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THE PLANETARY GEAR UNIT
The key advantages of epicyclic, or planetary, technology are: competitive price/performance ratio, compactness, modular design and reliability, all achieved even in extreme situations. This makes the planetary train a suitable alternative to conventional gear pairs for many applications in a variety of industrial sectors.
Operating principle of planetary reduction gear unit with fixed ring gear [industrial and mobile applications]:
Input drive is applied to a central or sun gear (1) by which three or more pinions, or planet gears (2), are set in rotation; these in turn rotate in mesh with the internal teeth of a fixed annulus or ring gear (3). The shafts of the planet gears (4), mounted to a planet carrier (5), are translated along a circumferential trajectory and made thus to revolve around the sun gear. The result is that the planet carrier (5), to which the output assembly is mounted (shaft, bearings, seals etc.), rotates at a lower speed than that of the sun gear (1).
Operating principle of planetary reduction gear unit with rotating ring gear (or gearcase) [mobile applications]:
Input drive is applied to a central or sun gear (1) by which three or more pinions, or planet gears (2), are set in rotation. The shafts of the planet gears (4) are mounted to a planet carrier (5), which is fixed. The rotation of the planet gears (2) is transmitted to a movable annulus or ring gear (3). As a result, the ring gear (3) rotates at a lower speed than that of the sun gear (1).
WHAT ARE THE ADVANTAGES OF THE PLANETARY GEAR UNIT?
WEIGHT
A planetary gearbox weighs about 2/3 less than a correspondingly rated traditional gear unit, which means that supporting structures can be made lighter, and maintenance is made easier in the event that the unit needs to be removed.
DIMENSIONS
The planetary gearbox is significantly more compact, and therefore easier to install, than traditional units (worm, coaxial, parallel/right angle shafts).
COST
Thanks to high volume production of planetary trains, substantial economies of scale are obtainable, with the result that prices are highly competitive when compared to those of correspondingly rated traditional gear units.
HIGH TORQUE
The planetary gear train is characterized by multiple points of meshing contact, and with loads spread across at least three planet gears, high torques can be transmitted even with a unit of relatively compact dimensions.
REVERSIBILITY
Planetary gearboxes function in the same way and deliver the same performance in both directions of rotation. This is a notable advantage in the case of machines that alternate regularly between clockwise and anticlockwise rotation.
HIGH TRANSMISSION RATIOS
Using standard planetary reduction stages, units with transmission ratios of up to 3000 can be supplied.
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