基于多自由度的小波包滚动轴承故障诊断方法

快速谱峭度图是滚动轴承故障诊断的有效方法,然而,该方法有可能将最佳频带分割到不同区域,造成对故障信息的识别能力不足,并且对随机冲击噪声的免疫力较弱。根据滚动轴承故障激发多个固有频率的特点以及平均降噪原理,提出多自由度小波包诊断方法,选取适当数量的小波包子带信号,将所选子带信号的频谱平均处理,充分利用信号的有用信息,增强了对白噪声及随机冲击噪声的免疫力。对滚动轴承故障仿真信号及实测信号分别应用快速有限冲击响应(FIR),谱峭度方法,小波包谱峭度方法以及多自由度小波包诊断方法的对比分析,表明多自由度小波包诊断方法对白噪声及随机冲击噪声具有更强的免疫力,验证了该方法的有效性及实用性。

Spectra of seismic force reduction factors of MDOF systems normalized by two characteristic periods

Seismic force reduction factor(SFRF) spectra of shear-type multi-degree-of-freedom(MDOF) structures are investigated. The modified Clough model, capable of considering the strength-degradation/hardening and stiffnessdegradation, is adopted. The SFRF mean spectra using 102 earthquake records on a typical site soil type(type C) are constructed with the period abscissa being divided into three period ranges to maintain the peak features at the two sitespecific characteristic periods. Based on a large number of results, it is found that the peak value of SFRF spectra may also exist for MDOF, induced by large high-mode contributions to elastic base shear, besides the mentioned two peak values. The variations of the stiffness ratio λk and the strength ratio λF of the top to bottom story are both considered. It is found that the SFRFs for λF ≤λk are smaller than those for λF > λk. A SFRF modification factor for MDOF systems is proposed with respect to SDOF. It is found that this factor is significantly affected by the story number and ductility. With a specific λF(= λk0.75), SFRF mean spectra are constructed and simple solutions are presented for MDOF systems. For frames satisfying the strong column/weak beam requirement, an approximate treatment in the MDOF shear-beam model is to assign a post-limit stiffness 15%-35% of the initial stiffness to the hysteretic curve. SFRF spectra for MDOF systems with 0.2 and 0.3 times the post-limit stiffness are remarkably larger than those without post-limit stiffness. Thus, the findings that frames with beam hinges have smaller ductility demand are explained through the large post-limit stiffness.

Dynamics of Sea Ice and Spectrum of Ice Force

Spectrum and self-excite characters are the two significant characters of the dynamics of sea ice. The spectrum character of sea ice is mainly shown by the spectrum of ice force. The spectrum character of the sea ice is its intrinsic attributes. When the spectrum of ice force from the dynamic response of ice and structure interaction are evaluated, the effect of dynamic character of the structure must be eliminated. In this paper, the ice force spectrum at Bohai Bay and Liaodong Bay is evaluated from the displacement and strain responses of a single degree and a multi-degree freedom structure. The evaluated ice force spectrum can be used to define the spectrum character of ice in the analysis of ice induced vibration.

Development of Five-Finger Multi-DoF Myoelectric Hands with a Power Allocation Mechanism

To be used as five-fingered myoelectric hands in daily living, robotic hands must be lightweight with the size of human hands. In addition, they must possess the DoFs （degrees of freedom） and high grip force similar to those of human hands. Balancing these requirements involves a trade-off; ideal robotic hands have yet to sufficiently satisfy both requirements. Herein, a power allocation mechanism is proposed to improve the grip force without increasing the size or weight of robotic hands by using redundant DoFs during pinching motions. Additionally, this mechanism is applied to an actual five-fingered myoelectric hand, which produces seven types of motions necessary for activities of daily living and realizes a -60% improvement in fingertip force, allowing three fingers to pinch objects exceeding 1 kg.