JP2008193177A - Image scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image scanner capable of scanning an image of high picture quality which suppresses the generation of moire without adding a driving mechanism for changing a relative distance between a line sensor for scanning a carried document and the scanning surface of the document. <P>SOLUTION: The line sensor 40 scans a document carried along a carrier path 12 through first glass 18 and scans the document set on second glass 20 through the second glass 20. When a CR motor 65 which is a driving source of the line sensor 40 is driven, a relative distance between the line sensor 40 and the scanning surface 25 of the document on the first glass 18 is changed. A scanner 10 is set to a first mode for reading out the document through the first glass 18 in a state that the relative distance is made approximately coincident with a focal distance of the line sensor 30 or a second mode for scanning the document through the first glass 18 in a state that the relative distance is made different from the focal distance of the line sensor 40. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image reading apparatus including an automatic document feeder (ADF) and a flat bed scanner (FBS).

  2. Description of the Related Art Conventionally, there has been known an image reading apparatus including an automatic document conveyance mechanism (hereinafter also simply referred to as “ADF”) and a flat bed scanner (hereinafter also simply referred to as “FBS”). This image reading apparatus includes a contact image sensor such as a CIS (Contact Image Sensor) that reciprocates with respect to the platen glass. The document placed on the platen glass is optically read by the image sensor while the image sensor is moved along the platen glass. A document placed on the document table of the ADF is optically read by an image sensor disposed at a predetermined reading position in the course of being conveyed along the conveyance path.

  It is known that when a halftone document such as a printed material is read by the image sensor described above, interference fringes called so-called moire are generated. Patent Document 1 discloses a configuration in which the line sensor is moved up and down to change the relative distance between the reading surface of the document placed on the platen glass and the line sensor in order to reduce the occurrence of moire.

  The image reading apparatus described in Patent Document 1 includes an image reading unit including a charge coupled device (CCD) and a rod lens array mounted on a carriage. The image reading unit includes an actuator in which an egg-shaped disc cam is provided on the rotation shaft of the stepping motor. The image reading unit is mounted on the carriage with the peripheral surface of the disc cam in contact with the carriage. When the stepping motor is driven, the disc cam rotates and the distance between the image reading unit and the carriage is changed. As a result, the distance between the image reading unit and the platen glass is changed.

  Japanese Patent Application Laid-Open No. 2004-228561 measures an MTF (Modulation Transfer Function) value based on an image signal obtained by reading a focus detection chart, and changes the height of the image reading unit based on the MTF value. Is described. This image reading apparatus has two reading modes, a photographic original mode and a printed original mode. In the photo original mode, the image reading unit is arranged at a height at which the MTF value is maximized, and the original on the platen glass is read. In the printed document mode, the image reading unit is arranged at a height at which the MTF value is about 40% of the maximum value, and the document on the platen glass is read.

  Patent Document 2 describes that the relative distance is adjusted by changing the height of the line sensor, as in the image reading apparatus disclosed in Patent Document 1. The image reading apparatus described in Patent Document 2 includes a rail whose longitudinal direction is the direction in which the CIS moves. The CIS moves on the rail along the rail. The rail has an oval cross section in a direction perpendicular to the longitudinal direction (axial direction), and is rotated around the axial direction by operation of a lever to function as a disc cam. As the rail rotates, the CIS approaches or moves away from the platen glass. That is, the relative distance between the CIS and the reading surface of the original on the platen glass is changed by operating the lever. Patent Document 2 describes that a jack is provided between the support plate on which the CIS is placed and the CIS, and the CIS is moved up and down by the jack by operating a knob.

  Patent Document 3 describes the use of a moire prevention plate when reading a document in which moire occurs. The moire prevention plate is a transparent member on which a document is placed, and is disposed on the platen glass. A document on which moiré is generated is placed on a moire prevention plate disposed on a platen glass. As described above, the moire prevention plate is interposed between the platen glass and the original, thereby separating the distance between the line sensor and the original. Since the original is read by the line sensor while being out of focus, the occurrence of moire is reduced.

JP 2002-171391 A JP 2002-262032 A JP-A-9-65078

  Incidentally, in the image reading apparatus described in Patent Document 1, it is necessary to provide a drive mechanism that moves the line sensor up and down in order to switch the reading mode of the document. This is the same when the configuration disclosed in Patent Document 2 is used, and there is a problem that the configuration of the apparatus becomes complicated and the manufacturing cost increases.

  The image reading apparatus described in Patent Document 3 requires a troublesome operation for the user such as disposing a moire prevention plate in order to reduce the occurrence of moire.

  It should be noted that a configuration capable of suppressing the occurrence of moire when reading a document conveyed by ADF is not disclosed in any patent document.

  The present invention has been made in view of such problems, and suppresses the generation of moiré without adding a drive mechanism for changing the relative distance between a line sensor that reads a conveyed document and the reading surface of the document. An object of the present invention is to provide an image reading apparatus capable of reading a high-quality image.

  (1) An image reading apparatus according to the present invention includes a first transmission member provided in a path through which a document is conveyed, a second transmission member on which the document is placed, and a first light transmission member or the first transmission member from a light source. (2) A contact type line sensor that irradiates a document through a transmissive member and reads reflected light from the document for each main scanning line, and moves the line sensor so as to face the first transmissive member or the second transmissive member. A drive unit that drives the drive unit to change the relative distance between the reading surface of the document on the first transmission member and the line sensor, and the control unit sets the relative distance to the focus of the line sensor. A first mode in which a document is read through the first transmission member by the line sensor in a state where the line sensor is substantially coincided with the distance, or in a state in which the control unit makes the relative distance different from the focal length of the line sensor. Sa by comprising a setting unit that sets a second mode for reading a document through the first transmissive member.

  The image reading apparatus of the present invention is configured to be able to read a document to be conveyed and a document placed on the second transmission member. The line sensor is arranged at a position facing the first transmission member by the driving unit when reading the conveyed document. In the process of transporting the original along the path, the line sensor irradiates light through the first transmission member, and the reflected light is read for each main scanning line. The line sensor is moved along the second transmission member by the drive unit when reading the document placed on the second transmission member. In the process, the original is irradiated with light through the second transmission member by the line sensor, and the reflected light is read for each main scanning line. The drive unit is driven by a control unit. By this driving, the relative distance between the reading surface of the original on the first transmitting member and the line sensor is changed. That is, the relative distance is changed using a drive source of the line sensor.

  The image reading apparatus is set to the first mode or the second mode by the setting unit. In the first mode, the line sensor is arranged by the control unit at a position where the relative distance substantially coincides with the focal length of the line sensor. In this state, the conveyed document is read by the line sensor through the first transmission member. Since the document is read with the line sensor in focus, a clear image of the document can be obtained. In the second mode, the line sensor is arranged at a position where the relative distance is different from the focal length by the control unit. In this state, the conveyed document is read by the line sensor through the first transmission member. Since the document is read in a state where the resolution of the line sensor is reduced, an image of the document in which the generation of moire is suppressed or an image of the document with a blurred image can be obtained.

  (2) The reading surface of the first transmission member may be inclined with respect to the plane on which the line sensor moves.

  With the above configuration, the relative distance can be easily changed without newly adding a member for changing the relative distance.

  (3) It is preferable that the reading surface of the first transmission member is separated from the plane on which the line sensor moves on the downstream side of the reading path in the path with respect to the upstream side in the document transport direction.

  With the above configuration, the document being conveyed is pressed against the first transmission member. For this reason, the relative distance is prevented from changing due to the floating of the document with respect to the first transmitting member.

  (4) In the image reading apparatus of the present invention, the thickness changes in a stepped shape or a wedge shape in the direction in which the line sensor moves, and the line sensor and the first sensor are in a state where the line sensor faces the first transmission member. The 1st spacer interposed between 1 permeation | transmission members may be provided.

  The first spacer changes in a stepped shape or a wedge shape in the moving direction of the line sensor. For this reason, the line sensor is moved toward or away from the first transmission member by being moved by the drive unit.

  (5) A reference member that is read by the line sensor as a lightness reference of the line sensor is provided, and the control unit changes the relative distance between the reading surface of the reference member and the line sensor by driving the drive unit. It may be a thing.

  With the above configuration, the distance between the reference member and the reading surface can be matched. It is possible to prevent a light amount difference from occurring between the light amount when the line sensor reads the original through the first transmission member and the light amount when the line sensor reads the reference member.

  (6) The reading surface of the reference member may be inclined with respect to a plane on which the line sensor moves.

  With the above configuration, the relative distance can be easily changed without newly adding a member for changing the relative distance between the line sensor and the reference member.

  (7) In the image reading apparatus of the present invention, the thickness of the line sensor changes in a stepped shape or a wedge shape in the direction in which the line sensor moves, and the line sensor and the reference member are in a state where the line sensor faces the reference member. You may provide the 2nd spacer interposed between.

  The second spacer changes in thickness in a stepped shape or a wedge shape in the moving direction of the line sensor. For this reason, the line sensor is moved toward or away from the reference member by being moved by the drive unit.

  (8) A reception unit that receives selection of the first mode or the second mode is provided, and the setting unit may set the first mode or the second mode based on the selection received by the reception unit. Good.

  Thereby, the resolving power of the line sensor is easily changed according to the user's selection.

  (9) The control unit causes the line sensor to perform an operation of reading a test document on which a predetermined pattern is recorded at a plurality of positions having different relative distances through the first transmission member. An arithmetic unit that obtains an MTF (Modulation Transfer Function) value for each of the plurality of positions based on the image signal of the test document obtained in the above, and the line sensor is operated by the drive unit in the first mode or the second mode. A determination unit that determines a reading position to be arranged for each mode based on each MTF value.

  The test document is, for example, a black and white pattern recorded thereon. The test document is read by the line sensor through the first transmission member. The line sensor is moved with respect to the first transmission member by the driving unit. The position of the line sensor with respect to the first transmission member is changed, and the test document is read by the line sensor. Thereby, an image signal of the test document is obtained for each position where the line sensor is arranged. An MTF value is obtained for each position of the line sensor based on these image signals, and reading positions for the first mode and the second mode are determined based on each MTF value. The conveyed document is read through the first transmission member in a state where the line sensor is arranged at different reading positions when the first mode is set and when the second mode is set.

  (10) A document tray on which a document conveyed along the path is placed, a first notification unit for notifying that the first test document is placed on the document tray, and the first notification unit. A first determination unit configured to determine whether or not a first test document is placed on the document tray in response to the notification; a second notification unit configured to notify that the second test document is to be placed on the document tray; A second determination unit that determines whether or not a second test document is placed on the document tray in response to a notification from the second notification unit, and the determination unit places the first test document. The reading position for the first mode is determined on the condition that the first determination unit has determined that the second test document has been placed, and the second determination unit determines that the second test document has been placed. The reading position for the mode may be determined.

  When the user places a first test document on the document tray in response to the notification from the first notification unit, the reading position for the first mode is determined. When the user receives a notification from the second notification unit and places the second test document on the document tray, the reading position for the second mode is determined.

  (11) The determining unit may determine a position where the MTF value is maximized as a reading position for the first mode.

  By setting the image reading apparatus to the first mode, the original is read with the line sensor in focus. Therefore, a clear document image can be obtained as compared with the case where the second mode is set.

  (12) The determination unit may determine a position where the MTF value is less than a maximum value and equal to or greater than a predetermined threshold as a reading position for the second mode.

  By setting the image reading apparatus to the second mode, the document is read with the line sensor out of focus. For this reason, an image in which the occurrence of moire is suppressed or a blurred image is obtained compared to the case where the first mode is set.

  (13) The determination unit may determine a position having a shorter relative distance corresponding to the MTF value as the reading position on condition that a plurality of the same MTF values are obtained by the calculation unit.

  This prevents the image of the read original from becoming extremely unclear when the original floats on the first transmission member.

