External force iterative estimation algorithm based on precise friction model

Abstract

The invention discloses an external force iterative estimation algorithm based on an accurate friction model. The method comprises the following steps: establishing a multi-factor coupled accurate friction model; total torque, speed and temperature-related friction torque of the robot are calculated, initial comprehensive load torque, load torque and load-related friction torque are determined, and iterative calculation tolerance is preset; entering an iterative loop, firstly updating a load torque, and calculating a load-related friction torque; calculating a load torque variation after iteration, judging the magnitude of a tolerance between the load torque variation and preset iterative calculation, and stopping iteration until the requirement is met; and outputting a final external force estimation value. According to the external force iterative estimation algorithm based on the precise friction model, an original multi-parameter system is decomposed into a plurality of relatively independent subsystems, the independent influence of each parameter on the external force is clearly revealed, so that the precision of external force estimation is effectively improved, high-precision perception can be realized through iterative calculation dynamic decoupling, and the accuracy of external force estimation is improved. And the external force estimation precision is further improved.

Description

Technical Field

[0001] This invention relates to the field of robot external force estimation algorithm technology, specifically to an iterative external force estimation algorithm based on an accurate friction model. Background Technology

[0002] External force estimation methods are mainly divided into two categories: one is based on the direct acquisition of external forces by force / torque sensors; the other is sensorless external force estimation based on motor current information. The former, by adding sensors, increases structural complexity and manufacturing costs. Sensorless external force estimation techniques are mainly divided into two categories: one is a direct calculation method based on a dynamic model, which derives the external force by establishing a current-torque mapping relationship; the other is an observer-based estimation method, which uses a state observer to decouple the system's momentum changes, thereby achieving external force estimation.

[0003] According to invention patent application CN117549308B, published on July 12, 2024, a method, terminal, and medium for estimating external forces on a robot are disclosed. The method is a sensorless method for estimating external forces on a robot, mainly including the following steps: estimating the robot's dynamic parameters using a parameter identification method; and estimating the external forces acting on the robot by combining the external force estimation state-space equation and the observer design method. Its main technical advantages are: utilizing the robot's dynamic model and the disturbance observer design method, it is possible to perceive the forces acting on the robot at low cost and with high reliability. Combining robust linear regression, iterative weighted least squares, and physical feasibility constraints can significantly reduce the robot's model error. By adaptively correcting the observation error of the observer system, the observation results are ensured to have a certain robustness to abnormal measurements, thus achieving accurate external force estimation.

[0004] In existing technologies, the parameters in dynamic models used for external force estimation often exhibit complex coupling relationships. In these models, a change in one parameter not only affects its directly related force components but also influences other parameters and their corresponding force components through complex interactions. Therefore, this paper proposes an iterative external force estimation algorithm based on an accurate friction model. This algorithm aims to address the problem of complex coupling relationships between parameters in existing external force estimation models, where a change in one parameter affects the remaining parameters and their corresponding force components. Summary of the Invention

[0005] The purpose of this invention is to provide an iterative estimation algorithm for external forces based on an accurate friction model, which aims to solve the problem that there are complex coupling relationships between the parameters of the external force estimation model in the prior art, and that a change in one parameter will affect the other parameters and the corresponding external force components.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an iterative estimation algorithm for external forces based on an accurate friction model, comprising the following steps: An accurate friction model with multiple coupled factors is established, as shown below: ; Calculate the total torque of the robot Friction torque related to speed and temperature Determine the initial comprehensive load torque Load torque Load-related frictional torque Preset iterative calculation tolerance; Enter the iterative loop, first update the load torque. And calculate the load-related frictional torque. ; After each iteration, the change in load torque is calculated, and the difference between the change in load torque and the preset iteration tolerance is determined until the requirement is met, at which point the iteration stops. Output the final estimated external force value.

[0007] Preferably, the multi-factor coupled accurate friction model is constructed based on a conventional dynamic model, coupling a speed-corrected friction model, a temperature-corrected friction model, and a load model of friction torque.

[0008] Preferably, the total torque of the robot Calculate using the following formula: ; in, Let n be the motor constant, n be the gear ratio of the reducer, and I be the current.

[0009] Preferably, the combined load torque is calculated according to the following formula: ; And make the initial load torque equal to the initial combined load torque, where, This represents the actual total torque value of the wheel module.

