JP5039734B2 - Document reading apparatus and image recording apparatus having the same - Google Patents

Description

  The present invention relates to a document reading apparatus of an image recording apparatus, and more particularly to an optical system of the document reading apparatus.

  In a conventional document reading apparatus, a document is irradiated with light and the reflected light is guided to a solid-state imaging device such as a CCD to electrically read a document image. Further, in a conventional document reading apparatus, an automatic document feeder (hereinafter referred to as ADF) is used when reading a plurality of documents continuously.

  ADF is a device that automatically takes out a plurality of documents placed on a paper feed tray one by one, transports them to a document reading position called a slit glass section using a plurality of transport rollers, and finally ejects them to a paper discharge tray. It is. The ADF repeats the above-described single sheet take-out, transport, and discharge until there are no more documents on the paper feed tray.

  On the other hand, the conveyed document moves on the slit glass portion. An optical system comprising a light source that irradiates light on a document, a plurality of folding mirrors that guide scattered light reflected from the document, a lens that collects scattered light, and a solid-state imaging device that electrically reads the scattered light have. When the ADF is used, the document reading device reads an image with the optical system in a state where the document is conveyed without being stopped.

  Incidentally, in order to improve the reading productivity of the document reading apparatus, it is necessary to increase the reading speed. However, when the reading speed is increased, the amount of light received per unit time of the solid-state imaging device is reduced, leading to deterioration of the image quality of the read image. As a method for solving this, there is a method of increasing the document irradiation light so that the amount of received light per unit time of the solid-state imaging device does not decrease, that is, a method of increasing the irradiation light amount.

  However, when the amount of irradiation light is increased, the temperature inside the aircraft is increased. In particular, during reading of a large amount of originals by ADF, the light source unit continues to stop directly below the slit glass (hereinafter referred to as “static exposure”), so that there is a disadvantage that the slit glass and its vicinity become high temperature.

In order to improve the problem of temperature rise due to such a light source, a proposal has been made to detect the temperature in the vicinity of the light source when reading a document and stop sending the document when the temperature exceeds a preset temperature, and then start again after cooling. ing. (See Patent Document 1)
In order to improve the temperature rise due to the light source, a cold mirror is used for the reflecting mirror provided on the back of the light source to reduce the radiation of infrared rays toward the slit glass, and the light source unit reciprocates during exposure scanning as a cooling means. Proposals have been made to prevent temperature rise by providing a small cooling fan that operates in conjunction with exercise. (See Patent Document 2)

JP 08-262590 A Japanese Patent Laid-Open No. 2001-7998

  However, the proposal of Patent Document 1 has a problem in that reading productivity is inevitably lowered because sending of the document is stopped during cooling. Further, the proposal of Patent Document 2 has a problem that the cooling fan does not operate unless the light source unit scans, and therefore cannot be used when ADF is used, that is, when the light source unit is subjected to static exposure.

  The present invention provides a document reading apparatus equipped with an optical system that has improved such conventional problems.

  A document reading apparatus according to an embodiment of the present invention includes an automatic document feeder that conveys a document, a light source that irradiates the document, and a light source side surface that obtains reflected light from the document by light emitted from the light source Slit glass provided with an infrared reflective / visible light transmissive coating, one or more folding mirrors that guide the reflected light through the slit glass, and a lens that forms an image of the reflected light guided to these mirrors The solid-state imaging device that converts the reflected light imaged by the lens into an electrical signal, the infrared transmission / visible light reflection mirror applied to the back surface of the light source, and the infrared transmission / visible light reflection mirror that is transmitted Infrared reflective / visible light transmitting mirror for reflecting infrared light, and slit glass coated with the infrared reflective / visible light transmissive mirror and the infrared reflective / visible light transmissive coating. An infrared absorbing member for absorbing the infrared rays reflected by the, characterized in that it has a cooler for cooling the infrared absorption member.

  With such a configuration, it is possible to realize an increase in the amount of light of the xenon lamp light source corresponding to high-speed reading while efficiently avoiding the temperature rise in the body caused by the light source and the temperature rise of the slit glass.

