Collimating direct-drive joint and transmission transparency design method thereof

Abstract

The invention discloses a collimated direct-driven joint and a transmission transparency design method thereof, and belongs to the field of robot joint design. The method comprises the following steps: determining key parameters needing collaborative optimization of a speed reducer and a motor based on a transmission transparency evaluation system containing quick response capability and torque sensing capability; and carrying out relevance matching and synchronous optimization design on key parameters in order to simultaneously improve the capabilities of the two aspects. The transmission transparency design method of the system is established for the first time, and the interaction safety and response performance of the joints are remarkably improved through parameter collaborative optimization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of robots, in particular to the design of robot joints, and more particularly to a design method for improving the transmission transparency of a quasi-parallel drive joint and a quasi-parallel drive joint manufactured using the method. BACKGROUND

[0002] There are three types of robot joints: rigid joints, elastic joints, and quasi-parallel drive joints. Among them, the quasi-parallel drive joint has great application potential in humanoid robots due to its small axial size, fast response, low cost, and high interaction safety. Transmission transparency is a key indicator for measuring the interaction safety and dynamic performance of a quasi-parallel drive joint, which directly affects the ability of the robot to perceive and respond to external forces. However, there is currently a lack of a systematic and quantitative method to guide the design of quasi-parallel drive joints to improve their transmission transparency, which restricts the optimization of joint performance and thus affects the technical maturity and industrial landing of humanoid robots. Therefore, there is an urgent need to establish a method that can clearly guide the design and effectively improve the transmission transparency of quasi-parallel drive joints. SUMMARY

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

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: In a first aspect, the present application provides a transmission transparency design method for a quasi-parallel drive joint, which comprises: Based on a transmission transparency evaluation system, determining the key parameters that need to be optimized in coordination in the reducer and motor design stages of the quasi-parallel drive joint, the key parameters at least including the forward drive efficiency, reverse drive efficiency, and moment of inertia of the reducer, and the cogging torque and moment of inertia of the motor; With the goal of simultaneously improving the fast response capability and torque perception capability in the transmission transparency evaluation system, performing correlation matching and synchronous optimization design on the key parameters to obtain the reducer and motor design parameters that meet the pre-set joint requirement specifications.

[0005] Preferably, the transmission transparency evaluation system includes the ratio of the reverse drive torque to the maximum output torque, the torque control bandwidth for evaluating the fast response capability, and the correlation between the motor current and the output torque for evaluating the torque perception capability.

[0006] In a second aspect, the present application provides a quasi-parallel drive joint, the reducer and motor of which are designed and manufactured using the design method described above.

[0007] Compared with the prior art, the present application has the following advantages: 1. The first complete set of collinear drive joint transmission transparency evaluation system and quantitative design method is proposed, which fills the gap of systematic design theory in this field.

[0008] 2. By revealing the internal relationship between transmission transparency performance indicators (such as counter-torque ratio) and underlying component design parameters (such as reducer efficiency, motor tooth slot torque), a clear direction and basis for design optimization is provided.

[0009] 3. Creatively propose to match and optimize the key parameters of the reducer and motor in a "correlation", rather than independent design, so as to systematically and collaboratively improve the fast response ability and torque perception ability of the joint, and ultimately realize the overall optimization of transmission transparency, significantly improve the interactive safety and dynamic performance of the robot joint. BRIEF DESCRIPTION OF DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings, wherein: Figure 1 It is a typical structure profile schematic diagram of collinear drive joint.

[0011] Figure 2 It is a schematic diagram of the transmission transparency evaluation system of the collinear drive joint proposed by the present application.

[0012] Figure 3 It is a schematic diagram of the relationship between transmission transparency test indicators and reducer and motor design parameters.

[0013] Figure 4 It is a whole design flow chart of the high transmission transparency collinear drive joint of the present application.

[0014] Figure 5 It is a reducer optimization design flow chart in the present application.

[0015] Figure 6 It is a structure diagram of 2K-H planetary reducer.

