Image reading device and image forming device

An image reading device, includes an illumination optical system which has a light source unit configured to emit light being illuminating light to an illuminated object; an optical member configured to have a plurality of reflecting plates and collect the light emitted from the light source unit; and a plurality of reflecting members, the light emitted from the light source unit being collected by the optical member, and the collected light being reflected by the plurality of reflecting members to illuminate a reading target area on the illuminated object, and at least one reflecting surface of the optical member or the plurality of reflecting members having a relief structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading device which is used in such as a digital copy machine or an image scanner, and an image forming device including the image reading device.

2. Description of the Related Art

In recent years, the development of the light emitting diode (LED) has been carried out actively, and brightness of LED elements has risen rapidly. Generally, advantages of LED are, for example, long life, high efficiency, high anti-acceleration character and monochrome luminescence, etc., and numerous applications of LED in the field of illumination are expected.

As an application, LED is used as a manuscript illuminating device of an image reading device such as a digital copy machine or an image scanner.

Various methods arc proposed for the application of LED which is employed by the image reading device. For example, JP 2006-67551A, JP 2006-42016A, JP 2005-241681A disclose that a plurality of LEDs are lined up in parallel with a main-scanning direction of a manuscript, and light emitted from the plurality of LEDs is diffused without giving any optical effect in the main-scanning direction, and the light is collected by reflecting surfaces in a sub-scanning direction, thus illuminance on a reading target area on a manuscript surface is heightened. Further, JP 2005-311662A discloses that a plurality of LEDs are lined up in parallel with a main-scanning direction of a manuscript, and light emitted from the plurality of LEDs is diffused without giving any optical effect in the main-scanning direction, and the light is collected by a lens in a sub-scanning direction, thus illuminance on a reading target area on a manuscript surface is heightened.

Here, the desired kind of illuminance or illuminance distribution on the manuscript surface will be explained.

As illustrated inFIG. 1, in an image reading device used in a digital copy machine or an image scanner, information included in a manuscript is input into an imaging device such as CCD through a readout lens.FIG. 2is a top view of a manuscript surface illustrated inFIG. 1viewed from the above. The image reading device is in a state such that only information of a long and thin reading target area illustrated inFIG. 2is capable of being input into the imaging device, when an optical system is in a fixed state. Then, by moving the entire device illustrated inFIG. 1, or moving an illumination optical system in conjunction with reflecting mirrors, the reading target area is moved in a direction of an arrow inFIG. 2. The entire manuscript can be read out by inputting information into the imaging device sequentially while moving the reading target area.

At this time, the amount of light entering the imaging device per unit time is required to be increased to move the reading target area illustrated inFIG. 2at a high speed (to shorten reading time per one sheet of the manuscript), and a high illuminance to the manuscript surface is preferable. From this viewpoint, the methods of restricting light in the sub-scanning direction disclosed in the above-mentioned patent documents are appropriate.

Meanwhile, uniform illuminance distribution is preferable in general.FIG. 3illustrates a conjugate relationship of the manuscript surface and the imaging device, and an example of the illuminance distribution on the manuscript surface is illustrated by a solid line and a dotted line. The solid line in the figure represents an illuminance distribution on the manuscript surface at a predetermined point, and the dotted line represents a changed illuminance distribution by such as an influence of a vibration from outside at a predetermined moment. As illustrated by the solid line or the dotted line inFIG. 3, when there is unevenness in the illuminance distribution on the manuscript surface, illuminance at a position on an imaging surface corresponding to a position on the manuscript surface where the illuminance is high, is high as well, and vice versa. During moving the reading target area in the direction of the arrow illustrated inFIG. 2and reading the entire manuscript, if a relationship of the manuscript and the illumination is always the same, illuminance distribution with such unevenness can be corrected by an image data processing. However, unevenness in density is generated in a scanned image if the relationship of the manuscript and the illumination is changed from a state illustrated by the solid line to a state illustrated by the dotted line instantaneously during this period, and a quality of the image decreases.

Therefore, as illustrated inFIG. 4, in general, it is preferable that the illuminance distribution over the entire reading target area be uniform. Illuminance distribution on the imaging surface would not change even if a positional relationship of the manuscript and the illumination shifts, for example, by receiving a vibration from the outside, if the illuminance distribution is uniform.

