Harmonic reducers mainly consist of three key parts: the wave generators, the flexsplines, and the circular splines.
The wave generators are the "power engines" of the harmonic reducers. They usually consist of elliptical cams and flexible ball bearings that fit over the cams. Sometimes, they are made up of rocker arms with rollers on both ends. Their role is to provide the initial power input for the entire transmission system, much like car engines provide the power source for a vehicle's movement.
The flexsplines are very distinctive components. They are thin-walled, cylindrical external gears typically made of a metal material with good elasticity, allowing them to undergo elastic deformation under the influence of the wave generators. Imagine the flexsplines as rubber gears that can flexibly change their shape under external forces. Their outer surfaces are machined with precise gear teeth that mesh with the teeth of the circular splines to achieve motion and power transmission.
The circular splines are rigid internal gears, like solid fortresses, providing stable support for the entire transmission system. Their inner surfaces are also machined with gear teeth that match those of the flexsplines, and they usually have more teeth than the flexsplines. During operation, the circular splines are generally fixed in place and serve as reference points for the entire transmission process.
These three components work closely together to accomplish the high-precision speed reduction task of the harmonic reducers. Their coordination is like a carefully choreographed dance, with each part playing a critical role in its position, indispensable to the whole.
When not assembled, the inner holes of the flexsplines are circular. After the wave generators are inserted into the inner holes of the flexsplines, since the lengths of the wave generators are slightly larger than the diameters of the inner holes of the flexsplines, it's similar to fitting larger eggs into slightly smaller eggshells; the flexsplines are stretched into elliptical shapes.
In the direction of the major axes of these ellipses, the teeth of the flexsplines fully engage with the fixed circular splines, much like two tightly interlocking gears. In the direction of the minor axes, the teeth are completely separated with no contact whatsoever. In other areas, depending on the rotational position of the flexsplines, the teeth are either in the state of "engaging in", gradually entering engagement, or "disengaging", gradually leaving engagement.
When the wave generators start to rotate, something magical happens. Because the circular splines are fixed, the rotation of the wave generators forces the flexsplines to continuously deform, with the major and minor axes and the "engaging in" and "disengaging" positions constantly changing. The teeth of the flexsplines start by engaging, gradually enter full engagement, and then transition to disengaging, eventually leaving engagement, repeating this cycle continuously, forming a consistent, regular motion.
During this process, as the wave generators rotate, one tooth of the flexsplines moves from engaging with one tooth of the circular splines to re-engaging with that same tooth on the circular splines, the flexsplines just complete one rotation, while the wave generators have rotated many times. The ratio of the number of rotations of the wave generators to the number of rotations of the flexsplines is the reduction ratio of the harmonic reducers, which explains why harmonic reducers can achieve high-precision speed reduction with large transmission ratios.
Throughout the entire motion process, the deformation of the flexsplines, when viewed as a development around their circumference, manifests as continuous simple harmonic waves. This is the origin of the term "harmonic" drive. This unique transmission method allows harmonic reducers to stand out among many reducers, becoming indispensable key components in robotics and other precision equipment.
