Code reader and code reading method

Abstract

To reduce the frequency of maintenance, such as cleaning, in reading a code attached to a bottom surface of a workpiece through a gap of a conveyance apparatus, thereby reducing the burden of a user.SOLUTION: A code reader 1 includes: an imaging unit having a Scheimpflug optical system; a control unit which executes decoding a code attached to a workpiece on the basis of an image output from the imaging unit; and an enclosure storing the imaging unit and the control unit, and having a first side surface with a light-receiving window formed thereon and a mounting surface which is different from the first side surface and having a mounting structure. When the enclosure is set, via the mounting surface, on an external horizontal or vertical fixed surface which is located on the side of a conveyance apparatus and below a conveyance surface, the Scheimpflug optical system forms an in-focus range which is extended in a longitudinal direction of a gap of the conveyance apparatus.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a code reader and a code reading method for reading a code attached to a workpiece transported by a transport device. [Background technology]

[0002] This type of code reader is used, for example, when reading a code attached to a workpiece transported by a transport device at a logistics site. The code reader disclosed in Patent Document 1 is configured to be able to read the code attached to the bottom surface of the workpiece, and uses the gaps in the transport device to read the code. That is, when the transport device is composed of multiple conveyors, there are gaps between the conveyors arranged in the transport direction. By installing the code reader facing upward directly below the gap between the conveyors, when the workpiece being transported passes through the gap between the conveyors, the code reader irradiates illumination light toward the bottom surface of the workpiece and receives the reflected light from the bottom surface to generate a code image. The code area of ​​the generated code image is decoded and the information obtained is used to identify and sort the workpiece. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Publication No. 2013 / 0292470 [Patent Document 2] U.S. Patent No. 6,783,068 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the code reader in Patent Document 1 is installed directly below the gap between conveyors lined up in the conveying direction. The code reader in Patent Document 1 is incorporated into the housing of a checkout system used in retail stores and supermarkets, so it is easy to provide sufficient space directly below the gap in the conveyors. However, since the installation conditions of conveyors at logistics sites and the like vary depending on the conditions of each site, there may be cases where it is not possible to secure space to install a code reader directly below the gap in the conveyors as in Patent Document 1, making installation difficult.

[0005] It is conceivable to install a code reader to the side of the transport device and below the transport surface, but since an image of the gap in the transport device would be captured from the side of the transport device B diagonally upward as shown in Fig. 25, if the in-focus range 92 is formed symmetrically with respect to the lens optical axis 91, it is difficult to fully include the longitudinal direction of the gap in the transport device B within the in-focus range 92. Therefore, the code reader 100 cannot read the code depending on the position where the code is attached on the bottom surface of the workpiece W.

[0006] Therefore, it is conceivable to use a Scheimpflug optical system in which the focal range is formed asymmetrically with respect to the lens optical axis. As in Patent Document 2, a code reader with a Scheimpflug optical system is publicly known, but it is premised on reading a code attached to the top or side of a workpiece from above the conveying surface, and does not assume reading a code attached to the bottom surface of a workpiece from the side of the conveying device and below the conveying surface.

[0007] Even if it were possible to use the code reader of Patent Document 2 to attempt to read the code attached to the bottom surface of the workpiece from the side of the conveying device and below the conveying surface, since the focal range of the Scheimpflug optical system is asymmetric with respect to the lens optical axis, it is difficult to know how much the focal range is inclined with respect to the code reader, compared to a code reader whose focal range is formed symmetrically with respect to the lens optical axis as shown in Figure 25. Therefore, with regard to a code reader having a Scheimpflug optical system, it is not easy to adjust the attitude and position of the housing and install it so that it is focused in the longitudinal direction of the gap in the conveying device.

[0008] The present disclosure has been made in consideration of such points, and its purpose is to facilitate the installation of a code reader capable of reading a code attached to the bottom surface of a workpiece from the side of a conveying device and below the conveying surface. [Means for solving the problem]

[0009] In order to achieve the above object, in this aspect, a code reader capable of reading a code attached to a bottom surface of a workpiece conveyed by a conveying device having a plurality of conveying mechanisms provided with gaps in a conveying direction from below a horizontal conveying surface of the conveying device through the gaps. The code reader includes a Scheimpflug optical system including a lens that collects reflected light from the bottom surface of the workpiece and an image sensor having a light receiving surface inclined with respect to the optical axis of the lens, an imaging unit that generates and outputs an image based on the amount of light received at the light receiving surface, a control unit that executes a decoding process on the code attached to the workpiece based on the image output from the imaging unit, and a housing that houses the imaging unit and the control unit and has a first side surface provided with a light receiving window that transmits the reflected light, and an attachment surface that is different from the first side surface and has an attachment structure. When the housing is installed via the mounting surface on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the Scheimpflug optical system of the imaging unit forms a focused range extending in the longitudinal direction of the gap.

[0010] By fixing the mounting surface of the housing to a horizontal or vertical surface that is generally used as an external fixed surface, the housing can be oriented so that a range in focus is formed in the longitudinal direction of the gap of the conveying device. The height position can be adjusted by moving the housing while maintaining the orientation, for example, using the height from the top surface of the housing to the focal plane obtained based on the image actually captured or the Scheimpflug optical system and the housing design, making installation easy.

[0011] When the housing is installed via the mounting structure on the external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the plane formed by the light receiving window intersects with the horizontal plane. The code reader of Patent Document 1 is installed facing upwards directly below the gap between the conveyors arranged in the conveying direction. Facing upwards means that the light projecting window through which the illumination light passes and the light receiving window through which the reflected light passes face directly upwards and are horizontal. However, since many workpieces are handled at the logistics site, dust and debris are likely to be generated. In particular, dust and debris may fall from the workpiece due to vibrations caused by the conveyors when the workpiece is conveyed and vibrations caused when the workpiece is handed over from one conveyor to another. The dust and debris fall downwards through the gaps between the conveyors and accumulate on the upper surface of the code reader of Patent Document 1. Since the light projecting window and the light receiving window are provided on the upper surface of the code reader, dust and debris accumulate on the light projecting window and the light receiving window, which leads to a decrease in reading performance, and therefore regular maintenance such as cleaning is required, which is a heavy burden on the user. Since the plane formed by the light receiving window intersects with the horizontal plane, dust and dirt are less likely to accumulate compared to the conventional light receiving window that faces directly upward when installed, so that the frequency of maintenance such as cleaning can be reduced, reducing the burden on the user.

[0012] The imaging unit is configured to continuously image the bottom surface of the workpiece that is exposed through the gap of the conveying device and is within the focused range, and output multiple images that include a portion of the code attached to the bottom surface of the workpiece.

[0013] The control unit can generate a composite image based on the multiple images output from the imaging unit, and perform a decoding process on the code attached to the bottom surface of the work based on the composite image.

[0014] Since the gap between the conveying devices is generally expected to be several mm to several tens of mm, it may not be possible to capture the entire code attached to the bottom surface of the workpiece in one image capture. According to this configuration, when the workpiece conveyed by the conveying device passes through the gap between the conveying mechanisms, the bottom surface of the workpiece is continuously imaged by the imaging unit from below the conveying surface of the conveying device. If a code is attached to the bottom surface of the workpiece, multiple images each showing a part of the code are output to the control unit. The control unit executes a decoding process on the code attached to the bottom surface of the workpiece based on a composite image generated using the multiple images.

[0015] The control unit may perform geometric correction on each of the plurality of images output from the imaging unit, and generate the composite image by synthesizing the plurality of processed images on which the geometric correction has been performed. For example, when the bottom surface of the workpiece exposed through the gap is captured in the plurality of images in a trapezoid shape with one end on the near side of the imaging unit as a long side and the other end on the far side of the imaging unit as a short side, the control unit may perform keystone correction on the trapezoid shape of the plurality of images. That is, since the near side of the imaging unit is captured larger than the far side, for example, a geometric correction such as keystone correction is performed before generating the composite image, making it possible to obtain a composite image suitable for decoding processing.

[0016] When the housing is installed with the light receiving window aligned to face the longitudinal direction of the gap of the transport device, the imaging unit may be configured so that the range in which the Scheimpflug optical system is focused extends in the longitudinal direction of the gap of the transport device. In other words, by focusing the Scheimpflug optical system on the gap of the transport device, optimal conditions are achieved for reading the code attached to the bottom surface of the workpiece.

[0017] The image sensor may have a plurality of imaging elements arranged in a row direction and a column direction. In this case, when the light receiving window is aligned to face the longitudinal direction of the gap of the transport device, the row direction of the image sensor may correspond to the longitudinal direction of the gap of the transport device, and the column direction of the image sensor may correspond to the transport direction of the transport device, and the image sensor may be configured to be able to partially read out signals of imaging elements in a row corresponding to the gap of the transport device among the plurality of imaging elements. In other words, when imaging through the gap of the transport device, only the part corresponding to the gap of the transport device is required in the field of view of the image sensor, so partial reading can be easily performed by aligning the row direction of the image sensor with the direction in which the gap of the transport device extends.

[0018] When the housing is installed via the mounting surface on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the imaging unit may be configured to be able to directly image the bottom surface of the workpiece through the gap.

