JP2012085004A - Optical line sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical line sensor device for discrimination comprising sensor elements of a new shape for avoiding occurrence of moire because occurrence of moire is inevitable when a sensor for discrimination is developed and the discrimination function itself is inhibited.SOLUTION: The optical line sensor device comprises a light source which irradiates a moving medium with a plurality of light beams while switching with time, light receiving units 14, 15 where sensor elements are arranged one-dimensionally in a direction y perpendicular to the moving direction x of the medium and detect light transmitted the medium or reflected thereon, and a signal processing unit 27 which discriminates the information of the medium by processing the optical detection signal of the light receiving units 14, 15. Observation width b of the sensor element in the moving direction of the medium and the arrangement pitch p of sensor elements arranged one-dimensionally satisfy a relation b>p.

Description

  The present invention relates to an optical line sensor device, and more particularly to a discrimination-use optical line sensor device for the purpose of discriminating securities and banknotes.

With recent remarkable improvements in printing technology and copying technology, counterfeiting of banknotes, securities, etc. is becoming more and more sophisticated, and to accurately identify and eliminate these in order to maintain the national social order Is important. In particular, in a device that handles banknotes such as ATMs and banknote processors, there is a strong demand for a higher-speed and higher-performance discrimination system for authenticity determination purposes.
As a method for discriminating these bills and securities, pattern identification using an optical line sensor device has been used for some time.

  The optical line sensor device includes a reduction optical line sensor device combining a reduction lens, a mirror, and a CCD, and a contact type optical line sensor device using an equal magnification optical system such as a selfoc lens, and the reduction optical system is a system. The unit price is low, the resolution can be easily adjusted, and there is an advantage that the depth of focus is deep. However, there are disadvantages that the volume of the sensor is increased and dust and foreign matter are liable to enter. Therefore, a contact type optical line sensor device that is easy to maintain has been widely used recently.

The optical line sensor device reads an image from three directions of front, back, and transmission of a target medium as counterfeiting becomes more sophisticated and the detection signal processing technology of the sensor advances.
In addition, the optical line sensor device irradiates light of a wavelength including ultraviolet light outside the visible region together with the human visible light region, color information by visible light irradiation, fluorescent color information of the medium by ultraviolet light irradiation, etc. What reads an image in at least two or more wavelength bands has become the mainstream these days.

For this reason, the current optical line sensor device for discrimination is equipped with a plurality of types of LEDs so that the mounted light source unit can emit light in a wide wavelength range from ultraviolet light to visible light. Are sequentially switched to emit light, and the respective light detection signals are collected in the light receiving unit to obtain image data of each condition, and authenticity determination is performed based on this.
In the optical line sensor device, in order to read a transmission image or a reflection image of a medium during movement of a medium such as securities or bills, the line sensor is disposed above or below a position where the medium passes. The sensor element of this line sensor employs a photodiode of amorphous silicon or single crystal silicon.

  The line sensor is a sensor IC chip in which each sensor element is arranged on a straight line and combined with a driver IC that converts a light detection signal of each sensor element into a line signal, or a photodiode and a signal processing driver are integrated. Are arranged on a straight line, and these are mounted on a substrate. Recently, an optical line sensor device using a sensor IC chip is widely used from the viewpoint of cost and production efficiency.

  Conventional sensor IC chips are being devised to reduce the size of the IC as much as possible. The pitch (pixel pitch) in the horizontal direction (one-dimensional array direction) of each sensor IC chip is related to the size of the required pixel (“pixel” means the smallest unit that is optically read on the medium), It is determined according to the required pixel size. However, the length (corresponding to the observation width) of the sensor IC chip in the vertical direction (the direction perpendicular to the one-dimensional array direction, the direction in which the medium moves) does not necessarily relate to the pixel size. This is because the vertical pixel size on the medium can be adjusted by setting the moving speed of the medium and the exposure time.

Therefore, the number of chips that can be taken out from one silicon wafer can be increased as the length of the sensor IC chip in the vertical direction is reduced. For this reason, the shape of the photodiode on the sensor IC chip has been devised to reduce the length in the vertical direction without degrading the performance.
For the above reasons, the pixel shape of the photodiode of the conventional sensor IC chip is a square or a rectangle with a short vertical direction, and it meets the market demand by reducing the pixel size without changing the pixel pitch. Is the current situation.

JP 2004-355262 A

  A light source that illuminates a medium usually includes a plurality of light source elements having different light emission characteristics, and has a structure in which color information is obtained by switching these light source elements. The vertical line density (resolution) on the medium is determined by the number of light source colors to be switched while the medium is moving and how many times the data is to be acquired per unit distance. For example, if data is acquired four times per 1 mm of the moving distance of the medium and the number of light source colors to be switched is 2, the resolution is 8 lines / mm.

Recently, it has become possible to read highly accurate images by increasing the speed of signal processing, and further, it has been desired to improve the discrimination function by identifying even the characters and numbers of the medium, and the resolution is 2 or more / mm, preferably In order to read numbers and characters on a medium, a resolution of 4 lines / mm or more has been demanded.
However, when developing an optical line sensor device having an advanced discrimination function such as securities or banknotes, moire that inhibits the discrimination function of the read image may occur depending on the print pattern of the target medium. Moire refers to a phenomenon in which each sensor element arranged on a straight line at an equal pitch and a striped image cause interference, and the light detection signal of each sensor element fluctuates periodically. If a noticeable moire is detected, an accurate image cannot be read and the discrimination function is inhibited.

