JP2023047216A - Strain wave gear device - Google Patents

Abstract

To provide a strain wave gear device that has power transmission efficiency improved in a practical range.SOLUTION: A strain wave gear device 1 has internal gear teeth 2, flexible external gear teeth 3, and a strain wave generator 4 that causes the external gear teeth 3 to produce a strain wave motion. The strain wave generator 4 has a bearing 6 fitted to the inner circumferential surface of the external gear teeth 3. An outer race 6a of the bearing 6 has a degree of elasticity found by formula (1) below. (1): Degree of elasticity (N/mm2)=E×I×(1/D4), E: modulus of longitudinal elasticity, I: cross-sectional second moment, D: outer diameter of outer race, and the degree of elasticity in a range of 7.8×10-5-2.7×10-2.SELECTED DRAWING: Figure 1

Description

The present invention relates to strain wave gearing.

Strain wave gearing is characterized by high precision, high reduction ratio, and light weight. Therefore, the strain wave gearing is mainly used as a speed reducer for robots, but the power transmission efficiency of the strain wave gearing is lower than that of a general planetary gear.

Conventionally, as a method of improving the power transmission efficiency of a wave gear device, for example, focusing on the engagement between an internal gear and an external gear, the tooth profile of the internal gear and the tooth profile of the external gear are set ( For example, see Patent Documents 1 and 2.).

JP 2017-166649 A JP 2018-159458 A

However, the above-described conventional strain wave gearing still has room for improvement in terms of improving power transmission efficiency within a range that can withstand practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a strain wave gearing in which the power transmission efficiency is improved within a practically acceptable range.

A strain wave gear device according to the present invention includes an internal gear, a flexible external gear, and a wave generator for generating a wave motion in the external gear. , a strain wave gear device having a bearing fitted to the inner peripheral surface of the external gear,
The outer ring of the bearing has a degree of elasticity determined by the following formula (1),
Elasticity (N/mm ² )=E×I×(1/D ⁴ ) (1)
E: Modulus of longitudinal elasticity, I: Moment of inertia of area, D: Outer diameter of outer ring Further, the elasticity is 7.8×10 ⁻⁵ to 2.7×10 ⁻² . According to the strain wave gearing of the present invention, the power transmission efficiency is improved within a practical range.

In the strain wave gearing according to the present invention, it is preferable that the longitudinal elastic modulus E (GPa) of the outer ring is 0.4-200. In this case, the power transmission efficiency is further improved while maintaining workability.

In the strain wave gearing according to the present invention, it is preferable that the outer ring is made of resin or light metal. In this case, power transmission efficiency is improved by a simple means of selecting materials.

In the strain wave gearing device according to the present invention, the outer ring is made of bearing steel, and the thickness ratio (%) of the thickness of the outer ring to the outer diameter of the outer ring is 1.2 to 2.1. is preferred. In this case, power transmission efficiency can be improved by a simple method of setting the thickness ratio within the above range while using an existing bearing material.

In the strain wave gearing according to the present invention, the outer ring is supported by rolling elements, and at least one of the surface of the rolling element and the raceway surface of the rolling element in the outer ring or the inner ring has a A hard layer having a hardness higher than that of the substrate layer may be provided. In this case, power transmission efficiency is further improved.

ADVANTAGE OF THE INVENTION According to this invention, the strain wave gearing which improves the power transmission efficiency within the range which can be put into practical use can be provided.

1 is a diagram schematically showing a strain wave gearing according to a first embodiment of the present invention; FIG. It is a figure which expands and shows the area|region X of FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG. 2; FIG. 6 is a strain wave gearing according to a second embodiment of the present invention, and is a diagram schematically showing a part of a bearing of the strain wave gearing. FIG. 10 is a strain wave gearing according to a third embodiment of the present invention, and is a diagram schematically showing a part of a bearing of the strain wave gearing. 4 is a line graph showing specific numerical results of power transmission efficiency obtained from Example 2 according to the present invention and specific numerical results of power transmission efficiency obtained from a comparative example with respect to Example 2; .

