Cycloidal pin wheel harmonic transmission device

Abstract

A cycloidal pin wheel harmonic transmission device includes camshaft, flexible bearing, flexible wheel, roller pins and rigid wheel. The flexible bearing is mounted on the camshaft with elliptical shape. The flexible wheel has inner ring cooperated with outer ring of the flexible bearing, and outer teeth surface contacted with each roller pin. The roller pins are evenly disposed inside semicircular groove of the rigid wheel. The flexible wheel is fixedly connected with inner ring and the rigid wheel is fixedly connected with outer ring of the main bearing. Both teeth height and root have cycloidal teeth profiles reduces the risk of breakage failure, possible to obtain larger engagement without deep engaging distance. Teeth width is large, used for the engagement, the surface specific pressure is small. It is possible to withstand large torque to reduce the amount of deformation of the flexible wheel, and to greatly improve the longevity.

Claims

1. A cycloidal pin wheel harmonic transmission device, characterized in that, the device comprises a camshaft, a flexible bearing, a flexible wheel, roller pins and a rigid wheel, wherein: the flexible bearing is mounted on the camshaft with an elliptical shape, the flexible wheel has an inner ring cooperated with an outer ring of the flexible bearing, and an outer teeth surface contacted with each of the roller pins, the roller pins are evenly disposed inside a semicircular groove of the rigid wheel, and the flexible wheel is fixedly connected with an inner ring of a main bearing, and the rigid wheel is fixedly connected with an outer ring of the main bearing, the flexible wheel has a teeth profile obtained by offsetting a curve equidistantly toward a center of the flexible wheel by a given distance, the curve satisfying the following equations:
x=E*Cos(t(Z−1))+R*Cos(t); and
y=E*Sin(t*(Z−1))+R*Sin(t), x and y are center coordinates of the roller pins with respect to time t using the center of the flexible wheel as a coordinate origin, E is an eccentricity of planetary motion, Z is a number of the roller pins, and R is a radius of the roller pins.

2. The cycloidal pin wheel harmonic transmission device according to claim 1, characterized in that, the camshaft is closely fitted together with an inner ring of the flexible bearing, so as to form a wave generator; and the inner ring of the flexible wheel is closely fitted together with the outer ring of the flexible bearing.

3. The cycloidal pin wheel harmonic transmission device according to claim 1, characterized in that, the roller pins are circumferentially and evenly disposed inside the semicircular groove of the rigid wheel.

4. The cycloidal pin wheel harmonic transmission device according to claim 1, characterized in that, the flexible wheel is constructed to have a cup-shape; a bottom of the flexible wheel is designed as a through hole, and the inner ring of the main bearing is provided with a threaded hole corresponding to the through hole of the flexible wheel, so as to be fixedly connected with it by using a screw; the rigid wheel has an outer ring provided with a threaded hole, and the outer ring of the main bearing is provided with a through hole corresponding to the threaded hole of the rigid wheel, so as to be fixedly connected with it also by using a screw; and the main bearing is a crossed roller bearing.

5. The cycloidal pin wheel harmonic transmission device according to claim 1, wherein the given distance is the radius of the roller pins.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings, used in the describing of the embodiments of the present invention or the description of the prior art, will be briefly explained below. The drawings, referred to in the following description, are only certain exemplary embodiments of the present invention, and it is obvious to those skilled in the art that, other drawings may be obtained from the drawings mentioned above without any creative work.

(2) FIG. 1 is a schematic diagram showing the principle of the structure of a cycloidal pinwheel harmonic transmission;

(3) FIG. 2 is an exploded schematic diagram of the cycloidal pin wheel harmonic transmission;

(4) FIG. 3 is a cross-sectional view showing the structure of the cycloidal pin wheel harmonic transmission;

(5) FIG. 4 is a front view of the cycloidal pinwheel harmonic transmission;

(6) FIG. 5 is a schematic diagram showing the engaging state when the camshaft of the cycloidal pin wheel harmonic transmission rotates at a fixed angle; and

(7) FIG. 6 is a schematic diagram showing the principle of forming the epicycloid.

DETAILED DESCRIPTION

(8) All of the features disclosed in this specification or all of the steps of methods or processes disclosed herein may be combined in any manner, except for mutually exclusive features and/or steps.

(9) Any features, disclosed in the specification including any additional claims, abstract and drawings, may be replaced by other equivalent or alternative features which may achieve similar functions, unless specifically stated. That is to say, each of the features is only one example of a series of equivalent or similar features, unless specifically stated.

(10) As shown in FIGS. 1 to 4, a flexible bearing 2 is mounted on a camshaft 1 with a elliptical shape. The inner ring of the flexible wheel 3 and the outer ring of the flexible bearing 2 are cooperated with each other. The outer teeth surface of flexible wheel 3 is in contact with each of the roller pins 4. The roller pins 4 is evenly disposed inside the semicircular groove of the rigid wheel 5. The inner ring of a main bearing 6 is fixedly connected with the flexible wheel 2, and the outer ring of the main bearing 6 is fixedly connected with the rigid wheel 5.

(11) Specifically, a cam shaft 1, used in the present invention, is closely fitted together with the inner ring of the flexible bearing 2, so as to form a wave generator. The inner ring of the flexible wheel 3 is closely fitted together with the outer ring of the flexible bearing 2. Due to the outer shape of the camshaft 1, which presents an elliptical curve, theoretically, the inner ring of the flexible bearing 2, the outer ring of the flexible bearing 2, and the inner ring of the flexible wheel 3 are equidistant curves of the ellipse of the camshaft 1.

