| The doctoral dissertation is concerned with theoretical investigation and 3D CAD/CAE simulation of globoid and cylindrical worm-gear drives. Four major contributions have been made: (1) theoretical investigation of globoid and cylindrical worm-gear drives; (2) a novel 3D modelling approach - Virtual Reality Machining (VRM), (3) 3D simulations of tooth contact analyses of the worm-gear drives, and (4) a feasible procedure for loaded multi-tooth contact analysis of the cylindrical worm-gear drive using the finite element method. Theoretical investigation has been carried out on two categories of worm-gear drives. A globoid worm-gear drive generally comprises a globoid worm and its generating gear. Two types of globoid worm-gear drives, a globoid worm meshing with an involute gear (GI) and a globoid worm meshing with a plane gear (GP), have been involved in this investigation. A novel cylindrical worm-gear drive, which comprises an involute cylindrical worm and an involute helical gear, has also been involved in this investigation. According to the spatial gear meshing theory, mathematical models of globoid and cylindrical worm-gear drives have been established. The general meshing equation, the meshing line equation, and the tooth surface equation have been derived. Furthermore, the feasibility of the cylindrical worm-gear drive has been originally proved via an analytical method. These worm-gear drives have their respective advantages, such as the globoid worm-gear drive with high-load capacity, good lubrication, and compact size; and the cylindrical worm-gear drive with point contact, simple manufacture, and precision transmission. These new developments will lay the foundation for further research into these special worm-gear drives. All 3D modelling methods can be classified as two kinds according to modelling procedure: direct modelling approach and indirect modelling approach. An novel VRM approach has been developed. 3D models of products can be produced by means of simulation of the actual machining process in a virtual reality environment. The VRM approach has many distinct advantages such as parametric and fast modelling, appropriate for optimum design, beneficial to manufacturing and assembly, and available for the state of art design. It is a significant progress in 3D modelling techniques and modem gear research fields. The 3D models of globoid worms (GI worm and GP worm) have been successfully built using the VRM approach. Since the tooth geometry is extremely complicated, 3D whole models of globoid worms have not been reported in literature. The virtual simulations of three types of worm-gear drives have been carried out. The characteristics of the worm- gear drives, such as tooth contact pattern, tooth contact region, lubrication condition, and engaged teeth, can be much more clearly displayed using their 3D assembly models than using the conventional 2D sketches. A feasible finite element modelling method for loaded multi-tooth contact analysis of the cylindrical worm-gear drive has been developed. The whole FE assembly model of the cylindrical worm-gear drive has been successfully built based on the 3D models transferred from Pro/Engineer into ANSYS via IGES interface. The contact pairs have been suitably selected to simulate the actual transmission. A general and reliable finite element analysis (FEA) procedure using the advanced surface-to-surface technique has been developed to predict tooth contact stresses, loaded tooth contact patterns, load distributions, and tooth deformations in ANSYS. The analysis results agree well with the predication of the theoretical investigation conducted previously. Using the technique and procedure developed in this research, researchers and engineers will be able to get substantial benefits from the loaded tooth contact analysis. |