A strain wave gearing according to an embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a strain wave gearing according to the first embodiment of the present invention. The wave gear device 1 has an internal gear 2 , a flexible (including elasticity) external gear 3 , and a wave generator 4 that causes the external gear 3 to generate wave motion. The wave generator 4 has an outer ring 6 a fitted to the inner peripheral surface of the external gear 3 .

The wave generator 4 is assembled to the inner peripheral surface of the external gear 3 to deform the external gear 3 in a non-circular shape, thereby forming a meshing portion P with the internal gear 2 in the external gear 3 and The meshing portion P is moved in the circumferential direction of the internal gear 2. - 特許庁

In this embodiment, the internal gear 2 has a plurality of internal teeth 2a and an annular body 2b. The plurality of internal teeth 2a protrude radially inward from the inner circumference of the annular main body 2b. In this embodiment, the internal gear 2 is fixed to, for example, a housing (not shown) of the strain wave gearing 1 . That is, in this embodiment, the internal gear 2 is a fixed gear. Furthermore, in this embodiment, the internal gear 2 is a rigid gear with high rigidity. The internal gear 2 is made of, for example, iron-based materials such as cast iron, alloy steel, and carbon steel, light metal alloys such as magnesium alloys, aluminum alloys, and titanium alloys, or single light metals, PEEK (polyetheretherketone), and PPS (polyphenylene sulfide). , POM (polyoxymethylene) and other engineering plastics.

Further, in this embodiment, the external gear 3 has a plurality of external teeth 3a and an annular main body 3b. The plurality of external teeth 3a protrude radially outward from the outer circumference of the annular main body 3b. The external gear 3 is a flexible gear having flexibility. The external gear 3 can be mechanically deformed and restored, for example, by forming the annular main body 3b thin. When the annular main body 3b is formed thin, the material for forming the external gear 3 can be metal or resin material, for example. In addition, the external gear 3 is made of, for example, a flexible material (for example, a thin material made of alloy steel, carbon steel, light metal, or a flexible resin material such as engineering plastic). can be transformed and restored.

Further, in this embodiment, the wave generator 4 includes a wave generating core 5 and bearings 6 .

In this embodiment, the wave-generating core 5 is connected to the drive shaft 7 . The drive shaft 7 is connected to a power source such as a motor (not shown). The wave generation core 5 is a member having high rigidity, like the internal gear 2 . The outer peripheral surface of the wave generating core 5 functions like a cam, for example. In this embodiment, the rotation axis of the drive shaft 7 is coaxial with the axis O of the strain wave gearing 1 . This allows the wave-generating core 5 to rotate around the axis O. As shown in FIG. The wave-generating core 5 has a non-circular shape. In this embodiment, the wave-generating core 5 is of the two-lobe type. As shown in FIG. 1, the two-lobe shape has an elliptical shape when viewed from the axial direction (a line of sight from the direction of the axis O). In FIG. 1, reference numeral 5a denotes the vertex of the wave generating core 5 on the long axis side. The vertex 5a on the long axis side is arranged on the long axis.

In this embodiment, the bearing 6 allows relative rotation between the external gear 3 and the wave generating core 5 . In this embodiment, the bearing 6 has an outer ring 6a, an inner ring 6b and rolling elements 6c. Examples of bearings having such a configuration include rolling bearings such as roller bearings and ball bearings (for example, deep groove ball bearings). Furthermore, in this embodiment, the outer ring 6a and the inner ring 6b are flexible. Thereby, the outer ring 6a and the inner ring 6b can be deformed according to the contour shape of the wave generating core 5, respectively. The bearing 6 can be made of, for example, a resin material such as PTFE (polytetrafluoroethylene), PEEK (polyetheretherketone), POM (polyoxymethylene), or fiber-reinforced plastic. again. The bearing 6 can be made of, for example, a light metal alloy such as a titanium alloy, an aluminum alloy, a magnesium alloy, or a single light metal.

