JP7535449B2 - Wave gear device, actuator and cover body - Google Patents

Description

The present disclosure generally relates to a wave gear device, an actuator, and a cover body, and more specifically to a wave gear device, an actuator, and a cover body that include a rigid internal gear, a flexible external gear, and a wave generator.

Patent Document 1 discloses that the surface of a flexible external gear in a strain wave gear device (flexible meshing gear device) is treated by nitriding.

The wave gear device has an annular rigid internal gear, a cup-shaped flexible external gear placed inside it, and an elliptical wave generator fitted inside it. The flexible external gear has a cylindrical body and external teeth formed on the outer circumferential surface of the body. The flexible external gear is bent into an elliptical shape by the wave generator, and the external teeth located at both ends of the long axis of the elliptical shape mesh with the internal teeth formed on the inner circumferential surface of the rigid internal gear.

When the wave generator is rotated by a motor or the like, the meshing positions of the two gears move in the circumferential direction, and a relative rotation occurs between the two gears according to the difference in the number of teeth between the internal and external teeth (2N (N is a positive integer)). Here, when the rigid internal gear side is fixed, a rotational output is obtained from the flexible external gear side that is significantly reduced in accordance with the difference in the number of teeth between the two gears.

JP 2001-59153 A

However, because the wave gear device transmits power by meshing the internal and external teeth while bending the flexible external gear, foreign matter such as metal powder or nitrides may be generated due to wear between the internal and external teeth, especially after long-term use. If such foreign matter gets into the bearings of the wave generator, damage may occur to the surfaces of the outer ring, inner ring, or rolling elements (balls) of the bearings, which may affect the reliability of the wave gear device.

This disclosure has been made in consideration of the above-mentioned reasons, and aims to provide a strain wave gear device, actuator, and cover body that are less susceptible to deterioration in reliability.

A wave gear device according to one aspect of the present disclosure includes an annular rigid internal gear having internal teeth, an annular flexible external gear having external teeth and arranged inside the rigid internal gear, and a wave generator arranged inside the flexible external gear to cause a deflection in the flexible external gear. The wave gear device deforms the flexible external gear as the wave generator rotates about a rotation axis, meshes a part of the external teeth with a part of the internal teeth, and rotates the flexible external gear relative to the rigid internal gear according to the difference in the number of teeth with the rigid internal gear. The wave generator has a non-circular cam that is driven to rotate about the rotation axis, and a bearing arranged between the outer peripheral surface of the cam and the inner peripheral surface of the flexible external gear. The wave gear device further includes a cover member arranged to face the bearing from one side of the rotation axis. The cover member faces the bearing with a gap between it and the outer ring of the bearing, preventing foreign matter from entering the inside of the outer ring from one side of the rotating shaft.

The actuator according to one aspect of the present disclosure includes the wave gear device, a drive source that rotates the cam, and an output section that extracts the rotational force of the flexible external gear as an output.

The cover body according to one aspect of the present disclosure is used as the cover member for the strain wave gear device.

The present disclosure has the advantage that reliability is less likely to decrease.

Fig. 1A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to embodiment 1. Fig. 1B is an enlarged view of an area Z1 in Fig. 1A. 2A and 2B are schematic diagrams of the strain wave gear device as viewed from the input side of the rotating shaft with a cover member removed. 3A and 3B are schematic exploded perspective views of the strain wave gear device as viewed from the output side and input side of the rotary shaft, respectively. FIG. 4 is a cross-sectional view showing a schematic configuration of an actuator including the above-mentioned strain wave gear device. 5A and 5B are enlarged views of the periphery of a head portion of a cover member in the strain wave gear device. FIG. 6 is a cross-sectional view showing an example of a robot using the above-mentioned strain wave gear device. Fig. 7A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to embodiment 2. Fig. 7B is an enlarged view of a main portion of Fig. 7A. Fig. 8A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to a first modified example of embodiment 2. Fig. 8B is an enlarged view of a main portion of Fig. 8A. Fig. 9A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to a second modified example of embodiment 2. Fig. 9B is an enlarged view of a main portion of Fig. 9A. 10A, 10B, and 10C are cross-sectional views of essential parts showing schematic configurations of strain wave gear devices according to third, fourth, and fifth modified examples of the second embodiment, respectively. Fig. 11A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to embodiment 3. Fig. 11B is an enlarged view of a main portion of Fig. 11A.

(Embodiment 1)
(1) Overview Below, an overview of the wave gear device 1 according to this embodiment will be described with reference to Figures 1A to 4. All of the drawings referred to in this disclosure are schematic diagrams, and the ratios of size and thickness of each component in the drawings do not necessarily reflect the actual dimensional ratios. For example, the tooth shapes, dimensions, number of teeth, etc. of the internal teeth 21 and external teeth 31 in Figures 2A to 3B are merely shown schematically for the purpose of explanation, and are not intended to be limited to the shapes shown in the drawings.

The wave gear device 1 according to this embodiment is a gear device including a rigid internal gear 2, a flexible external gear 3, and a wave generator 4. In this wave gear device 1, an annular flexible external gear 3 is arranged inside an annular rigid internal gear 2, and a wave generator 4 is arranged inside the flexible external gear 3. The wave generator 4 bends the flexible external gear 3 into a non-circular shape, thereby partially meshing the external teeth 31 of the flexible external gear 3 with the internal teeth 21 of the rigid internal gear 2. When the wave generator 4 rotates, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the rigid internal gear 2, and a relative rotation according to the difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 is generated between the two gears (rigid internal gear 2 and flexible external gear 3). If the rigid internal gear 2 is fixed, the flexible external gear 3 will rotate in response to the relative rotation of the two gears. As a result, the flexible external gear 3 produces a rotational output that is reduced at a relatively high reduction ratio according to the difference in the number of teeth between the two gears.

The wave generator 4, which causes the flexible external gear 3 to bend, has a non-circular cam 41 that is driven to rotate around the input rotation axis Ax1 (see FIG. 1A) and a bearing 42. The bearing 42 is disposed between the outer peripheral surface 411 of the cam 41 and the inner peripheral surface 301 of the flexible external gear 3. The inner ring 422 of the bearing 42 is fixed to the outer peripheral surface 411 of the cam 41, and the outer ring 421 of the bearing 42 is elastically deformed by being pressed by the cam 41 via the ball-shaped rolling body 423. Here, the outer ring 421 can rotate relative to the inner ring 422 by the rolling of the rolling body 423, so when the non-circular cam 41 rotates, the rotation of the inner ring 422 is not transmitted to the outer ring 421, and a wave motion is generated in the external teeth 31 of the flexible external gear 3 pressed by the cam 41. As a result of the wave motion of the external teeth 31, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the rigid internal gear 2 as described above, and relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2.

In short, in this type of wave gear device 1, the wave generator 4 having the bearing 42 bends the flexible external gear 3, while the internal teeth 21 and the external teeth 31 mesh to transmit power. Therefore, particularly with long-term use, foreign matter X1 such as metal powder or nitrides (see FIG. 5A) may be generated due to wear between the internal teeth 21 and the external teeth 31. If such foreign matter X1 enters the bearing 42, damage may occur to the surface of any of the outer ring 421, the inner ring 422, and the rolling element 423 of the bearing 42, which may affect the reliability of the wave gear device 1. The wave gear device 1 according to this embodiment has the following configuration, which mainly suppresses the entry of foreign matter X1 into the bearing 42 and makes it less likely to cause a decrease in reliability.

That is, as shown in Figures 1A to 3B, the wave gear device 1 according to this embodiment includes an annular rigid internal gear 2 having internal teeth 21, an annular flexible external gear 3 having external teeth 31, and a wave generator 4. The flexible external gear 3 is arranged inside the rigid internal gear 2. The wave gear device 1 deforms the flexible external gear 3 in accordance with the rotation of the wave generator 4 about the rotation axis Ax1, meshing a part of the external teeth 31 with a part of the internal teeth 21, and rotating the flexible external gear 3 according to the difference in the number of teeth with the rigid internal gear 2. The wave generator 4 includes a non-circular cam 41 and a bearing 42. The cam 41 is driven to rotate about the rotation axis Ax1. The bearing 42 is arranged between the outer peripheral surface 411 of the cam 41 and the inner peripheral surface 301 of the flexible external gear 3. This wave gear device 1 further includes a cover member 5. The cover member 5 is disposed so as to face the bearing 42 from one side of the rotating shaft Ax1. The cover member 5 faces the bearing 42 with a gap G1 (see FIG. 1B) secured between the cover member 5 and the outer ring 421 of the bearing 42, and prevents foreign matter X1 from entering the inside of the outer ring 421 from one side of the rotating shaft Ax1.

According to this aspect, the cover member 5 arranged to face the bearing 42 from one side of the rotating shaft Ax1 prevents the foreign matter X1 from entering the inside of the outer ring 421 of the bearing 42 from one side of the rotating shaft Ax1. Therefore, even if foreign matter X1 such as metal powder or nitrides is generated due to wear between the internal teeth 21 and the external teeth 31 due to long-term use of the wave gear device 1, the entry of such foreign matter X1 into the bearing 42 (inside the outer ring 421) is suppressed. As a result, damage to the surfaces of the outer ring 421, inner ring 422, rolling element 423, etc. of the bearing 42 due to the foreign matter X1 is unlikely to occur, and the reliability of the wave gear device 1 is unlikely to decrease due to damage to the bearing 42. Therefore, the wave gear device 1 according to this embodiment has the advantage that the reliability is unlikely to decrease. And, since the wave gear device 1 according to this embodiment is unlikely to decrease in reliability even when used for a long period of time, this leads to a longer life and higher performance of the wave gear device 1.

As shown in FIG. 4, the wave gear device 1 according to this embodiment constitutes an actuator 100 together with a driving source 101 and an output unit 102. In other words, the actuator 100 according to this embodiment includes the wave gear device 1, a driving source 101, and an output unit 102. The driving source 101 rotates the cam 41. The output unit 102 extracts the rotational force of the flexible external gear 3 as an output.

The cover member 5 of the strain wave gear device 1 according to this embodiment constitutes the cover body 10 (see FIG. 1A). In other words, the cover body 10 according to this embodiment is used as the cover member 5 for the strain wave gear device 1. In other words, the cover body 10 is the cover member 5.

The actuator 100 and cover body 10 according to this embodiment have the advantage that the reliability of the strain wave gear device 1 is less likely to deteriorate.

(2) Definition In the present disclosure, "annular" means a ring-like shape that forms an enclosed space (region) at least in a plan view, and is not limited to a circular shape (annular shape) that is a perfect circle in a plan view, but may be, for example, an elliptical shape, a polygonal shape, etc. Furthermore, even if the shape has a bottom 322, such as a cup-shaped flexible external gear 3, if its body 321 is annular, it is called an "annular" flexible external gear 3.

In this disclosure, "hinder" means to impede or hinder, and does not mean to completely block. In other words, the cover member 5 that hinders the intrusion of the foreign object X1 into the inside of the outer ring 421 only needs to hinder the intrusion of the foreign object X1 into the inside of the outer ring 421, and does not necessarily need to completely block the foreign object X1. In other words, the presence of the cover member 5 only needs to suppress the intrusion of the foreign object X1 into the inside of the outer ring 421, and as a result, the amount of the foreign object X1 that intrudes into the inside of the outer ring 421 needs to be reduced. Of course, the cover member 5 may completely block the intrusion of the foreign object X1 into the inside of the outer ring 421.

In this disclosure, "foreign matter" refers to a substance other than the original components of the harmonic gear device 1, and examples include metal powder or nitrides that are generated due to wear between the internal teeth 21 and the external teeth 31. In other words, the foreign matter X1 that is prevented from entering the inside of the outer ring 421 by the cover member 5 is not limited to substances that are generated due to wear inside the harmonic gear device 1, but also includes, for example, dirt, sand, dust, etc. that enter from the outside of the harmonic gear device 1.

