An externally excited harmonic speed reducer

Abstract

This invention discloses an externally excited harmonic reducer. The reducer includes a coaxially arranged externally excited harmonic generator, a gear shaft, a cage, and rollers. The externally excited harmonic generator has an inner cam, the inner contour of which has at least one radial protrusion. The gear shaft is a rigid shaft with circumferentially distributed external teeth on its outer cylindrical surface. The cage has circumferentially distributed radial grooves, each groove housing a roller. The roller simultaneously contacts and is constrained by the inner cam surface, the groove surface, and the external tooth surface. The number of external teeth on the gear shaft is equal to the sum or difference between the number of protrusions on the inner cam and the number of grooves. The cage is fork-shaped, with grooves formed between adjacent transmission forks. The transmission forks can generate slight bending elastic deformation to adaptively compensate for differences in tooth consistency. This invention eliminates the need for a flexible wheel, avoiding the problem of short fatigue life of flexible elements, reducing machining accuracy requirements, improving transmission efficiency, enhancing reliability, and extending service life.

Description

Technical Field

[0001] This invention relates to the field of mechanical transmission technology, and in particular to an externally excited harmonic reducer. Background Technology

[0002] Harmonic reducers are speed reduction transmission devices that rely on mechanical waves to transmit power and motion. Due to their large single-stage reduction ratio and high transmission accuracy, they are widely used in robotics, precision instruments, and automated equipment. Common harmonic reducers typically include a wave generator, a flexible wheel, and a rigid wheel. An elliptical cam on the wave generator, with the aid of a thin-walled bearing, causes the flexible wheel to elastically deform. The external teeth of the flexible wheel mesh with the internal teeth of the rigid wheel, thus achieving speed reduction between input and output. This type of structure relies on flexible elements to generate elastic mechanical waves for meshing, which has the disadvantage of short fatigue life of the flexible elements.

[0003] To avoid the short fatigue life of flexible components, various attempts have been made to replace the external teeth of the flexible gear with "live teeth" (such as the "external wave type compound rolling live tooth reducer" disclosed in CN102562956B). However, these attempts have not been widely adopted due to the extremely high requirements for the consistency of machining accuracy among multiple teeth, the difficulty in controlling the mating clearance, high cost, and poor reliability. Specifically, the live tooth frame of existing live tooth reducers is a rigid integral structure, and the working position of each live tooth is entirely determined by the machining accuracy of the transmission gear, harmonic generator, and live tooth frame. When multiple live teeth engage simultaneously, the dimensional tolerances, form and position tolerances, and center gear tooth pitch tolerances of each component accumulate into transmission errors, causing some live teeth to bear excessive loads and others to disengage, accelerating wear and reducing transmission accuracy. Summary of the Invention

[0004] The purpose of this invention is to provide an externally excited harmonic reducer, which achieves speed reduction transmission through a structure combining an externally excited harmonic generator, a rigid gear shaft, a cage, and rollers. The cage is configured as a fork shape, and the slight bending elasticity of the fork is used to compensate for the consistency differences between multiple teeth, thereby achieving high-efficiency and long-term reliable speed reduction transmission with appropriate machining accuracy and low cost.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: an externally excited harmonic reducer, comprising an externally excited harmonic generator, a gear shaft, a cage, and rollers mounted on the cage, arranged around the same rotation axis; the externally excited harmonic generator has an outer ring, and an inner cam is disposed inwardly on the outer ring, the inner contour of the inner cam having at least one protrusion; the gear shaft is a rigid shaft, and a plurality of external teeth are evenly distributed on its outer cylindrical surface; the cage is provided with a plurality of circumferentially distributed and radially radiating grooves, each groove accommodating one roller; the roller simultaneously interacts with the surface of the inner cam and the... The surface of the groove and the surface of the external teeth are in contact and constrained by all three; the number of external teeth of the gear shaft is equal to the sum of the number of protrusions of the inner cam and the number of grooves, or equal to the difference between the number of grooves and the number of protrusions of the inner cam; the retainer is a thin-walled cylindrical shape, one end of which is a rigid base, and the other end is provided with a plurality of transmission forks distributed along the circumference. Two adjacent transmission forks together with the base form a fork shape, and the space between two adjacent transmission forks forms the groove. The transmission fork is a slender structure that can produce a small amount of bending elastic deformation to compensate for the consistency difference between the plurality of rollers.

