JP2007312247A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image reader capable of preventing transfer of an adhesive foreign matter to reading glass for reading an image of an original to be conveyed and generation of distortion and a density error in the read image on the rear edge of the original. <P>SOLUTION: The image reader optically reads an original image at a reading position A while conveying the original right above the reading glass 12. On the reading glass 12, a guide sheet 30 which forms level difference so that an image surface of the original to be conveyed does not contact the reading glass 12 is installed on the upstream side in the original conveyance direction B from the reading position A. When the rear edge of the original passes the reading position A through the guide sheet 30, the rear edge of the original falls onto the reading glass 12. A scale factor and density of the image read at such a fallen state are compensated. Otherwise, positions of a lens of a reading optical system and an exposure lamp are varied when the read edge of the original passes the reading position A to compensate the reading scale factor and the density. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image reading apparatus, and more particularly to a sheet-through type image reading apparatus used as an image input apparatus in a copying machine, a scanner, or the like.

  Conventionally, as an image reading apparatus for optically reading an image of a document, a platen set method for reading an image of a document placed on a platen glass, and a document are conveyed one by one, and an image of the document is read during conveyance. The sheet-through method was used alone or in combination. The sheet-through method has advantages in downsizing, low cost, low noise, high-speed image reading, and high print productivity, and has become the mainstream of image reading devices in monochrome copiers. The introduction is also desired.

  In the case of the sheet-through method, the image reading position is fixed on a transparent member (elongated reading glass), and the reading optical system is focused on the image surface of the document conveyed through the reading glass. A portion that is easily affected by foreign matter such as dust adhered to the glass and is shielded by the foreign matter becomes streak-like image noise in the read image.

  The foreign matter adhering to the reading glass is mainly sticky foreign matter such as the adhesive part of the tape affixed to the original or peeling of the adhesive, correction liquid, ball pen ink lump, eraser scraps, etc., and the original slides on the reading glass. Easy to be transferred to the part. Further, such a sticky foreign matter does not easily peel off and has a problem of causing image noise.

  Therefore, Patent Documents 1 and 2 disclose measures for conveying a document in a non-contact state with respect to the reading glass by providing a step on the upstream side of the reading glass in the document conveying direction. In this non-contact conveyance method, the adhesive foreign matter can be prevented from adhering to the reading glass.

  However, when the trailing edge of the document passes through the step, it loses its support and falls and contacts the reading glass. Since the original is conveyed at a position higher than the reading glass, the distance from the reading optical system changes in the direction until the trailing edge passes through the step and comes into contact with the reading glass. Due to such a change, the optical path length from the original surface to the lens of the reading optical system is shortened, which causes a problem that the read image is enlarged and distortion occurs. Similarly, since the document surface approaches the illumination lamp of the reading optical system, the image information is brighter than the normal reading position, and there is a problem that appropriate image information cannot be obtained.

Patent Document 2 intends to stabilize a document which is conveyed by an air flow while tilting a reading glass against a guide and is kept at the focus position of the reading optical system. However, a variation in distance from the reading optical system occurs when the trailing edge of the document passes through the step forming member, and image distortion and density error due to this change have not been solved.
JP-A-9-307695 JP 11-146140 A

  Accordingly, an object of the present invention is a sheet-through system, which prevents an adhesive foreign matter from being transferred to a transparent member for reading an image of a conveyed document and also provides a read image at the rear end of the document. An object of the present invention is to provide an image reading apparatus capable of eliminating the occurrence of distortion and density error.

In order to achieve the above object, an image reading apparatus according to the first invention comprises:
A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Image correcting means for correcting an image read when the rear end of the document passes through the reading means via the step forming member;
It is provided with.

  According to the image reading apparatus of the first invention, the document is conveyed by the step forming member while being floated from the transparent member, and the sticky foreign matter is prevented from being transferred from the document surface to the transparent member. . When the trailing edge of the document passes through the reading unit through the step forming member, the distance from the reading unit changes. In this case, since the read image is corrected by the image correction means, the distortion and / or density error of the image that has occurred conventionally is eliminated.

