Patent Description:
Compound harmonic gearboxes enable achieving a high power density. Such gearboxes may be used in machinery requiring high torque output at low speeds. Such gearboxes may also be compact and lightweight. <CIT> describes a shaft gear reducer.

Disclosed and defined in claim <NUM> is a compound harmonic gearbox.

In addition to of the above disclosed gearbox the gearbox may include a drive bearing including a drive bearing inner race connected to the wave generator, a drive bearing outer race connected to the flex spline, and a drive bearing rolling element therebetween.

In addition to one or more of the above disclosed aspects the drive bearing and the flex spline may have a same axial span and may be axially aligned with one another.

In addition to one or more of the above disclosed aspects the first radial outer shell of the first ground gear may be disposed against a first axial side of the output flange and a second radial outer shell of the second ground gear may be disposed against a second axial side of the output flange, whereby the output flange is partially encased in the housing.

In addition to one or more of the above disclosed aspects the stationary shaft may extend axially from a second axial end wall of the second ground gear and is secured to the first axial end wall of the first ground gear to thereby form the housing.

In addition to one or more of the above disclosed aspects the first axial end wall may include an opening that forms a keyway and the stationary shaft includes a key.

In addition to one or more of the above disclosed aspects the axial end of the stationary shaft may include a threaded tip configured to receive a nut to secure the first ground gear and the second ground gear to one another, thereby securing the housing at the output flange.

In addition to one or more of the above disclosed aspects the gearbox may include a plurality of support bearings respectively disposed on axially opposing ends of the flex spline.

In addition to one or more of the above disclosed aspects the flex spline may include a plurality of splines that are outer facing, including an output spline, a first ground spline on one side of the output spline and a second ground spline on another side of the output spline, so that the second ground spline is axially offset from the first ground spline, and the output spline is axially between the first ground spline and the second ground spline, whereby the flex spline is configured as a compound spline.

In addition to one or more of the above disclosed aspects the output flange may include output gear teeth that mesh with the output spline, the first ground gear may include first ground gear teeth that mesh with the first ground spline, and the second ground gear includes second ground gear teeth that mesh with the second ground spline.

In addition to one or more of the above disclosed aspects the first ground spline and the first ground gear teeth may be configured to mesh to thereby form a first gear ratio, and the output spline and the output gear teeth may be configured to mesh to thereby form a second gear ratio that differs from the first gear ratio to form a compound gear ratio.

In addition to one or more of the above disclosed aspects the second ground spline and the second ground gear teeth may be configured to mesh and form the first gear ratio.

In addition to one or more of the above disclosed aspects the second spur gear and the first ground gear teeth may be axially positioned at axially opposing ends of the stationary-shaft bearing; and a first support bearing of the plurality of support bearings is positioned axially intermediate the second spur gear and the first ground gear teeth.

In addition to one or more of the above disclosed aspects the gearbox mounting features may be threaded-holes.

Further disclosed is a method of operating the compound harmonic gearbox as defined in claim <NUM>.

Compound harmonic gearboxes may enable achieving a relatively high power density. Known compound harmonic gears, however, have a limited range of rotational motion. In view of such limitations, the disclosed embodiments provide a compound harmonic gearbox configured for continuous output rotation. Benefits of the disclosed compound harmonic gearbox include broader and more efficient application with earth moving equipment, power tools, robot end effectors, power steering gearboxes, power lift gates, and the like.

Turning to <FIG>, disclosed is a compound harmonic gearbox (gearbox) 100A according to an embodiment. The gearbox 100A includes ground gears generally referred to as <NUM> including a first ground gear 110A and a second ground gear 110B. The ground gears <NUM> are interconnected about a stationary shaft <NUM> to form a housing <NUM> (e.g., <FIG>). According to an embodiment only the first ground gear 110A includes gearbox mounting features <NUM>. The gearbox mounting features <NUM> may be threaded holes.

An output flange <NUM> is partially encased within the housing <NUM>. A flex spline <NUM> is within the housing <NUM>. The flex spline <NUM> drives the output flange <NUM> from gear meshing, discussed in greater detail below. A wave generator <NUM> is within the housing <NUM>. The wave generator <NUM> drives the flex spline <NUM> from impulses generated from rotation of the wave generator <NUM>.

