JP2002183712A - Method and device for visual inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve a problem of inefficiency that boards are indiscriminately failed by small error recognition in a visual inspection to recognize letters written on parts on the boards. SOLUTION: A letter processing unit 49 provided with a visual inspection device comprises a position assigning part 62 adapted to assign a position where the letters are extracted in an image displaying the parts on the board and an expecting data maintaining part 60 adapted to memorize the position. A recognition unit 66 extracts the letters from the assigned position for recognition. An expecting letter string assigning part 64 assigns expected letter strings to be recognized. A determination unit 68 compares the recognized letter strings with the expected letter strings and determines the acceptibility on the basis of conforming letter strings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a visual inspection method and a visual inspection device. The present invention particularly relates to a technique for inspecting a mounting state of an electronic component mounted on an object to be inspected such as a printed circuit board.

[0002]

2. Description of the Related Art In recent years, with the rapid development of the information society, personal computers and mobile phones have exploded. In addition to simply lowering the price of these products, one of the important factors behind the spread is the diversified designs and the downsizing of the equipment for realizing them. The downsizing of electronic devices has a great influence on the portability of the devices, and further accelerates the development competition for higher integration of electronic components.

To support high-density design of electronic components,
It is indispensable to realize not only the component mounting technology itself but also a technology for inspecting the mounting state. As one of such technologies, an ICT (In-Circuit Tester) for performing a contact-type test has been used for the appearance inspection of a printed circuit board (hereinafter, simply referred to as a “board”) after component mounting.
For example, BGA (Ball Grid Array) and CSP (Chip Si
As technologies such as ze Package and Chip Scale Package have emerged, the mounting method has changed and the density has been further increased, and as a result, it is becoming difficult to respond by a contact-type inspection device. Therefore, the demand for a non-contact type appearance inspection apparatus, particularly using an image recognition technique, is increasing.

[0004]

Here, characters indicating a model number, specifications, and the like are usually written on the surface of the component mounted on the board. 2. Description of the Related Art Conventionally, there has been known a technology for inspecting whether or not a mounted component is correct by recognizing the character. However, the size of these characters and the space between the characters may vary depending on the size of the component, or the printing may be blurred, so that it is not always easy to read. Under these circumstances, how to improve the accuracy of character recognition has been a major issue. In particular, even if most characters are read correctly, it is impossible to inspect it because it could not be read at one place, and it is impossible to judge it as misinstallation due to only one mistake in reading. ineffective.

The present inventor has made the present invention based on the above recognition, and an object of the present invention is to provide a technique for improving the efficiency of board inspection by a flexible character recognition standard.

[0006]

One embodiment of the present invention relates to a visual inspection method. This method is for inspecting a mounting state of a component mounted on an object to be inspected, and includes a process of obtaining an image in which the component mounted on the object to be inspected is projected, and a description of the process. The process of extracting and recognizing characters from the acquired image, and between a character string formed by the recognized characters and a predetermined expected character string,
Determining pass / fail based on the number of matching characters;
including.

[0007] The term "inspected object" as used herein mainly refers to a substrate on which various electronic components are mounted. “Appearance inspection” includes inspection items such as detection of erroneously mounted components. The “parts” include, for example, a package such as an IC in which a model number such as “SJ27456NP” is described, and a resistor or a capacitor in which a resistance value or a capacitance value such as “103” is described. "Based on the number of matching characters" is, for example, "when a character string of 9 characters is described, at least 8
If the characters match, the test is passed. "

According to this device, by reading the characters described in the component, it is possible to confirm whether the operation of the internal program of the component or the component type is correct.
In addition, since the pass / fail judgment is made based on the number of characters to be matched, it is possible to relax the reference according to the component. In addition, for example, a pass / fail judgment can be made by loosening or strictening the criterion according to the length of the character string.

Another embodiment of the present invention relates to a visual inspection apparatus. This apparatus inspects a mounting state of a component mounted on an inspection object, and acquires a captured image in which the component mounted on the inspection object is projected by scanning the inspection object. A scanning unit, a recognition unit that extracts and recognizes characters written on the component from the captured image, and a correspondence between a character string formed by the recognized characters and a predetermined expected character string. And a determination unit for determining whether or not the character is acceptable based on the result of the comparison of the characters.
Then, the determination unit may determine a pass when the number of characters matched in the comparison satisfies a predetermined determination condition that defines a minimum number of characters to be matched.