  In the image reading apparatus according to the first invention, the image correcting means corrects at least the magnification or density of the read image. Moreover, it is preferable to gradually perform the correction of the image in the correction start area, and an image that does not feel uncomfortable can be obtained.

An image reading apparatus according to the second invention is
A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Detecting means for detecting a paper passing state in which a document passes through the reading means through the step forming member;
Control means for changing the relative position of the reading means and the document according to the passing state of the document detected by the detecting means;
It is provided with.

  According to the image reading apparatus of the second invention, the document is conveyed by the step forming member while being floated from the transparent member, and the sticky foreign matter is prevented from being transferred from the document surface to the transparent member. . When the trailing edge of the document passes through the reading unit through the step forming member, the distance from the reading unit changes. In this case, since the relative position between the reading unit and the original is changed in accordance with the passing state of the original, the magnification change and / or the density change of the read image is eliminated.

  In the image reading apparatus according to the second aspect of the present invention, there is provided driving means that is controlled by the control means and changes the relative position between the reading means and the document. Further, the means for detecting the passing state of the original detects the timing at which the rear end of the original passes through the step forming member, or detects the conveyance height of the original.

  Embodiments of an image reading apparatus according to the present invention will be described below with reference to the accompanying drawings. In each embodiment, the same parts and the same parts are denoted by the same reference numerals, and redundant description is omitted.

(Image reader, see FIGS. 1-4)
FIG. 1 shows an image reading apparatus 1 according to an embodiment of the present invention. The image reading apparatus 1 includes a platen set method for reading an image of a document (not shown) placed on the platen glass 10 and a sheet-through method for reading the document D conveyed by the automatic document conveying device 20. In addition, a reading optical system (scanner) 50 is installed.

  Reading of an image by the platen set method is performed, for example, by irradiating a document placed on the platen glass 10 by a lamp 53 such as a rare gas fluorescent lamp, and reflecting light from the document surface via mirrors 54, 55, and 56. The light is incident on the imaging lens 57 and further imaged on the imaging unit (CCD color line sensor) 58. The lamp 53 and the mirror 54 are mounted on the first slider 51, and the mirrors 55 and 56 are mounted on the second slider 52, and are movable in the sub-scanning direction Y, respectively. A white reference plate 11 for performing shading correction is installed on the upstream side of the platen glass 10 in the sub-scanning direction Y.

  On the other hand, the automatic document feeder 20 includes a plurality of roller pairs 21, 22, 23, and 24. The documents D are picked up one by one from the tray 25, fed from the roller pairs 21, 22, 23 onto the reading glass 12, and read by the reading optical system 50 set immediately below the reading position A. 24 is discharged onto the tray 26.

  The image data read by the reading optical system 50 is transferred to the image processing unit 60 and further transferred to the laser scanning unit of the digital copying apparatus, and an image is formed on the paper by a known electrophotographic method. The document image reading process by the platen set method or the sheet through method and the image forming process by the electrophotographic method are well known, and detailed description thereof is omitted.

  FIG. 2 shows an enlarged cross-section of a document reading unit using the sheet-through method. Around the reading glass 12, document guide plates 25a, 25b, 26a, and 26b and a guide 27 for scooping up the document that has passed the reading position A are arranged. An original guide sheet 30 that functions as a step forming member is provided on the reading glass 12 upstream of the reading position A in the original conveying direction B so that the original being conveyed does not directly touch the reading glass 12. Is attached to the mounting plate 35 and arranged in contact with the surface of the reading glass 12.

  In the image reading apparatus 1, an original conveyed rightward while sliding on the upper surface of the original guide sheet 30 by the conveyance roller pairs 23 and 24 has a predetermined position at a reading position A depending on the thickness of the guide sheet 30. It is conveyed in a non-contact state with the reading glass 12, and the original image is read by the reading optical system 50 through the reading glass 12. Since there is a gap between the original surface and the reading glass 12, adhesive foreign matters such as correction liquid do not adhere to the reading glass 12.

  Specifically, the document guide sheet 30 is formed of a material having a thickness (step) of 0.65 mm and a low sliding resistance (preferably a friction coefficient μ: 0.3 or less) such as ultrahigh molecular weight polyethylene. .

