Cycloidal Sense

When choosing speed reducers, torque is what really matters. Compared to conventional helical gear reducers, cycloid discs are a said to provide a major improvement in tooth dynamics. The cycloidal design allows torque-transmitting parts to roll, not grind. And since cycloidal drives have no teeth, the problems often associated with toothed gears are eliminated.

The primary cause of wear, tooth breakage and catastrophic failure in helical gearboxes is usually the high-speed pinion. Cycloidal drives do not have a high-speed pinion or gear teeth. They do not operate in shear, but rather in compression.

In addition to not having gear teeth, cycloid drives have two-thirds of their reduction components in contact at all times. The pressure is distributed throughout these contact points and generates a smooth and efficient operation that eliminates downtime caused by tooth failure.

Conventional helical gears are less efficient than cycloid drives because of the bearing rolling friction, gear mesh friction, seal drag, churning of lubrication and the winding up of rotating components. With all this friction, conventional gear drives experience thermal limitations that require stopping operations to allow them to cool down. In comparison, the thermal ratings of cycloid drives exceed their mechanical capabilities.

The main components of the cycloidal drive are: the eccentric cam, the internally flanged output shaft, the cycloidal disc and the ring gear housing. These components operate so uniquely that they are able to not only withstand high shock loads, but keep the operation smooth and steady in shock conditions.

This type of gearing also is ideal for severe reversing and frequent stop-start operations and shock-load applications such as conveying and food processing.

How it works

As the eccentric (high-speed shaft) rotates, it rolls the cycloid discs around the internal circumference of the stationary ring gear. The resulting action is similar to that of a wheel rolling along the inside of a ring. As the wheel (cycloid discs) travels in a clockwise path around the ring (ring gear), the wheel turns in a counter-clockwise direction around its own axis.

In the reducer, the lobes (rather than teeth) of the cycloid discs engage successively with the pins of the fixed ring gear, thus providing a reverse rotation at a reduced speed.

For each complete revolution of the high-speed shaft, the cycloid discs advance a distance of one lobe in the reverse direction. Typically, there is one less lobe per cycloid disc than there are pins in the fixed ring gear. The reduction ratio of a reducer is equal to the number of lobes in each disc.

The movement of the cycloid discs is transmitted to the slow-speed shaft by the projection of pins through the bores of the discs. This two-disc system is used to increase torque capacities and offer a smooth, vibration-less drive.

Size for size, cycloidal speed reducers deliver substantially more torque than conventional speed reducers, making it possible to select a smaller, lower-cost reducer for almost any application. Because all contact between the torque-transmitting components is of a rolling nature rather than grinding or a sliding friction, cycloidal drives withstand an exceptionally long life while exhibiting minimal wear.

Selecting the wrong speed reducer may lead to failure or inefficiencies that can then lead to costly equipment and production downtime. If you are considering alternatives to conventional speed reducers, it is important to choose a gear mechanism that is optimal for each particular application.

Stefanie Burns is with the marketing department of Sumitomo Drive Technologies.

Cycloidal gearing

* Many teeth share the shock of overload.

* All torque-transmitting parts roll, not grind.

Conventional helical gearing

* Torque-transmitting parts grind.

* 1 or 2 teeth absorb the entire shock of overload.