JP2011188231A - Image reading apparatus - Google Patents

Abstract

An image color change caused by temperature drift of a white LED is suppressed to a range that is not perceived by humans, and color reproducibility of an image in a large amount and high-speed reading is ensured at a high level.
When a white LED is used as a component of a light source unit for illuminating a read original and the same original is read as a read original with the illumination of the white LED, each read image data at the start of reading is read. The junction temperature of the white LED is controlled so that the difference between the chromaticity of the pixel and the chromaticity of the corresponding pixel in the read image data at the end of reading is within a preset range.
[Selection] Figure 12

Description

  The present invention relates to an image reading apparatus.

  In general, as an image reading apparatus provided with an image sensor that reads a document surface as image information, a flat bed type image reading apparatus used for home use of about 10 ppm to 20 ppm, or 40 ppm to 100 ppm used for business use is used. There are faster image reading devices. Conventionally, fluorescent lamps and xenon (Xe) lamps have been used as the illumination light source unit of the image reading apparatus. However, these require an inverter circuit for driving, and are expensive as a system constituting the illumination light source unit. is there. In addition, a sufficient amount of light cannot be obtained until the temperature of the fluorescent tube has risen to some extent. In general, it takes about 30 seconds to 1 minute from the start of light emission until a sufficient amount of light is obtained. Meanwhile, an image reading apparatus equipped with a fluorescent lamp or a xenon lamp has a problem that reading of a document cannot be started. Or, it was necessary to warm the fluorescent lamp or the xenon lamp during standby.

  Therefore, in recent years, as a light source of an image reading apparatus, light is incident from an end portion of a light guide, and is refracted or reflected by a number of triangular wave-shaped light refraction areas and / or reflection areas provided on one side surface of the light guide. A linear illumination device that emits light linearly has been proposed (see, for example, “Patent Document 1”).

  Such linear illumination devices are beginning to be used in low-speed image reading devices for home use. In this linear illumination device, an LED such as a white LED or a three-color LED is used as a light source for allowing light to enter from the end of the light guide. If an LED is used, a sufficient amount of light can be obtained without preheating, so that reading of a document can be started immediately after the start of light emission. The luminous efficiency of these LEDs has reached the same level as conventional xenon lamps and fluorescent lamps due to recent remarkable technological development, and can be applied to high-speed image readers for business use that require a larger amount of light. The environment is becoming possible.

JP-A-10-150526

  However, the luminous efficiency of the LED has temperature dependency, and there arises a problem that the amount of light and chromaticity change depending on the temperature of the light emitting region of the LED. Therefore, the reading performance such as gradation and color reproducibility is greatly affected.

  In particular, a high-speed image reading apparatus requires a higher amount of light than a normal image reading apparatus, and uses a high-intensity white LED, so that it is necessary to flow a large current of 600 mA to 700 mA. For this reason, the temperature rise of the junction temperature (so-called junction temperature) is larger than that of the low-brightness product, so that the amount of change in the light amount and chromaticity change is also larger than that of the low-brightness product.

  Moreover, when such a high-speed image reading apparatus reads a large amount of originals at high speed and continuously, correction processing such as light quantity correction cannot be performed midway. Read quality, that is, the color of the read image changes greatly.

  The present invention solves such a conventional problem, and ensures stable gradation and color reproducibility even when a white LED is used in an illumination light source unit of a high-speed image reading apparatus. Objective.

  In order to achieve the above object, the present invention has a white LED as a component of a light source unit for reading originals, and starts reading when the same original is read and read continuously with the white LED illumination. The junction temperature of the white LED is set so that the average color difference between the chromaticity of each pixel in the read image data at the time and the chromaticity of the corresponding pixel in the read image data at the end of reading falls within a preset range. It is something to control.

  With this configuration, when a white LED is used for high-speed reading of several tens to 100 originals per minute, the color change of the image can be suppressed to a range that is not perceived by humans, and is large and continuous. The color reproducibility of the image in the high-speed reading can be ensured at a high level.

  According to the image reading apparatus of the present invention, the color reproducibility of an image can be ensured at a high level when a white LED is used to perform high-speed reading of several tens to 100 documents per minute.

1 is a front perspective view of an image reading apparatus according to an embodiment of the present invention. The perspective view which looked at the image reading apparatus in one Example of this invention from diagonally backward 1 is a schematic sectional view of an image reading apparatus according to an embodiment of the present invention. 1 is a control block diagram of an image reading apparatus according to an embodiment of the present invention. The figure which showed the structure of the image reading part of the image reading apparatus in one Example of this invention. 1 is a configuration diagram of an illumination light source unit used in an image reading apparatus according to an embodiment of the present invention. 1 is a configuration diagram of an illumination light source unit used in an image reading apparatus according to an embodiment of the present invention. The figure which showed the mode of the progress and reflection of the irradiation light of the light source unit for illumination used for the image reader in one Example of this invention 1 is a block diagram of a main control unit constituting an image reading apparatus according to an embodiment of the present invention. 1 is a configuration diagram of a white LED of an illumination light source unit used in an image reading apparatus according to an embodiment of the present invention. The figure which shows the relationship between the forward bias of white LED used for the image reading apparatus in one Example of this invention, and junction temperature. Explanatory drawing of LED drive control by the control part which comprises the image reading apparatus in one Example of this invention. The figure which shows the characteristic of LED which comprises the image reading apparatus in one Example of this invention. Explanatory drawing of LED drive control by the control part which comprises the image reading apparatus in one Example of this invention. The figure which shows the change of the wavelength profile of LED which comprises the image reading apparatus in one Example of this invention. The figure which shows the change of the wavelength profile of LED which comprises the image reading apparatus in one Example of this invention. 1 is a system configuration diagram used to obtain experimental data of an image reading apparatus according to an embodiment of the present invention. The figure which shows the experimental data which show the relationship between the junction temperature of LED of the image reading apparatus in one Example of this invention, and the chromaticity difference of a document. The figure which shows the characteristic regarding the lighting rate of LED of the image reading apparatus in one Example of this invention.

  Hereinafter, specific contents of the present invention will be described with reference to examples.

  FIG. 1 is a front perspective view of an image reading apparatus according to an embodiment of the present invention, and FIG. 2 is a perspective view of the image reading apparatus according to an embodiment of the present invention as viewed obliquely from the rear. In FIG. 1, a hopper table 2 attached to the front surface portion of the image reading apparatus 1 can be moved up and down by a motor and a lifting mechanism (not shown). A document guide 2 a provided on the upper surface of the hopper table 2 is slidable to align the widths of documents (not shown) stacked on the hopper table 2. A document (not shown) loaded on the hopper table 2 is fed into the housing of the image reading apparatus 1 from the paper feed port 3.

  The document fed into the image reading apparatus 1 is discharged from the front discharge port 4 and stacked on the discharge stocker unit 5. Depending on the thickness of the document fed from the sheet feeding port 3, the conveyance path (not shown) provided in the image reading apparatus 1 is switched to be provided on the rear surface side of the image reading apparatus 1 shown in FIG. In some cases, the paper is discharged from the rear discharge port 7.