  The document guide plate 25b regulates the posture of the document D being conveyed, and the clearance from the reading glass 12 is set to 1.2 mm in order to perform stable image reading. If the gap with the reading glass 12 is increased to 1.4 mm or more, the posture of the conveyed document is not stabilized, the paper passing property is deteriorated, and the density of the read image varies.

  Here, the behavior of the document passing through the reading position A will be described with reference to FIG. The document D is guided to the surface of the guide sheet 30 and fed onto the reading glass 12 (see FIGS. 3A and 3B), and has a gap from the reading glass 12 by the thickness of the guide sheet 30. It is conveyed (see FIGS. 3C and 3D). When the trailing edge of the document leaves the edge of the guide sheet 30, it falls onto the reading glass 12 (see FIG. 3E) and contacts the reading glass 12 at a distance L from the edge (see FIG. 3F).

  Thus, when the trailing edge of the document D passes through the edge of the guide sheet 30, the trailing edge of the document is at the reading position A according to the height h of the guide sheet 30 and the conveyance speed, as shown in FIG. m changes. Based on the change in the height m, an enlargement of magnification and an error in density information occur at the rear end of the read original image.

(Refer 1st Example and FIGS. 5-8)
Therefore, in the first embodiment, an image read when the trailing edge of the document passes the reading position A through the guide sheet 30 is corrected. Such image correction is performed, for example, by the image processing unit 60 shown in FIG.

  By the way, the distance (height m) of the conveyed document from the reading glass 12 can be obtained in advance by an experiment using a CCD laser displacement meter, for example. FIG. 5 shows the height m (vertical axis) of the image surface of the document on the downstream side in the conveyance direction B from the edge of the guide sheet 30. The horizontal axis is the distance from the edge of the guide sheet 30. Here, the thickness (step) of the guide sheet 30 is set to 0.65 mm, and the document conveyance speed is set to 177 mm / s.

  The document reading position A is set according to the relationship between the amount of exposure on the document surface such as a decrease in the exposure amount by the guide sheet 30 and the space at the reading position A. In the first embodiment, the reading position A is set at a distance of 6 mm from the edge. The document surface height m at the reading position A is 0.7 mm.

  The trailing edge of the document falls on the reading glass 12 after passing through the edge of the guide sheet 30. At this time, the height m of the document surface is 0 mm, and the amount of change in the height m is 0.7 mm. Since the distance from the edge to the reading position A is 6 mm, the image is read at the position where the document comes into contact with the reading glass 12 (height m = 0 mm) in the area from the rear end of the read image to 6 mm inside. .

When the document surface height m decreases, the following phenomenon occurs.
(1) In the reading optical system 50, the optical path length for reading the document surface is shortened, and the image in the area C shown in FIG.
(2) Since the original surface approaches the lamp 53, the amount of light reflected from the original surface increases, and the image information changes to a bright density.

  As for (1), as shown in FIG. 7, since the distance l2 between the imaging lens 57 and the imaging unit (CCD) 58 is constant, when the document surface height m changes, the reading magnification is ( L2 / L1) = (L2 ′ / L1 ′) times. However, since the document conveyance speed does not change, only the magnification in the main scanning direction X changes.

  Therefore, in the region C shown in FIG. 6B, if the read image is corrected to 1 / (L2 / L1) times in the main scanning direction X, an appropriate read image that matches the original image can be obtained. For example, the image processing unit 60 can easily correct the image by processing such as thinning out pixels.

  Specifically, when L2 = 432.2 mm, m = 0.7 mm, and l2 = 101.7 mm, it is 1.0016 times, so that the read image data is 1 / 1.0016 times in the main scanning direction X. You can reduce it.

  Regarding (2), the change in the amount of reflected light when the document surface height m changes can be obtained in advance by experiments. FIG. 8 shows the relationship between the document surface height m determined in advance and the read density (gradation). When the original surface comes into contact with the reading glass 12 (height m = 0 mm), the image is read with a density of about 3%.

  Therefore, in the area C shown in FIG. 6B, if the density of the read image is corrected to 3% dark by the image processing unit 60, a read image having an appropriate density matching the original image can be obtained.

