JP2020178340A - Image reading device and image forming device - Google Patents

Abstract

To provide an image reading device capable of suppressing degradation of the reading accuracy of the original image.SOLUTION: The image reading device includes: a sampling unit 311 that samples a piece of analog image data output from a CMOS image sensor 209; and a conversion unit 312 that AD-converts the data. A CPU 304 detects the temperature of the CMOS image sensor 209 by a thermistor 310. CPU 304 causes a pulse generation unit 313 to generate a sample hold timing signal such that the sampling unit 311 holds a sample at the timing corresponding to the temperature.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image reading device for reading an image formed on a manuscript (hereinafter referred to as "manuscript image") and an image forming device including the image reading device.

The image reading device reads the original image by irradiating the original with light from the light source and reading the reflected light with the image sensor. The original is placed on the platen glass of the image reader with the scanning target side facing down. When reading an image of a document placed on a platen glass, the image reader scans the document while moving a light source along one direction at the bottom of the platen glass to read the original image. The image reading device can also read a document image from the document being transported by using an ADF (Auto Document Feeder) that transports the document.

The image sensor included in the image reading device has a plurality of pixels arranged linearly in the width direction of the document. The width direction of the document is the main scanning direction during scanning. Such image sensors include CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal-Oxide-Semiconductor) image sensors. CMOS image sensors generally consume less power than CCD image sensors. In addition, the CMOS image sensor enables random access of pixels.

The CMOS image sensor converts the charge stored in each pixel into a voltage for each pixel by receiving light, and outputs the converted voltage as an analog signal (hereinafter, "analog image signal") through an output amplifier. The image signal is output from the image reader after performing predetermined processing such as AD conversion by AFE (Analog Front End) or the like. AFE samples an analog image signal at a predetermined cycle and converts it into a digital signal. ..

In a CMOS image sensor having a large number of pixels in the main scanning direction, the output amplifier is often arranged at the end of the CMOS image sensor in the main scanning direction. In such a configuration, the distance from the first pixel of the CMOS image sensor to the output amplifier is different from the distance from the second pixel of the CMOS image sensor to the output amplifier. As a result, the time required for the analog image signal output from the first pixel to be output from the output amplifier (output time) is until the analog image signal output from the second pixel is output from the output amplifier. It will be different from the time of.

If the output time varies from pixel to pixel, the analog image signal may not be sampled when the signal level of the analog image signal is stable. Specifically, there is a possibility that the analog image signal will be sampled at the timing when the signal level of the analog image signal fluctuates. Patent Document 1 discloses a technique of suppressing the influence of variation in output time due to the pixel position by changing the sampling timing by AFE according to the pixel position of the CMOS image sensor.

Japanese Unexamined Patent Publication No. 2010-74673

The output time varies not only with the pixel positions but also with the temperature of the CMOS image sensor. This is largely due to the temperature characteristics of the output amplifier in the CMOS image sensor. The temperature of the CMOS image sensor changes depending on the operating status of the image reader and the installation environment. That is, depending on the usage environment of the CMOS image sensor, the analog image signal may not be sampled when the output level of the analog image signal is stable. As a result, the reading accuracy of the original image is lowered.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent a decrease in reading accuracy of an image of a document.

The image reading device of the present invention includes a line sensor including a light emitting unit that irradiates a document with light, a plurality of light receiving elements arranged in a predetermined direction and receiving the light reflected by the document, and the line sensor. A reading means including an amplifier for amplifying an analog signal corresponding to the light receiving result of the light receiving element, a temperature detecting means for detecting the temperature of the reading means, and a sampling means for sampling the value of the analog signal output from the amplifier. A conversion means for converting a value sampled by the sampling means into a digital value, and a generation means for generating image data representing an image of the original document based on the digital value converted by the conversion means. When the temperature detected by the temperature detecting means is the first temperature, the sampling means samples the analog signal corresponding to the first light receiving element included in the plurality of light receiving elements at the first timing. Then, when the temperature detected by the temperature detecting means is a second temperature higher than the first temperature, the analog signal corresponding to the first light receiving element is sent to a second timing later than the first timing. It is characterized by sampling at the timing of.

According to the present invention, it is possible to prevent the reading accuracy of the original image from being lowered.

The block diagram of an image reader. Internal configuration diagram of the image reader. Explanatory drawing of the controller. The characteristic illustration of the thermistor. Explanatory drawing of sampling timing. The figure which shows the correlation of an analog image signal and a sample hold timing signal. Correlation diagram between the delay time of the analog image signal and the temperature of the output amplifier. A flowchart showing an image reading process. A flowchart showing an image scanning process when a plurality of originals are continuously scanned.

Hereinafter, embodiments will be described in detail with reference to the drawings.

