Cam suitable for light-weight high-load harmonic reducer

Abstract

The invention discloses a cam suitable for a light-weight high-load harmonic reducer. A method comprises the following steps: step 1, structural design: step 1.1, a foundation structure; step 1.2, key parameter matching; step 1.3, performing function adaptation; step 2, processing and manufacturing: step 2.1, early-stage preparation; step 2.2, rough machining; step 2.3, heat treatment; step 2.4, finish machining is carried out; step 2.5, detecting and calibrating; step 3, assembling and transmission: step 3.1, assembling process; and step 3.2, transmission principle. Compared with the prior art, the transmission mechanism has the advantages that the meshing performance and the bearing capacity are improved, the service life is prolonged, the transmission precision is guaranteed, and a compact structure is adapted.

Description

Technical Field

[0001] This invention relates to the field of harmonic reducer technology, and in particular to a cam suitable for use in lightweight, high-load harmonic reducers. Background Technology

[0002] Harmonic reducers consist of a rigid wheel, a flexible wheel, and a wave generator (including a cam and flexible bearings). The cam, as the core component of the wave generator, achieves meshing transmission by driving the flexible wheel to deform elastically. Its profile design directly determines the transmission accuracy, smoothness, and lifespan. Traditional cams often use an elliptical profile, suitable for second harmonic drives. However, with the increasing demands for lightweight, high-speed, low-noise, and high-load capacity in collaborative robots, precision equipment, and other fields, elliptical cams are gradually showing limitations in stress distribution and vibration control.

[0003] The existing harmonic reducer cam is the core component of the wave generator, mainly divided into two categories. Its core function is to drive the flex wheel to generate controllable elastic deformation and realize the tooth transmission: (1) Elliptical cam: The main body is elliptical and connected to the flex wheel through a flexible bearing. When rotating, it forces the flex wheel to deform symmetrically in both directions. The long axis area meshes and the short axis area disengages. The accuracy can reach ±30 arcseconds, which is suitable for precision scenarios such as industrial robot joints. (2) Combined cam: It adopts a three-stage structure of "cam-bearing-flex wheel bushing". The cam has a mounting shaft and is matched with a conventional bearing. The flex wheel bushing directly abuts against the outer ring of the bearing. The structure is more compact and has a stronger load-bearing capacity. In addition, some cam outer surfaces are provided with grooves, which cooperate with the grooves of the flex wheel and have built-in cylindrical rollers to improve the smoothness of motion.

[0004] Defects of existing harmonic reducer cams:

[0005] Defect 1. Stress concentration and easy damage: Cams are mostly thin-walled structures with poor rigidity. They bear large alternating loads during operation. The long shaft is subjected to both deformation force and meshing force, which can easily cause fatigue damage. It is a vulnerable part of the reducer.

[0006] Defect 2. Assembly and fit issues: When the elliptical cam opens the bearing, it will generate large assembly stress, which will easily damage the inner ring of the bearing; the stress distribution of the traditional structure is uneven, which affects the transmission stability.

[0007] Defect 3. Performance limitations: Elliptical type relies on flexible bearings, and although the transmission efficiency is high (92%-96%), the impact resistance is weak and it is not suitable for heavy loads; the combined type has slightly lower efficiency (88%-92%) and needs to balance accuracy and durability.

[0008] Defect 4. High difficulty in processing and inspection: The cam processing technology is complex, the rigidity is difficult to guarantee, and there is a lack of efficient inspection methods, which can easily affect the consistency of product quality. Summary of the Invention

[0009] To address the problems existing in the prior art, the present invention provides a cam suitable for use in lightweight high-load harmonic reducers.

[0010] The technical solution adopted by this invention to solve its technical problem is:

[0011] A cam suitable for use in a lightweight, high-load harmonic reducer, the method comprising the following steps:

[0012] Step 1, Structural Design:

[0013] Step 1.1. Basic structure: It consists of a hollow body and three evenly distributed arc-shaped protrusions. The protrusions are integrally formed with the body and are connected at intervals along the circumference. The outer wall is a smoothly transitioned arc contour.

