Lubricant sealing structure, strain wave gearing, and actuator

A strain wave gearing is provided with a lubricant sealing structure that prevents a lubricant from leaking to the outside through a gap between a hollow input shaft and an end plate. The lubricant sealing structure is provided with a labyrinth seal that seals the gap. The labyrinth seal is configured by a plurality of gap portions defined by an oil-repellent surface in which fine grooves are formed in a prescribed groove array pattern. The oil-repellent surface is also formed at an outer peripheral surface portion on an upstream side of the labyrinth seal. Leakage of a lubricant oil to outside of the device can be reliably prevented through the oil-repellent effect of the oil-repellent surface at the upstream side, the sealing effect of the labyrinth seal, and the oil-repellent effect from the oil-repellent surface of the labyrinth seal.

TECHNICAL FIELD

The present invention relates to a lubricant sealing structure used in a strain wave gearing, in an actuator that is provided with a strain wave gearing and a motor, and in other mechanical devices. More specifically, the present invention relates to a lubricant sealing structure that prevents lubricant from leaking out from the interior of a device to the exterior through a space between a first member and a second member that rotate relative to one another.

BACKGROUND ART

In strain wave gearings and other gearing devices, a rotation-side member such as an input shaft or an output shaft is supported by a device housing or other secured-side member via bearings. A gap is formed between the rotation-side member and the secured-side member.

Typically, the gap is sealed by an oil seal in order to prevent lubricant such as oil or grease with which the interior of the device is filled from leaking outside of the device or to other sites within the device through the gap.

Patent document 1 (JP 2006-258234 A) proposes a lubricant sealing structure in which the sealing properties of an oil seal are enhanced. In this lubricant sealing structure, a fluorine-based grease having oil repellency with respect to lubricant is applied to portions of a rotating member that are sealed by an oil seal, and the sealing properties are enhanced.

Lubricant sealing structures in which labyrinth seals are used in lieu of oil seals are also known. Patent document 2 (JP 2007-333054 A) proposes a roll bearing device provided with a labyrinth gap formed between a secured-side member and a rotation-side member, and an oil-repellent and water-repellent surface formed by coating the surfaces that form the labyrinth gap with an oil-repellent and water-repellent material. Patent document 3 (JP 2017-9085 A) proposes a contactless sealing device provided with a labyrinth flow path that is incorporated between an axle and a casing of a gearing device for a railway vehicle, the labyrinth flow path defined by an oil-repellent treated surface.

Moreover, surface texturing, in which fine grooves, etc., are machined into a designated surface, is known as a technique for modifying surfaces such as sliding surfaces. Patent document 4 (JP 2017-214996 A) proposes forming a periodic structure of recesses and protrusions in the form of a fine grating in a sliding surface, and preventing any increase in friction and any occurrence of burning caused by a deficiency of lubricant, through surface machining in which a femtosecond laser is used. Additionally, Patent document 5 (Japanese Patent No. 5465109) proposes interposing a lubricating fluid onto sliding surfaces between two members and forming very small grooves in the sliding surfaces through laser machining, thereby imparting a strong friction-reducing effect.

Patent Literature

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

It is an object of the present invention to provide a lubricant sealing structure with which it is possible, by using fine groove machining (surface texturing), to reliably prevent lubricant from leaking out through a gap portion between first and second members that rotate relative to one another.

Means of Solving the Problems

According to the present invention, there is provided a lubricant sealing structure that prevents lubricant from leaking out, from an interior of a device provided with a first member and a second member that rotate relative to one another about a central axis, through a gap portion between the first and second members, wherein

a labyrinth seal for sealing the gap is provided,

the labyrinth seal is formed between a first surface portion on a first-member side and a second surface portion on a second-member side, the first and second surface portions facing each other;

oil-repellent surfaces provided with oil repellency with respect to the lubricant are formed on each of the first and second surface portions;

an upstream-side oil-repellent surface provided with oil repellency is formed on at least one of a first upstream-side surface portion and a second upstream-side surface portion, the first upstream-side surface portion being connected to the first surface portion and located on an upstream side in a direction in which the lubricant leaks, and the second upstream-side surface portion being connected to the second surface portion and located on an upstream side in the direction in which the lubricant leaks;

each of the oil-repellent surfaces and the upstream-side oil-repellent surface is provided with surface texturing in which fine grooves are formed in a prescribed groove array pattern;

the fine grooves are provided with a groove width and a groove depth ranging from several microns to several tens of nanometers; and

the groove array pattern is such that the fine grooves are arrayed at spacings ranging from several microns to several tens of nanometers.

