JP2024065450A - Image reader - Google Patents

Abstract

[Problem] Even if the conveying speed is slow, the image can be prevented from becoming too bright, and the reading operation of the line image sensor follows the fluctuation of the conveying speed to obtain an image synchronized in the sub-scanning direction. [Solution] The image reading device has a conveying section that conveys the document, a driving means that drives the conveying section, a driving control means 80 that controls the rotational driving of the driving means, a rotation detection means 83, 84 that detects the rotation of the conveying section or the driving means and outputs a pulse signal according to the rotation, a light source 88 that irradiates light onto the conveyed document and a light source control means 87 that controls the lighting of the light source, a reading means 86 that picks up and reads the conveyed document in a line shape, and an imaging start timing generation means 85 that counts the pulse signals output from the rotation detection means and generates an imaging start timing signal for one line of the reading means every certain number of pulses. The imaging start timing generation means outputs a dummy imaging start timing signal when the period of the pulse signal becomes long and exceeds a certain time. [Selected Figure] Figure 2

Description

The present invention relates to an image reading device that reads document images in an image scanner, facsimile machine, etc., and is particularly suitable for use in an image reading device that uses a DC motor as a drive means, illuminates a document with a linear light source using an LED as a reading means, and captures the linear image with a CIS (Contact Image Sensor) line sensor.

In conventional image reading devices, a DC motor may be used as the motor for transporting the document. Although DC motors are low cost and easy to drive, they have the disadvantage that their speed is prone to fluctuations due to changes in the transport load, etc. Patent Document 1 discloses an image reading device that detects this speed fluctuation and sequentially reads and stores the data one line at a time using a one-dimensional image sensor. This image reading device is provided with an encoder that detects a through hole in the disk and outputs a detection signal using a photointerrupter that is arranged opposite to a part of a disk that is attached to the rotating shaft of the DC motor so as to be able to rotate integrally with it, and each time a detection signal is output from the encoder, a reading operation is performed by the image sensor.

Patent Document 2 also discloses an image reading device that, when the speed of a DC motor fluctuates, compares the detection signal of an encoder with the reading cycle of a line sensor, and discards unnecessary image data if there is a difference.

Japanese Patent Application Laid-Open No. 6-54132 JP 2021-97389 A

However, with the above-mentioned conventional technology, when the conveying speed fluctuates and becomes slow, particularly at low speeds such as immediately before conveying is temporarily stopped, the imaging time of the line sensor becomes longer, and electric charge accumulates due to the influence of the dark current of the line sensor, which may result in a bright image being output. Furthermore, when control such as that in Patent Document 2 is performed, the line sensor cannot read in synchronization with the encoder for detecting the conveying speed, and so an image that is not synchronized with the conveying direction may be output.

In view of the above-mentioned problems, an image reading device according to the present invention comprises:
A conveying unit that conveys the document;
A driving means for driving the conveying unit;
A drive control means for controlling the rotational drive of the drive means;
a rotation detection means for detecting the rotation of the conveying unit or the driving means and outputting a pulse signal in response to the rotation;
a light source for irradiating light onto the conveyed document, and a light source control means for controlling the lighting of the light source;
a reading means for imaging and reading the conveyed document in a line perpendicular to the conveying direction;
an imaging start timing generating means for counting the pulse signal output from the rotation detecting means and generating an imaging start timing signal for one line of the reading means every time a certain number of pulses are counted;
The imaging start timing generating means outputs a dummy imaging start timing signal when the period of the pulse signal output from the rotation detecting means becomes long and exceeds a certain period of time.

According to the present invention, even when the conveying speed is slowed, excessive accumulation of dark current charge in the line sensor can be prevented, preventing the image from becoming too bright. In addition, the reading operation of the line image sensor follows fluctuations in the conveying speed, making it possible to obtain an image that is synchronized in the sub-scanning direction.

