Study On Theories And Automatic Programming System Of CNC Hobbing Non-Circular Gears

Non-circular gears are used to achieve variable gear ratio transmission as mechanical transmission parts, they have many unique advantages compared with traditional institutions that are used to achieve the same aim. But because their wide range, complicated calculate and design, and difficult processing, non-circular gears design and manufacturing technology are always hot and difficult in manufacturing. However, the development of numerical control technology opens a new way of processing non-circular gears. As we know, CNC hobbing is the most widely used as a processing gears method, but now, many theoretical issues in CNC hobbing non-circular gears has not been solved, so CNC hobbing has not been play its due role for peocessing non-circular gears. Because of this, theories and automatic programming system are studied in this paper, and the main research contents are as follows:According to principle of hobbing, spur and helical non-circular gears tooth profile forming, motion models of CNC hobbing spur and helical non-circular gears are established by using the intermediary spur tooling rack methord, the helical tooling rack metheord and helical gear meshing theory respectively. Taking oval gears as example, motion models are proved to be correct by computer simulation.Based on motion models, mathematical models of spur and helical non-circular gears processed by hobbing are also established by using conjugate surface theory and tooth profile meshing fundamental theorem.Variable ratio electronic gearbox must be used for motion controlling of machine tool in order to process non-circular gears. The principle, classification and performance requirements of variable ratio electronic gearbox are described, and feedforward fuzzy self-tuning PID control is used for variable ratio electronic gearbox control. After this, based on motion models, variable ratio electronic gearbox transmission schemes of hobbing spur and helical non-circular gears are designed by using electronic gear function module and pulse frequency synthesis module that have been researched independently.A cubic B-spline curve interpolation algorithm is proposed, and the algorithm of interpolation control theory is discussed. The interpolation algorithm is verified by an example, and the result shows that this algorithm can not only guarantee processing precision but also can ensure processing efficiency. Then, this interpolation algorithm is applied to CNC hobbing non-circular gears, and specific interpolation control process is provided.A parametric and graphical automatic programming system for hobbing non-circular gears is developed. This system can be achieved non-circular gears3D modeling, motion simulation and programs of CNC hobbing automatic generation. The components, development ideas of system are described, the development process of the major functional modules in this system, how to settle the key problem such as software interfaces processing, and how to establish computing and technology libraries are also discussed in this article.Lastly, the specific running process is introduced by taking a pair of oval gears as example. The result shows that the system has good interface and reliable operation. Then, using the NC program geberated by the automatic programming system, a pair of non-circular gears is processed using multi-functional complex CNC machine tool which has been self-developed, and this system is proved to be correct by the result of processing.