Variable stiffness joint external force estimation method based on fusion of current and elastic deformation

Abstract

This invention provides a method for estimating the external force of a variable stiffness joint based on current information. The overall output torque of the joint is set as the sum of the output torques of the position drive module and the stiffness adjustment module, which more closely approximates the actual output torque, thereby improving the accuracy of external force estimation based on current information. Furthermore, all parameters in the dynamic model can be obtained through measurement or identification of dynamic parameters, further reducing the impact of model errors on external force estimation. This invention provides a method for estimating the external force of a variable stiffness joint based on the fusion of current and elastic deformation, improving the resolution of external force estimation under dynamic stiffness and enabling high-precision external force estimation of variable stiffness joints.

Description

Technical Field

[0001] This invention belongs to the field of variable stiffness joint technology for robots, specifically relating to a method for estimating external forces in variable stiffness joints based on the fusion of electric current and elastic deformation. Background Technology

[0002] This application is a divisional application of the patent filed on January 18, 2023, with application number 2023100885343 and invention title "A method and device for estimating external force of a variable stiffness joint".

[0003] Variable stiffness joints, with their compliant properties, are widely used in scenarios where robots interact with their surroundings. In complex interactive tasks, high-precision force sensing is an important future development direction. Traditional force sensing is mainly achieved through external force sensors; however, external force sensors are expensive and their application is limited by constraints such as complex structures and additional installation space.

[0004] In recent years, external force sensing methods other than force sensors have been developed. Chinese Patent 201410112717.5 discloses a method based on H... ∞ A filtered method for estimating the external force of a robotic arm is proposed, deriving a dynamic model without explicit acceleration. The external force is treated as a state variable in the state-space equation, based on H... ∞ Filtering is used to estimate external forces. Chinese Patent 202210279718.3 discloses a method for estimating tactile external forces of a robotic arm based on a mechanistic data hybrid model. It estimates external forces based on current information and uses a supervised statistical learning method of Gaussian process regression to train compensation terms for unmodeled residual dynamic models based on datasets, thereby compensating for unknown disturbances. Chinese Patent 202210207511.5 discloses a method and system for estimating robot external forces based on configuration Jacobi condition number optimization. It uses a generalized momentum observer to estimate the external forces acting on the robot and improves the accuracy of external force estimation by accurately modeling frictional forces. Configuration Jacobi condition number optimization is used to filter the robot configuration, suppressing the influence of joint torque noise and modeling errors on external force estimation.

[0005] However, force estimation based on current information requires an accurate dynamic model. For variable stiffness joints, which use a dual-drive configuration of position motor and stiffness adjustment motor, the complexity of the dynamic model and the unmodeled residual parts restrict the effectiveness of force estimation.

[0006] Since variable stiffness joints have internal compliance properties, external forces can be estimated by detecting the elastic deformation inside the joint. However, this method has a better external force estimation effect under quasi-static stiffness, but its external force estimation effect is often poor under dynamic stiffness.

[0007] Furthermore, for lever-type variable stiffness joints, the maximum allowable external torque of the joint is different under different stiffnesses. Ignoring this factor will lead to saturation output of the detection torque.

[0008] Therefore, how to achieve high-precision external force estimation for variable stiffness joints is an urgent problem to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, such as the complexity of dynamic models and the limitation of unmodeled residual parts in dynamics on the effectiveness of external force estimation, this invention provides a variable stiffness joint external force estimation method based on current information. The overall output torque of the joint is the sum of the output torques of the position drive module and the stiffness adjustment module, which is closer to the actual output torque and improves the accuracy of external force estimation based on current information. All parameters in the dynamic model can be obtained through measurement or dynamic parameter identification, further reducing the impact of model errors on external force estimation.

[0010] To address the problem of high-precision external force estimation for variable stiffness joints in existing technologies, this invention provides a method for estimating external forces for variable stiffness joints based on the fusion of current and elastic deformation. This method improves the resolution of external force estimation under dynamic stiffness and enables accurate high-precision external force estimation for variable stiffness joints.

[0011] Specifically, the present invention achieves the above-mentioned technical objectives through the following technical means.

[0012] This invention provides a method for estimating the external force of a variable stiffness joint based on current information, comprising the following steps:

[0013] Establish dynamic models for the position-driven module and the stiffness adjustment module:

[0014]

[0015] in, and These represent the moments of inertia of the position drive module and the stiffness adjustment module, respectively. and These represent the frictional forces of the position drive module and the stiffness adjustment module, respectively. and These represent the output torques of the position drive module and the stiffness adjustment module, respectively. and θ1 and θ2 represent the input torques of the position drive module and stiffness adjustment module, respectively; θ1 and θ2 represent the output angular displacements of the position drive module and stiffness adjustment module, respectively.

