JP4844227B2 - Image reader - Google Patents

Description

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

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

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

  The foreign matter adhering to the reading glass is mainly sticky foreign matter such as the adhesive part of the tape affixed to the original or peeling of the adhesive, correction liquid, ball pen ink lump, eraser scraps, etc., and the original rubs the reading glass. Easy to be transferred to the part. Further, such a sticky foreign matter does not easily peel off and has a problem of causing image noise. In addition, there is a problem that floating foreign matters such as paper dust and dust in the air scattered from the conveyed document stay on the reading glass and cause image noise. In the sheet-through method, since the document is conveyed while being held in contact with a guide plate by a roller or the like, stress is applied to the document mainly composed of paper, and paper powder falls from the document surface.

  Therefore, Patent Documents 1 and 2 disclose measures for conveying a document in a non-contact state with respect to the reading glass by providing a step on the upstream side of the reading glass in the document conveying direction. In this non-contact conveyance method, the adhesive foreign matter can be prevented from adhering to the reading glass. On the other hand, floating foreign substances are those that are caught in a document to be conveyed and discharged naturally when the document comes into contact with the reading glass. There is a case where the rear end of the document loses its support immediately after passing through the step and comes into contact with the reading glass, and the rear end of the document entrains floating foreign matter and discharges it from the reading glass.

  As described above, when the trailing edge of the document passes through the step, it loses its support and falls and contacts the reading glass. However, since the document continues to be conveyed, there is a certain distance until the trailing edge passes through the step and comes into contact with the reading glass, and floating foreign substances existing at this distance cannot be removed. When floating foreign matter accumulates from the step edge to the position where the rear edge of the document comes into contact with the reading glass, the foreign matter is scattered downstream in the conveyance direction due to contact with the conveyed document and wind pressure, and a large amount of foreign matter is read. As a result, a streak-like image noise is generated.

  In addition, the distance at which the trailing edge of the original cannot contact the reading glass increases as the original conveyance speed increases, so that it is necessary to set the image reading position at a sufficient distance from the step edge, and the size of the image reading apparatus increases. End up.

  Patent Document 3 discloses, as an improvement measure of Patent Document 1, a capture member that captures foreign matter between a step and a reading position. However, maintenance (replacement and cleaning) of the capture member is necessary and complicated.

By the way, in a monochrome image reading apparatus, in order to emphasize the reproducibility of characters, the reproducibility of high density portions such as characters is enhanced, and the reproducibility of low density portions such as original background is lowered, thereby reducing the character image. Since image processing that is clearly reproduced is performed, image noise due to minute floating foreign matters such as paper dust does not become so obvious. However, in color image reading devices, since it is necessary to reproduce gradations such as photographs, it is important to read subtle gradation changes in the original, so even minute floating foreign matters that did not become apparent when reading monochrome images are read. Fine streak noise is generated in the read image.
JP-A-9-307695 JP 11-146140 A Japanese Patent Laid-Open No. 2001-223832

  Accordingly, an object of the present invention is a sheet-through method, which prevents the sticky foreign matter from being transferred to a transparent member for reading an image of a conveyed document, and reliably prevents floating foreign matter. An object of the present invention is to provide an image reading apparatus which can be eliminated and can prevent the occurrence of streak noise in a read image.

In order to achieve the above object, an image reading apparatus according to the first invention comprises:
A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Moving means for moving either the transparent member or the step forming member substantially parallel to the document transport direction in a state where the step forming member is in contact with the transparent member;
L1 ≦ L2 where L1 is the distance from the position where at least a part of the document starts contact with the transparent member to the edge of the step forming member, and L2 is the amount of relative position change between the transparent member and the step forming member. In relation to
It said reading position are disposed in the document conveying direction downstream side of the distance L1 from the edge portion of the step forming member,
Changing the relative position change amount of the transparent member and the step forming member according to the conveyance speed at which the document passes through the reading position;
It is characterized by.
An image reading apparatus according to the second invention is
A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Moving means for moving either the transparent member or the step forming member substantially parallel to the document transport direction in a state where the step forming member is in contact with the transparent member;
L1 ≦ L2 where L1 is the distance from the position where at least a part of the document starts contact with the transparent member to the edge of the step forming member, and L2 is the amount of relative position change between the transparent member and the step forming member. In relation to
The reading position is disposed downstream of the distance L1 from the edge portion of the step forming member in the document conveying direction,
In addition, a sensor is provided for detecting a position at which at least a part of the document starts contact with the transparent member, and the transparent member or the step forming member is moved a distance greater than the contact start position detected by the sensor. Letting
It is characterized by.