In any method disclosed in the above-mentioned documents, to make the illuminance distribution in the main-scanning direction uniform, light from a point light source, namely an LED, is diffused directly without giving any optical action to the light. However, when such a method is adopted, a long distance is necessary from the light source to the manuscript surface when the number of light source is small, and there is a possibility that an illumination optical system from the light source to the manuscript surface gets larger. When increasing the number of light sources to miniaturize the illumination optical system, though the illuminance is improved and the illumination optical system can be further miniaturized, there are disadvantages such as a high cost and high power consumption.

SUMMARY OF THE INVENTION

At least an object of the present invention is to provide an image reading device with good illuminance distribution which includes a compact illumination optical system having few light sources. At least another object of the present invention is to provide an image forming device including the image reading device.

In light of the above, the present invention proposes, for example, an image reading device including an illumination optical system which has: a light source unit configured to emit light being illuminating light to an illuminated object; an optical member configured to have a plurality of reflecting surfaces and collect the light emitted from the light source unit; and a plurality of reflecting members. The light emitted from the light source unit is collected by the optical member, and the collected light is reflected by the plurality of reflecting members to illuminate a reading target area on the illuminated object, and at least one reflecting surface of the optical member or the plurality of reflecting members has a relief structure, which reflects incident light while diffusing the incident light.

In addition, the present invention proposes an image forming device including the image reading device described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a traveling direction of diffusion light emitted from a point light source is distributed irregularly (randomly) by a relief structure provided on a reflecting surface. A constitution of an image reading device according to the present invention will be explained.

FIG. 5Ais a cross-sectional view illustrating a main part of the image reading device according to the first embodiment of the present invention, andFIG. 5Bis a top cross-sectional view illustrating the main part of the image reading device according to the first embodiment of the present invention.

As illustrated inFIGS. 5A and 5B, an image reading device10includes an illumination optical system including: a light source unit8which has one LED1(a point light source) or a plurality of LEDs1arranged in rows as a light emitting device and a light source which emits light as illuminating light to an illuminated object (a manuscript surface in the present invention); a light guide device2which is an optical member having a plurality of reflecting plates2a,2b,2c,2dand having a function of collecting light; and reflecting members3,4. The image reading device10further includes a contact glass6which has a manuscript surface6a; an imaging optical system (not illustrated) which is configured to image light reflected from a reading target area6a1arranged on the manuscript surface6a; and a sensor (not illustrated) which is arranged at an imaging part of the imaging optical system and reads out an image of the manuscript. In addition, the contact glass6includes a first plane and a second plane each of which has an XY plane, and the first plane, which is not facing the illumination optical system, is the manuscript surface6a(an illuminated surface) where the manuscript is disposed. The reading target area6a1arranged on the manuscript surface6ahas a predetermined length and a predetermined width, and the manuscript is disposed on the reading target area6a1. Here, light emitted from the light source unit8is collected by the light guide device2, and the collected light is reflected by the reflecting members3and4respectively, and then the light transmits through the contact glass6and irradiates the manuscript on the manuscript surface6a, for details the reading target area6a1on the manuscript surface6a, which has the predetermined length and the predetermined width.

Moreover, a space under the contact glass6where the illumination optical system is disposed is divided into two divisions: a first region in which the light source unit8exists and a second region in which the light source8does not exist, by a virtual plane7. Here, the virtual plane7represents a plane that separates the manuscript surface6avertically and passes through the reading target area6a1, i.e. a plane through which light reflected from the manuscript (the reading target area6a1) and used for an image formation passes. The light source unit8, the light guide device2, and the reflecting member3are arranged in the first region, and the reflecting member4is arranged in the second region. Since the light emitted from the light source unit8is reflected by the reflecting member3and the reflecting member4respectively, and then enters into the reading target area6a1on the manuscript surface6a, the illumination light is irradiated from both sides of the virtual plane7across the virtual plane7, and a uniform illuminance distribution in a sub-scanning direction can be obtained.

