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Inside Harmonic Drives   


width=300With YB Components becoming Cone Drive distributors this year, we thought we’d take time to explain how the signature product of the harmonic drive-specialists actually works.

Using strain weave gearing, harmonic drives are innovative products as they boast three excellent benefits over other gears, namely zero-backlash characteristics and the reduction in both weight and space occupied by the gear housing.

Let’s take a peak under the hood and see how harmonic drives are able to produce such quality performance despite being smaller and weighing less than other gear types.

The Strain Weave Gearing Principle

Strain weave gearing is the alternative name for harmonic drives, and it is a form of mechanical gear system using a flexible spline with external teeth. The spline is deformed by a rotating elliptical plug so it can engage with the outer spline’s internal gear teeth.

The harmonic drives available through Cone Drive distributors work using a special operating principle centred around the elastic mechanics of metal. It is this principle, along with the fact they only consist of three basic parts, that gives harmonic drives their zero-backlash characteristics, as well as significantly reducing their size and weight.

The basic parts of a harmonic drive are the Wave Generator, Flexspline and Circular Spline.

Wave Generator

The Wave Generator of these gears available through YB Components, the UK’s leading Cone Drive distributors in Yorkshire, consists of a very thin, specially designed raced ball bearing fitted onto an elliptical hub. It works as a very efficient torque converter, and usually operates as the input.


The radially-compliant but torsionally-stiff Flexspline is also thin, but in the shape of a cylindrical jar or cup. It is made with alloy steel and features external teeth at the open end of the jar-shaped receptacle. The Flexspline deforms into the elliptical shape of the Wave Generator once it has been inserted, and is generally used as the output.

Circular Spline

The rigid Circular Spline has internal teeth that engage with the Flexspline’s external teeth, primarily at the main axis of the Wave Generator ellipse. This creates a concentrically-inscribed ellipse contained within a circle which should make contact at two points. Instead, the finite height of the gear teeth transform these contact points into contact regions.

In Conclusion

These three basic components combine with the special strain weave gearing operating principle to create a high reduction ratio despite being in a compact and lightweight housing. In addition, the three element construction of the harmonic drive means the size and weight of the gear do not vary with the reduction ratio.

Additional performance positives of the strain weave gearing principle also include  high torque and excellent positional accuracy, as well as reliable repeatability.

If you require any harmonic drives, then contact YB Components who are the UK’s leading Cone Drive distributors in Yorkshire. We keep local stocks of all such parts and more ready to ship out fast and free all over the UK and the rest of the world.