on the output signals from the micro-computer.
This paper shows some of the results obtained from the above research.

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In recent years, many studies on the adaptive control of an oilhydraulic servomechanism using a microcomputer have been done. A microcomputer has merits of flexibility of algorism and high computing accuracy. But the computing time of the discrete adaptive law is not short enough to control an oilhydraulic servomechanism in high frequency region. For control of an oilhydraulic servomechanism in higher frequency region, there are two method. One is a method of using a digital signal processor, and the other is a method of using an analog adaptive controller. The analog adaptive controller has a merit that its computing time is theoretically zero. In this study, the adaptive law was constructed in continuous time description and the adaptive controller was realized by an analog electronic circuit which was designed using a CAD program. And experiments were conducted to investigate the electrohydraulic servomechanism with the analog adaptive controller.

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Present study deals with the adaptive control of an electrohydraulic servomotor system. A explicit type model reference adaptive controller was designed to compensate parameter changes such as load and temperature. An experimental apparatus was constructed which consists of an electrohydraulic servovalve, a hydraulic motor, an inertial load and the adaptive controller with a microcomputer. Experiments were carried out to confirm the advantage of the adaptive control and to examine the effect of the parameter adjustment law and the sampling time on the behavior of the plant. The variable gain algorithm based on least square method was better as a parameter adjustment law than the constant gain algorithm. When the inertial load was large or when the sampling time was short, the plant became non least phase system and then the MRACS designed in this study could not control the plant stably.

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The paper deals with the adaptive positioning control of an electrohydraulic servo system which employs an input filter. This filter spreads a large control input over a period of sampling instants to prevent input saturation. As well, its use enables the proof of stability to be achieved using the standard technique even for unstable plants. A controller structure, which does not require feedback from the output of the input filter, is determined by considering the input filter to be a part of the unknown plant. The design is described in discrete-time form using the Euler operator which has better characteristics than the z operator in many respects. The simulation results are presented to show the performance of the controller.

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This research represents the design method of the repetitive controller of electro-hydraulic servovibrator and shows the result of experiments. In the vibration test of machine or in the fatigue test of material, it is required to control the waveform of periodic motion. From the internal model principle, the repetitive control is effective to this problem. To make the repetitive control system stable, it is necessary to design the stabilizing filter of the repetitive compensator and the series compensator appropriately. The performance index of wave distortion is defined and used to calculate the optimal design of these compensators. The size of actuator should be chosen to make the range of attainable amplitude wide enough to use. At the same time, the performance index of wave distortion should be small enough. The result of experiments of acceleration waveform control shows that the performance index of the wave distortion is 6.8% for the reference signal of triangular wave with fundamental frequency of 50Hz.

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Cartridge valve technology offers solutions in the situations where high integration level of hydraulic components are needed, like in the case of linear servo-packages. Valvistor, which is often regarded as a hydraulic transistor, is one of the most modern two-way cartridge valve designs both from the standpoint of the package integration level and the static and dynamic characteristics. In this paper, mathematical and experimental studies are made concerning the application of Valvistor in control of a differential cylinder. In addition, an example of an advanced construction of intelligent actuator is shown both from the standpoint of component packaging and control.

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The multipass ele ct ro-hydraul is redundant servo systems, in what each pass drives a load synchronously at the same time, is discussed. First, the model of a single-pass system is given. Then, the performances of the redundant system and the essence of force-fight occurring among passes is analysed. At last, based on the theory of decouping, the equalization technique is set forward to solve the force-fight among passes and the opt imal design method of equalization net work is given. Simulations and experiments prove it is convenient for practical use.

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In recent years, with the need to reduce the time required to complete the cycle of automatic assembly machines, the high speed driving of pneumatic cylinders has become an important subject of research. Under certain driving conditions, it has been found that the velocity response as well as the pressure response of the air in the cylinder chamber displays an oscillatory behavior. In this report, a detailed examination using a numerical analysis is conducted in order to grasp the nature of this phenomenon. From this result, it was found that this oscillatory phenomenon becomes increasingly evident in the velocity response as well as the pressure response when the pneumatic cylinder is driven at a high speed. Thus, an analysis is first conducted to investigate the cause of this oscillatory phenomenon. Thereafter, an ideal driving method for obtaining high speed is proposed where this oscillatory response of the velocity is used positively.