According to another aspect of the present invention, there is provided a visual inspection method for obtaining an image of a component mounted on an object to be inspected, and extracting a character written on the component from a photographed image. Recognition unit and the process of analyzing the recognition result in units of character strings on the assumption that the character string formed by the recognized characters is a character string indicating attribute information of the part And

The "attribute information" here is, for example, an IC
And a constant code such as a resistance value and a capacitance value.

A visual inspection apparatus according to yet another aspect of the present invention includes a scanning unit that scans an object to be inspected to obtain a photographed image of a component mounted on the object to be inspected, The recognition unit includes a recognition unit that extracts written characters from a captured image and recognizes the extracted characters, an analysis unit that analyzes a result of the recognition, and a candidate dictionary that holds a plurality of character string candidates to be written on components. Then, the analysis unit assumes that a character string formed by the recognized characters matches any of the candidates,
The analysis may be performed using a character string as a unit.

Any combination of the above components,
What replaced the components and expressions of the present invention among methods, apparatuses, systems, computer programs, and the like is also effective as an aspect of the present invention.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A visual inspection apparatus according to the present embodiment recognizes a character written on a component, and a character string formed by the character and a character string expected as a recognition result. And whether the mounting state of the component is acceptable or not is determined. The pass / fail judgment is made based on the number of matching characters.

FIG. 1 shows an example of an electronic component and a character string described on the surface thereof. (A) is an example of the external appearance of an IC package.
A character string of a constant code indicating the model number of C is described.
(B) is an example of the appearance of the resistor, and the surface of the resistor has “10”.
A character string of a constant code indicating a resistance value of “3” is described. The visual inspection device according to the present embodiment reads these character strings described on the parts.

FIG. 2 shows the configuration of the appearance inspection apparatus. This apparatus scans an inspection surface of an object to be inspected by a line sensor to form an image, and determines whether the component mounting state is acceptable or not by image recognition. By driving the scanning head perpendicular to the scanning direction by the line sensor, images for each line are sequentially obtained, and the inspection is completed by one-dimensional movement of the scanning head. Another type of visual inspection device is to move the inspection surface two-dimensionally, stop it, and repeat this process to take spots one after another. In that case, however, the mechanism system is generally complicated, and the inspection time is generally increased. Is often long. In that respect,
It is more advantageous to use a one-dimensional sensor as in the present embodiment.

The appearance inspection apparatus 10 includes a main unit 12
And a test unit 14. A support table 22 is provided below the test unit 14, and holds the substrate 1 as an object to be inspected. A scanning head 16 and a stepping motor 20 for driving the scanning head 16 are provided above the test unit 14.
A guide 18 such as a linear guide for supporting the scanning head 16
Is provided.

The scanning head 16 has an illumination unit 30, a lens 32 and a line sensor 34. These members are fixed on a frame 36. Lighting unit 30
Incorporates a half mirror and the like. Light reflected vertically upward from the substrate 1 is guided to the lens 32 by the half mirror, passes through the lens 32, and is input to the line sensor 34, which is a one-dimensional CCD sensor. The line sensor 34 scans the substrate 1 line by line and outputs the image data 54 thereof.

The main unit 12 controls the entire apparatus in its entirety, and can be realized by a CPU, a memory, or other LSI of an arbitrary computer in terms of hardware, and is loaded into the memory in terms of software. It is realized by a program having an appearance inspection function or the like. Here, functional blocks realized by their cooperation are illustrated. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

The head control unit 40 of the main unit 12 first outputs a lighting control signal 50 to the lighting unit 30 to realize different lighting states according to the contents of the test.
The head control unit 40 further includes a motor control signal 52
To the stepping motor 20 and the test start signal 56 to the memory control unit 42. Step control of the stepping motor 20 is performed by the motor control signal 52, and when the inspection is started, the scanning head 16
Move to the end of. Thereafter, each time one line is scanned, the scanning head 16 advances by one line by the motor control signal 52. On the other hand, with reference to the test start signal 56, the memory control unit 42 controls the writing of the image data 54 to the memory 44, and thereafter, the image data 54 is recorded line by line.

