This paper proposes a digital control method of a fully-bridged circuit system consisting of switching-valve-operated proportional-seat-valves. It offers freedom of pressure control to an inertia load compared to a conventional servovalve system, and has potential to reduce the power-loss of control throttles and to prevent cavitation in quick motion control of an inertia load. The two-port seat-valve combination is applied to motion control of a ram-cylinder of 300kN class hydraulic punching press for saving power consumption. Its fluid power system has two power-sources of low-pressure, high-flow-rates for quick ram motion and high-pressure, low-flow-rates for punching plates. The control system switches the power-sources by the active timing control of the fully-bridged seat-valves according to the load condition. As a result, the power consumption is saved by 60% compared to a conventional system.

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This paper deals with a method for designing an optimal valve control to suppress the shocks due to the surge pressures followed by column separation produced at various periods of an operating cycle of a hydraulic machine press without reducing the cycle time. In this method, the time-history waveform of the input voltage signal for the valve, which controls a certain operating period (e. g., decompression period), is assumed to be of a several-stage break-line mode from a specified initial value to a final one. These break points are found by means of a computer program for optimization so that a minimum value of valve operating time can be achieved under the prescribed conditions of the magnitude of surge pressure being lower than an allowable value. Experiments carried out on a small-sized model apparatus show the success of the present method.

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Modification of poppet structure was proposed to control poppoet displacement so that flow rate can be continuously controlled by pilot pressure. All attenuator was inserted into a pilot line to reduce pressure oscillation caused by PWM drive of a pilot valve. A proposed PWM-controlled logic valve was examined experimentally. Poppet was floated and its displacement was controlled by PWM signal. It was demonstrated that flow rate was continuously controlled by PWM signal. Effects of parameters of the attenuator were investigated experimentally.

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In this study, a high-speed on/off digital valve was developed for use in a hydraulic control system. The device basically consists of a poppet valve acting as the main valve, and a multilayered piezoelectric (PZT) actuator for driving the poppet valve. A hydraulic amplifier was adopted to increase the actuation of the PZT actuator to the poppet valve. A compensation mechanism was set up to reduce this temperature effect in the hydraulic actuation of the PZT actuator. This problem arises when the oil temperature increases and causes the valve displacement to fluctuate slightly.
The static and dynamic characteristics of the device were investigated by experiment and digital simulation. As a result, we found that the switching time of the valve is less than 0.7 ms. Moreover, the valve can be driven by a PWM carrier wave using frequencies of up to 500 Hz. Additionally, the validity of the temperature compensation mechanism was confirmed. Hence this valve may be determined as feasible device.

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Resistance spot welding technology of various coated steel and aluminum alloys is widely used. These welded materials contain base metal, coated layers of metal or cladding metal with different thermal conductivity, electrical conductivity and expansion-contraction properties. They require a proper variable electrode force control during a short welding time to avoid welding spattering, reduce welding defects and increase welding strength. However, a constant electrode force method is usually used in spot welding machines because of too low response speeds of air cylinders.
In this research, a dummy force control cylinder was made to simulate the analyses and experiments of structural parameters about a newly developed motion and force compound control cylinder. The dummy force control cylinder is the same sizes as the force control part of the new cylinder in pipe diameter, pipe lengthes and piston diameters. Its transient and frequency responses are mainly dependent on pipe diameter and piston stroke. Experiments indicate that the optimal parameters are about 0.5 (mm) piston stroke and 4-6 (mm) pipe diameter for a servovalve of 8 (mm) spool diameter and 1 (mm) stroke.

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This paper describes the simulations of PID control and PID parameter-scheduling method of an air cylinder system in a spot welding machine. A proper simulation model of the valve controlled air cylinder system is obtained to assess the effectiveness of given control systems. The set-up and set-down responses are analysed in these control systems. Simulation results for various input amplitudes are given to show the effectiveness of the proposed controllers.

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This paper deals with the development of a pneumatic on/off valve driven by impulsive force of a multilayer PZT actuator. The displacement of the actuator is so small that it is necessary to design an amplifying mechanism. However, it subtracts the advantages of this actuator. On the other hand, the actuator can snap off a contacting small object like a hammer when the voltage is applied rapidly. This type of action is called a flight hammer. Using this action we hav developed an on/off valve with a nozzle-flapper mechanism, which is normally closed by the air pressure and is opened for a short time by the PZT actuator with the help of the spring force. The application of this valve is to blow off small objects by the air pulse flows that are generated by the on/off action of the valve. The air jet could blow up a small steel ball up to 20cm in height.

