A force measurement method and system based on machine vision and negative Poisson's ratio structure

Abstract

A force measurement method and system based on machine vision and negative Poisson's ratio structure, comprising: using a negative Poisson's ratio structure as a substrate, placing the negative Poisson's ratio structure parallel to an industrial camera, and contacting the object to be measured with the negative Poisson's ratio structure; the industrial camera collects deformation pictures in real time, and obtains the corresponding external force value through the elastic deformation magnitude of the first frame picture and the last frame picture; after applying external force to the object to be measured, the negative Poisson's ratio structure produces elastic deformation, and the elastic modulus E of the substrate is introduced by utilizing the property that stress and strain are proportional to each other, and a conversion equation between the external force and the deformation variable is established, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate. The present invention provides a method for measuring external force based on machine vision, which utilizes the property that stress and strain are proportional to each other, introduces the elastic modulus E of the substrate, and establishes a conversion equation between the external force and the deformation variable, so that the measurement of the measured object is converted into the measurement of the deformation size of the substrate.

Description

Technical Field

[0001] The present invention belongs to the technical field of visual detection, and in particular relates to a force measurement method and system based on machine vision and a negative Poisson's ratio structure. Background Art

[0002] In the process of force and displacement monitoring, the traditional force measurement method is to use a torque sensor for detection. A special torsion strain gauge is pasted on the elastic shaft to be measured with strain glue to form a strain bridge. The electrical signal of the torsion of the elastic shaft can be tested by providing working power to the strain bridge. This limits the promotion of traditional contact sensors in actual engineering. In addition, since the two need to contact each other, the propagation of noise and interference between the two is inevitable, affecting the measurement accuracy of the sensor. Summary of the invention

[0003] The purpose of the present invention is to provide a force measurement method and system based on machine vision and negative Poisson's ratio structure to solve the problem of noise in the prior art affecting the measurement accuracy of the sensor.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A force measurement method based on machine vision and negative Poisson's ratio structure, comprising:

[0006] Using a negative Poisson's ratio structure as a substrate, placing the negative Poisson's ratio structure parallel to the industrial camera, and bringing the object to be measured into contact with the negative Poisson's ratio structure;

[0007] The industrial camera collects deformation images in real time, and obtains the corresponding external force value through the elastic deformation magnitude between the first frame and the last frame.

[0008] When external force is applied to the object to be measured, the negative Poisson's ratio structure produces elastic deformation. By utilizing the property that stress and strain are proportional, the elastic modulus E of the substrate is introduced, and a conversion equation between external force and deformation variable is established, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate.

[0009] Furthermore, the shape change of the negative Poisson's ratio structure caused by force is indirectly identified based on machine vision technology: the edge detection of the negative Poisson's ratio structure is performed based on the image, and the pixel coordinate values ​​of the discrete points distributed on the base structure in the image and their pixel displacement relative to the initial position are obtained.

[0010] Furthermore, the relationship between external force and stress is as follows:

[0011]

[0012] Where F is the load, is the stress; A is the cross-sectional area of ​​the substrate in contact with the element being measured.

[0013] Furthermore, the relationship between strain and stress of the measuring element is as follows:

[0014]

[0015] in, To measure the stress on the component, is the elastic modulus of the negative Poisson’s ratio structure, is the strain generated when the structure with negative Poisson's ratio is subjected to stress.

[0016] Furthermore, the positive strain becomes

[0017]

[0018] Where L is the length before deformation, is the deformation amount after deformation.

[0019] Furthermore, the camera's intrinsic and extrinsic parameter matrices are obtained through camera calibration, and the image taken by the camera is corrected to obtain an image with less distortion.

[0020] Furthermore, when the negative Poisson's ratio structure is placed parallel to the industrial camera, the camera head of the industrial camera is aimed at the base of the negative Poisson's ratio structure, and a gimbal is used to support the camera.

[0021] Furthermore, a force measurement system based on machine vision and negative Poisson's ratio structure includes:

[0022] The image acquisition module is used to place the negative Poisson's ratio structure in parallel with the industrial camera using the negative Poisson's ratio structure as a substrate, and to contact the object to be measured with the negative Poisson's ratio structure; the industrial camera collects deformation images in real time, and obtains the corresponding external force value through the elastic deformation magnitude of the first frame image and the last frame image;

[0023] The measurement conversion module is used to apply external force to the object to be measured, so that the negative Poisson's ratio structure produces elastic deformation. By utilizing the property that stress and strain are proportional, the elastic modulus E of the substrate is introduced to establish a conversion equation between external force and deformation variable, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate.