[0016] The moment of inertia in the dynamic model is obtained through dynamic parameter identification methods. and friction The accurate value;

[0017] Measuring current information I of position motor and stiffness adjustment motor p and I s The input torques of the position drive module and the stiffness adjustment module are calculated according to the following formula:

[0018]

[0019] Among them, K pi and K si These represent the total torque constants of the position drive module and the stiffness adjustment module, respectively;

[0020] The calculated input torques of the position drive module and stiffness adjustment module are substituted into the dynamic model of the position drive module and stiffness adjustment module for solution, so as to obtain the output torques of the position drive module and stiffness adjustment module.

[0021] The sum of the output torques of the position drive module and the stiffness adjustment module is calculated as the external force estimate I:

[0022]

[0023] This invention provides a method for estimating the external force of a variable stiffness joint based on the fusion of electric current and elastic deformation, comprising the following steps:

[0024] The external force estimate I is obtained by using the aforementioned external force estimation method based on the current information of a variable stiffness joint;

[0025] External force estimation based on elastic deformation information and stiffness values ​​of variable stiffness joints II;

[0026] Based on external force estimation I and external force estimation II, external force estimates based on the fusion of current and elastic deformation are obtained:

[0027] τ q =K τ τ ei +(1-K τ )τ ec

[0028] Where, τ ei For external force estimation I, τ ec For external force estimation II, K τ This is the fusion coefficient.

[0029] In one embodiment, the step of obtaining the fusion coefficient includes:

[0030] Design a stiffness zone controller and calculate the expected value of stiffness variables based on the estimated external force and maximum external moment constraint at the previous moment.

[0031] The expected value of the stiffness variable is applied to the motion control of the stiffness-adjusting motor to obtain the actual value of the stiffness variable;

[0032] Substituting the actual values ​​of the stiffness variables into the stiffness model yields the updated stiffness values, where the stiffness model is a function of the stiffness variables.

[0033] The obtained stiffness values ​​are substituted into the adaptive fusion coefficient model for calculation to obtain the adaptive fusion coefficients; the adaptive fusion coefficient model is as follows:

[0034]

[0035] in, R represents the absolute value of the derivative of joint stiffness K. w1 and R w2 All are positive integers, satisfying R w2 >R w1 .

[0036] Specifically, a stiffness zone controller is designed, and based on the estimated external force and maximum external moment constraint at the previous moment, the expected values ​​of the stiffness variables are calculated, including:

[0037] A stiffness region controller is designed based on the Lyapunov barrier function.

[0038] For lever-type variable stiffness joints, the Lyapunov barrier function used for stiffness region control is expressed as:

[0039]

[0040] Where η represents the function variable, η=|τ q | / τ em -η0; η0, η1, and η2 are all positive constants and satisfy η0 = η2 = 0.5, η1 < 0.5; τ q τ represents the estimated external torque. em This represents the maximum allowable external moment of the joint under a specific stiffness variable γ, and is related to the stiffness variable γ; |τ q | / τ em The value range is [0,1];

[0041] Based on the Lyapunov barrier function, stiffness adjustment is divided into three regions: stiffness increase region, stiffness decrease region, and constant stiffness region.

[0042] Based on the region involved by the Lyapunov barrier function, its derivative can be expressed as:

[0043]

[0044] Design suitable Make it satisfy To ensure that η is in the constant stiffness region, The expression is:

[0045]

[0046] Where, k η Let k be a constant representing how quickly the stiffness of a lever-type variable stiffness joint transitions from a stiffness-increasing region or a stiffness-decreasing region to a constant stiffness region, and k η Greater than 0;

[0047] According to the definition of η, the derivative of η can be expressed as:

[0048]

[0049] in, The derivative of the stiffness variable γ of the lever-type variable stiffness joint;

[0050] After further sorting, we obtained The expression:

[0051]

[0052] Among them, when stiffness adjustment is divided into three regions based on the Lyapunov barrier function, the parameter η of the Lyapunov barrier function is used.

[0053] When η>η1, it is the region of increased stiffness;

[0054] When η < -η1, this is the region where stiffness decreases;

[0055] When -η1 < η < η1, it is a region of constant stiffness.

[0056] In one embodiment, the step of obtaining the fusion coefficient is as follows:

[0057] Real-time acquisition of stiffness values;

[0058] The obtained stiffness values ​​are substituted into the adaptive fusion coefficient model for calculation to obtain the adaptive fusion coefficients; the adaptive fusion coefficient model is as follows:

[0059]

[0060] in, R represents the absolute value of the derivative of joint stiffness K. w1 and R w2 All are positive integers, satisfying R w2 >R w1 ;

[0061] The expression for the external force estimation II is:

[0062]

[0063] Where K(γ) represents the stiffness value, This indicates elastic deformation inside the joint.

[0064] In another embodiment, the expression for the external force estimation II is:

[0065]

[0066] Where K(γ) represents the stiffness value, This indicates elastic deformation within the joint;

[0067] At this point, the fusion coefficient is the preset value.

