JP6258809B2 - Optical information reader, control method and program for optical information reader - Google Patents

Description

  The present invention relates to an optical information reader, an optical information reader control method, and a program.

  Two-dimensional code readers (hereinafter referred to as readers) that read two-dimensional codes such as barcodes and QR codes (registered trademark) are widely used. An example of such a reader is described in Patent Document 1.

JP 2011-76519 A

  By the way, in order to accurately decode the two-dimensional code by the reader, it is necessary to adjust the distance between the reader and the two-dimensional code so that there is no blur. This is because although some blurring is allowed, a decoding error occurs in an image with large blurring. In a factory, a two-dimensional code is given to a workpiece (product) conveyed on a line or laser engraving is performed, and this is read by a reader for production management. When the leader is installed with respect to the line, the distance to the two-dimensional code of the workpiece is adjusted. However, due to variations in the height of the workpiece conveyed on the line, variations in the position of the workpiece with respect to the line, etc. The distance to the dimension code may deviate from an appropriate distance, and a decoding error may occur. Of course, the reader can decode the two-dimensional code even if some blur occurs, but it is required to install the reader after knowing how much variation is allowed in the distance between the reader and the two-dimensional code. . That is, if the range of distance that can achieve the desired reading success rate (referred to as allowable depth) can be presented to the user or the person in charge of installation, the success rate of decoding at the factory can be improved. This will also be important in reducing the waste of work due to decoding failures.

  SUMMARY An advantage of some aspects of the invention is that it provides an optical information reader capable of obtaining an allowable depth.

According to the present invention, for example,
An imaging unit that includes a focus adjustment mechanism and images a code provided on the workpiece;
Decoding means for decoding image data acquired by the imaging means;
When the adjustment amount in the focus adjustment mechanism is changed in a plurality of ways, the decoding result by the decoding unit is obtained for each image data acquired by the imaging unit for each adjustment amount, and the adjustment amount is converted. An allowable depth that is a distance from the imaging means to the work that is allowed in decoding the code based on the correspondence between the obtained distance from the imaging means to the work and the decoding result Computing means for computing
An optical information reading device is provided.

  According to the present invention, an optical information reading apparatus capable of obtaining an allowable depth is provided.

The figure which shows an example of an optical information reader Diagram for explaining allowable depth Diagram showing the relationship between reading distance and matching level The figure which shows an example of the function etc. which convert the lens extension amount into the reading distance Diagram showing an example of a reader The figure which shows an example of the computer which sets a reader The figure which shows an example of the user interface Flow chart showing allowable depth acquisition processing

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

  FIG. 1 is a diagram showing an example of a reader system (optical information reader). A line 1 is a conveyance belt that conveys a workpiece 2 that is an inspection object. The reader 3 is a two-dimensional code reader that reads and decodes a two-dimensional code. Note that the reader 3 itself is an optical information reading device in a narrow sense. The programmable logic controller (PLC 5) is a control device that controls the line 1 and the reader 3. The computer 4 is an information processing apparatus that sets operating conditions and the like for the reader 3 and acquires and displays a decoding result from the reader 3.

<Allowable depth (reading depth)>
2A and 2B are diagrams for explaining the allowable depth. FIG. 2A is a diagram showing that the allowable depth DD is found by moving the work 2 away from or closer to the reader 3. FIG. 2B is a diagram showing that the allowable depth DD is found by moving the reader 3 away from or closer to the work 2. 2A and 2B, RD is a reading distance from the tip position P0 of the reader 3 when the user installs the reader 3 to the two-dimensional code 6 provided on the surface of the workpiece 2. Is referred to as a reference distance (the reading distance is variable, but the reading distance when the permissible depth acquisition process is started is referred to as a reference distance). In order to grasp the permissible depth DD, the user checks the ease of reading (referred to as a matching level) while moving the workpiece 2 away from or closer to the reader 3, and achieves a desired matching level. The possible position Pf of the far side workpiece 2 and the position Pn of the near side workpiece 2 are found, and the distance from the tip position P0 to Pn of the reader 3 and the distance from the tip position P0 to Pf of the reader 3 are determined. Obtained as allowable depth DD. The matching level is calculated and displayed by the reader 3 or the computer 4. Note that the optical system of the reader 3 is not necessarily focused on the two-dimensional code 6 of the workpiece 2 at the initial position (reference position Pr). For this reason, the margin on the far side (far margin) Mf and the margin on the near side (near margin) Mn may not coincide with the reference distance RD. Therefore, if the position of the two-dimensional code 6 at the reference distance RD is the reference position Pr, the distance from the reference position Pr to the reading limit position Pn on the near side is the near margin Mn. The distance from the reference position Pr to the far-side reading limit position Pf is the far margin Mf. As shown in FIG. 2B, the allowable depth DD may be obtained by confirming the matching level at each reading distance while fixing the work 2 and moving the reader 3 away from or close to the work 2.