An image reading apparatus according to the third invention is
A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Moving means for moving the transparent member substantially parallel to the document conveying direction while the step forming member is in contact with the transparent member during the document reading operation;
The moving means can change the relative position change amount of the transparent member and the step forming member into a plurality of amounts,
When the distance from the position where at least a part of the document starts to contact the transparent member to the edge portion of the step forming member is L1, and any of the plurality of relative position change amounts is Lm and Ln. When the difference | Lm−Ln |, there is a relationship of L1 ≦ | Lm−Ln |
The reading position is disposed downstream of the distance L1 from the edge portion of the step forming member in the document conveying direction;
It is characterized by.

  According to the image reading apparatus of the present invention, the document is conveyed by the step forming member while being floated from the transparent member, and the sticky foreign matter is prevented from being transferred from the document surface to the transparent member. Then, either the transparent member or the step forming member is moved so as to be in the relationship of L1 ≦ L2 or in the relationship of L1 ≦ | Lm−Ln | substantially parallel to the document conveying direction. By pushing out the floating foreign material accumulated near the edge of the step forming member to a position where a part of the document comes into contact with the transparent member and bringing the document into contact with the floating foreign material, the floating foreign matter is caught in the document. It can be excluded from the transparent member. Accordingly, streak noise does not occur in the read image.

  In addition, the reading position can be set in the vicinity of the edge of the step forming member, and a dedicated member for cleaning floating foreign matters is not required, and the image reading apparatus can be reduced in size.

In the image reading apparatus according to the first, second and third inventions, it is the trailing edge portion of the document that starts contact with the transparent member at the distance L1. In the image reading apparatus according to the third invention, in accordance with the conveyance velocity through the document reading position, rather preferable to change the relative positional variation of the transparent member and the step forming member, further, the original You may provide the sensor for detecting the position which at least one part starts a contact with a transparent member.

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

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

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

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

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

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

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

  Further, the reading glass 12 is held by a holding member 13, and as shown in FIG. 3, the crank arm 15 connected to the shaft 14 of the holding member 13 is rotated once by the eccentric cam 16 by a drive motor (stepping motor) 17. By doing so, it reciprocates in parallel with the document conveying direction B. The amount of movement of the reading glass 12 can also be controlled by the number of drive pulses of the drive motor 17. The movement timing of the reading glass 12 will be described in detail later.

  Specifically, the document guide sheet 30 is formed of a material having a thickness (step) of 0.65 mm and a low sliding resistance (preferably a friction coefficient μ: 0.3 or less) such as ultrahigh molecular weight polyethylene. . If a material having low sliding resistance is used, the load when the reading glass 12 is moved is reduced, and troubles such as generation of abnormal noise can be prevented.

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

  Here, the behavior of the document passing through the reading position A will be described with reference to FIG. The document D is guided to the surface of the guide sheet 30 and fed onto the reading glass 12 (see FIGS. 4A and 4B), and has a gap from the reading glass 12 by the thickness of the guide sheet 30. It is conveyed (see FIGS. 4C and 4D). When the trailing edge of the document leaves the edge of the guide sheet 30, it falls onto the reading glass 12 (see FIG. 4E) and contacts the reading glass 12 at a distance L1 from the edge (see FIG. 4F). This distance L1 is obtained by experiment, and is about 2 mm when the document conveyance speed is 177 mm / s, and about 4 mm when the document conveyance speed is 329 mm / s.

  By the way, in the image reading apparatus 1, since the original is conveyed in a non-contact state with respect to the reading glass 12, adhesive foreign matter from the original is not transferred to the reading glass 12. On the other hand, floating foreign matters such as paper dust fall on the surface of the reading glass 12 from the original, and many of them are caught in the original being conveyed and discharged from the reading glass 12. However, some 10% of floating foreign matters such as paper dust and dust in the air remain on the reading glass 12 and in the vicinity of the edge of the document guide sheet 30 as indicated by reference numeral E in FIG. become.