[0010] Preferably, the load-related frictional torque is calculated based on a load model of the frictional torque, which is expressed as: ; in, and These are the linear and quadratic coefficients of the load torque, respectively.

[0011] As a preferred embodiment, the velocity-corrected friction model is expressed as follows: ; ; ; in, This refers to the Stribeck phenomenon. Indicates viscous friction. These are the static friction coefficient, the Coulomb friction coefficient, and the viscous friction coefficient, respectively. Stribeck's velocity coefficient, It is an exponential decay factor, usually taken as .

[0012] Preferably, the temperature-corrected friction model is expressed as: ; in, is a temperature coefficient, and represents the rate of change of Coulomb friction coefficient, Stribeck velocity, and viscous friction coefficient with temperature, respectively.

[0013] In the above technical solution, the external force iterative estimation algorithm based on an accurate friction model provided by the present invention has the following beneficial effects: Iterative calculations enable dynamic decoupling of the friction model. By decomposing the complex and interconnected multi-parameter system into multiple relatively independent subsystems, the independent influence of each parameter on external forces is clearly revealed, thereby effectively improving the accuracy of external force estimation. Furthermore, iterative calculations and dynamic decoupling enable high-precision sensing, further enhancing the accuracy of external force estimation. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0015] Figure 1 This is a schematic diagram of the external force estimation process using the iterative algorithm provided in the embodiments of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, an iterative estimation algorithm for external forces based on an accurate friction model includes the following steps: The dynamic model is established as follows: ; Calculate the total torque of the robot Friction torque related to speed and temperature Determine the initial comprehensive load torque Load torque Load-related frictional torque Preset iterative calculation tolerance; Enter the iterative loop, first update the load torque. And calculate the load-related frictional torque. ; After each iteration, the change in load torque is calculated, and the difference between the change in load torque and the preset iteration tolerance is determined until the requirement is met, at which point the iteration stops. Output the final estimated external force value.

[0018] The conventional dynamic equations of a robot can be expressed using second-order linear differential equations as follows: ; in For location, Angular velocity, For acceleration, The inertia matrix, The coupling matrix of Coriolis force and centrifugal force. This is the gravity matrix.

[0019] In this embodiment of the invention, the established dynamic model is the dynamic model of the wheel module, and it is an independently driven wheel.

[0020] The generalized coordinates of the independent drive wheel provided by this invention are based on the wheel rotation angle. It is uniquely determined that its kinematic relationship satisfies the following formula: ; in, The linear velocity of the wheel. The radius is the wheel radius.

[0021] As an embodiment of the present invention, based on the principle of rigid body composite motion in the Newton-Euler equations, the inertia of the independent drive wheel system provided in this embodiment of the present invention simultaneously considers the rotational inertia of the wheels. With the overall quality of the robot The equivalent translational inertia is expressed as: ; When the nonholonomic constraint pure rolling condition defined above is satisfied, the Coriolis force matrix is ​​a zero matrix, i.e. When the robot is on a level surface, or when its axis of rotation is parallel to the direction of gravity, the required gravitational torque is zero. If there is a road surface inclination angle ,but .

[0022] Considering frictional losses, external disturbances, and modeling uncertainties in the actual system, the extended equation of motion for a single wheel is as follows: ; in, This is the actual output torque. This refers to the external disturbance torque. For frictional torque, This is due to unmodeled errors. In the single-drive module provided in this application, modeling is based on the condition that the wheel module does not contact the ground and the rotation axis is parallel to the direction of gravity; therefore, rolling friction is not considered. The output torque of the single-drive wheel module includes drive torque, friction loss, and load torque. The relationship between the motor output torque and current can be expressed as: ; in, For motor constants, This is the rotor inertia of the motor. This represents the gear ratio of the reducer.

[0023] Frictional torque is described as a combination of various nonlinear frictional characteristics under sliding conditions, such as Coulomb friction and viscous friction. Experiments show that frictional characteristics depend on wheel speed, joint temperature, and load torque. Therefore, the comprehensive frictional torque can be expressed as: ; in, Friction is a term related to friction and velocity. Friction is a friction term that is related to temperature. This refers to friction terms related to friction and load.

[0024] The wheel module is made to rotate at a constant speed under no-load conditions, and its position is obtained. ,speed acceleration and temperature Data and information.

