Precise elastic parts are widely used as sensitive parts to gain feedback signals in the controlling instrument such as electro-hydraulic servo valve or the navigation system such as flexibleness gyro in the field of astronavigation, navigation and aviation. Their stiffness parameters directly correlated with the performances of corresponding system. Therefore, not only have a rather high standard been set for dimensional precision and geometrical precision of them, but also certain demands are made against theirs stiffness characteristic. Due to their complicated geometry, along with machining errors and changes of materials characteristic, it is impossible to gain the accurate values of the stiffness by calculation. So, measurement is the only way to assure the stiffness requirement in production. At present, as the production level is advanced with the technology of astronavigation and continuous development of aviation, higher accuracy and efficiency in measurement are demanded to meet them.Therefore, studies on the stiffness measuring of spring tubes, typical plastic parts, is of great importance in enhancing strength of national defense. This dissertation firstly summarizes the development of stiffness-measuring instrument for spring tubes, and sums up the current research status and problems in the stiffness measurement. In order to expand the theory research on it, one stiffness-measuring system is developed successfully according to the design index of the spring tubes, which can automatically load and output stiffness curve by multi-points measurement. Then one new method for deleting gross error based on Grey System Theory is proposed in experiment data processing to improve the measuring accuracy. Technology of data accumulation in GST is used to weaken the randomness of measured data and enhance the trend item to find out the data regularity. Experiments prove that the proposed method is especially effective when the testing data are few or no statistical laws.Secondly, in order to research on the poor accuracy in stiffness measurement of the stiffer spring tubes, measuring principle is presented and error sources in the measuring system are analyzed. In the measuring device, bending deformation of all parts and contact deformation between parts joined together are key factors affected the measuring accuracy. So relation between the theoretical deformation of the tubes and the detecting deformation is set up based on homogeneous coordinate transformation and vector chain method. One model for errors compensation is obtained for improving measuring accuracy. Contact deformation between the measuring rod and tube is the most critical factor affecting the measurement accuracy. So, one contact model and corresponding conformal contact equation are set up by considering the surface roughness and the contact characteristic. Numerical method is adopted to solve the contact model.Thirdly, one new method is proposed to measure the stiffness of the stiffer spring tubes, in which special clamp are designed for the directly measuring of the angular deformation of the spring tubes. In the new measuring device, the bending deformation and contact deformation occurred before can be avoided and the repeatability accuracy can be improved evidently, which is proved by error analysis for new device and experiments.Finally,lots of experimental studies on stiffness measurement of spring tubes are carried out. The results show that contact deformation affects the measuring accuracy seriously, the bending deformation of the foundation plate is the second factor and other deformation can be ignored. On the other hand, the experimental results are also show that as the values increase errors caused by deformation will wicked. By the experiments of comparison of two measuring method, one conclusion can be drawn, which is that for stiffer spring tubes new method is a good choice to obtain high accuracy, but there are little difference for non-stiffer ones. Measuring efficiency and stability can be improved by distributing proper method for different tubes, which Lays the groundwork for mass production of this kind of elastic parts. |