FIG. 1 is a schematic diagram of an image reading apparatus 10 as an example of a sheet feeding apparatus according to a first embodiment; FIG. 1 is a block diagram showing an electrical configuration of an image reading device according to a first embodiment; Schematic diagram of an encoder unit 84 according to the first embodiment. FIG. 1 is a schematic diagram showing a current flow in a storage element 89 according to a first embodiment; 1 is a flowchart showing an example of the operation of the image reading device 10 according to the first embodiment. 1 is a flowchart showing a start pulse generation process of the image reading device 10 according to the first embodiment. 1 is a flowchart showing a line sensor imaging process of the image reading device 10 according to the first embodiment. 1 is a flowchart showing an image acquisition process of the image reading device 10 according to the first embodiment. 1 is a timing chart showing the operation of the image reading device 10 according to the first embodiment; 11 is a flowchart showing a start pulse generation process of the image reading device 10 according to the second embodiment. 11 is a timing chart showing the operation of the image reading device 10 according to the second embodiment. 11 is a flowchart showing a start pulse generation process of the image reading device 10 according to the third embodiment. 1 is a flowchart showing a dummy pulse generation process of the image reading device 10 according to the first embodiment. 11 is a flowchart showing a dummy pulse generation process of the image reading device 10 according to the third embodiment. FIG. 1 is a schematic diagram showing a configuration of a CMOS image sensor according to a first embodiment;

First Embodiment
Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are examples for realizing the present invention, and the present invention is not limited to the following embodiments. The dimensions, materials, shapes, relative positions, etc. of the components of the present embodiment should be appropriately modified or changed depending on the configuration and various conditions of the device to which the present invention is applied, without departing from the spirit of the present invention.

Figure 1 is a schematic diagram of an image reading device 10 according to this embodiment.

<Apparatus Configuration>
The image reading device 10 is a device that transports one or more sheets S loaded on a loading platform 12 into the device one by one from a paper feed port, reads the images on the sheets, and discharges the sheets S to the outside of the device by a drive roller 20 and a driven roller 21. The sheets S to be read are, for example, office paper, checks, business cards, cards, etc., and may be thick or thin sheets.

The loading tray document detection sensor 13a is positioned at a position where it can detect sheets S loaded on the loading tray 12, and is equipped with a light emitting section and a light receiving section. The light emitted by the light emitting section is returned to the light receiving section by the light guide lens 13b provided on the opposite side of the transport path, and when sheets S are loaded, the light path is blocked, thereby detecting that sheets S have been loaded on the loading tray 12.

<Paper feeding>
A first conveying section 50 is provided as a sheet feeding mechanism that feeds the sheet S along the path RT. In this embodiment, the first conveying section 50 includes a feed roller 14 (feed roller) and a separation pad 30 arranged opposite the feed roller 14, and sequentially conveys the sheets S on the stacking table 12 one by one in the feeding direction D. The feed roller 14 is driven to rotate in the direction of the arrow in the figure (the direction in which the sheet S is conveyed) by a drive section 15 configured to transmit a driving force by a motor (not shown) via a transmission section. Note that the drive section 15 is illustrated on the outside of the image reading device 10 for the sake of explanation, but is actually disposed beside the feed roller 14. The drive section 15 is not limited to a single one, and may be configured by a plurality of motors, etc.

<Drive unit>
In the present embodiment, for example, the transmission unit connecting the drive unit 15 and the feed roller 14 is in a state in which the drive force is normally transmitted, and the drive force is interrupted when the sheet S is stopped. When the transmission of the drive force is interrupted by the transmission unit, the feed roller 14 is in a state in which it can rotate freely.

<Isolation structure>
The separation pad 30, which is disposed opposite the feed roller 14, is a member for separating the sheets S one by one, and is in pressure contact with the feed roller 14. To ensure this pressure contact state, a compressible sponge member 33 (elastic member) is provided on the separation pad 30. The sponge member 33 is configured to urge a first friction member 32 and a second friction member (described later) toward the feed roller 14 by the elastic force of the sponge member 33.

<Conveyor structure>
The second conveying section 51, which serves as a conveying mechanism located downstream of the first conveying section 50 in the conveying direction, has a drive roller 16 and a driven roller 17 driven by the drive roller 16, and conveys the sheet S conveyed from the first conveying section 50 downstream. A driving force is transmitted from the drive section 15 to the drive roller 16, and the drive roller 17 is driven to rotate. The driven roller 17 is in contact with the drive roller 16 with a constant pressure, and rotates together with the drive roller 16. The driven roller 17 may be configured to be biased against the drive roller 16 by a biasing unit (not shown) such as a spring.