[0014] Step 1.2. Key parameter matching: The total circumference of the outer wall of the cam is exactly equal to the inner wall circumference of the matching flexible bearing; the height of the protrusion is controlled between 0.1mm and 0.18mm to balance the amount of deformation and rigidity;

[0015] Step 1.3. Functional Adaptation: Designed for harmonic reducers, the flexible bearing is driven by three protrusions, which in turn forces the flexible wheel to form three symmetrical protrusions, thus achieving meshing transmission with the rigid wheel;

[0016] Step 2, Processing and Manufacturing:

[0017] Step 2.1. Preliminary preparation: Determine the contour curve, base circle radius, and protrusion size parameters; select alloy steel such as 20CrMnTi; and use forgings or high-precision bars for the blank.

[0018] Step 2.2. Rough machining: The inner hole, end face and outer surface of the base circle are machined by turning, and the protruding contour is initially shaped by milling, leaving a heat treatment allowance;

[0019] Step 2.3. Heat treatment: Carburizing and quenching or high-frequency induction hardening is used. The surface is heated at 1900℃ for 7-8 seconds to achieve a surface hardness of about 60HRC.

[0020] Step 2.4. Finishing: Use a CNC grinding wheel to finish the cam profile to ensure profile accuracy;

[0021] Step 2.5. Inspection and Calibration: The contour deviation is detected by a coordinate measuring machine, and the heat treatment effect is verified by a hardness tester;

[0022] Step 3: Assembly and Transmission

[0023] Step 3.1. Assembly process: First, fit the inner wall of the flexible bearing with the outer wall of the X-shaped cam, then fix the outer ring of the flexible bearing with the inner ring of the flex wheel to form an integrated wave generator of "cam-flexible bearing-flex wheel"; finally, use screws to fix the cam to the motor shaft through the shims, and apply thread-locking glue to the screws.

[0024] Step 3.2. Transmission principle: When the motor drives the cam to rotate, the three protrusions squeeze the flexible bearing and the flex wheel in sequence, causing the flex wheel to produce periodic three-wave elastic deformation. The protrusions and the rigid wheel alternately mesh and disengage, and the speed reduction transmission is achieved through the tooth difference. The motion law is precisely controlled by the cam profile curve.

[0025] The present invention also has the following additional technical features:

[0026] As a further specific optimization of the technical solution of the present invention: the profile needs to be symmetrical about two orthogonal axes to ensure uniform deformation of the flex wheel, avoid local stress concentration, and ensure transmission stability; the maximum radial deformation of the cam needs to match the radius of the neutral layer of the flex wheel to ensure consistent meshing depth and reduce transmission error; a high-order continuous motion law is adopted to avoid sudden changes in speed and acceleration and reduce vibration and noise during high-speed operation.

[0027] As a further specific optimization of the technical solution of the present invention: determine the base circle radius r0, where r0 is the minimum circumscribed circle radius of the cam; determine the maximum radial deformation Wmax, where Wmax is the distance from the base circle to the vertex of the profile; determine the intersection angle α, where α is the angle between two symmetrical profiles, usually taken as 90°; determine the profile transition fillet R, where R is 3-5mm.

[0028] As a further specific optimization of the technical solution of the present invention: the model is established with the origin of polar coordinates, and the contour curve adopts a "polynomial + sine composite curve" to ensure the continuity of curvature.

[0029] As a further specific optimization of the technical solution of this invention: 40CrNiMoA is selected for general scenarios and quenched and tempered to HRC50-55; 7075 aluminum alloy is used for lightweight scenarios; the contour surface is ground to IT5 precision, and DLC coating is sprayed on key contact surfaces to reduce the friction coefficient to below 0.08.

[0030] As a further specific optimization of the technical solution of the present invention: Finite element analysis (FEA) simulates the deformation process of the cam-driven flexure, optimizes the local curvature of the profile, and reduces the maximum stress of the flexure by 15%-20%; by analyzing the speed and acceleration curves through MATLAB or ADAMS, the acceleration fluctuation is ≤5% when running at high speed of 3000rpm.

[0031] As a further specific optimization of the technical solution of the present invention: the clearance between the flexible bearing and the flexible bearing is controlled at 0.001-0.003mm to ensure transmission accuracy.

[0032] Compared with the prior art, the advantages of this invention are:

[0033] Advantage 1. Improved meshing performance and load-bearing capacity: The structure with alternating and evenly distributed protrusions and transition circles can increase the number of meshing teeth between the flexible wheel and the rigid wheel (about 10% better than the meshing rate of traditional elliptical cams), disperse the force on a single tooth, and improve the overall load-bearing capacity and transmission stability.

