原子力显微镜(atomic force microscopy,AFM)在微纳米尺度力学测量领域有着广泛应用,其微悬臂梁探针的弹性常数是直接影响测量结果准确性的关键因素之一。弯曲法是标定微悬臂梁弹性常数的一类重要方法,基于弯曲标定原理提出了一种新的...原子力显微镜(atomic force microscopy,AFM)在微纳米尺度力学测量领域有着广泛应用,其微悬臂梁探针的弹性常数是直接影响测量结果准确性的关键因素之一。弯曲法是标定微悬臂梁弹性常数的一类重要方法,基于弯曲标定原理提出了一种新的技术实现方案,并研制了相应的标定系统。借助精密运动定位台使微悬臂梁接触超精密天平并产生弯曲,分别以天平和光杠杆机构同步测得接触力和梁的弯曲量,再根据胡克定律直接算得弹性常数。利用所研制的系统对多种型号的微悬臂梁进行了标定,实验结果表明该系统具有良好的准确性和重复性,测量相对标准差小于5%。展开更多
To improve the efficiency and amplify the exciting force of a shake table,a novel variable stiffness mechanism(VSM)constructed by four leaf spring-lever combinations(LSLCs)was designed.Three VSMs were installed in par...To improve the efficiency and amplify the exciting force of a shake table,a novel variable stiffness mechanism(VSM)constructed by four leaf spring-lever combinations(LSLCs)was designed.Three VSMs were installed in parallel on the traditional hydraulic shake table to constitute a resonant shake table(RST).The static model of the VSM and the dynamic model of the RST were constructed by considering the large deflection of leaf springs and the geometrical nonlinearity of L-shaped levers.The variable stiffness property of LSLCs was analyzed and verified through static experiments.The simulation and vibration experiments on the dynamic properties of the RST prototype were conducted.The results show that compared with traditional shake tables,the RST consumes lower exciting force in a specified frequency bandwidth when outputting the same displacement of vibration.Under a harmonic vibrational excitation,the RST is effective for vibration enhancement using broadband frequency resonance and can save energy to some extent.The broadband resonance technology exhibits considerable potential in practical engineering applications.展开更多
A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphr...A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral-derivative(PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.展开更多
文摘原子力显微镜(atomic force microscopy,AFM)在微纳米尺度力学测量领域有着广泛应用,其微悬臂梁探针的弹性常数是直接影响测量结果准确性的关键因素之一。弯曲法是标定微悬臂梁弹性常数的一类重要方法,基于弯曲标定原理提出了一种新的技术实现方案,并研制了相应的标定系统。借助精密运动定位台使微悬臂梁接触超精密天平并产生弯曲,分别以天平和光杠杆机构同步测得接触力和梁的弯曲量,再根据胡克定律直接算得弹性常数。利用所研制的系统对多种型号的微悬臂梁进行了标定,实验结果表明该系统具有良好的准确性和重复性,测量相对标准差小于5%。
基金The National Natural Science Foundation of China(No.41876218,51905210)。
文摘To improve the efficiency and amplify the exciting force of a shake table,a novel variable stiffness mechanism(VSM)constructed by four leaf spring-lever combinations(LSLCs)was designed.Three VSMs were installed in parallel on the traditional hydraulic shake table to constitute a resonant shake table(RST).The static model of the VSM and the dynamic model of the RST were constructed by considering the large deflection of leaf springs and the geometrical nonlinearity of L-shaped levers.The variable stiffness property of LSLCs was analyzed and verified through static experiments.The simulation and vibration experiments on the dynamic properties of the RST prototype were conducted.The results show that compared with traditional shake tables,the RST consumes lower exciting force in a specified frequency bandwidth when outputting the same displacement of vibration.Under a harmonic vibrational excitation,the RST is effective for vibration enhancement using broadband frequency resonance and can save energy to some extent.The broadband resonance technology exhibits considerable potential in practical engineering applications.
基金the National Natural Science Foundation of China(No.51475284)
文摘A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral-derivative(PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.
