Image reading device

Abstract

By providing a buffer circuit on the image reading unit side, the image reading control signal on the wiring between the control unit and the image reading unit is attenuated by the attenuation circuit to reduce noise. [Solution] The first circuit board provided in the lower housing includes an AD converter 301 that converts an analog image signal output by the image reading means 70 into a digital image signal, a control means 200 that controls the image reading means 70 and the AD converter 301, and an attenuation circuit 306 for attenuating the image reading control signal used by the control means 200 to control the image reading means 70. The second circuit board provided in the upper housing includes a buffer circuit 78 that receives the image reading control signal attenuated by the attenuation circuit 306, adjusts the voltage or shapes the waveform, and outputs the image reading control signal to the image reading means.

Description

Technical Field

[0001] The present invention relates to an image reading device for reading an image of a document.

Background Art

[0002] In an image reading device, the electrical connection between an image reading unit and a control unit that controls it is connected via a cable, and it is common to connect them at a distance.

[0003] Further, in the image reading device, as the image reading speed increases and the device becomes more multifunctional, the signals transmitted are becoming faster. As a result, the occurrence of crosstalk and radiated radio wave noise from the cable has become a problem. As a countermeasure, an image reading device that communicates using a differential signal for high-speed transmission (e.g., LVDS [Low Voltage Differential Signaling]) is known.

[0004] However, when communicating using a differential signal (LVDS) for high-speed transmission, an impedance-matched shielded cable is required for the cable, which is a factor in increasing costs. Therefore, devices have been proposed to minimize the use of the shielded cable for differential signals (LVDS) and to reduce the transfer speed.

[0005] For example, Patent Document 1 arranges a control board in a first housing, an image reading board in a second housing, and a relay board near the image reading unit, connects between the control board and the relay board with a differential signal for high-speed transmission, and connects a control signal converted from a differential signal (LVDS) to a single-ended signal between the relay board and the image reading unit board, thereby proposing an image reading device that suppresses the use of a differential signal (LVDS) cable.

[0006] Also, in Patent Document 2, means for generating a clock signal of a timing generation circuit is provided in an image reading unit arranged in a second housing. As a result, an image reading device has been proposed that enables the exclusion of a high-speed clock signal from the cable connection between a control unit arranged in a first housing and an image reading unit arranged in a second housing. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-16042 [Patent Document 2] Japanese Patent Publication No. 2003-110798 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Patent Document 1 describes how the shielded cable for differential signals (LVDS) can be made as short as possible by making the section for differential signals for high-speed transmission as short as possible. However, this does not change the fact that a shielded cable for differential signals (LVDS) is still used.

[0009] Furthermore, Patent Document 2 states that the image reading unit must be equipped with a differential signal (LVDS) transmission and reception circuit, and an analog front-end (AFE) that converts the analog image reading signal into a digital signal and transmits it to the control unit. This leads to an increase in the size of the image reading unit and, consequently, the overall size of the device. In addition, a shielded cable for differential signals (LVDS) may be required. [Means for solving the problem]

[0010] In view of the above, the image reading device according to the present invention is An image reading device comprising a lower housing on which a first substrate is provided and an upper housing on which a second substrate is provided, a delivery means for connecting the first substrate and the second substrate, and an image reading means provided on the first substrate for generating an image analog signal corresponding to the optical density information of a document, The aforementioned first substrate is An AD converter that converts the analog image signal output by the image reading means into a digital image signal, Control means for controlling the image reading means and the AD converter, The control means includes an attenuation circuit for attenuating an image reading control signal for controlling the image reading means. Equipped with, The second substrate is The present invention is characterized by having a buffer circuit that receives the image reading control signal attenuated by the attenuation circuit, adjusts the voltage or shapes the waveform, and outputs the image reading control signal to the image reading means. [Effects of the Invention]

[0011] According to the present invention, by providing a buffer circuit for image reading control signals on the image reading unit side, the image reading control signals on the wiring between the control unit and the image reading unit can be attenuated by the attenuation circuit, thereby reducing noise. [Brief explanation of the drawing]

