In the paper, a controller is designed with the fuzzy control and the special effective velocity compensation signal at the low speed range of the cylinder to overcome the stick-slip effect and obtain the high accuracy. The periodic chargeable compensation signal is designed according to the relationship between the friction force and the velocity, the fl ow rate of the valve, and the dead-zone of the servo valve; and, it's directly added to the conventional fuzzy control signal. The experimental results have shown the effect of the compensation signal, and that the accuracy of the control performance can be obtained and reached to the limit of the resolution of the pulse scale.

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Consideration is given to data-based dynamic modelling and positioning of a pneumatic servo-actuator with time delay due to friction and air compressibility. A Smith predictor-type control scheme is considered to improve the control behaviour. System non-linearity is verified by the inability of linear modelling to provide satisfactory prediction. Data based dynamic modelling is undertaken using the group method of data handling (GMDH) neural network, a feedforward type neural network, and the techniques show potential for prediction of non-linear behaviour. Hence the time delay effect to the closed-loop control can be removed by incorporating the trained nonlinear model as a predictor in the feedback path. Conventional feedback control with/without the predictor are compared, and it is shown that the time delay system stability is significantly improved by using the non-linear predictor. The effect of time delay is most significant at small stroke changes of fast response demand and experiments were undertaken around the mid-stroke, which is less damped than any other position.

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Pneumatic actuators are widely used as low cost actuators, but there is difficulty in the precise positioning of the actuators in general. The one main reason for this is that the characteristics of the actuators vary according to the positions due to the compressibility of air. Many papers on the trials to eliminate the effects of the variation of the characteristics have been published but the effective method to maintain the robustness of the position control is not found by now. We think that LTI (Linear Time Invariant) controllers are not adequate for the plants whose parameters change widely. In this report, we have adopted the scheduled controller to eliminate the effect of the variation of cylinder parameters, and designed the controller by making use of LMI (Linear Matrix Inequality). The experimental results show the effectiveness of the control systems.

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The difficulty caused by the non-linearity of a pneumatic servo system is overcome by linearization of input-output via Direct Feedback Linearization (DFL), and a state feedback controller is then designed using the linear system theory. Good dynamics and high disturbance force rejection level are achieved by putting the non-dominant poles near the imaginary axis and far away from origin, and high disturbance force rejection enables the system to have high precision and high stiffness. Nonlinear uncertainty of pseudo linear system resulting from the changing running conditions and the inaccuracy of the model are established together with its linear bound. The analysis completed by applying Zero Exclusion Principle (ZEP) showed the controller is robust. Experimental results proved that the nonlinear state feedback controller is robust; it has an accuracy of±0.02mm and a repeated accuracy (3σ) of ±0.05mm; the smallest step command the system can follow is 0.2mm; and it has a fairly high stiffness, too.

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Pneumatic vibration isolator is achieved through either passive or active control system, which offers the simple and reliable means to reduce the vibration of a platform system due to a vibration environment. In this paper, a pneumatic passive vibration isolation system is designed and fabricated. The maximum amplitude in Bode plot of the pneumatic passive vibration isolation system is about 6Hz and the value of the transmissibility is 4. Using adaptive control, the improvement of the peak frequency is not effective but the transmissibility can be reduced to be the value 2. The ER fl uid exhibits dramatic and reversible phase change in the presence of the electric field. After applying the ER fluid, the characteristics of the system proposed in the paper are improved and investigated via computer simulation.

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To understand the characteristics of the noise generated by impinging jet from a small-scale nozzle, the far field sound pressure level was studied. It was found that there was a critical pressure ratio according to different condition. Under this pressure ratio the noise intensity raised rapidly but wavily, and over this pressure ratio the noise intensity raised enhanced slowly but steadily with the increase of the pressure ratio. The critical pressure ratios will decrease when impinging gets oblique.

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Vacuum is frequently utilized for handling systems in factory automation. Because of the negative pressure, the state change of air is different from that of positive pressure systems during charge or discharge. However, pressure and temperature responses in the vacuum condition have not been examined up to now. Therefore, in this study the pressure and temperature responses of RC circuit in the vacuum condition is investigated.
As a result, the research can be summarized as follows:
1) When the positive and negative pressure are compared in the same pressure ratio, it is found that the heat transfer rate is larger in the positive pressure case, because of the larger mixing effect.
2) The temperature responses are determined by the thermal-time constants. Since the negative pressure gets smaller thermal-time constants which concerned the air density, the temperature responses show a smaller variation than those of positive pressure. Therefore, the pressure response is slower in the case of negative pressure.

