Packaging box surface character detection device

Abstract

The invention relates to the technical field of packaging box detection, in particular to a packaging box surface character detection device which comprises a character visual detection platform, a packaging box database, a visual detection interference unit, a character detection unit, a positioning detection unit and a panel control unit. According to the method, character detection interference analysis is preliminarily carried out from two points of the character detection equipment and the target packaging box, so that the influence of interference factors on a detection result is reduced, and multi-angle character detection evaluation analysis is carried out on the surface feature image of the target packaging box in an information feedback manner; according to the method, detection is carried out from multiple angles of image processing, character recognition, character size and character color, so that the accuracy and comprehensiveness of surface character detection of the target packaging box are improved, and meanwhile, character positioning detection evaluation analysis is carried out on the surface feature image, so that whether the position and direction of the surface character of the target packaging box are standard or not is intuitively known; and the detection precision of the characters on the surface of the target packaging box is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging box detection, and in particular to a device for detecting characters on the surface of a packaging box. Background Art

[0002] As one of the most commonly used products in life, packaging boxes are used in various products in life. With the improvement of people's living standards, more and more people pay more attention to the quality of life. The parameters on the packaging boxes are particularly important, such as the production date and related parameters on the food packaging boxes, the production date and parameters on the packaging boxes in the pharmaceutical production industry, etc.

[0003] In traditional manufacturing, enterprises use manual labor to complete the detection of character parameters on packaging boxes. However, manual detection has many factors such as low detection efficiency and easy fatigue, which cannot meet the production needs of enterprises. At the same time, existing visual inspection equipment cannot monitor and analyze the interference between the equipment itself and the product surface, which leads to the influence of interference factors on the detection results. It is also impossible to perform multi-angle detection of the characters on the surface of the packaging box, which is not conducive to the comprehensive detection of the characters on the surface of the packaging box and reduces the detection quality.

[0004] In view of the above technical defects, a solution is now proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a device for detecting characters on the surface of a packaging box to solve the technical defects mentioned above. The present invention initially performs character detection interference analysis from two points: the character detection device itself and the target packaging box itself, so as to reduce the influence of interference factors on the detection results. The surface feature image of the target packaging box is subjected to multi-angle character detection evaluation analysis by means of information feedback, that is, detection is performed from multiple angles such as image processing, character recognition, character size, and character color, thereby helping to improve the accuracy and comprehensiveness of character detection on the surface of the target packaging box. At the same time, character positioning detection evaluation analysis is performed on the surface feature image, so as to intuitively understand whether the position and direction of the characters on the surface of the target packaging box are consistent with the standard positioning and direction, which helps to improve the detection accuracy of characters on the surface of the target packaging box, and further improves the quality of character detection on the surface of the target packaging box.

[0006] The object of the present invention can be achieved by the following technical solutions: a device for detecting characters on the surface of a packaging box, comprising a character visual detection platform, a packaging box database, a visual detection interference unit, a character detection unit, a positioning detection unit and a panel control unit;

[0007] The character visual detection platform retrieves the detection interference information of the character detection device from the packaging box database, and sends the detection interference information to the visual detection interference unit;

[0008] The visual detection interference unit is used to perform character detection interference evaluation analysis on the received detection interference information, perform discrimination analysis on the obtained self-interference index and surface interference index, and obtain a normal signal or an interference signal;

[0009] The character detection unit is used to respond to the normal signal, collect the surface feature image of the target packaging box, and perform multi-angle character detection evaluation and analysis on the surface feature image, and send the obtained unqualified instruction or size difference instruction or standard signal or color difference signal to the panel control unit;

[0010] The positioning detection unit is used to respond to the standard signal, and at the same time perform character positioning detection, evaluation and analysis on the pre-processed surface feature image of the target packaging box, perform discrimination processing on the obtained distance deviation value Pk, and obtain a positioning signal or a deviation signal.

[0011] Preferably, the character detection interference evaluation and analysis process of the visual detection interference unit is as follows:

[0012] The running time period of the character detection device is collected and set as a time threshold, and the detection interference information of the character detection device within the time threshold is obtained, where the detection interference information includes a self-interference index and a surface interference index;

[0013] Discriminant analysis of self-interference index and surface interference index:

[0014] If the self-interference index is equal to zero and the surface interference index is equal to zero, a normal signal is generated;

[0015] If the self-interference index is not equal to zero and the surface interference index is not equal to zero, an interference signal is generated.