[0012] [Figure 1] A perspective view of an image reading device showing a first embodiment of the present invention, viewed from the front. [Figure 2] A cross-sectional view of the internal configuration of an image reading device showing a first embodiment of the present invention, viewed from the side. [Figure 3] Cross-sectional view of the image reading unit of an image reading device showing a first embodiment of the present invention. [Figure 4] Block diagram showing the electrical connections of an image reading device according to the first embodiment of the present invention. [Figure 5] A block diagram showing the detailed electrical connections between the control board and the image reading unit of an image reading device representing a first embodiment of the present invention. [Figure 6] An explanatory diagram illustrating an image sensor drive signal transmitted by the first image reading device of the present invention. [Figure 7] Block diagram showing the electrical connection between the buffer circuit and image sensor of an image reading device according to a second embodiment of the present invention. [Figure 8] An explanatory diagram illustrating a filter circuit of an image reading device showing a first embodiment of the present invention. [Figure 9] An explanatory diagram illustrating the internal configuration of the buffer circuit of an image reading device according to the first embodiment of the present invention. [Figure 10] Timing chart when the image sensor of the image reading device showing the first embodiment of the present invention operates

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the configurations described in the following embodiments are merely examples, and the scope of the present invention is not limited by the configurations described in the embodiments.

[0014] (First Embodiment) <Description of the Configuration of the Image Processing Apparatus> FIG. 1 is a perspective view of an image reading device 100 according to the first embodiment as seen from the front side. More precisely, it is a view from a direction perpendicular to the front panel 90 provided inclined on the front side of the image reading device 100, and is a view from slightly above the front in the state where the device is placed.

[0015] A touch panel 93 is provided on the front panel 90 at the upper front, and a display unit 94 is inside the device. Also, the touch panel 93 is substantially transparent and is provided so that the display unit 94 can be visually observed through the touch panel 93.

[0016] A mounting table 1 on which a plurality of transport media S are stacked is provided deeper than the front top surface, and a discharge tray 2 is provided at the front bottom.

[0017] A discharge opening 92 is provided in the lower panel 91 at the lower front, and the transport media S stacked on the mounting table 1 are configured to be discharged to the discharge tray 2 through the discharge opening 92.

[0018] <Description of the Internal Configuration of the Image Reading Device> FIG. 2 is a cross-sectional view of the internal configuration of the image reading device according to the first embodiment of the present invention as seen from the side.

[0019] The image reading device 100 transports one or more transport media S loaded on the mounting table 1 one by one along the path RT inside the device and discharges them into the discharge tray 2. The upper housing is rotatably mounted to the lower housing via a hinge 101, and the path RT is formed between them.

[0020] Here, the transport medium S is, for example, a sheet of OA paper, checks, cheques, business cards, or other types of cards, and may be a thick or thin sheet. Examples of cards include health insurance cards, driver's licenses, and credit cards. Booklets such as passports are also included.

[0021] When dealing with booklets, the booklets are placed in a transparent holder in an open state and then placed on the mounting platform 1, allowing the booklets to be transported together with the holder.

[0022] In addition to the above, the image reading device 100 reads images of the transport medium S within the path RT and performs image processing on those images.

[0023] <Paper feeding structure> A first transport unit 10 is provided as a transport mechanism for supplying the transport medium S along the route RT. The first transport unit 10 comprises a feed roller 11 and a separation roller 12 positioned opposite the feed roller 11, and sequentially transports the transport medium S on the mounting table 1 one by one in the transport direction D1.

[0024] The feed roller 11 receives driving force from the paper feed drive unit 3 via the transmission unit 5 and is rotated in the direction of the arrow in the figure (the positive direction that transports the transport medium S along the path RT).

[0025] The transmission unit 5, which connects the paper feed drive unit 3 and the feed roller 11, is normally configured to transmit driving force, but cuts off the driving force when the transport medium S is reversed or stopped. When the transmission of driving force to the feed roller 11 is cut off by the transmission unit 5, the feed roller 11 becomes capable of free rotation. Note that the transmission unit 5 does not need to be provided if the feed roller 11 is driven in only one direction.