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In this study a few modelling methods of air mass flow rates are compared. The calculation of masses is necessary, because air is a compressible fluid. The density of air, which has an effect on the mass, varies depending on variations in pressure and temperature. The behaviour of the temperature of air is also contemplated in the models. The methods are examined by comparing simulated responses with those measured from a real pneumatic system consisting of valve and actuator. The aim is not to find an exact mathematical model for mass flow through a pneumatic valve but to study how each modelling method affects the complete behaviour of circuit. A measured data from a pneumatic position servo is used as a reference for simulated results. The developed simulation models are implemented in mechanism dynamics analysis software ADAMS. A pneumatic component model generator is created into ADAMS by using macros. The pneumatic circuit models can be created by choosing required component models and defining technical information. The reason for building pneumatic circuit models in ADAMS is that the actuators can easily be connected with mechanisms and thus features such as the structural flexibility can be included in the simulation models.

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Electroencephalograms EEG and topographies of experimental subjects heard neumaticnoise have been measured. Auditory evoked potential AEP and event-related potential ERP occur one after another. Alpha waves disappear and beta waves appear as the result of analysis of frequency map. Loudness of pneumatic noise is estimated by Steavns power law used brain potential of beta wave in ERP.
In addition, physiological responses, namely, heart rate, respiration, and sweating have been measured. Influence on them through the autonomic nervous system is demonstrated. Explanation based on function of the brain is given. Subjects fall into two categories, using a personality test. Even subjects who are hard to feel the stress are influenced by the pneumatic noise. These results indicate that the pneumatic noiseis stressor.

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Pneumatic servo systems are used widely in industrial field. However, the dynamic characteristics often change with load mass and there are non-linear elements caused by air compressibility, various frictions and so on. Therefore, it is difficult for conventional linear control methods to accomplish satisfactory control performance. In addition, there is a problem that discrete-time models of pneumatic servo system have possibilities to become non-minimum phase by difference of the sampling period, change in load mass, and so on.
In this paper, for these problems, we propose a design scheme which combines a Model Reference Adaptive Control (MRAC) using delta-operator and a Neural Network (NN). In this design, even if the discrete-time model is non-minimum phase, it can be constructed by regarding approximate model of the plant expressed by delta-operator as minimum-phase model, and NN compensates for modeling error and the non-linearity of pneumatic servo systems.

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Servo pneumatic positioning control systems have the advantages of high response, easy maintenances and cleanliness, but the positioning accuracy is restricted by systems' non-linearity, such as friction force. In this study, a high precision pneumatic-piezoelectrical hybrid positioning control system is developed. Such a system contains a servo-pneumatic cylinder and a piezoelectric actuator. The servo pneumatic cylinder serves to coarse positioning with high speed and large stroke, and the piezoelectric actuator positions in fine stroke to compensate the influence of non-linearity to achieve large stroke, high response and high positioning accuracy. The overall control system becomes a complex dual-input single-output (DISO) control system. The test results show that the positioning accuracy for the large stroke of 180 mm can achieve 1μm.

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his paper presents a pneumatic servo system for trajectory tracking. To reduce the effects of friction force, seals are removed from the pneumatic actuator, and the slider of the actuator is mounted with externally pressurised air bearings. Previous studies of this pneumatic actuator show an accuracy of ±2 [μm] for step responses and low constant velocities control tests. In this paper, the pneumatic servo system is tested in the more demanding task of trajectory tracking. Considering the characteristics of the pneumatic servo system, it is clarified that the trajectory with constant jerk is better than trajectory with constant acceleration. An example for a displacement of 180 [mm] that is realised in 0.4 [s] is shown. Despite the slider reaches a high velocity of 0.8 [m/s], an accuracy of±50 [μm] is attained.

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Pneumostatic bearings are generally used in continuous positioning systems, machine tool slides and measuring robots. The stiffness of these air bearings can be increased by using control systems that control gap height as a function of applied load. In this paper the design and construction of a pneumatic proportional control system which controls the relative displacement by a back pressure displacement transducer and bearing supply pressure regulating valves is presented.
For this system both the steady state and transient behaviour of the bearing in different load condition were investigated theoretically and experimentally.