In this disclosure, "rigidity" refers to the property of an object to resist deformation when an external force is applied to the object and the object attempts to deform. In other words, an object that has rigidity is less likely to deform even when an external force is applied to it. In addition, in this disclosure, "flexibility" refers to the property of an object to elastically deform (bend) when an external force is applied to it. In other words, an object that has flexibility is more likely to elastically deform when an external force is applied to it. Therefore, "rigidity" and "flexibility" have opposing meanings.

In particular, in this disclosure, the "rigidity" of the rigid internal gear 2 and the "flexibility" of the flexible external gear 3 are used in a relative sense. In other words, the "rigidity" of the rigid internal gear 2 means that the rigid internal gear 2 has a high rigidity, at least relatively compared to the flexible external gear 3, meaning that it is less likely to deform even when an external force is applied. Similarly, the "flexibility" of the flexible external gear 3 means that the flexible external gear 3 has a high flexibility, at least relatively compared to the rigid internal gear 2, meaning that it is more likely to elastically deform when an external force is applied.

In addition, in this disclosure, one side of the rotating shaft Ax1 (the right side in FIG. 1A) may be referred to as the "input side," and the other side of the rotating shaft Ax1 (the left side in FIG. 1A) may be referred to as the "output side." In other words, in the example of FIG. 1A, the cover member 5 is disposed so as to face the bearing 42 from the "input side" of the rotating shaft Ax1. However, the "input side" and "output side" are merely labels used for explanation, and are not intended to limit the positional relationship between the input and output when viewed from the strain wave gear device 1.

In this disclosure, "non-circular" means a shape that is not a perfect circle, and includes, for example, an elliptical shape and an oval shape. As an example in this embodiment, the non-circular cam 41 of the wave generator 4 is elliptical. In other words, in this embodiment, the wave generator 4 bends the flexible external gear 3 into an elliptical shape.

In this disclosure, the term "elliptical shape" refers to any shape in which a perfect circle is compressed and the intersection of the major and minor axes perpendicular to each other is located at the center, and is not limited to a mathematical "ellipse" which is a curved line consisting of a set of points whose sum of distances from two fixed points on a plane is constant. In other words, the cam 41 in this embodiment may be a curved line consisting of a set of points whose sum of distances from two fixed points on a plane is constant, like a mathematical "ellipse," or may be an elliptical shape such as an oval rather than a mathematical "ellipse." As mentioned above, all of the drawings referred to in this disclosure are schematic diagrams, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. Therefore, for example, in Figures 2A and 2B, the shape of the cam 41 of the wave generator 4 is a somewhat exaggerated elliptical shape, but this is not intended to limit the actual shape of the cam 41.

In this disclosure, the "axis of rotation" refers to a virtual axis (straight line) that is the center of the rotational motion of a rotating body. In other words, the axis of rotation Ax1 is a virtual axis that does not have a physical entity. The wave generator 4 performs rotational motion around the axis of rotation Ax1.

In this disclosure, "internal teeth" and "external teeth" do not refer to individual "tooths," but rather to a collection (group) of multiple "teeth." In other words, the internal teeth 21 of the rigid internal gear 2 are made up of a collection of multiple teeth formed on the inner peripheral surface of the rigid internal gear 2. Similarly, the external teeth 31 of the flexible external gear 3 are made up of a collection of multiple teeth formed on the outer peripheral surface of the flexible external gear 3.

(3) Configuration Hereinafter, the detailed configuration of the strain wave gear device 1 and the actuator 100 according to this embodiment will be described with reference to FIGS. 1A to 4.

Figure 1A is a cross-sectional view showing the schematic configuration of the wave gear device 1, and Figure 1B is an enlarged view of region Z1 in Figure 1A. Figure 2A is a schematic view of the wave gear device 1 with the cover member 5 removed, viewed from the input side of the rotation axis Ax1 (right side of Figure 1A). Figure 2B is a schematic view of the wave gear device 1 including the cover member 5, viewed from the input side of the rotation axis Ax1. Figure 3A is a schematic exploded perspective view of the wave gear device 1, viewed from the output side of the rotation axis Ax1 (left side of Figure 1A). Figure 3B is a schematic exploded perspective view of the wave gear device 1, viewed from the input side of the rotation axis Ax1. Figure 4 is a cross-sectional view showing the schematic configuration of an actuator 100 including the wave gear device 1.

(3.1) Harmonic Gearing As described above, the harmonic gearing 1 according to this embodiment includes the rigid internal gear 2, the flexible external gear 3, the wave generator 4, and the cover member 5. In this embodiment, the materials of the components of the harmonic gearing 1, that is, the rigid internal gear 2, the flexible external gear 3, the wave generator 4, and the cover member 5, are metals such as stainless steel, cast iron, carbon steel for machine construction, chromium molybdenum steel, phosphor bronze, aluminum bronze, etc. The metals referred to here include metals that have been subjected to surface treatment such as nitriding.

In addition, in this embodiment, a cup-type wave gear device is exemplified as an example of the wave gear device 1. That is, the wave gear device 1 according to this embodiment uses a flexible external gear 3 formed in a cup shape. The wave generator 4 is combined with the flexible external gear 3 so as to be housed within the cup-shaped flexible external gear 3.

In addition, in this embodiment, as an example, the strain wave gear device 1 is used with the rigid internal gear 2 fixed to the input side case 111 (see FIG. 4) and the output side case 112 (see FIG. 4), etc. As a result, in conjunction with the relative rotation between the rigid internal gear 2 and the flexible external gear 3, the flexible external gear 3 rotates relative to the fixed member (the input side case 111, etc.).

Furthermore, in this embodiment, when the wave gear device 1 is used in the actuator 100, a rotational force is applied as an input to the wave generator 4, and a rotational force is extracted as an output from the flexible external gear 3. In other words, the wave gear device 1 operates with the rotation of the wave generator 4 as the input rotation and the rotation of the flexible external gear 3 as the output rotation. As a result, the wave gear device 1 can obtain an output rotation that is reduced at a relatively high reduction ratio compared to the input rotation.

Furthermore, in the wave gear device 1 according to this embodiment, the input side rotation axis Ax1 and the output side rotation axis Ax2 are on the same straight line. In other words, the input side rotation axis Ax1 and the output side rotation axis Ax2 are coaxial. Here, the input side rotation axis Ax1 is the rotation center of the wave generator 4 to which the input rotation is applied, and the output side rotation axis Ax1 is the rotation center of the flexible external gear 3 which generates the output rotation. In other words, in the wave gear device 1, an output rotation that is slowed down at a relatively high reduction ratio compared to the input rotation on the same axis is obtained.

The rigid internal gear 2 is also called a circular spline and is an annular part having internal teeth 21. In this embodiment, the rigid internal gear 2 has an annular shape, with at least the inner peripheral surface being a perfect circle in a plan view. The inner peripheral surface of the annular rigid internal gear 2 has internal teeth 21 formed along the circumferential direction of the rigid internal gear 2. The multiple teeth constituting the internal teeth 21 all have the same shape and are provided at equal pitch over the entire circumferential area of the inner peripheral surface of the rigid internal gear 2. In other words, the pitch circle of the internal teeth 21 is a perfect circle in a plan view. In addition, the rigid internal gear 2 has a predetermined thickness in the direction of the rotation axis Ax1. All of the internal teeth 21 are formed over the entire length of the rigid internal gear 2 in the thickness direction. All of the tooth traces of the internal teeth 21 are parallel to the rotation axis Ax1.

As described above, the rigid internal gear 2 is fixed to the input side case 111 (see FIG. 4) and the output side case 112 (see FIG. 4), etc. Therefore, the rigid internal gear 2 has a plurality of fixing holes 22 for fixing.

The flexible external gear 3 is also called a flex spline and is an annular part having external teeth 31. In this embodiment, the flexible external gear 3 is a part formed in a cup shape from a relatively thin-walled metal elastic body (metal plate). In other words, the flexible external gear 3 has flexibility due to its relatively small (thin) thickness. The flexible external gear 3 has a cup-shaped main body 32. The main body 32 has a body 321 and a bottom 322. The body 321 has a cylindrical shape in which at least the inner circumferential surface 301 is a perfect circle in a plan view when no elastic deformation occurs in the flexible external gear 3. The central axis of the body 321 coincides with the rotation axis Ax1. The bottom 322 is arranged on one opening surface of the body 321 and has a disk shape that is a perfect circle in a plan view. The bottom 322 is disposed on the opening on the output side of the rotation axis Ax1, out of a pair of openings on the body 321. As described above, the body 32, consisting of the body 321 and the bottom 322, has a bottomed cylindrical shape, i.e., a cup shape, that is open to the input side of the rotation axis Ax1. In this embodiment, the body 321 and the bottom 322 are integrally formed from a single metal member, thereby realizing a seamless body 32.

Here, the wave generator 4 is combined with the flexible external gear 3 such that the non-circular (elliptical) wave generator 4 is fitted inside the body 321. As a result, the flexible external gear 3 elastically deforms into a non-circular shape when it receives an external force from the wave generator 4 in the radial direction (direction perpendicular to the rotation axis Ax1) from the inside to the outside. In this embodiment, by combining the wave generator 4 with the flexible external gear 3, the body 321 of the flexible external gear 3 elastically deforms into an elliptical shape. In other words, a state in which no elastic deformation occurs in the flexible external gear 3 means a state in which the wave generator 4 is not combined with the flexible external gear 3. Conversely, a state in which elastic deformation occurs in the flexible external gear 3 means a state in which the wave generator 4 is combined with the flexible external gear 3.

In addition, external teeth 31 are formed along the circumferential direction of the body 321 at least on the end of the outer peripheral surface of the body 321 opposite the bottom 322 (the input side of the rotation axis Ax1). The multiple teeth constituting the external teeth 31 are all of the same shape and are arranged at equal pitch over the entire circumferential area of the outer peripheral surface of the flexible external gear 3. In other words, the pitch circle of the external teeth 31 is a perfect circle in a plan view when no elastic deformation occurs in the flexible external gear 3. The external teeth 31 are formed only within a certain width from the edge of the opening side (the input side of the rotation axis Ax1) of the body 321. All of the tooth traces of the external teeth 31 are parallel to the rotation axis Ax1.

In this embodiment, as described above, the rotation of the flexible external gear 3 is extracted as the output rotation. For this reason, the output section 102 (see FIG. 4) of the actuator 100 is attached to the flexible external gear 3. A plurality of mounting holes 33 are formed in the bottom section 322 of the flexible external gear 3 for mounting a shaft serving as the output section 102. Furthermore, a through hole 34 is formed in the center of the bottom section 322. The area around the through hole 34 in the bottom section 322 is thicker than other parts of the bottom section 322.

The flexible external gear 3 configured in this manner is placed inside the rigid internal gear 2. Here, the flexible external gear 3 is combined with the rigid internal gear 2 so that only the end of the outer circumferential surface of the body 321 opposite the bottom 322 (the input side of the rotation axis Ax1) is inserted inside the rigid internal gear 2. Here, external teeth 31 are formed on the outer circumferential surface of the flexible external gear 3, and internal teeth 21 are formed on the inner circumferential surface of the rigid internal gear 2. Therefore, when the flexible external gear 3 is placed inside the rigid internal gear 2, the external teeth 31 and the internal teeth 21 face each other.

Here, the number of teeth of the internal teeth 21 of the rigid internal gear 2 is 2N (N is a positive integer) more than the number of teeth of the external teeth 31 of the flexible external gear 3. In this embodiment, as an example, N is "1", and the number of teeth (of the external teeth 31) of the flexible external gear 3 is "2" more than the number of teeth (of the internal teeth 21) of the rigid internal gear 2. Such a difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 determines the reduction ratio of the output rotation to the input rotation in the strain wave gear device 1.

