JP2006215456A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of positioning a plurality of lenses for forming an image on an image sensor, on an optical path with a simple mechanism. <P>SOLUTION: The image reader is equipped with: a platen; the image sensor; a lens unit in which a plurality of lenses for forming the image of an original positioned on the platen on the image sensor are mounted; a stopper which abuts on the lens unit in a state where any lens is positioned on the optical path leading to the image sensor from the original; a motor; and a screw which transmits the motive power of the motor so as to move the lens unit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus including a plurality of lenses for forming an image of a document on an image sensor.

2. Description of the Related Art Conventionally, there has been known an image scanner that includes a plurality of lenses having different resolutions and switches lenses according to a document type (see, for example, Patent Document 1).
In order to read the document accurately, it is necessary to read the document in a state where the plurality of lenses are localized at accurate positions. However, according to the image scanner described in Patent Document 1, there is a problem that the position of the lens at the time of reading cannot be accurately determined due to the backlash of the gear device for reciprocating the lens by the power of the motor.

US Pat. No. 5,577,697

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading apparatus capable of accurately locating a plurality of lenses for forming an image on an image sensor at a target position with a simple mechanism.

(1) An image reading apparatus for achieving the above object includes a platen, an image sensor, a lens unit including a plurality of lenses for forming an image of a document positioned on the platen on the image sensor, A stopper that contacts the lens unit in a state where any of the lenses is located on an optical path from the document to the image sensor, a motor, and a screw that transmits the power of the motor to move the lens unit; An image reading apparatus comprising:

  Even if there is backlash in the transmission mechanism that moves the lens unit by transmitting the power of the motor, once the lens unit is brought into contact with the stopper, the transmission mechanism is engaged with no gap. In this state, in order for the lens unit to move from the driven side, an inertial force or an external force necessary to rotate the screw needs to act on the lens unit. In a power transmission mechanism having a screw such as a worm or a lead screw, the efficiency when rotating the driven side from the driven side is worse than the efficiency of rotating the driven side from the driven side. Therefore, according to the present invention, even if the static force of the motor is small, the lens unit can be accurately positioned at the target position, and the lens unit can be moved even by a motor having a small torque. That is, according to the present invention, a control circuit for forcibly stopping the motor, a spring for pressing the lens unit against the stopper, a motor having a large torque, and the like are unnecessary.

(2) The screw may be self-locking.
According to the present invention, in a state where the lens unit is in contact with the stopper, even if an inertial force or an external force is applied to the driven lens unit, the screw does not rotate due to self-locking. Never move. Therefore, according to the present invention, the stationary control of the motor becomes unnecessary.

(3) The image reading apparatus may further include a guide that supports the lens unit so as to be reciprocally movable. The screw may transmit power of the motor to reciprocate the lens unit.
According to the present invention, since the moving direction of the lens unit can be made parallel to the document surface, the image reading apparatus can be reduced in size.
(4) The screw may be a worm.
(5) The screw may be a lead screw.

Embodiments of the present invention will be described below based on a plurality of examples. In each of the embodiments, the component having the same reference sign corresponds to the component of the other embodiment having the reference sign.
(First Example)
FIG. 2 is a schematic diagram showing the internal structure of the image scanner 1 as the first embodiment of the image reading apparatus according to the present invention. The image scanner 1 is a so-called flatbed type that reads a document 34 placed on a document table 32 as a platen described in the claims.

The document table 32 is formed of a transparent plate such as a glass plate, and a document 34 such as a printed document, a photograph, a book, a 35 mm strip film, or a 35 mm mount film is placed on the board surface.
The main carriage 20 is slidably fitted to a guide rod 30 parallel to the surface of the document table 32. The main carriage 20 includes a first light source 24, a mirror 22, a lens unit 10, and an image sensor 28. The main carriage 20 is pulled by a belt hung on a pulley driven by a main carriage conveyance motor (not shown), and reciprocates in the directions of arrows X and Y in parallel with the surface of the document table 32. When the first light source 24, the mirror 22, the lens unit 10, and the image sensor 28 are conveyed by the main carriage 20 in the directions of arrows X and Y parallel to the surface of the document table 32, the main scanning range for reading the document moves. .

