JP2013138322A - Image reader and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a band-like dark part occurs in an image of an original when the image of the original is continuously imaged after a shadow of a tip of the original is imaged.SOLUTION: In an image reading unit 10 of a sheet-through method, a guide roller 46 is arranged in a position facing a first reading glass 13, a second plane section 46d of the guide roller 46 is made to face the first reading glass 13 before an original is read, a shadow at an original tip by a linear light source 11, which occurs in the second plane section 46d, is detected in a plurality of positions parallel to a main scanning direction and a tilt amount of the original is calculated. When the original is read, the guide roller 46 is rotated, an arc face 46c is made to face the first reading glass 13, and the arc face 46c is allowed to abut on a rear face of the original passing an original read position to guide it so that a distance of an original face from the first reading glass 13 becomes stable.

Description

The present invention relates to an image reading apparatus including an automatic document conveyance unit and an image forming apparatus including the image reading apparatus.
About.

As an image reading device for reading an image of a document, a so-called sheet-through type image reading device that reads a document image passing through a document reading position while conveying the document by an automatic document transport unit (hereinafter referred to as “ADF unit”). There is.
Usually, at the document reading position, a strip-shaped reading glass extending in the main scanning direction (a direction orthogonal to the document transport direction) is arranged. Below the reading glass, a linear light source parallel to the main scanning direction is arranged, and light emitted from the linear light source is reflected by the original passing through the reading glass, and the reflected light is By receiving light by the sensor and converting it into an electric signal, an original image is read.

In such a sheet-through type image reading apparatus, the position of the leading edge of the document is accurately detected in order to determine the reading start timing by the line sensor or to detect the skew state (skew) of the document. It is desirable.
Therefore, for example, Patent Document 1 proposes a technique for determining the reading position of the document leading edge by detecting the shadow of the document leading edge that appears on the background member arranged facing the reading glass at the document reading position. .

FIG. 9A is a partial perspective view showing a configuration around the reading position of the image reading apparatus according to the above-mentioned document, and FIG. 9B is a cross section taken along the virtual plane Y in FIG. FIG.
In the image reading apparatus of Patent Document 1, as shown in FIG. 9A, a columnar background member that faces the reading glass 305 across the original conveyance path and extends parallel to the longitudinal direction of the reading glass 305. 301 is rotatably provided.

The background member 301 guides the original G so as to be a fixed distance from the reading glass 305.
On the other hand, annular grooves 303, 302, and 304 are formed at the center and both ends in the axial direction of the background member.
As shown in FIG. 9B, the image reading apparatus is disposed below the reading glass 305 and on the upstream side of the background member 301 in the conveyance direction of the original G, and passes through the reading glass 305 to the background member 301. It has a linear light source 308 that emits light and a line sensor 309 that receives the reflected light.

  In Patent Document 1, immediately before the reading of the document image is started, a shadow of the leading edge of the document G projected on the bottom of the grooves 302, 303, and 304 of the background member 301 is imaged, and the shadow image data is obtained. Based on this, the position of the leading edge of the original G and the skew amount are detected.

JP 2001-77986 A

However, when the read document image is examined in the configuration of Patent Document 1, the brightness of the portion corresponding to the groove portion of the image is low, and the low brightness portion extends in a band shape in the sub-scanning direction. Turned out to be.
This is because a part of the light irradiated to the original passes through the original and is reflected by the background member, and a part of the light again passes through the original and is received by the line sensor. When a groove is provided in the background member as shown above, the reflection surface of the transmitted light of the document is distant only by that portion, and the return rate of the reflected light to the document is changed to a background member (not touching the back surface of the document or This is considered to be due to a significant decrease compared to the adjacent portion.

In recent years, from the viewpoint of resource saving, the opportunity to use thin paper as a manuscript has increased, and in this case, the amount of light transmitted through the manuscript increases, so the difference in brightness due to the difference in the return rate of the reflected light. Becomes increasingly prominent.
The present invention solves such a problem, and an object of the present invention is to make it easy to detect the shadow of the leading edge of a document and to prevent a belt-like low-lightness portion from occurring in a read document image. An object of the present invention is to provide a reading apparatus and an image forming apparatus provided with the same.

  In order to achieve the above object, an image reading apparatus according to the present invention passes through a reading position on a strip-shaped reading glass and prints an image of a document conveyed in a direction perpendicular to the longitudinal direction of the reading glass. A sheet-through type image reading apparatus that reads with a line sensor, and is arranged in parallel with the longitudinal direction, and a surface facing the reading glass is brought into contact with a back surface of a conveyed document so as to be close to the reading glass. A first member that is guided to pass through, a guide member that can be selectively switched to a second surface that is further away from the reading glass than the first surface, and the reading glass in the guide member Switching means for switching the opposing surface between the first and second surfaces, and a parallel to the longitudinal direction on the opposite side of the guide member of the reading glass, and transporting the document through the reading glass direction The linear light source that irradiates light obliquely from the flow side toward the guide member, and the switching so that the second surface of the guide member faces the reading glass when the leading edge of the document approaches the reading position. And controlling the image sensor to detect the position of the leading edge of the document by reading the shadow of the leading edge of the document projected on the second surface with the line sensor. Control means for controlling the switching means so that the surface of the paper faces the reading glass, and for controlling the original image to be picked up by a line sensor.

