METHOD OF MAKING STRAIN WAVE GEARING

Abstract

A method of making a strain wave includes the steps of a) providing a circular spline, a flexspline meshed with the circular spline, and an initial wave generator having an initial outer profile of a standard ellipse with a perimeter S.sub.0, and b) producing a modified wave generator rotatably fitted within the flexspline and having a modified outer profile with a perimeter S. A difference E.sub.S between the perimeter S of the modified outer profile and the perimeter S.sub.0 of the initial outer profile satisfies the equation E.sub.S=S−S.sub.0=0.1 m to 0.8 m, wherein m is the modulus of the flexspline. Through a special parameter design of the modified wave generator, the meshing ratio between the circular spline and the flexspline is increased, thereby improving the transmission accuracy and reducing the average load.

Claims

1. A method of making a strain wave gearing, comprising the steps of: a) providing a circular spline having an inner annular toothed portion, a flexspline rotatably mounted within the circular spline and provided with an outer annular toothed portion meshed with the inner annular toothed portion of the circular spline, and an initial wave generator capable of being rotatably fitted within the flexspline, the initial wave generator having an initial elliptical outer profile capable of being abutted against an inner profile of the flexspline, the initial elliptical outer profile having a perimeter S.sub.0 satisfying the equation S.sub.0=∫.sub.0.sup.2π√{square root over (∂.sub.0(r.sub.0).sup.2+r.sub.0.sup.2)}, wherein: r.sub.0 is a radius of curvature of the initial elliptical outer profile and satisfies the equation r.sub.0=√{square root over ((a sin θ).sup.2+(b cos θ).sup.2)}, 0≦θ≦2θ; a is a semi-major axis of the initial elliptical outer profile; b is a semi-minor axis of the initial elliptical outer profile; and θ is an eccentric angle of the initial elliptical outer profile; and b) producing a modified wave generator rotatably fitted within the flexspline, the modified wave generator having a modified elliptical outer profile derived from the initial elliptical outer profile and abutted against the inner profile of the flexspline, the modified elliptical outer profile having a perimeter S satisfying the equation S=∫.sub.0.sup.2π√{square root over (∂.sub.θ(r).sup.2+r.sup.2)}; wherein r is a radius of curvature of the modified elliptical outer profile and satisfies the equation r=√{square root over (x.sup.2+y.sup.2)}; x satisfies the equation x={a′+C.sub.a(sin(4θ′−(π/2))+1)}sin θ′, 0≦θ′≦2π; y satisfies the euqation y={b′+C.sub.b(sin(4θ′−(π/2))+1)}cos θ′, 0≦θ′≦2π; a′ is a semi-major axis of the modified elliptical outer profile, which is equal to the semi-major axis of the initial elliptical outer profile; b′ is a semi-minor axis of the modified elliptical outer profile, which is equal to the semi-minor axis of the initial elliptical outer profile; θ is an eccentric angle of the modified elliptical outer profile; C.sub.a is a semi-major modification factor; C.sub.b is a semi-minor modification factor; and C.sub.a and C.sub.b range from −0.2 m to 0.2 m, respectively, wherein m is a modulus of the flexspline; wherein a difference E.sub.S between the perimeter S of the modified elliptical outer profile and the perimeter S.sub.0 of the initial elliptical outer profile satisfies the equation E.sub.S=S−S.sub.0=0.1 m to 0.8 m, wherein m is the modulus of the flexspline.

2. The method as claimed in claiml, wherein the circular spline and the flexspline have a same modulus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic structural view of a strain wave gearing comprising a circular spline, a flexspline and an initial wave generator in accordance with the present invention.

[0010] FIG. 2 is a schematic drawing illustrating outer profiles of the initial wave generator and a modified wave generator in accordance with the present invention, in which the dash line indicates the outer profile of the initial wave generator, and the solid line indicates the outer profile of the modified wave generator derived from the outer profile of the initial wave generator.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Referring to FIGS. 1 and 2, a method of making a strain wave gearing provided by an embodiment of the present invention comprised the following steps.

[0012] a) Provide a strain wave gearing 10 composed of a rigid circular spline 20, a flexspline 30, and an initial wave generator 40, as shown in FIG. 1. For the strain wave gearing 10, an existing, commercially available strain wave gearing may be used.

[0013] Specifically, the circular spline 20 has an inner annular toothed portion 22. The flexspline 30 is rotatably mounted within the circular spline 20 and provided with an outer annular toothed portion 32 meshed with the inner annular toothed portion 22 of the circular spline 20. It is to be noted that the number of teeth of the inner annular toothed portion 22 of the circular spline 20 is two or more times of the number of teeth of the outer annular toothed portion 32 of the flexspline 30. Further, the circular spline 20 and the flexspline 30 have a same modulus. The modulus used in this invention is defined as the quotient obtained by dividing the gear pitch diameter by the number of teeth.