In addition, in this embodiment, as an example, the dimension of the outer teeth 31 in the tooth trace direction (direction parallel to the rotation axis Ax1) is smaller than the dimension of the inner teeth 21 in the tooth trace direction (direction parallel to the rotation axis Ax1). In other words, in the direction parallel to the rotation axis Ax1, the outer teeth 31 are contained within the range of the tooth trace of the inner teeth 21.

However, when no elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is not combined with the flexible external gear 3), the pitch circle of the external teeth 31, which form a perfect circle, is set to be slightly smaller than the pitch circle of the internal teeth 21, which also form a perfect circle. In other words, when no elastic deformation occurs in the flexible external gear 3, the external teeth 31 and the internal teeth 21 face each other with a gap between them and do not mesh with each other.

On the other hand, when the flexible external gear 3 is elastically deformed (when the wave generator 4 is combined with the flexible external gear 3), the body 321 bends into an elliptical shape (non-circular shape), so that the external teeth 31 of the flexible external gear 3 partially mesh with the internal teeth 21 of the rigid internal gear 2. In other words, when the flexible external gear 3 (body 321) is elastically deformed into an elliptical shape, the external teeth 31 located at both ends of the long axis direction of the elliptical shape mesh with the internal teeth 21, as shown in FIG. 2A. In other words, the major axis of the pitch circle of the external teeth 31 that draws an ellipse coincides with the diameter of the pitch circle of the internal teeth 21 that draws a perfect circle, and the minor axis of the pitch circle of the external teeth 31 that draws an ellipse is smaller than the diameter of the pitch circle of the internal teeth 21 that draws a perfect circle. In this way, when the flexible external gear 3 is elastically deformed, some of the teeth that make up the external teeth 31 mesh with some of the teeth that make up the internal teeth 21. As a result, in the wave gear device 1, it is possible to mesh a portion of the external teeth 31 with a portion of the internal teeth 21.

The wave generator 4, also known as a wave generator, is a component that causes deflection in the flexible external gear 3, generating wave motion in the external teeth 31 of the flexible external gear 3. In this embodiment, the wave generator 4 is a component whose outer periphery is non-circular in plan view, specifically, elliptical.

The wave generator 4 has a non-circular (elliptical) cam 41 and a bearing 42 attached to the outer periphery of the cam 41. In other words, the non-circular (elliptical) cam 41 is fitted inside the inner ring 422 of the bearing 42, and is combined with the cam 41. As a result, the bearing 42 elastically deforms into a non-circular shape when it receives an external force from the cam 41 in the radial direction (direction perpendicular to the rotation axis Ax1) from the inside to the outside of the inner ring 422. In other words, a state in which no elastic deformation occurs in the bearing 42 means a state in which the cam 41 is not combined with the bearing 42. Conversely, a state in which elastic deformation occurs in the bearing 42 means a state in which the cam 41 is combined with the bearing 42.

The cam 41 is a non-circular (elliptical here) part that is driven to rotate around the input side rotation axis Ax1. The cam 41 has an outer circumferential surface 411 (see FIG. 1B), and at least the outer circumferential surface 411 is made of a metal plate that is elliptical in plan view. The cam 41 has a predetermined thickness in the direction of the rotation axis Ax1. As a result, the cam 41 has the same rigidity as the rigid internal gear 2. However, the thickness of the cam 41 is smaller (thinner) than the thickness of the rigid internal gear 2. In this embodiment, as described above, the rotation of the wave generator 4 is the input rotation. Therefore, the input part 103 (see FIG. 4) of the actuator 100 is attached to the wave generator 4. A cam hole 43 for attaching a shaft as the input part 103 is formed in the center of the cam 41 of the wave generator 4.

The bearing 42 has an outer ring 421, an inner ring 422, and a number of rolling elements 423. In this embodiment, as an example, the bearing 42 is a deep groove ball bearing using balls as the rolling elements 423.

The outer ring 421 and the inner ring 422 are both annular parts. The outer ring 421 and the inner ring 422 are both made of a relatively thin elastic metal body (metal plate) and are formed into an annular shape. In other words, the outer ring 421 and the inner ring 422 are flexible because they are relatively small (thin). In this embodiment, the outer ring 421 and the inner ring 422 have an annular shape that is a perfect circle in a plan view when no elastic deformation occurs in the bearing 42 (when the cam 41 is not combined with the bearing 42). The inner ring 422 is one size smaller than the outer ring 421 and is disposed inside the outer ring 421. Here, since the inner diameter of the outer ring 421 is larger than the outer diameter of the inner ring 422, a gap is generated between the inner peripheral surface of the outer ring 421 and the outer peripheral surface of the inner ring 422.

The multiple rolling elements 423 are disposed in the gap between the outer ring 421 and the inner ring 422. The multiple rolling elements 423 are arranged in a line in the circumferential direction of the outer ring 421. The multiple rolling elements 423 are all metal balls of the same shape, and are provided at equal pitches over the entire circumferential area of the outer ring 421. Although not specifically shown here, the bearing 42 further has a retainer, and the multiple rolling elements 423 are held between the outer ring 421 and the inner ring 422 by the retainer.

In addition, in this embodiment, as an example, the dimension in the width direction (direction parallel to the rotation axis Ax1) of the inner ring 422 is the same as the thickness of the cam 41. The dimension in the width direction (direction parallel to the rotation axis Ax1) of the outer ring 421 is larger than the dimension in the width direction of the inner ring 422. In this embodiment, the outer ring 421 and the inner ring 422 are positioned such that the end faces on the output side of the rotation axis Ax1 are flush, as shown in FIG. 1B, so that the outer ring 421 protrudes relative to the inner ring 422 on the input side of the rotation axis Ax1. Furthermore, the dimension in the width direction of the outer ring 421 is smaller than the thickness of the rigid internal gear 2.

With this configuration of the bearing 42, when the cam 41 is assembled to the bearing 42, the inner ring 422 of the bearing 42 is fixed to the cam 41, and the inner ring 422 elastically deforms into an elliptical shape following the outer peripheral shape of the cam 41. At this time, the outer ring 421 of the bearing 42 is pressed by the inner ring 422 via the multiple rolling elements 423 and elastically deforms into an elliptical shape. Therefore, both the outer ring 421 and the inner ring 422 of the bearing 42 elastically deform into an elliptical shape. In this state where the bearing 42 is elastically deformed (when the cam 41 is assembled to the bearing 42), the outer ring 421 and the inner ring 422 form elliptical shapes that are similar to each other.

Even when the bearing 42 is elastically deformed, the gap between the outer ring 421 and the inner ring 422 is maintained substantially constant over the entire circumference of the outer ring 421 due to the presence of multiple rolling elements 423 between the outer ring 421 and the inner ring 422. In this state, the outer ring 421 can rotate relative to the inner ring 422 due to the rolling of multiple rolling elements 423 between the outer ring 421 and the inner ring 422. Therefore, when the cam 41 rotates around the rotation axis Ax1 while the bearing 42 is elastically deformed, the rotation of the cam 41 is not transmitted to the outer ring 421, and the elastic deformation of the inner ring 422 is transmitted to the outer ring 421 via the multiple rolling elements 423. In other words, in the wave generator 4, when the cam 41 rotates around the rotation axis Ax1, the outer ring 421 is elastically deformed so that the major axis of the elliptical shape formed by the outer ring 421 rotates around the rotation axis Ax1. Therefore, as a whole, the outer peripheral shape of the wave generator 4, which is elliptical when viewed from the input side of the rotation axis Ax1, changes with the rotation of the cam 41 so that its major axis rotates around the rotation axis Ax1.

The wave generator 4 configured in this manner is disposed inside the flexible external gear 3. Here, the flexible external gear 3 is combined with the wave generator 4 so that only the end of the inner circumferential surface 301 of the body 321 opposite the bottom 322 (the input side of the rotation axis Ax1) is fitted into the wave generator 4. At this time, the bearing 42 of the wave generator 4 is disposed between the outer circumferential surface 411 of the cam 41 and the inner circumferential surface 301 of the flexible external gear 3. Here, the outer diameter of the outer ring 421 in a state where no elastic deformation occurs in the bearing 42 (a state where the cam 41 is not combined with the bearing 42) is the same as the inner diameter of the flexible external gear 3 (body 321) in a state where no elastic deformation occurs. Therefore, the outer circumferential surface of the outer ring 421 in the wave generator 4 contacts the inner circumferential surface 301 of the flexible external gear 3 without any gap. Therefore, when elastic deformation occurs in the flexible external gear 3 (when the flexible external gear 3 is combined with the wave generator 4), the body 321 bends into an elliptical (non-circular) shape. In this state, the flexible external gear 3 is fixed to the outer ring 421 of the bearing 42.

The cover member 5 is disposed so as to face at least the bearing 42 from one side (input side) of the rotating shaft Ax1. The cover member 5 faces the bearing 42 with a gap G1 (see FIG. 1B) secured between it and the outer ring 421 of the bearing 42, and prevents foreign matter X1 (see FIG. 5A) from entering the inside of the outer ring 421 from one side (input side) of the rotating shaft Ax1. The cover member 5 will be described in detail in the section "(3.3) Cover member".

In the wave gear device 1 having the above-mentioned configuration, as shown in FIG. 2A, the body 321 of the flexible external gear 3 bends into an elliptical shape (non-circular shape), so that the external teeth 31 of the flexible external gear 3 partially mesh with the internal teeth 21 of the rigid internal gear 2. In other words, the flexible external gear 3 (body 321) elastically deforms into an elliptical shape, so that the external teeth 31 at two locations corresponding to both ends of the long axis direction of the elliptical shape mesh with the internal teeth 21. Then, when the cam 41 rotates around the rotation axis Ax1, the rotation of the cam 41 is not transmitted to the outer ring 421 and the flexible external gear 3, but the elastic deformation of the inner ring 422 is transmitted to the outer ring 421 and the flexible external gear 3 via multiple rolling elements 423. Therefore, the outer peripheral shape of the flexible external gear 3, which has an elliptical shape when viewed from the input side of the rotation axis Ax1, changes with the rotation of the cam 41 so that its major axis rotates around the rotation axis Ax1.

As a result, a wave motion is generated in the external teeth 31 formed on the outer peripheral surface of the flexible external gear 3. The generation of the wave motion of the external teeth 31 causes the meshing position between the internal teeth 21 and the external teeth 31 to move in the circumferential direction of the rigid internal gear 2, and a relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2. In other words, the external teeth 31 mesh with the internal teeth 21 at both ends in the major axis direction of the elliptical shape formed by the flexible external gear 3 (body portion 321), so that the meshing position between the internal teeth 21 and the external teeth 31 moves as the major axis of this elliptical shape rotates around the rotation axis Ax1. In this way, the wave gear device 1 according to this embodiment deforms the flexible external gear 3 in accordance with the rotation of the wave generator 4 around the rotation axis Ax1, meshing a part of the external teeth 31 with a part of the internal teeth 21, and rotating the flexible external gear 3 according to the difference in the number of teeth with the rigid internal gear 2.

As described above, in the wave gear device 1, the difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 determines the reduction ratio of the output rotation to the input rotation in the wave gear device 1. In other words, if the number of teeth of the rigid internal gear 2 is "V1" and the number of teeth of the flexible external gear 3 is "V2," the reduction ratio R1 is expressed by the following formula 1.

R1=V2/(V1-V2)...(Formula 1)
In other words, the smaller the difference (V1-V2) in the number of teeth between the rigid internal gear 2 and the flexible external gear 3, the larger the reduction ratio R1. The number of teeth V2 of the flexible external gear 3 is "202", the difference in the number of teeth (V1-V2) is "2", so from the above formula 1, the reduction ratio R1 is "100". In this case, when the cam 41 rotates one revolution (360 degrees) clockwise around the rotation axis Ax1 as viewed from the input side of the rotation axis Ax1, the flexible external gear 3 rotates one revolution (360 degrees) around the rotation axis Ax1. It rotates counterclockwise by the number difference of "2" (i.e. 3.6 degrees).

With the wave gear device 1 according to this embodiment, such a high reduction ratio R1 can be achieved with a combination of one gear stage (rigid internal gear 2 and flexible external gear 3).