  Various settings and commands are input to the image reading apparatus 1 from the input unit 6 shown in FIG. The original image data read in the image reading apparatus 1 is transmitted to an external host computer 100 connected via an interface (hereinafter referred to as I / F) 8. Reference numeral 9 denotes a connector for connecting a power cord, and reference numeral 10 denotes a door for performing maintenance and the like inside the image reading apparatus 1.

  Next, the internal structure of the image reading apparatus 1 will be described with reference to FIGS.

  FIG. 3 is a schematic sectional view of an image reading apparatus according to an embodiment of the present invention, and FIG. 4 is a control block diagram of the image reading apparatus according to an embodiment of the present invention. The description from here will be mainly made with reference to FIG. 3, and will be supplementarily described with reference to FIG.

  In FIG. 3, when the hopper table 2 is raised, the pickup roller 21 is pushed up by the uppermost surface of the document 11. The pickup roller 21 stops rising when the pickup roller 21 is almost equal to the height of the paper feed roller 22, and both the pickup roller 21 and the paper feed roller 22 start rotating by driving a motor (not shown). Of the plurality of originals 11 stacked on the hopper table 2, the uppermost original 11 a is fed to the paper feed port 3 (FIG. 1) by the pickup roller 21, and the rear discharge from the paper feed port 3 by the paper feed roller 22. It is conveyed in the direction of the mouth 7.

  The retard roller 23 is located below the paper feed roller 22 and rotates while being in contact with the paper feed roller 22, so that a plurality of documents 11 are simultaneously fed into the nip portion between the paper feed roller 22 and the retard roller 23. This is to prevent double feeding of the document 11 by utilizing the difference between the frictional force of the document 11 and the frictional force of the document 11 and the retard roller 23.

  When the loading amount of the document 11 decreases due to the sheet feeding, the position of the uppermost surface of the document 11 gradually decreases, and the pickup roller 21 also descends accordingly. The hopper height sensor S is a sensor that detects that the pickup roller 21 is within a predetermined height range depending on the position of the roller receiving cover 40. When it is detected by the hopper height sensor S that the pickup roller 21 has been lowered to a position lower than the predetermined height, the hopper table 2 is raised so that the pickup roller 21 rises again to the predetermined height. As a result, the document 11 is almost certainly fed to the nip point between the paper feed roller 22 and the retard roller 23, so that stable paper feed is performed. The document presence / absence sensor SA is a sensor that detects whether or not the document 11 is present when the hopper table 2 is raised.

  The document 11a conveyed by the pickup roller 21, the paper feed roller 22, and the retard roller 23 passes between the light emitting unit PD and the light receiving unit PS provided at a position opposite to the light emitting unit PD. Here, part of the spot light emitted from the light emitting part PD passes through the original 11a and enters the light receiving part PS. The thickness of the document 11a is determined based on the amount of transmitted light received by the light receiving unit PS.

  Thereafter, the document 11 a is transported by the transport roller 24 to a reading unit mainly including an illumination light source unit 57, an image sensor 58, a document glass 59, and a white reference plate 60. The driven roller 25 follows the rotation of the conveying roller 24. A paper feed sensor SB is provided on the upstream side of the transport roller 24, and a reading position sensor SC is provided on the downstream side.

  FIG. 5 is a diagram showing the configuration of the image reading unit of the image reading apparatus according to an embodiment of the present invention. The light source unit 57 for illumination, the image sensor 58, the document glass 59, and the white LED 74 are provided on the image reading unit. FIG. 6 is a view of the positional relationship of the white reference plate 60 as viewed from the direction in which the document 11a enters. The longitudinal direction of the original glass 59, that is, the left-right direction in FIG.

  The white reference plate 60 provided on the original glass 59 serves as a reference for correcting unevenness (shading) of the density level of each pixel of the image sensor 58 before the original 11a is read. The white reference plate 60 according to the first exemplary embodiment is provided not on the entire original scanning direction on the original glass 59 but only on a portion that does not affect the reading of the original 11a.

  Therefore, the reflected light of the light transmitted through the original glass 59 from the illumination light source unit 57 of FIG. 3 and irradiated onto the original 11a is reflected toward the portion where the white reference plate 60 is provided on the original glass 59. Is incident on the image sensor 58.

  Reference numerals 26, 28, 30, 32, 34, and 36 denote paper discharge rollers for discharging the document 11 from which images have been read to the front paper discharge port 4 or the rear paper discharge port 7. Reference numerals 27, 29, 31, 33, 35, and 37 are driven rollers that are driven by the paper discharge rollers 26, 28, 30, 32, 34, and 36, respectively. The paper discharge rollers 26, 28, 30, 32, 34, and 36 constitute a paper discharge roller group 56 shown in FIG.

  As described above, the image reading apparatus 1 according to the first exemplary embodiment has the front discharge port 4 (indicated by the arrow B) or the rear discharge port 7 according to the thickness of the document 11a shown in FIG. The paper discharge destination can be switched to any one (indicated by arrow A). The control unit 51 shown in FIG. 4 determines the thickness of the original 11a shown in FIG. 3 based on the amount of transmitted light emitted from the light emitting part PD and transmitted through the original 11a and received by the light receiving part PS. The transfer path switching unit 38 is switched to either the position H or the position L.

  In the image reading apparatus 1 according to the first exemplary embodiment, when the document 11a is thicker than a predetermined thickness in FIG. 3, the document 11a is placed at the rear portion with the conveyance path switching unit 38 at the position H in order to avoid bending or jamming of the document 11a. The paper is discharged from the paper discharge port 7. If the document 11a has a predetermined thickness or less, the image reading apparatus 1 sets the transport path switching unit 38 to the position L and discharges the document 11a to the front discharge port 4.

  In the control block diagram of the image reading apparatus according to the first embodiment shown in FIG. 4, the control unit 51 includes an MPU, a ROM, a RAM, an I / O, and the like. The motor 52 driven by the controller 51 drives the pickup roller 21, the paper feed roller 22, and the retard roller 23 via the clutch CL1. Further, the conveying roller 24 is driven through the clutch CL2, and the paper discharge roller group 56 is driven without passing through the clutch.

  Accordingly, when the clutch CL1 is turned on while the motor 52 is driven, the pickup roller 21, the paper feed roller 22, and the retard roller 23 are rotationally driven, and when the clutch CL1 is turned off, these rollers are free to rotate. . Similarly, when the clutch CL2 is turned on, the conveyance roller 24 is driven to rotate, and when it is turned off, the rotation becomes free. However, the discharge roller group 56 always rotates when the motor 52 is driven. A stepping motor is normally used as the motor 52, and the rotation speed can be easily controlled by setting from the control unit 51.

  The hopper height sensor S detects the height of the pickup roller 21 and monitors that the hopper table 2 is at an appropriate height. The document presence sensor SA detects whether or not the document 11 is set on the hopper table 2. The paper feed sensor SB is provided on the upstream side of the transport roller 24 in the transport direction. The control unit 51 determines that the document 11 a is sandwiched between the transport roller 24 and the driven roller 25 after a predetermined time has elapsed since the paper feed sensor SB detected the leading edge of the document 11 a.

