• Journal of Drive and Control
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• v.13 no.3
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• pp.15-23
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• 2016

The direct-drive servo valve(DDV) is a kind of one-stage valve because the main spool valve is directly driven by the dc motor. Since the DDV structure is simple, it is less expensive, more reliable, and offers a reduced internal leakage and a reduced sensitivity to fluid contamination. The control system of the DDV is highly nonlinear due to a current limiter, a voltage limiter, and the flow-force effect on the spool motion. The shape of the step response of the DDV-control system varies considerably according to the magnitudes of the step input and the load pressure. The system-design requirements mean that the overshoots should be less than 20%, and the errors at 0.02s should be less than 2%, regardless of the reference-step input sizes of 1V and 5V and the load-pressure magnitudes of 0MPa and 20.7MPa. To satisfy the system-design requirements, the PID-controller parameters of $K_c$, $T_i$ and $T_d$, and the derivative-feedback gain of $K_{der}$ are designed using the root locus and manual tuning.

• Journal of Drive and Control
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• v.15 no.1
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• pp.16-27
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• 2018

Hydraulic torque load simulator is essential to test and qualify the performance of various angle control systems. Typically a flapper-type second stage servovalve is applied to the load simulator, but here the direct drive servovalve, which is a kind of one-stage valve and affected by the large flow force, is applied. Since the torque load is applied not to the stationary shaft but to the rotating shaft of the angle control system, the controlled torque of load simulator is not accurate due to the rotating speed of the angle control system. A feedforward compensator is designed and applied to minimize the disturbance-like effect. A mathematical model is derived and linearized to analyze the stability, accuracy and responsiveness of the torque load simulator. The parameter effects of a controller, servovalve, hydraulic motor, rotating spring shaft are analyzed and summarized. The goodness of the linear analysis is verified by the digital computer simulations using both the linear and nonlinear mathematical models.

• Journal of Drive and Control
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• v.17 no.3
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• pp.15-25
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• 2020

The cycle time and power saving effect of a hydraulic hybrid injection molding machine using a servo motor are considered in this paper. In order to verify control characteristics, such as pressure and speed, experiments were performed with the hydraulic hybrid injection molding machine, clamping force of 110 ton. The power consumption and production cycle time of a conventional hydraulic injection molding machine were measured to compare its performances with the hydraulic hybrid injection molding machine. An injection molding machine with a clamping force of 1300 ton was used as the conventional machine, the hybrid machine was implemented by replacing its induction motors with servo motors. In the remodeled hybrid machine, experiments were performed to investigate how the displacement of the mold clamping pump affects the power consumption and production cycle time. The results showed that the production cycle time of the hybrid injection molding is similar to a conventional hydraulic injection molding machine but with a significant energy saving of about 40%.

• Journal of Drive and Control
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• v.9 no.4
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• pp.32-41
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• 2012

Most diagnosis methods for servo valves requires installing spool displacement sensor or flow sensor as well as pressure sensor. The measurement of flow is hard to implement and many kinds of servovalves or proportional direction valves do not have a built-in spool displacement sensor. In this study, static performances of servovalve or proportional-direction-valve are studied theoretically and a diagnosis technique, which uses only load pressure and input current signal, is assessed. An experimental setup was made based upon a personal computer and the LabVIEW graphical language. A series of diagnosis tests were performed and the analysis results showed it possible to measure the pressure gain, hysteresis and null bias in a relatively simple methodology.

• Journal of Drive and Control
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• v.15 no.2
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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.

• Journal of Drive and Control
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• v.13 no.2
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• pp.42-50
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• 2016

The conventional technique to measure the hysteresis and the null of servo valves is defined in ISO 10770-1 and based on load flow signal of the servo valve. A new technique based on the transmission line pressures is suggested in this study. The new measuring method was verified through a series of experiments. No hysteresis was observed between the spool displacement and the transmission line pressures, load pressure or each chamber pressure. Some hysteresis was observed between valve input and pressures, which was found to be the same as those of load flow and spool displacement for the valve input. By using the chamber pressures, the hysteresis and the null are easier to measure than the load pressure or differential pressure between those two chamber pressures because the chamber pressures showed sharp edges.

• Journal of Drive and Control
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• v.13 no.2
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• pp.26-33
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• 2016

This paper describes of a mathematical and real experimental analysis for a walking robot which uses servo valve driven hydraulic actuator. Recently, many researchers are developing a walking robot based on hydraulic systems for the difficult and dangerous missions such as walking in the rough terrain and carrying a heavy load. In order to design and control a walking robot, the characteristics of the hydraulic actuators in the joint through the view point of walking such as controllability and backdrivability must be analyzed. A general mathematical model was used for analysis and proceeds to position and pressure changes characteristic of the input and backdrivability experiment. The result shows the actuator is a velocity source, had a high impedance, the output stiffness is high in contact with the rigid external force. So stand above the controller and instruments that complement the design characteristics can be seen the need to apply a hydraulic actuator in walking robot.

• Journal of Drive and Control
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• v.16 no.2
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• pp.72-79
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• 2019

Despite the development of electronic components and microprocessors, hydraulic actuators are still being applied in various applications. In some applications, there is a desire to apply a hydraulic actuator with a relatively small position error to the system. Various studies have been conducted to reduce the position error of hydraulic actuators. In this paper, the position error of the hydraulic actuator when the hydraulic oil pressure is supplied is defined as the offset generated by the servo valve, and the method for correcting the servo valve offset has been studied. A method for compensating the servo valve offset was proposed and it was verified through experiments that the position error of the hydraulic actuator was reduced. We also compared the servo valve offset correction method and controller using the PID control and disturbance observer used to reduce the position error of the hydraulic actuator. No-load test and load test were performed to confirm the performance of the servo valve offset correction method. The results of the study were compared with those obtained by using the disturbance observer and PID control.

• Journal of Drive and Control
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• v.15 no.4
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• pp.48-54
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• 2018

The hydraulic servo actuator has always operated very precisely with high frequency and small displacement, and is used continuously for a long time. The hydraulic servo actuator of the test equipment used in the accelerated life test in order to guarantee the service life of the automotive parts failed earlier than the products before finishing the test. This study performed an analysis on the cause of the failure of the hydraulic servo actuator used in the test equipment, changed the design of the actuator to solve the root cause of the main failure mode, and developed the improved servo actuator. Based on above process, this study established a better performances and longer lifetime of the servo actuator after testing.

• Journal of Drive and Control
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• v.18 no.3
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• pp.1-7
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• 2021

In a hydraulic control system, since a hydraulic cylinder drives a relatively large mass of an object, an external load force acts as a disturbance on the control performance of the system. Additionally, as the hydraulic system is used for a long period, there are disturbances that occur gradually, such as a drop in supply pressure because of abrasion of the pump, oil leakage from a valve, and oil leakage from a cylinder. In this study, a state feedback controller based on a linearization technique is applied. To prevent the performance degradation of the controller from the load disturbance, an Extended Luenberger observer (ELO) is used for the Extended system. The case of using the proportional controller, which is a representative linear controller, and the result of using the controller designed in this study are compared and reviewed through simulation. Also, we propose an experimental gain-setting method for a state feedback controller that can be used at industrial sites, and examine how the stability and control performance of the system changes because of the disturbance inputs through the experimental results.