A collimating driven joint and its transmission transparency design method

Abstract

The application discloses a collimating driving joint and a transmission transparency design method thereof, and belongs to the field of robot joint design. The method comprises the following steps: based on a transmission transparency evaluation system comprising quick response ability and torque sensing ability, key parameters of a reducer and a motor which need to be cooperatively optimized are determined; and in order to simultaneously improve the two abilities, the key parameters are subjected to correlation matching and synchronous optimization design. The application firstly establishes a systematic transmission transparency design method, and through parameter cooperative optimization, the interactive safety and response performance of the joint are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of robotics, specifically relating to the design of robot joints, and more specifically to a design method for improving the transmission transparency of a collimated drive joint and a collimated drive joint manufactured using this method. Background Technology

[0002] Robot joints are mainly classified into three types: rigid joints, elastic joints, and quasi-direct-drive joints. Among them, quasi-direct-drive joints have shown great application potential in the field of humanoid robots due to their advantages such as small axial dimensions, fast response, low cost, and high interaction safety. Transmission transparency is a key indicator for measuring the interaction safety and dynamic performance of quasi-direct-drive joints, directly affecting the robot's ability to perceive and respond to external forces. However, the industry currently lacks a systematic and quantitative method to guide the design of quasi-direct-drive joints to improve their transmission transparency, which restricts the optimization of joint performance and consequently affects the technological maturity and industrialization of humanoid robots. Therefore, it is urgent to establish a method that can clearly guide the design and effectively improve the transmission transparency of quasi-direct-drive joints. Summary of the Invention

[0003] The present invention aims to overcome the shortcomings of the prior art and provide a systematic design method for high transmission transparency of quasi-direct drive joints and the resulting high-performance joints.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a method for designing the transparency of a quasi-direct drive joint transmission, comprising:

[0006] Based on the transmission transparency evaluation system, the key parameters that need to be optimized in the design stages of the reducer and motor of the quasi-direct drive joint are determined. The key parameters include at least the forward drive efficiency, reverse drive efficiency, and moment of inertia of the reducer, as well as the cogging torque and moment of inertia of the motor.

[0007] With the goal of simultaneously improving the rapid response capability and torque sensing capability in the transmission transparency evaluation system, the key parameters are correlated and synchronously optimized to obtain the design parameters of the reducer and motor that meet the preset joint requirements.

[0008] Preferably, the transmission transparency evaluation system includes the ratio of reverse drive torque to maximum output torque for evaluating rapid response capability, and torque control bandwidth, as well as the correlation between motor current and output torque for evaluating torque sensing capability.

[0009] Secondly, the present invention provides a quasi-direct drive joint, wherein the reducer and motor are designed and manufactured using the design method described above.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] 1. For the first time, a complete evaluation system and quantitative design method for the transparency of quasi-direct drive joint transmission were proposed, filling the gap in systematic design theory in this field.

[0012] 2. By revealing the intrinsic relationship between transmission transparency performance indicators (such as reverse drive torque ratio) and underlying component design parameters (such as reducer efficiency and motor cogging torque), a clear direction and basis are provided for design optimization.

[0013] 3. A creative approach is proposed to perform "correlation matching and synchronization optimization" on the key parameters of the reducer and motor, rather than designing them independently. This systematically and collaboratively improves the joint's rapid response capability and torque sensing capability, ultimately achieving overall optimization of transmission transparency and significantly enhancing the interactive safety and dynamic performance of the robot joint. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0015] Figure 1 This is a schematic cross-sectional view of a typical quasi-direct drive joint.

[0016] Figure 2 This is a schematic diagram of the quasi-direct drive joint transmission transparency evaluation system proposed in this invention.

[0017] Figure 3 This diagram illustrates the relationship between transmission transparency test parameters and the design parameters of the reducer and motor.

[0018] Figure 4 This is a flowchart illustrating the overall design of the high-transmission transparency collimating drive joint of the present invention.

[0019] Figure 5 This is a flowchart of the speed reducer optimization design in this invention.

[0020] Figure 6 This is a simplified structural diagram of the 2K-H planetary reducer.