  The reading position sensor SC is provided on the downstream side of the transport roller 24 in the transport direction. The control unit 51 starts reading processing of the document 11a by the illumination light source unit 57 and the image sensor 58 after a predetermined time has elapsed since the reading position sensor SC detected the leading edge of the document 11a. The paper discharge sensor SD detects that the document 11a is discharged from the front discharge port 4, and the paper discharge sensor SE detects that the document 11a is discharged from the rear discharge port 7. As described above, the paper discharge destination is switched by the transport path switching unit 38.

  The reflected light of the light emitted from the illumination light source unit 57 to the document 11 a is incident on the image sensor 58, converted from an optical signal to an electrical signal, and then output to the image processing circuit 63. The image processing circuit 63 performs image processing such as A / D conversion processing and binarization processing, and the obtained image data is written into the buffer 65 or 66. The image data in the buffer 65 or 66 is compressed by the compression circuit 68 and output to the external host computer via the I / F 8.

  Each of the buffer 65 and the buffer 66 has a capacity capable of storing uncompressed data for one sheet of the document 11a. The control unit 51 switches between the data writing by the image processing circuit 63 and the data reading by the compression circuit 68 and the buffer 65 and the buffer 66 by switching the switch 64 and the switch 67.

  The image processing circuit 63 notifies the control unit 51 of the completion of data writing to the buffer 65 or the buffer 66. When the data reading / compression / output to the host computer from the buffer 65 or 66 is completed, the compression circuit 68 notifies the control unit 51 to that effect. In this way, the control unit 51 always keeps track of which buffer the data is written to / read from and which buffer is in a write / read state.

  With such a configuration, for example, as described below, high-speed reading control exceeding several tens to 100 sheets per minute becomes possible. That is, when the first original 11 a is read, the switch 64 is switched to the buffer 65 side, and the first original data sent from the image processing circuit 63 is written into the buffer 65. Next, when reading the second original, the switch 64 is switched to the buffer 66 side, and the second original data sent from the image processing circuit is written into the buffer 66. Meanwhile, the switch 67 is switched to the buffer 65 side, and the first document data previously written in the buffer 65 is transmitted to the host computer (not shown) via the compression circuit 68 and the I / F 8. Further, when reading the third original, the switch 64 is switched to the buffer 65 again, and the third original data sent from the image processing circuit 63 is written into the buffer 65. In the meantime, the switch 67 is switched to the buffer 66 side, and the second original data written in the buffer 66 is transmitted to the host computer (not shown) via the compression circuit 68 and the I / F 8.

  When the fourth original is subsequently read, the switch 64 is switched to the buffer 66 again, and writing and reading to and from the buffer 65 and the buffer 66 are performed alternately.

  6 and 7 are configuration diagrams of an illumination light source unit used in the image reading apparatus according to an embodiment of the present invention. FIGS. 6A, 6B, and 7A are respectively for illumination. It is the top view of the light source unit 57, side CC 'sectional drawing, and front DD' sectional drawing. FIG. 7B is a partially enlarged perspective view of the illumination light source unit 57.

  The illumination light source unit 57 is the direction in which the front cross section shown in FIG. 7A can be seen in FIG. 3 and the central optical axis L1 of the illumination light emitted from the illumination light source unit 57 is as shown in FIG. It arrange | positions so that it may correspond with the optical axis L1 shown in FIG.

  As shown in FIGS. 6B and 7B, the light guide 71 has a light refraction / reflection surface 72 composed of a number of sawtooth-like surfaces provided on one side surface in the longitudinal direction. . The light guide 71 and the light refraction / reflection surface 72 are integrally formed by injection molding with a transparent resin. A number of sawtooth-shaped surfaces that are the light refraction / reflection surfaces 72 are configured to be formed on the bottom surface of the light guide 71.

  As a material for the transparent resin, heat-resistant acrylic, polycarbonate, amorphous polyolefin, and the like are suitable in consideration of translucency, heat resistance, and flowability of the resin during injection molding.

  A white LED 74 is mainly mounted on the LED circuit board 73 shown in FIGS. The LED circuit board 73 and the light guide 71 on which the white LED 74 is mounted are held by the connection portion 75. The guide rib 70 of the light guide 71 is guided by the positioning groove of the frame 79, and the connecting portion 75 is held on the end surface of the frame 79. The frame 79 is formed by extrusion molding of aluminum, and the surface thereof is subjected to black alumite treatment in order to absorb light leaked from the light guide 71.

  As shown in FIG. 6B, the light guide 71 is formed such that the cross-sectional area (diameter of the circle) decreases in the direction away from the white LED 74, that is, from the left to the right in FIG. 6B. Yes.

  The light shielding member 76 is, for example, a sponge such as white polyethylene or polyether foamed foam or silicone rubber, and closes the gap between the light guide 71 and the connecting portion 75.

  A reflector 77 shown in FIGS. 6A and 6B corresponds to the auxiliary reflector. For example, as shown in FIG. 7A, the reflector 77 has a reflective surface 77a described below formed on a black thin plate-like base member 77b made of a thermoplastic resin such as ABS by a fixing member such as an adhesive tape. It is formed by sticking and fixing.

  As the reflecting surface 77a, for example, the surface of a plastic film such as a polyester film is a reflective layer in which an aluminum foil is bonded with an adhesive in consideration of translucency and spectral characteristics, or a metal such as aluminum or chromium is vacuum-deposited. Alternatively, it is formed by sputtering or the like, and a protective layer obtained by thermocompression bonding of a thermoplastic film such as PET, PBT, PEN, PMMA, or polycarbonate is used.

  The reflector 77 formed in this way has guide ribs in, for example, square holes (not shown) provided in the reflector fixing member 77c with the reflection surface 77a in contact with the light refraction / reflection surface 72 of the light guide 71. 70 is inserted and is engaged with the light guide 71 by being pushed in from below.

  The light reflecting layer 80 is formed on the other end 78 of the light guide 71 shown in FIG. 6B by, for example, aluminum deposition or dipping. Alternatively, it may be formed by affixing an aluminum tape with a transparent adhesive on an aluminum foil to the other end 78, or may be configured by inserting a cap made of white resin into the other end 78. Good.

  FIG. 8 is a diagram showing the progress and reflection of the irradiation light of the illumination light source unit used in the image reading apparatus in one embodiment of the present invention.

First, among the light emitted from the white LED 74, the light component c ₁ emitted in the direction of the gap between the light guide 71 and the connecting portion 75 is the light component c ₁ if there is no light blocking member 76, as indicated by the broken arrow c ₂ . Since the light leaks directly from the gap between the light guide 71 and the connecting portion 75 to the outside, the illuminance on the original surface near the connecting portion 75 becomes extremely high, and the illuminance variation becomes large. However, since the light shielding member 76 is disposed in the gap between the light guide 71 and the connection portion 75, the light is not emitted in the direction of the document 11 after entering the light guide 71.

Next, among the light components other than these, the light component c ₃ that directly reaches the light refraction / reflection surface 72 is reflected and emitted in the document surface direction. The light component c ₄ incident on the light guide 71 at an angle greater than the critical angle will eventually reach the light refracting / reflecting surface 72 while repeating total reflection on the side surface of the light guide 71, where it will be refracted or reflected. The direction of travel can be bent suddenly. Thereafter, the light passes through the other side facing the light refraction / reflection surface 72 and is emitted to the upper outside of the light guide 71 to irradiate the document surface.