The third conveying section 52, which serves as a conveying mechanism located downstream of the second conveying section 51 in the conveying direction, includes a drive roller 20 and a driven roller 21 that is driven by the drive roller 20, and discharges the sheet S conveyed from the second conveying section 51 to the outside of the device. In other words, the third conveying section 52 functions as a discharge mechanism.

The driving force is transmitted from the driving unit 15 to the driving roller 20, which is then driven to rotate. The driven roller 21 is pressed against the driving roller 20 with a constant pressure, and rotates along with the driving roller 20. The driven roller 21 may be configured to be biased against the driving roller 20 by a biasing unit (not shown) such as a spring.

<Image reading structure and control>
In the image reading device 10 of the present embodiment, the second conveying section 51 and the third conveying section 52 convey the sheet S at a constant speed in order to read the image by the image reading units 18 and 19 disposed between the second conveying section 51 and the third conveying section 52. By always setting the conveying speed at this time to be equal to or higher than the conveying speed of the first conveying section 50, it is possible to reliably prevent the succeeding sheet S from catching up with the preceding sheet S. For example, in the present embodiment, the reduction ratio of the transmission section that transmits the drive from the drive section 15 to the first conveying section 50 is set to be greater than the reduction ratio of the transmission section that transmits the drive from the drive section 15 to the second conveying section 51 and the third conveying section 52 so that the conveying speed of the sheet S by the second conveying section 51 and the third conveying section 52 is faster than the conveying speed of the sheet S by the first conveying section 50.

Even if the conveying speed of the sheet S by the second conveying unit 51 and the third conveying unit 52 and the conveying speed of the sheet S by the first conveying unit 50 are the same, it is possible to form a minimum gap between the preceding sheet S and the succeeding sheet S by controlling the drive unit 15 to control only the drive of the first conveying unit 50 and intermittently shifting the timing at which the feed of the succeeding sheet S starts.

<Registration sensor>
The medium detection sensors 41 and 42 arranged downstream of the first transport unit 50 in the transport direction are examples of detection sensors (sensors for detecting the behavior and state of a sheet) arranged upstream of the image reading units 18 and 19 and downstream of the first transport unit 50 on the upstream side of the transport path RT, and detect the position of the sheet S transported by the first transport unit 50, more specifically, whether the end of the sheet S has reached or passed the detection position of the medium detection sensors 41 and 42. Various types of medium detection sensors 41 and 42 can be used, but in this embodiment, they are optical sensors that have a light emitting portion and a light receiving portion and detect the sheet S based on the principle that the intensity of received light (amount of received light) changes when the sheet S reaches or passes through. Note that the medium detection sensors 41 and 42 are not limited to the optical sensors described above, and may be, for example, sensors (image sensors, etc.) that can detect the end of the sheet S, or may be lever-type sensors protruding into the path RT.

<CIS placement>
The image reading units 18 and 19 located downstream of the medium detection sensors 41 and 42, for example, optically scan the transported document in a main scanning direction perpendicular to the transport direction (sub-scanning direction), convert the scanned image into an electric signal, and read the scanned image as image data. The image reading units 18 and 19 are equipped with a light source such as an LED, a line sensor arranged in a line, a lens array, and the like. In this embodiment, the image reading units 18 and 19 are arranged one on each side of the path RT, and read the front and back sides of the sheet S. However, the image reading units 18 and 19 may be arranged only on one side of the path RT to read only one side of the sheet S. In this embodiment, the image reading units 18 and 19 are arranged opposite each other across the path RT, but they may be arranged with an interval between them in the transport direction of the path RT, for example. In this embodiment, a CIS (Contact Image Sensor) is used as the line sensor, and this CIS is a document reading means, and is an example of the line sensor 86 shown in Fig. 2, and the image reading units 18 and 19 each include this line sensor 86, a light source 88, the above-mentioned lens array, etc. Also, the start pulse generating section 85 and the light source control means 87 are realized by ICs or the like arranged on the image reading boards of the image reading units 18 and 19, but are not limited to this. For example, a configuration may be adopted in which these functions are realized as part of the functions of the CPU 80.

<Block diagram explanation>
FIG. 2 is a block diagram showing the electrical configuration of the image reading device 10. As shown in FIG.