[0068] Compared with the prior art, this invention has outstanding substantive features and significant progress, specifically:

[0069] In estimating external forces based on current information, this invention comprehensively considers the dynamic information of the position drive module and the stiffness adjustment module, obtains the output torque of the position drive module and the stiffness adjustment module respectively, and uses the sum of the two as the overall output torque of the joint, making the overall output torque of the joint closer to the actual output torque and improving the accuracy of external force estimation based on current information. The dynamic model of each sub-drive also includes unknown parameters that can be identified through dynamic parameters and measurable angular displacements, further reducing the impact of model errors on external force estimation.

[0070] The external force estimation method for variable stiffness joints proposed in this invention, which integrates current and elastic deformation, achieves the fusion of external force estimation based on current and external force estimation based on elastic deformation information through a fusion coefficient. This overcomes the shortcomings of single external force estimation methods, improves the external force estimation effect under dynamic and quasi-static stiffness, and is suitable for variable stiffness joint systems that require high-precision external force estimation in force interaction scenarios.

[0071] In one embodiment, the present invention designs an adaptive fusion coefficient model based on stiffness variables. The adaptive fusion coefficient changes autonomously with the stiffness value, which can realize a smooth transition between the external force estimation value based on current and the external force estimation value based on elastic deformation, and avoid the jump of the external force estimation value.

[0072] This invention takes into account the different maximum allowable external torques of joints under different stiffnesses. Based on the maximum external torque constraint and the estimated external force value at the previous moment, a stiffness region variable controller is designed to realize the dynamic update of stiffness values, and the stiffness values ​​are closer to the actual stiffness values. By dynamically adjusting the stiffness variable, the stiffness is kept in the constant stiffness region, ensuring that the joint has a small stiffness.

[0073] This invention, based on real-time acquisition of stiffness values ​​and measurement of internal elastic deformation of joints, derives an external force estimation II based on elastic deformation information, thereby improving the resolution of external force estimation under dynamic stiffness. Attached Figure Description

[0074] Figure 1 This is a flowchart of the variable stiffness joint external force estimation method in Example 1;

[0075] Figure 2 This is a flowchart of the variable stiffness joint external force estimation method in Example 1;

[0076] Figure 3 This represents the correspondence between the maximum allowable external torque and the stiffness variable of a lever-type variable stiffness joint.

[0077] Figure 4 A simplified diagram of stiffness region control;

[0078] Figure 5 This is a schematic diagram of the adaptive fusion coefficients;

[0079] Figure 6 A comparison of the results of three different external force estimation methods. Detailed Implementation

[0080] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein similar or identical reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0081] The technical concept of this invention is as follows: In view of the shortcomings of the existing technology, such as the complexity of the dynamic model and the limitation of the effect of external force estimation by the unmodeled residual part of the dynamics, this invention provides a variable stiffness joint external force estimation method based on current information. The overall output torque of the joint is the sum of the output torques of the position drive module and the stiffness adjustment module, which is closer to the actual output torque and improves the accuracy of external force estimation based on current information. The parameters in the dynamic model can all be obtained by measurement or dynamic parameter identification, which further reduces the impact of model error on external force estimation.

[0082] The second technical concept of this invention is as follows: In view of the problem of needing to achieve high-precision external force estimation of variable stiffness joints in the prior art, this invention provides a variable stiffness joint external force estimation method based on the fusion of current and elastic deformation, which improves the resolution of external force estimation under dynamic stiffness and can accurately achieve high-precision external force estimation of variable stiffness joints.

[0083] The following will discuss exemplary embodiments of the invention in detail with reference to the accompanying drawings.

[0084] Example 1

[0085] like Figure 1 As shown, this embodiment provides a method for estimating the external force of a variable stiffness joint based on current information, including the following steps:

[0086] Establish dynamic models for the position-driven module and the stiffness adjustment module:

[0087]

[0088] in, and These represent the moments of inertia of the position drive module and the stiffness adjustment module, respectively. and These represent the frictional forces of the position drive module and the stiffness adjustment module, respectively. and These represent the output torques of the position drive module and the stiffness adjustment module, respectively. and θ1 and θ2 represent the input torques of the position drive module and stiffness adjustment module, respectively; θ1 and θ2 represent the output angular displacements of the position drive module and stiffness adjustment module, respectively.

[0089] The moment of inertia in the dynamic model is obtained through dynamic parameter identification methods. and friction The accurate value;

[0090] Measuring current information I of position motor and stiffness adjustment motor p and I s The input torques of the position drive module and the stiffness adjustment module are calculated according to the following formula:

[0091]

[0092] Among them, K pi and K si These represent the total torque constants of the position drive module and the stiffness adjustment module, respectively;

[0093] The calculated input torques of the position drive module and stiffness adjustment module are substituted into the dynamic model of the position drive module and stiffness adjustment module for solution, so as to obtain the output torques of the position drive module and stiffness adjustment module.

