JPH10222608A - Method and device for inspecting character - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically extract a character which is stereoscopically formed in a prescribed work like the vehicle number of an automobile, etc., with precision without receiving influence from an environment condition such as the change of surrounding light. SOLUTION: A laser height sensor 10 detects the heights of respective points on the surface of the work which is set in work feeding mechanism 12 and the height distribution picture of a work surface is formed in the picture memory 26 of a height distribution picture forming part 24. An inspecting part 22 separates a character part from a background part through the use of a height threshold value in the height distribution picture so as to extract the character. Then, an extracted character pattern is matched with a teaching pattern which is obtained from a teaching data storage part 28 so that it is inspected whether or not the character punched in the work is the correct one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for inspecting characters formed three-dimensionally on a workpiece, such as a chassis number stamped on a body part of an automobile.

[0002]

2. Description of the Related Art A chassis number stamped on a cowl outer panel (hereinafter referred to as "cowl") of an automobile is an important number serving as an identification number of the automobile. Inspection is taking place. At present, this inspection is generally performed by a visual inspection by an operator, and the enormous number of man-hours required for the inspection and the possibility of human error are problems.

In order to solve such a problem, a method of automatically checking a chassis number is disclosed in, for example, Japanese Patent Laid-Open No. 62-2487.
No. 6 has proposed a method disclosed in Japanese Patent Application Laid-Open No. HEI 6-206. In this conventional method, a cowl on which a chassis number is stamped is imaged by a television camera, and the imaged result is subjected to image processing to recognize the number.
Check that it is stamped correctly.

[0004]

The conventional method of recognizing a chassis number picked up by a camera by image processing is a method of recognizing characters based on a pattern of the intensity of reflected light on the cowl surface. However, since the chassis number is simply stamped on the metal cowl, the degree of light reflection differs depending on how light hits, and the pattern of reflected light intensity differs. That is, for example, even with the same chassis number, the pattern of the light and shade of the image obtained by capturing the environmental light (light from the surrounding light source) changes. Therefore, the conventional method has a problem that a number recognition error is likely to occur.

In the chassis number, it is important not only that the designated correct number is stamped, but also that the stamping quality, that is, whether the stamping is performed to a sufficient depth. However, in the above-mentioned conventional method, it was not possible to directly inspect the embossing depth of the number.

The present invention has been made to solve such a problem, and can automatically and three-dimensionally extract a character formed three-dimensionally by embossing or the like. It is an object of the present invention to provide an inspection method and an apparatus capable of directly inspecting quality such as an embossing depth.

[0007]

In order to achieve the above object, a character inspection method according to the present invention measures a height of each point on a work surface on which a character is formed three-dimensionally, and determines the height of each point. Forming a height distribution image of the work surface by associating the two-dimensional position with the height measurement value, and extracting and inspecting a character portion from the height distribution image based on the height measurement value of each point. It is characterized by the following.

In this configuration, utilizing the property that characters are formed three-dimensionally on the work, the height distribution of the work surface on which the characters are formed is measured, and the characters are extracted from the height distribution. Here, the work is a concept including various members on which a three-dimensional character is formed, such as a cowl of an automobile, a credit card, and a gas cylinder. Almost constant measurement results can be obtained for the height distribution of the work surface even when the conditions such as ambient light change.According to this configuration, characters on the work are always accurately extracted, and processing such as recognition is performed. It can be carried out. In this configuration, since the height distribution itself of the work surface is measured, the height (depth) of the character by stamping or the like is obtained.
Can be directly known, and the quality of characters formed on the work can be inspected. It is clear that such a configuration can be applied to inspection of not only characters in a narrow sense but also symbols and figures, and in this configuration and hereinafter, the term “character” refers to symbols and figures. The concept also includes

In a preferred aspect of the present invention, a height distribution of a reference surface of the work is obtained based on the height distribution image, and the reference distribution is determined based on a difference between the height distribution image and the height distribution of the reference surface. Form a height distribution image with surface curvature corrected,
Characters are extracted based on the corrected height distribution image.

Here, the reference plane refers to a plane which is a background of a three-dimensional character in the work, that is, a plane other than the part where the character is formed.

For example, a work on which a three-dimensional character is formed is not necessarily a perfect plane so that when a chassis number is stamped on a cowl, the cowl is bent by the stamping pressure. If the workpiece has a bend, the height distribution image of the surface of the workpiece (such as a cowl) includes the effect of the bend. Unless the influence of the bend is corrected, a character portion on the surface of the work may not be correctly extracted. This configuration is for correcting the influence of such bending of the work.

