A new check valve which can be closed at controlled speed and can prevent pipeline systems from waterhammer has been designed and manufactured (Fig.2). The Chinese National Patent-1986 and the Chinese National Invention Award-1987 have been conferred for it. The conventional fluid transients theory has been used for designing and calculating. Eight simulataneous equations were set up and solved by computer program. In order to carry out the calculation of transient analysis, it was necessary to know the resistance coefficient ξ as a function of Reynolds number Re and opening angle δ of the clapper, and to know the flow coefficient Cv as a function of Re and opening h of the needle valve. Therefore those values were measured by experiment. As these quantities have dimensionless, the values obtained from experiment are not only for this valve, but also for the valves of the same kind.

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This paper suggests a new method of pictorially describing the mathematical model of a hydraulic system by combining the advantages of block diagram and bond graph. The fundamental components are equal flow junction, equal effort junction, power transmission line, control line and various elements. The relationships between the variables are written in the block of every element. The differential relationship is used, so that is convenient t o list t he state equations from the diagram. A valve controlled motor system is used as an example so as to illustrate the procedures of drawing the state variable d iagram.

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The problems for high accuracy synchronous drive of mult ipass hydraulic position servo system is discussed in this paper. First, the constitution of mult ipass systems is analysed and simplified. Then, the Model Reference Adaptive Control (MRAC) is adopted t o improve t he dynamic response and the position synchronism accuracy of system, and to eliminite serious influences of various nonlinear factors. This paper has applied Lyapunov stability theory to design the adaptive control law and rat ionally simplified it. Simulations and experiments prove it is effective and successful. For engineering implementation, it is convenient as well.

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A robot electro-hydraulic servo system is a highly nonlinear system whose parameters are apt to be affected when its attitudes and payloads are varied in a larger extent, therefore the results of using conventional compensation are not satisfactory. A simple method, which has some anti-interference abilities, called simultaneous gain compensation, can obviously improve the dynamic response characteristic of the electro-hydraulic servo system, and is good for the stable accuracy of the system. In this paper the simulation study and the experiment study of the method have been worked out.

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The robots realized at present, are primarily developed for automation in factory, such as industrial robots. Recently, intelligent robot with vision etc. appeared, but the object of introduction doesn't change, so much.
New field of robot with more advanced functions is developing, whose object is inspection and maintenance of large plant such as nuclear generating facilities. But realization of this type of robot by present technology is very difficult, because it requires remote, mobile operation. It requires to solve many technical problems for development of advanced robot. Especially important problem for it, is locomotion technology of robot. There are crawler, wheel and rail transportation as the conventional locomotion techniques, but they have a peculiar drawback, that is lack of smoothness when there is obstacles in locomotion route.
In these cases, multi-legs articulated mechanism is suited well. So that, development work is busy in worldwide.In this time, Hitachi developed and demonstrated “Biped Robot” for TSUKUBA EXPO'85 in Goverment Theme Pavillion, under the cooperation of prof. Kato of Waseda University.
This articulated mechanism. realized highlevel autonomous two legs walk which simulates human walk by oil hydraulic technology. The features of this robot is that all components except electrical power source is mounted on robot trunk. That is, power supply, composed of oil pump and auxilliaries, controller, composed of microcomputer and amplifier etc. are all mounted on robot. As follows, details of the biped robot will be explained.

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Pneumatic actuators are cheaper and lighter and they can drive faster than any other robot actuators. So it is very interesting to use the pneumatic actuators such as air cylinder to the high accuracy robot systems. But in this case, the motion of robot tends to unstable by the air performance. To make stable the system, pole assignment control method is often used and the results by the electro-hydraulic cylinder driving system have been reported (1).
The pole assignment method reported in this paper is useful to the electro-pneumatic cylinder driving system theoretically. The experimental results of pole assignment control for actual robot arm system are shown by using air cylinders.

