On the realization of dynamic balancing machine

2022-08-01
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Discussion on the realization method of dynamic balancing machine

when the rotor material is evenly distributed, installed well, and rotates smoothly. In an ideal case, the support is only subjected to gravity, and the rotor only has static load when it rotates as it does not. When the rotor materials are distributed unevenly and installed improperly, the central inertia main shaft of the rotor does not coincide with the rotating shaft, resulting in inertia centrifugal force and centrifugal couple, causing additional rotating load on the support is called dynamic load

for the unbalanced rotor with constrained rotating axis, the dynamic unbalance will cause dynamic load on the support, which will not only cause vibration of the whole rotating machinery, generate noise, increase energy consumption, but also accelerate the wear of bearings, cause high-frequency fatigue damage of rotor components and forced vibration damage of support gearbox and some components, reduce the service life of rotating machinery, and even lead to major accidents in serious cases

for a rotor (such as a satellite) whose rotation axis is unconstrained, the dynamic imbalance will affect its attitude in space, and then affect its working quality

since these imbalances occur when the rotor is rotating, they generally need to be measured and corrected during rotation, so they are called dynamic balance. To a great extent, the effect of dynamic balance is restricted by the accuracy of the measurement system

in principle, the measuring system can be divided into soft support dynamic balancing machine and hard support dynamic balancing machine. The hard support dynamic balancing machine is a universal dynamic balancing machine which has been developed rapidly since the early 1970s. Since its calibration is independent of the rotor's M (mass) and I (moment of inertia), it only needs to be calibrated once (while the calibration coefficient of the soft support dynamic balancing machine varies with the rotor's M and I, so it needs to be recalibrated one by one for different types of rotors). In recent years, due to the continuous improvement of the structure, the electric measurement system has been increasingly improved, and the balance accuracy has been continuously improved. In addition to the strong universality, the soft support dynamic balancing machine is still used for the balance of ultra-high speed, high precision, small rotors and large quantities (such as crankshafts), the rest have been mostly replaced by the hard support dynamic balancing machine

the dynamic balancing machine is composed of the following parts: mechanical vibration measurement system (including vibration sensor and phase signal generator), driving system, electronic measurement system, correction device and safety protection device. Among them, the change of mechanical vibration measurement system is relatively slow, while the development of electrical measurement system is very rapid. Due to the increasing popularity of microcomputers, the computerized electrical measuring system has become a new trend in the design of dynamic balancing machines at home and abroad

it can be seen that the dynamic balance technology is a complex electromechanical integration technology, and it is also a key technology that restricts the development of the machinery industry. It directly affects the working quality and service life of various rotating machinery. The advanced industrial countries represented by Germany started early and developed rapidly in the field of dynamic balance research. Although China started not late, its development is slow due to various reasons. Most of the dynamic balancing machines used by domestic users are products from the 1960s and 1970s, with poor accuracy, many faults and low benefits, which have seriously affected the development of production and enterprises. Large enterprises or national key enterprises have spent huge amounts of foreign exchange to import dynamic balancing machines. Due to economic reasons, small and medium-sized enterprises can only continue to use outdated products, which, on the one hand, wastes a lot of valuable foreign exchange, on the other hand, still seriously affects the development of the machinery industry. In recent years, the design and manufacturing of domestic dynamic balancing machines have developed rapidly, but on the whole, some of them are imported models that have been eliminated or are about to be eliminated from abroad, and some are self-designed products in China, which have few functions and are not ideal in terms of precision and reliability. Therefore, the research and manufacturing of advanced dynamic balancing machines has become an urgent need for the development of the mechanical industry

in order to track the world's advanced dynamic balancing technology and improve the level of the domestic electrical measurement system, the author has made a systematic and in-depth study on the hardware and software of the microcomputer based electrical measurement system of the general hard support dynamic balancing machine, and developed an electrical measurement system with high precision, complete functions, simple operation and in line with the actual needs of China -- the microcomputer based electrical measurement system of the cab792 general hard support dynamic balancing machine

2 overall design scheme of the system

2.1 some factors affecting the system scheme

the main task of the dynamic balance electromechanical measuring system is to extract the amplitude and phase position information of the useful signals with the same frequency as the rotor rotation from the weak dynamic unbalance signals with interference obtained by the mechanical vibration measuring system. At the same time, it should also cooperate with the mechanical vibration measuring system to solve the plane separation (solution) of the rotor and the automatic phase determination of the rotor. This is the basic starting point of our electric measurement system design

this system is a general electric measuring system specially designed for the hard support dynamic balancing machine equipped with a moving coil speed sensor. Therefore, the following problems need to be considered:

① the hard support dynamic balancing machine is a force measuring balancing machine. Therefore, the unbalance signal output by the sensor is proportional to ω 3( ω—— Rotation angular speed of the rotor)

② high frequency noise of mechanical lever amplifier output

③ low frequency interference and transmission interference transmitted through the foundation

④ the balance speed of the rotor cannot be absolutely stable

⑤ in the process of signal filtering and amplification, it is necessary to consider how to reduce the interference of reference channel to small signal channel and the influence of ambient temperature change on DC zero drift

⑥ when realizing the goal of high precision and multi-function, it is necessary to consider how to give full play to the respective advantages of hardware and software to make the system obtain a high performance price ratio

2.2 composition of the system

according to the above considerations, the following principles are determined in the design and composition of the system:

① the triple integrator is used in the front-end stage to eliminate the ω 3. In order to ensure that the useful signal is not too small when operating at high speed, the speed of 180 ~ 5000r/min is divided into four speed ranges. Each speed range has its own cubic integrator. The speed range is divided as a common ratio, i.e. 180 ~ 5000r/min is divided into 180 ~ 387r/min, 388 ~ 835r/min, 836 ~ 1799r/min and 1800 ~ 5000r/min. In this way, the common ratio of calibration coefficients between adjacent intervals will be equal to 10

② select MDAC narrow-band automatic tracking filter. By reasonably selecting RC, bw-40db of hardware is controlled below 2Hz to facilitate the system to eliminate high and low frequency interference

③ select AD574 to speed up the pace of data collection to increase the sample size. The software performs multiple averaging to minimize near frequency interference and random interference

④ IBM-PC is selected as the host. On the premise of ensuring the measurement accuracy, the functions of the electrical measurement system are vigorously strengthened: multiple support modes, multiple display modes, multiple compensation modes, multiple gain control modes, multiple time averaging, multiple startup averaging, multiple correction calculation, multiple print out modes, automatic calibration and message service

the overall block diagram of the system is shown in Figure 1. X1, Y1, X2 and Y2 in the figure represent the components of the unbalance signal of the two support points on the X and Y axes

the following is a brief introduction to some parts of the system block diagram:

cubic integral circuit

according to the principle of the hard support dynamic balancing machine, the swing frame amplitude is proportional to the centrifugal force. The vibration signals at the two supports are detected by the moving coil speed sensor. Therefore, the measured vibration signal amplitude is proportional to the third power of the balance speed. The influence of balancing speed can be eliminated by setting up a cubic integrating circuit in the pre-processing. At the same time, due to the low-pass characteristics of the integrating circuit, it can suppress high-frequency noise and retain useful low-frequency vibration signals. The cubic integration circuit of the system is realized by a third-order Butterworth low-pass filter. The system divides the working speed into four speed ranges, corresponding to each speed range, there is a corresponding integrator channel (the speed range is realized by hardware)

manual/automatic gain control a turns off the compressor; Pressing the power switch gc

gain control AGC is designed to reduce the quantization error of a/d on the basis of expanding the range. The circuit makes full use of the a/d conversion accuracy and ensures that the index of the balancing machine will not be reduced due to the small signal. The gain control of the system can switch between manual control and automatic control. Generally, the "automatic gain control" mode is selected. When the interference is particularly strong and the fluctuation is large, the "manual gain control" mode is recommended

mdac correlation filtering

the output signal of the sensor of the dynamic balancing machine includes the signal with the same frequency as the rotor speed, deterministic interference and random interference. One of the main tasks of the electrical measurement system is filtering: suppressing various interferences and extracting useful signals, that is, signals with the same frequency as the rotor. When designing the filter, the narrower the bandwidth is, the higher the separation accuracy is. At the same time, a general dynamic balancing machine is required to work at different speeds; Even when balancing at a certain speed, the speed will shift due to various reasons. It is difficult and uneconomical to require it to be constant. Therefore, the automatic tracking bandpass filter is used in the system. When the rotating speed of the dynamic balancing machine is unstable, the center frequency of the tracking band-pass filter can automatically track the rotating speed, so as to ensure the stability of the spoke value and phase of the useful signal and improve the measurement accuracy. Because of the characteristics of MDAC filter, the system adopts MDAC correlation filter. The so-called correlation filtering is to select a pair of orthogonal signals sin ω 0t and COS ω 0t is used as the reference signal, and the signal f (T) is related to them respectively, then ω 0 the amplitude and phase of the frequency component

reference channel circuit

reference channel circuit mainly includes: ① speed measurement circuit; ② A decoding circuit providing channel address for the cubic integrator circuit to control the automatic switching of the integrator; ③ Provide the counter clock signal for the automatic gain control circuit (AGC), so that when the photoelectric pulse has output, the AGC circuit is allowed to act once every second; ④ Provide 360f0 and F0 signals for MDAC main filter circuit to control counter counting, so that EPROM can provide a complete sine and cosine waveform for MDAC

a/d conversion circuit

in order to realize multi-point average in software (equivalent to software low-pass filter), the system adopts AD574. AD574 is a fast 12 bit successive approximation a/d converter. It is the most widely used and affordable a/d converter in China. Because the chip contains high-precision reference voltage source and clock circuit, it can complete all a/d conversion functions without any external circuit and clock signal, which is very convenient for application

system interface circuit

system interface circuit refers to the part where the information processed by the hardware circuit is interfaced with the microcomputer through ISA bus. It mainly completes the following functions: ① input the a/d conversion results of 4-channel direct flow sent by the MDAC main filter circuit; ② Input 16 bit binary speed code; ③ Input 10 bit system status information code; ④ Output the address code of the multiplexer before controlling the a/d conversion circuit; ⑤ Output 4-bit manual/automatic gain control code and 2-bit control code for message service; Wait

3 system software analysis

the purpose of the computerization of the dynamic balance electromechanical measuring system is not mainly to improve the balance accuracy (in fact, the time averaging processing realized by software is also conducive to the stability of the reading, so as to reduce the reading error; moreover, the measurement accuracy of the system can be greatly improved and the defects of the hardware circuit can be compensated through nonlinear compensation and other algorithms), but to increase the function of the system. Computerization can reduce hardware overhead and increase system functions. There are many hardware functions, such as the solution of the soft support machine, the a-b-c-r1-r2 operation of the hard support machine, and various compensations

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