  Actually, the position at which the magnification change and the exposure amount change occur varies from machine to machine due to an attachment error of the guide sheet 30 or an attachment error of the document guide member. Therefore, if there is a “deviation” between the image correction start position (see arrow C ′ in FIG. 6B) and the position where the image starts to fluctuate, the image looks uncomfortable. Therefore, it is preferable to gradually change the degree of correction within a predetermined time in consideration of the variation due to the error at the image correction start position C ′. That is, when the correction level is gradually changed within a width of about 3 mm before and after the start position C ′, an image without a sense of incongruity due to variations can be obtained.

(Refer 2nd Example and FIGS. 9-11)
In the second embodiment, a sheet passing state in which the document passes through the reading position A through the guide sheet 30 is detected, and the relative position between the reading optical system 50 and the document is changed according to the detected sheet passing state. A good read image was obtained regardless of the height change of the surface.

  The timing at which the trailing edge of the document falls on the reading glass 12 after passing through the edge of the guide sheet 30 is to detect the trailing edge of the document upstream of the reading position A in the conveyance direction B as shown in FIG. This can be detected by installing the sensor SE1. That is, the timing t2 at which the trailing edge of the document passes through the edge of the guide sheet 30 is predicted from the timing t1 at which the trailing edge of the document is detected by the sensor SE1, and the reading optical system 50 will be described below at the timing t2. Move to.

  For example, the distance from the sensor SE1 to the reading position A is k0, the distance from the edge is k1, the distance from the edge to the reading position A is k2, and k0 = k1 + k2 = 30.9 mm, k2 = 6 mm, document conveyance speed v = 177 mm. In this case, the trailing edge of the document starts to fall through the edge after k1 / v = 0.14 s from the timing when it passes the sensor SE1. That is, the fluctuation of the document surface height m starts.

  Therefore, at the timing when the fluctuation of the document surface height m starts, the imaging unit (CCD) 58 or the imaging lens 57 is moved to a position where an appropriate magnification can be maintained. That is, as shown in FIG. 10, it is moved to a position where the relationship of L2: l2 = L1: l1 can be maintained.

  Specifically, when L2 = 432.2 mm, m = 0.7 mm, and l2 = 101.7 mm, the imaging unit (CCD) 58 is moved to the imaging lens 57 side by l2-l1 = 0.165 mm. Good. At this time, if the lamp 53 is moved away from the document surface and the amount of exposure light is reduced by about 3%, a read image having an appropriate density without distortion can be obtained.

  Since the moving amount of the image pickup unit (CCD) 58 and the lamp 53 is very small, an ultrasonic motor using a piezoelectric element that changes the displacement amount according to the input voltage as an actuator can be suitably used as the driving means. Ultrasonic motors have the advantages of small size, low noise, low vibration and high accuracy. As for the light quantity of the lamp 53, the same effect can be obtained by controlling the lighting voltage.

  Here, the control procedure in the second embodiment will be described with reference to FIG. First, when the sensor SE1 detects the trailing edge of the document (YES in step S1), a timer is started (step S2). Since the trailing edge of the document reaches the edge of the guide sheet 30 at the count value T1 of the timer, when the T1 is counted (YES in step S3), the ultrasonic motor is driven to drive the imaging unit (CCD) 58 and the lamp. 53 is moved to a predetermined position (step S4).

  When the reading of the document image is completed (YES in step S5, it can be determined from the count value of the timer that the trailing edge of the document has passed the reading position A), the ultrasonic motor is driven and the imaging unit (CCD) 58 and the lamp 53 are returned to their original positions (step S6).

(Refer to the third embodiment, FIGS. 12 and 13)
In the third embodiment, as in the second embodiment, a document passing state in which the document passes through the reading position A through the guide sheet 30 is detected, and the reading optical system 50 and the document are detected according to the detected sheet passing state. In order to obtain a good read image regardless of the height change of the document surface. In the second embodiment, the sheet passing state is detected based on the detection of the trailing edge of the document by the sensor SE1, but in the third embodiment, the height of the document conveyed at the reading position A is shown. The displacement sensor SE2 shown in FIG. Further, the positions of the image pickup unit (CCD) 58 and the lamp 53 are moved according to the height of the document surface, as in the second embodiment.