In this configuration, the height distribution of the reference surface of the work is obtained. The height distribution of the reference surface indicates the state of the curvature of the reference surface of the work. By taking the difference between the actually measured height distribution image and the height distribution of this reference plane, the relative height distribution of the character with respect to the reference plane can be obtained. This relative height distribution is equivalent to the height distribution when the reference plane is regarded as a plane. That is, according to this configuration, it is possible to obtain a height distribution image in which the influence of the bending of the work is corrected, and it is possible to accurately extract characters from the height distribution image.

In a preferred aspect of the present invention, the height distribution image is divided into a plurality of regions, and for each of these regions, a height of a reference plane of the region is determined based on a height measurement value of each point in the region. The height measurement value of each point in the height distribution image is corrected so that the reference plane height of each region becomes equal, and characters are extracted from the corrected height distribution image.

In this configuration, in order to correct the curvature of the reference surface of the work, the height distribution image of the work is divided into a plurality of regions, and the height of the reference surface of the work in the region is determined for each region. The height measurement value of each point in the height distribution image is corrected so that the reference plane height of each area is adjusted. By performing the correction so that the heights of the reference planes of the respective regions match each other, the value of the height of each point in the correction result indicates the relative height from the reference plane having a constant height. become. That is, according to this correction, it is possible to obtain the height distribution of each point when the reference plane of the work is regarded as substantially flat. As a result, in the corrected height distribution, the height of each point can be uniformly treated as the height from the plane. Therefore, in the subsequent image processing, for example, the character portion is subjected to a simple binarization process. Can be separated and extracted from the work itself. Furthermore, in this configuration, the height distribution image is divided into a plurality of regions, and the reference plane height is obtained for each region. Therefore, it is possible to cope with a case where the degree of bending of the work is not uniform over the entire work. it can.

In a further preferred aspect, the corrected height distribution image is binarized by using a required reference value for a height difference between the reference plane and a character portion as a threshold value, and a character is determined based on the binarization result. Is extracted.

For example, there is a case where a character is required to be formed with a sufficient height difference from a reference surface of a work, such as a case where a character is required to be stamped to a predetermined depth in a chassis number or the like. . In this configuration, the height distribution image is binarized based on the required height difference, that is, the required reference value. According to such a binarization process, it is possible to extract, from the height distribution image, a portion having a height difference that satisfies the required reference value. If the part extracted in this way is recognized as a character specified in advance,
That means that the character has a sufficient height difference with respect to the work reference plane. In other words, in this configuration, the character recognition processing is the inspection of the quality of the height difference of the character with respect to the work as it is. That is, according to this configuration, it is possible to simultaneously perform character recognition and quality inspection.

Further, the character inspection apparatus according to the present invention comprises a height measuring means for scanning a work surface on which a character is formed three-dimensionally and measuring the height of each point on the work surface; Height distribution image forming means for forming a height distribution image with the height measurement value of each point by the means as the pixel value of the pixel corresponding to the two-dimensional position of the point, and each pixel of the height distribution image Character extracting means for extracting characters by binarizing the value.

In this configuration, a height distribution image can be formed by using the measured height of each point on the work surface as a pixel value of a corresponding pixel, and the height distribution image is captured by a camera. Various image processing techniques such as a binarization process can be applied as in the case of the processed image. In this configuration, characters are extracted from the height distribution image, so that characters can be accurately extracted without being affected by ambient light or the like.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram showing a schematic configuration of a chassis number inspection apparatus according to the present embodiment. In this configuration, a work on which a chassis number is stamped (that is, a cowl in this case) is fixedly attached to a work feeding mechanism 12, and a laser height sensor 10 scans the surface of the work with a laser beam of spot light. Then, the height of each part of the work surface is detected based on the reflected light from the work surface.