The inspection unit 46 reads the image data 54 from the memory 44 in parallel with the scanning or after the scanning is completed, and judges pass / fail of each inspection item based on an inspection standard recorded in the inspection standard storage unit 48 in advance. I do. Inspection items include determination of misalignment of parts, missing parts, and missing solder, presence / absence of a solder bridge, and determination of polarity reversal. In the inspection reference storage unit 48, a judgment criterion or a reference image regarding pass / fail of the component mounting of the board 1 to be inspected is recorded in advance, and the pass / fail judgment is performed by applying the criterion or the image to the image actually acquired by the line sensor 34. A determination is made.

The character processing unit 49 performs an inspection which can be determined by recognizing characters from the board image. The character processing unit 49 stores the image data 54 from the memory 44.
Is read out, characters are recognized from the component area shown in the image, and pass / fail is determined based on the characters. The character processing unit 49 detects, for example, the correctness of a program inside a component or a mounted component.

FIG. 3 shows a detailed configuration of the character processing unit 49. The character processing unit 49 includes a position designation unit 62,
An expected data holding unit 60 and a recognition unit 66 are included. The position specifying unit 62 specifies a position where a character is to be extracted in an image in which the board and its components are projected. This position is, for example, "(20, 30)-(60, 200),
For example, "180 degrees" may be designated by coordinates and angles. The expected data holding unit 60 holds such position data in advance, and the position specifying unit 62 refers to this. The recognition unit 66 extracts and recognizes a character from the position specified by the position specifying unit 62.

The expected character string specification section 64 specifies an expected character string expected as a recognition result. The expected character string is held in advance by the expected data holding unit 60 in association with the position data, and the expected character string designation unit 64 refers to this.

The character processing unit 49 includes a judgment unit 6
8 and the judgment condition holding unit 70 are further held. The determination unit 68 compares corresponding characters between a character string formed by the characters recognized by the recognition unit 66 and the expected character string specified by the expected character string specifying unit 64. The determination unit 68 determines pass / fail based on the comparison result. The pass / fail judgment is made based on the number of matching characters when comparing two character strings. The determination condition holding unit 70 stores in advance a predetermined determination condition that defines the minimum number of characters to be matched. For example, if the judgment condition of “8 or 9 characters” is set,
It is assumed that the expected character string is “SJ27456NP” and the recognized character string is “5I2456NP”. The number of matching characters in the result of comparing these strings is 6 characters,
Since the judgment condition is not satisfied, it is judged as “fail”.

Different criteria may be set as the judgment conditions depending on the component. For example, for a component in which a character string with a relatively large number of characters is described, such as “SJ27456NP”, a slightly smaller number of characters may be set as the minimum number of characters to be matched instead of the total number of characters. On the other hand, "10
For a component in which a character string having a relatively small number of characters, such as “3”, the total number of characters may be set as the minimum number of characters to be matched. The configuration may be such that the determination condition can be set by the user's operation each time the inspection is performed.

FIG. 4 is a flowchart showing the procedure of the inspection in this embodiment. This inspection procedure is divided into a pre-processing stage and a main processing stage. First, the position specifying unit 62 specifies a position from which a character is to be extracted (S10). Next, the expected character string specifying unit 64 specifies the expected character string (S
12). Next, a determination condition is set (S14). The step of setting the above items is a preprocessing stage.

The following steps are the main processing steps. First, the recognition unit 66 extracts and recognizes a character from the position specified by the position specifying unit 62 (S16). Next, the determination unit 68 compares the recognized character string with the expected character string (S18). Also, the determination unit 68 calculates the number of matching characters (S20). Then, when the calculated number of characters satisfies the determination condition (S22Y), it is determined to be “pass” (S24), and when it is not satisfied (S22N), it is determined to be “fail” (S26).

(Second Embodiment) The appearance inspection apparatus of the present embodiment is different from the first embodiment in that the pass / fail judgment conditions based on the result of character recognition can be further relaxed.

FIG. 5 shows a detailed configuration of the character processing unit 49 in this embodiment. Character processing unit 49
Are the configuration of the character processing unit 49 in the first embodiment, the relaxation condition holding unit 72 and the relaxation setting unit 74.
Further included. The mitigation condition holding unit 72 holds, as the mitigation condition, a set of a plurality of types of characters that are allowed to be identified in the comparison between the recognized character string and the expected character string. Characters that allow identification are two or more characters that are likely to be misrecognized due to their approximate shape. Relaxation setting section 74
Sets the relaxation conditions. The mitigation setting unit 74 may set the mitigation condition according to the type of the component. The mitigation setting unit 74 may be configured to set the mitigation condition by the operation of the user every time the examination is performed. The determination unit 68 determines pass / fail based on the result of the comparison in consideration of the relaxation condition.