The first light source 24 and the second light source 36 are illumination devices such as a white cold cathode fluorescent lamp. The first light source 24 and the second light source 36 illuminate the document 34 placed on the document table 32.
The lens 12 or 13 (see FIG. 1) mounted on the mirror 22 and the lens unit 10 includes reflected light from the document 34 illuminated by the first light source 24 and transmitted light from the document 34 illuminated by the second light source 36. Is incident on the light receiving surface of the image sensor 28. At this time, the optical axis of either the lens 12 or 13 selected by the CPU 60 is localized on the optical path from the document 34 to the image sensor 28. Details of the lens unit 10 will be described later.

  The image sensor 28 is a so-called linear image sensor in which a large number of photoelectric conversion elements (not shown) composed of photodiodes or the like are linearly arranged. The image sensor 28 is mounted on the main carriage 20 so that a large number of photoelectric conversion elements are arranged in parallel with the central axis of the tubular first light source 24. Electric charges corresponding to the amount of received light are accumulated in each photoelectric conversion element of the image sensor 28 by photoelectric conversion. The electric charge accumulated in each photoelectric conversion element is transferred to the output unit of the image sensor 28 by a CCD (Charge Coupled Device). This charge transfer may be performed by CMOS (Complementary Metal Oxide Semiconductor). The analog signal output from the image sensor 28 is output to the AFE unit 76 (see FIG. 1).

FIG. 1 is a block diagram showing a main configuration of hardware of the image scanner 1.
The CPU 60 executes a program stored in the ROM 82 and controls each unit of the image scanner 1. The ROM 82 is a non-volatile memory that stores various programs, various data, and the like. These programs and various types of data are stored in the ROM 82 by downloading from a predetermined server via a network, reading from a computer-readable storage medium such as a removable memory (not shown), and the like. The RAM 74 is a memory that temporarily stores various programs and various data. The RAM controller 72 controls data transfer between the CPU 60, the AFE unit 76, the image processing unit 78, the external interface controller 80, and the like and the RAM 74.

The first light source controller 62 includes an inverter circuit, a control circuit, and the like (not shown), and controls the turning on and off of the first light source 24. The second light source controller 64 includes an inverter circuit, a control circuit, and the like, and controls turning on and off of the second light source 36.
The image sensor controller 70 is a drive circuit that outputs drive pulses necessary for driving the image sensor 28 to the image sensor 28, and includes, for example, a synchronization signal generator, a drive timing generator, and the like.

The main carriage controller 68 includes the above-described main carriage transport motor (not shown), a main carriage transport motor drive circuit, a control circuit, and the like. The main carriage controller 68 receives a main carriage conveyance control signal transmitted from the CPU 60, and controls the rotation direction, rotation speed, and the like of the main carriage conveyance motor.
The lens unit controller 66 includes a drive circuit and a control circuit for the motor 50 that drives the lens unit 10. The lens unit controller 66 receives a lens replacement signal transmitted from the CPU 60 and controls the rotation direction, rotation speed, and rotation angle of the motor 50.

The analog front end (AFE) unit 76 performs CDS (Correlated Double Sampling) processing, optical black clamp control for reproducing the black level of the image, level adjustment processing of the electric signal by adjusting the gain of the electric signal of the image, A scan image digitized by performing quantization processing or the like is stored in the RAM 74 via the RAM controller 72.
The image processing unit 78 is a DSP (Digital Signal Processor) that performs signal processing for performing image processing such as gamma correction and shading correction on the scanned image stored in the RAM 74 in cooperation with the CPU 60.

The external interface controller 80 connects the image scanner 1 and an external system such as a PC (Personal Computer) so that they can communicate with each other.
FIG. 3 is a perspective view showing the lens unit 10. The lens unit 10 is accommodated in a main carriage 20 and includes two lenses 12 and 13, a lens carriage 14, and a rack 16. The lens carriage 14 is slidably fitted to shafts 38 and 40 extending in the main scanning direction. The shafts 38 and 40 as guides described in the claims are fixed to the main carriage 20. A rail may be used as a guide for the lens carriage 14.