The image reading device 10 is entirely controlled by the CPU 80. The CPU 80 controls the speed of the drive motor 82 by issuing control instructions to a drive control unit 81, which controls the drive of the drive motor 82 (an example of a drive unit 15), based on the output signal of the encoder pulse generating unit 83, which is one of the encoder unit 84 and encoder pulse generating unit 83 that are rotation detection means for detecting the rotation speed of the drive motor 82 and generate a pulse signal synchronized with the rotation of the drive motor 82. The drive motor 82 is a drive means for conveying a sheet, and a DC motor is mainly used.

As shown in FIG. 3, the encoder unit 84 has a disk 123, a light emitter 124, and a light receiver 125. The disk 123 is provided on the rotation shaft of the drive motor 82 so as to rotate in accordance with the rotation of the drive motor 82. A plurality of slits 126 (light transmission holes) are formed in the disk 123. The light emitter 124 and the light receiver 125 are provided so as to face each other across the disk 123. The light emitter 124 irradiates light toward the disk 123. On the other hand, the light receiver 125 generates and outputs a pulse signal, which is an electrical signal according to the intensity of the received light. The signal value of the pulse signal is relatively large (High) while the light emitted by the light emitter 124 is received through the slit 126, and is relatively small (Low) while the light emitted by the light emitter 124 is blocked by the disk 123, and is generated into the desired pulse signal by the encoder pulse generating unit 83. For convenience, FIG. 3 shows a disk 123 with 12 slits 126, but an actual disk 123 will have hundreds of slits.

The start pulse generating unit 85 counts the pulses output from the encoder pulse generating unit 83, generates a start pulse every certain count number (number of pulses), and issues it to the line sensor 86. The certain count number differs depending on the resolution in the sub-scanning direction read by the image reading device, and it is desirable for the count number to detect the amount of rotation of the encoder when the sheet S advances a distance of one pixel of the desired resolution.

When the start pulse generating unit 85, which is the imaging start timing generating means, issues a start pulse, which is an imaging start timing signal, to the line sensor 86, the line sensor 86 starts imaging. That is, at this time, the start pulse of the start pulse generating unit 85 is also issued to the light source control means 87, and the light source control means 87 controls the lighting of the light source 88 so that it is lit for a certain period of time in synchronization with the start pulse. The light source 88 is made up of red, green, and blue LEDs, and in this embodiment, they are lit simultaneously to obtain a gray image. The light irradiated from the light source 88 is reflected by the sheet and enters the line sensor 86, and the line sensor 86 can read the image on the sheet.

Now, using FIG. 15, we will explain the configuration of the sensor part of a CMOS image sensor, which is an example of a line sensor. It has a photodiode 201 that photoelectrically converts incident light and accumulates an electric charge, and the charge of the photodiode is converted into a voltage by a capacitor 202. It has an amplifier 205 that amplifies the voltage of the capacitor 202, and when a signal corresponding to a start pulse is input to switches 203 and 204, the switches perform an ON/OFF operation. When switch 203 is turned ON, the electric charge accumulated in the photodiode 201 moves to the capacitor 202. When switch 204 is turned ON, the output voltage of amplifier 205, which is the amplified voltage of capacitor 202, is input to the CPU 80. In a CMOS image sensor, this circuit is provided for each pixel.

The medium detection unit 91 corresponds to the medium detection sensors 41 and 42 in FIG. 1. The storage element 89 is composed of an electric double layer capacitor or the like. The flow of current through the storage element 89 will be explained below with reference to FIG. 4.

In this embodiment, the host PC 200 connected to the image reading device 10 via USB is configured to supply current to the image reading device 10 via a USB cable. The current supply source may be a host PC or a power supply device such as an AC adapter. When current is supplied from the host PC 200, it is temporarily stored in the storage element 89 and supplied to the drive motor 82 and other electric circuits 96 that constitute the image reading device 10. The storage amount detection unit 90 detects the voltage of the storage element 89 and the current amount of the current sensor 95 to detect the storage amount of the storage element 89 and the current flowing through the connected load (drive motor 82, other electric circuits 96), and transmits it to the CPU 80. The CPU 80 issues instructions to the drive control unit 81 based on the information, controls the speed of the drive motor 82, etc., and reduces current consumption. In addition, if the voltage of the storage element 89 is below a certain level, the CPU 80 temporarily stops the drive motor 82, reduces current consumption, and stores charge in the storage element 89 so that the voltage is above a certain level.

