JP2011259164A - Image reading device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading device capable of improving reading image quality in the composition where a contact image sensor (CIS) reads a surface of an original under conveyance.SOLUTION: When the tip part of an original D guided by a conveyance guide 55 passes through a detection position X2 of a distance measuring sensor 51, the distance measuring sensor 51 detects a distance H to the original D to obtain a height Hα from a dustproof glass 50b of a CIS 50 for the original D based on the distance of the detected distance H. If the obtained Hα is not within an allowed tolerance range of the focal position in the CIS 50, the conveyance course of the original D is displaced by moving the conveyance guide 55 in the direction shown by an arrow B so that the obtained Hα can be within the allowed tolerance range.

Description

  The present invention relates to a sheet-through image reading apparatus that reads a document being conveyed while passing through a reading position of a contact image sensor, and an image forming apparatus including the same, and more particularly to a technique for improving read image quality.

An image reading apparatus used for a copying machine or the like is configured to display an image of a document while passing a document conveyed on a conveyance path by an automatic document conveyance device through a reading position of a contact image sensor (CIS). There is a sheet-through method to read.
In a contact image sensor, a light emitting element, a lens, and a light receiving element are usually arranged inside a casing that is open on the side facing the document conveyance path, and the opening of the casing is closed with translucent dust-proof glass. Consists of. When scanning a document being transported with a contact image sensor, the document surface is irradiated with light emitted from the light emitting element through the dust glass when the document passes over the dust glass of the contact image sensor. The reflected image light from the document surface is received by a light receiving element through a dust-proof glass and a lens and subjected to photoelectric conversion to obtain image information of the document.

  In the case of the sheet-through method, when a document is transported while being in close contact with the dust-proof glass surface of the contact image sensor, foreign matter such as paper dust from the document remains on the dust-proof glass surface of the contact image sensor, and the foreign material remains in the image. Since it appears as streak noise and the read image quality is deteriorated, it is often the case that the document is conveyed while being floated from the dust-proof glass surface.

JP 2008-283388 A JP 2008-205726 A

However, if the original is lifted from the surface of the dust-proof glass and transported, conditions such as the strength of the original will change depending on the type of document used (thickness, material, etc.) and the surrounding environment (temperature and humidity). As a result, the document transport path varies in the height direction from the dust-proof glass from time to time, and the height of the document surface from the dust-proof glass of the contact image sensor is likely to vary.
If the variation in the height falls within the tolerance range of the focal position in the contact image sensor, the read image quality does not deteriorate.

However, the contact-type image sensor has a shallow depth of focus due to the miniaturization, and the allowable tolerance range in reading is narrow, so the amount of deviation from the focal position of the document surface may not fall within the tolerance range. There is a risk of reducing the read image quality.
The present invention has been made in view of the above problems, and an image reading apparatus capable of improving reading image quality in a configuration in which a document surface of a document being conveyed is read by a contact image sensor, and the image reading apparatus An object of the present invention is to provide an image forming apparatus including the above.

  In order to achieve the above object, an image reading apparatus according to the present invention is a sheet-through type image reading apparatus that reads a document being conveyed while passing a reading position of a contact image sensor, and the document being conveyed is A guide member for guiding the image sensor to a reading position of the image sensor in a floating state, detection means for detecting the height of the document guided by the guide member from the image sensor, and the image sensor And the guide member relative to the height direction and a moving mechanism for moving the guide member in a direction away from the height direction, and a height of the document from the image sensor based on a detection value by the detection means. The image sensor and the guide member are moved relative to each other so that they are within the tolerance range of the focus position of the sensor. Characterized in that it comprises a movement control means for.

  The detection means is disposed at a position facing the document conveyance path, and detects the distance to the leading edge of the document immediately before the leading edge of the document being conveyed reaches the reading position of the image sensor. A detection sensor that detects the height based on a distance to the leading edge of the document detected by the detection sensor, and the movement control means detects the leading edge of the document by the detection sensor. Until the leading edge of the document reaches the reading position of the image sensor.

Here, the detection sensor detects a distance from the detection sensor at a central portion in the width direction of the document conveyance path in the leading end portion of the document.
Further, the moving mechanism is configured such that each of both ends of the guide member in the width direction of the document conveyance path can move in the height direction with respect to the image sensor with one side serving as a fulcrum. The detection means is a position facing the document conveyance path, and is arranged at each of one end side and the other end side across the width direction center of the document conveyance path, and the leading edge of the document being conveyed Comprises a pair of detection sensors for detecting the distance to the leading edge of the document at a position immediately before reaching the reading position of the image sensor, and based on the detection values detected by the pair of detection sensors, The height at each of one end side and the other end side in the width direction of the path is detected, and the movement control means is based on the height at one end side in the width direction of the document transport path detected by the detection means. The one end side of the guide member is moved in the height direction so that the height of the document from the image sensor is within the tolerance range on the one end side, and is detected by the detecting means. Based on the height of the other end side in the width direction of the document transport path, the guide member is arranged such that the height of the document from the image sensor is within the allowable tolerance on the other end side. The other end side is moved in the height direction.

  Here, a plurality of pairs of detection sensors including the first and second groups are arranged, and the pair of detection sensors belonging to the first group sandwiches the center in the width direction of the document conveyance path. And detecting the distance to the leading edge of the document at the first and second positions respectively separated from the center by a first distance, and the pair of detection sensors belonging to the second group are configured to detect the width of the document transport path. The movement control means detects the distance to the leading edge of the document at third and fourth positions that are separated from the center by a second distance that is longer than the first distance. When the document width of the document to be printed is W, the interval between the first position and the second position in the width direction is W1, and the interval between the third position and the fourth position in the width direction is W2. When W1 <W ≦ W2, it belongs to the first group When the detection result of the pair of detection sensors is used, and W2 <W, the movement in the height direction is executed using the detection result of the pair of detection sensors belonging to the second set. And

Further, the movement control means detects the leading edge of the document after the leading edge of the document is detected by the detecting means on each of the one end side and the other end side in the width direction of the document conveying path. The movement is executed until the position is reached.
In addition, it is possible to execute a job for continuously conveying a plurality of documents one by one at intervals, and reading the images of each document by sequentially passing through the reading positions. Of the originals, the movement is executed only for the first original conveyed first, and the process for prohibiting the movement is executed for the second and subsequent originals.

Here, the movement control means includes determination means for determining that the types of the plurality of documents are the same type, and executes the processing only when the determination is made, and when the determination is not made. The movement is executed for each of the plurality of documents.
Further, when a document transported in a posture in which the front surface is the lower surface side and the back surface is the upper surface side passes through the first reading position, the front surface of the document is read from below by the first reading means. When the original passes through the first reading position and then passes through the second reading position, the back surface of the original is read by the second reading means from above, and the second reading position is the reading position. It corresponds to a position, and the second reading means corresponds to the image sensor.

  An image forming apparatus according to the present invention includes the above-described image reading device, and an image forming unit that forms an image on a sheet based on image data read by the image reading device.

  In this way, even if the type of document and the surrounding environment vary, the height of the document surface of the document being conveyed from the contact image sensor is within the tolerance range of the focal position. Accordingly, it is possible to further improve the read image quality by suppressing the deterioration of the read image quality due to the deviation of the document surface from the focal position.

