JP6310997B2 - Image reading device - Google Patents

Description

  Embodiments described herein relate generally to an image reading apparatus.

  2. Description of the Related Art Conventionally, an image reading apparatus used by being connected to a POS (Point of Sales) terminal or the like is an imaging window in which an image of a code symbol attached to a product or an entire or part of an object image is formed on a casing. The code information (product code or the like) of the code symbol is acquired by decoding the captured image, and the feature amount is extracted from the captured image. Such an image reading apparatus captures a code symbol image or an object image by an image sensor such as a CCD (Charge Coupled Device) sensor.

  In addition, in this type of image reading apparatus, the imaging window is closed by a flat transmission plate made of glass or resin for the purpose of dust-proofing the imaging element.

  In addition, this type of image reading apparatus illuminates a code symbol or an object reading area, which is an imaging area of an image sensor, using an illumination device such as an LED (Light Emitting Diode). In the conventional image reading apparatus, in order to prevent the stray light caused by the light emitted from the illumination device being reflected by the transmission plate closing the imaging window from being incident on the imaging device, the light is irradiated near the end of the transmission plate. A lighting device is arranged.

  However, according to the prior art, the illumination device is arranged near the end of the dust-proof transmission plate, so that the illuminance decreases near the center of the imaging region of the image sensor compared to the vicinity of the imaging region near the illumination device. There is a problem that.

The image reading apparatus according to the embodiment includes a transmission plate, an imaging lens, a transparent substrate, an illumination device, and an optical path changing member. The transmission plate is a flat plate having transparency disposed in an imaging window opened in the housing. The imaging lens images reflected light from a subject located in a reading area having a certain resolution or higher among imaging areas formed outside the transmission plate on an imaging element. The transparent substrate is a flat plate that is provided between the transmission plate and the imaging lens and is disposed to face the transmission plate. The illumination device irradiates the reading area with illumination light. The optical path changing member is on the transparent substrate in the optical path of light rays that can be reflected from the incident surface or the exit surface of the transmissive plate and become stray light that reaches the image sensor, out of the light emitted from the illumination device. It is formed in a substantially circular shape and changes the optical path of the light beam.

FIG. 1 is a perspective view showing the overall configuration of a POS system using the image reading apparatus according to the first embodiment. FIG. 2 is a cross-sectional view illustrating a schematic configuration of an imaging apparatus included in the image reading apparatus. FIG. 3 is a schematic diagram showing an arrangement of a conventional lighting device. FIG. 4 is a schematic diagram illustrating an installation position of the lighting device. FIG. 5 is a schematic diagram illustrating an example of stray light. FIG. 6 is a schematic diagram showing an example of the arrangement of the light shielding members on the optical path of light rays that can become stray light. FIG. 7 shows an example of the light shielding member, where (a) is a plan view, (b) is a transverse side view, and (c) is a longitudinal side view. FIG. 8 shows an example of the light shielding member, where (a) is a plan view, (b) is a side view, and (c) is a front view. FIG. 9 is a schematic diagram illustrating an arrangement example of the optical path changing member according to the second embodiment. FIG. 10 is a schematic diagram showing a partially enlarged configuration of the optical path changing member.

  Hereinafter, the present embodiment will be described with reference to the drawings.

(First embodiment)
Here, FIG. 1 is a perspective view showing the overall configuration of the POS system 1 using the image reading apparatus 11 according to the first embodiment. Note that an arrow A in the drawing indicates the width direction (left-right direction) of the image reading device 11, an arrow B indicates the front in the front-rear direction of the image reading device 11, and an arrow C indicates the upper direction in the vertical direction of the image reading device 11. Show.

  As shown in FIG. 1, a POS (Point Of Sales) system 1 includes an image reading device 11 that is a vertical scanner and a POS terminal 12 that executes sales registration processing according to an image captured by the image reading device 11. I have. The image reading device 11 is erected at a substantially central portion on the soccer stand 10 on which a shopping cart or the like is placed. The POS terminal 12 is provided in the vicinity of one end of the soccer base 10. The image reading device 11 and the POS terminal 12 are connected to each other via a transmission path (not shown) so that they can communicate with each other. The image reading device 11 and the POS terminal 12 constitute a POS terminal unit.

