BACKLASH IN GEARS :PROS AND CONS EXPLAINED

Backlash may be defined as a clearance between mating gear teeth.It is built into speed reducers to let the gears mesh without binding and to provide space for a film of lubricating oil between the teeth. This prevents overheating and tooth damage.

Why Backlash Is Important

If a set of gears were to have “zero” backlash, it would mean the gears have been absolutely perfectly designed and manufactured, with no lubricant between them, and no thermal expansion or retraction interfering with the system. This simply isn’t realistic, so all gear systems must be designed with backlash in mind—especially ones that require more precision and control.

On the other hand, the same clearance causes lost motion between reducer input and output shafts, making it difficult to achieve accurate positioning in equipment such as instruments, machine tools, and robots. For these applications the backlash must be optimum.

There are few basic ways to reduce or optimize backlash: precision gears and modified gears.

Precision gears

Variables such as manufacturing errors, mounting tolerances, and bearing play often increase the amount of backlash in a speed reducer. Precision speed reducers minimize such imperfections by incorporating close-tolerance parts. Typically, they combine hardened precision gears (up to AGMA quality 14), ABEC quality 5 bearings, and machined housings with close tolerances on bearing bores.

Modified designs

Gear designs can be modified in several ways to cut backlash. Some methods adjust the gears to a set tooth clearance during initial assembly. With this approach, backlash eventually increases due to wear, which requires readjustment. Other designs use springs to hold meshing gears at a constant backlash level throughout their service life. They're generally limited to light load applications, though.

Common design methods include short center distance, spring-loaded split gears, plastic fillers, tapered gears, preloaded gear trains, and dual path gear trains.