[0019] That is, for example, if you try to image a workpiece through a gap from the side of a conveyor using a non-Scheimpflug optical system, it is difficult to focus on the conveyor surface. Although it is possible to read the code even if it is not in focus, it is more effective to focus and image the workpiece from directly below the gap in the conveyor, so in the case of a non-Scheimpflug optical system, it is common to install it directly below the gap in the conveyor as in the conventional installation position.

[0020] Here, it is conceivable to set an installation position on the side of the conveying device, install a code reader at this installation position, and take an image by adjusting the field of view to the gap of the conveying device and focusing on the conveying surface via a mirror. However, compared to taking an image directly below the conveying device via a mirror, when taking an image via a mirror from the side of the conveying device, it is necessary to tilt and adjust the angle not only in the short side direction of the mirror (approximately parallel to the conveying direction) but also in the long side direction of the mirror (approximately parallel to the long side direction of the gap of the conveying device), so that the arrangement adjustment of the mirror becomes complicated and a large tilt angle is required when tilting the mirror in the long side direction, which is likely to be restricted by the space below the conveying device and makes the layout difficult. Therefore, in the case of a non-Scheimpflug optical system, it was difficult to think of actively choosing to install the camera on the side of the conveying device rather than directly below the conveying device.

[0021] In contrast, in the present embodiment, when the housing of the code reader is installed to the side of the conveying device, the imaging unit directly images the bottom surface of the workpiece through the gap in the conveying mechanism without using a mirror, thereby enabling an installation state with high reading performance to be achieved without being restricted by the space below the conveying device.

[0022] The code reader may further include an external reflection member disposed outside the housing. When the housing is installed such that the optical axis of the lens inside the housing is substantially parallel to the conveying direction in a top view, the optical axis of the lens outside the housing is folded back by the external reflection member to a direction substantially parallel to the longitudinal direction of the gap of the conveying device in the top view, whereby the imaging unit can image the bottom surface of the workpiece via the external reflection member.

[0023] The angle between the plane formed by the light receiving window and the horizontal plane can be set to 45 degrees or more. This makes the light receiving window steeper, so that dust and dirt that falls from above can slide down the surface of the light receiving window more easily and are less likely to accumulate on the surface of the light receiving window.

[0024] That is, μ≦tan(θ) θ≧arctan(μ) If the above equation holds, foreign matter on the surface of the light-receiving window will easily slide off. For example, assuming that the coefficient of friction μ between glass, polycarbonate, etc. and other materials is usually 1 or less, if the light-receiving window is made of glass, polycarbonate, etc., then from the perspective of suppressing the accumulation of foreign matter, it is preferable that the angle between the surface of the light-receiving window and the horizontal plane be 45 degrees or more.

[0025] In another aspect, the present invention may be based on a code reading method in which a code attached to a bottom surface of a workpiece conveyed by a conveying device having a plurality of conveying mechanisms arranged with gaps in a conveying direction is read from a side of the conveying device and below the conveying surface through the gap by using a code reader including an imaging unit having a Scheimpflug optical system, a control unit for decoding an image output from the imaging unit, and a housing for housing the imaging unit and the control unit and having a first side surface on which a light receiving window is provided and an attachment surface different from the first side surface on which an attachment structure is provided. For example, the housing is installed via the attachment surface on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the Scheimpflug optical system of the imaging unit captures an image of the code attached to the bottom surface of the workpiece located in a focused range formed to extend in the longitudinal direction of the gap, and the control unit executes a decoding process on the code based on an image of the code located in the focused range. Effect of the Invention

[0026] As described above, the code reader of this embodiment can be easily installed by fixing it via the mounting surface of the housing to a commonly used horizontal or vertical external fixing surface, since the housing can be positioned in such a way that a range is formed in focus in the longitudinal direction of the gap in the conveying device. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a perspective view illustrating a code reader according to an embodiment of the present invention during operation. [Diagram 2]FIG. 2 is a block diagram of the code reader. [Diagram 3] FIG. 3 is a diagram for explaining the code reader during operation, as viewed from the upstream side in the conveying direction. [Figure 4] FIG. 4 is a plan view illustrating the code reader during operation. [Diagram 5] FIG. 5 is a schematic diagram showing the relationship between the Scheimpflug optical system and the focal plane. [Figure 6A] FIG. 6A is a diagram showing an image of a code attached to the bottom surface of a workpiece captured from the side of the transport device and below the transport plane. [Figure 6B] FIG. 6B is a diagram showing the relationship between the field of view, the focal plane, and the in-focus range of the code reader according to this embodiment. [Figure 7] FIG. 7 is a front view of the code reader. [Figure 8] FIG. 8 is a side view of the code reader. [Figure 9] FIG. 9 is a rear view of the code reader. [Figure 10A] FIG. 10A is a perspective view of the code reader as viewed from the front side. [Figure 10B] FIG. 10B is a perspective view of the code reader as viewed from the rear side. [Figure 11] FIG. 11 is a diagram showing an example in which the code reader is installed directly below the transport device. [Figure 12] FIG. 12 is a diagram showing an example in which a code reader whose light receiving window is angled at less than 90 degrees with respect to the horizontal plane is installed directly below the transport device. [Figure 13] FIG. 13 is a diagram showing an example in which a code reader whose light receiving window is angled at less than 90 degrees with respect to the horizontal plane is installed on the side of a transport device. [Figure 14] FIG. 14 is a diagram showing an example in which a code reader whose light receiving window is at an angle of more than 90 degrees with respect to the horizontal plane is installed directly below a transport device. [Figure 15A] FIG. 15A is a cross-sectional view taken along line XV-XV in FIG. [Figure 15B]FIG. 15B is a diagram illustrating a first example of the near illumination section and the far illumination section in FIG. 15A. [Figure 15C] FIG. 15C is a diagram illustrating a second example of the near illumination section and the far illumination section in FIG. 15A. [Figure 16] FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. [Figure 17] FIG. 17 is a diagram for explaining how the bottom surface of a workpiece is imaged during transportation. [Figure 18] FIG. 18 is a flowchart showing an example of a series of processes from imaging to outputting the read result. [Figure 19] FIG. 19 is a diagram for explaining a case where an image of the bottom surface of a workpiece being conveyed is captured from the side of the conveying device. [Figure 20] FIG. 20 is a diagram for explaining an example in which a plurality of code readers are installed. [Figure 21A] FIG. 21A is a diagram illustrating a first example in which the optical axes of a near illumination section and a far illumination section are provided substantially parallel to each other. [Figure 21B] FIG. 21B is a diagram illustrating a second example in which the optical axes of the near illumination section and the far illumination section are provided substantially parallel to each other. [Figure 22] FIG. 22 is a view corresponding to FIG. 4, showing a first example in which an external reflecting member is used. [Diagram 23] FIG. 23 is a view corresponding to FIG. 4, showing a second example in which an external reflecting member is used. [Figure 24] FIG. 24 is a side view showing a case where the workpiece is transported by a roller conveyor. [Diagram 25] FIG. 25 is a diagram showing the relationship between the field of view, the focal plane, and the in-focus range of a code reader in which the in-focus range is formed symmetrically with respect to the lens optical axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applications, or its uses.

[0029] Fig. 1 is a schematic diagram showing a code reader 1 according to an embodiment of the present invention during operation. Fig. 2 is a block diagram of the code reader. This example shows a case where the code reader 1 is used at a logistics site where multiple workpieces W are handled. At the logistics site, a conveying device B is installed for sequentially conveying multiple workpieces W in a predetermined conveying direction. The conveying direction of the workpieces W is indicated by arrow A, and therefore the right side of Fig. 1 is the upstream side of the conveying direction, and the left side of Fig. 1 is the downstream side of the conveying direction.

[0030] The conveying device B has a plurality of conveying mechanisms B1 and B2. Each of the conveying mechanisms B1 and B2 is, for example, a belt conveyor, and includes an upstream conveying mechanism B1 and a downstream conveying mechanism B2. The upper surfaces of the upstream conveying mechanism B1 and the downstream conveying mechanism B2 are the conveying surfaces. In this embodiment, the conveying direction of the work W is defined as the Y direction, the direction perpendicular to the Y direction on the conveying surface is defined as the X direction, and the direction perpendicular to both the X direction and the Y direction is defined as the Z direction. In the logistics field, the X direction and the Y direction are often approximately horizontal, but the Y direction may be inclined with respect to the horizontal plane. The X direction may be called the width direction of the conveying mechanisms B1 and B2, or the longitudinal direction of the gap of the conveying device B. The Z direction may be called the height direction (up and down direction). Note that this definition of the direction is for convenience of explanation, and does not limit the direction during use.

[0031] The upstream transport mechanism B1 and the downstream transport mechanism B2 are provided with a gap in the transport direction. The size (dimension) of the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2 is not particularly limited, but is set so that the smallest workpiece W to be transported is smoothly transferred from the upstream transport mechanism B1 to the downstream transport mechanism B2 without falling through the gap. The longitudinal dimension (dimension in the X direction) of the gap is approximately the same as the width (dimension in the X direction) of the transport mechanisms B1 and B2, but this is also not particularly limited.

[0032] The upstream transport mechanism B1 and the downstream transport mechanism B2 are supported on a floor surface C (shown in FIG. 3) by members such as legs B3. Because of this, the transport surfaces of the upstream transport mechanism B1 and the downstream transport mechanism B2 are positioned at a predetermined distance above the floor surface C, a space may be formed below the upstream transport mechanism B1 and the downstream transport mechanism B2.