However, not all of the light reaching the light refracting / reflecting surfaces 72 are reflected toward the inside of the light guide member 71, leaks some of the outside of the light guide 71 as light components c ₅ . The leaked light is reflected again toward the inside of the light guide 71 by the reflector 77 and is transmitted from the inside of the light guide 71 to the document surface, or is refracted or reflected again inside the light guide 71.

As described above, in the portion where the reflector 77 is present, most of the light leaking from the light refraction / reflection region 72 to the outside of the light guide 71 is reflected by the reflector 77 and travels toward the document surface. The efficiency of the emitted light increases, and the illuminance of the document increases. Furthermore, since the reflector 77 is disposed in the vicinity of the light refraction / reflection region 72 of the light guide 71, most of the light leaking outside is efficiently reflected and reused. In addition, among the light components incident on the light guide 71, the light component that has repeatedly undergone total reflection and reaches the other end 78 becomes a light component c ₆ that has been totally reflected again by the light reflecting layer 80, and is guided. By returning to the body 71 and being reused, there is little loss and it is used for document surface irradiation.

  Next, the main part of the present invention for the image reading apparatus 1 according to the first embodiment having the above-described configuration to perform high-speed reading of several tens to 100 or more originals per minute using a white LED. State.

  FIG. 9 is a block diagram of the main control unit constituting the image reading apparatus in one embodiment of the present invention. Of the control block diagram of the image reading apparatus in the first embodiment shown in FIG. It is the block diagram which extracted the part concerned.

  When the control unit 51 outputs a drive signal (WLED) (not shown) to the LED drive circuit 82 provided therein, the LED drive circuit 82 drives and lights the white LED 74 mounted on the illumination light source unit 57. Then, the white illumination light WL is emitted from the white LED 74 and irradiated on the document 11a. A part of the illumination light WL is reflected by the original 11a, and a part BL1 to BL3 of the reflected light BL is red, green, and blue on the CCD 84 via the SELFOC lens 83 mounted on the image sensor 58. The light enters the image pickup devices 84R, 84G, and 84B (here, only one image pickup device of each color is representatively displayed, but actually there are more image pickup devices for each color).

  When each of the image pickup devices 84R, 84G, 84B receives light, received light detection signal voltages VR, VG, VB are output and input to the video amplifiers 85R, 85G, 85B, respectively, and amplified. As will be described later, the amplification degree of each of the video amplifiers 85R, 85G, and 85B is designed to be changeable according to the lighting rate by the LED driving circuit 82 of the white LED 74 described later. The amplified output signal voltages AR, AG, AB from the video amplifiers 85R, 85G, 85B are converted from analog signals to digital signals by the A / D converter 86 and input to the image processing circuit 63.

  The control unit 51 performs accumulation and transmission of image data, control of the amplification degree of the video amplifiers 85R, 85G, and 85B to the image sensor 58 and the image processing circuit 63 via the buses B1 and B2, respectively. The CCD 84, the A / D converter 86, and the image processing circuit 63 operate in synchronization with the clock signal VCLK output from the image processing circuit 63. The control signal SI-RGB is a control signal for controlling a shift register built in the CCD 84.

  FIG. 10 is a configuration diagram of a white LED of an illumination light source unit used in an image reading apparatus according to an embodiment of the present invention. FIG. 10 (a) is a perspective view from above, and FIG. 10 (b) is from below. FIG. 10C is a perspective view of the WW ′ cross section in FIG. 10A or 10B. As the white LED 74 in the first embodiment, LXML-PWC1-0100 manufactured by Lumileds is employed. In FIG. 10B, which is a perspective view from the bottom, 74A is an anode electrode, 74C is a cathode electrode, and 74T is a heat dissipation pad.

  Further, 74H in FIG. 10C is an LED chip that emits blue light, and a compound semiconductor such as gallium nitride is epitaxially grown on a silicon substrate. 74G is a phosphor for emitting yellow light when excited by the light emission beam of the LED chip, and 74F is a silicon lens for condensing the light emission beam of the white LED 74. Reference numeral 74I denotes a thermal pad for dissipating heat generated by power loss at the junction of the LED chip 74H to the outside.

  FIG. 11 is a diagram showing the relationship between the forward bias Vf of the white LED used in the image reading apparatus in one embodiment of the present invention and the junction temperature Tj. As shown in FIG. 11, the forward bias Vf of the white LED 74 described in FIG. 10 and the junction temperature Tj are approximately proportional to each other, and the forward bias Vf decreases linearly as the junction temperature Tj increases. I understand that. Therefore, if the voltage between the anode electrode 74A and the cathode electrode 74C of the white LED 74 shown in FIG. 10B is measured, the relationship between the forward bias Vf and the junction temperature Tj shown in FIG. It becomes possible to know the junction temperature Tj indirectly.

  The control unit 51 in FIG. 9 incorporates data in which the relationship between the forward bias Vf and the junction temperature Tj shown in FIG. 11 is tabulated, and the LED drive circuit 82 includes the anode electrode 74A and the cathode electrode of the white LED 74. A circuit for measuring the voltage between 74C is also provided. As a result, the control unit 51 can indirectly know the junction temperature Tj of the white LED 74 via the LED drive circuit 82.

  Alternatively, although not shown in the first embodiment, temperature detecting means such as a temperature sensor may be disposed in the vicinity of the white LED 74 so that the junction temperature Tj of the white LED 74 can be measured more directly.

  Hereinafter, the LED drive control which is the main part of the present invention will be described in detail.

  FIG. 12 is an explanatory diagram of LED drive control by the control unit constituting the image reading apparatus according to the embodiment of the present invention. FIG. 13 is a diagram showing the characteristics of the LEDs constituting the image reading apparatus in one embodiment of the present invention, and shows the relationship between the heat radiation pad temperature of the white LED and the relative luminous flux, that is, the light quantity. FIG. 14 is an explanatory diagram of LED drive control by the control unit constituting the image reading apparatus according to the embodiment of the present invention, and shows an example of temporal change in the lighting rate of the white LED.

  The biggest feature in FIG. 12 is that the method of LED drive control is different between section I and section II. This point will be described in detail below.

  As described above, when the control unit 51 shown in FIG. 9 outputs the drive signal WLED to the LED drive circuit 82, the LED drive circuit 82 drives and lights the white LED 74 mounted on the illumination light source unit 57. . FIG. 12A shows the state of the drive signal WLED.

  When the drive signal WLED is turned on, the white LED 74 shown in FIGS. 9 to 10 is turned on. In the first embodiment, the white LED 74 is continuously lit. Then, as shown in FIG. 12B, the junction temperature Tj of the white LED 74 rapidly rises with time.

  The relationship between the temperature of the heat dissipating pad 74T constituting the white LED 74 and the relative luminous flux, that is, the light amount is as shown in FIG. 13, and the light amount decreases as the temperature of the heat dissipating pad 74T rises. Naturally, the temperature of the heat radiation pad 74T and the junction temperature Tj are proportional to each other. Therefore, when the junction temperature Tj of the white LED 74 increases, the amount of light emitted from the white LED 74 also decreases. Accordingly, the amount of light incident on the image pickup devices 84R, 84G, and 84B of the CCD 84 shown in FIG. 9 is inevitably reduced. As a result, as shown in FIG. 12C, the received light detection signal voltages VR, VG, VB from the image pickup devices 84R, 84G, 84B decrease in proportion to the amount of incident light.

