Moving coil type full electric feedback servo valve automatic detection system

Abstract of the paper: Taking the MK moving coil type fully electric feedback servo valve produced by Japan KYB Industry Co., Ltd. as an example, the characteristics of the moving coil type fully electric feedback servo valve are introduced, and the test method of the moving coil type fully electric feedback servo valve is described in detail. And the principle of the automatic detection system, and the test results of the MK valve using the automatic detection system are given.
    1 Introduction The
    most typical and most commonly used traditional electro-hydraulic servo valve is the double-nozzle flapper-type spool valve force feedback servo valve, which uses a torque motor as an electro-mechanical conversion device, and the double-nozzle flapper valve is a hydraulic amplifying element. The feedback lever and the spring tube constitute mechanical feedback. Although the torque motor has the advantages of high natural frequency and compact structure, in order to limit nonlinearity, the output displacement of the torque motor armature is generally very small, and the manufacturing accuracy is high. The mechanical feedback formed by the force feedback rod and the spring tube makes the torque motor resistant Poor pollution and high price.
    The moving-coil force motor does not change the length of the air gap when it moves in the air gap, and has the characteristics of large displacement. The force motor directly drives the spool valve, which can increase the anti-pollution ability of the valve. In the early moving coil type force motor servo valve, in order to make full use of the linearity of the force motor, the spool stroke is large, and the stiffness of the centering spring is generally small, and the moving coil and the pilot valve spool are connected together, and the moving part has a large mass, resulting in The frequency of the force motor is low and the response speed is slow. With the development of electronic technology and sensor technology, it is no longer difficult to increase the output force of the force motor by increasing the driving current of the moving coil force motor. The use of advanced displacement detection technology to achieve high-precision detection of the valve core position is not only feasible but also economical. Therefore, in recent years, almost all servo valves with high frequency response and large flow rate above hundreds of Hz have adopted a moving coil type force motor structure. This article takes the MK servo valve produced by Japan KYB Industry Co., Ltd. as an example to analyze the characteristics of the moving coil servo valve and its detection problems.
    2 Features of MK valve and its amplifier
    MK electro-hydraulic servo valve is a kind of electro-hydraulic servo valve with full electric feedback, two-stage drive and two-position closed loop. It has the characteristics of high frequency response, high precision, good pollution resistance and stable performance. Compared with force feedback, the use of electrical feedback not only simplifies the structure of the servo valve, but also provides a technical basis for changing the characteristics of the valve with electrical parameters.
    Figure 1 is the electrical schematic diagram of the moving coil type full electric feedback MK valve and its amplifier. The servo valve is composed of a pilot valve, a main valve and a pressure reducing valve. The pilot stage is mainly composed of a moving coil force motor, a spool valve and an eddy current displacement sensor. The electrical part is completely dry, and the spool is directly moved when the moving coil is moving. The displacement of the spool is detected and fed back by the embedded eddy current displacement sensor. The input to the amplifier forms an electrical closed loop. This method of direct action plus electrical feedback makes its structure particularly simple and greatly improves reliability. The main valve is driven by the pilot stage, and the main spool is connected to the iron core of the embedded differential transformer displacement sensor. The displacement of the main spool is detected by the differential transformer displacement sensor and fed back to the input of the amplifier to form a second level of feedback. The pressure reducing valve is located between the main valve and the pilot valve to ensure that the pilot valve can obtain a stable oil supply pressure. The servo amplifier is composed of power amplifier, main valve loop, addition circuit, DC power supply and detection circuit, and its current drive capability is ±3.5 A@±48V. The sensor and amplifier are placed close to the servo valve, responsible for processing and amplifying the displacement signal of the pilot valve and the main valve spool, and converting the displacement signal into an electrical signal of 4-20 mA. This kind of current transmission method greatly improves the anti-interference ability of the system.

1. Pilot valve 2. Pressure reducing valve 3. Main valve Fig. 1 The electrical principle diagram of the moving coil type full electric feedback MK valve and its amplifier
    can be seen from Fig. 1, this kind of full electric feedback, two-stage drive, dual position The closed-loop electro-hydraulic servo valve itself is a complex and precise control system integrating mechanical, electrical, and hydraulic. Testing its performance parameters and quality indicators is not only an important means to measure its performance, but also to adjust electrical parameters to ensure its normal , High-efficiency, stable operation and necessary means of strengthening maintenance.
    3 The composition principle of the automatic detection system
    can be known from the above analysis: the performance detection of the moving coil type full electric feedback MK valve is actually the performance detection of the full electric feedback electro-hydraulic servo system. In order to ensure that the impedance effect of the detection system does not affect the performance of the MK valve and the adjustment of its parameters, the detection system should not only complete the detection functions of the pilot valve, the main valve’s flow characteristics, pressure leakage characteristics, spool displacement characteristics, and frequency characteristics, but also Take isolation measures and effective anti-interference technology to ensure that the performance of the valve is not affected.
  Figure 2 is a block diagram of the composition of the automatic detection system. The system software is realized under the WINDOWS environment, with good man-machine interface and operability. The system hardware is mainly composed of a monitoring computer, an excitation signal generating unit, a sensor and its transmission unit, a signal acquisition and processing unit, a detection result output unit, a test device and a servo valve under test.