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Internal model control (IMC) has a number of advantages for enhancing control performance. IMC can minimize disturbance greatly. IMC is attractive for industrial users because it has only one tuning paramete. In this paper, we propose an intelligent control method in which IMC control is combined with neural networks (NN). NN is used to get the suitable control parameter when the plant contains non-linear elements. We apply the proposed intelligent control method for a pneumatic servo system which usually contains non-linearity. The effectiveness of the proposed design method is confirmed by experiments using the existent pneumatic servo system.

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In this paper, a new proportional solenoid developed for a miniature 4/3-way directional control valve will be introduced. The new proportional solenoid has two-dimensional structure and a pivoting armature. The most advantageous feature of this solenoid is that its mechanical parts can be easily manufactured and assembled. The working principle and design example of the new proportional solenoid, its application to the activation of a 4/3-way directional valve and the evaluation of its control performance in position control loop will be reported.

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The use of digital modulating valves for the development of pneumatic servosystems is becoming a widely employed technique. The main requirement for the valves is low response time, and typically it involves the size to be relatively small. The paper deals about the possibility to use small, fast response valves coupled with larger, and slower, valves inorder to obtain fast response and wide bandwidth in large size servosystems. The faster valves provide the system with the capability to obtain high precision, while the larger valves allow high flows in order to increase the fastness of the system.

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Dry-cutting/grinding system utilizing compressed cold air is environment-friendly machining since it uses nocutting/grinding oil and the cutting chips are easy to recycle. In this system, the control valve dealing with the cold air of -10--30°C has to satisfy both the insulation from heat sources around and the linkage with an externalvalve-actuator. The former is avoidance from heat transfer and the latter is connection with heat conductor. For there quirement of two contrary functions, we have developed an electro-pneumatic valve that equips both the vacuuminsulation layer inside and the latch-mechanism using the magnetic force of a permanent magnet. The thermal transmittance of the developed valve, which is the index of the heat conduction into the cold air, indicates about onethirtieth of the conventional value.

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The continuous trend within the factory automation and process control to use intelligent peripheral field devices increasingly leads to an extended function range of proportional pneumatic valves and drives. Typical requests in his area are:
-interfacing to a digital communication system
-line-up support
-diagnostic and service functions
-error messages/alarm
-compatibility/exchangeability
In the area of process control there is a demand to lower the installation costs and to transfer the energy and the control signal via the same wire. For this reason the presented valve is characterised by a reduced electrical power consumption. The pilot control stage operates according to the spool valve principle and reduces the pneumatic power consumption substantially, too. The maximum electrical power consumption of the entire valve including the connection of the field bus and the electrical amplifier stage amounts to less than 1W.

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A poppet type brake pressure control valve, which the output pressure is proportional to the input displacement, is developed to use in the hydraulic control system for friction brake of railway rolling stock. Internal feedback structure isdesigned to eliminate the reliability problem of the pressure transducer, and the poppet type valve is utilized to reducethe internal leakage, which is a problem of the conventional control valve when the electrical supply is under failure.Compensation methods for the disadvantages of poppet valve and the stability are considered together with the structure of the valve. Static and linearized dynamic models of the valve are determined to study the effects and to decide the parameters of valve. The stability and performance of valve are studied and confirmed experimen tally. The experimental results show that the response of out put pressure is improved compared with the conventional pneumaticbrake system.

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This paper proposes a new construction of the relief valve with pilot G-π bridge hydraulic resistances network. The valve's static characteristics are studied theoretically. The formulas for designing the relief valve with zero static pressure override are obtained. The static performances of the relief valve are experimentally investigated. The theoretical and experimental results show that the relief valve developed in this paper is un-sensitive to flow rate, i.e.when the overflow increases the control pressure is kept constant.

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Flow control valves play an important role in the control of fluid power systems. Literature presents a great deal of works concerning hydraulic valves, nevertheless it seems to be lacking in studies on this typology of valve.
In this work a simple mathematical model has been used in order to obtain steady state characteristics of a generic two way flow control valve connected to a constant pressure supply circuit and a resistance type hydraulic load. The model has been later applied to the real geometry of a commercial valve.
Dynamic behaviour analysis has been carried out by the use of a simulation tool. Simulating the dynamics of the valve, subjected to various load conditions, may suggest how to analyse the sensitivity of the valve to variations of the valve parameters, since a quick response essentially depends on the presence of damping orifices inside the valve.