  Therefore, the control unit 51 illustrated in FIG. 9 performs an operation of increasing the amplification degree of each of the video amplifiers 85R, 85G, and 85B in order to compensate for a decrease in the amount of incident light from the white LED 74 to the image pickup devices 84R, 84G, and 84B. This is indicated by the section I in FIG. The control in the section I is “LED lighting rate constant + video amplifier amplification degree control”.

  More specifically, the control in the section I is as follows: “The lighting rate of the white LED 74 is constant, and the illumination light from the illumination light source unit 57 is reflected by the read original 11a and is sent to the image sensors 84R, 84G, 84B. It may be said that this is performed by the “first control means for changing the amplification degree of each of the video amplifiers 85R, 85G, 85B (variable amplification means) according to the amount of incident light”.

  The white LED 74 sufficiently exceeds the target light amount immediately after the start of lighting, and decreases to the vicinity of the target light amount level after several minutes (temperature characteristic where the light amount is negative). Therefore, in the section I, control is performed to keep the output level of the video amplifier constant by changing the amplification degree of the video amplifier from 0.9 to 0.95, for example. On the other hand, the xenon tube, which is a conventional light source, has the highest luminous efficiency at around 40 ° C., and it takes a few minutes to reach the target light amount at the start of light emission from a low temperature (the light amount is a positive temperature characteristic). That is, a waiting time until the document reading starts is required. As described above, if the change in the initial light quantity of the white LED is corrected by the amplification factor of the video amplifier immediately after the start of lighting, the document is read immediately after the lighting without warming up during standby like a xenon tube. Therefore, standby power can be greatly reduced.

  Note that the “lighting rate” of the white LED 74 referred to here indicates the ratio of the time during which the current If is actually passed through the white LED 74 in the constant section TL smaller than the section I, as shown in FIG. is there. As a result, the amount of light emitted from the white LED can be controlled.

  In the section I of FIG. 12 in the first embodiment, the lighting rate of the white LED 74 is 100%. However, depending on the case, the lighting rate may be slightly reduced from the beginning.

  The increase in the junction temperature Tj of the white LED 74 shown in FIGS. 9 to 10 does not continue indefinitely, and the increase naturally stops in about one minute to several minutes from the start of lighting due to thermal resistance or the like. That is, it has an upper limit value of the natural temperature rise.

  In an experiment using one sample of the white LED 74 of the first embodiment, the ambient temperature of the white LED 74 that is continuously lit (that is, having a lighting rate of 100%) is normal temperature, that is, the junction temperature Tj at 25 ° C. The increase stops at about 140 ° C., as indicated by the dashed line curve in FIG. Incidentally, the absolute maximum rating of the junction temperature Tj of the white LED 74 in the first embodiment is 150 ° C., and the upper limit of the natural rise of the junction temperature Tj is within the allowable range if limited to the above measurement conditions. Become.

  However, there are of course individual differences in the white LED 74, and there may be a higher upper limit temperature for the natural rise of the junction temperature Tj. Further, the absolute maximum rating of 150 ° C. of the junction temperature Tj is not necessarily guaranteed completely by the manufacturer, and may be destroyed at a temperature lower than this.

  Furthermore, the experimental data of the alternate long and short dash line curve in FIG. 12B shows the case where the ambient atmosphere temperature of the white LED 74 is room temperature. Actually, even if the external temperature of the image reading apparatus 1 is normal temperature, the internal temperature of the image reading apparatus 1 during the reading operation reaches approximately 50 ° C. to 60 ° C. That is, the ambient ambient temperature of the illumination light source unit 57 including the white LED 74 can actually be 50 ° C. to 60 ° C. This means that the probability that the upper limit of the natural rise of the junction temperature Tj exceeds the absolute maximum rating of 150 ° C. or reaches the actual breakdown temperature is further increased.

  Therefore, if the increase in the junction temperature Tj of the white LED 74 is lower than the upper limit of the natural rise at the maximum lighting rate, preferably lower than the upper limit of the natural rise at the maximum lighting rate at room temperature (25 ° C. to 27 ° C.). The possibility of destruction of the white LED 74 can be further reduced.

  Furthermore, it has been experimentally found that not only the light emission amount of the white LED 74 decreases as the junction temperature Tj increases (as shown in FIG. 13 above), but also changes the wavelength characteristics. . This is shown in FIG. 15 and FIG.

  FIGS. 15 and 16 are diagrams showing changes in the wavelength profile of the LEDs constituting the image reading apparatus in one embodiment of the present invention. FIG. 15A shows the junction temperature Tj of the white LED 74 from 25 ° C. to 110 ° C. The figure which shows the change of the wavelength profile when it raises, FIG.15 (b) is the figure which expanded the change of the 1st peak wavelength vicinity in Fig.15 (a). FIG. 16 is an enlarged view of the change in the vicinity of the second peak wavelength in FIG.

  Here, FIG. 15 (b) particularly pays attention. FIG. 15B shows that the junction temperature Tj increases from 25 ° C. to 110 ° C., and the first peak wavelength is shifted by about 5 nm. So-called “temperature drift” occurs. This means that if the image reading apparatus equipped with the white LED 74 continues to read the same document 11 for a long time, the color information of the document 11 read at the start of reading and the color information of the document 11 read last. It shows that a so-called “color shift” occurs in the meantime.

  Therefore, the amount of color misregistration actually generated with the increase in the junction temperature Tj of the white LED 74 in Example 1 was measured and confirmed by the method described below.

  The confirmation method is demonstrated using FIG. 16, FIG. FIG. 17 is a system configuration diagram used to obtain experimental data of the image reading apparatus in one embodiment of the present invention.

  First, a standard measurement document 11b shown in FIG. 17A is prepared (the actual product is a color gradation chart). The matrix coordinates 1A,..., 1L, 2A,..., 22L on the standard document 11b are measured in the measurement environment shown in FIG. That is, the read data by the image reading apparatus 1 in one embodiment of the present invention and the read data by the standard colorimeter 90 are compared.

  The colorimeter 90 is, for example, a standard light source mainly called D65 (light source for measuring object color illuminated by daylight including ultraviolet region. CIE and ISO reference light, color temperature is 6504k, not shown). And a spectrophotometer (not shown) typified by Spectrolino manufactured by GRETAG. The light emitted from the standard light source is irradiated onto the standard original 11b, and the spectrophotometer is used to spectroscopically reflect the reflected light of each color cell on the matrix coordinates 1A,..., 1L, 2A,. Measure reflectivity. From the measured spectral reflectance, tristimulus values under a standard light source are calculated, and further color values (Lab, etc.) are calculated.

  The color meter 90 may have a device block that calculates tristimulus values from these measured spectral reflectances and further obtains color values. Further, even if the color coordinates on the matrix coordinates 1A,..., 1L, 2A,..., 22L of the document 11b are designated in advance, the spectral reflectance can be continuously and automatically measured. good.

  In any case, the chromaticity of each color cell on the matrix coordinates 1A, ..., 1L, 2A, ..., 22L of the standard document 11b is measured and calculated by the color meter 90 as described above. .

