Learn about harmonic gear reducer in one minute

Learn about harmonic gear reducer in one minute
The harmonic gear reducer is composed of a fixed internal tooth rigid wheel, a flexible wheel, and a wave generator that deforms the flexible wheel radially. The harmonic gear reducer is a new transmission structure in the gear reducer. It uses flexible gears to generate controllable elastic deformation waves, causing relative staggered teeth between the teeth of the rigid wheel and the flexible wheel to transmit power and motion. This kind of transmission is essentially different from general gear transmission, and has particularity in meshing theory, collective calculation and structural design. Harmonic gear reducer has the advantages of high precision and high bearing capacity. Compared with ordinary reducer, because it uses 50% less material, its volume and weight are reduced by at least 1/3.

Like planetary gear transmission, harmonic gear transmission is also composed of three basic components: a fixed internal toothed rigid wheel, a flexspline (that is, an elastic thin-walled cup whose base is connected to the driven shaft" at the generatrix at the beginning of the flexspline Make a ring gear on top”) and a wave generator that deforms the flexspline radially. The teeth with the same modulus are cut on the rigid wheel and the flexible wheel, but the number of teeth is different, that is, the number of teeth of the flexible wheel is two less than that of the rigid wheel. The tooth number difference of the harmonic drive represents the deformation wave number of the flexspline. The most common is the harmonic drive with wave number w-2. In the free state (without generator), the two wheels are in a concentric position, and the tooth gaps of the rigid wheel and the flexible wheel are uniform. The generator installed in the flexible wheel deforms the flexible wheel radially and becomes an ellipse.
At this time, on the long axis of the ellipse, the teeth mesh along the entire working height, while on the short axis, a radial gap is formed between the tooth tips. During the rotation of the generator, the shape of the flexspline is always close to the above-mentioned shape.

The harmonic gear reducer is composed of three main components: rigid wheel, flexible wheel, and wave generator. Among them, the wave generator is the driving part, and one of the rigid wheel and the flexible wheel is the driven part. The fixed rigid wheel is a rigid internal gear, and the flexible wheel is an easily deformable thin-walled cylindrical external gear. Together they have a triangular (or involute) tooth profile, and the pitches of the two are equal, but the rigid wheel is better than the flexible wheel A few more teeth (usually two teeth). 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 motive body, one of the flexible wheel and the rigid wheel is the driven body, and the other is the fixed part.

Before assembling, the flexspline and its inner hole are circular. After the wave generator is installed in the inner hole of the flexspline, the length of the wave generator is slightly larger than the diameter of the inner hole of the flexspline. The wheel is completely meshed with the fixed rigid wheel in the direction of the long axis of the ellipse, and completely separated in the direction of the short axis. The rest of the teeth are either in the state of "engaging in" or "engaging out" depending on the rotation position of the flexible wheel. . Because the rigid wheel is fixed, when the wave generator rotates counterclockwise, the flexible wheel rotates clockwise. When the wave generator rotates continuously, the positions of the long and short shafts of the flexspline and the "engagement" and "engagement" continue to change. The teeth of the flexspline change from engagement to engagement, and then engagement to engagement. The exit steering is disengaged, so that the reciprocating cycle forces the flexible wheel to continuously rotate.
When the flexspline rotates with the wave generator, when one of the teeth meshes with one tooth of the rigid wheel to mesh with this tooth on the rigid wheel again, the flexspline rotates exactly once, and the wave generator rotates For many turns, the ratio of the number of turns of the wave generator to the number of turns (1 turn) of the flexspline is the reduction ratio of the harmonic gear reducer, so the reduction ratio is very large. In the whole movement process, the deformation of the flexspline is a continuous simple harmonic shape on the expanded view of the flexspline circumference. Therefore, this transmission is called a harmonic gear transmission.
Harmonic gear reducers can be divided into single wave, double wave and triple wave according to the number of their mechanical waves. The most commonly used is double wave transmission. In harmonic drive, the difference between the number of teeth of the rigid wheel and the flexible wheel should be equal to an integer multiple of the mechanical wave number, which is usually equal to the wave number.