CN113931990B

CN113931990B - Harmonic drive cam

Info

Publication number: CN113931990B
Application number: CN202111012432.0A
Authority: CN
Inventors: 侍威; 郑继贵; 张兆晶; 黄玉平; 赵守军; 杨斌; 张茸
Original assignee: Beijing Research Institute of Precise Mechatronic Controls
Current assignee: Beijing Research Institute of Precise Mechatronic Controls
Priority date: 2021-08-31
Filing date: 2021-08-31
Publication date: 2023-04-14
Anticipated expiration: 2041-08-31
Also published as: CN113931990A

Abstract

A characteristic curve of a harmonic drive cam is that low-angle frequency cosine waves and high-angle frequency cosine waves are added on the basis of a cosine function, the tendency of radial reduction at the long axis of the cam is reduced by utilizing the low-angle frequency cosine terms, and the deformation at the short axis of the cam is changed by utilizing the high-angle frequency cosine terms, so that the deformation of the long axis of the cam is smaller than that of the short axis. The invention improves the comprehensive performance of harmonic drive, and the harmonic drive cam characteristic curve can increase the harmonic drive wrap angle and improve the harmonic drive bearing capacity.

Description

Harmonic drive cam

Technical Field

The invention relates to a harmonic drive cam, and belongs to the field of harmonic gear drive research.

Background

The profile (characteristic curve) of the cam, which is an important part of harmonic gear transmission, has a decisive influence on the performance of the harmonic. The characteristic curves of the cam commonly used at present are cosine curves, ellipse curves, resal curves, four rollers, eccentric discs and other profiles.

The existing characteristic curves basically have the problems that the change range of the wrap angle of the cam is limited, and free adjustment is difficult to realize, so that the stress change of a flexible gear in the transmission wrap angle range of the harmonic gear is violent, and the bearing capacity of the harmonic gear is relatively poor.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the novel harmonic drive cam is provided, the cam profile is changed according to different application requirements, the comprehensive performance of harmonic drive is improved, the harmonic drive cam characteristic curve can increase a harmonic drive wrap angle, and the harmonic drive bearing capacity is improved.

The technical scheme adopted by the invention is as follows: a characteristic curve of a harmonic drive cam is that low-angle frequency cosine waves and high-angle frequency cosine waves are added on the basis of a cosine function, the tendency of radial reduction at the long axis of the cam is reduced by utilizing the low-angle frequency cosine terms, and the deformation at the short axis of the cam is changed by utilizing the high-angle frequency cosine terms, so that the deformation of the long axis of the cam is smaller than that of the short axis.

The cam characteristic curve equation is as follows:

ρ＝R+A×cos(θ)+B×cos(2θ)+C×cos(4θ)；

wherein theta is a polar angle, and R is a characteristic curve circle radius when the characteristic curve is not deformed; A. b and C are both coefficients.

And B = k · m, wherein k is a cam deformation coefficient, and m is a gear module of a flexible gear matched with the cam in the harmonic reducer.

When the reduction ratio is more than or equal to 100, k = 1.0-1.1; k =0.95 to 1 when the reduction ratio is 80 to 100; when the reduction ratio is 30 to 80, k =0.85 to 0.95.

The cam deformation amount ω = a × cos (θ) + B × cos (2 θ) + C × cos (4 θ).

Deformation omega at long axis of cam ₁ = A + B + C, amount of deformation omega at minor axis ₂ ＝-B+C，C≤-A/2。

Compared with the prior art, the invention has the advantages that:

(1) The cam has the advantages of flexible parameter adjustment and capability of realizing random deformation of deformation quantities at the positions of the major axis and the minor axis of the ellipse-like shape under the condition of unchanged perimeter.

(2) The cam can realize the gradual reduction of the deformation near the long shaft and the rapid increase of the deformation near the short shaft, thereby being beneficial to the large bearing of the harmonic gear transmission at the long shaft and the rapid exit of the engagement at the short shaft and ensuring the high efficiency of the transmission.

(3) The cam has the advantages of continuous curve, no speed abrupt change point and convenient production and processing.

Drawings

FIG. 1 is a harmonic drive component diagram;

fig. 2 is a comparison of cam characteristic curves.

Detailed Description

The invention is described with reference to the accompanying drawings.

As shown in figure 1, the harmonic gear transmission pair comprises a flexible gear 1, a rigid gear 2 and a cam 3, wherein the cam 3 is a shock wave source for generating harmonic transmission fluctuation.

According to the invention, low-angular frequency and high-angular frequency cosine waves are added on the basis of the original cosine cam characteristic curve to adjust the wrap angle range of the cam, so that the characteristic curve near the long axis of the cam changes slowly and changes more intensely at the position closer to the short axis of the cam, the harmonic transmission bearing capacity is enhanced, the equivalent ball load is reduced, and the service life of the flexible bearing is prolonged. Fig. 2 is a comparison of cam profiles.

The cam characteristic curve equation is as follows:

ρ＝R+A×cos(θ)+B×cos(2θ)+C×cos(4θ)；

wherein: where θ is the polar angle (from the major axis), and R is the characteristic curve radius when undeformed. A. B and C are both coefficients.

B = k · m, wherein k is a cam deformation coefficient, and m is a gear module of a flexible gear matched with a cam in the harmonic reducer;

k = 1.0-1.1 for the reduction ratio is more than or equal to 100; k =0.95 to 1 for a reduction ratio of 80 to 100; the reduction ratio is 30 to 80, k =0.85 to 0.95.

A＝(0.2～0.3)×B；

Cam deformation amount: ω = a × cos (θ) + B × cos (2 θ) + C × cos (4 θ);

wherein, the deformation omega of the long axis of the cam ₁ = A + B + C, amount of deformation ω in minor axis ₂ ＝-B+C；

Radial direction of the cam: ρ = ω + R;

in order to realize the equal perimeter of the deformed characteristic curve and the undeformed characteristic curve of the cam, the deformation of the cam at the short axis is larger than that at the long axis, namely-omega ₂ ≥ω ₁ Thereby obtaining the product with the C less than or equal to-A/2.

The present invention has not been described in detail, partly as is known to the person skilled in the art.

Claims

1. A harmonic drive cam is characterized in that a cam characteristic curve is that low-angle frequency cosine waves and high-angle frequency cosine waves are added on the basis of a cosine function, the tendency of radial reduction at a long axis of the cam is reduced by using a low-angle frequency cosine term, and the deformation at a short axis of the cam is changed by using a high-angle frequency cosine term, so that the deformation of the long axis of the cam is smaller than that of the short axis;

the cam characteristic curve equation is as follows:

ρ＝R+A×cos(θ)+B×cos(2θ)+C×cos(4θ)；

wherein theta is a polar angle, and R is a characteristic curve circle radius when not deformed; A. b and C are both coefficients;

2. The harmonic drive cam as in claim 1, wherein when the reduction ratio is not less than 100, k = 1.0-1.1; k =0.95 to 1 when the reduction ratio is 80 to 100; when the reduction ratio is 30 to 80, k =0.85 to 0.95.

3. A harmonic drive cam as claimed in claim 2, wherein the cam deflection ω = a × cos (θ) + B × cos (2 θ) + C × cos (4 θ).

4. The harmonic drive cam as in claim 3 wherein the amount of deformation ω is about the major axis of the cam ₁ = A + B + C, amount of deformation ω in minor axis ₂ ＝-B+C，C≤-A/2。