The inner ring 6 b of the bearing 6 is attached to the outer peripheral surface of the wave generating core 5 . As a result, the bearing 6 is assembled to the wave generating core 5 so that the shape of the bearing 6 becomes the contour shape of the wave generating core 5 . However, the inner ring 6b can be formed integrally with the wave generating core 5. FIG. That is, according to the present invention, the inner ring 6b can be constructed as part of the wave-generating core 5 .

The outer ring 6 a of the bearing 6 is attached to the inner peripheral surface of the external gear 3 . The outer ring 6a has flexibility. As a result, the bearing 6 can support the flexible external gear 3 so that the shape of the external gear 3 conforms to the contour shape of the wave generating core 5 . In this embodiment, the wave-generating core 5 is two-lobed. Therefore, as shown in FIG. 1 , the external gear 3 bends in an elliptical shape along with the bearing 6 according to the shape of the wave generating core 5 . As a result, meshing portions P between the internal gear 2 and the external gear 3 are formed at two positions on the long axis side of the wave generating core 5 between the internal gear 2 and the external gear 3. be done.

In the wave gear device 1 , when the wave generator 4 is rotated, the wave generating core 5 of the wave generator 4 can be rotated relative to the external gear 3 . In the strain wave gearing 1, there is a tooth number difference between the number of teeth _ZF of the external teeth 3a of the external gear 3 and the number of teeth _ZR of the internal teeth 2a of the internal gear 2. Therefore, when the wave generator 4 is rotated, relative rotation occurs between the internal gear 2 and the external gear 3 due to the difference in the number of teeth. As a result, when the wave generator 4 is rotated, the meshing portion P of the external gear 3 moves in the circumferential direction of the internal gear 2 in a direction opposite to the rotational direction of the wave generator 4 . In this embodiment, the meshing portion P moves relative to the internal gear 2 in a direction opposite to the direction of rotation of the wave generator 4 each time the wave generating core 5 rotates about the axis O by 180 degrees. That is, in this embodiment, the input rotation from the wave generator 4 is inverted and output as the reduced speed rotation from the external gear 3 .

As described above, the strain wave gearing 1 performs deceleration by meshing the external teeth 3a of the external gear 3 and the internal teeth 2a of the internal gear 2 at two meshing portions P on the long axis side. Since the speed reduction ratio at this time is determined by the number of teeth of the external teeth 3a and the internal teeth 2a, it is possible to realize a high speed reduction ratio compared to other speed reducers. The strain wave gearing 1 is used, for example, as a speed reducer for a robot.

On the other hand, the power transmission efficiency of the conventional strain wave gearing is lower than that of the general planetary gearing. The main reason for this is the frictional resistance, viscous resistance and agitation resistance in the bearing 6 in the wave generator 4 . Here, referring to FIG. 2, the frictional resistance depends on, for example, the normal force N and the coefficient of dynamic friction μ received at the sliding portion between the outer ring 6a and the rolling element 6c. Frictional resistance is relatively large in a mechanism such as a strain wave gearing in which a large vertical force is generated at the long shaft of the cam. Therefore, the conventional strain wave gearing inevitably suffers a large loss in power transmission efficiency.

Therefore, the present invention aims to reduce the frictional force F generated inside the bearing 6 and improve the power transmission efficiency in the wave gear device 1 .

Here, the frictional force F(N) can be defined by F=μ×N.

From the above formula, the frictional force F(N) is proportional to the normal force N. In this embodiment, the wave generator 4 is of two-lobe type. In this case, the normal force N is the reaction force required to deform the perfectly circular bearing 6 into an elliptical shape according to the outer peripheral shape of the wave generating core 5 . Therefore, the normal force N becomes smaller as the bearing 6 becomes more deformable. In the present invention, the ease of deformation of the bearing 6 is quantitatively evaluated by the bending stiffness EI (=E×I), and the normal force N is reduced by reducing the value.

According to the present invention, the outer ring 6a has elasticity determined by the following formula (1).
Elasticity (N/mm ² )=E×I×(1/D ⁴ ) (1)
E: Modulus of longitudinal elasticity, I: Moment of inertia of area, D: Outer diameter of outer ring 6a It is the diameter of the outer ring 6a at a certain time.