[0094] The sum of the output torques of the position drive module and the stiffness adjustment module is calculated as the external force estimate I:

[0095]

[0096] In estimating external forces based on current information, this invention comprehensively considers the dynamic information of the position drive module and the stiffness adjustment module, obtains the output torque of the position drive module and the stiffness adjustment module respectively, and uses the sum of the two as the overall output torque of the joint, making the overall output torque of the joint closer to the actual output torque and improving the accuracy of external force estimation based on current information. The dynamic model of each sub-drive also includes unknown parameters that can be identified through dynamic parameters and measurable angular displacements, further reducing the impact of model errors on external force estimation.

[0097] Example 2

[0098] This embodiment provides a method for estimating external forces in variable stiffness joints based on the fusion of current and elastic deformation, such as... Figure 2 As shown, it includes the following steps:

[0099] External force estimation I is obtained using the external force estimation method based on the current information of a variable stiffness joint as described in Example 1;

[0100] External force estimation based on elastic deformation information and stiffness values ​​of variable stiffness joints II;

[0101] Based on external force estimation I and external force estimation II, external force estimates based on the fusion of current and elastic deformation are obtained:

[0102] τ q =K τ τ ei +(1-K τ )τ ec

[0103] Where, τ ei For external force estimation I, τ ec For external force estimation II, K τ This is the fusion coefficient.

[0104] It is understandable that the fusion coefficients can be pre-set according to the application scenario's requirements for external force estimation I and external force estimation II.

[0105] In this embodiment, an expression for the external force estimation II is given, specifically:

[0106]

[0107] Where K(γ) represents the stiffness value, This indicates the elastic deformation inside the joint, which is measured using additional sensors.

[0108] In use, the external force estimation II can be obtained by substituting the real-time stiffness value and the measured elastic deformation inside the joint into the external force estimation II expression.

[0109] This embodiment achieves the fusion of external force estimation based on current and external force estimation based on elastic deformation information by using a fusion coefficient. This overcomes the shortcomings of a single external force estimation method, improves the external force estimation effect under dynamic and quasi-static stiffness, and is suitable for variable stiffness joint systems that require high-precision external force estimation in force interaction scenarios.

[0110] Example 3

[0111] This embodiment provides one step for obtaining the fusion coefficient in Embodiment 2, such as... Figure 2 As shown, specifically:

[0112] Design a stiffness region controller based on the estimated external force τ from the previous moment. q and maximum external moment constraint τ em The expected value of the stiffness variable γ was calculated. d .

[0113] The specific steps are as follows:

[0114] Step 1: Design a stiffness region controller based on the Lyapunov barrier function.

[0115] For lever-type variable stiffness joints, the Lyapunov barrier function used for stiffness region control is expressed as:

[0116]

[0117] Where η represents the function variable, η=|τ q | / τ em -η0; η0, η1, and η2 are all positive constants and satisfy η0 = η2 = 0.5, η1 < 0.5; τ q τ represents the estimated external torque. em This represents the maximum allowable external moment of the joint under a specific stiffness variable γ, and is related to the stiffness variable γ; |τ q | / τ em The value range is [0,1].

[0118] like Figure 3 As shown, the maximum allowable external torque τ of the joint em Constrained by both the maximum compression and rated torque of the elastic element, τ is not a constant value, but rather related to the stiffness variable γ: τ is within the range [0, γ1]. em τ increases with increasing γ, and this process is mainly constrained by the maximum compression of the elastic element; in the interval [γ1, γ2], τ em It is a constant value and is subject to the rated torque constraint.

[0119] Understandably, due to |τ q | / τ emThe value range of η is [0,1]. Therefore, by introducing η0 and defining η0 = η2 = 0.5, η can be made to be between [-0.5, 0.5].

[0120] Step 2, based on the Lyapunov barrier function, divides the stiffness adjustment into three regions: a stiffness-increasing region, a stiffness-decreasing region, and a constant stiffness region; specifically as follows... Figure 4 As shown, the region division is based on the parameter η.

[0121] Specifically, when η>η1, |τ q | / τ em When the ratio is close to or greater than 1, the external torque τ acting on the joint q Approaching or exceeding the maximum withstandable moment τ at this stiffness em Increase the stiffness K to allow the maximum allowable torque τ. em It also increases to ensure that the external forces on the joint are within the acceptable range, hence it is called the "stiffness increase zone";

[0122] When η < -η1, |τ q | / τ em When the ratio is close to 0, the external torque τ acting on the joint is... q Much smaller than the maximum allowable moment τ at this stiffness em By controlling the stiffness K to decrease, the resolution of external force estimation is improved, hence it is called the "stiffness reduction region";

[0123] When -η1 < η < η1, |τ q | / τ em Within a reasonable range, the joint has a suitable external force estimation resolution, while the torque it bears is also less than the maximum allowable torque τ. em At this point, the joint is in the "constant stiffness region" and no adjustment is made to the stiffness.