  The cause of this moire will be described with reference to FIG. Moire occurs both in the vertical direction and in the horizontal direction. Moire generated in the vertical direction will be described below. The y direction in FIG. 6 indicates the arrangement (lateral direction) of the sensor elements of the sensor module, and the x direction indicates the medium feeding direction (vertical direction). As for the color of the light source, it is assumed that green (G) is repeatedly emitted once every two times, such as green (G) → other colors → green (G) → other colors. By intermittently reading the sensor element of the sensor module, eight observation lines are generated on the medium per 1 mm in the vertical direction. That is, the resolution in the x direction is 8 lines / mm.

In FIG. 6, the vertical distribution of the input image is shown on the right side of the observation line. The input image has a sine wave shape for convenience. A sensor output signal observed by the sensor element is indicated by a thick broken line, and a moire image included in the sensor output signal is indicated by a thick broken line. When reading such periodic images, moire occurs.
Here, when the distance that the medium travels in the x direction for each light emission is “a” and the width of the observation window of the sensor element in the x direction is “b”, the vertical width of the observation line is (a + b). Since green (G) is emitted once every two times, the period of the observation line in the x direction is 2 (a + b). If the cycle of the input image is 2 (a + b) + δ (0 <δ <a + b), the cycle of the generated moire is 4 (a + b) ² / δ.

When moiré occurs in this way, for facsimile and scanner applications, if an image containing moire is output as it is, the product value is lost. Usually, various image processing such as complementary processing, error diffusion method, halftone method, and resolution change are performed. By applying this technique, a device has been devised to prevent moire from appearing in the output image.
However, in the line sensor device for discrimination use, it is necessary to read the authenticity and damage precisely, and further, the time required to introduce image processing software into the process in order to judge the authenticity immediately after reading the image on the device. It seems that there is no room.

In addition, in line sensor devices for discrimination applications, it is possible to reduce the resolution by software or optically blur such as a low-pass filter to erase moire, but this makes it possible to read an accurate image that is the purpose of the discrimination sensor There is a drawback that the function itself is degraded.
In the present invention, the occurrence of moire is unavoidable in order to develop a high-resolution discrimination application sensor, and this impedes the discrimination function itself, so that it is provided with a sensor element having a new shape to avoid the occurrence of moire. An object is to provide an optical line sensor device.

  The optical line sensor device for differential use according to the present invention includes a light source that irradiates the medium by temporally switching a plurality of lights having different spectral characteristics while the medium is moving, and a direction in which the sensor element is different from the moving direction of the medium. A light receiving unit that detects light transmitted or reflected by the medium, and a signal processing unit that determines information on the medium by processing a light detection signal of the light receiving unit, The relation between the observation width b of the sensor element along the moving direction of the medium and the arrangement pitch p of the sensor elements in which the sensor elements are arranged one-dimensionally satisfies the relation of b> p.

  According to this configuration, the size of the sensor element is increased in the direction in which the medium moves, and the ratio of the length in the one-dimensional direction of the sensor element to the length in the direction of movement of the medium is greater than 1. ing. As described in [Background Art], the shape of the sensor element of the conventional sensor IC chip is a square or a rectangle with a short vertical direction (a direction perpendicular to the one-dimensional array direction). There is a significant feature in the shape that the ratio between the length in the one-dimensional direction and the length in the vertical direction is larger than 1, that is, the length is long. It is possible to easily overlap the observation line currently read by the sensor element with the observation line previously read by the same sensor element. As a result, the occurrence of moire can be reduced, and a good-quality image that can be identified is obtained.

The observation width b of the sensor element, a reading resolution N that is the number of times the plurality of lights are switched over time per unit moving distance of the medium, and a specific spectral characteristic during the time switching of the plurality of lights. The relationship with the number of repetitions of light emission n (n is an integer of 2 or more)
b> = (n−1) / N (1)
It is preferable to satisfy the formula: According to this configuration, the observation line currently read by the sensor element and the observation line read by the same sensor element before can be reliably overlapped.

In the sensor element of the present invention, the ratio of the length in the one-dimensional direction to the length in the vertical direction is more preferably 1.25 or more.
The optical line sensor device of the present invention may adopt a 1 × magnification reading method in which a sensor module is read in close contact with a medium.

  As described above, according to the present invention, the occurrence of moire at the time of reading is reduced by employing rectangular pixels in which the size of the sensor element in the vertical direction opposite to the reduction direction of the conventional sensor IC chip is specially increased. It has a high discrimination function. In addition, by increasing the size of the sensor element in the vertical direction, the area of one pixel when optically reading is increased, leading to an improvement in optical reading sensitivity.

It is sectional drawing which shows the optical line sensor apparatus which detects the image of media, such as securities and a banknote. It is a front view which shows the element arrangement | sequence of a sensor module. It is a side view of a sensor module which shows a mode that medium S moves to the x direction from the paper surface left to the right (comparative example). FIG. 6 is a side view of the sensor module showing how the medium S moves in the x direction from the left to the right of the drawing (Example). 4 is a graph depicting the relationship between an observation width b and a reading resolution N in the present invention. It is a figure for demonstrating the cause of generation | occurrence | production of moire.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing a differential use optical line sensor device that detects an image of securities, banknotes and the like (hereinafter referred to as “medium S”), and banknote transport for transporting the medium S linearly in the x direction. The detection units 12 and 13 having the same configuration are disposed opposite to each other across the path 11. The banknote conveyance path 11 conveys the medium S straightly in a posture along the conveyance direction x. The coordinate systems x, y, and z in FIG. 1 are orthogonal to each other.