  Incidentally, the matching level is a parameter indicating how easy the reader 3 can read the two-dimensional code 6 when the reader 3 successfully reads the two-dimensional code 6. There are only two reading results for each reading of the two-dimensional code 6: success and failure. Therefore, even if attention is paid only to whether the decoding succeeds or fails, it is not known how much time the decoding succeeds. Therefore, a measure called matching level is used in the industry. Since the matching level calculation method itself is already well known in the art, its details are omitted here.

  FIG. 3 shows an example of a graph showing the relationship between the reading distance between the reader / work and the matching level, and an example of a user interface (UI) that displays the allowable depth, the near margin, and the far margin. FIG. 3 shows an example in which the reference distance RD is 170 mm. In FIG. 3, UML is a predetermined threshold condition set by the user. The UML here is an allowable lower limit matching level. In this example, the near limit distance that satisfies UML is 130 mm, and the far distance is 220 mm. Therefore, the allowable depth is 130 mm to 220 mm. Moreover, since the reference distance RD is 170 mm and the limit distance on the near side is 130 mm, the near margin is 40 mm. Since the reference distance RD is 170 mm and the far-side limit distance is 220 mm, the far margin is 50 mm.

  If the permissible depth or the like can be presented to the user in this way, it becomes possible to specifically understand the range in which the distance from the reader 3 to the two-dimensional code 6 of the work 2 should be kept. However, in the method shown in FIGS. 2A and 2B, the user needs to move the workpiece 2 up and down and the reader 3 up and down. In particular, a cable or the like is connected to the reader 3, and it is not easy to move the reader 3 manually. Furthermore, decoding results need to be obtained for a large number of positions, which would be a huge work. On the other hand, it is also possible to employ a focus adjustment mechanism (AF mechanism) in the optical system of the reader 3. The AF mechanism is a mechanism for driving the optical system so as to focus on the subject. Therefore, in the present embodiment, the AF mechanism is driven to adjust the in-focus position, the adjustment amount is converted into the distance between the reader 3 and the work 2, and the correspondence between the converted distance and the decoding result is obtained. An optical information reader that calculates the allowable depth based on the above is provided. As a result, the user can grasp the allowable depth without moving the reader 3 or the work 2.

<Method of converting AF adjustment amount into reading distance>
The AF mechanism generally performs focusing (focusing) by extending a part or all of the lenses of the optical system or changing the refractive index of the liquid lens. Here, for convenience of explanation, it is assumed that the lens is extended. Therefore, if data indicating the relationship between the lens feed amount (AF adjustment amount) and the read distance is created in advance, the feed amount can be converted into the read distance based on this data. The reading distance is the distance from the tip position P0 of the reader 3 to the two-dimensional code 6 of the workpiece 2.

  FIG. 4 is a diagram illustrating an example of a correspondence relationship between the lens extension amount and the reading distance. Such a relationship can be obtained by conducting an experiment on the reader 3 or executing a simulation. By storing this in a storage device as a table or function, the lens extension amount can be converted into a reading distance. For example, a table or a function is created by measuring the reading distance for each of the 12 lens feed amounts. The approximation function may be generated by a mathematical approximation method such as a least square method. Moreover, you may obtain | require the value which exists between two measured values by performing an interpolation process with respect to a measured value. As the lens extension amount, for example, the rotation speed (rotation amount) of a motor that adjusts the position of the lens can be adopted. In the case of a liquid type lens, instead of this, the relationship (table, function, etc.) between the applied voltage (AF adjustment amount) and the reading distance is obtained in advance and stored in the storage unit, and the applied voltage is determined by referring to this relationship. Can be converted into reading distance. As described above, the data for converting the AF adjustment amount into the reading distance is generated when the reader 3 is shipped from the factory, so that the user can save time and effort.

