JP2006060407A - Light source unit, image reader, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source unit with which a desired illuminance distribution and a desired light distribution can be obtained. <P>SOLUTION: In an image reader equipped with a light source having a cold-cathode tube 25 and an LED array 26, the LED array 26 sets an illuminance distribution of individual LEDs so that an illuminance characteristic distribution of the cold-cathode tube 25 is interpolated. The illuminance distribution is set by adjusting the size, array intervals, luminance, spectral characteristics, etc., of the LEDs, and these objects to be adjusted can be combined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus that reads a document image, a light source device used in the image reading apparatus, and an image forming apparatus including the image reading apparatus.

  In an image forming apparatus such as a copying machine, a scanner, or a facsimile, in order to convert image information of a document into an electric signal, an image is optically applied to a line sensor in which a large number of fine photoelectric conversion elements are linearly arranged at equal intervals. Thus, an electric signal is sequentially obtained while scanning the original in a direction orthogonal to the arrangement of the photoelectric conversion elements. As a method of projecting an original on a line sensor, it is common to irradiate the original with a light source such as a lamp and form an image of the reflected light on the line sensor via an imaging lens or the like. As a light source, a light source such as a fluorescent lamp or a halogen lamp has been used. However, in recent years, the lamp has been shifted to a cold cathode tube having a relatively long life and good stability. The cold cathode tube has a drawback that the illuminance is lower than that of the light source described above, but this has also been increased in output, and has been adopted in color scanners and color copying machines. On the other hand, an idea of using an LED, which is a semiconductor element, as a light source has been born and is being put into practical use, but has some drawbacks. One is that the illuminance is extremely low. In particular, since it is still lower than that of a cold cathode tube, increasing the reading speed is a major issue. Furthermore, when a number of LEDs are arranged in an array in the main scanning direction, each is a point light source, so there is a problem that the illuminance falls at the joint and it is difficult to obtain a smooth illuminance distribution as a result. .

Therefore, for example, in Patent Document 1, an organic LED is adopted as a light source, a line sensor is improved, and a plurality of photoelectric conversion elements are integrated as a solid light emitting element and a photoelectric conversion element on a transparent glass substrate. It has been proposed to reduce the size of the reading device by forming and arranging it on individual lines. Further, Patent Document 2 proposes to irradiate a transparent original with light emitting means having different wavelengths, and Patent Document 3 discloses that an LED light source can reduce the number of LEDs mounted and has good light output. An invention is disclosed in which characteristics are obtained. Further, Patent Document 4 proposes a hybrid light source in which the light source is composed of at least one color cold cathode tube and an LED.
JP 2000-106617 A JP 2000-253284 A JP 2001-339577 A JP 2000-32219 A

  However, there are manufacturing and technical problems to obtain the target characteristics for the illuminance, illuminance distribution, or light distribution of the LED array light source, and even if it can be realized, it is disadvantageous in terms of cost. Met.

  The present invention has been made in view of the actual situation of the prior art, and an object of the present invention is to use a hybrid light source and to obtain desired illuminance distribution and light distribution characteristics at low cost. It is in.

  In order to achieve the above object, the first means sets the illuminance distribution of the LED array so as to interpolate the illuminance characteristic distribution of the cold cathode tube light source in a light source device having a cold cathode tube and an LED array as light sources. It is characterized by being.

  A second means is characterized in that, in the first means, the illuminance distribution of the LED array is set by adjusting the size of each LED of the LED array.

  A third means is characterized in that, in the first means, the illuminance distribution of the LED array is set by adjusting an arrangement interval of individual LEDs of the LED array.

  A fourth means is characterized in that, in the first means, the illuminance distribution of the LED array is set by adjusting the luminance of each LED of the LED array.

  A fifth means is characterized in that, in the first means, the illuminance distribution of the LED array is set by adjusting spectral characteristics of individual LEDs of the LED array.

  A sixth means is characterized in that, in any one of the first to fifth means, the cold-cathode tube and the LED array each have a light emission characteristic of three wavelengths.

  The seventh means is characterized in that the image reading apparatus includes the light source device according to any one of the first to sixth means.

  According to an eighth means, the image forming apparatus includes an image reading apparatus according to the seventh means and an image forming means for forming an image on a recording medium based on image information read by the image reading apparatus. It is characterized by.

  In the embodiments described later, the light source corresponds to the light source 15, the cold cathode tube corresponds to the cold cathode tube 25, and the LED array corresponds to the LED array 26.

