Calculation and influencing factors of backlash of planetary gearbox

Release Time：

2025-02-22

We know that for planetary gear reducers used in high-precision transmission applications, there are usually strict control requirements for their backlash. So, how is backlash defined, how is backlash calculated for planetary reducers, and what are the influencing factors?

Calculation and influencing factors of backlash of planetary gearbox
We know that for planetary gear reducers used in high-precision transmission applications, there are usually strict control requirements for their backlash. So, how is backlash defined, how is backlash calculated for planetary reducers, and what are the influencing factors?
1) Definition of backlash of planetary gearbox

The backlash of a planetary gearbox, also known as the return clearance, refers to the angular displacement of the gearbox's output or input when the gearbox rotates clockwise and counterclockwise while fixing the input or output end, producing a certain torque at the output or input end. It is generally expressed in degrees and is measured in arcmin, where 1 degree equals 60 arcmin.
Backlash is an important parameter of precision planetary gearboxes, and the lower the value, the higher the accuracy. Generally, high-precision types are defined within 3 arc minutes, and low precision types are defined above 15 arc minutes. The backlash has a significant impact on the performance and lifespan of the gearbox. If the backlash is too large, it will cause obvious relaxation during reverse rotation, affecting the positioning accuracy and motion stability of the gearbox. Conversely, if the backlash is too small, it will cause meshing interference or jamming, increasing the friction and wear of the gearbox, thereby reducing its lifespan.

3) Factors affecting the backlash of planetary gearboxes

According to the definition and calculation of backlash in planetary gearboxes mentioned above, the main influencing factors of backlash in planetary gearboxes are closely related to the influencing factors of backlash in gear pairs, mainly including the following three categories:
a、 The manufacturing errors of gears themselves, including pitch errors, tooth thickness tolerances, radial runout, helix deviation, etc. of each gear component in each planetary gear system;
b、 Manufacturing and installation errors related to gear components, including center distance error, ring gear installation error, sun gear installation error, planetary carrier installation error, planetary carrier pin hole position error, etc;
c、 Other influencing factors include bearing clearance, changes in operating temperature, and torsional deformation of shafts and gear components.
The impact of the above three factors on the backlash of the planetary gearbox decreases in order. Therefore, the main measures to improve the backlash of the planetary gearbox are: 1) improving the machining accuracy of the gears and reducing the designed meshing backlash of the gear pair; 2) Eliminate the spline clearance of planetary transmission connections at all levels; 3) Improve the machining position accuracy of planetary carrier pin holes and the positioning accuracy of gear ring installation, ensuring the accuracy of gear installation center distance; 4) Reduce the bearing clearance appropriately, such as applying appropriate preload force to tapered bearings to eliminate axial clearance.