1 is a schematic diagram showing the overall configuration of a document reading apparatus that is an embodiment of the present invention. FIG. 2 is a schematic diagram showing a specific configuration of the optical system of the first embodiment in FIG. 1. FIG. 3 is a schematic diagram showing a heat pump as a cooler in FIG. 2. FIG. 3 is a schematic diagram showing a heat pipe as a cooler in FIG. 2. FIG. 5 is a schematic diagram of a partial cross section of the cooler in FIG. FIG. 3 is a schematic diagram showing a water cooling device as a cooler in FIG. 2. FIG. 3 is a schematic diagram showing a specific configuration of the optical system of the second embodiment in FIG. 1.

  Hereinafter, embodiments of the present invention will be described in detail.

  First, a schematic configuration of the ADF used in this embodiment will be described with reference to FIG.

  The ADF includes a paper feed tray 1, a pickup roller 2 that feeds a document P from the paper feed tray 1, a plurality of transport rollers 3 that transport the fed document P, and a registration roller 4 that controls the posture of the document P. After the original P passes through the slit glass 11, the discharge roller 5 and the discharge tray 6 are conveyed to the discharge tray 6.

  In the ADF having such a configuration, the document P is stacked on the sheet feeding tray 1. When a start button on a control panel (not shown) is pressed, the pickup roller 2 is lowered, and only the uppermost part of the document P is fed to the transport roller 3a. The orientation of the first document is controlled by the registration roller 4 and then conveyed onto the slit glass 11 at the document reading position by the transport roller 3b and the transport roller 3c. On the slit glass 11, the original P is read and the image is read without being stopped. The document is directly discharged to the discharge tray 6 by the discharge roller 5 through the transfer roller 3d and the transfer roller 3e. The above operation is repeated until there are no more originals P stacked on the paper feed tray 1. Since the other parts are structures relating to the double-sided reading of the document, description thereof is omitted.

  On the other hand, the light from the xenon lamp light source 12 irradiates the original P moving on the slit glass 11, and the reflected light L (scattered light on the original) from the original is reflected by the lens 14 by the plurality of folding mirrors 13. An image is formed and converted into an electric signal by the solid-state imaging device 15.

  Next, the optical system in the above embodiment will be described more specifically.

  As shown in FIG. 2, the optical system includes a xenon lamp light source 12, a slit glass 11 for obtaining reflected light L from the original by the irradiation light of the xenon lamp light source 12, and the original from the original through the slit glass 11. First to third folding mirrors 13a, 13b, 13c for guiding the reflected light L of the lens, a lens 14 for imaging the reflected light L guided to the third folding mirror 13c, and the reflected light imaged by the lens 14 A solid-state imaging device 15 that converts L into an electrical signal, an infrared absorbing member 21, and a cooler 22 that cools the infrared absorbing member 21 are provided.

  The slit glass 11 described above is held by the slit glass holding unit 23. An infrared reflective / visible light transmissive coating 24 is applied to the surface of the slit glass 11 on the xenon lamp light source 12 side. A cold mirror 25 is provided on the back surface of the xenon lamp light source 12. Further, on the back side of the xenon lamp light source 12, a dichroic mirror 27 is disposed so as to reflect the infrared ray 26 emitted from the xenon lamp light source 12 and guide it to the infrared absorbing member 21. The cooler 22 for forcibly cooling the infrared absorbing member 21 is disposed so as to be in contact with the back surface of the infrared absorbing member 21.

  As the slit glass 11 provided with the above-described infrared reflective / visible light transmissive coating 24, for example, a solar heat reflective glass developed by the National Institute of Advanced Industrial Science and Technology can be used. This is a glass that transmits visible light and reflects heat rays (infrared rays), developed by Kazuhiko Tonooka and Senior Researcher Naoto Kikuchi of the Functional Oxide Group of the Institute for Electronics Research.

Since this glass can effectively reflect near infrared rays with strong thermal action while securing daylighting by solar radiation, it is expected to contribute to energy saving by using it as a window glass for buildings, houses, vehicles and the like. A laminated structure with titanium oxide and silicon oxide as the main raw materials was formed on a glass substrate using a sputtering method and the like, and the heat ray reflection with high wavelength selectivity was realized by controlling the thickness of each layer to the nanometer order. The developed solar heat reflecting glass has a visible light transmittance of 82% (actual measurement value), and the reflectance with respect to heat ray energy during solar radiation is estimated to be about 50%. (National Institute of Advanced Industrial Science and Technology; press release)
The aforementioned cold mirror is a mirror with an optical thin film that transmits infrared rays and reflects visible light. This is a wavelength selective mirror for infrared region in which dielectric materials with different refractive indexes are coated on white plate glass alternately. It reflects 90% or more of visible light (400-700nm) and transmits 80% or more of near infrared light. To do. The reflected light does not contain heat rays. Further, because of the dielectric multilayer coating, there is almost no light absorption by the film. By processing this cold mirror on the back side of the xenon lamp light source, infrared rays on the back side of the xenon lamp light source are transmitted. On the other hand, visible light is reflected, and only the visible light can be irradiated on the front surface. Since the light reflected in this way does not contain infrared rays, it is possible to prevent the slit glass from becoming hot. Further, the visible light reflected by the cold mirror is irradiated on the front surface, and only the light amount irradiated on the front surface is increased, and the light amount corresponding to high-speed reading can be secured.