The wave gear device 1 only needs to include at least the rigid internal gear 2, the flexible external gear 3, the wave generator 4, and the cover member 5, and may further include components such as the spline bush 113 described in the "(3.2) Actuator" section.

(3.2) Actuator Next, the configuration of the actuator 100 according to this embodiment will be described in more detail.

As shown in FIG. 4, the actuator 100 according to this embodiment includes the wave gear device 1 according to this embodiment, a drive source 101, and an output unit 102. That is, the actuator 100 includes the drive source 101 and the output unit 102 in addition to the rigid internal gear 2, flexible external gear 3, wave generator 4, and cover member 5 that constitute the wave gear device 1. The actuator 100 also includes an input unit 103, an input side case 111, an output side case 112, a spline bush 113, a spacer 114, a first fastener 115, a second fastener 116, and an attachment plate 117 in addition to the wave gear device 1, the drive source 101, and the output unit 102. In this embodiment, the actuator 100 also includes input side bearings 118 and 119, an input side oil seal 120, output side bearings 121 and 122, and an output side oil seal 123.

In this embodiment, the materials of the components of the actuator 100 other than the driving source 101, the input side oil seal 120, and the output side oil seal 123 are metals such as stainless steel, cast iron, carbon steel for mechanical construction, chromium molybdenum steel, phosphor bronze, or aluminum bronze.

The driving source 101 is a power generating source such as a motor (electric motor). The power generated by the driving source 101 is transmitted to the cam 41 of the wave generator 4 in the wave gear device 1. Specifically, the driving source 101 is connected to a shaft serving as the input unit 103, and the power generated by the driving source 101 is transmitted to the cam 41 via the input unit 103. This enables the driving source 101 to rotate the cam 41.

The output unit 102 is a cylindrical shaft arranged along the rotation axis Ax2 on the output side. The central axis of the shaft serving as the output unit 102 coincides with the rotation axis Ax2. The output unit 102 is held in the output side case 112 so that it can rotate around the rotation axis Ax2. The output unit 102 is fixed to the bottom 322 of the main body 32 of the flexible external gear 3, and rotates together with the flexible external gear 3 around the rotation axis Ax2. In other words, the output unit 102 extracts the rotational force of the flexible external gear 3 as an output.

The input unit 103 is a cylindrical shaft arranged along the input side rotation axis Ax1. The central axis of the shaft as the input unit 103 coincides with the rotation axis Ax1. The input unit 103 is held by the input side case 111 so that it can rotate around the rotation axis Ax1. The input unit 103 is attached to the cam 41 of the wave generator 4 and rotates together with the cam 41 around the rotation axis Ax1. In other words, the input unit 103 transmits the power (rotational force) generated by the drive source 101 as an input to the cam 41. In this embodiment, as described above, the input side rotation axis Ax1 and the output side rotation axis Ax2 are on the same straight line, so the input unit 103 and the output unit 102 are located on the same axis.

The input side case 111 holds the input part 103 via input side bearings 118, 119 so that the input part 103 can rotate. The pair of input side bearings 118, 119 are arranged side by side with a gap between them along the rotation axis Ax1. In this embodiment, the shaft serving as the input part 103 penetrates the input side case 111, and the tip of the input part 103 protrudes from the input side end face of the rotation axis Ax1 of the input side case 111 (the right end face in FIG. 4). The gap between the input part 103 and the input side end face of the rotation axis Ax1 of the input side case 111 is sealed by an input side oil seal 120.

The output side case 112 holds the output part 102 via output side bearings 121, 122 so that the output part 102 can rotate. The pair of output side bearings 121, 122 are arranged side by side with a gap between them along the rotation axis Ax2. In this embodiment, the shaft serving as the output part 102 penetrates the output side case 112, and the tip of the output part 102 protrudes from the end face (left end face in FIG. 4) of the output side of the rotation axis Ax1 in the output side case 112. The gap between the output part 102 and the end face of the output side of the rotation axis Ax1 of the output side case 112 is sealed by an output side oil seal 123.

Here, as shown in FIG. 4, the input side case 111 and the output side case 112 are connected to each other in a state in which the rigid internal gear 2 of the wave gear device 1 is sandwiched from both sides in a direction parallel to the rotation axis Ax1. Specifically, the input side case 111 contacts the rigid internal gear 2 from the input side of the rotation axis Ax1, and the output side case 112 contacts the rigid internal gear 2 from the output side of the rotation axis Ax1. In this way, the input side case 111 is fastened and fixed to the output side case 112 by screws (bolts) through the multiple fixing holes 22 with the rigid internal gear 2 sandwiched between the input side case 111 and the output side case 112. As a result, the input side case 111, the output side case 112, and the rigid internal gear 2 are connected to each other and integrated. In other words, the rigid internal gear 2, together with the input side case 111 and the output side case 112, constitute the outer shell of the actuator 100.

The spline bush 113 is a cylindrical part for connecting the shaft serving as the input part 103 to the cam 41. The spline bush 113 is inserted into the cam hole 43 formed in the cam 41, and the shaft serving as the input part 103 is inserted into the spline bush 113 so as to pass through the spline bush 113. Here, the movement of the spline bush 113 relative to both the cam 41 and the input part 103 is restricted in the rotation direction centered on the rotation axis Ax1, and in the direction parallel to the rotation axis Ax1, it is movable at least relative to the input part 103. This realizes a spline connection structure as a connection structure between the input part 103 and the cam 41. Therefore, the cam 41 is movable along the rotation axis Ax1 relative to the input part 103, and rotates together with the input part 103 around the rotation axis Ax1.

In this embodiment, the spline bushing 113 connects the shaft as the input portion 103 not only to the cam 41 but also to the cover member 5. Therefore, the spline bushing 113 is inserted not only into the cam hole 43 but also into the cover hole 53 formed in the cover member 5. Here, the movement of the spline bushing 113 relative to both the cover member 5 and the input portion 103 in the rotation direction centered on the rotation axis Ax1 is restricted, and in the direction parallel to the rotation axis Ax1, it is movable at least relative to the input portion 103. This realizes a spline connection structure as a connection structure between the input portion 103 and the cover member 5. Therefore, the cover member 5 is movable along the rotation axis Ax1 relative to the input portion 103 and rotates together with the input portion 103 around the rotation axis Ax1.

The spacer 114 is a part that fills the gap between the spline bushing 113 and the cam 41. The first fastener 115 is a part that prevents the spline bushing 113 from coming off the cam 41 and the cover member 5. The first fastener 115 is, for example, an E-ring, and is attached to the spline bushing 113 so as to contact the cover member 5 from the input side of the rotation axis Ax1. The second fastener 116 is a part that prevents the input part 103 from coming off the spline bushing 113. The second fastener 116 is, for example, an E-ring, and is attached to the input part 103 so as to contact the spline bushing 113 from the output side of the rotation axis Ax1.

The mounting plate 117 is a part for attaching the shaft serving as the output part 102 to the bottom part 322 of the flexible external gear 3. Specifically, the mounting plate 117 is fastened to the flange part of the output part 102 with screws (bolts) passing through the multiple mounting holes 33, with the area around the through hole 34 in the bottom part 322 sandwiched between the mounting plate 117 and the flange part of the output part 102. In this way, the shaft serving as the output part 102 is fixed to the bottom part 322 of the flexible external gear 3.

(3.3) Cover Member Next, the configuration of the cover member 5 (cover body 10) of the strain wave gear device 1 according to this embodiment will be described in more detail with reference to FIGS. 1A to 3B.

The cover member 5 is a plate-shaped part that covers the bearing 42 from one side (input side) of the rotation axis Ax1. The cover member 5 is a non-circular (elliptical) part. The cover member 5 is made of a metal plate with at least the outer circumferential surface that is elliptical in plan view. The cover member 5 has a predetermined thickness in the direction of the rotation axis Ax1. However, the thickness of the cover member 5 is smaller (thinner) than the thickness of the rigid internal gear 2. As a result, the cover member 5 has a higher rigidity than the flexible external gear 3 and a lower rigidity than the rigid internal gear 2.

The cover member 5 has a base portion 51 and an umbrella portion 52. The base portion 51 is a metal plate that is elliptical when viewed from one side (input side) of the rotation axis Ax1. The umbrella portion 52 is an annular portion that is the outer periphery of the cover member 5 when viewed from one side (input side) of the rotation axis Ax1. In other words, the base portion 51 is located inside the umbrella portion 52. In this embodiment, the umbrella portion 52 is also formed with at least an elliptical outer periphery when viewed from one side (input side) of the rotation axis Ax1. In this embodiment, the outer periphery of the umbrella portion 52 and the outer periphery of the base portion 51 are both similar to the outer periphery of the cam 41. In addition, the base portion 51 and the umbrella portion 52 are integrally formed from a single metal member, thereby realizing a seamless cover member 5.

The cover member 5 is disposed so as to face at least the bearing 42 from the input side of the rotation axis Ax1, thereby covering the bearing 42 from the input side of the rotation axis Ax1. In other words, the cover member 5 is combined with the wave generator 4 so as to overlap from the input side of the rotation axis Ax1. In this embodiment, the cover member 5 is combined with the wave generator 4 so that most of the cover member 5 fits between both sides of the rigid internal gear 2 in the thickness direction in a direction parallel to the rotation axis Ax1. As shown in FIG. 1A, only a part of the thickness direction of the cover member 5 protrudes from the rigid internal gear 2 to the input side of the rotation axis Ax1. As a result, the cover member 5 prevents the foreign object X1 from entering from one side (input side) of the rotation axis Ax1 to the inside of the outer ring 421. However, the cover member 5 is disposed so as to face the bearing 42, with a certain or more gap G1 secured between the cover member 5 and the outer ring 421 of the bearing 42. Therefore, the cover member 5 does not come into contact with the outer ring 421.

In this embodiment, the cover member 5 has a shape and size that covers at least the entire wave generator 4 when viewed from one side of the rotation axis Ax1. Furthermore, the cover member 5 has an outer peripheral shape that is the same as that of the flexible external gear 3. Therefore, as shown in FIG. 2B, when viewed from the input side of the rotation axis Ax1, the cover member 5 covers not only the bearing 42, but also the entire wave generator 4 including the cam 41, and also the flexible external gear 3.

In this way, the cover member 5 has a non-circular portion corresponding to the cam 41 at a portion facing the bearing 42 when viewed from one side of the rotation axis Ax1. In this embodiment, the entire cover member 5 consisting of the base portion 51 and the umbrella portion 52 has a non-circular shape (here, an elliptical shape) similar to the cam 41 when viewed from one side of the rotation axis Ax1. Therefore, while the cover member 5 covers the entire wave generator 4 when viewed from the input side of the rotation axis Ax1, it hardly protrudes from the wave generator 4. Furthermore, the wave generator 4 does not protrude from the cover member 5. In other words, the cover member 5 and the wave generator 4 (cam 41 and bearing 42) have elliptical shapes that are similar to each other and have major axes in the same direction when viewed from one side of the rotation axis Ax1, as shown in FIG. 2B.

In addition, in this embodiment, as described above, the cover member 5 is connected to the shaft serving as the input portion 103 by the spline bushing 113. Therefore, a cover hole 53 for attaching the shaft serving as the input portion 103 is formed in the center of the base portion 51. The cover hole 53 has the same shape as the cam hole 43 of the cam 41 when viewed from one side (the input side) of the rotation axis Ax1.

In this embodiment, the cover member 5 rotates at the same speed as the cam 41. That is, the cover member 5 rotates together with the cam 41 relative to the rigid internal gear 2. Therefore, when the cam 41 rotates one revolution (360 degrees) clockwise around the rotation axis Ax1 as viewed from the input side of the rotation axis Ax1, the cover member 5 also rotates one revolution (360 degrees) clockwise around the rotation axis Ax1. In this embodiment, as described above, a spline connection structure is used as the connection structure between the input part 103, the cam 41, and the cover member 5, so that the cover member 5 rotates at the same speed as the cam 41. Furthermore, by rotating the cover member 5 and the cam 41 at the same speed, the cover member 5 and the wave generator 4 (cam 41 and bearing 42) maintain an elliptical shape that is similar to each other and has a major axis in the same direction as viewed from one side of the rotation axis Ax1.