[0124] It is understandable that the constant stiffness region is the desired region, and the purpose of stiffness adjustment is to keep the stiffness within the constant stiffness region.

[0125] Step 3, based on the region involved by the Lyapunov barrier function, its derivative is expressed as:

[0126]

[0127] Step 4, design a suitable Make it satisfy To ensure that η is in the constant stiffness region, The expression is:

[0128]

[0129] Where, k ηLet k be a constant representing how quickly the stiffness of a variable stiffness joint transitions from a region of increasing stiffness or decreasing stiffness to a region of constant stiffness, and k η It is greater than 0, and its value can be selected according to actual needs.

[0130] The constant stiffness region can guarantee the external torque τ q The maximum allowable moment τ under a certain stiffness em This also ensures that the joint is in a low stiffness and high external force resolution; therefore, it is necessary to keep η in the constant stiffness region as much as possible, so as to avoid the stiffness being in a constant adjustment process and save energy.

[0131] Furthermore, when the direction of the external torque changes, |τ q | / τ em The ratio fluctuates around 0. By setting a minimum stiffness value, stiffness fluctuations can be avoided.

[0132] Step 5, according to the definition of η, η = |τ q | / τ em -η0 expresses the derivative of η as:

[0133]

[0134] in, The derivative of the stiffness variable γ of the variable stiffness joint reflects the magnitude of the stiffness adjustment rate and affects how fast the stiffness adjustment is.

[0135] Step 6, after further processing, obtain The expression:

[0136]

[0137] As can be seen, in this embodiment, considering the different maximum allowable external torques of the joint under different stiffnesses, a stiffness region controller was designed. By adjusting the stiffness variable, it is ensured that η is in the constant stiffness region, which guarantees that the joint has good external force estimation resolution and avoids saturation output of the detected torque.

[0138] After calculating the expected value γ of the stiffness variable d Then, considering the expected value γ of the stiffness variable calculated by the stiffness zone controller... d This is only a theoretical value; therefore, the expected value γ of the stiffness variable will also be considered. d Motion control applied to the stiffness-adjusting motor yields the actual value γ of the stiffness variable. r This enables real-time updates of stiffness variables.

[0139] Furthermore, when applied to discrete-time control systems, the stiffness variable γ is expressed as:

[0140]

[0141] Among them, t i This represents the i-th sampling time; Δt is the system's sampling period, t i+1 =t i +Δt.

[0142] The actual value of the stiffness variable γ r Substituting into the stiffness model K(γ), we obtain the updated stiffness value K(γ). r ).

[0143] The obtained stiffness value K(γ) r Substitute the values ​​into the adaptive fusion coefficient model for calculation to obtain the adaptive fusion coefficients; the adaptive fusion coefficient model is as follows:

[0144]

[0145] in, R represents the absolute value of the derivative of joint stiffness K. w1 and R w2 All are positive integers, satisfying R w2 >R w1 .

[0146] like Figure 5 As shown, the adaptive fusion coefficient K calculated according to step S2 τ The diagram illustrates the adaptive fusion coefficient K. τ According to Self-regulation, when At that time, K τ The value is 1, and the external force estimation based on current information plays a dominant role; when At that time, K τ When the value is 0, the external force estimation based on elastic deformation information plays a dominant role; when At that time, the estimated value of external force was calculated by combining the current and elastic deformation.

[0147] By adapting the fusion coefficient K τ The design of the expression in the form of a sine curve can achieve a smooth transition between the external force estimation value based on current and the external force estimation value based on elastic deformation, avoiding jumps in the external force estimation value.

[0148] This invention takes into account the different maximum allowable external moments of joints under different stiffnesses. Based on the maximum external moment constraint and the estimated external force value at the previous moment, a stiffness region variable controller is designed to realize the expected value γ of the stiffness variable. d The dynamic update, after calculating the expected value γ of the stiffness variable. dThen, considering the expected value γ of the stiffness variable calculated by the stiffness region variable controller... d This is only a theoretical value; therefore, the expected value γ of the stiffness variable will also be considered. d Motion control applied to the stiffness-adjusting motor yields the actual value γ of the stiffness variable. r Using the actual value of stiffness variable γ r The calculated stiffness value is closer to the actual stiffness value. Based on this dynamic actual stiffness value, the joint deformation of the variable stiffness joint during motion control can be accurately quantified.

[0149] The stiffness region variable controller dynamically adjusts according to the stiffness range, ensuring that the stiffness is in a constant stiffness region. This guarantees that the joint has low stiffness, improves the accuracy of external force estimation, and thus simultaneously meets the requirements of interactive safety and external force estimation resolution performance indicators.