InFIG. 5, a length direction of the reading target area6a1(a main-scanning direction, an up and down direction inFIG. 5B) is set as an X direction; a width direction of the reading target area6a1(the sub-scanning direction, a right and left direction inFIG. 5B) is set as a Y direction, and a direction (an up and down direction inFIG. 5A) through which the light used for the image formation of the reflected light from the reading target area6a1passes is set as a Z direction. In addition, in the following embodiments, relationships between the virtual plane7and the first region and the second region are defined similar to those in the present embodiment. In particular, except for changes such as the type of an optical member, the arrangements and constitutions of the virtual plane7and the first region and the second region are similar to those in the present embodiment.

Moreover, the LED1is the point light source which emits white light. For example, a single-chip type white light-emitting diode which uses a fluorescent material, or a white light-emitting diode which consists of at least two kinds of chips of a light-emitting diode each of which emits a different color of light, and which emits white light by the color mixture, is preferable.

The light guide device2includes a plurality of reflecting plates2a,2b,2c, and2dwhich are integrated. Each of reflecting surfaces of the reflecting plates2a,2b,2c, and2dcan be a flat surface, or curved surface. Moreover, each of the reflecting surfaces can be provided with an aluminum coating or a reflective sheet to improve the reflection efficiency.

The reflecting plates2aand2bare arranged such that they sandwich the light emitted from the light source unit8in the Z direction, and as illustrated inFIG. 5A, the reflecting plates2aand2bare disposed with an angle such that from an entry side to an exit side of the light guide device2, an interval between the reflecting plates2aand2bincreases. Thus, light that diffuses outside in the Z direction from a front direction of the light source unit8(LED1), which is a part of the light emitted from the light source unit8(LED1), can be reflected by the reflecting plates2aand2band be collected in the front direction of the light source unit8. In addition, the reflecting plates2cand2dare arranged such that they sandwich the light emitted from the light source unit8in the X direction and are disposed in parallel. Thus, light that diffuses outside in the X direction from the front direction of the light source unit8(LED1), which is a part of the light emitted from the light source unit8(LED1), can be reflected by the reflecting plates2cand2dand be used to illuminate the manuscript effectively. Thus, the light emitted from the light source unit8is collected by the light guided device2and enters the reflecting members3and4.

For example, the reflecting plates2a,2b,2c, and2dcan be integrated by adhering with an adhesive, or formed and shaped integrally, or be integrated by combining two pairs of moldings.

Each of the reflecting plate3and the reflecting plate4reflects the light collected by the light guide device2and directs the light to the reading target area6a1on the manuscript surface6a. That is to say, in the first region the light from the light guide device2is reflected by the reflecting plate3and is directed to the reading target area6a1on the manuscript surface6a, and in the second region the light from the light guide device2is reflected by the reflecting plate4and is directed to the reading target area6a1on the manuscript surface6a.

Each of the reflecting surfaces of the reflecting members3and4is a flat surface, and to improve the reflection efficiency, each of the reflecting surfaces is aluminum coated or provided with a reflective sheet.

Moreover, a fine relief structure for reflecting while scattering the incident light, is formed on the reflecting surfaces of the reflecting members3and4.FIGS. 6A and 6Billustrate enlarged sectional views of the relief structure formed on the reflecting surfaces of the reflecting members3and4.FIG. 6Ais a sectional view of the reflecting member3(or4) cut in the main-scanning direction (the X direction), andFIG. 6Bis a sectional view of the reflecting member3(or4) cut in the sub-scanning direction (the Y direction). Hereafter, the relief structure of the reflecting member3will be explained, and the reflecting member4is formed with a similar relief structure.

The relief structure of the reflecting member3includes a one-dimensional grating (a grating structure) in which a plurality of rectangular grooves (concave portions) c′ are formed in parallel on a substrate a′. The plurality of grooves (concave portions) c′ are arranged such that a length direction of each of the grooves c′ is perpendicular to the X direction, which is a length direction of the reading target area6a1, therefore, a cross section of the plurality of grooves (the concave portions) c′ in the X direction is a structure of a plurality of rectangular convex portions b′ lined up at a regular interval (a width of one groove (one concave portion) c′), as illustrated inFIG. 6A. On the other hand, a cross-section of the plurality of grooves (the concave portions) c′ in the sub-scanning direction (the Y direction) is a structure of a plane with a height of B of the convex portion b′ formed continuously on the substrate a′, as illustrated inFIG. 6B. It is necessary to suitably select such as a size of an asperity, an incident angle of light, and a reflecting angle of light, to avoid reflecting light of a specific wavelength only, though it is desirable that such a relief structure has a diffraction grating structure. Such a relief structure is formed by a well-known method such as the pattern etching by the photoresist.