Next, the shape of the base portion 51 will be described in more detail. The base portion 51 has a recessed portion 511 on the outer periphery of the surface on the output side of the rotation axis Ax1. As shown in FIG. 3A, the recessed portion 511 forms a step on the outer periphery of the base portion 51 such that the surface on the output side of the rotation axis Ax1 is recessed. The recessed portion 511 is formed around the entire circumferential direction of the base portion 51. Here, the side and bottom surfaces of the recessed portion 511 are perpendicular to each other. Therefore, an "inner corner" that is a right angle in cross section is formed within the recessed portion 511, as shown in FIG. 1B.

The base part 51 is combined with the wave generator 4 so that the corners of the outer ring 421 of the bearing 42 are accommodated in the recess 511. That is, as shown in FIG. 1B, the recess 511 of the base part 51 accommodates the inner corners of the input side end face of the rotation axis Ax1 of the outer ring 421. In this embodiment, the gap G1 between the cover member 5 and the outer ring 421 of the bearing 42 is smallest in the recess 511. However, the cover member 5 faces the bearing 42 with the gap G1 secured between the cover member 5 and the outer ring 421 of the bearing 42, and the cover member 5 and the outer ring 421 do not come into contact with each other even in the recess 511. More specifically, a radial gap G11 (perpendicular to the rotation axis Ax1) exists between the side surface of the recess 511 and the inner peripheral surface 424 of the outer ring 421. Furthermore, a gap G12 in the thrust direction (direction parallel to the rotation axis Ax1) exists between the bottom surface of the recess 511 and the input side end face of the rotation axis Ax1 of the outer ring 421. The gap G1 between the cover member 5 and the outer ring 421 includes these gaps G11 and G12.

The gaps G11 and G12 are both set to dimensions that do not interfere with each other even when taking into account the processing and assembly errors of each part, and are set to 0.05 mm or more and 1.0 mm or less, for example. It is more preferable that the gaps G11 and G12 are both 0.1 mm or more, and more preferably 0.5 mm or less.

The recessed portion 511 is formed around the entire circumference of the base portion 51. In this embodiment, the entire cover member 5 has an elliptical shape similar to the cam 41 when viewed from one side of the rotation axis Ax1. Therefore, the above-mentioned gap G1 is ensured around the entire circumference of the outer ring 421. In other words, the gap G1 is ensured approximately uniformly around the circumference of the outer ring 421.

The base portion 51 also has a constricted portion 512 in the area inside the recessed portion 511 on the surface on the output side of the rotation axis Ax1. As shown in FIG. 3A, the constricted portion 512 is a portion in which the thickness of the base portion 51 is made smaller (thinner) than the central portion of the base portion 51 by recessing the surface on the output side of the rotation axis Ax1 except for the central portion of the base portion 51. The constricted portion 512 is formed around the entire circumferential direction of the base portion 51. The constricted portion 512 makes it possible to reduce the weight of the cover member 5 while ensuring the rigidity required for the cover member 5.

Furthermore, the base portion 51 has a recess 513 in an annular region around the cover hole 53 on the surface on the input side of the rotation axis Ax1. As shown in FIG. 3B, the recess 513 is formed by recessing the surface on the input side of the rotation axis Ax1 except for the center of the base portion 51, making the thickness of the base portion 51 smaller (thinner) than that of the center of the base portion 51. The recess 513 is formed around the entire circumferential circumference of the base portion 51. The recess 513 allows the cover member 5 to be made lighter while still ensuring the rigidity required for the cover member 5.

Next, the shape of the umbrella portion 52 will be described in more detail. As shown in FIG. 1B, the umbrella portion 52 is formed so that the distance from the rotation axis Ax1 gradually increases from the bearing 42 side toward one side (input side) of the rotation axis Ax1. In other words, the umbrella portion 52 has an outer peripheral surface 521 that is inclined with respect to the rotation axis Ax1 so that the distance (radius) from the rotation axis Ax1 gradually increases the farther away from the bearing 42. Therefore, the umbrella portion 52 has a triangular shape in cross section as shown in FIG. 1B. Such an umbrella portion 52 is formed around the entire circumference of the cover member 5 in the circumferential direction.

The cover member 5 is configured to ensure a predetermined gap even in the umbrella portion 52 with respect to the outer ring 421 of the bearing 42, and further with respect to the flexible external gear 3 and the rigid internal gear 2. Of the outer ring 421, the flexible external gear 3, and the rigid internal gear 2, the guide portion 23 provided on the rigid internal gear 2 has the narrowest gap with the umbrella portion 52. The guide portion 23 faces the umbrella portion 52 with a certain gap or more between it and the guide portion 23. As shown in FIG. 1B, the guide portion 23 is a portion that protrudes from the end face of the internal teeth 21 of the rigid internal gear 2 on the input side of the rotation axis Ax1 toward the input side of the rotation axis Ax1.

The guide portion 23 has an inclined surface 231 inclined with respect to the rotation axis Ax1 so that the distance (radius) from the rotation axis Ax1 gradually increases toward one side (input side) of the rotation axis Ax1. The inclined surface 231 of the guide portion 23 is parallel to the outer peripheral surface 521 of the umbrella portion 52. As a result, the umbrella portion 52 can secure a certain amount of gap between the rigid internal gear 2 and the guide portion 23 while narrowing the gap between the rigid internal gear 2 and the guide portion 23. The gap (spacing) between the umbrella portion 52 and the guide portion 23 is set to a dimension that does not interfere with each other even when considering the processing error and assembly error of each part, and is set to 0.05 mm or more and 1.0 mm or less, as an example. The gap (spacing) between the umbrella portion 52 and the guide portion 23 is more preferably 0.1 mm or more, and more preferably 0.5 mm or less. In this embodiment, the guide portion 23 and the rigid internal gear 2 are integrally formed from one metal member.

In this embodiment, the cover member 5 is configured to not allow liquid to pass through. In other words, the liquid is blocked by the cover member 5 and does not pass through the cover member 5. In this disclosure, the "liquid" includes liquid or gel-like substances. The "gel-like" here means a state having intermediate properties between liquid and solid, and includes a colloidal state consisting of two phases, a liquid phase and a solid phase. For example, the "gel-like" includes a state called a gel or sol, such as an emulsion in which the dispersion medium is in a liquid phase and the dispersoid is in a liquid phase, and a suspension in which the dispersoid is in a solid phase. The "gel-like" also includes a state in which the dispersion medium is in a solid phase and the dispersoid is in a liquid phase. In other words, the liquid blocked by the cover member 5 is an object that has a constant volume if the temperature and pressure are constant and has the properties of a fluid that does not have a fixed shape. In other words, the liquid blocked by the cover member 5 is a fluid (fluid) other than a gas. "Fluid" here includes both Newtonian and non-Newtonian fluids.

In the wave gear device 1, for example, liquid or gel-like lubricant 54 (see FIG. 5A) is injected into the meshing portions between the internal teeth 21 and the external teeth 31, and between the outer ring 421 and the inner ring 422 of the bearing 42, etc. Since the lubricant 54 is a liquid, the cover member 5 at least blocks the lubricant 54. This makes it difficult for the lubricant 54 to seep into the cover member 5.

In addition, in this embodiment, the cover member 5 has oil repellency. The cover member 5 may have oil repellency in its entirety, but at least a part of it may have oil repellency. In this embodiment, the cover member 5 is partially coated with an oil repellent coating, for example, a fluorine compound, and the oil repellent coated part of the cover member 5 has oil repellency. Specifically, the outer peripheral surface 521 of the umbrella portion 52 of the cover member 5 has oil repellency. As an example, when a lubricant (oil) as the lubricant 54 is applied to the oil repellent part of the cover member 5, the static contact angle of the cover member 5 with the droplet of the lubricant 54, that is, the contact angle of the cover member 5 with the oil, is preferably 25 degrees or more. The "oil contact angle" here means the contact angle with oil, that is, the angle formed by the oil droplet and the solid surface when the oil droplet made of the lubricant 54 (lubricant) adheres to the solid surface (the surface of the part of the cover member 5 with oil repellency).

(4) Operation Next, the operation of the strain wave gear device 1 according to this embodiment will be described with reference to FIGS. 5A and 5B.

Figures 5A and 5B are enlarged views of the periphery of the umbrella portion 52 of the cover member 5 in Figure 1B. In order to explain the function of the cover member 5, Figures 5A and 5B illustrate a foreign object X1 that is prevented from entering the inside of the outer ring 421 by the cover member 5, but this is not intended to include the foreign object X1 as a component of the wave gear device 1. Also, Figures 5A and 5B illustrate a lubricant 54 held between the outer ring 421 and the cover member 5, but this is not intended to stipulate the shape and amount of the lubricant 54 in the manner illustrated.

As described above, the cover member 5 is disposed so as to face at least the bearing 42 from the input side of the rotating shaft Ax1, thereby covering the bearing 42 from the input side of the rotating shaft Ax1. As a result, the cover member 5 prevents the intrusion of foreign matter X1 from one side (the input side) of the rotating shaft Ax1 into the inside of the outer ring 421. Therefore, even if foreign matter X1 such as metal powder or nitrides is generated due to wear or the like occurring between the internal teeth 21 and the external teeth 31, the foreign matter X1 is unlikely to intrude into the inside of the outer ring 421 (between the outer ring 421 and the inner ring 422).

In particular, in the wave gear device 1, power transmission by meshing between the internal teeth 21 and the external teeth 31 involves slippage in both the tooth profile direction and the tooth trace direction, so that foreign matter X1 is likely to be generated due to wear. Furthermore, although a lubricant 54 is used, the flow speed of the lubricant 54 in the rotational speed range used in the wave gear device 1 is relatively low, and it is difficult to expect the effect of washing away the generated foreign matter X1 with the lubricant 54. If such foreign matter X1 enters the bearing 42, damage will occur to the surface of any of the outer ring 421, inner ring 422, and rolling element 423 of the bearing 42, which may affect the reliability of the wave gear device 1. In other words, if the foreign matter X1 enters between the outer ring 421 and inner ring 422 of the bearing 42, the foreign matter X1 will be caught by the rolling element 423, and damage may occur to the surface of any of the outer ring 421, inner ring 422, and rolling element 423. In the wave gear device 1 according to this embodiment, the cover member 5 prevents foreign matter X1 from entering the bearing 42, making it less likely that reliability will decrease.

As an example, if flaking occurs on the inner circumferential surface (rolling surface) of the outer ring 421 due to the ingress of foreign matter X1, this may impair the function of the bearing 42 and interfere with the operation of the harmonic gear device 1. In the harmonic gear device 1 according to this embodiment, the cover member 5 can drastically reduce the ingress of foreign matter X1 into the bearing 42, which leads to improved reliability of the harmonic gear device 1. In particular, reliability is less likely to decrease even during long-term use, which ultimately leads to a longer life and higher performance of the harmonic gear device 1.

Moreover, the cover member 5 secures a certain gap G1 between the cover member 5 and the outer ring 421 of the bearing 42, and does not come into contact with the outer ring 421. Therefore, even if a relative movement occurs between the cover member 5 and the outer ring 421 of the bearing 42 when the harmonic gear device 1 is driven, frictional resistance between the cover member 5 and the outer ring 421 and wear of the cover member 5 or the outer ring 421 are unlikely to occur. In other words, in this embodiment, the cover member 5 rotates with the cam 41, and the outer ring 421 rotates with the flexible external gear 3, so that a relative rotation occurs between the cover member 5 and the outer ring 421 according to the difference in the number of rotations (reduction ratio) between the cam 41 and the flexible external gear 3. At this time, since the gap G1 is secured between the cover member 5 and the outer ring 421, frictional resistance and wear of the cover member 5 or the outer ring 421 are unlikely to occur, and the provision of the cover member 5 is unlikely to cause a malfunction in the operation of the harmonic gear device 1.