  (14) A partition unit that divides the reading area of the line sensor in the conveyed document into a plurality of areas based on information input from the outside, and the determination unit determines a reading position for the second mode. The controller determines for each of the plurality of areas, and the controller controls the reading position determined by the determiner for each area partitioned by the partition during the reading of the conveyed document in the second mode. The position of the line sensor may be changed.

  Information is input from the outside. The reading area of the conveyed document is divided into a plurality of areas based on this information. In this case, the reading position for the second mode is determined for each partitioned area. In the second mode, the conveyed document is read by the line sensor through the first transmission member. During reading of the original, the reading position of the line sensor is changed for each area. As a result, the resolution of the line sensor is changed depending on the area, and the document is read. As a result, the obtained image of the manuscript is suppressed as a whole, and moire is suppressed, and the image is blurred in some areas.

  (15) An emphasis unit for emphasizing an image of the document read by the line sensor is provided. The emphasis unit performs an emphasis process on the image of the document obtained in the first mode with a first emphasis coefficient. The document image obtained in the two modes may be enhanced with a second enhancement coefficient larger than the first enhancement coefficient.

  The document image read by the line sensor is enhanced by the enhancement unit. The document image obtained in the second mode is enhanced with a higher enhancement coefficient than the document image obtained in the first mode. By reading the document in the second mode, the occurrence of moire is suppressed and the image is prevented from being blurred.

  According to the present invention, a clear original image can be obtained by setting the first mode, and an image in which the occurrence of moire is suppressed can be obtained by setting the second mode. Therefore, it is possible to obtain a high-quality original image by switching modes according to the type of original and the reading resolution.

  Embodiments of the present invention will be described below with reference to the drawings as appropriate. In addition, this embodiment is only an example of this invention, and it cannot be overemphasized that embodiment can be changed suitably in the range which does not change the summary of this invention.

[First Embodiment]
FIG. 1 is a perspective view showing an external configuration of the scanner 10 according to the first embodiment of the present invention, and shows a state in which a document cover 17 is opened.

  A scanner 10 (an example of an image reading apparatus according to the present invention) has a scanner function for reading an image of a document. In the present embodiment, the present invention will be described using the scanner 10 having only the scanner function as an example. However, the image reading apparatus according to the present invention is not limited to the scanner 10. The image reading apparatus according to the present invention may be realized as a copier, a facsimile machine, or a multi function device having a plurality of functions.

  As shown in FIG. 1, the scanner 10 includes a document table 11. The document table 11 functions as a flat bed scanner (FBS). The document table 11 has a substantially rectangular parallelepiped housing 15. A line sensor 40 (see FIGS. 2 and 3) is provided inside the housing 15. In the scanner 10, an image of a document is read by the line sensor 40.

  As shown in FIG. 1, the scanner 10 includes a document cover 17. The document cover 17 is for bringing a document placed on a second glass 20 (an example of a second transmission member of the present invention), which will be described later, into close contact with the second glass 20. The document cover 17 is provided so as to be openable and closable with respect to the document table 11. Specifically, the document cover 17 is rotatably connected to the document table 11 via a hinge (not shown) on the back side of the document table 11. The document cover 17 includes an automatic document feeder (ADF) 28.

  FIG. 2 is a schematic cross-sectional view showing a part of the conveyance path 12 in the scanner 10 according to the first embodiment of the present invention.

  As shown in FIGS. 1 and 2, the ADF 28 conveys the document placed on the document tray 22 to the paper discharge tray 23 along the conveyance path 12. That is, the conveyance path 12 is a path along which the document is conveyed. In FIG. 2, the original tray 22 and a part of the conveyance path 12 on the original tray 22 side are omitted. The document tray 22 (see FIG. 1) and the paper discharge tray 23 (see FIG. 2) are provided on the document cover 17 so that the document tray 22 is arranged in two upper and lower stages with the document tray 22 on the upper side. The conveyance path 12 is provided inside the ADF 28 so as to have a substantially U shape in the horizontal direction when viewed in a vertical cross section. The conveyance path 12 is continuously formed as a passage having a predetermined width through which a document can pass by members, guide plates, guide ribs, and the like that constitute the ADF 28 body. The document tray 22 and the paper discharge tray 23 are connected by the transport path 12.

  A plurality of rollers 73 (see FIG. 4) for conveying the document are disposed in the conveyance path 12. Although not shown in the figure, the roller 73 includes a so-called pickup roller, separation roller, transport roller, and paper discharge roller. A driving force is transmitted to each of these rollers 73 from a single motor 72 (see FIG. 4). The rotational force of each roller 73 is transmitted to the document, and the document is transported along the transport path 12 from the document tray 22 toward the paper discharge tray 23. As shown in FIG. 2, a first glass 18 (an example of a first transmission member of the present invention) is provided in the middle of the conveyance path 12. When the document cover 17 is closed, the document placed on the document tray 22 is transported along the transport path 12 by the ADF 28 and passes over the first glass 18. At that time, the image of the original is read by the line sensor 40 standing under the first glass 18. The original is further conveyed and discharged to the paper discharge tray 23.

  As shown in FIG. 1, a first glass 18 and a second glass 20 are disposed on the top surface of the upper cover 16 that constitutes a part of the housing 15. The first glass 18 is a transmission plate made of a transparent glass plate, an acrylic plate, or the like. When an original is placed on the original tray 22 and an instruction to start reading the original is issued, the line sensor 40 is disposed at a position facing the first glass 18 (see, for example, FIG. 6). The document on the document tray 22 is transported along the transport path 12 by the ADF 28. In the process, the image of the document conveyed on the first glass 18 is read by the line sensor 40 through the first glass 18.

  The second glass 20 (see FIG. 1) is for placing a document when the document table 11 is used as an FBS. The second glass 20 is a transmission plate made of a transparent glass plate, an acrylic plate, or the like. When an original is placed on the second glass 20 and an instruction to start reading the original is issued, the line sensor 40 is moved in the sub-scanning direction of the original (the direction indicated by the arrow 38) so as to face the second glass 20. . In the process, the image of the document on the second glass 20 is read by the line sensor 40 through the second glass 20.

  A partition member 51 (see FIGS. 1 and 2) is provided between the first glass 18 and the second glass 20 on the top surface of the document table 11. The partition member 51 is a long member that extends in the depth direction of the scanner 10 (the direction indicated by the arrow 39) similarly to the first glass 18 and the second glass 20. As shown in FIG. 2, the partition member 51 has a substantially L-shaped cross section in the width direction of the scanner 10. One end (the right side in FIG. 2) of the first glass 18 in the short direction is supported by the partition member 51. The partition member 51 is used as a document positioning reference when placing the document on the second glass 20. The partition member 51 has a display indicating the center position, the positions of both ends of various document sizes such as A4 (Japanese Industrial Standards A row No. 4) size and B5 (Japanese Industrial Standards B row No. 5) size. The document is placed on the second glass 20 with the center position marked on the partition member 51 as a reference.

  The upper surfaces of the first glass 18 and the second glass 20 are exposed when the document cover 17 is opened (see FIG. 1). By closing the document cover 17, the entire upper surface of the document table 11 including the first glass 18 and the second glass 20 is covered with the document cover 17. A document retainer 19 (see FIG. 1) that covers the second glass 20 is provided on the lower surface of the document cover 17. The document retainer 19 is composed of a sponge, a white plate and the like in order to retain the document placed on the second glass 20. When the document cover 17 is closed, the document placed on the second glass 20 is pressed toward the second glass 20 by the document cover 17 via the document presser 19. In addition, since the first glass 18 is provided on the upper surface of the document table 11, the document cover 17 is closed to constitute a part of the transport path 12. For this reason, the ADF 28 is used in a state where the document cover 17 is closed with respect to the document table 11.

  FIG. 3 is a plan view showing the internal configuration of the document table 11. FIG. 3 shows a state in which the upper cover 16 is removed.

  As shown in FIG. 3, an image reading unit 14 is provided inside the housing 15 of the document table 11. The image reading unit 14 reads a document through the first glass 18 or the second glass 20. The image reading unit 14 includes a line sensor 40, a carriage 41, a guide shaft 42, and a belt driving mechanism 43.

  The line sensor 40 irradiates the original with light from a light source and reads reflected light from the original for each main scanning line. As the line sensor 40, a reading device having a short focal length is used. In the present embodiment, the line sensor 40 is a so-called contact image sensor (CIS). Although not shown in the drawing, the line sensor 40 includes a light source, a lens, and a light receiving element. The line sensor 40 irradiates the original with light from the light source through the first glass 18 or the second glass 20. In other words, the line sensor 40 irradiates the original conveyed by the ADF 28 with light through the first glass 18, or irradiates the original placed on the second glass 20 with light through the second glass 20. The line sensor 40 condenses the reflected light from the document on a light receiving element by a lens and converts it into an electrical signal (image signal). Thereby, an image of a document is obtained. The light receiving elements of the line sensor 40 are arranged side by side in the main scanning direction (direction indicated by the arrow 39) of the document, for example, in units of chips. The light source and lens of the line sensor 40 are arranged in the same direction as the light receiving element.

  The carriage 41 has the line sensor 40 mounted on the upper side thereof (see FIG. 2). Inside the housing 15, a guide shaft 42 is installed over the width direction (left and right direction in FIG. 3). The carriage 41 is fitted with the guide shaft 42. The carriage 41 is driven by the belt drive mechanism 43 and moves on the guide shaft 42 in the direction indicated by the arrow 38. Rollers 30 (see FIGS. 2 and 3) are provided on the upper surface of the carriage 41 corresponding to both ends of the carriage 41 in the longitudinal direction. Each roller 30 is pivotally supported by the carriage 41 so as to be able to roll in the moving direction of the carriage 41 (the direction indicated by the arrow 38). Each roller 30 protrudes upward from the upper surface of the carriage 41 evenly. A guide member 34 (see FIG. 2) is provided on the upper surface side of the housing 15. The guide member 34 is an elongated flat plate member that extends in the moving direction of the carriage 40. The guide member 34 is disposed along a trajectory along which the roller 30 moves. Each roller 30 abuts on the back surface of the guide member 34 (see FIG. 2). Thereby, a certain gap is formed between the upper surface of the line sensor 40 and the back surface of the second glass 20. The focal point of the line sensor 40 coincides with the upper surface of the second glass 20 due to this constant gap. As the rollers 30 roll, the carriage 41 is smoothly moved along the guide member 34. Since the line sensor 40 is mounted on the carriage 41, the line sensor 40 is moved to face the first glass 18 or the second glass 20.

  The belt drive mechanism 43 (see FIG. 3) includes a drive belt 44, a drive pulley 45, and a driven pulley 46. As shown in FIG. 3, the drive pulley 45 and the driven pulley 46 are respectively provided at both ends of the housing 15 in the width direction. The drive belt 44 is an endless ring having teeth on the inside, and is stretched between the drive pulley 45 and the driven pulley 46. A driving force is transmitted to the shaft of the driving pulley 45 from a CR (carriage) motor 65 (corresponding to the driving unit of the present invention: see FIG. 4). The drive belt 44 is rotated by the rotation of the drive pulley 45, and the line sensor 40 mounted on the carriage 41 is moved to face the first glass 18 or the second glass 20. For example, a stepping motor is used as the CR motor 65. The position of the line sensor 40 in the width direction of the scanner 10 (the direction indicated by the arrow 39) is monitored by measuring the number of steps of the CR motor 65.

