Patent Description:
Strain wave gearings are provided with characteristics such as being small and lightweight and having high rotational precision, high load capacity, and a high reduction ratio, and are therefore used in industrial robots, NC machinery, etc. Required speed ratios of strain wave gearings differ depending on the applications of the gearings, and products having different speed ratios are therefore prepared. A reduction gear converts torque and rotational speed without altering the output of a motor, and maximum torque and maximum rotational speed of a gearing containing the reduction gear are therefore determined when the speed ratio is determined. With prior-art strain wave gearings, one strain wave gearing is provided per motor. Therefore, it has been the case that when the speed ratio of the strain wave gearing is set to a certain level, the maximum torque, maximum rotational speed, and other indices of performance of the gearing are set to a certain level in accordance with the speed ratio.

<CIT> proposes a configuration in which, in order to obtain a rotation output of two degrees of freedom from one rotation input, two strain wave mechanisms are provided and a wave generator of one strain wave mechanism can be engaged with and disengaged from an input shaft via a clutch.

<CIT> discloses a strain wave gearing according to the preamble of independent claim <NUM>.

The purpose of the present invention is to provide a speed ratio switching type strain wave gearing in which a speed ratio of a rotation output relative to one rotation input can be switched to two stages or multiple stages by means of a simple configuration.

A speed ratio switching type strain wave gearing of the present invention comprises:.

In this speed ratio switching type strain wave gearing, for example, the wave generator is a rotation input element and the externally toothed gear is a rotation output element. One of the first and second internally toothed gears, which are in a rotation-enabled state, is switched by the clutch mechanism to a rotation-disabled fixed state.

For example, the first internally toothed gear is switched to a rotation-disabled fixed state. When the wave generator rotates in this state, relative rotation occurs between the first external teeth of the externally toothed gear and the first internally toothed gear restricted from rotating, the relative rotation corresponding to the difference in the number of teeth between these two gears. The externally toothed gear rotates because the first internally toothed gear is fixed. The second internally toothed gear, which is meshed with the second external teeth of the externally toothed gear, is in a rotation-enabled state and therefore rotates integrally with the externally toothed gear. Therefore, rotation output, which is reduced in speed in accordance with the difference in the number of teeth between the first external teeth and the first internally toothed gear, is extracted from the externally toothed gear.

The clutch mechanism switches the second internally toothed gear to a rotation-disabled fixed state and returns the first internally toothed gear to a rotation-enabled state. Rotation input delivered to the wave generator thereby becomes rotation output reduced in speed in accordance with difference in the number of teeth between the second external teeth of the externally toothed gear and the second internally toothed gear, and this rotation output is extracted from the externally toothed gear. Thus, the speed ratio of the rotation output obtained from one rotation input can be switched to two stages. The speed ratio of the rotation output can be switched to multiple stages by increasing the number of the sets of external teeth formed on the cylinder of the externally toothed gear. It is possible to realize a strain wave gearing having a compact and simple configuration with which one rotation input can be reduced in speed at a speed ratio of two or more levels and outputted.

Below are descriptions, made with reference to the drawings, of speed ratio switching type strain wave gearings according to embodiments to which the present invention is applied.

<FIG> is a front view of a speed ratio switching type cup strain wave gearing according to Embodiment <NUM>, and <FIG> is a cross-sectional view of the same. The speed ratio switching type cup strain wave gearing <NUM> (referred to below simply as the "strain wave gearing <NUM>") is provided with a first internally toothed gear <NUM>, a second internally toothed gear <NUM>, an externally toothed gear <NUM> having a cup shape, a wave generator <NUM>, and a clutch mechanism <NUM>.