The relative rotational speed between the cover member 5 and the outer ring 421 depends on the difference in rotational speed between the cam 41 and the flexible external gear 3 (reduction ratio), but if the reduction ratio is relatively high, the relative rotational speed between the cover member 5 and the outer ring 421 will also be large. As a result, if frictional resistance occurs between the cover member 5 and the outer ring 421, the power transmission efficiency of the wave gear device 1 will decrease significantly, and starting performance may also be affected in harsh environments such as cold regions. In the wave gear device 1 of this embodiment, the gap G1 between the cover member 5 and the outer ring 421 makes it less likely for such frictional resistance to cause problems, and the reliability of the wave gear device 1 is greatly improved.

In the strain wave gear device 1 according to this embodiment, as described above, for example, the meshing portion between the internal teeth 21 and the external teeth 31, and between the outer ring 421 and the inner ring 422 of the bearing 42, etc., are filled with a liquid or gel-like lubricant 54. As an example, the lubricant 54 is a liquid lubricant (oil). When the strain wave gear device 1 is in use, the lubricant 54 also enters between the outer ring 421 of the bearing 42 and the cover member 5, as shown in Figures 5A and 5B. Specifically, the lubricant 54 enters at least a part of the gap G1 (see Figure 1B) between the outer ring 421 and the cover member 5, and seals at least a part of the gap G1. In short, in this embodiment, at least a part of the gap G1 between the outer ring 421 and the cover member 5 is filled with the lubricant 54.

5A and 5B, the lubricant 54 is filled in the entire gap G1 so as to fill both the radial gap G11 between the outer ring 421 and the cover member 5 and the thrust gap G12. Furthermore, in this embodiment, the lubricant 54 is filled in the entire gap G1 formed around the entire circumference of the outer ring 421. The space on the input side (right side of FIG. 5A) of the rotating shaft Ax1 and the space on the output side (left side of FIG. 5A) of the rotating shaft Ax1 can be connected through the gap G1 with respect to the cover member 5. In this way, the gap G1 forming a bottleneck connecting the inside and outside of the cover member 5 is filled with the lubricant 54. Therefore, the space on the input side of the rotating shaft Ax1 and the space on the output side of the rotating shaft Ax1 are shielded by the lubricant 54. Therefore, the intrusion of the foreign matter X1 from one side (input side) of the rotating shaft Ax1 to the inside of the outer ring 421 is more reliably prevented.

Here, the lubricant 54 is held in the gap G1 between the outer ring 421 and the cover member 5 by capillary action. In other words, the gap G1 between the outer ring 421 and the cover member 5 is relatively narrow, and when the gap G1 is filled with the lubricant 54, the lubricant 54 is held in the gap G1 by capillary action. Therefore, the gap G1 is maintained in a state filled with the lubricant 54. The magnitude of the holding force due to the capillary action also changes depending on the "wettability" between the outer ring 421 and the cover member 5 and the lubricant 54. Therefore, it is preferable that at least the portion of the cover member 5 facing the gap G1, that is, the side surface of the recessed portion 511 and the bottom surface of the recessed portion 511, does not have oil repellency.

In addition, in the wave gear device 1 according to this embodiment, the cover member 5 has an umbrella portion 52, so that the umbrella portion 52 is expected to have the effect of shaking off the foreign matter X1 outward by centrifugal force. In other words, the umbrella portion 52 is formed so that the distance from the rotation axis Ax1 gradually increases from the bearing 42 side toward the input side of the rotation axis Ax1. Therefore, even if foreign matter X1 such as metal powder or nitride is generated due to wear or the like that occurs between the internal teeth 21 and the external teeth 31 and this foreign matter X1 adheres to the outer peripheral surface 521 of the umbrella portion 52, it is possible to shake off the foreign matter X1 outward (to the input side of the rotation axis Ax1).

In other words, as the cover member 5 rotates, centrifugal force acts on the foreign object X1 attached to the outer peripheral surface 521 of the umbrella portion 52 in a direction away from the rotation axis Ax1. As a result, the foreign object X1 attached to the outer peripheral surface 521 of the umbrella portion 52 moves along the outer peripheral surface 521 in a direction away from the rotation axis Ax1, that is, toward the input side of the rotation axis Ax1, as shown in FIG. 5A. As a result, the foreign object X1 moves in a direction away from the bearing 42, and is finally discharged to the input side of the rotation axis Ax1 from the cover member 5, as shown in FIG. 5B. At this time, the foreign object X1 is discharged through between the outer peripheral surface 521 of the umbrella portion 52 and the inclined surface 231 of the guide portion 23. In other words, the gap between the umbrella portion 52 and the guide portion 23 forms a discharge path for the foreign object X1. According to such a function of the umbrella portion 52, the generated foreign object X1 can be shaken off to the outside of the cover member 5, so that the foreign object X1 is less likely to accumulate inside the cover member 5.

Furthermore, as described above, the cover member 5 has oil-repellent properties on the outer peripheral surface 521 of the umbrella portion 52. Therefore, foreign matter X1 that is oily due to the lubricant 54 or the like is less likely to remain on the umbrella portion 52 and is more likely to be shaken off to the outside of the cover member 5.

(5) Application Examples Next, application examples of the strain wave gear device 1 and the actuator 100 according to this embodiment will be described with reference to FIG.

Figure 6 is a cross-sectional view showing an example of a robot 9 using the strain wave gear device 1 according to this embodiment. This robot 9 is a horizontal articulated robot, a so-called SCARA (Selective Compliance Assembly Robot Arm) type robot.

As shown in FIG. 6, the robot 9 is equipped with two wave gear devices 1 and a link 91. The two wave gear devices 1 are provided at two joints in the robot 9, respectively. The link 91 connects the two joints. In the example of FIG. 6, the wave gear device 1 is a top hat type wave gear device, not a cup type. In other words, the wave gear device 1 illustrated in FIG. 6 uses a flexible external gear 3 formed in a top hat shape. Also, the cover member 5 is not illustrated in FIG. 6.

(6) Modifications The first embodiment is merely one of various embodiments of the present disclosure. Various modifications of the first embodiment are possible depending on the design, etc., as long as the object of the present disclosure can be achieved. In addition, all drawings referred to in this disclosure are schematic drawings, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. Modifications of the first embodiment are listed below. The modifications described below can be applied in appropriate combination.

The wave gear device 1 is not limited to the cup type described in the first embodiment, but may be, for example, a top hat type, a ring type, a differential type, a flat type (pancake type), or a shield type.

The cover member 5 only needs to be arranged so as to face the bearing 42 from one side of the rotating shaft Ax1, and is not required to be arranged on the input side of the rotating shaft Ax1 with respect to the bearing 42 as in the first embodiment. In other words, the cover member 5 may be arranged so as to face the bearing 42 from the output side of the rotating shaft Ax1. In this case, the cover member 5 prevents the intrusion of the foreign object X1 from the output side of the rotating shaft Ax1 into the inside of the outer ring 421.

Furthermore, the cover member 5 may be arranged so as to face the bearing 42 from one side of the rotating shaft Ax1, and a pair of cover members 5 may be arranged on the input side and output side of the rotating shaft Ax1 with respect to the bearing 42, respectively. In this case, the cover members 5 prevent the intrusion of the foreign object X1 from the input side and output side of the rotating shaft Ax1 into the inside of the outer ring 421.

The configuration of the actuator 100 is not limited to the configuration described in the first embodiment, and can be modified as appropriate. For example, the connection structure between the input section 103 and the cam 41 and cover member 5 is not limited to a spline connection structure, and an Oldham coupling or the like may be used. By using an Oldham coupling as the connection structure between the input section 103 and the cam 41 and cover member 5, it is possible to offset the misalignment between the input side rotation axis Ax1 and the wave generator 4 (cam 41), and further to offset the misalignment between the rigid internal gear 2 and the flexible external gear 3. Furthermore, the cam 41 and cover member 5 do not need to be movable along the rotation axis Ax1 relative to the input section 103.

In addition, application examples of the harmonic gear device 1 and actuator 100 according to this embodiment are not limited to the horizontal multi-joint robot described above, but may be, for example, industrial robots other than horizontal multi-joint robots, or non-industrial robots. Examples of industrial robots other than horizontal multi-joint robots include vertical multi-joint robots and parallel link robots. Examples of non-industrial robots include domestic robots, nursing robots, and medical robots.

The bearing 42 is not limited to a deep groove ball bearing, but may be, for example, an angular contact ball bearing. Furthermore, the bearing 42 is not limited to a ball bearing, but may be, for example, a roller bearing, such as a cylindrical roller bearing, a needle roller bearing, or a tapered roller bearing, in which the rolling elements 423 are not ball-shaped "rollers."

In addition, the material of each component of the strain wave gear device 1 or the actuator 100 is not limited to metal, but may be, for example, a resin such as engineering plastic.

Furthermore, it is not essential for the wave gear device 1 that the cover member 5 rotate at the same speed as the cam 41; for example, the cover member 5 does not have to rotate relative to the rigid internal gear 2.

Furthermore, it is sufficient that the guide portion 23 is provided on the rigid internal gear 2, and it is not essential for the wave gear device 1 that the guide portion 23 is formed integrally with the rigid internal gear 2 from a single metal member. For example, the guide portion 23, which is a separate part from the rigid internal gear 2, may be provided on the rigid internal gear 2 by being fixed to the rigid internal gear 2 by bonding or the like. Furthermore, a plate material may be fixed to the inner peripheral surface of the input side case 111 to which the rigid internal gear 2 is fixed, and this plate material may function as the guide portion 23.

The lubricant 54 is not limited to a liquid substance such as lubricating oil (oil), but may be a gel-like substance such as grease.

(Embodiment 2)
7A and 7B, the wave gear device 1A according to this embodiment differs from the wave gear device 1 according to embodiment 1 in the configuration of a cover member 5A. Hereinafter, configurations similar to those in embodiment 1 will be denoted by the same reference numerals and descriptions thereof will be omitted as appropriate.

Figure 7A is a cross-sectional view showing the schematic configuration of strain wave gear device 1A, and Figure 7B is an enlarged view of a main portion of Figure 7A (the range corresponding to area Z1 in Figure 1A).

In this embodiment, the wave gear device 1A has a pair of cover members 5A. Of the pair of cover members 5A, one cover member 5A faces the bearing 42 from the input side of the rotation shaft Ax1, and the other cover member 5A faces the bearing 42 from the output side of the rotation shaft Ax1. In other words, the wave gear device 1A has a pair of cover members 5A that are respectively arranged on the input side and output side of the rotation shaft Ax1 with respect to the bearing 42.

With this configuration, the bearing 42 is sandwiched between the pair of cover members 5A in a direction parallel to the rotation axis Ax1. Therefore, the pair of cover members 5A prevent the intrusion of foreign matter X1 into the inside of the outer ring 421 from both sides of the rotation axis Ax1.

The shape of each cover member 5A also differs from the cover member 5 in embodiment 1. In this embodiment, the pair of cover members 5A have symmetrical shapes in a direction parallel to the rotation axis Ax1, so the following describes the shape of one of the pair of cover members 5A.

That is, in this embodiment, the cover member 5A has a base portion 51 and a protruding portion 55, as shown in FIG. 7B. The base portion 51 is a metal plate that is elliptical when viewed from one side (input side) of the rotation axis Ax1. The protruding portion 55 also has at least an elliptical outer periphery when viewed from one side (input side) of the rotation axis Ax1. In this embodiment, the outer periphery of the protruding portion 55 and the outer periphery of the base portion 51 are both similar to the outer periphery of the cam 41. In addition, the base portion 51 and the protruding portion 55 are integrally formed from a single metal member, thereby realizing a seamless cover member 5A.

