Perhaps the most apparent is to improve precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound can be suffering from gear and housing components as well as lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the error of over-specifying the motor. Remember, the insight pinion on the planetary should be able deal with the motor’s result torque. What’s more, if you’re using a multi-stage gearhead, the output stage must be strong enough to soak up the developed torque. Obviously, using a more powerful motor than necessary will require a bigger and more costly gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, output low backlash planetary gearbox torque is definitely a linear function of current. So besides protecting the gearbox, current limiting also defends the motor 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 at the same time in mesh. Although you can’t really totally remove noise from this assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries fits the shape of electric motors. Thus the gearhead could be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are usually more costly than lighter duty types. However, for rapid acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead may be viewed as a mechanical springtime. The torsional deflection caused by the spring action adds to backlash, compounding the consequences of free shaft motion.
Servo-grade gearheads incorporate many 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 type of bearings supporting the output shaft depends upon the strain. High radial or axial loads generally necessitate rolling element bearings. Small planetaries can often manage with low-cost sleeve bearings or various other economical types with relatively low axial and radial load ability. For larger and servo-grade gearheads, heavy duty result shaft bearings are often required.
Like the majority of gears, planetaries make noise. And the faster they run, the louder they get.
Low-backlash planetary gears are also available in lower ratios. Although some types of gears are usually limited by about 50:1 or more, planetary gearheads lengthen from 3:1 (solitary stage) to 175:1 or more, depending on the number of stages.