In the image reading apparatus according to the present invention, when imaging the shadow of the leading edge of the document, the guide member has a first surface that faces the reading glass when the surface facing the reading glass is the second surface. The length of the shadow in the document transport direction is increased by the distance from the document as compared to when the image is, so that the shadow can be imaged with emphasis.
Thereafter, the guide member is moved to the first position, and an image of the document is captured in a state where the document is guided toward the reading glass.

Thus, the floating of the original from the reading glass is suppressed, and the gap between the original and the guide member is entirely reduced in the longitudinal direction of the reading glass. "Transmitted light amount") can also be suppressed as a whole.
Therefore, in the longitudinal direction, the amount of transmitted light varies because the gap between the document and the guide member is locally different, and the dark portion is generated more than the conventional configuration in which the read image has a band-like dark portion. Can be suppressed.

Further, the control means completes imaging of the shadow of the leading edge of the document until the leading edge of the document reaches the document reading position on the reading glass, and the first surface of the guide member It is desirable to control the switching means so as to face the glass.
The control means preferably converts the gradation of the image signal output from the line sensor so that the contrast of the captured image of the shadow at the leading edge of the document by the line sensor is enhanced.

Further, the guide member is a columnar rotating body that can rotate around an axis parallel to the longitudinal direction, and the first surface and the second surface are formed at different positions in the circumferential direction. The switching means is preferably configured to switch the surface facing the reading glass by rotating the rotating body.
Here, the guide member has a brush along the longitudinal direction that removes foreign matter on the surface of the reading glass as it rotates, at a position different from the first and second surfaces of the circumferential surface. It is desirable that they are provided in rows.

Further, it is preferable that the line sensor further includes a calculation unit that calculates an inclination with respect to the document conveyance direction based on a result of imaging the shadow of the document tip at a plurality of different positions in the longitudinal direction.
The present invention may be an image forming apparatus provided with the image reading apparatus.

1 is a schematic diagram illustrating a configuration of an image forming apparatus including an image reading apparatus according to an embodiment of the present invention. It is a schematic diagram for demonstrating the structure of the said image reading apparatus. It is a perspective view which shows the structure of the guide roller provided in the said image reading apparatus. (A)-(c) is a schematic diagram for demonstrating the arrangement | positioning position of the said guide roller, and the shadow state of the document front-end | tip part reflected on the said guide roller. It is a block diagram which shows the control part of the said image reading apparatus, and its control object. It is a flowchart which shows the execution procedure of the image reading process performed in the said control part. FIG. 6 is a diagram illustrating a state of γ correction used when capturing a shadow of a leading edge of a document and capturing a document image. (A) And (b) is a schematic diagram for demonstrating rotation operation | movement of the said guide roller. (A) is a fragmentary perspective view which shows the structure of the conventional image reading apparatus, (b) is the sectional drawing.

Hereinafter, an embodiment of an image forming apparatus provided with an image reading apparatus according to the present invention will be described by taking as an example a case where it is applied to an electrophotographic copying machine.
FIG. 1 is a schematic diagram for explaining the configuration of the copying machine according to the present embodiment.
The copying machine 1 includes an image reading unit A and an image forming unit B as shown in FIG.
The image reading unit A includes an image reading unit 10 provided with a strip-shaped first reading glass 13 and a plate-like second reading glass 16 having a larger area than the first reading glass 13 on the upper surface, In addition, an ADF unit 40 provided above the image reading unit 10 is provided.

In addition, every time the image reading unit A in the present embodiment reads an image of a document one by one, the image reading unit A detects the skew of the document and performs skew correction on the read image data.
The image reading unit 10 can selectively execute image reading in both the sheet-through method and the scanner movement method, and the ADF unit 40 is set on the document feed tray 40a when the sheet-through method is executed. The originals D are separated from the original bundle one by one, passed through the first reading glass 13, and then discharged onto the original discharge tray 40b.

Detailed configurations of the image reading unit 10 and the ADF unit 40 will be described later.
On the other hand, the image forming unit B forms a toner image based on the image data read by the image reading unit A, and applies it to the recording sheet S supplied from the paper supply unit 30 provided below the image forming unit B. The toner image is transferred and fixed.
Hereinafter, the image forming unit B will be described.

<Image forming unit>
As shown in FIG. 1, the image forming unit B is moved horizontally in the intermediate transfer belt 22 below the intermediate transfer belt 22 and the intermediate transfer belt 22 driven around in the direction of arrow X by a drive source (not shown). The process units 23Y, 23M, 23C, and 23K are provided along the portion.