  In Example 1, it is assumed that the results are, for example, Lab (1Af),..., Lab (1Lf), Lab (2Af),.

  Next, the same standard document whose chromaticity is measured and calculated by the colorimeter 90 is read by the image reading apparatus 1 of the first embodiment. At this time, the junction temperature Tj of the white LED 74 mounted on the illumination light source unit 57 in the image reading apparatus 1 is monitored by a method such as monitoring Vf as described above.

  The image reading apparatus 1 is connected to the PC 10 via the cable 8a. Since the RGB image data of the standard document 11b is sent from the image reading apparatus 1 to the PC 10, it is on the matrix coordinates 1A,..., 1L, 2A,. The tristimulus values of each color cell are calculated, and further the color values are obtained. In the first embodiment, the chromaticity of each color cell at the junction temperature Tj of the white LED 74 is, for example, Lab (1Af),..., Lab (1Lf), Lab (2Af),. ).

  By the method described above, the matrix coordinates 1A,..., 1L, 2A,... Of the standard document 11b measured and calculated using the reading device 1 and the standard colorimeter 90 in the first embodiment of the present invention. The color difference data shown in FIG. 18A was obtained using the chromaticity of each color cell on 22L.

  FIG. 18 is a diagram showing experimental data showing the relationship between the junction temperature of the LED of the image reading apparatus and the chromaticity difference of the original in one embodiment of the present invention.

18 (a) and 18 (b), Av. ΔE is the matrix coordinates 1A,..., 1L, 2A,..., 22L of the standard document 11b by the image reading apparatus 1 of the first embodiment (see FIG. 17B) at an arbitrary junction temperature Tj. Each difference between the chromaticity when each color cell on the top is read and the chromaticity when each color cell corresponding to the standard document 11b is read with the standard colorimeter 90 (see FIG. 17B) is averaged. It is the value. That is, if there are n color cells on the matrix coordinates 1A,..., 1L, 2A,.
Av. ΔE = [{Lab (1ATj) −Lab (1Af)} +... + {Lab (1LTj) −Lab (1Lf)} + {Lab (2ATj) −Lab (2Af)} +... + Lab (22ATj ) -Lab (22Af)}] / n (Formula 1)
It is indicated.

  In Example 1, Av. ΔE will be referred to as “average color difference”.

  18A shows an “average color difference” when the junction temperatures Tj of the LEDs 74 mounted on the illumination light source unit 57 of the image reading apparatus 1 (see FIG. 17B) are 26 ° C., 73 ° C., and 110 ° C., respectively. Is shown. Further, “ΔE110−ΔE26” in FIG. 18A indicates the average color difference Av. When the junction temperature Tj is 26 ° C. and 110 ° C. The difference of ΔE is shown. This difference directly represents the change in chromaticity of the standard document 11b (see FIG. 17B) due to the increase in the junction temperature Tj.

  If ΔE26 is at the start of reading and ΔE110 is at the end of reading, “ΔE110−ΔE26” is the recognized chromaticity and reference chromaticity information at the start of reading. And the average value of the color difference from the average chromaticity and the difference between the recognized chromaticity at the end of reading and the average value of the color difference of the reference chromaticity information.

  In the measurement and calculation results shown in FIG. 18A, “ΔE110−ΔE26 = 1.6”. That is, when the junction temperature Tj of the LED 74 mounted on the light source 57 of the image reading apparatus 1 (see FIG. 17B) is 26 ° C. and 110 ° C., it is linked to the temperature drift of the main wavelength shown in FIG. This also shows that the color of the image changes.

  As an index, an operator who specializes in color can identify a color difference of 0.4 or more, and a general person can discriminate a color difference of 2.5 or more. The measurement and calculation result “ΔE110−ΔE26 = 1.6” shown in FIG. 18A can be discriminated by an operator specialized in color according to the above identification criteria, but can be distinguished by a general person. It will be a level that is not connected.

  However, the junction temperature Tj and the average color difference Av. There is a proportional relationship with ΔE as shown in FIG. If the junction temperature Tj continues to rise as it is, the chromaticity deviation from 26 ° C. will be 2.5 or more, and the general person may be able to recognize that the color of the image to be observed has changed. is there. Furthermore, as described above, considering the individual differences of the white LEDs 74, the possibility can be further increased.

  This means that if the same document 11 is read in large quantities continuously, the rate of change between the image data of the document 11 read first and the image data of the document 11 read last increases. Indicates that the color of the image has changed. That is, the color reproducibility of an image in a large amount and continuous reading cannot be guaranteed.

  Accordingly, the present invention has the white LED 74 as one component of the illumination source light source unit 57 for the read original, and the same original 11 (the same standard original 11a in the case of the first embodiment) is continuously generated by the illumination of the white LED 74. When reading, the average color difference between the chromaticity of each pixel in the read image data at the start of reading and the chromaticity of the corresponding pixel in the read image data at the end of reading is within the “preset range”. The junction temperature Tj of the white LED 74 is controlled so as to fall within the range. More specifically, the increase in the junction temperature Tj of the white LED 74 is suppressed to be lower than the natural increase upper limit value at the maximum lighting rate (100% in the first embodiment, that is, continuous lighting).

  Alternatively, the white LED 74 is provided as a component of the illumination light source unit 57 for the reading document 11, and the same document 11 (the same standard document 11 a in the first embodiment) is continuously read as the reading document 11 by the illumination of the white LED 74. When reading, a difference between the average chromaticity between the read image data at the start of reading and the reference image data and the average chromaticity between the read image data at the end of reading and the reference image data is set in advance. The junction temperature Tj of the white LED may be controlled so as to be within the range.

  Then, even if the same original 11 is read in large quantities, the color between the image data of the original 11 read first and the image data of the original 11 read last. Can be suppressed to the extent that a person does not notice that the color of the read image has changed. That is, the color reproducibility of an image in a large amount and continuous high-speed reading can be ensured at a high level.

  It should be noted that where the above-mentioned “preset range” is set is arbitrary, but as described above, it is appropriate to set it to 2.5 or less, which cannot be distinguished by at least ordinary people. It is done. Alternatively, in the case of an image reading apparatus for an industry that emphasizes the color of an image, there is a possibility that the value is 0.4 or less.

  In order to realize these, in Example 1 of the present invention, as shown in FIG. 12, the lighting rate of the white LED 74 is varied according to the junction temperature Tj of the white LED 74 at the same time as entering the section II (FIG. 12). (D)), control is performed to vary the gain (gain) of the video amplifier in accordance with the lighting rate (FIG. 12 (e)). That is, “variable lighting rate + video gain variable control according to lighting rate”.

  More specifically, the control in the section II is as follows: “The lighting rate is made variable in accordance with the junction temperature Tj of the white LED 74, and the video amplifiers 85R, 85G, 85B (variable amplification means are changed in accordance with the lighting rate of the white LED 74”. It may be said that this is performed by the “second control means for changing the respective amplification degrees”).

  The lighting rate of the white LED 74 and the amplification factor of the video amplifier are in an inversely proportional relationship. FIG. 19A shows an example in which the lighting rate and the amplification factor of the video amplifier are converted into table data. Based on this table data, in the section II, for example, the same control as that shown in FIGS. 12D and 12E is performed.