[0021] Figure 7 This is a simplified schematic diagram of an external rotor motor. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] This invention provides a method for designing the transparency of a quasi-direct drive joint transmission, comprising:

[0024] Based on the transmission transparency evaluation system, the key parameters that need to be optimized in the design stages of the reducer and motor of the quasi-direct drive joint are determined. The key parameters include at least the forward drive efficiency, reverse drive efficiency, and moment of inertia of the reducer, as well as the cogging torque and moment of inertia of the motor.

[0025] With the goal of simultaneously improving the rapid response capability and torque sensing capability in the transmission transparency evaluation system, the key parameters are correlated and synchronously optimized to obtain the design parameters of the reducer and motor that meet the preset joint requirements.

[0026] It should be further explained that the transmission transparency evaluation system includes:

[0027] The ratio of reverse drive torque to maximum output torque, and torque control bandwidth, are used to evaluate fast response capability.

[0028] The correlation between motor current and output torque is used to evaluate torque sensing capability.

[0029] The optimization design of the reducer specifically includes:

[0030] Determine the preliminary parameters of the reducer that meet the joint requirements, including the width of the internal gear, gear material, and module;

[0031] Establish and analyze the relationship between the transmission ratio and the forward and reverse drive efficiency of the reducer in order to determine the optimal transmission ratio;

[0032] Using the number of gear teeth and the displacement coefficient as design variables, and the reducer mass, strength, dimensions, concentricity, adjacency, and installation conditions as constraints, the optimization objectives are to minimize the moment of inertia and maximize the efficiency of forward and reverse driving. Multi-objective optimization design is then performed.

[0033] The reducer is a 2K-H type planetary reducer, such as Figure 1As shown, the system includes a sun gear 1, a motor rotor 2, a motor stator 3, an internal gear 4, planetary gears 5, bearings 6, an encoder 7, a control board 8, and a rotating frame 9. Its forward drive efficiency is calculated based on the meshing efficiency of the sun gear 1 and planetary gears 5, the meshing efficiency of the planetary gears 5 and internal gear 4, the efficiency of bearing 6, and the lubrication efficiency; the reverse drive efficiency is calculated based on the corresponding reverse meshing efficiency.

[0034] The optimization design of the motor specifically includes:

[0035] Based on the predetermined relationship between motor mass and axial dimension and air gap radius, the air gap radius of the motor is initially determined;

[0036] Using the axial dimension of the permanent magnet as the design variable, the output torque and speed requirements as constraints, and minimizing the moment of inertia and cogging torque as the optimization objective, a multi-objective optimization design is performed.

[0037] The motor is an external rotor type permanent magnet synchronous motor, and its cogging torque is characterized and optimized by a model that includes the number of stator slots, rotor position angle and harmonic coefficients.

[0038] The optimization of the ratio of the reverse drive torque to the maximum output torque is related to the transmission ratio, reverse drive efficiency, and moment of inertia of the reducer, as well as the moment of inertia and cogging torque of the motor; the optimization of the torque control bandwidth is related to the moment of inertia of the reducer and the motor; the optimization of the correlation between the motor current and the output torque is related to the forward drive efficiency and reverse drive efficiency of the reducer, as well as the current-torque characteristic curve of the motor.

[0039] The method is optimized based on a pre-established quantitative correlation model between the transmission transparency index and design parameters, wherein:

[0040] The ratio of the reverse drive torque to the maximum output torque is mainly related to the transmission ratio, reverse drive efficiency, moment of inertia of the reducer, and the moment of inertia and cogging torque of the motor.

[0041] The torque control bandwidth is mainly related to the rotational inertia of the reducer and the motor.

[0042] The correlation between motor current and output torque is mainly related to the forward drive efficiency and reverse drive efficiency of the reducer, as well as the current-torque characteristics of the motor.

[0043] The present invention also provides a quasi-direct drive joint, wherein the reducer and motor are designed and manufactured using the aforementioned design method.

[0044] The following detailed description of the quasi-direct drive joint transmission transparency design method provided by the present invention is based on specific embodiments.

