JP2006174038A - Image sensor unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain uniform reflection characteristics by reducing unevenness of an amount of reflected light due to position variations or the like of manuscript paper regarding a contact type image sensor. <P>SOLUTION: When the field angle of a lens array constituting the image sensor is set to θ1, an irradiation angle of illumination light emitted from a light guide body to an original manuscript is set in the range of ≥θ1 and <30° on the basis of an optical axis of the lens array. Consequently, the image sensor with the improved illumination depth characteristics and the reduced unevenness of the illumination light is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus such as an image scanner, a facsimile, or a copying machine, and more particularly to an image sensor unit provided in an image reading unit that reads reflected light from a document surface.

2. Description of the Related Art Conventionally, in an image reading apparatus such as an image scanner, a facsimile, or a copying machine, a sensor unit mounting method in the image reading apparatus is roughly divided into the following two.
A document is fixed on a document support in the image reading apparatus, and the sensor unit is fixed to a flat bed type image reading apparatus that moves and reads, and the document sheet on the document support is moved and read. First, an example of a flat bed type conventional image reading apparatus is shown in FIG. Here, an example of a flat bed type image reading apparatus using a contact image sensor (hereinafter abbreviated as CIS) is shown. Hereinafter, a configuration example of a conventional contact image sensor will be described. FIG. 4 is a structural sectional view of a conventional contact image sensor, and shows a case where there is only one light guide 42. The close contact image sensor has a light source for irradiating a document, and receives reflected light from a document sheet through a lens by a light receiving portion formed by a photoelectric conversion element, and converts it into an electrical signal.

  In the figure, reference numeral 43 denotes a frame that supports the constituent members, 44 denotes a lens array that forms an optical image of the document on the sensor array 45, and 45 includes a plurality of light receiving units that photoelectrically convert the optical image of the document into electrical signals. A linear sensor array 46 is a sensor substrate on which the sensor array is mounted, and 41r, 42g, and 43b are light sources composed of LEDs for illuminating the document, and are arranged on the end face of the light guide 42 that extends in the longitudinal direction. Has been. The light source unit 41 includes a light guide 42 that takes in the light emitted from the LED and is designed so that the amount of illumination light is substantially uniform over the length of one line of the document reading unit. Reference numeral 47 denotes a connector for connecting a sensor signal to an external device, and reference numeral 48 denotes a transparent glass original support table for supporting the original paper 49.

  In general, the light guided into the light guide 42 is reflected by a reflecting unit provided on the opposite side of the emitting unit and irradiated from the lens unit, and the illumination light is directed to the original paper at an angle of approximately 45 degrees. Go. In particular, when it is necessary to improve the reflection characteristics, it is preferable to arrange titanium oxide powder or aluminum powder as a reflecting material in the reflecting portion by means such as printing.

  FIG. 5 shows a high-speed sheet feed type image sensor and an image reading apparatus using the same. In the figure, an example is shown in which two light guides are incorporated in order to increase the brightness of the light source. Reference numeral 25 denotes a document transport roller. By transporting the document paper between the rollers, a predetermined paper transport path W is set, and the document-side focal point 26 of the lens array is set at the center. In this case, there is a problem that the height of the original paper fluctuates in both the direction of the optical axis of the lens array, that is, the original side focal point 26 with the mechanical conveyance of the original paper.

Moreover, regarding the irradiation angle of this illumination light, it is disclosed in patent document 1 that it is centering on 30-50 degree | times, and also arrange | positioning close to a lens array is disclosed. (For details, see Patent Document 1)
Japanese Patent Laid-Open No. 11-17903, FIG. 24 and others

  However, the above conventional example has the following problems. In other words, for example, when scanning a book with a book open or when reading uneven document paper, the illumination intensity of the image sensor is shallow, so the amount of illumination light decreases at a position slightly away from the document support table. The amount of light that can be collected on the sensor array by the lens array is reduced, and as a result, the spread portion is displayed in black, so that improvement in image quality has been demanded.

  Even if the original information has a uniform density, if the original paper fluctuates in the optical axis direction of the lens array, the amount of illumination light on the original surface perpendicular to the optical axis of the lens array changes and image reading is performed. There has been a problem that unevenness of density depending on the height of the reading position is likely to occur in the output image of the apparatus.

  In the flat bed type image reading apparatus, the document-side focal point of the lens array is set slightly above the document-side surface position of the document support so that a document with an uneven surface can be easily read. However, when the height fluctuates in the optical axis direction of the lens array, there is a problem that density unevenness is likely to occur.

In view of such circumstances, the present invention provides a contact-type image sensor unit having an illuminating device, and by adjusting an incident angle of an optical axis indicating the maximum amount of illumination light emitted from the illuminating device, The present invention provides a sensor unit in which the variation in the amount of reading light is small with respect to the height variation.