[0006] Specifically, the cage of this invention adopts a fork-shaped structure, with the transmission fork being a slender elastic body that can undergo slight bending elastic deformation along the circumference under the thrust of the rollers. When machining dimensional errors and assembly errors of the transmission components cause a roller to slightly lead or lag behind its theoretical position, the corresponding transmission fork generates a corresponding amount of elastic deformation, automatically adjusting the circumferential position of that roller so that all rollers can participate in meshing simultaneously and uniformly. This "elastic adaptive" mechanism eliminates the problem of individual rollers being overloaded or losing contact due to machining errors in rigid cage designs, improving transmission efficiency, enhancing reliability, and extending service life. Attached Figure Description

[0007] Figure 1 This is an embodiment of an externally excited harmonic reducer. The schematic diagram of the overall structure along the longitudinal section along the axial direction shows an embodiment in which the number of protrusions of the inner cam is one. Figure 2 for Figure 1 The schematic diagram of the overall structure of the embodiment shown along a section perpendicular to the axis of rotation illustrates the externally excited harmonic generator, gear shaft, cage, rollers, and their mating relationships. Figure 3 Another embodiment of the externally excited harmonic reducer is shown in the overall structural schematic diagram along a section perpendicular to the rotation axis, illustrating an embodiment with two protrusions on the inner cam. Figure 4The schematic diagram of the cage shows the slight bending elasticity of the drive fork along the circumferential direction under the action of roller thrust; Figure 5 This is a three-dimensional structural diagram of various cage embodiments, showing multiple implementations of the cage base, slide, cutout, and fork; Note: No cross-sectional lines have been added to the rollers and harmonic bearings in the figure to keep the drawing simple and easy to read.

[0008] Markings: 10-Base, 11-Housing, 12-Support bearing; 20-External harmonic generator, 21-Outer ring, 22-Inner cam, 23-Harmonic bearing; 30-Cage, 31-Base, 32-Slide groove, 33-Slit, 34-Drive fork, 34'-Deformed drive fork; 40-Roller; 50-Gear shaft, 51-External gear; IN-Input shaft, OUT-Output shaft, e-Eccentricity of the eccentric inner cam. Detailed Implementation

[0009] Example 1: Externally excited harmonic reducer with a single-protruding internal cam. For example... Figure 1 and Figure 2 As shown, the externally excited harmonic reducer of this embodiment includes a base 10, a housing 11, and an externally excited harmonic generator 20, a cage 30, a roller 40, and a gear shaft 50 arranged around the same rotation axis.

[0010] The externally excited harmonic generator 20 has an outer ring 21, and an inner cam 22 is disposed inwardly on the outer ring 21. In this embodiment, the inner cam 22 has one protrusion, that is, the inner cam 22 is an inner cylindrical hole eccentric to the rotation axis, and the eccentricity is e. The externally excited harmonic generator 20 also includes a harmonic bearing 23, and the inner cam 22 is formed by the inner hole of the inner ring of the harmonic bearing 23.

[0011] The gear shaft 50 is a rigid shaft, and multiple external teeth 51 are evenly distributed on its outer cylindrical surface.

[0012] The cage 30 has multiple radially radiating grooves 32 evenly distributed around its circumference, each groove 32 accommodating a roller 40. The rollers 40 are needle rollers, with an outer diameter matching the width of the groove 32. The needle rollers can only slide radially within the groove 32. The rollers 40 and the cage 30 are positioned within the radial space between the externally excited harmonic generator 20 and the gear shaft 50. The rollers 40 simultaneously contact and are constrained by the surfaces of the inner cam 22, the groove 32, and the outer gear 51.

