| The gear transmission is the most common transmission form in the machinery transmission. The cylindrical gear transmission with a fixed-transmission ratio has been used widely among them. In some fields, such as textile industry and light industry, some mechanisms that can achieve variable transmission ratios will be used .Because of the special request to the techniques. the circle gear hardly meet the request of this kind of transmission while noncircular gear transmission can realize present request of movement with its special characteristic in kinematics and geometry. But it were not used widely in industry. It is mainly because designing and machining non-circular gear is very difficult. If computer science and numerical control technology will be applied in designing and machining non-circular gears, making non-circular gears will be easy. So the non-circular gears get the increasingly extensive application in all kinds of machinery.This paper mainly researches ellipse gears because non-circular gear has many types . In the detailed elementary theory foundation, it gives computer-aided design of pitch circle of non-circular gears in order to verify if parameter of designing to be rationality or not . At present the main non-circular gear's processing method is gear hobbing. To the gear hobbing, this paper offers three methods of manufacturing and their merits and demerits through the examples.This paper is divided into five parts-prefaces, the basis theory of non-circular, CAD of non-circular, numerical control manufacturing methods of non-circular and summarization.The first part of this paper summarizes the development history ofnon-circular gears, introduces the newest development of computer science and numerical control technology applied in non-circular gears and methods of non-circle gear manufacturing.The second part introduces the basic theory of non-circle gear designing and manufacturing in detail ;specially expatiates the compute methods of pitch circles of non-circular gears and judgment whether the pitch curve is closed ;the compute method of the pitch circle's radius and the judgment whether the pitch circle is convex; whether the pressure angle is right. Some common kinds of pitch circles are also introduced. Then the methods of forming tooth profile are analyzed .The content will provide theoretical foundation for CAD.The third part analyses program of pitch circle creation of non-circle gear and presents the designing and judgment program when giving transmission ratio function of non-circular gear, offers examples of CAD and program flow chart and idea of profile circle creation of non-circle gear.In the forth part,the principle of processing non-circular gears by CNC hobbling machine tools is discussed, its mathematical model is derived. The principle and disadvantages of traditional interpolation methods such as equivalent arc length and equivalent angle method are introduced. Based on these, the new interpolation method that pitch circle is fitted by cubic spline is proposed. This part researches its interpolation principle and the pre-processing and the algorithm of real-time interpolation. It provides examples of using pitch circle's tangent to envelope pitch circle .Besides, it also provides examples that pitch circle is fitted by equivalent arc length method and cubic spline method It points out that the cubic spline method could well guarantee the machining quality, efficiency and stability.The last part is the summary of this paper. It sums up the result of this paper and point out the shortage and subsequent research content.
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