An input shaft <NUM> includes an input gear <NUM> that drives the wave generator <NUM>. The input shaft <NUM> extends along an axial direction A (axially) through an input-shaft channel <NUM> in the first ground gear 110A. The input-shaft channel <NUM> extends axially through a first axial end wall 210A of the first ground gear 110A. With the disclosed configuration the output flange <NUM> may rotate completely, (e.g., more than <NUM> degrees clockwise or counterclockwise) around the stationary shaft <NUM> with rotation of the input shaft <NUM> in the same direction (or in an opposing direction, depending on the harmonic gears configuration).

The input gear <NUM> forms a first spur gear. An axial end <NUM> of the wave generator <NUM> forms a second spur gear 230A. The input gear <NUM> and second spur gear 230A mesh to enable the input gear <NUM> to drive the wave generator <NUM>.

One or more input-shaft bearings <NUM> are disposed in the input-shaft channel <NUM> for rotational positioning the input shaft <NUM>. The input shaft <NUM> is offset along a radial direction R (radially) from an axial center A of the stationary shaft <NUM>.

A stationary-shaft bearing <NUM> is provided between the stationary shaft <NUM> and the wave generator <NUM>. A portion <NUM> of the stationary shaft <NUM> forms a stationary-shaft inner race. A stationary-shaft bearing outer race <NUM> is disposed against the wave generator <NUM>. A stationary-shaft bearing rolling element <NUM> is disposed between the stationary shaft <NUM> and the stationary-shaft bearing outer race <NUM>.

A drive bearing <NUM> (e.g., <FIG>) is disposed between the wave generator <NUM> and the flex spline <NUM>. The drive bearing <NUM> includes a drive bearing inner race <NUM> disposed against the wave generator <NUM>. A drive bearing outer race <NUM> is disposed against the flex spline <NUM>. A drive bearing rolling element <NUM> is between the drive bearing inner race <NUM> and the drive bearing outer race <NUM>. The drive bearing <NUM> has a same axial span as the flex spline <NUM>. The drive bearing <NUM> is axially aligned
with the flex spline <NUM>.

A first radial outer shell <NUM> of the first ground gear 110A is disposed against a first axial side <NUM> of the output flange <NUM>. A second radial outer shell <NUM> of the second ground gear 110B is disposed at a second axial side <NUM> of the output flange <NUM>. From this configuration the output flange <NUM> is partially encased in the housing <NUM>. There would be an axial clearance <NUM> between both axial sides of the output flange <NUM> and the outer shells <NUM>, <NUM>. This clearance <NUM> would allow for motion between the output flange <NUM> and the outer ground shells of the ground gear <NUM>.

The stationary shaft <NUM> extends axially from a second axial end wall 210B of the second ground gear 110B toward the first ground gear 110A. The stationary shaft <NUM> is secured to the first axial end wall 210A of the first ground gear 110A, as discussed in further detail below. This configuration forms the housing <NUM>.

The first axial end wall 210A includes an opening <NUM>. The opening <NUM> forms a keyway. An axial end <NUM> of the stationary shaft <NUM> forms a key <NUM>. This configuration prevents relative rotational motion between the ground gears <NUM> when connected. The axial end <NUM> of the stationary shaft <NUM> is includes threaded tip <NUM> configured to receive a nut <NUM>. The nut <NUM> secures the ground gears <NUM> to one another. This configuration secures the housing <NUM> at the output flange <NUM>, leaving the clearance <NUM> between the output flange <NUM> and the outer shells <NUM>, <NUM>.

The gearbox 100A further includes a plurality of support bearings <NUM> (e.g., <FIG>). The plurality of support bearings <NUM> include a first support bearing 412A and a second support bearing 412B. The plurality of support bearings <NUM> are positioned at axially opposing ends of the flex spline <NUM> and drive bearing <NUM>. According to a disclosed embodiment, the plurality of support bearings <NUM> are ball bearings.

The flex spline <NUM> includes a plurality of splines <NUM> (e.g., <FIG>) to thereby form a compound spline. For example, the flex spline <NUM> includes a first ground spline 420A, a second ground spline 420B and an output spline 420C. The second ground spline 420B is axially offset from the first ground spline 420A. The output spline 420C is axially intermediate the first ground spline 420A and the second ground spline 420B. Each of the first ground spline 420A, the second ground spline 420B and the output spline 420C are outer facing splines.