[0016] Preferably, the self-interference index represents the number of deviations of the numerical value corresponding to the self-interference information from a preset threshold, and the self-interference information includes the vertical distance between the visual detection head of the character detection device and the workbench, and the brightness of the shooting light; the surface interference index represents the area corresponding to the surface defects of the character areas on each surface of the target packaging box, and the surface defects include wrinkles and stains, dividing the surface of the target packaging box into character areas and blank areas.

[0017] Preferably, the multi-angle character detection evaluation and analysis process of the character detection unit is as follows:

[0018] The surface feature image of the target packaging box within the time threshold is obtained, and the surface feature image is preprocessed. The preprocessing includes scaling and cropping. The image information of the preprocessed surface feature image is obtained. The image information includes picture clarity and picture resolution, and the image information is discriminated and processed:

[0019] If there is a value corresponding to the image information that is lower than a preset threshold, a correction instruction is generated;

[0020] If there is no image information corresponding to a value lower than a preset threshold, a feedback instruction is generated;

[0021] Preferably, when generating a feedback instruction: obtaining a pre-processed surface feature image, performing character extraction on the pre-processed surface feature image, setting a character string composed of the character extraction of the pre-processed surface feature image as a character recognition string, and performing recognition detection and analysis on the character recognition string to obtain a qualified instruction or an unqualified instruction;

[0022] When a qualified instruction is generated: the character area of ​​the preprocessed surface feature image is obtained, and then the area corresponding to the character area of ​​the preprocessed surface feature image is obtained, and it is set as the regional character area, and the regional character area is discriminated to obtain a consistent instruction or a size difference instruction.

[0023] Preferably, when generating a consistent instruction: obtaining the maximum grayscale value and the minimum grayscale value of the character area of ​​the preprocessed surface feature image, constructing the character grayscale interval according to the maximum grayscale value and the minimum grayscale value of the character area of ​​the preprocessed surface feature image, and performing discriminant analysis on the character grayscale interval:

[0024] If the minimum grayscale value in the character grayscale interval is greater than or equal to the minimum grayscale value in the standard character grayscale interval, and the maximum grayscale value in the character grayscale interval is less than or equal to the maximum grayscale value in the standard character grayscale interval, a standard signal is generated;

[0025] If the condition that the minimum grayscale value in the character grayscale interval is greater than or equal to the minimum grayscale value in the standard character grayscale interval and the maximum grayscale value in the character grayscale interval is less than or equal to the maximum grayscale value in the standard character grayscale interval is not satisfied, a color difference signal is generated.

[0026] Preferably, the character positioning detection evaluation and analysis process of the positioning detection unit is as follows:

[0027] Obtain a preprocessed surface feature image of the target packaging box within a time threshold, obtain four angles of the target packaging box in the surface feature image, and set the four angles of the target packaging box in the surface feature image as parameter positioning points, obtain the minimum straight-line distance between each character and each parameter positioning point in the processed surface feature image, and set the minimum straight-line distance between each character and each parameter positioning point as a first distance, a second distance, a third distance, and a fourth distance, obtain the minimum straight-line distance between each character and each parameter positioning point in the standard surface feature image, and set the minimum straight-line distance between each character and each parameter positioning point in the standard surface feature image as a first standard distance, a second standard distance, a third standard distance, and a fourth standard distance;

[0028] The differences between the first distance, the second distance, the third distance and the fourth distance and the first standard distance, the second standard distance, the third standard distance and the fourth standard distance are obtained and set as the distance deviation value Pk, where k=1, 2, 3, 4, and the distance deviation value Pk is discriminated:

[0029] If the distance deviation value Pk is equal to the preset distance deviation value threshold, a positioning signal is generated;

[0030] If the distance deviation value Pk is not equal to the preset distance deviation value threshold, a deviation signal is generated.