Further, according to the present invention, said elasticity (N/mm ² ) is in the range of 7.8×10 ⁻⁵ to 2.7×10 ⁻² . More preferably, the elasticity (N/mm ² ) is in the range of 7.8×10 ⁻⁵ to 5.9×10 ⁻⁴ , as will be apparent from the examples below.

In the above formula (1), E×I represents bending rigidity (N·mm ² ) and is also called bending rigidity EI. The bending stiffness EI is the product of the modulus of longitudinal elasticity E and the moment of inertia I. The term (1/D ⁴ ) multiplied by the bending stiffness EI is a correction term based on the outer diameter D of the bearing 6 . This correction term is a correction term for equalizing the difference in size of the strain wave gearing. Specifically, if the size of the strain wave gearing is changed, the thickness (t) and width (w) of the bearing are also changed accordingly. Therefore, the moment of inertia of area also changes greatly according to changes in the thickness (t) and width (w) of the bearing 6 . In order to absorb the change in elasticity due to the change in the geometrical moment of inertia, a correction term based on the outer diameter D of the outer ring 6a is used for leveling.

If the flexural rigidity EI of the outer ring 6a of the bearing 6 is reduced to the limit where the strength required for the strain wave gearing 1 can be secured, the force required to elastically deform the bearing 6 can be reduced within a practically durable range. be. As a result, the frictional force F generated between the outer ring 6a and the rolling elements 6c of the bearing 6 is also reduced within a range that can withstand practical use. As a result, reduction in the power transmission efficiency of the strain wave gearing 1 can be suppressed.

In the strain wave gearing 1, the bending rigidity EI is set so that the elasticity (N/mm ² ) satisfies the range of 7.8×10 ⁻⁵ to 2.7×10 ⁻² . When the elasticity (N/mm ² ) is 2.7×10 ⁻² or less, the power transmission efficiency is improved compared to the conventional strain wave gearing having no configuration according to the present invention. Further, when the elasticity (N/mm ² ) is 7.8×10 ⁻⁵ or more, it is possible to improve power transmission efficiency while maintaining durability and workability. Therefore, if the elasticity (N/mm ² ) is set to satisfy the range of 7.8×10 ⁻⁵ to 2.7×10 ⁻² , the bending rigidity EI of the outer ring 6a can be reduced to a range that can withstand practical use. can be reduced to the limit where the required strength can be secured.

Therefore, according to the strain wave gearing 1, the bearing 6 is easily deformed within a range that can withstand practical use. improves.

In particular, in the strain wave gearing 1, the longitudinal elastic modulus E (GPa) of the outer ring 6a is preferably in the range of 0.4-200. When the modulus of longitudinal elasticity E (GPa) is 200 or less, the power transmission efficiency is further improved as compared with the conventional strain wave gearing that does not have the configuration according to the present invention. Further, when the modulus of longitudinal elasticity E (GPa) is 0.4 or more, the outer ring 6a of the bearing 6 can obtain rigidity that can support the external gear 3 in a more stable state. This improves power transmission efficiency. In addition, in this case, the workability of the outer ring 6a can also maintain the conventional workability. Therefore, if the longitudinal elastic modulus E (GPa) of the outer ring 6a is in the range of 0.4 to 200, the power transmission efficiency is further improved while maintaining workability.

Further, in the strain wave gearing 1, the outer ring 6a is preferably made of resin or light metal. In this case, power transmission efficiency is improved by a simple means of selecting materials. Examples of the resin include resin materials such as PEEK (polyetheretherketone), POM (polyoxymethylene), PTFE (polytetrafluoroethylene), and fiber-reinforced plastics. Further, the light metal may be, for example, a light metal alloy such as a titanium alloy, an aluminum alloy, a magnesium alloy, or a single light metal. In addition, the constituent material of the outer ring 6a does not have to be a single material. The material of the outer ring 6a can be a combination of resin and light metal. Alternatively, the constituent material of the outer ring 6a may be a combination of at least any two of resin, light metal and iron material. Also, the inner ring 6b can be made of the same material as the outer ring 6a.

