Traditional valve controlled hydraulic drives have an inherent power loss, due to the throttling over the valves, which limits the maximum system efficiency. Pump controlled direct drives do not have this inherent limitation, but are limited when it comes to controlling asymmetric cylinders, why most solutions that have tried to overcome this problem have incorporated some kind of accumulator. In the present paper a new concept is presented, modelled and analyzed, and it is shown that the concept overcomes the problem with asymmetric cylinders, without the use of an accumulator. The paper first presents an analysis of the general concept, showing that both cavitation and excessive pressure build up needs to be handled by the system, after which the system is presented and modelled. Finally both simulation and experimental results are presented showing the validity of the concept.

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Temperature and behavior of a piston motor slipper were examined using a test rig. The experimental setup comprised a tester, a hydraulic circuit, control units, and measuring instruments. The tester included a servomotor and a chamber enclosing two piston assemblies with slippers, a rotating disk, displacement sensors, and thermocouples. The sliding surface diameter of the test slipper was 32 mm; the test oil was hydraulic oil with VG46. Tests were conducted at supply pressures up to 35 MPa, rotational speeds up to 26.7 s⁻¹, and oil temperature of 30–50°C. The pad temperature increased with the supply pressure and rotational speed. The pad established a temperature gradient, being maximized near the slightly-outer trailing edge and minimized near the leading edge. The temperature differences were influenced by the rotational speed, but were almost independent of the supply pressure.

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A theory of order reduction is applied to the optimized finite element model of pipeline dynamics. Depending on the number of elements of the model, the order of the model can become very large. A technique to reduce the order of the finite element model is investigated while the reduced-order model still holds accuracy. Balanced realization and state elimination based on Hankel singular value are applied as the order reduction theory. As a result of order reduction, the number of order has been much decreased. The reduced-order model shows a good agreement with experimental results. Real-time simulation is possible by the reduced-order finite element model.

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In hydraulic systems with pressure levels above 21 MPa, as being typical in mobile applications, piston units are the first choice. Especially axial piston pumps in swash plate design offer technical benefits and enable compact and efficient designs. Worth mentioning here as an example is the power take off (PTO) and the efficient controllability by use of variable displacements. Nevertheless, the tribological contacts in these robust and widely used components are highly stressed and determine the efficiency of the units. Due to the kinematics each piston is highly loaded by lateral forces and therefore the piston-bushing contact represents the area where the tribological knowledge is essential for wear-resistant and efficient design. Besides materials, macro and micro geometry, local loads and movement lead to friction losses. This paper describes the theoretical kinematics of the inclined piston and a sensor for measuring the rotation of the piston in the pressurised piston-bushing contact, which enables to fill the knowledge gap regarding the rotational movement of the piston under operational conditions.

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The study of displacement machines, and in particular external gear pumps has improved the understanding of the important features of operation. Applying these underlying phenomena to new design methodologies has brought new advances in quieter machines by designing for the reduction of fluid-borne noise, cavitation, and pressure peaks. The present work seeks to expand on the previous modeling and experimental efforts by directly considering the effect that design changes to the pump and to the system are predicted to apply on the sound emitted from displacement machines and the attached lines. In particular, the current document focuses on efforts related to the noise propagation from the pump into the hydraulic lines, and out of the lines to the environment by comparing the model to experimentally measured values for the fluid and air-borne noise.

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In this paper, a novel structure for bilateral control in master-slave system composed of flexible pneumatic robot arms is presented. From our previous study, it is needed to apply the brake mechanism on the master arm and it perhaps can be a bilateral control by taking into account the force factor in both master and slave arms. The compact and lightweight brake mechanism can avoid patients from injury by limiting and stopping the movement of master arm when it moves in the dangerous area or angle during the therapy. The control system consists of flexible pneumatic cylinders, potentiometers, quasi-servo valves, accelerometers and a microcomputer. The analytical model of the master-slave control is explained and the control performances using the brake system are investigated. The experimental results show that the attitude control can be achieved by using the proposed master arm with the pneumatic brake mechanism and proposed analytical model. Thus, this master-slave control with the brake mechanism has a potential for application in rehabilitation field.

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This paper describes the control of the rubberless artificial muscle antagonistic drive system. The rubberless artificial muscle is a pneumatic artificial muscle that uses no rubber tube. It can contract by low pressure, but it has nonlinear characteristics including hysteresis characteristics. For this study, we apply the rubberless artificial muscle to an antagonistic drive system. Then we control an antagonistic position and antagonistic force. A position feedback control system with linearization by a mechanical equilibrium model showing the static characteristic of the rubberless artificial muscle is applied. In addition, contraction force is controlled by another force feedback control system. From experimentally obtained result, it was confirmed that the antagonistic position is almost identical to the target position. Furthermore, antagonistic force is also controlled appropriately even if the antagonistic position is moving.

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The pressure method for leak test of vessels measures decrease of charged gas pressure assuming that it indicates the leak. Temperature control is important in this test. Whereas industrial standards define test duration of several days, production lines for vessels cannot accept such long test time; they can spend only several minutes for the testing. The flowrate of the leak of gas is determined by geometric parameters, pressure and gas properties. This paper shows that a geometric parameter derived from dimensions of leakage channels, which is named as leak coefficient, is known, any leak by given pressure and gas viscosity will be readily found. This paper shows methods to estimate the geometric parameter. Through experiments of leak test for a 147 L vessel, the temperature compensation was studied measuring temperature distributions in and the surface of the test vessel installing 17 thermocouples. The relationship between the measuring time and the ability of leak detection was also studied.

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An experimental study of the dynamic behaviors of a pneumatic cylinder is presented, and the relation between the friction characteristics and the vibration characteristics is discussed. In the experiments, a pneumatic cylinder is operated in upward or downward motion. The piston velocity was varied to investigate dynamic friction characteristics and their effect on the vibration characteristics. Step input signals or half-period sinusoidal input signals were supplied to flow control valves when measuring dynamic friction characteristics. When the frequency of the sinusoidal signal and the stepwise velocity are increased, the size of the hysteresis loop is increased. A stick-slip motion takes place more easily in upward motion. Finally, the effect of the dwell time on the dynamic friction characteristic is examined. The break-away force increases with the increase of the dwell time, but the dwell time for the break-away force to become the constant value (the maximum static friction force) considerably differs in the operation direction.

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