[0033] The code reader 1 is installed at an installation position set to the side of the conveying device B and below the conveying surface of the conveying device B. That is, as shown in Fig. 1, when the edge of the width direction of the conveying device B is projected vertically downward, the edge is located on an imaginary straight line L1. The imaginary straight line L1 is a straight line extending in the Y direction. The side of the conveying device B outboard of the imaginary straight line L1 in a top view can be defined as the side of the conveying device B. As also shown in Figs. 3 and 4, the installation position of the code reader 1 in this embodiment is set to the side of the conveying device B and directly beside the gap between the conveying mechanisms B1 and B2.

[0034] The dashed line indicated by the reference numeral 8 in FIG. 1 and FIG. 2 indicates the field of view of the imaging unit 3 (shown in FIG. 2) of the code reader 1, the details of which will be described later. The code reader 1 is installed at an installation position so that the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2 is included in the field of view of the imaging unit 3. Therefore, the code reader 1 of this embodiment is a stationary type. The operation of this stationary code reader 1 is when the operation of reading the codes of the workpieces W transported by the transport device B is performed in sequence. The code reader 1 can be fixed to a vertical fixing surface of a frame F fixed to a floor surface C as shown in FIG. 3 via a mounting structure 71 described later, but it may also be fixed via a stand or bracket (not shown), or it may be directly placed and fixed on the floor surface C, or it may be fixed to the transport mechanisms B1 and B2, or it may be fixed to the leg B3, and the installation target is not particularly limited.

[0035] Since the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2 is included in the field of view of the imaging unit 3, when the bottom surface of the workpiece W being transported passes through the gap, the bottom surface can be imaged by the imaging unit 3. A code may be attached to the bottom surface of the workpiece W. If a code is attached to the bottom surface of the workpiece W, the code reader 1 is installed at an installation position below the transport surface of the transport device B, so that the code attached to the bottom surface of the workpiece W can be read through the gap from below the transport surface of the transport device B.

[0036] The code attached to the work W includes both barcodes and two-dimensional codes. Examples of two-dimensional codes include QR code (registered trademark), micro QR code, data matrix (Data code), Veri code, Aztec code, PDF417, and Maxi code. Two-dimensional codes are classified into stack type and matrix type, and the present invention can be applied to any two-dimensional code. The code may be attached to the work W by directly printing or engraving it, or by printing it on a label and then attaching it to the work W, and the means and method are not important.

[0037] 1, the code reader 1 is connected to a computer 200 and a programmable logic controller (PLC) 201 by signal lines 200a and 201a, respectively, but this is not limiting, and the code reader 1, the computer 200, and the PLC 201 may each have a built-in wireless communication module, and the code reader 1 may be connected to the computer 200 and the PLC 201 by wireless communication. The PLC 201 is a control device for sequentially controlling the conveying device B and the code reader 1, and a general-purpose PLC may be used. The computer 200 may be a general-purpose or dedicated electronic computer, a portable terminal, or the like.

[0038] Moreover, during operation, the code reader 1 receives a read start trigger signal that specifies the start timing of code reading from the PLC 201 via the signal line 201a. Then, the code reader 1 captures an image of the code and decodes it based on the read start trigger signal. The decoded result is then transmitted to the PLC 201 via the signal line 201a. Thus, during operation of the code reader 1, the read start trigger signal is repeatedly input and the decoded result is repeatedly output via the signal line 201a between the code reader 1 and an external control device such as the PLC 201. Note that the read start trigger signal may be input and the decoded result may be output via the signal line 201a between the code reader 1 and the PLC 201 as described above, or via other signal lines not shown. For example, a sensor for detecting the arrival of the work W may be directly connected to the code reader 1, and the read start trigger signal may be input from the sensor to the code reader 1.

[0039] As shown in FIG. 2, the code reader 1 includes an illumination unit 2, an imaging unit 3, a control unit 4, a storage unit 5, and a communication unit 6. The control unit 4 includes an imaging control unit 41 that controls the imaging unit 3, an illumination control unit 42 that controls the illumination unit 2, a code detection unit 43, and a decoding unit 44. The storage unit 5 can be configured with a readable and writable storage device such as an SSD (Solid State Drive). The storage unit 5 can store, for example, various programs, decoded results, image data, setting information, and the like, and includes a decoded result storage unit 51, an image data storage unit 52, and a setting storage unit 53. Although not shown, the decoded result storage unit 51, the image data storage unit 52, and the setting storage unit 53 may be provided in separate storage devices.

[0040] The communication unit 6 is a part that executes communication with the computer 200 and the PLC 201. The setting information by the computer 200 is received by the control unit 4 via the communication unit 6. In addition, the control unit 4 receives a reading start trigger signal from the PLC 201 via the communication unit 6. The decoded result by the code reader 1 is transmitted to the computer 200 and the PLC 201 via the communication unit 6. In addition, the communication unit 6 receives the dimensions of the gaps formed between the multiple conveying mechanisms B1 and B2 of the conveying device B and the conveying speed of the conveying device B. The dimensions of the gaps and the conveying speed can be input in advance by the user to the computer 200 or the like. The input dimensions of the gaps and the conveying speed are stored in the computer 200, and the dimensions of the gaps and the conveying speed are received and acquired by the communication unit 6 after being transmitted from the computer 200.

[0041] The lighting unit 2 is a part that irradiates illumination light onto the workpiece W, and the illumination range of the lighting unit 2 includes the gap between the upstream conveying mechanism B1 and the downstream conveying mechanism B2. Since the code reader 1 is installed to the side of the conveying device B and below the conveying surface of the conveying device B, the lighting unit 2 irradiates illumination light from below the conveying surface toward the gap. As a result, when the bottom surface of the workpiece W being conveyed passes through the gap between the upstream conveying mechanism B1 and the downstream conveying mechanism B2, the bottom surface can be illuminated by the lighting unit 2. If a code is attached to the bottom surface of the workpiece W, the code attached to the bottom surface of the workpiece W can be illuminated by the lighting unit 2.

[0042] The illumination unit 2 has a near illumination unit 2a and a far illumination unit 2b. The near illumination unit 2a is a part that irradiates illumination light onto the near side of a focal plane 7 (shown in FIG. 6B) of a Scheimpflug optical system 31 described later. The far illumination unit 2b is a part that irradiates illumination light onto the far side of the focal plane 7 of the Scheimpflug optical system 31. The near illumination unit 2a and the far illumination unit 2b each include a light emitting body such as a light emitting diode (LED: Light Emission Diode) or the like.

[0043] The illumination unit 2 and the imaging unit 3 may be integrated, or the illumination unit 2 and the imaging unit 3 may be separate. The illumination unit 2 is controlled by an illumination control unit 42, which switches the illumination unit 2 on and off and changes the brightness when it is on. When a reading start trigger signal is input from the PLC 201, the illumination control unit 42 turns on the illumination unit 2 for a predetermined time and turns it off after the predetermined time has elapsed.

[0044] The imaging unit 3 is a part that captures an image of the workpiece W through the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2, generates a code image including a code, and outputs it to the control unit 4. The imaging unit 3 has a Scheimpflug optical system 31, a pre-processing circuit 32, and a plane mirror 33. As also shown in FIG. 5, the Scheimpflug optical system 31 has a lens 31a and an image sensor 31b having a light receiving surface inclined with respect to the optical axis 10 of the lens 31a. The lens 31a is an imaging lens that collects reflected light from the bottom surface of the workpiece W. The light incident on the lens 31a is emitted toward the light receiving surface of the image sensor 31b and forms an image on the light receiving surface.

[0045] The plane mirror 33 is a member for directing the light incident on the imaging unit 3 to the lens 31a. That is, in this example, since the Scheimpflug optical system 31 is included, the focal plane 7 is formed so as to extend in the V direction of the image sensor 31b. FIG. 6A shows a state in which the code attached to the bottom surface of the workpiece W is imaged from the side of the conveying device B and below the conveying surface. FIG. 6A also shows the shape of the focal plane 7 formed on the light receiving surface of the image sensor 31b, where the near side is relatively close to the code reader 1, and the far side is relatively far from the code reader 1. As shown in FIG. 6A, the gap between the workpiece W and the conveying device B appears larger on the near side than on the far side. That is, on the image sensor 31b, the bottom surface of the workpiece W seen through the gap between the conveying device B is captured in a trapezoid shape with one end on the near side, which is relatively close to the imaging unit 3, as the long side, and the other end on the far side, which is relatively far from the imaging unit 3, as the short side.

[0046] 6B, the field of view of the imaging unit 3 is indicated by reference numeral 8, and the in-focus range is indicated by reference numeral 9. Also, the optical axis (the optical axis of the lens 31a) extending through the center of the field of view 8 is indicated by reference numeral 10. In this manner, the Scheimpflug optical system 31 has the inclination of the focal plane 7 in the V direction of the image sensor 31b. Compared to the code reader shown in FIG. 25 in which the in-focus range 92 is formed symmetrically with respect to the lens optical axis 91, the code reader 1 of this embodiment makes it possible to fully include the longitudinal direction of the gap of the conveying device B within the in-focus range 9.