  The dichroic mirror described above is a kind of mirror made using a special optical material, and reflects light of a specific wavelength and transmits light of other wavelengths. Among them, there are those targeting the near ultraviolet to near infrared region. In this mirror, a thin film such as a dielectric multilayer film is formed on a mirror surface to reflect a specific wavelength and transmit the other wavelengths to obtain the above-described characteristics. Unlike the optical filter, this dichroic mirror does not use absorption, and has a feature of excellent durability. By utilizing a mirror in which the specific wavelength to be reflected is set in the infrared region, the infrared light transmitted by the cold mirror can be reflected to a specific location.

  The infrared absorbing member 21 described above is for absorbing infrared rays, and a black-plated sheet metal, heat ray absorbing glass, or the like can be used. The heat ray absorbing glass is a glass colored by adding a small amount of a metal component such as iron, nickel, and cobalt into the plate glass composition, and can efficiently absorb infrared rays by the metal component. This infrared absorbing member 21 can absorb the infrared light reflected by the dichroic mirror 27 and the infrared reflective / visible light transmissive coating 24.

  The above-described cooler 22 is for forcibly cooling the infrared absorbing member 21 that has generated heat due to absorption of infrared rays. For example, a heat pump, a heat pipe, a water cooling device, a cooling gel, or the like can be used.

  FIG. 3 shows a specific example of the heat pump. A heat pump pipe 221 is placed in contact with the back surface of the infrared absorbing member 21. This pipe is a passage for the refrigerant, and the compressed refrigerant is sent through the lower pipe (arrow a). Then, heat is absorbed by contact with the infrared absorbing member 21, and the compressed refrigerant becomes a vapor state and moves to a refrigerant compression device (not shown) through the upper pipe (arrow b). In this compressor, the vaporized refrigerant is compressed again into a liquid state, and then supplied to the infrared absorbing member 21 through the lower pipe. In this way, the heat of the infrared absorbing member 21 can be forcibly cooled.

  As described above, a heat pump is a cooler that uses heat absorption due to evaporation of a liquid (referred to as a refrigerant) and heat dissipation due to solidification of the evaporated refrigerant. This is a system that cools and heats the air by efficiently drawing and moving the heat in the atmosphere using a compressor. In this embodiment, the heat of the infrared absorbing member 21 is reduced by causing a cooling phenomenon in the pipe that is in contact with the infrared absorbing member 21 by circulating the refrigerant and a heating phenomenon in the pipe that is not in contact with the infrared absorbing member 21. Forced cooling.

  Fig. 4 shows a specific example of a heat pipe. The heat pipe 222 is placed in contact with the back surface of the infrared absorbing member 21. This pipe has a D-shaped cross section only at the portion in contact with the infrared absorbing member 21, and the other is a circular shape.

  A schematic configuration of the heat pipe will be described in detail with reference to FIG. A heat pipe conducts heat at high speed. Inside the tube 51, a wick 52 (wire mesh or cloth), which is a porous material, is attached. The pipe 51 contains hydraulic fluid such as water. When the evaporation section 53 is heated, the hydraulic fluid evaporates (arrow 54), takes heat (arrow 55), and flows to the condensation section 56 (thick arrow). In the condenser 56, the vapor is condensed by cooling (arrow 57) and releases heat (arrow 58). In this way, heat is transferred from the evaporation section 53 to the condensation section 56. The water condensed in the condensing unit 56 returns from the condensing unit 56 to the evaporating unit 53 due to the capillary action of the wick 52. Note that the inside of the pipe is vacuum-sealed so that the working fluid is easily evaporated. Further, the cooling phenomenon can be efficiently caused by cooling the condensing unit 56 with a fan (not shown). In this embodiment, the heat of the infrared absorbing member 21 was forcibly cooled by causing a cooling phenomenon in the pipe in contact with the infrared absorbing member 21 and a heating phenomenon in the pipe not in contact with the infrared absorbing member 21.