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A measurement technique had been developed to detect the variation of vane space pressure in a pneumatic vane motor during time. The investigated motor is a small dimensions and high speed one, and due to these characteristics it can be used in robotics. To evaluate instantaneous pressure a piezoresistive pressure transducer had been fitted in the driver rotor and during tests it rotates with the rotor. Being the motor dimensions reduced, it can rotate at a very high speed, consequently the pressure frequency is very high. A pressure frequency telemetric system had been used to transmit the pressure data from the rotor parts to the static ones. In this way we have not a cable transmission but a radio transmission from the rotor to the static parts. Results obtained from an extensive series of experimental tests carried out in laboratory in various operating configurations are presented.

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The present paper shows the investigation of the fatigue life of a hydraulic servo controlled log crane boom structure. The coupled dynamics of the hydraulic driven log crane is simulated using ADAMS. After analyzing the dynamics of the system the results obtained are utilized in the ANSYS finite element program to determine the stress history of the boom. During the simulation the stress range occurrences are calculated using Rainflow-algorithm. The fatigue life at a certain location of structure is then calculated by means of the hot spot stress approach. In this approach the fatigue strength, in form of S-N curves, is based structural hot spot stresses.
By employing the designing method mentioned above the effects of variations in the parameters of a P-, PD-and P+acceleration feedback joint controllers on the fatigue life of a crane boom structure are investigated. The goal of the study is to highlight the importance to compromise between the control properties and fatigue life in the design of a servo controlled working machine boom.

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This paper deals with hydraulic active suspension br wheeled hydraulic excavator. In this study, a combined control method for both the posture keeping and the vibration elimination is proposed, and verified in experiment. The posture keeping control is realized by a variable stiffness control, and the vibration control is based on the skyhook damping theory. The result shows that the control can not only well eliminate the vibrationon the body of the excavator during its high speed moving, but also well keep the posture of the chassis horizontal while the excavator is in digging or swing operation.

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Surge pressure problems at the lower pressure side of the hydraulic system of an active suspension system for passenger cars is investigated by experiments and numerical analyses. In the numerical analyses, the method of characteristics was used for simulating unsteady flow in the hydraulic system and gas discrete model was adopted for estimating gas volume variation in separated liquid column. Also, effective techniques for smoothing surge pressure in the return line of the hydraulic system were suggested.

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In this paper, a mathematical model for a semi-active damper, in which a pressure regulating mechanism similar to a balanced piston type relief valve is built-in, is derived. The Numerical simulation results of the damping force characteristics are in good agreement with the experimental ones. It implies that the mathematical model is available. Furthermore, effects of various parameters on the stability of the system are investigated on the basis of this model.

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Switching-and proportional-solenoid valves are mass-produced components for electrohydraulic servomechanisms. Quality of a servomechanism depends on the valve-dynamics and it is important for valves to respond as quick as possible. Main delay of a valve is resulted usually from the time-constant of solenoidinductance. It is compensated easily by energizing the solenoid with a highvoltage over-excitation circuit. However more quick operation is prevented from the eddy-current in the magnetic circuit. It interferes to permeate magnetic-flux into an armature. This paper clarifies the affect of eddy current on the switching speed of on/off-and proportional-solenoids by measuring the transient characteristics of the electric current and magnetic fl ux-flow, and next by calculating transient flux-flow on the process of permeating into the armature with the aid of newly-programmed FEM analysis. Over-excitation energizing and low-conductive material shorten the delay of a switching-solenoid valve from 7.9 ms to 0.8 ms and of a proportional valve from 40 ms to 1.7 ms.

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Primarily in use at present is the nozzle flapper type servo valve providing with a torque motor.
It is not in all cases appropriate for construction machines requiring large flow, owing to small control flow of the nozzle flapper.
To deal with this situation, the linear motor servo valve using a magnet for a proportional solenoid has been developed.
By driving metering spool directly by a linear motor, neutral leak is kept small and control flow increases.
This valve operates independently of supply pressure fluctuation, i.e, pressure compensating characteristics.
For large stroke of the linear motor, the orifice diameter is large, thus greatly lessening the possibility of contamination failure of the valve.
Frequency response of the main spool is as much as 70Hz.
This valve is thus shown suitable for construction machines.