[0016] Figure 7 It is a principle diagram of outer rotor motor. DETAILED DESCRIPTION

[0017] In order to make the objects, technical solutions and advantages of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0018] The present application provides a collimation drive joint transmission transparency design method, comprising: Based on the transmission transparency evaluation system, the key parameters of the collimation drive joint that need to be optimized in the reducer and motor design stage are determined, and the key parameters at least include the forward drive efficiency, the reverse drive efficiency, the rotational inertia of the reducer, and the cogging torque and the rotational inertia of the motor; In order to simultaneously improve the quick response ability and the torque sensing ability in the transmission transparency evaluation system, the key parameters are associated and matched and are synchronously optimized and designed to obtain the reducer and motor design parameters that meet the preset joint demand specifications.

[0019] It needs to be further explained that the transmission transparency evaluation system comprises: The ratio of the reverse drive torque to the maximum output torque, and the torque control bandwidth are used to evaluate the quick response ability; The correlation of the motor current and the output torque is used to evaluate the torque sensing ability.

[0020] The optimization design of the reducer comprises: The preliminary parameters of the reducer that meet the joint demand specifications are determined, including the inner gear width, the gear material and the modulus; The relationship between the transmission ratio and the forward drive efficiency and the reverse drive efficiency of the reducer is established and analyzed to determine the optimal transmission ratio; The gear tooth number and the modification coefficient are taken as the design variables, the mass, the strength, the outer shape size, the concentric condition, the adjacent condition and the installation condition of the reducer are taken as the constraints, and the minimization of the rotational inertia and the maximization of the forward and reverse drive efficiencies are taken as the optimization objectives to perform the multi-objective optimization design.

[0021] The reducer is a 2K-H type planetary reducer, as shown in Figure 1 The forward drive efficiency is calculated based on the meshing efficiency of the sun gear 1 and the planetary gear 5, the meshing efficiency of the planetary gear 5 and the inner gear 4, the bearing 6 efficiency and the lubrication efficiency; and the reverse drive efficiency is calculated based on the corresponding reverse meshing efficiency.

[0022] The optimized design of the motor specifically includes: 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.

[0023] 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 coefficient.

[0024] 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.

[0025] 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 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. The torque control bandwidth is mainly related to the rotational inertia of the reducer and the motor. 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.

[0026] The present invention also provides a quasi-direct drive joint, wherein the reducer and motor are designed and manufactured using the aforementioned design method.

[0027] The following detailed description of the quasi-direct drive joint transmission transparency design method provided by the present invention is based on specific embodiments.

[0028] Example 1 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.

[0029] 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.

[0030] 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. Figure 5-7 The paper elaborates on the specific optimization design process of the reducer and motor.

[0031] Reducer optimization design (taking the 2K-H planetary reducer as an example): 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.

[0032] 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.

[0033] wherein the reducer mass and the rotational inertia are calculated by the following formulas respectively: (1); (2); wherein, is the inner gear pitch circle radius; is the inner gear material density; is the transmission ratio; is the swing frame width; is the inner gear width; is the ratio of the inner gear outer diameter to the pitch circle diameter. By optimizing the rotational inertia, the joint acceleration and bandwidth can be improved; by optimizing the forward and reverse efficiency, the energy consumption can be reduced, the heat can be reduced, and the linearity of torque transmission and perception can be improved.

[0034] The total engagement efficiency of the reducer is calculated by the following formula: (3); wherein, is the gear engagement efficiency; is the bearing efficiency; is the lubrication efficiency.