FIG. 7illustrates the incidence of light to the reflecting member3(or4) having the relief structure illustrated inFIGS. 6A and 6B, and reflection of the light thereof. Lines with arrows in the figure are light rays (incident light Lin and reflected light Lout).

First of all, the incident light Lin to a top surface of the convex portion b′ is reflected to a direction line-symmetric to a perpendicular line of the cross-section in the Figure (a specular reflection) and advances as the reflected light Lout. On the other hand, light that has entered the concave portion c′ is reflected plural times in the concave portion c′ as illustrated inFIG. 7, and then is emitted in a random direction which has a different angle with the light reflected by the top surface of the convex portion b′. Due to a part of reflected light from the reflecting surfaces advancing in a random direction on the cross-section in the figure, thus it can obtain an uniform illuminance distribution in the length direction of the reading target area6a1(the main-scanning direction), even if the interval of the LEDs1is constant. It is preferable that if the relief structure be a diffraction grating since a diffusion degree by the reflection rises further, here, for example, only the diffusion effect by the reflection which can be expressed by the Snell's law will be explained.

There is no advantage in providing the relief structure if there are too few reflection frequencies in the concave portion c′, therefore it is preferable that there be a large number of reflection frequencies. However, a problem arises in that energy attenuates after the reflection. The illuminance on the reading target area6a1decreases remarkably when it is a structure in which reflection occurs too many times. For example, if each of the reflecting surfaces of the reflecting members3and4is formed with an aluminum thin film, since a degree of reflection of aluminum is almost 90% at each incident angle of light, energy of the light will be reduced to 90% after one time of reflection, to 81% after two times, 73% after three times, and finally 48%, lower than 50%, after seven times of reflection.

Consequently, it is preferable to set a ratio (B/A) of the height B of the convex portion b′ to the width A of the concave portion c′ of the relief structure to 0.692 or more than 0.692. As a result, the reflection frequency of light becomes less than seven times, and a remarkable decrease of illuminance and a reduction of the contribution to illumination of light that enters into the reading target area6a1from a random direction can be avoided. Here, the above-mentioned ratio is set on a basis such that an emitting angle of light emitted from the LED1is within a half-value angle with respect to the front direction of the LED.

Here, the half-value angle will be explained.

Usually, the light intensity of light, emitted at a light emitting angle of sixty degrees from an LED (a bare chip type LED) which is not provided with a refraction member such as a lens, to its light emitting device (chip) has 50% energy of that of light emitted in the front direction of the LED. An angle at which light having 50% energy of that of light emitted in the front direction of the LED is emitted is called a “half-value angle”. For example, as illustrated inFIG. 5B, the light intensity of light entering to the reflecting member3with an incident angle of sixty degrees from the LED1which is represented by a heavy line has 50% energy of that of light emitted from the LED1in the front direction (the right direction in the figure), thus the half-value angle is sixty degrees. In this invention, the light energy of light emitted from such a general bare chip type LED at a half-value angle is restricted to be not less than 50% energy of that after reflection.

In the second embodiment, the constitutions of the LED1or the LEDs1and the light guide device2, and the arrangement of the reflecting members3and4are similar to those in the first embodiment (similar constitution as illustrated inFIG. 5), and as illustrated inFIG. 8, a relief structure on each of the reflecting surfaces of the reflecting members3and4is formed in a shape of triangle. That is, the relief structure of the reflecting member3(or4) includes a one-dimensional grating (a grating structure) in which a plurality of inverted triangular grooves (concave portions) c1are formed on the substrate a′ in parallel. Hereat, the plurality of grooves (concave portions) c1are arranged such that a length direction of each of the grooves (concave portions) c1is perpendicular to the X direction which is the length direction of the reading target area6a1; therefore, a cross-section of the plurality of grooves (concave portions) c1in the X direction is a structure of a plurality of triangular convex portions b1lined up in a row, as illustrated inFIG. 8. On the other hand, a cross section of the plurality of grooves (concave portions) c1in the sub-scanning direction (the Y direction) is a structure of a plane with a height of B of the convex portion b1formed continuously on the substrate a′.