[0024] Compared with the prior art, the present invention has the following technical effects:

[0025] The invention discloses a method for measuring external force based on machine vision. The method utilizes the property that stress and strain are in proportional relationship, introduces the elastic modulus E of the substrate, establishes a conversion equation between the external force and the deformation variable, and converts the measurement of the measured quantity into the measurement of the deformation size of the substrate.

[0026] Furthermore, after the camera is calibrated, the camera's intrinsic and extrinsic parameter matrices can be obtained to correct the images subsequently taken by the camera, thereby obtaining images with relatively small distortion, making the measurement more accurate.

[0027] Furthermore, using a gimbal to support the camera can obtain stable image information. The gimbal can capture the object to be measured by clamping the industrial camera and rotating it to the corresponding position. This setting greatly increases the accuracy of the measurement results.

[0028] Furthermore, the camera types are not limited and the selection range is wide. Infrared cameras or ordinary cameras can be selected according to different application environments. This setting expands the application scope of this measurement method.

[0029] Furthermore, the choice of substrate is not restricted and can be a negative Poisson's ratio structure of any cell structure, and its function is to convert the external force measurement of the measured object into the deformation size measurement of the negative Poisson's ratio structure through the negative Poisson's ratio structure.

[0030] In summary, the solution provided by the present invention has high reliability, high detection accuracy, strong practicability, and can effectively solve the problems existing in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the device based on the negative Poisson's ratio structure

[0032] Figure 2 This is a schematic diagram of the deformation of a negative Poisson's ratio structure under tension as the base.

[0033] Figure 3 This is a schematic diagram of deformation under pressure when a negative Poisson's ratio structure is used as the base. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] The invention discloses a force measurement method based on machine vision and negative Poisson's ratio structure, belonging to the field of machine vision technology. The device comprises: an industrial camera, a camera bracket, a substrate, and a lens. By calibrating the camera, the internal and external matrix parameters of the camera are obtained, so that the distortion of the captured image is extremely small. By applying external force to the object to be measured, the substrate will produce corresponding deformation. The industrial camera takes a deformed picture, and after data processing, the applied external force value is output.

[0038] S1. Using a negative Poisson's ratio structure as a substrate, placing the negative Poisson's ratio structure parallel to the industrial camera 2, and the object to be measured is in contact with the negative Poisson's ratio structure.

[0039] S2. The camera collects deformation images in real time and transmits the data to the GPU. The GPU calculates the elastic deformation between the first frame and the last frame, and outputs the corresponding external force value through the computer processing module.

[0040] S3. Obtain the camera's intrinsic and extrinsic parameter matrices through camera calibration, and correct the images subsequently taken by the camera to obtain images with relatively small distortion.

[0041] S4. After an external force is applied to the object being measured, the negative Poisson's ratio structure produces elastic deformation. By using the property that stress and strain are proportional, the elastic modulus E of the substrate is introduced, and the conversion equation between external force and deformation variable is established, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate.

[0042] The relationship between external force and stress is as follows:

[0043]

[0044] Where F is the load, is the stress. A is the cross-sectional area of ​​the substrate in contact with the element being measured.

[0045] The relationship between strain and stress of the measuring element is as follows:

[0046]

[0047] in, To measure the stress on the component, is the elastic modulus of the negative Poisson’s ratio structure, is the strain generated when the structure with negative Poisson's ratio is subjected to stress.

[0048] The positive strain is

[0049]

[0050] Where L is the length before deformation, is the deformation amount after deformation.

[0051] The negative Poisson's ratio structure sample that can be used for the substrate of the present invention will produce lateral contraction when subjected to a force in the vertical direction. In the present invention, the negative Poisson's ratio structure produces elastic deformation after being subjected to force, and the camera captures the structural deformation image, and the deformation size is obtained through analysis. According to the conversion equation between the external force and the deformation variable, the magnitude of the external force on the structure is finally output.

[0052] The device includes an industrial camera 2, a pan / tilt platform 1 for supporting the industrial camera 2, and a lens 3. The industrial camera 2 is placed parallel to a negative Poisson's ratio structure 4.

[0053] Since the negative Poisson's ratio structure has unique tensile expansion characteristics, the negative Poisson's ratio structure is used as a substrate and is brought into contact with the object to be measured. The shape change of the negative Poisson's ratio structure caused by the force is indirectly identified based on machine vision technology.

[0054] Applying an external force to the object being measured will cause the negative Poisson's ratio structure to deform accordingly.