  It can be detected that the rear end of the original passes through the guide sheet 30 and the height m changes at the reading position A by installing a displacement sensor SE2 on the back side of the reading position A. The displacement sensor SE2 irradiates the document surface with laser light at the reading position A, and the output voltage changes based on the amount of received reflected light and the light reception angle, and can accurately detect the height m of the document surface. It is. Therefore, if the detected value m0 of the document surface height is equal to or greater than the predetermined threshold value m1 by the displacement sensor SE2, the image pickup unit (CCD) 58 is moved to a position where an appropriate magnification can be maintained, assuming that the document trailing edge starts to drop. At the same time, the lamp 53 is moved to a position where an appropriate amount of exposure light can be maintained.

  Here, the control means in the third embodiment will be described with reference to FIG. First, the height of the original surface at the reading position A is detected by the displacement sensor SE2 (step S11). When the detected value m0 exceeds the threshold value m1 (YES in step S12), the ultrasonic motor is driven to image the image pickup unit. The (CCD) 58 and the lamp 53 are moved to predetermined positions (step S13).

  When the reading of the document image is completed (YES in step S14, it can be determined that the trailing edge of the document has passed the reading position A by the displacement sensor SE2), the ultrasonic motor is driven and the imaging unit (CCD) is driven. 58 and the lamp 53 are returned to their original positions (step S15).

(Other examples)
The image reading apparatus according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

  In particular, the configuration of the mechanism for conveying the document and the reading optical system is arbitrary. In addition, regarding the reading glass, the example in which the reading glass is arranged in the horizontal direction has been described, but the reading glass may be arranged in an inclined manner. In this case, either the form in which the reading glass is inclined so as to gradually rise downstream with respect to the document conveyance direction or the form in which the reading glass is inclined so as to gradually fall downstream may be employed.

It is a schematic block diagram which shows one Example of the image reader which concerns on this invention. It is a principal part expanded sectional view of the image reading apparatus shown in FIG. It is explanatory drawing regarding the behavior of the original document which passes a reading position. FIG. 6 is an explanatory diagram illustrating a state in which a document trailing edge falls on a reading glass. 6 is a graph showing a change in document surface height with respect to a distance from an edge of a guide sheet in the first embodiment. It is explanatory drawing which shows the magnification state of the read image. FIG. 3 is an optical path diagram for explaining magnification correction of a read image in the first embodiment. It is a graph which shows the change of the reading density with respect to the document surface height. FIG. 10 is a cross-sectional view showing the arrangement of document trailing edge detection sensors in the second embodiment. In a 2nd Example, it is an optical path figure for demonstrating the magnification correction of the read image. In 2nd Example, it is a flowchart figure which shows an example of a control procedure. In 3rd Example, it is sectional drawing which shows arrangement | positioning of a displacement sensor. In 3rd Example, it is a flowchart figure which shows an example of a control procedure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image reader 12 ... Reading glass (transparent member)
20 ... Automatic document feeder 30 ... Document guide sheet (step forming member)
DESCRIPTION OF SYMBOLS 50 ... Reading optical system 60 ... Image processing part A ... Reading position D ... Original document SE1, SE2 ... Sensor

Claims (7)

A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Image correcting means for correcting an image read when the rear end of the document passes through the reading means via the step forming member;
An image reading apparatus comprising:   The image reading apparatus according to claim 1, wherein the image correcting unit corrects at least the magnification or density of the read image.   The image reading apparatus according to claim 1, wherein the image correction unit gradually performs correction of an image in a correction start area. A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Detecting means for detecting a paper passing state in which a document passes through the reading means through the step forming member;
Control means for changing the relative position between the reading means and the document according to the passing state of the document detected by the detection means;
An image reading apparatus comprising:   The image reading apparatus according to claim 4, further comprising a driving unit that is controlled by the control unit to change a relative position between the reading unit and the document.   6. The image reading apparatus according to claim 4, wherein the detection unit detects a timing at which a rear end of the document passes through the step forming member.   6. The image reading apparatus according to claim 4, wherein the detection unit detects a conveyance height of the document.

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