Harmonic drive

A Ellipto or stress wave transmission and wave gear, also known by the English name strain wave gear (SWG ) is a gear with an elastic transmission element, which is characterized by high transmission ratio and stiffness. Manufacturer of such transmissions are the Harmonic Drive AG, Harmonic Drive LLC and the Harmonic Drive Systems In. Harmonic Drive is a registered trademark of Harmonic Drive AG.

Construction

A sliding wedge consists of three elements:

• One elliptical steel disc with aufgeschrumpftem bearings and thin deformable race, called the Wave Generator. The harmonic drive pictured works without roller bearing ring. The elliptical shape of the inner bright disk is in the image hard to see. Law it is highlighted as dark gray ellipse. The steel plate is the drive of the gear.
• A deformable cylindrical steel sleeve with external teeth, the so-called flex spline. In the figures, it is the brown-red timing belt. The steel sleeve is the output.
• A rigid cylindrical outer ring with internal teeth, the circular spline. In the picture on the left it is hard to make out, on the right marked in light gray. At the top and bottom of his teeth and the flexible spline mesh.

The external teeth of the steel bush has less teeth than the inner teeth of the outer ring.

Operation

The driven elliptical disk deforms the thin-walled steel sleeve about the outer ring of the ball bearing. Thus, the external teeth of the steel bush engages in the region of the large axis of the ellipse with the internal teeth of the outer ring. Holding the outer race fixed, in one revolution of the drive disc, the steel sleeve ( the output ) corresponding to the smaller number of teeth from the outer ring remains.

Due to the high numbers of teeth of fine serrations obtained very large translations. For example, the translation in z = 202 ​​teeth on the internal gear, and z = 200 in the steel sleeve 200:2 = 100 In hundred revolutions of the elliptical disk, the deformable steel bush rotates once.

Approx. 30 % of the teeth are involved in the transmission of power. Together with the high reduction ratio ( from 30:1 to 320:1 for is technically possible as the default ) the harmonic drive is very stiff and backlash. Depending on the model, the positioning accuracy is better than 30 ". The transmission is compact and maintenance-free. A harmonic drive is for axis drives for robots, drives in flight simulators, tracking of large parabolic antennas, in motor vehicles ( Dynamic Steering), in machine tools and in drives of printing machines.

Unlike Zykloidgetrieben Ellipto or corrugated gears have a slightly lower moment of shock, but build much easier due to the smaller number of components.