[0150] The adaptive fusion coefficient K is obtained through the stiffness variable. τ The design of the expression in the form of a sine curve can achieve a smooth transition between the external force estimation value based on current and the external force estimation value based on elastic deformation, avoiding jumps in the external force estimation value.

[0151] Example 4

[0152] This embodiment provides another step for obtaining the fusion coefficient, specifically including:

[0153] Real-time acquisition of stiffness values;

[0154] The obtained stiffness values ​​are substituted into the adaptive fusion coefficient model for calculation to obtain the adaptive fusion coefficients; the adaptive fusion coefficient model is as follows:

[0155]

[0156] in, R represents the absolute value of the derivative of joint stiffness K. w1 and R w2 All are positive integers, satisfying R w2 >R w1 .

[0157] Example 5

[0158] In this embodiment, the variable stiffness joint is defined as a lever-type variable stiffness joint system, such as... Figure 2 As shown, a specific implementation method for estimating external forces is presented.

[0159] The specific steps are as follows:

[0160] Step A: Obtain stiffness values ​​in real time;

[0161] Step A1: Design a stiffness region controller based on the estimated external force τ from the previous moment. q and maximum external moment constraint τ em The expected value of the stiffness variable γ was calculated. d .

[0162] The specific steps are as follows:

[0163] Step 1: Design a stiffness region controller based on the Lyapunov barrier function.

[0164] For lever-type variable stiffness joints, the Lyapunov barrier function used for stiffness region control is expressed as:

[0165]

[0166] Where η represents the function variable, η=|τ q | / τ em -η0; η0, η1, and η2 are all positive constants and satisfy η0 = η2 = 0.5, η1 < 0.5; τ q τ represents the estimated external torque. em This represents the maximum allowable external moment of the joint under a specific stiffness variable γ, and is related to the stiffness variable γ; |τ q | / τ em The value range is [0,1].

[0167] like Figure 3 As shown, the maximum allowable external torque τ of the joint em Constrained by both the maximum compression and rated torque of the elastic element, τ is not a constant value, but rather related to the stiffness variable γ: τ is within the range [0, γ1]. em τ increases with increasing γ, and this process is mainly constrained by the maximum compression of the elastic element; in the interval [γ1, γ2], τ em It is a constant value and is subject to the rated torque constraint.

[0168] Understandably, due to |τ q | / τ em The value range of η is [0,1]. Therefore, by introducing η0 and defining η0 = η2 = 0.5, η can be made to be between [-0.5, 0.5].

[0169] Step 2, based on the Lyapunov barrier function, divides the stiffness adjustment into three regions: a stiffness-increasing region, a stiffness-decreasing region, and a constant stiffness region; specifically as follows... Figure 4 As shown, the region division is based on the parameter η.

[0170] Specifically, when η>η1, |τ q | / τ em When the ratio is close to or greater than 1, the external torque τ acting on the jointq Approaching or exceeding the maximum withstandable moment τ at this stiffness em Increase the stiffness K to allow the maximum allowable torque τ. em It also increases to ensure that the external forces on the joint are within the acceptable range, hence it is called the "stiffness increase zone";

[0171] When η < -η1, |τ q | / τ em When the ratio is close to 0, the external torque τ acting on the joint is... q Much smaller than the maximum allowable moment τ at this stiffness em By controlling the stiffness K to decrease, the resolution of external force estimation is improved, hence it is called the "stiffness reduction region";

[0172] When -η1 < η < η1, |τ q | / τ em Within a reasonable range, the joint has a suitable external force estimation resolution, while the torque it bears is also less than the maximum allowable torque τ. em At this point, the joint is in the "constant stiffness region" and no adjustment is made to the stiffness.

[0173] It is understandable that the constant stiffness region is the desired region, and the purpose of stiffness adjustment is to keep the stiffness within the constant stiffness region.

[0174] Step 3, based on the region involved by the Lyapunov barrier function, its derivative is expressed as:

[0175]

[0176] Step 4, design a suitable Make it satisfy To ensure that η is in the constant stiffness region, The expression is:

[0177]

[0178] Where, k η Let k be a constant representing how quickly the stiffness of a variable stiffness joint transitions from a region of increasing stiffness or decreasing stiffness to a region of constant stiffness, and k η It is greater than 0, and its value can be selected according to actual needs.

[0179] The constant stiffness region can guarantee the external torque τ q The maximum allowable moment τ under a certain stiffness em This also ensures that the joint is in a low stiffness and high external force resolution; therefore, it is necessary to keep η in the constant stiffness region as much as possible, so as to avoid the stiffness being in a constant adjustment process and save energy.

[0180] Furthermore, when the direction of the external torque changes, |τ q | / τ em The ratio fluctuates around 0. By setting a minimum stiffness value, stiffness fluctuations can be avoided.

