JP2010200231A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader which can attain high-speed signal transmission and also can suppress noise radiation from metal frames and crosstalks, using a flexible flat cable that attains both flexibility and high impedance. <P>SOLUTION: The image reader includes a metal frame 2; a reading unit 4 for reading an image of an original document through its reciprocal movement, inside a box defined by the metal frame 2 and an original document base glass 3; a control board 10 for receiving image information; and a flexible flat cable 11. A conductive film 13a is provided in a surface of the U-shaped bent flexible flat cable 11, facing the inner wall of the metal frame and extending to the farthest point of the U shape, as viewed from the reading unit 4 when the reading unit 4 reaches a position where the original document base glass side of the U-shaped bent flexible flat cable becomes longest in extension. A conductive film 13b is provided in a surface of the flexible flat cable 11 opposite to the surface to be extended from the farthest point of the U shape to the control board 10 and is connected to the conductive film 13a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image reading apparatus for reading a document such as a document or a photograph, converting the read information into digital data, and outputting the digital data to a processing apparatus such as a computer or a printer.

  2. Description of the Related Art Image reading devices are widely used as means for reading image information on a document such as a printed matter or a photograph and outputting the information to a processing device such as a computer or a printer.

  FIG. 5 schematically shows an image reading apparatus according to a conventional example. The image reading apparatus 101 includes a box-shaped metal frame 102, a document table glass 103 disposed on the upper surface thereof, and a document table glass. And an openable / closable document cover 105 disposed on 103. When reading a document, the document is placed on the platen glass 103, the document cover 105 is closed, and the document is pressed onto the glass. Next, the reading unit 104 provided in the metal frame 102 scans in parallel with the glass plane of the document table glass 103 to read an image on the document. The reading unit 104 incorporates an unillustrated light source for document irradiation, a mirror, a lens, and an image sensor.

  In this type of image reading apparatus, since the light source, the mirror, the lens, and the imaging sensor for irradiating the document are integrated, the lens and the imaging sensor are fixed, and the image reading apparatus in which the light source and the mirror reciprocate, The advantage is that the overall height of the device can be reduced and the size can be reduced.

  In the metal frame 102 of the image reading apparatus 101, a reading unit 104, a belt 106 for driving the reading unit, driving members such as a guide shaft 107, a motor 108 and a gear 109, a control board 110, and a flexible flat cable 111 are incorporated. ing. The rotating shaft of the motor 108 drives the belt 106 via a gear 109. A part of the belt 106 is fixed to the reading unit 104, and reciprocates in the axial direction of the guide shaft 107 (main scanning direction) in the glass plane area of the document table glass 103 by forward and reverse rotation of the motor 108. Thus, the image on the original is read. The read image information is converted into digital data by an AD conversion circuit in the reading unit 104 and transmitted to the control board 110 via the flexible flat cable 111. The digital data is subjected to predetermined image processing on the control board 110 and then transferred to a processing device such as a computer or a printer.

  The flexible flat cable 111 is a cable having a strip-shaped signal line formed by arranging a plurality of independent linear conductive patterns in parallel on a flexible substrate (base film such as polyimide), and is called FFC. The flexible flat cable 111 is arranged to be bent in a U shape, and is flexibly deformed so as not to prevent the reading unit 104 from reciprocating smoothly in the main scanning direction. The flexible flat cable 111 has flexibility, that is, flexibility, but also has appropriate tension, that is, toughness. When the flexible flat cable 111 is deformed into a U-shape, the repulsive force to return to the original I-shape is external. Work in the direction. Therefore, the flexible flat cable 111 presses against the bottom 102b of the metal frame 102 in the section 111b on the control board 110 side, and tends to float toward the upper part 102a of the metal frame 102 in the section 111a on the reading unit 104 side. . Therefore, the flexible flat cable 111 is not damaged by being caught in the reading unit 104 that reciprocates.

  In recent years, digital data transmitted through the flexible flat cable 111 tends to increase the transmission rate in order to improve the reading image quality and the reading speed per unit time. For this reason, it is one of the major problems of the image reading apparatus to suppress radiation noise that increases due to high speed digital data transmitted through the flexible flat cable 111. The effect of this radiated noise on other electronic devices is called EMI (Electro Magnetic Interference), which causes malfunction of electronic devices. Therefore, the frequency band that poses a problem with radiated noise is determined and the amount of radiation is regulated. . In addition, electronic device manufacturers need to design and manufacture products so as to comply with this regulation.

  As described above, in this type of image reading apparatus, the section 111a on the reading unit 104 side is formed on the upper part 102a of the metal frame 102 in the flexible flat cable 111 bent in a U shape in order to reduce the height of the apparatus. Proximity or contact situations occur. At that time, the flexible flat cable 111 is electrically coupled to the bottom portion 102b and the upper portion 102a of the metal frame 102 to supply a high-frequency current, and radiation noise suddenly increases in a specific frequency band using the metal frame 102 as a radiation source. There is a problem of increasing.