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The 2D pressure control valve is a piloted pressure control valve designed with two motions of a single spool. The rotary motion combining a hydraulic bridge forms the pilot stage of the valve to control the pressure of a spool chamber, while another spool chamber is directly connected to the load pressure. The hydraulic bridge (pilot stage) is developed with the concept of pressure linear distribution along a damping pipe under small Reynolds Number and has a significant effect on both static and dynamic characteristics of the valve. The rotary motion of the spool is actuated by a digital electrical-to-mechanical interface. The interface mainly composed of a stepper motor connected to the valve as an actuator though a proper coupling and a digital valve controller which is basically a one-chip computer system. The core part of the controller for the stepper motor is an algorithm which will keep stepper motor under continuous control. In this way the quantitative accuracy and the response of the valve are simultaneously sustained. In this paper the structural parameter affecting the characteristics are analyzed and discussed. And the dynamic properties of the valve under the actuation of the stepper motor are tested.

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The dynamic characteristics of a proportional solenoid control single stage pressure relief valve is studied theoretically through modeling and simulation, supported by existing experimental result. Based on an existing model for the estimation of pressure loss coefficients the overall steady state pressure flow characteristics of the valve are determined. A detailed dynamic model has been developed and studied within the MATLAB-SIMULINK environment. The nonlinearities have been considered via the use of appropriate SIMULINK blocks. Detail valve geometry is considered in order to model the valve accurately. The solenoid is modelled as a nonlinear resistor/inductor combination. The spool valve assembly is modelled as a spring/mass/damper system with the consideration of inertia and damping effects. The inductance parameters are described as a function of displacement and current. The detailed modelling has resulted in a good comparison between simulation and measurement. The overall dynamic behaviour has been shown to be dominated by the solenoid characteristic relating force to applied voltage.

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In mobile hydraulic applications, such as the bucket functions of a wheel loader, there are often repetitive tasks which would benefit from some level of automation. Machine efficiency, working accuracy and reduced operator fatigue are possible benefits. From an economic stand point, the automation must be realized with inexpensive and reliable components, which means minimizing the complexity and number of physical components. For these reasons, it was of interest to introduce some level of automation to the bucket functions of a wheeled loader using proportional valves. In this paper the problems of achieving flow control in a load sensing system employed on the wheel loader using proportional valves are addressed. In particular, development of a flow control strategy involving mapping of the valve pressure/flow characteristics is investigated.

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Servovalve torque-motors are controlled changing magnetic flux through air gaps at the armature ends. The traditional theory gives the torque on the armature assuming uniform distribution of the flux over the air gaps. However, experimental facts contradict with the assumption because the flux density becomes uneven by the fringing at the gaps. To express the torque with acceptable accuracy, two coefficients are necessary. The first is the ratio of the mean flux density and the flux density at the center of the gap. The second is the ratio of mean of squared flux density and the square of the flux density at the center of the gap. This paper explains the necessity of these coefficients and presents the procedure to find them. The obtained result forms a part of design criteria for servovalve torque-motors.

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Diesel engine performance can be improved and emissions reduced by improving the power density and combustion cycle efficiency. It can be done by increasing combustion pressure and engine speed which also necessitates improving the controllability of the engine. One of the key elements in improving overall controllability of the engine is the valvetrain. During recent years various camless valvetrain designs for automotive size engines have been introduced, but in bigger engines camless valve actuation is only applied to low speed two stroke marine diesels. Feasible way to realize camless valve actuation in modern and future medium speed diesels is electrohydraulic valvetrain. It, how ever, has numerous shortcomings and difficulties to overcome.
An electrohydraulic valvetrain for experimental engine, having performance characteristics twice the level of current medium speed engines, has been developed. Valvetrain offers significant benefits in comparison to traditional cam actuated valvetrain. Valvetrain is able to operate up to engine speed of 1600 rpm and combustion pressure of 400 bar at speed level twice the tradional cam actuation. Hydraulic peak power of the valvetrain is approx 100 kW and shortest controlled actuation time is approx 6 ms for 18 mm stroke. Main challenges in valvetrain design are are keeping the continuous power consumption at reasonable level, controlling the valve speed, precission of valve timing and dynamics of the system in whole as well as individual components.
The paper will introduce the system and component design of the prototype system. System and component performance is discussed on basis of Amesim simulation models. Control system design, realization and valvetrain prototype testing are also discussed.

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In this paper, the authors have shown that amplitudes of self-excited oscillations occurring in a poppet valve circuit are significantly affected by oil column separation. The numerical simulation has indicated that the magnitude of amplitude of self-excited oscillations is reduced into half in the large amplitude region by the effect of oil column separation.