In particular, in the strain wave gearing 1, the outer ring 6a is made of bearing steel (for example, SUJ2), and the thickness ratio (%), which is the ratio of the thickness t of the outer ring 6a to the outer diameter D of the outer ring 6a, is , 1.2 to 2.1.

Referring to FIG. 1, the thickness ratio (%) is defined as follows.
Thickness ratio (%) = t/D (2)
D: outer diameter of outer ring 6a, t: thickness of outer ring 6a

When the thickness ratio (%) is in the range of 1.2 to 2.1, the thickness ratio (%) of the outer ring 6a is set within the range (1.2 to 2.1) while using the existing bearing material of bearing steel. .1) can improve power transmission efficiency.

On the other hand, the frictional force F(N) is also proportional to the dynamic friction coefficient μ. The coefficient of dynamic friction μ generally decreases as the hardness of the sliding surface increases. Therefore, by forming a hard layer on the sliding surface between the rolling elements 6c and the outer ring 6a, the dynamic friction coefficient μ can be reduced, and the reduction in the power transmission efficiency of the strain wave gearing 1 can be further suppressed.

In the strain wave gearing 1, the outer ring 6a is supported by rolling elements 6c. Therefore, in the present embodiment, at least one of the surface of the rolling element 6c and the raceway surface of the rolling element 6c in the outer ring 6a or the inner ring 6b is provided with a hard layer having higher hardness than the base material layer of the outer ring 6a. , the power transmission efficiency is further improved. Here, the raceway surface of the rolling element 6c refers to at least one of the inner peripheral surface of the outer ring 6a and the outer peripheral surface of the inner ring 6b.

Materials used for the hard layer include, for example, materials having hardness higher than that of bearing steel, and a specific example thereof is DLC (diamond-like carbon). Moreover, when the hard layer is formed by a surface hardening treatment, the surface hardening treatment is not limited to a specific surface treatment. Examples of such surface effect treatments include chrome plating, nitriding, and carburizing. The hard layer can be formed on either the rolling element 6c or the raceway surface of the rolling element 6c. Alternatively, the hard layer can be formed on both the rolling elements 6c and the raceway surfaces of the rolling elements 6c. In this case, power transmission efficiency is most improved. Further, according to the present invention, the outer ring 6a can be made of a multi-layered structure, the inner layer having the raceway grooves can be made of a hard layer such as iron, and the outer layer can be made of a material having a low longitudinal elastic modulus E such as resin. Further, according to the present invention, the inner ring 6b can be made of multiple layers, the outer layer as a raceway surface can be made of a hard layer such as iron, and the inner layer can be made of a material having a low longitudinal elastic modulus E such as resin.

FIG. 4 is a strain wave gearing according to a second embodiment of the present invention, and is a diagram schematically showing a part of the bearing 6 of the strain wave gearing. In this embodiment, the shape of the outer ring 6a of the bearing 6 is changed. In this embodiment, the outer peripheral surface of the outer ring 6a is provided with a plurality of grooves 6d spaced apart in the circumferential direction. If the groove 6d is provided in the outer ring 6a, the outer ring 6a can be easily bent starting from the groove 6d. That is, the bending rigidity EI of the outer ring 6a can be reduced by providing the groove 6d in the outer ring 6a. This makes it easier to bend the outer ring 6a. Therefore, according to this embodiment, the power transmission efficiency can be improved as compared with a wave gear device without the groove 6d.

Specifically, the groove 6d is formed as a groove that is recessed radially inward toward the axis O. Further, in this embodiment, the groove 6d extends parallel to the axis O, that is, parallel to the axial direction. Furthermore, in this embodiment, the groove 6d is a long groove formed to reach the axial end of the outer ring 6a. Further, referring to FIG. 4, the power transmission efficiency can be improved by processing the outer ring 6a of the bearing 6 so that the degree of elasticity is within the above range. For example, by providing a V-shaped (wedge-shaped) long groove or a U-shaped long groove in the outer ring 6a of the bearing 6, the elasticity can be set within the above range.