1 is a diagram illustrating a configuration of a copier according to a first embodiment. FIG. 2 is a diagram illustrating a configuration of an image reading unit provided in a copying machine. FIG. 4 is an enlarged view illustrating a configuration example of a conveyance guide provided in an image reading unit. FIG. 6 is a diagram schematically showing how a distance H from the back side of a document D is detected by a distance measuring sensor. FIG. 2 is a diagram illustrating a configuration of a reading control unit provided in a copying machine. It is a flowchart which shows the content of a guide displacement control process. It is a figure which extracts and shows only the content of the modification of a guide displacement control process. FIG. 10 is a conceptual diagram for explaining a conveyance guide support mechanism according to Embodiment 2; 10 is a flowchart showing the content of a guide displacement control process according to the second embodiment. It is a flowchart which shows the content of the subroutine of a sensor determination process. It is a flowchart which shows the content of the subroutine of guide movement control.

Hereinafter, an embodiment of an image forming apparatus provided with an image reading apparatus according to the present invention will be described with reference to the drawings, taking a multifunction digital copying machine (hereinafter referred to as “copying machine”) as an example.
[Embodiment 1]
<Overall configuration of copier>
FIG. 1 is a schematic diagram showing the configuration of the copying machine according to the present embodiment.

As shown in the figure, the copying machine includes an image reading unit 1, an image forming unit 2, a paper feeding unit 3, a main body control unit 4, and a reading control unit 5.
The image reading unit 1 is configured to be able to read a document image by both a sheet-through method that is one of fixed optical systems and a scanner moving method that is one of moving optical systems. Here, the sheet-through method is a method of reading a document being conveyed (moved) at a fixed reading position while the optical system is stationary (fixed). With the scanner movement method, with the document stationary, the mirror that guides the reflected light from the document surface to the reading sensor is moved relative to the document, and the optical path length from the document surface to the reading sensor is always kept constant. This is a reading method.

The present embodiment has a so-called Dual Scan reading function capable of reading images on the front (front) surface and back (back) surface of a document without inverting the document in the sheet-through method. Each reading method and function can be selected by the user.
The image reading unit 1 includes a scanner unit 10 having a sheet-through glass 13 and a platen glass 16 provided on the upper surface, and an automatic document feeder (ADF) 40 provided above the scanner unit 10. I have.

The automatic document transport unit 40 transports the documents placed on the document feed tray 40 a one by one onto the sheet through glass 13 of the scanner unit 10.
The scanner unit 10 applies a fluorescent light 11 that is a linear light source to a front surface of a document conveyed on the sheet-through glass 13 by the automatic document conveyance unit 40 or a document placed on the platen glass 16. The reflected light is guided to a CCD (Charge Coupled Device) sensor 12 as a reading sensor through the reduction optical system 15. The CCD sensor 12 generates image data corresponding to the document image by photoelectrically converting the received reflected light of the document, and sends the generated image data to the reading control unit 5. As the fluorescent lamp 11, a rare gas fluorescent lamp such as a xenon lamp, an external electrode fluorescent lamp, or the like is usually used.

  An image on the back side (back side) of the document is read by a contact image sensor (CIS) provided in the automatic document feeder 40. A contact image sensor (hereinafter referred to as “CIS”) 50 is disposed at a position downstream of the sheet-through glass 13 in the document conveyance direction, and an image on the back side of the document D passes through the CIS 50. The read image data is sent to the reading control unit 5.

The image forming unit 2 forms an image based on image data output from the CCD sensor 12 of the scanner unit 10, image data output from the CIS 50, and the like. The image forming unit 2 includes an intermediate transfer belt 22, an image forming unit 23Y, 23M, 23C, and 23K.
The image forming units 23Y, 23M, 23C, and 23K are arranged along the intermediate transfer belt 22, and are respectively yellow (Y), magenta (M), cyan (C), and black (K) toner images. Form. Since the image forming units 23Y to 23K all have the same configuration, only the image forming unit 23K will be described, and thus other description will be given.

  The image forming unit 23K includes a photosensitive drum 24K, a charger 25K, an exposure device 26K, a developing device 27K, and a primary transfer roller 28K. The outer circumferential surface of the photosensitive drum 24K is uniformly charged by the charger 25K. The exposure device 26K emits a light beam toward the photosensitive drum 24K by a drive signal based on the image data generated by the scanner unit 10, and exposes and scans the surface of the charged photosensitive drum 24K. An electrostatic latent image is formed on the surface.

The electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 24K is developed with toner by the developing device 27K, and the toner image is electrostatically transferred onto the intermediate transfer belt 22 by the primary transfer roller 28K. On the intermediate transfer belt 22, the toner images of each color Y to K are transferred and overlapped to form a color toner image.
In parallel with the toner image forming operation, the paper feeding unit 3 feeds the recording sheets S one by one from any one of the plurality of paper feeding cassettes 31 accommodated therein, and a secondary transfer roller 21 is provided. It is conveyed to the secondary transfer position. The secondary transfer roller 21 electrostatically transfers the toner image on the intermediate transfer belt 22 onto the recording sheet S. As a result, an image is formed on the recording sheet S.

  When performing dual scan reading in the sheet-through method, a toner image forming operation is sequentially performed for each image on the front surface and the back surface of a single document, and the document that is transferred onto the intermediate transfer belt 22 A toner image representing the front surface is transferred to the first recording sheet S fed from the paper feeding unit 3, and subsequently transferred onto the intermediate transfer belt 22. The image is transferred to the second recording sheet S from the sheet feeding unit 3.

The recording sheet S on which the toner image has been transferred is discharged and discharged onto the discharge tray 20a after the toner image is melted and pressed on the recording sheet S by heating and pressing in the fixing unit 29. Residual toner remaining on the intermediate transfer belt 22 without being transferred to the recording sheet S is removed by the cleaner 20b.
In the above description, an example of an image forming operation by a so-called single-sided copy function that forms an image only on one side (one side) of the recording sheet S has been described. In the case of an apparatus having a copy function, an image on the front surface of a document is formed and fixed on one surface of one recording sheet S, and then the recording sheet S is reversed by a switchback mechanism. In this state, the sheet can be conveyed again to the secondary transfer position, and a double-sided copy job for forming an image on the back side of the document on the other side of the recording sheet S can be executed.

The main body control unit 4 controls the operation of each unit in an integrated manner to smoothly execute a copy operation, and the reading control unit 5 controls each unit in the image reading unit 1 to execute a document image reading operation.
<Configuration of Image Reading Unit>
FIG. 2 is a schematic configuration diagram of the image reading unit 1.
As shown in the figure, the sheet-through glass 13 provided on the upper surface of the scanner unit 10 extends long in a direction (main scanning direction) perpendicular to the conveyance direction of the document conveyed by the automatic document conveyance unit 40. It has a plate shape and is provided on the side of the scanner unit 10 on the upstream side in the document conveyance direction (sub-scanning direction). The platen glass 16 on which the document is placed is provided on the downstream side in the document transport direction (sub-scanning direction) with respect to the sheet through glass 13 with an appropriate interval from the sheet through glass 13. Further, a reference plate 9 having a white reference surface for correcting the shading of the CCD sensor 12 is provided between the sheet-through glass 13 and the platen glass 16 with the white reference surface facing downward.

  In the shading correction of the CCD sensor 12, the light emitted from the linear light source 11 in the stopped state after the first slider 18 has moved to the position immediately below the reference plate 9 in the direction indicated by the arrow A by the driving force of the scanner motor 81. Is irradiated onto the white reference surface, and the reflected light of the irradiated light from the white reference surface is changed from the first mirror 15b mounted on the first slider 18 to the second mirror 15c mounted on the second slider 19. This is performed by the CCD sensor 12 receiving light through the third mirror 15d and the reduction lens 15e.