<Control unit>
FIG. 5 is a block diagram showing an electronic configuration of the reader 3. The camera unit (imaging means) of the reader 3 includes an image sensor 10, an optical system 9, an AF mechanism 11, an illumination unit 12, and the like. The image sensor 10 is an image sensor such as a CCD or CMOS that converts an image of a two-dimensional code formed through the optical system 9 into an electrical signal. The AF mechanism 11 is a mechanism for adjusting the position and refractive index of the focusing lens in the optical system 9. The illumination unit 12 has one or more light emitting elements and is a unit that illuminates a two-dimensional code. The decoding unit 13 is a unit that decodes the image data 32 of the two-dimensional code acquired by the image sensor 10 and writes the decoding result 31 in the storage unit 30. The communication unit 14 is a unit that communicates with the PLC 5 and the computer 4. The display unit 15 is a liquid crystal display device, a light emitting diode, or the like, and is a unit that visually outputs information. The display unit 15 includes, for example, character information that is the decoding result 31 of the two-dimensional code, a reading success rate (success rate when a plurality of reading processes are executed), and a matching level (read margin indicating ease of reading). ), PPC (a value indicating how many pixels a single cell constituting the two-dimensional code corresponds to), allowable depth, near margin, far margin, and the like may be displayed. The input unit 16 is a unit that receives an input operation such as a switch. The control unit 20 is a unit that comprehensively controls each unit of the reader 3. The control unit 20 has various functions, but these may be realized by a logic circuit or may be realized by executing software. The autofocus control unit (AF control unit) 21 is a unit that controls the AF mechanism 11. The imaging control unit 22 is a unit that controls the amount of illumination light of the illumination unit 12 and controls the exposure time (shutter speed) of the imaging device 10.

  The calculation unit 23 executes various calculation processes. For example, the calculation unit 23 changes the adjustment amount in the AF mechanism 11 through the AF control unit 21 in a plurality of ways. For example, when the calculation unit 23 starts the permissible depth acquisition process, the AF control unit 21 changes the adjustment amount of the AF mechanism 11 so that the focal point of the optical system is changed to the near side with respect to the workpiece 2 and decodes. The unit 13 is caused to acquire the decoding result for the near side. For example, the AF mechanism 11 moves the lens to the closest position, and then changes the lens feed amount from the reference position to the reference position. The image sensor 10 acquires image data at each step and supplies the image data to the decoding unit 13. When this is completed, the AF control unit 21 changes the lens extension amount of the AF mechanism 11 so that the focal point of the optical system is changed to the far side with respect to the workpiece 2. The image sensor 10 acquires image data at each step and supplies the image data to the decoding unit 13. Note that the AF mechanism 11 may continuously change from the closest lens extension amount to the far side lens extension amount. On the other hand, the calculation unit 23 causes the decoding unit 13 to decode each image data 32 acquired by the imaging device 10 for each adjustment amount, and acquires a decoding result 31. Further, the calculation unit 23 obtains a correspondence relationship between the reading distance from the image sensor 10 to the work 2 and the decoding result 31. The reading distance from the image sensor 10 to the workpiece 2 is obtained by converting the adjustment amount of the AF mechanism 11. The computing unit 23 computes an allowable depth that is a reading distance from the image sensor 10 to the work 2 that is allowed for decoding the code based on this correspondence. Further, the calculation unit 23 may calculate the above-described near margin or far margin and display the calculated margin on the display unit 15. The setting unit 24 sets a threshold condition for the decoding result 31 in advance. The threshold condition is a criterion for the allowable depth. This threshold condition is the UML described with reference to FIG. For example, the calculation unit 23 causes the AF control unit 21 to continuously change the lens extension amount from the closest lens extension amount to the far side lens extension amount, of which the lens extension amount at which the matching level is greater than or equal to UML. It may be converted into a reading distance, and the reading distance and the matching level may be recorded in association with each other. That is, since the matching level is less than UML from the closest lens extension amount to a certain lens extension amount, recording is omitted. In addition, when the reading distance exceeds the reference distance and is changed to a reading distance on the far side, when the matching level becomes less than UML, the adjustment of the lens extension amount is stopped and the acquisition process of the allowable depth is also stopped. May be.