[0034] Advantage 2. Extended service life: The outer circumference of the cam is equal to the inner circumference of the mating device, so that it fits tightly after installation and does not expand under overload, reducing wear between the cam and the flexible bearing and flex wheel, and extending the service life of the core components.

[0035] Advantage 3. Ensure transmission accuracy: By optimizing the contour curve design, the meshing backlash can be reduced, achieving near-zero backlash transmission. Combined with high-precision machining (such as long and short axis symmetry control), it meets the requirements of precision control.

[0036] Advantage 4. Adaptable to compact structure: Inheriting the inherent advantages of harmonic reducers, it achieves a large transmission ratio (50-320 for a single stage) in a small volume, which is suitable for the lightweight design requirements of robots and precision equipment. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the cam structure dimensions of the present invention. Detailed Implementation

[0038] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Example 1

[0039] A cam suitable for lightweight, high-load harmonic reducers is described. The X-shaped cam has a four-convex symmetrical structure and is mainly used in harmonic reducers. It is realized through three steps: structural design, processing and manufacturing, and assembly and transmission. The core is to drive the flexible wheel to generate four-wave meshing motion, thereby improving transmission stability.

[0040] The method for designing and manufacturing a cam includes the following steps:

[0041] Step 1: Structural Design

[0042] Step 1.1. Basic structure: It consists of a hollow body and three evenly distributed arc-shaped protrusions. The protrusions are integrally formed with the body and are connected at intervals along the circumference. The outer wall is a smoothly transitioned arc contour.

[0043] Step 1.2. Key parameter matching: The total circumference of the outer wall of the cam is exactly equal to the inner wall circumference of the matching flexible bearing to ensure a tight fit during assembly, which will not damage the bearing and can transmit stable driving force; the height of the protrusion is controlled between 0.1mm and 0.18mm to balance deformation and rigidity.

[0044] Step 1.3. Functional adaptation: Designed for harmonic reducers, the flexible bearing is driven by three protrusions, which in turn forces the flexible wheel to form three symmetrical protrusions, which mesh with the rigid wheel (which has 3 more teeth than the flexible wheel) to achieve transmission.

[0045] Step 2, Processing and Manufacturing:

[0046] Step 2.1. Preliminary preparation: Determine parameters such as contour curve, base circle radius, and protrusion size, and select alloy steel such as 20CrMnTi (for heavy-duty scenarios). The blank should be a forging or high-precision bar stock.

[0047] Step 2.2. Rough machining: The inner hole, end face and outer surface of the base circle are machined by turning, and the protruding contour is initially shaped by milling, leaving a heat treatment allowance.

[0048] Step 2.3. Heat treatment: Carburizing and quenching or high-frequency induction hardening (heating at 1900℃ for 7-8 seconds) is used to make the surface hardness reach about 60HRC, thereby improving wear resistance and fatigue strength.

[0049] Step 2.4. Finishing: Use CNC grinding (CBN grinding wheel) to finish the cam profile to ensure profile accuracy; grind the chamfer to remove burrs and avoid assembly damage.

[0050] Step 2.5. Inspection and Calibration: Use a coordinate measuring machine to check the contour deviation and a hardness tester to verify the heat treatment effect to ensure that the parameters meet the design requirements.

[0051] Step 3, Assembly and Transmission:

[0052] Step 3.1. Assembly process: First, fit the inner wall of the flexible bearing with the outer wall of the X-shaped cam (since the circumference is equal, there is no stress in the fit), then fix the outer ring of the flexible bearing with the inner ring of the flex wheel to form an integrated wave generator of "cam-flexible bearing-flex wheel"; finally, use screws to fix the cam to the motor shaft through the shims, and apply thread sealant to the screws to prevent loosening.

[0053] Step 3.2. Transmission principle: When the motor drives the cam to rotate, the three protrusions squeeze the flexible bearing and the flex wheel in sequence, causing the flex wheel to produce periodic three-wave elastic deformation. The protrusions and the rigid wheel alternately mesh and disengage, and the speed reduction transmission is achieved through the tooth difference. The motion law is precisely controlled by the cam profile curve. Example 2

[0054] The core design principle of cam design and fabrication methods:

[0055] Principle 1. Symmetrical Coordination Principle: The profile must be symmetrical about two orthogonal axes to ensure uniform deformation of the flexible wheel, avoid local stress concentration, and ensure smooth transmission.