[0047] The image sensor 31b includes light receiving elements such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) that converts the image of the code obtained through the lens 31a into an electric signal. An image including the code is generated based on the amount of light received on the light receiving surface of the image sensor 31b. The image sensor 31b has a plurality of imaging elements arranged in row and column directions, and is configured so that the row direction is approximately the same as the direction from the near side to the far side of the focal plane of the Scheimpflug optical system 31. The aspect ratio of the image sensor 31b is set smaller than the aspect ratio of a light receiving window 67 described later. The image sensor 31b is configured to be able to partially output a signal from an imaging element corresponding to the light receiving window 67 among the plurality of imaging elements.

[0048] That is, assuming that a line sensor is used as the image sensor, high-speed readout is possible, but the frame rate for reading the code becomes extremely high, which may increase the amount of heat generated by the illumination unit 2. In this regard, in this embodiment, an area sensor in which multiple image pickup elements are arranged in row and column directions is used as the image sensor 31b, and only the portion corresponding to the light receiving window 67 (some of the rows) is partially read out, thereby making it possible to achieve both heat suppression and high-speed readout.

[0049] The image generated by the image sensor 31b is input to a pre-processing circuit 32. The pre-processing circuit 32 may be provided as necessary and is not essential.

[0050] The pre-processing circuit 32 is configured with an integrated circuit such as an FPGA (Field Programmable Gate Array), and is a part that performs various pre-processing on the image output from the image sensor 31b. The pre-processing includes, for example, various filter processes. The imaging unit 3 outputs the image that has been pre-processed by the pre-processing circuit 32 to the control unit 4. The pre-processing by the pre-processing circuit 32 may be performed as necessary, and an image that has not been pre-processed may be output to the control unit 4. The image output to the control unit 4 is stored in the image data storage unit 52 of the storage unit 5.

[0051] The imaging unit 3 is controlled by the imaging control unit 41. When a read start trigger signal is input from the PLC 201, the imaging control unit 41 generates an image by exposing for a preset exposure time. The imaging control unit 41 controls the imaging unit 3 to apply a preset gain to the image generated by the image sensor 31b, and also executes a process of amplifying the brightness of the image by digital image processing. The imaging control unit 41 also determines the frame rate (the number of images taken per second) of the imaging unit 3 based on the size (gap width) of the gap between the transport mechanisms B1 and B2 received by the communication unit 6 and the transport speed. For example, the imaging control unit 41 increases the frame rate of the imaging unit 3 as the transport speed increases. The frame rate can be set in the range of, for example, 500 fps to 5000 fps. The higher the frame rate, the stronger the light required to obtain sufficient brightness with a short exposure time, and the heat generation amount of the illumination unit 2 increases proportionally.

[0052] 7 to 10, the code reader 1 includes a housing 60 that houses the illumination unit 2, the imaging unit 3, and the control unit 4. The housing 60 may be configured to house the imaging unit 3 and the control unit 4, but not the illumination unit 2. In this case, the illumination unit 2 is configured as an illumination unit separate from the housing 60 that houses the imaging unit 3 and the control unit 4, but is controlled in synchronization with the control unit 4 when the workpiece W is imaged.

[0053] The housing 60 has a first side surface 61, a second side surface 62, a third side surface 63, and a fourth side surface 64, as well as a top surface 65 and a bottom surface 66. In this embodiment, the depth direction (front-rear direction), left-right direction, and top-bottom direction of the housing 60 are defined as shown in Figs. 7 to 10, but this definition is for convenience of explanation and does not limit the actual usage posture of the code reader 1. In addition, the number of sides is not limited to six, and a shape having six or more sides is also acceptable.

[0054] According to the above definition, the first side surface 61 is a surface (front surface) located on the front side of the housing 60, and has a shape long in the vertical direction. The second side surface 62 is adjacent to the left edge of the first side surface 61 and extends toward the back side of the housing 10, and is a surface (left side surface) located on the left side of the housing 60. The third side surface 63 is adjacent to the right edge of the first side surface 61 and extends toward the back side of the housing 10, and is a surface (right side surface) located on the right side of the housing 60. The fourth side surface 64 is a surface (rear surface) located on the rear side of the housing 60, and has a shape long in the vertical direction like the first side surface 61. The first side surface 61 and the fourth side surface 64 are approximately parallel to each other. In addition, the second side surface 62 and the third side surface 63 are approximately parallel to each other.

[0055] An upper edge of the fourth side surface 64 is located lower than an upper edge of the first side surface 61, and when the vertical dimension of the first side surface 61 is compared with the vertical dimension of the fourth side surface 64, the first side surface 61 is longer. The upper surface 65 is inclined so as to be positioned lower toward the back side of the housing 60 in order to correspond to the difference in vertical dimension between the first side surface 61 and the fourth side surface 64. On the other hand, the lower surface 66 extends approximately horizontally.

[0056] The first side surface 61, the third side surface 63, the fourth side surface 64, the top surface 65, and the bottom surface 66 of the housing 60 are integrally molded, and are configured, for example, as one part. Therefore, the first side surface 61, the third side surface 63, the fourth side surface 64, the top surface 65, and the bottom surface 66 configure a member whose left side is entirely open. A member configuring the second side surface 62 is fastened from the left side to the member configured by the first side surface 61, the third side surface 63, the fourth side surface 64, the top surface 65, and the bottom surface 66. In this way, a sealed housing 60 is configured.

[0057] As shown in FIG. 7, the first side surface 61 is provided with a light receiving window 67 that transmits reflected light from the bottom surface of the workpiece W into the inside of the housing 60. The light receiving window 67 is made of a transparent material having a short side direction and a long side direction. Examples of materials that constitute the light receiving window 67 include glass and resin materials such as polycarbonate. The long side direction of the light receiving window 67 coincides with the long side direction of the first side surface 61, i.e., the up-down direction of the housing 60, and the short side direction of the light receiving window 67 coincides with the left-right direction of the housing 60. In addition, the light receiving window 67 is provided offset to the right from the center of the first side surface 61 in the left-right direction.

[0058] The light receiving window 67 forms a plane extending along the up-down and left-right directions of the housing 60. The plane formed by the light receiving window 67 intersects with the plane formed by the focal plane 7 of the Scheimpflug optical system 31. The plane formed by the light receiving window 67 can also be defined as a virtual plane including the front surface (or back surface) of the light receiving window 67. Note that the light receiving window 67 does not have to be a perfect plane, and may be a gently curved surface that can be optically regarded as a plane.

[0059] 1 to 3, when the housing 60 is installed below the transport surface of the transport device B, the installation position and installation angle, etc. of the housing 60 are adjusted so that the focal range (depth of field) 9 of the Scheimpflug optical system 31 includes the gap of the transport device B and the focal plane 7 of the Scheimpflug optical system 31 is approximately parallel to the transport surface. When the housing 60 is installed in this manner, the light receiving window 67 is provided so that the plane formed by the light receiving window 67 intersects with the horizontal plane.

[0060] The installation position of the code reader 1 is not limited to the side of the transport device B. That is, for example, as shown in FIG. 11, if there is sufficient space available directly below the transport device B, the code reader 1 can be installed directly below the transport device B. For example, when the housing 60 is installed so that the optical axis of the lens 31a is approximately parallel to the transport direction A in a top view, the imaging unit 3 can be configured to be able to image the bottom surface of the workpiece W from the installation position through the mirror D as an external reflection member. In this case, the mirror D extending in an approximately vertical direction is installed on the side of the transport device B, and the reflected light from the bottom surface of the workpiece W is made to enter the mirror D, is folded back downward, and is made to enter the light receiving window 67. The code reader 1 according to the example shown in FIG. 11 is configured to include an external reflection member (mirror D) arranged outside the housing 60.

[0061] In this example, the angle at which the light receiving window 67 intersects with the horizontal plane is 90 degrees, but this is not limited to this, and when the code reader 1 is installed directly below the transport device B as shown in Fig. 12, the inclination angle α of the light receiving window 67 with respect to the horizontal plane E may be less than 90 degrees. The inclination angle α may be, for example, 20 degrees or more, or 45 degrees or more.

[0062] 13, a code reader 1 in which the angle of the light receiving window 67 is less than 90 degrees with respect to the horizontal plane E may be installed on the side of the transport device B. Also, as shown in Fig. 14, a code reader 1 in which the angle of the light receiving window 67 is more than 90 degrees with respect to the horizontal plane E may be installed directly below the transport device B. In this case, similar to the example shown in Fig. 11, the reflected light from the bottom surface of the workpiece W is made to enter the mirror D, is turned downward, and is made to enter the light receiving window 67.

[0063] Dust and debris are likely to fall onto the housing 60 installed below the transport surface of the transport device B, but since the light receiving window 67 is arranged to be inclined with respect to the horizontal plane E, dust and debris are less likely to accumulate on the light receiving window 67 compared to a light receiving window facing directly upward. In this embodiment, the light projection window 68 also faces in the same direction as the light receiving window 67, so dust and debris are also less likely to accumulate on the light projection window 68. In particular, as shown in Figure 14, since the angle of the light receiving window 67 with respect to the horizontal plane E exceeds 90 degrees, dust and debris hardly adheres to the light receiving window 67.

[0064] In the case of FIG. 12, the angle of the light receiving window 67 with respect to the horizontal plane E is less than 90 degrees. However, if this angle were set to 45 degrees or more, foreign matter on the surface of the light receiving window would be more likely to slide off.

