Research On High Accuracy Dynamic Unbalancing Measurement Based On Fully Compliant Tandem Vibration System

Dynamic unbalancing of rotation machinery is one of sources of harmful vibration and noise, which affects life-span, reliability, and operation performance of the product. That is also a common problem in the course of manufacturing and application of rotation parts. It is meaningful to research high accuracy dynamic unbalancing measurement.Vibration system and electrical measurement system are the core components of the dynamic balancing equipment. To improve the performance of the dynamic unbalancing measurement equipment for outboard rotor, this paper presents some new methods during the course of unbalancing signal transmission, acquisition and processing, with the results that smaller minimum achievable residual unbalance, better plane separation performance and long-term stability is realized in unbalancing measurement. In brief, this research includes:1. Some points on outboard rotor unbalancing measurement, including the structure characteristics of the general vibration system, the mechanism of force relation effect, and the plane separation performance, are analyzed in depth. The design ideas for novel vibration system are proposed to improve measurement accuracy and long-tem stability.2.Starting from the concept of instantaneous motion center in theoretic mechanics, a novel fully compliant tandem vibration system with 2 DOF is presented. Its structure combines the advantage of the general overhanging beam structure with high balancing efficiency and the simple beam structure with good plane separation performance. Moreover, it has bigger distance between measuring planes and stable vibration center. Flexure hinges, which are considered as plastic element, are introduced to novel vibration system to provide higher sensitivity, low stiffness and damp in the direction of motion and force transmission in order that the minimum achievable residual unbalance is reduced. The transducers are installed on the same radial measuring plane, the performance changes in transducers caused by environment factor is reduced, the results for this vibration system in long-term operation is more accurate measurement with lower requirement for a second correction run.3. The kinematic model of vibration system is established and the kinematics differential equations are obtained. On the basis of analyzing unbalancing response, the plane separation equations are achieved. By energy method, the theoretic expressions of the equivalent stiffness, nature frequencies and sensitivity of vibration system are induced. Static and modal analyses of vibration system are performed by ANSYS finite element method to prove the reliability of the theoretical model. The influence of geometrical parameters of flexure hinges and structure parameters of vibration system on nature frequencies, sensitivity and stress distribution are researched in depth by FEM. Based on the above obtained results, an optimum design procedure is developed to determine vibration system.4. High performance electronic circuits is designed and implemented to achieve high accuracy dynamic unbalancing measurement. Includes: designing signal conditioning circuit (charge amplifier, selecting frequency and filter) for piezoelectric transducers, designing processing circuit for photodiode sensor to improve phase resolution and establish velocity and rotation direction of the principal axis, designing controlling circuit for motor based on 16-bit microprocessor XC167. The measuring and controlling programmer is realized by KeilC167.5. As the unbalancing signal being immerged under the strong background noises and varied frequency disturbances, the improved empirical modal decomposition method and an adaptive IIR lattice notch filter realized by all-pass filter are separately proposed to extract dynamic unbalancing signal. the original vibration signal can be adaptively decomposed into a definite number of orthogonal intrinsic mode functions arranged in order from high frequency to low frequency by empirical modal decomposition method. The auto-regression prediction model is introduced to eliminate the influence of end effects on balancing signal. The power spectral density is adopted to identify unbalancing signal from all intrinsic modal functions. On adaptive IIR lattice notch filter realized by all-pass filter, a novel algorithm is presented. The time-averaged estimation of cross correlation of the present instantaneous input signal and the past output signal is employed to update step-size. The convergence rate in a low SNR situation is considerably improved. The normalized power factor is introduced to control the variation of step-size in its steady-state bounds. This technique prevents algorithm from diverging due to the influence of biggish power input signal and improves the robustness of algorithm. The experiment results validate the effectiveness of the above two methods.6.The parameters of dynamic unbalancing signal, which are measured by the general methods, must be picked up by integral-period sampling. The phase difference correction method is presented to measure the parameters of random sampling unbalancing signal. The frequency of the measured signal has no influence on the sampling frequency when adopting this method and the measured signal needs not to be picked up by integral-period sampling. The proper windows function is selected to eliminate energy leakage error, and the length of the windows function should be the integer times of the period of unbalancing signal to eliminate harmonic disturbances. The experimental results validate the presented method can achieve high accuracy parameters measurement of dynamic balancing signal.Finally, the extensive experiments are made to prove the effectiveness of the presented dynamic unbalancing measurement system, including plane separation performance, phase accuracy, minimum achievable residual unbalance and repeatability. These achievements in paper can supply theoretical guidance and reference to improve the performance of national dynamic unbalancing measurement equipment.