[0026] The separation roller 12, positioned opposite the feed roller 11, is a roller for separating the conveyed medium S one sheet at a time, and is in constant pressure contact with the feed roller 11. To ensure this pressure contact, the separation roller 12 is provided to be swingable and is configured to be biased toward the feed roller 11.

[0027] The separation roller 12 receives driving force from the paper feed drive unit 3 via the torque limiter 12a and is rotated in the direction of the solid arrow (opposite to the forward direction of the feed roller 11).

[0028] When the separation roller 12 is in contact with the feed roller 11, the torque limiter 12a restricts the transmission of driving force, causing it to rotate in the direction of rotation with the feed roller 11 (in the direction of the dashed arrow). As a result, when multiple conveying media S are conveyed to the contact area between the feed roller 11 and the separation roller 12, two or more conveying media S are prevented from being conveyed downstream, leaving one behind.

[0029] It should be noted that such a separation mechanism is not necessarily required; any feeding mechanism that sequentially feeds the transport medium S one by one along the path RT will suffice. Alternatively, instead of a configuration like the separation roller 12, a separation pad that applies frictional force to the transport medium S may be pressed against the feed roller 11 to achieve a similar separation effect.

[0030] <Conveying Structure> The second conveying unit 20 includes a drive roller 21 and a driven roller 22 that moves in accordance with the drive roller 21. It is located downstream of the first conveying unit 10 in the conveying direction and conveys the conveying medium S that has been conveyed from the first conveying unit 10 to the downstream side.

[0031] The drive roller 21 receives driving force from a conveying drive unit 4 such as a motor and is rotated in the direction of the arrow in the figure. The driven roller 22 presses against the drive roller 21 with constant pressure and rotates along with the drive roller 21. The driven roller 22 may be configured to be biased against the drive roller 21 by a biasing unit (not shown) such as a spring.

[0032] The third conveying unit 30 includes a drive roller 31 and a driven roller 32 that moves in accordance with the drive roller 31. It is located downstream of the second conveying unit 20 in the conveying direction and conveys the conveyed medium S that has been conveyed from the second conveying unit 20 to the discharge tray 2. In other words, this third conveying unit 30 functions as a discharge mechanism.

[0033] The drive roller 31 receives driving force from a conveying drive unit 4 such as a motor and is rotated in the direction of the arrow in the figure. The driven roller 32 presses against the drive roller 31 with constant pressure and rotates along with the drive roller 31. The driven roller 32 may be configured to be biased against the drive roller 31 by a biasing unit (not shown) such as a spring.

[0034] <Image reading position detection structure> The image reading position detection sensor 50 detects whether the end of the transport medium S, which is transported by the first transport unit 10, has reached or passed the detection position.

[0035] Various types of image reading position detection sensors 50 can be used. In this embodiment, it is an optical sensor comprising a light-emitting unit 51 and a light-receiving unit 52, and detects the transport medium S by changing the light-receiving intensity (amount of light received) when the transport medium S arrives or passes through.

[0036] Furthermore, the image reading position detection sensor 50 is not limited to the optical sensor described above. For example, a sensor capable of detecting the end of the transport medium S (such as an image sensor) may be used, or a lever-type sensor protruding from the path RT may also be used.

[0037] In this embodiment, the image reading position detection sensor 50 is placed on the upstream side in the transport direction of the second transport unit 20, but the image reading position detection sensor 60 may be placed on the downstream side in the transport direction. In addition, both image reading position detection sensors 50 and 60 may be placed.

[0038] <Control board> A control board 190 (first board) for controlling the image reading device 100 is located at the bottom rear of the lower housing (lower housing) of the image reading device 100.

[0039] The control board 190 is connected to the image reading unit 70 (70a and 70b) via flat cables 80a and 80b (see Figure 4) inside the device. More specifically, it is connected to the image reading board (second board) of the image reading unit 70. It is also connected to the image reading position detection sensors 50 and 60 via a cable 81 (not shown).