[0181] Step 5, according to the definition of η, η = |τ q | / τ em -η0 expresses the derivative of η as:

[0182]

[0183] in, The derivative of the stiffness variable γ of the variable stiffness joint reflects the magnitude of the stiffness adjustment rate and affects how fast the stiffness adjustment is.

[0184] Step 6, after further processing, obtain The expression:

[0185]

[0186] As can be seen, in this embodiment, considering the different maximum allowable external torques of the joint under different stiffnesses, a stiffness region controller was designed. By adjusting the stiffness variable, it is ensured that η is in the constant stiffness region, which guarantees that the joint has good external force estimation resolution and avoids saturation output of the detected torque.

[0187] Step A2, after calculating the expected value γ of the stiffness variable. d Then, considering the expected value γ of the stiffness variable calculated by the stiffness zone controller... d This is only a theoretical value; therefore, the expected value γ of the stiffness variable will also be considered. d Motion control applied to the stiffness-adjusting motor yields the actual value γ of the stiffness variable. r This enables real-time updates of stiffness variables.

[0188] Furthermore, when applied to discrete-time control systems, the stiffness variable γ is expressed as:

[0189]

[0190] Among them, t i This represents the i-th sampling time; Δt is the system's sampling period, t i+1 =t i +Δt.

[0191] Step A3, change the actual value of the stiffness variable γ r Substituting into the stiffness model K(γ), we obtain the updated stiffness value K(γ). r ).

[0192] Step B: Obtain the adaptive fusion coefficients.

[0193] Step B1, Design the adaptive fusion coefficient model:

[0194]

[0195] Where K represents joint stiffness, R represents the absolute value of the derivative of joint stiffness K. w1 and R w2 All are positive integers, satisfying R w2 >R w1 ;

[0196] Step B2, update the stiffness value K(γ) r Substituting into the adaptive fusion coefficient model, the adaptive fusion coefficient K is obtained. τ .

[0197] Step C, obtain external force estimation I based on the current information of the variable stiffness joint:

[0198] In practice, the following steps are included:

[0199] Step C1: Establish the dynamic models of the position drive module and the stiffness adjustment module.

[0200] The dynamic model is expressed as follows:

[0201]

[0202] in, and These represent the moments of inertia of the position drive module and the stiffness adjustment module, respectively, and are unknown parameters; and These represent the frictional forces of the position drive module and the stiffness adjustment module, respectively, and are unknown parameters; and These represent the output torques of the position drive module and the stiffness adjustment module, respectively. and θ1 and θ2 represent the input torques of the position drive module and stiffness adjustment module, respectively; θ1 and θ2 represent the output angular displacements of the position drive module and stiffness adjustment module, respectively.

[0203] Step C2: Obtain the moment of inertia in the dynamic model using the dynamic parameter identification method. and friction The accurate value;

[0204] Step C3: Measure the motor current values ​​of the position drive module and the stiffness adjustment module, and calculate the input torque of the position drive module and the stiffness adjustment module according to the following formula:

[0205]

[0206] Among them, K pi and K si These represent the total torque constants of the position drive module and the stiffness adjustment module, respectively, reflecting parameters such as the motor torque constant and reduction ratio; I p and I s These represent the motor current values ​​for the position drive module and the stiffness adjustment module, respectively.

[0207] Step C4: Substitute the calculated input torques of the position drive module and stiffness adjustment module into the dynamic models of the position drive module and stiffness adjustment module for solution, and obtain the output torques of the position drive module and stiffness adjustment module. and

[0208] Step C5: The output torque of the position drive module and the stiffness adjustment module is... and The operation yields an external force estimate I based on current information:

[0209] As can be seen, in this embodiment, the dynamic model is decoupled and split into the dynamic model of the position drive module and the dynamic model of the stiffness adjustment module, thereby reducing the high-order dynamic model to the control of each sub-drive, simplifying the model and reducing the control difficulty; the dynamic model of each sub-drive includes unknown parameters that can be identified through dynamic parameters and measurable angular displacement, further reducing the impact of model error on external force estimation.

[0210] Step D, based on the elastic deformation information of the variable stiffness joint and the updated stiffness value K(γ) r Obtaining External Force Estimation II:

[0211]

[0212] Step E, based on the adaptive fusion coefficient K τ External force estimation Iτ ei and external force estimation IIτ ec To obtain an estimate of the external force based on the fusion of current and elastic deformation:

[0213] τ q =K τ τ ei +(1-K τ )τ ec .

[0214] like Figure 6The figure shows an experimental comparison of three different external force estimation methods in a lever-type variable stiffness joint scenario. The average absolute value of the errors of the three different external force estimation results is shown below:

[0215]

[0216]

[0217] It can be seen that the external force estimation based on elastic deformation has a good external force estimation effect under quasi-static stiffness, but the external force estimation effect under dynamic stiffness is poor.

