US 8,555,505 B2Granted

Maximum meshable tooth profile having non-positive deflection in flat wave gear device

AssigneeHarmonic Drive Systems Inc.

InventorShoichi Ishikawa

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Abstract

In a flat wave gear device, there is determined a rack-approximated movement locus Lc1 of a flexible externally toothed gear with respect to an S-side rigid internally toothed gear accompanying rotation of a wave generator. ρOPT is a minimum value of the radius of curvature of the movement locus Lc1, and is determined from an evolute e of the movement locus Lc1. A convex arc having a radius ρ (ρ≦ρOPT) is used in a main part of a tooth profile of the flexible externally toothed gear. A parallel curve c that is set apart from a movement locus Lc2 by the arc radius ρ is used on a main part of a tooth profile to be generated on the S-side rigid internally toothed gear. The movement locus Lc2 accounts for the actual number of teeth, and is obtained from a center A of a convex arc of the flexible externally toothed gear being drawn with respect to the rigid internally toothed gear. In a flat wave gear device that is provided with a flexible externally toothed gear having a non-positive deflection (κ≦1) tooth profile, a tooth depth of the flexible externally toothed gear can be increased, whereby ratcheting torque is increased and meshing can occur continuously over an entire range of a movement locus; and a load capacity of the flat wave gear device is increased.

A flat wave gear device, comprising:

a D-side rigid internally toothed gear;
an S-side rigid internally toothed gear disposed in parallel in a coaxial state with the D-side rigid internally toothed gear;
an annular flexible externally toothed gear disposed in a coaxial state within the D-side and the S-side rigid internally toothed gears;
and
a wave generator for causing a cross-section of the flexible externally toothed gear given perpendicularly with respect to an axis thereof to flex elliptically and the resulting shape to rotate;
a number of teeth on the D-side rigid internally toothed gear being the same as a number of teeth on the flexible externally toothed gear, and a number of teeth on the S-side rigid internally toothed gear having 2n more teeth, n being a positive integer, than the number of teeth on the flexible externally toothed gear;
the flat wave gear device having a tooth profile derived from the following method:
using both the flexible externally toothed gear and the S-side rigid internally toothed gear as spur gears of module m;
setting κmn, wherein κ≦1, and −κmn as a degree of radial flexing on, respectively, a major and minor axis of an elliptically shaped rim neutral line of the flexible externally toothed gear, a line passing through the center part along a thickness direction of a tooth root rim when the flexible externally toothed gear is deformed into an elliptical shape, in the cross-section of the flexible externally toothed gear given perpendicularly with respect to the axis;
determining a rack-approximated movement locus of the flexible externally toothed gear with respect to the S-side rigid internally toothed gear accompanying rotation of the wave generator;
taking ρOPT as a minimum value of a radius of curvature of the movement locus;
and
using a convex arc having a radius ρ, wherein ρ≦ρOPT, on a main part of a tooth profile of the flexible externally toothed gear;
wherein the method for setting the tooth profile in the flat wave gear device further comprises:
determining the movement locus using formula (1);
determining an evolute of the movement locus using formula (2);
and
determining the radius of curvature ρOPT using formula (3), with θ=π in formula (2)
⁢
x
=
0.5
⁢
mn
⁡
(
θ
-
κ
⁢
⁢
sin
⁢
⁢
θ
)
⁢
⁢
⁢
y
=
-
κ
⁢
⁢
mn
⁡
(
1
-
cos
⁢
⁢
θ
)
(
1
)
x
=
mn
⁡
[
0.5
⁢
(
θ
-
κ
⁢
⁢
sin
⁢
⁢
θ
)
+
2
⁢
{
0.25
⁢
(
1
-
κ
⁢
⁢
cos
⁢
⁢
θ
)
2
+
κ
2
⁢
sin
2
⁢
θ
}
1.5
κ
⁡
(
κ
-
cos
⁢
⁢
θ
)
⁢
cos
⁢
{
tan
-
1
⁢
0.5
⁢
(
1
-
κ
⁢
⁢
cos
⁢
⁢
θ
)
κ
⁢
⁢
sin
⁢
⁢
θ
}
]
⁢
⁢
y
=
mn
⁡
[
κ
⁢
⁢
cos
⁢
⁢
θ
-
1
+
2
⁢
{
0.25
⁢
(
1
-
κ
⁢
⁢
cos
⁢
⁢
θ
)
2
+
κ
2
⁢
sin
2
⁢
θ
}
1.5
κ
⁡
(
κ
-
cos
⁢
⁢
θ
)
⁢
sin
⁢
{
tan
-
1
⁢
0.5
⁢
(
1
-
κ
⁢
⁢
cos
⁢
⁢
θ
)
κ
⁢
⁢
sin
⁢
⁢
θ
}
]
(
2
)
⁢
ρ
OPT
=
0.25
⁢
mn
⁢
⁢
(
1
+
κ
)
2
κ
.
(
3
)

248 more elements

Facts

Application

12/926,698Filed 6 Dec 2010 · division

Priority

JP 2007-3136294 Dec 2007

Published

US 2011/0138952 A116 Jun 2011

Granted

15 Oct 2013

Term ends

Not estimatedThe source records don’t support an estimate.

Classification9 codes

G01B 5/202
For measuring contours or curvatures: of gears
F16H 55/0833
Profiling: flexible toothed member, e.g. harmonic drive
Y10T 29/49462
Method of mechanical manufacture: gear making
Y10T 29/49467
Gear making: gear shaping

Abstract

Claims4