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This paper describes the effects of asymmetricity of pneumatic cylinders on the frequency responses of a valve-controlled cylinder system, wherein an uneven-underlap valve and an asymmetric cylinder, which has an inertia load with Coulomb and viscous frictions, are used. The system is analyzed theoretically.
Experiments of the frequency response of valve-controlled asymmetric cylinder system were carried out using three cylinders, two of which are asymmetric. The effects of the spool amplitude (input signal), the supply pressure and the asymmetricity of cylinders on the frequency response of the system were studied.
The theoretical results agreed fairly well with the experimental ones.

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In this text we discuss the idea of the distributed control using the Independent Intelligent Actuators the new building blocks in machine. automation. We show the merits of such a system and easiness of using. We then discuss the system structure on the levels of programming, controlling, communication and hardware and we show the specification of the Independent Intelligent Actuator. After these discussions we examine the practical implementation of the Independent Intelligent Actuator and the in-machine communication system in depth. We show some experimental results on the areas of controlling and communication. Finally we discuss the overall system.

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Compared with hydraulic systems, the positional control of pneumatic systems is much more difficult because of the high compressibility of air. A pneumatic system, in which several cylinders are connected with each other in series, can be used to acquire a reliable and accurate positional control at the high speed. Especially it is interested when the stroke of each cylinder in some unit varies in a sequence of 2 powered integers starting from 0, the total output displacements of the system could be any integer in this unit from 0 to N2-1 where N is the number of cylinders.
In this research, the ON-OFF actions of each cylinder was controlled by a microcomputer, and a triangular shaped digital output has been taken as an example. This paper reports the dynamic characteristics of such systems investigated by computer simulation.

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Thispaper describes a servo controlfor pneumatic cylinder drive systems in whichpressure control is emphasized to improve the system response. Based on the block diagram of the system, decoupling of pressure change and motion of load was discussed first. Next, the pressure control system in which feedback compensation of pressure derivatives was used and gains were changed adaptively according to the piston position was proposed. By using this control system, the pressure response is quite improved and the constant and same dynamics for two pressure chambers are assured. Furthermore, P-D position control system was discussed for cylinder drive systems.
The effectiveness of this control method was certified by numerical simulation and experiment.

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An investigation is carrried out to a new type of electro-pneumatic digital pressure valve, in which pressure smooth drop in capillary damper tubes is exploited to transform the angular displacement of a stepper motor into pressure signal and to control the valve outlet pressure further. First the mathematical model of the valve is built up and its static property is discussed. The pulse response of the valve is then analysed through both linearized and numerically simulating methods. The electropneumatic digital pressure valve is experimentally tested to verify the correctness of theoretical analysis. Through comparison between theoretical and experimental results it is concluded that the new type of the electro-pneumatic digtal pressure valve has good stability, high responding speed and simple configuration.

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This paper describes an experimental study to compare a method of testing the effective area of solenoid valve in a flow discharging from a tank, (JIS), with that in a steady flow, (ISO DRAFT). It became clear:
(1) In the discharging method, the effective areas agreed with those in the ISO method, within 5% deviation, including expected error and the effect of heat transfer from the tank
(2) The discharging method could be used as equivalent to the ISO method for practical use
(3) A change of state in the tank could be approximated as a polytropic change with a constant polytropic index
(4) Mass flow rate from the tank was smaller than that calculated from the above approximation
(5) The reason was supposed to be due to a temperature distribution developved inside the tank, and the presumption was experimentally confirmed.