[0040] Furthermore, the device receives power from an external power supply (not shown) to drive it, and when connected via a wired connection to an external device (not shown), information is communicated via an external communication cable 82 (see Figure 4).

[0041] In this embodiment, the control board 190 is positioned at the bottom of the rear side of the image reading device 100, but it may also be positioned parallel to the path RT. Furthermore, it may be located on the upper housing side of the front panel 90. In short, the placement of the control board 190 is not particularly restricted; it simply needs to be located within the device.

[0042] <Image reading structure> Figure 3 is a cross-sectional view of the image reading unit 70 of an image reading device 100 according to one embodiment of the present invention.

[0043] The image reading unit 70 is positioned opposite the second transport unit 20 and the third transport unit 30. In the following description, these will be referred to as image reading units 70a and 70b, respectively. Image reading units 70a and 70b are sensor units with the same structure, positioned symmetrically across the path RT.

[0044] The image reading unit 70a optically scans the original document and converts the optical density information of the original document into an electrical signal to read it as image data. It is equipped with an optical unit 75a, an image reading light source 74a, and an image sensor 76a. A white reference plate 72a is also provided for shading correction of the opposing reading unit.

[0045] The optical unit 75a includes an optical element that forms an optical path that guides the light from the transport medium, generated when the light from the image reading light source 74a irradiates the transport medium, to the line sensor. The optical path may be provided by various structures, and the optical element can also be made up of various materials.

[0046] The image reading light source 74a is equipped with an LED, fluorescent lamp, or the like for irradiating the transport medium with light. The light reflected from the transport medium or white reference plate 72 located at the irradiation position is received by the image sensor 76 of the image reading unit 70, and the image sensor 76 generates a signal corresponding to the amount of light received by each photoelectric conversion element.

[0047] The image sensor 76a is a line sensor extending in one direction, with multiple photoelectric conversion elements arranged in that direction. Each photoelectric conversion element outputs a signal corresponding to the intensity of the received light. In this embodiment, the direction in which the line sensor extends (main scanning direction) is positioned perpendicular to the transport direction of the transport medium (sub-scanning direction).

[0048] Furthermore, the image reading unit 70a is sealed to prevent contamination of the transport medium S with paper dust or other materials. Therefore, the transport medium S passes through the path RT, which is sandwiched between the glass surfaces 77a and 77b.

[0049] Since the image reading unit 70b has the same structure as the image reading unit 70a, its explanation will be omitted.

[0050] <Block diagram of the image reading device> Figure 4 is a block diagram showing the electrical connection according to the first embodiment of the present invention.

[0051] The control board 190 is equipped with components for controlling the image reading device 100. In this embodiment, it is equipped with a control unit 200, an AD conversion unit 301, a ROM 302, a RAM 303, a power supply unit 304, a light source drive unit 305, and filter circuits 306a and 306b.

[0052] The control unit 200 consists of a CPU, microcontroller, etc., and is responsible for the control, calculation, and information transfer of the entire device. The aforementioned paper feed drive unit 3, transport drive unit 4, transmission unit 5, image reading position detection sensors 50 and 60, image reading units 70a and 70b, AD conversion unit 301, touch panel 93, display unit 94, ROM 302, RAM 303, and light source drive unit 305 are connected to it.

[0053] The control unit 200 performs control functions such as image reading control (image sensor 76, image reading light source 74), motor drive control (paper feed drive unit 3, transport drive unit 4), drive transmission control (transmission unit 5), and light emission intensity control (image reading position detection sensors 50 and 60).

[0054] Furthermore, the control unit 200 includes a communication unit 202 and an image processing unit 207.

[0055] The communication unit 202 communicates with external devices (not shown). Communication standards include wired connections such as USB, LAN, and SCSI, and wireless connections such as wireless LAN and Bluetooth®. In the case of a wired connection, it connects to the external device via an external communication cable 82.

[0056] The image processing unit 207 processes the digital image data output from the AD conversion unit 301 and outputs the processed image data to the RAM 303.