The process units 23Y, 23M, 23C, and 23K form toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Since the process units 23Y to 23K have the same configuration except for the color of the toner to be filled, only the configuration of the process unit 23K will be described as a representative.
The process unit 23K has a charging unit 25K, an exposure unit 26K, and a developing unit 27K around the photosensitive drum 24K.

The outer circumferential surface of the photosensitive drum 24K is uniformly charged by the charger 25K.
The exposure unit 26K modulates and drives the laser light source based on the image data acquired by the image reading unit A, and exposes and scans the surface of the charged photosensitive drum 24K. Thereby, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 24K.
The electrostatic latent image is developed with K color toner by the developing device 27K.

Further, a primary transfer roller 28K is provided above the photosensitive drum 24K at a position sandwiching the intermediate transfer belt 22.
The primary transfer roller 28K forms an electric field with the photosensitive drum 24K. As a result, the toner image on the photosensitive drum 24K is transferred onto the intermediate transfer belt 22 by the action of the electric field.

  Similarly, primary transfer rollers 28Y, 28M, and 28C are respectively provided above the other process units 23Y, 23M, and 23C with the intermediate transfer belt 22 interposed therebetween. The Y, M, and C color toner images formed on the respective photosensitive drums are transferred onto the intermediate transfer belt 22. A full-color image is formed by transferring the toner images of each color of Y, M, C, and K at the same position on the intermediate transfer belt 22 in an overlapping manner.

The toner image transferred onto the intermediate transfer belt 22 is transported to a secondary transfer position facing the secondary transfer roller 21 by the rotating operation of the intermediate transfer belt 22.
A plurality of paper feed cassettes 31 are provided in the paper feed unit 30 provided below the image forming unit B.
When the toner image is formed in the image forming unit B, the paper feeding unit 30 feeds the recording sheets S one by one from one of the paper feeding cassettes 31 specified by the user via an operation panel (not shown), and performs secondary processing. Transport to transfer position.

The secondary transfer roller 21 electrostatically transfers the toner image on the intermediate transfer belt 22 onto the recording sheet S.
The toner remaining on the intermediate transfer belt 22 without being transferred to the recording sheet S is removed by the cleaner 20b.
A fixing device 29 is provided above the secondary transfer position, and the recording sheet S that has passed the secondary transfer position is conveyed to the fixing device 29.

The recording sheet S on which the toner image is transferred is heated and pressed by the fixing device 29. As a result, the toner image transferred to the recording sheet S is fixed on the recording sheet S.
Then, the recording sheet S on which the toner image is fixed is discharged onto the recording sheet tray 20a.
Next, a detailed configuration of the image reading unit 10 in the image reading unit A will be described.

<Image Reading Unit of Image Reading Device>
FIG. 2 is a schematic diagram for explaining the configuration of the image reading unit A.
The image reading unit 10 includes an optical system 10a that reads an image in a housing 10b, a reading control unit 17 that executes predetermined processing on the read image data, and the like.
Here, on the upper surface of the housing 10b, as described above, the strip-shaped first reading glass 13 and the first reading glass 13 are provided so as to cover almost the entire upper surface. A flat plate-like second reading glass 16 is provided.

The optical system 10a includes a first slider 18 and a second slider 19, a reduction lens 15e, a line sensor 12, and the like.
The line sensor 12 is formed by mounting a CCD (Charge Coupled Device) having a plurality of photoelectric conversion elements arranged in a straight line on a substrate.
The linear light source 11 and the first mirror 15b are mounted on the first slider 18, and are slid in the direction of arrow G by a drive motor (not shown).

On the second slider 19, the second mirror 15c and the third mirror 15d are installed at an angle of 90 degrees, and are the same at a speed that is 1/2 that of the first slider 18 by wire driving using a moving pulley. Configured to move in the direction.
The linear light source 11 irradiates light over the entire width direction of the document (in the sheet-through type reading, the entire length of the first reading glass 13 in the longitudinal direction).

As the linear light source 11, a rare gas linear light source such as a fluorescent lamp or a xenon lamp, an outer electrode linear light source, an LED, or the like is usually used.
When reading an image of a document placed manually on the second reading glass 16 (scan movement method), the first slider 18 slides in the direction of the arrow G while the second light source 11 reads the second reading. After irradiating light toward the document placed on the glass 16, it is turned off and returned to the home position.

  As described above, the second slider 19 provided with the second mirror 15c and the third mirror 15d is configured to slide in the same direction at half the moving speed of the first slider 18, so that the document An image of a document placed on the second reading glass 16 can be read by the line sensor 12 after being reduced and projected by the reduction lens 15e, while keeping the optical distance from the surface to the reduction lens 15e constant. it can.

  On the other hand, when the image of the document D conveyed on the first reading glass 13 by the ADF unit 40 is read (sheet through method), the first slider 18 has the linear light source 11 as shown in FIG. The first reading glass 13 is maintained at a position (hereinafter referred to as a “sheet through position”) where light can be emitted toward the document from a position slightly upstream from a position just below the center in the document conveyance direction.