  The reading condition control unit 25 is a unit that controls imaging conditions such as exposure time and illumination light amount, and image processing conditions (such as filter coefficients) in the decoding unit 13. Appropriate imaging conditions and image processing conditions change due to the influence of external light on the workpiece 2 conveyed on the line 1. Therefore, the reading condition control unit 25 searches for a more appropriate reading condition and sets it in the AF control unit 21, the imaging control unit 22, and the decoding unit 13. The reading condition control unit 25 fixes the reading condition without changing it while the calculation unit 23 is executing the processing for obtaining the allowable depth. This is because the reading condition affects the matching level, and if the reading condition fluctuates, an accurate allowable depth cannot be obtained. Therefore, the calculation unit 23 starts an allowable depth acquisition process after the reading condition is determined by the reading condition control unit 25. The storage unit 30 is a storage device such as a memory. The decoding result 31 acquired by the decoding unit 13, the image data 32 acquired by the image sensor 10, the data set in the reader 3 by the setting device such as the computer 4, The setting data 33, which is data set through the input unit 16, is stored.

  FIG. 6 is a block diagram showing functions of the computer 4. If the size of the reader 3 is reduced, it becomes difficult to set all the functions of the reader 3 with only the display unit 15 and the input unit 16 of the reader 3. Therefore, some or all of the setting data 33 may be created by the computer 4 and transferred to the reader 3. The CPU 40 is a unit that controls each unit included in the computer 4 based on a program stored in the storage unit 50. The UI control unit 43, which is a function of the calculation unit 41, generates a user interface for setting the imaging conditions of the reader 3 and the user interface for displaying the decoding result 31, the image data 32, and the like output from the reader 3. To be displayed on the display unit 61. The UI control unit 43 displays an allowable depth, a near margin, a far margin, a distance from the reader 3 to the workpiece 2 (reading distance), a graph (such as FIG. 3) showing a correspondence relationship between the reading distance and the decoding result. You may display on the part 61. FIG. When a part of the graph is designated by the input unit 62, the UI control unit 43 may display the reading distance corresponding to the designated part on the display unit 61. For example, the user may move the pointer with a pointing device that is a part of the input unit 62 and superimpose the pointer on a desired position on the graph. The UI control unit 43 and the calculation unit 41 may acquire the coordinates of the pointer and calculate the corresponding reading distance on the graph from the coordinates. The calculation unit 41 is a unit that executes the various calculation processes described above instead of the calculation unit 23 of the reader 3. When the calculation performance of the calculation unit 23 of the reader 3 is low and the calculation performance of the calculation unit 41 of the computer 4 is high, the calculation unit 41 of the computer 4 may execute most calculation processes. The setting unit 42 is a unit that sets control parameters such as imaging conditions and UML in the reader 3. The communication unit 63 is connected to the communication unit 14 of the reader 3 by wire or wireless, and receives the decoding result 31 and the image data 32 and transmits the setting data 33 generated by the setting unit 42. The storage unit 50 is a memory, a hard disk drive (HDD), a solid state drive (SSD), or the like.

<Example of user interface>
FIG. 7 is a diagram illustrating an example of user interfaces 70a and 70b for displaying a graph indicating a correspondence relationship between a decoding result and a reading distance. In the user interface 70a, the pointer 71 has not yet designated a part of the graph. The UI control unit 43 updates the display position of the pointer 71 in conjunction with the operation of the pointing device of the input unit 62. When the coordinates of the pointer 71 coincide with the coordinates of the graph, the UI control unit 43 obtains a reading distance corresponding to the coordinates, and pops up the reading distance. In FIG. 7, the pop-up unit 72 includes the reading distance and image data acquired at the reading distance, but it is sufficient that at least the reading distance is included. Also, by displaying the image data, the user can visually grasp the image of the two-dimensional code and understand the relationship between the matching level and the image. Confirming the image of the two-dimensional code will help the user to change the UML.

<Flowchart>
The reader 3 has an operation mode and a setting mode. The operation mode is a mode in which reading of a two-dimensional code is performed on a plurality of workpieces 2 that are actually conveyed on the line 1. The setting mode is a mode in which the reading conditions of the reader 3 are set and the allowable depth and the like are presented to the user.