Here, the principle of height measurement in the present embodiment will be described with reference to FIG. As shown in FIG. 2, in the present embodiment, a laser beam 110 emitted from a semiconductor laser 40 is focused on a surface of a work 100 by a scanning optical system 60, and one of diffused laser beams reflected by the surface of the work 100. Part (reflected light 120) is
An image is formed on an SD (Position Sensitive Device) 50. Here, the PSD 50 is arranged so as to capture reflected light in a direction different from the “height” direction (the vertical direction in FIG. 2) as the measurement target. When the height of the work 100 changes to H0, H1, and H2 due to such an arrangement relationship, the image forming position of the reflected light 120 from the surface of the work 100 on the PSD 50 also changes to P0, P1, and P2, respectively. Therefore, from the position where the light is focused on the PSD 50, the work 100
The height of the laser reflection point 130 on the surface can be determined. Since the PSD 50 outputs an analog signal corresponding to the image forming position of the incident light, this signal is processed by an arithmetic circuit to obtain a laser reflection point 130 on the surface of the workpiece 100.
Can be calculated.

The above is the principle of height measurement in the present embodiment. Next, a specific configuration of the height measuring system according to the present embodiment will be described with reference to FIG. Note that FIG. 3 is merely a conceptual illustration of the device configuration, and is shown in a more simplified manner than an actual device. In particular, the mechanical parts such as the work (cowl) 100, the inspection table 30, and the table driving unit 32 are greatly simplified in the drawing.

In FIG. 3, a work 100 is fixedly mounted on an inspection table 30, and can be driven in a y direction shown by a table driving section 32 including a motor and the like.

The semiconductor laser 40 emits infrared laser light having a wavelength of 830 nm (nanometers). This laser light is collimated by an optical system (not shown). The parallel beam obtained as a result is reflected by the polygon mirror 42 and focused by the fθ lens 44 for projecting light to form a spot having a diameter of about 20 μm on the surface of the work 100. The laser light thus focused is reflected (scattered) on the surface of the work 100.

In the present embodiment, of the reflected light of the laser light from the work 100, the light in two predetermined directions is transmitted to the PSD 50a,
The height is measured by guiding to 50b. For this reason, the light reflected in the predetermined two directions reflected by the surface of the work 100 is reflected and refracted by the optical path conversion units 46a and 46b, respectively, and guided to the fθ lenses 44a and 44b for receiving light. The transmitted light is reflected by the polygon mirror 42, and the PSD 50 is reflected by the light receiving lenses 48a and 48b.
a, 50b. As a result, a signal indicating the height of the reflection point is output from the PSDs 50a and 50b according to the above-described principle.

In the present embodiment, the reflected light in two directions (that is, two PSDs) is used for measuring the height because there is a possibility that the detection may be omitted in one direction. That is, as shown in FIG. 4, when the reflection point of the laser beam from the semiconductor laser 40 is located at the embossed portion 100a of the work 100, the reflected light does not reach the PSD 50 depending on the positional relationship between the PSD 50 and the reflection point. In some cases, the height cannot be measured. On the other hand, if a configuration is employed in which reflected light in two directions is captured using two PSDs as in the present embodiment, reflected light can be captured in at least one of the two PSDs. In this case, the height is calculated based on both of the output signals of the two PSDs or one of the signals that can be received. In the present embodiment, in order to simplify the signal processing, the configuration of the light receiving optical system is
It is desirable to use a configuration in which reflected light in two directions symmetrical to each other with respect to the direction perpendicular to the surface (ie, the “height” direction) is used. In addition, for characters having a relatively simple shape such as a chassis number, detection light can be sufficiently prevented from being reflected by reflected light in two directions as described above. It is also conceivable that two directions are not enough. In such a case, although the optical system becomes somewhat complicated, the configuration may be such that the number of PSDs is increased and reflected light in more directions is used.

In this embodiment, the laser beam emitted from the semiconductor laser 40 scans the surface of the workpiece 100 in the x direction shown in FIG. At this time, the scanning speed on the surface of the work 100 is determined by the fθ lens 44.
Is maintained at a constant speed. In this embodiment, the height of each point on the scanning line is measured at a pitch of 20 μm according to this scanning. When the scanning of one line in the x direction by the rotation of the polygon mirror 42 is completed, the work 100 is sent by the table driving unit 32 by one line width in the y direction, that is, about 20 μm in this example. Scanning is performed. By repeating such processing, in the present embodiment, a chassis number area of 160 mm (x direction) × 30 mm (y direction) on the surface of the work 100 is scanned, and the height of each point of about 20 μm pitch in the area is scanned. Is required. It should be noted that the prototype of the present applicant could scan the chassis number area in about 5 seconds.