[0013] The number of external teeth 51 on the gear shaft 50 is equal to the sum of the number of protrusions on the inner cam 22 of the externally excited harmonic generator 20 (1 in this embodiment) and the number of slide grooves 32 on the cage 30, that is, the number of external teeth = the number of slide grooves + 1 (e.g., ...). Figure 2(As shown in the attached figure). Alternatively, the number of external teeth = the number of grooves - 1 (not shown in the attached figure).

[0014] A support bearing 12 is installed inside the base 10. The retainer 30 is installed between the base 10 and the support bearing 12 via an interference fit with the base 31 and is fixed to the base 10 as a whole. This structure is compact and is particularly advantageous for applications with high space requirements, such as humanoid robot joints.

[0015] Working principle: The externally excited harmonic generator 20 is connected to the input shaft IN and rotates. The inner cam 22 pushes the roller 40 to slide radially within the slide groove 32, thereby pushing the external teeth 51 of the gear shaft 50, causing relative rotational motion between the gear shaft 50 and the cage 30. If the gear shaft 50 is fixed, the cage 30 is connected to the output shaft OUT; if the cage 30 is fixed, the gear shaft 50 is connected to the output shaft OUT (as used in this embodiment). The rotational speed of the output shaft OUT is lower than that of the input shaft IN, achieving a speed reduction function.

[0016] Example 2: Externally excited harmonic reducer with double-protruding inner cam. For example... Figure 3 As shown, the difference between this embodiment and Embodiment 1 is that the inner cam 22 has two protrusions, meaning the inner cam 22 is an inner elliptical cylindrical hole centered on the rotation axis. Correspondingly, the number of external teeth 51 on the gear shaft 50 is equal to the sum of 2 and the number of grooves 32 (number of external teeth = number of grooves + 2). Alternatively, the number of external teeth = number of grooves - 2 (not shown in the attached figures). The roller 40 is a spherical ball bearing, with the outer diameter of the ball bearing matching the width of the groove 32. The ball bearing can only slide radially within the groove 32. The remaining structure and working principle are the same as in Embodiment 1.

[0017] Shift fork elastic compensation mechanism: such as Figure 4 As shown, the cage 30 is a thin-walled cylindrical shape. One end of the cylinder is a rigid base 31, and the other end is provided with multiple drive forks 34 distributed along the circumference. Two adjacent drive forks 34 together with the base 31 form a fork shape. The space between two adjacent drive forks 34 forms a groove 32. The drive forks 34 have a slender structure and can produce a small amount of bending elastic deformation (as shown in the deformed drive fork 34') to compensate for the consistency differences between the multiple rollers 40. The cylindrical surface of the cage 30 is provided with a narrow slit 33 along the axial direction. The slit 33 is located at the bottom of the groove 32, or in the middle of the drive fork 34, dividing the drive fork 34 in two.

[0018] During transmission, due to machining dimensions, form and position errors, and assembly errors of various transmission components, a certain roller 40 may slightly lead or lag behind its theoretical position, meaning there is a slight difference between its actual contact position and its theoretical position. The circumferential thrust exerted by this roller on the adjacent transmission fork 34 increases, causing the transmission fork 34 to undergo a slight bending elastic deformation, causing the circumferential position of the roller 40 to slightly retract, thereby reducing its contact pressure. Conversely, when a certain roller 40 slightly lags behind, the elastic restoring force of the transmission fork 34 causes its circumferential position to slightly advance. Through this elastic adaptive mechanism, all rollers 40 can participate in meshing simultaneously and uniformly, avoiding the problem of a few teeth bearing the main load or jamming and being unable to rotate, as in rigid cage designs.