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The work is a current extension of work on the conception, design and performance of an air motor powered servodrive for a 20 kg payload industrial situation. The earlier work involved dynamic modelling (using bond graphs) and simulation to help design the system, and response measurements on a prototype system. Fixed parameter feedback control was used. In parallel with that brushless d.c. motor, hydraulic motor, and hydraulic cylinder servodrives designed and similarly analysed, and comparisons were made with the airmotor servodrive's performance.
The airmotor servodrive's performance was sufficiently encouraging to warrant further development. The system is nonlinear, and the load impedance it would experience in real life could change continually during its working cycle. It was considered highly probable that an appropriate adaptive control strategy will significantly improve the controlled performance of the system. Such a strategy, using the model reference approach, has been devised and implemented on digital simulation. A hardware system using software control will later be assembled to seek validation of the findings of the simulation.
The paper presents the servodrive system and the adaptive control strategy developed, and the simulated performance of the loaded system under adaptive control for several conditions.

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The constant adaptation gain algorithm has been often applied to the MRAC of electro-hydraulic servo system. This paper describes the application of the MRAC with the constant trace algorithm to a pneumatic servo system. The response of the MRAC of the plant without feedback is compared with that of the MRAC of the plant with feedback, whose response was rather smooth and stable. It is cleared that the power spectra of control inputs upof both MRAC systems, obtained by FFT, differ remarkably. The effectiveness of the constant trace algorithm in the MRAC was shown by the experiments of the sudden changes of the feedback gain of the plant during the control. It is shown that the limiter of the control input is very effective to stabilize the MRACS where the response speed of a reference model is much faster than that of the plant.

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To study the feasibility of an electropneumatic servomechanism, it is necessary to simulate the charging or discharging process of a chamber by using a servovalve.
Both servoamplifier and servovalve behaviour are taken into account by the combination of a non-linear element and a transfer function deduced from the frequency response of the torque motorspool assembly. The effective area of each servovalve orifice is a function of the input current and the pressure ratio, which has been calculated from experimental data. The model which has been retained for a chamber is equivalent to the Jebar's model. The chosen state variables arc the total internal energy and the mass of the gas which is contained in a chamber. The heat transfer coefficient is supposed to depend on the pressure and the temperature. Simulated results have been obtained by using A. C. S. L. language. A comparison between experimental and simulated results is presented.

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The ready studies show that the characteristics of an electropneumatic servo control system (EPSCS) can be improved remarkably by employing of the state-feedback technique. But the control error of such a system cannot be ignored, especially when there exits large external disturbance, and its stiffness is not satisfied.
In this paper, the authors propose a robust control scheme, and develop a design method for robust controller, when the controlled object or plant is unstable, as in the case of EPSCS.
The robust controller is drived by system error and it can eliminate the error to zero. So, as confirmed by simulations and experiments, the system has almost infinite stiffness and can follow the input signal perfectly.

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For realizing an opto-fluidic system without any mechanical moving part, opto-fluidic converter employing a photoacoustic cell as the control port of a laminar proportional amplifier was investigated. Carbon black was used as a light absorber of the photoacoustic cell. Effects of the incident light intensity, the light modulating frequency, the absorber thickness, and the cell length on the photoacoustic pressure amplitude are clarified. Conversion characteristics of the opto-fluidic converter are also reported.

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The paper concerns the construction and the simulation testing of a motion synchronization system of two pneumatic cylinders operating parallelly under different loads. The sinchronizer comprises the fluidic amplifier controlled by the slidingspool valve distributing the air flow into the cylinders. The fluidic amplifier is controlled by the pressure signal from the valve output.On the basis of the mathematical model the simulation of operation of two cylinders working parallelly with synchronizing valve has been carried out. The results has been compared with the simulation of two cylinders working parallelly without synchronizing valve. The aim of the simulation testing was to optimize the construction of the synchronizing system.
displacement of the piston rods of both cylinders x₁/t/, x₂/t/ on the way cylinders stokes.
The experimental results allow to state that aplication of the synchronizing valve with the fluidic amplifier essentialy improves the characteristics of the system, decreasing the displacement difirence of cylinders by about 50 /e.g.for the load difference 900 N, the displacement difference is 21, while the system without synchronization showed the difference of 43%/.
The selection of the amplification factor of fluidic element and of the springs which holding sliding spool in midposition has the most important influence the working of the synchronizing system.

