High-precision low-noise harmonic reducer

Abstract

The high-precision low-noise harmonic reducer comprises a wave generator, a flexible gear and a rigid gear, the wave generator is embedded into the flexible gear and used for driving the flexible gear to generate elastic deformation, and the flexible gear and the rigid gear are in meshing transmission; the wave generator comprises a cam and a flexible bearing arranged on the cam in a sleeving mode, the cam profile of the cam is a cosine cam profile, the flexible bearing is of a four-point contact ball bearing structure, and the flexible bearing is in interference fit with the cam and the flexible gear; a gear ring of the flexible gear is of an involute tooth profile structure, and a correspondingly meshed rigid gear tooth ring is of a conjugate tooth profile conjugate with the involute tooth profile. Through accurate matching of a specific parameter involute tooth profile of the flexible gear and a conjugate tooth profile of the rigid gear, meshing precision and stability are remarkably improved; the first-order derivative and the second-order derivative of the cosine cam contour are continuous, so that the deformation speed and the acceleration of the flexible gear are stably changed, sudden impact is avoided, and the operation noise is greatly reduced; and flexible gear carburizing and quenching, rigid gear hardening and tempering and cam nitriding treatment are further carried out, and the deformation resistance can be improved.

Description

Technical Field

[0001] This invention relates to the field of wave generator processing technology, specifically to a high-precision, low-noise harmonic reducer. Background Technology

[0002] Harmonic reducers are precision transmission mechanisms that rely on the elastic deformation of flexible gears to transmit motion and power. They have advantages such as large transmission ratio, small size, light weight, and smooth transmission, and are widely used in high-end equipment fields such as industrial robots, aerospace equipment, and precision machine tools.

[0003] In existing technologies, the design and manufacturing schemes of harmonic reducers have many limitations: First, the flexure gears mostly adopt standard involute tooth profiles and have unreasonable displacement coefficient designs, which easily lead to tooth overlap interference after long-term operation. At the same time, the flexure gear tooth surfaces are not specifically modified, resulting in uneven distribution of meshing contact pressure, aggravated fatigue deformation of the flexible gears, increased transmission clearance, and decreased positioning accuracy. Second, the wave generator cams generally adopt elliptical profiles, which cause sudden changes in speed and acceleration during the deformation of the flexure gear, resulting in deformation impact and stress concentration. Noise increases significantly under high-speed operation conditions. The single-row flexible bearings used in some schemes have insufficient deformation resistance, further aggravating vibration and noise problems. Third, the materials and heat treatment processes of the flexure gear, rigid gear, and flexible bearings are poorly matched. The wear resistance of the flexure gear tooth surface is insufficient, and the rolling elements and raceways of the flexible bearing are prone to wear, resulting in a short overall service life of the reducer and high maintenance costs. Fourth, the rigid gear tooth profiles mostly adopt a design that simply adapts to the flexure gear tooth profile without conjugate optimization based on the meshing principle, which limits meshing smoothness and load-bearing capacity.

[0004] In response to the core deficiencies of the existing technologies, there is an urgent need to develop a harmonic reducer that combines high precision, low noise, and long lifespan to meet the high-performance application requirements of high-end equipment. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a harmonic reducer with high precision and low noise performance.

[0006] The technical solution of this invention is to provide a high-precision, low-noise harmonic reducer with the following structure: It includes a wave generator, a flexible wheel, and a rigid wheel. The wave generator is embedded inside the flexible wheel and drives it to undergo elastic deformation. The flexible wheel meshes with the rigid wheel for transmission. The wave generator includes a cam and a flexible bearing sleeved on the cam. The cam's cam profile is a cosine cam profile. The flexible bearing is a four-point contact ball bearing structure, and it is interference-fitted with the cam and the flexible wheel. The flexible wheel's gear ring adopts an involute tooth profile structure, and the corresponding meshing rigid wheel gear ring adopts a conjugate tooth profile that is conjugate to the involute tooth profile. The cam and the input shaft are connected by an involute spline with a spline module of 1mm, 18 teeth, a pressure angle of 30°, and a fit accuracy of H7 / h6, ensuring backlash-free power transmission.