[0031] The beneficial effects of the present invention are as follows:

[0032] (1) The present invention preliminarily performs character detection interference analysis from two points: the character detection device itself and the target packaging box itself, to determine whether the character detection device and the packaging box itself cause interference to the detection result, so as to manage and adjust the character detection device or the packaging box to reduce the influence of interference factors on the detection result, which helps to improve the accuracy of the detection result;

[0033] (2) The present invention performs multi-angle character detection, evaluation and analysis on the surface feature image of the target packaging box by means of information feedback to determine whether the quality of the characters on the surface of the target packaging box is qualified, that is, detection is performed from multiple angles such as image processing, character recognition, character size, and character color, thereby helping to improve the accuracy and comprehensiveness of the detection of characters on the surface of the target packaging box. At the same time, character positioning detection, evaluation and analysis are performed on the surface feature image so as to intuitively understand whether the position and direction of the characters on the surface of the target packaging box are consistent with the standard positioning and direction, which helps to improve the detection accuracy of the characters on the surface of the target packaging box and further improve the detection quality of the characters on the surface of the target packaging box. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below in conjunction with the accompanying drawings;

[0035] Figure 1 It is a flowchart of the system of the present invention;

[0036] Figure 2 It is a local reference analysis diagram of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

[0038] Embodiment 1:

[0039] See also Figure 1 to Figure 2 As shown, the present invention is a device for detecting characters on the surface of a packaging box, comprising a character visual detection platform, a packaging box database, a visual detection interference unit, a character detection unit, a positioning detection unit and a panel control unit, wherein the packaging box database is connected to the character visual detection platform in a one-way communication manner, the character visual detection platform is connected to the visual detection interference unit in a one-way communication manner, the visual detection interference unit is connected to the character detection unit and the panel control unit in a one-way communication manner, the character detection unit is connected to the positioning detection unit and the panel control unit in a one-way communication manner, and the positioning detection unit is connected to the panel control unit in a one-way communication manner;

[0040] The character visual detection platform retrieves the detection interference information of the character detection device from the packaging box database, and sends the detection interference information to the visual detection interference unit. The visual detection interference unit is used to perform character detection interference evaluation and analysis on the received detection interference information, so as to manage and adjust the character detection device or packaging box to reduce the influence of interference factors on the detection results. The specific character detection interference evaluation and analysis process is as follows:

[0041] The running time period of the character detection device is collected and set as a time threshold, and the detection interference information of the character detection device within the time threshold is obtained, where the detection interference information includes a self-interference index and a surface interference index;

[0042] In the embodiment of the present invention, the self-interference index indicates the number of deviations of the value corresponding to the self-interference information from the preset threshold value. The self-interference information includes the vertical distance between the visual detection head of the character detection device and the workbench, the brightness of the shooting light, etc. It should be noted that the larger the value of the self-interference index, the greater the risk of abnormal operation efficiency of the character detection device.

[0043] In the embodiment of the present invention, the surface interference index represents the area corresponding to the surface defects of the character area on each surface of the target packaging box. The surface defects include wrinkles, stains, etc. The surface of the target packaging box is divided into a character area and a blank area. It should be noted that the larger the value of the surface interference index is, the greater the risk of surface character detection deviation is.

[0044] Discriminant analysis of self-interference index and surface interference index:

[0045] If the self-interference index is equal to zero and the surface interference index is equal to zero, a normal signal is generated;

[0046] If the self-interference index is not equal to zero and the surface interference index is not equal to zero, an interference signal is generated, and the normal signal or the interference signal is sent to the panel control unit. After receiving the normal signal or the interference signal, the panel control unit immediately displays the preset warning text corresponding to the normal signal or the interference signal, so as to manage and adjust the character detection equipment or the packaging box to reduce the impact of interference factors on the detection results.

[0047] Embodiment 2:

[0048] When a normal signal is generated, the character detection unit is used to respond to the normal signal, collect the surface feature image of the target packaging box, and perform multi-angle character detection evaluation and analysis on the surface feature image to determine whether the quality of the characters on the surface of the target packaging box is qualified, that is, to detect from multiple angles such as image processing, character recognition, character size, and character color, thereby helping to improve the accuracy and comprehensiveness of the detection of characters on the surface of the target packaging box, and at the same time help to improve the quality of character printing or coding on the surface of the target packaging box. The specific multi-angle character detection evaluation and analysis process is as follows:

[0049] The surface feature image of the target packaging box within the time threshold is obtained, and the surface feature image is preprocessed. The preprocessing includes scaling, cropping, etc., and the image information of the preprocessed surface feature image is obtained. The image information includes picture clarity, picture resolution, etc., and the image information is discriminated and processed:

[0050] If there is a value corresponding to the image information that is lower than a preset threshold, a correction instruction is generated. When the correction instruction is generated, the surface feature image corresponding to the correction instruction is preprocessed again to reduce the impact of image processing on character detection;

[0051] If there is no image information corresponding to a value lower than a preset threshold, a feedback instruction is generated;

[0052] When a feedback instruction is generated: the pre-processed surface feature image is obtained, characters are extracted from the pre-processed surface feature image, and the character string composed of the characters extracted from the pre-processed surface feature image is set as a character recognition string, and recognition detection analysis is performed on the character recognition string:

[0053] If the character recognition string and the standard character recognition string are in one-to-one correspondence, a qualified instruction is generated;

[0054] If the character recognition string does not correspond to the standard character recognition string one by one, an unqualified instruction is generated and sent to the panel control unit. After receiving the unqualified instruction, the panel control unit immediately displays the preset warning text corresponding to the unqualified instruction so as to process the target packaging box;

[0055] When a qualified instruction is generated: the character area of ​​the preprocessed surface feature image is obtained, and then the area corresponding to the character area of ​​the preprocessed surface feature image is obtained, and it is set as the regional character area, and the regional character area is discriminated:

[0056] If the area of ​​the regional characters is equal to the preset regional character area threshold, a consistent instruction is generated;

[0057] If the area of ​​the regional characters is not equal to the preset area character area threshold, a size difference instruction is generated and sent to the panel control unit. After receiving the size difference instruction, the panel control unit immediately displays the preset warning text corresponding to the size difference instruction, so as to manage the target packaging boxes with character size differences, thereby helping to improve the character printing or coding quality of the target packaging boxes;

[0058] When a consistent instruction is generated: the maximum grayscale value and the minimum grayscale value of the character area of ​​the preprocessed surface feature image are obtained, the character grayscale interval is constructed according to the maximum grayscale value and the minimum grayscale value of the character area of ​​the preprocessed surface feature image, and the character grayscale interval is discriminated and analyzed:

[0059] If the minimum grayscale value in the character grayscale interval is greater than or equal to the minimum grayscale value in the standard character grayscale interval, and the maximum grayscale value in the character grayscale interval is less than or equal to the maximum grayscale value in the standard character grayscale interval, a standard signal is generated;

[0060] If the condition that the minimum grayscale value in the character grayscale interval is greater than or equal to the minimum grayscale value in the standard character grayscale interval, and the maximum grayscale value in the character grayscale interval is less than or equal to the maximum grayscale value in the standard character grayscale interval is not satisfied, a color difference signal is generated, and the standard signal or the color difference signal is sent to the panel control unit. After receiving the standard signal or the color difference signal, the panel control unit immediately displays the preset warning text corresponding to the standard signal or the color difference signal, so as to perform detection from multiple angles such as image processing, character recognition, character size, and character color, thereby helping to improve the accuracy and comprehensiveness of character detection on the surface of the target packaging box, and at the same time helping to improve the quality of character printing or coding on the surface of the target packaging box.

[0061] Embodiment three:

[0062] When the standard signal is generated, the positioning detection unit is used to respond to the standard signal, and at the same time, the character positioning detection evaluation analysis is performed on the pre-processed surface feature image of the target packaging box, so as to intuitively understand whether the position and direction of the characters on the surface of the target packaging box are consistent with the standard positioning and direction, which helps to improve the detection accuracy of the characters on the surface of the target packaging box, and further improve the detection quality of the characters on the surface of the target packaging box. The specific character positioning detection evaluation analysis process is as follows:

[0063] Obtain a preprocessed surface feature image of the target packaging box within a time threshold, obtain four angles of the target packaging box in the surface feature image, and set the four angles of the target packaging box in the surface feature image as parameter positioning points, obtain the minimum straight-line distance between each character and each parameter positioning point in the processed surface feature image, and set the minimum straight-line distance between each character and each parameter positioning point as a first distance, a second distance, a third distance, and a fourth distance, obtain the minimum straight-line distance between each character and each parameter positioning point in the standard surface feature image, and set the minimum straight-line distance between each character and each parameter positioning point in the standard surface feature image as a first standard distance, a second standard distance, a third standard distance, and a fourth standard distance;

