Types Of Cycloid Gears

Gearboxes with involute toothing are used in general in mechanical engineering. A disadvantage of this type of toothing is the sliding friction between the teeth. If you pair the teeth with a roller, we recommend the cycloid toothing, which in this case achieves better efficiency and has less wear. In addition, it can usually be manufactured with little or no backlash. Helical gear units with parallel axes and coaxial eccentric gear units are possible.

A distinction can be made between the following designs:

• Type A1: classic grisson
• Type A2: Grisson coaxial classic multiple
• Type A3: Grisson coaxial, single row, multiple
• Type B1: Classic cycloid eccentric gear
• Type B2: Cycloid external eccentric gear
• Type C1: Compur gearbox
• Type C2: Compur external gear
• Type D1: Cycloid Akbar gear
• Type D2: Cycloid Akbar external gear
• Type E1: reciprocally built cycloid Akbar gear

The inexpensive design: the Grisson gear

The standard grisson gear has two roller rings and a thumb cam shaft with two thumb curves offset by 180 °. This thumb shaft is mounted axially parallel to the roller wheel shaft. The thumb curves represent envelopes of the epicycloids and form curves and countercurves between two roles. This construction is a simple and inexpensive design with good efficiency.

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Picture gallery with 14 pictures

The standard grisson gearbox can be turned into a coaxial eccentric gearbox by attaching an eccentric shaft. For this purpose, offset cranks are attached to the thumb shaft, which are driven by the central eccentric shaft via a circular disk. The coaxial gearbox can then be equipped with several thumb shafts and can thus be designed to be very resilient. The statics of the output stage either have a favorable symmetrical pair of forces, an equilateral triangle or equilateral polygons as a force corner depending on the arrangement of the thumb shafts. It therefore has the advantages of planetary gears, however, with rolling toothing friction.

If the 180 ° offset thumb curves are not attached to a shaft but each thumb curve receives a separate shaft that is offset by 180 ° in pairs, the coaxial grisson gear can also be designed with a roller ring. The construction is very short. Other designs are conceivable, such as: inside thumb waves or thumb curves offset by 120 ° with three roller rings. The gears are suitable for fast movements. The translations can range from i = 5: 1 to approx. 30: 1.

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Develop, optimize and understand gearboxes

Classic cycloid eccentric gear

The gearbox is driven as standard with a centrally located eccentric and moves the cycloid-toothed eccentric wheel, which rolls on the rollers arranged in the housing. Bores in the eccentric wheel turn the central roller ring connected to the output shaft. Usually the gearboxes are placed twice (180 ° rotated) or triple (120 ° rotated) axially one behind the other to compensate for the very large bearing forces of the eccentric shaft and the unbalance.

The same gearbox can also be designed with the outside roller ring rotating and the inside roller ring standing. The cycloid-toothed eccentric wheel then only makes a wobbling eccentric movement without rotation.

In the case of the cycloid external eccentric gear, the outer wheel carrying the cycloid curve is arranged eccentrically rotating. The eccentric is remodeling on the outside. The cycloid cam wheel rolls on an inner, centrally positioned roller ring. The same gearbox can also be designed differently.

The cycloid cam wheel only makes an eccentric movement without rotation around a roller ring fixed in the housing. The cycloidal cam wheel rotates an inner roller ring that is connected to the output shaft. The ratios of single-stage gearboxes are approx. I = 8: 1 to i = 120: 1.

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An overview of the world of gears

For small translations: the Compur gear

The Compur gearbox has an outer cycloidal cam ring which is fixed to the housing while stationary and another cycloidal cam ring which is connected on the inside to the output shaft in a rotating manner. A roller ring swung out by an eccentric is arranged between the two cycloid cam rings.

In the case of the Compur external gearbox, the arrangement is basically the same as that of the Compur gearbox, but the inner cam disc is held here so that the outside rotates. Compur gearboxes are mainly suitable for smaller gear ratios that cannot be achieved with simple cycloid gearboxes.

Builds compactly: the cycloid Akbar gearbox

If two cycloid cam wheels are connected to each other and swung out via a central eccentric, the cyclo-Akbar gearbox is created. There is a stationary, stationary central roller ring and a second, centrally rotating roller ring. A cycloid cam wheel rolls in the stationary roller ring and continues to rotate both wheels. The second cycloid cam wheel rotates the second central roller ring which is connected to the output shaft.

The cycloid-Akbar external gearbox is created in the same way as with the cycloid gearbox. Cycloid Akbar gearboxes have to be built compactly for the largest translations.

If a cycloid-Akbar internal gear is arranged in a cycloid-Akbar external gear, the two gears can be braced against each other and thus can be preloaded absolutely free of play and adapted to the external load. Maul Konstruktionen designs and supplies these cycloid gears on request. (ud)

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Cycloid and planetary gears compared

* Erich Maul is managing director of Maul Konstruktionen GmbH, Aachen.