The semiconductor laser 40, polygon mirror 42, fθ lenses 44, 44a and 44b in FIG.
Optical path conversion units 46a, 46b, light receiving lenses 48a, 48
b and the PSDs 50a and 50b are components of the laser height sensor 10 in FIG. The inspection table 30 and the table driving unit 32 are components of the work feed mechanism 12 in FIG.

Returning to the description of FIG. 1, the laser height sensor 10 detects two PSDs at each laser reflection point.
The height signals output from 50a and 50b are A / D converted and output as height measurement values. Laser height sensor 10
Outputs, for example, a height measurement value as 8-bit digital data with a height direction resolution of 20 μm. That is, in this case, the height can be measured in a range of a height difference of about 5 mm.

On the other hand, the work feed mechanism 12 is controlled by the feed control unit 14 to execute work feed. In the present embodiment, the work feeding mechanism 1 is operated by the following mechanism.
2 is synchronized with the laser beam scanning by the laser height sensor 10. That is, a timing signal serving as a reference for beam scanning is input from the laser height sensor 10 to the main control unit 16, and the main control unit 16 generates a timing signal serving as a reference for work feeding based on the timing signal, and performs feed control. Notify part 14. The feed control unit 14 supplies a drive command to the work feed mechanism 12 according to the timing signal, and the work feed mechanism 12 moves the work according to the drive command. The main control unit 1
Reference numeral 6 controls the overall operation of the character inspection apparatus, in addition to adjusting the synchronization between the laser beam scanning and the work feed.

The height measurement values of each point sequentially output from the laser height sensor 10 in response to such scanning are input to the height distribution image forming unit 24 of the number inspection unit 20.
The height distribution image forming unit 24 sequentially stores the input height measurement values of each point in the image memory 26. Here, the height measurement value of each point is stored as the pixel value of the pixel in the image memory 26 corresponding to the two-dimensional position of each point. In order to realize such data writing, the main control unit 16
Generates a write control signal based on a timing signal from the laser height sensor 10 and supplies the write control signal to the height distribution image forming unit 24. The height distribution image forming unit 24 writes the height measurement value of each point to the corresponding pixel of the image memory 26 according to the writing control signal. As a result of the above processing, a height distribution image having a height measurement value of each point in the chassis number area as a pixel value is formed in the image memory 26. This height distribution image is displayed on the screen of the first display unit 18a via the main control unit 16, and can be visually confirmed by the operator.
This display is realized by using the height measurement value stored as each pixel value in the image memory 26 as a pixel density value or color value.

The inspection unit 22 of the number inspection unit 20 extracts the chassis number from the height distribution image formed on the image memory 26, and determines whether or not the chassis number is a correct number, and all the chassis numbers. Check if the character is stamped to the required depth. This inspection is performed by collating (pattern matching) each character of the extracted chassis number with a pattern image stored in the teaching data storage unit 28. Here, the teaching data storage unit 28 stores a pattern image when each character used for the chassis number is correctly stamped. Using this, the inspection unit 22 inspects whether a correct character is imprinted for each digit of the chassis number. That is, the inspection unit 22 obtains, from a chassis number management database (not shown), information on the correct chassis number to be stamped on the work currently being inspected, and, based on this information, a pattern image of a correct character of each digit of the chassis number. Are sequentially extracted from the teaching data storage unit 28 and sequentially compared with the character pattern of each digit of the chassis number extracted from the height distribution image. By such processing, it can be inspected whether or not the correct chassis number is stamped with a predetermined quality. The result of this inspection is displayed on the second display section 18b. The details of the inspection process in the inspection unit 22 will be described later. The inspection unit 22 includes a DSP (digital
(A signal processor).

Next, an overall processing procedure in the apparatus of the present embodiment will be described with reference to FIG. First, the work (cowl) on which the chassis number is stamped is set on the inspection table 30 of the work feed mechanism 12 by an operator's hand or by an automatic setting mechanism (S10). Then, the inspection table 30 moves to a predetermined measurement position facing the laser height sensor 10 under the control of the feed control unit 14 (S1).
2). Then, the height distribution of the work is detected by the laser height sensor 10, and the inspection of the chassis number is performed based on the distribution (S14). When the inspection of the chassis number is completed, the inspection table 30 returns to the initial position (S16), and the work is taken out (S18).

Next, the procedure for checking the chassis number in the above processing will be described in more detail with reference to FIG. FIG.
Shows processing for each character (number, symbol) in the chassis number. In the inspection of one chassis number, the process of FIG. 6 is repeated by the number of digits of the chassis number. Each step in FIG. 6 is executed by the inspection unit 22.

