I. Working Principle of Harmonic Reducer
A harmonic reducer, also known as a harmonic gear reducer, is a speed reduction device consisting of three basic components: a fixed internal gear, a flexible gear (i.e., an elastic thin-walled sleeve whose base is connected to the driven shaft, "with a gear ring made on the generatrix at the beginning of the flexible gear"), and a wave generator that causes radial deformation of the flexible gear.
Before assembly, the flexible wheel and its inner bore are circular. After the wave generator is inserted into the inner bore of the flexible wheel, because the length of the wave generator is slightly larger than the diameter of the inner bore of the flexible wheel, the flexible wheel expands into an elliptical shape. This forces the flexible wheel to fully engage with the fixed rigid wheel along the major axis of the ellipse and completely disengage along the minor axis. The teeth at other points are either in an "engaged" or "disengaged" state depending on the rotational position of the flexible wheel. Since the rigid wheel is fixed, when the wave generator rotates counterclockwise, the flexible wheel rotates clockwise. As the wave generator rotates continuously, the major and minor axes of the flexible wheel, as well as the "engaged" and "disengaged" positions, constantly change. The flexible wheel teeth change from engaged to disengaged, then from engaged to disengaged, and so on, in a continuous cycle of engagement, disengagement, disengagement, engagement, and so on, forcing the flexible wheel to rotate continuously.
As the flex wheel rotates with the wave generator, when one of its teeth engages with a tooth on the rigid wheel and then engages with that tooth again, the flex wheel completes one revolution. Meanwhile, the wave generator rotates many revolutions. The ratio of the number of revolutions of the wave generator to the number of revolutions of the flex wheel (one revolution) is the reduction ratio of the harmonic gear reducer, hence its high reduction ratio. Throughout the entire motion, the deformation of the flex wheel forms a continuous simple harmonic waveform on the unfolded diagram of its circumference; therefore, this transmission is called a harmonic gear transmission.
Harmonic gear reducers can be classified according to the number of mechanical waves: single-wave, double-wave, and triple-wave, with double-wave transmission being the most common. In harmonic transmission, the difference in the number of teeth between the rigid wheel and the flexible wheel should be an integer multiple of the number of mechanical waves, usually taken as equal to the number of waves.
II. Differences between harmonic reducers and RV reducers
Harmonic reducers and RV reducers are both common speed reduction devices used to reduce the rotational speed of moving mechanical parts and provide greater torque output. Although they can achieve similar functions, there are some important differences in their structure and working principle.
First, harmonic reducers and RV reducers operate on different principles. Harmonic reducers utilize the principle of harmonic vibration to achieve speed reduction, while RV reducers achieve speed reduction by connecting gears of different structures in series.
The harmonic reducer employs the principle of elliptical displacement and consists of an external gear, an internal gear, and a flexible ring. When the drive shaft rotates, harmonic vibrations are generated between the external gear and the flexible ring, thereby changing the relative position of the internal and external gears to achieve speed reduction. The harmonic reducer features a compact structure, a high reduction ratio, and high transmission efficiency.
The RV reducer consists of a toroidal gear and a helical gear. The toroidal gear is fixed to the output shaft, and the helical gear connects it to the input shaft to achieve speed reduction. Due to its simple structure, large capacity, and ability to achieve high reduction ratios, the RV reducer is widely used in industrial production.
Secondly, harmonic reducers and RV reducers also differ in structure. Harmonic reducers have a relatively complex structure, consisting of multiple components, including a drive shaft, flexible rings, and internal and external gears. These components require precise machining and assembly to ensure the reducer's proper operation. In contrast, RV reducers have a simpler structure, containing only toroidal gears and helical gears, making them easier to manufacture and maintain.
Harmonic reducers and RV reducers also differ somewhat in their application areas. Harmonic reducers, due to their high reduction ratio and small size, are suitable for applications with strict size requirements but high demands for torque output and transmission accuracy, such as precision machinery, robots, and solar tracking systems. RV reducers, on the other hand, are suitable for industrial automation equipment requiring larger output torque and reduction ratios, such as CNC machine tools and packaging machinery.
In addition, harmonic reducers and RV reducers also have some characteristics and problems during use. Due to their complex structure, harmonic reducers require a long period of operation and debugging to achieve optimal performance. Furthermore, harmonic reducers have relatively high manufacturing costs and are therefore more expensive.
In summary, although both harmonic reducers and RV reducers are common speed reduction devices, they differ in their working principles, structures, and application areas. Choosing the appropriate reducer based on specific application requirements and budget is crucial for the performance and efficiency of mechanical equipment.
