The Harmonic Drive® strain wave gear is made up of three basic components. These are first of all the so-called wave generator, an elliptical steel disc that forms the heart of the gear unit, which has a centric hub and a special thin, elliptically deformable ball bearing. The wave generator is also connected to the motor shaft. Secondly, the wave generator consists of the flexspline – a deformable, cylindrical steel bushing with teeth arranged around its outer circumference – and the circular spline. The latter surrounds both the wave generator and the flexspline as a rigid, cylindrical outer ring, with teeth along its inner circumference. What is significant is the number of teeth – the outer toothing of the flexspline has fewer teeth than the inner toothing of the circular spline. The difference in number is frequently two.

The central features and advantages of the strain wave gear compared to other, more conventional types of gear unit, are primarily due to the combination of its simple construction and the unique principle of elastic deformation found in steel gear wheels. Harmonic Drive® gears display absolute play-free performance throughout their service life and maintain a high level of torsional rigidity over the whole torque range. With smaller dimensions and a lower weight compared with conventional gear types, they are suitable for use in lighter and more compact applications and systems. Owing to their high reduction ratios and the fact that they consist of three basic components and have a coaxial orientation, strain wave gears can be easily integrated into existing applications.