[0019] Multiple implementation schemes for the cage: such as Figure 5 As shown, the cage 30 can be implemented in several ways. In one embodiment, the notch 33 is located at the bottom of the groove 32, and the drive fork 34 is an independent cantilever structure. In another embodiment, the notch 33 is located in the middle of the drive fork 34, dividing the drive fork 34 into two parts to form a double cantilever structure. In yet another embodiment, two adjacent drive forks 34 are joined together at their ends, enclosing the space of the groove 32 between them into a cylindrical hole shape to accommodate the case where the roller 40 is a spherical ball bearing, with the roller 40 accommodated within the cylindrical hole groove 32. All these embodiments can achieve slight bending elastic deformation of the drive fork 34; the specific choice depends on the required elastic stiffness, transmission accuracy, and load-bearing capacity.

Claims

1. An externally excited harmonic reducer, comprising a base (10) and a housing (11), characterized in that, The device includes an externally excited harmonic generator (20), a gear shaft (50), a cage (30), and rollers (40) mounted on the cage (30) arranged around the same rotation axis. The externally excited harmonic generator (20) has an outer ring (21) with an inner cam (22) arranged inwardly. The inner contour of the inner cam (22) has at least one radial protrusion. The gear shaft (50) is a rigid shaft with a plurality of circumferentially distributed external teeth (51) on its outer cylindrical surface. The cage (30) has a plurality of circumferentially distributed and radially radiating grooves (32), each groove (32) accommodating one roller (40). The rollers (40) are needle rollers or ball bearings, and the outer diameter of the rollers (40) is the same as the width of the grooves (32). The rollers (40) and the cage (30) are arranged around the externally excited harmonic generator (20) and the cage (30). Within the radial space between the gear shafts (50), the roller (40) simultaneously contacts and is constrained by the surfaces of the inner cam (22), the slide groove (32), and the outer tooth (51); the number of the outer teeth (51) of the gear shaft (50) is equal to the sum of the number of protrusions of the inner cam (22) and the number of slide grooves (32), or equal to the difference between the number of slide grooves (32) and the number of protrusions of the inner cam (22); the retainer (30) is a thin-walled cylindrical shape, with a rigid base (31) at one end and multiple transmission forks (34) distributed along the circumference at the other end. Two adjacent transmission forks (34) together with the base (31) form a fork shape, and the space between two adjacent transmission forks (34) forms the slide groove (32). The transmission fork (34) is a slender structure that can produce a small amount of bending elastic deformation to compensate for the consistency difference between the multiple rollers (40).

2. The externally excited harmonic reducer according to claim 1, characterized in that, The retainer (30) has a narrow slit (33) on its cylindrical surface along the axial direction. The slit (33) is located at the bottom of the groove (32) or in the middle of the transmission fork (34) to divide the transmission fork (34) into two.

3. The externally excited harmonic reducer according to claim 1, characterized in that, The inner cam (22) has one or two protrusions; when the number of protrusions is one, the inner cam (22) is an inner cylindrical hole that is eccentric to the rotation axis; when the number of protrusions is two, the inner cam (22) is an inner elliptical cylindrical hole whose center is located on the rotation axis.

4. The externally excited harmonic reducer according to claim 1, characterized in that, The externally excited harmonic generator (20) is used to connect to the input shaft (IN); when the gear shaft (50) is fixed, the cage (30) is connected to the output shaft (OUT); when the cage (30) is fixed, the gear shaft (50) is connected to the output shaft (OUT).

5. The externally excited harmonic reducer according to claim 1, characterized in that, The externally excited harmonic generator (20) includes a harmonic bearing (23), and the inner cam (22) is formed by the inner ring bore of the harmonic bearing (23).

6. The externally excited harmonic reducer according to claim 1, characterized in that, The base (10) is provided with a support bearing (12), and the base (31) is installed between the base (10) and the support bearing (12) by interference fit, and is fixed to the base (10) as a whole.

7. The externally excited harmonic reducer according to claim 1, characterized in that, The two adjacent drive forks (34) are joined together at the end, forming a cylindrical hole in the space of the groove (32) between them to accommodate the case where the roller (40) is a spherical ball; the roller (40) is accommodated in the cylindrical groove (32).

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