The line sensor 12 detects reflected light from the incident original, generates an image signal corresponding to the amount of received light, and outputs the image signal to the reading control unit 17.
The reading control unit 17 generates image data corresponding to the document image based on the signal output from the line sensor 12.
<ADF unit of image reading apparatus>
As shown in FIG. 2, the ADF unit 40 has a document feed tray 40a on which a document D from which an image is read is placed.

The document feed tray 40a is provided with a document sensor 40c that detects the size of the placed document D in the transport direction.
The document D placed on the document feed tray 40a is lifted by the lift plate 40d and brought into contact with the pickup roller 42, whereby the document D is moved from the document feed tray 40a into the transport path 49 (indicated by an arrow E). (In the direction shown)

The document D transported in the transport path 49 passes between the feeding roller pair 43 including the feeding roller 43a and the flange roller 43b to which the torque limiter is attached, so that only one sheet is Then, it is conveyed to the first registration roller pair 44b.
The pickup roller 42 and the feeding roller 43a are driven by the same drive source (not shown), for example, via a timing belt.

Further, a document detection sensor S1 for detecting a document to be conveyed is provided on the downstream side of the first registration roller pair 44b in the document conveyance direction.
The first registration roller pair 44b adjusts the posture of the single document D to be transported so as not to tilt as much as possible with respect to the transport direction, and transports it to the pre-reading roller pair 45 disposed below.

The pre-reading roller pair 45 is arranged on the upstream side in the document conveyance direction (the same direction as the sliding direction of the first slider 18 indicated by the arrow G) along the upper surface of the first reading glass 13. The first registration roller pair 44b is rotationally driven by a drive motor (not shown).
The document D sent out from the first registration roller pair 44b is sent through the pre-reading roller pair 45 so as to pass over the first reading glass 13 at a predetermined timing.

When the document D passes over the first reading glass 13, images of the lower surface (first surface) of the document D facing the first reading glass 13 are the first mirror 15 b, the second mirror 15 c, It is read by the line sensor 12 through the three mirrors 15d and the reduction lens 15e.
In the image reading unit A in the present embodiment, a long guide roller 46 extending in the main scanning direction is provided at a position facing the surface of the first reading glass 13 across the conveyance path of the document D.

  The guide roller 46 is used as a background of the transported document for detecting the tilt of the transported document D when reading the image of the document D, and the document surface of the document D is first read when the document is read. It is also used for cleaning the surface of the first reading glass 13 when the original D is not conveyed and is guided so as to pass through the glass 13 while maintaining a predetermined distance set in advance. .

The detailed configuration of the guide roller 46 will be described later.
The document D that has passed over the first reading glass 13 passes through the post-reading roller pair 47b, and is then discharged onto the document discharge tray 40b by the document discharge roller pair 48 ahead.
The pre-reading roller pair 45, the post-reading roller pair 47b, and the document discharge roller pair 48 are rotationally driven by the same drive source (not shown), for example, and the document D is moved on the first reading glass 13 at a predetermined speed. Let it pass.

The document D is transported so that the center in the width direction orthogonal to the transport direction coincides with the center in the longitudinal direction of the first reading glass 13 (center passing).
In the present embodiment, when the document passes over the surface of the first reading glass 13, the shadow of the leading edge of the document is projected onto the guide roller 46, and this shadow is imaged by the image reading unit 10. The image of the original is taken.

The shadow imaging result is used to perform skew correction on the image data of the document read subsequent to the shadow imaging.
Hereinafter, the configuration of the guide roller 46 will be described.
<Background material>
FIG. 3 is a perspective view of the guide roller 46. For convenience, the central portion in the longitudinal direction is not shown.

The guide roller 46 includes a main body portion 46a, a plurality of brush portions 46f planted in rows in the longitudinal direction of a part of the peripheral surface of the main body portion 46a, and a support shaft portion 46e protruding from both end portions of the main body portion 46a. Become.
As shown in FIG. 3, the main body 46a has a cylindrical body that is parallel to the axial center line G0 and intersects with each other at a predetermined angle (in this embodiment, 90 [°]) (however, The first plane portion 46b and the second plane portion 46d, and an arc surface 46c having a radius r1 of about 7 mm, which is viewed from the axial direction. The central angle θ1 of the arc centered on the axis G0 is set to be about 150 [°].

The length of the main body 46a in the axial direction is slightly longer than the total length in the longitudinal direction of the first reading glass 13, and the plurality of brush parts 46f are arranged in a row in the longitudinal direction on the first flat surface 46b. It is flocked.
The length of the brush portion 46f is set so that the tip end portion of the brush portion 46f is in sliding contact with the upper surface of the first reading glass 13 by the rotation of the main body portion 46a, whereby the main body portion 46a is rotationally driven. Accordingly, foreign matters such as paper dust attached on the first reading glass 13 are removed by the tip of the brush portion 46f.