The externally toothed gear <NUM> has a cup shape provided with a flexible cylinder <NUM> capable of flexing in a radial direction, a diaphragm <NUM> extending radially inward from a rear end of the cylinder <NUM>, and an annular rigid boss <NUM> formed integrally on an internal peripheral edge of the diaphragm <NUM>. A first number of first external teeth <NUM> and a second number of second external teeth <NUM> are formed on an external peripheral surface <NUM> of the cylinder <NUM>. Specifically, the first external teeth <NUM> are formed on the external peripheral surface <NUM> of the cylinder <NUM>, on a distal-end side portion thereof. The second external teeth <NUM> are formed on the external peripheral surface <NUM>, in a portion adjacent to the first external teeth <NUM> along an axis 1a.

The first internally toothed gear <NUM> is disposed in a position where the gear <NUM> concentrically encircles the first external teeth <NUM> in the externally toothed gear <NUM>. First internal teeth <NUM> formed on the first internally toothed gear <NUM> partially mesh with the first external teeth <NUM>, and the number of first internal teeth <NUM> is different from the number of first external teeth <NUM>. The second internally toothed gear <NUM> is aligned with the first internally toothed gear <NUM> along the axis 1a, and is in a position where the gear <NUM> concentrically encircles the second external teeth <NUM> in the externally toothed gear <NUM>. Second internal teeth <NUM> formed on the second internally toothed gear <NUM> partially mesh with the second external teeth <NUM>, and the number of second internal teeth <NUM> is different from the number of second external teeth <NUM>.

The wave generator <NUM> causes the portions in the cylinder <NUM> of the externally toothed gear <NUM> where the first and second external teeth <NUM>, <NUM> are formed to flex in the radial direction. Due to this flexing, the first external teeth <NUM> partially mesh with the first internal teeth <NUM> and the second external teeth <NUM> partially mesh with the second internal teeth <NUM>. In the present example, the portions of the cylinder <NUM> where the first and second external teeth <NUM>, <NUM> are formed are caused by the wave generator <NUM> to flex into an ellipsoidal shape, and at both long-axis ends of the ellipsoid, the first and second external teeth <NUM>, <NUM> respectively mesh with the first and second internal teeth <NUM>, <NUM>. Therefore, the difference in the number of teeth between the first internal teeth <NUM> and the first external teeth <NUM> and the difference in the number of teeth between the second internal teeth <NUM> and the second external teeth <NUM> are both set to 2n (n being a positive integer).

The wave generator <NUM> includes a cylindrical hub <NUM>, a rigid plug <NUM> mounted on an external peripheral surface of the hub <NUM> via an Oldham coupling <NUM>, and a wave bearing <NUM>. The rigid plug <NUM> includes an ellipsoidal external peripheral surface 53a. The wave bearing <NUM> is secured by being press-fitted in an ellipsoidally flexed state to the ellipsoidal external peripheral surface 53a.

The clutch mechanism <NUM> includes a ring-form clutch member <NUM> capable of sliding in the direction of the axis 1a, and a sliding mechanism <NUM> that causes the clutch member <NUM> to slide in the direction of the axis 1a. Engaging teeth <NUM> (splines) are formed on a circular internal peripheral surface of the clutch member <NUM>. Engaging teeth <NUM>, <NUM> (splines) capable of engaging with the engaging teeth <NUM> from the direction of the axis 1a are respectively formed on the circular external peripheral surfaces of the first and second internally toothed gears <NUM>, <NUM>. The clutch member <NUM> is able to slide in a direction parallel to the axis 1a, between an engagement position of engaging with the engaging teeth <NUM> of the first internally toothed gear <NUM> and an engagement position of engaging with the engaging teeth <NUM> of the second internally toothed gear <NUM>.