[0025] Friction torque can be obtained The expression: ; During the uniform motion of the single-wheel module, Therefore, inertial torque Meanwhile, ignoring external disturbances... And assume .

[0026] Combining the above formula for the relationship between motor output torque and current, and friction torque The formula yields the linear relationship between frictional torque and motor current: ; in, Let n be the motor constant, n be the gear ratio of the reducer, and I be the current.

[0027] The velocity-corrected friction model provided in this embodiment of the invention is specifically represented as follows: ; ; ; in, This refers to the Stribeck phenomenon. Indicates viscous friction. These are the static friction coefficient, the Coulomb friction coefficient, and the viscous friction coefficient, respectively. Stribeck's velocity coefficient, It is an exponential decay factor, usually taken as , can be represented as: ; ; ; In lubrication mechanisms, the primary reason friction is affected by temperature lies in the changes in the physical properties of the lubricant, such as viscosity and ultimate shear stress. The ultimate shear stress of the lubricant decreases non-linearly with increasing temperature. Furthermore, viscosity typically exhibits an exponential relationship with temperature. Therefore, it is reasonable to assume that viscous friction will decrease with increasing temperature. Conventional friction models in existing technologies can only be used under relatively stable conditions. Therefore, a temperature-dependent parameter is introduced to construct a temperature-corrected friction model, as shown below: ; in, is a temperature coefficient, and represents the rate of change of Coulomb friction coefficient, Stribeck velocity, and viscous friction coefficient with temperature, respectively.

[0028] The established load model for frictional torque is as follows: ; in, and These are the linear and quadratic coefficients of the load torque, respectively, which determine the degree of influence of the load torque on the friction torque. (Sign function) This reflects the consistency between the frictional torque and the velocity direction.

[0029] By combining the analysis of the effects of speed, temperature, and load on frictional torque, and integrating the speed-corrected friction model, temperature-corrected friction model, and load model of frictional torque, a comprehensive friction model for the sliding region can be obtained: ; That is, a precise friction model that takes into account the coupling of multiple factors such as wheel speed, temperature, and load torque.

[0030] During actual operation, the I, q, and values ​​of the wheel system are collected. T, then perform initialization processing; Calculate the total torque of the robot Friction torque related to speed and temperature Determine the initial comprehensive load torque Load torque Load-related frictional torque Preset iterative calculation tolerance; Enter the iterative loop, first update the load torque. And calculate the load-related frictional torque. ; After each iteration, the change in load torque is calculated, and the difference between the change in load torque and the preset iteration tolerance is determined until the requirement is met, at which point the iteration stops. Output the final estimated external force value.

[0031] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0032] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0033] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0034] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0035] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0036] The embodiments of this application also provide a specific implementation of an electronic device capable of implementing all the steps in the methods described above, wherein the electronic device specifically includes the following: Processor, memory, communications interface, and bus; The processor, memory, and communication interface communicate with each other through the bus. The processor is used to invoke a computer program stored in the memory. When the processor executes the computer program, it implements all the steps in the method described in the above embodiments. For example, when the processor executes the computer program, it implements the following steps: An accurate friction model with multiple coupled factors is established, as shown below: ; Calculate the total torque of the robot Friction torque related to speed and temperature Determine the initial comprehensive load torque Load torque Load-related frictional torque Preset iterative calculation tolerance; Enter the iterative loop, first update the load torque. And calculate the load-related frictional torque. ; After each iteration, the change in load torque is calculated, and the difference between the change in load torque and the preset iteration tolerance is determined until the requirement is met, at which point the iteration stops. Output the final estimated external force value.

[0037] Embodiments of this application also provide a computer-readable storage medium capable of implementing all steps of the methods in the above embodiments. The computer-readable storage medium stores a computer program that, when executed by a processor, implements all steps of the methods in the above embodiments. For example, when the processor executes the computer program, it implements the following steps: An accurate friction model with multiple coupled factors is established, as shown below: ; Calculate the total torque of the robot Friction torque related to speed and temperature Determine the initial comprehensive load torque Load torque Load-related frictional torque Preset iterative calculation tolerance; Enter the iterative loop, first update the load torque. And calculate the load-related frictional torque. ; After each iteration, the change in load torque is calculated, and the difference between the change in load torque and the preset iteration tolerance is determined until the requirement is met, at which point the iteration stops. Output the final estimated external force value.

