US 2026/0185594 A1Published application

Strain wave gearing and externally toothed gear

AssigneeHarmonic Drive Systems Inc.

InventorNorio SHIROKOSHI

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Abstract

An externally toothed gear (3) of a strain wave gearing (1) is provided with external teeth (34), the tooth profile of which gradually changes along the tooth trace direction. The external teeth (34) are each provided with an external tooth portion (341) that is capable of meshing with internal teeth (24) of an internally toothed gear (2), and an external tooth extension portion (342) that does not mesh with the internal teeth (24). The external tooth extension portions (342) have a tapered tooth profile that tapers off, and serves as a guide for instances when the external teeth (34) are inserted between the internal teeth (24). The tooth profile (342c) of the external tooth extension portions (342) is slightly smaller than the tooth profile (341c) at first ends (341a) of the external tooth portions (341), to which the external tooth extension portions (342) are linked. The tooth profile (342c) does not protrude in the tooth depth direction or the tooth thickness direction from the tooth profile (341c) due to misalignment of a molding die. It is easy to carry out fitting work for inserting the externally toothed gear (3) into the internally toothed gear (2) using the external tooth extension portions (342) as a guide.

Claims4

Dependent claims

A strain wave gearing (1) comprising a rigid internally toothed gear (2), a flexible externally toothed gear (3) that is coaxially disposed on an inner side of the internally toothed gear (2), and a wave generator (4) that is fitted to an inner side of the externally toothed gear (3), the externally toothed gear (3) being a molded article, the strain wave gearing (1) being characterized in that:

external teeth (34) of the externally toothed gear (3) are each provided with
an external tooth portion (341) that is capable of meshing with internal teeth (24) of the internally toothed gear (2), and
an external tooth extension portion (342) that is formed at a position set off from the internal teeth (24) in a tooth trace direction (W) and does not contribute to meshing with the internal teeth (24);
the external tooth portions (341) are each such that at least a top land circle diameter gradually decreases from a first end (341a) on one side in the tooth trace direction (W) toward a second end (341b) on the other side in the tooth trace direction (W), with a first draft angle for die molding in a first direction (W1) along the tooth trace direction (W) being formed;
the external tooth extension portions (342) are external tooth insertion guides when the external teeth (34) are inserted between the internal teeth (24) from the first-end (341a) side along the tooth trace direction (W), the external tooth extension portions (342) extending, continuously with the first ends (341a) of the external tooth portions (341), in a direction away from the first ends (341a) along the tooth trace direction (W);
and
the top land circle diameter of the external tooth extension portions (342)
is less than the top land circle diameter of the external tooth portions (341) at the first ends (341a) of the external tooth portions (341), and
gradually decreases from connection ends (342a), which are linked to the first ends (341a), as a distance from the connection ends (342a) along the tooth trace direction (W) increases, with a second draft angle for die molding in a second direction (W2) opposite a direction of the first draft angle being formed.

6 more elements

An externally toothed gear (3) of a strain wave gearing (1), the externally toothed gear (3) comprising a cylindrical barrel part (31) that is capable of flexing in a radial direction, a diaphragm (32) that extends radially inward from one end (31b) of the cylindrical barrel part (31), and external teeth (34) that are formed on an outer-peripheral-surface portion on an open-end (31a) side of the cylindrical barrel part (31), the open end (31a) being the other end of the cylindrical barrel part (31), the externally toothed gear (3) being a molded article in which the external teeth (34) are formed integrally with the cylindrical barrel part (31) using a molding die, the externally toothed gear (3) being characterized in that:

the external teeth (34) are each provided with
an external tooth portion (341) that is capable of meshing with internal teeth (24) of an internally toothed gear (2) of the strain wave gearing (1), and
an external tooth extension portion (342) that does not contribute to meshing with the internal teeth (24);
the external tooth portions (341) are each such that at least a top land circle diameter gradually decreases from a first end (341a) on one side in a tooth trace direction (W) toward a second end (341b) on the other side in the tooth trace direction (W), with a first draft angle for die molding in a first direction (W1) along the tooth trace direction (W) being formed;
the external tooth extension portions (342) are external tooth insertion guides when the external teeth (34) are inserted between the internal teeth (24) from the first-end (341a) side along the tooth trace direction (W), the external tooth extension portions (342) extending, continuously with the first ends (341a) of the external tooth portions (341), in a direction away from the first ends (341a) along the tooth trace direction (W);
and
a top land circle diameter of the external tooth extension portions (342)
is less than a top land circle diameter of the external tooth portions (341) at the first ends (341a) of the external tooth portions (341), and
gradually decreases from connection ends (342a), which are linked to the first ends (341a), as a distance from the connection ends (342a) along the tooth trace direction (W) increases, with a second draft angle for die molding in a second direction (W2) opposite a direction of the first draft angle being formed.

6 more elements

Dependencies are inferred from the claim text.