Further, the second flat portion 46d and the circular arc surface 46c are white or a color having lightness close to white.
In the guide roller 46, each support shaft portion 46e rotates to a side plate (not shown) constituting the housing of the ADF unit 40 so that the axis G0 is in a horizontal state parallel to the first reading glass 13. Further, one of them is connected to a background member drive source (not shown) capable of controlling the rotation angle, such as a pulse motor, and is driven to rotate.

Prior to reading the document, when correcting shading and reading the document image, the rotation angle is set so that the arc surface 46C faces the first reading glass 13, and the skew of the document is detected. In doing so, the rotation angle is set so that the second flat portion 46d faces the first reading glass 13.
In the present embodiment, the background member drive source (not shown) may be a servo motor with a built-in angle detection mechanism such as a rotary encoder.

The second flat surface portion 46d is used to detect the inclination of the original by projecting the shadow of the front end of the original.
4A to 4C are schematic diagrams for explaining the shadow state of the leading end of the document projected onto the second flat surface portion 46d of the guide roller 46. FIG.
As shown in FIG. 4A, the guide roller 46 is stopped at a rotational position where the second flat portion 46d and the surface of the first reading glass 13 are in parallel.

At this time, the stop position of the first slider 18 at the time of sheet through is set so that the image reading position C is almost the center of the second flat surface portion 46d in the document transport direction.
At this time, the distance between the second flat surface portion 46d and the first reading glass 13 is set to be a predetermined distance D1, and in this embodiment, the value of the distance D1 is set to 4 [mm], for example. It is said.

  Since the linear light source 11 is arranged upstream of the reading position C in the document conveying direction, the shadow is projected onto the second flat portion 46d immediately before the leading edge of the document reaches the reading position C. . Therefore, by reading this shadow (hereinafter referred to as “leading edge shadow”) with the line sensor 12, it is possible to detect the positions of the leading edge of the document at a plurality of points in the main scanning direction. It can be easily detected.

If the document is skewed, a shadow starts to be projected first on one side near both ends of the second flat portion 46d.
4B and 4C, the location where the tip shadow starts to be projected is surrounded by a two-dot chain line, and the points from P1 to Pn are the line sensors 12 in the case of imaging the tip shadow. Indicates the reading position.

When the tip of the tip shadow reaches any of the reading points P1 to Pn, the light receiving intensity of the image sensor of the line sensor 12 corresponding to one of the light receiving intensity reading points rapidly decreases. Can be detected.
FIG. 4C shows a state where the shadow tip has reached the reading point P3.
Here, at time t0, the shadow tip reaches the reading point P3, at time t1, the shadow tip reaches the reading point P4, and at time t2, the shadow tip reaches the reading point P5. When the distance is reached, the distance between the reading points P3 and P5 in the direction orthogonal to the document conveyance direction is L1, the time from time t0 to time t2 is Δt, and the document conveyance speed is V. θ3 is obtained by the following equation.

<Formula 1> θ2 = Tan ((V × Δt) / L1)
<Reading Control Unit of Image Reading Device>
FIG. 5 is a block diagram illustrating a configuration of a control system of the image reading unit A.
The reading control unit 17 includes a CPU, a clock, a ROM, a RAM, an EEPROM, and the like. The reading control unit 17 communicates with a control unit (not shown) in the image forming unit B, conveys a document by the ADF unit 40, and the image reading unit 10. Controls reading operation by.

That is, the reading control unit 17 executes document reading processing for reading an image of a document in the image reading unit 10 and detects a skew of the document. Then, based on the detection result of the skew of the document, a known skew correction is performed on the image data of the document, and then the image data is output in the image forming unit B.
Further, the reading control unit 17 includes two rollers, a pickup roller 42 and a feeding roller 43a, a registration roller pair 44b, a pre-reading roller pair 45, a post-reading roller pair 47b, and a document discharge roller pair 48 in the ADF unit 40. The three roller pairs are connected to the document conveying drive sources M1, M2 and M3 for driving the respective roller pairs, and also connected to the background member drive unit M4 for driving the guide roller 46 to rotate. ing.

<Control contents in document reading process>
FIG. 6 is a flowchart showing the control content of the document reading process executed by the reading control unit 17.
When the user places a bundle of documents on the document feed tray 40a of the ADF unit 40 and presses a start key on an operation panel (not shown), the reading control unit 17 is controlled via the control unit in the image forming unit A. An instruction to start reading a document is transmitted to.

  When the reading control unit 17 receives a document reading instruction from the control unit in the printer unit B (step S <b> 101), the rotation position of the guide roller 46 is set so that the second flat surface portion 46 d faces the first reading glass 13. (Initial rotation position) is set (step S102), and the document D placed on the document feed tray 40a is fed out onto the document transport path by the pickup roller 42, and the other rollers are also rotated at a predetermined timing. Is started (step S103).