(Refer 1st Example and FIGS. 5-8)
Therefore, in the first embodiment, before the original is conveyed to the reading position A, the reading glass 12 is moved from the home position (the position shown in FIG. 5A) by the drive motor 17 and the eccentric cam 16 by a distance L2. A reciprocating movement (moving speed is 8.2 mm / s) upstream in the document conveying direction B (see FIGS. 5B and 5C). Thus, the floating foreign matter E remaining in the vicinity of the edge of the document guide sheet 30 is pushed out by the edge of the guide sheet 30 to a position where the rear end of the document contacts the reading glass 12. Thereafter, the floating foreign material E is caught at the rear end of the conveyed document D (refer to FIG. 5D) and is removed from the reading glass 12 by the conveyance of the document.

  That is, when the step of the guide sheet 30 is 0.65 mm and the document conveying speed is 177 mm / s, the distance L1 is 2 mm. Therefore, if the reading glass 12 is reciprocated by L2 (2 mm or more), floating foreign matter E can be removed from the reading glass 12 by being caught at the rear end of the document, and the occurrence of streak noise in the read image can be eliminated. Further, since the guide sheet 30 is formed of a member having low sliding resistance, the surface of the reading glass 12 is not damaged.

  Although the relative movement between the guide sheet 30 and the reading glass 12 described above is effective every time a document is conveyed, the stage where accumulation of the floating foreign matter E does not affect as noise (not much) It may be executed at a stage where it does not grow significantly).

  In the above description, the reading glass 12 is moved. However, the reading glass 12 may be fixed and the document guide sheet 30 may be reciprocated. FIG. 6 shows a state in which the floating foreign substance E moves when the document guide sheet 30 is reciprocated.

  Incidentally, the distance L1 at which the trailing edge of the document comes into contact with the reading glass 12 varies depending on the document conveyance speed and the weight (basis weight) of the document. Therefore, if the contact relationship between the original and the reading glass 12 is detected by a sensor and the movement distance L2 is controlled, the floating foreign matter E can be surely eliminated.

  That is, as shown in FIG. 7, the displacement sensors SE1, SE2, and SE3 are arranged along the document conveyance direction B, and the document conveyance height is measured. The displacement sensors SE1, SE2, SE3 are CCD displacements that irradiate a document conveyed on the reading glass 12 with a laser beam and output a voltage corresponding to the height of the document surface from the amount and angle of the reflected light received. A sensor can be suitably used.

  More specifically, the sensors SE1, SE2, and SE3 output 0V by irradiating the surface of the reading glass 12, and the output changes by 1V when the document surface height changes by 0.1 mm. 8A, 8B, and 8C, the document SE is conveyed at a height of 0.6 mm from the glass surface, and the sensor SE1 when the trailing edge of the document falls from the edge of the guide sheet 30 at the timing t1. , SE2 and SE3. When the trailing edge of the document passes through the sensors SE1, SE2, and SE3, the reflected laser beam is not received and the output voltage is saturated at 10V.

  In this example, since the outputs of the sensors SE1 and SE2 have not decreased to 0V, the document height does not reach the glass surface (the document trailing edge is not in contact with the reading glass 12). The output of the sensor SE3 is reduced to 0V, and it is detected that the trailing edge of the document has come into contact with the reading glass 12 at the position from the sensor SE2 to the sensor SE3. That is, since the trailing edge of the document is in contact with the edge of the guide sheet 30 at 4 to 6 mm, the reading glass 12 may be moved by 6 mm or more.

  Similarly, although the sensor SE1 does not detect contact, if the sensors SE2 and SE3 detect contact, the rear end of the document is in contact with the edge of the guide sheet at 2 to 4 mm. What is necessary is just to move 4 mm or more. If all of the sensors SE1, SE2 and SE3 detect contact, the trailing edge of the document is in contact within 2 mm from the edge of the guide sheet, so the reading glass 12 may be moved by 2 mm or more.

  As described above, if the position where the trailing edge of the document contacts the reading glass 12 is detected and the reading glass 12 is reciprocated according to the detected position, the time required for the reciprocating movement can be shortened, and the period during document conveyance is limited. The reading glass 12 can be efficiently cleaned in a long time.