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Starting from previous papers [1], where hydrostatic transmissions automotive controls functionalities were investigated, an embedded electronic control system was designed. It is based on a low cost electronic control unit, controlling a hydrostatic transmission with a variable displacement axial piston pump and an axial piston dual displacement motor. The pump displacement control strategy, which depends on diesel engine working point and delivery pressure, is based on a fully customisable engine performance map. Special control strategies superimposed on this strategy and depending on autorecognized working mode, that allowed excellent performance in the vehicle field test phase to be reached. Special diagnostic strategies were introduced, based on functional and congruence controls, relying on fault recovery systems, to maintain the system in a high safety condition and to modify automatically the system working mode in case of fault occurrence. This approach allows reductionof overall risks for the operator and the environment.

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The Composite Fuels Laboratory at the University of Oklahoma has designed and built two new fueling stations to produce and provide an alternative fuel, trademark Super-Gas^TM to be used for vehicle propulsion. Two fluid power systems have been designed and adapted to accomplish these requirements. Both the fluid power system and the automatic controller control the processes to produce Super-Gas^TM in a safety and reliable way. This paper will present the fluid power circuits and controller designs for the particular fueling stations. This design system has the capability to either produce the fuel on board the vehicle (BOB) or transfer it to the vehicle tank as a common fueling station. Super-Gas^TM is a liquid fuel mixture composed of a light hydrocarbon and compressed natural gas and it has somecharacteristics that make it behave as a hydraulic fluid.
Super-Gas^TM made using the bubbling on board type design (BOB) produces 10 Gallon of the mixture in approximately 8 minutes on board the vehicle. A diaphragm pump was used to transfer the light hydrocarbon (LPG). The fast fuel design (FFS) has shown to produce the same amount of fuel in a time range from 5 to 7 minutes, but at any vehicle tank pressure, without reduction in the volumetric efficiency as long the circuit controls the flashing issue. It uses a basic concept of a drive piston pump.
The paper will discuss technical hurdles that remain for improving the designs.

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The noise from hydraulic systems is highly correlated to the system pressure ripple, appearing as a response to introduced flow transients. One of the main origins for flow transients is the hydrostatic pump. In order to reduce the pump generated flow ripple magnitude and its frequency content, several design features have been developed. However, even though they may have very good influences on the flow ripple, their sensitivities to changes in operational conditions are considerable. This implies that a pump optimised for minimizing flow ripple at one specific operational condition, may give severe flow ripple as the conditions are changed. When choosing a design feature for a pump, it is important that the pump behaves satisfactory throughout the whole range of operational conditions. It is therefore necessary to be aware of the plausible conditions to which the pump will be exposed.
In this paper, the sensitivities for changes in the operational conditions are analysed for three different design features. The insensitivities to operational conditions toghether with over-all flow ripple reductions in relation to implementation cost for different design features is a fair figure of merit, enabling mutual comparisons to be made.

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The load simulator is required for the performance test of the vibro-hammering machine for construction work, which can realize the dynamic characteristics of the various types of the ground. The hydraulic servomechanism is applied to the load simulator to realize the equivalent dynamic characteristics of the ground. The magnitude and the phase angle of the mechanical impedance of the simulator on an operating vibration frequency are controlled to coincide with the reference impedance using the iterative control method, according to applied force and velocity of the vibro-hammering machine.
The performances of the load simulator are confirmed experimentally using an experimental apparatus. The accuracy of the impedance of the simulator and the number of iteration are discussed for the applied control algorithm.
The maximum operating frequency is realized at 50Hz which is applicable for super high frequency vibro-hammering work. The results show the possibility of practical use of this control method.

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The design of machines has considerably changed its face in the last decades. Most evident is the strong role electronics has gathered in many of the former purely mechanically working machines, plants, or devices. Today Mechatronics is the word used to describe technical systems operating mechanically with respect to at least some kernel functions with more or less electronics supporting fluid power, electrical or mechanical parts decisively.
In all fluid power applications a load has to be controlled by an actuator in respect of speeds and forces. A new dimension of the ways to look upon these control aspects is to use a control valve (proportional or servo valve), which is capable of controlling both flow and pressure. These types of components are available today and this has led to an enormous impact on system design and moved it into the mechatronic field. Closed loop servo drive technology is increasingly becoming the norm in machine automation, where the operators are demanding greater precision, faster operation and simpler adjustment. There is also an expectation that the price of increasing the level of automation should be contained within acceptable limits. Examples are material handling, mobile equipment, plastics, steel plants, mining, oil exploration and automotive testing.
The object of this paper is to give knowledge about design and function of mechatronic systems with fluid power actuation. The focus is set on system aspects where control and measurement techniques are central parts.

