Michalec, a British scholar, defines a high-quality gear with a tolerance of 0.0254-0.002 54 mm (0.001-0.0001 inch) as a precision gear. Precision gears are widely used in industry and national defense, especially in instruments, automatic control devices and high-speed devices, such as servo mechanisms and machine tools. In order to achieve this goal, it is necessary to consider the transmission backlash of gears. This parameter is an important standard to evaluate the transmission accuracy of gears.

The transmission backlash indicates that the gear is not consistent with the theoretical working state in the actual transmission process, that is to say, there is error in the actual transmission of the gear, which is also the main source of the gear position error. As the name implies, backlash is a pair of gears in the process of meshing transmission, which has a great impact on the dynamic response performance of gears.

At present, the demand for precision gears in China’s market is growing explosively, but the domestic gear production and manufacturing level is still far behind the developed countries such as Europe and the United States. There are only a few domestic manufacturers that can manufacture precision gears on a large scale, which leads to a large proportion of precision gears in China relying on imports. Therefore, it is very important to reduce the transmission error of precision gear to improve the gear manufacturing level and reduce the cost.

(1) Based on the analysis of the source and meshing situation of the transmission backlash, and through the approximate vertical relationship between the meshing line and the tooth profile, the theoretical calculation formula of the transmission backlash of the planetary gear is obtained, and the error between the theoretical value and the experimental value of the transmission backlash is 3.3%.

(2) The calculated result is the maximum value of the backlash of the gear drive, but in fact, it is impractical for each tolerance to reach the maximum value for the free tolerance. For parts with more free tolerance, the calculated results will be different from the measured results, so it is necessary to use mathematical statistics to calculate the back difference.

(3) In order to reduce the transmission return difference, the spring loaded scissor gear can be used, or it can be adjusted properly by skilled workers during assembly.