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 is also 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 input pinion on the planetary should be able deal with the motor’s output torque. What’s more, if you’re using a multi-stage gearhead, the result stage should be strong enough to soak up the developed torque. Certainly, using a better motor than necessary will require a bigger and more expensive gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, result torque is definitely a linear function of current. Therefore besides safeguarding the gearbox, current limiting also defends 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 you can’t really totally get rid of noise from such an assembly, there are several methods to reduce it.
As an ancillary benefit, the geometry of planetaries matches the form of electric motors. Thus the gearhead can 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 quick acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead could be viewed as a mechanical springtime. The torsional deflection caused by the spring action increases backlash, compounding the consequences of free shaft movement.
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-gear shafts. Stiff or “rigid” gearheads tend to be the costliest of planetaries.
The kind of bearings supporting the output shaft depends on the strain. High radial or axial loads generally necessitate rolling element bearings. Small planetaries could get by with low-price sleeve bearings or additional 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 quicker they operate, the louder they obtain.
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