[0007] Preferably, the polar equation of the cosine cam profile is: r = R0 + w·cos(nθ); where r is the polar diameter (i.e., the distance from any point on the cosine profile to the origin), R0 is the base circle radius of the cam (valued at 17.78 mm), w is the maximum deformation of the cam (valued at 0.25 mm), n is the harmonic order (valued at 2, corresponding to a dual-wave harmonic reducer), and θ is the polar angle (the angle between the polar diameter and the polar axis, ranging from 0° to 360°). The cosine cam profile allows for a smooth transition during the deformation process of the flexspline, reducing deformation impact and stress concentration.

[0008] Preferably, the flexible bearing includes an inner ring, an outer ring, and a plurality of rolling elements disposed between the inner ring and the outer ring; the rolling elements are made of zirconia ceramic material, and the inner ring and the outer ring are made of GCr15 bearing steel material.

[0009] Preferably, the surface of the rolling element is polished to a roughness Ra≤0.01μm; the inner and outer rings are quenched and tempered to a hardness of HRC60-64; and the raceways of the inner and outer rings are designed with a convexity of 0.001-0.003mm.

[0010] Preferably, the involute tooth profile is generated using the standard involute equation, and the polar coordinate equation is: r=rb / cosα; Where r is the polar radius at any point on the involute, rb is the base circle radius of the flexure, and α is the pressure angle of the involute at that point; The formula for calculating the base circle radius rb of the flexure is: rb=0.5*mzcosα0; where m is the module, z is the number of teeth, and α0 is the pitch circle pressure angle.

[0011] Preferably, the specific parameters of the involute tooth profile of the flexible gear are: module 0.254mm, number of teeth 200, pitch circle pressure angle 28.6°, addendum coefficient 0.875, clearance coefficient 0.25, displacement coefficient 0 < x < 0.2, and meshing clearance 0.5-2μm; the displacement coefficient is a positive displacement design, used to improve the meshing depth and avoid overlapping interference on both sides of the tooth profile.

[0012] Preferably, the flexible gear adopts an axially modified design, with the tooth surface being drum-shaped along the axial direction. The modification amount is 0.01-0.03mm, in order to reduce the contact pressure during meshing and increase the meshing stiffness.

[0013] As a preferred embodiment, the method for generating the conjugate tooth profile of the rigid wheel is as follows: under the premise that the cosine convex profile of the wave generator and the involute tooth profile parameters of the flexible wheel are determined, the envelope method is used to generate the tooth profile based on the gear meshing principle; by establishing the motion equation of the flexible wheel tooth profile and combining it with the elastic deformation displacement equation of the flexible wheel under the drive of the wave generator, the coordinate values ​​of each discrete point of the rigid wheel tooth profile are calculated, and then the complete tooth profile is generated by smooth fitting using a cubic spline interpolation algorithm; the generation process is constrained by the constant meshing clearance to ensure meshing accuracy.

[0014] Preferably, the inner side of the rigid wheel gear ring is provided with a polyurethane elastic noise reduction coating with a thickness of 0.1-0.2mm and a diamond-shaped anti-slip texture on the surface of the coating. The anti-slip texture is processed by laser engraving, with a texture spacing of 0.5mm and a depth of 0.02mm. The coating is bonded and fixed by epoxy resin adhesive, and the curing conditions are 80℃×2h.

[0015] Preferably, the flexible wheel is made of 20CrMnTi alloy structural steel, which has been carburized and quenched to a thickness of 0.8-1.2mm and a surface hardness of HRC58-62; the rigid wheel is made of 40Cr alloy structural steel, which has been quenched and tempered to a hardness of HRC28-32; and the cam surface is nitrided to a thickness of 0.15-0.25mm.

