What is a Planetary Gear?

2020-07-01

A planetary gear (also known as epicyclic gear train) appears to be quite complex. It is certainly true that it takes a skilled gear engineer to master all of the intricate aspects of designing the planetary gear system. But if you are looking for a more basic understanding of planetary gears, you have come to the right place.

What is a Planetary Gear?

A planetary gear set consists of three types of gears including a sun gear, planet gears (also called satellite gears), and a ring gear. The sun gear is located at the center and transmits torque to the planet gears which are typically mounted on a moveable carrier. The strength of the planetary gearhead is usually determined by the size of the sun gear. Larger sun gears will allow for higher torque values. The planet gears orbit around the sun gear and mesh with an outer ring gear. Planetary gear systems can vary in complexity from very simple to intricate compound systems, depending on the application.

Why is it Called a Planetary Gear?

The planetary gear set (also named planetary gearhead) got its name because of how the different gears move together. In a planetary gearhead, we see a sun (solar) gear, ring gear, and two or more planet gears. Normally, the sun-gear is driven and thus move the planet gears locked in the planet carrier and form the output shaft. The ring gears have a fixed position with the outside world. This looks similar to our planetary solar system and that is where the name comes from.

In practice, we often speak from the perspective of the use of planetary gearhead for industrial automation. That is why we call the sun-gear the input shaft, the planet gears and carrier the output shaft and the ring gear the housing.

What are the Advantages of the Planetary Gear System?

√ Coaxial arrangement of the input shaft and output shaft

√ Load distribution to several planetary gears

√ Many gear ratio options due to the combination of several planet stages

√ Suitable as planetary switching gear due to fixing this or that part of the planetary gearhead

√ Favorable low noise

√ Suitability for a wide range of applications

Where is the Planetary Gearhead Usually Used (In the Transmission)?

Planetary gear systems can produce the torque needed because the load is shared among multiple planet gears. This arrangement also creates more contact surfaces and a larger contact area between the gears than a traditional parallel axis gear system. Because of this, the load is more evenly distributed. Therefore the gears are more resistant to damage.

The construction makes the Planetary Gearheads, in combination with ZHAOWEI DC micro motors, ideal for high torque, low speed and high-performance applications. In most cases, the gear train of the input stage is made of plastic to keep noise levels as low as possible at higher RPM‘s. Sometimes, powder metallurgy is also a kind of common technology that planetary gearheads often adopt. A metal input stage is also available for extreme loads. The gearhead is mounted to the motor with a threaded flange to render a solid fit.

Such a combination contributes to a wide range of applications like:

√ In a robot to increase the torque

√ In a printing press to reduce the speed of the rollers

√ For precise positioning

√ In a packaging machine for reproducible products

What are the purchase criteria for a planetary gearhead? That is difficult to answer because it is highly dependent on where the gearhead is used precisely. First of all, the primary specifications (eg.: torque, backlash, ratio) must be correct, but then the secondary (eg.: corrosion resistance, noise level, construction) and the tertiary (eg.: delivery time, price, global availability, service) are important.

More specifically, here are the main processes that you should pay attention to:

1) Choose shaft shape. There are D-type, circular, double flat, hexagon, pentagon, and square.

Then, choose suitable bearings, which are often divided into two types including porous bearing and rolling bearing.

2) Choose materials for satellite gears and sun gears in micro planetary gearheads. There are plastic gears, materials made by powder metallurgy, and hardware processing. ZHAOWEI has metal and plastic shells for them in micro planetary gearheads, suitable for any application that you need within reach.

3) The single-stage planetary gear can not meet the large planetary gear transmission ratio. Sometimes it needs 2-stage or 3-stage or even 4-stage to meet the requirements of the larger transmission ratio. As the number of planetary gears increases, the distribution of the load increases and therefore the torque that can be transmitted.

4) Choose a suitable kind of motor. ZHAOWEI supplies optional motors, such as brushed DC motors, DC brushless motors, stepper motors, and coreless motors, which can match with your micro planetary gearhead for better performance.

Note: As for more details (voltage, current, gear ratio, diameter torque, etc.), ZHAOWEI also provides related information as well as customized service for you.