As shown in FIG. 6, the inspection section 22 first extracts a rough character area of a character to be inspected from the height distribution image formed in the image memory 26 by laser scanning (S20). That is, in the chassis number, since the arrangement position of each character is predetermined, a rough character area is determined based on the position information in consideration of an error, and the height distribution of the character area is extracted from the image memory 26. .

Next, the inspection unit 22 performs plane correction on the height distribution data of the extracted area (S22). The plane correction is a process of removing a bending component of the work surface itself from the height distribution data and obtaining a height distribution when the work surface is a plane. According to this processing, the relative height (depth) of the embossed portion with respect to the work surface can be obtained. The necessity of this plane correction will be described below.

In the case of the undercarriage number, the work inevitably bends to some extent due to the pressure at the time of stamping (the work may be actively bent to improve the strength). On the other hand, the laser height sensor 10 can determine only an absolute height with respect to a certain reference. Here, in order to extract characters from the height distribution image, a binarization process is required. However, the binarization process is directly performed on the absolute height distribution image obtained by the laser height sensor 10. However, the following problems arise.

FIGS. 7A and 7B are diagrams for explaining this problem. FIG. 7A shows the inscription state of a certain character, and FIG. 7B shows the binarization result. Here, in the lower part of (a), an alternate long and short dash line showing the height of the binarization threshold 300 is shown together with the AA cross section of the upper part. As shown in FIG. 7, when the work surface 200 itself has a bend, even if the embossing section 210 is embossed at a sufficient depth with respect to the work surface 200, the inclination of the work surface 200 itself is reduced. Due to the influence, a part of the embossing part 210 becomes higher than the threshold value 300,
In the binarization result (b), a part of a character (an embossed portion) may be missing. In such a case, the stamped portion is not recognized as a correct character even though the stamp is correctly (ie, to a sufficient depth). Therefore, as the work surface 200 is necessarily bent, correction of the influence of the work surface bending, that is, plane correction processing is required to realize the inspection of the chassis number.

Next, the plane correction processing in this embodiment will be described. In the present embodiment, as shown in FIG.
First, the character area 400 extracted in S20 is further divided into a plurality of small blocks 410, and each block 4
10 is subjected to a correction process. The division into the fine blocks 410 is because the curvature (inclination) of the work surface is not necessarily uniform over the entire inside of the character area, and therefore, it may not be possible to perform a sufficient correction if the correction is performed uniformly on the entire character area. Because there is. This example is shown in FIG. In FIG. 9, as shown in FIG.
0 is inclined as a whole, and the work surface 200 is also bent in a convex shape inside the character area. In the case of a work in which a chassis number is stamped, it is general that the work is entirely bent in a convex shape as shown in FIG. In such a height distribution, for example, with respect to the height measurement value at each point of the AA section, a predetermined number of correction points 220 set for the entire character area are changed as shown in FIG. Horizontal plane 3
It is assumed that the correction has been performed so as to be lined up on the top 10. This horizontal plane 3
Reference numeral 10 is a virtual reference plane for a work, and a threshold 300 is set at a predetermined depth (height) with respect to this reference plane. In this case, due to the influence of the convex bending of the work surface 200, as shown in FIG.
It is also conceivable that it does not reach 00. In this case, even if the character is stamped at a sufficient depth with respect to the work surface 200, the character itself is not detected, or it is not determined that the character is stamped at a sufficient depth. It will be. Here, it is conceivable to perform correction using a correction formula that takes into account convex bending, but the degree of bending of the work surface due to embossing varies depending on the shape of each character and various conditions at the time of embossing. Therefore, it is practically difficult to set a uniform correction formula that can be used in all cases. Therefore, in the present embodiment, this problem is solved by dividing the character area into a plurality of minute blocks and performing correction for each block.

The correction processing in each block is as follows. That is, first, as shown in FIG. 10, the height measurement values, which are the pixel values of each pixel in the block, are totaled, and a frequency distribution (histogram) indicating the frequency of the height is created. Then, the height of the maximum frequency in the frequency distribution is set as the height of the reference plane of the block. Here, the reference plane is a part other than the part where the character is imprinted on the work surface. In the present embodiment, the height of the maximum frequency in the block is set as the height of the reference plane of the block in consideration of the bending of the reference plane itself.

