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Analysis of Flexspline Stress and Tooth Wear in Harmonic Gear Drive

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Tutor: DiWenJie
School: Harbin Institute of Technology
Course: Mechanical Design and Theory
Keywords: Harmonic gear drive,Flexspline,FEM,Tooth wear,Discretization
CLC: TH132.43
Type: Master's thesis
Year:  2008
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Abstract:
Because harmonic gear drive have many merits such as big ratio of transmission, small volume and light weight, high drive accuracy, little return difference and so on, it has been applied successfully to many fields including aerospace, atomic reactor and high-energy accelerator, radar system, robot, military field, optical instrument and general machine. Though almost all fields involved harmonic gear drive have been studied by many domestic and foreign scholars, a lot of works still require to do. Such as the problem of fatigue strength and wear of gear teeth which mainly influence the life of harmonic drive is one of the most important research in harmonic gear drive. So it is very significant to study harmonic gear drive. This article mainly study the fatigue strength and the wear of gear teeth.The theory and characteristic of harmonic gear is described in this article at first. Based on the experimental result the stress and displacement of flexspline are analyzed. This is the basic theory in studying of flexspline. The displacement of flexspline is large and this is a large displacement of geometry non-linear problem. Then, according to achievements that have been achieved and shortages on study of harmonic drive at the present time, by applying elastic theory and non-linear finite element method, a 3-D model of flexspline is established. The model is analyzed by finite element contact method in order to gain stress of flexspline. The load on flexspline tooth is calculated. The stress of flexspline under load is analyzed. At last, on the basis of the model, some geometrical parameters of flexspline are analyzed and the recommendatory values of these parameters are given based on the changes of flexspline’s stress. This can help the designers a lot to design the flexspline.This article will study the wear of tooth contour face by boundary element method. A wear model is established after studying mesh character and, on the basis of the Archard formula, a formula, by which the contact stress, the wear coefficient and the sliding distance are considered, is derived for determining the theoretical wear of the flexible tooth. When calculating the wear, the tooth contour is discretized into a series of points and by calculating the wear at the points the whole tooth contour after wearing can be obtained. The stress and the sliding distance can be obtained by the geometrical characteristic of the involute at the first meshing process. The coordinates of the points after wearing can be calculated with the vertical wear value and the original coordinates. With the coordinates after wearing and cubic polynomial spline function the tooth contour function after wearing can be obtained. Then, next step of wear will be calculated with the stress and sliding distance which has been modified according to the tooth contour function after wearing. The modifying times of contour line will be decided by calculation precision. This function can be used to calculate the wear value after any work time and forecast the work life according to the maximal permitted wear value.
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