The first ground gear 110A includes first ground gear teeth 430A. The first ground gear teeth 430A mesh with the first ground spline 420A. The second ground gear 110B includes second ground gear teeth 430B. The second ground gear teeth 430B mesh with the second ground spline 420B. The output flange <NUM> includes output gear teeth 430C. The output gear teeth 430C mesh with the output spline 420C. Each of the first ground gear teeth 430A, the second ground gear teeth 430B and the output gear teeth 430C are inner facing teeth.

The plurality of splines <NUM> are configured to mesh with the ground gears <NUM> and the output flange <NUM> according to different gear ratios. The first ground spline 420A and the first ground gear teeth 430A have a first gear ratio (Ratio <NUM>, below). The second ground spline 420B and the second ground gear teeth 430B also have the first gear ratio. The output spline 420C and the output gear teeth 430C have a second gear ratio (Ratio <NUM>, below) that differs from the first gear ratio. The splines <NUM> are integral to same structure, that is, the flex spline <NUM>. Thus the different gear ratios together form a compound gear ratio (Compound Ratio, below). The compound gear ratio provides a differential motion between the ground gears <NUM> and the output flange <NUM>.

The compound gear ratio is represented as the difference of the individual gear ratios: <MAT> <MAT> <MAT>.

The second spur gear 230A and the first ground gear teeth 430A are axially positioned at axially opposing ends of the stationary-shaft bearing <NUM> (e.g., <FIG>). The first support bearing 412A is positioned axially intermediate the second spur gear 230A and the first ground gear teeth 430A.

Turning to <FIG>, disclosed is a second compound harmonic gearbox (the second gearbox) 100B according to an illustrative example not forming part of the invention according to the appended claims. Aspects of the second gearbox 100B shall be identified as by same reference numbers as aspects of the gearbox 100A of <FIG>. Differences, if any, are those expressly identified below.

The second gearbox 100B includes ground gears generally referred to as <NUM> including a first ground gear 110A and a second ground gear 110B. The ground gears <NUM> are interconnected about a stationary shaft <NUM> to form a housing <NUM> (e.g., <FIG>). According to an embodiment only the first ground gear 110A includes gearbox mounting features <NUM>. The gearbox mounting features <NUM> may be threaded holes.

An input shaft <NUM> includes an input gear <NUM> that drives the wave generator <NUM>. The input shaft <NUM> extends radially through an input-shaft channel <NUM> in the first ground gear 110A. The input-shaft channel <NUM> extends radially through a first radial outer shell <NUM> of the first ground gear 110A. With the disclosed configuration the output flange <NUM> may rotate completely, more than <NUM> degrees clockwise or counterclockwise, around the stationary shaft <NUM> with rotation of the input shaft <NUM> in one direction or another direction. As illustrated, the input shaft <NUM> and output flange <NUM> rotate perpendicularly to one another.

The input gear <NUM> forms a first bevel gear. An axial end <NUM> of the wave generator <NUM> forms a second bevel gear 230B. The input gear <NUM> and second bevel gear 230B mesh to enable the input gear <NUM> to drive the wave generator <NUM>.

One or more input-shaft bearings <NUM> are disposed in the input-shaft channel <NUM> for rotational positioning the input shaft <NUM>.

A stationary-shaft bearing <NUM> is provided between the stationary shaft <NUM> and the wave generator <NUM>. A portion <NUM> of the stationary shaft <NUM> forms a stationary-shaft bearing inner race. A stationary-shaft bearing outer race <NUM> is disposed against the wave generator <NUM>. A stationary-shaft bearing rolling element <NUM> is disposed between the stationary shaft <NUM> and the stationary-shaft bearing outer race <NUM>.

A drive bearing <NUM> (e.g., <FIG>, which is equally applicable in this embodiment) is disposed between the wave generator <NUM> and the flex spline <NUM>. The drive bearing <NUM> includes a drive bearing inner race <NUM> disposed against the wave generator <NUM>. A drive bearing outer race <NUM> is disposed against the flex spline <NUM>. Drive bearing rolling elements <NUM> are between the drive bearing inner race <NUM> and the drive bearing outer race <NUM>. The drive bearing <NUM> has a same axial span as the flex spline <NUM>. The drive bearing <NUM> is axially aligned with the flex spline <NUM>.

