Harmonic reducer wave generator capable of bearing axial load

Abstract

The invention relates to the technical field of harmonic reducer wave generators, and discloses a harmonic reducer wave generator capable of bearing axial load, which comprises a rigid gear, a flexible gear and a wave generator, the wave generator is arranged in the flexible gear, the flexible gear is arranged in the rigid gear, the inner ring of the rigid gear is meshed with the outer ring of the flexible gear through teeth, and the inner ring of the rigid gear is meshed with the outer ring of the flexible gear. The long shaft part of the flexible gear is in contact with the rigid gear, the short shaft part of the flexible gear does not participate in action, the wave generator comprises an oval cam and a flexible bearing, and the oval cam is arranged in the flexible bearing; the flexible bearing comprises a bearing inner ring, a bearing outer ring and balls, the bearing inner ring and the bearing outer ring are each provided with two channels, the distance between the two channels of the inner ring is smaller than that between the two channels of the outer ring, and when the multiple balls are arranged in the corresponding channels in the bearing inner ring and the bearing outer ring, the contact points of the balls and the outer ring and the contact points of the balls and the inner ring are connected through the connecting line of the centers of the balls. And a certain included angle is formed between the bearing and the radial direction of the bearing and is generally about 15 degrees. The flexible bearing can bear a certain axial load, the bearing capacity of the speed reducer can be greatly improved, the precision service life of the speed reducer can be greatly prolonged, the application field and range of the speed reducer are expanded, and the flexible bearing is simple in structure and convenient to install.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of harmonic reducer wave generator, and particularly relates to a harmonic reducer wave generator capable of bearing axial load. BACKGROUND

[0002] Harmonic drive is a device for motion or power transmission by using elastic deformation wave of flexible components, which has the advantages of simple structure, large transmission ratio, stable transmission, high precision, low noise and high transmission efficiency, and is widely used in space technology, radar communication, machine tool, instrument, precision optical equipment and other fields.

[0003] Referring to the drawings Figure 1 , Figure 2 in the accompanying drawings, the harmonic gear reducer in the prior art mainly consists of a wave generator 113, a flexspline 112 and a rigid gear 111. The wave generator 113 has various structures, and the flexible bearing cam type wave generator is one of them, which can comprehensively control the deformation of the flexspline. The flexible bearing cam type wave generator in the prior art consists of an oval cam 1131 placed in a flexible bearing 1132. The wave generator 113 is placed inside the flexspline 112, and due to the action of the oval cam 1131, the flexspline 112 forms an ellipse with the flexible bearing 1132, and when placed inside the rigid gear 111, only the long axis part is in contact with the rigid gear, and the short axis part does not participate in the work. Since the number of teeth of the rigid gear is more than that of the flexspline, when the cam drives the flexible component to rotate, with each rotation, the flexspline rotates a certain number of teeth relative to the rigid gear through the meshing of the teeth, thereby achieving the purpose of speed reduction.

[0004] The flexible bearing cam type wave generator in the prior art has the advantages of large transmission ratio, high transmission precision and small error, but also has the defect that it is difficult to withstand excessive load due to the thin flexible bearing, which eliminates the radial clearance and has a contact angle of zero, and it is difficult to withstand excessive load in use. Therefore, this type of product is mainly used in small size and low rated load occasions. If the load is large, an RV reducer is generally selected.

[0005] The flexible bearing of the commonly used harmonic reducer wave generator is mainly designed by referring to the form of deep groove ball bearing, but the deep groove ball bearing is designed, manufactured and used on the basis that the inner and outer rings and rolling elements of the traditional rigid bearing are rigid and cannot be plastically deformed. The specific explanation is as follows: Referring to the drawings Figure 3 (a), due to the need of process, the bearing has a radial clearance before installation. Referring to the drawings Figure 3(b) shown, during installation, through the inner and outer ring axial displacement, respectively, to eliminate the play. The rolling body and the rolling contact, and pre-loaded a certain load (pre-load, excess play), to ensure the smooth operation of the bearing. Due to the existence of play, after the installation is completed, the stress direction of the bearing (through the center of the steel ball, the line connecting the contact point of the steel ball and the outer raceway and the inner raceway) and the bearing radial direction forms a certain angle (generally 5-7 °), so that it can also withstand the appropriate axial force while mainly bearing the radial force.

