What The Tech: What is a plan­e­tary gear and how does it work?

A gearbox, or ‘trans­mis­sion’, is the link between the motor and the appli­ca­tion. Its task is to generate a higher torque on the appli­ca­tions, reduce the speed of the motor, increase posi­tioning accu­racy, and compen­sate for mass inertia. A plan­e­tary gear has a partic­u­larly high power density for this purpose.

The plan­e­tary wheels are used to transmit power, and the inter­nally toothed ring gear limits their orbit. A planet carrier, which is connected to all planets, conveys the power as a down­force.
The deci­sive factor here is the gear reduc­tion ratio “i” – in other words, the trans­la­tion into the slow speed. It repre­sents the ratio of the speed at the input to the speed at the output and is deter­mined by the ratio of the ring gear to the sun gear. In single-stage trans­mis­sions, a gear reduc­tion ratio of three to ten is common. Higher gear reduc­tion ratios are also possible depending on the trans­mis­sion. If the right trans­mis­sion is selected for an appli­ca­tion, the motor can even be smaller – saving costs in terms of procure­ment and oper­a­tion.

Plan­e­tary gears also enable very precise posi­tioning, which is why they are used in barriers and access control systems in subways and airports, for example. In contrast to simpler solu­tions, low-back­lash plan­e­tary gears have lower forces acting on the gear wheels, since the torque is distrib­uted along the gear wheels over a large contact area. This means that the design can be more compact, makes the plan­e­tary gear more durable, and enables low-noise oper­a­tion with no break in the fric­tional connec­tion. Thanks to its seam­less design, the trans­mis­sion can be used in the hygienic design zone in the food and phar­ma­ceu­tical indus­tries. Or in other areas of indus­trial drive tech­nology – such as intral­o­gis­tics and shuttle drives. There are different types depending on the require­ments – whether perfor­mance, robust­ness and dura­bility, or smooth oper­a­tion is needed.