  In addition to this issue, there is another issue. In the reciprocating motion of the reading unit 104, the flexible flat cable 111 bent in a U shape is bent by its own weight as the number of sections floating from the metal frame 102 increases, and the inner surfaces approach each other. When the inner surfaces of the flexible flat cable 111 are close to each other, the band-like signal lines inside the flexible flat cable are electrically coupled to each other, so-called crosstalk occurs, and the signal waveform received by the control board 110 is disturbed. . Avoiding this crosstalk is another issue.

  In order to simultaneously solve the above two problems, namely, suppression of radiation noise from the metal frame and avoidance of crosstalk, a conductive film is wound around both sides of the flexible flat cable, and both ends are connected to the ground potential. So-called double-sided shield FFC is effective.

  As disclosed in Patent Document 1 (Japanese Utility Model Laid-Open No. 58-19415), the double-sided shield FFC functions as a so-called electrostatic shield for the internal signal line. Even if the surface of the U-shaped flexible flat cable facing the inner wall of the metal frame is close to or in contact with the upper part of the metal casing, the band-like signal inside the flexible flat cable is obtained due to the effect of electrostatic shielding. Electrical coupling from the line to the upper part of the metal frame can be suppressed. Thereby, it becomes possible to suppress noise emission from the metal frame. Moreover, even if the inner surfaces of the both sides of the flexible flat cable bent into a U-shape are close to each other, the band-like signal lines inside the flexible flat cable are electrically coupled by the electrostatic shielding effect. Can be avoided. That is, crosstalk is avoided and the signal waveform received by the control board is not disturbed. In this way, both suppression of radiation noise and avoidance of crosstalk can be realized.

Japanese Utility Model Publication No. 58-19415

  However, since the impedance of the double-sided shielded FFC is significantly lower than that of a normal FFC, it has become difficult to cope with a signal transmission system that is increasing in speed.

  In recent years, it has become essential to ensure the characteristic impedance of a line at a predetermined value in response to a demand for high-speed transmission signals. For example, in the LVDS (Low Voltage Differential Signaling) transmission method that is mainstream in the field of high-speed signal transmission, a low-amplitude current of 3.5 mA is passed through the pair wiring. In this method, a voltage having an amplitude of 350 mV generated at both ends of a 100Ω termination resistor arranged near the receiving side IC is detected by the receiving side IC input terminal. In the LVDS system, it is necessary to match the impedance of the transmission line to 100Ω, which is the same as the termination resistance, in order to prevent the deterioration of the waveform quality due to reflection.

  However, if the double-sided shield FFC is manufactured to be thin enough to satisfy the flexibility, the coupling between the signal transmission line and the shield, that is, the ground is strengthened, the impedance is lowered, and it is difficult to secure 100Ω.

  Therefore, if a distance between the signal transmission line and the shield is ensured in order to ensure a predetermined high impedance, the flexibility is significantly impaired due to the thickness of the insulating material. If the flexibility is impaired, a large load is applied to the reading unit, so that it is necessary to increase the driving force of the motor. In addition, the pressure at which the FFC comes into contact with the inner wall of the metal frame is remarkably increased, and the risk of the FFC being damaged due to rubbing increases. Therefore, it is difficult to apply the double-sided shield FFC to an image reading apparatus that requires high-speed signal transmission.

  Conversely, if the value of the terminating resistor is decreased in accordance with the decrease in the impedance of the transmission line, while the current amplitude of the signal transmitted from the transmitting IC is increased, the voltage amplitude detected at the receiving IC input terminal is increased. The predetermined threshold voltage can be 350 mV, and the threshold condition of the receiving IC can be satisfied. However, there is a problem that the power consumption of the transmission side IC and the energy of radiation noise increase in proportion to the increase in current amplitude. For example, if the current amplitude is doubled, there is a possibility that the power consumption and radiation noise of the transmission side IC will increase up to twice. Therefore, it is difficult to change the configuration of the peripheral circuit in accordance with the low impedance of the double-sided shield FFC for an image reading apparatus that requires high-speed signal transmission.

  The present invention provides an image reading apparatus that realizes high-speed signal transmission while achieving both flexibility and high impedance of a flexible flat cable, and enables suppression of radiation noise from crosstalk and metal frames. It is intended.