[0057] The AD (analog / digital) conversion unit 301 is a converter that amplifies and offsets the minute analog signal output from the image sensor 76, and then converts it into digital image data.

[0058] ROM302 is a non-volatile storage device for storing data such as program data from the control unit 200 and correction data from the pixel processing unit 207.

[0059] RAM303 is a high-speed access storage device for temporarily storing data such as some of the program data from the control unit 200 and image data acquired from the image reading sensor 70.

[0060] The power supply unit 304 is a voltage conversion circuit unit that generates the power necessary to drive the image reading device 100 from an external power supply (not shown), such as an AC adapter. A DC / DC converter, LDO, or the like is used for voltage conversion.

[0061] The light source drive unit 305 is a drive circuit for illuminating the light source to a desired brightness, and consists of a constant current circuit, a PWM control circuit, and a voltage conversion circuit for the light source. The drive circuit may utilize discrete circuits using transistors or a dedicated driver IC for driving the light source.

[0062] Filter circuits 306a and 306b are circuits that cut or pass specific frequency bands of a signal and are used to block noise. In this embodiment, filter circuits are used, but any attenuation circuit will suffice, and so-called damping resistors consisting only of resistors may also be used.

[0063] Furthermore, although filter circuits 306a and 306b have the same function, their circuit constants differ because the distance between the control board 190 and the image reading units 70a and 70b is different, resulting in different required attenuation levels.

[0064] The image reading units 70a and 70b are equipped with components that control the image reading operation of the image reading device 100. In this embodiment, they are equipped with image sensors 76a and 76b, image reading light sources 74a and 74b, and buffer circuits 78a and 78b.

[0065] The image reading light source 74a is a light source that provides reflected light for image formation to the image sensor 76a. An LED or similar light source is used.

[0066] The image sensor 76a is a photoelectric conversion element that converts reflected light for image formation into analog image data signals, and it has photoelectric conversion elements on a single line. For this reason, it is necessary to read them sequentially, and they are read based on the image reading control signal output from the control unit 200.

[0067] Image sensors can be broadly classified into two types: CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors, and their control mechanisms differ.

[0068] A CCD sensor receives light using a photodiode, converts it into an electric charge, stores it, and then moves that charge to the next element in a bucket brigade-like fashion, ultimately converting the charge into a voltage.

[0069] On the other hand, a CMOS sensor converts light received by a photodiode into electric charge and stores it, and then an amplifier in each element converts the charge into a voltage. By successively switching switches attached to each photodiode arranged in a grid, each element is read out directly, pixel by pixel.

[0070] In this embodiment, the output image reading control signal is the image reading signal for the CMOS sensor, but the same can be done with an image reading control signal for a CCD sensor.

[0071] The buffer circuit 78a is a circuit that increases the driving capability of the signal transmitted from the control unit 200 to drive the image sensor 76a, and also performs waveform shaping.

[0072] Note that the image sensor 76b, image reading light source 74b, and buffer circuit 78b have the same functions as the image sensor 76a, image reading light source 74a, and buffer circuit 78a, so their explanation will be omitted.

[0073] Flat cables 80a and 80b are wires in which conductors are arranged in parallel and an insulator is crimped onto them in a thin, plate-like shape. They are used for connecting electronic components and circuit boards in movable parts, areas with limited space, and in housings. In this embodiment, they are used to connect the control board 190 and the image reading unit 70.

[0074] Furthermore, although flat cables 80a and 80b have the same function, their cable lengths differ because the distance between the control board 190 and the image reading units 70a and 70b is different.

[0075] Cable 81 is a wire used to connect the control board 190 and the image reading position detection sensors 50 and 60.

[0076] The external communication cable 82 is a wire used to connect external equipment (not shown) via a wired connection.

[0077] Ferrite cores 85a and 85b are core rods made of ferrite magnetic material, and are attached to enclose the flat cables 80a and 80b. In this way, the flat cables 80a and 80b and the ferrite cores 85a and 85b form a coil (inductor).

[0078] As a result, it has the same impedance as an inductor in an electronic component, which increases with higher frequencies, acting as a low-pass filter that blocks high-frequency currents and attenuates high-frequency noise.