  When the document is read by the sheet through method, the document D placed on the document feed tray 40a of the automatic document transport unit 40 is sent out from the document feed tray 40a to the document transport path 40c by the pickup roller 42. And conveyed to the separation roller pair 43. The separating roller pair 43 includes a separating roller 43a and a sheet feeding roller 43b. The separating roller pair 43 separates the document D conveyed between the separating roller 43a and the sheet feeding roller 43b one by one and passes through the conveying roller pair 43d. Then, it is conveyed to the registration roller pair 44. The registration roller pair 44 conveys one conveyed document D to a pre-reading roller pair 45 with a predetermined posture and at a predetermined timing.

The pre-reading roller pair 45 conveys the document D sent from the registration roller pair 44 toward the sheet-through glass 13 and passes it over the surface of the sheet-through glass 13.
A cleaning roller 49 is disposed on the sheet-through glass 13 at a position facing the sheet-through glass 13.
The cleaning roller 49 includes a rotating body main body portion having a D-shaped cross section having an arc surface on the peripheral surface, and a brush member attached to a flat portion of the rotating body main body portion, and guides the document D in the document transport direction. It has a guide function and a function of cleaning the surface of the sheet-through glass 13. Specifically, when the document D is transported on the sheet-through glass 13, the arcuate surface of the main body of the rotating body is in a posture facing the document transport path 40c (the posture shown in FIG. 2). A non-contact state (a state shown in FIG. 2) in which a gap (space) is formed between the glass 13 and the glass 13 is guided to the downstream in the document transport direction by the arc surface. While the document D passes through the gap between the cleaning roller 49 and the sheet-through glass 13, the scanner unit 10 causes the document D to face the document D (on the side of the document D facing the sheet-through glass 13). Image) is read.

On the other hand, at a predetermined timing not during document conveyance, a driving motor (not shown) composed of a stepping motor is driven to rotate one or more times, and the tip of the brush member is the surface of the sheet-through glass 13 during the rotation. The dust such as paper dust adhering to the surface of the sheet-through glass 13 is swept away by rubbing while being in contact with the sheet and cleaned.
The document D that has passed over the sheet-through glass 13 is conveyed toward the CIS 50 along the guide surface 69 by the conveyance guide 55 via the post-reading roller pair 46.

The CIS 50 includes a main body 50a disposed in the housing, and a dust-proof glass 50b provided on the side facing the document conveyance path 40c and preventing dust and the like from entering the housing.
Since the CIS 50 is a known sensor, the details are omitted, but the outline is as follows. In other words, the main body 50a is arranged in a row along the main scanning direction between a light-emitting unit composed of a large number of LEDs and the like, a light-receiving unit composed of a large number of photodiodes, and the like, and between the light-receiving unit and the dust-proof glass 50b. And a long imaging lens in the main scanning direction, and the light emitted from the light emitting portion passes through the dust-proof glass 50b and passes directly under the CIS 50 (the original document D) The surface of D facing the CIS 50 is irradiated.

Then, the reflected light of the irradiated light from the back surface of the document D is received by the light receiving unit through the dust-proof glass 52 and the imaging lens, and the received reflected light is photoelectrically converted, so that Image data of the back side image is generated. Note that a contact image sensor may be used, and a CIS having a configuration different from the above may be used.
The document D transported by the transport guide 55 passes directly under the CIS 50 while being lifted from the surface of the dust-proof glass 50b of the CIS 50 (in a non-contact state), and then sent to the discharge roller pair 48 through the transport roller pair 47. The paper is discharged out of the apparatus by the discharge roller pair 48 and is stored on the discharge tray 40b. Each roller provided in the automatic document feeder 40 is rotationally driven by the driving force of the carry motor 82.

  The conveyance guide 55 is supported by an apparatus main body (not shown) so as to be movable in a direction approaching and separating from the CIS 50 (direction indicated by an arrow B), and the conveyance path of the document D to be conveyed is the CIS 50. The position of the position relative to the CIS 50 is controlled so as to fall within the allowable tolerance of the focal length (tolerance with respect to the focal position as a reference). This guide displacement control is executed by the reading control unit 5. Details of the guide displacement control will be described later.

A document leading edge detection sensor 53 is disposed at a position downstream of the sheet-through glass 13 and upstream of the post-reading roller pair 46 in the document transport direction and facing the document transport path 40c. The document leading edge detection sensor 53 includes, for example, an optical sensor, detects the leading edge (document leading edge) of the document D being conveyed, and sends the detection signal to the reading control unit 5.
In the scanner unit 10, when reading a document by the sheet-through method, the first slider 18 is moved to a position below the sheet-through glass 13 (position in FIG. 2: sheet-through position). The front surface of the document D passing over the sheet-through glass 13 is irradiated by the fluorescent lamp 11 of the first slider 18 that is stationary at the sheet-through position.

The light reflected from the front surface of the document D is changed in optical path by the first mirror 15b, the second mirror 15c, and the third mirror 15d, and is connected to the light receiving surface of the CCD sensor 12 by the reduction lens 15e. Imaged.
On the other hand, when the original on the platen glass 16 is read not by the sheet-through method but by the scanner movement method, the automatic document feeder 40 is opened upward and the original is set on the platen glass 16 by the user. The first slider 18 is moved in the direction indicated by the arrow A in FIG. The second slider 19 moves in the same direction at half the moving speed of the first slider 18 so as to follow the movement of the first slider 18, and the distance (optical path length) from the document surface to the CCD sensor 12 is increased. The reflected light of the document is guided to the CCD sensor 12 while being always kept constant. The second slider 19 is also moved along with the movement of the first slider 18 when the first slider 18 is moved to a position directly below the reference plate 9 during the shading correction of the CCD sensor 12 described above. is there.

The document feed tray 40a is provided with a document size detection sensor 8 for detecting the size of the placed document D. Information indicating the document size detected by the document size detection sensor 8 is sent to the reading control unit 5.
<Configuration of transport guide>
FIGS. 3A and 3B are enlarged views of the cross section of the conveyance guide 55.

As shown in both figures, the conveyance guide 55 is disposed opposite to the surface of the dust-proof glass 50b of the CIS 50 at an interval, and the upper surface is a guide surface 69 for conveying the document D.
The conveyance guide 55 is provided over a length from a position upstream of the post-reading roller pair 46 in the document conveyance direction to a position downstream of the conveyance roller pair 47 in the document conveyance direction. The conveyance guide 55 is provided with notches 46c and 47c at a portion where the lower roller 46b of the post-reading roller pair 46 is located and a portion where the lower roller 47b of the conveyance roller pair 47 is located, The lower rollers 46b and 47b are pressed against the upper roller 46a of the post-reading roller pair 46 and the upper roller 47a of the conveying roller pair 47 from below through the notches 46c and 47c.

The conveyance guide 55 is supported movably in a direction approaching and separating from the surface of the dust-proof glass 50b of the CIS 50 (a direction indicated by an arrow B). Here, the conveyance guide 55 is configured to be supported by a frame (not shown) on the apparatus main body side.
Specifically, the conveyance guide 55 is provided with side surfaces 62 that are bent downward on both ends of the guide surface 69 in the front-rear direction of the apparatus (perpendicular to the paper surface) (in FIG. Only the side surface 62 is shown.), And each side surface 62 is provided with kerfs 64a and 64b extending in a direction parallel to the direction indicated by the arrow B.