FIG. 6 shows a table of relaxation conditions. In the setting item column 84, names of setting items such as “setting 1” and “setting 2” are defined. In the first character column 86 and the second character column 88, two characters that are confusing in appearance from each other are set. The setting state column 90 indicates a state of whether the setting is valid or invalid for each setting item. For example, in the figure, the setting for identifying the alphabet “I” and the number “1” as “setting 1” is set to “valid”, and the number “7” and the number “1” as “setting 2”. Is set to “invalid”.
In addition, settings are made for confusing characters such as “5” and “S”, “Q” and “O”, and “0” and “O”.

Here, it is assumed that the settings 2 and 3 shown in FIG. 6 are validated. If the model number “SJ27456NP” of the IC exemplified in the first embodiment is “5I21456”
Even if it is recognized as "NP", "S" and "5", "7"
And “1” are identified, so the number of matching characters is eight. Therefore, the judgment condition is "8 or 9 characters"
However, the standard is more flexible than in the first embodiment in that it is determined to be “passed”.

FIG. 7 is a flowchart showing the procedure of the inspection in this embodiment. First, each step of S30 to S34 is the same as each step of S10 to S14 of the first embodiment. After the determination condition is set (S34), the user is inquired whether or not the relaxation condition should be set. If the user desires the setting (S36Y), the relaxation setting unit 7
4 sets the relaxation condition (S38). The step of setting the above items is a preprocessing stage.

The following steps are the main processing steps. First, the recognition unit 66 extracts and recognizes a character from the position specified by the position specifying unit 62 (S40). Next, the determination unit 68 compares the recognized character string with the expected character string (S42). Further, the determination unit 68 calculates the number of matching characters (S44). Then, when the calculated number of characters satisfies the determination condition (S46Y), it is determined to be "passed" (S60). On the other hand, the determination condition is not satisfied (S4
6N), and when the relaxation condition is not set (S48N), it is determined as "fail" (S58). Also,
If the criterion condition is not satisfied, but the relaxation condition is set (S48Y), the mismatched character is replaced with an approximate character based on the relaxation condition (S50). Then, the recognition character string after the replacement is compared with the expected character string (S52). Next, the number of matching characters is determined by the determination unit 6.
8 is calculated (S54). Then, when the calculated number of characters satisfies the determination condition (S56Y), it is determined to be "pass" (S60), and when the determination condition is not satisfied (S5).
6N) It is determined as "fail" (S58).

(Third Embodiment) The appearance inspection apparatus of the present embodiment is different from the first and second embodiments in that the result of character recognition is analyzed and the recognition result is supplemented according to the analysis result. For example, in the case of a resistor or a capacitor, numerical values described as a resistance value or a capacitance value have a regularity, and characters other than characters according to the rules are not described. Therefore, by analyzing the recognition result based on the rule and modifying the recognition result, the reliability of the recognition result can be increased even for characters that are difficult to recognize.

FIG. 8 shows a detailed configuration of the character processing unit 49 in this embodiment. Character processing unit 49
Is the analysis unit 76 and the candidate dictionary holding unit 7 in addition to the configuration of the character processing unit 49 in the first embodiment.
8 is further included. The analysis unit 76 analyzes the recognition result on a character string basis, on the assumption that the recognition character string is a character string indicating attribute information of the component. The analysis unit 76 analyzes with reference to the candidate dictionaries of the candidate dictionary holding unit 78.

The candidate dictionary holding unit 78 holds a plurality of character string candidates to be described in the parts in the candidate dictionary. This candidate is a character string indicating component attribute information, and is described according to a predetermined rule. For example, the resistance value and the capacitance value are E
It is limited to a 3-digit to 4-digit constant code called a series. Then, for example, in the case of the numerical value of the E24 series, the numerical values of the upper two digits are 10, 11, 12, 13, 15, 16,
18, 20, 22, 24, 27, 30, 33, 36, 3
9, 43, 47, 51, 56, 62, 68, 75, 8
2, 91. Also, the third digit of the E24 series usually indicates a factorial number, and is therefore limited to a number from 0 to 6. The candidate dictionary holding unit 78 holds combinations of these numerical values as candidates. The candidate dictionary holding unit 78 may hold a plurality of dictionaries in which constant codes are classified by component. The analysis unit 76 may switch the dictionary to be referred according to the component to be inspected.

