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The term "Backlash" originated from gear engineering discipline. In JIS terminology, this word is described as: Play that exists between a pair of engaged gears' tooth surfaces. When described as a distance of an arc on the engagement pitch circle, it is called "Circumference Direction Backlash", when described as the shortest distance between two opposing tooth surfaces is called "Normal Line Backlash".
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| Generally, some play is required in machinery systems. Gears will not function if all back is eliminated. It is inevitable to have small back-play in any gear train in operation. Same can be said for Triangular and Trapezoidal Screw systems, and it would be difficult to hand-rotate without some "play". However, it is possible to eliminate this backlash in ball screw systems, making possible to ensure accurate positioning in reversing applications. |
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| Causes for ball screw backlash are: |
1) Axial clearance
2) Axial elastic deformation of nut
3) Elongation and contraction of screw shaft
4) Axial deformation due to tortional forces |
| The entire drive train mechanism must be taken in consideration when considering the subject of Backlash. |
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| There is a method of backlash reduction caused by axial clearance and deformation of the contacting surfaces. It is called "Preloading" and is applied during ball screw assembly. This "Preload" is not to be confused with applied load on the system, but should be understood as internally built-in load. |
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