  FIG. 8 is a flowchart showing an allowable depth acquisition process. Each step of the acquisition process will be described with reference to FIG. The user adjusts the distance (reading distance) between the reader 3 and the work 2 so that the reader 3 can read the two-dimensional code provided on the work 2. Usually, the leader 3 is fixed to a support member, and the distance from the workpiece 2 can be adjusted. The user confirms the matching level displayed on the display unit 15 and adjusts the distance between the reader 3 and the work 2 so that the matching level is maximized. The reading distance in this state becomes the reference distance. When the reference distance is determined, the user operates the input unit 16 to cause the control unit 20 to start an allowable depth acquisition process.

  In S800, the setting unit 24 sets the threshold value UML based on the value input through the input unit 16 or the computer 4. The setting unit 24 may display a message or the like for prompting the setting of the UML on the display unit 15.

  In step S <b> 801, the reading condition control unit 25 determines the reading condition based on the image data acquired by the image sensor 10, sets the imaging condition in the imaging control unit 22, and sets the image processing condition in the decoding unit 13. The reading condition control unit 25 searches and sets the AF adjustment amount, illumination light quantity, exposure time, image processing conditions, etc. so that the decoding result is the best.

  In S <b> 802, the calculation unit 23 obtains a reference distance by converting the lens extension amount of the AF mechanism 11 acquired through the AF control unit 21 into a reading distance.

  In step S <b> 803, the AF control unit 21 controls the AF mechanism 11 to adjust the lens extension amount by one step so that the focal position of the optical system moves to the near side. Here, the reading distance is gradually reduced from the reference distance. In step S804, the imaging control unit 22 causes the imaging device 10 to perform imaging to acquire image data, and causes the decoding unit 13 to perform decoding processing on the image data. The decoding unit 13 performs a decoding process on the image data and acquires a decoding result. In step S <b> 805, the calculation unit 23 determines whether the two-dimensional code has been successfully decoded based on the decoding result output from the decoding unit 13. In a two-dimensional code, there are only two results of success or failure as a result of reading each time. Therefore, for example, the calculation unit 23 performs N readings for one position (reading distance), counts the number of successes, obtains the average number of successes (reading success rate), and the reading success rate is 0%. If it exceeds, it may be determined that the reading has succeeded, and if the reading success rate is 0%, it may be determined that the reading has failed. If the reading is successful, the process advances to step S807, and the calculation unit 23 obtains a matching level based on the decoding result, obtains a reading distance from the lens feed amount, and stores them in the storage unit 30. On the other hand, if the reading is unsuccessful, the process proceeds to S806, where the calculation unit 23 obtains a matching level based on the decoding result, and determines whether the matching level is equal to or higher than a threshold value. If the matching level is equal to or greater than the threshold, the reading distance has not yet reached the near limit distance. Therefore, the process returns to S803, and the lens feed amount is adjusted by one step to the near side. Thereafter, the processing of S803 to S807 is repeatedly executed until the reading distance reaches the near limit distance. On the other hand, when the matching level is less than the threshold value, the near limit distance is determined, that is, the near margin (difference between the reference distance and the near limit distance) is also determined. Therefore, it progresses to S808.

  In step S808, the AF control unit 21 controls the AF mechanism 11 so that the reading distance returns to the reference distance, and adjusts the lens extension amount of the AF mechanism 11.

  In step S809, the AF control unit 21 controls the AF mechanism 11, and adjusts the lens feed amount by one step so that the focal position of the optical system moves to the far side. Here, the reading distance is gradually increased from the reference distance. In step S810, the imaging control unit 22 causes the imaging element 10 to perform imaging to acquire image data, and causes the decoding unit 13 to execute decoding processing on the image data. The decoding unit 13 performs a decoding process on the image data and acquires a decoding result. In S811, the calculation unit 23 determines whether the two-dimensional code has been successfully decoded based on the decoding result output from the decoding unit 13. If the reading is successful, the process proceeds to S813, where the calculation unit 23 obtains a matching level based on the decoding result, obtains a reading distance from the lens feed amount, and stores them in the storage unit 30. On the other hand, if the reading is unsuccessful, the process proceeds to S812, where the calculation unit 23 obtains a matching level based on the decoding result, and determines whether the matching level is equal to or higher than a threshold value. If the matching level is greater than or equal to the threshold value, the reading distance has not yet reached the far limit distance. Therefore, the process returns to S809, and the lens feed amount is adjusted one step to the far side. Thereafter, the processes of S809 to S813 are repeatedly executed until the reading distance reaches the far limit distance. On the other hand, when the matching level becomes less than the threshold value, the far side limit distance is determined, that is, the far margin (the difference between the reference distance and the far side limit distance) is also determined. Therefore, it progresses to S814.