One detection unit 12 has a dimension in the length direction (y direction in FIG. 1) that is considerably larger than the dimension in the thickness direction (z direction in FIG. 1) and the dimension in the width direction (x direction in FIG. 1). It has an elongated shape. The detection unit 12 includes an elongated box-shaped casing 16 having an opening in the lower direction, an elongated plate-shaped translucent cover 17 attached to the casing 16 so as to close the opening, and a casing. 16 and a unit main body U housed in 16.
The translucent cover 17 is formed of a transparent material such as glass, and is chamfered so as to be thinner at both ends in the width (x) direction so that the thickness becomes thinner toward the tip side. This chamfering is to prevent the medium S from becoming a hindrance when passing through the detection unit 12. In addition, as the translucent cover 17, you may use the integrally molded resin molded product which minimized the level | step difference of the junction part.

  In the unit main body U, a sensor module (including an image detection sensor such as a CCD and a signal processing unit) 14 is disposed on the opposite side to the translucent cover 17. The sensor module 14 has an elongated shape like the unit body U, and is mounted in the housing 16 with its length (y) direction coincided with the length (y) direction of the unit body U. . The sensor module 14 has its image detection direction directed to the translucent cover 17.

  In the unit main body U, a rod lens array 25 having an elongated shape in the length (y) direction is arranged in parallel with the sensor module 14. The rod lens array 25 is a lens element for forming an image of the medium S as an upright image at an equal magnification on the photosensitive surface of the sensor module 14. The rod lens array 25 is attached to the housing 16 in a state where the positions of the unit main body U in the width (x) direction and the length (y) direction are entirely superimposed on the sensor module 14.

  The sensor module 14 sets the detection area (observation line) of the image to be captured via the rod lens array 25 outside the translucent cover 17 by a predetermined distance (this detection area is indicated by R1 in FIG. 1). A line connecting the detection area R1 and the sensor module 14 is parallel to the z-axis. As a matter of course, the detection area R1 is also an elongated area in the length (y) direction, like the unit body U.

With the above configuration, the sensor module 14 can form an image existing in the detection area R <b> 1 set outside the translucent cover 17 on one side of the unit body U via the rod lens array 25. .
In addition, in the unit main body U, an elongated light source 19 that can irradiate light obliquely toward the detection area R1 is provided along with the rod lens array 25 (the direction of light in FIG. 1). Is indicated by a broken line). The light source 19 is attached to the housing 16 in a state parallel to the sensor module 14 and the rod lens array 25 along the length (y) direction of the unit body U.

The light source 19 includes a light guide 38 made of a transparent material such as an elongated glass having a length substantially equal to or longer than that of the sensor module 14 and a light emitting element 29 made of a semiconductor element that irradiates the light guide 38. is doing.
Further, as shown in FIG. 1, the casing 16 is provided with a reflecting plate portion 34 for guiding light emitted from the light guide resin 38 obliquely downward. Like the unit body U, the reflecting plate portion 34 has an elongated shape in the length (y) direction and has a parallel groove along the length (y) direction. The light emitter 19 is accommodated in the groove. Yes. One side of the groove that accommodates the light emitter 19 spreads in a horn shape as it is separated from the light guide resin 38 in the thickness (−z) direction, but the other surface of the groove is cut horizontally. This is to prevent the irradiation light from the light guide resin 38 from becoming an obstacle when traveling to the detection area R1.

  A plurality of, specifically five, light emitting elements 29 in the light emitter 19 are provided. Each light emitting element 29 is capable of emitting three light emitting elements (LED elements) 29A to 29C each capable of independently irradiating visible light in a desired wavelength region and ultraviolet light (UV) having a wavelength of 300 nm to 400 nm. An element 29D and a light emitting element 29E capable of emitting infrared light (IR) having a wavelength of 800 nm or more are included. Each light emitting element 29A-29E is provided with a predetermined electrode terminal (not shown), and they are connected by wire bonding or the like. The light emitting elements 29A to 29C irradiate light of any three wavelength regions of visible light, ultraviolet light, and infrared light of a plurality of colors corresponding to three primary colors such as red, green, blue (RGB) or cyan, magenta, and yellow, for example. It is possible.

Each of the light emitting elements 29A to 29E can irradiate light of a different wavelength region into the light guide resin 38. For this reason, the light emitting elements 29A to 29E are selected by selecting an electrode terminal to apply a voltage to each element. It has a circuit configuration that can switch light in time and emit light.
The casing 16 is formed with a bottom wall portion 35 for preventing light from the light emitter 19 from leaking to the sensor module 14 inside, and the bottom wall portion 35 has an optical path of the sensor module 14. An opening is formed only in the opening, and the rod lens array 25 is attached to the opening. The reflection plate portion 34 and the bottom wall portion 35 may be integrally formed as shown in FIG.

  The other detection unit 13 is opposed to the detection unit 12 in a posture reversed 180 degrees around an axis along the length (y) direction with the banknote transport path 11 in between. That is, the detection unit 13 is provided with an opening in the upper direction of the elongated box-shaped housing 21, and the translucent cover 22 is attached to the housing 21 so as to close the opening. The detection unit 13 and the detection unit 12 face each other with the main surfaces of the translucent covers 17 and 22 parallel to the banknote transport path 11 with a gap of 1.5 to 3 mm.