(12) More specifically, the roller pins 4 are circumferentially and evenly disposed inside the semicircular groove of the rigid wheel 5. In order to prevent the roller pins 4 from disengaging axially, the semicircular groove of the rigid wheel 5 is needed to be designed as a structure with a rib. Also, in order to prevent the interference with the flexible wheel 2, the inner diameter of the rib should not be less than the diameter of the circle, along which the roller pins 4 are distributed.

(13) Further, the flexible wheel 3 is a cup-shaped structure. The bottom of the flexible wheel 3 is designed with a through hole. The inner ring of the main bearing 6 is provided with a threaded hole, corresponding to the through hole of the flexible wheel 3, so as to fixedly connect the main bearing 6 with the flexible wheel 3 by using screws. The outer ring of the rigid wheel 5 is provided with a threaded hole. The outer ring of the main bearing 6 is provided with a through hole, corresponding to the threaded hole of the rigid wheel 5, so as to fixedly connect the main bearing 6 with the rigid wheel 5 by also using screws. The main bearing 6 is a cross-roller bearing, which may support both radial load and bear axial load, as well as support bending moment.

(14) Furthermore, in theory, the design parameters of the teeth profile of the flexible wheel 3 are respectively defined as: the radius R of the reference circle, along which the centers of the roller pins 4 are disposed on the rigid wheel 5; the number Z of the roller pins 4; the radius R of the roller pins 4; and the eccentricity E of the planetary movement. Taking the center of the flexible wheel 3 as the coordinate origin, the parameter equation of the center coordinate (x, y) of the roller pins 4 with respect to the time t is as follows.
x=E*Cos(t*(Z−1))+(R−E)*Cos(t)
y=E*Sin(t*(Z−1))+(R+E)*Sin(t)

(15) The teeth profile of the flexible wheel 3 is an equidistant curve of the center curve of the roller pins 4. The offset amount of the equidistant curve is equal to the radius of the roller pins 4, and the offset is performed in a direction toward the center. In order to make the roller pins 4 tangent to the flexible wheel 3, it is required that the eccentricity E of the planetary movement is equal to half the difference between the long semi-axis and the short semi-axle of the camshaft 1.

(16) Furthermore, the elliptical teeth profile, mentioned above, is not convenient to process and cannot be used. In the present invention, the teeth profile of the flexible wheel 3 is obtained by the following method.

(17) The designing equations used herein are as follows:
x=E*Cos(t*(Z−1))+R*Cos(t)
y=E*Sin(t*(Z−1))+R*Sin(t)

(18) Wherein, the eccentricity E is equal to half of the difference between the long semi-axis and the short semi-axis of the camshaft 1; R is equal to the radius of the circle, along which the roller pins 4 are distributed; and Z is the number of the roller pins 4. If the curve is offset equidistantly toward the center, with an offset distance equal to half of the roller pins 4, the curve in a free state of flexible wheel 3 would be obtained. When the camshaft 1 is embedded into the flexible bearing 2, and when the flexible wheel 3 is embedded into the flexible bearing 2, the curve of the flexible wheel 3 is changed, because of the ellipse of the cam shaft 1. As a result, the roller pins 4 is tangent to the flexible wheel 2 at all positions.

(19) While working, when the camshaft 1 is loaded into the flexible bearing 2, and when the flexible bearing 2 is loaded into the flexible wheel 3 in turn, the flexible wheel 3 is forced to elastically deform and appear an elliptical shape. This results in that, the root of the teeth of the flexible wheel 3 at the long axis is embedded into the roller pins 4, so as to form a state in which the root of the teeth is tangent, and in which the top of the of the teeth of the flexible wheel 3 at the short axis is also tangent to the roller pins 4. As a result, a contact holding state is maintained. When the cam shaft 1 is continuously rotated, the flexible wheel 3 is forced to constantly deform. The position, where the flexible wheel 3 and the roller pins 4 are in contact with each other, constantly changes, which results in a so-called misalignment motion and thus realizes a movement transmission.

(20) Further, as shown in FIG. 5, if it is assumed that the rigid wheel 5 is fixed, when the camshaft 1 is rotated to be at 0 degree, the flexible wheel 2 and the rigid wheel 5 coincide at position indicated by the arrow. When the camshaft 1 rotates clockwise to be at 180 degree, as shown by the arrow of the flexible wheel in the figure, the flexible wheel 2 then rotates a distance equal to one tooth counterclockwise. When the camshaft 1 is rotated clockwise to be at 360 degree, as shown by the arrow of the flexible wheel in the figure, the flexible wheel 2 then rotates a distance equal to two teeth counterclockwise. Therefore, when the rigid wheel is fixed and the flexible wheel rotates, the reduction ratio is equal to half of the teeth number of the flexible wheel 2.

(21) The camshaft 1 is shaped with an ellipse by the method of numerical control machining. The flexible wheel 2 is processed by slow wire or by using a hob. The rigid wheel 5 is processed by the method of numerically controlled milling machine, slow wire or gear shaping. It can be seen that the processes above are very simple.

(22) The roller pins 4 are formed of the material of bearing steel, whose hardness after heat treatment may be up to HRC60-62 and roughness Ra may be up to above 0.4. It is beneficial to reduce wear and improve life.

(23) As shown in FIG. 6, the cycloidal wheel 201 is fixed, while the roller pins 202 moves relative to the cycloidal wheel in particular certain regularity. The movement regularity may be determined by the mechanism and the transmission ratio of the reducer. At the periphery of the cycloidal wheel, the roller pins continuously move according to a given movement regularity. On the periphery of the cycloidal wheel, the outer circle of the roller pins forms a continuous closed envelope, and this envelope is also the teeth profile curve of the cycloidal wheel.

(24) The above is only some particular embodiments of the present invention. The scope of the present invention is not limited thereto. Any changes or substitutions, which may be obtained by those skilled in the art without any creative effort, are included within the scope of the present invention. Therefore, the claimed scope of the invention should be defined by the appended claims.