[0006] Referring to the description attached Figure 3 (c) shown, the prior art harmonic reducer wave generator used flexible bearing is by the cam oval long axis direction, radial clearance (cam installation, oval long axis direction is excess). Cam long axis size is greater than the inner diameter of the bearing, when the cam is pressed into the bearing inner ring, the bearing inner ring produces radial direction expansion deformation, the long axis direction eliminates the installation play of the bearing, and the pre-load requirement makes the actual contact angle of the bearing zero.

[0007] The relationship between the axial force F1, the radial force F2, the resultant force F and the contact angle θ: the radial force F2 = the axial force F1 / tan θ; When the contact angle θ is very small and close to 0, as long as there is a certain axial force, the radial force will be infinite.

[0008] The inventor of the harmonic reducer also considers this problem, which is to increase a cross-roller bearing in the axial direction to ensure that the axial displacement is eliminated and the axial force is prevented. In practice, due to the error of machining precision and assembly precision of parts, it is difficult to ensure that there is no absolute axial displacement, and thus a very small axial force is generated, which will form a very large radial force. This is also the main problem encountered in the practice of harmonic reducers. Light loss precision, serious failure and even rupture of the outer ring of the flexible bearing are also reasons why harmonic reducers cannot be used in working conditions with relatively large working loads. The size of the rated load of the harmonic reducer is also an important indicator to measure the quality of the product.

[0009] In the past decade, the design and manufacture of harmonic reducers in China have made great progress, but there is still some gap compared with similar foreign products (mainly Japanese Hamernik HD). The main problems are precision, service life and load capacity. Generally speaking, the load capacity of similar products in China is about 20% lower than that of foreign products. SUMMARY

[0010] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a harmonic reducer wave generator capable of bearing axial load, which enables the flexible bearing to bear a certain axial load, greatly improves the load capacity and precision life of the reducer, expands its application field and range, and has simple structure and convenient installation.

[0011] The application adopts the following technical scheme: a harmonic reducer wave generator capable of bearing axial load, comprising a rigid wheel, a flexible wheel and a wave generator, the wave generator is arranged in the flexible wheel, the flexible wheel is arranged in the rigid wheel, the inner ring of the rigid wheel is engaged with the outer ring of the flexible wheel through teeth, the long shaft part of the flexible wheel is in contact with the rigid wheel, and the short shaft part of the flexible wheel does not participate in action, the wave generator comprises an elliptical cam and a flexible bearing, and the elliptical cam is arranged in the flexible bearing; the flexible bearing comprises a bearing inner ring, a bearing outer ring and balls, double channels are arranged on the bearing inner ring and the bearing outer ring, and a plurality of balls are arranged in corresponding channels on the bearing inner ring and the bearing outer ring, so that the contact angle between the stress direction of the ball in the channel and the radial force direction is 10°-20°, and the two contact angles are equal in value and opposite in direction.

[0012] Further, the bearing inner ring and the bearing outer ring are integrated structures.

[0013] Further, the contact angle between the stress direction of the ball in the channel and the radial force direction is 15°.

[0014] Further, the ball eliminates the clearance in the channel through radial displacement.

[0015] Further, the elliptical cam is arranged in the bearing inner diameter of the bearing inner ring, so that the radial force is added, and the radial and axial clearances of the ball in the channel are eliminated.

[0016] Further, by controlling the channel position difference, channel size and clearance of the bearing inner ring and the bearing outer ring, the ball forms a certain contact angle in the channel.

[0017] Compared with the prior art, the application has the following beneficial effects: 1. The harmonic reducer wave generator capable of bearing axial load, wherein the contact angle between the stress direction of the ball in the channel and the radial force direction is about 15°, so that the flexible bearing can bear a certain axial load, the load-carrying capacity and precision life of the reducer can be greatly improved on the basis of the same manufacturing process level, and the application field and range of the reducer are expanded.

[0018] 2. The harmonic reducer wave generator capable of bearing axial load, wherein the bearing inner ring and the bearing outer ring are integrated structures, which are different from the structure design of the traditional double-row angular contact ball bearing, that is, the outer ring is integrated, the inner ring is two bodies, and a separation pad is added, so that the wave generator structure of the application is simpler and more convenient to install.