[0079] Furthermore, when current flows through the inductor constructed as described above, a magnetic flux is generated in the ferrite core, and the energy of the current is converted into magnetic energy. As the current changes, this magnetic flux is converted back into current by electromagnetic induction.

[0080] In this case, not all of the magnetic flux energy is converted back into current energy; some is lost as magnetic loss. Therefore, a portion of the noise current passing through the wire is lost as magnetic loss.

[0081] Furthermore, although ferrite cores 85a and 85b are provided in this embodiment, they are not necessarily required depending on the noise radiation level. Alternatively, only one of the ferrite cores 85a or 85b may be provided.

[0082] <Detailed block diagram between the control board and the image reading unit> Figure 5 is a block diagram detailing the electrical connections between the control board and the image reading unit (particularly the image reading board) of an image reading device according to the first embodiment of the present invention. Note that the configurations of branches a and b are common to all of this block diagram and will therefore be omitted from the explanation.

[0083] The flat cable 80 is constructed by arranging conductors 501 to 512 side by side.

[0084] Wires 501, 502, and 503 are light source drive lines for illuminating the light source for the image reading sensor. In this embodiment, color separation is performed by the light source in order to acquire a color image. Therefore, drive lines are provided to illuminate three colors: red, blue, and green.

[0085] In this embodiment, a drive line was used to illuminate three colors, but this does not limit the number of colors. Furthermore, it does not limit the number of colors.

[0086] The conductor 504 is a power supply line that supplies power voltage to the image sensor 76 and buffer circuit 78 on the image reading unit.

[0087] The lead wire 505 is an image sensor drive signal line for driving the image sensor 76. The image sensor drive signal output from the control unit 200 is output from the image sensor drive signal line 505 after noise removal via the filter circuit 306. After that, it is waveform shaped via the buffer circuit 78 and then input to the image sensor 76. Here, the image sensor 76 is divided into multiple channels in its main scanning direction, and an image reading signal line is output in parallel for each channel. Figure 5 shows an example where it is divided into three channels.

[0088] Conductors 507, 509, and 511 are image reading signal lines output from the image sensor 76. Outputting them in parallel helps to suppress the acceleration of the drive signal. Although this embodiment uses three outputs, the number of outputs is not limited.

[0089] Furthermore, the image reading signal lines 507, 509, and 511 are positioned between the ground lines 506, 508, 510, and 512 in the pattern lines on the image reading unit 70, the flat cable 80, and the control board 190. This ensures a return path for each image reading signal line, suppressing radiated noise and crosstalk.

[0090] <Diagram illustrating the transmitted image sensor drive signal> Figure 6 is an explanatory diagram illustrating the image sensor drive signal transmitted by the image reading device according to the first embodiment. In this explanation, the clock signal with the highest frequency used to drive the image sensor will be used.

[0091] Figure 6(a) shows the image sensor drive signal output from the control unit 200. The voltage amplitude is sufficiently high, and the rise and fall times are also steep.

[0092] However, if the signal is transmitted directly to the image sensor 76 in this manner, waveform reflection and crosstalk will occur due to the long transmission line length and the difference in impedance at the connection point between the circuit board and the cable, resulting in waveform distortion (overshoot, undershoot, ringback, ringing, step).

[0093] Figure 6(a) on the right shows a magnified view explaining each type of waveform distortion. Overshoot is a phenomenon where the rising edge of a square wave exceeds the power supply voltage (H level). Undershoot is a phenomenon where the falling edge of a square wave falls below ground (L level). These can cause damage to components in a circuit or shorten their lifespan.

[0094] Ringback refers to the waveform on the reaction side of overshoot and undershoot. Ringing, on the other hand, is an unstable oscillation state in which overshoot and undershoot and ringback repeatedly occur until it gradually stabilizes at an L level or H level.

[0095] Furthermore, a "step" is a phenomenon where a signal pauses briefly, like a landing on a staircase, during its rising or falling phase. This can lead to misinterpretations of L-level and H-level signals, or cause timing violations.