Then, the reading control unit 17 turns on the linear light source 11 and activates the line sensor 12 to start detecting the leading edge of the document (step S104).
This detection is performed by repeatedly referring to the signal output from the image sensor of the pixel corresponding to the detection points P1 to Pn in order from P1 among the signals output from the line sensor 12 in a predetermined cycle.

As the document progresses, the shadow at the leading edge is projected onto the second flat portion 46d, and the shadow is eventually detected by the line sensor 12, but the surface on which the shadow is projected is originally set. Since the distance from the position of the original surface is farther upward, the outline of the shadow imaged by the line sensor 12 may be slightly blurred.
Therefore, the reading control unit 17 has a large γ correction coefficient value as indicated by L2 in FIG. 7 as a γ curve used for gradation conversion processing of the read image data when starting the detection of the leading end of the document in step S104. (See FIG. 7), the contrast of the image is enhanced, and the detection accuracy of the edge portion of the shadow corresponding to the leading edge of the document is improved.

  After the start of detection, it is determined whether or not a shadow at the leading edge of the document is detected at any of the detection points P1 to Pn (step S105). If it is detected (step S105: YES), the time is measured from that point. After a predetermined time has elapsed (step S106: YES), the document skew amount is calculated as described above based on the detection data detected during this time (step S107), and the guide roller 46 is quickly rotated. Thus, the arcuate surface 49c is made to face the first reading glass 13 (step S108: see FIG. 8A).

  Here, the distance D2 between the surface of the arcuate surface 49c and the first reading glass 13 is smaller than the first flat surface portion 46d (in the present embodiment, 1.6 [mm]), and the document Since the back surface of the guide is guided in such a way that it is pressed slightly toward the first reading glass 13, the optical path length from the document surface to the reduction lens 15e is stabilized at a predetermined value determined in advance by design when reading the image of the document. Therefore, a clear image can be read by the line sensor 12.

  The “predetermined time” in step S106 is at least the guide roller from the time (t1) when the detected portion actually reaches the document reading position C after the shadow at the specific position of the leading edge of the document is detected. 46 is a time (t3 ≦ t1−t2) obtained by subtracting the time (t2) required to rotate the circular arc surface so that the arc surface faces the line sensor 12, and at least 2 in the maximum skew amount that can normally occur. A value that is longer than the time required to detect the shadow at the leading edge of the document at the detected points is determined and set in advance.

As can be seen from FIG. 4A, when the leading edge of the document G reaches the position E, the shadow projected on the second flat surface is detected by the line sensor 12, and when the leading edge reaches the position F, the leading edge is detected by the line sensor 12. Therefore, the time t1 is a value obtained by dividing the distances E to F by the document conveyance speed V.
Therefore, if the distance between the linear light source 11 and the reading position C in the document conveyance direction is a fixed value, the time t1 is increased as the distance D1 between the second flat portion 46d and the first reading glass 13 is increased. Within that time, the document skew amount can be detected and the guide roller 46 can be switched to the arcuate surface 49c with certainty.

Further, the calculation of the skew amount in step S107 is calculated from the difference in detection time at the detection points where the distance between the two points is as far as possible out of the detection data at the two or more detection points acquired within the predetermined time. Is desirable. In addition, it is good also as an average value of the skew amount obtained from the detection data of a plurality of sets of two points.
Thereafter, document reading is started, and the image signal read by the line sensor 12 is subjected to known data processing and then stored in the image memory (step S109). At this time, the reading control unit 17 performs γ correction by returning to the normal γ correction coefficient value as indicated by L 1 in FIG. 7 read by the line sensor 12.

Subsequently, the reading control unit 17 determines whether or not the trailing edge of the document has passed the document reading position on the first reading glass 13 (step S110).
This determination is made based on, for example, whether or not a predetermined time has elapsed since the output of the document detection sensor S1 provided on the upstream side of the pair of pre-reading rollers 45 in the document transport direction is switched from ON to OFF. Here, the predetermined time is a time required for the document to be conveyed from the detection position of the document detection sensor S1 to the document reading position.

The document reading is continued until the trailing edge of the document passes the document reading position on the first reading glass 13 (step S110: NO), and when it passes (step S110: YES), the document reading is finished (step S110: YES). Step S111).
Subsequently, the reading control unit 17 rotates the guide roller 46, and as shown in FIG. 8B, the surface of the first reading glass 13 is cleaned by the brush unit 46f to clean foreign matters such as paper dust. (Step S112).

  As described above, when the guide roller 46 rotates once along the document conveyance direction, the portion facing the first reading glass 13 is the second flat surface portion 46d → the circular arc surface 46c → the brush portion 46f → the second portion. The flat portions 46d are arranged in this order, so that only the guide roller 46 rotates once, the leading edge shadow is imaged, the document is guided, and the surface of the first reading glass 13 is smoothly cleaned. Be able to.