(Refer to the second embodiment, FIG. 9)
The configuration of the second embodiment is the same as that of the first embodiment, but the reading glass 12 is moved downstream in the document conveyance direction B before the document is conveyed to the reading position A. Here, the step is 0.65 mm, the document conveyance speed is 177 mm / s, and L1 is 2 mm.

  FIG. 9A shows a state before the document is conveyed, and floating foreign matter E is accumulated near the edge of the guide sheet 30. When the reading glass 12 is moved to the downstream side in the 2 mm original conveying direction B before the original is conveyed to the reading position A, the floating foreign matter E is exposed at a position 2 mm from the edge (see FIG. 9B). ). Next, when the document D is conveyed, the trailing edge entrains the floating foreign substance E (see FIG. 9C) and removes it from the reading glass 12 (see FIG. 9D). Thereafter, the reading glass 12 is returned to the home position shown in FIG.

  Even in the second embodiment, the same effect can be obtained even if the guide sheet 30 is moved. In this case, the guide sheet 30 is moved upstream in the transport direction B before the document is transported to expose the floating foreign matter E.

(Refer 3rd Example and FIGS. 10-12)
In the third embodiment, the reading glass 12 is moved to the upstream side in the conveyance direction B at a constant speed during reading of the original image, and the streak noise caused by the foreign matter is detected from the feature of the foreign matter read by the CCD color line sensor 58. However, the present invention is applied to a system that complements image information that is missing from surrounding image data due to streak noise.

  As shown in FIG. 10, the document image is read in the order of R, G, and B. In the complementary system using the glass movement, the foreign matter E adhering to the reading glass 12 moves in the direction opposite to the document conveying direction B together with the reading glass 12, and the foreign matter E is easily recognized. That is, streak noise is generated in the reading arrangement order of the CCD color line sensor 58, and the streak noise interval generated when passing through each pixel is the time during which the moving speed V of the reading glass 12 moves the pixel interval L. Is equal to the distance at which the sensor 58 reads an image. The read original image and the noise due to the foreign matter E are sorted, and only the noise can be removed by processing the image data.

  However, this complementary system based on glass movement has a problem that foreign matter E cannot be removed as shown in FIG. That is, during reading of the image, the reading glass 12 is moved to the upstream side in the conveyance direction B at a constant speed (see FIGS. 11A and 11B), so that the trailing edge of the document D has passed through the edge of the guide sheet 30. At this time, the foreign matter E remains in the vicinity of the edge (see FIG. 11B). Thereafter, the reading glass 12 returns to the home position (FIG. 11C), but the foreign matter E is accumulated on the glass 12 without being excluded.

  When the foreign matter E is accumulated and covers all the RGB pixels, color separation cannot be performed, and surrounding image information cannot be distinguished from a noise image due to foreign matter reading, and noise cannot be detected or complemented. As a result, the image quality is significantly deteriorated.

  Therefore, in the third embodiment, in the complementary system using glass movement, the movement amount of the reading glass 12 is changed in two steps, Lm and Ln, in order to remove the foreign substance by bringing the trailing edge of the document into contact with the foreign substance. I did it.

  Here, a case where the step is 0.65 mm, the document conveyance speed is 177 mm / s, and L1 is 2 mm will be described as an example. In synchronization with the start of reading the image of the original, the reading glass 12 starts to move upstream in the conveyance direction B (see FIG. 12A). The moving speed at this time is 8.2 mm / s when the document is letter size (short side 216 mm). Therefore, the image reading is completed when moving Lm (10 mm) (FIGS. 11B and 11C). At this time, the floating foreign matter E accumulated on the edge of the guide sheet 30 does not come into contact with the document D and is not removed from the glass 12.

  When the reading is finished and the reading glass 12 returns to the home position, the foreign matter E is exposed at a position corresponding to the glass movement amount Lm. However, since the next original D is conveyed without contact with the glass 12, the foreign matter E is not excluded (see FIG. 12D).

  Therefore, at the time of reading the image of the next document, the moving speed of the reading glass 12 is reduced to 6.5 mm / s or less and the moving amount is set to Ln (8 mm or less). That is, L1 ≦ | Lm−Ln |. As a result, the foreign material E with the trailing edge of the next original exposed at the position Lm-Ln is caught and removed from the glass 12 (see FIGS. 12E and 12F).