[0096] The waveform distortions mentioned above become harmonic components of the digital signal, which travel through circuit board patterns and conductors such as cables, causing radiated noise.

[0097] The harmonic components of digital signals increase radiated noise. Therefore, the signal is attenuated using filter circuit 306. Signal attenuation requires a low-pass filter circuit that allows low-frequency components of the input voltage to pass through while blocking high-frequency components.

[0098] An example of a low-pass filter circuit is shown in Figure 8. Figure 8 is an RC low-pass filter composed of a resistor (R) and a capacitor (C). With this filter configuration, the cutoff frequency fc is fc = 1 / 2πRC, which blocks harmonic components.

[0099] In this embodiment, the attenuation circuit is an RC low-pass filter, but it may also be an attenuation circuit consisting only of a resistor, known as a damping resistor. Alternatively, it may be a circuit consisting of multiple stages of the RC filter circuit shown in this embodiment.

[0100] Next, Figure 6(b) shows the image sensor drive signal attenuated by the filter circuit 306. This filter circuit also limits the amount of drive current that can be output from the control unit 200.

[0101] Furthermore, the filter circuit 306 also reduces the voltage range of the signal amplitude VH-VL. Therefore, if the filter circuit constants are set to attenuate the signal so strongly that the effects of ringing and reflection disappear, it may prevent subsequent stages from operating. In such cases, the ferrite core 85 should be used in conjunction with the filter circuit.

[0102] However, as shown in Figure 6(b), if the output voltage of the drive signal input to the image sensor 76 is attenuated below VH and the drive current is reduced, there is a possibility that the image sensor 76 may not be able to be driven completely.

[0103] Therefore, in order to shape the waveform and ensure sufficient drive current, the image sensor drive signal is input to the image sensor 76 via the buffer circuit 78. Figure 9(a) shows an example of the circuit configuration of the buffer circuit 78. By using a circuit configuration like that shown in Figure 9(a), waveform shaping against signal attenuation can be performed without logic conversion.

[0104] Furthermore, although this embodiment does not perform logic conversion and uses a buffer circuit 78, it is also possible to configure the control unit 200 to invert the logic and output it, and to use an inverter circuit, and the method of waveform shaping in response to signal attenuation is not limited. In the present invention, a circuit that performs waveform shaping, including an inverter circuit, is referred to as a buffer circuit.

[0105] Figure 9(b) shows an example of an inverter circuit configuration. The inverter circuit has three stages. Therefore, the signal is inverted three times, and the output signal is an inverted version of the input signal.

[0106] Figure 6(c) shows the image sensor drive signal output from the buffer circuit 78. An output equivalent to that shown in Figure 6(a) before attenuation is input to the image sensor 76. However, this is just one example, and the image sensor drive signal output from the buffer circuit 78 does not necessarily have to be equivalent to the output before attenuation in Figure 6(a); it is sufficient that the output voltage is configured to drive the image sensor 76.

[0107] Furthermore, by adding spread spectrum, which intentionally modulates the clock frequency of the image sensor drive signal, the energy is not concentrated at a single frequency but spread out, thus further reducing radiated noise.

[0108] In this embodiment, the flat cable 80 is assumed to be a general-purpose product, but it is also possible to use a shielded flat cable with added shielding functionality. However, since shielded flat cables have capacitive components, the image reading signal output from the image sensor 76 will also be attenuated. Therefore, if higher speed and image quality are required, it is preferable to use a configuration that does not use a shielded flat cable.

[0109] As described above, according to this embodiment, the image sensor drive signal line on the flat cable can be output in a low-noise state by attenuating it with a filter circuit, enabling high-speed image reading in an inexpensive and compact configuration. In this embodiment, the image sensor drive signal is attenuated by the resistance component of the filter circuit, but this is not limited to this, and attenuation of the image sensor drive signal may be achieved by other circuit configurations arranged for other purposes.

[0110] Figure 10 shows the timing chart when the image sensor 76 is in operation. The image sensor 76 is driven by two control signals, the SP (Start Pulse) signal and the CLK (Clock) signal.