The present invention increases the illumination depth of the illuminating device by moving the optical axis of the irradiating light from the light guide toward the document table in a direction perpendicular to the document table as much as possible. However, an object of the present invention is to obtain a good image reading apparatus as a result of suppressing the decrease in the amount of light.
The present invention includes an illuminating device that illuminates a document sheet disposed on a transparent document support table, a lens array that images reflected light from the document sheet, and a plurality of pixels that convert the reflected light into an electrical signal. An image sensor unit comprising a sensor array,
The angle of view of the lens array is θ1,
When the angle of intersection of the illumination light optical axis emitted from the illumination device and directed to the document is θ2 with respect to the lens optical axis of the lens array,
θ1 <θ2 <30 °
This is an image sensor unit.

According to the present invention, the illumination depth can be increased by changing the irradiation angle of the illumination light, and even when the position of the document on the document support changes, it is possible to suppress a change in the amount of reading light. . Therefore, a large amount of light can be obtained while improving the light condensing performance of the illumination device, and thus the amount of light read per unit time is increased and high-speed reading is possible. In addition, it is possible to realize an image sensor unit in which the output fluctuation is small with respect to the fluctuation of the vertical position of the document.

In the configuration of the present invention, the image sensor unit according to the present invention is configured as follows. By using a conventional image sensor unit and devising the shape of the frame for fixing the image sensor unit or the shape of the frame receiving portion, the angle of the light beam incident on the document support table is made lower than before. That is, the angle of view of the lens array is θ1, the optical axis passing through the lens array toward the sensor array is the reference axis, and among the illumination light emitted from the light guide and traveling straight toward the document, When the angle formed by is θ2,
It is characterized in that θ1 <θ2 <30 °.
Hereinafter, the present invention will be described in detail by way of examples.

An example of a contact image sensor using the image sensor unit of the present invention is shown in FIG.
The light source 12 stored in the sensor frame 13 has an LED light source 11 disposed on the end face thereof. The light emitted therefrom is guided into the light guide and can irradiate the original paper 19 in a line shape in the longitudinal direction. The light emitted from the light guide enters the original support 18 and irradiates the original paper 19 thereon. Next, the light reflected by the original paper is collected by the lens array 14, formed on the photoelectric conversion element 15 disposed on the sensor substrate 16, and photoelectrically converted into an electric signal. The image signal is sent to a control circuit (not shown) through an external terminal 17 attached to the lower part of the sensor substrate to form an image.

  At this time, the light emitted from the light guide irradiates the reading position of the original paper in a line shape, but the light quantity actually has a light quantity distribution in the horizontal direction and the height direction of the original paper. It is desirable that the light amount distribution does not change as much as possible even when the document sheet is lifted from the document support table.

  As shown in FIG. 1, a line extending vertically from the center of the lens array 14 is defined as a lens optical axis, and an axis indicating the maximum amount of light emitted from the light guide is defined as an illumination light optical axis. Here, the irradiation angle means an angle θ2 at which these two optical axes intersect. In the figure, the light beam emitted from the light guide is drawn in a straight line, but the actual light beam is refracted and changes its angle when entering the document support table, and returns to the original angle when it exits into the air. The substantial angle of θ2 is constant. Therefore, in the present application, in order to simplify the drawing, it is drawn with a straight line.

  In this example, the irradiation angle θ2 was adjusted to 27 degrees by inserting a spacer between the light guide and the frame. Further, on the opposite side of the light guide emitting portion, aluminum powder is formed as a reflecting member by a printing method to increase the reflection efficiency.

  FIG. 3 is a graph showing the relationship between the distance from the document support table and the illuminance on the horizontal axis. A spacer is placed on the document support table shown in FIG. 1, and the amount of light reaching the sensor array is measured as an electric signal output of the line sensor by changing the distance from the document sheet. In the figure, the sensor output at the position on the document support table is standardized as 1.

  The curve in FIG. 3 (II) shows the result of the present embodiment, and FIG. 2 (I) shows a comparative example according to the prior art. When the light amount on the document support base is set to 1, the light amount is reduced by about 30% at a position 2 mm away in the conventional example, whereas the light guide body of this application is about 10% and maintains a high light amount. You can see that Furthermore, even if it is 8 mm away, it has a light amount of 40%, and it can be seen that a decrease in illuminance is remarkably suppressed.

  In general, when the book is opened and placed on the document support table, in the conventional example, the amount of light is reduced at the binding portion far from the document support table, and the binding portion may be printed black. The amount of blackening can be significantly reduced by using.