  The document conveyed by the ADF 28 is moved along the first glass 18. An image of the original is read through the first glass 18 by the line sensor 40 disposed below the first glass 18. For this reason, on the upper surface of the first glass 18, a document reading surface 25 (see FIG. 2) by the line sensor 40 is formed. Here, the reading surface 25 is a reading area of the line sensor 40 in the first glass 18. In other words, the image of the document passing over the first glass 18 is read by the line sensor 40 in the reading region 25 on the upper surface of the first glass 18. As shown in FIG. 2, the reading surface 25 is inclined with respect to a plane on which the line sensor 40 moves (a plane parallel to the paper surface of FIG. 3: hereinafter also referred to as “moving plane”). In the present embodiment, the reading surface 25 is separated from the moving surface on the downstream side (the right side in FIG. 2) from the upstream side (the left side in FIG. 2) in the transport direction of the document in the transport path 12 (see FIG. 2). . For this reason, the original document being conveyed is pressed against the first glass 18. As a result, it is possible to prevent the relative distance between the upper surface of the line sensor 40 and the reading surface 25 from being changed due to the floating of the document with respect to the first glass 18.

  The line sensor 40 is moved to face the first glass 18 by the driving force applied from the CR motor 65. The driving of the CR motor 65 is controlled by a control unit 55 (see FIG. 4) described later. The control unit 55 corresponds to a control unit, a setting unit, a reception unit, a calculation unit, a determination unit, a first notification unit, a first determination unit, a second notification unit, a second determination unit, and a partition unit of the present invention. As described above, the reading surface 25 of the first glass 18 is inclined with respect to the moving surface. The controller 55 drives the CR motor 65 to move the line sensor 40 (carriage 41) in the direction indicated by the arrow 38. Depending on the position of the line sensor 40, the position of the reading surface 25 moves in the short direction of the first glass 18 (see FIG. 6). Thereby, the control unit 55 changes the relative distance between the reading surface 25 of the document on the first glass 18 and the line sensor 40 (hereinafter also referred to as “first relative distance”) (D1 in FIG. 6). To D3). Since the first relative distance is changed using the CR motor 65 that is the drive source of the line sensor 40, the first relative distance can be changed with a simple configuration. That is, the first relative distance can be easily changed without newly adding a member for changing the first relative distance. By changing the first relative distance, the focus of the line sensor 40 can be changed with respect to the reading surface 25 of the document, and the document conveyed by the ADF 28 can be read.

  Note that the inclination angle of the reading surface 25 with respect to the moving surface is not particularly limited. However, the inclination angle is preferably set based on the MTF (Modulation Transfer Function) characteristic of the line sensor 40. When the inclination angle is increased, the change in the first relative distance with respect to the movement of the line sensor 40 is increased. Conversely, when the inclination angle is reduced, the change in the first relative distance due to the movement of the line sensor 40 is reduced. Therefore, when using a reading device with a very narrow focus range as the line sensor 40, it is preferable to set the tilt angle to be small. On the contrary, when using a reading device with a relatively wide focus range as the line sensor 40, the tilt angle may be set larger. Further, the reading surface 25 may be separated from the moving surface on the upstream side with respect to the downstream side in the transport direction of the document in the transport path 12. However, in order to prevent the document from floating with respect to the reading surface 25, it is preferable that the reading surface 25 is separated from the moving surface on the downstream side of the document conveying direction upstream side.

  As shown in FIG. 2, a platen 49 is provided above the first glass 18. The surface of the platen 49 facing the first glass 18 extends along the first glass 18 in the depth direction of the scanner 10 (the direction indicated by the arrow 39). The platen 49 is attached to a member (not shown) constituting the ADF 28 via a coil spring 35. Although not shown in the figure, convex portions projecting toward the first glass 18 are provided at both ends of the platen 49 in the longitudinal direction. By this convex portion, when the document cover 17 is closed, the first glass 18 and the platen 49 are arranged to face each other with a predetermined interval. The predetermined interval is set slightly longer than the thickness of the document. For this reason, the document is smoothly conveyed along the first glass 18 without being restricted by the platen 49.

  As shown in FIGS. 1 and 2, a reference member 37 is provided on the opposite side of the second glass 20 across the first glass 18. The reference member 37 is provided on the back surface of the upper cover 16. The reference member 37 is an image that is read by the line sensor 40 as a lightness reference of the line sensor 40. That is, the reference member 37 is used for adjusting the light amount of the line sensor 40 and acquiring white reference data 90 to 92 (see FIG. 5). The light amount adjustment and the acquisition of the white reference data 90 to 92 will be described in detail later. The reference member 37 is a thin-film strip-shaped member having substantially the same length as the line sensor 40 in the main scanning direction of the line sensor 40, and the surface facing the line sensor 40 is white. The reference member 37 is attached to the back surface of the inclined portion 48 formed on the upper cover 16. The inclined portion 48 is inclined at the same inclination angle as the first glass 18 with respect to the moving surface. For this reason, the reading surface 27 of the reference member 37 is inclined with respect to the moving surface at substantially the same angle as the first glass 18. Here, the reading surface 27 does not indicate the entire back surface of the reference member 37 but means a surface of the reference member 37 that is read by the line sensor 40. As shown in FIG. 2, the first glass 18 and the reference member 37 are inclined in line symmetry with respect to the width direction of the scanner 10.

  The controller 55 drives the CR motor 65 to move the line sensor 40 (carriage 41), whereby the relative distance between the reading surface 27 of the reference member 37 and the line sensor 40 (hereinafter referred to as “second relative distance”). Change). Since the second relative distance is changed using the CR motor 65 that is a drive source of the line sensor 40, the second relative distance can be changed with a simple configuration. That is, the second relative distance can be easily changed without newly adding a member for changing the second relative distance between the line sensor 40 and the reference member 37. By changing the second relative distance, the focus of the line sensor 40 can be changed and the reading surface 27 can be read.

  As shown in FIG. 1, an operation panel 13 is provided in the upper front portion of the scanner 10. The operation panel 13 includes a liquid crystal display for displaying various information, an input key for the user to input information, and the like. The scanner 10 operates based on an operation input from the operation panel 13. A user's operation input for instructing to start reading a document placed on the second glass 20 or a document placed on the document tray 22 is performed from the operation panel 13. The scanner 10 is operated not only by an instruction from the operation panel 13 but also by an instruction connected to a computer and transmitted from the computer via a scanner driver or the like.

  FIG. 4 is a block diagram illustrating a configuration example of the control unit 55 of the scanner 10. FIG. 5 is a block diagram illustrating a configuration example of the image processing circuit 79.

  The control unit 55 controls the overall operation of the scanner 10. As shown in FIG. 4, the control unit 55 mainly includes a CPU (Central Processing Unit) 56, a ROM (Read Only Memory) 57, a RAM (Random Access Memory) 58, and an EEPROM (Electrically Erasable and Programmable ROM) 59. It is configured as a microcomputer. The control unit 55 is connected to the motor control circuit 124, the motor control circuit 125, the reading control circuit 126, the image processing control circuit 127, the panel control circuit 128, and the sensor input circuit 129 via the bus 60.

  The ROM 57 stores a control program for controlling various operations of the scanner 10 by the CPU 56. The RAM 58 is a storage area or a work area for temporarily storing various data used when the control program is executed by the CPU 56. As shown in FIG. 5, the RAM 58 includes a first light amount adjustment value 101, a second light amount adjustment value 102, a third light amount adjustment value 103, first white reference data 90, second white reference data 91, and third white reference. Data such as data 92 is stored. These data will be described in detail later.

  The RAM 58 stores the reading mode information 24 (see FIG. 4). The reading mode information 24 is information indicating a document reading mode set by the control unit 55 based on an operation input from the operation panel 13. Reading of the original conveyed by the ADF 28 is performed based on the reading mode information 24. In the present embodiment, the control unit 55 includes a normal mode (corresponding to the first mode of the present invention), a moire reduction mode (an example of the second mode of the present invention), and a blurring mode (an example of the second mode of the present invention). ) Is set. The normal mode is a reading mode in which the control unit 55 reads the document through the first glass 18 with the line sensor 40 in a state where the first relative distance is substantially matched with the focal length of the line sensor 40. In other words, the normal mode is a reading mode in which the original is read in a state where the line sensor 40 is focused on the reading surface 25 of the original on the first glass 18. The moire reduction mode and the blurring mode are reading modes in which the control unit 55 reads the original through the first glass 18 by the line sensor 40 in a state where the first relative distance is different from the focal length of the line sensor 40. Note that the first relative distance is greatly different between the moire reduction mode and the blurring mode. The moiré reduction mode is a reading mode in which the original is read with the focus of the line sensor 40 slightly shifted from the original reading surface 25 of the first glass 18. In the blurring mode, a partial area of the document (outside the blurring area described later) is read with the focus of the line sensor 40 slightly shifted from the reading surface 25, and the focus of the line sensor 40 is largely shifted from the reading surface 25. This is a reading mode for reading the remaining area of the document (in a blur area described later).

  Note that the reading mode information 24 may be set based on an instruction transmitted from a computer instead of an operation input from the operation panel 13. In the present embodiment, a mode in which the second mode of the present invention includes two reading modes, a moire reduction mode and a blur mode, will be described, but the second mode may be any one of these modes. In other words, the control unit 55 may set the normal mode or the moire reduction mode, or set the normal mode or the blur mode.

  The EEPROM 59 stores various settings, flags, and the like that should be retained even after the power is turned off. In the present embodiment, the EEPROM 59 stores a first position 31, a second position 32, and a third position 33. The position information is information indicating the reading position in the sub-scanning direction where the line sensor 40 is arranged with respect to the reading mode information 24 set in the RAM 58. The first position 31 is a reading position where the line sensor 40 is in focus with respect to the reading surface 25. The second position 32 is a reading position where the line sensor 40 is slightly out of focus from the reading surface 25. The third position 33 is a reading position where the focus of the line sensor 40 is further shifted from the reading surface 25 as compared to the second position 32.

  FIG. 6 is a schematic cross-sectional view illustrating the reading position of the line sensor 40, where (A) is a reading position corresponding to the first position 31, (B) is a reading position corresponding to the second position 32, and (C). Indicates a reading position corresponding to the third position 33.

  The reading mode information 24 in the RAM 58 is set to the normal mode, and the document conveyed by the ADF 28 is read. The image of the original is read on the reading surface 25 in a state where the line sensor 40 is disposed at the reading position corresponding to the first position 31 (see FIG. 6A). Since the first position 31 is a position where the line sensor 40 is in focus with respect to the reading surface 25, a clear document image with high resolution can be obtained. That is, the normal mode is a reading mode suitable for reading a photographic document or the like in which moiré is unlikely to occur.

  The reading mode information 24 in the RAM 58 is set to the moire reduction mode, and the document conveyed by the ADF 28 is read. The image of the original is read on the reading surface 25 in a state where the line sensor 40 is disposed at the reading position corresponding to the second position 32 (see FIG. 6B). Since the second position 32 is a position where the focus of the line sensor 40 is shifted from the reading surface 25, an image of a document in which the occurrence of moire is suppressed can be obtained. That is, the moire reduction mode is a reading mode suitable for reading a halftone document in which moire tends to occur.

  The reading mode information 24 in the RAM 58 is set to the blur mode, and the document conveyed by the ADF 28 is read. In the original, an image outside a blur area to be described later is read in a state where the line sensor 40 is disposed at a reading position corresponding to the second position 32 (see FIG. 6B). Further, the image of the remaining area (in the blur area) is read from the document in a state in which the line sensor 40 is disposed at the reading position corresponding to the third position 33 (see FIG. 6C). As a result, the occurrence of moiré is suppressed with respect to the image outside the blur area, and an image of the original that is blurred until the image in the blur area cannot be identified is obtained. That is, the blur mode is a reading mode suitable for blurring and reading a partial area of the document. The method for determining the first position 31, the second position 32, and the third position 33, and the document reading operation in each reading mode will be described in detail later.

  The document image (image data) read by the line sensor 40 through the first glass 18 is enhanced (sharpened) by a filter processing circuit 85 (see FIG. 5) described later. The EEPROM 59 stores coefficients (enhancement coefficients) 75 and 76 used for this enhancement process. The first coefficient 75 (an example of the first enhancement coefficient of the present invention) and the second coefficient 76 (an example of the second enhancement coefficient of the present invention) will be described in detail later.