  The element arrangement in the housing 21 is provided with a light emitter 23 that irradiates the back surface of the medium S from the bottom to the top in addition to the light emitter 24 having the same configuration as the light emitter 19 described above. It has been. Since the light emitter 23 is disposed relative to the sensor module 14 of the detection unit 12, the light emitted from the light emitter 23 and transmitted through the medium S passes through the rod lens array 25 and enters the sensor module 14. The Similarly to the light emitter 19 described above, each of the light emitters 23 includes five light emitting elements that can individually irradiate light in a desired wavelength region.

  With this configuration, the sensor module 14 of the upper detection unit 12 shown in FIG. 1 can detect a transmission image in the detection area R1 of the lower detection unit 13 shown in FIG. Further, the sensor module 14 of the upper detection unit 12 shown in FIG. 1 can detect a reflected image irradiated from the upper light emitter 19 shown in FIG. 1 and reflected by the detection area R1, and the lower side shown in FIG. The sensor module 15 of the detection unit 13 can detect the reflected image of the detection area R2 irradiated from the light emitter 23.

The light emitting body 19 and the light emitting body 23 are controlled to emit light by temporal switching so that the transmitted image and the reflected image do not enter the sensor module 14 at the same time.
With the above configuration, a transmission image or a reflection image of an object irradiated through the light-transmitting covers 17 and 22 on the surface of the housing is applied to the surface of the sensor modules 14 and 15 through the rod lens arrays 25 and 26 at the same magnification. Formed as a standing image.

The determination unit 30 compares the transmission image data or the reflection image data of the medium S read by the sensor element with each of, for example, master data to determine authenticity, denomination, contamination, and the like. -Implemented by a computer executing a program recorded in a predetermined storage medium S such as a ROM or a hard disk.
Next, FIG. 2 is a front view showing the element arrangement of the sensor modules 14 and 15. The sensor modules 14 and 15 are sensor ICs in which a plurality of sensor elements (each composed of a photodiode, a phototransistor, etc.) arranged linearly in the y direction, a signal processing unit 27, and a driver unit 31 are integrated. Chips are arranged and mounted on a substrate. The driver unit 31 is a circuit part that generates and supplies a bias current for driving the sensor element, and the signal processing unit 27 is a circuit part that reads and processes a light detection signal of the sensor element. Although the kind of sensor element is not limited, for example, a silicon PN diode or a PIN diode is used.

An arrangement pitch of a plurality of sensor elements arranged linearly in the y direction is indicated by “p”. The arrangement pitch p of the sensor elements is substantially equal to the size of one sensor element in the y direction. The observation width that the sensor element can read the medium S at the moment when the medium S moves in the x direction is indicated by “b”.
By exposing these plurality of sensor elements at once, an observation line along the y direction can be set on the surface of the medium S. The width of the observation line in the x direction is basically determined by the observation width b of the sensor element. However, in actuality, there is an exposure time of the sensor element, and during this time, the medium S moves in the x direction. .

  The arrangement pitch p in the y direction of the sensor modules 14 and 15 determines the maximum resolution in the y direction. For example, if the pitch p is set to 125 μm, it can be read with a resolution of 8 lines / mm in the y direction. When reading with lower resolution, the signals of sensor pixels adjacent in the y direction may be short-circuited. For example, it is possible to change the resolution to 4 lines / mm by short-circuiting two adjacent pixels and reading them as one pixel. It is also possible to change the resolution to 2 lines / mm by short-circuiting 4 pixels.

On the other hand, the moving speed of the medium S in the x direction is “v”. The moving speed v is set to, for example, 1500 mm to 2000 mm / sec in an ATM or banknote processing machine. The time from the start of exposure of one light emitting element to the start of exposure of the next light emitting element (exposure cycle T) can be arbitrarily set according to the intensity of the light source, the wavelength sensitivity of the sensor element, and the like. For example, it is set to 0.5 to 1.0 milliseconds.
The distance that the medium S moves in the x direction during one exposure period T is vT. This distance is written as “a”. This distance a determines the reading resolution N (N = 1 / a) in the x direction. For example, if the distance a is 125 μm, it can be read with a resolution of N = 8 lines / mm in the x direction.

While the medium S moves in the x direction, the signal processing unit 27 exposes the sensor elements arranged in a line over the exposure period T, whereby an observation line having a predetermined width along the y direction on the surface of the medium S. Can be set. The width of the observation line along the x direction is the sum (a + b) of the distance a and the observation width b of the sensor element.
Each of the light emitting elements 29A to 29E is assumed to emit light while being switched in time by selecting an electrode terminal that applies a voltage to each element. Here, paying attention to a light emitting element of a specific color, the number of times the light emitting element emits light repeatedly (how many times it emits light once) is represented by a multiple n of the exposure period T. For example, when attention is paid to a green (G) light emitting element and green (G) is emitted once every two times, such as green (G) → other color → green (G) → other color, n = 2. If green (G) is emitted once every three times, such as green (G)-> other colors-> other colors-> green (G)-> other colors-> other colors-> green (G) n = 3.

