Perhaps the most obvious is to improve precision, which is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound is also affected by gear and housing components along with lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the error of over-specifying the electric motor. Remember, the input pinion on the planetary should be able handle the motor’s output torque. What’s more, if you’re using a multi-stage gearhead, the output stage should be strong enough to absorb the developed torque. Obviously, using a more powerful motor than necessary will require a larger and more expensive gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, result torque is certainly a linear function of current. So besides protecting the gearbox, current limiting also protects the engine and drive by clipping peak torque, which may be from 2.5 to 3.5 times continuous torque.
In each planetary stage, five gears are simultaneously in mesh. Although it’s impossible to totally get rid of noise from this assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Therefore the gearhead can be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are generally more costly than lighter duty types. However, for rapid acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In this kind of applications, the gearhead could be seen as a mechanical springtime. The torsional deflection resulting from the spring action increases backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate several construction features to minimize torsional stress and deflection. Among the more common are large diameter output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads tend to be the most costly of planetaries.
The kind of bearings supporting the output shaft depends upon the strain. High radial or axial loads generally necessitate rolling component bearings. Small planetaries could get by with low-cost sleeve bearings or various other economical types with fairly low axial and radial load capacity. For larger and servo-grade gearheads, heavy duty result shaft bearings are often required.
Like the majority of gears, planetaries make sound. And the faster they run, the louder they obtain.
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