However, when the height of the maximum frequency is set as the reference plane height, there is a possibility that the height of the embossed portion of the block including the embossed portion is erroneously set as the reference plane height. In order to avoid this, in the present embodiment, the maximum frequency height is not used as the reference plane height for the block including the embossed portion. Here, whether or not the embossed portion is included is determined based on the difference between the height of the maximum frequency of the block and the height of the highest point (or the lowest point). That is, in the present embodiment, the size of the block is set to be small to some extent, and it is considered that the height difference of the reference surface of the work in the block is small. Therefore, when the difference between the maximum frequency height and the highest point (or lowest point) height of a block is larger than a certain level, it is highly possible that the block includes a stamped portion. Therefore, in the present embodiment, the difference between the maximum frequency height and the highest point (or lowest point) height is compared with a predetermined threshold value, and if the difference is larger than the threshold value, the block includes a stamped portion. At this stage, the reference surface height is not set for the block. For example, when a character is engraved on the work surface 200 as in the example of FIG. 7 or the like, the maximum frequency height is low in a block including the engraved portion. What is necessary is just to determine the presence or absence of the notched portion. Conversely, the positive character may be determined based on the difference between the maximum frequency height and the minimum point height. The determination as to whether the block includes the embossed portion is not limited to the above method, and may be performed based on, for example, a difference between the height of the highest point and the height of the lowest point of the block.

By such a process, each block constituting the character area is in a state in which the reference plane height is set or not set. For example, in the example of FIG. 11, blocks b, e,
The reference plane height is not set for f, and the reference plane height is set for each block other than b, e, and f.

In this embodiment, a block for which the reference plane height is not set has eight blocks (8
Then, the median (median value) is set as the reference plane height of the block. By such processing, the reference plane heights of all the blocks constituting the character area are obtained.

In this embodiment, for a block that does not include a stamped portion, the height of the maximum frequency of the block is basically used as it is as the reference plane height. It is also conceivable that there is a large deviation from the value of the maximum frequency height of surrounding blocks due to the influence of. Considering the continuity of the work surface, it is unlikely that the height of the reference surface suddenly changes greatly.In such a block, the value that greatly deviates from the actual height of the reference surface due to the effects of noise, etc. is the largest. It is considered that the value is a frequency value. Therefore, in the present embodiment, the following median filter processing is performed to correct the reference surface height of such a block to an appropriate value. That is, in the present embodiment, for a block determined not to include the embossed portion, the reference plane height of the block (that is, the maximum frequency height) and the reference plane height of the block 8 near the block 8 ( That is, the difference from the maximum frequency height is calculated. If any of the differences is larger than a predetermined threshold, the maximum frequency height of the block is regarded as including noise, and a median having a reference plane height near 8 is used instead of the maximum frequency height. Reset to the reference plane height of the block. By such a process, for a block whose maximum frequency height is significantly different from that of the surrounding blocks, an appropriate value obtained from the surrounding reference plane height is set as the reference plane height.

By the above processing, the height of the reference plane is set to an appropriate value for all the blocks constituting the character area.

When the reference plane heights are obtained for all the blocks in this manner, the height data of all the pixels is corrected so that the reference plane heights of all the blocks become equal. This correction is performed based on the following equation.

[0047]

(Height after correction) = {(height measurement value) − (reference height of block)} + (common reference height) That is, for each pixel, the height of that pixel is measured. The difference between the value and the reference plane height of the block including the pixel is obtained, and the height measurement value of each pixel is corrected by adding a predetermined common reference plane height to the difference. FIG. 12 is a diagram conceptually illustrating this correction processing. In this correction process, as shown in FIG. 12, the height of each point on the actual work surface 200 is shifted so that the height of the reference plane of each block matches the common reference plane height 500. The correction result 200a obtained by this processing can be said to represent the height distribution of each point when the curved work reference plane is extended to a plane. According to this correction processing, a distribution of a pure embossing depth (height) itself, in which the influence of the bending of the reference surface of the work is removed, is obtained as a correction result. In the plane correction processing described above, the height distribution of the work reference plane is determined from the height distribution image formed in the image memory 26, and the difference between the height distribution of the reference plane and the height distribution image is calculated. By taking this, it can be said that it is a process of obtaining a distribution indicating the depth (height) of the embossment relative to the reference plane.