In the embodiment of the present invention, it is assumed that the three light emitting elements 29A to 29C (RGB) are sequentially switched to emit light, and the number of repetitions when focusing on a specific color light emitting element (red (R)) is n = 3. And
FIG. 3 shows a side view of the sensor module 14 as seen from the y direction. The medium S is assumed to move in the x direction from left to right on the paper surface, and the three light emitting elements 29A to 29C of the light source 19 or the light source 23 are temporally switched, and red (R) → green (G) → blue (B). → ... and will change. 3A shows a red (R) emission state, FIG. 3B shows a green (G) emission state, and FIG. 3C shows a blue (B) emission state. In the figure, the exposure period T of each color, the distance a in which the medium S moves during the exposure period T, and the observation width b in the x direction (vertical direction) of each sensor element of the sensor module 14 are shown.

FIG. 3 (a) shows the first moment of reading the medium S under red light emission. The width (indicated as R (1)) by which the medium S is read is “b”.
FIG. 3B shows a time point when the sensor element is switched to reading under the next green emission after reading one line under the red emission. While proceeding from FIG. 4A to FIG. 4B, the medium S has advanced a distance a. Therefore, the width in the x direction (observation line width) read by the sensor element in red is a + b.

  FIG. 3C shows a point in time when the reading is switched to reading of the sensor element under the next blue light emission after reading one line under the green light emission. While proceeding from FIG. 4B to FIG. 4C, the medium S further proceeds by the distance a. Therefore, the width in the x direction (the width of the observation line) read by the sensor element in green is a + b. At this time, the tip of the portion read by the sensor element in red is advanced by 2a from the right end (indicated by x1) of the observation width of the sensor element. Here, since the width of the observation line read by the sensor element with red light is a + b, only the rear end ba − (= a + b−2a) is still passing under the sensor element ( (Refer FIG.3 (c)).

  FIG. 3D shows the moment when the sensor element is read for one line under blue light emission and then switched to reading with the sensor element under the next red light emission. While proceeding from FIG. 3C to FIG. 3D, the medium S further proceeds by the distance a. At this time, the rear end of the portion read by the sensor element under “front” red emission is advanced by 3a− (a + b) from the right end x1 of the observation width of the sensor element. At this time, the next medium S is read under red light emission (displayed as R (2)).

  FIG. 3E is a graph showing the exposure amount distribution of the observation line read by the sensor element with red light. The exposure amount gradually increases until the distance a is measured from the right end of the portion, and the exposure amount between the point of the distance a and the point of the distance (ba) becomes a peak, and the distance (b− The exposure amount gradually decreases from the point a) to the point of distance (a + b). The width of the observation line is (a + b).

  As can be seen from FIG. 3 (d), between the rear end of the portion read by the sensor element under “front” red light emission and the right end x1 of the observation width of the sensor element, “3a− (a + b)” There is a portion (indicated by “e”) that cannot be read in red. If this non-reading portion e exists, the observation line read by the sensor element under red light emission becomes discontinuous in the x direction, which causes a moire as shown in FIG.

Therefore, the width b in the x direction of the sensor element is set so that there is no “part that cannot be read in red” of 3a− (a + b), that is, 3a− (a + b) = <0. Rewriting the inequality sign 3a- (a + b) = <0 results in b> = 2a. If the reading resolution N in the x direction (N = 1 / a) is used, b> = 2 / N.
FIG. 4 is a schematic diagram illustrating a state in which the medium S moves in the x direction from the left to the right on the paper surface when the condition b = 2a is satisfied.

  FIG. 4A shows the first moment when the sensor element reads the medium S under red light emission. The read line width, that is, the observation width of the medium S is “b” (indicated as R (1)). FIG. 4B shows a point in time after the sensor element reads one line under red light emission, the sensor element switches to green reading under the next green light emission. While proceeding from FIG. 4A to FIG. 4B, the medium S advances by a distance a. Therefore, the width in the x direction read by the sensor element under red light emission is a + b. FIG. 4C shows a time point when the sensor element reads one line under green light emission and then switches to reading the sensor element under the next blue light emission. While proceeding from FIG. 4B to FIG. 4C, the medium S further proceeds by the distance a. Therefore, the width in the x direction read by the sensor element under green light emission is a + b. At this time, the tip of the portion read by the sensor element under red light emission is advanced by 2a from the right end x1 of the observation width of the sensor element. Here, since the full width of the portion read by the sensor element under red light emission is a + b, only the portion b−a at the rear end is still passing under the sensor element (FIG. 4C). )).

  FIG. 4D shows a time point when the sensor element reads one line under blue light emission and then switches to reading the sensor element under the next red light emission. While proceeding from FIG. 4C to FIG. 4D, the medium S further proceeds by the distance a. At this time, the tip of the portion read by the sensor element under the “previous” red light emission is advanced by 3a from the right end x1 of the observation width of the sensor element. The rear end of the portion read by the sensor element under the “front” red light emission is advanced by 3a− (a + b) from the right end x1 of the observation width of the sensor element. In this embodiment, b = 2a. Therefore, 3a- (a + b) = 0. At this time, the sensor element reads the next medium S under red light emission (displayed as R (2)).

FIG. 4E is a graph showing the exposure amount of the portion read by the sensor element under red light emission. The exposure amount gradually increases until the distance a is measured from the right end of the portion, and the exposure amount between the point of the distance a and the point of the distance (ba) becomes a peak, and the distance (b− The exposure amount gradually decreases from the point a) to the point of distance (a + b).
As can be seen from FIG. 4D, there is an “unreadable portion” between the rear end of the portion read by the “front” sensor element under red light emission and the right end x1 of the observation width of the sensor element. No longer exists. Since this non-reading portion does not exist, the observation lines read by the sensor elements under red light emission exist continuously, and the moire as shown in FIG. 6 does not occur.