[0045] Example 1

[0046] The core of this invention lies in establishing a systematic design process from performance targets to design parameters. First, a transmission transparency evaluation system is defined. For example... Figure 2 As shown, this system comprises two dimensions: first, rapid response capability, evaluated by the ratio of joint reverse drive torque to maximum output torque (a smaller ratio indicates easier reverse drive and faster response) and torque control bandwidth (higher bandwidth indicates faster dynamic response); second, torque sensing capability, evaluated by the correlation between motor current and output torque (higher correlation indicates more accurate current-sensing of output torque). The establishment of this system provides clear optimization objectives for the entire design process.

[0047] Secondly, clearly defining the correlation model between performance indicators and design parameters is the foundation for targeted optimization. For example... Figure 3 As shown, the ratio of the joint's reverse drive torque to its maximum output torque is mainly related to the reducer's transmission ratio, the reducer and motor's moment of inertia, the reducer's reverse drive efficiency, and the motor's cogging torque. Optimizing these parameters (such as improving reverse drive efficiency and reducing cogging torque) can effectively reduce the reverse drive force, thereby improving rapid response capability, making the joint easier to be driven by external forces, and improving interaction safety. The torque control bandwidth is mainly related to the reducer and motor's moment of inertia. Reducing the moment of inertia can directly increase the bandwidth, enabling the joint to track torque commands faster and improving dynamic response speed. The correlation between motor current and output torque is related to the reducer's forward drive efficiency, reverse drive efficiency, and the motor's own current-torque relationship curve (linearity). Improving forward / reverse efficiency and optimizing the motor's electromagnetic design to improve current-torque linearity can enhance the correlation, improve the joint's torque sensing accuracy, and achieve more precise force control.

[0048] Based on the above evaluation system and correlation model, the overall design process proposed in this invention is as follows: Figure 4 As shown below. Figures 5-7 The paper elaborates on the specific optimization design process of the reducer and motor.

[0049] Reducer optimization design (taking the 2K-H planetary reducer as an example):

[0050] The first step is to determine the width of the internal gear based on the overall requirements of the joint (such as mass, shape, torque, and speed). Gear material (determines density) ) and modulus Preliminary parameters are obtained. The transmission ratio is generated. With the positive drive efficiency of the reducer Reverse drive efficiency The relationship curve is used to determine the optimal transmission ratio. This step initially filters out the transmission ratio range that is beneficial to transmission transparency from an efficiency perspective.

[0051] The second step, after determining parameters such as the transmission ratio, is to perform multi-objective optimization. The design variable is the number of teeth on the sun gear. Number of planetary gear teeth Number of teeth on internal gears And its displacement coefficient. The constraint condition is the mass of the reducer. The optimization objectives include considering gear contact and bending strength, overall dimensions, and the concentricity, adjacency, and assembly conditions of the planetary gear train. The goal is to minimize the rotational inertia of the reducer. Minimize, while maximizing positive drive efficiency and reverse drive efficiency maximize.

[0052] Among them, the mass of the reducer and moment of inertia The calculation formulas are as follows:

[0053] (1);

[0054] (2);

[0055] In the formula, The pitch circle radius of the internal gear; The density of the internal gear material; The transmission ratio; The width of the rotating frame; The width of the internal gear; This is the ratio of the outer diameter of the internal gear to the pitch circle diameter. By optimizing the moment of inertia, the acceleration and bandwidth of the joint can be increased; by optimizing forward and reverse efficiency, energy consumption, heat generation, and the linearity of torque transmission and sensing can be reduced.

[0056] Total meshing efficiency of the reducer The formula is:

[0057] (3);

[0058] In the formula: For gear meshing efficiency; For bearing efficiency; For lubrication efficiency.