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To apply a pneumatic robot to not only conventional simple tasks but also more rigorous ones, a servo type control is required. Since it has some high nonlinear properties, some type of adaptive control strategy should be adopted to improve its conrol performance. In this kind of robot, the simplicity of control algorism is also important.
In this study, an adaptive variable structure control scheme is developed on the basis of the well-known variable structure system theory. This control scheme confines a phase-plane trajectory on the switching line momentarily rotated adaptively to the phase-state of controlled system. It can suppress the chattering often encountered in the usual sliding mode control with a fixed switching line, to achieve a smooth response. Further, it can automatically generate the specified phase-plane trajectory heading toward the desired position asymptotically.
As a result of the application to the PTP type position control of an articulated pneumatic robot, the expected control performance can be well attained. Some advantages of this control method are the simplicity of a control algorism and the flexibility in the decision of control parameter values. Its availability may be verified.

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Aservovalve/cylinderposition control system is studied for the case when a simplified first-order transfer function may be considered a sufficiently accurate representation of the system dynamics.Digital filters are then included in the feedback and error loop of the system, and the new closed-loop transient responseis theoretically derived. Filter coefficients, are then determined by an explicit solution to the closed-loopresponseequationby specifying the first three desired response values. The stability of this approach is also investigated for variations in the electrohydraulic system parameters.An excellent comparison between measurement and theory is established.

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A pneumatic transmission line is widely used for measurement and control systems. Therefore it is necessary to calculate dynamic responses of the line. The Brown's model of the pneumatic transmission line gives sufficiently accurate responses, but it needs troublesome calculations including Bessel functions. In this study, a new reduced model is proposed, which is presented by first or second order system and time delay system. So calculatations using the reduced model can be very easily carried out. In experiments, tests of step responses and frequency responses were conducted. The reduced model showed a good agreement with the exact solution and experimental results. The new reduced model is very useful for designing a real control system with pneumatic lines.

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The present study deals with the estimation of the dynamic characteristics of the hydraulic system used in an injection molding machine. It is usually not easy to estimate its dynamic behavior, however, because the characteristics of the plastics as a load is not well analyzed. The aim of this study is to estimate the dynamic behavior of the plastics in the mold by bond-graph simulation. The hydraulic components used in the hydraulic circuit were decomposed into simple elements which were replaced with corresponding bond-graph elements, and finally a bond-graph diagram for the hydraulic circuit was obtained. On the other hand, six models for the behavior of the plastics had been assumed, and after calculation using those models these results were compared with experimental results. One of them was selected as the most preferable model, which best simulates the behavior of the plastics.

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In this paper, the method ofcontrolling a hydraulic load tester tosimulate a desired mass-damper system isdescribed. Two cylinders are located in asame axis and the rods are rigidlyconnected with each other. A load testpattern, which is specified in timesequence, is adopted as examinations. Wepropose two kinds of method to control theload simulator:(1) a feedback controlwhich is theoretically derived to makethe loading system simulate an actualload;(2) a feedforward control which makesthe response of output load pressure fairlygood. In both methods, the relationbetween the velocity and load pressureagrees closely with the given load characteristics.

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A basic method for the time domainsimulation of fluid transmissionlines is introduced in this paper.First of all, accurate approximationare made for propagation operatorr and characteristic impedanceZc in the distributed parametermodel of the lines. Then, the methodof Fast Inversion Laplace Transformis applied to deal with the inversionLaplace transform of the modelwhere propagation operator and characteristicimpedance are replacedby their accurate approximations. Inaddition, by means of the method andcharacteristics method a set ofrational polynomial approximationsobtained in previous papers is confirmedin time domain for sevenunique transfer matrix elements inthe distributed parameter model. Theresearch is meaningful for simulationof hydraulic systems and fluidmeasurement using the dynamic modelof fluid transmission lines.

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This paper deals with chaotic oscillationsoccuring in a hydraulic circuitconsisting of a poppet valve and a pipelineterminating at a constant pressure tank.The circuit with a long pipeline becomesunstable and various kinds of oscillationsare self-excited. In this study, it isshown by digital simulations that irregularsolutions are obtained from a deterministicmathematical model for the dynamics of thecircuit in addition to periodic or almostperiodic oscillations. The irregular solutionswhich are considered as a kind ofchaotic phenomena are classified into (a) period-doubling type, (b) Ruelle-Takenstype, and (c) intermittent type.
Experimental results are qualitatively in good agreement with theoretical ones.

