Perhaps the most apparent is to improve precision, which is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the guts distance of the tooth mesh. Sound is also affected by gear and housing materials and also lubricants. In general, expect to spend more for quieter, smoother gears.
Don’t make the mistake of over-specifying the motor. Remember, the input pinion on the planetary must be able manage the motor’s result torque. What’s more, if you’re utilizing a multi-stage gearhead, the result stage must be strong enough to absorb the developed torque. Obviously, using a better motor than required will require a bigger and more expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, result torque is definitely a linear function of current. Therefore besides protecting the gearbox, current limiting also shields 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 eliminate noise from this assembly, there are several methods to reduce it.
As an ancillary benefit, the geometry of planetaries fits the form of electric motors. Therefore the gearhead could be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are usually more expensive than lighter duty types. However, for speedy acceleration and deceleration, a servo-grade gearhead may be the only sensible choice. In such applications, the gearhead may be viewed as a mechanical spring. The torsional deflection resulting from the spring action increases backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate many construction features to reduce torsional stress and deflection. Among the more prevalent are large diameter output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads have a tendency to be the costliest of planetaries.
The kind of bearings supporting the output shaft depends on the load. High radial or axial loads generally necessitate rolling component bearings. Small planetaries could manage with low-cost sleeve bearings or other economical types with fairly low axial and radial load ability. For larger and servo-grade gearheads, heavy duty output shaft bearings are often required.
Like most gears, planetaries make noise. And the faster they operate, the louder they get.
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