In the strain wave gearing <NUM> having this configuration, for example, the wave generator <NUM> is a rotation input element, and a rotating input shaft <NUM> is connected to the wave generator as shown by imaginary lines. The externally toothed gear <NUM> is a rotating output element, and an output member <NUM> is connected to the rigid boss <NUM> as shown by imaginary lines. The first external teeth <NUM> and the second external teeth <NUM> of the externally toothed gear <NUM> partially mesh with the first internally toothed gear <NUM> and the second internally toothed gear <NUM>, respectively. For example, the clutch member <NUM> is caused to mesh with the second internally toothed gear <NUM>, the second internally toothed gear <NUM> is switched to a rotation-disabled fixed state, and the other first internally toothed gear <NUM> remains able to rotate. When the wave generator <NUM> rotates, relative rotation occurs between the second external teeth <NUM> of the externally toothed gear <NUM> and the fixed second internally toothed gear <NUM>, the relative rotation corresponding to the difference in the number of teeth between these two gears. The externally toothed gear <NUM> rotates and rotation reduced in speed at a speed ratio corresponding to the difference in the number of teeth is outputted from the externally toothed gear <NUM> to the output member <NUM>.

When the clutch member <NUM> is caused to slide toward the first internally toothed gear <NUM>, the clutch member <NUM> disengages from the second internally toothed gear <NUM> and engages with the first internally toothed gear <NUM>. The first internally toothed gear <NUM> switches to a rotation-disabled fixed state, and relative rotation occurs between the first internally toothed gear <NUM> and the first external teeth <NUM>, the relative rotation corresponding to the difference in the number of teeth. Therefore, input rotation is reduced in speed by the externally toothed gear <NUM> at a speed ratio corresponding to the difference in the number of teeth between the first internally toothed gear <NUM> and the first external teeth <NUM>, and speed-reduced rotation is outputted from the externally toothed gear <NUM> to the output member <NUM>.

A limited time is needed for a speed-changing action to take place via the clutch member <NUM>. The clutch member <NUM> is engaged with and disengaged from the first and second internally toothed gears <NUM>, <NUM>, which rotate integrally with the externally toothed gear <NUM> at comparatively low speeds. It is therefore possible to minimize the incidence of anomalous events caused by the speed-changing action being in progress.

In the present example, the wave generator <NUM> is a rotation input element and the externally toothed gear <NUM> is a rotation output element. Conversely, if the wave generator <NUM> is a rotation output element and the externally toothed gear <NUM> is a rotation input element, input rotation can be increased at a different speed ratio and extracted as increased rotation output.

Furthermore, the present invention can be applied to a top hat strain wave gearing provided with an externally toothed gear having a top hat shape, and to a flat strain wave gearing (see <FIG>) provided with a cylindrical externally toothed gear.

<FIG> is a cross-sectional view of Modification <NUM> of the strain wave gearing <NUM>. The basic configuration of the strain wave gearing <NUM> shown in <FIG> is the same as that of the strain wave gearing <NUM>; therefore, the corresponding parts are denoted by the same symbols and descriptions thereof are omitted. The strain wave gearing <NUM> includes a number of wave generators corresponding to the number of speed-change levels. This is preferable because torque capacity thereby increases.

Specifically, the strain wave gearing <NUM> includes a first wave generator 5A that causes ellipsoidal flexure in the portion of the cylinder <NUM> of the externally toothed gear <NUM> where the first external teeth <NUM> are formed, and a second wave generator 5B that causes ellipsoidal flexure in the portion where the second external teeth <NUM> are formed. The first wave generator 5A includes a first rigid plug 53A having an ellipsoidal external peripheral surface (a first non-circular external peripheral surface), and a first wave bearing 54A mounted on the ellipsoidal external peripheral surface. Similarly, the second wave generator 5B includes a second rigid plug 53B having an ellipsoidal external peripheral surface (a second non-circular external peripheral surface), and a second wave bearing 54B mounted on the ellipsoidal external peripheral surface. In the present example, the first rigid plug 53A and the second rigid plug 53B are formed from a single component.

Flexure referred to as coning occurs in the cup-shaped externally toothed gear <NUM>. The wave generator 5B, which is disposed on the diaphragm <NUM> side of the externally toothed gear <NUM>, is preferably less of an ellipsoid than the wave generator 5A disposed on the opposite side, in accordance with there being less flexure caused by coning. Additionally, there is preferably a greater speed ratio on the side of the second external teeth <NUM> positioned on the diaphragm side where there is less flexure.