In the lubricant sealing structure according to the present invention, the oil-repellent surfaces in which a groove array pattern of fine grooves has been produced are formed in the first and second surface portions forming the labyrinth seal for sealing the gap between the first and second members. Additionally, the upstream-side oil-repellent surfaces are formed on the first and second upstream-side surface portions positioned further upstream than the labyrinth seal in the direction in which the lubricant leaks. The lubricant leaking through the gap deforms into spheroids after being repelled by the upstream-side oil-repellent surfaces. The dimensions of the gap in the labyrinth seal are made smaller than the size (diameter) of the spheroidal lubricant, whereby the flow of lubricant into the gap forming the labyrinth seal is suppressed. Additionally, because the labyrinth seal is formed by the oil-repellent surfaces, the flow of lubricant into the labyrinth seal is suppressed.

In the lubricant sealing structure according to the present invention, the oil-repelling effect produced by the upstream-side oil-repellent surface formed by implementing surface texturing through fine groove machining, the sealing effect produced by the labyrinth seal, and the oil-repelling effect produced by the oil-repellent surface that regulates the labyrinth seal operate synergistically, and exceptional sealing properties are achieved and maintained. The lubricant is thereby reliably prevented from leaking from the lubricant enclosure portions in the interior of the device to, inter alia, the exterior of the device.

Any of the following array patterns (1) to (5) can be employed as the groove array pattern for imparting oil repellency to the member surfaces. Additionally, a composite array pattern in which a plurality of array patterns selected from among these array patterns are combined can also be employed.

(1) An array pattern in which the fine grooves extend, at the spacings, in a straight line, curve, or undulating form in a direction following the central axis of the device.

(2) An array pattern in which the fine grooves extend, at the spacings, in a straight line, curve, or undulating form in a circumferential direction centered on the central axis.

(3) An array pattern in which the fine grooves extend, at the spacings, in a straight line, curve, or undulating form in a direction inclined relative to the direction following the central axis.

(4) An array pattern in which the fine grooves extend in a spiral at the spacings.

(5) An array pattern in which the fine grooves are formed in a mesh at the spacings.

In the lubricant sealing structure according to the present invention, an oil reservoir having large gap dimensions can be formed in part of the gap portion constituting the labyrinth seal. Lubricant that has penetrated the gap portion of the labyrinth seal is trapped in the oil reservoir, whereby leakage of the lubricant can be reliably prevented.

In cases where the oil reservoir is formed, an oil absorber composed of a non-woven fabric or another porous material can be mounted in the oil reservoir. The lubricant can be reliably prevented from flowing downstream from the oil reservoir.

Additionally, the inner peripheral surface portion of the oil reservoir can be configured as an oleophilic surface provided with oleophilic properties with respect to the lubricant. This makes it possible to efficaciously prevent the lubricant that has collected in the oil reservoir from flowing downstream.

A gap portion in which the gap dimensions gradually decrease toward the direction in which the lubricant leaks can be formed in part of the gap portion constituting the labyrinth seal. For example, a gap portion having a wedge shape in cross-section can be formed. Suitably setting the gap dimensions of this gap portion makes it easier for the lubricant to be trapped in the gap portion and makes it possible to efficaciously prevent the lubricant from flowing downstream.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of a lubricant sealing structure to which the present invention is applied are described below with reference to the accompanying drawings. The embodiments described below illustrate cases where the lubricant sealing structure according to the present invention is applied to a strain wave gearing and to an actuator provided with a strain wave gearing and a motor. The present invention also can similarly be applied to gear-type reducers and other rotation-transmitting devices other than strain wave gearings.

FIG.1Ais a schematic longitudinal cross-sectional view of a strain wave gearing according to embodiment 1 of the present invention. The strain wave gearing1is provided with: disc-form end plates2and3that face each other across a prescribed spacing in the direction of a central axis1a; a hollow input shaft4that extends coaxially through central portions of the end plates2,3; and a wave gear mechanism5that is incorporated between the end plates2,3in a state of coaxially surrounding the hollow input shaft4. The hollow input shaft4is supported by the end plates2,3, with ball bearings6,7interposed therebetween, in a state that allows rotation. The wave gear mechanism5is provided with an annular rigid internally toothed gear8, a top-hat-shaped elastic externally toothed gear9, an ellipsoidally contoured wave generator10, and cross-roller bearing11that supports the internally toothed gear8and the externally toothed gear9in a state that allows relative rotation.