[0056] Principle 2. Meshing and Matching Principle: The maximum radial deformation of the cam must match the radius of the neutral layer of the flexspline to ensure consistent meshing depth and reduce transmission errors.

[0057] Principle 3. Dynamic stability principle: Adopt high-order continuous motion laws to avoid sudden changes in speed and acceleration, and reduce vibration and noise during high-speed operation. Example 3

[0058] Key parameter design for cam design and fabrication methods:

[0059] Design 1. Determination of basic parameters:

[0060] Core parameter system: base circle radius r0 (minimum circumscribed circle radius of the cam), maximum radial deformation Wmax (distance from the base circle to the profile vertex), cross angle α (angle between two symmetrical profiles, usually 90°), profile transition fillet R (generally 3-5mm, to avoid stress concentration).

[0061] Typical parameter example: X-shaped cam adapted to type 20 harmonic reducer, base circle radius r0=18mm, maximum radial deformation Wmax=0.22mm, cross angle α=90º, transition fillet R=3.5mm.

[0062] Design 2. Contour Curve Design:

[0063] Design core: The model is established with the origin of polar coordinates (the center of rotation of the cam), and the contour curve adopts a "polynomial + sine composite curve" to ensure the continuity of curvature.

[0064] Key constraints: The joints of each segment of the contour must satisfy the continuity of displacement, velocity, and acceleration, and the maximum radius of curvature must not be less than 1.2 times the radius of the rolling element of the flexible bearing.

[0065] Design 3. Material and Process Selection:

[0066] Material selection: 40CrNiMoA (quenched and tempered to HRC50-55) is used for general applications to ensure strength and wear resistance; 7075 aluminum alloy (hard anodized) is used for lightweight applications, reducing weight by more than 25%.

[0067] Precision manufacturing process: The contoured surfaces are ground (IT5 precision), and key contact surfaces are coated with DLC coating to reduce the coefficient of friction to below 0.08, thereby extending service life.

[0068] Design 4. Simulation and Optimization Verification:

[0069] Finite element analysis (FEA): Simulates the deformation process of a cam-driven flexure, optimizes the local curvature of the profile, and reduces the maximum stress of the flexure by 15%-20%.

[0070] Kinematic simulation: Velocity and acceleration curves are analyzed using MATLAB or ADAMS to ensure no impact peaks and acceleration fluctuations ≤5% during high-speed (3000rpm) operation.

[0071] Clearance optimization: The clearance between the bearing and the flexible bearing is controlled within 0.001-0.003mm to ensure transmission accuracy. Example 4

[0072] Verification of the effectiveness of cam design and fabrication methods in practical applications:

[0073] Verification Scenario 1: Industrial Robot Joints

[0074] In the joint of a certain type of six-axis industrial robot, the X-shaped cam harmonic reducer of this invention was used. After 3,000 hours of continuous operation testing, the maximum stress of the flexible wheel was reduced by 18%, and the transmission error was controlled within ±15 arcseconds. Compared with the traditional elliptical cam solution, the joint motion stability was improved by 25%, and no failures caused by bearing or cam wear occurred.

[0075] Verification Scenario 2: Precision CNC Machine Tool Spindle

[0076] It is applied to the spindle transmission system of high-precision CNC machine tools. By optimizing the contour curve (using a fifth-order polynomial + sine composite curve), zero backlash transmission is achieved, and the spindle radial runout is ≤0.002mm, meeting the IT3 level machining accuracy requirements. At the same time, because the cam and the flexible bearing are closely fitted, after 5000 hours of operation, the wear of the core components is only 1 / 3 of that of the traditional solution.

[0077] Scenario 3: Lightweight Arm of Collaborative Robot

[0078] To address the need for lightweight collaborative robots, 7075 aluminum alloy cams (40% lighter than steel cams) are used, along with DLC coating treatment. While ensuring load-bearing capacity (rated torque increased by 10%), the overall weight of the robot is reduced by 15%. According to actual tests, the vibration acceleration fluctuation is ≤3% during high-speed movement (2m / s), which meets the safety standards for human-robot collaboration.

