• 유공압시스템학회논문집
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• 제3권1호
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• pp.1-6
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• 2006

A servo actuator with a valve using MR (Magneto-Rheological) fluid is proposed for fluid control systems. The MR fluid is well known as a functional fluid whose apparent viscosity is controlled by the applied magnetic field strength. The pressure in the MR cylinder can be controlled by the applied magnetic field strength. Good points of the MR cylinder are more simple, compact and reliable structure than a conventional oil hydraulic cylinder. The experimental results show that the MR cylinder could be used as a servo actuator.

• 유공압시스템학회논문집
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• 제6권2호
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• pp.1-6
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• 2009

The APU(Auxiliary Power Unit) needs a set of complex pipeline for the fuel supply system where some of the main valves controlling the flow rate consist of the servo valve worked with a torque motor. The input electric current produces an induced magnetic field almost perpendicular to the background magnetic filed generated by fixed permanent magnets. The induced torque deforms the tubular bushing, and directly rotates an armature, which can open and close the valve. In this study, we start from a basic analytic model using a simple electro-magneto-statics, and expand our model to the three-dimensional one computationally applying a commercial code named COMSOL. The result is compared with each other, and reasonable numerical data are obtained for the dynamic behavior and multi-physics system.

• 드라이브 ㆍ 컨트롤
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• 제15권2호
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• pp.32-37
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• 2018

The power plants use turbine output control devices to supply or shut off steam to high pressure and low-pressure steam turbines connected to generators. This turbine output control device is driven by a hydraulic servo actuator. The gas flows into the hydraulic servo actuator during periodic inspection or normal operation, and the resulting adiabatic compression of the gas raises the internal temperature of the actuator to $500^{\circ}C$. This temperature increase causes the seals to burn and show wear and tear, resulting in failure. In this study, an air vent valve was installed to allow gas inside the hydraulic servo actuator to flow large quantities of air at the beginning of the operation and after the periodic inspection. Gas was passed through for only minute flow during normal operation of the power plant. By applying the air vent valve, it improves the reliability of the hydraulic servo actuator by discharge the gas appropriately to improve the life of the seal.

• 대한기계학회논문집A
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• 제20권8호
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• pp.2480-2490
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• 1996

This paper presents a new type of hydraulic servo chllinder which is characterized by its simple construction and an ubtegrated feedback mechanism. Piston position of the cylinder is controlled by eletrical input and mechamical feedback deduced from its own structure. Hydraulic pressure in each cylinder room is controlled by a poppet valve. The poppet is activated by a solenoid and is linked to the piston. Solenoid input current pulls up the poppet, which results in pressure drop and thus piston motion. The piston motion generates pull down force on the poppet by the linkage and the motion stops at equilibrium. In that way the piston position is controlled by an expernal input current. Characteristics of the servo cylinder is verified by stability analysis, tranient vehavior and steady state positing for step input. Design parameter analyses have been executed by derivation of analytical approximate solutions and by computer simulations. A prototype hydraulic servo cylinder is developed and tested. The experimental results show successful function of the servo cylinder and consistency with the theoritical results.

• 한국정밀공학회지
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• 제17권10호
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• pp.162-169
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• 2000

A Direct Drive Valve(DDV) hydraulic actuation system which is commonly used as an aircraft's control surface driving actuator has multi-loop control structure to ensure its safety operation. However, because of not perfect matching of one self channel characteristics with the others, the servo valve driving current of each channel can be widely different. Therefore, the long-time use of DDV actuator without any correction of these channel current offsets will cause the problem of performance or life expectancy degradation due to unwanted heats in the linear motor. A current equalization loop structure which can minimizes current offsets between channels is introduced and designed. The performance of the current equalization loop is investigated and verified through the analytic and experimental ways.

• 동력기계공학회지
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• 제6권3호
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• pp.71-77
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• 2002

In this study, a dynamic model of proportional pressure control valve using the bond graph and a predictive controller are presented in the form of dynamic matrix control which is concerned with a design method of digital controller for the electro hydraulic servo system. The bond graph can be utilized for all types of systems which involve power and energy, and it is applied to a propotional pressure control valve in this study. Recently, many researchers suggested that better control performance could be obtained by means of the predictive controls with future reference input, future control output and future control error. The Predictive controller is very practical because the controller can be easily applicable to a personal computer or a microprocessor. This study investigates through numerical simulations that hydraulic system with the predictive controller shows very good control performances.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.54-59
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• 1994

In this study, a high-speed servo valve with no outer leakage is developed, which is used to drive flexible hydraulic actuators (FHA) for extreme environments. In the valve, multilayered PZT devices are used to drive a spool directly and quickly. A bellows is also used to prevent outer leak from the clearance between the spool and the sleeve. Employing a disturbance observer, the lack of the system damping of the valve is improved by feeding back the estimated velocity of the spool, as well as the estimated disturbance is fed back to eliminate effectively the hysteresis between input voltage and output displacement of the PZT devices.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.507-514
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• 2001

Direct drive servovalve(DDV) is a kind of one-stage valve since the rotary motion of DC motor is directly transferred to the linear motion of valve spool through the link. Since the structure of DDV is simple, it is less expensive, more reliable and offers reduced internal leakage and reduced sensitivity to fluid contamination. However, the flow force effect on the spool motion is significant such that it induces large steady-state error in a step response. If the proportional control gain is increased to reduce the steady-state error, the system becomes unstable. In order to satisfy the system design requirements, the classical controller is designed using the analytical Bode method.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1992년도 추계학술대회 논문집
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• pp.249-254
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• 1992

Hydrostatic Bearings have been applied to ultra high precision machine tools and precision instruments, because of their low friction characteristic, high load carrying capacity and high moving accuracy at all range of speed. In regard to realizing the Hydrostatic Bearing, various restrictors such as capillary, orifice, diaphram valve, spool valve, and etc can be used. However, their stiffness and flexibility are not sufficient in practical use for ultra precision machine tool elements. In this study dynamic equations were derived and the dynamic characteristics were simulated for both orifice and flow control servo valve. Simulation was carried out on the condition that static and sinusoidal dynamic loads were applied to the table of CNC jig Boring machine. The simulation results indicate the improvement of the performance of the Bearing system when flow control servo valve has been used as restrictor of Hydrostatic Bearing.

• 한국정밀공학회지
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• 제15권1호
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• pp.109-116
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• 1998

This paper is concerned with effective operating method of pneumatic on-off valves for improving position control accuracy, valve life-time and position settling time using modified pulse width modulation with dead-zone (MPWMD). The pneumatic system using on-off valves has advantage of simple construction and low cost compared with a system with servo-valves. The performance of the proposed control method is investigated experimentally for the position control of a pneumatic cylinder using on-off valves. Experimental results show that the proposed algorithm for valve operation can be used to obtain fast and accurate position control compared to the conventional PWMD algorithm. It is also shown that the use of the proposed MPWMD algorithm for the position control significantly reduces the number of valve switching and noise.