  In S <b> 814, the calculation unit 23 determines an allowable depth from the near limit distance and the far limit distance, and displays the allowable depth on the display unit 15. As a result, the user can grasp the allowable depth. The calculation unit 23 may cause the display unit 15 to display both or one of the near margin and the far margin together with the allowable depth or instead of the allowable depth. In addition, the calculation unit 23 may create a graph indicating the correspondence between the matching level stored in the storage unit 30 and the reading distance and display the graph on the display unit 15. Note that these display processes may be executed by the computer 4 as described above.

<Summary>
The reader 3 includes an AF mechanism 11 that adjusts the in-focus position of the optical system, an image sensor 10 that images the two-dimensional code 6 provided on the work 2, and a decoding unit that decodes image data acquired by the image sensor 10. 13. When the adjustment amount in the AF mechanism 11 is changed in a plurality of ways, the calculation unit 23 acquires the decoding result by the decoding unit 13 for each image data acquired by the imaging device 10 for each adjustment amount, and calculates the adjustment amount. A correspondence relationship between the read distance obtained by conversion and the decoding result is obtained, and an allowable depth is calculated based on the correspondence relationship. Thus, an optical information reading apparatus capable of obtaining the allowable depth is provided. Note that the calculation unit 41 of the computer 4 may execute part or all of the calculation processing of the calculation unit 23.

  The display units 15 and 61 may function as an allowable depth display unit that displays the allowable depth calculated by the calculation units 23 and 41. As a result, the user can visually grasp the allowable depth.

  As described with reference to FIGS. 3 and 8, the calculation unit 23 satisfies the threshold level condition (eg, UML) based on the correspondence between the distance from the image sensor 10 to the work and the decoding result. Of the reading distances, the distance closest to the work 2 (near limit distance) and the distance farthest from the work 2 (far limit distance) are calculated, and the work is measured from the distance closest to the work 2 to the work. On the other hand, the farthest distance may be output as the allowable depth. This makes it possible to clearly grasp the reading distance on the near side that can satisfy the threshold condition and the reading distance on the far side. That is, since the user can grasp the allowable depth, it will be possible to efficiently readjust the reading distance in consideration of variations in the workpiece 2. That is, the reading distance of the reader 3 can be adjusted so that the reading of the two-dimensional code is successful even if the variation in height of the workpiece 2 becomes maximum. Thereby, it becomes possible to reduce the discard rate of the workpiece | work 2 by not being able to read a two-dimensional code. Even if the workpiece 2 is at an acceptable level as a product, if the two-dimensional code is not correctly printed, affixed or stamped, the product management cannot be performed and the workpiece 2 is discarded. This means that even if a reading failure occurs due to insufficient setting of the reading distance of the work 2, the work 2 is discarded. Since unnecessary disposal of the work 2 leads to an increase in manufacturing cost of the work 2, such reading failure must be reduced. This is especially true if the workpiece 2 is an expensive part such as an engine block. In the present embodiment, as long as the permissible depth of the reader 3 can be presented to the user, the user can easily set the reading distance correctly, and unnecessary disposal of the workpiece 2 can be reduced.

  The user may set UML that is a threshold condition through the setting units 24 and 42. It is expected that the appropriate UML varies depending on the installation environment of the workpiece 2 and the line 1. Therefore, the user may set an appropriate UML based on his / her own experience.

  As described with reference to FIG. 2, the calculation units 23 and 41 are close to each other, which is the difference between the reference distance RD that is the actual reading distance from the work 2 to the image sensor 10 and the reading distance closest to the work 2. The direction margin Mn may be calculated. Further, the calculation units 23 and 41 and the display units 15 and 61 may function as a near margin display means for displaying the near margin. As a result, the user will be able to clearly grasp the proximity margin Mn.