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The cataract is a disease in which crystalline lenses get opacified because of aging or others. In the treatment of heavy cataract, opacified lenses must be replaced with artificial lenses. The PEA isrecently a major technique for removing opacified lenses. There is, however, a problem called as surge phenomenon still to be solved in the PEA. The surge phenomenon is that an intracameral pressure accidentally falls down to an extreme and this would invite a possibility of blindness in worst case. Though there exist some passive countermeasures against it, but not enough to secure the safety of surgical operation. This paper describes of how to control an intracameral pressure by employing modem control theory. By our fabricated modeled eye we could simulate a surge phenomenon. Having designed a state-predictive LQ servo system, we succeeded to restrict the surge to an allowable level.

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Hydraulic cylinders are typical actuators in force control applications. The friction force is the most serious disturbance of a force control, when the piston does not move. When the piston is moving the volume flow and changes in the controlled volume are disturbances. In this study the force control is realized as the piston side pressure control of a hydraulic cylinder. Three different ways to control the pressure are compared. The 3-way valve is used in this study. The influence of the piston movement and spring force on the performance of the force control is studied experimentally. The theoretical background of force and pressure controls is presented. Experimental results are shown and different solution compared. Two different ways to modify the conventional PI controller are presented and tuned to fulfill the system requirements.

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In this study, we investigated a tele-robotics system for a construction machine.The system consists of a servocontrolled construction robot, two joysticks for controlling the robot from a remote place, and a 3-degrees-of-freedom motion base. The operator of the robot sits on the motion base and controls the robot bilaterally from a remote place. The role of the motion base is to realistically simulate the motion of the construction robot. As a tool for assisting the operator, a stereo video graphic of the operation field is projected on a screen.If, in addition to the video graphics, computer graphics (CG) of the robot were to be presented to the operator, the tasking efficiency could be expected to increase. To confirm this, a CG of a virtual robot was created, and its effectiveness for a task involving carrying an object was determined in this study. This system can present the position or shape of the task object by means of a stereo vision system. The results of the experiment clarified that tasking time was shortened effectively even for amateur operators. Thus, the usefulness of the developed CG system was confirmed.

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In teleoperation field robotic system such as hydraulically actuated robotic excavator, the maneuverability andconvenience is the most important in the operation of robotic excavator. Particularly the force information is importantin dealing with digging and leveling operation in the teleoperated excavator. This paper presents a new force reflectingjoystick in a velocity-force type bilateral teleoperation system. The master system is electrical joystick and the slavesystem is hydraulic cylinder. Particularly pneumatic motor is used newly in the master joystick for force reflection andthe information of the pressure of slave cylinder is measured and utilized as force feedback signal. This paper alsoproposes a novel force-reflection gain selecting algorithm based on artificial neural network. Finally a series ofexperiments are conducted under various load conditions using a laboratory-made one axis slave cylinder and loadsimulator.

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A wave power converter: Pendulor, works with 40% efficiency at an optimal condition. Irrespective of change the wave climate, anAutonomous Optimization Control (AOC) adjusts hydrostatic power transmission to keep the Pendulor in the best match with thewaves. This is a new system to know the wave climate from the Pendulor motion. AOC improves the system reliability and solvesload sharing problem in the HST lines.

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A hydraulic transformer may be looked upon as a type of secondary controlled machine. As other secondarycontrolled machines, hydraulic transformers require closed loop control. High efficiency, as a consequence ofenergy recovery possibilities and good controllability have motivated the use of secondary controlled machines, mainly motors. The hydraulic transformer adds some further attractive properties concerning control of linearloads, i.e. cylinders. However, there are still design issues that have to be improved.
In previous studies of the new Innas Hydraulic Transformer (IHT) concept, the low-speed operating andstart/stop sequences have been found to be the most critical operating conditions. Here losses of stick-slipnature are dominant due to the combination of varying driving torque and small inertia.
In the paper conceptual control strategies are presented. The design is simulated and evaluated concerningthe low-speed operation of the IHT. Basis for the study is a detailed simulation model describing the transformerat a high level of detail and with good agreement between simulations and measurements.

