Working principle of harmonic gear reducer

A harmonic gear reducer is a type of transmission structure consisting of a fixed inner tooth rigid wheel, a flexible wheel, and a wave generator that causes radial deformation of the flexible wheel. The harmonic gear reducer is a new type of transmission structure in gear reducers, which uses flexible gears to generate controllable elastic deformation waves, causing relative misalignment between the teeth of the rigid wheel and the flexible wheel to transmit power and motion. This type of transmission is fundamentally different from general gear transmission, and has special characteristics in meshing theory, set calculation, and structural design. Harmonic gear reducers have the advantages of high precision and high load-bearing capacity. Compared with ordinary reducers, they use 50% less materials and reduce their volume and weight by at least 1/3.

Composition and structure

The harmonic gear reducer is composed of three main components: a rigid wheel, a flexible wheel, and a wave generator. Among them, the wave generator is the active component, and one of the rigid and flexible wheels is the driven component. A fixed rigid wheel is a rigid internal gear, while a flexible wheel is a thin-walled cylindrical external gear that is prone to deformation. They both have a triangular (or involute) tooth shape and have equal circumferential pitches, but the rigid wheel has several more teeth (usually two teeth) than the flexible wheel. The wave generator consists of an elliptical disk and a flexible ball bearing, or a rotating arm with rollers at both ends. Usually, the wave generator is the original body, one of the flexible wheels and steel wheels is the driven body, and the other is the fixed component.

working principle

Before assembly, the flexible wheel and its inner hole are circular. After the wave generator is installed into the inner hole of the flexible wheel, due to the length of the wave generator being slightly larger than the diameter of the inner hole of the flexible wheel, the flexible wheel is supported into an oval shape, forcing the flexible wheel to fully mesh with the fixed rigid wheel in the long axis direction of the ellipse and completely separate in the short axis direction. The teeth in other parts may be in a "meshing" state depending on the rotation position of the flexible wheel, Or in a "meshing out" state: due to the fixed rigid wheel, when the wave generator rotates counterclockwise, the flexible wheel rotates clockwise. When the wave generator rotates continuously, the long and short axes of the flexible wheel, as well as the positions of "meshing in" and "meshing out", constantly change.

 

The flexible wheel teeth turn from meshing in to meshing out, and then from meshing out to meshing out, and so on, meshing in, meshing out, disengagement, meshing in, meshing... reciprocating cycles, Force the flexible wheel to rotate continuously. During the rotation of the flexible wheel with the wave generator, when one of the teeth engages with a tooth on the rigid wheel and then again with this tooth on the rigid wheel, the flexible wheel rotates exactly one turn. At this time, the wave generator rotates many times, and the ratio of the number of turns of the wave generator to the number of turns of the flexible wheel (1 turn) is the reduction ratio of the harmonic gear reducer, so its reduction ratio is very large. In the whole movement process, the deformation of the flexspline is a continuous simple harmonic waveform on the unfolded diagram of the flexspline circumference, so this drive is called harmonic gear drive: the harmonic gear reducer can be divided into single wave, double wave and three waves according to the number of mechanical skills, of which the most commonly used is double wave transmission. In harmonic transmission, the tooth number difference between the rigid wheel and the flexspline should be an integral multiple of the mechanical wave number, usually taken as equal to the wave number.

advantage

1. Large transmission speed ratio: Single stage harmonic gear transmission speed ratio ranges from 70 to 320, which can reach, 000 in some devices, and multi-stage transmission speed ratio can reach over 30000. It can be used not only for deceleration, but also for speed increase situations.

2. High load-bearing capacity: This is because there are many teeth that mesh simultaneously in harmonic gear transmission, and the number of teeth that mesh simultaneously in double wave transmission can reach more than 30% of the total number of teeth. Moreover, the flexible wheel uses high-strength materials, and the teeth are in surface contact.

3. High transmission accuracy. This is because there are many teeth engaged at the same time in harmonic gear transmission, and the error is averaged, that is, the multi tooth engagement has mutual compensation effect on the error, so the transmission accuracy is high. Under the same gear accuracy level, the transmission error is only about 114 of the ordinary cylindrical gear transmission. At the same time, the radius of the wave generator can be changed by the proud amount to increase the deformation of the flexible wheel, making the backlash very small, and even achieving no backlash meshing. Therefore, the harmonic gear reducer has a small transmission clearance and is suitable for reverse rotation

4. High transmission efficiency and smooth motion: Due to the uniform radial movement of the flexible gear teeth during the transmission process, even with high input speed, the relative slip speed of the gear teeth is still extremely low (which is 1% of that of ordinary involute gear transmission), so the wear of the gear teeth is small and the efficiency is high (up to 69% and 96%). Additionally, due to the meshing in and out, both sides of the gear participate in work, so there is no impact phenomenon, Smooth movement;

5. Simple structure, fewer parts, and convenient installation. There are only three basic components, and the input and output shafts are coaxial, so the structure is simple and installation is convenient

6. Small size and light weight: Compared with general reducers, when the output torque is the same, the volume of harmonic gear reducers can be reduced by 2/3, and the weight can be reduced by 2/2.

7. It can transmit movement to confined space. With the flexibility of flexible wheels, this valuable advantage of wheel drive is incomparable with other existing drives.