  FIG. 6 shows a specific example of the water cooling device. A metal tube 223 of a water cooling device is provided on the back surface of the infrared absorbing member 21. The metal tube 223 has a D shape only at the portion in contact with the infrared absorbing member 21, and the others are circular. A vinyl hose 224 is connected to the metal tube 223. Cooling water circulating through the cooling device enters a radiator (not shown) at the end of the vinyl hose 224 and is cooled here. With this water cooling device, the heat of the infrared absorbing member 21 can be forcibly cooled.

  The mechanism of the water cooling system is the same as that of the radiator mounted on the car. The mechanism is a structure in which the metal tube containing water absorbs the heat of the infrared absorbing member, and the water is cooled and circulated by a radiator installed outside the case. In order to enhance the cooling effect, the radiator is cooled by passing a large amount of cooling water through a narrow passage. In the present embodiment, the heat of the infrared absorbing member 21 was forcibly cooled by cooling the metal tube 223 brought into contact with the infrared absorbing member 21 and cooling the cooling water with a radiator.

  Next, the operation of the optical system in the document reading apparatus as described above will be described with reference to FIG.

  First, as described above, the original P is moved onto the slit glass 11 by ADF. The irradiation light on the front surface of the xenon lamp light source 12 irradiates a document moving on the slit glass 11. At this time, the infrared rays 26 (broken lines) in the irradiation light irradiated to the slit glass 11 from the xenon lamp light source 12 are reflected by the infrared reflective / visible light transmissive coating 24 coated on the slit glass 11. The reflected infrared ray 26 is absorbed by the infrared absorbing member 21. The infrared absorbing member 21 that generates heat by the absorbed infrared ray 26 is forcibly cooled by the cooler 22.

  Since the cold mirror 25 is processed on the back side of the xenon lamp light source 12 on the back side of the xenon lamp light source 12, only the infrared ray 26 is transmitted and visible light is reflected. Since the reflected visible light is applied to the slit glass 11, the amount of light with respect to the slit glass 11 increases. Here, the infrared rays 26 transmitted through the cold mirror 25 are reflected by the dichroic mirror 27 and absorbed by the infrared absorbing member 21. The absorbed infrared rays 26 are forcibly cooled by the cooling means 22 as described above.

  On the other hand, the reflected light L from the original is imaged by the lens 14 via the folding mirrors 13a, 13b and 13c, and converted into an electric signal by the solid-state imaging device 15.

  In this way, the infrared rays radiated from the xenon lamp light source 12 are collected on the infrared absorbing member 21 by the infrared reflection / visible light transmission coating 24 and the dichroic mirror 27, and cooled by the cooling means 22, resulting from the infrared rays 26 from the light source 12. The temperature rise of the machine body and the slit glass can be efficiently avoided. Furthermore, since the visible light on the back surface of the light source 12 is reflected by the cold mirror 25 and irradiated on the front surface, the light quantity of the xenon lamp light source corresponding to high-speed reading can be increased.

  FIG. 7 shows a schematic diagram of the optical system of the second embodiment of the present invention. This optical system includes a xenon lamp light source 12, a slit glass 11 held by a slit glass holding unit 23 for obtaining reflected light L from an original by irradiation light of the xenon lamp light source 12, and through the slit glass 11 First to third folding mirrors 13a, 13b, 13c for guiding the reflected light L of the document, a lens 14 for imaging the reflected light L from the document guided to the third folding mirror 13c, and imaging by the lens 14 A solid-state image sensor 15 is provided for converting the reflected light L from the original document into an electrical signal.

  The xenon lamp light source 12 is in a state of being thermally sealed with a dichroic mirror 27 on the front, a light source sealing wall 31 on the side, and a cold mirror 25 on the back. The infrared absorbing member 21 is disposed so as to contact the back surface of the cold mirror 25. The cooler 22 for forcibly cooling the infrared absorbing member 21 is disposed so as to be in contact with the back surface of the infrared absorbing member 21.