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In a large scale oil hydraulicsystem having repeatedly operatedactuator, such as a large scaleforging press, pressure surgesoften occur due to the recombinationof oil column in a return lineattached to the downstream side ofa directional control valve.Especially, the pressure surgesappear very severe ones at acertain valve operating frequency.These pressure surges restrict theoperating frequency of thehydraulic system. But there are fewreports about the above mentionedphenomenon.
In this study, therefore, the authors investigate the exactreason why such severe pressuresurges occur at a certain range ofvalve operating frequency. And forthat purpose, the relationshipbetween pressure surges and valveoperating frequency is studied byexoeriments and numericalcomputations.

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A new type of hydraulicpressure intensifier was previouslyproposed by the author, which operateson the principle that an oilhammer is generated continuously inthe pipeline by the on-off operationof a solenoid operated valve, locatedat the downstream end of the pipeline, and only the high pressure fluid isdischarged through a check valve. Inaddition, a method to utilize theintensifier for pressure control of ahydraulic cylinder by adjusting apulse to the solenoid operated valvewas already proposed.
In this paper, a pressure control system utilizing this intensifieris developed to generate a waveform according to a desired input.The empirical formula which relatesthe pulse width to the correspondingpressure increase is established inadvance and memorized in a computer.When the desired pressure is given tothe computer, it calculates the pulsewidth automatically through the empiricalformula and sends a pulse to asolenoid operated valve. Since thissystem is digitally controlled usinga micro computer, it has an advantagof having an option for a learningfunction.

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Cavitation erosion due to impingement of cavitating jet was experimentally studied with specimens of aluminum alloy in hydraulic oil, high water content fluids (HWCFs), and tap water. The behavior of cavitating jet was observed through instantaneous photographs. Probability distributions of cavity cloud existence were obtained from an analysis of the instantaneous photographs taken from the side of the jet. The behaviour of impinging cavity clouds was also observed. Furthermore, the damaged surfaces of the specimens were examined by using scanning electron microscope.

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This paper treats the experimental research of the erosion of the poppet valve chamber by changing the configuration of the poppet valves and seats and the pressure of the poppet valve chamber.
As the result of the experiment, the following became clear: 1) The erosion in the valve chamber is the result of the cavitation and jet. 2) There occur extreamly erosion in the case of the diverging flow than parallel and converging flow. 3) Erosion has its maximum value against the back pressure, and at this time the noise level becomes maximum. 4) Ersion of the valve chamber become small according to an increase in the diameter of the valve chamber. 5) Effective and simple preventive measure of the erosion is presented.

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Pump cavitation has always been a serious problem. The determination of pump cavitation inception is an important matter for preventing pump from cavitation damage. Based on the authors' research on pump cavitation characteristics with signal analysis technique, it is found that once cavitation occurs, a particular low frequency fluctuation component of outlet pressure with higher amplitudes than that in non-cavitating condition appears. Its nature of association with cavitation inception indicates that the appearance of this low frequency component can perhaps be used as an indirect indicator for pump cavitation inception. The experimental observation results with piston and gear pumps at different speeds are shown. A discussion and preliminary theoretical analysis are also given in this paper.

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The interaction of moving expansion waves with junctions of branched duct is theoretically studied. Two cases of the interaction are studied both analytically and numerically. One is the interaction of expansion waves with a single junction. The other is the interaction in the case of a double junction. As an analytical approach, a quasi-steady flow model is utilized. As a numerical approach, the method of chracteristics is used. The strengths of the transmitted and reflected waves are shown for many different combinations of the cross-sectional areas and the angles of the side branches and the strengths of incident expansion waves. The numerical results show clealy how transmitted and reflected waves develop with time in the transient process of the interaction.