On the apparatus main body side, support frames corresponding to the respective side surfaces 62 are provided at positions facing the respective side surfaces 62 of the conveyance guide 55. , 64b are provided to be fitted into the protrusions 65a and 65b.
The conveyance guide 55 can be freely translated along the direction in which the cut grooves 64a and 64b extend (the direction indicated by the arrow B) in a state where the projections 65a and 65b of the support frame are fitted in the cut grooves 64a and 64b. It has become. Here, the projection is fitted into the kerf, but the present invention is not limited to this. The conveyance guide 55 may be configured to be movable in parallel, and instead of the configuration in which the protrusion is fitted in the kerf, a configuration in which the conveyance guide 55 can be directly moved by the rail may be used. In the present embodiment, only the conveyance guide 55 is configured to be movable in the direction indicated by the arrow B with respect to the frame (not shown) on the apparatus main body side.

The conveyance guide 55 is bent at a substantially right angle toward the upstream side in the document conveyance direction from the lower end of the side surface 66a and a side surface 66a bent downward at a substantially right angle from the downstream end of the guide surface 69 in the document conveyance direction. A bottom surface 66b is provided.
A guide displacement motor 56 fixed to a frame (not shown) on the apparatus main body side is disposed below the bottom surface 66b of the conveyance guide 55 and at a central position in the apparatus front-rear direction. An eccentric cam 57 is attached to the rotation shaft 561 of the guide displacement motor 56, and the peripheral surface of the eccentric cam 57 and the bottom surface 66b of the conveyance guide 55 are in contact with each other.

  When the guide displacement motor 56 is driven and the eccentric cam 57 rotates, the rotational movement of the eccentric cam 57 moves straight in the direction indicated by the arrow B by an amount corresponding to the eccentric amount of the eccentric cam 57. The position of the conveyance guide 55 relative to the CIS 50 can be displaced by converting the movement of the conveyance guide 55 in the direction of the arrow B by being converted into motion. Here, the bottom surface 66b of the conveyance guide 55 is always in contact with the peripheral surface of the eccentric cam 57 by the weight of the conveyance guide 55, but a configuration in which a spring biasing force or the like is applied may be employed.

  FIG. 3A shows that the distance (interval) of the surface of the guide portion 67 of the conveyance guide 55 (the portion of the conveyance guide 55 facing the dust-proof glass 50b of the CIS 50) from the surface of the dust-proof glass 50b of the CIS 50 is h1. 3 shows the position of the conveyance guide 55 with respect to the CIS 50, and FIG. 3B shows the position of the conveyance guide 55 with respect to the CIS 50 when the distance is h2 (> h1). Yes. A position indicated by a symbol R indicates a reading position of the document D in the document transport direction of the CIS 50.

The CIS 50 is fixed on a support plate 50c, and the support plate 50c is fixedly supported by a frame (not shown) on the apparatus main body side. On the support plate 50c, a distance measuring sensor 51 is arranged at a position upstream of the CIS 50 in the document conveyance direction and in the center in the longitudinal direction of the apparatus (corresponding to a position 131 in FIG. 8 described later).
The distance measuring sensor 51 irradiates the measurement target (the back side of the document D) with infrared rays emitted from the infrared LED, and receives the infrared rays reflected by the measurement target with a PSD (Position Sensitive Detector), thereby making contactless. It is a distance detection sensor that detects the distance from the measurement object.

  FIG. 4 is a diagram schematically illustrating how the distance H from the back surface of the document D is detected by the distance measuring sensor 51, and the infrared rays emitted from the distance measuring sensor 51 are indicated by broken lines. The distance H is a distance between the center portion of the document D in the longitudinal direction of the apparatus (corresponding to the width direction of the document conveyance path) and the distance measuring sensor 51. An upper guide plate 41a is disposed between the distance measuring sensor 51 and the document D. The upper guide plate 41a is provided with a through hole 41b at a portion facing the distance measuring sensor 51. The distance H can be detected when infrared rays pass through the through hole 41b.

  The distance H is used to detect the height of the document D from the CIS 50 as will be described later. If the distance D is detected as close as possible to the CIS 50, the accuracy of document height detection can be improved. It is desirable that the document is disposed at a position upstream of the CIS 50 and in the immediate vicinity of the CIS 50 and detected at a position immediately before the leading edge of the document D reaches the reading position R. The document detection position by the distance measuring sensor 51 is not limited to the center in the width direction of the document transport path, and may be, for example, the end in the width direction depending on the apparatus configuration.

Based on the magnitude of the distance H detected by the distance measuring sensor 51, guide displacement control for controlling the position of the conveyance guide 55 relative to the CIS 50 is executed. Information indicating the distance H is sent to the reading control unit 5.
<Configuration of reading control unit>
FIG. 5 is a diagram illustrating a configuration of the reading control unit 5.

As shown in the figure, the reading control unit 5 includes a CPU 91, a guide displacement processing unit 92, a timer 93, and the like, and these can communicate with each other.
The CPU 91 has a built-in ROM 94 and RAM 95, reads a program for executing an image reading operation stored in the ROM 94, and controls the operations of the scanner unit 10 and the automatic document feeder 40 in the image reading unit 1. To perform a smooth image reading operation. Further, when there is an instruction from the main body control unit 4, for example, an instruction to read an original, an original image is read based on the instructed reading mode (Dual Scan reading function or the like), and an original image obtained by reading is read. Processing such as sending data to the main body control unit 4 is executed. The RAM 95 is a work area for the CPU 91.

The guide displacement processing unit 92 executes a guide displacement control process, and the timer 93 is used in the guide displacement control process.
<Contents of guide displacement control processing>
FIG. 6 is a flowchart showing the content of the guide displacement control process. This process is executed separately for each original as a process for the original when the original is read using the sheet-through dual scan reading function.

As shown in the figure, it is determined whether or not the leading edge of the document D being conveyed has been detected by the document leading edge detection sensor 53 (step S1).
When it is determined that the leading edge of the document has been detected (“YES” in step S1), the timer 93 starts counting (counting up) (step S2). Then, it is determined whether or not the count value Tc of the timer 93 has reached a predetermined value To (step S3). Here, the predetermined value To is the document conveyance path 40c between the detection position of the document leading edge detection sensor 53 (X1 shown in FIG. 4) and the detection position of the distance measuring sensor 51 (X2 shown in FIG. 4) in the document conveyance direction. This is a value obtained by dividing the upper distance L by the document conveying speed V.

Therefore, the fact that the count value Tc has reached the predetermined value To means that the leading edge of the document D detected by the document leading edge detection sensor 53 has reached the detection position X2 of the distance measuring sensor 51. The distance L and the document conveyance speed V are determined by the apparatus configuration, and information indicating a predetermined value To corresponding to the apparatus is stored in the ROM 94 in advance for each apparatus.
When it is determined that the count value Tc has reached the predetermined value To (“YES” in step S3), the timer 93 is stopped, the count value Tc is reset to zero (step S4), and the distance measuring sensor 51 is used. Detection of the distance H to the back side of the document D is executed (step S5).

For the detection of the distance H, a method is used in which the output value from the distance measuring sensor 51 is sampled at a predetermined period and an average of a plurality of sampled output values is taken. For example, if the leading edge of the document is the starting point (0 [mm]), sampling is executed a plurality of times at the leading edge of the document in the range from the starting point to the trailing edge of about 5 [mm].
When the distance H is detected, the leading edge of the document D is directed toward the guide portion 67 of the transport guide 55, and the document D is transported along the guide surface 69 due to its own weight. If the document D is transported in a state of being in close contact with the guide surface 69, the position of the document transport path in the height direction from the CIS 50 when the document passes immediately below the CIS 50 does not vary.

