The Advantages and Applications of Strain Wave Generator Gearings

A strain wave generator gear is a highly precise, backlash-free, compact gearing product that provides an extraordinary amount of speed reduction. Utilizing a unique operating principle based on the elastic mechanics of metals, the strain wave gear achieves a very high reduction ratio in a compact envelope. While this type of gearhead is less common than traditional spur or planetary technologies, it is nevertheless ideal for use in many popular industries, including applications like exoskeletons and X-ray machines within medical and industrial spaces.

Strain Wave Generator Gearing Components

This type of mechanical gearing system consists of only three precision components: the wave generator, the flex spline, and the circular spline. Let’s cover each below:

1.	Wave Generator. The wave generator is composed of a thin raced ball bearing and an elliptical hub. The race of the ball bearing is fitted onto the hub, causing the outer race of the bearing to deform into an elliptical shape. It is usually directly attached to the motor shaft.
2.	Flex Spline. The flex spline is a thin-walled cylindrical cup with gear teeth on its external surface. This component fits over the wave generator and assumes its elliptical shape. It is usually fitted to the output of the gear.
3.	Circular Spline. The circular spline is a rigid ring with internal teeth (usually two more teeth than the flex spline). The teeth of the flex spline engage with the teeth of the circular spline across the major axis of the wave generator ellipse. It is typically mounted onto a housing.

 

Working Principles of Strain Wave Generator Gearings

When the wave generator is put inside the flex spline, the flex spline is forced into an elliptical shape that causes the teeth of the flex spline to engage with the teeth of the circular spline at two opposite regions across the major axis of the ellipse. For every 180-degree clockwise rotation of the wave generator, the flex spline teeth are advanced counterclockwise by one tooth in relation to the circular spline. Each complete clockwise rotation of the wave generator results in the flex spline moving counterclockwise by two teeth from its original position relative to the circular spline. Because the gear teeth are always fully engaged in a region along the major axis, these gearheads have zero backlash and a high torque-carrying capacity.

Advantages of Strain Wave Generator Gearings

Strain wave generator gearings are typically used in applications that require extremely high reduction ratio and high torque in a compact package, as well as excellent positional accuracy and repeatability. Here are a few advantages of employing strain wave generator gearings:

•	Extremely high single stage reduction ratios 30:1 to 320:1 in a very compact and lightweight package
•	Space and weight savings (compared to other gearhead types)
•	Excellent positional accuracy and repeatability
•	High torque capacity
•	Zero backlash
•	High efficiency
•	Long lifetimes
•	Low noise

Applications of Strain Wave Generator Gearings

Though strain wave generator gearings aren’t ideal for every application, they are well-suited for a specific set of applications that fit within the unique needs described above.

Here are a few popular examples and how they use this gearhead technology:

•	Aerospace and Defense. Strain wave generator gearings were originally developed for aerospace applications because of their low weight and high single-stage reduction ratio in a compact design. These characteristics make this gearing the ideal choice for many satellite drives and space missions.
•	Exoskeletons. Exoskeletons are external support structures that assist mobility-impaired persons to perform movements and daily tasks. These structures are also used in many applications to perform auxiliary functions, including carrying and lifting heavy loads that otherwise would subject workers to considerable stress for an extended period. These devices employ strain wave generator gears, which are used in combination with a very compact electric motor, to ease the workload of users wearing them; this helps prevent physical stress and improve working efficiency.
•	Industrial Robots. Robots are used worldwide in many industries to carry out various tasks like building assemblies at faster rates. Such tasks necessitate higher accuracy with excellent repeatability for producing correct assemblies without wasting time. Hence, such markets are ideal opportunities for strain wave generator gears.
•	Machine Tools – Multi-Spindle Lathe. Strain wave generator gearings are used in the actuator for the automated adjustment of tool wear in the machine.
•	Medical Equipment – X-Ray Machines. These gearings are utilized to position the X-ray source precisely over the patient.

Think your application could benefit from strain wave generator gears? Get in touch with our experts to discuss!