In this embodiment, the power is supplied from the host PC 200, temporarily stored in the power storage element 89, and then supplied to the load. However, it is also possible to provide an AC adapter or a power supply unit within the image reading device and receive power from these limited power sources. Temporarily storing power in the power storage element 89 allows stable operation even in the event of a sudden load change, but the power storage element 89 is not necessary.

Next, an example of the operation of the image reading device 10 will be described with reference to FIG. 5. When an instruction to start reading (S101) is given from the host PC 200 or the like, it is confirmed whether a sheet is loaded on the loading tray 12 of the image reading device 10 (S102). If a sheet is loaded, a DC motor, which is an example of the drive motor 82, is driven and sheet transport begins (S103). If there is no sheet on the loading tray 12, the device waits until a sheet is placed, or if no sheet is detected after a certain period of time has passed, it may return an error to the host PC 200 indicating that there is no sheet.

When the drive motor 82 is driven (S103), the disk 123 attached to the shaft of the drive motor 82 rotates, a pulse signal is output from the encoder unit 84, and the start pulse generator 85 starts counting the encoder pulses generated by the encoder pulse generator 83 (S104).

Now, with reference to Figures 6 and 13, an example of the operation of counting the encoder pulses to generate a start pulse and an example of the operation of generating a dummy pulse will be described. When the start pulse generating unit 85 detects the rising edge of the encoder pulse output from the encoder pulse generating unit 83 (Yes in S201 and S205), the internal counter counts up in the start pulse generating process shown in Figure 6. In the dummy pulse generating process shown in Figure 13, the internal counter counts up and time measurement starts (S206).

In the start pulse generation process shown in FIG. 6, when the encoder pulse count reaches six pulses (Yes in S202), the count number is reset (S203), and the start pulse generating unit 85 generates a start pulse that instructs the line sensor 86 to start imaging (S204). In the configuration of this embodiment, it is assumed that an image is read at a resolution of 300 dpi, and when the encoder pulse count reaches six pulses, the sheet is transported a distance equivalent to one dot at a resolution of 300 dpi.

On the other hand, in the dummy pulse generation process shown in FIG. 13, when the rising edge of the next encoder pulse is detected (Yes in S207), the time measurement is reset (S208). When a certain time has passed without the next encoder pulse being detected (Yes in S209), the start pulse generating unit 85 generates a dummy pulse to the line sensor 86 (S210). If the certain time has not passed, the process returns to S207.

Even if a dummy pulse is generated, the encoder pulse count continues. The operations in Figures 6 and 13 are repeated until the DC motor stops.

Returning to FIG. 5, when the medium detection unit 91 (resist sensor) detects the leading edge of the sheet being conveyed (Yes in S105), the sheet reading operation is started (S106). Here, the time until the sheet reading operation is started may be the time when the leading edge of the sheet reaches the line sensor 86.

The imaging operation of the line sensor 86 will be described with reference to FIG. 7. When the line sensor 86 detects a start pulse or a dummy pulse (Yes in S301), it starts imaging (S302). When the light source control means 87 detects a start pulse or a dummy pulse, it turns on the light source 88 (S303). The lighting time of the light source 88 is adjusted in advance to achieve the desired brightness of the image. The light source 88 is turned on for this adjusted time, and when a certain time has passed (Yes in S304), the light source control means 87 turns off the light source (S305). When the next start pulse or dummy pulse is detected (S306), the line sensor 86 stops imaging, outputs the captured image signal to a subsequent circuit (not shown), and starts imaging the next line. The start pulse or dummy pulse detected in S306 is the pulse detected in S301 in the next line.

Next, the image acquisition operation of the image signal output from the line sensor 86 (S107 in FIG. 5) will be explained using FIG. 8.

First, in S401, the image signal output from the line sensor 86 is determined to be either a signal captured by a start pulse or a signal captured by a dummy pulse. The CPU 80 recognizes the timing at which the dummy pulse was output based on information from the encoder pulse generating unit 83 and the start pulse generating unit 85. If the image signal was captured by a start pulse, it passes through an amplifier circuit and an A/D conversion circuit (not shown) and is then stored in memory as image data (S403). If the image signal was captured by a dummy pulse, it is not stored in memory as it is an unnecessary image signal (S402).