  However, in practice, the leading edge of the document D is guided by the guide surface 69 of the conveyance guide 55 because the stiffness of the document changes or curls due to the size, material, and surrounding environment of the document. In some cases, some of the paper is conveyed while being in close contact with the guide surface 69, and some of the paper is conveyed with a slight lift from the guide surface 69, so that there are many variations in the conveyance path of the document. Since the CIS 50 and the distance measuring sensor 51 are fixedly arranged, if there is a variation in the transport path of the document whose distance H is to be detected, the size of the distance H also changes by the amount of the variation. .

  Even when the document D is conveyed while being in close contact with the guide surface 69, the distance between the thin document and the thick document is equal to the distance H, that is, from the dust-proof glass 50b of the CIS 50. The height of the document D (the distance between the dust-proof glass 50b of the CIS 50 and the back surface of the document D) differs. Some thin paper and thick paper are extremely thin and thick, and the distance H changes depending on the type of document according to the difference in thickness.

Based on the detection value (distance) H of the distance measuring sensor 51, the height Hα (FIG. 4) of the back surface of the document D being conveyed from the surface of the dust-proof glass 50b of the CIS 50 is obtained (step S6). The calculation of Hα uses an expression represented by Hα = H−Hβ, where Hβ (fixed value: FIG. 4) is the distance from the distance measuring sensor 51 to the surface of the dust-proof glass 50b in the height direction.
The calculated value according to this formula is a value that is assumed to be obtained by measuring with the distance measuring sensor 51 when the dust-proof glass 50b of the CIS 50 is positioned between the distance measuring sensor 51 and the document D. Although the actual height of the document D (document height) at the reading position R of the CIS 50 is not shown as it is, it is almost the same value in the configuration of the present embodiment, so this calculated value is used as an approximate value. Yes. Note that there are cases where approximation cannot be performed depending on the configuration. In such a case, a correction coefficient can be obtained in advance from an experiment or the like and applied to the above equation. It can be said that the processing in the above steps S5 and S6 functions as a detection unit that detects the height (distance) of the document D guided by the conveyance guide 55 (guide member) from the dust-proof glass 50b of the CIS 50.

It is determined whether or not the calculated height Hα is within the tolerance range of the focus position in the CIS 50 (step S7). The tolerance range can be expressed as follows.
That is, the position of the surface of the dust-proof glass 50b of the CIS 50 is the origin (0 [mm]), and the focal position at the reading position R of the CIS 50 is at a position X [mm] in the height direction from the origin. When the allowable tolerance in the direction (+) away from the surface of the dust-proof glass 50b is Y [mm] and the allowable tolerance in the approaching direction (−) is Z [mm], the minimum value (X−Z) <X <maximum value (X + Y) The range from the minimum value to the maximum value in () can be set as the tolerance range of the focus position.

Specifically, for example, if X = 0.5 [mm] and Y = Z = 0.3 [mm], the tolerance range is within a range of 0.2 to 0.8 [mm]. Become.
If it is determined that the height Hα is within the allowable tolerance range (“YES” in step S7), the processing is terminated as it is.
When it is determined that the height Hα is not within the allowable tolerance range, that is, out of the allowable tolerance range (“NO” in step S7), the height Hα is greater than the maximum allowable tolerance range (X + Y). Whether or not (step S8).

If it is determined that the height Hα is greater than the maximum value (X + Y) (“YES” in step S8), the position of the conveyance guide 55 is displaced from the current position in a direction approaching the CIS 50 (step S9), and the process is performed. finish.
The displacement of the conveyance guide 55 is performed by rotating the eccentric cam 57 by a rotation angle corresponding to the displacement amount by driving the guide displacement motor 56, and the displacement amount is a value corresponding to the difference between Hα and X. . When the conveyance guide 55 is brought closer to the CIS 50 by this difference, the conveyance path of the document D guided by the conveyance guide 55 can be moved closer to the CIS 50 as much as the shift, and the document D against the surface of the dust-proof glass 50b of the CIS 50 can be moved. The height of the back surface can be adjusted to the focal position X [mm].

Here, when the circumferential surface of the eccentric cam 57 is divided by 1 °, such as 1 °, 2 ° ·· 359 °, from the reference position over the entire circumference, and the angle is set to each angle. The amount of movement of the conveyance guide 55 in the direction of arrow B relative to when the eccentric cam 57 is located at the reference position is obtained in advance from experiments, and each rotation angle is associated with the amount of movement. Is done.
Then, the current rotation angle of the eccentric cam 57 is detected, and from how many times the eccentric cam 57 is rotated from the detected current rotation angle, the conveyance guide 55 is moved by an amount corresponding to the displacement amount. The eccentric cam 57 is rotated from the associated rotation angle and information on the amount of movement, and the eccentric cam 57 is rotated by the calculated rotation angle. Information in which each rotation angle is associated with the amount of movement of the conveyance guide 55 is stored in advance in the ROM 94 or the like, and the rotation angle corresponding to the amount of displacement is read, and the eccentric cam 57 is read by the read rotation angle. Rotation drive of the guide displacement motor 56 is controlled so as to rotate.

  On the other hand, if it is determined that the height Hα is not larger than the maximum value (X + Y), that is, smaller than the minimum value (X−Z) (“NO” in step S8), the position of the conveyance guide 55 is set to the current position. It is displaced in a direction away from the CIS 50 (step S10), and the process is terminated. The amount of displacement at this time is also a value corresponding to the difference between Hα and X. When the conveyance guide 55 is moved away from the CIS 50 by this difference, the height of the back surface of the document D with respect to the surface of the dust-proof glass 50b of the CIS 50 can be adjusted to the focal position X [mm].

In the above description, only the conveyance guide 55 is displaced in the direction of the arrow B. However, when the conveyance path of the document D cannot be displaced by this alone, the conveyance guide 55 and the post-reading roller pair 46 are conveyed. It can be considered that the roller pair 47 is configured to be movable together.
The processes from Steps S4 to S10 are executed after the leading edge of the document D being conveyed passes the detection position X2 of the distance measuring sensor 51 and reaches the reading position R of the CIS 50. Thus, even when the transport path of the document varies depending on the document type or the like, when the leading edge of the document reaches the reading position R and reading of the document image is started, the transport of the document D when passing the reading position R is performed. Since the path (the height of the document D from the dust-proof glass 50b) is within the allowable tolerance range with respect to the focal position of the CIS 50, the read image quality can be improved.

  It is desirable that the conveyance guide 55 is moved (finished) before the leading edge of the document reaches the reading position R. For example, the transport guide 55 is moved by the time when several millimeters from the leading edge of the document pass the reading position R. Even if the configuration is completed, the image quality deterioration does not appear to be noticeable. This is because the range of several millimeters from the leading edge of the document is usually an area where no image is formed. The same can be said for the second embodiment, which will be described later, regarding the configuration related to the time until the end of the movement of the transport guide 55.

  In the above description, the guide displacement control process is executed for each conveyed document, and the position of the conveyance guide 55 with respect to the CIS 50 is adjusted to an appropriate position with respect to the document. When executing a job that sequentially conveys images at intervals, and sequentially passes through the reading position and reads the image of each document, the first document to be read (1 It is also possible to adopt a configuration in which the guide displacement control process is executed only on the second sheet and not executed on the second and subsequent documents.