  In order to achieve the above object, an image reading apparatus according to the present invention includes a box-shaped metal frame having an opening on an upper surface, an original table glass disposed so as to cover the opening, the metal frame, and the original table. A reading unit that is disposed inside a box made of glass and that reciprocates to read an image of a document placed on the platen glass, and a control board that receives and processes image information read by the reading unit And a flexible flat cable arranged in a U-shape between the reading unit and the control board, wherein the flexible flat cable is arranged in a U-shape. When the reading unit reaches the position where the platen glass side of the flexible flat cable is longest, the platen glass of the flexible flat cable is In the first part located on the first side, the first conductive film disposed on the first surface of the flexible flat cable, and the second part of the flexible flat cable excluding the first part, A second conductive film disposed on a second surface of the flexible flat cable; and a conductive connection portion that connects the first and second conductive films to each other; The first surface is a surface of the both sides of the flexible flat cable that faces the inner wall of the metal frame, and the second surface is a surface opposite to the first surface. To do.

  In addition to realizing a flexible flat cable that achieves both flexibility and high impedance, it is possible to suppress radiation noise from the metal frame and to avoid crosstalk due to the proximity of the flexible flat cable itself.

  Also, by making the deformation of the flexible flat cable according to the reciprocating movement of the reading unit smoother, the reciprocating movement of the reading unit can be made faster, and the number of originals read per unit time can be increased. Become.

1 is a schematic diagram illustrating an image reading apparatus according to Embodiment 1. FIG. It is a figure explaining the structure of the flexible flat cable by Example 1 in three cross sections. It is a figure explaining the mode of a deformation | transformation of the flexible flat cable by Example 1. FIG. It is a figure explaining the structure of the flexible flat cable by Example 2 in the cross section of three places. It is a schematic diagram explaining the image reading apparatus by a prior art example.

The best mode for carrying out the present invention will be described with reference to the drawings.

  1 to 3 relate to the first embodiment. FIG. 1 is a schematic view of the image reading apparatus according to the present embodiment as viewed from the side, and FIG. 2 illustrates cross sections taken along lines A, B, and C in FIG. .

  In FIG. 1, an image reading apparatus 1 is provided on a box-shaped metal frame 2 having an opening on the upper surface, a platen glass 3 disposed so as to cover the opening, and a platen glass 3. And an openable document cover. In reading the original, the original is placed on the original platen glass 3, the original cover is closed, and the original is pressed onto the glass. Next, the reading unit 4 arranged inside the box composed of the metal frame 2 and the platen glass 3 scans (reciprocates) in parallel with the glass plane of the platen glass 3, thereby causing an image of the original. Read. The reading unit 4 incorporates a light source for document irradiation, a mirror, a lens, and an image sensor.

  The control board 10 is connected to the reading unit 4 via the flexible flat cable 11, receives the read image information, and performs predetermined processing. A plurality of signal lines 12 are arranged on the flexible flat cable 11, and conductive films 13a, 13b, and 13c are arranged outside. The first conductive film 13 a is connected to the ground of the reading unit 4, and the second conductive film 13 b is connected to the ground of the control board 10. The conductive films 13a and 13b are connected to each other by a conductive film 13c constituting a conductive connection portion. That is, the reading unit 4 and the ground of the control board 10 are connected via the conductive films 13a, 13b, and 13c.

  As shown in FIG. 2, the flexible flat cable 11 is constituted by a flexible substrate 14, and a base film such as polyimide is used for the flexible substrate 14. A plurality of signal lines 12 are arranged inside the flexible substrate 14, and conductive films 13a, 13b, and 13c are bonded together to constitute a flexible flat cable 11 that is a shield FFC.

  FIG. 1 shows a state in which the reading unit 4 has reached the longest position on the platen glass side of the flexible flat cable 11 bent into a U-shape. As can be seen from FIG. 1, in the first portion from the reading unit 4 to the farthest point position U of the U-shape, the first of the both sides of the flexible flat cable 11 that faces the inner wall of the metal frame 2. A first conductive film 13a is provided on the surface. Further, in the remaining second portion excluding the first portion from the position B at the farthest point of the U-shape to the control board 10, the inner wall of the metal frame 2 is formed on both sides of the flexible flat cable 11. A second conductive film 13b is provided on the second surface opposite to the facing surface.

  As shown in FIG. 2A, even if the signal line 12 is close to the upper part 2a of the metal frame 2 at the position A, the metal frame 2 is separated from the signal line 12 by the electrostatic shielding effect of the conductive film 13a. The electrical coupling to the upper part 2a of the metal frame 2 is suppressed, and noise emission from the metal frame 2 is suppressed. Further, even if the signal lines 12 are close to each other at the position C close to the bottom 2b of the metal frame 2 as shown in FIG. 2C, the signal lines are connected to each other due to the electrostatic shielding effect of the conductive film 13b. Can be prevented from being electrically coupled. That is, crosstalk is suppressed and the signal waveform received by the control board 10 is not disturbed.

  The flexible flat cable 11 is a single-sided shield from the section from the position B to the reading unit 4 and the section from the position B to the control board 10, so that it has sufficient flexibility and ensures a predetermined high impedance. it can.