[0055] The edge detection of the negative Poisson's ratio structure is performed based on the image, and the pixel coordinate values ​​of the discrete points distributed on the base structure in the image and their pixel displacement relative to the initial position are obtained.

[0056] In summary, the method for measuring force based on machine vision and negative Poisson's ratio structure of the present invention has flexible and diverse optional structures, simple overall design, and independent components without physical connection.

[0057] In yet another embodiment of the present invention, a force measurement system based on machine vision and a negative Poisson's ratio structure is provided, which can be used to implement the above-mentioned force measurement method based on machine vision and a negative Poisson's ratio structure. Specifically, the system includes:

[0058] The image acquisition module is used to place the negative Poisson's ratio structure in parallel with the industrial camera using the negative Poisson's ratio structure as a substrate, and to contact the object to be measured with the negative Poisson's ratio structure; the industrial camera collects deformation images in real time, and obtains the corresponding external force value through the elastic deformation magnitude of the first frame image and the last frame image;

[0059] The measurement conversion module is used to apply external force to the object to be measured, so that the negative Poisson's ratio structure produces elastic deformation. By utilizing the property that stress and strain are proportional, the elastic modulus E of the substrate is introduced to establish a conversion equation between external force and deformation variable, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate.

[0060] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A force measurement method based on machine vision and negative Poisson's ratio structure, characterized in that: include: Using a negative Poisson's ratio structure as a substrate, placing the negative Poisson's ratio structure parallel to the industrial camera, and bringing the object to be measured into contact with the negative Poisson's ratio structure; The industrial camera collects deformation images in real time, and obtains the corresponding external force value through the elastic deformation magnitude between the first frame and the last frame. When an external force is applied to the object to be measured, the negative Poisson's ratio structure produces elastic deformation. By using the property that stress and strain are proportional, the elastic modulus E of the substrate is introduced, and the conversion equation between the external force and the deformation variable is established, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate. The relationship between external force and stress is as follows: F=σA Where F is the load, σ is the stress, and A is the cross-sectional area of ​​the substrate in contact with the element being measured.

2. A force measurement method based on machine vision and negative Poisson's ratio structure according to claim 1, characterized in that: The shape change of the negative Poisson's ratio structure caused by force is indirectly identified based on machine vision technology: the edge detection of the negative Poisson's ratio structure is performed based on the image, and the pixel coordinate values ​​of the discrete points distributed on the base structure in the image and their pixel displacement relative to the initial position are obtained.

3. The force measurement method based on machine vision and negative Poisson's ratio structure according to claim 1, characterized in that: The relationship between strain and stress of the measuring element is as follows: σ=Eε Among them, σ is the stress on the measuring element, E is the elastic modulus of the negative Poisson's ratio structure, and ε is the strain generated by the negative Poisson's ratio structure after being subjected to force.

4. The force measurement method based on machine vision and negative Poisson's ratio structure according to claim 1, characterized in that: The positive strain is Among them, L is the length before deformation, and △L is the deformation after deformation.

5. The force measurement method based on machine vision and negative Poisson's ratio structure according to claim 1, characterized in that: The camera’s intrinsic and extrinsic parameter matrices are obtained through camera calibration, and the image taken by the camera is corrected to obtain an image with less distortion.

6. The force measurement method based on machine vision and negative Poisson's ratio structure according to claim 1, characterized in that: When the negative Poisson's ratio structure is placed parallel to the industrial camera, the camera head of the industrial camera is aligned with the base of the negative Poisson's ratio structure, and a gimbal is used to support the camera.

7. A force measurement system based on machine vision and negative Poisson's ratio structure, characterized in that: include: An image acquisition module is used for placing the negative Poisson's ratio structure in parallel with the industrial camera using the negative Poisson's ratio structure as a substrate, and bringing the object to be measured into contact with the negative Poisson's ratio structure; The industrial camera collects deformation images in real time, and obtains the corresponding external force value through the elastic deformation magnitude between the first frame and the last frame. The measurement conversion module is used to apply external force to the measured object, so that the negative Poisson's ratio structure produces elastic deformation. By using the property that stress and strain are proportional, the elastic modulus E of the substrate is introduced to establish a conversion equation between external force and deformation variable, so that the measurement of the measured object is converted into the measurement of the elastic deformation size of the substrate; The relationship between external force and stress is as follows: F=σA Where F is the load, σ is the stress, and A is the cross-sectional area of ​​the substrate in contact with the element being measured.

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