FIG. 5 is a strain wave gearing according to a third embodiment of the present invention, and is a diagram schematically showing a part of the bearing 6 of the strain wave gearing. In this embodiment, a hole portion B6 is provided inside the outer ring 6a. The hole B6 is a closed space inside the outer ring 6a. If the hole portion B6 is provided inside the outer ring 6a, a hole (space) is formed inside the outer ring 6a, so the longitudinal coefficient E is lowered. As a result, the bending stiffness EI can be lowered equivalently to the embodiment of FIG. This makes it easier to bend the outer ring 6a. Therefore, according to this embodiment, it is possible to improve the transmission efficiency as compared with a strain wave gearing having no air holes.

In the third embodiment shown in FIG. 5, the holes B6 are simply holes, but the holes B6 may be impregnated with a material having a low longitudinal elastic modulus E such as resin. Moreover, when the size of the pores is large, the pores become starting points of fatigue fracture. For this reason, it is desirable that the size of the pores (specifically, the average pore diameter, that is, the average diameter of the pores) is evenly dispersed at several tens of μm or less.

Next, examples of the present invention will be described.

Table 1 below shows the results of power transmission efficiency measurements. The measurement results include the power transmission efficiency measurement results obtained in Examples 1 to 6 according to the present invention, and the power transmission efficiency obtained in Comparative Examples 1 to 2 for comparison with Examples 1 to 6. and the measurement results of

Table 1 shows the elasticity of the outer ring 6a (N/mm ² ), the thickness t (mm) of the outer ring 6a, the thickness ratio (%) of the outer ring 6a, and the outer ring 6a of the bearing 6 for each example and comparative example. are also shown. The power transmission efficiency is measured using the wave generator 4 as an input. The input rotation speed (rpm) was set to three types of 100 rpm, 500 rpm, and 1000 rpm in the range of 100 to 1000 rpm. Moreover, the load torque (N·m) was measured at 1.0. In particular, in Example 6, a hard layer made of DLC is formed on the rolling elements 6c, the raceway surface (inner peripheral surface) of the outer ring 6a, and the raceway surface (outer peripheral surface) of the inner ring 6b of the bearing 6. There are four types of power transmission efficiency: ◎: power transmission efficiency of 50% or more, ○: power transmission efficiency of 40% or more and less than 50%, △: power transmission efficiency of 30% or more and less than 40%, ×: power transmission efficiency of less than 30%. evaluated with

Next, Table 2 below shows the comprehensive judgment results of Examples 1 to 6 and Comparative Examples 1 and 2, taking practicality into consideration. Items for comprehensive evaluation include power transmission efficiency, processing difficulty, and durability. The overall evaluation is an evaluation that takes into consideration the power transmission efficiency, the difficulty of processing, and the durability. Comprehensive evaluation was made into 4 types of ⊚: very good, ∘: good, Δ: slightly good, and ×: bad. In this comprehensive evaluation, it was determined that a strain wave gearing device with a comprehensive evaluation of Δ or higher was practical.

Here, Example 1 is an example corresponding to the invention according to claim 3 of this application. In Example 1, the outer ring 6a and the inner ring 6b of the bearing 6 are made of PTFE (polytetrafluoroethylene) of a resin material (longitudinal elastic modulus E=4.0×10 ² N/mm ² ), and the outer ring 6a and the inner ring 6b are The thickness is 0.8 mm. On the other hand, in Comparative Example 2, the resin material is the same PTFE, and the thickness of the outer ring 6a and the inner ring 6b is 0.5 mm. In both cases, the bending rigidity is reduced by reducing the longitudinal elastic modulus E and the thickness of the outer ring 6a by changing the material, and good power transmission efficiency can be obtained. is too thin, has problems with durability, and cannot withstand practical use.

