Perhaps the most apparent is to increase precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the guts distance of the tooth mesh. Sound can be suffering from gear and housing components in addition to lubricants. In general, expect to spend more for quieter, smoother gears.
Don’t make the mistake of over-specifying the motor. Remember, the insight pinion on the planetary should be able handle the motor’s result torque. Also, if you’re using a multi-stage gearhead, the output stage should be strong enough to absorb the developed torque. Certainly, using a better motor than necessary will require a larger and more costly gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is certainly a linear function of current. So besides safeguarding the gearbox, current limiting also protects the electric 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 concurrently in mesh. Although you can’t really totally get rid of noise from this assembly, there are several ways to reduce it.
As an ancillary benefit, the geometry of planetaries fits the form of electric motors. Hence 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 speedy acceleration and deceleration, a servo-grade gearhead may be the only sensible choice. In such applications, the gearhead could be viewed as a mechanical spring. The torsional deflection caused by the spring action adds to backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate a number of construction features to reduce torsional stress and deflection. Among the more prevalent are large diameter result shafts and beefed up support for satellite-equipment shafts. Stiff or “rigid” gearheads tend to be the most costly of planetaries.
The type of bearings supporting the output shaft depends on the load. High radial or axial loads usually necessitate rolling component bearings. Small planetaries could manage with low-price low backlash planetary gearbox sleeve bearings or other economical types with relatively low axial and radial load capability. For bigger and servo-grade gearheads, heavy duty result shaft bearings are often required.
Like most gears, planetaries make sound. And the quicker they run, the louder they get.
Low-backlash planetary gears are also available in lower ratios. Although some types of gears are usually limited to about 50:1 or more, planetary gearheads prolong from 3:1 (single stage) to 175:1 or more, depending on the amount of stages.