  That is, when a plurality of documents that are continuously conveyed are of the same type (thin paper, thick paper, etc.), the strength of the originals is the same, and the environment around the apparatus during one job execution is the same. If there is no significant change, it is assumed that the document transport path is the same for the first document and the second and subsequent documents. In this case, if the conveyance guide 55 is displaced to an appropriate position with respect to the first document, the second and subsequent documents can be read within the allowable tolerance of the CIS 50 in the same manner as the first document. It will be possible.

FIG. 7 is a flowchart showing the content of the guide displacement control process in the case of adopting a configuration for switching whether or not the displacement control of the conveyance guide 55 is executed between the first sheet and the second and subsequent sheets. Only the different parts are shown. It is to be noted that the control process is executed each time a document is fed out and conveyed one by one, as described above.
First, it is determined whether or not the originals of the set original bundle are of the same type (step S15). This determination is made based on information input from the user indicating whether or not they are of the same type. Here, for example, the user can input the information via an input means such as an operation panel (not shown) before executing the job, and the input information (the same type or different) Information) is temporarily stored, and each time a document is conveyed, the stored information is read to determine whether or not they are of the same type.

  If it is determined that the types are not the same (“NO” in step S15), the process proceeds to step S1. In this case, displacement control of the conveyance guide 55 is executed for each original document. If it is determined that they are of the same type (“YES” in step S15), it is determined whether or not the conveyed document is the first document (step S16). This determination is made by setting the first document that is first fed out from the start of job execution among the set of document bundles as the first sheet.

If it is determined that it is the first document ("YES" in step S16), the process proceeds to step S1. In this case, displacement control of the conveyance guide 55 is executed for the first document.
If it is determined that the document is not the first document, that is, the second and subsequent documents ("NO" in step S16), the movement of the conveyance guide 55 is prohibited and the control process is terminated as it is. In this case, the displacement control of the conveyance guide 55 is not executed.

With such a configuration, it is not necessary to perform processing such as distance detection by the distance measuring sensor 51 (step S5) and determination within the allowable tolerance range (steps S6 and S7) while maintaining a read image quality exceeding a certain level. Accordingly, the processing load on the CPU 91 is reduced and the number of times the guide displacement motor 56 is driven is reduced, so that the overall power consumption of the motor can be reduced.
In the above description, it is determined whether or not a plurality of documents that are continuously conveyed are of the same type. For example, a plurality of documents that are set are likely to be of the same type, and a plurality of documents are assumed to be of the same type. In the case of continuously conveying a single document, the displacement control of the conveyance guide 55 is uniformly performed only on the first sheet without performing the above determination, and the displacement is not performed on the second and subsequent sheets. Compared to a configuration in which no control is performed at all, a certain degree of image quality improvement can be expected.

[Embodiment 2]
In the above embodiment, the transport guide 55 is configured to be movable in the direction indicated by the arrow B with respect to the CIS 50. However, in this embodiment, the front and rear ends of the transport guide 55 are individually provided. In this respect, this embodiment is different from the first embodiment. Hereinafter, in order to avoid duplication of description, the description of the same contents as those of Embodiment 1 is omitted, and the same components are denoted by the same reference numerals.

FIG. 8 is a conceptual diagram for explaining the support mechanism of the transport guide 55 in the present embodiment, and shows a view when the transport guide 55 is viewed from the direction indicated by the arrow G in FIG. .
As shown in FIG. 8, a displacement drive unit 110a is disposed on the front side of the apparatus in the front-rear direction of the apparatus (corresponding to the width direction of the document conveyance path) below the conveyance guide 55, and the displacement drive unit 110b on the rear side of the apparatus. Is arranged.

The displacement driving units 110a and 110b include eccentric cams 111a and 111b that contact the bottom surface 66b of the conveyance guide 55, and guide displacement motors 112a and 112b that rotationally drive the eccentric cams 111a and 111b.
The displacement drive unit 110a is for displacing the front end of the transport guide 55 along the direction of arrow B, and the displacement drive unit 110b is the end of the transport guide 55 on the rear side of the device in the direction of arrow B. It is for displacing along.

The conveyance guide 55 is allowed to move in the above height direction up to an amount corresponding to the maximum eccentricity of the eccentric cam with one end in the longitudinal direction of the apparatus as a fulcrum. In this way, it is supported by a frame (not shown) on the apparatus main body side.
For example, when only the guide displacement motor 112a on the front side of the apparatus is driven to rotate, the eccentric cam 111a rotates, and the end of the transport guide 55 on the front side of the apparatus has an arrow corresponding to the amount of eccentricity of the eccentric cam 111a. Move along the direction indicated by B. At this time, the rear end portion of the conveyance guide 55 is maintained in contact with the eccentric cam 111b and is not displaced in the direction indicated by the arrow B.

On the contrary, when only the guide displacement motor 112b on the rear side of the apparatus is driven to rotate, the eccentric cam 111b rotates, and the conveyance guide 55 is moved behind the apparatus by an amount corresponding to the eccentric amount of the eccentric cam 111b. The side end moves along the direction indicated by arrow B. At this time, the end portion of the conveyance guide 55 on the front side of the apparatus is kept in contact with the eccentric cam 111a and is not displaced in the direction indicated by the arrow B.
By individually driving and controlling the guide displacement motors 112a and 112b, the apparatus front side and the rear side of the conveyance guide 55 can be independently displaced in the direction along the arrow B, and the conveyance guide 55 can be moved with respect to the horizontal posture. The first inclined posture in which the front side is raised and the rear side of the device is lowered, and conversely, the second inclined posture can be switched to the second inclined posture in which the front side of the device is lowered and the rear side of the device is raised.

  In this way, the conveyance guide 55 is configured to be switchable between the first and second inclined postures even when the document D is conveyed in an inclined posture in which one side is raised and the other side is lowered before and after the apparatus. In order to allow individual adjustment of the position of the conveyance guide 55 in the height direction with respect to the CIS 50 so that both the front side and the rear side of the document D are within the allowable tolerance of the CIS 50 It is.

In order to perform position adjustment on the front side and the rear side of the apparatus, in this embodiment, distance measuring sensors for detecting the height of the document D from the CIS 50 are respectively provided on the front side and the rear side of the apparatus. Separately provided on each side.
In FIG. 8, three distance measuring sensors 121a, 122a, 123a are arranged on the support plate 125a on the front side of the apparatus at intervals in the front-rear direction of the apparatus, and three distance measuring sensors 121b, 122b, An example is shown in which 123b is arranged at intervals in the same direction. A one-dot chain line 131 in the drawing indicates the center position of the document transport path in the front-rear direction (width direction) of the apparatus, and the document D is transported in the width direction so that the center thereof matches the position of the one-dot chain line 131.

Each distance measuring sensor reaches the document when the document being conveyed passes through the position at a position that is the same distance from the position 131 in the front-rear direction of the apparatus across the position 131 at the center in the width direction of the document conveyance path. Sensors that detect the distance between them constitute one set.
Specifically, it is a set of distance measuring sensors 121a and 121b, a set of distance measuring sensors 122a and 122b, and a set of distance measuring sensors 123a and 123b. The reason why three sets of sensors are provided is that when a document having a different width in the front-rear direction of the apparatus is conveyed, the set of distance measuring sensors used for detection is properly used according to the size of the width.