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On a view point of a human-machine interface, the vocal sound is an effective medium of communication between human beings and machines both sides. Mechanism of phonation for living being is much complicated. Human phonetic organs consist of the lungs, the vocal cords, and the vocal tract. The phonemic characteristics of the vowels are determined by the frequency of the vocal cords producing fundamental sound and by the resonant behavior of the vocal tract modifying the sound to a voice. The purpose of this study is to make a human-like robot that utters sounds by a mechanical phonetic organ instead of an ordinary electrical approach. Vocal cords and a vocal tract model for mechanism of human-like phonation has been developed and Japanese five articulated vowels have been experimentally investigated by the developed resonant part.

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The position control of a pneumatic cylinder at high speed and high accuracy is very difficult due to nonlinearities of its movement because of the air compressibility or the sliding frictions. In this study, above problems, the improved pulse driving control method is proposed to overcome. The position is controlled by the pulse driving high response on-off valves. In this control method, the phase plane trajectory is confined on the switching line using differential pressure. This position control is executed, the dynamic response and the position accuracy are experimentally examined.
As a result, obtained characteristics are so satisfactory that the efficiency of the proposed control method are ascertained.
And we have developed a positioning controller of a pneumatic cylinder with this control method. It has been used as a pneumatic servo robot in an actual product assembly lines.

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In this paper, new bang-bang control methods by means of learning law and fuzzy reasoning are proposed for a pneumatic positioning system in which a pneumatically driven brake is built in the cylinder. Two schemes to stop the piston rod are discussed. One is that the piston rod is stopped by brake, and the other is that the piston rod is stopped by chamber pressures. Controllers are designed to determine the bang-bang control inputs, the positions of the piston rod, for switching valves to satisfy the terminal position and the braking condition through analyzing the previous cyclic data. Experimental results show that the proposed controllers possess the capability of obtaining fast convergence of position error, especially for periodic actuations. Owing to ease in implementation, this pneumatic positioning system has been having a prospect in the industrial automation.

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Intending to lighten hard physical labor of a nurse carring a patient in her arm, a powered suit which supports the muscular force of the nurse was developed. The powered suit consists of shoulers, arms, waist, and legs, made of aluminum, and is fitted on the nurse. The powered suit was originated with the concept of master and slave system in one body. The arms, waist and legs have pneumatic rotary actuators. The pneumatic actuator consists of concentric round boxes sliding each other. The movement of the arms, waist and legs of the nurse were sensed with strain sensors made with conductive rubber.
This paper gives design and the characteristics of the powered arm, waist and leg using the slide box type pneumatic actuators verifing its practicability.

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Intending to explore the possibility of an optical control robot without interposing any electrical signal, a pneumatic control robot arm controlled with a new differential optofl uidic interface was developed. The interface employs opposed light absorbing nozzle walls in a laminar proportional fluid amplifier. The fluidic output signal of the interface was amplified by a three-stage proportional amplifier gain block. Robot arm has two members and two joints moved by pneumatic rotary actuators. Two membrane type booster amplifiers with two staged nozzle-flapper valves were used to amplify the power of the output signals of the gain block so far as enough to drive the rotary actuator. PID control was applied to the robot arm system and the feasibility of the optical control was proved.

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A FLexible microactuator. FMA. has potential to reproduce human friendly actuation because ofits smoothness in motion. It is made of fiber-reinforced silicon-nibber which bends or stretches in proportion to pressures of internal three chambers. The mechanism is yen- simple and enables gentle miniature robots without conventional link mechanism. Two kinds of multi-fingered robot-hand are developed. One is four FMA-fingers arranged symmetrically. and the other is five FMAfingers with a palm like a human hand. Four-fingered hand can tighten a bolt skillfully. Five-fingered hand can hold soil and fragile timings such as fruit or glasses.

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For the maximum supply pressure of 62 MPa (the maximum load of 15 kN) and the maximum speed of rotation of 25 S^-1, the characteristics of circular hydrostatic thrust bearings for high pressure hydraulic pumps and motors in mixed to fluid film lubrication were studied experimentally. The diameter of the bearings tested was 20 mm and their surface was roughened in the region of 0.02 to 5μmRa. A fluid tested was an ISO VG 32 hydraulic fluid. The frictional torque and the leakage flow rate were measured. The power losses were increased as the supply pressure, speed of rotation and surface roughness became large. The minimum power loss was obtained by a ratio of the load to the maximum hydrostatic load-carrying capacity being close to unity. Introducing a representative power loss, one could normalize the power losses in the supply pressure ranging from 0.98 to 62 MPa and the speed of rotation ranging from 1.7 to 25 S^-1.

