Study On Mechanical Properties Of Precise Micro Motion Platform Considering Temperature Effect

Precision micro-motion stage was widely applied in biological engineering, medical sciences, micro-mechanical manufacturing, aerospace and other frontier fields. Micro-motion stage tends to work in temperature-varying environment, which cause the stage to produce thermal stress and thermal deformation, and decrease the precision. So the study on mechanical properties of a precision micro-motion stage considering temperature effects has important theoretical and practical significance. Considering temperature effects, the modelling, performance analysis and synthesis of micro-motion stage were carried out by using finite element method in this paper. The main content is listed as follows:(1) In order to reduce the temperature effects on micro-motion stage, the comparative analysis of temperature effects on four kinds of typical flexure hinge with straight-beam, circular, elliptic and parabolic section is carried out, so that we can choose reasonably the flexure hinge used to design compliant mechanisms. The flexure hinge is divided into two variable cross-section beam elements, and the initial strain caused by temperature change is accounted into. The principle of minimum potential energy is applied to derive the thermal load vector and stiffness matrix of four kinds flexure hinge, and the mass matrix is obtained by employing Lagrange equation. And the mechanical model of the flexure hinges is obtained. The comparative analysis of the precision, thermal stress and thermal vibration of the compliant four-link mechanism is carried out based on the finite element model of the flexure hinge. The analysis results showed that the thermal errors of circular hinge is largest, and parabolic one, elliptic and straight-beam is smallest; The sequence of thermal stress from large to small is circular, elliptic, parabolic and straight-beam flexure hinge; The thermal vibration resonant frequency of the straight-beam hinge is minimum, the circular and elliptic one is second, parabolic is maximum, and it illustrated that the straight-beam hinge is more susceptible to temperature changes. But the amplitude of the parabolic hinge at the resonant frequency is maximum, and the thermal vibration is larger.(2) In order to accurately analyze the influence of the temperature effect on the mechanical properties of micro-motion stage, the finite element method is applied to build its mechanical model. In order to validate the precision of the proposed mechanical model, the comparative analysis with results of ANSYS is carried out, and the difference range is 3.3%~11.3%. The results showed that the theoretical model is close to ANSYS, and the proposed model can accurately illustrate the static and dynamic properties. Thus it is effective for optimization design of micro-motion stage. The analysis of temperature effects on stage’s properties was carry out based on the model. The results showed that temperature change has important effect on precision of stage; it can reduce the thermal errors through choosing structure parameters properly; it produced thermal vibration under the impact of temperature effect; temperature change produced thermal stress. In a word, temperature effect on the stage can’t be neglected. It needs exercise optimal design based on the model and the analysis results in order to reduce the impact on the temperature effect of stage.(3) As a bridge micro-motion stage, the optimization of structure parameters and configuration design of the stage are presented to reduce temperature effects. First, the temperature effects are decreased from the perspective of optimizing the structure parameters. The optimization model was obtained by taking structure parameters which is sensitive to thermal error as the design variables, thermal error and maximum thermal stress as the object, the natural frequency as the constraint. The operation precision would be increased while the thermal stress was decreased by the structural parameters optimized design. The results show that the optimization model meets the constraints condition and the thermal error of stage decreased 44.35%, which indicated the effectiveness of the optimization model. Then, reducing the temperature effect from the perspective of designing the stage configuration, the symmetrical and complementary bridge mechanism were proposed to reduce temperature effects as the symmetry of the structure could offset temperature effects of each other. The results show that the symmetrical and complementary stage could reduce thermal error, and thermal error of the symmetrical stage was smaller comparing with the complementary stage at the same temperature change.(4) In order to achieve robust of one-dimensional micro-motion stage, using taguchi robust design method and taking the temperature change and the thermal expansion coefficient as the noise factor, the combination of structure parameters which made the performance fluctuation of the stage achieve least was obtained to reduce the effect of temperature change on the stage based on parameters design of static and dynamic performance. For static robust design, the mechanical model was established by using finite element method, and the best combination of control factor was obtained by the orthogonal design and the analysis of main effect. The results showed that the mean value of thermal error decreased 16.03%, its variance decreased 12.07% and the SNR increase 1.1%. Because the desired output of the stage can be varied from the input displacements during the course of the micro-operation, it is necessary to carry out the dynamic robust design. The dynamic SNR is used to reflect the fluctuation of output displacement under the effect of the temperature change and the thermal expansion coefficient, and the sensitivity between input displacement and the output displacement was characterized by the dynamic sensitivity. The best combination of structure parameters was obtained by the orthogonal design and the analysis of main effect. Comparing the mean and standard deviation of the output displacements before optimization and after optimization under the influence of the same noise factors, the results show that the SNR and sensitivity of the dynamic characteristic values are larger, that is to say, the mean of the optimized output displacement increases, and standard deviation becomes smaller, which indicated the feasibility of the design ideas.