The operations from S106 to S107 in FIG. 5 are repeated until the medium detection unit 91 detects the rear end of the sheet and the entire sheet is imaged by the line sensor 86. When the imaging operation of the entire sheet is completed (S109), the image data stored in the memory undergoes a predetermined image processing (S110) and is then output to the host PC 200 or the like (S111). If there are still sheets on the loading tray 12, the imaging operation is repeated until a stop operation is performed from the host PC or the like (S112). If there are no more sheets on the loading tray 12, the imaging operation is completed and the drive motor 82 is stopped (S113).

Here, we will use Figure 9 to explain the relationship between the encoder pulse, start pulse, dummy pulse, and image signal.

The start pulse generating unit 85 generates a start pulse every time it counts six encoder pulses. When the start pulse is generated, the line sensor 86 starts capturing images. The light source 88 also turns on for a fixed period of time in synchronization with the start of line sensor capturing images. The light source 88 is turned ... advance so that an image of the desired brightness can be obtained. The image signal captured in the nth section after the start of line sensor capturing images is output from the line sensor 86 at the start of the next n+1th section, converted into digital data by an amplifier and A/D converter (not shown), and stored in a storage device such as a memory.

In the example of Figure 9, the period of the encoder pulse is lengthened from the 15th pulse onwards due to the slower rotation speed of the drive motor 82.

Because the start pulse generating unit 85 cannot detect the encoder pulse, it cannot generate a start pulse, and the line sensor imaging time is extended. When the line sensor imaging time is extended, the line sensor 86 continues imaging during that period. The light source 88 is only lit for a predetermined period of time, but the line sensor 86 accumulates unnecessary charges due to dark current and the influence of light entering from outside, even when the light source 88 is not lit. If the imaging time of the line sensor 86 is extended, the amount of accumulated unnecessary charges becomes large, resulting in an image signal that is brighter than the actual brightness.

In this embodiment, to prevent this, as explained with reference to FIG. 13, when the start pulse generating unit 85 fails to detect the encoder pulse for a certain period of time or more, it generates a dummy pulse instead of a start pulse, which is used as a trigger to start imaging by the line sensor. The n+3th time the line sensor starts imaging in FIG. 9 is the section where imaging is triggered by the dummy pulse. This prevents the imaging time of the line sensor 86 from becoming too long, and prevents the continued accumulation of unnecessary charge. Note that the image signal captured with this dummy pulse is not written to memory, as it is an image signal from a position that is not actually needed.

Even if a dummy pulse is generated, the start pulse generating unit 85 continues to count the encoder pulses. When the 19th encoder pulse is detected, the start pulse generating unit 85 generates a start pulse. This start pulse causes the line sensor 86 to capture an image for the n+4th time. The image signal captured at this time is an image signal for the correct position, so it is A/D converted and stored in memory.

If there is little time difference between the start of the n+3th imaging and the start of the n+4th imaging, there is a possibility that there will not be enough time to read out the image signal from the line sensor 86, so the start of the n+4th imaging may be configured to be delayed.

In this embodiment, the start pulse generating unit 85 measures the time between rising edges of the encoder pulses output from the encoder pulse generating unit 83 to generate a dummy pulse, but it may be configured to measure the time between start pulses and output a dummy pulse when a certain period of time has elapsed.

It may also be configured so that the charge accumulated in the photodiode 201 is reset by a dummy pulse.

In addition, in this embodiment, the red, green, and blue colors of the light source 88 are simultaneously lit to obtain a gray image, but a color image can also be obtained by configuring the light source 88 to be switched between red, green, and blue for each line. In this case, three pieces of image data (red, green, and blue) are obtained to obtain one line's worth of image data, and the number of counts of the encoder pulses is adjusted so that the sheet advances a distance equivalent to one line of the desired resolution when the three images of red, green, and blue are obtained.

By configuring as described above, even if the speed of the drive motor 82 slows down or stops, the imaging time of the line sensor 86 is prevented from becoming too long, and an image of uniform brightness can be obtained.

Second Embodiment
A second embodiment of the present invention will now be described with reference to the drawings. The configuration of the device is the same as that of the first embodiment.

An example of the operation of this embodiment will be described with reference to FIG. 10. In this embodiment, the operation of acquiring a color image by turning on multiple light sources of red and then green using a start pulse signal as a trigger will be described.