[0016] With the above structure, the high-precision, low-noise harmonic reducer of the present invention has the following advantages compared with the prior art: 1. This invention significantly improves meshing accuracy and stability by precisely matching the involute tooth profile of the flexible wheel with the conjugate tooth profile of the rigid wheel using specific parameters; combined with the positive displacement design of 0 < x < 0.2, it greatly increases the meshing depth and avoids tooth overlap interference; the axial drum-shaped modification reduces the contact pressure to below 175MPa, a reduction of more than 30%, significantly increases the meshing stiffness, reduces the transmission error to 33 Arc sec, and achieves a repeatability accuracy of 36 Arc sec, effectively reducing vibration and tooth surface wear.

[0017] 2. The cosine convex profile of this invention has continuous first and second derivatives, which makes the deformation speed and acceleration of the flexible wheel change smoothly without sudden impact. Combined with the ceramic rolling element flexible bearing (low coefficient of friction) and the polyurethane noise reduction coating of the rigid wheel (absorbs vibration energy), the operating noise at the rated speed is ≤55dB, which is 15-20dB lower than the prior art, and the operating noise is significantly reduced.

[0018] 3. This invention uses a combination of materials and processes, including 20CrMnTi carburizing and quenching for the flexible wheel, 40Cr tempering for the rigid wheel, and nitriding for the cam, to ensure the wear resistance and strength of the core components. The four-point contact structure of the flexible bearing, the raceway convexity design, and the interference fit enhance the resistance to deformation and the transmission stability, delay the fatigue failure of the flexible wheel, and extend the overall service life of the reducer by more than 50% compared with the prior art, thus significantly reducing maintenance costs.

[0019] 4. The positive displacement design increases the tooth surface contact area and, combined with the improved meshing stiffness, significantly enhances the reducer's load-bearing capacity, making it suitable for the heavy-duty operating conditions of high-end equipment. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention.

[0021] Figure 2 This is a schematic diagram of the flexible bearing in this invention.

[0022] Figure 3 This is a backlash test diagram for the present invention.

[0023] Figure 4 This is a torsional stiffness test diagram of the present invention.

[0024] Figure 5 This is a transmission error test diagram for the present invention.

[0025] Figure 6 This is a noise test diagram of the present invention.

[0026] Explanation of reference numerals in the attached figures: 1. Wave generator; 11. Cam; 12. Flexible bearing; 121. Inner ring; 122. Outer ring; 123. Rolling element; 2. Flexible wheel; 3. Rigid wheel. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] In the description of this invention, it should be understood that the terms "inner" and "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0029] like Figures 1-6 As shown, this invention discloses a high-precision, low-noise harmonic reducer, which includes a wave generator 1, a flexible wheel 2, and a rigid wheel 3. The wave generator 1 is embedded inside the flexible wheel 2 and is used to drive the flexible wheel 2 to undergo elastic deformation. The flexible wheel 2 meshes with the rigid wheel 3 for transmission.

[0030] The wave generator 1 includes a cam 11 and a flexible bearing 12 sleeved on the cam 11. The cam profile of the cam 11 adopts a cosine cam profile. The polar coordinate equation of the cosine cam profile of the cam 11 is: r = R0 + w·cos(nθ); where r is the polar diameter (i.e., the distance from any point on the cosine profile to the origin), R0 is the base circle radius of the cam (value is 17.78mm), w is the maximum deformation of the cam (value is 0.25mm), n is the harmonic order (value is 2, corresponding to a dual-wave harmonic reducer), and θ is the polar angle (the angle between the polar diameter and the polar axis, with a value range of 0°-360°), i.e., r = 17.78 + 0.25·cos(2θ); the cosine cam profile can make the deformation process of the flexible wheel smooth and reduce deformation impact and stress concentration. The surface of the cam 11 is nitrided, and the nitriding layer thickness is 0.2mm.

[0031] The flexible bearing 12 adopts a four-point contact ball bearing structure. The flexible bearing 12 includes an inner ring 121, an outer ring 122, and several rolling elements 123 disposed between the inner ring 121 and the outer ring 122. The rolling elements 123 are made of zirconia ceramic material and have a polished surface with a surface roughness Ra=0.008μm. The inner ring 121 and outer ring 122 are made of GCr15 bearing steel and have undergone quenching and tempering treatment, with a hardness of HRC60-64. The raceways of the inner ring 121 and outer ring 122 have a convex design with a convexity value of 0.002mm.

