用于钢轨温度应力检测的电容式位移传感器的结构研究

【作者】 饶莉；

【导师】 丁杰雄；

【作者基本信息】 电子科技大学 ， 机械制造及其自动化， 2005， 硕士

【摘要】 本文介绍了一种用于钢轨温度应力检测的电容式位移传感器结构方案。该传感器是基于传统测量方法和标定轨长测量轨温的原理基础上设计出来的。将自由轨段与固定轨段平行安装,当环境温度改变时,固定轨段受扣件阻力及道床阻力的作用不能伸缩,产生了温度应力,而自由钢轨能自由伸缩,产生了长度的变化,即发生了应变,而这应变就是由于钢轨内部温度应力的释放而产生的。因而固定轨段的瞬时自然长度(即标定轨长)与自由钢轨的瞬时自然长度之差就反映了固定轨段的温度应力的大小。这个“瞬时自然长度之差”是通过电容式位移传感器进行检测的。在该检测方法中,将传感器动极安装在自由轨段上,传感器定极安装在固定轨段上,两极板间的位移就是固定轨段(标定轨长)与自由钢轨的瞬时自然长度差。当环境温度变化时,固定轨段的瞬时自然长度不变,而自由钢轨会发生伸缩,瞬时自然长度变化,从而推动电容的动极移动,极板间距改变,电容值变化。因此,通过测量电容值的变化可检测出固定钢轨的温度应力。由于钢轨温度应变量只有数十微米,为了提高传感器的灵敏度,同时降低后续电路设计的难度,设计了一种双柔性的平行四杆柔性铰链位移放大机构。这种机构既能减少不必要的传递误差、安装误差,又能降低加工难度,同时减小传感器的体积。在对位移放大机构的设计时,分析了位移放大机构的放大倍数和运动情况并对柔性铰链的参数进行了设计。同时还通过ANSYS 有限元仿真软件对位移放大机构进行有限元建模分析,优化了位移放大机构的结构及其参数。同时,利用ANSYS 对传感器电容的电场情况进行了仿真分析。为了减小边缘效应,对电容的极板进行了改进,增加了保护环。仿真比较了加保护环前后的电容电场的变化,优化了电容两极板的结构参数。最后,分析了位移放大机构对传感器的灵敏度、线性度等参数的影响,以实现对传感器的参数进一步优化设计。更多还原

【Abstract】 The structure scheme of the capacitive displacement sensor that tests temperaturestress of seamless railroad is described. Based on traditional measure technique andcalibrated length technique of rail, the sensor is designed in draft. The free rail and thefixed rail are installed by parallel. When the environmental temperature changes, thefixed rail can not flex because of the resistances of fasteners and rail bed. And thetemperature stress is produced. At the same time, the free rail can flex and change itslength by the release of rail’s temperature stress. Accordingly, the difference betweenthe instantaneous natural length of the free rail and the fixed rail, which is tested bythe capacitive displacement sensor, reflects the magnitude of temperature stress. In thetest method, the moving electrode is installed on the free rail and the stable electrodeis installed on the fixed rail. The displacement of the two electrodes is the differencebetween the instantaneous natural length of the free rail and the fixed rail. When theenvironmental temperature is changed, the length of fixed rail is not changed, but thefree rail can flex and its length is changed. The free rail pushes the moving electrode,and the distance between the electrodes is changed. As a result, the capacitance ischanged. Thereby, the temperature stress is tested through the change of thecapacitance.The temperature strain is only tens of microns in a convenience distance. Inorder to improve the sensor’s sensitivity and reduce the difficulty in circuit’s design,the displacement amplifier is designed which is double flexible parallel mechanism.The mechanism can reduce the transferring error, the installing error, and the sensor’svolume. With regard to the displacement amplifier’s design, on one hand, it’samplificatory multiple and the movement are analyzed, and the parameters of flexiblehinge are designed. On the other hand, the model of FEM for the structure of theflexible hinges amplifier (HIA) is set up, and the HIA is analyzed and optimized.The model of FEM for electric field is set up and analyzed. To decreaseinfluence by the field changes caused by the spacer, the electrode of capacitance isimproved by applying the guard electrodes. The electric field with guard electrodescompare with the electric field without guard electrodes. The parameters of thecapacitance are optimized.Finally, the affect of the sensor’s sensitivity and linearity by the HIA isanalyzed and the sensor is optimized.更多还原