  According to the present invention, desired illuminance distribution and light distribution can be obtained, and high image quality can be achieved. In addition, the specifications required for the cold-cathode tube light source can be widely taken, the development period can be shortened, and a total cost reduction can be expected.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 is a perspective view of a scanner as an image reading apparatus according to an embodiment of the present invention, FIG. 2 is a plan view showing an original platen portion of the scanner of FIG. 1, and FIG. 3 is a first view when an ADF is used in a cyro-through system. FIG. 4 is a diagram illustrating a reading position of the traveling body, and FIG. 4 is a diagram illustrating a relationship between the first traveling body and the second traveling body when the original is read by the flat bed method.

  The scanner includes a scanner body 1, a cover portion 2 that covers the upper surface of the scanner body 1, and a sheet-through ADF (automatic document feeder) 3 that is attached to the cover portion 2. The scanner body 1 includes a housing 11, a contact glass 12 serving as a document table, a reading window 13 for reading a document by sheet through, a reference white plate 14 for shading correction, and a light source 15 for irradiating the document. The first traveling body 16 and a second traveling body 18 that guides reflected light from the first traveling body 16 to the CCD substrate 17 are configured. Although not shown, a condensing lens made of a lens block is disposed between the second traveling body 17 and the CCD substrate 17.

  The first traveling body 16 includes a light source 15 that irradiates the document, and a first mirror 21 that sends reflected light from the document to the second traveling body 18. When reading the document with the contact glass 12, the first traveling body 16 is driven by a driving motor (not shown) to move in the sub-scanning direction to scan the document with respect to the document fixed on the contact glass 12. When continuously reading a plurality of documents using the ADF 3 by the sheet-through method, as shown in FIG. 3, scanning is performed by reading a document that is fixed under the reading window 13 and passes through the reading window 13. I do. At this time, the document is pulled out in the direction of arrow A.

  The second traveling body 18 includes second and third mirrors 22, 23, and the reflected light from the first traveling body 16 is guided to the CCD substrate 17 by these mirrors 22, 23, and is converted into an electrical signal by the CCD substrate 17. Converted.

  As shown in FIG. 4, the light source 15 includes a cold cathode tube 25 and an LED array 26. The cold cathode tubes 25 and the LED array 26 are disposed on the upper part of the first traveling body 16. The cold cathode tube 25 is provided with an optical opening 25a obliquely. In the case of the sheet-through method, the cold cathode tubes 25 and the LED arrays 26 do not necessarily have to arrange the light sources on the same traveling body. For example, the first traveling body 16 is provided with the cold cathode tubes 25. The LED array 26 may be divided and arranged in the casing 11. The light emitted from the light source 15 to the document is guided to the first mirror 21 of the first traveling body 16 as reflected light. The mirror image falling on the first mirror 21 is further reflected by the second and third mirrors 22 and 23 of the second traveling body 18 and guided to a lens (not shown) that forms an image on the CCD of the CCD substrate 17. . Reference numeral 19 denotes a background plate in the reading window 13.

  As described above, the light source 15 can be combined with the cold cathode tube 25 and the LED array 26 to compensate for the respective disadvantages and to adopt the advantages. That is, when comparing the light source of the cold cathode tube 25 and the light source of the LED array 26, the LED array 26 is lighter in weight, lower in power consumption (low voltage drive), and smaller in size than the cold cathode tube 25 (layout). However, it has the disadvantages of low illuminance and large variations in illumination distribution. On the other hand, cold cathode tubes are heavier because of glass compared to LED arrays, have large power consumption (high voltage drive), large noise, low layout freedom, normal life span, and long rise time (dark start characteristics) However, it has disadvantages such as small design freedom, but it has the advantages of high illuminance and smooth distribution of illuminance. Therefore, there are merits of hybridization in compensating for each of these disadvantages and adopting the advantages. Therefore, in the present invention, according to various characteristics such as illuminance distribution and spectral distribution of the cold cathode tube, the disadvantages are complemented by combining the characteristics of the individual LEDs constituting the arrayed LED light source, and ideal light source characteristics are obtained. It has gained.

  FIG. 5 is a graph showing the illuminance distribution in the main scanning direction of the cold cathode tube and the LED array. The light source preferably has a flat distribution as a general illuminance distribution. However, for example, as shown in FIG. 5, the cold cathode tube may have illuminance at both ends lower than that at the center when viewed in the main scanning direction. Therefore, for the cold cathode fluorescent lamp 25 having such an illuminance distribution, the LED array 26 increases the illuminance at both ends in the longitudinal direction, and the illuminance in the longitudinal direction, that is, the main scanning direction is almost the same in the entire light source 15. Thus, the merit of the hybrid light source is derived by changing the shape and arrangement of the individual LEDs constituting the LED array 26.

