Cycloidal Gearbox

Here you can get about Cycloidal Gearbox working principle.

Cycloidal drive or cycloidal speed reducer is a mechanism for reducing the speed of an input shaft by a certain ratio. Cycloidal speed reducers are capable of relatively high ratios in compact sizes with very low backlash. The input shaft drives an eccentric bearing that in turn drives the cycloidal disc in an eccentric, cycloidal motion.

What IS Cycloidal Gearbox

Cycloidal gearboxes or reducers consist of four basic components: a high-speed input shaft, a single or compound cycloidal cam, cam followers or rollers, and a slow-speed output shaft. The input shaft attaches to an eccentric drive member that induces eccentric rotation of the cycloidal cam. In compound reducers, the first track of the cycloidal cam lobes engages cam followers in the housing.

Cylindrical cam followers act as teeth on the internal gear, and the number of cam followers exceeds the number of cam lobes. The second track of compound cam lobes engages with cam followers on the output shaft and transforms the cam’s eccentric rotation into concentric rotation of the output shaft, thus increasing torque and reducing speed.

Cycloidal Gearbox Working

As the disc rotates, the lobes of the cycloidal disc act like teeth and engage with pins on a stationary ring gear. The cycloidal disc also has roller pins that protrude through the disc, and these pins attach to an output disc which transfers motion to an output shaft.

A cycloidal gearbox uses the principles of cycloidal gears to provide high gear ratios (often 100:1 or greater) with excellent torsional stiffness, good shock load capacity, stable backlash over the gearbox life, and low wear.

There are various designs of cycloidal gearboxes, but the basic principle consists of an input shaft that is eccentrically mounted to a drive member or bearing, which drives a cycloidal disc in an eccentric motion. As the disc rotates, the lobes of the cycloidal disc act like teeth and engage with pins on a stationary ring gear. The cycloidal disc also has roller pins that protrude through the disc, and these pins attach to an output disc which transfers motion to an output shaft.

The number of lobes (teeth) on the cycloidal disc is lower than the number of pins (teeth) on the ring gear, which provides speed reduction and torque multiplication. To prevent “wobbling” of the output shaft, the roller pins connected to the output disc are mounted in holes slightly larger than the pin diameter. A single cycloidal disc experiences unbalanced forces, which can be compensated by using a second cycloidal disc, offset from the first by 180 degrees.

Cycloidal gears are much more difficult to manufacture than involute gears, requiring extremely accurate manufacturing and assembly. But they do offer significant benefits in some applications. First, they can provide transmission ratios up to 300:1 in a relatively small package — especially concerning the length of the gearbox — since they don’t require “stacking” of gear stages as planetary designs do.

Cycloidal gears also experience lower friction and less wear on the tooth flanks due to their rolling contact and lower Hertzian contact stress. And their good torsional stiffness and capacity to withstand shock loads make them ideal for heavy industrial applications that also require servo precision and stiffness.

Advantages

  • Having a wider flank as compared to Involute gears they are considered to have more strength and hence can withstand further load and stress.
  • The contact in case of cycloidal gears is between the concave surface and the convex flank. This results in less wear and tear.
  • No interference occurs in these types of gears.

Disadvantages

  • Due to the eccentric nature of the drive, if the cycloidal disk is not balanced by a second disk or a counterweight, it will generate vibration which will propagate through the driven shafts and the body.
  • This will cause increased wear on the exterior teeth of the cycloidal disk, as well as component bearings.
  • With two discs the static imbalance is corrected but a small dynamic imbalance remains, this is generally considered acceptable for most applications but to reduce vibration high speed drives use three (or more) discs to allow the imbalance to be corrected, the outer discs move in unison and in opposition to the middle one which is twice as massive.

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