The externally toothed gear9is provided with a flexible cylindrical barrel part9bon which external teeth9aare formed, a disc-form diaphragm9cthat spreads radially outward from the end of the cylindrical barrel part9b, and an annular rigid boss9dformed integrally with the outer peripheral edge portion of the diaphragm9c. The opening-end-side portion of the cylindrical barrel part9bwhere the external teeth9aare formed is disposed coaxially inside the internally toothed gear8. The wave generator10is coaxially fitted into the inner side of the opening-end-side portion of the cylindrical barrel part9b. The wave generator10is provided with a plug part10aformed integrally with the outer peripheral surface portion of the hollow input shaft4, and a wave bearing10bmounted on the ellipsoidal outer peripheral surface of the plug part10a. The cylindrical barrel part9bof the externally toothed gear9is flexed into an ellipsoidal shape by the wave generator10, and portions of the external teeth9apositioned at both long-axis ends of the ellipsoidal shape mesh with internal teeth8aof the internally toothed gear8.

The boss9dof the externally toothed gear9is sandwiched between the end plate2and an outer race12of the cross-roller bearing11from both sides along the central-axis1adirection, and these three members are securely fastened in this state. The internally toothed gear8is sandwiched between the end plate3and an inner race13of the cross-roller bearing11from both sides along the central-axis1adirection, and these three members are securely fastened in this state.

The hollow input shaft4is a rotation-inputting member linked to a motor, etc. When the hollow input shaft4rotates, the wave generator10rotates integrally therewith, and the positions where the externally toothed gear9meshes with the internally toothed gear8move in the circumferential direction. The two gears8,9undergo relative rotation that corresponds to the difference between the numbers of teeth of the two gears8,9. For example, the end plate2to which the externally toothed gear9is fastened is configured as a secured-side member, the end plate3to which the internally toothed gear8is fastened is configured as a rotation-outputting member, and relative rotation (reduced rotation) is outputted from the end plate3.

Examples of lubricated portions in the interior of the strain wave gearing1include the portions where the externally toothed gear9and the internally toothed gear8mesh, the portions where the externally toothed gear9and the wave generator10contact each other, sliding sections of the cross-roller bearing11and the wave bearing10bof the wave generator10, and sliding sections of the ball bearings6,7. Lubricant sealing structures for preventing lubricant enclosed in or applied to these portions from leaking from the interior of the strain wave gearing1to the exterior are incorporated into the strain wave gearing1. The strain wave gearing1according to the present example is provided with a site1B where a lubricant sealing structure provided with a labyrinth seal20is incorporated, a site1C where a lubricant sealing structure provided with a labyrinth seal30is incorporated, and a site1D where a lubricant sealing structure provided with a labyrinth seal40is incorporated.

The lubricant sealing structure provided with the labyrinth seal20at the site1B creates a seal between the end plate2and one shaft end section4aof the hollow input shaft4, and prevents lubricant from leaking out from a portion of the ball bearing6and from a lubricant enclosure portion26located between the hollow input shaft4and the externally toothed gear9between the end plates2,3. The lubricant sealing structure provided with the labyrinth seal30at the site1C creates a seal between the end plate3and the other shaft end section4bof the hollow input shaft4, and prevents lubricant from leaking out from a portion of the ball bearing7and from the lubricant enclosure portion26. The lubricant sealing structure provided with the labyrinth seal40at the site1D creates a seal between the outer race12and the inner race13of the cross-roller bearing11, and prevents lubricant from leaking out from a portion of the cross-roller bearing11and from a lubricant enclosure portion46formed between the externally toothed gear9, the cross-roller bearing11, and the internally toothed gear.

(Lubricant Sealing Structure at Site1B)

FIG.1Bis an illustrative diagram of the lubricant sealing structure provided with the labyrinth seal20that creates a seal between the end plate2and the shaft end section4aof the hollow input shaft4. The one shaft end section4aof the hollow input shaft4is rotatably supported in the end plate2via the ball bearing6. The shaft end section4aof the hollow input shaft4protrudes toward the exterior of the device through a central portion of the end plate2. A gap that allows communication from the ball-bearing6side (lubricant-enclosure-portion26side) to the exterior of the device is formed between the end plate2and the shaft end section4aof the hollow input shaft4. The gap is sealed by the labyrinth seal20.

An annular member22is mounted in the gap between the end plate2and the shaft end section4aof the hollow input shaft4. The annular member22is securely press-fitted onto an outer peripheral surface portion4cof the shaft end section4aof the hollow input shaft4. An annular protrusion2athat protrudes inward is formed on the inner peripheral surface of the end plate2so as to face the annular member22in the axial direction. The labyrinth seal20is formed between a surface portion2bon the annular-protrusion2aside of the end plate2and a surface portion22aon the annular-member22side of the hollow input shaft4, the surface portion22afacing the surface portion2b.