[0059] For a 2K-H planetary reducer (internal gear fixed, sun gear input, carrier output), when the number of teeth on the planet gears is greater than the number of teeth on the sun gear, its forward transmission meshing efficiency is... The calculation formula is:

[0060] (4);

[0061] Reverse transmission meshing efficiency The calculation formula is:

[0062] (5);

[0063] in, When the transmission is in the forward direction, the meshing efficiency between the sun gear and the planet gears; When the transmission is in the forward direction, the meshing efficiency between the planetary gear and the internal gear; When the transmission is in reverse, the meshing efficiency of the sun gear and planet gears; The meshing efficiency between the planetary gears and the internal gear when the transmission is in reverse. The calculation formulas are as follows:

[0064] (6);

[0065] (7);

[0066] (8);

[0067] (9);

[0068] In the formula, The coefficient of meshing friction; The gear pressure angle; , These are the pressure angles of the addendum circles of the sun gear and planet gear, respectively. The engagement angle; The gear tooth pitch; When the transmission is in the forward direction, the degree of overlap between the sun gear and the planet gears is measured. When the transmission is in the forward direction, the degree of overlap between the planetary gears and the internal gears; For forward transmission, the partial end face overlap is calculated based on the length of the sun gear tooth tip meshing line; For forward transmission, the partial end face overlap is calculated based on the length of the planetary gear tooth tip meshing line; For forward transmission, the partial end face overlap is calculated based on the length of the meshing line at the tooth tip of the internal gear; When the transmission is in reverse, the degree of overlap between the planetary gears and the sun gear; When the transmission is in reverse, the degree of overlap between the internal gear and the planetary gear; When the transmission is in reverse, the partial end face overlap is calculated based on the length of the sun gear tooth tip meshing line; When the transmission is in reverse, the partial end face overlap is calculated based on the length of the planetary gear tooth tip meshing line; For reverse transmission, the partial end face overlap is calculated based on the length of the meshing line at the tip of the internal gear. Modeling and optimizing these efficiency formulas can accurately predict and improve the energy loss of the reducer in different transmission directions, which is key to improving transmission transparency (especially reverse drive characteristics and torque sensing linearity).

[0069] Optimized motor design (taking an external rotor permanent magnet synchronous motor as an example):

[0070] First, according to the motor mass formula (in The air gap radius of the motor; , For rotor and stator densities; , For rotor and stator lengths; , Generate a mass-to-dimensional relationship diagram for the rotor and stator thicknesses, and initially select a smaller air gap radius while satisfying constraints. This helps reduce the size and weight of the motor.

[0071] Then, multi-objective optimization was performed. The main design variable was the axial length of the permanent magnet. and thickness The constraint is that the output torque must be satisfied. No-load speed Rated torque and rated speed The optimization objective is the motor's rotational inertia. Minimize and cogging torque minimize.

[0072] The formula for calculating the moment of inertia of an electric motor (external rotor) is:

[0073] (10);

[0074] optimization This can further improve the overall dynamic response of the system.

[0075] Cogging torque It is an important factor affecting the counter-driving force and torque pulsation, and its calculation formula is:

[0076] (11);

[0077] In the formula, The angle between the rotor and the specified stator centerline when the rotor rotates to a certain position; Remanence of permanent magnets; , These are the outer radius of the stator and the inner radius of the rotor, respectively. This refers to the axial length of the permanent magnet. It is the least common multiple of the number of armature poles and the number of slots; The vacuum permeability; Here are the coefficients related to the motor structure; n is the harmonic order. Optimize cogging torque. It can significantly reduce the fluctuation of the joint's counter-drive force and the torque pulsation during operation, thereby directly improving the rapid response smoothness and torque sensing accuracy in transmission transparency.

[0078] Finally, the optimized reducer and motor parameters are integrated to complete the detailed mechanical, electrical, and software design of the joint. Prototype testing is then used to verify whether the transmission transparency index meets the design requirements. If not, feedback is fed back to the parameter allocation step for iterative optimization.

[0079] Example 2

[0080] Design a collimated direct-drive joint for the elbow joint of a humanoid robot. First, determine the required specifications: maximum output torque. =50 Nm Rated torque =20 Nm The mass does not exceed 0.8 kg Outer diameter less than 80 mm .

[0081] Requirements Analysis and Quality Allocation: Based on whole-machine simulation and experience, a total joint mass target of 0.75 is set. kg The initial target mass for the reducer is 0.42. kg The target mass of the motor (including the casing) is 0.28. kg .