[0065] That is, μ≦tan(θ) If θ≧arctan(μ), then foreign matter on the surface of the light-receiving window 67 will be more likely to slide off. For example, assuming that the coefficient of friction μ between glass, polycarbonate, etc. and other materials is normally 1 or less, in order to prevent foreign matter from accumulating, if the light-receiving window 67 is made of glass, polycarbonate, etc., then it is preferable for the angle it makes with the horizontal plane E to be 45 degrees or more.

[0066] 1 to 3 and 11 to 14, when the housing 60 is installed, the distance between the light receiving window 67 and the gap of the transport device B, the orientation of the light receiving window 67 with respect to the gap, etc. are determined. When the housing 60 is installed in this manner with the light receiving window 67 aligned so as to face the longitudinal direction of the gap of the transport device B, the imaging unit 3 is configured so that the range (depth of field) in which the Scheimpflug optical system 31 is in focus includes the gap of the transport device B. At this time, the gap is included in the middle part of the depth of field of the Scheimpflug optical system 31.

[0067] As shown in FIG. 7, the first side surface 61 is provided with a light projection window 68 that transmits the illumination light emitted from the illumination unit 2 to the outside of the housing 60. In this embodiment, the light receiving window 67 and the light projection window 68 are made of a common transparent material, and the area to the right of the dashed dotted line L2 in FIG. 7 is the light receiving window 67, and the area to the left of the dashed dotted line L2 is the light projection window 68. In this manner, the light receiving window 67 and the light projection window 68 are provided adjacent to each other in the left-right direction. Like the light receiving window 67, the light projection window 68 also has a short side direction and a long side direction, and the long side direction coincides with the long side direction of the first side surface 61. The light receiving window 67 and the light projection window 68 may be made of separate materials.

[0068] As shown in FIG. 10B, the code reader 1 includes a heat dissipation fin (heat dissipation section) 69 for dissipating heat generated in the illumination section 2 to the outside of the housing 60. The heat dissipation fin 69 is disposed on the second side surface 62 of the housing 60. Specifically, the second side surface 62 located on the left side of the housing 60 is made of a material having high thermal conductivity, such as an aluminum alloy, and the heat dissipation fin 69 is integrally formed with the member constituting the second side surface 62. Therefore, the heat dissipation fin 69 is also made of a material having high thermal conductivity. The heat dissipation fin 69 may be a separate body from the second side surface 62.

[0069] The heat dissipation fin 69 protrudes leftward from the second side surface 62 and extends in the vertical direction. A plurality of heat dissipation fins 69 having this shape are provided at intervals in the depth direction. The heat dissipation fins 69 are adjacent to the illumination unit 2 of the housing 60 in the left-right direction, which improves the heat dissipation efficiency of the illumination unit 2.

[0070] A cooling fan 70 is provided in the vertical middle of the heat dissipation fins 69. The fan 70 is controlled by, for example, the control unit 4, and is configured to operate when the temperature of the housing 60 reaches or exceeds a predetermined temperature. The fan 70 sends outside air to the heat dissipation fins 69, making it possible to perform forced air cooling. The fan 70 and heat dissipation fins 69 may be provided as needed.

[0071] As shown in FIG. 10B, the housing 60 has a second side surface 62 as an attachment surface on which an attachment structure 71 is provided, which is different from the first side surface 61 on which the light receiving window 67 is provided. As shown in FIG. 6B, when the code reader 1 (housing 60) is located to the side of the transport device B and below the transport surface and is fixed to a vertical fixing surface of a frame F arranged on a floor surface C via the mounting surface, the Scheimpflug optical system of the imaging unit 3 forms a range in focus extending in the longitudinal direction of the gap of the transport device B. By fixing the mounting surface of the housing to a general horizontal or vertical surface as an external fixing surface, the housing 60 can be positioned so that a range in focus is formed in the longitudinal direction of the gap of the transport device B. The focal surface may be parallel to the transport surface.

[0072] The mounting structure 71 may be, for example, a plurality of screw holes, and the housing 60 may be fixed to the frame F using a screw for each screw hole. However, the mounting structure 71 may be a plurality of bolts, and the housing 60 may be fixed to the frame F using a nut for each bolt, or may be a structure that can be fixed with a clamp metal fitting. The mounting structure 71 may be provided on the heat dissipation fin 69 or the fan 70 arranged on the second side surface 62. The mounting surface is not limited to the second side surface 62, and the mounting structure 71 may be provided on a surface other than the first side surface on which the light receiving window 67 and the light projecting window 68 are provided, that is, at least one of the second side surface, the third side surface 63, the fourth side surface 64, the upper surface 65, and the lower surface 66, so as not to interfere with the irradiation of the illumination light by the illumination unit 2 and the reception of the light by the imaging unit 3. For example, if the upper surface 65 or the lower surface 66 is used as the mounting surface, the mounting structure 71 may be placed and fixed on a plate or the like provided protruding from the frame F as an external horizontal fixing surface via the mounting surface. The mounting surface may be directly attached to the fixed surface, or may be indirectly attached to the fixed surface using an intermediate part such as a bracket. That is, even if the mounting surface is the second side surface 62, it may be attached to a horizontal fixed surface via the mounting structure 71 and an intermediate part.

[0073] A surface that is approximately parallel to the focal plane 7 of the Scheimpflug optical system may be provided on at least a part of the upper surface 65. Since the conveying surface of the conveying device B is generally horizontal, by placing a level on the upper surface 65, the installation state of the housing 60 in which the focal plane 7 is parallel to the conveying surface can be achieved with higher accuracy.

[0074] 7, when the housing 60 is viewed from the front, that is, when viewed from a direction directly facing the light-receiving window 67, the illumination unit 2 is disposed adjacent to the light-receiving window 67 in the short side direction (left-right direction) of the light-receiving window 67. The fact that the illumination unit 2 is adjacent to the light-receiving window 67 in the short side direction means that the optical axis (illumination optical axis) of the illumination unit 2 and the optical axis of the lens 31a of the imaging unit 3 are close to each other, and the field of view of the imaging unit 3 is brightly illuminated by the illumination unit 2.

[0075] In the illumination unit 2, the positions where the optical axes of the illumination units 2a and 2b intersect with the focal plane 7 are different in the direction in which the focal plane extends so as to suppress the deficiency of illuminance on the far side of the imaging unit 3 relative to the near side of the imaging unit 3 on the focal plane 7 of the Scheimpflug optical system 31, or to make the illuminance on the far side equal to or greater than the illuminance on the near side. This makes it possible to suppress the deficiency of the amount of reflected light received from the far side relative to the amount of reflected light received from the near side of the imaging unit 3, and an image with more uniform luminance is generated on the near side and far side of the imaging unit 3, so that both codes close to the imaging unit and codes far from the imaging unit can be read in a short time. Note that an image with more uniform luminance on the near side and far side of the imaging unit 3 is, for example, an image in which the average luminance value of a dark code on the far side is 50% or more of the average luminance value of a bright code on the near side, and more preferably, an image in which the average luminance value of a dark code on the far side is 60% or more of the average luminance value of a bright code on the near side.

[0076] In order to provide different amounts of light for the far and near sides, the illumination unit 2 has a near illumination unit 2a and a far illumination unit 2b. The far illumination unit 2b differs from the near illumination unit 2a in at least one of the optical axis angle with respect to the focal plane 7 of the Scheimpflug optical system 31 or the light flux.

[0077] 15A, 15B, and 15C, the near-use illumination unit 2a having an optical axis L3 that intersects with the focal plane 7 on the near side of the focal plane 7 relative to the far side of the focal plane 7 and the far-use illumination unit 2b having an optical axis L4 that intersects with the focal plane 7 on the far side of the focal plane 7 in the illumination unit 2 according to this embodiment have different optical axis angles with respect to the focal plane 7 of the Scheimpflug optical system 31, and the optical axis L3 and the optical axis L4 intersect in a region before reaching the focal plane 7. In other words, the angle of the optical axis L3 of the near-use illumination unit 2a with respect to the focal plane 7 is configured to be larger than the angle of the optical axis L4 of the far-use illumination unit 2b with respect to the focal plane 7.

[0078] In the first example shown in FIG. 15B, the area where the illumination light of the near illumination unit 2a and the illumination light of the far illumination unit 2b overlap on the focal plane 7 is biased toward the far side. The second example shown in FIG. 15C is different from the first example in FIG. 15B in that the overlapping area is reduced by narrowing the light distribution angle of each illumination unit, while the luminous flux of the far illumination unit 2b is made larger than the luminous flux of the near illumination unit 2a. In both cases of FIG. 15B and FIG. 15C, the illuminance shortage on the far side relative to the near side of the focal plane 7 can be suppressed, or the illuminance on the far side can be made equal to or greater than the illuminance on the near side. As a result, by suppressing the luminance shortage on the far side relative to the luminance on the near side of the image output by the imaging unit 3, an image with more uniform luminance on the near side and the far side of the imaging unit 3 can be generated, thereby improving the reading efficiency.

[0079] 15A, the near field illumination unit 2a and the far field illumination unit 2b are arranged adjacent to each other on a first side surface 61 of the housing 60, i.e., from the light projection window 68 toward the inside of the housing 60. The near field illumination unit 2a is arranged on the first side surface 61 side, and the far field illumination unit 2b is arranged on the rear side of the near field illumination unit 2a.