  The rack 16 is fixed to the lens carriage 14 and meshes with a spur gear 46 that is rotatably supported by the main carriage 20. The motor 50 is connected to a worm 52 as a “screw” in the claims, and meshes with a worm wheel 48 (see FIG. 4) coaxial with the spur gear 46. The advance angle γ of the worm 52 is smaller than the friction angle between the worm 52 and the worm wheel 48. When the motor 50 is driven, the worm 52, the worm wheel 48, and the spur gear 46 are driven, and the lens unit 10 moves in parallel with the document table 32. The lenses 12 and 13 are fixed to the lens carriage 14. The lenses 12 and 13 have different resolutions. The resolution for reading an image can be changed to the set resolution by localizing the optical axis of one of the lenses 12 and 13 to the central optical path according to the set resolution. The central optical path is an optical path that extends from the center of the main scanning line in a direction perpendicular to the main scanning line and reaches a predetermined pixel near the center of the image sensor 28 via the mirror 22. The stoppers 42 and 44 are fixed to the main carriage 20. When the moving lens carriage 14 comes into contact with the stopper 42 or 44, its movement in the moving direction is stopped by the drag force. When the lens carriage 14 is in contact with the stopper 42, the optical axis of the lens 13 is localized in the central optical path, and when the lens carriage 14 is in contact with the stopper 44, the optical axis of the lens 12 is localized in the central optical path. 42 and 44 are fixed. The lenses 12 and 13 may be lenses having the same resolution.

Next, the operation of each part at the time of lens replacement will be described.
4A is a schematic view of the driving system of the lens unit 10 as viewed from the side opposite to the document table 32, FIG. 4B is a schematic view in which the meshing portion of the rack 16 and the spur gear 46 is enlarged, and FIG. ) Is a schematic view showing a meshing portion of the worm wheel 48 and the worm 52.
The CPU 60 controls the lens unit controller 66 according to the document type and resolution setting input by the user on a PC (not shown) connected via the external interface controller, and according to the document type and the set resolution. The lens unit 10 is moved so that the optical axis of the lens 12 or 13 is positioned on the central optical path. Hereinafter, the operation of moving the lens 13 on the central optical path from the state where the lens 12 is on the central optical path will be described in detail.

  The lens unit controller 66 drives the motor 50 to move the lens carriage 14 by a preset amount of movement in the direction in which the lens carriage 14 approaches the stopper 42. Here, the preset amount of movement is set according to the distance between the optical axes of the lenses 12 and 13, and is sufficient for the lens carriage 14 to move and come into contact with the stoppers 42 and 44 during lens replacement. And When the motor 50 is rotating, as shown in FIG. 4B, each tooth of the spur gear 46 has a tooth surface 90 of the rack 16 in which the tooth surface 90 on the front side in the traveling direction is on the front side in the traveling direction of each tooth. 92 abuts. When the lens carriage 14 comes into contact with the stopper 42, the lens carriage 14 stops in a state where the tooth surface 90 on the front side in the traveling direction of the spur gear 46 contacts the tooth surface 92 on the rack 16 on the front side in the tooth traveling direction. . In order for the lens carriage 14 to move in a direction away from the stopper 42 from the state where the lens carriage 14 abuts on the stopper 42 and stops, the tooth surface is moved by the tooth surface 92 on the front side in the direction away from the stopper 42. The spur gear 46 must be rotated by pushing back the tooth surface 90 of the spur gear 46 that is in contact with 92. However, since the advance angle γ of the worm 52 is smaller than the friction angle of the tooth surface, the worm 52 does not rotate even if the worm wheel 48 receives a rotational force due to vibration or the like via the spur gear 46. That is, the lens carriage 14 is localized in a state where it abuts against the stopper 42 as long as the motor 50 does not generate a driving force.