  FIG. 3 shows how the flexible flat cable 11 is deformed when the reading unit 4 is reciprocated. FIG. 3A shows a state in which the reading unit 4 is located at the longest position on the side of the platen glass of the flexible flat cable 11 bent into a U-shape, which is the same state as FIG.

  FIG. 3B shows a state in which the reading unit 4 is at an approximately midpoint of the document scanning range, and FIG. 3C shows reading at a position where the side of the platen glass of the flexible flat cable 11 bent into a U-shape is the shortest. The unit 4 is present.

  The flexible flat cable 11 in FIG. 3 shows a section where the conductive film 13a is disposed by a dotted line, and a section where the conductive film 13b is disposed by a one-dot chain line.

  In the state of FIG. 3A, since the platen glass side of the flexible flat cable 11 bent into a U-shape is the longest, the floating section of the flexible flat cable 11 is most bent by its own weight, and the signal lines 12 are connected to each other. Close to each other and crosstalk is likely to occur. From this state, the shorter the floating section of FIGS. 3B and 3C and the flexible flat cable 11, the less the deflection due to its own weight, and the less likely it is to generate crosstalk. Therefore, the range shown by the alternate long and short dash line in which the conductive film 13b for avoiding crosstalk is provided is sufficient in the range shown in the figure.

  On the other hand, the section indicated by the dotted line is in a state where the conductive film 13a exists on the surface facing the upper portion 2a of the metal frame 2 in the entire document scanning range in which the reading unit 4 moves in parallel. 12 is reliably suppressed from being electrically coupled to the upper portion 2a of the metal frame 2.

  According to the first embodiment, a flexible flat cable having both flexibility and high impedance is mounted to realize high-speed signal transmission, and radiation noise suppression from the metal frame and crosstalk due to the proximity of the flexible flat cable itself are achieved. Avoidance is possible.

  FIG. 4 illustrates the second embodiment. The plurality of signal lines 12 include a high-speed signal line 16 and a ground line 17 connected to the reading unit 5 and the ground of the control board 10. The conductive films 13a, 13b, and 13c are disposed only in a portion along the high-speed signal line 16 that is a part of the plurality of signal lines 12, and are connected to the ground line 17 in the portion of the conductive film 13c. Yes.

  A plurality of signal lines 12 arranged in the cable have so-called high-speed signals such as image signals and device drive signals (clocks) for capturing the image signals that have a fast signal rise speed and a short repetition cycle. A high-speed signal line 16 for transmitting a signal is included. A high-speed signal is likely to cause radiation noise and crosstalk because of its large energy as a noise source. On the other hand, the plurality of signal lines 12 include many control signals and power supplies that are slow in speed. These signals and power supply have low energy as a noise source.

  Therefore, if the conductive films 13a, 13b, and 13c are provided only in a part along the high-speed signal line 16 such as an image signal or a device drive signal, radiation noise suppression and crosstalk avoidance can be realized.

  With this configuration, since the volume occupied by the conductive film in the flexible flat cable can be reduced, in addition to the effects of the first embodiment, the flexibility of the flexible flat cable can be improved.

  According to the present embodiment, since the deformation of the flexible flat cable according to the reciprocating motion of the reading unit becomes smoother, the reciprocating motion of the reading unit can be increased, and the number of originals read per unit time can be increased. It becomes possible.

DESCRIPTION OF SYMBOLS 1 Image reader 2 Metal frame 3 Original plate glass 4 Reading unit 10 Control board 11 Flexible flat cable (FFC)
12 Signal lines 13a, 13b, 13c Conductive film 14 Flexible substrate 16 High-speed signal line 17 Ground line

Claims (2)

A box-shaped metal frame having an opening on the upper surface;
A platen glass arranged to cover the opening;
A reading unit that is disposed inside a box composed of the metal frame and the platen glass, and that reciprocates to read an image of the document placed on the platen glass;
A control board for receiving and processing image information read by the reading unit;
In an image reading apparatus comprising: a flexible flat cable disposed in a U shape between the reading unit and the control board;
The flexible flat cable is
When the reading unit reaches the position where the platen glass side of the flexible flat cable bent in a U-shape is the longest, the first is located on the platen glass side of the flexible flat cable. The first conductive film disposed on the first surface of the flexible flat cable,
In the second portion of the flexible flat cable excluding the first portion, a second conductive film disposed on the second surface of the flexible flat cable;
A conductive connecting portion for connecting the first and second conductive films to each other;
The first surface of the flexible flat cable is a surface of the both surfaces of the flexible flat cable that faces the inner wall of the metal frame, and the second surface is a surface opposite to the first surface. An image reading apparatus comprising: The flexible flat cable includes a plurality of signal lines including a high-speed signal line,
The image reading apparatus according to claim 1, wherein the first and second conductive films are disposed only in a portion along the high-speed signal line.

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