[0064] The differences between the first distance, the second distance, the third distance and the fourth distance and the first standard distance, the second standard distance, the third standard distance and the fourth standard distance are obtained and set as the distance deviation value Pk, where k=1, 2, 3, 4, and the distance deviation value Pk is discriminated:

[0065] If the distance deviation value Pk is equal to the preset distance deviation value threshold, a positioning signal is generated;

[0066] If the distance deviation value Pk does not meet the preset distance deviation value threshold, a deviation signal is generated, and the positioning signal or the deviation signal is sent to the panel control unit. After receiving the positioning signal or the deviation signal, the panel control unit immediately displays the preset warning text corresponding to the positioning signal or the deviation signal, so as to intuitively understand whether the position and direction of the characters on the surface of the target packaging box are consistent with the standard positioning and direction, which is helpful to improve the detection accuracy of the characters on the surface of the target packaging box;

[0067] In the embodiment of the present invention, when Pk=P1, it represents the difference between the first distance and the first standard distance, when Pk=P2, it represents the difference between the second distance and the second standard distance, when Pk=P3, it represents the difference between the third distance and the third standard distance, and when Pk=P4, it represents the difference between the fourth distance and the fourth standard distance;

[0068] In summary, the present invention preliminarily performs character detection interference analysis from two points: the character detection device itself and the target packaging box itself, to determine whether the character detection device and the packaging box itself cause interference to the detection result, so as to manage and adjust the character detection device or the packaging box to reduce the influence of interference factors on the detection result, which helps to improve the accuracy of the detection result. The surface feature image of the target packaging box is subjected to multi-angle character detection evaluation analysis by means of information feedback to determine whether the quality of the characters on the surface of the target packaging box is qualified, that is, detection is performed from multiple angles such as image processing, character recognition, character size, and character color, which helps to improve the accuracy and comprehensiveness of the detection of characters on the surface of the target packaging box. At the same time, the surface feature image is subjected to character positioning detection evaluation analysis, so as to intuitively understand whether the position and direction of the characters on the surface of the target packaging box are consistent with the standard positioning and direction, which helps to improve the detection accuracy of the characters on the surface of the target packaging box, and further improve the detection quality of the characters on the surface of the target packaging box.

[0069] The threshold is set to facilitate comparison. The size of the threshold depends on the amount of sample data and the number of bases set by technicians in this field for each group of sample data; as long as it does not affect the proportional relationship between the parameter and the quantized value.

[0070] The above formulas are obtained by collecting a large amount of data for software simulation and selecting a formula that is close to the actual value. The coefficients in the formula are set by technical personnel in this field according to actual conditions. The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited to this. Any technical personnel familiar with the technical field within the technical scope disclosed by the present invention, according to the technical solution and the inventive concept of the present invention, make equivalent replacement or change, which should be covered within the protection scope of the present invention.

Claims

1. A device for detecting characters on the surface of a packaging box, characterized in that: It includes a character vision detection platform, a packaging box database, a visual detection interference unit, a character detection unit, a positioning detection unit and a panel control unit; The character visual detection platform retrieves the detection interference information of the character detection device from the packaging box database, and sends the detection interference information to the visual detection interference unit; The visual detection interference unit is used to perform character detection interference evaluation analysis on the received detection interference information, perform discrimination analysis on the obtained self-interference index and surface interference index, and obtain a normal signal or an interference signal; The character detection unit is used to respond to the normal signal, collect the surface feature image of the target packaging box, and perform multi-angle character detection evaluation and analysis on the surface feature image, and send the obtained unqualified instruction or size difference instruction or standard signal or color difference signal to the panel control unit; The positioning detection unit is used to respond to the standard signal, and at the same time perform character positioning detection, evaluation and analysis on the pre-processed surface feature image of the target packaging box, perform discrimination processing on the obtained distance deviation value Pk, and obtain a positioning signal or a deviation signal.

2. A device for detecting characters on the surface of a packaging box according to claim 1, characterized in that: The character detection interference evaluation and analysis process of the visual detection interference unit is as follows: The running time period of the character detection device is collected and set as a time threshold, and the detection interference information of the character detection device within the time threshold is obtained, where the detection interference information includes a self-interference index and a surface interference index; Discriminant analysis of self-interference index and surface interference index: If the self-interference index is equal to zero and the surface interference index is equal to zero, a normal signal is generated; If the self-interference index is not equal to zero and the surface interference index is not equal to zero, an interference signal is generated.

