Comments:
A Planetary Gearbox is a set of gears, shafts, and bearings that are enclosed in
a housing and are arranged in a way that resemble a solar system, with one or more
planet gears orbiting around a sun gear. Such gearboxes are known as speed reducers.
They convert input speed (typically provided by an electric motor as shown above)
into a lower output speed while correspondingly creating higher torque. In other
words, gear-boxes reduce RPM (revolutions per minute), turning it into power for
use in low-RPM high-torque applications. Gearboxes come in different arrangements
including planetary (as shown), bevel, cycloid, helical, harmonic, spur, and worm.
Larger planetary gearboxes exist for industrial processes, providing output torque
in excess of 6,000,000 pounds per square inch. The input power to the illustrated
planetary gearboxes comes from a small electric motor (as shown).
How a Planetary Gearbox works
The planetary system has 3 main components: a central sun gear, a planet carrier
(carrying one or more planet gears - 3 on each of the four stages in this example)
, and an annulus (an outer ring). The central sun gear is orbited by planet gears.
The planet gears are meshed with the sun gear. An outer ring (the annulus) has teeth
facing inward that also mesh with the planet gears.
There are several configurations for planetary systems. Typical configurations require
that out of the 3 components: one is the input, one is the output, and one is stationary.
For example, one configuration is where the sun gear is the input , the annulus is
the output, and the planet carrier is stationary. In this configuration, the input
shaft rotates the sun gear. The planet gears rotate on their own axes, simultaneously
applying a torque to the rotating planet carrier, that in turn applies torque to
the output shaft (which in this case is the annulus).
The rate at which the gears rotate (gear ratio) is determined by the number of teeth
in each gear. The torque (power output) is determined by both the number of teeth
and by which component in the planetary system is stationary.
The advantages of a Planetary Gearbox
The planetary gearbox arrangement is an ingenious engineering design that offers
many advantages over traditional gearbox arrangements. One advantage is its unique
combination of both compactness and outstanding power transmission efficiencies.
Typical efficiency losses in a planetary gearbox arrangement is only 3% per stage.
This type of efficiency ensures that a high proportion of the energy being input
into the gearbox is multiplied and transmitted into torque, rather than being wasted
on mechanical losses inside the gearbox.
Another advantage of the planetary gearbox arrangement is load distribution. Because
the load being transmitted is shared between multiple planets, torque capability
is greatly increased. The more planets in the system, the greater load ability and
the higher the torque density.
The planetary gearbox arrangement also creates greater stability (it's a balanced
system) and increased rotational stiffness.
Possible disadvantages to the planetary arrangement include design complexity and
accessibility issues.
Artwork comments from Griff
This private illustration project took a total of 3 days to complete. Applications
used: tS7.6, GWai Parallax 2.0, GWai Specular, Adobe Photoshop CS4 and various plug-ins,
Adobe illustrator CS4, Adobe Fireworks CS4.