  Thus, in the image scanner 1, the worm 52 cannot be rotated from the lens unit 10 side by using the self-locking worm gear for the transmission mechanism that moves the lens unit 10. Therefore, in the image scanner 1 according to the first embodiment of the present invention, the lens carriage 14 can be localized at the position in contact with the stoppers 42 and 44 even if the static force of the motor 50 is small. Further, since a spring for pressing the lens unit 10 against the stoppers 42 and 44 is not required, it is not necessary to move the lens unit 10 against a restoring force of the spring or the like. Therefore, the torque required for the motor 50 can be reduced. Further, since the lens unit 10 does not move unless the motor 50 generates a driving force, a servo mechanism for stopping the motor 50 is unnecessary.

(Second embodiment)
FIG. 5 is a schematic diagram showing an image scanner 1 according to the second embodiment of the present invention. The lens unit 11 includes a plurality of lenses 12 and 13, a lens carriage 14, and a nut 102. The nut 102 is fixed to the lens carriage 14. The lead screw 100 is directly connected to the rotating shaft of the motor 50 and meshes with the nut 102. When the motor 50 rotates, the lead screw 100 rotates and the lens carriage 14 moves linearly together with the nut 102. When the lens carriage 14 comes into contact with the stopper 42 or 44, the lens carriage 14 stops in a state where the tooth surface on the front side in the moving direction of the lead screw 100 is in contact with the tooth surface of the nut 102 on the front side in the moving direction of the tooth. . Hereinafter, the case where the lens carriage 14 is in contact with the stopper 42 and stopped will be described. In order for the lens carriage 14 to move away from the stopper 42 from the state where the lens carriage 14 has come into contact with the stopper 42 and stopped, the tooth surface on the front side of the nut 102 in the direction away from the stopper 42 is used. The lead screw 100 must be rotated by pushing back the tooth surface of the abutting lead screw 100. However, since the lead angle of the lead screw 100 is smaller than the friction angle of the tooth surface between the lead screw 100 and the nut 102, the self-lock works and the lead screw 100 does not rotate even if the nut 102 receives a propulsive force due to vibration or the like. That is, the lens carriage 14 is localized in a state where it abuts against the stopper 42 as long as the motor 50 does not generate a driving force.

  As described above, in the image scanner 1, the lead screw 100 cannot be rotated from the lens unit 10 side by using the self-locking lead screw and nut for the transmission mechanism that moves the lens unit 10. Therefore, in the image scanner 1 according to the second embodiment of the present invention, the lens carriage 14 can be localized at the position where it abuts against the stoppers 42 and 44 even if the static force of the motor 50 is small.

  The present invention can also be applied to a mirror moving image scanner that moves the main scanning range by fixing the positions of the image sensor and the lens with respect to the document table 32 and moving a plurality of mirrors in conjunction with each other. The present invention can also be applied to a sheet feed type in which the main scanning range is moved by moving the document 34 in the sub-scanning direction during image reading. Furthermore, the present invention can also be applied to a copying machine or a facsimile provided with an image reading function.

1 is a block diagram according to a first embodiment of the present invention. 1 is a schematic diagram showing an internal structure of an image scanner according to a first embodiment of the present invention. 1 is a perspective view showing a lens unit according to a first embodiment of the present invention. FIG. 3 is a schematic diagram showing a driving system for a lens unit according to the first embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an image scanner according to a second embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image scanner (image reading apparatus), 10 lens unit, 11 lens unit, 12 lens, 13 lens, 28 image sensor, 32 manuscript stand (platen), 34 manuscript, 38 shaft (guide), 40 shaft (guide), 42 Stopper, 44 Stopper, 50 Motor, 52 Worm (screw), 100 Lead screw (screw)

Claims (5)

The platen,
An image sensor;
A lens unit equipped with a plurality of lenses for forming an image of the document positioned on the platen on the image sensor;
A stopper that comes into contact with the lens unit in a state where any of the lenses is positioned on an optical path from the document to the image sensor;
A motor,
A screw for transmitting the power of the motor to move the lens unit;
An image reading apparatus comprising:   The image reading apparatus according to claim 1, wherein the screw is self-locking. A guide that supports the lens unit in a reciprocating manner;
The image reading apparatus according to claim 1, wherein the screw transmits power of the motor to reciprocate the lens unit.   The image reading apparatus according to claim 1, wherein the screw is a worm.   The image reading apparatus according to claim 1, wherein the screw is a lead screw.

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