The harmonic drive consists of three basic components: the wave generator, the flexible wheel, the wheel. Three components can be fixed one, the other two one for the initiative, one for the drive, can achieve deceleration or speed (fixed transmission ratio), can also be converted into two inputs, an output, composed of differential drive (its principle Figure)

When the wheel is fixed, the wave generator is active, the flexible wheel is driven: the flexible wheel is deformed under the action of the elliptical cam, and the soft wheel teeth at both ends of the long side of the wave generator are completely meshed with the wheel teeth; In the short axis at both ends of the soft wheel teeth and the wheel just teeth completely disengaged; in the wave generator long axis and short axis of the interval, the soft wheel teeth and just wheel teeth in a semi-meshing state, known as And then gradually withdraw from the engagement in a semi-disengaged state, known as the out of the mouth. As the continuous rotation of the wave generator, making the engagement, fully engaged, out, completely off the four cases in turn change, endless cycle. Since the Rou wheel is less than the number of teeth of the wheel, the soft wheel turns the angle of the two teeth in the opposite direction when the wave generator rotates for one week, thus achieving a large reduction ratio.