In the present example, the speed ratio is switched to two stages, but the strain wave gearing can also be configured such that the speed ratio is switched to three stages or multiple stages of a number greater than three, as in Embodiment <NUM> described hereinafter. A number of the sets of external teeth corresponding to the number of switching levels is preferably formed on the externally toothed gear, and the same number of internally toothed gears is preferably included.

<FIG> is a cross-sectional view of Modification <NUM> of the strain wave gearing <NUM>. The basic configuration of the strain wave gearing <NUM> shown in <FIG> is the same as that of the strain wave gearing <NUM>; therefore, the corresponding parts are denoted by the same symbols and descriptions thereof are omitted.

In the speed-changing configurations in the strain wave gearings <NUM>, <NUM> (see <FIG> and <FIG>) previously described, the engaging teeth <NUM>, <NUM> (splines) are provided to the external peripheral surfaces of the first and second internally toothed gears <NUM>, <NUM>, the ring-form clutch member <NUM> having the engaging teeth <NUM> cut into the inner side is selectively caused to mesh with the first and second internally toothed gears <NUM>, <NUM>, the clutch member <NUM> is moved in the direction of the axis 1a, and the first and second internally toothed gears <NUM>, <NUM> are switched between being fixed and free.

In the strain wave gearing <NUM> shown in <FIG>, clutch mechanisms 6A, 6B are provided respectively to the first and second internally toothed gears <NUM>, <NUM>. Speed is changed by switching the clutch mechanisms 6A, 6B between on and off. The clutch mechanisms 6A, 6B are, for example, multiplate clutches. Various clutches can be used as the clutch mechanisms. For example, band type clutches can also be used, in which clutch bands are disposed so as to enclose the first and second internally toothed gears <NUM>, <NUM> from the outer peripheral sides thereof.

<FIG> is a cross-sectional view of a speed ratio switching type flat strain wave gearing according to Embodiment <NUM> of the present invention. A speed ratio switching type flat strain wave gearing <NUM> (referred to below simply as the "strain wave gearing <NUM>") can switch a speed ratio to three stages, and includes a first internally toothed gear <NUM>, a second internally toothed gear <NUM>, a third internally toothed gear <NUM>, a drive-side internally toothed gear <NUM>, a cylindrical externally toothed gear <NUM>, a wave generator <NUM>, and a clutch mechanism <NUM>.

The externally toothed gear <NUM> includes a flexible cylinder <NUM> capable of flexing in the radial direction. A first number of first external teeth <NUM>, a second number of second external teeth <NUM>, a third number of third external teeth <NUM>, and a fourth number of fourth external teeth <NUM> are formed on an external peripheral surface of the cylinder <NUM>. In the external peripheral surface of the cylinder <NUM>, the first through fourth external teeth <NUM>-<NUM> are aligned in this order from one end toward another end in the direction of an axis 100a.

The first internally toothed gear <NUM> is disposed in a position where the gear <NUM> concentrically encircles the first external teeth <NUM> in the externally toothed gear <NUM>. First internal teeth <NUM> formed on the first internally toothed gear <NUM> are able to mesh with the first external teeth <NUM>, and the number of first internal teeth <NUM> is different from the number of first external teeth <NUM>. The second internally toothed gear <NUM> is aligned with the first internally toothed gear <NUM> in the direction of the axis 100a, and is disposed in a position where the gear <NUM> concentrically encircles the second external teeth <NUM> in the externally toothed gear <NUM>. Second internal teeth <NUM> formed on the second internally toothed gear <NUM> are able to mesh with the second external teeth <NUM>, and the number of second internal teeth <NUM> is different from the number of second external teeth <NUM>. The third internally toothed gear <NUM> is aligned with the second internally toothed gear <NUM> in the direction of the axis 100a, and is disposed in a position where the gear <NUM> concentrically encircles the third external teeth <NUM> in the externally toothed gear <NUM>. Third internal teeth <NUM> formed on the third internally toothed gear <NUM> are able to mesh with the third external teeth <NUM>, and the number of third internal teeth <NUM> is different from the number of third external teeth <NUM>.