[0035] For a 2K-H planetary reducer (inner gear fixed, sun gear input, swing frame output), when the number of planet gear teeth is greater than the number of sun gear teeth, the forward transmission engagement efficiency is calculated by the following formula: (4); The reverse transmission engagement efficiency is calculated by the following formula: (5); wherein, is the engagement efficiency of the sun gear and the planet gear when transmitting forward; is the engagement efficiency of the planet gear and the inner gear when transmitting forward; is the engagement efficiency of the sun gear and the planet gear when transmitting reverse; is the engagement efficiency of the planet gear and the inner gear when transmitting reverse. The calculation formulas are as follows: (6); (7); (8); (9); wherein, is the meshing friction coefficient; is the pressure angle of the gear; , are the addendum circle pressure angles of the sun gear and the planet gear, respectively; is the meshing angle; is the gear pitch; is the degree of coincidence of the sun gear and the planet gear when the transmission is in the forward direction; is the degree of coincidence of the planet gear and the ring gear when the transmission is in the forward direction; is the partial face coincidence degree calculated by the length of the addendum meshing line of the sun gear when the transmission is in the forward direction; is the partial face coincidence degree calculated by the length of the addendum meshing line of the planet gear when the transmission is in the forward direction; is the partial face coincidence degree calculated by the length of the addendum meshing line of the ring gear when the transmission is in the forward direction; is the degree of coincidence of the planet gear and the sun gear when the transmission is in the reverse direction; is the degree of coincidence of the ring gear and the planet gear when the transmission is in the reverse direction; is the partial face coincidence degree calculated by the length of the addendum meshing line of the sun gear when the transmission is in the reverse direction; is the partial face coincidence degree calculated by the length of the addendum meshing line of the planet gear when the transmission is in the reverse direction; is the partial face coincidence degree calculated by the length of the addendum meshing line of the ring gear when the transmission is in the reverse direction. Modeling and optimizing these efficiency formulas can accurately predict and improve the energy loss of the reducer in different transmission directions, which is the key to improving transmission transparency, especially the reverse driving characteristics and torque perception linearity.

[0036] Optimization design of motor (taking outer rotor permanent magnet synchronous motor as an example): First, generate a mass and size relationship diagram according to the motor mass formula (wherein is the motor air gap radius; , is the rotor and stator density; , is the rotor and stator length; , is the rotor and stator thickness) to preliminarily select a smaller air gap radius which helps to reduce the volume and mass of the motor.

[0037] Then, multi-objective optimization is performed. The design variables are mainly the axial length and thickness of the permanent magnet. The constraint conditions are the output torque , no-load speed , rated torque , and rated speed The optimization target is motor inertia Minimize cogging torque Minimize.

[0038] The formula for calculating the motor inertia (outer rotor) is: (10) ; Optimization Can further improve the overall dynamic response of the system.

[0039] Cogging torque is an important factor affecting the counterforce and torque ripple, and its formula is: (11) ; In the formula, is the angle between the rotor rotating to a certain position and the specified stator centerline; is the residual magnetism of the permanent magnet; , are the outer radius of the stator and the inner radius of the rotor, respectively; is the axial length of the permanent magnet; is the least common multiple of the number of armature poles and the number of slots; is the vacuum permeability; is a coefficient related to the motor structure; n is the harmonic number. Optimize cogging torque Can significantly reduce the joint counterforce fluctuation and torque ripple during operation, thereby directly improving the rapid response smoothness and torque perception accuracy in transmission transparency.

[0040] Finally, the optimized reducer and motor parameters are integrated to complete the detailed mechanical, electrical and software design of the joint, and whether the transmission transparency index meets the design requirements is verified through prototype testing. If not, feedback to the parameter allocation step for iterative optimization.

[0041] Example 2 Design a quasi-straight drive joint for a humanoid robot elbow joint. First, determine the requirements: maximum output torque =50 Nm , rated torque =20 Nm , mass not more than 0.8 kg , outer diameter less than 80 mm .

[0042] Requirement analysis and mass allocation: according to the whole machine simulation and experience, set the total mass of the joint target to 0.75 kg . Preliminary allocation of reducer mass target 0.42 kg , motor (including shell) mass target 0.28 kg .

[0043] Preliminary design and parameter optimization of the reducer: Preliminary parameters: the material is 20CrMnTi (density p =7850 kg / m 3 ), the inner gear width b =10 mm , the modulus m =0.6. According to the efficiency model (equations (4)-(9)), the target transmission ratio n =10 is selected.

[0044] Optimization process and results: the number of sun gear teeth , the number of planet gear teeth (3), the number of inner gear teeth and the modification coefficient , , are variables. With the constraints of meeting the strength (contact stress <1200MPa), assembly conditions and mass <0.42kg, the NSGA-II algorithm is used for multi-objective optimization, and the objectives are the minimum moment of inertia , the maximum forward efficiency and the maximum reverse efficiency .

