Development Of Stiffness Surveying Instrument For Precise Elastic Elements In Electro-Hydraulic Servo Valve Based On Charge-Coupled Device

Electro-hydraulic servo valve is often used as control device in aerospace and navigation industries, where precise elastic elements are widely used as sensitive parts to obtain feedback signal by the stress deformation. Therefore, the stiffness parameters of the precise elastic elements are so directly related to the performance of control device or navigation as to be strictly controlled during production.Feedback stem and spring tube are commonly used elastic elements in electro-hydraulic servo valve. In this dissertation, the measurement principle and method of feedback stem and spring tube are analyzed, and a stiffness surveying instrument based on CCD (Charge-coupled Device) are developed.Firstly, the overall scheme is carried out based on the measurement principle analysis. A step motor controlled by computer pushes a parallel beam type transducer to load the measured part in this system, which makes the transducer the loading element and the measuring element at the same time. The force signal acquired would be transferred to the computer after processed by the circuit through a HY-6120 digital I/O board. Changing images of the measured part are acquired by the CCD camera and transferred to the computer for processing to get the displacement value. Then the computer calculates the stiffness value based on the force signal and displacement value gained before and display it on the screen. Meanwhile, the stiffness curve would be drawn according to the result data.Secondly, the mechanical structure of this system is designed, which mainly includes the clamping structure, the loading structure, the location and adjustment structure for CCD and the light source, and other auxiliary functions structure. The mechanical structure is the foundation of the system. Moreover, it is highly required due to the sophisticated dimensions of the measured parts, which makes this part the key to the system.Thirdly, the control circuit and the VC++ program are designed on the basis of the step motor and the transducer selected before. The program consists of six modules, which are the step motor drive control module, the force signal acquisition and processing module, the CCD drive and image acquisition module, the image processing module, the stiffness value calculation and drawing module, and the document processing module. Among those modules, the image processing module is the most important one as it directly related to the final measuring accuracy.Finally, two types of feedback stems and one type of spring tube are measured as samples after debugging of the control circuit and program based on the mechanical structure. According to the analysis of the experimental results, adjustment and improvement for the system are taken, and suggestion for the future work is put forward.