  The image reading device 11 includes an imaging device 17, a keyboard 21, a display 19, and the like. The imaging device 17 optically captures an image of a code symbol (barcode, two-dimensional code, etc.) attached to a product and an entire or part of an object image through the imaging window 16 facing the operator. . The keyboard 21 is provided with various keys for registering products that cannot be registered with code symbols or object images. The display 19 displays the product name, price, etc. of the product registered for the operator and the shopper in accordance with the sales registration process by the POS terminal 12.

  Next, the configuration of the imaging device 17 will be described in detail. Here, FIG. 2 is a cross-sectional view illustrating a schematic configuration of the imaging device 17 included in the image reading device 11.

  As shown in FIG. 2, the imaging device 17 includes a housing 15 having an imaging window 16 that is open. The imaging device 17 includes an imaging unit 14 and a lighting device 13 in the housing 15. Here, the imaging region D of the imaging unit 14 is a region between the line L1 and the line L2 in FIG.

  The casing 15 is formed in a substantially rectangular parallelepiped box shape, and an imaging window 16 is formed on the front wall 15a thereof. The casing 15 faces an operator (not shown) located in front of the casing 15. The imaging window 16 is formed in a substantially rectangular shape when viewed from the front.

  The imaging window 16 is closed by a transmissive flat plate 18 for the purpose of dust-proofing the imaging unit 14. The transmission plate 18 is made of, for example, glass or resin. The transmission plate 18 is supported by the housing 15. Specifically, the transmission plate 18 is supported by the casing 15 by being fixed to a peripheral portion of the imaging window 16 on the inner surface of the casing 15 by a fixing means such as adhesion.

  The illumination device 13 transmits the illumination light I to the imaging region D of the imaging unit 14 through the transmission plate 18 and illuminates the object existing in the imaging region D. The illuminating device 13 has a plurality of LEDs (Light Emitting Diodes) as light sources, and is provided along a side portion for each pair of side portions of the imaging window 16. That is, the lighting device 13 is provided in a pair of left and right with the imaging unit 14 interposed therebetween. A pair of illuminating device 13 becomes a right-and-left symmetrical (plane symmetry) structure. The light source is not limited to a plurality of LEDs, and may be a single LED.

  The outline of the illumination light I from the illumination device 13 is indicated by lines L3 and L4, and lines L5 and L6 in FIG. Reference numeral 20 is a light shielding member that functions as an optical path changing member that changes the optical path of a predetermined light beam of the illumination light I from the illumination device 13, which will be described in detail later.

  Although not particularly illustrated, the imaging unit 14 includes an imaging element 14a such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and an imaging lens 14b. As shown in FIG. 2, the optical axis F of the imaging unit 14 (imaging lens 14 b) extends along the front-rear direction of the image reading device 11 (imaging device 17) and passes through the imaging window 16.

  More specifically, the imaging unit 14 images a reading target located in a reading area E formed outside the imaging window 16 in the housing 15. Here, in FIG. 2, the reading area E is generally an area between the line L <b> 6 and the transmission plate 18 in the imaging area D.

  Here, the reading area E will be described. The imageable range of the imaging device 14a of the imaging unit 14 is determined by the characteristics of the imaging lens 14b. The imaging lens 14b of the present embodiment is a fixed focus lens, and the focus position (the position where the focus is best) is at a position away from the lens tip by a certain distance. When the product that is the imaged object is placed at the focal position, the resolution is the highest, the image can be clearly captured, and the product that is the imaged object is placed in a direction approaching or moving away from the imaging element 14a from the focal position. The image is out of focus and the resolution is low. For example, in order to decode a barcode, it is necessary to measure the width of each color (for example, black and white) bar forming the barcode from the image data of the product acquired by the image sensor 14a. Disappear. Therefore, a range of a certain resolution or more in the imaging region D becomes a reading region E in which a code symbol can be extracted from image data by an image processing board (not shown).

  In other words, the imaging unit 14 receives reflected light that is reflected from an object to be read that is located in the reading area E in front (outside) of the imaging window 16 and that has entered the housing 15 from the imaging window 16. Placed in position. The imaging unit 14 captures an image by imaging the reflected light from the object incident into the housing 15 through the imaging window 16 through the imaging lens 14b and outputs image data.