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In the present study, flow visualization is conducted in hydraulic holding valves in order to reduce cavitation noise. The hydraulic holding valves of poppet type are used to prevent sudden fall of load in unexpected case in oil hydraulic systems. New type of hydraulic holding valve are developed to reduce the noise and cavitation. Tests are conducted in half cut models of the valve for measurement of noise and for flow visualization in case of converging flow. Test facilities are designed to control flow rate, upstream pressure, downstream pressure, and valve lift.

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The paper is concerned with the development of an analytical model for the transmission characteristics of fluidborne pressure ripples in hydraulic flexible hoses with finite length under anchored end conditions, as an extension to the previous researches for the hoses with relatively long length [1, 2]. The model is obtained in transfer matrix form relating the pressure and flow ripples at hose upstream and downstream, by considering the effect of possible longitudinal resonance of the hose in addition to the anisotropic viscoelasticity of the hose wall and the coupled vibration of the hose and the fluid. It is applied to predict the transfer matrix parameters of the hoses with different lengths. By the comparison of the predicted and measured results, it is shown that the model yields fairly good results in a frequency range up to around 3kHz and even may accurately predict what existing models failed to predict, i.e., the influence of longitudinal resonance of the hose wall on the wave propagation of fluid in the hose.

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A new technique for an active-adaptive attenuator for wide-band random pressure pulsation in liquid piping systems, which controls feed-forwardly the secondary source by the progressive wave component of fluid-borne vibration detected at the upstream of the pipeline and the capability to change system parameters owing to a programmable digital filter, is presented together with computer simulation and experimental results. The adaptive feed-forward control structure is based on the so-called “Filtered-X LMS algorithm”. It is established by the test on the small-sized experimental pipeline that the pressure pulsation in a down stream pipe of the secondary source can be reduced by at least 20 dB for almost all harmonics of around 10 to 800 Hz, while maintaining the stability, even in the case where uncontrolled system parameters such as acoustic properties, dynamic characteristics of secondary source, etc., change with time. It is also shown that the computer simulation agrees well quantitatively with the experimental results and thus can be applied successfully to system design.

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In fluid power systems, cavitation under unsteady flow conditions plays an important role regarding their dynamic characteristics. To clarify the feature of unsteady cavitation, cavitation of long orifices in unsteady flows was studied. Sinusoidal and stepwise flows were obtained from a variable displacement piston pump. Cavitation was detected mainly in the pressure ripples obtained by a pressure sensor located at the outlet of the orifice. Also, a video-camera was used to observe the cavitation clouds. The test results, related to inception and desinence of cavitation choking, were mainly shown as the relationship between cavitation number and the amplitude and frequency (0.0 1.0 Hz) in case of the sinusoidal flow-, and the step height of the stepwise flow.
Also, by the finite volume method, the two- and three-dimensional distributions of pressure and velocity in the long orifice were obtained. The low pressure region which occurred just behind the inlet corner of the orifice was verified. The theoretical results can explain the experimental ones.

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A new ultrasonic cavitation detecting method has been developed to study behabior of cavitation in the oil hydraulic equipments. As cavitation is very harmfull to the performance and reliability of the oil hydraulic equipments, it is very useful to have a real time cavitation detecting method. In this study, a single piston eccentric cam driven test pump with a spool valve was used. This test rig simulates the main feature of an axial piston pump and is convenient to investigate cavitation phenonina because of its sipmlicity and the transparent windows on the pumping chamber. In this rig, ultrasonics waves caused by the cavitation were detected with a piezoelectric sensor. Correlations between measured pressure flactuations in the pumping chamber, suction pipe and delivery pipe, a visually observed result and ultrasonic waves were well explained. Finally the sensor was installed on the surface of an actual axial piston pump to detect cavitation successfully.

