Non Circular Gears

Abstract- In most of the industries, use of circular gears is much restricted due to high size to surface areas ratio. The necessity of developing and using non-circular gears becomes prominent and even more profitable. Due to advanced manufacturing processes, the costs of production of such non-circular gears have also proven to be advantageous. The non-circular gears are of various shapes viz. square, elliptical, triangular, etc. Such non-circular gears increase the surface area to a much larger extent, which results in more power transmission and maximum work output, hence found in many industrial applications. Some of the common requirements handled by non-circular gears include converting a constant input speed into a variable output speed,

Litvin who had developed the enveloping theory. The enveloping theory was mainly based on obtaining tooth surface as the envelope of the family of tool surfaces and the main features were as following: - the noncircular gear could be manufactured with the same tools as that used for manufacturing of circular ones; the conjugated tooth shape could be obtained by the imaginary rolling of the tool centrode over the given gear, considering a proper kinematics. The generation of the non circular gears is shown in fig. 2, in which centrodes of non circular gears 1 and 2 are meshing with the rack cutter 3 as shown. The rack cutter rolls on the centrode represented by the straight line t-t ie; a common tangent to centrodes 1 and 2 and also rolls over the two centrodes. The Rack cutter translates along the common tangent t-t and also rotates about its instantaneous center of rotation I. Accordingly the tooth surfaces of the two gears are in mesh with the rack cutter at the same time, and the two gears have conjugated

Many scientists have focused their attention on finding new manufacturing methods, on improving the existing models and finding solutions for incorporating noncircular gears into various mechanisms.

The first step in non-circular gear generation is the design of conjugated centrodes; few approaches, generally based on rolling theory, are mentioned in the literature. The real challenge has been proved to be the further step, i.e. the generation of the tooth profile on various centrode shapes. Methods such as enveloping theory, analytical developments and virtual gear manufacture have been developed, bearing in mind the basic condition – avoidance of undercutting.

The non-circular gear manufacture was developed by copying or rolling, using special designed equipment and kinematics. Electron discharge machining and rapid prototyping are also
Technologies mentioned in the references. The increased potential in non-circular gear design and manufacture explains the relatively new and continuous researches on these non-conventional gears