[0045] Example of optimized parameters: a group of Pareto optimal solutions is obtained, and one of them is selected: =20, =18, =58, =0.42, =0.35, =0.1. The calculated mass of this scheme is =0.41 kg , the moment of inertia is =1.7×10 － 4 kg · m 2 . Substitute the tooth profile parameters into equations (6), (7), (8) and (9), take =0.08, and calculate =0.993, =0.992, =0.992, =0.991, and then substitute into equations (4) and (5) to calculate the forward drive efficiency =0.945 and the reverse drive efficiency =0.918 (about 92%).

[0046] Comparative Example (conventional design): conventional design is performed to meet the same transmission ratio and strength requirements, without specifically optimizing the reverse efficiency and inertia. The conventional design scheme parameters can be: = 15, = 21, = 57, standard displacement. Its reverse efficiency ≈ 0.86, moment of inertia = 2.1 x 10 －4 kg · m 2 Compared with the conventional design, the reverse efficiency of the optimized scheme of the present embodiment is improved by about 6 percentage points, and the moment of inertia is reduced by about 19%.

[0047] Motor preliminary design and parameter optimization: Preliminary parameters: based on mass distribution and size constraints, the air gap radius = 21 mm is preliminarily selected according to the mass formula relationship diagram, the number of stator slots = 12, the number of pole pairs = 5, the residual magnetism of the permanent magnet = 1.2 T , the pole arc coefficient = 0.8.

[0048] Optimization process and results: taking the permanent magnet axial length and thickness as variables. With the constraints of meeting the no-load speed > 8000 rpm and the rated point efficiency > 85%, the multi-objective optimization is performed with the objective of minimizing the moment of inertia and the peak value of the cogging torque .

[0049] Optimized parameter example: the optimized solution is obtained: = 20 mm , = 3.5 mm . Through electromagnetic finite element simulation verification, the output torque of the scheme meets the requirements, the moment of inertia = 5.2 x 10 －5 kg · m 2 The cogging torque waveform conforms to formula (11), and its peak value is calculated as 0.16 Nm , which accounts for 0.8% of the rated torque 20 Nm .

[0050] Comparative Example (conventional design): conventional motor design aiming at the same output torque and speed, not specially optimized for cogging torque, its cogging torque peak value Generally up to 0.4-0.5 Nm , about 2%-2.5% of the rated torque. It can be seen that the cogging torque peak value of the embodiment is reduced by about 60%-70%.

[0051] Integration and testing: integrate the optimized reducer and motor parameters, complete the joint detailed design and manufacture the prototype. Perform performance comparison test under the same test conditions (temperature 25°C, same control algorithm).

[0052] Prototype test results of the embodiment: Back-drive torque to maximum output torque ratio: 11.5%.

[0053] Torque control bandwidth (-3dB): 152 Hz .

[0054] Linear correlation coefficient of motor current and output torque: 0.996.

[0055] Prototype test results of the comparative example (using a reducer and motor of conventional design): Back-drive torque to maximum output torque ratio: 22%.

[0056] Torque control bandwidth (-3dB): 88 Hz .

[0057] Linear correlation coefficient of motor current and output torque: 0.965.

[0058] Test result analysis: compared with the comparative example not optimized by the method of the present application, the collimating drive joint obtained by the collaborative optimization design method of the embodiment has significantly improved in three core indicators representing transmission transparency: back-drive torque ratio is reduced by about 48%, control bandwidth is increased by about 73%, and current-torque correlation coefficient is increased to close to 1. This fully verifies the effectiveness of the design method proposed in the present application in systematically improving the transmission transparency of the collimating drive joint.

[0059] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, any equivalent structural transformation made under the inventive concept of the present application, or direct / indirect application in other related technical fields, should be included in the protection scope of the present application.

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 the design parameters of the reducer and motor that meet the preset joint requirements.

2. The method according to claim 1, characterized in that, 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.

3. The method according to claim 1 or 2, 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.

4. The method according to claim 3, 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.

5. The method according to claim 1 or 2, 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.

6. The method according to claim 5, 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.

7. The method according to claim 2, characterized in that, 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.

8. The method according to claim 1 or 2, characterized in that, 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 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. The torque control bandwidth is mainly related to the rotational inertia of the reducer and the motor. 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.

9. 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 8.

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