[0079] The above detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

Claims

1. A cam adapted for use in a lightweight high-load harmonic reducer, the cam comprising: The method comprises the following steps: Step 1, structure design: Step 1.

1. Basic structure: composed of a hollow body and three uniformly distributed arc protrusions, the protrusions are integrally formed with the body, are connected in circumferential direction, and the outer side wall is a smooth transition circular arc profile; Step 1.

2. Key parameter matching: the total circumference of the cam outer side wall is completely equal to the inner wall circumference of the matched flexible bearing; the protrusion height is controlled within 0.1mm-0.18mm, balancing the deformation and rigidity; Step 1.

3. Function adaptation: for the design of a harmonic reducer, the three protrusions drive the flexible bearing, and then force the flexible gear to form three symmetrical protrusions to realize meshing transmission with the rigid gear; Step 2, processing and manufacturing: Step 2.

1. Preliminary preparation: determine the profile curve, base circle radius, protrusion size parameters, select 20CrMnTi alloy steel, and use forged pieces or high-precision bar stock as the blank; Step 2.

2. Rough machining: process the inner hole, end face and base circle outer surface by turning, and mill the protrusion profile to reserve the heat treatment allowance; Step 2.

3. Heat treatment: adopt carburizing quenching or high-frequency induction quenching, heat at 1900℃ for 7-8 seconds, so that the surface hardness reaches about 60HRC; Step 2.

4. Finishing: use CBN grinding wheel for precise grinding of the cam profile to ensure profile accuracy; Step 2.

5. Detection and calibration: detect the profile deviation by a three-coordinate measuring machine, and verify the heat treatment effect by a hardness tester; Step 3, assembly and transmission Step 3.

1. Assembly process: first, fit the inner wall of the flexible bearing with the outer wall of the X-shaped cam, then fix the outer ring of the flexible bearing with the inner ring of the flexible gear, and form an integrated wave generator of "cam-flexible bearing-flexible gear"; finally, fix the cam on the motor shaft through the gasket with screws, and apply thread glue to the screws; Step 3.

2. Transmission principle: when the motor drives the cam to rotate, the three protrusions successively press the flexible bearing and the flexible gear, making the flexible gear produce periodic three-wave elastic deformation, the protrusions alternately mesh with and disengage from the rigid gear, and the speed reduction transmission is realized through the gear difference, and the motion law is accurately controlled by the cam profile curve.

2. The cam according to claim 1, adapted for use in a lightweight high-load harmonic reducer, wherein: The profile needs to be symmetrical about two orthogonal axes to ensure uniform deformation of the flexible gear; the maximum radial deformation of the cam needs to match the neutral layer radius of the flexible gear to ensure consistent meshing depth; high-order continuous motion law is adopted to avoid sudden changes in speed and acceleration.

3. The cam according to claim 1, wherein: Determine the base circle radius r0, which is the minimum circumscribed circle radius of the cam; determine the maximum radial deformation Wmax, which is the distance from the base circle to the profile vertex; determine the intersection angle α, which is the included angle between the two symmetrical profiles, usually 90°; determine the profile transition fillet R, which is 3-5mm.

4. The cam according to claim 1, wherein: Establish the model with the polar coordinate origin, and use "polynomial + sinusoidal composite curve" for the profile curve to ensure continuous curvature.

5. The cam according to claim 1, wherein: In general scenarios, select 40CrNiMoA, quench and temper to HRC50-55; in lightweight scenarios, use 7075 aluminum alloy; the profile surface is processed by grinding with IT5 level precision, and the key contact surface is sprayed with DLC coating to reduce the friction coefficient to below 0.

08.

6. The cam according to claim 1, wherein: Finite element analysis (FEA) is used to simulate the deformation process of cam-driven flexspline, and the local curvature of the profile is optimized to reduce the maximum stress of the flexspline by 15%-20%. The speed and acceleration curves are analyzed by MATLAB or ADAMS, and the acceleration fluctuation is less than or equal to 5% when the flexspline runs at high speed of 3000 rpm.

7. The cam according to claim 1, wherein: The matching gap of the flexspline and the flexible bearing is controlled within 0.001-0.003 mm to ensure the transmission accuracy.

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