[0032] The flexible bearing 12 is interference-fitted with the cam 11 and the flexure 2, with an interference of 0.003 mm. The cam 11 is connected to the input shaft by an involute spline with a spline module of 1 mm, 18 teeth, a pressure angle of 30°, and a fit accuracy of H7 / h6.

[0033] The gear ring of flexure 2 adopts an involute tooth profile structure. The involute tooth profile is generated using the standard involute equation, and the polar coordinate equation is: r=rb / cosα, where r is the polar diameter at any point on the involute, rb is the base circle radius of the flexure, and α is the pressure angle of the involute at that point. The formula for calculating the base circle radius rb of the flexure is: rb=0.5*mzcosα0, where m is the module, z is the number of teeth, and α0 is the pressure angle of the special pitch circle adapted to the harmonic reducer transmission.

[0034] The specific parameters of the involute tooth profile of the flexible gear 2 are: module 0.254mm, number of teeth 200, pitch circle pressure angle 28.6°, addendum coefficient 0.875, clearance coefficient 0.25, and displacement coefficient x=0.2 (within the positive displacement range of 0<x<0.2). The meshing clearance is controlled at 2μm. The displacement coefficient is a positive displacement design, which is used to improve the meshing depth and avoid overlapping interference on both sides of the tooth profile.

[0035] The flexible gear 2 adopts an axial profile design, with the tooth surface being drum-shaped along the axial direction. The profile is 0.02mm, which makes the contact area between the flexible gear 2 and the rigid gear 3 reasonably distributed with a wider middle and narrower ends, effectively reducing the local contact pressure on the tooth surface and increasing the meshing stiffness.

[0036] Flexible wheel 2 is made of 20CrMnTi alloy structural steel, which is carburized and quenched. The carburized layer thickness is 1.0mm and the surface hardness is HRC60.

[0037] The rigid wheel 3 gear ring meshing with the flexible wheel 2 adopts a conjugate tooth profile that is conjugate to the involute tooth profile. The rigid wheel 2 has 202 teeth (which, together with the 200 teeth of the flexible wheel, achieves a dual-wave transmission reduction ratio). The method for generating the conjugate tooth profile of the rigid wheel 3 is as follows: under the premise that the cosine cam profile of the wave generator 1 and the involute tooth profile parameters of the flexible wheel 2 are determined, the envelope method is used to generate it based on the gear meshing principle; by establishing the motion equation of the flexible wheel tooth profile and combining it with the elastic deformation displacement equation of the flexible wheel 2 driven by the wave generator 1, the coordinate values ​​of each discrete point of the rigid wheel 3 tooth profile are calculated, and then the complete tooth profile is generated by smooth fitting using a cubic spline interpolation algorithm; the generation process is constrained by a constant meshing clearance to ensure meshing accuracy.

[0038] The inner side of the steel wheel 3 gear ring is coated with a polyurethane elastic noise reduction coating with a thickness of 0.15mm and a diamond-shaped anti-slip texture on the surface. The anti-slip texture is processed by laser engraving, with a texture spacing of 0.5mm and a depth of 0.02mm. The coating is bonded and fixed with epoxy resin adhesive and cured at 80℃ for 2 hours. The steel wheel 3 is made of 40Cr alloy structural steel, which is heat treated to achieve a hardness of HRC30.