  Specifically, in the front-rear direction of the apparatus, the distance between the document detection position of the distance measurement sensor 121a and the document detection position of the distance measurement sensor 121b is W1, and the document detection position of the distance measurement sensor 122a and the document detection position of the distance measurement sensor 122b. Is W2 (> W1), and the distance between the original detection position of the distance measuring sensor 123a and the original detection position of the distance measuring sensor 123b is W3 (> W2). If W has a relationship of W1 <W ≦ W2, a set of distance measuring sensors 121a and 121b is used.

If W2 <W ≦ W3, a pair of distance measuring sensors 122a and 122b is used, and if W3 <W, a pair of distance measuring sensors 123a and 123b is used.
As the document width increases, the distance sensor set disposed at a position farther outward from the center 131 in the width direction of the document conveyance path is used for the distance H at both ends of the document in the width direction. This is because the size can be easily detected.

  When the document D is in an inclined posture, both ends are more likely to be out of the tolerance range of the CIS 50 than the center in the width direction, so that the distance H is detected in the portion as close as possible to both ends in the width direction of the document. Thus, the image quality can be improved by adjusting the position of the conveyance guide 55 so as to fall within the allowable tolerance range. Hereinafter, the set of distance measuring sensors 121a and 121b is referred to as an inner set, the set of distance measuring sensors 122a and 122b is referred to as an intermediate set, and the set of distance measuring sensors 123a and 123b is referred to as an outer set.

FIG. 9 is a flowchart showing the contents of the guide displacement control process according to the present embodiment.
As shown in the figure, a sensor determination process for determining a set of ranging sensors to be used for detection is executed (step S21).
FIG. 10 is a flowchart showing the contents of a subroutine for sensor determination processing.
As shown in the figure, the document size of the document D being conveyed is detected (step S31). The document size is detected based on the detection result of the document size detection sensor 8.

The document width W is obtained from the document size (step S32). Here, information indicating the document width W for each document size is stored in advance in the ROM 94 or the like, and the document W is obtained by referring to the information.
It is determined whether or not the document width W has a relationship of W1 <W ≦ W2 (step S33). If it is determined that the relationship of W1 <W ≦ W2 is satisfied (“YES” in step S33), the set of sensors to be used is determined as the inner set (121a and 121b) (step S34), and the guide displacement is determined. Return to the main routine of the control process.

On the other hand, if it is determined that the document width W does not have a relationship of W1 <W ≦ W2 (“NO” in step S33) and has a relationship of W2 <W ≦ W3 (“YES” in step S35). ”), The group of sensors to be used is determined as an intermediate group (122a and 122b) (step S36), and the process returns to the main routine of the guide displacement control process.
If it is determined that the document width W does not have a relationship of W2 <W ≦ W3 (“NO” in step S35), it is determined that the relationship of W3 <W is established and the set of sensors to be used is outside. The set (123a and 123b) is determined (step S37), and the process returns to the main routine of the guide displacement control process. Hereinafter, in each set, the distance measuring sensor on the front side of the apparatus may be distinguished from the sensor a and the distance measuring sensor on the rear side may be distinguished from the sensor b.

Returning to FIG. 9, the processes of steps S1 to S4 are sequentially executed. The contents of each processing from these steps S1 to S4 are the same as described above.
When the timer reset in step S4 is executed, in step S22, the distance H (front) from the two distance measuring sensors constituting the determined sensor set to the front side portion of the document D being conveyed by the sensor a. And the distance H (rear) to the rear part of the document D is detected by the sensor b.

In step S23, the heights Hα (front) and Hβ (rear) of the document surface from the surface of the dust-proof glass 50b of the CIS 50 are obtained based on the detection values H (front) and (rear) of the sensors a and b. This method of determination is the same as described above before and after the apparatus.
Then, guide movement control for moving the conveyance guide 55 based on the heights Hα (front) and Hβ (rear) is executed (step S24), and the guide displacement control process is ended.

FIG. 11 is a flowchart showing the contents of a guide movement control subroutine.
As shown in the figure, it is determined whether or not the calculated height Hα (front) is within the allowable tolerance range in the height direction of the CIS 50 (step S41). This determination method is the same as the method according to step S7.
If it is determined that the height Hα (front) is within the allowable tolerance range (“YES” in step S41), the process proceeds to step S45. On the other hand, if it is determined that it is out of the allowable tolerance range (“NO” in step S41), it is determined whether or not the height Hα (previous) is larger than the maximum value of the allowable tolerance range (step S42). This determination method is the same as in step S8.

  If it is determined that the height Hα (front) is larger than the maximum value (“YES” in step S42), the front position of the transport guide 55 is displaced from the current position toward the CIS 50 (step S43), and the minimum value is reached. If it is determined that it is smaller (“NO” in step S42), the position on the front side of the conveyance guide 55 is displaced in the direction away from the CIS 50 with respect to the current position (step S44), and the process proceeds to step S45. The displacement of the position on the front side of the transport guide 55 is performed by driving the displacement driving unit 110a disposed on the front side of the apparatus, and the drive control uses the same method as in steps S9 and S10.

In step S45, it is determined whether or not the calculated height Hα (rear) is within a tolerance range in the height direction of the CIS 50. This determination method is the same as in step S7.
If it is determined that the height Hα (after) is within the allowable tolerance range (“YES” in step S45), the process returns. On the other hand, if it is determined that it is out of the allowable tolerance range (“NO” in step S45), it is determined whether the height Hα (after) is larger than the maximum value of the allowable tolerance range (step S46). This determination method is the same as in step S8.

  If it is determined that the height Hα (rear) is larger than the maximum value (“YES” in step S46), the rear position of the conveyance guide 55 is displaced in the direction approaching the CIS 50 from the current position (step S47), and the minimum If it is determined that the value is smaller (“NO” in step S46), the rear position of the conveyance guide 55 is displaced in the direction away from the CIS 50 with respect to the current position (step S48), and the process returns. The displacement of the position on the rear side of the conveyance guide 55 is performed by driving the displacement driving unit 110b disposed on the rear side of the apparatus, and the drive control uses the same method as in steps S9 and S10.

In this way, the height Hα from the CIS 50 falls within the allowable tolerance of the CIS 50 at each of both ends in the width direction of the document D being conveyed, so that the reading image quality can be further improved. it can.
In the above description, the document width W of the conveyed document D is obtained from the document size. However, the present invention is not limited to this. For example, if there is a sensor that can detect the document width W, the sensor may be used to detect the document width W. Further, as long as the user can input the value of the document width W, it may be obtained from the input value.

[Modification]
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.
(1) In the above embodiment, the document D is transported along the guide surface 69 of the transport guide 55 by its own weight. However, the document transported on the transport guide 55 using, for example, suction means. A configuration may be adopted in which D is transported so as to be drawn toward the guide portion 67 of the transport guide 55. As the suction means, for example, a suction fan can be used.

  Specifically, a suction fan is disposed below the conveyance guide 55 and a plurality of small-diameter through holes are provided in the guide portion 67 of the conveyance guide 55. The suction fan is driven to draw the air on the document conveyance path side to the suction fan side through the through hole provided in the conveyance guide 55, thereby attracting the document D being conveyed to the guide surface 69 side of the conveyance guide 55. By applying a suction force in the direction, the conveyance path of the document D can be brought closer to the guide surface 69.