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EHL system does not need conventional hydraulic equipment. This is possible to save space and energy.EHL press machine is consisted of five components, such as master cylinder, slave cylinder, servomotor, ball screw, etc. Master cylinder and slave cylinder are coupled by fluid line. Master cylinder reciprocalmotion is made possible by suitable choice of area ratio of both cylinders. Slave cylinder is driven bymaster cylinder and the former force is amplified by the area ratio of the former and the latter. Accumulator is used for compensation of fluid expansion due to temperature change. Semi-closedcontrol of EHL press machine is simple but positioning accuracy is not sufficient due to compression offl uid. Therefore full closed control is required for good position accuracy. We tried application of thissystem to the clamping device of 10-ton load. By this combination, tact time becomes as small as 3second.

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This paper examines how to handle redundancy in mobile hydraulic cranes. Four different strategies are presented andsimulated on a model of a rigid crane coupled to a hydraulic system. By integrating the power of the pump (flow timesthe pressure), it can be determined how much energy the different strategies use. The strategies are, (i) minimum normsolution in joint space, (ii) minimum norm solution in actuator space, (iii) minimizing forces in the cylinders, and (iv) moving only two cylinders at once to reduce throttling losses in the system. Based on the experiments presented in thispaper, it is the opinion of the authors that strategy (iv) is the simplest to implement, is the most robust, and gives thebest energy results of the strategies tested.

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A new method of estimating wave speed in a pipe is proposed. A continuity equation of pipe flow can be arranged so that wave speed is included in a coefficient term which relates differentiation of pressure with respect to time and differentiation of flow rate with respect to distance along a pipe axis. The wave speed will be calculated from the differentiation signals using a pipeline dynamics model, which is an optimized finite element model. Bootstrap algorithms are applied to estimation of wave speed included in the coefficient. Both simulation and experiment are carried out to examine the estimation method. The influence of experimental conditions and calculation parameters on the wave-speed estimation was investigated.

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A new simulation technique called the “system modal approximation” method for fluid transients in compound fl uid-line systems composed of many line elements is developed and presented. This new method is based on numerical modal approximation of the frequency transfer function itself of the output to the input, considering the total system dynamics. This simulation technique also has the feature that the line elements with any kinds of the dynamic characteristics can be applicable because only the numerical data of the frequency response of transfer matrix parameters of individual line element is needed, and that the computation time is very short because the output in time domain can be calculated by the simple algebraic expression in the form of a recurrence formula. Simulation results of this method for the pressure transients in typical three kinds of compound fluid-line are compared with both the solutions from the method of characteristics and experimental results, and the superiority of this technique in easy applicability, flexibility, accuracy, computation time, etc. are demonstrated.

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There are some hydraulic actuators, which operates periodically. This led to a pulsating pressure in a hydraulic line. When a hydraulic actuator is placed at the tip of the crane, the hydraulic line consists of hoses because there are moving joints. The pulsating pressure decreases the reliability of the hydraulic hoses and fittings.
It is possible to reduce the pressure oscillation by help of different dampers e.g. an accumulator or a T-pipe. This paper studies the properties of the T-pipe when the operating frequency of the actuator was quite low. The result was that the T-pipe works well even at the frequency 33Hz.
The maximum working pressure of the hose is higher if the nominal size of the hose is smaller. When several small hoses are installed parallel those can be use even high oil flows. This way can be integrated the high working pressure and high oil flow. One benefit is that the hydraulic line, which is realised by several parallel installed small hoses, is more flexible than one big hose. These kinds of parallel hose systems were studied by calculating the maximum power level of different hose concepts with special interesting of price. Results show that two or several hose concept is cheapest at the power level over 100kW.

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Flexible hosepipes are often used in an oil-hydraulic system. In highly pressurized hydraulic systems, big changes of pressure and flow rate in the components cause oscillation and deformation of the flexible hosepipe itself. Those phenomena may cause destruction of the hosepipes if a natural frequency of a valve should coincide with that of a hosepipe system. Some studies have been performed on pressure propagation in the hosepipes, which were conducted by considering the dynamic characteristics of the internal fluid combined with the characteristics of the hosepipe wall. However, these models could not explain the mechanism of the oscillation and deformation. From a viewpoint of safety, the mathematical model must represent such mechanism. The objective of this study is to propose the mathematical model of the flexible hosepipes, which contains the characteristics of the internal fluid, a flexible hosepipe itself and their interactions. All the numerical results were compared with experimental results. The bondgraph method was used for modeling.