In the example of FIG. 4, the state in which the medium S moves when b = 2a is satisfied is shown, but b> 2a may be used. In this case, the observation lines read by the sensor elements under the same color of light emission are continuously present while partially overlapping, and an effect of preventing the occurrence of moire can be achieved.
In the embodiment of FIG. 4 described above, the number of repetitions of light emission when focusing on a light emitting element of a specific color is set to “3”, and the medium S is cyclically switched. Therefore, it is necessary to set the width b in the x direction of the sensor element so that there is no non-reading portion of 3a− (a + b), that is, 3a− (a + b) = <0. Rewriting the inequality sign 3a- (a + b) = <0 yielded b> = 2a. Therefore, when the reading resolution N in the x direction is N, the observation width b in the x direction of the sensor elements of the sensor module 14 needs to be “2 / N” or more.

  However, the number of repetitions of light emission when focusing on a specific color light-emitting element is not necessarily three. For example, “2” may be used. At this time, the width b in the x direction of the sensor element is set so that there is no non-reading portion of 2a− (a + b), that is, 2a− (a + b) = <0. Rewriting the inequality sign 2a- (a + b) = <0 results in b> = a. If read resolution N in the x direction (N = 1 / a) is used, b> = 1 / N. Therefore, if the reading resolution N in the x direction is N, the observation width b in the x direction of the sensor elements of the sensor module 14 needs to be equal to or greater than the “1 / N”.

  Further, the number of repetitions of light emission when focusing on a light emitting element of a specific color may be “4”. As described above, when an infrared (IR) light source is included, the number of light source colors is “4”. In this case, 4a− (a + b) = <0 so that 4a− (a + b) = <0. Set the width b. Rewriting the inequality sign 4a- (a + b) = <0 results in b> = 3a. If the reading resolution N in the x direction is used, b> = 3 / N.

Generally, when the number of repetitions of light emission when focusing on a light emitting element of a specific color is n (n is an integer of 2 or more), an observation width b along the moving direction of the medium and a reading resolution N in the x direction Relationship
b> = (n−1) / N (1)
It becomes.

The following are numerical examples. The arrangement pitch p in the y direction determines the maximum resolution in the y direction, which corresponds to the manufacturing size of the sensor element to be manufactured. Usually, it is set to about 90 to 100 μm.
(A) Latest discriminating application The reading resolution N in the x direction of the optical line sensor device is 2 to 12 / mm. For example, it is assumed that the number of repetitions of light emission is 2 at the resolution of 8 lines / mm in the x direction when attention is paid to a light emitting element of a specific color. The observation width b in the x direction of the sensor pixel, which is less likely to cause moire, is calculated using the above equation (1) and may be 125 μm or more.

(B) A case is assumed in which reading is performed with the number of repetitions of light emission 3 when focusing on a light emitting element of a specific color at a resolution of 8 lines / mm in the x direction. The observation width b in the x direction of the sensor pixel for preventing moire from occurring may be 2/8 = 250 μm or more.
(C) Assume a case where reading is performed with the number of repetitions of light emission 3 when focusing on a light emitting element of a specific color at a resolution of 12 lines / mm in the x direction. The observation width b in the x direction of the sensor pixel for preventing moire from occurring may be 2/12 = 167 μm or more.

Usually, since the arrangement pitch p per light emitting element in the y direction of the line sensor is about 90 to 100 μm, according to the present invention, the size of the light emitting element is 125 μm or more, or a vertical width of 167 μm or more with respect to the lateral width. A novel rectangular shape that cannot be assumed by a conventional square sensor IC chip is an effective means of the present invention.
In the present invention, as a new shape that does not exist in the conventional square sensor shape, the size of the light-emitting element is limited to a shape and a rectangle having a vertical width larger than 1 times the horizontal width.

In addition, a rectangular shape in which the size of the light emitting element is 1.25 times or more the width is a preferable shape. More preferably, it becomes 1.5 times or more.
FIG. 5 is a graph depicting the relationship between the observation width b and the reading resolution N when the arrangement pitch p per light emitting element in the y direction of the line sensor is assumed to be 0.1 mm and n = 2. is there. The equation (1) is drawn as a hyperbola. A region where “observation width b is larger than p” is indicated by oblique hatching. Further, the region where “the observation width b is larger than p and b> = 1 / N” is shown by cross hatching.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, the present invention can be applied to a combination in which one sensor module is omitted and only one transmissive light source unit is provided as a simple type for cost reduction purposes. In addition, various modifications can be made within the scope of the present invention.

12, 13 Detection unit 14, 15 Sensor module 19, 23, 24 Light emission source 27 Signal processing unit 30 Determination unit S Medium such as securities, banknotes U Unit body

The optical line sensor device reads an image from three directions of front, back, and transmission of a target medium as counterfeiting becomes more sophisticated and the detection signal processing technology of the sensor advances.
Moreover, the optical line sensor device irradiates ultraviolet light and infrared light outside the visible region from a light source together with the human visible light region, color information by visible light irradiation, fluorescent color information of the medium by ultraviolet light irradiation, etc. What reads an image in at least two or more wavelength bands has become the mainstream these days.