The operation flows of Figs. 5, 7, and 8 shown in the first embodiment are the same in this embodiment. Fig. 10 explains the operation after the start pulse or dummy pulse is generated. When the start pulse or dummy pulse is detected (S501), the start pulse generating unit 85 counts the time T1 with a built-in timer (S502) and generates a red imaging start signal to the line sensor 86 (S503). This time T1 may be set to 0 and the imaging start signal may be generated simultaneously with the start pulse or dummy pulse, or may be delayed slightly. Although the explanation is omitted, when the imaging start signal is generated, the line sensor 86 starts imaging one line as in the first embodiment, and the light source control means 87 turns on the red of the light source 88, and imaging of one line of the red image signal is performed. The same applies to the subsequent green and blue imaging operations.

Then, the start pulse generating unit 85 generates a green imaging start signal (S505) after a time T2 has elapsed since generation of the red imaging start signal (S504). The time T2 is set to be equal to or longer than the imaging time for one line. Next, after a time T3 has elapsed since the green imaging start signal (S506), a blue imaging start signal is generated (S507). These times T2 and T3 may be calculated by the CPU 80 counting the clock.

Here, we will use Figure 11 to explain the relationship between the start pulse, dummy pulse, line sensor imaging start signal, and image signal.

The start pulse generating unit 85 generates a start pulse every time it counts six encoder pulses. When the start pulse is generated, a line sensor imaging start signal is generated for the line sensor 86 after time T1 has elapsed. The light source control means 87 switches the light source 88 between red, green, and blue for each line sensor imaging start signal.

The lighting time is adjusted in advance for each color so that an image of the desired brightness can be obtained. An image is captured in response to a line sensor imaging start signal, and the charge accumulated in the line sensor 86 is output in response to the next line sensor imaging start signal, converted to digital data by the amplifier and A/D converter shown in the figure, and stored in a storage device such as a memory.

Next, the imaging operation when a dummy pulse is generated will be described. After the 15th encoder pulse, the period is extended due to the slower rotation speed of the motor, etc. After the blue line sensor imaging start signal of the n+2th line, the next line sensor imaging start signal cannot be generated due to the inability to detect the encoder pulse, so the blue imaging time is extended. If the blue imaging time becomes long, the amount of unnecessary charge accumulated becomes large and only the blue image signal becomes brighter than the desired brightness. To prevent this, when the start pulse generating unit 85 cannot detect the encoder pulse for a certain period of time or more, it generates a dummy pulse instead of a start pulse, and generates a line sensor imaging signal using this as a trigger. The n+3th line sensor imaging start in FIG. 11 is the section where imaging is performed using the dummy pulse as a trigger. Since the image signal captured with this dummy pulse becomes an image signal of an unnecessary position, the red, green, and blue image data of the n+3th line are discarded without being stored in memory.

By using the above configuration, even if the speed of the drive motor 82 slows down or stops, the imaging time of the line sensor 86 is prevented from becoming too long, and an image with uniform brightness can be obtained.

Third Embodiment
A third embodiment of the present invention will now be described with reference to the drawings. The configuration of the device is the same as that of the first embodiment.

In the third embodiment, an example is described in which the amount of charge stored in the storage element 89 is detected and it is determined whether or not to generate a dummy pulse.

Figures 12 and 14 are flow charts showing part of the operation of this embodiment. Steps S601 to S604 in Figure 12 are the same as those explained in Figure 6 in the first embodiment, so the explanation will be omitted.

In FIG. 14, in the dummy pulse generation process, when the rising edge of the encoder pulse is detected (S605), the time measurement is started until the next rising edge is detected (S606). When the rising edge of the next encoder pulse is detected (S607), the time measurement is reset (S608). When a certain time has passed without the next encoder pulse being detected (S209), the start pulse generating means 85 notifies the CPU 80 that it is in a state to generate a dummy pulse. Next, the CPU 80 obtains the amount of charge stored in the storage element 89 by the storage amount detection unit 90. At this time, if the amount of charge stored in the storage element 89 is equal to or less than a certain reference value (S610), the CPU 80 instructs the start pulse generating unit 85 to generate a dummy pulse, and the start pulse generating unit 85 generates a dummy pulse (S611). Here, the reference value of the amount of charge stored in the storage element 89 is a judgment value for whether there is a sufficient amount of charge to supply power to the drive motor 82.

If the amount of charge stored in the storage element 89 is equal to or greater than a certain reference value, the CPU 80 determines that the speed reduction of the drive motor 82 is temporary, and instructs the start pulse generating unit 85 to stop generating dummy pulses (S612), and waits for the next encoder pulse to be detected.