[0039] like Figures 3-6 As shown, the performance test data of this invention were all tested using a professional harmonic reducer comprehensive performance test bench. The specific test results are shown in Table 1 below: Test Project Test value Test conditions Tooth gap 9 Arc sec ±1N·m Torsional stiffness 31230~34638 N·m / rad ±50N·m Transmission error 33 Arc sec 500r / min Repeatability 36 Arc sec 500r / min noise 51dB 2000 r / min, 50 N·m Table 1 This invention organically combines a flexible wheel design with specific parameter involute tooth profile + positive displacement + axial drum-shaped modification, a wave generator design with cosine cam profile + ceramic rolling element four-point contact flexible bearing, a rigid wheel design with envelope method conjugate tooth profile + polyurethane noise reduction coating, and targeted material heat treatment processes to achieve the technical goals of high precision, low noise, and long life. Specific features are as follows: Wave generator design: The cam profile is a cosine curve, driving the flex wheel to deform without impact; the flexible bearing adopts a four-point contact ball bearing structure, the rolling element is made of zirconia ceramic material, the inner and outer ring raceways have a convex design, and it adopts an interference fit of 0.002-0.005mm with the cam and flex wheel; the cam and the input shaft are connected by an involute spline, with a fit accuracy of H7 / h6.

[0040] Tooth profile and flexible gear design: The flexible gear ring adopts an involute tooth profile with a module of 0.254mm, 200 teeth, and a pressure angle of 28.6°, combined with a positive displacement design of 0 < x < 0.2 to improve the meshing depth and avoid tooth overlap interference; the flexible gear tooth surface adopts an axial drum-shaped modification with a modification amount of 0.01-0.03mm to reduce contact pressure and increase meshing stiffness.

[0041] Rigid wheel design: The rigid wheel gear ring adopts a conjugate tooth profile generated based on the envelope method and cubic spline interpolation algorithm, with constant meshing clearance as the constraint condition; a polyurethane elastic noise reduction coating is set on the inner side of the rigid wheel gear ring, and anti-slip texture is processed by laser engraving process to improve the noise reduction effect and coating adhesion.

[0042] Materials and heat treatment processes: The flexible wheel is made of 20CrMnTi carburized and quenched, with a surface hardness of HRC58-62; the rigid wheel is made of 40Cr quenched and tempered, with a hardness of HRC28-32; the cam surface is nitrided, with a nitrided layer thickness of 0.15-0.25mm. The materials and processes of each component are well matched to ensure wear resistance and strength.

[0043] Through the above improvements, the present invention has the following beneficial effects compared with the prior art: 1. This invention significantly improves meshing accuracy and stability by precisely matching the involute tooth profile of the flexible wheel with the conjugate tooth profile of the rigid wheel using specific parameters; combined with the positive displacement design of 0 < x < 0.2, it greatly increases the meshing depth and avoids tooth overlap interference; the axial drum-shaped modification reduces the contact pressure to below 175MPa, a reduction of more than 30%, significantly increases the meshing stiffness, reduces the transmission error to 33 Arc sec, and achieves a repeatability accuracy of 36 Arc sec, effectively reducing vibration and tooth surface wear.

[0044] 2. The cosine convex profile of this invention has continuous first and second derivatives, which makes the deformation speed and acceleration of the flexible wheel change smoothly without sudden impact. Combined with the ceramic rolling element flexible bearing (low coefficient of friction) and the polyurethane noise reduction coating of the rigid wheel (absorbs vibration energy), the operating noise at the rated speed is ≤55dB, which is 15-20dB lower than the prior art, and the operating noise is significantly reduced.

[0045] 3. This invention uses a combination of materials and processes, including 20CrMnTi carburizing and quenching for the flexible wheel, 40Cr tempering for the rigid wheel, and nitriding for the cam, to ensure the wear resistance and strength of the core components. The four-point contact structure of the flexible bearing, the raceway convexity design, and the interference fit enhance the resistance to deformation and the transmission stability, delay the fatigue failure of the flexible wheel, and extend the overall service life of the reducer by more than 50% compared with the prior art, thus significantly reducing maintenance costs.

[0046] 4. The positive displacement design increases the tooth surface contact area and, combined with the improved meshing stiffness, significantly enhances the reducer's load-bearing capacity, making it suitable for the heavy-duty operating conditions of high-end equipment.