[0014] For the initial wave generator, a physical, commercially available wave generator or a virtual wave generator may be used. As shown in FIG. 1, the initial wave generator 40 is rotatably fitted within the flexspline 30 and has an outer profile 41 of a standard ellipse. The initial elliptical outer profile 41 of the initial wave generator 40 is abutted against an inner profile of the flexspline 30. As a result, when the wave generator 40 is driven to rotate by a power source (not shown), the flexspline 30 will be pushed and deformed by the outer profile 41 of the wave generator 40, causing the inner annular toothed portion 22 of the circular spline 20 to be completely meshed with the outer annular toothed portion 32 of the flexspline 30 in the major axis direction of the wave generator 40 and completely disengaged from the outer annular toothed portion 32 of the flexspline 30 in the minor axis direction of the wave generator 40. Thus, the circular spline 20 can be rotated by the flexspline 30 to achieve the effect of torque output.

[0015] The initial elliptical outer profile 41 of the initial wave generator 40 has a perimeter S.sub.0 satisfying the equation S.sub.0=∫.sub.0.sup.2π√{square root over (∂.sub.θ(r.sub.0).sup.2+r.sub.0.sup.2)}, wherein:

[0016] r.sub.0 is a radius of curvature of the initial elliptical outer profile 41 and satisfies the equation r.sub.0=√{square root over ((a sin θ).sup.2+(b cos θ).sup.2)}, 0≦θ≦2π;

[0017] a is a semi-major axis of the initial elliptical outer profile 41 of the initial wave generator 40;

[0018] b is a semi-minor axis of the initial elliptical outer profile 41 of the initial wave generator 40; and

[0019] θ is an eccentric angle of the initial elliptical outer profile 41 of the initial wave generator 40.

[0020] b) Produce a modified wave generator 42 by modifying the initial wave generator 40 and mount the modified wave generator 42 inside the flexspline 30 in lieu of the initial wave generator 40, so as to complete the strain wave gearing 10 of the present invention.

[0021] Specifically, the modified wave generator 42 is configured having a modified elliptical outer profile 43, which is derived from the initial elliptical outer profile 41 of the initial wave generator 40 and is abutted against the inner profile of the flexspline 30 when the modified wave generator 42 is rotatably fitted within the flexspline 30. The modified elliptical outer profile 43 is configured having a perimeter S satisfying the equation S=∫.sub.0.sup.2π√{square root over (θ.sub.θ(r).sup.2+r.sup.2)}; wherein:

[0022] r is a radius of curvature of the modified outer profile 43 of the modified wave generator 42 and satisfies the equation r=√{square root over (x.sup.2+y.sup.2)};

[0023] x satisfies the equation x={a′+C.sub.a(sin(4θ′−(π/2))+1)}sin θ′, 0≦θ′≦2π;

[0024] y satisfies the equation x={a′+C.sub.a(sin(4θ′−(π/2))+1)}sin θ′, 0≦θ′≦2π;

[0025] a′ is a semi-major axis of the modified elliptical outer profile 43 of the modified wave generator 42, which is equal to the semi-major axis of the initial elliptical outer profile 41 of the initial wave generator 40;

[0026] b′is a semi-minor axis of the modified elliptical outer profile 43 of the modified wave generator 42, which is equal to the semi-minor axis of the initial elliptical outer profile 41 of the initial wave generator 40;

[0027] θ′ is an eccentric angle of the modified elliptical outer profile 43 of the modified wave generator 42;

[0028] C.sub.a is a semi-major modification factor, C.sub.b is a semi-minor modification factor, and C.sub.a and C.sub.b range from −0.2 m to 0.2 m, respectively, wherein m is a modulus of the flexspline.

[0029] Further, the modified wave generator 42 is configured in a way that a difference E.sub.S between the perimeter S of the modified elliptical outer profile 43 and the perimeter S.sub.0 of the initial elliptical outer profile 41 satisfies the equation E.sub.S=S−S.sub.0=0.1 m to 0.8 m, wherein m is the modulus of the flexspline 30.

[0030] With the wave generator 42, which has the elliptical outer profile 43 modified from the initial elliptical outer profile 42 of an initial wave generator 40 and is installed inside the flexspline 30, during the operation of the wave generator 42 to rotate the flexspline 30 relative to the circular spline 20, engaging and disengaging frequency between the outer annular toothed portion 32 of the flexspline 30 and the inner annular toothed portion 22 of the circular spline 20 is increased, thereby increasing the number of teeth in mesh, and thus, the strain wave gearing 10 provided by the present invention can achieve a high meshing ratio and a high level of transmission accuracy and can also reduce the average load of the teeth.