Next, Example 2 is also an example corresponding to the invention according to claim 3 of this application. In Example 2, the outer ring 6a and the inner ring 6b of the bearing 6 are made of PEEK resin material (longitudinal elastic modulus E=3.00×10 ³ N/mm ² ), and the thickness of the outer ring 6a and the inner ring 6b is 0.8 mm. and Here, Table 3 shows specific numerical results obtained by measuring the power transmission efficiency of Example 2. Table 3 shows that the outer ring 6a and the inner ring 6b of the bearing 6 are made of bearing steel (SUJ2) (longitudinal elastic modulus E = 2.08 × 10 ⁵ N/mm ² , elasticity = 4.1 × 10 ^-2 N/ mm ² ), and specific numerical results obtained by measuring the power transmission efficiency of Comparative Example 1 in which the thickness of the outer ring 6a and the inner ring 6b is 0.8 mm are also shown. Moreover, in FIG. 6, Table 3 is shown with a line graph.

As shown in Table 3 and FIG. 6, as a result of a comparative test of the power transmission efficiency of both Example 2 and the conventional technology, the power transmission efficiency of Example 2 was 50% or more, whereas the conventional technology The power transmission efficiency of the technology is about 22 to 30%, and we were able to confirm an improvement in power transmission efficiency of about two times. Further, when the material of the outer ring 6a of the bearing 6 is PEEK, the thickness ratio (%) is preferably 2.4% to 4.4%. If the thickness ratio (%) is less than 2.4%, the thickness of the outer ring 6a including the inner ring 6b becomes too thin, and a sufficient raceway groove depth cannot be secured. In this case, there is concern that the rolling elements 6c may come off. On the other hand, if the thickness ratio (%) is more than 4.4%, the thickness t of the outer ring 6a becomes too thick, and the elasticity (N/mm ² ) becomes too large. , the power transmission efficiency deteriorates. Therefore, when the material of the outer ring 6a of the bearing 6 is PEEK, the thickness ratio (%) is preferably 2.4% to 4.4%. In Example 2, PEEK was used as the resin material for the outer ring 6a and the inner ring 6b. A light metal alloy or a light metal simple substance may be used, and the longitudinal elastic modulus E is desirably in the range of 0.4 GPa to 200 GPa.

Examples 3 to 5 are examples corresponding to the invention according to claim 4 of this application. The outer ring 6a and the inner ring 6b of the bearing 6 were made of bearing steel (SUJ2), and the thickness ratio (%) was changed from 2.4% in Comparative Example 1 to 2.1%, 1.5%, and 1.2%, respectively. In this example, only the thicknesses of the outer ring 6a and the inner ring 6b are changed. As the thickness t of the outer ring 6a is reduced, the bending rigidity EI is reduced, and the power transmission efficiency can be improved as compared with the first comparative example. In this case, the thickness ratio (%) is preferably 1.2% to 2.1%. If the thickness ratio (%) is less than 1.2%, the outer ring 6a and the inner ring 6b are too thin. Therefore, it becomes difficult to manufacture the outer ring 6a, and the durability is lowered. In addition, when the thickness ratio (%) is more than 2.1%, the thickness is almost the same as in Comparative Example 1 and becomes too thick, so the elasticity (N/mm ² ) becomes too large. As a result, power transmission efficiency is not improved. Therefore, if the thickness ratio (%) is 2.1% or less, the reduction in transmission efficiency loss due to changes in thickness is reduced, and the power transmission efficiency is not significantly improved. Therefore, the thickness ratio (%) is more preferably 1.2% to 2.1%.

Referring to Table 2, according to the relationship between Examples 1 to 6 and Comparative Examples 1 and 2, the elastic degree (N/mm ² ) of the strain wave gearing 1 is 7.8×10 ⁻⁵ to 2.7×10 −5 . The range of 10 ⁻² is satisfied, and it is clear that the power transmission efficiency is improved within a range that can withstand practical use. More preferably, as in Examples 1, 2 and 4, said elasticity (N/mm ² ) ranges from 7.8×10 ⁻⁵ to 1.0×10 ⁻² .