[0019] 3. A harmonic reducer wave generator capable of bearing axial load, the present application controls the difference in the position of the groove of the inner ring and the outer ring of the bearing, the size of the groove and the play, so that the ball forms a certain contact angle in the groove; the elliptical cam is placed in the inner diameter of the inner ring of the bearing, so that the radial force eliminates the radial and axial play of the ball in the groove, and the overall structure is simple. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the structure of a harmonic gear reducer using a flexible bearing cam wave generator in the prior art; Figure 2 is a sectional view of a harmonic gear reducer using a flexible bearing cam wave generator in the prior art; Figure 3 is a schematic diagram of three states of a deep groove ball bearing; wherein 3(a) is a sectional view of a deep groove ball bearing in a free state, wherein 3(b) is a sectional view of a general deep groove ball bearing in a working state, and wherein 3(c) is a sectional view of a flexible bearing used in the existing wave generator to eliminate radial play; Figure 4 is a schematic diagram of the structure of a harmonic reducer wave generator capable of bearing axial load according to the present application; Figure 5 is a schematic diagram of the upper part structure of a harmonic reducer wave generator capable of bearing axial load according to the present application.

[0021] Figure 6 is the difference in the position of the groove of the inner ring and the outer ring of the bearing when two sets of bearings are used in pairs; Figure 7 is the difference in the position of the groove of the inner ring and the outer ring of the bearing when the bearing is used according to the present application;

[0022] Figure 8 is the protrusion or recess of a single bearing inner ring and outer ring.

[0023] In the figure: the rigid wheel-1; the flexible wheel-2; the wave generator-3; the elliptical cam-31; the flexible bearing-32; the bearing inner ring-321; the bearing outer ring-322; the ball-323; the groove-324. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with specific reference to specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict.

[0025] The purpose of the present invention is to provide a harmonic reducer wave generator capable of bearing axial loads in view of the defects of the prior art. Example 1

[0026] This embodiment provides a harmonic reducer wave generator capable of bearing axial load, referring to Figure 4 As shown, the wave generator 3 includes a rigid pulley 1, a flexspline 2, and a wave generator 3. The wave generator 3 is placed inside the flexspline 2, which is itself placed inside the rigid pulley 1. The inner ring of the rigid pulley 1 meshes with the outer ring of the flexspline 2 through teeth. The long axis of the flexspline 2 contacts the rigid pulley 1, while the short axis of the flexspline 2 does not participate in the movement. The wave generator 3 is a flexible bearing cam type wave generator. The wave generator 3 includes an elliptical cam 31 and a flexible bearing 32. The elliptical cam 31 is placed inside the flexible bearing 32.

[0027] Reference Figure 5 As shown, the flexible bearing 32 includes a bearing inner ring 321, a bearing outer ring 322 and balls 323. The bearing inner ring 321 and the bearing outer ring 322 are both provided with double-track grooves 324. A plurality of balls 323 are arranged in the corresponding grooves 324 on the bearing inner ring 321 and the bearing outer ring 322, so that the contact angle between the force direction of the balls 323 in the groove 324 and the radial force direction is 10°~20°, and the two angles are in opposite directions; specifically, in this embodiment, the contact angle between the force direction of the balls 323 in the groove 324 and the radial force direction is 15°. According to the calculated relationship between the axial force F1, the radial force F2, the resultant force F and the contact angle θ, it can be seen that the flexible bearing 32 can withstand about 27% of the axial force and can withstand a certain axial / radial load. On the basis of the same manufacturing process level, it can greatly improve the load-bearing capacity and precision life of the reducer, and expand its application field and scope.

[0028] Reference Figure 5As shown, the bearing inner ring 321 and the bearing outer ring 322 in the embodiment are one-piece structures. The contact angle of a general double-row angular contact ball bearing (double-groove) is determined by the difference between the distance between the two grooves of the bearing inner ring and the distance between the two grooves of the outer ring, the shape of the grooves of the inner and outer rings, and the bearing play. Since it is difficult to ensure the dimensional accuracy of parts, especially the groove spacing and groove shape, with general machining accuracy, it is difficult to ensure consistency. Therefore, double-row angular contact ball bearings with certain precision are designed with the outer ring as one piece and the inner ring as two pieces. An isolation pad is usually added between the two inner rings. During installation, the axial displacement of the inner ring eliminates the play, and the resulting error is concentrated as the distance between the groove positions of the two inner rings. The height of the isolation pad is adjusted. The flexible bearing 32 in the embodiment eliminates the play by radial displacement of the ball 323 in the groove 324, so it does not need to leave space for axial movement. The bearing inner ring 321 and the bearing outer ring 322 are designed as one piece. The elliptical cam 31 is placed in the bearing inner diameter of the bearing inner ring 321, which applies a radial force to eliminate the radial and axial play of the ball 323 in the groove 324. By controlling the position difference of the grooves 324 of the bearing inner ring 321 and the bearing outer ring 322, the groove size and the play, a certain contact angle (10-20°) is formed for the ball 323 in the groove 324.