  In addition, it is possible to increase the illumination depth by reducing the irradiation angle. However, if the irradiation angle θ2 is reduced, it is easy to capture regular reflection light, which increases noise. This will be described in detail below. In this embodiment, a lens array having an angle of view at which the lens array can capture light is 12 degrees. For example, when the irradiation angle is smaller than 12 degrees, the specularly reflected light having a high light amount reflected from the document surface or the like surely enters the angle of view of the lens and forms an image around the sensor array. Such specularly reflected light becomes stray light and becomes a noise component when taken into the sensor array. For this reason, it is essential that the irradiation angle is greater than the angle of view of the lens array.

  Furthermore, when the irradiation angle θ2 is close to the angle of view θ1 of the lens array, the possibility of specularly reflected light entering the angle of view increases due to the unevenness of the original paper, especially noise when reading a black image. However, there is a problem that it is likely to be displayed as a white spot. Therefore, in practice, the lower limit of the irradiation angle is preferably twice the angle of view of the lens array, that is, about 2 × θ1.

  FIG. 2 shows a case where two light guides which are different embodiments of the present invention are used. In general, this type of sensor unit can reduce the reading time per line by increasing the amount of irradiation light, and therefore can increase the number of readings per time, and is applied to a high-speed scanner or the like.

  The optical axis indicating the maximum amount of illumination light emitted from the two light guides is adjusted to 27 degrees by adjusting the positional relationship between the light guide and the frame with a spacer or the like. Designed to be The CIS unit of this system was also able to suppress the difference in light amount depending on the reading position of the document as in the first embodiment.

  As a result, as in the case of the first embodiment, the illumination depth can be increased, and it is possible to suppress a portion that becomes black even with respect to a document having a depth, such as when a book is widened.

(Comparative example)
FIG. 4 is a cross-sectional view of a conventional contact image sensor showing the illumination depth characteristics shown in FIG. The image sensor unit is the same as the structure shown in FIG. 1 except that the irradiation angle to the original paper is set to 45 degrees.

  In the figure, the light emitted from the LED element is guided to the light guide 42 and irradiates the original paper 49 in a line form through the original support 48. The reflected light is guided to the photoelectric conversion element 45 disposed on the sensor substrate 46 through the SELFOC lens array 44 and converted into an electric signal based on the same principle as the present invention.

  As shown in FIG. 3I, it can be seen that the amount of light suddenly decreases as the position of the original paper increases.

An embodiment of a flat bed type image scanner using the image sensor unit of the present invention will be described.
FIG. 7 is a perspective view showing the appearance of the image scanner. In the figure, reference numeral 71 denotes a contact image sensor of the present invention. 74 is a drive motor, 75 is a wire, 76 is a glass plate as a document support table, and 77 is a pressure plate for document paper.

  By driving the drive motor 74 and mechanically moving the wire 75, the CIS 71 can move in the reading direction (scanning direction) and read the image of the document. The CIS is configured as a sensor unit in which an illuminating unit is integrated, and reflected light from an illuminated original is condensed on a photoelectric conversion element by a lens array (not shown) in the CIS, and image information for each line. Is output as In this way, sheet-like image information can be read and output.

In the image scanner equipped with the CIS unit of the present invention, it is possible to realize an image scanner which is less affected by the position fluctuation and unevenness of the original paper and can output stable image information.

1 is a cross-sectional view of a configuration of a contact image sensor according to a first embodiment of the present invention. FIG. 5 is a cross-sectional view of a configuration of a contact image sensor according to a second embodiment of the present invention. An example using two light guides is shown. The figure which shows the illumination depth characteristic at the time of using the contact type image sensor of this invention and a prior art example. The horizontal axis indicates the change from the focal position, and the vertical axis indicates the light amount fluctuation. The cross-sectional view of the configuration of a conventional contact image sensor. The figure which shows an example of the sheet feed type image reader using the contact | adherence type image sensor of a prior art example. The figure which shows an example of the sheet feed type image reading apparatus using the contact | adherence type image sensor of this application. The figure which shows an example of the flatbed type image reading apparatus using the image sensor of this invention.

Explanation of symbols

θ1 An angle of view θ2 indicating an area in which the light from the lens array is scattered. Angle at which the optical axis of the illumination light intersects the lens optical axis 11 LED light source 12 Light guide 13 Frame 14 Selfoc lens array 15 Photoelectric conversion element 16 Sensor substrate 18 Document support table 19 Document paper

Claims (3)

An illumination device that illuminates a document sheet disposed on a transparent document support table, a lens array that forms an image of reflected light from the document sheet, and a sensor array that includes a plurality of pixels that convert the reflected light into an electrical signal; An image sensor unit comprising:
The angle of view of the lens array is θ1,
When the angle of intersection between the optical axis of the lens array and the optical axis of the illumination light emitted from the illumination device and directed to the document is θ2,
θ1 <θ2 <30 °
An image sensor unit characterized by being. The relationship between θ1 and θ2 is
2xθ1 <θ2 <30 °
The image sensor unit according to claim 1, wherein: An image reading apparatus comprising the image sensor unit according to claim 1.

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