The labyrinth seal20according to the present example is an axial labyrinth seal and is such that gap portions21a,21c,21eextending in the axial direction and gap portions21b,21dextending in the radial direction are alternatingly formed from the upstream side toward the downstream side in the direction in which lubricant leaks. The gap portions21ato21eare such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the radial-direction gap dimensions of the furthest-upstream gap portion21ain the labyrinth seal20are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

An oil-repellent surface provided with oil repellency with respect to the lubricant is formed on the surface portion2bon the end-plate2side where the gap portions21ato21eare formed. InFIG.1B, a dotted pattern is used to indicate the region on the surface portion2bwhere the oil-repellent surface is formed. Oil-repellent surfaces are also formed on the surface portion22aof the annular member22that faces the surface portion2bon the end-plate2side, and on an outer peripheral surface portion4dof the hollow input shaft4. A dotted pattern is also used to indicate the regions on the surface portion22aand the outer peripheral surface portion4dwhere the oil-repellent surfaces are formed. On the shaft end section4aof the hollow input shaft4, oil-repellent surfaces (upstream-side oil-repellent surfaces) are formed not only on the outer peripheral surface portion4dwhere the gap portion21ais formed but also on an outer peripheral surface portion4d1 (upstream-side surface portion) extending from the outer peripheral surface portion4dto a site at which an outer race of the ball bearing6is mounted.

The oil-repellent surfaces according to the present example are provided with surface texturing in which fine grooves are formed in a prescribed groove array pattern so as to achieve oil repellency with respect to the enclosed lubricant. The fine grooves are provided with a groove width and a groove depth ranging from several microns to several tens of nanometers, and the groove array pattern is such that the fine grooves are arrayed at spacings ranging from several microns to several tens of nanometers. For example, fine grooves25that form the oil-repellent surface on the outer peripheral surface portion4dof the hollow input shaft4extend in the circumferential direction and are arrayed at fixed intervals in the direction of the central axis1a, as is schematically shown inFIG.1B.

A variety of groove array patterns can be employed as the groove array pattern of the fine grooves25that form the oil-repellent surface. For example, it is possible to use a groove array pattern in which fine grooves25extending in a straight line, curve, or undulating form in a direction following the central axis1aare formed at fixed intervals in the circumferential direction. The fine grooves25may form a groove array pattern in which fine grooves25extending in a straight line, curve, or undulating form in a circumferential direction centered on the central axis1aare formed at fixed intervals in the central-axis1adirection. It is also possible to employ a groove array pattern configured from fine grooves25extending in a straight line, curve, or undulating form in a direction that is inclined relative to the direction following the central axis1a. It is additionally possible to employ a groove array pattern configured from fine grooves25extending in a spiral at a fixed pitch in the central-axis1adirection. Furthermore, it is also possible to employ a reticulate groove array pattern in which fine grooves25extending in the central-axis1adirection and fine grooves25extending in the circumferential direction intersect. It is moreover possible to employ a groove array pattern having a configuration in which the aforementioned groove array patterns overlap.

As described above, a seal is created between the hollow input shaft4and the end plate2by the labyrinth seal20, and the lubricant is prevented from leaking to the exterior of the device. Because the gap portions21ato21econstituting the labyrinth seal20are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal20is efficaciously prevented from flowing out toward the exterior of the device. Furthermore, the outer peripheral surface portion4d1 of the hollow input shaft4is also configured as an oil-repellent surface (upstream-side oil-repellent surface). Lubricant flowing into the labyrinth seal20from the ball-bearing6side is repelled by this oil-repellent surface, and deforms into spheroidal grains just before penetrating the gap portion21aof the labyrinth seal20. Because the radial-direction gap dimensions of the gap portion21aare smaller than the diameter of the spheroidal lubricant grains thus formed, penetration of the lubricant into the gap portion21ais suppressed. Additionally, because the downstream-side gap portions among the gap portions21ato21econstituting the labyrinth seal20are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions.

In the present example, the gap dimensions at individual radial-direction positions are the same in each of the gap portions21a,21c,21eextending in the axial direction. Additionally, the gap dimensions in the axial direction are the same in each of the gap portions21b,21dextending in the radial direction. It is also possible to use gap portions in which the gap dimensions gradually decrease from the interior of the device toward the exterior (i.e., gap portions having a wedge-shaped cross-section).