The first radial outer shell <NUM> of the first ground gear 110A is disposed against a first axial side <NUM> of the output flange <NUM>. A second radial outer shell <NUM> of the second ground gear 110B is disposed against a second axial side <NUM> of the output flange <NUM>. From this configuration the output flange <NUM> is partially encased in the housing <NUM>.

The stationary shaft <NUM> extends axially from a second axial end wall 210B of the second ground gear 110B toward the first ground gear 110A. The stationary shaft <NUM> is secured to a first axial end wall 210A of the first ground gear 110A, as discussed in further detail below. This configuration forms the housing <NUM>.

The first axial end wall 210A includes an opening <NUM>. The opening <NUM> forms a keyway. An axial end <NUM> of the stationary shaft <NUM> is formed to include a key <NUM>. This configuration prevents relative rotational motion between the ground gears <NUM> when connected. The axial end <NUM> of the stationary shaft <NUM> is includes threaded tip <NUM> configured to receive a nut <NUM>. The nut <NUM> secures the ground gears <NUM> to one another. This configuration secures the housing <NUM> at the output flange <NUM>, leaving the clearance <NUM> between the output flange <NUM> and the outer shells <NUM>, <NUM>.

The second bevel gear 230B and the first ground gear teeth 430A are at axially positioned at axially opposing ends of the stationary-shaft bearing <NUM> (e.g., <FIG>). The first support bearing 412A is positioned axially intermediate the second bevel gear 230B and the first ground gear teeth 430A.

The above configurations are balanced to react all generated loads through the gearbox mounting features <NUM> on the first ground gear 110A. From the above configuration an external movable structure connected to the output flange <NUM> may rotate relative to an external stationary structure connected to the first ground gear 110A and the input shaft <NUM>. Such external stationary structure and external movable structure may be components of, for example, earth moving equipment, power tools, robot end effectors, power steering gearboxes, power lift gates, and the like.

Claim 1:
A compound harmonic gearbox (100A) comprising:
a first ground gear (110A) and a second ground gear (110B) being interconnected about a stationary shaft (<NUM>) to form a housing (<NUM>),
wherein only the first ground gear (110A) includes gearbox mounting features (<NUM>);
an output flange (<NUM>) partially encased within the housing (<NUM>);
a flex spline (<NUM>) within the housing (<NUM>) that drives the output flange (<NUM>);
a wave generator (<NUM>) within the housing (<NUM>) that drives the flex spline (<NUM>);
an input shaft (<NUM>) with an input gear (<NUM>) that drives the wave generator (<NUM>),
the input shaft (<NUM>) extending through the first ground gear (110A),
wherein the output flange (<NUM>) rotates completely around the stationary shaft (<NUM>) by rotating the input shaft (<NUM>);
and characterized in that :
the input shaft (<NUM>) extends through an input-shaft channel (<NUM>) in a first radial outer shell (<NUM>) of the first ground gear (110A);
one or more input-shaft bearings (<NUM>) are disposed in the input-shaft channel (<NUM>) for rotational positioning of the input shaft (<NUM>); and
the input shaft (<NUM>) extends radially through the first radial outer shell (<NUM>); and
the input gear (<NUM>) defines a first bevel gear and an axial end of the wave generator (<NUM>) defines a second bevel gear (230B) that meshes with the input gear (<NUM>);
the input shaft (<NUM>) extends axially through a first axial end wall (<NUM>) and is radially offset from an axial center (A) of the stationary shaft (<NUM>); and
the input gear (<NUM>) defines a first spur gear, and an axial end of the wave generator (<NUM>) defines a second spur gear that meshes with the first spur gear, and
wherein the input shaft (<NUM>) extends radially through the first radial outer shell (<NUM>) of the first ground gear (110A); and
the gearbox (100A) further comprising:
a stationary-shaft bearing (<NUM>),
wherein:
a portion (<NUM>) of the stationary shaft (<NUM>) defines a stationary-shaft bearing inner race (<NUM>);
a stationary-shaft bearing outer race (<NUM>) is connected to the wave generator (<NUM>); and
a stationary-shaft bearing rolling element (<NUM>) is disposed therebetween.