Conventional sensor IC chips are being devised to reduce the size of the IC as much as possible. The pitch (pixel pitch) of each sensor IC chip in the horizontal direction (one-dimensional array direction : this direction may be referred to as the sub-scanning direction ) is the minimum required pixel (“pixel” is optically read on the medium). It is determined according to the required pixel size. However, the length (corresponding to the observation width) of the vertical direction of the sensor IC chip (the direction perpendicular to the one-dimensional array direction, the direction in which the medium moves : this direction may be referred to as the main scanning direction ) is not necessarily the size of the pixel. Not tied. This is because the vertical pixel size on the medium can be adjusted by setting the moving speed of the medium and the exposure time.

A light source that illuminates a medium usually includes a plurality of light source elements having different light emission characteristics, and has a structure in which color information is obtained by switching these light source elements. The vertical line density ( reading resolution) on the medium is determined by the number of light source colors to be switched while the medium is moving and how many times data is to be acquired per unit distance. For example, when data is acquired four times per 1 mm of the moving distance of the medium and the number of light source colors to be switched is 2, the reading resolution is 8 lines / mm.

Recently, it has become possible to read highly accurate images by increasing the speed of signal processing, and further, it has been desired to improve the discrimination function by identifying even the characters and numbers of the medium, and the resolution is 2 or more / mm, preferably In order to read numbers and characters on a medium, a resolution of 4 lines / mm or more has been demanded.
However, when developing an optical line sensor device having an advanced discrimination function such as securities or banknotes, moire that inhibits the discrimination function of the read image may occur depending on the print pattern of the target medium. There are moire in the sub-scanning direction (horizontal direction) and moire in the main scanning direction (vertical direction). Moire in the horizontal direction refers to a phenomenon in which each sensor element arranged on a straight line at an equal pitch and a striped image cause interference, and a light detection signal of each sensor element fluctuates periodically. In the case of vertical moire, when the target medium moves in the main operation direction and is periodically read by each sensor element, the reading cycle of the sensor interferes with the stripe pattern in the main scanning direction of the image, and each sensor A phenomenon in which the light detection signal of the element fluctuates periodically. If a noticeable moire is detected, an accurate image cannot be read and the discrimination function is inhibited.

Mode crack is that obtained also occurs in the transverse direction to the longitudinal direction, in this specification, explaining moire occurring below the longitudinal direction. The cause of this moire will be described with reference to FIG. The y direction in FIG. 6 indicates the arrangement (lateral direction) of the sensor elements of the sensor module, and the x direction indicates the medium feeding direction (vertical direction). As for the color of the light source, it is assumed that green (G) is repeatedly emitted once every two times, such as green (G) → other colors → green (G) → other colors. By intermittently reading the sensor element of the sensor module, four green observation lines are generated per 1 mm in the vertical direction on the medium. That is, the green resolution in the x direction is 4 lines / mm.

In FIG. 6, the vertical distribution of the input green image is shown on the right side of the observation line. The input image has a sine wave shape for convenience. It shows the sensor output signal by a bold broken line for the observed green sensor element. Thus, when reading an image of a periodic moire is generated interferes with the observation line.
Here, if the distance that the medium travels in the x direction for each light emission is Tang # and the width in the x direction of the observation window of the sensor element is T, the vertical width of the observation line is (a + b). Since green (G) is emitted once every two times, the green pitch in the x direction of the observation line is 2 (a + b). When the pitch of the green image which is input 2 (a + b) + δ (0 <δ <a + b), the pitch of the moire regarding green generated by theory of well-known moiré, and ^{4 (a + b) 2 /} δ Become. It is also well known from the theory that the smaller the difference in the shades of the observation line, the smaller the difference in the shades of moire.

According to this configuration, the size of the sensor element is increased in the direction in which the medium moves, and the ratio of the length in the one-dimensional direction of the sensor element to the length in the direction of movement of the medium is greater than 1. ing. As described in [Background Art], the shape of the sensor element of the conventional sensor IC chip is a square or a rectangle with a short vertical direction (a direction perpendicular to the one-dimensional array direction). There is a significant feature in the shape that the ratio between the length in the one-dimensional direction and the length in the vertical direction is larger than 1, that is, the length is long. It is possible to easily overlap the observation line currently read by the sensor element with the observation line previously read by the same sensor element. In other words, if the sensor element is lengthened vertically, the difference in light and shade of the observation line becomes smaller, and the difference in light and shade of moire becomes smaller. Thus, the occurrence of moire can be reduced and a good-quality image that can be identified is obtained.

When the observation width b of the sensor element, the reading resolution N that is the number of times the plurality of lights are switched over time per unit moving distance of the medium, and light of a specific color among them, light is emitted once. When n is the number of switches from when the light is emitted to the next time (n is an integer of 2 or more) , these relationships are
b> = (n−1) / N (1)
It is preferable to satisfy the formula: According to this configuration, it is possible to reliably overlap the observation line currently read by the sensor element and the observation line of the color read by the same sensor element last time. In other words, by doing this, the difference in the shade of the observation line becomes small, and the moire becomes inconspicuous.

With the above configuration, the sensor module 14 can form an image existing in the detection area R <b> 1 set outside the translucent cover 17 on one side of the unit body U via the rod lens array 25. .
In addition, in the unit main body U, an elongated light source 19 that can irradiate light obliquely toward the detection area R1 is provided along with the rod lens array 25 (the direction of light in FIG. 1). Is indicated by a one-dot chain line ). The light source 19 is attached to the housing 16 in a state parallel to the sensor module 14 and the rod lens array 25 along the length (y) direction of the unit body U.