For example, as shown inFIG.1E, the gap portion21acan be configured such that the radial-direction gap dimensions thereof gradually decrease from the lubricant-enclosure-portion26side toward the exterior of the device. For example, an inner peripheral surface portion2con the surface portion2bon the end-plate2side where the gap portion21ais formed is to be configured as a tapered inner peripheral surface. In this case, at least the minimum gap dimensions of the gap portion21aare to be set to values that are less than the diameter of the lubricant grains formed into spheroids on the oil-repellent surface. Gap portions in which the gap dimensions gradually decrease toward the downstream side can also be applied in a similar manner to the lubricant sealing structures described below and to lubricant sealing structures in embodiment 2 that shall be described later.

(Lubricant Sealing Structure at Site1C)

FIG.1Cis an illustrative diagram of the lubricant sealing structure provided with the labyrinth seal30that creates a seal between the end plate3and the other shaft end section4bof the hollow input shaft4. The shaft end section4bof the hollow input shaft4is rotatably supported in the end plate3via the ball bearing7. The shaft end section4bof the hollow input shaft4protrudes toward the exterior of the device through a central portion of the end plate3. A gap that allows communication from the ball-bearing7side (lubricant-enclosure-portion26side) to the exterior of the device is formed between the end plate3and the shaft end section4bof the hollow input shaft4. The gap is sealed by the labyrinth seal30.

An annular member32is mounted in the gap between the end plate3and the shaft end section4bof the hollow input shaft4. The annular member32is securely press-fitted onto an outer peripheral surface portion4eof the shaft end section4bof the hollow input shaft4. An annular protrusion3athat protrudes inward is formed on the inner peripheral surface of the end plate3so as to face the annular member32in the axial direction. The labyrinth seal30is formed between a surface portion3bon the annular-protrusion3aside of the end plate3and a surface portion32aon the annular-member32side, the surface portion32afacing the surface portion3b.

In the labyrinth seal30according to the present example, gap portions31a,31c,31eextending in the axial direction and gap portions31b,31dextending in the radial direction are alternatingly formed from the upstream side toward the downstream side in the direction in which lubricant leaks. The gap portions31ato31eare such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the radial-direction gap dimensions of the furthest-upstream gap portion31ain the labyrinth seal30are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

The surface portion3bon the end-plate3side where the gap portions31ato31eare formed is an oil-repellent surface provided with oil repellency with respect to the lubricant. InFIG.1C, a dotted pattern is used to indicate the range over which the oil-repellent surface is formed. The surface portion32aof the annular member32that faces the surface portion3bis also configured as an oil-repellent surface. A dotted pattern is also used to indicate the range over which the oil-repellent surface on the surface portion32ais formed. On the shaft end section4bof the hollow input shaft4, an oil-repellent surface (upstream-side surface portion) is also formed on part of an outer peripheral surface portion4fat which the ball bearing7is mounted. The oil-repellent surfaces have the same configurations as the oil-repellent surfaces of the labyrinth seal20described above, and therefore are not described here.

An oil reservoir is formed in the gap portion31aof the labyrinth seal30. Specifically, a groove32bof rectangular cross-section that extends in the circumferential direction is formed in the inner peripheral surface of the annular protrusion3aof the end plate3. The oil reservoir, in which the radial-direction gap dimensions are greater than those at other portions in the gap portion31a, is formed by the groove32b. The groove32bis filled with a porous material, such as an oil absorber33composed of a non-woven fabric. Furthermore, a bottom surface portion and both inner peripheral side surface portions of the groove32bare subjected to surface treatment and configured as oleophilic surfaces provided with oleophilic properties with respect to the lubricant. InFIG.1C, cross-hatching is used to indicate the range over which the oleophilic surfaces are formed.

The lubricant flows out from the ball-bearing7side in the interior of the device to the gap between the hollow input shaft4and the end plate3. The lubricant is prevented from leaking to the exterior of the device by the labyrinth seal30. Additionally, because the downstream-side gap portions among the gap portions31ato31econstituting the labyrinth seal30are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions31ato31econstituting the labyrinth seal30are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal30is efficaciously prevented from flowing out toward the exterior of the device. Moreover, lubricant flowing from the ball-bearing7side toward the labyrinth seal30is repelled by the oil-repellent surface formed on the outer peripheral surface portion4fof the shaft end section4bof the hollow input shaft4, and deforms into spheroidal grains just before penetrating the gap portion31aof the labyrinth seal30. Because the radial-direction gap dimensions of the gap portion31aare smaller than the diameter of the spheroidal lubricant grains thus formed, the flow of the lubricant into the gap portion31ais suppressed.