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In hydraulic system, because of the compressibility of the bubbles contained in oil, the working efficiency and the accuracy of position control will decrease. Moreover, the equipment will be damaged when bubbles collapse This subject topic of this paper is to investigate the mechanism of bubbles formation in Air/Hydro system on the basis of fluid transients theory. We found the negative pressure occured in the system, it leaded to the bubbles formation.According to these reasons, we gives some methods to deal with the problem. Besides the computation model is presented through system simplifying, the essential equations and the boundary conditions are established, and some results were gotten. At the same time, the experimental table was built for duplicating the bubble formed phenomenon, and the pressure of several specific points are obtained under different conditions We found the results of calculation are coincided with the these of experiment. it proves the computation model and boundary conditions are reasonable.At the end of this paper some conclusions are gived.

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This paper reports on the use of a commercial CFD package to model the flow fields and bubble trajectories in the cylinder of a reciprocating plunger pump during the suction stroke. The predicted behaviour of bubbles is compared with results obtained from a previously-reported flow visualisation study of a mock pump. The good qualitative agreement provides the basis for using the CFD model to examine the effect of changes to the pump valve and cylinder geometries.

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This paper describes a computer software package developed to assist the designer of fluid power systems. A variety of component models are selected from the icon library and system circuit can be sketched on the graphic monitor. The input data for component can be provided from the theoretical and experimental analysis, and from manufacture's catalog. For each component the modularized modeling and programming techniques are presented, and for each system the node table is automatically generated to check the continuity and compatibility conditions. A vector icon editor is developed under Motif and imbedded to facilitate the addition of new components. Being the X-window system based on Unix, this software has merits in portability, extensibility, and multi-user environment. The simulation results are confirmed to be consistent with those of other software and experiments.

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The synthesis of systems to provide a required load motion is a demanding task. This paper presents a systems design approach to solving this problem. The design process has two distinct phases:(i) synthesis of a mechanism capable of performing the desired motion;(ii) synthesis of a hydraulic drive for the mechanism, compatible with the required motion.
Kinematic synthesis is performed by using the software package CAMFORD which can compare the motions of alterna tive mechanisms capable of performing a specified task. Required force- or torque-time relationships to drive the mechanism is also determined. A fluid power circuit capable of providing the required torque and motion characteristics is then designed using the BATHfp simulation package.
Design of a high-speed cutting machine illustrates integrated use of the two packages. The transient and steady-state response of the resulting system are presented. The advantages of using the systems approach in machine design are outlined.

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This paper describes a simulation technique for resonator hoses which are used in the hydraulic systems of automobiles. In order to calculate the characteristics of resonator hose in a circuit, a distributed parameter model considering the effect of the leakage through the wall of the inner tube has been developed. In calculation, the method of characteristics was employed to take into account the non-linearity of the leakage. The validity of the model was confirmed by experimental results. Furthermore, the flow characteristics of the inner tube of the resonator hoses were tested to obtain better simulated results. Using this simulation model, the effect of parameters such as leakage coefficient, length of the inner tube, and pressure loss in the inner tube were investigated.

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The aerodynamic electrohydraulic servo load simulator is a type of passive force system. The active motion of the fin drive system causes a big displacement disturbance to the load system. So that an additional flow companied with disturbance force is produced in the load system. In this paper, we discuss the disturbance force of the system starting, and normal and abnormal component of disturbance force.

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In locking up torque converter, there exists shift shock according to lockup pressure and this shift shock degrades shift quality. To enhance the lockup shift quailty, the closed-loop lockup controller is necessary. Th high-order modeling of hydraulic lockup system is constructed including hydraulic circuit and power transmission system. The lockup closed-loop controller tracking the desired engine and turbine speed difference trajectory is designed. In this lockup controller, Time Delay Control and optimization technique on setting control parameters are used.

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This paper proposes a pressure regulation system for a pump by use of a vortex amplifier (VA) whose supply nozzle is angled to reverse direction of main vortex. VA is inserted just before the suction port of the pump, and its load pressure is feedbacked to the control port of VA. It is shown by simulation and experiment that a fairly wide region of constant pressure can be obtained against change of the load flow. The characteristic is further improved by installing a “core bar” in the low pressure bubble region on the center axis of the vortex chamber.

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In order to reduce fuel consumption and exhaust gases from road vehicles in city traffic, it has been considered technically reasonable to recover vehicle kinetic energy that might otherwise be lost as heat during braking. A energy recovery system using a rotating flywheel seems to be advantageous for vehicle applications due to its high energy density. The authors propose a Constant Pressure System (CPS) which is a simple hydraulic drive system for enginefl ywheel hybrid vehicles. CPS can easily realize power transmission and vehicle traction control. In this study, analytical modeling and simulations for the flywheel hybrid vehicle using CPS are presented to evaluate its fuel saving potential. Simulations were performed based on the experimental efficiency data of a FFC (Fluid Force Couple) type pump/motor. Simulation results indicate that it is possible to improve fuel economy in urban driving schedules.