The drive-side internally toothed gear <NUM> is aligned with the third internally toothed gear <NUM> in the direction of the axis 100a, and is in a position where the gear <NUM> concentrically encircles the fourth external teeth <NUM> in the externally toothed gear <NUM>. Internal teeth <NUM> formed on the drive-side internally toothed gear <NUM> are able to mesh with the fourth external teeth <NUM>, and the number of internal teeth <NUM> is set to be the same as the number of fourth external teeth <NUM> so that the internal teeth <NUM> rotate integrally with the externally toothed gear <NUM>.

The wave generator <NUM> causes radial flexure in the portions of the cylinder <NUM> of the externally toothed gear <NUM> where the first through fourth external teeth <NUM>-<NUM> are formed. Due to this flexure, the first external teeth <NUM> partially mesh with the first internal teeth <NUM>, the second external teeth <NUM> partially mesh with the second internal teeth <NUM>, the third external teeth <NUM> partially mesh with the third internal teeth <NUM>, and the fourth external teeth <NUM> partially mesh with the internal teeth <NUM>. In the present example, the portions of the cylinder <NUM> where the first through fourth external teeth <NUM>-<NUM> are formed are caused by the wave generator <NUM> to flex into an ellipsoidal shape, and at both long-axis ends of the ellipsoid, the first through fourth external teeth <NUM>-<NUM> respectively mesh with the first, second, and third internal teeth <NUM>, <NUM>, <NUM> and the internal teeth <NUM>. Therefore, the difference between the number of first internal teeth <NUM> and first external teeth <NUM>, the difference between the number of second internal teeth <NUM> and second external teeth <NUM>, and the difference between the number of third internal teeth <NUM> and third external teeth <NUM> are all set to 2n (n being a positive integer).

The wave generator <NUM> includes a rigid plug <NUM> fixed to a rotation input shaft <NUM> shown by imaginary lines, four fixed-width ellipsoidal external peripheral surfaces <NUM>-<NUM> formed on an external peripheral surface portion of the rigid plug <NUM>, and wave bearings <NUM>-<NUM> mounted on the ellipsoidal external peripheral surfaces <NUM>-<NUM>. The wave bearings <NUM>-<NUM> are disposed in positions corresponding to the portions of the externally toothed gear <NUM> where the first through fourth external teeth <NUM>-<NUM> are formed.

The clutch mechanism <NUM> includes a ring-form clutch member <NUM> capable of sliding in the direction of the axis 100a and a sliding mechanism <NUM> that causes the clutch member <NUM> to slide in the direction of the axis 100a. Engaging teeth <NUM> (splines) are formed on a circular internal peripheral surface of the clutch member <NUM>. Engaging teeth <NUM>, <NUM>, <NUM> capable of engaging with the engaging teeth <NUM> from the direction of the axis 100a are formed respectively on the circular external peripheral surfaces of the first through third internally toothed gears <NUM>-<NUM>. The clutch member <NUM> is able to slide in sequence to engaging positions where the clutch member <NUM> can selectively engage with the engaging teeth <NUM>, <NUM>, <NUM> of the first through third internally toothed gears <NUM>-<NUM>.