  According to the third embodiment, since the reading glass 12 is moved while the document is being transported, it is possible to transport the document with a close interval between the documents, and to perform image reading in a time efficient manner.

(Other examples)
The image reading apparatus according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof. In particular, the configuration of the mechanism for conveying the document and the reading optical system is arbitrary.

It is a schematic block diagram which shows one Example of the image reader which concerns on this invention. It is a principal part expanded sectional view of the image reading apparatus shown in FIG. It is a schematic sectional drawing which shows the moving mechanism of reading glass. It is explanatory drawing regarding the behavior of the original document which passes a reading position. It is operation | movement explanatory drawing in 1st Example. It is other operation | movement explanatory drawing in 1st Example. It is explanatory drawing which shows arrangement | positioning of the sensor in 1st Example. It is a graph which shows the output voltage of the said sensor. It is operation | movement explanatory drawing in 2nd Example. It is explanatory drawing of original image reading. It is explanatory drawing which shows the behavior of the foreign material in the complementation system by glass movement. It is operation | movement explanatory drawing in 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image reader 12 ... Reading glass (transparent member)
17 ... Driving motor 20 ... Automatic document feeder 30 ... Document guide sheet (step forming member)
50 ... Reading optical system A ... Reading position D ... Original SE1, SE2, SE3 ... Sensor

Claims (8)

A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Moving means for moving either the transparent member or the step forming member substantially parallel to the document transport direction in a state where the step forming member is in contact with the transparent member;
L1 ≦ L2 where L1 is the distance from the position where at least a part of the document starts contact with the transparent member to the edge of the step forming member, and L2 is the amount of relative position change between the transparent member and the step forming member. In relation to
It said reading position are disposed in the document conveying direction downstream side of the distance L1 from the edge portion of the step forming member,
Changing the relative position change amount of the transparent member and the step forming member according to the conveyance speed at which the document passes through the reading position;
An image reading apparatus. A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Moving means for moving either the transparent member or the step forming member substantially parallel to the document transport direction in a state where the step forming member is in contact with the transparent member;
L1 ≦ L2 where L1 is the distance from the position where at least a part of the document starts contact with the transparent member to the edge of the step forming member, and L2 is the amount of relative position change between the transparent member and the step forming member. In relation to
The reading position is disposed downstream of the distance L1 from the edge portion of the step forming member in the document conveying direction,
In addition, a sensor is provided for detecting a position at which at least a part of the document starts contact with the transparent member, and the transparent member or the step forming member is moved a distance greater than the contact start position detected by the sensor. Letting
An image reading apparatus. In the case where images of a plurality of originals are continuously read, the transparent document is passed between the rear end of the first original conveyed continuously after the read position and the front end of the subsequent original reaching the read position. image reading apparatus according to claim 1 or claim 2, characterized in that moving member or the step forming member. 3. The image reading apparatus according to claim 1, wherein the transparent member or the step forming member is moved each time a document is conveyed. A document conveying means for sending out the documents one by one and passing the reading position;
Reading means for optically reading an image of a document conveyed at the reading position;
A transparent member disposed between the document conveyed at the reading position and the reading unit;
A step forming member having a predetermined thickness disposed on the transparent member and upstream of the reading position in the document conveying direction;
Moving means for moving the transparent member substantially parallel to the document conveying direction while the step forming member is in contact with the transparent member during the document reading operation;
The moving means can change the relative position change amount of the transparent member and the step forming member into a plurality of amounts,
When the distance from the position where at least a part of the document starts to contact the transparent member to the edge portion of the step forming member is L1, and any of the plurality of relative position change amounts is Lm and Ln. When the difference | Lm−Ln |, there is a relationship of L1 ≦ | Lm−Ln |
The reading position is disposed downstream of the distance L1 from the edge portion of the step forming member in the document conveying direction;
An image reading apparatus. Image reading apparatus according to any one of claims 1 to 5, characterized in that to initiate contact with the transparent member by the distance L1 is a trailing edge portion of the document. The image reading apparatus according to claim 5 , wherein the relative position change amount of the transparent member and the step forming member is changed according to a conveyance speed at which the document passes through the reading position. A sensor for detecting a position at which at least a part of the document starts contact with the transparent member, and the transparent member or the step forming member is moved by a distance greater than or equal to the contact start position detected by the sensor; The image reading apparatus according to claim 5, wherein:

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