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There has been a dramatic increase in the use of unmanned vehicles in worldwide marine fields. In marine engineering the high power density of hydraulics is without doubt the main advantage. Underwater operation makes special demands on components and systems. With an increasing surrounding pressure, the fits and tolerances in hydraulic components change and alters the performance characteristics. Hence it is necessary to carryout laboratory investigations to develop basic components of a hydrostatic transmission system which would ultimately propel and steer underwater vehicles.
Performance characteristics of a commercial hydraulic motor are tested under hydrostatic pressures upto 50 bar. A test set-up has been designed to subject the hydraulic motor to variable surrounding pressures upto 50 bar. The test rig and instrumentation are described. Dynamic tests are performed on the hydraulic motor, and the test results of the investigations are discussed.

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The semi-empirical method is employed in modelling a commercially used counter balance valve for hydraulic crane circuit simulation applications. By means of the method the analytical model of the valve is brought into a form in which the number of the parameters whose values can be determined from the measured characteristic curves is small. The particular problems apparent when modelling the counter balance valves such as description of high seal friction and complicated flow force characteristic are solved by using pure empirical functions.

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This paper deals with the stability of a relief valve of balanced piston type. Governing equations of 9th order and its linearized form, x = Ax, are derived and the cracking characteristics and the stability are numerically investigated. The theoretical cracking characteristics of the relief valve is indicated to be in good agreement with experimental results. The characteristic equation, (sI-A) = 0, is solved numerically and the stability of the system including supply line dynamics is examined by the signs of the real parts of characteristic roots. It is pointed out that the pilot valve stability governs in the system stability.

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The requirements to improve hydraulic components for higher performances are increasingly growing. and predictions of flow fields inside components are necessary for the improvement. Among hydraulic components, poppet valves are principal ones as hydraulic control valves. The present study focuses on the flow in a poppet valve and analyzes it numerically using streamline coordinates method. In order to confirm the validity of the numerical results. the pressures acting on the valve-body surface are compared with experimental results. The analyses are conducted for laminar flow and potential flow. The comparison between the two cases suggests that the internal flow in practice. which is usually turbulent flow, can be predicted to a certain extent by these analyses.

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The analysis and the evaluation of the steady-state flow forces acting on the spool of hydraulic valves is a keyaspect in performance assessment of many working conditions. These flow forces are generated by the different pressures on the spool faces caused by the high gradients of velocity near the metering orifice edge. In some working conditions these forces can cause significant instabilities in valve operation and a better insight is needed, with respect to classical approximations, in order to acquire informations on its causes and to guide design changes.
An experimental and numerical analysis has been carried out in order to analyse the overall force needed to operate a valve spool in different working conditions in a controlled environment.
From the experimental side, test results were used in order to identify critical operating conditions, and C.F.D. fl ow analysis (computational fluid dynamics based on the finite element method) was checked against the measured value of the operating force in order to tune a numerical model for a parametric investigation of valve flow characteristic. The paper focuses on the numerical aspect of the study, highlighting possibilities offered by C.F.D. in hydraulics, its expected degree of approximation, and problems in comparing numerical results with experimental evidence. Some detail considerations are reserved to a sensitivity analysis on aspects usually unknown in setting up a numerical C.F.D. analysis, such as turbulence model parameters and effect of geometric simplification.

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Karman Vortex velocimeter which is applicable to liquid and gas was developed in this study. In this case, the Karman vortex generator of a very small diameter (φ0.1-0.7) is set perpendicular to the flow and a parallel laser beam (φ1) from laser diode passes through downstream of the generator. This beam is refracted by the density change resulted from the Karman vortex. The refracted light is detected by the photo-diode and the frequency is measured with FFT. The generator is heated to strengthen the magnitude of the signal. Three generators of three different diameter (φ0.3, 0.5, 0.7) are used to measure the velocities of three different points simultaneously and nine generators of same diameter (φ0.1) are used to switch the measuring point instantly by switching the electrical charge to the generators.