[0080] The near-field illumination unit 2a has a near-field light-emitting board 2c, one or more near-field light-emitting elements 2d, and a near-field illumination lens 2e. The near-field light-emitting board 2c is disposed toward the lower end in the housing 60, and is inclined with respect to the horizontal plane so as to be positioned higher toward the back side of the housing 60. The code reader 1 includes a near-side support member 71 that supports the near-field light-emitting board 2c on the second side surface 62. The near-side support member 71 is fixed to the second side surface 62, and is formed so as to protrude from the second side surface 62 toward the inside of the housing 60, and extends in a direction intersecting with the second side surface 62. A surface facing downward of the near-field light-emitting board 2c is fixed to a portion of the near-side support member 71 that protrudes toward the inside of the housing 60.

[0081] The near-use illumination unit 2a and the heat dissipation fin 69 are thermally connected via the near-side support member 71. That is, the near-side support member 71 is made of, for example, an aluminum alloy or a resin material as a material having thermal conductivity. Grease or the like for improving thermal conductivity is interposed between the near-side support member 71 and the second side surface 62 and between the near-side support member 71 and the near-use light-emitting board 2c. This makes it easier for heat emitted by the near-use light-emitting element 2d to be transferred to the heat dissipation fin 69 via the near-use light-emitting board 2c and the near-side support member 71. "Thermal connection" means that the connection is made in a state where heat can easily move and without any heat insulating material interposed.

[0082] A plurality of near-use light-emitting elements 2d are arranged (mounted) on the upward surface of the near-use light-emitting substrate 2c in a state of being lined up in the depth direction of the housing 60. The near-use illumination lens 2e is provided so as to cover the light-emitting surface of each near-use light-emitting element 2d. The optical axis of the near-use illumination unit 2a is indicated by a dashed dotted line L3. The optical axis L3 of the near-use illumination unit 2a is directed toward the near side of the focal plane 7 of the Scheimpflug optical system 31, and the orientation of the near-use light-emitting substrate 2c, i.e., the orientation of the near-use light-emitting element 2d, is set and the near-use illumination lens 2e is designed so that such an optical axis L3 is formed.

[0083] The long-distance illumination section 2b has a long-distance light-emitting board 2f, one or more long-distance light-emitting elements 2g, and a long-distance illumination lens 2h. The long-distance light-emitting board 2f is disposed adjacent to the rear end of the near-distance light-emitting board 2c, and is inclined with respect to the horizontal plane so that the far-distance light-emitting board 2f is positioned higher toward the rear of the housing 60. The inclination angle of the long-distance light-emitting board 2f with respect to the horizontal plane is larger than the inclination angle of the near-distance light-emitting board 2c with respect to the horizontal plane, and therefore the long-distance light-emitting board 2f has a steeper inclination than the near-distance light-emitting board 2c.

[0084] The code reader 1 includes a far-side support member 72 that supports the far-field light emitting board 2f on the second side surface 62. The far-side support member 72 is fixed to the second side surface 62 and is formed so as to protrude from the second side surface 62 toward the inside of the housing 60. A downward surface of the far-field light emitting board 2f is fixed to a portion of the far-side support member 72 that protrudes toward the inside of the housing 60. The far-field illumination section 2b and the heat dissipation fin 69 are thermally connected via the far-side support member 72, similar to the far-field illumination section 2b.

[0085] On the upward surface of the far-field light emitting substrate 2f, a plurality of far-field light emitting elements 2g are arranged (mounted) in a line in the depth direction of the housing 60. The number of far-field light emitting elements 2g is set to be greater than the number of near-field light emitting elements 2d. This makes the amount of light emitted by the far-field illumination section 2b greater than the amount of light emitted by the near-field illumination section 2a.

[0086] The long-distance illumination lens 2h is provided so as to cover the light-emitting surface of each long-distance light-emitting element 2g. The optical axis of the long-distance illumination unit 2b is indicated by a dashed line L4. The optical axis L4 of the long-distance illumination unit 2b is directed toward the long-distance side of the focal plane 7 of the Scheimpflug optical system 31, and the orientation of the long-distance light-emitting substrate 2f, i.e., the orientation of the long-distance light-emitting element 2g, is set and the long-distance illumination lens 2h is designed so that such an optical axis L4 is formed.

[0087] The inclination angle of the far-field light-emitting board 2f of the far-field illumination section 2b with respect to the lower surface 66 adjacent to the first side surface 61 is larger than the inclination angle of the near-field light-emitting board 2c of the near-field illumination section 2a with respect to the lower surface 66, and the far-field light-emitting board 2f is disposed higher than the near-field light-emitting board 2c with respect to the lower surface 66. As a result, the range in which illumination light from the illumination section 2 (particularly the near-field illumination section 2a) can be irradiated can be brought closer to the first side surface 61 of the housing 60, so that the housing 60 can be installed at a position closer to the transport device B, and the height of the housing 60 can also be reduced, so that a code reader 1 that is easy to install even in a logistics site or the like where installation space is likely to be restricted can be realized.

[0088] As an example of the configuration of the housing 60, in this embodiment, the second side surface 62 is made of a metal plate, and members such as the near side support member 71, the far side support member 72, the sensor mounting bracket 80, the upper mounting bracket 81, the lower mounting bracket 84, and the control board 90 are arranged and fixed on the metal plate, and each member is covered with a cover member having a surface other than the second side surface 62 (i.e., the first side surface 61, the third side surface 63, the fourth side surface 64, the upper surface 65, and the lower surface 66), and the inside of the housing 60 is sealed together with the metal plate. The cover member is made of a metal material or a resin material. If the cover member is made of a metal material, the housing 60 can be made more robust, and if the cover member is made of a resin material, the housing 60 can be made lighter. The heat dissipation fins 69 are arranged to extend from the surface opposite to the surface on which each member of the metal plate (second side surface 62) is arranged.

[0089] 16, the housing 60 includes a partition member 75 that is disposed between the illumination unit 2 and the imaging unit 3 and optically separates the illumination unit 2 from the imaging unit 3. The partition member 75 is made of a resin material, a metal material, or the like having light blocking properties, and includes a side plate portion 75a (also shown in FIG. 15) formed so as to protrude from the second side surface 62 toward the inside of the housing 60, and a vertical plate portion 75b connected to the end of the side plate portion 75a on the inside of the housing 60. As a result, the illumination light irradiated from the illumination unit 2 is emitted to the outside of the housing 60 only from the light projection window 68, making it difficult for stray light to enter the imaging unit 3.

[0090] The imaging unit 3 is disposed toward the upper end within the housing 60. When the light receiving window 67 is used as a reference, the upper end within the housing 60 corresponds to one end in the longitudinal direction of the light receiving window 67. Therefore, the imaging unit 3 is disposed toward one end in the longitudinal direction of the light receiving window 67 within the housing 60. On the other hand, the lower end within the housing 60 corresponds to the other end in the longitudinal direction of the light receiving window 67 when the light receiving window 67 is used as a reference. Therefore, the illumination unit 2 is disposed toward the other end in the longitudinal direction of the light receiving window 67 within the housing 60.

[0091] The image sensor 31b of the imaging unit 3 is disposed at the rear side within the housing 60 and is fixed to the second side surface 62 by a sensor mounting bracket 80. The light receiving surface of the image sensor 31b faces the front side. The lens 31a of the imaging unit 3 is disposed at the front side of the image sensor 31b within the housing 60 and is fixed to the second side surface 62. The optical axis of the lens 31a extends in the depth direction of the housing 60. The plane mirror 33 of the imaging unit 3 is disposed at the front side of the lens 31a within the housing 60 and is fixed to the second side surface 62 by an upper mounting bracket 81. The reflective surface of the plane mirror 33 faces diagonally downward.

[0092] The code reader 1 is housed in the housing 60 and includes an internal reflection member 83 that folds back light incident on the imaging unit 3. The internal reflection member 83 is disposed near the lower end of the housing 60 and is fixed to the second side surface 62 by a lower mounting bracket 84. The front end of the internal reflection member 83 is positioned near the lower end of the light receiving window 67. On the other hand, the rear end of the internal reflection member 83 is positioned closer to the front than the rear end of the housing 60. The reflection surface of the internal reflection member 83 faces upward, and is inclined so that the reflection surface is located higher toward the rear. The internal reflection member 83 is disposed below and the imaging unit 3 is disposed above, and light incident from above through the light receiving window 67 is folded back by the internal reflection member 83 to be incident on the image sensor 31b. This allows the height dimension of the housing 60 to be shortened and the code reader 1 to be made compact.

[0093] 8 to 10, the code reader 1 includes a marker 59. The marker 59 is provided on the upper surface 65 of the housing 60, and is controlled by the control unit 4 to be switched between a lit state and an unlit state. The marker 59 is a member for indicating success or failure of code reading to the user by color, and glows, for example, green when successful and red when unsuccessful or abnormal.

[0094] The code reader 1 includes a connector unit 85 that is connected to the outside. The computer 200, the PLC 201, a power source, and the like are connected to the connector unit 85. The connector unit 85 is provided on the rear side of the housing 60 so as to face the outside of the housing 60. Specifically, a recess 64a is provided on the fourth side surface 64 of the housing 60, and the connector unit 85 is attached to the inner side surface 64b of the recess 64a. In this embodiment, an example is shown in which a plurality of connector units 85 are provided at intervals from each other in the vertical direction, but the number of connector units 85 can be set arbitrarily. The connector unit 85 has an insertion port 85a into which a terminal (not shown) of a wiring line or the like is inserted. Since the insertion port 85a opens toward the right, the terminal of the wiring line can be inserted into each insertion port 85a from the right side of the housing 60.