FIG. 6 is a diagram showing an example of changing the shape and interval of the LED array along the main scanning direction. In the embodiment of FIG. 6, in order to make the illuminance in the main scanning direction of the LED array 26 substantially the same, the size of each LED 26a is increased 1) at both ends.
2) Reduce the illuminance by changing the arrangement interval of the individual LEDs 26a.
3) Or the illuminance is adjusted by changing the shape of the single LED 26a.
Three specific methods are shown. Thus, an LED array having a luminance distribution as shown in FIG. 7 is provided. Although FIG. 6 shows three types of illuminance adjustment methods, it is needless to say that it is not necessary to use all three types.

  In the embodiment of FIG. 6, an arbitrary illuminance distribution is obtained by changing or combining the shapes of individual LEDs. In this case, however, it is difficult to align the array as an array when the LEDs have individual shapes. There is. Therefore, in the embodiment shown in FIG. 7, the shape of each LED is unified, and an arbitrary illuminance distribution is obtained by changing the luminance of each LED.

  FIG. 7 is a diagram showing an example of changing the luminance of the LED array along the main scanning direction. That is, some LEDs have the same shape but different luminance due to different transmittance of the condenser lens and output of the chip. In this embodiment, such LEDs are combined into an array to aim for a correction effect. Further, by individually controlling the duty of the LEDs (controlling the light emission interval), it is possible to change the brightness of each LED even when the LED combination is exactly the same.

  In each of the above-described embodiments, the illuminance distribution in the main scanning direction is described here as an example. However, the illuminance distribution also exists in the sub-scanning direction, which is effective for correction in this case.

  An image reading apparatus of a type that reads an original image in color is also provided. In color reading, not only illuminance but also chromaticity (spectral) is an important characteristic. Generally, color reading is realized by emitting light of wavelengths of R, G, and B which are the three primary colors. In the cold-cathode tube, phosphors corresponding to respective wavelengths are applied, and when the application is uneven or it is difficult to obtain a desired spectrum, the light source of the LED array 26 is the same as in the above-described embodiments. It is possible to obtain the necessary spectrum by complementing with.

  FIG. 8 is a graph showing the color spectrum of the light source device in the color image reading device, where (a) shows the spectral state of the cold cathode tube and (b) shows the spectral state of the LED array. As can be seen from FIG. 8A, in the cold cathode fluorescent lamp, the B level is lower than the R and G levels. Therefore, in order to raise the level of B and average the overall spectral level, the emission wavelengths of the LEDs for the three primary colors can be complemented by making them as shown in FIG. Furthermore, it is possible to complement even when the spectrum of the cold cathode fluorescent lamp is not uniform by finely changing the spectrum of each LED.

1 is a perspective view illustrating an appearance of an embodiment of a scanner including an image reading device according to the present invention. FIG. 2 is a plan view showing an original table portion of the scanner of FIG. 1. It is a figure for demonstrating the fixed position of the 1st driving | running | working body at the time of ADF use. It is a figure for demonstrating the relationship between a 1st traveling body and a 2nd traveling body. It is a graph which shows the illumination distribution of the main scanning direction of a cold cathode tube and an LED array. It is a figure which shows the example which changes the shape and space | interval of a LED array along the main scanning direction. It is a figure which shows an example which changes the brightness | luminance of a LED array along the main scanning direction. It is a graph which shows the color spectrum of the light source device in the image reader for color, (a) shows the spectral state of a cold cathode tube, (b) shows the spectral state of an LED array, respectively.

Explanation of symbols

1 scanner body 11 housing 12 contact glass 13 reading window 13
15 Light source 16 1st traveling body 1
17 CCD substrate 18 Second traveling body 18
25 Cold cathode tube 25a Light aperture 26 LED array 26a LED

Claims (8)

In a light source device having a cold cathode tube and an LED array as a light source,
An illuminance distribution of the LED array is set so as to interpolate an illuminance characteristic distribution of the cold-cathode tube light source.   The light source device according to claim 1, wherein the illuminance distribution of the LED array is set by adjusting the size of each LED of the LED array.   2. The light source device according to claim 1, wherein the illuminance distribution of the LED array is set by adjusting an arrangement interval of individual LEDs of the LED array.   2. The light source device according to claim 1, wherein the illuminance distribution of the LED array is set by adjusting the luminance of each LED of the LED array.   2. The light source device according to claim 1, wherein the illuminance distribution of the LED array is set by adjusting spectral characteristics of individual LEDs of the LED array.   6. The light source device according to claim 1, wherein each of the cold cathode fluorescent lamp and the LED array has a light emission characteristic of three wavelengths.   An image reading apparatus comprising the light source device according to claim 1. An image reading apparatus according to claim 7;
Image forming means for forming an image on a recording medium based on image information read by the image reading device;
An image forming apparatus comprising:

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