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This paper treats stick-slip vibrations occurring in a typical computer controlled hydraulic servo system. The relevant system consists of hydraulic cylinder, servo-valve and personal computer. First, experiment was performed to reveal three different types of vibrations occurring in a conventional feedback control system. Detailed numerical analysis has been then performed to identify the main factors for occurrence of these self-excited vibrations. It is shown that the control signal generated through the D/A converter causes stick-slip vibration of small amplitude over the wide range of the control feedback gain. Increasing the feedback gain results in the other type of stick-slip vibration of larger amplitude due to the locally increased flow gain within the underlap of the servo-valve.

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In this paper, a FUZZY + PI control strategy for electro- hydraulic servo fatigue testing machine based on micro computer is introduced. The robust nature of fuzzy control gives the control systema good anti-disturbance ability, and the adding of MD control to the system improves the system's static accuracy and the elimination of wave distortion. Good static and dynamic performances are gotten in step response, robust performance and waveform following experiment of this FUZZY+PI control system. Experimental resultsprove that the introduced control strategy is quite successful in electro-hydraulic servo fatigue testing machine, and it can also be used in other electro-hydraulic servo system.

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A condition monitoring technique based on vibration measurements and evaluation by means of neural networks has previously been investigated. Preliminary results were promising. In this work, the reliability and the sensitivity of the method are discussed. This study has used a simulation approach to study the sensitivity. An experimentally verified simulation model which yields the internal forces in the pump has been used in combination with experimentally found transfer functions to find the vibration on the surface of the pump housing. Different designs of the valve plate have been studied to simulate an increased internal leakage in the pump. For the evaluation of simulation or measurement results, neural networks are used.

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So far, Numerical prediction of flow has been. developed mainly by Neumann type computer Nv hich is serial processing. The aim of this study is to carry out, . from two sides of soft ware and hardware. this computation by neural-network which is the parallel processing and to reduce the operation time. For the first step, neura.1-network simulator was used to confirm the possibility. Seconsly. the electrical circuit, which calculate finite difference equation of. flow was developed and parallel computat, ion by using the circuits each of which was configured in grids was carried out, . The comparison among the finite difference method, the neural-no, work simulator and the electrical circuit was done and good coincidence was obtained.

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A monitoring camera, which is set on the top of a mobil crane boom br the purposeofkeeping the operation safe and easy, plays an important role as an another eye br a crane operator. Recentlya total length of a mobil crane has been increased much more and a crane boom has been lightened. As the result, the stiffness of the crane boom becomes low. These low stiffness and lengthening cause the amplification of a small oscillation which is negligible for a conventional one. The new device for damping the oscillation is needed.
In the present study we developed a new oil-damper to stabilize the oscillation and investigated its characteristics in the simulation as well as in the experiment. Simulation is based on Bond graphs method. Simulation results agree well with the experiment.

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In this paper a K-type fluid filter is theoretically studied. the impedance matching theorem and this filter model of hydraulic system are put forward. A lot of experimental work is done for finding out the optimal value of filter parameters. For a well designed filter, 85% pressure fluctuation after filter and its 60% before filter can be filtrated.

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This paper shows the coupling motion characteristics of an electrohydraulic parallel link servomechanism with three degrees of freedom. A parallel link with multi degrees of freedom consists of multi cylinder servo systems, and an end effector. The motion of these servo systems has interaction with each other. Its analysis is not easy, because the dynamics of the system is Try complicated. To make it simple, spring-damper model is applied for the cylinder servo system. The characteristics of coupling motion is represented by frequency response of coupling amplitude ratio with the parameters of equivalent natural frequency ω_ei and damping ratio ζ_ei.

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The problem on suppressing forced and self-excited oscillations in control systems can be solved by inserting special correcting devices into pipe lines. A correct choice of a scheme, parameters and locations of the devices is determined by the type of the problem. The paper presents the design method using some generalised approaches which are suitable for solving both problem.

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CLSS (Closed-Center-type Load Sensing Systems) for fluid power controls in hydraulic excavators are capable of controlling complex motions of multiple actuators with high accuracy against varying loads under varying engine speed conditions, with expectations for improved controllability and compatibility of hydraulic excavators to many kinds of works in which attachments are used. Conversely, operators have made the best use of the characteristics of conventional fluid power systems, in which each actuator speed is varied by inertia or engine speed change.
Accordingly in 1993, a range of new hydraulic excavators were introduced, equipped with newly developed CLSS's, which are suitable for either traditional excavator use or new electrical operation, including automatic electronic control by microcomputer.

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