  As shown in FIG. 4, a drive circuit 71 is connected to the motor control circuit 124. A drive circuit 66 is connected to the motor control circuit 125. A line sensor 40 and an AFE (Analog Front End) circuit 78 are connected to the reading control circuit 126. An image processing circuit 79 is connected to the image processing control circuit 127. The operation panel 13 is connected to the panel control circuit 128. A document detection sensor 36 is connected to the sensor input circuit 129.

  The drive circuit 71 drives the motor 72. The motor 72 is configured to be rotatable in both forward and reverse directions. The drive circuit 71 receives the output signal from the motor control circuit 124 and generates a pulse signal for rotating the motor 72. Based on this pulse signal, the motor 72 is rotated. The motor 72 applies a driving force to the roller 73 and is a driving source in the ADF 28. The control unit 55 counts the number of pulses of the pulse signal generated by the drive circuit 71. Thereby, the number of steps of the motor 72 is counted. The counted number of steps is temporarily stored in the RAM 58.

  The image reading unit 14 executes a document reading operation and outputs an image of the document as an image signal. The image reading unit 14 includes a line sensor 40, a carriage 41, a CR motor 65, and a drive circuit 66. The drive circuit 66 supplies a drive signal to the CR motor 65 based on the phase excitation signal or the like input from the motor control circuit 125. The CR motor 65 is a stepping motor, for example. The CR motor 65 rotates in response to the drive signal. Thereby, the carriage 41 is reciprocated. The drive circuit 66 also adjusts the operating current for turning on the light source of the line sensor 40. Further, the control unit 55 controls the image reading unit 14 based on a control program stored in the ROM 57, so that the light amount adjustment values 101, 102, 103 and the white reference data 90, 91 in addition to the document reading operation. , 92 are acquired.

  The line sensor 40 irradiates light on a document placed on the second glass 20 or a document conveyed on the first glass 18 by the ADF 28 from a light source, and reads the document image line by line. The read image is output from the line sensor 40 to the AFE circuit 78 as an image signal (image data).

  The line sensor 40 is moved by the carriage 41 so as to face the second glass 20 on which the document is placed. In this process, the line sensor 40 repeats the operation of irradiating the original from the light source through the second glass 20 and outputting the reflected light from the original as an image signal of one line. Thereby, an image of the entire document placed on the second glass 20 is obtained.

  The line sensor 40 is moved by the carriage 41 and disposed at a position facing the first glass 18. In this state, the document placed on the document tray 22 is transported along the transport path 12 by the ADF 28. In this process, the line sensor 40 repeats the operation of irradiating the original from the light source through the first glass 18 and outputting the reflected light from the original as an image signal of one line. As a result, an image of the entire document passing over the first glass 18 is obtained.

  The AFE circuit 78 samples and holds analog image signals output from the line sensor 40, digitally converts the sampled and held image signals, and serializes them. The digital conversion is a process of converting an analog image signal output from the line sensor 40 into a digital signal composed of a digital code having a predetermined number of bits. This digital conversion is performed by an analog / digital converter. The analog image signal input to the AFE circuit 78 is output to the image processing circuit 79 as a digital image signal of, for example, 8 bits (256 gradations: 0 to 255).

  As shown in FIG. 5, the image processing circuit 79 includes a sampling circuit 81, a dark correction circuit 82, a shading correction circuit 83, a γ correction circuit 84, a filter processing circuit 85, a resolution conversion circuit 86, a color conversion processing circuit 87, and A binarization processing circuit 88 is included.

  The sampling circuit 81 samples the image signal output from the AFE circuit 78. The dark correction circuit 82 corrects the image signal output from the sampling circuit 81 in order to correct the variation between the light receiving elements of the line sensor 40. This image signal correction is performed based on the black reference data stored in the RAM 58. The black reference data is data obtained by reading a reference member (not shown) in a state where the line sensor 40 turns off the light source.

  The shading correction circuit 83 performs shading correction on the image signal output from the dark correction circuit 82. By performing the shading correction, variations between the light receiving elements of the line sensor 40 and the light sources are corrected. The shading correction by the shading correction circuit 83 is performed based on any of the white reference data 90, 91, 92. A document image signal read in a state where the line sensor 40 is disposed at a reading position corresponding to the first position 31 is subjected to shading correction based on the first white reference data 90. The image signal of the document read in a state where the line sensor 40 is disposed at the reading position corresponding to the second position 32 is subjected to shading correction based on the second white reference data 91. The document image signal read in a state where the line sensor 40 is disposed at the reading position corresponding to the third position 33 is subjected to shading correction based on the third white reference data 92.

  The filter processing circuit 85 performs enhancement (sharpening) processing on the image signal of the document. The emphasis process is a process for emphasizing a change in shading of an image signal of a document. The enhancement process is performed by subtracting a secondary differential value or the like from the target pixel. The filter processing circuit 85 emphasizes the image signal of the document based on the following equation (1).

  In the arithmetic expression of Expression 1, g (x, y) is image data after enhancement processing. f (x, y) is input image data input to the filter processing circuit 85. h is a filter coefficient. H for subtracting the secondary differential value from the pixel of interest is shown in Equation 2 below.

  In the arithmetic expression of Expression 2, when k is increased, the secondary differential value to be subtracted increases and the degree of emphasis increases. Therefore, k is an enhancement coefficient. In the present embodiment, the enhancement coefficient k is changed according to the reading position (the first position 31 to the third position 33) where the line sensor 40 is disposed. When the image signal of the document is obtained in a state where the line sensor 40 is disposed at the reading position corresponding to the first position 31, the first coefficient 75 is used as the enhancement coefficient k. When the image signal of the document is obtained with the line sensor 40 placed at the reading position corresponding to the second position 32, the second coefficient 76 is used as the enhancement coefficient k. The coefficients 75 and 76 are set so that the second coefficient 76 is larger than the first coefficient 75.

  The γ correction circuit 84, the resolution conversion circuit 86, the color conversion processing circuit 87, and the binarization processing circuit 88 are well known and will not be described in detail.

  The panel control circuit 128 generates a signal for controlling the liquid crystal display of the operation panel 13 based on an instruction from the control unit 55. The panel control circuit 128 includes an interface circuit that transmits information input from the operation panel 13 to the control unit 55.

  The sensor input circuit 129 removes noise from the output signal (sensor signal) from the document detection sensor 36 (see FIG. 4) and outputs the signal to a predetermined output destination. The document detection sensor 36 detects the presence or absence of a document in the document tray 22 (see FIG. 1), and is arranged at a predetermined position on the document tray 22. The document detection sensor 36 is a mechanical sensor in the present embodiment. The document detection sensor 36 includes a transmission type optical sensor (photo interrupter) and a shielding member pivotally supported. In the photo interrupter, a light emitting unit that emits light and a light receiving unit that receives light emitted from the light emitting unit are arranged to face each other. The document detection sensor 36 outputs a sensor signal based on the fact that light is received by the light receiving portion of the photo interrupter. In a state where the shielding member is in a position that blocks the optical path between the light emitting unit and the light receiving unit, the light emitted from the light emitting unit is blocked by the shielding member and is not received by the light receiving unit. Since the shielding member is detected, the document detection sensor 36 is in the OFF state. When a document is placed on the document tray 22, the document contacts the shielding member and the shielding member is rotated. As a result, the shielding member leaves the position where the optical path of the photo interrupter is blocked. For this reason, the light emitted from the light emitting unit is received by the light receiving unit. That is, the document detection sensor 36 is turned on. As described above, since the state of the document detection sensor 36 is changed by placing the document on the document tray 22, the control unit 55 controls the document tray 22 based on the sensor signal output from the sensor input circuit 129. The presence or absence of a document can be determined.

  The processing for setting the reading position is performed at a predetermined timing such as when the power is turned on or when a predetermined operation input is performed by the user. Further, the process for setting the reading position may be executed when a predetermined time elapses from the previous reading position setting process or when the power is turned on after the predetermined time elapses. FIG. 7 to FIG. 10 are flowcharts showing a processing procedure when processing for setting a reading position is performed when the scanner 10 is powered on. Note that the processing of the scanner 10 described based on the following flowchart is performed according to a command issued by the control unit 55 based on a control program stored in the ROM 57.

  The control unit 55 determines whether the power of the scanner 10 is turned on based on whether a predetermined operation input is performed by the user from the operation panel 13 (S1). When the control unit 55 determines that the power is not turned on (S1: NO), it enters a standby state. When it is determined that the power of the scanner 10 is turned on (S1: YES), the control unit 55 determines whether the reading position of each mode is stored (S2). Specifically, the control unit 55 determines whether or not the first position 31, the second position 32, and the third position 33 are stored in the EEPROM 59. When the control unit 55 determines that all the reading positions are stored (S2: YES), the process ends.

  When the control unit 55 determines that any one of the first position 31, the second position 32, and the third position 33 is not stored (S2: NO), the first position 31 is stored. It is determined whether or not (S3). When it is determined that the first position 31 is not stored in the EEPROM 59 (S3: NO), the control unit 55 notifies that the first test document 98 is to be placed on the document tray 22 (S4). For example, the control unit 55 causes the operation panel 13 to display a message such as “Please set the first test document on the document tray”.

  FIG. 11 is a schematic diagram illustrating an example of the first test document 98. FIG. 12 is a schematic cross-sectional view showing how the reading position of the line sensor 40 is changed.

  As shown in FIG. 11, the first test original 98 is obtained by recording white and black stripe patterns (an example of a predetermined pattern according to the present invention) at a pitch of 150 lpi (line per inch). The first test document 98 is placed on the document tray 22 such that the pattern arrangement direction (the left-right direction in FIG. 11) matches the depth direction of the scanner 10 (the direction indicated by the arrow 39). Note that the pitch of the black and white pattern is not limited to 150 lpi, and may be changed as appropriate according to the performance of the line sensor 40 and the like.

  The control unit 55 determines whether or not the first test document 98 is placed on the document tray 22 based on the sensor signal output from the document detection sensor 36 (see FIG. 4) (S5). When the control unit 55 determines that the first test document 98 is not placed on the document tray 22 (S5: NO), the process of step S4 is continued. When determining that the first test document 98 is placed on the document tray 22 (S5: YES), the control unit 55 controls the CR motor 65 (see FIG. 4) to move the line sensor 40 to the reading start position. (S6). The reading start position is the left end of the readable range (see FIG. 2) of the line sensor 40 with respect to the first glass 18 (see FIG. 12A). The control unit 55 controls the motor 72 (see FIG. 4) to convey the first test original 98 along the conveyance path 12 by a predetermined amount. As a result, the black and white pattern recorded on the first test document 98 is arranged above the first glass 18. Then, the control unit 55 reads the first test document 98 through the first glass 18 by the line sensor 40 (S7). In the process of step S7, the image of the first test document 98 is read for one line or several lines. The control unit 55 obtains the MTF value based on the image signal of the first test document 98 read by the process of step S7 and the following equation (3) (S8).

  In the arithmetic expression of Expression 3, Imax is the maximum density of the input image. In other words, Imax is the theoretical value of the highest density of the image recorded on the first test document 98. Imin is the minimum density of the input image. In other words, Imin is a theoretical value of the minimum density of the image recorded on the first test document 98. Dmax is the maximum density of the output image. Dmin is the minimum density of the output image.

  Following the processing of step S8, the control unit 55 determines whether or not the first set number (six in this embodiment) of MTF values has been acquired (S9). When it is determined that the six MTF values have not been acquired (S9: NO), the control unit 55 controls the CR motor 65 to move the line sensor 40 toward the reading end position (see FIG. 12) by the first distance. Move (S10). By performing the processing of step S10, the reading position of the line sensor 40 is changed. In other words, the first relative distance is changed. The reading surface 25 of the first glass 18 is separated from the moving surface of the line sensor 40 on the downstream side from the upstream side in the document transport direction. For this reason, the first relative distance increases as the line sensor 40 is moved. The reading end position is the right end of the readable range (see FIG. 2) of the line sensor 40 with respect to the first glass 18 (see FIG. 12C).