[0029] The two sets of bearings are used in pairs, and the ultimate goal is that there is no gap in the axial and radial directions of the two sets of bearings, and the steel balls are in close contact with the inner and outer ring raceways, so that the two sets of bearings become one, and the contact points of the steel balls and the outer ring raceways form a certain angle relative to the radial direction of the bearing through the center of the steel ball and the connecting line of the contact points of the steel ball and the inner ring, so that the bearing can also bear a certain axial force (the directions of the two forces are opposite) while mainly bearing the radial force. Figure 6 As shown (the dimensions marked in the figure, the upper one is the distance between the groove positions of the two sets of bearing outer rings, the lower one is the distance between the groove positions of the two sets of bearing inner rings, and the dimension chain marked at the lower left is half the difference between the groove spacing of the two sets of bearing outer rings and the groove spacing of the two sets of bearing inner rings). To achieve the above purpose, according to the geometry of mechanics, the hypotenuse corresponds to the diameter of the steel ball, which is fixed and known, so the key is the opposite side, that is, the difference between the distance between the groove positions of the two sets of bearing outer rings and the distance between the groove positions of the two sets of bearing inner rings.

[0030] This position difference, as shown on a single set of bearings, is the height difference (which can also be understood as the axial play of the bearing) in the axial direction between the bearing outer ring plane and the bearing inner ring plane after the bearing has an axial displacement (that is, the outer ring and the inner ring move in opposite axial directions). The bearing term is called protrusion or concave amount. The inner ring is higher than the outer ring, which is called protrusion, and the inner ring is lower than the outer ring, which is called concave amount.

[0031] There are many factors that affect the amount of protrusion and recess, including groove shape error, groove curvature radius error, groove diameter size error, groove position error, clearance error and many other factors. Due to the limitations of process technology and equipment, it is difficult to strictly control them. The way the bearing industry solves this problem is to strictly control the above errors as much as possible during the processing process to keep them within an acceptable range. Finally, for a single set of finished bearings, use special instruments to check the protrusion or recess of each set of bearings, such as Figure 8 As shown, for the selected bearings, select two sets with the algebraic sum of protrusion or recess amount of zero and use them in pairs ( Figure 8 The dimension marked in the figure is the protrusion or recess. For example, one set of bearings has a protrusion of 0.003mm and the other has a recess of 0.003mm. When these two sets of bearings are paired, when the flat surfaces of the outer rings touch, the flat surfaces of the inner rings also touch, and there is no clearance in both the radial and axial directions, achieving the effect of using a set (two bearings).

[0032] The bearings involved in this invention cannot be made into a two-piece structure due to their thin wall thickness. Therefore, previous harmonic generators could only use single-row ball bearings. With the improvement of processing technology, equipment advancement, and the emergence of new processing and testing methods, it has become possible to make the inner and outer rings of the bearings into one piece, such as Figure 7 (The dimensions marked in the figure are: the distance between the two grooves of the bearing outer ring on the top, the distance between the two grooves of the bearing inner ring on the bottom, and the dimension marked on the far right of the dimension chain marked below is: half of the difference between the groove spacing of the bearing outer ring and the groove spacing of the inner ring.) The means for implementing the present invention include: The groove shape error can be corrected by using diamond rollers. The shape of the groove is determined by the shape of the diamond roller, which can basically ensure the consistency of the groove shape. Servo control technology is now very mature. The existing equipment can be modified to add a private servo control system in the axial direction. After grinding one groove, it moves axially to the designed position and continues to grind the next groove. The current private servo control accuracy can reach 0.001mm, so the difference in the groove position of a batch can be completely controlled within 0.003mm. The equipment adds an active measurement system to measure the mutual difference between the two groove diameters of the same ring. During grinding, the groove diameter size is randomly measured. This technology has been relatively mature in bearing processing and is mainly used in the grinding of the inner diameter of the bearing. With the introduction of this technology in the groove grinding process, it is not difficult to control the size dispersion within 0.003mm at the current process level.