  Next, the installation position of the illumination device 13 will be described in detail.

  In the conventional image reading apparatus, in order to prevent stray light from being incident on the image sensor due to the light emitted from the illumination device being reflected by the transmission plate closing the imaging window, in the vicinity of the end of the transmission plate The lighting device was arranged. This point will be described with reference to FIG. As shown in FIG. 3, the conventional image reading apparatus does not generate stray light. Therefore, the imaging region d of the imaging unit 14 is an area defined by an optical path that is folded back with the exit surface of the dust-proof transmission plate 50 as a reflection surface, Alternatively, outside of any wider region g (hereinafter referred to as an equivalent imaging region) among the regions defined by the optical path where the imaging region d of the imaging unit 14 is folded with the incident surface of the transmission plate 50 as the reflecting surface. Therefore, the illumination device 51 is provided in the vicinity of the transmission plate 50. In FIG. 3, only one side of the illumination device 51 is shown for the sake of simplicity.

  However, in the conventional image reading apparatus, the optical path length from the illumination device 51 located outside the equivalent imaging region g and in the vicinity of the transmission plate 50 is a position close to the illumination device 51 on the transmission plate 50 (in FIG. 3). , L11) and a substantially central position (L12 in FIG. 3) of the equivalent imaging region g in the transmission plate 50 are greatly different. For this reason, the illuminance that is inversely proportional to the square of the optical path length is too bright in the vicinity of the imaging region d near the illumination device 51 in the transmission plate 50, and near the approximate center of the reading region e near the transmission plate 50 in the transmission plate 50. Even if the light from a plurality of LEDs is superimposed, there is a problem that the image becomes too dark.

  Here, FIG. 4 is a schematic diagram showing the installation position of the illumination device 13. In FIG. 4, only one side of the illumination device 13 is shown for ease of explanation. As shown in FIG. 4, in the image reading apparatus 11 of the present embodiment, an equivalent imaging is performed outside the imaging region D in order to uniformly illuminate a product to be read placed near the transmission plate 18. The illumination device 13 is disposed inside the region G. In addition, the illumination device 13 is disposed at a position where the distance to the vicinity of the periphery of the imaging region D on the transmission plate 18 and the distance to the vicinity of the approximate center of the equivalent imaging region G on the transmission plate 18 are substantially the same.

In this case, if the number of light sources (portions that emit light from the illumination device 13) is n, the illuminance at the center is different, so the illuminance near the center is about n times that of the periphery, and the center is It can be used when you want to brighten it. When trying to make the illuminance of the entire reading area E uniform, the illuminance from each light source is inversely proportional to the square of the optical path length from the light source. That is, when the distance to the periphery is Lo and the distance to the center is Lc, the ratio of illuminance between the periphery and the center is
1 / (Lo) ² : 1 / (Lc) ²
It becomes. When it is approximated that the light sources overlap in the central part and are not significantly affected by other light sources in the peripheral part, ,
(Lc) ² / (n × (Lo) ² )
It becomes. In order to set this to 1, the value obtained by dividing the distance Lo to the vicinity of the imaging region D in the transmission plate 18 by the distance Lc to the vicinity of the approximate center in the vicinity of the imaging window 16 in the region of the transmission plate 18 is obtained.
Lc / Lo = √n
It turns out that In practice, 1 ≦ Lc / Lo ≦ √n between these two poles
It is desirable to arrange a light source at

  However, when the illumination device 13 is arranged inside the equivalent imaging region G as shown in FIG. 4, the reflected light from the transmission plate 18 passes through the entrance pupil of the imaging lens 14 b of the imaging unit 14 and the imaging element 14 a. Stray light that reaches FIG. 5 is a schematic diagram illustrating an example of stray light. As shown in FIG. 5, among the light emitted from the illuminating device 13, a light beam L10 that is reflected by the entrance surface or the exit surface of the transmission plate 18 and reaches the image sensor 14a through the entrance pupil of the imaging lens 14b It is stray light. These stray lights are superimposed on regular light that is reflected from the product to be read and incident on the image sensor 14a. For this reason, when stray light is generated, there is a problem that the image reading is hindered.