The light source 19 includes a light guide 38 made of a transparent material such as an elongated glass having a length substantially equal to or longer than that of the sensor module 14 and a light emitting element 29 made of a semiconductor element that irradiates the light guide 38. is doing. In the light guide 38, the light irradiated from the light emitting element 29 is emitted toward the detection area R1.
More housing 16, as shown in FIG. 1, the reflective plate portion 34 for guiding light emitted from the light guide 3 8 in the detection area R1 is provided. Like the unit body U, the reflecting plate portion 34 has an elongated shape in the length (y) direction and has a parallel groove along the length (y) direction. The light emitter 19 is accommodated in the groove. Yes. One side of the groove for accommodating the light emitter 19 has a thickness from the light guide 3 8 (-z) spreads the horn shape as the distance in the direction, the other surface of the groove being cut horizontally. This is to avoid an obstacle when irradiating light from the light guide 3 8 proceeds to the detection area R1.

Each light-emitting element 29A~29E is capable irradiated with light of different wavelength regions in the light guide 3 in 8, the light emitting element 29A~29E by selecting the electrode terminal for applying a voltage to this end each element The circuit configuration can emit light by switching over time.
The casing 16 is formed with a bottom wall portion 35 for preventing light from the light emitter 19 from leaking to the sensor module 14 inside, and the bottom wall portion 35 has an optical path of the sensor module 14. An opening is formed only in the opening, and the rod lens array 25 is attached to the opening. The reflection plate portion 34 and the bottom wall portion 35 may be integrally formed as shown in FIG.

While the medium S moves in the x direction, the signal processing unit 27 exposes the sensor elements arranged in a line over the exposure period T, whereby an observation line having a predetermined width along the y direction on the surface of the medium S. Can be set. The width of the observation line along the x direction is the sum (a + b) of the distance a and the observation width b of the sensor element.
Each of the light emitting elements 29A to 29E is assumed to emit light while being switched in time by selecting an electrode terminal that applies a voltage to each element. Here, paying attention to a light emitting element of a specific color, the number of times that the light emitting element emits light repeatedly (how many times it emits once) is represented by a number n that is switched until the light emitting element emits light next time. For example, when attention is paid to a green (G) light emitting element and green (G) is emitted once every two times, such as green (G) → other color → green (G) → other color, n = 2. If green (G) is emitted once every three times, such as green (G)-> other colors-> other colors-> green (G)-> other colors-> other colors-> green (G) n = 3.

FIG. 3 (a) shows the first moment of reading the medium S under red light emission. The width (indicated as R (1)) in which the medium S is read is t.
FIG. 3B shows a time point when the sensor element is switched to reading under the next green emission after reading one line under the red emission. While advances in Figure 3 (a) (b), the medium S is advanced by a distance a. Therefore, the width in the x direction (observation line width) read by the sensor element in red is a + b.

FIG. 3C shows a point in time when the reading is switched to reading of the sensor element under the next blue light emission after reading one line under the green light emission. While advances in Figure 3 (b) (c), the medium S is advanced by further distance a. Therefore, the width in the x direction (the width of the observation line) read by the sensor element in green is a + b. At this time, the tip of the portion read by the sensor element in red is advanced by 2a from the right end (indicated by x1) of the observation width of the sensor element. Here, since the width of the observation line read by the sensor element with red light is a + b, only the rear end ba − (= a + b−2a) is still passing under the sensor element ( (Refer FIG.3 (c)).

FIG. 3D shows the moment when the sensor element is read for one line under blue light emission and then switched to reading with the sensor element under the next red light emission. While proceeding from FIG. 3C to FIG. 3D, the medium S further proceeds by the distance a. At this time, the rear end of the portion read by the sensor element under “front” red emission is advanced by e = 3a− (a + b) from the right end x1 of the observation width of the sensor element. At this time, the next medium S is read under red light emission (displayed as R (2)).

In general, when paying attention to a light emitting element of a specific color, if the number to be switched between light emission once and appearing next is n (n is an integer of 2 or more), an observation width b along the moving direction of the medium, The relationship with the reading resolution N in the x direction is
b> = (n−1) / N (1)
It becomes.

Claims (4)

In the optical line sensor device for the purpose of identifying media such as securities, banknotes,
A light source that irradiates the medium by temporally switching a plurality of lights having different spectral characteristics during the movement of the medium;
A light receiving unit that detects light transmitted or reflected by the sensor element in a one-dimensional manner in a direction different from the moving direction of the medium;
A signal processing unit for determining information of the medium by processing a light detection signal of the light receiving unit;
The relationship between the observation width b of each sensor element along the moving direction of the medium and the arrangement pitch p of the sensor elements in which the sensor elements are arranged one-dimensionally satisfies the relationship b> p. Line sensor device. b> = 1.25p
The optical line sensor device according to claim 1, satisfying the relationship: The observation width b of the sensor element, a reading resolution N that is the number of times the plurality of lights are switched over time per unit moving distance of the medium, and a specific spectral characteristic during the time switching of the plurality of lights. The relationship with the number of repetitions of light emission n (n is an integer of 2 or more)
b> = (n−1) / N
The optical line sensor apparatus of Claim 1 or Claim 2 which satisfy | fills Formula.   The optical line sensor device according to any one of claims 1 to 3, which employs an equal magnification reading method in which a sensor module is read in close contact with a medium.

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