[0033] By following these technical indicators and selecting the inner and outer ring groove diameters to control the clearance error within 0.003mm, the angular error in both directions of the bearing can be within plus or minus 1°. This fully meets the use standards for paired bearings (according to international standards, the angular error of paired angular contact bearings is generally no more than plus or minus 3°, and the current industry standard is to control it within plus or minus 1°).

[0034] To better achieve the performance of the harmonic reducer wave generator of the present invention, the distance error between the two grooves 324 provided on the bearing inner ring 321 and the distance error between the two grooves 324 provided on the bearing outer ring 322 should not exceed ±1μm. The groove profile error, that is, the error in the groove curvature radius, of the grooves 324 provided on the bearing inner ring 321 and the bearing outer ring 322 should be less than 3μm. The error between the diameters of the two grooves 324 provided on the bearing inner ring 321 and the bearing outer ring 322 should also be less than 3μm. This is because the radial clearance is controlled by the groove diameter size (the dimension from the upper bottom to the lower bottom of the groove) in conjunction with the size of the ball 323. The radial clearance error determines the bearing angular error.

[0035] The present invention discloses a harmonic reducer wave generator capable of withstanding axial loads. The contact angle between the force direction and the radial force direction of the balls 323 within the channel 324 is approximately 15°, enabling the flexible bearing 32 to withstand approximately 27% of the axial force, thus enabling it to withstand a certain axial load. This significantly improves the reducer's load-bearing capacity, precision lifespan, and application scope, while maintaining the same manufacturing process. The bearing inner ring 321 and outer ring 322 are both integrally designed, unlike conventional double-row angular contact ball bearings, which have a single outer ring and two inner rings with an additional isolation pad. This makes the present invention's wave generator simpler in structure and easier to install.

[0036] The present invention controls the position difference, groove size and clearance of the groove 324 of the bearing inner ring 321 and the bearing outer ring 322, so that the ball 323 forms a certain contact angle in the groove 324; the elliptical cam 31 is placed in the bearing inner diameter of the bearing inner ring 321, so that the radial direction force is applied to eliminate the radial and axial clearances of the ball 323 in the groove 324, and the overall structure is simple.

[0037] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A harmonic reducer wave generator capable of bearing axial load, comprising a rigid wheel (1), a flexible wheel (2) and a wave generator (3), wherein the wave generator (3) is placed inside the flexible wheel (2), the flexible wheel (2) is placed inside the rigid wheel (1), the inner ring of the rigid wheel (1) and the outer ring of the flexible wheel (2) are meshed through teeth, and the long axis portion of the flexible wheel (2) is in contact with the rigid wheel (1), characterized in that: The wave generator (3) includes an elliptical cam (31) and a flexible bearing (32), wherein the elliptical cam (31) is placed inside the flexible bearing (32); the flexible bearing (32) includes a bearing inner ring (321), a bearing outer ring (322) and a ball (323), wherein the bearing inner ring (321) and the bearing outer ring (322) are both provided with a double-channel groove (324), and a plurality of the balls (323) are arranged in the corresponding grooves (324) on the bearing inner ring (321) and the bearing outer ring (322), so that the contact angle between the force direction of the ball (323) in the groove (324) and the radial force direction is 10° to 20°, and the two contact angles are equal in value and opposite in direction.

2. The harmonic reducer wave generator capable of bearing axial load according to claim 1, characterized in that: The bearing inner ring (321) and the bearing outer ring (322) are both integral structures, and both the inner ring and the outer ring have double-row grooves.

3. The harmonic reducer wave generator capable of bearing axial load according to claim 2, characterized in that: Due to the difference between the inner ring groove spacing and the outer ring groove spacing, the contact angle between the force direction of the ball (323) in the groove (324) and the radial force direction is 15°.

4. The harmonic reducer wave generator capable of bearing axial load according to claim 3, characterized in that: The ball (323) eliminates clearance in the groove (324) by radial displacement, and there is no room for axial movement.

5. The harmonic reducer wave generator capable of bearing axial load according to claim 4, characterized in that: By placing the elliptical cam (31) in the inner diameter of the bearing inner ring (321), radial force is applied to eliminate radial and axial clearances of the ball (323) in the groove (324).

6. The harmonic reducer wave generator capable of bearing axial load according to claim 4, characterized in that: By controlling the position difference, groove size and clearance of the groove (324) of the bearing inner ring (321) and the bearing outer ring (322), the ball (323) forms a contact angle of a certain size in the groove (324).

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