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Offshore, marine, aircraft and other complex engineering systems operate in harsh environmental and operational conditions and must meet stringent requirements of reliability, safety and maintainability. To reduce the high cost of development of new systems in these fields improved design management techniques and a vast array of computer aided techniques are applied during design and testing stages. Failure Modes and Effects Analysis (FMEA) is generally used in the above industries to reduce design risks. At present FMEA cannot be carried out automatically. Although various FMEA software tools exist, they basically provide data management for a manual analysis. It is generally recognised that failure analyses are usually carried out after the system has been designed, and often after it has been manufactured. If any fundamental design flaws or safety risks in the system are identified at this stage then modifications to the hardware are often costly. The software tool for automated FMEA is based on qualitative modelling of generalised information flow (energy, information or mass) in a system, recognising that the primary functions of mechanical, electrical, thermal and/or hydraulic systems (or their combination) as well as modem neuromechanic systems (also called mechatronic systems in the mechanical domain) are the generation, transmission and conversion of energy. The paper explains some underlying principles of software operation and provides a description of the software

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When hydraulically driven machine is constructed it is often hard to study the effects of alternative hydraulic components and systems on its behavior because it is time-consuming to install and replace the components in the real construction. An effective and timesaving method is presented. The method is based on a real-time hydraulics simulation model which is simulated while running the real machine construction. The main idea of this method is to get the real hydraulics, connected with the mechanism, to behave like the virtual hydraulics does. When managed, the variations can easily be made in the simulation model and their effects then be seen from the behavior of real construction. Also, properties of mechanics like flexibility, gaps and friction quite often difficult to model are automatically included.

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In the procedure of the hydraulic control system design, a linearized approximate equation described by the first order terms of Taylor's series has been widely used. Such a linearized equation is effective just near the operating point. However, pressure and flowrate in actual hydraulic systems are usually not confined near an operating point. This study suggests a new linearized equation for servovalve modelling as a modified form of the conventional linearized equation. And also, methods to determine effective operating points for the new linearized equation and the conventional linearized equation are proposed. From the evaluations of time responses and frequency responses obtained from simulations for a hydraulic control system, the effectiveness of the new linearized equation and the methods to determine effective operating points is confirmed.

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In the article the dynamic processes in an axial-reciprocating hydraulic motor and mechanical drive are considered. The mathematical model of an axial-reciprocating hydraulic motor is presented, where the flow of fluid in each cylinder of the motor and the interaction of liquid with the piston are taken into account. The flow of fluid in a hydraulic system is described by a system of equations of a hyperbolic type, which is solved by the characteristics method. For example, the mathematical simulation of the activity of an axial-reciprocating motor in a hydraulic system together with the mechanical drive is shown.

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Electrohydraulic servovalve play a major role in many feedback control systems. They find applications in CNC machine tools, aircraft, remote controlled mechanisms and all kinds of of high and mobile applications. The analyzed servovalve uses a nozzle and receiver holes to generate a differential pressure which is then used to move precision spool valve incorporating some type of feedback device. Hence, if the nozzle movement can be controlled in some way, preferably by a low power electrical signal, then the resulting device would seem to offer the ideal interface between low-power electronics and high power output hydraulics. The performance of the valve depends on many parameters. An attempt has been made to study the steady-state operation of a jet pipe flow control servovalve using nite Element Analysis (FEA) and theoretical method. Jet pipe servovalve have two main assemblies; the torque motor (first stage) and the valve assembly (second stage). Between the first and second stages, the feedback spring is connected to stabilize the servovalve operation. Solid modeling is a prerequisite for this analysis. Solid model of the servovalve was developed using SDRC IDEAS software. The finite element formulation of the desired component assemble consisting of the torque motor armature, armature bush, flexure tube, jet pipe, jet pipe nozzle, second stage feedback spring was subsequently carried out and simulated with appropriate boundary conditions. From the FEA it is possible to predict the jet pipe deflection, armature rotation as well as spool displacement for a given torque input at the armature.

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In order to improve the characteristics of a control valve, it is necessary to precisely predict the flow inside. Under these Circumstances a method using so called streamline coordinates has been developed. In this method, one of the coordinates is chosen along a streamline, and the other coordinate orthogonal with streamlines. A control valve has several restrictions, and the flows through them form flow jets with free discontinuous surfaces. The streamline-coordinate method can solve such a problem, since a free surface consists of streamlines. The important characteristics of a hydraulic control valve include the flow coefficient at its metering orifice and axial forces acting on the valve body. These characteristics can be numerically predicted using the streamline-coordinate method. Those characteristics of poppet and spool valves are analyzed by the streamline-coordinate method, and the usefulness of this method is shown.

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