The base portion 51 is disposed inside the flexible external gear 3. A first gap G21 is formed between the outer peripheral surface 514 of the base portion 51 and the inner peripheral surface 301 of the flexible external gear 3, which face each other in a direction perpendicular to the rotation axis Ax1. That is, the base portion 51 has an elliptical shape whose outer peripheral shape is slightly smaller than the inner peripheral surface 301 of the flexible external gear 3, as viewed from one side (input side) of the rotation axis Ax1. Therefore, the outer peripheral surface 514 of the base portion 51 disposed inside the flexible external gear 3 faces the flexible external gear 3 with the first gap G21 secured between it and the inner peripheral surface 301 of the flexible external gear 3, and does not come into contact with the flexible external gear 3. More specifically, a first gap G21 exists in the radial direction (direction perpendicular to the rotation axis Ax1) between the outer peripheral surface 514 of the base portion 51 and the inner peripheral surface 301 of the flexible external gear 3.

The convex portion 55 protrudes from the base portion 51 and is inserted inside the outer ring 421. A second gap G22 is formed between the outer peripheral surface 551 of the convex portion 55 and the inner peripheral surface 424 of the outer ring 421, which face each other in a direction perpendicular to the rotation axis Ax1. That is, the convex portion 55 has an elliptical shape whose outer peripheral shape is slightly smaller than the inner peripheral surface 424 of the outer ring 421 when viewed from one side (input side) of the rotation axis Ax1. Therefore, the outer peripheral surface 551 of the convex portion 55 arranged inside the outer ring 421 faces the outer ring 421 while securing the second gap G22 between it and the inner peripheral surface 424 of the outer ring 421, and does not come into contact with the outer ring 421. More specifically, a second gap G22 in the radial direction (direction perpendicular to the rotation axis Ax1) exists between the outer peripheral surface 551 of the convex portion 55 and the inner peripheral surface 424 of the outer ring 421.

In addition, a third gap G23 is formed between the base portion 51 and the outer ring 421, which face each other in the direction of the rotation axis Ax1. The first gap G21 and the second gap G22 are connected through the third gap G23. That is, the base portion 51 faces the outer ring 421 while securing the third gap G23 between the end face of the outer ring 421 in the direction of the rotation axis Ax1, and does not contact the outer ring 421. More specifically, a third gap G23 in the thrust direction (direction parallel to the rotation axis Ax1) exists between the base portion 51 and the outer ring 421. And, as shown in FIG. 7B, the first gap G21 and the second gap G22 in the radial direction are connected by the third gap G23. The gap G2 between the cover member 5A and the outer ring 421 and the flexible external gear 3 includes the first gap G21, the second gap G22, and the third gap G23.

The first gap G21, the second gap G22, and the third gap G23 are all set to dimensions that do not interfere with each other even when taking into account the processing errors and assembly errors of each part, and are set to 0.05 mm or more and 1.0 mm or less, as an example. It is more preferable that the first gap G21, the second gap G22, and the third gap G23 are all 0.1 mm or more, and more preferably 0.5 mm or less.

That is, a crank-shaped gap G2 is formed in cross section between the cover member 5A and the outer ring 421 and the flexible external gear 3 by the first gap G21, the second gap G22, and the third gap G23. The space on the input side (right side of FIG. 7A) of the rotating shaft Ax1 and the space on the output side (left side of FIG. 7A) of the rotating shaft Ax1 can be connected through the gap G2 with respect to the cover member 5A. In this way, the gap G2 forming a narrow passage connecting the inside and outside of the cover member 5A adopts a complex labyrinth structure as described above, thereby improving the sealing performance of the cover member 5A. This more reliably prevents the intrusion of the foreign object X1 from one side (input side or output side) of the rotating shaft Ax1 to the inside of the outer ring 421. Moreover, the third gap G23 in the thrust direction is particularly maintained at a constant minimum gap without elastic deformation of the outer ring 421 and the flexible external gear 3, making it easy to prevent the foreign object X1 from passing through the gap G2. The first gap G21 and the second gap G22 in the radial direction can also be maintained at a constant minimum gap without elastic deformation of the outer ring 421 and the flexible external gear 3, making it possible to prevent the foreign object X1 from passing through the gap G2.

Furthermore, in this embodiment, the cover member 5A has a constricted portion 515 (see FIG. 10A) in the area surrounding the cover hole 53. As shown in FIG. 7A, the constricted portion 515 is a portion in which the thickness of the cover member 5A is made smaller (thinner) than the center portion of the cover member 5A by recessing both sides in the thickness direction (direction parallel to the rotation axis Ax1). The constricted portion 515 is formed around the entire circumference of the cover member 5A in the circumferential direction. The constricted portion 515 makes it possible to reduce the weight of the cover member 5A while ensuring the rigidity required for the cover member 5A.

In this embodiment, it is also preferable that the gap G2 is filled with lubricant 54.

Figure 8A is a cross-sectional view showing the schematic configuration of a wave gear device 1B according to a first modified example of embodiment 2, and Figure 8B is an enlarged view of a main part of Figure 8A (the range corresponding to region Z1 in Figure 1A). In the wave gear device 1B according to the first modified example of embodiment 2, the cover member 5 described in embodiment 1 is used instead of one of the pair of cover members 5A described in embodiment 2 that faces the bearing 42 from the input side of the rotation axis Ax1. In this configuration, the umbrella portion 52 of the one cover member 5 that faces the bearing 42 from the input side of the rotation axis Ax1 can shake off the generated foreign matter X1 to the outside of the cover member 5, making it difficult for the foreign matter X1 to accumulate inside the cover member 5.

Figure 9A is a cross-sectional view showing the schematic configuration of a strain wave gear device 1C according to a second modified example of embodiment 2, and Figure 9B is an enlarged view of a main portion of Figure 9A (the range corresponding to region Z1 in Figure 1A). In the strain wave gear device 1C according to the second modified example of embodiment 2, of the pair of cover members 5A described in embodiment 2, one cover member 5A that faces the bearing 42 from the input side of the rotation axis Ax1 is replaced with a cover member 5C having a different shape. In addition to the base portion 51 and protrusion portion 55 similar to those of cover member 5A, cover member 5C further has an umbrella portion 52.

As shown in FIG. 9B, the umbrella portion 52 of the cover member 5C protrudes from the surface of the base portion 51 on the opposite side of the bearing 42 in the thickness direction. The umbrella portion 52 is formed so that the distance from the rotation axis Ax1 gradually increases from the bearing 42 side toward one side (input side) of the rotation axis Ax1. In other words, the umbrella portion 52 has an outer peripheral surface 521 inclined with respect to the rotation axis Ax1 so that the distance (radius) from the rotation axis Ax1 gradually increases as it moves away from the bearing 42. Such an umbrella portion 52 is formed around the entire circumference of the cover member 5 in the circumferential direction. In this configuration, in one cover member 5C facing the bearing 42 from the input side of the rotation axis Ax1, the umbrella portion 52 functions to shake off the generated foreign matter X1 to the outside of the cover member 5C, so that the foreign matter X1 is less likely to accumulate inside the cover member 5C.

Figures 10A, 10B, and 10C are cross-sectional views of essential parts showing the schematic configurations of strain wave gear devices 1D, 1E, and 1F according to the third, fourth, and fifth modified examples of embodiment 2, respectively.

In the wave gear device 1D according to the third modified example of the second embodiment, as shown in FIG. 10A, the shape of the cover member 5D is different from that of the cover member 5A described in the second embodiment. Instead of the convex portion 55, the cover member 5D has a groove portion 56 on the surface of the base portion 51 at a portion facing the outer ring 421. The groove portion 56 is formed around the entire circumference of the base portion 51 in the circumferential direction. Furthermore, the outer ring 421 has a rib 425 protruding from the end face in the direction of the rotation axis Ax1. The rib 425 is formed around the entire circumference of the outer ring 421 in the circumferential direction. The rib 425 is inserted into the groove portion 56. Here, a gap G3 is secured between the cover member 5D and the outer ring 421, including between the rib 425 and the groove portion 56. The gap G3 has a labyrinth structure similar to the gap G2 at the rib 425 and the groove portion 56, so that the sealing performance of the cover member 5D is improved.

In the wave gear device 1E according to the fourth modified example of the second embodiment, as shown in FIG. 10B, the shape of the cover member 5E is different from that of the cover member 5A described in the second embodiment. In the cover member 5E, the base portion 51 itself is disposed inside the outer ring 421. That is, when viewed from one side (input side) of the rotation axis Ax1, the base portion 51 has an elliptical shape whose outer peripheral shape is slightly smaller than the inner peripheral surface 424 of the outer ring 421. Here, the cover member 5E has a rib 57 protruding from the outer peripheral surface 514 of the base portion 51. The rib 57 is formed over the entire circumference of the base portion 51 in the circumferential direction. Furthermore, the outer ring 421 has a groove portion 426 on its inner peripheral surface. The groove portion 426 is formed over the entire circumference of the outer ring 421 in the circumferential direction. The rib 57 is inserted into the groove portion 426. Here, a gap G4 is secured between the cover member 5E and the outer ring 421, including between the rib 57 and the groove portion 426. Gap G4 has a complex labyrinth structure with rib 57 and groove 426, similar to gap G2, improving the sealing performance of cover member 5E. Furthermore, gap G4 is filled with lubricant 54.

In the wave gear device 1F according to the fifth modified example of the second embodiment, as shown in FIG. 10C, the shape of the cover member 5F is different from that of the cover member 5E according to the sixth modified example of the second embodiment. The cover member 5F has a rib 58 protruding from the outer peripheral surface 514 of the base portion 51. The outer peripheral shape of the rib 58 is slightly smaller than the inner diameter in the width direction of the outer ring 421. The rib 58 is formed around the entire circumference of the base portion 51 in the circumferential direction. Furthermore, the outer ring 421 has a groove portion 427 on the inner peripheral surface. The groove portion 427 is formed around the entire circumference of the outer ring 421 in the circumferential direction. The inner diameter of the outer ring 421 is different on the inside and outside with the groove portion 427 in between, and is larger on the outside of the groove portion 427. The rib 58 faces the groove portion 427. Here, a gap G5 is secured between the cover member 5F and the outer ring 421, including between the rib 58 and the groove portion 427. Gap G5 has a labyrinth structure with ribs 58 and grooves 427, similar to gap G2, improving the sealing performance of cover member 5F. Furthermore, gap G5 is filled with lubricant 54.

Furthermore, it is not essential that the various cover members 5A to 5F described in embodiment 2 are provided in pairs, and only one may be provided so as to face the bearing 42 from one side of the rotation axis Ax1.

The configuration of embodiment 2 (including modifications) can be applied in appropriate combination with the configuration described in embodiment 1 (including modifications).

(Embodiment 3)
11A and 11B, the strain wave gear device 1G according to this embodiment differs from the strain wave gear device 1A according to embodiment 2 in the configuration of a cover member 5G. Hereinafter, configurations similar to those in embodiment 2 will be denoted by the same reference numerals and descriptions thereof will be omitted as appropriate.

Figure 11A is a cross-sectional view showing the schematic configuration of the strain wave gear device 1G, and Figure 11B is an enlarged view of a main portion of Figure 11A (the range corresponding to area Z1 in Figure 1A).

In this embodiment, the pair of cover members 5G have symmetrical shapes in a direction parallel to the rotation axis Ax1, so the following describes the shape of one of the pair of cover members 5G.

That is, in this embodiment, the cover member 5G faces only the bearing 42 of the wave generator 4 from one side of the rotation axis Ax1. In other words, the cover member 5G is a part formed in an annular shape similar to the bearing 42. The cover member 5G is fixed to the inner ring 422 of the bearing 42.