[0111] The SP signal is used to reset the charge accumulated in each pixel of the image sensor 76, and the CLK signal is used to transfer the output signal of each pixel. As shown in Figure 5, both signals are branched and input according to each sensor row. Furthermore, the sensor row may be further divided into pixel blocks.

[0112] When the image sensor drive signal is transmitted without the buffer circuit 78, as in the conventional method, the waveform becomes distorted due to the capacitive component of the transmission line. If the image sensor 76 is driven based on this distorted SP signal, a delay occurs in the output timing of the image signal from the sensor array or pixel block.

[0113] In contrast, with the buffer circuit 78 of the present invention, although a slight delay Td occurs as shown in Figure 6, it can be limited to a slight delay of a certain value caused by the configuration of the buffer circuit 78. Therefore, when the image sensor 76 is driven based on the SP signal from the buffer circuit 78, the timing difference of the output of the image signal from the sensor array or pixel block can be suppressed.

[0114] (Second embodiment) The image reading device according to the second embodiment of the present invention shows an alternative configuration of the electrical connection between the buffer circuit and the image sensor within the image reading unit.

[0115] Figure 7 is a block diagram showing the electrical connection between the buffer circuit and the image sensor of the image reading device according to this embodiment.

[0116] Figure 7(a) shows a configuration in which buffer circuits are arranged in parallel for each sensor row. This configuration allows for the driving of high-speed sensors that require more power. Furthermore, because the buffer circuits can be placed as close to each sensor as possible, the distance over which the attenuated image sensor drive signal travels becomes longer, allowing for longer signal lines that operate in a lower-noise state.

[0117] Figure 7(b) shows a configuration in which a buffer circuit 78d is added before the configuration in Figure 7(a). With this configuration, the effect of reflections from subsequent branching can be absorbed by the buffer circuit 78d, resulting in a lower noise state.

[0118] In this embodiment, a buffer circuit is arranged in parallel for each sensor row, but it is also possible to arrange buffer circuits in parallel for every few sensor rows. [Explanation of Symbols]

[0119] 70 Image reading unit 74 Image reading light source 76 Image Sensors 78 Buffer Circuit 80 Flat Cable 81 Cable 82 External communication cable 100 Image reading device 190 Control board 200 Control Unit 202 Communications Department 207 Image Processing Unit 301 AD Conversion Unit 305 Light source drive unit 306 Filter Circuit 501 Image reading light source (red) drive line 502 Image reading light source (green) drive line 503 Image reading light source (blue) drive line 504 Power supply line 505 Image sensor drive line 506 Ground Line 507 Image reading signal line 508 Grand Line 509 Image reading signal line 510 Ground Line 511 Image reading signal line 512 Grand Line

Claims

1. An image reading device comprising a lower housing on which a first substrate is provided, an upper housing on which a second substrate is provided, a distribution means for connecting the first substrate and the second substrate, and an image reading means provided on the first substrate for generating an image analog signal corresponding to the optical density information of the original, The first substrate is An AD converter that converts the analog image signal output by the image reading means into a digital image signal, Control means for controlling the image reading means and the AD converter, The control means includes an attenuation circuit for attenuating an image reading control signal for controlling the image reading means. Equipped with, The second substrate is An image reading device characterized by comprising a buffer circuit that receives the image reading control signal attenuated by the attenuation circuit, adjusts the voltage or shapes the waveform, and outputs the image reading control signal to the image reading means.

2. The image reading device according to claim 1, characterized in that the delivery means is a flat cable.

3. The image reading device according to claim 1, characterized in that a magnetic material is attached to a part of the delivery means.

4. The image reading device according to claim 1, characterized in that the image reading means is divided into a plurality of channels and outputs a plurality of analog image signals corresponding to the channels in parallel.

5. The image reading device according to claim 4, characterized in that a ground is wired between a plurality of image analog signals within the delivery means.

6. The image reading device according to claim 1, characterized in that the image reading control signal is provided with spread spectrum.

Images