  After the reading position of the line sensor 40 is changed by the process of step S10, the processes of steps S7 and S8 are performed in a state where the line sensor 40 is disposed at the reading position. The control unit 55 repeats the processes of step S7, step S8, and step S10 in order, so that the first test original 98 is first placed at a plurality of (six in the present embodiment) positions with different first relative distances. The line sensor 40 is caused to execute an operation of reading through the glass 18. And the control part 55 calculates | requires MTF value for every six positions based on the image signal of the 1st test original 98 obtained by this operation | movement.

  FIG. 13 is a diagram showing the MTF characteristics obtained by reading the first test document 98.

  In FIG. 13A, the horizontal axis changes by moving the line sensor 40 by driving the CR motor 65 and the relative relationship between the line sensor 40 and the reading surface 25 of the first test document 98 in the first glass 18. The distance, that is, the first relative distance is shown. The vertical axis represents the MTF value. FIG. 13A shows MTF values corresponding to six reading positions having different first relative distances. “1” on the horizontal axis corresponds to the first relative distance between the line sensor 40 and the first test document 98 when the line sensor 40 is disposed at the reading start position (see FIG. 12A). “6” on the horizontal axis corresponds to the first relative distance between the line sensor 40 and the first test document 98 in a state where the line sensor 40 is disposed at the reading end position (see FIG. 12C). As shown in FIG. 13A, the line sensor 40 is arranged at the reading position (see FIG. 12B) corresponding to the first relative distance whose horizontal axis is “3.1” in the MTF curve 68. The MTF value of the image signal obtained in is the largest.

  In the present embodiment, the first distance is set so that the reading position of the line sensor 40 is changed to six positions between the reading start position and the reading end position in order to acquire six MTF values. Has been. The first distance is set based on the distance from the reading start position to the reading end position and the first set number. Note that the number of MTF values to be acquired is not limited to six. For example, ten MTF values may be acquired by changing the first distance.

  When it is determined that the six MTF values have been acquired (S9: YES), the control unit 55 determines the reading position where the MTF value is maximized as the temporary reading position (S11). Specifically, the control unit 55 obtains the MTF curve 68 (see FIG. 13A) from the six MTF values obtained by repeating the processes of steps S8 to S10. Since the method for obtaining the MTF curve 68 from the MTF value is well known, the description of the method is omitted here. The control unit 55 determines the position of the line sensor 40 having the maximum MTF value from the MTF curve 68 as the temporary reading position. Here, in the MTF characteristic of FIG. 13A, the MTF value corresponding to the first relative distance whose horizontal axis is represented by “3.1” is the maximum. Therefore, the control unit 55 determines the reading position (see FIG. 12B) of the line sensor 40 at which the horizontal axis is the first relative distance represented by “3.1” as the temporary reading position. The temporary reading position may be determined without obtaining the MTF curve 68. That is, the control unit 55 may determine the maximum value among the six MTF values and determine the reading position of the line sensor 40 corresponding to the MTF value as the temporary reading position. The temporary reading position is temporarily stored in a predetermined area of the RAM 58.

  As shown in FIG. 8, after performing the process of step S <b> 11, the control unit 55 moves the line sensor 40 from the temporary reading position to the position where the first distance is returned to the reading start position side (S <b> 13). Specifically, the control unit 55 rotates the CR motor 65 in the direction opposite to the process of step S10, and moves the line sensor 40 arranged at the reading end position to the position returned by the half. The control unit 55 reads the first test document 98 in the same manner as the process of step S7 (S14). Then, the control unit 55 obtains the MTF value based on the image signal of the first test document 98 read again by the process of step S14 as in the process of step S8 (S15).

  The control unit 55 determines whether or not the first set number (here, 6) of MTF values has been acquired (S16). The process of step S16 is performed in the same manner as the process of step S9. When determining that the six MTF values have not been acquired (S16: NO), the control unit 55 controls the CR motor 65 to move the line sensor 40 toward the reading end position by the second distance (S17). . The second distance is set to about 20% of the first distance in the present embodiment. For this reason, by performing the process of step S17, the reading position of the line sensor 40 is finely changed compared to the process of step S10.

  After the reading position of the line sensor 40 is changed by the process of step S17, the processes of step S14 and step S15 are performed in a state where the line sensor 40 is arranged at the reading position. The controller 55 repeats the processes of step S14, step S15, and step S17, so that the first test original 98 is at a plurality of (here, six) positions having different first relative distances before and after the provisional reading position. The line sensor 40 is caused to execute an operation of reading the image through the first glass 18. And the control part 55 calculates | requires MTF value for every six positions based on the image signal of the 1st test original 98 obtained by this operation | movement.

  In FIG. 13B, the horizontal axis indicates the first relative distance between the line sensor 40 and the first test document 98 that is changed by moving the line sensor 40 before and after the provisional reading position “3.1”. ing. The vertical axis represents the MTF value. FIG. 13B shows MTF values corresponding to six reading positions before and after the provisional reading positions having different first relative distances.

  When it is determined that the six MTF values have been acquired (S16: YES), the control unit 55 determines the reading position where the MTF value is maximized as the first position 31 (S18). Specifically, the control unit 55 obtains the MTF curve 69 (see FIG. 13B) from the six MTF values obtained by repeating the processing of step S14 to step S17. The control unit 55 determines the position of the line sensor 40 that maximizes the MTF value from the obtained MTF curve 69 as the first position 31. Here, in the MTF characteristic of FIG. 13B, the MTF value corresponding to the first relative distance whose horizontal axis is represented by “3.4” is the maximum. Therefore, the control unit 55 sets the reading position (see FIG. 6A) of the line sensor 40 at the first relative distance D1 (see FIG. 6A) whose horizontal axis is represented by “3.4”. 1 position 31 is determined. The process of step S18 is performed on the condition that the control unit 55 determines that the first test document 98 is placed on the document tray 22 in step S5. The first position 31 is information indicating a reading position for the normal mode. The first position 31 is stored in the EEPROM 59. Thereby, when the reading mode is set to the normal mode, the line sensor 40 is arranged at the reading position corresponding to the first position 31 by the CR motor 65 when the original is read through the first glass 18.

  When it is determined that the first position 31 is stored in the EEPROM 59 (S3: YES), or when the process of step S18 is performed, the control unit 55 determines whether or not the second position 32 is stored in the EEPROM 59. Judgment is made (S21). When it is determined that the second position 32 is not stored in the EEPROM 59 (S21: NO), the control unit 55 notifies that the second test document 99 is to be placed on the document tray 22 (S22). For example, the control unit 55 causes the operation panel 13 to display a message such as “Please set the second test document on the document tray”.

  FIG. 14 is a schematic diagram illustrating an example of the second test document 99.

  As shown in FIG. 14, the second test document 99 is obtained by recording white and black stripe patterns at a pitch of 75 lpi. The second test document 99 is placed on the document tray 22 so that the pattern arrangement direction (the left-right direction in FIG. 14) matches the depth direction of the scanner 10 (the direction indicated by the arrow 39). The pitch of the black and white stripe pattern is not limited to 75 lpi, and may be appropriately changed according to the performance of the line sensor 40 and the like.

  The control unit 55 determines whether or not the second test document 99 is placed on the document tray 22 based on a sensor signal output from the document detection sensor 36 (see FIG. 4) (S23). When the control unit 55 determines that the second test document 99 is not placed on the document tray 22 (S23: NO), the process of step S22 is continued. When it is determined that the second test document 99 is placed on the document tray 22 (S23: YES), the control unit 55 moves the line sensor 40 to the reading start position (S24) as in the process of step S6. The controller 55 controls the motor 72 to convey the second test document 99 along the conveyance path 12 by a predetermined amount. As a result, the black and white pattern recorded on the second test document 99 is arranged above the first glass 18. Then, the control unit 55 reads the second test document 99 through the first glass 18 by the line sensor 40 (S25). The control unit 55 obtains the MTF value based on the image signal of the second test document 99 read by the process of step S25 and the arithmetic expression of the above expression 3 (S26).

  The control unit 55 determines whether or not the second set number (11 in this embodiment) of MTF values has been acquired (S27). When the control unit 55 determines that eleven MTF values have not been acquired (S27: NO), the control unit 55 controls the CR motor 65 to move the line sensor 40 to the reading end position (see FIG. 12C) side. Move by 3 distances (S28). As a result, the first relative distance between the line sensor 40 and the second test document 99 is changed. The third distance is a distance set based on the distance from the reading start position to the reading end position and the third set number. Therefore, for example, if the second set number is changed, it is changed accordingly.

  After the reading position of the line sensor 40 is changed by the process of step S28, the processes of steps S25 and S26 are performed in a state where the line sensor 40 is disposed at the reading position. The control unit 55 reads the second test document 99 through the first glass 18 at a plurality of (here, 11) positions having different first relative distances by repeating the processes of step S25, step S26, and step S28. Is executed by the line sensor 40. And the control part 55 calculates | requires an MTF value for every 11 positions based on the image signal of the 2nd test original 99 obtained by this operation | movement.

  FIG. 15 is a diagram showing the MTF characteristics obtained by reading the second test document 99.

  In FIG. 15, the horizontal axis changes by moving the line sensor 40 by driving the CR motor 65, that is, the relative distance between the line sensor 40 and the reading surface 25 of the second test document 99 on the first glass 18, that is, The first relative distance is shown. The vertical axis represents the MTF value. FIG. 15 shows MTF values corresponding to 11 reading positions having different first relative distances.

  When it is determined that 11 MTF values have been acquired (S27: YES), the controller 55 obtains the maximum MTF value (S29). Specifically, the control unit 55 obtains the MTF curve 63 (see FIG. 15) from the 11 MTF values obtained by repeating the processes of steps S25 to S28. Then, the control unit 55 determines the peak of the MTF curve 63 and obtains the maximum value of the MTF value. Here, as shown in FIG. 15, the MTF value corresponding to the first relative distance whose horizontal axis is represented by “3.5” is the maximum value.

  The control unit 55 determines the second position 32 as a position where the MTF value is less than the maximum value obtained in the process of step S29 and is equal to or greater than 80% of the maximum value (an example of a predetermined threshold in the present invention) ( S30). Specifically, the control unit 55 obtains an MTF value that is 80% of the maximum value obtained in step S29. For example, when the maximum value is 1, the MTF value is 0.8. The control unit 55 determines the position of the line sensor 40 corresponding to the obtained MTF value (here, 0.8). As is apparent from FIG. 15, there are two positions of the line sensor 40 where the MTF value is 0.8, with the position where the MTF value is the maximum. In other words, two identical MTF values are determined. On the condition of this, the control unit 55 determines the reading position (see FIG. 6B) having a shorter first relative distance corresponding to the MTF value as the second position 32. The process in step S30 is performed on condition that the control unit 55 determines that the second test document 99 is placed on the document tray 22 in step S23. Here, if the reading position having a longer first relative distance is set to the second position 32, the light emitted from the light source of the line sensor 40 to the original when the original floats on the first glass 18 occurs. The amount of light is greatly reduced. When the reading position with the shorter first relative distance is determined as the second position 32, the image of the read original becomes extremely unclear when the original floats on the first glass 18. It is prevented. The second position 32 is a reading position for the moire reduction mode. The second position 32 is stored in the EEPROM 59. As a result, when the reading mode is set to the moire reduction mode, the line sensor 40 is arranged at the reading position corresponding to the second position 32 by the CR motor 65 when the original is read through the first glass 18. As shown in FIG. 6B, the line sensor 40 is arranged at a reading position where the first relative distance is D2. Note that 80% of the maximum value of the MTF value is an example of a predetermined threshold, and may be appropriately changed according to the degree of moire.