[0218] The force estimation based on current information has a stable force estimation effect under both dynamic and quasi-static stiffness conditions, but its force estimation effect under quasi-static stiffness conditions is worse than that based on elastic deformation.

[0219] The external force estimation method proposed in this invention, which integrates current and elastic deformation, combines the advantages of both types of information, improves the external force estimation effect under dynamic and quasi-static stiffness, and has the smallest average value of the overall absolute error in terms of external force estimation error.

[0220] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the scope of the invention. Any person skilled in the art can make modifications without departing from the scope of the invention; all equivalent modifications made in accordance with the invention should be covered by the scope of the invention.

Claims

1. A method for estimating external forces in a variable stiffness joint based on the fusion of electric current and elastic deformation, characterized in that, Includes the following steps: The external force estimate I is obtained by using a variable stiffness joint external force estimation method based on current information; The variable stiffness joint external force estimation method based on current information includes the following steps: Establish dynamic models for the position-driven module and the stiffness adjustment module: in, and These represent the moments of inertia of the position drive module and the stiffness adjustment module, respectively. and These represent the frictional forces of the position drive module and the stiffness adjustment module, respectively. and These represent the output torques of the position drive module and the stiffness adjustment module, respectively. and These represent the input torques of the position drive module and the stiffness adjustment module, respectively. and These represent the output angular displacements of the position drive module and the stiffness adjustment module, respectively. The moment of inertia in the dynamic model is obtained through dynamic parameter identification methods. , and friction , The accurate value; Measuring motor current information of the position drive module and stiffness adjustment module and The input torques of the position drive module and the stiffness adjustment module are calculated according to the following formula: in, and These represent the total torque constants of the position drive module and the stiffness adjustment module, respectively; The calculated input torques of the position drive module and stiffness adjustment module are substituted into the dynamic model of the position drive module and stiffness adjustment module for solution, so as to obtain the output torques of the position drive module and stiffness adjustment module. The sum of the output torques of the position drive module and the stiffness adjustment module is calculated as the external force estimate I: External force estimation based on elastic deformation information and stiffness values ​​of variable stiffness joints II; Real-time acquisition of stiffness values; the steps for real-time acquisition of stiffness values ​​include: Design a stiffness zone controller and calculate the expected value of stiffness variables based on the estimated external force and maximum external moment constraint at the previous moment. The expected value of the stiffness variable is applied to the motion control of the motor in the stiffness adjustment module to obtain the actual value of the stiffness variable; Substituting the actual values ​​of the stiffness variables into the stiffness model yields the updated stiffness values, where the stiffness model is a function of the stiffness variables. The obtained stiffness values ​​are substituted into the adaptive fusion coefficient model for calculation to obtain the adaptive fusion coefficients; the adaptive fusion coefficient model is as follows: in, Indicates joint stiffness The absolute value of the derivative, and All are positive numbers, satisfying ; Based on external force estimation I and external force estimation II, external force estimates based on the fusion of current and elastic deformation are obtained: in, For external force estimation I, For external force estimation II, For adaptive fusion coefficients.

2. The method for estimating external forces in a variable stiffness joint based on the fusion of current and elastic deformation as described in claim 1, characterized in that, Design a stiffness zone controller, and calculate the expected values ​​of stiffness variables based on the previous time-stress estimate of external forces and the maximum external moment constraint, including: A stiffness region controller is designed based on the Lyapunov barrier function. For lever-type variable stiffness joints, the Lyapunov barrier function used for stiffness region control is expressed as: in, Represents function variables, ; , , All are positive numbers and satisfy , ; This represents the estimated external torque; Represents a specific stiffness variable The maximum allowable external moment of the lower joint, and the stiffness variable related; The range of values ​​is ; Based on the Lyapunov barrier function, stiffness adjustment is divided into three regions: stiffness increase region, stiffness decrease region, and constant stiffness region. Based on the region involved by the Lyapunov barrier function, its derivative can be expressed as: Design suitable To satisfy To ensure Located in the constant stiffness region, The expression is: in, Let be a constant representing how quickly the stiffness of a lever-type variable stiffness joint transitions from a region of increasing stiffness or decreasing stiffness to a region of constant stiffness, and Greater than 0; according to The definition will The derivative is expressed as: in, Represents the stiffness variable of a lever-type variable stiffness joint. The derivative; After further sorting, we obtained The expression: 。 3. The method for estimating external forces in a variable stiffness joint based on the fusion of current and elastic deformation as described in claim 2, characterized in that: When dividing stiffness adjustment into three regions based on the Lyapunov barrier function, the parameters of the Lyapunov barrier function are used as the basis. ; when At this time, it represents the region where stiffness is increased; when At this time, it is a region where stiffness decreases; when At that time, it is a region of constant stiffness.

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