[0082] Preliminary design and parameter optimization of the speed reducer:

[0083] Preliminary parameters: The selected material is 20CrMnTi (density) ρ =7850 kg / m 3 ), set the width of the internal gear b =10 mm Modulus m =0.6. Based on the efficiency model (formulas (4)-(9)), the target transmission ratio is selected. n =10.

[0084] Optimization process and results: based on the number of teeth on the sun gear Number of planetary gear teeth (3), number of teeth on the internal gear and displacement coefficient , , As variables. To meet the requirements of strength (contact stress <1200MPa), assembly conditions, and mass. With a constraint of <0.42kg, the NSGA-II algorithm is used for multi-objective optimization, with the objective being the rotational inertia. Minimum, positive efficiency Maximum and reverse efficiency maximum.

[0085] Example of optimized parameters: A set of Pareto optimal solutions is obtained, and one example is selected: =20, =18, =58, =0.42, =0.35, =0.1. The calculated mass of this scheme is... =0.41 kg Moment of inertia =1.7×10 － 4 kg · m 2 Substitute the tooth profile parameters into formulas (6)(7)(8)(9) and take... =0.08, calculated as follows =0.993, =0.992, =0.992, =0.991, then substitute into formulas (4) and (5) to calculate the positive drive efficiency. =0.945, reverse drive efficiency =0.918 (approximately 92%).

[0086] Comparative Design (Conventional): A conventional design is used to meet the same transmission ratio and strength requirements, without specifically optimizing reverse efficiency and inertia. The parameters for the conventional design may be: =15, =21, =57, standard displacement. Its reverse efficiency, calculated using the same formula, is... ≈0.86, moment of inertia =2.1×10 －4 kg · m 2 Compared to the conventional design, the optimized scheme in this embodiment improves the reverse efficiency by approximately 6 percentage points and reduces the moment of inertia by approximately 19%.

[0087] Preliminary design and parameter optimization of the motor:

[0088] Preliminary parameters: Based on mass distribution and dimensional constraints, and referring to the relationship diagram of the mass formula, the air gap radius is initially selected. =21 mm Number of stator slots =12, the extreme pair number =5, Remanence of permanent magnet =1.2T Polar arc coefficient =0.8.

[0089] Optimization process and results: Based on the axial length of the permanent magnet and thickness As variables. Constraints include no-load speed > 8000 rpm and rated efficiency > 85%, with rotational inertia as the variable. and cogging torque peak Minimize as the objective for multi-objective optimization.

[0090] Example of optimized parameters: Obtain the optimized solution: =20 mm , =3.5 mm Electromagnetic finite element simulation verified that the output torque of this scheme meets the requirements, and the moment of inertia... =5.2×10 －5 kg · m 2 The cogging torque waveform conforms to the description of formula (11), and its peak value is... The calculated value is 0.16. Nm Relative to rated torque 20 Nm It accounted for 0.8%.

[0091] Comparative Example (Conventional Design): A conventional motor design aimed at achieving the same output torque and speed, without specifically optimizing cogging torque; its peak cogging torque... Typically, it can reach 0.4-0.5. Nm This accounts for approximately 2%-2.5% of the rated torque. Therefore, the peak cogging torque of this embodiment is reduced by approximately 60%-70%.

[0092] Integration and Testing: Integrate the optimized reducer and motor parameters, complete the detailed joint design, and manufacture a prototype. Conduct performance comparison tests under the same test conditions (temperature 25°C, same control algorithm).

[0093] The prototype test results for this embodiment are as follows:

[0094] Ratio of reverse drive torque to maximum output torque: 11.5%.

[0095] Torque control bandwidth (-3dB): 152 Hz .

[0096] The linear correlation coefficient between motor current and output torque is 0.996.

[0097] Comparative prototype (using a conventionally designed reducer and motor) test results:

[0098] Ratio of reverse drive torque to maximum output torque: 22%.

[0099] Torque control bandwidth (-3dB): 88 Hz .

[0100] The linear correlation coefficient between motor current and output torque is 0.965.