In addition, in the second embodiment, if a ratio (B/A) of the height B of the convex portion b1to the width A of the concave portion c1of the relief structure is set to 0.692 or more than 0.692, a uniform illuminance distribution and predetermined illuminance can be obtained, without the reflection frequency of light emitted at the half-value angle, i.e., sixty degrees, exceeding seven times.

In the third embodiment, the constitutions of the LED1or me LEDs1and the light guide device2, and the arrangement of the reflecting members3and4are similar to those in the first embodiment (similar constitution as illustrated inFIG. 5), and as illustrated inFIG. 9, a relief structure on each of the reflecting surfaces of the reflecting members3and4is formed in a trapezoidal shape. That is, the relief structure of the reflecting member3(or4) includes a one-dimensional grating (a grating structure) in which a plurality of inverted trapezoidal grooves (concave portions) c2are formed on the substrate a′ in parallel. Hereat, the plurality of grooves (concave portions) c2are arranged such that a length direction of each of the grooves c2is perpendicular to the X direction, which is the length direction of the reading target area6a1; therefore, a cross-section of the plurality of grooves (concave portions) c2in the X direction is a structure of a plurality of trapezoidal convex portions b2lined up at a regular interval, as illustrated inFIG. 9. On the other hand, a cross-section of the plurality of grooves (the concave portions) c2in the sub-scanning direction (the Y direction) is a structure of a plane with a height of B of the convex portion b2formed continuously on the substrate a′.

In addition, in the third embodiment, if a ratio (B/A) of the height B of the convex portion b2to the width A of the concave portion c2of the relief structure is set to 0.692 or more than 0.692, a uniform illuminance distribution and predetermined illuminance can be obtained, without the reflection frequency of light emitted at the half-value angle, i.e., sixty degrees, exceeding seven times.

In the fourth embodiment, to improve the light use efficiency, the constitutions of the LED1or the LEDs1and the light guide device2, and the arrangement of the reflecting members are similar to those in the first embodiment (similar constitution as illustrated inFIG. 5), and as illustrated inFIG. 10, reflecting members5aand5b, at least one of which has a curved reflecting surface (a concave surface), instead of the flat reflecting surfaces of the reflecting members3and4, are used. Two curved reflecting members are used inFIG. 10, although the improvement of illuminance of the reading target area6a1(improvement of the light use efficiency) can be achieved with only one curved reflecting member.

In addition, each of the reflecting members5aand5bhas a relief structure in a rectangular shape similar to those on the reflecting members3and4in the first embodiment. However, as illustrated inFIG. 11, pitches of rectangular asperities are nonuniform, differing to the case in the first embodiment. In particular, a width A of a concave portion c′ (an interval between adjacent convex portions b′) decreases as the concave portion c′ becomes near a center of a main-scanning direction (the X direction) of the reflecting member5a(or the reflecting member5b), and increases as the concave portion c′ becomes near an end of the reflecting member5a(or the reflecting member5b). Such a structure is effective in such a case, i.e., when an arrangement interval between the LEDs1, for example, decreases gradually from a center to a periphery of a space where the LEDs1are disposed, and a uniform illuminance in a center more than that in a periphery of the reading target area6a1is necessary.

In the fifth embodiment the constitutions of the LED1or the LEDs1, the light guide device2, and the reflecting members5aand5bare similar to those in the fourth embodiment (similar constitution as illustrated inFIG. 10), and on at least one of the reflecting surfaces of the reflecting plates2a,2b,2cand2dof the light guide device2, a relief structure in a rectangular shape similar toFIG. 6is provided. Due to the relief structure or a rough structure in a grain shape being provided on the at least one of the reflecting surfaces of the reflecting plates2a,2b,2cand2dof the light guide device2, uneven illuminance of illumination light can be improved further, which it is preferable.