When the amount of electricity stored in the storage element 89 is decreasing, sufficient power cannot be supplied to the drive motor 82, so the drive motor 82 slows down or temporarily stops driving and waits until the charge in the storage element 89 is sufficient (for example, a predetermined value that exceeds a reference value). In this case, the intervals between occurrences of the encoder pulses gradually become longer as the speed decreases, and the drive motor eventually stops.

Because the encoder pulse cannot be detected, the imaging time for one line is also longer, and as a result, the line sensor 86 accumulates unnecessary charge, resulting in a bright image. To prevent this, in the first and second embodiments, a dummy pulse is generated, but even if a large load is suddenly placed on the conveying system, the drive motor 82 may give in to the load and temporarily slow down, causing the encoder pulse to be extended. If the amount of stored electricity in the storage element 89 is sufficient, the power that can be supplied to the drive motor 82 is sufficient, so the drive motor only slows down temporarily, and it can quickly return to normal speed. Therefore, even if a dummy pulse is not generated, the imaging time will not be extended to the point where the image becomes too bright.

By using the above configuration, it is possible to prevent dummy pulses from being generated due to sudden speed fluctuations, and to obtain images with uniform brightness.

REFERENCE SIGNS LIST 10 Image reading device 12 Loading platform 13a Loading platform document detection sensor 13b Light guide lens 14 Feed rollers 16, 20 Drive rollers 17, 21 Driven rollers 18, 19 Image reading unit 30 Separation pad 32 First friction member
33 sponge members 41, 42 medium detection sensor 50 first conveying section 51 second conveying section 52 third conveying section 80 CPU
81 Drive control section 82 Drive motor 83 Encoder pulse generating section 84 Encoder section 85 Start pulse generating section 86 Line sensor 87 Light source control means 88 Light source 89 Power storage element 90 Power storage amount detecting section 91 Medium detecting section 123 Disk 124 Light emitter 125 Light receiver 126 Slit 201 Photodiode 202 Capacitor 203 Switch 204 Switch 205 Amplifier

Claims (6)

A conveying unit that conveys the document;
A driving means for driving the conveying unit;
A drive control means for controlling the rotational drive of the drive means;
a rotation detection means for detecting the rotation of the conveying unit or the driving means and outputting a pulse signal in response to the rotation;
a light source for irradiating light onto the conveyed document, and a light source control means for controlling the lighting of the light source;
a reading means for imaging and reading the conveyed document in a line perpendicular to the conveying direction;
an imaging start timing generating means for counting the pulse signal output from the rotation detecting means and generating an imaging start timing signal for one line of the reading means every time a certain number of pulses are counted;
The image reading device according to claim 1, wherein the imaging start timing generating means outputs a dummy imaging start timing signal when the period of the pulse signal output from the rotation detecting means becomes long and exceeds a certain period of time. The image reading device according to claim 1, characterized in that when the dummy imaging start timing signal is output, the signal of the reading means captured by the dummy imaging start timing signal is not captured. A storage element for temporarily storing power supplied from an external source;
a charge amount detection means for detecting the amount of charge stored in the charge storage element,
3. The image reading apparatus according to claim 1, wherein the drive control means controls a rotation speed of the drive means in accordance with the amount of charge detected by the amount of charge detection means. The image reading device according to claim 3, characterized in that the control means stops driving the drive means when the amount of charge in the storage element detected by the charge amount detection means falls below a reference value, and waits until the storage element is charged. The imaging start timing generating means
When the amount of charge in the storage element detected by the charge amount detection means is equal to or greater than a reference value,
Even if the period of the pulse signal exceeds the certain time, a dummy imaging start timing signal is not output,
When the charge amount of the storage element detected by the charge amount detection means becomes equal to or less than a reference value,
5. The image reading device according to claim 4, wherein a dummy image pickup start timing signal is output when the period of the pulse signal exceeds the certain time. a second imaging start timing generating means for counting a clock and generating a second imaging start timing signal using the imaging start timing signal as a trigger;
The light source is a multi-color light source,
6. The image reading device according to claim 1, wherein the light sources of the plurality of colors are switched on and turned on in accordance with the imaging start timing signal and the second imaging start timing signal.

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