Figure 2 Block diagram of the composition of the automatic detection system
    (1) Monitoring computer The
    monitoring computer adopts an industrial control machine, which is the main control machine of the entire test system. Through a friendly man-machine interface, it is responsible for receiving user instructions, monitoring and managing the working status of intelligent instruments such as the program-controlled signal generator, BCDGPIB data conversion unit, 1253 gain phase analyzer, PM3384 four-channel digital-analog combined oscilloscope, etc. according to the test purpose. And is responsible for controlling the DSP interface board to complete the simulated acquisition, analysis and processing of the measured. At the same time, the monitoring computer realizes the display and printout of the test status and results through a large-screen display and a printer.
    Through the IEEE488 bus, the monitoring computer communicates with intelligent instruments such as the programmable signal generator, BCDGPIB data conversion unit, 1253 gain phase analyzer, PM3384 four-channel digital-analog combined oscilloscope, and completes the working status of these intelligent instruments such as working mode and range Work such as setting up and obtaining test data.
    (2) Excitation signal generation unit The
    excitation signal generation unit includes two parts, one is the programmable signal generator, and the other is the excitation signal output part of the 1253 gain phase analyzer. The programmable signal generator can generate sine waves, triangle waves, pseudo-random signals, step signals, etc. The excitation signal output of the 1253 gain phase analyzer is a sine wave. The monitoring computer operates the excitation signal generating unit through the IEEE488 bus, sets the signal type, amplitude and other parameters, and generates various excitation signals required by the test project.
    (3) Sensor and its transmission unit The
    sensor and its transmission unit are important components of the servo valve detection system. The physical quantities that characterize the performance or state of the tested servo valve, such as pressure, flow, temperature and other parameters, need to be converted into electrical signals by the corresponding sensors, and then processed and displayed by the transmitter or secondary instrument, and sent to the signal The acquisition and processing unit performs analysis and processing.
    Pressure detection adopts PDCR-961 pressure sensor and DPI-280 digital pressure display instrument of British DRUCK company, range is 0～35 MPa, accuracy is ±0.1%; flow measurement adopts VSE1, VSE 2, VC0 produced by German VSE GmbH .2 and VSE0.04 4 types of gear flow sensors, the secondary instrument uses MFI digital flow indicator, the performance parameters of the flow sensor are shown in Table 1; Temperature range: -50～150℃, accuracy 0.5℃.
     The pressure and flow digital display instrument can also output analog quantity (4～20 mA/0～10 V) and BCD digital quantity while displaying.
Table 1 Flow sensor performance and application
model VSE2 VSE1 VC0.2 VSE0. 04 Linearity (%) 0.3 0.3 1 0.3 Measuring range (L/min) 1.5～125 0.8～16 0.2～16 0.04～4 Flow characteristic flow characteristic Leakage characteristics
    (4) Signal acquisition and processing unit The
    signal acquisition and processing unit is mainly composed of signal conditioner, DSP interface board, BCDGPIB data conversion unit, 1 253 gain phase analyzer, PM3384 four-channel digital-analog combined oscilloscope and monitoring Computer and other components, responsible for the isolation, amplification, filtering, acquisition, processing and other functions of the signal from the sensor.
    In addition to the functions of amplifying, blocking and filtering analog signals from sensors or secondary meters, the signal conditioner also provides the isolation function of analog signals, which effectively eliminates the influence of the sensor ground network on the test system. The input and output of the servo amplifier and the pilot valve spool displacement and main valve spool displacement signals are isolated by the conditioner and connected to the test system, thus avoiding the influence of the test system on the servo valve and servo amplifier, and ensuring the servo valve and servo amplifier The normal work and the independence of parameter adjustment.
    While the DSP interface board collects the analog signal from the signal conditioner, the monitoring computer collects the BCD digital quantity from the secondary instrument through the BCDGPIB data conversion unit, so that online calibration and zero adjustment of the analog quantity can be easily realized. The static characteristic curve of the servo valve is drawn using digital calibrated analog quantity, which not only ensures the data accuracy of the static characteristic of the servo valve, but also ensures the resolution and integrity of the static characteristic curve of the servo valve.
    The frequency characteristics can be completed by the 1253 gain phase analyzer, and the results are transmitted to the monitoring computer via the IEEE488 bus for secondary processing, and then displayed, printed and output by the monitoring computer.
    The step characteristics are collected by PM3384 four-channel-analog combined oscilloscope, and then displayed and printed after analysis and processing by the monitoring computer.
    (5) Test result output unit
    XY recorder, large screen display, printer and PM3384 four-channel-analog oscilloscope constitute the test result output unit of the test system.
    4 Test circuit and experiment
    (1) The static characteristic test of the static characteristic test circuit and the experimental
    electro-hydraulic servo valve mainly includes the no-load control flow characteristic, the pressure gain characteristic and the internal leakage characteristic. From these 3 characteristic curves, one can find Obtain the characteristic parameters such as flow gain, linearity, hysteresis, symmetry, polarity, pressure gain, zero offset and internal leakage of the electro-hydraulic servo valve.
    Figure 3 is the static characteristic test loop diagram of the electro-hydraulic servo valve. In order to ensure that the test system is not disturbed when the spool moves, a proportional amplifier, proportional valve, servo valve P, T port pressure sensor and PI regulator are used to form the pressure closed loop of the test loop, thereby satisfying the servo valve in the flow characteristic test. The valve pressure drop is basically maintained at a constant requirement. During the no-load control flow characteristic test, open the shut-off valves 1, 3, 5, 6, and 7, and close the shut-off valve 8. Pressure gain characteristics and <