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Intending to develop a plane bending fatigue testing machine of a cantilever having a long life without maintenance, a fluidic oscillator using supersonic bistable device has been designed and tested. This machine which a new type fluidic oscillator is applied into has some advantages. That is, it can deflect a test piece with jet stream, it can be used in high frequency range of testing vibration, and it has no mechanical vibration of machine itself. Therefore it is of use for impact plane bending fatigue test of a test piece fi xed as a cantilever.
The new type fluidic oscillator is a kind of the loaded oscillator with the bifurcated channels of each outlet. A tank or tube as a capacitance is connected with one of the bifurcated channels, and the other of them constructs one of two opposite nozzles. A fatigue test piece is set between these opposite nozzles forming flapper-nozzle confi guration and is vibrated by the alternately impinging jets.
The supersonic fluidic oscillator with some special features mentioned above has been designed and tested. And the oscillation mechanism has been explained by a simple analytical model.

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Jet pumps, vortex amplifiers and Y-joints are examples of “fluid-dynamic 3-terminal elements” (3TE). There are many other such devices all of which have useful flow controlling effects. An interesting form of classification results from considering 3TE to operate in just two flow-states, in this case those with zero flow in one terminal are chosen. This gives four distinct flow-state classes. Having identified these flow states the pressure states are classified in terms of ideal lossless operation, absolute gain and amplitude modulation. These attributes are represented graphically using the indefinite circle-diagram. A table is drawn-up with 20 device-types resulting from the 4 flow states and 5 types of pressure classifications. Further subclassification is possible. The origin and significance of the various types of “reverse flow diverters” is then made clear along with other types of junctions, vortex devices and diverters which are established fluidic components.

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Effects of difference in the poppet shape on the characteristics of oil hydraulic poppet valves are studied, under in particular the flow conditions with cavitation. The flow rate and thrust characteristics, noise level and cavitation occurrence limit are measured with the five different shaped poppet valves: type (A) the normal cone, type (B) with a plane on the top, type (C) the cylindrical, types (D) and (E) with a flange around the skirt and the top of the poppet.
As a result, it is mainly revealed that the plane placed on the top of type (B) has a great effect in the case of the converged flow application, the difference of the seat angle of type (C) makes great changes in the valve characteristics in the diverged flow, and the flanges in types (D) and (E) have a effect on the compensation of flow force or changing the direction of the flow force.

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A proportional poppet valve is a new oil-hydraulic valve whose main poppet lift is linearly controlled by a pilot valve. Like a usual and simple oil-hydraulic valve, the total flow rate of this new poppet valve is influenced by load pressure. The present paper describes a new compensation method to decrease the influence of load pressure, and this new method is named as area compensation method. The area compensation method is based on the design of top and bottom areas of the main poppet. From detailed experiments and analysis, this new compensation method has been found to be effective and practical. The structure of the proportional poppet valve designed by this area compensation method is simple. The analysis of static characteristics is easily and accurately performed.

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A pressure relief valve design is analysed, and a computer simulation compared with experimental measurement. The valve is one of a specialist type which utilises a controlled pressure differential across the main spindle to regulate its motion and therefore to regulate the pressure rate of rise in the system. Some predictions concerning the dynamic behaviour for a range of parameter variations are also presented.

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Automotive automatic power transmissions have some pressure control valves which control the pressure of wet-clutches or band- brakes. Recent transmissions have replaced hydro-mechanical valves with electro-hydraulic valves for the improvement of shift quality of gear changes. A conventional proportional pressure control valve is controlled by asolenoid with a triangular leakage path of magnetic flux which causes lower reproducibility and productibity. And it is difficult for a single stage valve to control high flow rates. Here, we have designed a new type of proportional solenoid with a rectangular leakage path in magnetic circuit with an aid of FEM analysis, and controlled a secondary valve by a primary valve with a spool of 2 mm in diameter. The dynamics of the valve and the presssure control system are simulated by bond graphs which manipulate nonlinear elements symbolically.

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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.

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