  Therefore, the imaging device 17 of the image reading device 11 according to the present embodiment reflects the light emitted from the illumination device 13 on the incident surface or the emitting surface of the transmission plate 18 and passes through the entrance pupil of the imaging lens 14b. A light shielding member 20 that functions as an optical path changing member that shields the light beam L10 is provided in the optical path of the light beam L10 that can become stray light reaching the element 14a.

  Here, FIG. 6 is a schematic diagram illustrating an arrangement example of the light shielding member 20 on the optical path of a light beam that can become stray light. In the example shown in FIG. 6B, the light L10 is shielded to prevent stray light from reaching the imaging element 14a through the entrance pupil of the imaging lens 14b of the imaging unit 14 on the optical path of the light L10 that can become stray light. The member 20 is provided.

  As shown in FIG. 6B, since the light shielding member 20 is disposed on the light beam L10, the optical path closer to the imaging unit 14 than the light shielding member 20 is eliminated, so that stray light does not reach the imaging element 14a. .

  FIG. 7 shows an example of the light shielding member 20, wherein (a) is a plan view, (b) is a transverse side view, and (c) is a longitudinal side view. As shown in FIG. 7, the light shielding member 20 is mainly composed of a flat plate-like transparent substrate 20a formed of glass, resin, or the like. The light shielding member 20 includes a light shielding pattern 20b on the transparent substrate 20a by screen printing with a light shielding ink such as a black paint having a high light shielding property. The printing position of the light shielding pattern 20b is determined by analyzing the optical path of light rays that can be stray light according to the installation position of the light shielding member 20 and the installation position of the illumination device 13. It should be noted that the light shielding member 20 is preferably disposed as close as possible to the transmission plate 18 in order to suppress the range of the reading area shielded by the light shielding member 20 as much as possible.

  The transparent substrate 20 a of the light shielding member 20 has a hole 20 c in a portion corresponding to the imaging region D of the imaging unit 14. The edge portion of the hole 20c is rounded and rounded so as not to generate scattered light. Further, as shown in FIG. 7, the transparent substrate 20a of the light shielding member 20 is arranged so that the angle of the light emitted from the lighting device 13 is not changed as much as possible, and the inner peripheral portion 20e of the hole 20c and the outer periphery of the transparent substrate 20a. The portion 20d is inclined at an angle that is parallel to the light beam from the nearest illumination device 13.

  As described above, according to the image reading apparatus 11 of the first embodiment, a uniform illuminance distribution can be obtained in the reading region E of the transmission plate 18 without generating stray light.

  In the present embodiment, the light shielding member 20 is applied as an optical path changing member that shields the light beam L10 that may become stray light. However, the present invention is not limited to this. For example, a light shielding member 30 as shown in FIG. 8 may be applied as the optical path changing member. FIG. 8 shows an example of the light shielding member 30, where (a) is a plan view, (b) is a side view, and (c) is a front view. As shown in FIG. 8, the light shielding member 30 is formed of sheet metal or the like, and includes a disk-shaped light shielding pattern 30b on a flat substrate 30a. The base body 30a is parallel to the direction of the light beam L10 that can be stray light. On the other hand, the light shielding pattern 30b faces in a direction orthogonal to the direction of the light beam L10 that can become stray light. The light shielding pattern 30b is provided with a reflective coating in order to eliminate light reflection.

  Further, in the case where an optical member (for example, a lens) that suppresses the light spreading angle is provided for the LED of the lighting device 13, the optical member (for example, the lens) is screen-printed with a light-shielding ink. A light shielding pattern may be formed. Also in this case, the printing position of the light shielding pattern is determined by analyzing the optical path of the light beam that can become stray light according to the installation position of the optical member (for example, lens) and the installation position of the illumination device 13.

(Second Embodiment)
Next, a second embodiment will be described. In addition, the same part as 1st Embodiment mentioned above is shown with the same code | symbol, and description is also abbreviate | omitted. This embodiment differs from the image reading apparatus 11 according to the first embodiment in that an optical path changing member 40 that bends the optical path of the light beam L10 that can be stray light is applied as the optical path changing member instead of the light shielding members 20 and 30. Is different.