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Unique, high pressure CFRP hydraulic cylinder incorporated stroke sensor was developed. As a first step of development, a unique CFRP-METAL joint using. a filament-winding method was developed, which had a high strength and high fatigue limit. In this method, strength of carbon fiber is fully exhibited. Effectiveness of the method was confirmed by the models of hydraulic cylinder. The joint strength of rod was more than 390 MPa and the tube endured more than 106 times impul-sive dynamic pressure of 27 MPa.
Second, we developed integrated, smart stroke sensor, suitable for CFRP cylinder construction.
By combining above two key technologies, we manufactured complete 21 MPa rating CFRP hydraulic cylinder incorporated stroke sensor. Stroke of the cylinder is 500mm, inner dia. is 50mm and rod dia. is 28mm. The weight of manufactured cylinder is 4.7 kg, less than 1/3 of steel cylinder and 1/6 of commercial steel cylinder including stroke sensor.

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Utilization of ocean wave power is one of our dreams.
A system introduced here “Pendulor” has pendulums which resonate in the exciting wave motion and the pendulums drive a generator via hydrostatic drive system. We believe, this “Pendulor” would bring the dream in our life. The combination of the pendulum (mechanical power transfer) and the HST (hydraulic power transfer) gave 40% overall efficiency in ocean testing, having a basic matching of their huge thrust force -low speed features. The Pendulor absorbs wave force and makes little reflecting waves so effectively that the caisson attached it can become an improved breakwater.
25 yen/kWH or 9.4 yen/kWH are expected using a proto-type Pendulor designed here, including with or without caisson cost.

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The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned experimental program complemented by a flow visualization study. The moving surface was provided by rotating solid and scooped cylinders located at the leading edge, the trailing edge, or the upper leading edge of the airfoil. Results suggest that the concept is quite promising leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of the angle of attack (α).
A flow visualization study using a water tunnel with food colouring as marker substantiates, rather spectacularly, effectiveness of the moving surface boundary layer control and qualitatively confirms complex character of the flow as predicted by the experimental data.

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The present paper concerns the unsteady laminar incompressible flow between two parallel disks with a fluid source at the center of the disk (s). Both the flow rate of the source and the gap width between the disks are varied arbitrarily with time and independently of each other. Such a flow often appears in a nozzle-flapper valve or in a statical pressure bearing such as the piston shoes of a swash type axial piston pump. Series solutions to the Navier-Stokes equations are obtained, on the basis of an asymptotic expansion in the radial direction and a new theory of “multifold series expansion” for the time variable. The solutions describe precisely the non-linear interaction between the two coexisting flows. Experiments were carried out for the case where both the gap width and source flow were varied sinusoidally. The solutions agree well with the experimental results over a wide range of the flow conditions.

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The thermoelastic behavior of hydrostatic thrust bearings is analyzed numerically. Mineral oils, HWCF, sea water, and tap water are studied as lubricants. The physical properties of lubricants are expressed as a function of temperature and pressure. The heat transfer and thermoelastic distortion of the bearing pad are considered. The performance of bearings is evaluated by the load carrying capacity, mass flow rate, and friction torque. The effect of temperature and pressure on the physical properties of mineral oils is greater than that on HWCF, sea water, and tap water. The load carrying capacity is scarcely influenced by the types of lubricant, the angular velocity, and the fluid film profile. The fluid film thickness influences the mass flow rate and the friction torque. The inclination of the bearing pad increases the mass flow rate and the moment-load carrying capacity. The distortion due to pressure in the fluid film increases the mass flow rate.

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This paper, firstly, describes the generation of small pitch parallel line chatter marks on the workpiece surface. Experimental results show that the pressure pulsation produced by the vane pump makes the wheelhead and the work table of the machine vibrate which results in small pitch chatter mark formation. The installation of an in-line type accumulator to the hydraulic line is effective in suppressing this type of chatter mark. Secondly, the causes of the unexpected change of the chatter mark pattern corresponding to the wheel rotation are also investigated. It is found that the speed and stroke of the work table and the hydraulic oil temperature vary with operating time. As a result, the chatter marks may change their appearances in spite of constant machine settings. It is also found that by using the developed special control device, it has been possible to keep the speed and stroke of the work table constant and also to obtain the most preferable chatter mark pattern.

