Papers by Keyword: Servo Valve

Abstract: In this paper, a hydrostatic bearing controlled by servo-valve for precise closed-loop oil-film gap control is developed. Due to the increasing demands of larger dimension, heavier load and higher precision for current and future machine tools, the development of hydrostatic bearing has become a more and more important issue over the past decades. Nowadays, the most commonly used active pressure feedback restrictor for hydrostatic bearing is membrane type, in which a thin and flexible metal sheet serves as the key component to meter the hydraulic oil flow precisely. However, the membrane type pressure feedback restrictor is not quite suitable for extremely heavy load. Therefore, an alternative to design the active restrictor for hydrostatic bearing using servo-valve is presented in this paper. Different controllers are also designed and compared in this paper. There are two significant features regarding the proposed design. The first one is the introduced orifice restrictor inside the servo-valve which avoids the influence of possible oil temperature variation. The second feature is the introduced closed-loop oil-film gap control scheme that widens the application range effectively. Finally, a test rig of servo-valve controlled hydrostatic bearing is implemented and the experimental results prove the validity of the hydrostatic bearing with the proposed servo-valve and the closed-loop gap control scheme.

Abstract: Because hydraulic actuator has higher power and force density, it is normally used in heavy load manipulator robots and industrial equipment which require high torque. Also, the hydraulic actuator is applied to underwater robots that need high performance maneuver in underwater operations. The force control has benefits to those kind of robots to ensure compliance with user or environment. However, the hydraulic actuator is difficult to control forces due to the non-linearity characteristic of the hydraulic servo system. In this paper, we propose a force control method with compensation of force derivative and natural velocity feedback. We also describe a method of applying it to the real system. In order to evaluate the effect of the proposed control method, the simulations and experiments were performed.

Abstract: The mechanical part of the 2D servo valve is mainly a hydraulic servo screw mechanism, by which the rotary motion of the spool is turned to linear sliding. A step motor is utilized to rotate the spool and functions as the electrical-to-mechanical transformer. For studying the different influences of 2D valve's pilot circular and full arch structure on its dynamic characteristics of servo screw mechanism, a step response and sine response experiment device was designed, and the experiments were done. The experimental results show that the full arch structure type step response time is about 1.6 ms (abbreviation of millisecond), the circular type about 3ms, proved that the full bow structure can significantly improve the dynamic characteristic of servo screw mechanism, it is also be proved by sinusoidal frequency response experiments.

Abstract: The paper presents a circuit topology favorable to drive piezoelectric actuators for high frequency servo valve. It begins with a short overview of different energy-saving PZA drive types and their tradeoff between efficiency and circuit complexity. Then the mechanical structure and equivalent model of the piezoelectric servo valve are described. And the circuit topology including an energy-saving oscillator, an efficient DC bias power and a repetitive controller especially for tracking reciprocating motion, is proposed. The efficiency-improved PZA drive is then derived from the above design. Finally, the drive together with the servo valve is tested in the simulation experiments.

Abstract: In regular electrical upsetting process, the process parameters were determined by the experience. During working, these parameters were constant and could not be controlled online. In this paper a new proportionate valve and various velocity top anvils, electrical upsetting system is introduced. Based on the bulb temperature measured at the time of operation proportionate valve will vary the upset pressure to obtain the bulb without crack or fold. The control strategy includes two key parts: sensing the temperature and controlling it by varying the power intensity in the circuit through controlling the upset pressure. And the different anvil position and anvil velocity will be used to change the bulb shape based on the valve profile. This control strategy also includes two key parts: Velocity of anvil is directly proportional to height of bulb, in various positions various velocity will be used to form a different shape of bulb without defects.

Abstract: During the processing of the servo valve spool machining, the overlap of valve spool's each edge should take zero grinding. The grinding processes including spool overlap test and grinding. In this paper, the authors used a new test method, which simulates working condition of servo valve. Hydraulic cylinder is used as the load of servo valve in this test method, and the hydraulic cylinder is in no-load operation. This test method realized the automatic switch of test valve, and it determined the amount of grinding through complete measuring four edges overlap values, furthermore, it realized measuring the total amount of overlap, thus reflect the flow characteristics of a valve. This is a new automatic method for measuring servo valve overlap.

Abstract: Structure and working principle of the two-stage moving coil electro-hydraulic servo valve has been analyzed. Through Laplace transformation to get the transfer function by the dynamic equations of the moving coil force motor, the displacement and current double closed loop control to simulate the force output characteristics, ignoring the electromagnet and valve clearance of hysteresis effect, the simulation model was established based on AMESim. The main simulation parameters was determined by the means of measuring and calculating, the control parameters of the pilot spool and the main spool were optimized based on the step response. Inputting the same multiple superimposed sine excitation signal to the physical prototype and simulation models, comparing the simulation and experimental results in the time domain and frequency domain, the correctness of simulation model was proved.

Abstract: There are some problems in moving coil linear motor for Electro-hydraulic servo valve, such as big weight, small electromagnetic force, long response time and small bandwidth. After simulation analysis on permanent magnet placement and permanent magnet magnetization direction, it is found that distribution of magnetic field lines is uneven, magnetic flux density is low, and magnetic field lines are not vertical with the coil current direction. To solve these problems, a new type of linear force motor with 5 rings stack Halbach permanent magnet array structure is put forward. Through using the new structure, the weight and volume of motor can be reduced, and the electromagnetic force can be increased. Simulation results show that for the new structure, under the coil displacement change, the output electromagnetic force changes little and can maintain good linearity. Using permanent magnet with same volume, the electromagnetic force produced by new force motor is 2.5 times as it is produced by current motor. If the electromagnetic forces produced by two structures are same, the step response time of new type can be decreased of 14.3%, and the bandwidth can be improved to 2 times.

Abstract: The jet pipe electro-hydraulic servo valve is a typical two-stage flow control servo valve, its static and dynamic characteristics are analyzed in this paper. The interaction of the mechatronic and hydraulic system is considered by multidomain simulation tool, the all key parameters are tunable and this provides the optimal possibility to develop a high-performance jet pipe electro-hydraulic servo valve.

Abstract: A device used in measuring composite stiffness of armature components (CSAC) is developed according to the proposed definition of CSAC. Couple exerting and measuring mechanism, rotary actuator structure and fixture of armature components are introduced in this paper.