[0038] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on its differences from other embodiments. In particular, for hardware + program embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. Although the embodiments in this specification provide the method operation steps as shown in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-inventive means. The order of steps listed in the embodiments is merely one possible execution order among many steps and does not represent the only execution order. In actual device or terminal product execution, the methods can be executed in the order shown in the embodiments or drawings or in parallel (e.g., in a parallel processor or multi-threaded processing environment, or even a distributed data processing environment). The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, product, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, product, or apparatus. Without further limitations, the presence of other identical or equivalent elements in the process, method, product, or apparatus that includes said elements is not excluded. For ease of description, the above devices are described in terms of function, divided into various modules. Of course, in implementing the embodiments of this specification, the functions of each module can be implemented in one or more software and / or hardware, or the module implementing the same function can be implemented by a combination of multiple sub-modules or sub-units, etc. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division; in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings or direct couplings or communication connections may be through some interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms. This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing device to produce a machine, such that the instructions, which are executable by the processor of the computer or other programmable data processing device, produce instructions for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0039] Those skilled in the art will understand that the embodiments of this specification can be provided as methods, systems, or computer program products. Therefore, the embodiments of this specification can take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, the embodiments of this specification can take the form of computer program products implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The various embodiments in this specification are described in a progressive manner, and similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. In the description of this specification, the reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., means that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the embodiments of this specification.

[0040] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Furthermore, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as features of different embodiments or examples, without contradiction. The above descriptions are merely embodiments of this specification and are not intended to limit the embodiments of this specification. Various modifications and variations can be made to the embodiments of this specification by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the embodiments of this specification should be included within the scope of the claims of the embodiments of this specification.

Claims

1. An iterative estimation algorithm for external forces based on an accurate friction model, characterized in that, Includes the following steps: An accurate friction model with multiple coupled factors is established, as shown below: ； Calculate the total torque of the robot Friction torque related to speed and temperature Determine the initial comprehensive load torque Load torque Load-related frictional torque Preset iterative calculation tolerance; Enter the iterative loop, first update the load torque. And calculate the load-related frictional torque. ; After each iteration, the change in load torque is calculated, and the difference between the change in load torque and the preset iteration tolerance is determined until the requirement is met, at which point the iteration stops. Output the final estimated external force value.

2. The external force iterative estimation algorithm based on an accurate friction model according to claim 1, characterized in that, The precise friction model with multi-factor coupling is constructed based on the conventional dynamic model, coupling a speed-corrected friction model, a temperature-corrected friction model, and a load model of friction torque.

3. The external force iterative estimation algorithm based on an accurate friction model according to claim 1, characterized in that, The robot's total torque Calculate using the following formula: ； in, Let n be the motor constant, n be the gear ratio of the reducer, and I be the current.

4. The external force iterative estimation algorithm based on an accurate friction model according to claim 1, characterized in that, The combined load torque is calculated according to the following formula: ； And make the initial load torque equal to the initial combined load torque, where, This represents the actual total torque of the robot module.

5. The external force iterative estimation algorithm based on an accurate friction model according to claim 2, characterized in that, The load-related frictional torque is calculated based on the load model of the frictional torque, which is expressed as follows: ； in, and These are the linear and quadratic coefficients of the load torque, respectively.

6. The external force iterative estimation algorithm based on an accurate friction model according to claim 1, characterized in that, The change in load torque is calculated according to the following formula: ； in, This refers to the load torque for this iteration. This is the load torque calculated in the previous calculation.

7. The external force iterative estimation algorithm based on an accurate friction model according to claim 2, characterized in that, The velocity-corrected friction model is expressed as follows: ； ； ； in, This refers to the Stribeck phenomenon. Indicates viscous friction. These are the static friction coefficient, the Coulomb friction coefficient, and the viscous friction coefficient, respectively. Stribeck's velocity coefficient, It is an exponential decay factor.

8. The external force iterative estimation algorithm based on an accurate friction model according to claim 2, characterized in that, The temperature-corrected friction model is expressed as follows: ； in, is a temperature coefficient, and represents the rate of change of Coulomb friction coefficient, Stribeck velocity, and viscous friction coefficient with temperature, respectively.

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