基于小波变换的拖拉机旋耕作业载荷谱同步加速

    Synchronous acceleration of the load spectrum for tractor rotary tillage operation based on wavelet transform

    • 摘要: 拖拉机旋耕作业载荷谱中小载荷循环占据大量时间,导致室内可靠性试验时间长,效率低。该研究针对常用载荷谱加速方法对多类型载荷加速效果有限的问题,提出基于小波变换的旋耕作业载荷谱同步加速方法。该方法结合小波变换和Hilbert包络分析实现大损伤片段的识别和提取,基于旋耕作业载荷的时域同步性实现载荷谱加速;提出伪损伤加速效率指标(pesudo-damage acceleration efficiency, PDAE)对加速效果进行评价,确定了适用于拖拉机旋耕作业载荷谱的最优加速参数,加速后的载荷谱时间保留比为81.32%,动力输出轴(power take-off, PTO)转矩载荷的伪损伤保留比为98.99 %,悬挂载荷谱的伪损伤保留比为97.56 %。与常用损伤保留加速方法相比,本文加速方法在保留载荷损伤特征的基础上节省10.07%的时间,具有更高的加速效率。开发拖拉机旋耕载荷谱台架加载平台并开展应用试验,结果表明,加载平台对PTO转矩载荷谱和悬挂载荷谱的平均复现误差分别为−7.53%和−2.48%,能够实现载荷谱复现模拟旋耕作业工况。研究结果可为拖拉机载荷测试以及加速疲劳可靠性试验提供参考和技术支撑。

       

      Abstract: Load spectrum has been widely used in indoor reliability tests on quality verification, in order to improve the efficiency and accuracy of tractor products. However, a large amount of time has been occupied by small load cycles in the load spectrum of tractor tillage during operation, leading to long testing, high energy consumption, and low efficiency. Fortunately, the large and extensive load spectrum can be accelerated for the equivalent real lifetime of tractor products. The equivalent load spectrum is called the accelerated load spectrum. Nevertheless, the conventional acceleration of the load spectrum cannot simultaneously accelerate the multiple types of load in real time. In this study, a synchronized acceleration approach was proposed for the load spectrum of tractor rotary tillage using wavelet transform. Loading application experiments were also carried out to verify the synchronously accelerated load spectrum. Firstly, the operation loads of tractor tillage were collected using the peak-over threshold model. The load spectrum of 1-time extrapolated tillage was obtained for the acceleration research. Subsequently, the wavelet transform analysis with Hilbert envelope was implemented to synchronously accelerate the tillage load spectra. Daubechies wavelet basis function (DbN) was used to decompose the load signal. The wavelet coefficients were reconstructed for the wavelet components at different scales. The cumulative sum-of-square of wavelet components was computed to represent the load damage contribution across all scales. A threshold was set to identify the segments with significant damage. As such, the high-damage segments were extracted using Hilbert envelope analysis. Finally, synchronization acceleration was achieved, according to the time-domain synchronicity of the tillage load spectrum. In addition, the pseudo-damage acceleration efficiency (PDAE) index was proposed to evaluate the acceleration efficiency of the load spectrum. Ultimately, the optimal acceleration parameters were then determined suitable for the operation load spectra of tractor tillage. In the power take-off (PTO) torque load spectrum, the Db1 wavelet was used better at a threshold step size of 16 for the acceleration; In the suspension load spectrum, the Db7 wavelet was used better at a threshold step size of 18 for the acceleration. The better synchronization acceleration was achieved for the load spectrum of the 1-time extrapolated tillage, with a time retention ratio of 81.32% for the accelerated load spectrum, a pseudo-damage retention ratio of 98.99% for the PTO torque load spectrum, and a pseudo-damage retention ratio of 97.56% for the suspension load spectrum. A comparison was made on the statistical characteristic parameters from the improved and traditional damage-retention-based acceleration. The comparative results show that the improved acceleration saved 10.07 percentage point in time retention ratio compared to the damage retention method, while retaining the characteristics of load damage, indicating the higher acceleration efficiency. After that, the mean- and amplitude-frequency histograms of the accelerated load spectrum were obtained using rain flow cycle counting. The accuracy of the acceleration was verified to explore the high acceleration efficiency of the wavelet. Finally, a loading bench test was carried out on the tillage load spectrum. A fuzzy PID controller-based loading control algorithm was also proposed for the tillage load spectrum. Bench loading application tests were also conducted using the accelerated tillage load spectrum. The test results indicate that the loading bench shared a response error of -7.53% for the PTO torque load spectrum and a response error of -2.48% for the suspension load spectrum. The overall error of the loading bench for the rotary tillage load spectrum fully met the actual requirements of the loading application. Dynamic loading was achieved under the tillage working conditions. This research can also provide theoretical references and platform support for the tractor load testing and accelerated fatigue reliability test.

       

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