The analysis unit 76 analyzes on the assumption that the recognized character string matches any of the character string candidates, and selects a candidate by determining which constant code is closest to the character string candidate. For example, it is assumed that a character string written on a component is a character string that can be read as both “103” and “703”. Here, according to the E24 series, the upper two digits do not become “70”, so the analysis unit 76 selects the candidate “103”. As described above, in the present embodiment, since character string candidates are limited, even if a character whose recognition is uncertain is included, the reliability of the recognition result can be increased.

The analysis unit 76 determines whether a character that does not match the rule of the candidate is included in the recognized character string.
The unmatched character may be notified to the user. For example, the analysis unit 76 may automatically convert characters that did not match the rule to matching characters. For example, the analysis unit 76 may ask the user whether to perform an automatic conversion that matches the rule.

FIG. 9 is a flowchart showing the procedure of the inspection in this embodiment. First, in the preprocessing stage, S
Steps 80 to S84 are the same as the preprocessing steps in the first embodiment.

The following steps are the main processing steps. First, the recognition unit 66 extracts and recognizes a character from the position specified by the position specifying unit 62 (S86). Next, the analysis unit 76 analyzes the recognition result and selects a candidate closest to the recognized character string from the dictionary (S88).
Next, the selected candidate is compared with the expected character string (S9).
0), if they match (S92Y), it is determined as "pass"(S94); if they do not match (S92N), it is determined as "fail" (S96).

(Fourth Embodiment) In the appearance inspection apparatus of this embodiment, a table of characters having similar shapes is set.
The third embodiment is different from the third embodiment in that a similar character table is referred to when analyzing a recognition result.

FIG. 10 shows a detailed configuration of the character processing unit 49 in this embodiment. Character processing unit 49
Includes an approximate table holding unit 80 and a table setting unit 82 in addition to the configuration of the character processing unit 49 in the third embodiment. The approximation table holding unit 80 holds an approximation table defining a plurality of types of characters having similar shapes. This approximate table is almost the same as the table shown in FIG. 6 described above, and approximate characters such as “I” and “1”, “7” and “1”, and “5” and “S” are associated with each other. Have been. When the analysis unit 76 determines that the recognized character string does not match any of the candidates, the analysis unit 76 replaces characters that do not match the rules of the candidates with similar characters, and selects a candidate.

The table setting section 82 sets an approximate table. The table setting unit 82 may set an approximation table according to the component type. For example, for components such as resistors and capacitors for which only numbers are to be described, a setting may be made to replace alphabets with numbers that approximate the alphabet.
For example, "I" and "1" and "S" and "5" may be set to be identified with each other. The table setting unit 82 may set valid / invalid for each similar character set,
This setting may be switched by a user operation.

FIG. 11 is a flowchart showing the procedure of the inspection in this embodiment. First, S100 to S10
4 is the same as S80 to S84 in the third embodiment. After the setting of the determination condition (S104), if the user desires to set the approximation table (S106Y), valid / invalid is set for each set of similar characters (S10).
8). The above steps are the preprocessing stage.

The following steps are the main processing steps. First, the recognition unit 66 extracts and recognizes a character from the position specified by the position specifying unit 62 (S110). Next, the analysis unit 76 analyzes the recognition result. If a candidate for a character string that matches the recognized character string is not included in the dictionary (S112N), a character that does not match the rule of the candidate is replaced with an approximate character (S114). ). Then, a candidate that matches the character string after replacement is selected from the dictionary (S11).
6). Next, the selected candidate is compared with the expected character string (S118).
(S122), and if not satisfied (S120)
N) is determined to be "fail" (S124).

The present invention has been described based on several embodiments. These embodiments are exemplifications, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and that such modifications are also within the scope of the present invention. is there. Less than,
Modifications will be described.

The analysis unit 76 in the third and fourth embodiments analyzes on the assumption that the recognized character string matches any of the candidates included in the dictionary, but the recognized character string does not match any of the candidates. If it is determined that the above condition is satisfied, the above-mentioned premise may be released. In this case, the user may be notified that they did not match. Alternatively, the result of the analysis with the assumption canceled may be temporarily or permanently registered in the candidate dictionary. Furthermore, the user may be asked whether to register in the candidate dictionary.

