Strain wave gearing
Strain wave gearing (also known as harmonic gearing) is a type of mechanical gear system that uses a flexible spline with external teeth, which is deformed by a rotating elliptical plug to engage with the internal gear teeth of an outer spline.
The German company Harmonic Drive SE manufactured the first series-produced gears under the product name or registered trademark Harmonic Drive.
Strain wave gearing has some advantages over traditional gearing systems such as helical or planetary gears, including:
- no backlash,
- compactness and light weight,
- high gear ratios,
- reconfigurable ratios within a standard housing,
- good resolution and excellent repeatability (linear representation) when repositioning inertial loads,
- high torque capability,
- coaxial input and output shafts.
High gear reduction ratios are possible in a small volume (a ratio from 30:1 up to 320:1 is possible in the same space in which planetary gears typically only produce a 10:1 ratio).
Disadvantages include a tendency for 'wind-up' (a torsional spring rate) in the low torque region.
Strain wave gearing is commonly used in robotics and aerospace. It can provide gear reduction but may also be used to increase rotational speed, or for differential gearing.