Although in the above-mentioned embodiments, examples where the relief structure is provided on at least one of the reflecting surfaces of the reflecting members3and4(or5aand5b) are explained, the relief structure can be provided on at least one of the reflecting surfaces of the reflecting plates2a,2b,2cand2dof the light guide device2, without providing the relief structure on the reflecting surfaces of the reflecting member3and4(or5aand5b).

Next, a constitution of an image forming device100according to the present invention will be explained.

FIG. 12is a schematic view illustrating the image forming device100having an image reading device200according to the present invention.

In the image reading device200, a manuscript (an illuminated object)202is disposed on a contact glass201(the contact glass6inFIG. 5A), i.e. a manuscript surface, and an illuminating section not shown, having a constitution according any one of the first to the fifth embodiments, which is provided at a first traveling body203arranged under the contact glass201, illuminates the manuscript202. Reflected light from the manuscript202is reflected by a first mirror203aof the first traveling body203, and then is reflected by a first mirror204aand a second mirror204bof a second traveling body204, and then is led to an imaging lens205, and is imaged on a line sensor206. In addition, the present invention can be applied to a color image reading device by providing the line sensors206corresponding to each color of RGB, with a similar constitution.

When scanning in the length direction of the manuscript, the first traveling body203moves to the right inFIG. 12at a speed of V, and at the same time the second traveling body204moves to right at a speed of ½V, which is a half of the speed of the first traveling body203; therefore an optical path length from the manuscript202to the line sensor206is kept constant, and the entire manuscript can be read out at a constant magnification.

The image forming device100includes a latent image carrier111in a drum shape, a charge roller112as a charging device, and a developing device113, and a transfer roller114and a cleaning device115are arranged in the surroundings of the latent image carrier111. A corona charger can be used as the charging device. In addition, an optical scanning device117which receives manuscript information from outside such as an image reading part and performs optical scanning by laser beam LB is provided, and “exposure by the laser beam” LB is performed between the charge roller112and the developing device113.

When forming an image, the latent image carrier111, which is a photoconductive photoreceptor, is rotated clockwise at a constant speed, and a surface of the latent image carrier111is uniformly charged by the charge roller112, and receives the exposure by the optical writing of the laser beam LB of the optical scanning device117, and an electrostatic latent image is formed. The formed electrostatic latent image includes a so-called negative latent image where an image area is exposed and a so-called positive latent image where a non-image area is exposed. Any one of the above-mentioned electrostatic latent images is visible by using a toner for the electrostatic latent image development in the developing device113. Hereat, four developing devices113are provided each of which corresponds to each of four colors of YMCK; therefore the image forming device can form a color image.

A cassette118storing transfer paper P is provided detachablely to a main body of the image forming device100. In a state that the cassette118is attached to the image forming device100, as illustrated inFIG. 12, one piece of transfer paper on the top of the stored transfer paper P is fed by a paper feeding collar120, and an end of the fed one piece of transfer paper P is caught by a pair of resist rollers119. The pair of resist rollers119feed the one piece of transfer paper P to a transfer part, synchronously with a timing of moving a toner image on the latent image carrier111to a transfer position. The fed one piece of transfer paper P is superimposed with the toner image in the transfer part and the toner image is an electrostatic image transferred by an action of the transfer roller114. The one piece of transfer paper P transferred with the toner image is sent to a fixing device116, and the toner image is fixed in the fixing device116, and then is ejected onto a catch tray123by a pair of delivery rollers122, passing through a feeding path121. The surface of the latent image carrier111after transferring of the toner image is cleaned by the cleaning device115, and residual toner and paper dust or the like are removed.

According to an aspect of the present invention, it can provide an image reading device having a compact illumination optical system in which the number of light sources is small and illuminance unevenness is little. In addition, it can provide an image forming device which is capable of forming a good image while being compact, by using the image reading device.

It should be noted that although the present invention has been described with respect to exemplary embodiments, the invention is not limited thereto. In view of the foregoing, it is intended that the present invention cover modifications and variations provided they fall within the scope of the following claims and their equivalent.

The entire contents of Japanese patent application No. JP 2007-228756, filed on Sep. 4, 2007, of which the convention priority is claimed in this application, are incorporated hereinto by reference.