  FIG. 19 is a diagram showing characteristics relating to the LED lighting rate of the image reading apparatus according to an embodiment of the present invention. FIG. 19A shows, for example, before the image reading apparatus 1 of FIG. This is table data created using the white reference plate 60 on the illumination light source unit 57, the image sensor 58, and the original glass 59 on which the white LED 74 is mounted.

  From here, the positional relationship among the illumination light source unit on which the white LED is mounted, the image sensor, the original glass, and the white reference plate provided thereon will be further described with reference to FIG. Illumination light WL emitted from the illumination light source unit 57 in FIG. 5 once passes through the original glass 59 and irradiates the original 11a passing through the original conveyance path 12 in FIG. 59, and enters the image sensor 58. As a result, the document 11a can be read.

  The illumination light source unit 57 emits not only the reflected light BL of the illumination light WL from the document 11 but also the light BW that is reflected by the white reference plate 60 provided on the document glass 59 and enters the image sensor 58. There is also. However, since the white reference plate 60 is disposed outside the assumed position 13 of the document 11 on the document conveyance path 12, the illumination light WL and the reflected light BL for reading the document are not blocked.

  In such a configuration, when the reflected light BL from the illumination light source unit 57 by the white reference plate 60 is detected by the image sensor 58 and the detected value is used, it is mounted on the illumination light source unit 57 shown in FIG. Table data indicating the relationship between the lighting rate of the white LED 74 and the amplification factor of the video amplifier 85 can be created.

  FIG. 19B shows an example of measurement data when the table data is created. In the first embodiment, as shown in the row P of FIG. 19B, the lighting rate of the white LED 74 (see FIG. 9) mounted on the illumination light source unit 57 is changed in increments of 100% to 5%. Yes. Then, the output voltages from the image sensors (see FIG. 9) 84R, 84G, 84B of the image sensor 58 at the respective lighting rates are as shown in the row Q of FIG. It differs depending on the elements 84R, 84G, and 84B.

  Accordingly, as shown in row T of FIG. 19B, the amplified output signal voltages AR, AG, AB from the video amplifiers 85R, 85G, 85B of the respective colors are always at a constant voltage value ( In the first embodiment, the gains GR, GG, GB of the video amplifiers 85R, 85G, 85B are set so as to be “5V”. The result is, for example, as shown in row T of FIG. If the row P and the row S in the measurement data example shown in FIG. 19B are extracted, the relationship between the lighting rate of the white LED 74 mounted on the illumination light source unit 57 and the amplification degree GR, GG, GB of the video amplifier 85. The table data shown in FIG.

  Returning to FIG. 12, the control in the section I (hereinafter referred to as “control I”), that is, the control in the section II from “constant LED lighting rate + video amplifier amplification degree control” (hereinafter referred to as “control II”), That is, where to set the switching junction temperature for switching to “variable LED lighting rate + video gain variable control according to the lighting rate” depends on where the increase convergence target value of the junction temperature Tj is set.

  In Example 1, when the ambient atmosphere temperature is normal temperature (25 ° C.), the maximum lighting rate of the white LED 74 is 100%, that is, the natural rise upper limit value of the junction temperature Tj when the white LED 74 is continuously lit is 140 ° C. .

  Therefore, in the first embodiment, as shown in FIG. 12, the target value of the rising convergence of the junction temperature Tj is set to 110 ° C., the switching junction temperature is set to 100 ° C., and the control method is set when the temperature reaches 100 ° C. Is transferred from Control I to Control II.

  The natural rise upper limit value and the rise convergence target value of the junction temperature Tj when the white LED 74 is continuously lit are not limited to the values shown in the first embodiment. Since the natural rising temperature upper limit value when continuously lit is different depending on the white LED 74 to be adopted, the rising convergence target value of the junction temperature Tj and the switching junction temperature are also different.

  However, if at least the increase target value of the junction temperature Tj of the white LED 74 is set lower than the natural increase temperature upper limit value, the change in the color reproducibility of the image due to the temperature drift of the white LED 74 is suppressed to a range that is not perceived by humans. There is no difference in being able to.

  Of course, the increase convergence target temperature may be any temperature as long as it is lower than the natural increase temperature upper limit. The image reading apparatus 1 usually has an operation guarantee temperature. This shows a temperature range outside the image reading apparatus 1 in which the reading operation is guaranteed. Correspondingly, the junction temperature Tj of the white LED 74 (see FIG. 9) before the reading operation is started after the operation of the apparatus is paused for a long time and the internal temperature becomes equal to the external temperature is the image reading apparatus. 1 seems to be at one of the temperatures within the guaranteed operating range.

  When the image reading apparatus 1 starts the reading operation, the temperature inside the apparatus is expected to be higher than the temperature outside the image reading apparatus 1. However, it is considered that the junction temperature Tj of the white LED 74 is at least higher than the upper limit of the operation guarantee temperature of the image reading apparatus 1 at the time before the reading operation is started after the internal temperature becomes equal to the external temperature. You don't have to. If so, the operation of the image reading apparatus 1 itself is not guaranteed.

  When the operation of the image reading apparatus 1 is guaranteed, the operation of the image reading apparatus 1 is paused for a long time, and the junction of the white LED 74 before the reading operation is started after the internal temperature becomes equal to the external temperature. The temperature Tj is always equal to or lower than the upper limit of the operation guarantee temperature of the image reading apparatus 1.

  Therefore, the increase and convergence target value of the junction temperature Tj of the white LED 74 is higher than the upper limit of the guaranteed operating temperature of the image reading apparatus 1 in which the white LED 74 is mounted as a part of the illumination light source unit 57 of the reading document 11 and is white. What is necessary is just to set lower than the natural temperature rising upper limit of junction temperature Tj of LED74.

  The switching junction temperature Tj from the so-called “control I” to “control II” is higher than the upper limit of the guaranteed operating temperature of the image reading apparatus 1 in which the white LED 74 is mounted as a part of the illumination light source unit 57 and is white. What is necessary is just to set lower than the raise convergence target value of the junction temperature Tj of LED74.

  9 again, the image reading apparatus 1 according to the first embodiment of the present invention includes variable lighting means that can change the lighting rate of the white LED 74 and the illumination light source unit 57 that includes the white LED 74. A CCD 84 that receives the reflected light BL from the reading original 11a of the illumination light WL, and video amplifiers 85R, 85G, and 85B (variable amplification means) that amplify the light reception detection signal voltages VR, VG, and VB of the CCD 84; First control means for changing the amplification degree of the video amplifiers 85R, 85G, and 85B in accordance with the amount of incident light of the reflected light BL reflected by the image sensor 84, and the junction temperature Tj of the white LED 74, with the lighting rate of the white LED 74 constant. Accordingly, the lighting rate of the white LED 74 is varied, and the video amplifiers 85R, 85G, 85 are changed according to the lighting rate. And a second control means for changing the degree of amplification of the document, and when reading a plurality of read originals 11a continuously, first, reading is started by the first control means in section I of FIG. After that, it is possible to enter the section II in FIG. 12 and switch to the second control means.