The oil reservoir filled with the oil absorber33is formed in the gap portion31aof the labyrinth seal30. Lubricant that has penetrated the labyrinth seal30is trapped in the oil reservoir and prevented from flowing out toward the downstream side (toward the exterior of the device). Because the inner peripheral surface portions of the groove forming the oil reservoir are configured as oleophilic surfaces, the lubricant trapped in the oil reservoir is efficaciously prevented from flowing out toward the downstream side by this configuration as well. Thus, the sealing effect produced by the labyrinth seal30, the effect produced by the oil-repellent surface, and the effect produced by the oil reservoir provided with the oil absorber and the oleophilic surfaces make it possible to reliably prevent the lubricant from leaking to the exterior of the device.

(Lubricant Sealing Structure at Site1D)

The lubricant sealing structure provided with the labyrinth seal40that seals a gap between the outer race12and the inner race13of the cross-roller bearing11is described next.FIG.1Dis an illustrative diagram of the lubricant sealing structure provided with the labyrinth seal40that creates a seal between the outer race12and the inner race13. A gap that allows communication from a raceway groove14to the exterior of the device is formed between outer race12and the inner race13. The gap is sealed by the labyrinth seal40. The labyrinth seal40is formed between an inner-peripheral-side surface portion12aof the outer race12and an outer-peripheral-side surface portion13aof the inner race13, the outer-peripheral-side surface portion13afacing the inner-peripheral-side surface portion12a.

In the labyrinth seal40, gap portions41a,41c,41eextending in the axial direction and gap portions41b,41dextending in the radial direction are alternatingly formed along the direction from the lubricant-enclosure-portion side toward the exterior of the device. The gap portions41ato41eare such that the downstream-side gap portions are narrower than the upstream-side gap portions.

The inner-peripheral-side surface portion12aof the outer race12where the gap portions41ato41eare formed is an oil-repellent surface provided with oil repellency with respect to the lubricant. InFIG.1D, a dotted pattern is used to indicate the range over which the oil-repellent surface is formed. The outer-peripheral-side surface portion13aof the inner race13that faces the inner-peripheral-side surface portion12ais also configured as an oil-repellent surface. InFIG.1D, a dotted pattern is also used to indicate the range over which the oil-repellent surface on the outer-peripheral-side surface portion13ais formed. The oil-repellent surfaces are configured in the same manner as the oil-repellent surfaces of the labyrinth seal20described above, and therefore are not described here.

The lubricant flows out from the raceway-groove14side of the cross-roller bearing11in the interior of the device to the gap between the outer race12and the inner race13. The lubricant is prevented from leaking to the exterior of the device by the labyrinth seal40. Additionally, because the downstream-side gap portions among the gap portions41ato41econstituting the labyrinth seal40are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions41ato41econstituting the labyrinth seal40are regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal40is efficaciously prevented from flowing out toward the exterior of the device. Thus, the sealing effect produced by the labyrinth seal40and the oil-repelling effect produced by the oil-repellent surface make it possible to reliably prevent the lubricant from leaking to the exterior of the device via the gap.

FIG.2Ais a schematic longitudinal cross-sectional view of an actuator provided with the lubricant sealing structure according to the present invention. The actuator100is a hollow actuator provided with a hollow section extending through the center thereof, and is provided with a motor110and a strain wave gearing120. The motor110is provided with a hollow motor shaft111, a rotor112attached to the outer peripheral surface of the hollow motor shaft111, and a stator113that coaxially surrounds the rotor112. The hollow motor shaft111is rotatably supported, at both ends thereof, by a motor housing116with ball bearings interposed therebetween (only one ball bearing114is shown in the drawings).

The motor housing116is provided with a large-diameter attachment flange117at the front end thereof. The strain wave gearing120is coaxially attached to the front surface of the attachment flange117. The strain wave gearing120is provided with a rigid internally toothed gear121, a top-hat-shaped flexible externally toothed gear122, a wave generator123, a cross-roller bearing124that supports the internally toothed gear121and the externally toothed gear122in a state that allows relative rotation, and a disc-form output shaft125.

The wave generator123is provided with a hollow input shaft126that is coaxially linked to the hollow motor shaft111, and an ellipsoidally contoured plug127being formed integrally with the outer peripheral surface of the hollow input shaft126. A wave bearing128is mounted on the ellipsoidal outer peripheral surface of the plug127. A cylindrical barrel part of the externally toothed gear122, on which external teeth122aare formed, is flexed into an ellipsoidal shape by the wave generator123, and the external teeth partially meshes with internal teeth121aof the internally toothed gear121.