Specifically, the cover member 5G has a main plate 501, a first side plate 502, and a second side plate 503. The main plate 501 is a plate-shaped member formed in an annular shape when viewed from one side of the rotation axis Ax1. The first side plate 502 protrudes from the inner peripheral edge of the main plate 501 toward the bearing 42 along the rotation axis Ax1. The second side plate 503 protrudes from the outer peripheral edge of the main plate 501 toward the bearing 42 along the rotation axis Ax1. In other words, the first side plate 502 and the second side plate 503 face each other in the radial direction and are connected by the main plate 501. The main plate 501, the first side plate 502, and the second side plate 503 are integrally formed from a single metal member, thereby realizing a seamless cover member 5G.

The cover member 5G is flexible due to its relatively small (thin) thickness. Therefore, if the inner ring 422 elastically deforms while the cover member 5G is fixed to the inner ring 422, the cover member 5G will elastically deform in response to the deformation of the inner ring 422.

Here, the main plate 501 faces the bearing 42 from one side of the rotation axis Ax1 with a gap between the end face of the bearing 42. Then, the first side plate 502 is pressed into the gap between the inner ring 422 and the cam 41, and the cover member 5G is fixed to the inner ring 422 by the first side plate 502. Meanwhile, the second side plate 503 is inserted into the gap between the outer ring 421 and the flexible external gear 3, but the second side plate 503 ensures a gap G6 between the outer ring 421 and the flexible external gear 3.

According to the above configuration, the cover member 5G faces the bearing 42 with a gap G6 secured between the cover member 5G and the outer ring 421 of the bearing 42. Even this cover member 5G has the function of preventing foreign matter X1 from entering the inside of the outer ring 421 from one side (input side) of the rotating shaft Ax1.

Furthermore, it is not essential that a pair of cover members 5G are provided as described in embodiment 3, and only one may be provided so as to face the bearing 42 from one side of the rotation axis Ax1.

The configuration of embodiment 3 (including modifications) can be applied in appropriate combination with the configurations (including modifications) described in embodiment 1 or embodiment 2.

(summary)
As described above, the wave gear device (1, 1A to 1G) according to the first aspect includes an annular rigid internal gear (2) having internal teeth (21), an annular flexible external gear (3) having external teeth (31) and arranged inside the rigid internal gear (2), and a wave generator (4). The wave generator (4) is arranged inside the flexible external gear (3) and causes a deflection in the flexible external gear (3). The wave gear device (1, 1A to 1G) deforms the flexible external gear (3) in accordance with the rotation of the wave generator (4) about the rotation axis (Ax1), meshing a part of the external teeth (31) with a part of the internal teeth (21), and rotating the flexible external gear (3) relative to the rigid internal gear (2) in accordance with the difference in the number of teeth between the rigid internal gear (2) and the flexible external gear (3). The wave generator (4) has a non-circular cam (41) that is driven to rotate about a rotation shaft (Ax1), and a bearing (42) that is arranged between an outer peripheral surface (411) of the cam (41) and an inner peripheral surface (301) of the flexible external gear (3). The wave gear device (1, 1A to 1G) further includes a cover member (5, 5A to 5G) that is arranged to face the bearing (42) from one side of the rotation shaft (Ax1). The cover member (5, 5A to 5G) faces the bearing (42) with gaps (G1 to G6) secured between the cover member (5, 5A to 5G) and an outer ring (421) of the bearing (42), and prevents a foreign object (X1) from entering the inside of the outer ring (421) from one side of the rotation shaft (Ax1).

According to this embodiment, even if foreign matter (X1) is generated due to wear or the like that occurs between the internal teeth (21) and the external teeth (31) when the strain wave gear device (1, 1A-1G) is used for a long period of time, the intrusion of such foreign matter (X1) into the bearing (42) is suppressed. Therefore, there is an advantage in that a decrease in reliability is unlikely to occur.

In the first embodiment of the wave gear device (1, 1A to 1G) according to the second aspect, the cover member (5, 5A to 5G) rotates at the same speed as the cam (41).

According to this embodiment, even if the bearing (42) elastically deforms, the cover member (5, 5A to 5G) can follow the elastic deformation of the bearing (42).

In the wave gear device (1, 1A to 1G) according to the third aspect, in the second aspect, the cover member (5, 5A to 5G) has a cap portion (52) that is formed so that the distance from the rotating shaft (Ax1) gradually increases from the bearing (42) side toward one side of the rotating shaft (Ax1).

According to this embodiment, the foreign matter (X1) attached to the umbrella portion (52) can be moved in a direction away from the bearing (42) by centrifugal force.

The wave gear device (1, 1A to 1G) according to the fourth aspect is the same as the third aspect, but further includes a guide portion (23) that is provided on the rigid internal gear (2) and faces the bevel portion (52) with a certain gap or more between them.

According to this embodiment, the movement of the foreign matter (X1) attached to the umbrella portion (52) due to centrifugal force can be guided.

In the wave gear device (1, 1A to 1G) according to the fifth aspect, in any of the first to fourth aspects, the cover member (5, 5A to 5G) has a non-circular portion that corresponds to the cam (41) when viewed from one side of the rotating shaft (Ax1) at a portion facing the bearing (42).

According to this embodiment, the amount of protrusion of the cover member (5, 5A to 5G) from the wave generator (4) can be kept relatively small.

In the wave gear device (1, 1A to 1G) according to the sixth aspect, in any of the first to fifth aspects, at least a portion of the gap (G1 to G6) between the outer ring (421) and the cover member (5, 5A to 5G) is filled with a lubricant (54).

According to this embodiment, sealing using a lubricant (54) can be achieved.

In the wave gear device (1, 1A to 1G) according to the seventh aspect, in the sixth aspect, the lubricant (54) is held in the gap (G1 to G6) between the outer ring (421) and the cover member (5, 5A to 5G) by capillary action.

According to this embodiment, there is no need for a member to hold the lubricant (54).

In the strain wave gear device (1, 1A to 1G) according to the eighth aspect, in any of the first to seventh aspects, the cover member (5, 5A to 5G) has a base portion (51) that is arranged inside the flexible external gear (3). A first gap (G21) is formed between the outer peripheral surface (514) of the base portion (51) and the inner peripheral surface (301) of the flexible external gear (3), which face each other in a direction perpendicular to the rotation axis (Ax1).

According to this embodiment, a bottleneck is formed at the first gap (G21), making it easier to prevent the foreign object (X1) from entering the inside of the outer ring (421).

In the strain wave gear device (1, 1A to 1G) according to the ninth aspect, in the eighth aspect, the cover member (5, 5A to 5G) further has a protrusion (55) that protrudes from the base portion (51) and is inserted inside the outer ring (421). A second gap (G22) is formed between the outer peripheral surface (551) of the protrusion (55) that faces the inner peripheral surface (424) of the outer ring (421) in a direction perpendicular to the rotation axis (Ax1).

According to this embodiment, a bottleneck is formed at the second gap (G22), making it easier to prevent the foreign object (X1) from entering the inside of the outer ring (421).

In the wave gear device (1, 1A to 1G) according to the tenth aspect, a third gap (G23) is formed between the base portion (51) and the outer ring (421) that face each other in the direction of the rotation axis (Ax1) in the ninth aspect. The first gap (G21) and the second gap (G22) are connected through the third gap (G23).

According to this aspect, the first gap (G21), the second gap (G22), and the third gap (G23) form a bottleneck, making it easier to prevent the foreign matter (X1) from entering the inside of the outer ring (421).

In the strain wave gear device (1, 1A to 1G) according to the eleventh aspect, in any of the first to tenth aspects, the cover member (5, 5A to 5G) is configured to be impermeable to liquids.

According to this embodiment, the cover member (5, 5A to 5G) can block the liquid.

In the wave gear device (1, 1A to 1G) according to the twelfth aspect, in any of the first to eleventh aspects, the cover member (5, 5A to 5G) has oil repellency.

According to this embodiment, oily foreign matter (X1) is less likely to adhere to the cover member (5, 5A to 5G).

The actuator according to the thirteenth aspect includes a wave gear device (1, 1A-1G) according to any one of the first to twelfth aspects, a drive source (101) that rotates the cam (41), and an output section (102) that extracts the rotational force of the flexible external gear (3) as an output.

This has the advantage that reliability is less likely to decrease.

The cover body (10) according to the fourteenth aspect is used as a cover member (5, 5A to 5G) for the wave gear device (1, 1A to 1G) according to any one of the first to twelfth aspects.

This has the advantage that reliability is less likely to decrease.

The configurations according to the second to twelfth aspects are not essential to the wave gear device (1, 1A to 1G) and may be omitted as appropriate.

REFERENCE SIGNS LIST 1, 1A to 1G Harmonic gear device 2 Rigid internal gear 3 Flexible external gear 4 Wave generator 5, 5A to 5G Cover member 10 Cover body 21 Internal teeth 23 Guide portion 31 External teeth 41 Cam 42 Bearing 51 Base portion 52 Convex portion 54 Lubricant 55 Convex portion 100 Actuator 101 Driving source 102 Output portion 411 Outer peripheral surface 421 Outer ring Ax1 Rotating shaft G1 to G6 Gap G21 First gap G22 Second gap G23 Third gap X1 Foreign object

Claims (14)

an annular rigid internal gear having internal teeth;
an annular flexible external gear having external teeth and disposed inside the rigid internal gear;
a wave generator disposed inside the flexible external gear and causing the flexible external gear to deflect;
a wave gear device in which the flexible external gear is deformed in accordance with rotation of the wave generator about a rotation axis, a portion of the external teeth is meshed with a portion of the internal teeth, and the flexible external gear is rotated relative to the rigid internal gear in accordance with a difference in the number of teeth between the flexible external gear and the rigid internal gear,
The wave generator includes:
A non-circular cam that is driven to rotate around the rotation shaft;
a bearing disposed between an outer circumferential surface of the cam and an inner circumferential surface of the flexible external gear;
a cover member disposed on one side of the rotating shaft so as to face the bearing,
the cover member faces the bearing with a gap between the cover member and the outer ring of the bearing, and prevents foreign matter from entering the inside of the outer ring from one side of the rotating shaft.
Wave gear device. The cover member rotates at the same speed as the cam.
The strain wave gear device according to claim 1 . The cover member has an umbrella portion formed so that the distance from the rotating shaft gradually increases from the bearing side toward one side of the rotating shaft.
The strain wave gear device according to claim 2. The rigid internal gear further includes a guide portion that faces the bevel portion with a certain gap therebetween.
The strain wave gear device according to claim 3. the cover member has a non-circular portion, which corresponds to the cam when viewed from one side of the rotation shaft, at a portion facing the bearing;
The wave gear device according to any one of claims 1 to 4. At least a portion of the gap between the outer ring and the cover member is filled with a lubricant.
The wave gear device according to any one of claims 1 to 5. The lubricant is held in the gap between the outer ring and the cover member by capillary action.
The strain wave gear device according to claim 6. The cover member has a base portion disposed inside the flexible external gear,
a first gap is formed between an outer circumferential surface of the base portion and an inner circumferential surface of the flexible external gear, the outer circumferential surface of the base portion and the inner circumferential surface of the flexible external gear facing each other in a direction perpendicular to the rotation axis;
The wave gear device according to any one of claims 1 to 7. the cover member further includes a protrusion protruding from the base portion and inserted into the inner side of the outer ring,
a second gap is formed between an outer circumferential surface of the convex portion and an inner circumferential surface of the outer ring that face each other in a direction perpendicular to the rotation axis;
The strain wave gear device according to claim 8. a third gap is formed between the base portion and the outer ring which face each other in a direction of the rotation axis,
The first gap and the second gap are connected through the third gap.
The strain wave gear device according to claim 9. The cover member is configured to be impermeable to liquids.
The wave gear device according to any one of claims 1 to 10. The cover member has oil repellency.
The wave gear device according to any one of claims 1 to 11. A wave gear device according to any one of claims 1 to 12,
A drive source that rotates the cam;
and an output section that outputs the rotational force of the flexible external gear as an output.
Actuator. A cover member is used in the wave gear device according to any one of claims 1 to 11.
Cover body.