The above is the contents of the plane correction processing in S22. Referring back to FIG. 6, when the plane correction processing in S22 is completed, the height distribution of the correction result is subjected to binarization processing and labeling processing well known in the image processing field (S2).
4) The part of the embossed character is separated from the background and extracted (S
26). In step S26, high-frequency noise is removed by performing a small area removing process of excluding a region having a small area from the character portion among the regions labeled by the binarization and labeling process.

Then, the inspection unit 22 compares the character extracted in S26 with the pattern data of the correct character obtained from the teaching data storage unit 28 (see FIG. 1) (that is, performs pattern matching processing) to extract the character. It is checked whether the extracted character is a correct character (S28). The result of this character inspection, that is, the result of pass or fail is displayed on the second display unit 18b for each character.

Here, since the chassis number needs to be clearly stamped, a required standard of the stamping depth is determined for each company, and stamping quality is managed. In the present embodiment, the required standard of the embossing depth is used as a binarization threshold in the binarization processing in S24. By using such a binarization threshold, if the embossing depth of a part of the character is below the required standard,
In the value conversion result, that part is missing from the character, and as a result, it is not recognized as a correct character in the inspection in S28. Conversely, if the character is determined to be a correct character in the inspection at S28, it indicates that the entire character has been sufficiently stamped to the required depth. As described above, in the present embodiment, by using the required standard of the embossing depth as the binarization threshold, it is possible to simultaneously perform the inspection of whether or not the character is correct and the inspection of the embossing depth. If only character identification is required, the binarization threshold may be another value.

When the character inspection is completed as described above, a chipping inspection is finally performed (S30). This chipping inspection is processing for checking whether there is a possibility that the character type (printed character) of the character mounted on the engraving machine is chipped. In this process, the inspection unit 22
Inspects the character pattern extracted from the height distribution of the plane correction result for the possibility of chipping as follows.

In this example, different inspection processes are performed on a character having a loop portion such as "0" or "8" and a character having no loop portion such as "1" or "4".

For a character having a loop portion, the checking unit 22
Performs an edge detection process well known in the field of image processing on a character pattern, and checks the number of loops formed by the detected edges. FIG. 13 shows, by way of example, the state of the edge of the character “0” when there is (a) no chipping and (b) there is a chipping. As can be seen from the figure, "0" indicates that there is no chipping (in a normal case), two edge loops (edge loops 600a and 600b).
However, if there is a chip, only one edge loop (edge loop 600c) can be formed. As described above, in a character having a loop portion, if a part of the character shape is missing, the number of edge loops is smaller than in a normal case. In the present embodiment, by utilizing this property, the number of edge loops of the extracted character pattern is compared with the number of correct edge loops of the character, and if they are different, it is determined that the character pattern may be missing. I do. That is, in the present apparatus, the number of normal edge loops is registered for each character having a loop portion, and the inspection unit 22 determines the number of edge loops of the extracted character pattern in the registered normal state. Compare with the value to determine the possibility of chipping.

For a character having no loop portion, the possibility of chipping is determined by focusing on a portion of the character shape which is presumed to be easily chipped. For example, in the case of the character “1”, one of the parts that is presumed to be easily lost is a part 700 shown in FIG. In order to determine the lack of the part 700, in the present embodiment, the distance a from the vertical stroke portion of “1” to the end of the base stroke is calculated, and the distance a is calculated from a predetermined lower limit to an upper limit. If it is within the range, it is determined to be normal, and if the distance a is out of the range, it is determined that there is a possibility of chipping. As described above, in the present embodiment, the distance from a predetermined reference position to the end of the part is calculated for a part that is presumed to be easily missing of each character, and the character is determined based on whether or not this distance is within the normal range. Determine the possibility of missing a type. For this reason, in the present apparatus, information of a part which is presumed to be easily missing for each character (the position of the part, a point for calculating the distance, and the like) is registered, and the inspection unit 22 performs chipping based on this information. Inspection.

When the inspection unit 22 determines that there is a possibility that the character shape is missing by the above method, the inspection unit 22 displays the second display unit 1.
A warning is displayed at 8b. When this warning is displayed, the operator visually checks the character shape of the stamping machine to check for chipping, and if there is a chipping, performs necessary processing such as character character replacement.

The above is the procedure of a series of inspection processing for one character of the chassis number in the present embodiment. By repeating these series of processes for each digit of the chassis number, it is possible to determine the suitability of the entire chassis number. It should be noted that the apparatus prototyped by the present applicant was able to execute a series of inspection processes shown in FIG. 6 in about one second for each character.