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-precision, low-noise harmonic reducer, comprising a wave generator (1), a flexible wheel (2), and a rigid wheel (3), wherein the wave generator (1) is embedded inside the flexible wheel (2) and is used to drive the flexible wheel (2) to undergo elastic deformation, and the flexible wheel (2) meshes with the rigid wheel (3) for transmission; characterized in that, The wave generator (1) includes a cam (11) and a flexible bearing (12) sleeved on the cam (11). The cam (11) has a cosine cam profile. The flexible bearing (12) has a four-point contact ball bearing structure. The flexible bearing (12) is interference-fitted with the cam (11) and the flexible wheel (2). The gear ring of the flexible wheel (2) has an involute tooth profile structure. The gear ring of the corresponding meshing rigid wheel (3) has a conjugate tooth profile that is conjugate to the involute tooth profile.

2. The high-precision, low-noise harmonic reducer according to claim 1, characterized in that, The polar equation of the cosine profile of the cam (11) is: r = R0 + w·cos(nθ); Where r is the polar radius, R0 is the base circle radius of the cam, w is the maximum deformation of the cam, n is the harmonic order, and θ is the polar angle.

3. The high-precision, low-noise harmonic reducer according to claim 1, characterized in that, The flexible bearing (12) includes an inner ring (121), an outer ring (122) and a plurality of rolling elements (123) disposed between the inner ring (121) and the outer ring (122); the rolling elements (123) are made of zirconium oxide ceramic material, and the inner ring (121) and the outer ring (122) are made of GCr15 bearing steel material.

4. A high-precision, low-noise harmonic reducer according to claim 3, characterized in that, The surface of the rolling element (123) is polished; the inner ring (121) and the outer ring (122) are quenched and tempered; the raceways of the inner ring (121) and the outer ring (122) are designed with a convexity.

5. A high-precision, low-noise harmonic reducer according to claim 1, characterized in that, The involute tooth profile of the flexible wheel (2) is generated using the standard involute equation, and the polar coordinate equation is: r=rb / cosα; Where r is the polar radius at any point on the involute, rb is the base circle radius of the flexure, and α is the pressure angle of the involute at that point; The formula for calculating the base circle radius rb of the flexure is: rb=0.5*mzcosα0; where m is the module, z is the number of teeth, and α0 is the pitch circle pressure angle.

6. A high-precision, low-noise harmonic reducer according to claim 5, characterized in that, The specific parameters of the involute tooth profile of the flexible wheel (2) are: module 0.254mm, number of teeth 200, pitch circle pressure angle 28.6°, tooth addendum coefficient 0.875, tooth clearance coefficient 0.25, displacement coefficient 0 < x < 0.2, and meshing clearance 0.5-2μm; the displacement coefficient is a positive displacement design, used to improve the meshing depth and avoid overlapping interference on both sides of the tooth profile.

7. A high-precision, low-noise harmonic reducer according to claim 1, characterized in that, The flexible wheel (2) adopts an axial profile design, with the tooth surface being drum-shaped along the axial direction.

8. A high-precision, low-noise harmonic reducer according to claim 1, characterized in that, The method for generating the conjugate tooth profile of the rigid wheel (3) is as follows: under the premise that the cosine convex profile of the wave generator (1) and the involute tooth profile parameters of the flexible wheel (2) are determined, the envelope method is used to generate the tooth profile based on the gear meshing principle; by establishing the motion equation of the flexible wheel tooth profile and combining the elastic deformation displacement equation of the flexible wheel (2) driven by the wave generator (1), the coordinate values ​​of each discrete point of the tooth profile of the rigid wheel (3) are calculated, and then the complete tooth profile is generated by smooth fitting using the cubic spline interpolation algorithm; the generation process is constrained by the constant meshing clearance to ensure meshing accuracy.

9. A high-precision, low-noise harmonic reducer according to claim 8, characterized in that: The inner side of the tooth ring of the rigid wheel (3) is provided with a polyurethane elastic noise reduction coating, and the surface of the coating has a diamond-shaped anti-slip texture.

10. A high-precision, low-noise harmonic reducer according to claim 1, characterized in that: The flexible wheel (2) is made of 20CrMnTi alloy structural steel and is carburized and quenched; the rigid wheel (3) is made of 40Cr alloy structural steel and is quenched and tempered; the cam surface is nitrided.

Images