[0095] The image sensor 31b is disposed directly above the connector section 85. The illumination section 2 and the internal reflection member 83 are disposed between the light receiving window 67 and the connector section 85. That is, since the lens 31a, the image sensor 31b, and the plane mirror 33 constituting the imaging section 3 need to be disposed at intervals in the depth direction of the housing 60, it is difficult to secure a space for disposing the connector section 85 at the top of the housing 60. However, since the illumination section 2 and the internal reflection member 83 can be shorter in the depth direction of the housing 60 than the imaging section 3, in this embodiment, it is possible to secure a space for disposing the connector section 85 on the back side of the illumination section 2 and the internal reflection member 83 without increasing the size of the housing 60.

[0096] When the code reader 1 is installed as shown in Figs. 1 to 3, the bottom surface of the workpiece W transported by the transport device B is exposed downward from the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2. The depth of field of the imaging unit 3 of the code reader 1 installed as shown in Figs. 1 to 3 includes the bottom surface of the workpiece W exposed from the gap in the transport device B. This allows the imaging unit 3 to directly image the bottom surface of the workpiece W through the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2. "Directly" means that the imaging unit 3 images the bottom surface of the workpiece W without going through a reflective member such as a mirror.

[0097] When installed as shown in Figures 1 to 3, the light receiving window 67 is aligned with the gap of the conveying device B, and in this state, the row direction of the image sensor 31b corresponds to the extension direction of the gap of the conveying device B, and the column direction of the image sensor 31b corresponds to the conveying direction of the conveying device B (the direction indicated by arrow A in Figure 1).

[0098] Therefore, as shown in FIG. 17, the imaging unit 3 continuously captures the bottom surface of the workpiece W that is exposed through the gap of the conveying device B and is included in the depth of field of the imaging unit 3, thereby outputting a plurality of images in which a part of the code attached to the bottom surface of the workpiece W is captured. The upper side of FIG. 17 shows the upstream conveying mechanism B1 and the downstream conveying mechanism B2 conveying the workpiece W as viewed from below, and the workpiece W is conveyed as shown from left to right. Since the dimension of the code in the conveying direction is longer than the gap between the upstream conveying mechanism B1 and the downstream conveying mechanism B2, only a part of the code in the conveying direction is exposed downward from the gap between the upstream conveying mechanism B1 and the downstream conveying mechanism B2. As shown in the lower side of FIG. 17, a plurality of images in which a part of the code in the conveying direction is captured are sequentially output from the imaging unit 3. The plurality of images output from the imaging unit 3 are input to the control unit 4. The image output from the imaging unit 3 becomes an image that is elongated in the longitudinal direction of the gap between the upstream conveying mechanism B1 and the downstream conveying mechanism B2 by geometric correction described later.

[0099] (Details of control unit 4) The control unit 4 is a part that generates a composite image based on the multiple images output from the imaging unit 3, and executes a decoding process on the code attached to the bottom surface of the workpiece W based on the composite image. As shown in Fig. 2, a specific configuration example of the control unit 4 can be, for example, a configuration example including a microcomputer having a central processing unit, ROM, RAM, etc. An imaging control unit 41, an illumination control unit 42, a code detection unit 43, and a decoding unit 44 are configured by hardware included in the control unit 4, software executed by the control unit 4, etc.

[0100] The code detection unit 43 of the control unit 4 is a unit that identifies a code area based on the code image output from the imaging unit 3 and detects a code from the identified code area. The decode unit 44 of the control unit 4 is a unit that decodes the code detected by the code detection unit 43. Specifically, since the code is represented by black and white binary data, the decode unit 44 decodes the black and white binary data. A table showing the correspondence between encoded data can be used for the decoding. Furthermore, the decode unit 44 checks whether the decoded result is correct or not according to a predetermined check method. If an error is found in the data, the decode unit 44 uses an error correction function to calculate the correct data. The error correction function differs depending on the type of code. The details of the code detection unit 43 and the decode unit 44 will be specifically described below.

[0101] The details of the process by the control unit 4 will be described below based on the flowchart shown in Fig. 18. This flowchart starts when the operation of the code reader 1 is started. After the start, in step SA1, a read start trigger signal is input from the PLC 201 to the code reader 1. When the read start trigger signal is input, the illumination control unit 42 turns on the illumination unit 2, and the imaging control unit 41 causes the imaging unit 3 to capture an image and generate an image.

[0102] The area surrounded by the two-dot chain line in FIG. 19 is the image output from the imaging unit 3. In this embodiment, since the code reader 1 is installed to the side of the transport device B, the bottom surface of the workpiece W is imaged from diagonally below. Therefore, unlike the case where the image is taken from directly below, a geometric change occurs according to the installation angle of the code reader 1 as shown in FIG. 19. Specifically, in the multiple images output from the imaging unit 3, the bottom surface of the workpiece W exposed from the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2 appears as a trapezoid with one end on the near side of the focal plane of the Scheimpflug optical system 31 as the long side and the other end on the far side of the focal plane of the Scheimpflug optical system 31 as the short side.

[0103] For this reason, in step SA2 of the flowchart shown in Fig. 18, the code detection unit 43 performs keystone correction on the trapezoidal shapes of the multiple images as geometric correction. Specifically, the code detection unit 43 acquires information related to the installation angle of the code reader 1. The information related to the installation angle of the code reader 1 may be information input by the user when setting up the code reader 1, or may be information automatically detected by the code reader 1. The code detection unit 43 performs geometric correction on each of the multiple images output from the imaging unit 3 based on the information related to the installation angle of the code reader 1. As a result, an image similar to that when imaged from directly below the workpiece W is obtained.

[0104] In step SA3, the code detection unit 43 synthesizes the multiple processed images that have been geometrically corrected in step SA2 to generate a composite image including the code. In step SA4, it is determined whether the number of times imaging by the imaging unit 3 has reached a designated number. This number is set to a number that allows the entire code to be imaged. If the determination in step SA4 is NO, the process proceeds to step SA1, where imaging, geometric correction, and image synthesis are repeated until the entire code is imaged. If the determination in step SA4 is YES, the process proceeds to step SA5.

[0105] In step SA5, the code detection unit 43 applies multiple edge extraction filters to the image synthesized in step SA3 to extract edges of different frequencies to generate multiple edge images, and then performs integration processing of the multiple edge images. The code detection unit 43 determines the code candidate position based on the result of the edge integration processing. That is, in the edge-processed image, it is possible to estimate that an area where many pixels with high brightness values ​​are concentrated is a code area.

[0106] For example, the code detection unit 43 can generate a heat map image that indicates the likelihood of a code in order to search for the position of a code in a code image. That is, the code detection unit 43 quantifies the feature amount of the code, generates a heat map in which the magnitude of the feature amount is assigned to each pixel value, and extracts a code candidate area on the heat map in which a code is likely to exist. As a specific example, there is a method of acquiring the feature portion of the code in an area that is relatively hot (has a large feature amount) in the heat map. When multiple feature portions are acquired, they can be extracted by prioritizing them and stored in a RAM or the like. By using the heat map image, it becomes possible to detect the code area at high speed. The decoding unit 44 decodes the code searched for by the code detection unit 43.

[0107] (Effects of the embodiment) The code reader 1 according to the present embodiment can be fixed to a horizontal or vertical surface, which is a common external fixed surface located to the side of the transport device B and below the transport surface, via the mounting surface of the housing, so that the housing can be oriented so that a range in focus is formed in the longitudinal direction of the gap of the transport device B. The height position can be adjusted by moving the housing while maintaining the orientation, for example, using an image to be actually captured or the height from the top surface of the housing to the focal plane obtained based on the Scheimpflug optical system and the housing design, making installation easy. In addition, since the plane formed by the light receiving window 67 in the above installation state intersects with the horizontal plane, dust and dirt are less likely to accumulate on the light receiving window 67. In addition, since the code reader 1 is installed to the side of the transport device B, the light receiving window 67 is disposed at a position outside the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2. As a result, dust and dirt that have fallen from the gap between the upstream transport mechanism B1 and the downstream transport mechanism B2 are less likely to adhere to the light receiving window 67. The same applies to the light projection window 68. This reduces the frequency of maintenance such as cleaning, thereby easing the burden on the user.

[0108] Furthermore, when the housing 60 is installed so that the depth of field of the Scheimpflug optical system 31 includes the gap of the transport device B, the longitudinal direction of the light receiving window 67 can be made to correspond to the longitudinal direction of the gap of the transport device B. This makes it possible to capture an image of the code attached to the workpiece W through the gap of the transport device B. At this time, since the illumination unit 2 is adjacent to the light receiving window 67 in the short direction, the illumination optical axis and the optical axis of the lens 31a of the imaging unit 3 are close to each other, and the field of view of the imaging unit 3 is brightly illuminated by the illumination unit 2. This allows an image with the brightness required for decoding processing to be obtained.

[0109] (Other embodiments) The above-described embodiment is merely illustrative in all respects and should not be construed as limiting. Furthermore, all modifications and variations within the scope of the claims are within the scope of the present invention.