Then, the image data of the read original is subjected to skew correction and output to the control unit of the image forming unit (step S113).
This skew correction is performed, for example, by shifting the image data once stored in the page memory of the image memory to another page memory by shifting the memory address so as to eliminate the skew amount obtained in step S107.

  However, when data for one line read from the line sensor 12 is first stored in the page memory, it may be stored while shifting the memory address while correcting skew, or the image reading unit does not perform skew correction. The read image data and the data of the skew amount for each page may be transmitted to the control unit of the image forming unit B and the skew correction may be performed by the control unit of the image forming unit B.

If the most recently transported document is the final document (step S113: YES), the image reading process is terminated. If the document is not the final document, the processes in and after step S102 are repeatedly executed to obtain the next document. The skew amount is detected and the original is read.
Here, whether or not the most recently transported document is the final document is determined, for example, if the document sensor (not shown) provided on the upstream side of the registration roller pair 44b in the document transport direction has not detected the document. The control unit 17 determines that the most recently transported document is the final document, and determines that the document is not the final document if the document sensor detects the document.

  As described above, when detecting the shadow of the leading edge of the document, since the guide roller 46 is located away from the first reading glass 13, the distance between the guide roller 46 and the document increases. Since the length of the shadow in the document transport direction increases, it is possible to increase the time from the detection of the shadow until the leading edge of the document actually reaches the reading position. During this time, the skew amount is detected and the guide roller 46 is rotated. be able to.

Further, in the present embodiment, since the shadow can be projected over the entire length of the second flat surface portion 46d, various sizes can be used as compared with the configuration in which the conventional shadow detection is limited to the groove portion. Can be used for any manuscript.
For example, when a document having a narrow width (the length in a direction perpendicular to the document conveyance direction is short) is to be read, in the conventional image reading apparatus, the width of the document is larger than the pitch of the grooves arranged in the background member. If it is narrow, shadows cannot be detected at two or more grooves, and skew cannot be detected, but this embodiment can be flexibly handled by increasing the value of the detection point Pn.

Further, in the conventional image reading apparatus, the groove portion of the background member shows through and there is a problem in the image quality of the read image. However, the guide roller 46 in the present embodiment is flat in the main scanning direction and has a step. Therefore, such show-through (low brightness part) does not occur.
As described above, the arcuate surface 49c of the line sensor 12 is white and is also used as a white reference plate in known shading correction. The timing for acquiring the correction coefficient in the shading correction can be set at the time of turning on the power to the image reading apparatus and / or at the start of the first reading operation in each image reading job.

In the latter case, in the flowchart of FIG. 6, the guide roller 46 is rotated immediately after step S101 so that the circular arc surface 49c faces the first reading glass 13, the linear light source 11 is turned on, and correction for shading correction is performed. A coefficient is acquired, and after reading in step S109, the data for each line is subjected to shading correction based on the correction coefficient.
<Modification>
(1) In the above embodiment, the ADF unit 40 is configured to automatically convey an image on the document surface side so that the image reading unit 10 can read the image. Image readers that simultaneously read the front and back surfaces have appeared.

In such an image reading apparatus, as shown by a two-dot chain line in FIG. 2, a document back side reading unit 141 is provided on the document transport path of the ADF unit 40, thereby reading an image on the back side of the document.
Here, the document back surface reading unit 141 is an array sensor or the like in which a plurality of image sensors are arranged in a direction orthogonal to the document conveyance direction. The document back surface reading unit 141 extends in the arrangement direction of the image sensors and includes the back surface of the document. A linear light source (not shown) is provided slightly upstream in the document transport direction from the side image reading position.

In the case of such an image reading apparatus, since the distance from the first reading glass 13 to the reading position of the document back surface reading unit 141 is short, the skew amount is unlikely to change during this period. The skew correction of the image on the back side of the document may be performed using the skew amount obtained by detecting the projected shadow.
Of course, there are two points in FIG. 2 when there is a high possibility that the skew amount will change due to an increase in the distance from the first reading glass 13 to the reading position of the document back side reading unit 141 by design. As indicated by the chain line, a guide roller 142 similar to the guide roller 46 is provided at a position facing the document back side reading unit 141 across the document conveyance path, and the document skew is detected again, and the document is based on this. The skew correction of the back side image may be executed.

(2) In the above embodiment, the guide roller 46 is rotated and moved when the document is read to guide the back side of the document by the arc surface 46c closer to the first reading glass 13, and the guide roller is detected when the leading end of the document is detected. 46 is rotated so that the second flat surface portion 46d farther from the first reading glass 13 is opposed to the arc surface 46c.
As a result, the shadow of the leading edge of the document can be projected greatly, the amount of skew can be acquired at an early stage, and the surface of the guide roller 46 that faces the first reading glass 13 before the leading edge of the document reaches the reading position. A sufficient time can be secured for switching from the two flat surface portions 46d to the circular arc surface 46c.