  (2) In the above embodiment, the CIS 50 is the fixed side and the conveyance guide 55 is the movable side. However, the present invention is not limited to this. If the CIS 50 and the conveyance guide 55 are configured to be relatively displaceable in the perspective direction, the height of the document D from the CIS 50 is adjusted so that the conveyance path of the document D being conveyed is within the allowable tolerance of the CIS 50. It becomes possible to do. From this, it is possible to adopt a configuration in which, for example, the CIS 50 is movable and the conveyance guide 55 is fixed, or both the CIS 50 and the conveyance guide 55 are movable.

(3) In the above embodiment, the configuration example using the CIS 50 as the reading unit for reading the back side of the document in Dual Scan reading has been described. However, the CIS 50 is not limited to the configuration for reading the back side of the document. CIS may be used as means for reading the front surface.
That is, when the position for reading the front side of the document is the first reading position and the position for reading the back side of the document is the second reading position (position R above), the front side of the document D is the lower side. When the document D passes through the first reading position, the front surface of the document D is moved from the lower side to the first reading position when the document D passes through the first reading position. After reading by the reading means and passing through the first reading position, the document D is conveyed obliquely upward toward the second reading position. When the document D passes through the second reading position, the back surface of the document D is In the configuration in which the second reading means reads from the second reading means and passes through the second reading position and then discharged outside the apparatus, the second reading means is CIS50 in the above embodiment. For example, the first reading means uses CIS. There is also a possibility.

Further, even in a configuration in which one side of a document is read using one reading unit without having a Dual Scan reading function, a configuration using CIS for the reading unit can be adopted.
(4) In the above embodiment, the mechanism for displacing the conveyance guide 55 by the eccentric cam 57 is used. However, the mechanism for moving the conveyance guide 55 as a guide member is not limited to this, and other mechanisms such as screws are used. A feed mechanism may be used. Needless to say, the numerical values such as the focal length and tolerance of the CIS 50 are not limited to those described above.

  (5) In the above-described embodiment, an example in which the image reading apparatus according to the present invention is applied to a digital copying machine has been described. However, a sheet-through that reads an original image using a contact image sensor such as a scanner or a facsimile machine. Applicable to general image reading apparatus. Further, the present invention can be applied to an apparatus that reads an image in monochrome without being limited to color. Furthermore, the present invention can be applied to an image forming apparatus having the above-described image reading apparatus and an image forming unit that forms an image on a sheet based on image data read by the image reading apparatus.

  Further, the above embodiment and the above modification examples may be combined.

  The present invention can be widely applied to sheet-through type image reading apparatuses.

DESCRIPTION OF SYMBOLS 1 Image reading part 2 Image formation part 5 Reading control part 8 Original size detection sensor 40c Original conveyance path 50 CIS
50a CIS main body 50b Dust-proof glass 51, 121a, 121b, 122a, 122b, 123a, 123b Distance sensor 53 Document leading edge detection sensor 55 Transport guide 56, 112a, 112b Guide displacement motor 57, 111a, 111b Eccentric cam 69 Guide surface 92 Guide displacement processing unit 110a, 110b Displacement driving unit hα Document height H Distance from distance measuring sensor to document surface R Reading position

Claims (10)

A sheet-through type image reading apparatus that reads a document being conveyed while passing a reading position of a contact image sensor,
A guide member that guides the document being conveyed to a reading position of the image sensor in a state of floating from the image sensor;
Detecting means for detecting a height of the document guided by the guide member from the image sensor;
A moving mechanism for moving the image sensor and the guide member relatively in the height direction and in a direction away from the height direction;
Based on the detection value by the detection means, the image sensor and the guide member are moved relative to each other so that the height of the document from the image sensor is within the tolerance range of the focal position of the image sensor. Movement control means for causing
An image reading apparatus comprising: The detection means includes
A detection sensor that is disposed at a position facing the document conveyance path and detects the distance to the leading edge of the document at a position immediately before the leading edge of the document being conveyed reaches the reading position of the image sensor;
Based on the distance to the leading edge of the document detected by the detection sensor, the height is detected,
The movement control means includes
2. The movement is performed after the leading edge of the document is detected by the detection sensor and before the leading edge of the document reaches the reading position of the image sensor. Image reading device. The detection sensor is
3. The image reading apparatus according to claim 2, wherein a distance from the detection sensor is detected at a central portion in a width direction of the document conveyance path among the leading end portions of the document. The moving mechanism is
Each of both ends of the guide member in the width direction of the document conveyance path is configured to be movable in the height direction with respect to the image sensor, with one side serving as a fulcrum.
The detection means includes
The position facing the document transport path, which is disposed at each of the one end side and the other end side across the center in the width direction of the document transport path, and the leading edge of the document being transported is the reading position of the image sensor A pair of detection sensors for detecting the distance to the leading edge of the document at a position immediately before reaching
Based on the detection values detected by the pair of detection sensors, the height of each of the one end side and the other end side in the width direction of the document conveyance path is detected,
The movement control means includes
Based on the height of one end side in the width direction of the document transport path detected by the detecting means, the height of the document from the image sensor at the one end side falls within the allowable tolerance range. And moving one end side of the guide member in the height direction,
Based on the height of the other end side in the width direction of the document conveyance path detected by the detecting means, the height of the document from the image sensor on the other end side falls within the allowable tolerance range. The image reading apparatus according to claim 1, wherein the other end side of the guide member is moved in the height direction. The pair of detection sensors are arranged in a plurality of sets including the first and second sets,
The pair of detection sensors belonging to the first set are:
Detecting the distance to the leading edge of the document at first and second positions respectively spaced apart from the center by a first distance across the center in the width direction of the document transport path;
A pair of detection sensors belonging to the second set are:
Detecting the distance to the leading edge of the document at third and fourth positions respectively spaced apart from the center by a second distance longer than the first distance across the center in the width direction of the document transport path;
The movement control means includes
When the width of the document to be conveyed is W, the distance between the first position and the second position in the width direction is W1, and the distance between the third position and the fourth position in the width direction is W2. , When W1 <W ≦ W2, the detection results of the pair of detection sensors belonging to the first set are used, and when W2 <W, the detection results of the pair of detection sensors belonging to the second set are used. The image reading apparatus according to claim 4, wherein the movement in the height direction is executed by using. The movement control means includes
In each of one end side and the other end side in the width direction of the document transport path,
6. The movement is performed between the time when the leading edge of the document is detected by the detecting means and the time when the leading edge of the document reaches the reading position of the image sensor. Image reading apparatus. It is possible to execute a job for continuously conveying a plurality of originals one by one at intervals, and reading the images of each original by sequentially passing through the reading positions.
The movement control means includes
The processing is executed only for a first original conveyed among the plurality of originals, and processing for prohibiting the movement is executed for second and subsequent originals. The image reading apparatus according to any one of 1 to 6. The movement control means includes
Determining means for determining that the types of the plurality of documents are the same;
8. The image reading according to claim 7, wherein the process is executed only when the determination is made, and when the determination is not made, the movement is executed for each of the plurality of documents. apparatus. When a document transported in a posture where the front surface is the lower surface side and the back surface is the upper surface side passes through the first reading position, the first reading means reads the front surface of the document from below, When the original passes through the first reading position and then passes through the second reading position, the back side of the original is read from above by the second reading means,
The image reading apparatus according to claim 1, wherein the second reading position corresponds to the reading position, and the second reading unit corresponds to the image sensor. An image reading apparatus according to any one of claims 1 to 9,
An image forming unit that forms an image on a sheet based on image data read by the image reading device;
An image forming apparatus comprising:

Images