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Gearhead offers `lowest possible` backlash

19 February, 2011

The Swiss manufacturer maxon motor has produced a planetary gearhead that, it claims, comes as close to exhibiting zero backlash as is technically feasible. The 32mm-diameter GP 32 BZ gearhead is aimed at applications demanding highly accurate positioning, such as precision assembly and dosing systems.

Designing low-backlash gears is usually either costly, or it results in reduced efficiencies – or often a combination of the two. maxon doesn’t call its new gearhead “backlash-free”, but says that it offers the lowest possible backlash, with an average value of between 0.15 and 0.5 degrees.

It achieves this by mounting the planetary wheels of the gearhead’s last stage in pairs on their shaft. They are loaded in a radial direction by half the pitch and are linked to each other by torsion springs. The wheels are mounted slightly askew from each other, so that the leading tooth flank of one of the planetary wheels is in contact with one flank of the hollow wheel, while the trailing tooth flank of the second planetary wheel touches the other hollow wheel’s flank, thus almost eliminating the backlash and providing extremely smooth operation.

The diagram (above) depicts the output stage of the low-backlash planetary gearhead, highlighting (1) the planetary carrier; (2) the axis; (3) a pair of planetary wheels; and (4) the torsion spring that connects the wheels.

During high-load phases – when loads exceed the tension force of the preloaded planetary wheel pairs – backlash increases slightly. But as the load decreases, the preload force of the planetary wheels comes into play again, minimising the backlash. This results in the gearhead operating with “insignificantly low” backlash under high loads, and returning to backlash-reduced operation automatically once below the defined torque limit. This behaviour is maintained for the life of the gearhead, with the backlash tending to diminish over time.

The gearhead can deliver a maximum continuous torque of 0.75–4.5mNm and offers a choice of one to three stages of reduction, providing ratios from 3.7:1 to 236:1. It has a claimed efficiency of up to 90%. The output shaft is designed to carry high loads in both axial and radial directions.

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