An annular boss122cof the externally toothed gear122is sandwiched between the attachment flange117and an outer race124aof the cross-roller bearing124, and these three members are securely fastened in this state. The internally toothed gear121is sandwiched between an inner race124bof the cross-roller bearing124and the output shaft125, and these three members are securely fastened in this state. Output rotation of the motor110is inputted from the hollow motor shaft111to the wave generator123. When the wave generator123rotates, the internally toothed gear121rotates at a reduced speed, and reduced-speed rotation is outputted from the output shaft125linked to the internally toothed gear121to a load side (not shown).

Examples of lubricated portions in the interior of the strain wave gearing120include the portions where the externally toothed gear122and the internally toothed gear121mesh, the portions where the externally toothed gear122and the wave generator123contact each other, and the cross-roller bearing124and the wave bearing128of the wave generator123. A site2B of a lubricant sealing structure provided with a labyrinth seal140, a site2C of a lubricant sealing structure provided with a labyrinth seal150, and a site2D of a lubricant sealing structure provided with a labyrinth seal160are incorporated into the strain wave gearing120in order to prevent lubricant from leaking from lubricant enclosure portions131,132in the interior of the strain wave gearing120to the exterior of the device or toward the motor110.

(Lubricant Sealing Structure at Site2B)

FIG.2Bis an illustrative diagram of the site of the lubricant sealing structure provided with the labyrinth seal140that creates a seal between the hollow input shaft126and the output shaft125. The space between the hollow input shaft126, which rotates at high speed, and the output shaft125, which rotates at a reduced speed, is sealed by the lubricant sealing structure provided with the labyrinth seal140. An internal space in the externally toothed gear122in which the wave bearing128is disposed is a lubricant enclosure portion131(refer toFIG.2A) in which is enclosed lubricant supplied, inter alia, to the wave bearing128or to sliding portions between the wave bearing128and the externally toothed gear122. A gap that passes through from the wave bearing128positioned toward the interior of the device to the exterior of the device is formed between the hollow input shaft126and the output shaft125. The gap is sealed by the labyrinth seal140. The labyrinth seal140is formed between an inner-peripheral-side surface portion125aof the output shaft125and a shaft-end-side surface portion126aof the hollow input shaft126, the shaft-end-side surface portion126afacing the inner-peripheral-side surface portion125a.

The labyrinth seal140is an axial labyrinth seal and is such that gap portions141a,141c,141eextending in the radial direction and gap portions141b,141d,141fextending in the axial direction are alternatingly formed along the direction from the lubricant sealing structure toward the exterior of the device. The gap portions141ato141eare such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the axial-direction gap dimensions of the furthest-upstream gap portion141ain the labyrinth seal140are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

An oil-repellent surface provided with oil repellency with respect to the lubricant is formed on the inner-peripheral-side surface portion125aof the output shaft125where the gap portions141ato141fare formed. Additionally, an oil-repellent surface (upstream-side oil-repellent surface) is also formed on an outer peripheral surface portion125b(upstream-side surface portion) that is connected to the inner side of the device (upstream side in the direction in which lubricant leaks) with respect to the gap portion141a. Furthermore, an oil-repellent surface is additionally formed on the surface portion126aof the hollow input shaft126. InFIG.2B, a dotted pattern is applied along surface portions where the oil-repellent surfaces are formed in order to indicate these surface portions. The oil-repellent surfaces are surface portions in which fine grooves are formed in a prescribed groove array pattern in the same manner as with the oil-repellent surfaces on the labyrinth-seal20side in embodiment 1 described above, and therefore are not described here.

The lubricant flows out from the interior of the device to the gap between the hollow input shaft126and the output shaft125. Because the lubricant is sealed by the labyrinth seal140, the lubricant is prevented from leaking to the exterior of the device. Additionally, because the downstream-side gap portions among the gap portions141ato141fconstituting the labyrinth seal140are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions141ato141fare regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal140is efficaciously prevented from flowing out toward the exterior of the device. Moreover, lubricant flowing into the labyrinth seal140is repelled by the oil-repellent surface formed on the outer peripheral surface portion125bof the output shaft125, and deforms into spheroidal grains just before penetrating the gap portion141aof the labyrinth seal140. Because the axial-direction gap dimensions of the gap portion141aare smaller than the diameter of the spheroidal lubricant grains thus formed, the flow of the lubricant into the gap portion141ais suppressed.

Thus, the oil-repelling effect produced by the upstream-side oil-repellent surface, the sealing effect produced by the labyrinth seal140, and the oil-repelling effect produced by the oil-repellent surface that regulates the labyrinth seal140make it possible to reliably prevent the lubricant from leaking to the exterior of the device.