3. A device for detecting characters on the surface of a packaging box according to claim 2, characterized in that: The self-interference index indicates the number of deviations of the numerical value corresponding to the self-interference information from the preset threshold. The self-interference information includes the vertical distance between the visual detection head of the character detection equipment and the workbench, and the brightness of the shooting light. The surface interference index indicates the area corresponding to the surface defects of the character areas on each surface of the target packaging box. The surface defects include wrinkles and stains, and the surface of the target packaging box is divided into character areas and blank areas.

4. The device for detecting characters on the surface of a packaging box according to claim 1, characterized in that: The multi-angle character detection evaluation and analysis process of the character detection unit is as follows: The surface feature image of the target packaging box within the time threshold is obtained, and the surface feature image is preprocessed. The preprocessing includes scaling and cropping. The image information of the preprocessed surface feature image is obtained. The image information includes picture clarity and picture resolution, and the image information is discriminated and processed: If there is a value corresponding to the image information that is lower than a preset threshold, a correction instruction is generated; If there is no image information corresponding to a value lower than a preset threshold, a feedback instruction is generated.

5. A device for detecting characters on the surface of a packaging box according to claim 4, characterized in that: When generating a feedback instruction: obtaining a pre-processed surface feature image, performing character extraction on the pre-processed surface feature image, setting a character string composed of the character extraction of the pre-processed surface feature image as a character recognition string, and performing recognition detection and analysis on the character recognition string to obtain a qualified instruction or an unqualified instruction; When a qualified instruction is generated: the character area of ​​the preprocessed surface feature image is obtained, and then the area corresponding to the character area of ​​the preprocessed surface feature image is obtained, and it is set as the regional character area, and the regional character area is discriminated to obtain a consistent instruction or a size difference instruction.

6. A device for detecting characters on the surface of a packaging box according to claim 5, characterized in that: When a consistent instruction is generated: the maximum grayscale value and the minimum grayscale value of the character area of ​​the preprocessed surface feature image are obtained, the character grayscale interval is constructed according to the maximum grayscale value and the minimum grayscale value of the character area of ​​the preprocessed surface feature image, and the character grayscale interval is discriminated and analyzed: If the minimum grayscale value in the character grayscale interval is greater than or equal to the minimum grayscale value in the standard character grayscale interval, and the maximum grayscale value in the character grayscale interval is less than or equal to the maximum grayscale value in the standard character grayscale interval, a standard signal is generated; If the condition that the minimum grayscale value in the character grayscale interval is greater than or equal to the minimum grayscale value in the standard character grayscale interval and the maximum grayscale value in the character grayscale interval is less than or equal to the maximum grayscale value in the standard character grayscale interval is not satisfied, a color difference signal is generated.

7. The device for detecting characters on the surface of a packaging box according to claim 1, characterized in that: The character positioning detection evaluation and analysis process of the positioning detection unit is as follows: Obtain a preprocessed surface feature image of the target packaging box within a time threshold, obtain four angles of the target packaging box in the surface feature image, and set the four angles of the target packaging box in the surface feature image as parameter positioning points, obtain the minimum straight-line distance between each character and each parameter positioning point in the processed surface feature image, and set the minimum straight-line distance between each character and each parameter positioning point as a first distance, a second distance, a third distance, and a fourth distance, obtain the minimum straight-line distance between each character and each parameter positioning point in the standard surface feature image, and set the minimum straight-line distance between each character and each parameter positioning point in the standard surface feature image as a first standard distance, a second standard distance, a third standard distance, and a fourth standard distance; The differences between the first distance, the second distance, the third distance and the fourth distance and the first standard distance, the second standard distance, the third standard distance and the fourth standard distance are obtained and set as the distance deviation value Pk, where k=1, 2, 3, 4, and the distance deviation value Pk is discriminated: If the distance deviation value Pk is equal to the preset distance deviation value threshold, a positioning signal is generated; If the distance deviation value Pk is not equal to the preset distance deviation value threshold, a deviation signal is generated.

Images