[0101] Test Result Analysis: Compared to the comparative example not optimized using the method of this invention, the quasi-direct drive joint obtained through the aforementioned collaborative optimization design method in this embodiment achieves significant improvements in all three core indicators characterizing transmission transparency: the reverse drive torque ratio is reduced by approximately 48%, the control bandwidth is increased by approximately 73%, and the current-torque correlation coefficient is improved to near 1. This fully verifies the effectiveness of the design method proposed in this invention in systematically improving the transmission transparency of quasi-direct drive joints.

[0102] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the inventive concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, should be included within the protection scope of the present invention.

Claims

1. A method for designing transparency in a quasi-direct drive joint transmission, characterized in that, include: Based on the transmission transparency evaluation system, the key parameters that need to be optimized in the design stages of the reducer and motor of the quasi-direct drive joint are determined. The key parameters include at least the forward drive efficiency, reverse drive efficiency, and moment of inertia of the reducer, as well as the cogging torque and moment of inertia of the motor. With the goal of simultaneously improving the rapid response capability and torque sensing capability in the transmission transparency evaluation system, the key parameters are correlated and synchronously optimized to obtain reducer and motor design parameters that meet the preset joint requirements. The transmission transparency evaluation system includes: The ratio of reverse drive torque to maximum output torque, and torque control bandwidth, are used to evaluate fast response capability. The correlation between motor current and output torque is used to evaluate torque sensing capability. The optimization of the ratio of the reverse drive torque to the maximum output torque is related to the transmission ratio, reverse drive efficiency, and moment of inertia of the reducer, as well as the moment of inertia and cogging torque of the motor; the optimization of the torque control bandwidth is related to the moment of inertia of the reducer and the motor; the optimization of the correlation between the motor current and the output torque is related to the forward drive efficiency and reverse drive efficiency of the reducer, as well as the current-torque characteristic curve of the motor. The method is optimized based on a pre-established quantitative correlation model between the transmission transparency index and design parameters, wherein: The ratio of the reverse drive torque to the maximum output torque is related to the gear ratio, reverse drive efficiency, moment of inertia of the reducer, and the moment of inertia and cogging torque of the motor. The torque control bandwidth is related to the rotational inertia of the reducer and the motor. The correlation between the motor current and the output torque is related to the forward drive efficiency and reverse drive efficiency of the reducer, as well as the current-torque characteristics of the motor.

2. The method according to claim 1, characterized in that, The gearbox design is optimized, specifically including: Determine the preliminary parameters of the reducer that meet the joint requirements, including the width of the internal gear, gear material, and module; Establish and analyze the relationship between the transmission ratio and the forward and reverse drive efficiency of the reducer in order to determine the optimal transmission ratio; Using the number of gear teeth and the displacement coefficient as design variables, and the reducer mass, strength, dimensions, concentricity, adjacency, and installation conditions as constraints, the optimization objectives are to minimize the moment of inertia and maximize the efficiency of forward and reverse driving. Multi-objective optimization design is then performed.

3. The method according to claim 2, characterized in that, The reducer is a 2K-H type planetary reducer. Its forward drive efficiency is calculated based on the meshing efficiency of the sun gear and planet gears, the meshing efficiency of the planet gears and internal gears, the bearing efficiency, and the lubrication efficiency; the reverse drive efficiency is calculated based on the corresponding reverse meshing efficiency.

4. The method according to claim 1, characterized in that, The motor design is optimized, specifically including: Based on the predetermined relationship between motor mass and axial dimension and air gap radius, the air gap radius of the motor is initially determined; Using the axial dimension of the permanent magnet as the design variable, the output torque and speed requirements as constraints, and minimizing the moment of inertia and cogging torque as the optimization objective, a multi-objective optimization design is performed.

5. The method according to claim 4, characterized in that, The motor is an external rotor type permanent magnet synchronous motor, and its cogging torque is characterized and optimized by a model that includes the number of stator slots, rotor position angle and harmonic coefficients.

6. A quasi-direct drive joint, characterized in that, The reducer and motor are designed and manufactured using the design method described in any one of claims 1 to 5.

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