Wednesday - 01/02/2017 18:57
Torque multiplication: Gearheads provide a mechanical advantage when mounted to the motor output shaft.
The number of gears, and the number of teeth on each, create a mechanical advantage defined by a ratio. If a motor generates 100 lb-in. of torque, attaching a 5:1 gearhead generates output torque approaching 500lb-in. depending on gearhead efficiency.
Speed reduction: Gearheads are often called gear reducers because most increase output torque while decreasing output speed. A motor running at 1,000 rpm fitted with a 5:1 ratio gearhead outputs 200 rpm. This speed reduction improves system performance because many motors do not operate efficiently at low rpm.
Consider a stone-grinding mechanism that must run at 15rpm. At this speed, motor cogging makes grindingwheel rotation inconsistent. The variable resistance of the stone being ground also renders wheel rotation unpredictable.
In contrast, fitting a 100:1 gearhead to the motor lets the latter run at 1,500 rpm. The motor-gear-head combination provides more-consistent output force and smooth wheel rotation despite friction and load variations.
Inertia matching: Over the past 20 years, servomotor manufacturers have introduced lightweight materials, dense copper windings, and high-energy magnets for motors that generate more torque for a given frame size. While beneficial, this trend has increased the risk of inertial mismatches between servomotors and the loads they control.
Should load inertia significantly exceed that of the motor, it causes excessive overshoot or increased settling times — both of which decrease production line throughput. On the other hand, a motor too large for an application has a high initial cost and consumes more power to accelerate its own inertia.
Here, a gearhead can help match motor inertia to load inertia, resulting in a more-responsive system. The motor experiences reflected inertia equal to the load inertia divided by the square of the gearhead ratio. Rapid startand- stop applications benefit most from wellmatched motor and load inertias.
Cost savings: Using a gearhead to multiply torque, reduce speed, and match inertia also helps cut system cost by permitting smaller motors and drives. Consider an application requiring 200lb-in. at 300rpm.
Driving this load with a servomotor alone (assuming industry-standard performance characteristics) necessitates a 142-mm frame size and a drive supplying 30A continuous.
Such a system costs about ,000. In contrast, including a gearhead cuts motor and gearhead frame size to 90mm — and the resulting mechanical advantage permits a smaller drive as well. Such a system costs about ,300.

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