|
|
 |
The innovative concept of the "Harmonic Drive®" and its unique mechanism are the brainchild of an American inventor, C.W. Musser. An inventing genius, Musser holds upward of 1,500 patents, and these cover not only his specialty field of mechanical engineering, but also a more extensive swath that includes physics, chemistry and biology. Prior to Musser, efforts had been focused on increasing the rigidity of gear mechanisms in order to attain the supreme objective - i.e. conveying driving power and motion in a faster and more accurate method than before.
Contrary to that general trend, Musser's Harmonic Drive® theory is based on elastic dynamics and concerns itself with making use of the flexibility of metal. His theory has since been celebrated the world over as a revolutionary method for driving force transmission. |
 |
 |
|
| Basically, the Harmonic Drive® -- which was developed to take advantage of the elastic dynamics of metal -- is generally made up of just three components: a wave generator, a flexspline and a circular spline. Depending on its shape, the Harmonic Drive® is sometimes made up of four components; but even this four-component Harmonic Drive® is based on the same principle of motion. You can easily grasp the Harmonic Drive's unique mechanism from the way its teeth mate with one another. |
•Wave Generator
The wave generator is a component having small ball bearings built into the outer circumference of the elliptical cam. The inside raceway of the bearings is fixed to the cam while the outer raceway is subjected to elastic deformation via the ball bearings. The wave generator is usually attached to the input shaft.
•Flexspline
The flexpline is a thin cup-shaped metal rim component with external teeth. The bottom of the flexspline (cup bottom) is called the diaphragm. The diaphragm is usually attached to the output shaft.
•Circular Spline
The circular spline is a rigid steel ring with internal teeth. The circular spline has two teeth more than the flexpline and is usually fixed to a casing. |
 |
 |
The flexspline is deflected by the wave generator into an elliptical shape causing the flexspline teeth to engage with those of the circular spline at the major axis of the wave generator ellipse, with the teeth completely disengaged across the minor axis of the ellipse. |
 |
When the wave generator is rotated clockwise with the circular spline fixed, the flexspline is subjected to elastic deformation and its tooth engagement position moves by turns relative to the circular spline. |
 |
When the wave generator rotates 180 degrees clockwise, the flexspline moves counterclockwise by one tooth relative to the circular spline. |
 |
When the wave generator rotates one revolution clockwise (360 degrees), the flexspline moves counterclockwise by two teeth relative to the circular spline because the flexspline has two fewer teeth than the circular spline. In general terms, this movement is treated as output power. |
 |
|
1. High-speed reduction ratio
A Harmonic Drive® has high single-stage coaxial reduction ratios of 1/30 to 1/320. This is why the Harmonic Drive® provides high efficiency gearing without using complex mechanisms and structures.
2. Free of backlash (lost motion)
Different from the ordinary tooth-with-tooth mating mechanism, the Harmonic Drive® operates with very little -- nearly zero -- backlash, which is an essential characteristic for motion control.
3. High precision
With the Harmonic Drive®, high positional/ rotational accuracy is assured because 1) it has many simultaneous-mating teeth built-in, and 2) because these teeth mate with one another in two symmetrical positions at 180 degrees. This means influences of tooth pitch errors and accumulated pitch errors on rotational accuracy are equalized to assure high positional/ rotational accuracy.
4. Small numbers of components and ease of assembly
Effective speed reduction ratios are possible with only three basic components, and since all three components are co-axially aligned, the Harmonic Drive® can be easily built into component-assembled products, allowing for simple configurations.
5. Small-sized and lightweight
Machinery/equipment can be made smaller and lighter because the Harmonic Drive® provides the same levels of torque and speed reduction ratios as conventional gearing mechanisms, while being less than 1/3 the size of conventional products in terms of capacity and less than 1/2 the weight.
6. High torque capacity
The flexspline is made of special steel with a higher resistance to fatigue. Different from the typical driving force transmission apparatus, every tooth is subjected to very little force yet provides a high torque capacity. Because 1) the number of simultaneously mating teeth in the flexspline accounts for some 30% of the total number of teeth, and 2) these teeth come into contact with one another face to face, every tooth is subjected to a minimum of force while providing a maximum of torque.
7. High efficiency
The mating portion of each tooth is subjected to very little slide motion. Therefore, motion loss due to friction is reduced substantially, enabling the Harmonic Drive® to maintain a high level of efficiency, and allowing driving motors to be made smaller.
8. Quiet, vibration-free operation
With the Harmonic Drive®, quiet and vibration-free operations are possible because the teeth do not come into rolling contact with one another, and as the circumferential speed of each tooth is low, the teeth provide a well-balanced force.
|
 |
|
|