The configuration for switching the distance between the surfaces facing the first reading glass 13 in this way is not limited to the rotational movement of the guide roller 46, but a configuration for sliding and switching between surfaces that are near and far away, or one A mechanism for moving the surface close to or away from the first reading glass 13 may be used.
(3) In the above embodiment, the reading control unit 17 is provided in the image reading unit 10, but the present invention is not limited to this. For example, a configuration in which the control system provided in the image forming unit B also serves as the reading control unit 17 may be employed.

(4) In the above embodiment, the leading edge shadow is detected for the purpose of correcting the skew of the document, but the present invention is not limited to this.
For example, the amount of deviation Z in the document transport direction between the shadow reaching the image reading position and the document leading edge is obtained from the relative positional relationship between the linear light source 11, the document, and the second flat surface portion 46d. Since the position of the leading edge of the document can also be detected by imaging, it is used only for detecting the leading edge shadow, detecting the leading edge position of the document, and determining the image reading start timing. It doesn't matter.

(5) In the embodiment, the second flat portion 46d is white or a color having lightness close to white. However, the present invention is not limited to this.
For example, the second flat surface portion 46d only needs to have a color having a brightness that can recognize the tip shadow projected on the second flat surface portion 46d.
Further, in order to detect the inclination of the tip shadow, the member that projects the tip shadow is preferably a plane such as the second flat portion 46d. Since it is possible to detect, the surface of the member on which the tip shadow is projected may be a surface other than a plane in some cases.

(6) In the above embodiment, the copying machine has been described as an image forming apparatus provided with an image reading device. However, the present invention is not limited to this, and the present invention can also be applied to an image forming apparatus such as a copying machine or a facsimile. Further, it may be a device dedicated to image reading having only an image reading function.
The contents of the above embodiment and the above modification may be combined as much as possible.

  INDUSTRIAL APPLICABILITY The present invention is suitable as a technique for picking up a leading edge shadow and detecting the leading edge position and skew in an image reading apparatus that reads an image of a document passing through a document reading position.

DESCRIPTION OF SYMBOLS 1 Copier 10 Image reading unit 11 Linear light source 12 Line sensor 13 First reading glass 15e Reduction lens 18 First slider 19 Second slider 22 Intermediate transfer belt 23Y, 23M, 23C, 23K Process unit 40 ADF unit 40c Document sensor 42 Pickup roller 44b Registration roller pair 43 Feeding roller pair 45 Pre-reading roller pair 46 Guide roller 46a Main body part 46b First plane part 46c Arc surface 46d Second plane part

Claims (7)

A sheet-through type image reading apparatus that reads an image of a document that passes through a reading position in a belt-shaped reading glass and is conveyed in a direction perpendicular to the longitudinal direction of the reading glass with a line sensor,
A first surface that is arranged in parallel to the longitudinal direction and that is opposed to the reading glass and guides the surface to be in contact with the back surface of the document being conveyed so as to pass near the reading glass; A guide member selectively switchable to a second surface farther from the reading glass than the surface;
Switching means for switching the facing surface of the guide member to the reading glass between the first and second surfaces;
A linear shape that is disposed in parallel to the longitudinal direction on the opposite side of the reading glass from the guide member, and irradiates light obliquely from the upstream side in the document transport direction toward the guide member through the reading glass. A light source;
When the leading edge of the document approaches the reading position, the switching means is controlled so that the second surface of the guide member faces the reading glass, and the shadow of the leading edge of the document projected on the second surface is removed. Control is performed so that the position of the leading edge of the document is detected by taking an image with the line sensor, and when the document image is read, the switching means is controlled so that the first surface of the guide member faces the reading glass. An image reading apparatus comprising: control means for controlling an image to be picked up by a line sensor. The control means completes the imaging of the shadow of the leading edge of the document until the leading edge of the document reaches the document reading position on the reading glass, and the first surface of the guide member is formed on the reading glass. The image reading apparatus according to claim 1, wherein the switching unit is controlled so as to face each other.   2. The control unit according to claim 1, wherein the control unit converts a gradation of an image signal output from the line sensor so that a contrast of a captured image of a shadow at the leading edge of the document by the line sensor is enhanced. Image reading apparatus. The guide member is a cylindrical rotating body that is rotatable around an axis parallel to the longitudinal direction, and the first surface and the second surface are formed at different positions in the circumferential direction,
The image reading apparatus according to any one of claims 1 to 3, wherein the switching unit is configured to switch a surface facing the reading glass by rotating the rotating body. In the guide member, brushes for removing foreign substances on the surface of the reading glass as it rotates are arranged in rows along the longitudinal direction at positions different from the first and second surfaces on the circumferential surface. The image reading apparatus according to claim 4, wherein the image reading apparatus is provided. 6. The calculating unit according to claim 1, further comprising: a calculating unit configured to calculate an inclination of the line sensor with respect to a document transport direction based on imaging results of a shadow of a document tip at a plurality of different positions in the longitudinal direction. The image reading apparatus described in 1.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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