  The light source sealing wall 31 is made of ceramic that is difficult to conduct heat. Ceramics is a so-called “Seto” structure and has a structure in which heat is not easily transmitted by having a large number of bubbles. In addition, since it is easy to break in the structure of only ceramics, it is conceivable to use a structural material in which a sheet metal is coated with heat-resistant ceramics. Since the dichroic mirror, cold mirror, and cooler have been described above, they are omitted.

  The operation of the optical system in the document reading apparatus as described above will be described with reference to FIG.

  First, as described above, the original P is moved onto the slit glass 11 by ADF. The irradiation light on the front surface of the xenon lamp light source 12 irradiates a document moving on the slit glass 11. At this time, of the irradiation light emitted from the xenon lamp light source 12, the infrared light is reflected by the front dichroic mirror 27, and only visible light is transmitted and reaches the slit glass 11. The infrared light reflected here passes through the cold mirror 25 on the back surface and is absorbed by the infrared absorbing member 21. The infrared absorbing member 21 that has generated heat due to the absorbed infrared rays is forcibly cooled by the cooler 22.

  On the back side of the xenon lamp light source 12, the irradiation light emitted from the xenon lamp light source 12 transmits only infrared rays through the cold mirror 25 and reflects visible light. The reflected visible light passes through the dichroic mirror disposed on the front surface and is irradiated onto the slit glass 11, so that the amount of light with respect to the slit glass 11 increases. Here, the infrared rays transmitted through the cold mirror 25 are absorbed by the infrared absorbing member 21 in the same manner as described above, and the infrared absorbing member 21 that has generated heat due to the absorbed infrared rays is forcibly cooled by the cooler 22.

  On the other hand, the reflected light L from the original is imaged by the lens 14 by the folding mirrors 13a, 13b, and 13c, and converted into an electric signal by the solid-state imaging device 15.

  By adopting such a configuration, it is possible to efficiently increase the light quantity of the xenon lamp light source corresponding to high-speed reading while efficiently avoiding the temperature rise in the body and the temperature rise of the slit glass caused by the xenon lamp light source 12. I can do it.

DESCRIPTION OF SYMBOLS 11 ... Slit glass 12 ... Xenon lamp 13 ... Folding mirror 14 ... Lens 15 ... Solid-state image sensor 21 ... Infrared absorption member 22 ... Cooler 23 ... Slit glass holding part 24 ... Infrared reflective and visible light transmission coating 25 ... Cold mirror 26 ... Infrared 27… Dichroic mirror 31… Light source sealed wall L… Visible light

Claims (10)

A document transport device for transporting a document;
A light source for illuminating the document;
A slit glass with an infrared reflective / visible light transmissive coating on the light source side surface to obtain light reflected from the original by the light emitted from the light source,
One or more folding mirrors that guide the reflected light through the slit glass;
A lens for imaging the reflected light guided to these mirrors;
A solid-state imaging device that converts the reflected light imaged by the lens into an electrical signal;
An infrared transmissive / visible light reflecting mirror applied to the back surface of the light source;
An infrared reflecting / visible light transmitting mirror that reflects infrared rays transmitted from the infrared transmitting / visible light reflecting mirror;
An infrared ray absorbing member that absorbs infrared rays reflected by the infrared reflection / visible light transmission mirror and the slit glass coated with the infrared reflection / visible light transmission coating;
A document reading apparatus comprising a cooler for cooling the infrared absorbing member.   The document reading device according to claim 1, wherein the slit glass provided with the infrared reflective / visible light transmissive coating is a solar heat reflective glass. The document conveying device includes:
A paper tray,
A pick-up roller that feeds documents from this paper feed tray;
A plurality of transport rollers for transporting the fed document;
A registration roller for controlling the orientation of the document;
A discharge roller for conveying the original to the discharge tray after passing through the slit glass;
The document reading apparatus according to claim 2 , wherein the document reading apparatus is an automatic document feeder configured with a discharge tray. The document reading apparatus according to claim 3 , wherein the infrared reflection / visible light transmission mirror is a dichroic mirror. The document reading apparatus according to claim 4 , wherein the infrared transmission / visible light reflection mirror is a cold mirror. The document reading apparatus according to claim 5 , wherein the infrared absorbing member is heat ray absorbing glass. The document reading device according to claim 6 , wherein the cooler is a heat pump. The document reading device according to claim 6 , wherein the cooler is a heat pipe. The document reading device according to claim 6 , wherein the cooler is a water cooling device. An image recording apparatus comprising the document reading apparatus according to claim 6 .

Images