[0110] Fig. 20 is a diagram showing a case where a code reader 1 is installed on each side of a conveying device B. As shown in this figure, by installing multiple code readers 1 so as to image the workpiece W from opposite directions, it is possible to accommodate a conveying device B having a wide width in the X direction and to reduce blind spots. The shape of the workpiece W is not particularly limited, and may be a cylindrical workpiece W as shown in Fig. 20. The code reader 1 of the present disclosure images the workpiece W from diagonally below, so that it is possible to expand the range in which the code affixed to the part of the workpiece W that is not in contact with the conveying surface can be read, even for a cylindrical workpiece W.

[0111] In the above-described embodiment, as shown in Fig. 15B and Fig. 15C, the inclination angles of the optical axes of the near use illumination unit 2a and the far use illumination unit 2b with respect to the focal plane 7 are different in side view. This allows the near use illumination unit 2a and the far use illumination unit 2b to be made compact and the height dimension of the housing 60 to be shortened, but this is not limited thereto. For example, as shown typically in Fig. 21A and Fig. 21B, the optical axes of the near use illumination unit 2a and the far use illumination unit 2b may be arranged to be substantially parallel, that is, the inclination angles of the optical axes with respect to the focal plane 7 may be substantially the same.

[0112] In the case of FIG. 21A, the area where the illumination light from the near-use illumination unit 2a and the illumination light from the far-use illumination unit 2b overlap on the focal plane 7 is biased toward the far side rather than the near side of the focal plane 7. In the case of FIG. 21B, the light distribution angle of the illumination light from the near-use illumination unit 2a and the illumination light from the far-use illumination unit 2b is narrowed compared to FIG. 21A, and the area where they overlap on the focal plane 7 is made smaller, while the luminous flux of the far-use illumination unit 2b is made larger than the luminous flux of the near-side illumination unit 2a. In either case, by suppressing the illuminance shortage on the far side relative to the near side of the focal plane 7, or by making the illuminance on the far side equal to or greater than the illuminance on the near side, the luminance shortage on the far side relative to the luminance on the near side of the image output by the imaging unit 3 is suppressed, and therefore an image with more uniform luminance on the near side and far side of the imaging unit 3 can be generated, and reading efficiency can be improved.

[0113] 22, when the code reader 1 is installed on the side of the transport device B, a mirror (external reflection member) D1 may be used to reflect light. The mirror D1 may be attached to the housing 60, or may be attached to a member separate from the housing 60. This is an effective installation method when it is not possible to ensure sufficient installation space on the side of the transport device B to align the light receiving window 67 so that it faces the longitudinal direction of the gap in the transport device B.

[0114] 23, when the code reader 1 is installed directly below the transport device B, a mirror (external reflection member) D2 may be used to reflect light. The mirror D2 may be attached to the housing 60, or may be attached to a member separate from the housing 60. When almost no installation space can be secured to the side of the transport device B, the code reader 1 can be installed directly below the transport device B.

[0115] In both cases of Figures 22 and 23, when the housing 60 is installed so that the optical axis 10 of the lens inside the housing 60 is approximately parallel to the conveying direction (Y direction) when viewed from above, the optical axis 10 of the lens outside the housing 60 is folded back by a mirror (external reflective member) D2 to a direction (X direction) approximately parallel to the longitudinal direction of the gap of the conveying device B when viewed from above, so that the imaging unit 3 is configured to be able to image the bottom surface of the workpiece W via the external reflective member D2.

[0116] As shown in Fig. 24, the transport device B may be configured by a roller conveyor. That is, the transport device B has a plurality of rollers B4 that rotate around a horizontal axis and a frame B5 that supports the rollers B4. A transport mechanism is configured by each roller B4 and an axis B6 that rotates each roller B4. A gap is provided between the rollers B4, B4 adjacent to each other in the transport direction. The code reader 1 is configured to be able to read the code attached to the bottom surface of the workpiece W through the gap between the rollers B4, B4 adjacent to each other in the transport direction.

[0117] Furthermore, the code reader 1 in this embodiment is not limited to the installation position described above, but can also be installed at the same height as the conveying surface or higher than the conveying surface, which allows it to be used to read codes attached to the side or top surface of the workpiece W in addition to codes attached to the bottom surface of the workpiece W. [Industrial Applicability]

[0118] As described above, the code reader according to the present disclosure can be used, for example, to read a code attached to a workpiece. [Explanation of symbols]

[0119] 1 Code Reader 2. Lighting section 3. Imaging unit 4. Control section 6. Communications Department 31 Scheimpflug Optical System 31a Lens 31b Image sensor 60 Case 61 First aspect 62 Second aspect 67 Light receiving window 83 Internal reflective material 85 Connector part B. Conveyor device B1 Upstream transport mechanism B2 Downstream transport mechanism D Mirror (external reflective material) Double work

Claims

1. A code reader capable of reading a code attached to a bottom surface of a workpiece transported by a transport device having a plurality of transport mechanisms arranged with gaps in a transport direction from below a lateral and horizontal transport surface of the transport device through the gaps, An imaging unit having a Scheimpflug optical system consisting of a lens that collects reflected light from the bottom surface of the workpiece and an image sensor having a light receiving surface inclined with respect to the optical axis of the lens, generating and outputting an image based on the amount of light received on the light receiving surface; A control unit that executes a decoding process on the code attached to the work based on the image output from the imaging unit; a housing that houses the imaging unit and the control unit, the housing having a first side surface on which a light receiving window that transmits the reflected light is provided, and an attachment surface that is a surface different from the first side surface and on which an attachment structure is provided, A code reader in which, when the housing is installed via the mounting surface on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the Scheimpflug optical system of the imaging unit forms a focused range extending in the longitudinal direction of the gap.

2. 2. The code reader according to claim 1, A code reader in which, when the housing is installed via the mounting structure on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the plane formed by the light receiving window intersects with a horizontal plane.

3. 2. The code reader according to claim 1, The imaging unit continuously images the bottom surface of the workpiece exposed through the gap of the conveying device and included within the range of focus, thereby outputting a plurality of images in which a part of the code attached to the bottom surface of the workpiece is captured; The control unit generates a composite image based on the multiple images output from the imaging unit, and performs a decoding process on the code attached to the bottom surface of the work based on the composite image.

4. The code reader according to claim 3, The control unit performs geometric correction on each of the plurality of images output from the imaging unit, and combines the plurality of processed images on which the geometric correction has been performed to generate the combined image.

5. The code reader according to claim 4, In the plurality of images output from the imaging unit, the bottom surface of the workpiece exposed from the gap is captured in a trapezoid shape having a long side at one end near the imaging unit and a short side at the other end far from the imaging unit, The control unit performs keystone correction as the geometric correction on the trapezoidal shapes of the multiple images.

6. 2. The code reader according to claim 1, A code reader in which, when the housing is installed with the light receiving window aligned so that it faces the longitudinal direction of the gap of the conveying device, the imaging unit is configured so that the focused range of the Scheimpflug optical system extends in the longitudinal direction of the gap of the conveying device.

7. 7. The code reader according to claim 6, The image sensor includes a plurality of image pickup elements arranged in rows and columns; When the light receiving window is aligned to face the longitudinal direction of the gap of the conveying device, a row direction of the image sensor corresponds to the longitudinal direction of the gap of the conveying device, and a column direction of the image sensor corresponds to the conveying direction of the conveying device; The image sensor is configured to be able to partially read out signals from imaging elements in a row corresponding to the gap of the conveying device, among the plurality of imaging elements.

8. 2. The code reader according to claim 1, A code reader in which, when the housing is installed via the mounting surface on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface, the imaging unit is configured to be able to directly image the bottom surface of the workpiece through the gap.

9. 2. The code reader according to claim 1, The code reader further includes an external reflecting member disposed outside the housing, A code reader configured such that when the housing is installed such that the optical axis of the lens inside the housing is approximately parallel to the conveying direction when viewed from above, the optical axis of the lens outside the housing is folded back by the external reflective member to a direction approximately parallel to the longitudinal direction of the gap of the conveying device when viewed from above, thereby enabling the imaging unit to image the bottom surface of the workpiece through the external reflective member.

10. The code reader according to claim 2, A code reader, wherein an angle between a plane formed by the light receiving window and the horizontal plane is 45 degrees or more.

11. A code reading method for reading a code attached to a bottom surface of a workpiece transported by a transport device having a plurality of transport mechanisms arranged with gaps in a transport direction from a side of the transport device and below a transport surface through the gap, the code reading method comprising: an imaging unit having a Scheimpflug optical system; a control unit that decodes an image output from the imaging unit; and a housing that houses the imaging unit and the control unit and has a first side surface on which a light receiving window is provided and an attachment surface different from the first side surface on which an attachment structure is provided, the code reading method comprising: reading a code attached to a bottom surface of a workpiece transported by a transport device having a plurality of transport mechanisms arranged with gaps in a transport direction from a side of the transport device and below a transport surface through the gap, the code reading method comprising: The housing is installed via the mounting surface on an external horizontal or vertical fixed surface located to the side of the conveying device and below the conveying surface; The Scheimpflug optical system of the imaging unit captures an image of a code attached to a bottom surface of the workpiece located within a focused range formed to extend in the longitudinal direction of the gap; The code reading method further comprises the step of: executing a decoding process on the code by the control unit based on an image in which the code is located within the focused range.

Images