  If the control unit 55 determines that the second position 32 is stored (S21: YES), or after performing the process of step S30, is the third position 33 (see FIG. 4) stored in the EEPROM 59? It is determined whether or not (S32). When the control unit 55 determines that the third position 33 is stored (S32: YES), the process ends. When it is determined that the third position 33 is not stored (S32: NO), the control unit 55 notifies the user that the third test document (not shown) is to be placed (S33). For example, the control unit 55 displays a message such as “Please set the third test document on the document tray” on the operation panel 13. Note that the third test document is one in which white and black stripe patterns are recorded at a pitch of 50 lpi, for example.

  The control unit 55 determines whether or not the third test document is placed on the document tray 22 (S34). The process of step S34 is performed in the same manner as the process of step S5. When the control unit 55 determines that the third test document is not placed on the document tray 22 (S34: NO), the process of step S33 is continued. When it is determined that the third test document is placed on the document tray 22 (S34: YES), the control unit 55 moves the line sensor 40 to the reading start position (S35) in the same manner as in step S6. The control unit 55 controls the motor 72 to convey the third test document along the conveyance path 12 by a predetermined amount. As a result, the black and white pattern recorded on the third test document is arranged above the first glass 18. Then, the control unit 55 reads the third test document through the first glass 18 by the line sensor 40 (S36). The control unit 55 obtains the MTF value based on the image signal of the third test document read by the process of step S36 and the arithmetic expression of the above expression 3 (S37).

  The control unit 55 determines whether a third set number (for example, 8) of MTF values has been acquired (S38). When it is determined that the eight MTF values have not been acquired (S38: NO), the control unit 55 controls the CR motor 65 to move the line sensor 40 to the reading end position (see FIG. 12C) side. Move by 4 distances (S39). As a result, the first relative distance between the line sensor 40 and the reading surface 25 of the second test document 99 in the first glass 18 is changed. The fourth distance is set based on the distance from the reading start position to the reading end position and the third set number.

  After the reading position of the line sensor 40 is changed by the process of step S39, the processes of step S36 and step S37 are performed in a state where the line sensor 40 is disposed at the reading position. The control unit 55 repeats the processes of step S36, step S37, and step S39, thereby reading the third test document through the first glass 18 at a plurality of (here, 8) positions having different first relative distances. The line sensor 40 is executed. And the control part 55 calculates | requires an MTF value for every position of 8 places based on the image signal of the 3rd test original document obtained by this operation | movement.

  When it is determined that eight MTF values have been acquired (S38: YES), the controller 55 obtains the maximum MTF value (S40). The process of step S40 is performed in the same manner as the process of step S29. That is, the process of step S40 is performed by obtaining an MTF curve from eight MTF values obtained by repeating the processes of step S36 to step S39, and determining the MTF value corresponding to the peak.

  The control unit 55 determines the position where the MTF value is less than 20% of the maximum value obtained in step S40 as the third position 33 (S41). Specifically, the control unit 55 obtains an MTF value that is 20% of the maximum value obtained in step S40. For example, when the maximum value is 1, the MTF value is 0.2. The control unit 55 determines the position of the line sensor 40 corresponding to the obtained MTF value (here, 0.2). Similar to the MTF curve 68 (see FIG. 13A) and the MTF curve 63 (see FIG. 15), the MTF curve obtained from the MTF value obtained in step S37 is a curve having a peak at the center. For this reason, two identical MTF values are determined from the MTF curve. The control unit 55 determines the reading position (see FIG. 6C) having the shorter first relative distance as the third position 33. The third position 33 is a reading position for the blur mode. The third position 33 is stored in the EEPROM 59. As a result, when the reading mode is set to the blur mode, the line sensor 40 is arranged at the reading position corresponding to the third position 33 by the CR motor 65 when reading the blur region of the document through the first glass 18. As shown in FIG. 6C, the line sensor 40 is arranged at the reading position where the first relative distance is D3. In the present embodiment, when the reading mode is set to the blur mode, an image outside the blur area of the document is read in a state where the line sensor 40 is disposed at a reading position corresponding to the second position 32. That is, in the blur mode, the document conveyed by the ADF 28 is read while changing the reading position of the line sensor 40 during reading. The document reading in the blur mode will be described in detail later.

  Thus, the first test original 98 (see FIG. 11) is read by the line sensor 40 through the first glass 18. The line sensor 40 is moved with respect to the first glass 18 by the CR motor 65. The position of the line sensor 40 with respect to the first glass 18 is changed, and the first test document 98 is read by the line sensor 40. Thereby, an image signal of the first test document 98 is obtained for each position where the line sensor 40 is disposed. Based on these image signals, the MTF value is obtained for each position of the line sensor 40 (see FIG. 13). Based on each MTF value, a first position 31 that is information indicating a reading position for the normal mode (see FIG. 6A) is determined. Similarly, the second position 32, which is information indicating the reading position (see FIG. 6B) for the moire reduction mode, is determined using the second test document 99 (see FIG. 14). Further, the third position 33 which is information indicating the reading position (see FIG. 6C) for the blur mode is determined using the third test document.

  As described above, the control unit 55 sets the reading position where the line sensor 40 is disposed by the CR motor 65 in the normal mode, the moire reduction mode, or the blurring mode based on each MTF value obtained by changing the reading position. Decide every time.

  Note that three patterns for determining the positions of the first position 31 to the third position 33 are recorded instead of the three sheets of the first test original 98, the second test original 99, and the third test original. The first position 31 to the third position 33 may be determined using a single test document. In this case, a test document in which three patterns are recorded side by side in the depth direction of the scanner 10 (the direction indicated by the arrow 39) is used. The control unit 55 reads the image of each pattern individually by changing the reading range of the test document in the main scanning direction. And the control part 55 determines the 1st position 31-the 3rd position 33 based on each acquired image. In this case, the time and effort for the user to place the test document on the document tray 22 is reduced. Alternatively, a test document in which three patterns are recorded side by side in the document transport direction may be used. In this case, it is only necessary to individually read the image of each pattern by changing the pattern arranged on the first glass 18 by conveying the test document.

  In the present embodiment, the three patterns are used to determine the first position 31 to the third position 33. However, the predetermined pattern used to determine these reading positions is one. It may be one. For example, the first position 31 to the third position 33 may be determined using only the first test original 98 without using the second test original 99 and the third test original. In this case, the control unit 55 determines the reading position corresponding to the maximum value of the MTF characteristic obtained by reading the pattern of the first test document 98 as the first position 31. Then, the control unit 55 determines the reading position corresponding to the MTF value that is 80% of the maximum value as the second position 32, and sets the reading position corresponding to the MTF value that is 50% of the maximum value to the third position. Position 33 is determined. That is, the number of patterns used for determining the first position 31 to the third position 33 is arbitrary.

  FIGS. 16 to 18 are flowcharts showing a procedure of processes performed in the scanner 10 when reading a document conveyed by the ADF 28.

  Based on the sensor signal output from the document detection sensor 36, the controller 55 determines whether or not a document is placed on the document tray 22 (S50). When the control unit 55 determines that no document is placed on the document tray 22 (S50: NO), a standby state is entered. When it is determined that the document is placed on the document tray 22 (S50: YES), the control unit 55 determines whether the reading mode is selected by a predetermined operation from the operation panel 13 (S51). When it is determined that the reading mode is not selected (S51: NO), the control unit 55 notifies the user that the reading mode is selected (S52). Specifically, the control unit 55 displays, for example, a message such as “Please select a reading mode” and selectable reading modes (in this embodiment, a normal mode, a moire reduction mode, and a blurring mode) on the operation panel. 13 is displayed. The process of step S52 is continued until the control unit 55 determines that the reading mode is selected in the process of step S51. When it is determined that the reading mode has been selected (S51: YES), the controller 55 stores the information in the RAM 58 as the reading mode information 24 (see FIG. 4) (S53). As described above, the control unit 55 accepts the selection of the normal mode, the moire reduction mode, or the blurring mode and sets one of the modes in the RAM 58. Note that the normal mode may be set as a default of the reading mode so that, for example, the normal mode is set when an instruction to start reading the document is issued without selecting the reading mode.

  The controller 55 determines whether or not a document reading start command is input based on the presence or absence of a predetermined operation input from the operation panel 13 (S54). If the control unit 55 determines that a document reading start command has not been input (S54: NO), the process returns to step S54. When the control unit 55 determines that a reading start command has been input (S54: YES), the reading mode information stored in the RAM 58 indicates whether the reading mode is set to the normal mode, the moire reduction mode, or the blurring mode. 24 based on the determination (S55).

  When it is determined that the reading mode is set to the normal mode (S55: normal mode), the control unit 55 moves the line sensor 40 to the reading position corresponding to the first position 31 with respect to the reference member 37 (see FIG. 2). (S56). In this reading position, a relative distance (second relative distance) between the line sensor 40 moved downward of the reference member 37 by driving of the CR motor 65 and the reading surface 25 of the reference member 37 is arranged at the first position 31. The position is substantially equal to the relative distance (first relative distance) between the line sensor 40 and the original reading surface 25 of the first glass 18. For example, the first relative distance and the second relative distance are stored in advance by associating the reading position of the line sensor 40 with respect to the first glass 18 and the corresponding reading position of the line sensor 40 with respect to the reference member 37. Can be substantially matched. That is, the distance between the reference member 37 and the reading surface 25 can be matched. It is possible to prevent a light amount difference between the light emitted from the light source of the line sensor 40 to the reading surface 25 of the first glass 18 and the light emitted from the light source of the line sensor 40 to the reading surface 27 of the reference member 37. .

  The control unit 55 acquires the first light amount adjustment value 101 and the first white reference data 90 (see FIG. 5) (S57). The control unit 55 first irradiates the light source of the line sensor 40 toward the reading surface 27 of the reference member 37 with a small amount of light. Then, the control unit 55 gradually increases the light amount of the light source until the output from the light receiving element of the line sensor 40 reaches a predetermined value, and the light amount when the received light amount reaches the predetermined value is set to the first light amount adjustment value 101. Get as. That is, the first light amount adjustment value 101 is the light amount of the light source at which the light receiving amount of the light receiving element of the line sensor 40 becomes a predetermined value. Subsequently, the control unit 55 irradiates the reading surface 27 of the reference member 37 with the light amount of the first light amount adjustment value 101 from the light source of the line sensor 40. Then, the control unit 55 acquires the first white reference data 90 by converting the reflected light from the reading surface 27 into an electric signal by the light receiving element of the line sensor 40. The first light amount adjustment value 101 and the first white reference data 90 acquired by the process of step S57 are stored in the RAM 58.

  The control unit 55 reads the document conveyed by the ADF 28 by the line sensor 40 disposed at the reading position corresponding to the first position 31 (S58). Specifically, the control unit 55 controls the CR motor 65 to move the line sensor 40 disposed opposite to the reference member 37 to a reading position (see FIG. 6A) corresponding to the first position 31. Then, the control unit 55 causes the line sensor 40 to perform an operation of reading a document conveyed on the first glass 18 at a reading position corresponding to the first position 31. As a result, the image of the document is read in a state where the focus of the line sensor 40 is substantially aligned with the reading surface 25 of the document on the first glass 18. Therefore, a clear original image can be obtained as compared with the case where the line sensor 40 is arranged at another position and the original is read. The document image (image signal) read in this way is processed by the AFE circuit 78, the sampling circuit 81, and the dark correction circuit 82.

  The shading correction circuit 83 corrects the shading of the original image processed by the dark correction circuit 82 based on the first white reference data 90 acquired in the process of step S57 (S59). The filter processing circuit 85 enhances the shading-corrected document image based on the first coefficient 75 stored in the EEPROM 59 (S60). As described above, the filter processing circuit 85 emphasizes the original image obtained in the normal mode with the first coefficient 75. The emphasized original image is processed by the resolution conversion circuit 86, the color conversion processing circuit 87, and the binarization processing circuit 88 and then stored in a predetermined area of the RAM 58.