(Lubricant Sealing Structure at Site2C)

FIG.2Cis an illustrative diagram of the site of the lubricant sealing structure provided with the labyrinth seal150that creates a seal between the strain wave gearing120and the motor110. The lubricant is prevented from leaking from the strain-wave-gearing120side toward the motor110side by this lubricant sealing structure. The ball bearing114is mounted between an inner peripheral edge section117aof the attachment flange117and a shaft end section111aof the hollow motor shaft111, the shaft end section111afacing the inner peripheral edge section117a. The distal end of the shaft end section111aof the hollow motor shaft111protrudes toward the strain-wave-gearing120side through the attachment flange117. The hollow input shaft126of the strain wave gearing120is securely linked in a coaxial manner to the shaft end section111aof the hollow motor shaft111.

A gap is formed between the inner peripheral edge section117aof the attachment flange117and the hollow input shaft126that faces the inner peripheral edge section117a. The gap is sealed by the labyrinth seal150. The labyrinth seal150is formed between a surface portion117bof the inner peripheral edge section117aof the attachment flange and a surface portion126cof the hollow input shaft126, the surface portion126cfacing the surface portion117bfrom the axial direction.

In the labyrinth seal150, gap portions151a,151c,151eextending in the radial direction and gap portions151b,151dextending in the axial direction are alternatingly formed along the direction from the strain-wave-gearing120side toward the motor110side. The gap portions151ato151eare such that the downstream-side gap portions are narrower than the upstream-side gap portions. Furthermore, the axial-direction gap dimensions of the furthest-upstream gap portion151ain the labyrinth seal150are set to values that are less than the diameter of lubricant grains, which are formed into spheroids after being repelled by an oil-repellent surface that shall be described below.

An oil-repellent surface provided with oil repellency with respect to the lubricant is formed on the surface portion117bof the inner peripheral edge section117aof the attachment flange where the gap portions151ato151eare formed. Additionally, an oil-repellent surface is also formed on the surface portion126con the shaft end of the hollow input shaft126that faces the surface portion117b. Furthermore, an oil-repellent surface (upstream-side oil-repellent surface) is additionally formed on an outer peripheral surface portion126d(upstream-side surface portion) on the inner side of the device with respect to the gap portion151a. InFIG.2C, a dotted pattern is applied along surface portions where the oil-repellent surfaces are formed in order to indicate these surface portions. The oil-repellent surfaces are surface portions in which fine grooves are formed in a prescribed groove array pattern in the same manner as with the oil-repellent surfaces on the labyrinth-seal20side in embodiment 1 described above, and therefore are not described here.

The lubricant flows out from the interior of the device to the gap between the hollow input shaft126and the inner peripheral edge section117aof the attachment flange. Because the lubricant is sealed by the labyrinth seal150, the lubricant is prevented from leaking to the exterior of the device. Additionally, because the downstream-side gap portions among the gap portions151ato151econstituting the labyrinth seal150are narrower than the upstream-side gap portions, lubricant that has penetrated the upstream-side gap portions is efficaciously prevented from flowing into the downstream-side gap portions. Furthermore, because the gap portions151ato151eare regulated by the oil-repellent surfaces, lubricant that has penetrated the labyrinth seal150is efficaciously prevented from flowing out toward the exterior of the device. Moreover, lubricant flowing into the labyrinth seal150is repelled by the oil-repellent surface formed on the outer peripheral surface portion126don the shaft end of the hollow input shaft126, and deforms into spheroidal grains just before penetrating the gap portion151aof the labyrinth seal150. Furthermore, because the axial-direction gap dimensions of the gap portion151aare smaller than the diameter of the spheroidal lubricant grains thus formed, the flow of the lubricant into the gap portion151ais suppressed.

Thus, the oil-repelling effect produced by the upstream-side oil-repellent surface of the labyrinth seal150, the sealing effect produced by the labyrinth seal150, and the oil-repelling effect produced by the oil-repellent surface that regulates the labyrinth seal150make it possible to reliably prevent the lubricant from leaking to the exterior of the device.

(Lubricant Sealing Structure at Site2D)

FIG.2Dis an illustrative diagram of the site of the lubricant sealing structure between the outer race124aand the inner race124bof the cross-roller bearing124. The site2D of the lubricant sealing structure provided with the labyrinth seal160is disposed at a portion of the cross-roller bearing124that supports the externally toothed gear122and the internally toothed gear121in a state that allows relative rotation. Specifically, the lubricant sealing structure is disposed in order to seal a gap portion between the outer race124aand the inner race124bof the cross-roller bearing124. This lubricant sealing structure is substantially identical to the lubricant sealing structure in which the labyrinth seal40is used, which is shown inFIG.1Dwithin embodiment 1.

Therefore, no specific description thereof is given here.