  As described with reference to FIG. 2, the calculation units 23 and 41 are far distances that are differences between the reference distance RD that is the actual reading distance from the workpiece 2 to the image sensor 10 and the reading distance that is farthest from the workpiece 2. The margin Mf may be calculated. The calculation units 23 and 41 and the display units 15 and 61 may function as a far margin display unit that displays a far margin. Accordingly, the user can clearly grasp the far margin Mf.

  The AF control unit 21 changes the focus adjustment amount of the AF mechanism 11 stepwise, and the image sensor 10 captures a two-dimensional code provided on the work 2 for each focus adjustment amount and outputs image data. May be. As a result, the user manually adjusts the reading distance many times and is relieved from the trouble of performing imaging every time.

  The reading condition control unit 25 may control reading conditions including the imaging conditions of the image sensor 10 and the image processing conditions in the decoding unit 13. The calculation unit 23 starts an allowable depth acquisition process after the reading condition is determined. As described above, by executing the process for obtaining the allowable depth after appropriately adjusting the reading conditions, a more accurate allowable depth will be obtained. Similarly, the reading condition control unit 25 may fix the reading condition without changing it while the calculation unit 23 executes the processing for obtaining the allowable depth. By making the reading conditions constant, a more accurate allowable depth will be required.

  As described with reference to FIG. 8, when the allowable depth acquisition process is started, the AF control unit 21 changes the focus of the optical system of the image sensor 10 to the near side with respect to the workpiece. 11, the decoding unit 13 is caused to acquire the decoding result for the near side, and when the decoding unit 13 completes the acquisition of the decoding result for the near side, the image sensor 10 The adjustment amount of the AF mechanism 11 may be changed so that the focal point of the optical system is changed, and the decoding unit 13 may acquire the decoding result for the far side. As a result, decoding results can be obtained efficiently from the near side to the far side.

  As described with reference to FIGS. 3 and 7, the calculation units 23 and 41 and the display units 15 and 61 may function as a graph display unit that displays a graph indicating a correspondence relationship between the reading distance and the decoding result. As a result, the user can grasp the characteristics of the relationship between the reading distance and the decoding result.

  As described with reference to FIG. 7, the input unit 62 and the pointer 71 may function as designation means for designating a part of the graph indicating the correspondence. The UI control unit 43 and the display unit 61 may function as a distance display unit that displays the distance from the image sensor 10 corresponding to the portion designated by the pointer 71 to the workpiece. Thereby, the user can display the reading distance corresponding to the desired matching level in the graph by a simple operation.

  The decoding result is, for example, the reading success rate for the two-dimensional code 6, the reading margin that is an index of readability, or the image data obtained by the image sensor 10 with one cell constituting the two-dimensional code 6. It may be a PPC indicating how many pixels it corresponds to. There are various indicators of decoding results required by the user. Therefore, an index of the decoding result required by the user may be obtained and displayed.

  In this embodiment, the allowable depth is not calculated from the reading success rate of the image data acquired by the imaging means. The permissible depth is obtained based on the decoding result that is the result of decoding the image data. In the example shown in FIG. 3, the vertical axis represents the matching level obtained by decoding the image data, rather than the luminance, contrast ratio, and the like of the acquired image data itself. In the code reader, the decoding result, which is the result of decoding the image, is more important for the user than the sharpness of the image. Therefore, the reading distance and the allowable depth are calculated based on the decoding result. If the reading distance and the allowable depth are calculated from the image data, even if the decoding result is not good, it may be calculated that it is within the allowable depth. This is because the distance at which the image data is sharp and the distance at which the decoding result is excellent do not always match.

  DESCRIPTION OF SYMBOLS 1 ... Line, 2 ... Work, 3 ... Reader, 4 ... Computer, 5 ... Programmable logic controller (PLC)

Claims (17)