  When the control unit 55 determines that the reading mode is set to the moire reduction mode (S55: moire reduction mode), the line sensor 40 corresponds to the second position 32 with respect to the reference member 37 (see FIG. 2). Move to the reading position (S61). This reading position is arranged at a reading position where the second relative distance between the line sensor 40 moved downward of the reference member 37 by driving the CR motor 65 and the reading surface 25 of the reference member 37 corresponds to the second position 32. This position is substantially equal to the first relative distance between the line sensor 40 and the original reading surface 25 of the first glass 18.

  The control unit 55 acquires the second light amount adjustment value 102 and the second white reference data 91 (see FIG. 5) (S62). The process of step S62 is performed in the same manner as the process of step 57 except that the reading position of the line sensor 40 with respect to the reference member 37 is different. The second light amount adjustment value 102 and the second white reference data 91 acquired by the process of step S62 are stored in the RAM 58.

  The control unit 55 reads the document conveyed by the ADF 28 by the line sensor 40 disposed at the reading position corresponding to the second position 32 (S63). Specifically, the control unit 55 controls the CR motor 65 to move the line sensor 40 disposed to face the reference member 37 to a reading position (see FIG. 6B) corresponding to the second position 32. Then, the control unit 55 causes the line sensor 40 to perform an operation of reading a document conveyed on the first glass 18 at a reading position corresponding to the second position 32. Thereby, the image of the document is read with the focus of the line sensor 40 slightly shifted from the reading surface 25 of the document on the first glass 18. The document image (image signal) read in this way is processed by the AFE circuit 78, the sampling circuit 81, and the dark correction circuit 82.

  The shading correction circuit 83 corrects the shading of the document image processed by the dark correction circuit 82 based on the second white reference data 91 acquired in the process of step S62 (S64). The filter processing circuit 85 enhances the shading-corrected document image based on the second coefficient 76 stored in the EEPROM 59 (S65). As described above, the filter processing circuit 85 emphasizes the original image obtained in the moire reduction mode with the second coefficient 76. The second coefficient 76 is a coefficient having a larger value than the first coefficient 75. For this reason, the document image read in step S63 is more emphasized than the document image read in step S58. By reading the document in the moire reduction mode, the generation of moire is suppressed and the image is prevented from being blurred. The emphasized original image is processed by the resolution conversion circuit 86, the color conversion processing circuit 87, and the binarization processing circuit 88 and then stored in a predetermined area of the RAM 58.

  When the control unit 55 determines that the reading mode is set to the blur mode (S55: blur mode), whether or not information for specifying the blur region is input based on the presence / absence of a predetermined operation from the operation panel 13 is determined. Is determined (S66). Here, the blur area is an area that is blurred and read out of the reading area of the document conveyed by the ADF 28. When it is determined that the information for designating the blur area has not been input (S66: NO), the control unit 55 notifies the user that the blur area is to be designated (S67). For example, the control unit 55 causes the operation panel 13 to display a message such as “Please specify a blur area”. The process of step S67 is continued until YES is determined in the process of step S66.

  If the control unit 55 determines that the information for designating the blur area has been input (S66: YES), the controller 55 divides the read area of the document into the blur area and the outside of the blur area (S68). As described above, the control unit 55 divides the reading area of the line sensor 40 in the document conveyed by the ADF 28 into a plurality of areas (here, two areas) based on information input from the outside.

  The control unit 55 moves the line sensor 40 to the reading position corresponding to the second position 32 with respect to the reference member 37 (S69). The control unit 55 acquires the second light amount adjustment value 102 and the second white reference data 91 as in the process of step S62 (S70). The acquired second light amount adjustment value 102 and second white reference data 91 are stored in the RAM 58. The control unit 55 moves the line sensor 40 to the reading position corresponding to the third position 33 with respect to the reference member 37 (S71). The reading position corresponds to a reading position in which the second relative distance between the line sensor 40 moved downward of the reference member 37 by driving the CR motor 65 and the reading surface 25 of the reference member 37 corresponds to the third position 33. This is a position that is substantially equal to the first relative distance between the line sensor 40 disposed in the first glass 18 and the reading surface 25 of the original on the first glass 18. The control unit 55 acquires the third light amount adjustment value 103 and the third white reference data 92 as in the process of step S57 (S72). The acquired third light amount adjustment value 103 and third white reference data 92 are stored in the RAM 58.

  As shown in FIG. 18, the control unit 55 reads the document conveyed by the ADF 28 by the line sensor 40 disposed at the reading position corresponding to the second position 32 (S74). Specifically, the control unit 55 controls the CR motor 65 to move the line sensor 40 disposed to face the reference member 37 to a reading position (see FIG. 6B) corresponding to the second position 32. Then, the control unit 55 causes the line sensor 40 to perform an operation of reading a document conveyed on the first glass 18 at a reading position corresponding to the second position 32. Thereby, the image of the document is read with the focus of the line sensor 40 slightly shifted from the reading surface 25 of the document on the first glass 18.

  The control unit 55 determines whether or not the blurred region of the document conveyed by the ADF 28 has reached the reading surface 25 (see FIG. 6C) on the first glass 18 (S75). The determination in step S75 is made based on the information on the blur area divided in step S68 and the number of steps of the motor 72 (see FIG. 4) after the ADF 28 starts conveying the document. When it is determined that the blur area has not reached (S75: NO), the control unit 55 determines whether or not the document has passed over the first glass 18 (S76). If the control unit 55 determines that the document has not passed over the first glass 18 (S76: NO), the process returns to S74.

  When the control unit 55 determines that the blur area has arrived (S75: YES), the line sensor in which the document conveyed by the ADF 28 is arranged at the reading position corresponding to the third position 33 (see FIG. 6C). 40 (S77). Specifically, the control unit 55 controls the CR motor 65 to move the line sensor 40 disposed at the second position 32 to a reading position corresponding to the third position 33. Then, the control unit 55 causes the line sensor 40 to perform an operation of reading a document conveyed on the first glass 18 at a reading position corresponding to the third position 33. Thereby, the image of the document is read with the focus of the line sensor 40 being extremely shifted from the reading surface 25 of the document on the first glass 18.

  As described above, the control unit 55 determines the reading position for the blur mode for each of a plurality of areas (in the present embodiment, inside the blur area and outside the blur area). Then, the control unit 55 changes the position of the line sensor 40 for each area (in the blur area and outside the blur area) during reading of the conveyed document in the blur mode. As a result, the resolution of the line sensor 40 is changed depending on the area, and the document is read. As a result, the obtained image of the original is obtained by blurring the image in a part of the area.

  The control unit 55 determines whether or not the blur region has passed through the reading surface 25 (see FIG. 6C) of the first glass 18 corresponding to the reading position of the third position 33 (S78). The determination in step S78 is performed based on the information on the blurred area divided in the process in step S68 and the number of steps of the motor 72 after the ADF 28 starts conveying the document. When the control unit 55 determines that the blur area has not passed (S78: NO), the process of step S77 is continued. If the control unit 55 determines that the blur area has passed (S78: YES), the process proceeds to step S76. When it is determined that the document has passed over the first glass 18 (S76: YES), the control unit 55 determines that the document has been read.

  The document image (image signal) read by the processes in steps S74 and S77 is processed by the AFE circuit 78, the sampling circuit 81, and the dark correction circuit 82. When the control unit 55 determines YES in the process of step S76, the shading correction circuit 83 corrects the shading of the image outside the blur area based on the second white reference data 91 acquired by the process of step S70 (S79). . Further, the shading correction circuit 83 corrects the shading of the image in the blur area based on the third white reference data 92 acquired by the process of step S72 (S80).

  The filter processing circuit 85 performs an enhancement process on the image outside the blurred region subjected to the shading correction based on the second coefficient 76 (see FIG. 5) stored in the EEPROM 59 (S81). The emphasized image in the blur area and the image outside the blur area are processed by the resolution conversion circuit 86, the color conversion processing circuit 87, and the binarization processing circuit 88, and then stored in a predetermined area of the RAM 58.

  In the blur mode, information for designating a blur area is input from the operation panel 13. The reading area of the document conveyed by the ADF 28 is divided into a blur area and a blur area based on this information. In the blur mode, the reading position of the line sensor 40 is determined for each partitioned area. In the present embodiment, the reading position of the line sensor 40 that reads outside the blur area is determined as the second position 32, and the reading position of the line sensor 40 that reads inside the blur area is determined as the third position 33. For this reason, the reading position of the line sensor 40 is changed between reading in the blurred area and reading outside the blurred area in the document. Thereby, the document is read by changing the resolving power of the line sensor 40 in the blur area and outside the blur area. As a result, the obtained image of the manuscript is suppressed as a whole, and moire is suppressed, and the image is blurred in some areas.

  As described above, the scanner 10 is set to the normal mode, the moire reduction mode, or the blurring mode. In the normal mode, the line sensor 40 is arranged by the control unit 55 at a position where the first relative distance substantially coincides with the focal length of the line sensor 40. Since the original is read with the line sensor 40 in focus, a clear image of the original can be obtained. In the moiré reduction mode and the blurring mode, the line sensor 40 is arranged at a position where the first relative distance is different from the focal length of the line sensor 40 by the control unit 55. Since the original is read in a state where the resolution of the line sensor 40 is reduced, an image of the original in which the occurrence of moire is suppressed or an image of the original in which the image is blurred is obtained as compared with the normal mode. Note that the reading mode is switched based on an operation input from the operation panel 13. That is, the resolution of the line sensor 40 is easily changed according to the user's selection.

  When one of the three reading modes is set, the CR motor 65 is driven by the control unit 55, and the first relative distance between the reading surface 25 of the document on the first glass 18 and the line sensor 40 is changed. The That is, the first relative distance is changed using the drive source of the line sensor 40. For this reason, high-quality image reading with suppressed moire is performed without adding a drive mechanism for changing the first relative distance between the line sensor 40 that reads the conveyed document and the reading surface 25 of the document. be able to.

  Here, the form in which the area outside the blurred area of the document is read by the line sensor 40 arranged at the reading position corresponding to the second position 32 has been described, but the area outside the blurred area of the document corresponds to the first position 31. It may be read by the line sensor 40 arranged at the reading position. That is, an image outside the blurred area in the document may be read in the same manner as in the normal mode. In this case, the first white reference data 90 is used in place of the second white reference data 91 for shading correction on the document image. In addition, the first coefficient 75 is used in place of the second coefficient 76 in the enhancement process for the document image.

  The second glass 20 according to the present embodiment may be configured to be movable up and down in the height direction of the scanner 10.

  FIG. 19 is a schematic diagram showing the lifting mechanism 110 for the second glass 20.

  As shown in FIG. 19, the elevating mechanism 110 includes a fixing member 111, a slide member 112, support members 113 and 114, and coil springs 115, 116, 117, and 118. Support members 113 and 114 are fixed to both ends of the second glass 20 in the depth direction of the scanner 10 (the direction indicated by the arrow 39). The fixing member 111 supports the support member 113 via the coil springs 115 and 116. The fixing member 111 is fixed to the housing 15. The slide member 112 supports the support member 114 via the coil springs 117 and 118. The slide member 112 is provided to be slidable in the depth direction of the scanner 10 with respect to the housing 15. A driving force from a motor (not shown) is transmitted to the slide member 112. The slide member 112 slides by receiving this driving force. The fixed member 111 and the slide member 112 are provided with inclined surfaces 118 and 119 that descend toward the second glass 20. A contact surface 120 parallel to the inclined surface 118 is formed on the support member 113. A contact surface 121 parallel to the inclined surface 119 is formed on the support member 114.