[0049]

According to the present invention, a board can be inspected efficiently by recognizing characters written on components on the board on a flexible basis.

[Brief description of the drawings]

FIG. 1 is a diagram exemplifying an electronic component and a character string described on a surface thereof.

FIG. 2 is a functional block diagram illustrating a configuration of a visual inspection device.

FIG. 3 is a character processing unit 49 according to the first embodiment.
FIG. 3 is a functional block diagram showing a detailed configuration of FIG.

FIG. 4 is a flowchart illustrating an inspection procedure according to the first embodiment.

FIG. 5 is a character processing unit 49 according to the second embodiment.
FIG. 3 is a functional block diagram showing a detailed configuration of FIG.

FIG. 6 is a diagram showing a table of relaxation conditions.

FIG. 7 is a flowchart illustrating an inspection procedure according to the second embodiment.

FIG. 8 shows a character processing unit 49 according to the third embodiment.
FIG. 3 is a functional block diagram showing a detailed configuration of FIG.

FIG. 9 is a flowchart illustrating an inspection procedure according to the third embodiment.

FIG. 10 shows a character processing unit 4 according to a fourth embodiment.
9 is a functional block diagram showing a detailed configuration of No. 9.

FIG. 11 is a flowchart illustrating an inspection procedure according to a fourth embodiment.

[Explanation of symbols]

1 board, 10 appearance inspection device, 12 main unit, 14 test unit, 49 character processing unit, 60 expected data holding unit, 62 position designation unit,
64 expected character string specification part, 66 recognition unit,
68 judgment unit, 70 judgment condition holding unit, 72
Relaxation condition storage unit, 74 relaxation setting unit, 76 analysis unit, 78 candidate dictionary storage unit, 80 approximate table storage unit, 82 table setting unit.

Claims (7)

[Claims] 1. A method for inspecting a mounted state of a component mounted on an object to be inspected, the method comprising: obtaining an image in which a component mounted on the object to be inspected is projected; Extracting a recognized character from the image and recognizing the character; determining whether the character is acceptable or not based on the number of matching characters between a character string formed by the recognized character and a predetermined expected character string Performing a visual inspection method. 2. An apparatus for inspecting a mounted state of a component mounted on an object to be inspected, wherein a scanned image of the part mounted on the object to be inspected is acquired by scanning the object to be inspected. A recognition unit that extracts and recognizes characters written on the component from the photographed image, between a character string formed by the recognized characters and a predetermined expected character string. A determination unit that determines pass / fail based on a comparison result of corresponding characters, wherein the determination unit determines a minimum number of characters to be matched by the number of characters matched in the comparison. A visual inspection apparatus characterized in that a pass is determined when the condition is satisfied. 3. A relaxation setting unit configured to set a plurality of types of characters that are allowed to be identified in the comparison as a relaxation condition, and the determination unit determines a pass / fail based on a result of the comparison in consideration of the relaxation condition. The visual inspection device according to claim 2, wherein the determination is made. 4. A method for inspecting a mounting state of a component mounted on an object to be inspected, the method comprising: obtaining an image in which a component mounted on the object to be inspected is projected; A recognition unit that extracts a character from the photographed image and recognizes the character string, on the assumption that a character string formed by the recognized character is a character string indicating attribute information of the part, Analyzing the recognition result as a unit. 5. An apparatus for inspecting a mounted state of a component mounted on an object to be inspected, wherein a scanned image of the part mounted on the object to be inspected is obtained by scanning the object to be inspected. A recognition unit that extracts and recognizes characters written on the component from the captured image, an analysis unit that analyzes the result of the recognition, and a candidate for a character string to be written on the component. A plurality of candidate dictionaries, wherein the analysis unit analyzes on a character string basis on the assumption that a character string formed by the recognized characters matches any of the candidates. A visual inspection device characterized by performing. 6. The candidate dictionary has a constant code of the component as the candidate, and the analysis unit determines which of the constant codes a character string formed by the recognized characters is closest to. The appearance inspection apparatus according to claim 5, wherein a candidate is selected by the determination. 7. A table setting unit for setting a table defining a plurality of types of characters having similar shapes, wherein the analysis unit sets a character string formed by the recognized characters to any of the candidates. The visual inspection device according to claim 5, wherein when it is determined that the characters do not match, the plurality of similar characters are replaced and a candidate is selected.