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The oil bath lubrication used for a gear unit, is affected by the agitation loss at temperature rise. In order to reduce the agitation loss, it is necessary not only to measure agitation loss torque but also to visualize the agitation appearance. The purpose of this paper is to clarify the behaviors of lubricant flow in the K-H-V planetary gear unit used in those of hydraulic drive systems for heavy machines. In the visualization experiment, visualization equipment containing transparent liquid paraffin lubricant was used, and agitation losses of the equipment were measured. The lubricant flow in the planetary gear unit is discussed in terms of the change in position and movement of each component. Further, some parts in the equipment were modified and carried out the visualization and measurement of agitation losses. We discuss about the behaviors of the lubricant flow vs. agitation loss characteristics relationship.

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The dynamic characteristics between flowrate and pressure difference of a couple of cylindrical chokes in series are investigated experimentally by making use of a cylindrical choke type instantaneous flowmeter, which has been proposed and developed recently by authors. As a result, it is confirmed that the dynamic characteristics are greatly influenced due to the existence of co-axial unsteady jet caused by the upstream choke and are quite different from those of independently connected choke characteristics without the existence of jet flow. In addition, a simple mathematical model is proposed, the results are in good agreement with the experimental results. It is also confirmed experimentally that the newly devised rectifiers set up in front of chokes are valid to avoid the influence of the unsteady jet flow.

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This paper discusses an applicaton of the hydraulic oscillator utilizing the self -exited vibration phenomenon to a flowrate meter which detects the flowrate in the form of a vibratory member frequency.
The hydraulic oscillator is constituted not to cause the pulsation of the flowrate when the fluid passes through it, and the frequency characteristics are improved to confom with a flowrate meter.
The approximated equations of motion for the vibratory member are obtained and solved by means of digital computer.
The experiments are conducted by varying the ratio of a main spring constant to an auxiliary spring constant. The experimental frequency characteristics almost agree with the theoretical. It is confirmed by the theoretical and experimental study that the hydraulic oscillator is applicable to a flowrate meter.

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In this paper, a new method using Pattern Recognition Techniques (PRT) to measure the particulate contaminents in hydraulic fluid is presented. From the enlarged digital images of the particulate contaminents, the number and size of the particles can be measured, the particle size distribution can be counted up, and some physical properties of the particles can be estimated. All the values of the characteristic parameters of the particulate contaminents are collected and processed in a shortime (about 23 minutes) by the combined system of a close-up video camera and an IBMPC/ XT microcomputer with an image processing board installed. With such a system, initial experiments have been done by the authors and good results have been achieved.

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This paper describes the gas-liquid separation for various hydraulic systems those can be used in the microgravity environment such as space. Methods for the separation of gas entrained in silicone oil and in liquid nitrogen are proposed. The principle of gas-liquid separation for silicone oil is based on the electrostatic force, and the principle for liquid nitrogen on a newly devised reducing plug with a heating filter.
A concept of the microgravity experiment for evaluating the performance of the gas-liquid separation methods for both silicone oil and liquid nitrogen developed is also provided. In the microgravity experiment an aircraft is employed.
The visualisation experiment in microgravity environment aimed at the understandings of the fluidic behaviors of the gas-liquid two phase flow consisting of silicone oil and air bubbles was carried out prior to the development of gas-liquid separation methods.

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The performance of a newly developed bubble elimination system is analyzed. The system consists of a circular body for a swirled flow supplied tangentially, equiped with a throttle valve downward and a valve for discharging bubbles upward.
A strong swirl superimposed on an averaged laminar flow during the initial state is found to decay exponentially with the distance from the entrance at the far downstream. As a result, for Reynolds numbers greater than a suitable value an adverse pressure gradient is produced, exerting a backward force on the bubbles to be discharged.
In addition, universal velocity distributions and pressure contours downward are shown.

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