An imaging unit that includes a focus adjustment mechanism and images a code provided on the workpiece;
Decoding means for decoding image data acquired by the imaging means;
When the adjustment amount in the focus adjustment mechanism is changed in a plurality of ways, the decoding result by the decoding unit is obtained for each image data acquired by the imaging unit for each adjustment amount, and the adjustment amount is converted. An allowable depth that is a distance from the imaging means to the work that is allowed in decoding the code based on the correspondence between the obtained distance from the imaging means to the work and the decoding result Computing means for computing
An optical information reading apparatus comprising:   The optical information reading apparatus according to claim 1, further comprising an allowable depth display unit that displays the allowable depth calculated by the calculation unit.   The computing means is based on a correspondence relationship between a distance from the imaging means to the work and the decoding result, and is a distance that the decoding result satisfies a predetermined threshold condition and is the closest distance to the work. The distance farthest from the work is calculated, and the distance from the distance closest to the work to the distance farthest from the work is output as the allowable depth. The optical information reading device described.   The optical information reading apparatus according to claim 3, further comprising setting means for setting the threshold condition.   The calculation means calculates a proximity margin that is a difference between a reference distance that is an actual distance from the work to the imaging means and a distance that is closest to the work. 5. The optical information reading device according to 4.   6. The optical information reading apparatus according to claim 5, further comprising a near margin display means for displaying the near margin.   7. The calculation unit according to claim 3, wherein the calculation unit calculates a far margin that is a difference between a reference distance that is an actual distance from the workpiece to the imaging unit and a distance farthest from the workpiece. The optical information reader according to any one of the above.   8. The optical information reading apparatus according to claim 7, further comprising a far margin display means for displaying the far margin. An autofocus control unit for controlling the focus adjustment mechanism;
The autofocus control unit changes the focus adjustment amount of the focus adjustment mechanism,
9. The optical information according to claim 1, wherein the imaging unit images a code provided on the workpiece for each focus adjustment amount and outputs image data. 10. Reader. A reading condition control means for controlling a reading condition including an imaging condition of the imaging means and an image processing condition in the decoding means;
10. The optical information reading apparatus according to claim 1, wherein the calculation unit starts the permissible depth acquisition process after the reading condition is determined. 11.   The optical information reading apparatus according to claim 10, wherein the reading condition control unit fixes the reading condition without changing while the calculation unit performs the processing for obtaining the allowable depth.   When the permissible depth acquisition process is started, the autofocus control unit changes the adjustment amount of the focus adjustment mechanism so that the focus of the optical system of the imaging unit is changed closer to the workpiece. The decoding means acquires the decoding result for the near side, and when the decoding means completes the acquisition of the decoding result for the near side, the optical system of the imaging means is located far from the workpiece. The optical information reading apparatus according to claim 9, wherein an adjustment amount of the focus adjustment mechanism is changed so that a focus is changed, and the decoding unit is caused to acquire a decoding result for the far side.   13. The optical information according to claim 1, further comprising a graph display unit that displays a graph indicating a correspondence relationship between a distance from the imaging unit to the workpiece and the decoding result. Reader. Designation means for designating a part of the graph indicating the correspondence;
The optical information reading apparatus according to claim 13, further comprising a distance display unit that displays a distance from the imaging unit to the workpiece corresponding to a portion designated by the designation unit.   The decoding result is a PPC indicating a reading success rate for the code, a reading margin that is an index of readability, or a number of pixels corresponding to one cell constituting the code in the image data. The optical information reading device according to claim 1, wherein the optical information reading device is provided. A control method for an optical information reading apparatus, comprising: a focus adjustment mechanism, and an imaging means for imaging a code provided on a work; and a decoding means for decoding image data acquired by the imaging means,
Obtaining the decoding result by the decoding means for each image data obtained by the imaging means for each adjustment amount while changing the adjustment amount in the focus adjustment mechanism in a plurality of ways, and obtaining the adjustment amount A correspondence relationship between the distance from the imaging means to the workpiece and the decoding result is obtained, and an allowable depth that is a distance from the imaging means to the workpiece that is allowed to decode the code is calculated based on the correspondence relationship. A control method characterized by that. A program that is executed by an optical information reading device that includes a focus adjustment mechanism and includes an imaging unit that images a code provided on a workpiece, and a decoding unit that decodes image data acquired by the imaging unit, In the optical information reader,
Obtaining a decoding result by the decoding unit for each image data acquired by the imaging unit for each adjustment amount while changing the adjustment amount in the focus adjustment mechanism in a plurality of ways, and obtaining the conversion amount The correspondence between the distance from the imaging means to the workpiece and the decoding result is obtained, and the allowable depth that is the distance from the imaging means to the workpiece that is allowed to decode the code based on the correspondence is calculated. A program characterized by letting