  The slide member 112 receives the driving force from the motor and slides in a direction close to the fixed member 111 (left direction in FIG. 19). The support member 113 is pushed up by the inclined surface 118 and the support member 114 is pushed up by the inclined surface 119, and the second glass 20 is raised. The coil springs 115 and 117 are contracted as the second glass 20 rises, and accumulate a spring force that pushes the second glass 20 downward. The coil springs 116 and 118 are stretched as the second glass 20 is raised, and store a spring force that pulls the second glass 20 downward. The slide member 112 slides in a direction away from the fixed member 111 (right direction in FIG. 19) when the motor is rotated in the reverse direction. The support members 113 and 114 are moved downward along the inclined surfaces 118 and 119 by the spring force accumulated by the coil springs 115 to 118, and the second glass 20 is lowered.

  As described above, the document reading surface 25 of the first glass 18 is inclined with respect to the moving surface of the line sensor 40. For this reason, as the line sensor 40 moves, the height of the reading surface 25 corresponding to the line sensor 40 changes. By moving the second glass 20 up and down so that the upper surface of the second glass 20 and the height of the reading surface 25 coincide with each other, the reading mode is changed even in the FBS and the original placed on the second glass 20 is read. Is possible. That is, even in the FBS, it is possible to read a document in the above-described normal mode, moire reduction mode, and blur mode.

[Second Embodiment]
The second embodiment of the present invention will be described below. The second embodiment is the same as the first embodiment except that the first glass 18 and its peripheral configuration, and the reference member 37 and its peripheral configuration are different. Therefore, the description of the other configurations is omitted. The

  20 and 21 are schematic cross-sectional views showing a part of the conveyance path 12 in the scanner 10 according to the second embodiment of the present invention.

  In the scanner 10 according to the second embodiment of the present invention, the first glass 18 and the reference member 37 are provided in parallel with the moving surface of the line sensor 40. Further, on the back surface of the guide member 34, first spacers 94 are provided on the upstream side and the downstream side in the document transport direction with respect to the first glass 18. The first spacer 94 is interposed between the line sensor 40 and the first glass 18 with the line sensor 40 facing the first glass 18. The first spacer 94 has a thickness that changes stepwise in the direction in which the line sensor 40 moves (the direction indicated by the arrow 38 in FIG. 20). The first spacer 94 is formed with a stepped portion 26 whose thickness increases stepwise from the upstream side to the downstream side in the conveyance direction of the document conveyed by the ADF 28. On the other hand, the carriage 41 has step portions 50 at both ends in the longitudinal direction where the rollers 30 are provided. The step portion 50 is formed so as to increase stepwise from the downstream side to the upstream side in the transport direction of the document transported by the ADF 28 corresponding to the step portion 26.

  The guide shaft 42 is supported by the housing 15 so as to be movable up and down while being biased upward. The carriage 41 moves in the direction indicated by the arrow 38 so that the stepped portion 50 of the carriage 41 moves up and down the stepped portion 26. For example, the carriage 41 moves from the downstream side in the document transport direction toward the upstream side (see FIGS. 20 and 21). As a result, the height of the line sensor 40 mounted on the carriage 41 changes. As a result, the first relative distance, which is the relative distance between the line sensor 40 and the original reading surface 25 of the first glass 18, is changed from D5 to D6. 20 and 21, the first spacer 94 is provided with two step portions 26 so that the first relative distance is changed to two steps. However, the number of steps of the step portions 26 is increased to increase the number of steps. One relative distance may be changed in three steps or more.

  The second spacers 96 are provided on both sides of the reference member 37 in the width direction of the scanner 10 (the direction indicated by the arrow 38). The second spacer 96 is interposed between the line sensor 40 and the reference member 37 with the line sensor 40 facing the reference member 37. The second spacer 96 has the same shape as the first spacer 94. That is, the thickness of the second spacer 96 changes stepwise in the direction in which the line sensor 40 moves (the direction indicated by the arrow 38). When the line sensor 40 is moved to face the reference member 37, the second relative distance between the line sensor 40 and the reading surface of the reference member 37 is changed stepwise.

  FIG. 22 is a schematic cross-sectional view showing the first spacer 104 and the second spacer 106.

  The first spacer and the second spacer in the present invention are not limited to the first spacer 94 and the second spacer 96. That is, the first spacer and the second spacer in the present invention are the first spacer 104 and the second spacer 106 whose thickness changes in a wedge shape in the moving direction of the line sensor 40 as shown in FIG. Also good.

FIG. 1 is a perspective view showing an external configuration of the scanner 10 according to the first embodiment of the present invention, and shows a state in which a document cover 17 is opened. FIG. 2 is a schematic cross-sectional view showing a part of the conveyance path 12 in the scanner 10 according to the first embodiment of the present invention. FIG. 3 is a plan view showing the internal configuration of the document table 11. FIG. 4 is a block diagram illustrating a configuration example of the control unit 55 of the scanner 10. FIG. 5 is a block diagram illustrating a configuration example of the image processing circuit 79. FIG. 6 is a schematic cross-sectional view illustrating the reading position of the line sensor 40, where (A) is a reading position corresponding to the first position 31, (B) is a reading position corresponding to the second position 32, and (C). Indicates a reading position corresponding to the third position 33. FIG. 7 is a flowchart illustrating a processing procedure when processing for setting a reading position is performed when the scanner 10 is powered on. FIG. 8 is a flowchart showing a processing procedure when processing for setting a reading position is performed in the scanner 10 when the power is turned on. FIG. 9 is a flowchart showing a procedure of processing when the scanner 10 performs processing for setting a reading position when the power is turned on. FIG. 10 is a flowchart showing a procedure of processing when the scanner 10 performs processing for setting a reading position when the power is turned on. FIG. 11 is a schematic diagram illustrating an example of the first test document 98. FIG. 12 is a schematic cross-sectional view showing how the reading position of the line sensor 40 is changed. FIG. 13 is a diagram showing the MTF characteristics obtained by reading the first test document 98. FIG. 14 is a schematic diagram illustrating an example of the second test document 99. FIG. 15 is a diagram showing the MTF characteristics obtained by reading the second test document 99. FIG. 16 is a flowchart showing a procedure of processing performed in the scanner 10 when reading a document conveyed by the ADF 28. FIG. 17 is a flowchart showing a procedure of processing performed in the scanner 10 when reading a document conveyed by the ADF 28. FIG. 18 is a flowchart showing a procedure of processing performed in the scanner 10 when reading a document conveyed by the ADF 28. FIG. 19 is a schematic diagram showing the lifting mechanism 110 for the second glass 20. FIG. 20 is a schematic cross-sectional view showing a part of the conveyance path 12 in the scanner 10 according to the second embodiment of the present invention. FIG. 20 is a schematic cross-sectional view showing a part of the conveyance path 12 in the scanner 10 according to the second embodiment of the present invention. FIG. 22 is a schematic cross-sectional view showing the first spacer 104 and the second spacer 106.

Explanation of symbols

10... Scanner (an example of an image reading apparatus according to the present invention)
12 ... Conveying path (corresponding to the path of the present invention)
13 ... Operation panel 18 ... 1st glass (an example of the 1st transmission member of the present invention)
20 ... 2nd glass (an example of the 2nd transmission member of the present invention)
25, 27 ... reading surface 31 ... first position 32 ... second position 33 ... third position 37, 53 ... reference member 40 ... line sensor 55 ... control unit ( (Corresponding to a control unit, a setting unit, a reception unit, a calculation unit, a determination unit, a first notification unit, a first determination unit, a second notification unit, a second determination unit, and a partition unit)
65... CR motor (corresponding to the drive unit of the present invention)
75 ... 1st coefficient (an example of the 1st emphasis coefficient of the present invention)
76 ... 2nd coefficient (an example of the 2nd emphasis coefficient of this invention)
85... Filter processing circuit (corresponding to the emphasis unit of the present invention)
94, 104 ... first spacer 96, 106 ... second spacer 98 ... first test document (an example of a test document of the present invention)
99: Second test document (an example of a test document of the present invention)

Claims (15)

A first transmission member provided in a path along which the document is conveyed;
A second transmission member on which a document is placed;
A contact-type line sensor that irradiates a document with light from a light source through the first transmission member or the second transmission member and reads reflected light from the document for each main scanning line;
A drive unit that moves the line sensor to face the first transmission member or the second transmission member;
A controller that changes the relative distance between the reading surface of the document on the first transmission member and the line sensor by driving the driving unit;
A first mode in which the control unit reads the document through the first transmission member with the relative distance approximately equal to the focal length of the line sensor, or the control unit determines the relative distance to the line sensor. And a setting unit that sets a second mode in which the line sensor reads the original through the first transmission member in a state that is different from the focal length of the image reading apparatus.   The image reading apparatus according to claim 1, wherein a reading surface of the first transmission member is inclined with respect to a plane on which the line sensor moves.   3. The image reading apparatus according to claim 2, wherein the reading surface of the first transmission member is separated from the plane on which the line sensor moves on the downstream side of the path along the conveyance direction of the document.   A first thickness interposed between the line sensor and the first transmission member in a state in which the thickness changes in a stepped shape or a wedge shape in the moving direction of the line sensor, and the line sensor faces the first transmission member. The image reading apparatus according to claim 1, further comprising a spacer. A reference member that is read by the line sensor as a lightness reference of the line sensor,
The image reading apparatus according to claim 1, wherein the control unit changes the relative distance between the reading surface of the reference member and the line sensor by driving the driving unit.   The image reading apparatus according to claim 5, wherein a reading surface of the reference member is inclined with respect to a plane on which the line sensor moves.   And a second spacer interposed between the line sensor and the reference member in a state where the thickness changes in a stepped shape or a wedge shape in a direction in which the line sensor moves, and the line sensor faces the reference member. Item 6. The image reading apparatus according to Item 5. A reception unit for receiving selection of the first mode or the second mode;
The image reading apparatus according to claim 1, wherein the setting unit sets the first mode or the second mode based on a selection received by the receiving unit. The control unit causes the line sensor to perform an operation of reading a test document in which a predetermined pattern is recorded at a plurality of positions having different relative distances through the first transmission member,
An arithmetic unit for obtaining an MTF (Modulation Transfer Function) value for each of the plurality of positions based on the image signal of the test document obtained by the operation;
The determination part which determines the reading position in which the said line sensor is arrange | positioned by the said drive part in the said 1st mode or the said 2nd mode for every mode based on each said MTF value. The image reading apparatus described in 1. A document tray on which documents conveyed along the path are placed;
A first notification unit for notifying that the first test document is to be placed on the document tray;
A first determination unit for determining whether or not a first test document is placed on the document tray in response to a notification from the first notification unit;
A second notification unit for notifying that the second test document is to be placed on the document tray;
A second determination unit that determines whether or not a second test document has been placed on the document tray in response to notification by the second notification unit;
The determination unit determines a reading position for the first mode on the condition that the first determination unit determines that the first test document is placed, and the second test document is placed when the second test document is placed. The image reading apparatus according to claim 9, wherein the reading position for the second mode is determined on the condition that the two determining unit determines.   The image reading apparatus according to claim 9 or 10, wherein the determination unit determines a position where the MTF value is maximum as a reading position for the first mode.   The image reading apparatus according to claim 9, wherein the determination unit determines a position where the MTF value is less than a maximum value and is equal to or greater than a predetermined threshold as a reading position for the second mode.   The determination unit determines a position having a shorter relative distance corresponding to the MTF value as the reading position on condition that a plurality of the same MTF values are obtained by the calculation unit. An image reading apparatus according to claim 1. Based on information input from the outside, a partition unit that partitions the reading area of the line sensor in the conveyed document into a plurality of areas,
The determination unit determines a reading position for the second mode for each of the plurality of regions,
The said control part changes the position of the said line sensor to the reading position determined by the said determination part for every area | region divided by the said division part during reading of the said document conveyed in the said 2nd mode. The image reading apparatus according to any one of 9 to 13. An emphasis unit for emphasizing an image of a document read by the line sensor;
The enhancement unit enhances the document image obtained in the first mode with a first enhancement coefficient, and the document image obtained in the second mode is a second larger than the first enhancement coefficient. The image reading apparatus according to claim 1, wherein enhancement processing is performed using an enhancement coefficient.

Images