  Here, FIG. 9 is a schematic diagram illustrating an arrangement example of the optical path changing member 40 according to the second embodiment. In the example shown in FIG. 9B, the optical path of the light beam L10 is bent on the optical path of the light beam L10 that can become stray light so that the stray light does not reach the imaging element 14a through the entrance pupil of the imaging lens 14b of the imaging unit 14. An optical path changing member 40 is provided.

  As shown in FIG. 9B, since the optical path changing member 40 is arranged on the light beam L10, the direction of the light beam L10 closer to the imaging unit 14 than the optical path changing member 40 is changed. Will never reach.

  FIG. 10 is a schematic view showing a part of the configuration of the optical path changing member 40 in an enlarged manner. As shown in FIG. 10, the optical path changing member 40 is mainly composed of a flat transparent substrate 40a formed of glass, resin or the like. The optical path changing member 40 includes an optical path changing unit 40b that changes an optical path (at least one of an angle and a position) of the light beam L10 in the transparent substrate 40a. The position of the optical path changing unit 40b is determined by analyzing the optical path of a light beam that can become stray light according to the installation position of the optical path changing member 40 and the installation position of the illumination device 13. Although not particularly illustrated, the transparent substrate 40 a of the optical path changing member 40 has a hole in a portion corresponding to the imaging region D of the imaging unit 14, similarly to the transparent substrate 20 a of the light shielding member 20.

  As shown in FIG. 10, the optical path changing unit 40b is a recess that is a substantially conical recess formed on the transparent substrate 40a. The inside of the recess is an air layer. More specifically, the shape of the optical path changing unit 40b is a shape whose cross section is a hyperbola. That is, the conical tip of the optical path changing unit 40b is rounded and rounded so as to be gentle. Further, the edge of the optical path changing unit 40b is rounded and rounded to prevent the light from being scattered and causing stray light.

  The change destination of the optical path of the light beam L10 by the optical path changing member 40 is preferably in the reading area E. By doing so, it is possible to increase the illuminance of illumination with respect to the product to be read placed near the transmission plate 18.

  By providing such an optical path changing member 40, it is possible to prevent the light beam L10 that can be stray light from reaching the imaging element 14a through the entrance pupil of the imaging lens 14b of the imaging unit 14.

  As described above, according to the image reading apparatus 11 of the second embodiment, a uniform illuminance distribution can be obtained in the reading region E of the transmission plate 18 without generating stray light.

  In the present embodiment, the optical path changing portion 40b of the optical path changing member 40 is a substantially conical recess having a hyperbolic cross section. However, the present invention is not limited to this, and the substantially conical shape having a hyperbolic cross section. It may be a convex part.

  In each of the above-described embodiments, the POS terminal unit configured by the image reading device 11 and the POS terminal 12 has been described. However, the present invention is not limited to this, and the function of the image reading device 11 and the POS terminal 12 is provided. You may make it apply to the apparatus of a stand structure. As a single device having the functions of the image reading device 11 and the POS terminal 12, there is a self-checkout device (hereinafter simply referred to as self-POS) that is installed and used in a store such as a supermarket.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 Image reader 13 Illumination device 14 Imaging part 16 Imaging window 18 Transmission board 20,30,40 Optical path change member

JP 2011-141862 A

Claims (5)

A transmissive flat plate having transparency disposed in the imaging window opening in the housing;
An imaging lens that forms an image on reflected light from a subject located in a reading region having a certain resolution or higher among imaging regions formed outside the transmission plate;
A flat transparent substrate provided between the transmission plate and the imaging lens and disposed opposite to the transmission plate;
An illumination device for irradiating the reading area with illumination light;
Of the light emitted from the illuminating device , is formed in a substantially circular shape on the transparent substrate in the optical path of light rays that can be reflected by the incident surface or the exit surface of the transmission plate and reach the image sensor, An optical path changing member for changing the optical path of the light beam;
An image reading apparatus comprising: The optical path changing member is a concave portion or a convex portion provided on the transparent substrate.
The image reading apparatus according to claim 1. The optical path changing member is formed of a light shielding ink .
The image reading apparatus according to claim 1. The optical path changing member has a shape whose cross section is a hyperbola,
The image reading apparatus according to claim 1. The optical path changing member changes an optical path to the reading region;
The image reading apparatus according to claim 1.

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