As described above, in the present embodiment, the distribution of the height of the work surface itself is detected by the laser height sensor, and characters are extracted from this height distribution and inspected. Characters can always be detected and inspected with high accuracy without being affected by. In the inspection of individual characters, the height distribution image is divided into small blocks, the height of the reference plane is determined for each block, and the height distribution of the entire character area is determined so that the reference plane heights match. Since the image is plane-corrected, the embossing depth (height) of the character can be accurately detected without being affected by variations in the surface shape of the reference surface itself.

The plane correction processing in the above embodiment is based on the assumption that the degree of curvature of the reference surface of the work is not uniform and cannot be known in advance. In such a case, it is also possible to perform plane correction by subtracting the reference plane shape from the height distribution obtained by the laser height sensor.

In the above embodiment, the height distribution image plane-corrected in S22 can be stored on an optical disk or the like, and used as a substitute for a vehicle number.

In the above-described embodiment, the inspection of the chassis number is taken up. However, the inspection method of the present invention is not limited to the inspection of the chassis number, and the three-dimensional characters formed on the work can be used. In general, the inspection is widely applicable.

[0061]

As described above, according to the present invention,
Since the height distribution of the work surface itself is detected and characters are extracted and inspected from this height distribution, characters can always be extracted and inspected with high accuracy without being affected by changes in ambient light. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a chassis number inspection device according to the present invention.

FIG. 2 is an explanatory diagram of a principle of height measurement in the device of the embodiment.

FIG. 3 is a diagram illustrating a configuration of a height measuring system in the apparatus according to the embodiment.

FIG. 4 is a diagram for explaining a possibility of detection omission in height measurement.

FIG. 5 is a flowchart illustrating an overall processing procedure of the apparatus according to the embodiment.

FIG. 6 is a flowchart showing a detailed processing procedure of a chassis number inspection;

FIG. 7 is an explanatory diagram of a mechanism of occurrence of character detection failure due to bending of a work.

FIG. 8 is an explanatory diagram of block division of a character area.

FIG. 9 is a diagram for explaining the necessity of block division.

FIG. 10 is a diagram for explaining a method of obtaining the height of a reference plane of a block from a height distribution image.

FIG. 11 is a diagram for explaining a procedure for obtaining a reference plane height of each block.

FIG. 12 is a conceptual explanatory diagram of a plane correction process based on a reference plane height.

FIG. 13 is a diagram for explaining the concept of a method for checking for missing characters having a loop portion.

FIG. 14 is a diagram for explaining the concept of a character missing inspection method without a loop portion.

[Explanation of symbols]

10 Laser height sensor, 12 Work feed mechanism, 14
Feed control unit, 16 main control unit, 18a first display unit, 1
8b second display unit, 20 number inspection unit, 22 inspection unit, 24 height distribution image forming unit, 26 image memory,
28 Teaching data storage unit.

Claims (5)

[Claims] 1. A height distribution of the work surface by measuring a height of each point on a work surface on which a character is formed three-dimensionally and associating a two-dimensional position of each point with a height measurement value. A character inspection method, comprising: forming an image; extracting a character portion from the height distribution image based on a height measurement value of each point; and inspecting the extracted character portion. 2. The method according to claim 1, wherein a height distribution of a reference plane of the workpiece is obtained based on the height distribution image, and a difference between the height distribution image and the height distribution of the reference plane is determined. A character inspection method, comprising: forming a height distribution image in which the curvature of the reference plane has been corrected; and extracting characters based on the corrected height distribution image. 3. The method according to claim 1, wherein the height distribution image is divided into a plurality of regions, and for each of these regions, a reference plane of the region based on a height measurement value of each point in the region. The height measurement value of each point in the height distribution image is corrected so that the reference plane height of each area becomes equal, and characters are extracted from the corrected height distribution image. Features method. 4. The method according to claim 2, wherein the corrected height distribution image is binarized using a required reference value for a height difference between the reference plane and a character portion as a threshold value,
Character extraction is performed based on the binarization result. 5. A height measuring means for scanning a work surface on which characters are three-dimensionally formed and measuring the height of each point on the work surface, and a height measurement value of each point by the height measuring means. A height distribution image forming means for forming a height distribution image having pixel values of pixels corresponding to the two-dimensional position of each point, and binarizing each pixel value of the height distribution image. A character inspection apparatus, comprising: character extraction means for extracting characters; and inspecting the extracted characters.