Further, referring to Examples 1 and 2, it is clear that one method of suppressing the bending rigidity EI is to change the material of the outer ring 6a to a material having a low longitudinal elastic modulus E.

Also, referring to Examples 3 to 5, it is clear that the second method of suppressing the bending rigidity EI is to reduce the thickness t of the outer ring 6a. Here, in FIG. 3, the outer ring 6a of the bearing 6 is shown in the AA section of FIG. In FIG. 3, the symbol w is the axial width of the outer ring 6a. Further, in FIG. 3, symbol t is the thickness of the outer ring 6a. Referring to FIG. 3, the geometrical moment of inertia I of the outer ring 6a is I=(w×t ³ )/12. Therefore, the geometrical moment of inertia I is proportional to the cube of the thickness t of the outer ring 6a. Therefore, by reducing the thickness t of the outer ring 6a, the bending rigidity EI can be reduced.

As a third method for suppressing the bending rigidity EI, the geometrical moment of inertia I can be reduced by changing the cross-sectional shape and internal structure of the outer ring 6a. Specific examples include the above second and third embodiments.

Furthermore, Example 6 is an example corresponding to the invention according to claim 5 of this application. In this embodiment, a hard layer made of DLC is formed on the rolling elements 6c, the sliding surface (inner peripheral surface) of the outer ring 6a, and the sliding surface (outer peripheral surface) of the inner ring 6b. It can be seen that this suppresses the dynamic friction coefficient of the sliding portion, which contributes to the frictional force F, thereby improving the power transmission efficiency. In addition, although DLC is described as the hard layer in the present embodiment, as described above, the hard layer is not limited to DLC. good.

The foregoing merely exemplifies a plurality of embodiments and examples according to the present invention, and various modifications are possible within the scope of the claims. In this embodiment, the strain wave gearing 1 has been described as a two-lobe type, but the present invention is different. It is not limited to a two-lobe shape. According to the invention, the wave-generating core 5 may be multi-lobed. Specific examples of the wave generating core 5 include, for example, a triangular three-lobe shape and a quadrilateral four-lobe shape. Further, in the above description, the power transmission path of the strain wave gearing device 1 has the wave generator 4 as an input and the external gear 3 as an output, but is not limited to this.

1: Strain wave gearing, 2: Internal gear, 2a: Internal tooth, 2b: Annular body, 3: External gear, 3a: External tooth, 3b: Annular body, 4: Wave generator, 5: Wave generation Core 5a: Vertex 6: Bearing 6a: Outer ring 6b: Inner ring 6c: Rolling element 6d: Groove 7: Driving shaft B6: Hole P: Meshing part

Claims (5)

An internal gear, a flexible external gear, and a wave generator for generating wave motion in the external gear, wherein the wave generator is located on the inner peripheral surface of the external gear. A wave gear device having a bearing that fits into
The outer ring of the bearing has a degree of elasticity determined by the following formula (1),
Elasticity (N/mm ² )=E×I×(1/D ⁴ ) (1)
E: Modulus of longitudinal elasticity, I: Moment of inertia of area, D: Outer diameter of outer ring Further, the elastic degree is 7.8×10 ⁻⁵ to 2.7×10 ⁻² . The strain wave gearing according to claim 1, wherein the outer ring has a longitudinal elastic modulus E (GPa) of 0.4 to 200. 3. A wave gear device according to claim 2, wherein said outer ring is made of resin or light metal. 2. The outer ring according to claim 1, wherein the outer ring is made of bearing steel, and the thickness ratio (%), which is the ratio of the thickness of the outer ring to the outer diameter of the outer ring, is 1.2 to 2.1. strain wave gearing. The outer ring is supported by rolling elements, and at least one of the surface of the rolling elements and the raceway surface of the rolling elements in the outer ring or the inner ring is coated with a hard material having a higher hardness than the base layer of the outer ring. A strain wave gearing according to any one of claims 1 to 4, wherein layers are provided.

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