  The switching point from the first control means to the second control means is set as the aforementioned “switching junction temperature”. As a result, the difference from the chromaticity of the corresponding pixel in the read image data at the end of reading can be kept within a preset range, for example, 2.5 or less.

  If the junction temperature Tj of the white LED 74 exceeds the switching junction temperature at the time of starting the continuous reading, the continuous reading is performed using the second control means without going through the first control means. May be started. As a result, an increase in the junction temperature Tj of the white LED 74 can be suppressed, and the destruction thereof can be prevented.

  As described above, when the image reading apparatus is configured as in the present invention, the white LED 74 has a temperature drift when the white LED is used to perform high-speed reading of the document 11 exceeding several dozen to 100 sheets per minute. The color change of the image can be suppressed to a range that is not perceived by humans, and the color reproducibility of the image in a large amount and continuous high-speed reading can be ensured at a high level.

  In addition, the white LED 74 naturally has individual differences due to mass production. As a result, the natural LED temperature upper limit of the junction temperature Tj may exceed the rating and the white LED 74 may be destroyed, or the white LED 74 may be destroyed before the rating is exceeded. If the image reading apparatus 1 is configured as described above, the white LED 74 can be prevented from being destroyed.

  Furthermore, in a conventional image reading apparatus that employs a xenon tube that takes about 30 seconds to 1 minute to stabilize the light amount as a light source unit for reading illumination, a mechanism for heating the xenon tube during standby is required. If a white LED is used in a light source unit for reading illumination as in the present invention, a sufficient amount of light can be obtained almost simultaneously with lighting. Therefore, such a warming mechanism becomes unnecessary, and the configuration of the image reading apparatus can be simplified. In addition, since no power is required to warm the illumination light source unit during standby, standby power of the image reading apparatus can be suppressed.

  The image reading apparatus according to the present invention senses a change in the color of an image due to a temperature drift of the white LED when a white LED is used for high-speed reading of several tens to 100 documents per minute. Since the color reproducibility of images in a large amount and continuous high-speed reading can be ensured at a high level, the image reading device can be used for business purposes, for example, at a high speed exceeding 40 ppm to 100 ppm. Etc. are possible.

DESCRIPTION OF SYMBOLS 1 Image reader 2 Hopper table 2a Document guide 3 Paper feed port 4 Front discharge port 5 Paper discharge stocker unit 6 Input unit 7 Rear paper discharge port 8 Interface (I / F)
9 Connector 10 Door 11 Document 11a, 11b Document 12 Document transport path 13 Original document position 21 Pickup roller 22 Paper feed roller 23 Retard roller 24 Transport roller 25 Driven roller 26, 28, 30, 32, 34, 36 Paper discharge roller 27 , 29, 31, 33, 35, 37 Driven roller 38 Transport path switching unit 40 Roller receiving cover 51 Control unit 52 Motor 56 Paper discharge roller group 57 Light source unit for illumination 58 Image sensor 59 Original glass 60 White reference plate 63 Image processing circuit 64, 67 Switch 65, 66 Buffer 68 Compression circuit 70 Guide rib 71 Light guide 72 Light refraction / reflection surface 73 LED circuit board 74 White LED
74A Anode electrode 74C Cathode electrode 74T Radiation pad 75 Connection portion 76 Light shielding member 77 Reflector 77a Reflective surface 77b Base member 77c Reflector fixing member 78 Other end portion 79 Frame 80 Light reflecting layer 82 LED drive circuit 83 Selfoc lens 84 CCD
84R, 84G, 84B Image sensor 85, 85R, 85G, 85B Video amplifier 86 A / D converter 90 Colorimeter B1, B2 Bus BL, BL1-BL3 Reflected light CL1, CL2 Clutch PD Light emitting part PS Light receiving part S Hopper height Sensor SA Document presence sensor SB Paper feed sensor SC Reading position sensor SD, SE Paper discharge sensor SI-RGB Control signal Tj Junction temperature VCLK Clock signal Vf Forward bias WL Illumination light WLED drive signal VR, VG, VB Light reception detection signal voltage AR , AG, AB Amplified output signal voltage

Claims (7)

It has a white LED as a component of a light source unit for reading a document,
When continuously reading the same original as the reading original by the illumination of the white LED,
The junction of the white LED so that the average color difference between the chromaticity of each pixel in the read image data at the start of reading and the chromaticity of the corresponding pixel in the read image data at the end of reading falls within a preset range. An image reading device for controlling temperature. The image reading apparatus according to claim 1, wherein an increase in the junction temperature of the white LED is suppressed to be lower than a natural increase upper limit value at a maximum lighting rate. The increase convergence target value of the junction temperature of the white LED is set to be higher than the upper limit of the operation guarantee temperature of the image reading device and lower than the upper limit of the natural increase temperature of the junction temperature of the white LED. The image reading apparatus described. Variable lighting means capable of varying the lighting rate of the white LED;
An imaging element that receives reflected light from the reading original of illumination light from the illumination light source unit;
Variable amplification means for amplifying the output of the image sensor,
First control means for making the lighting rate of the white LED constant and changing the amplification degree of the variable amplification means according to the amount of incident light of the reflected light by the imaging device;
A second control unit that varies the lighting rate according to the junction temperature of the white LED and changes the amplification degree of the variable amplifying unit according to the lighting rate;
2. The image reading apparatus according to claim 1, wherein when the plurality of read originals are continuously read, the first control unit can start reading and then switch to the second control unit. 3. The increase target value of the junction temperature of the white LED is
It is set higher than the upper limit of the guaranteed operating temperature of the image reading apparatus and lower than the upper limit of the natural rise temperature of the junction temperature of the white LED,
The switching junction temperature of the white LED for switching from the first control unit to the second control unit is higher than the upper limit of the operation guarantee temperature of the image reading device, and the junction temperature of the white LED is increased. The image reading apparatus according to claim 4, wherein the image reading apparatus is set lower than a convergence target value. Variable lighting means capable of varying the lighting rate of the white LED;
An imaging element that receives reflected light from the reading original of illumination light from the illumination light source unit;
Variable amplification means for amplifying the output of the image sensor,
First control means for making the lighting rate of the white LED constant and changing the amplification degree of the variable amplification means according to the amount of incident light of the reflected light by the imaging device;
A second control unit that varies the lighting rate according to the junction temperature of the white LED and changes the amplification degree of the variable amplifying unit according to the lighting rate;
The white LED junction temperature rise convergence target value is set higher than the upper limit of the operation guarantee temperature of the image reading device and lower than the natural rise temperature upper limit value of the white LED junction temperature,
The switching junction temperature of the white LED for switching from the first control means to the second control means is higher than the upper limit of the operation guarantee temperature of the image reading device,
And it is set lower than the increase convergence target value of the junction temperature of the white LED, at the time of starting to read a plurality of the read originals continuously,
The continuous reading is started using the second control unit from the beginning without going through the first control unit when the junction temperature of the white LED exceeds the switching junction temperature. Image reading apparatus. It has a white LED as a component of a light source unit for reading a document,
When continuously reading the same original as the reading original by the illumination of the white LED,
The difference between the average chromaticity between the read image data at the start of reading and the reference image data and the average chromaticity between the read image data at the end of reading and the reference image data is within a preset range. An image reading device for controlling the junction temperature of the white LED.