In the strain wave gearing <NUM> having this configuration, for example, the wave generator <NUM> is a rotation input element, and the rotation input shaft <NUM> is connected thereto. The drive-side internally toothed gear <NUM>, which rotates integrally with the externally toothed gear <NUM>, is a rotation output element, and an output member <NUM> is connected thereto. For example, the clutch member <NUM> is engaged with the second internally toothed gear <NUM>, the second internally toothed gear <NUM> is switched to as rotation-disabled fixed state, and the other first and third internally toothed gears <NUM>, <NUM> remain able to rotate. When the wave generator <NUM> rotates, relative rotation occurs between the second external teeth <NUM> of the externally toothed gear <NUM> and the fixed second internally toothed gear <NUM>, the relative rotation corresponding to the difference in the number of teeth between these two gears. The externally toothed gear <NUM> rotates and rotation reduced in speed at a speed ratio corresponding to the difference in the number of teeth is outputted from the drive-side internally toothed gear <NUM>, which rotates integrally with the externally toothed gear <NUM>, to the output member <NUM>. Similarly, rotation output at a different speed ratio is obtained by causing the clutch member <NUM> to slide toward the first internally toothed gear <NUM> or the third internally toothed gear <NUM>.

In the present example, the wave generator <NUM> is a rotation input element and the drive-side internally toothed gear <NUM> is a rotation output element. Conversely, if the wave generator <NUM> is a rotation output element and the drive-side internally toothed gear <NUM> is a rotation input element, input rotation can be increased at a different speed ratio and extracted as increased rotation output. A multiplate clutch and other various clutch mechanisms can also be used as the clutch mechanism <NUM>. Furthermore, the speed ratio can be switched to three stages in the present example, but the clutch mechanism can also be configured such that the speed ratio can be switched to two stages or to multiple stages of more than three, as in the case of Embodiment <NUM>.

Claim 1:
A speed ratio switching type strain wave gearing (<NUM>; <NUM>) comprising:
an externally toothed gear (<NUM>; <NUM>) including a cylinder (<NUM>; <NUM>) capable of flexing in a radial direction, a predetermined number of first external teeth (<NUM>; <NUM>) formed on an external peripheral surface of the cylinder (<NUM>; <NUM>), and a predetermined number of second external teeth (<NUM>; <NUM>) formed on the external peripheral surface of the cylinder (<NUM>; <NUM>), the second external teeth (<NUM>; <NUM>) being formed in a different position along an axial direction from the first external teeth (<NUM>; <NUM>) in the external peripheral surface of the cylinder (<NUM>; <NUM>), with the number of the first external teeth (<NUM>; <NUM>) and that of the second external teeth (<NUM>; <NUM>) being the same or different;
a rigid first internally toothed gear (<NUM>; <NUM>) which is disposed in a position of concentrically encircling the first external teeth (<NUM>; <NUM>), and which includes first internal teeth (<NUM>; <NUM>) that partially mesh with the first external teeth (<NUM>; <NUM>);
a rigid second internally toothed gear (<NUM>; <NUM>) which is disposed in a position of concentrically encircling the second external teeth (<NUM>; <NUM>), and which includes second internal teeth (<NUM>; <NUM>) that partially mesh with the second external teeth (<NUM>; <NUM>);
a wave generator (<NUM>; <NUM>) that causes the cylinder (<NUM>; <NUM>) of the externally toothed gear (<NUM>; <NUM>) to flex in the radial direction, causes the first external teeth (<NUM>; <NUM>) to partially mesh with the first internal teeth (<NUM>; <NUM>), and causes the second external teeth (<NUM>; <NUM>) to partially mesh with the second internal teeth (<NUM>; <NUM>);
characterized in that
the speed ratio switching type strain wave gearing (<NUM>; <NUM>) further comprises a clutch mechanism (<NUM>; <NUM>) that is able to switch one of the first internally toothed gear (<NUM>; <NUM>) and the second internally toothed gear (<NUM>; <NUM>), which are in a rotation-enabled state, to a rotation-disabled fixed state,
the number of the first external teeth (<NUM>; <NUM>) and that of the first internal teeth (<NUM>; <NUM>) are different, and
the number of the second external teeth (<NUM>; <NUM>) and that of the second internal teeth (<NUM>; <NUM>) are different.