(Image reader)
FIG. 1 is a configuration diagram of the image reading device 1 of the present embodiment. Further, FIG. 2 is an internal configuration diagram of the image reading device 1. The image reading device 1 includes a reading device 100 and a cover 103. The cover 103 is attached to the reading device 100 so as to be openable and closable (rotatable). In FIG. 1, the cover 103 is open with respect to the reading device 100. In FIG. 2, the cover 103 is in a closed state with respect to the reading device 100.

The reading device 100 includes a platen glass 102 on which the document 101 to be read is placed. On the surface of the cover 103 on the platen glass 102 side, a white pressing plate for pressing the document 101 placed on the platen glass 102 toward the platen glass 102 when the cover 103 is closed. 104 is provided. The reading device 100 includes a scanning glass 207 on the same surface as the platen glass 102. A white reference plate, which is a reference member used for shading correction, is provided inside the reading device 100 of the frame 106 between the platen glass 102 and the scanning glass 207.

A reading unit 105A for reading a document image is provided inside the reading device 100 at the bottom of the platen glass 102. The reading unit 105A is a substantially rectangular parallelepiped optical sensor, and reads a document image from the document 101 with the longitudinal direction as the main scanning direction. When reading the document 101 placed on the platen glass 102, the reading unit 105A reads the document 101 while moving in the sub-scanning direction orthogonal to the main scanning direction by a motor (not shown).

The cover 103 includes a document transport section 107. The document transporting unit 107 can sequentially transport a plurality of documents onto the scanning glass 207 when the cover 103 is in the closed state. When the scanning unit 105A reads the document conveyed to the scanning glass 207 by the document conveying unit 107, the scanning unit 105A reads the conveyed document directly under the scanning glass 207.

The document transport unit 107 includes a document tray 201 on which the document 101 is loaded and a paper output tray 215 on which the document 101 is ejected after reading the image. The document tray 201 can load a plurality of documents 101. The document transfer unit 107 includes a pickup roller 202, a separation roller 203, 204, a front transfer roller 205, a lead roller 206, a pressing roller 212, 216, a rear transfer roller 213, and a paper ejection roller 214.

The pickup roller 202 feeds the documents in order from the document 101 placed on the top of the documents loaded on the document tray 201. The separation rollers 203 and 204 separate the originals one by one in order to prevent a plurality of sheets from being fed at the same time. For example, the separation roller 203 rotates in the direction of transporting the originals, and the separation roller 204 does not rotate, so that the originals are separated one by one.

The separation rollers 203 and 204 convey the separated document 101 to the front transfer roller 205. The front transfer roller 205 is a pair of rollers that conveys the document 101 to the lead roller 206. The lead roller 206 is a pair of rollers, and conveys the document 101 to the reading position A by the reading unit 105A. The reading position A is located above the scanning glass 207 when the cover 103 is in the closed state. The reading unit 105A reads the image of the first surface of the document 101 conveyed at the reading position A via the scanning glass 207. A document tip detection sensor 211 that detects the tip of the document 101 in the transport direction is provided on the upstream side of the reading position A in the transport direction of the document 101. The reading unit 105A starts reading the document image after a predetermined time from the timing when the document tip detection sensor 211 detects the tip of the document 101.

The reading position A is provided between the pressing roller 212 and the pressing roller 216. The pressing rollers 212 and 216 press the document 101 toward the scanning glass 207 so that the document 101 does not float from the scanning glass 207.

The rear transfer rollers 213 are a pair of rollers, and transfer the document 101 that has passed the reading position A to the reading position B. The document transport unit 107 includes a reading unit 105B. The reading unit 105B reads the image of the second surface of the document 101 conveyed at the reading position B via the scanning glass 207. The reading unit 105B starts reading the document image after a predetermined time from the timing when the document tip detection sensor 211 detects the tip of the document 101.
The paper ejection roller 214 is a pair of rollers, and ejects the document 101 to the paper ejection tray 215. The scanned original document 101 is placed on the output tray 215.

The reading unit 105A provided inside the reading device 100 includes a light emitting unit 208 as a light source, an image sensor (CMOS image sensor in this embodiment) 209, and an optical component group. The light emitting unit 208 includes a light emitting element such as an LED (Light Emitting Diode), and irradiates the document 101 with line-shaped light in the main scanning direction. The light applied to the document 101 is reflected and guided to the CMOS image sensor 209 by the optical component group. The CMOS image sensor 209 is a line sensor in which a plurality of pixels (light receiving elements) are arranged in a line in the main scanning direction. The reflected light from the document 101 guided by the optical component group is received by each pixel. The CMOS image sensor 209 outputs an electric signal (analog image signal) which is an analog signal according to the reflected light received by each pixel. This analog image signal represents, for example, the luminance value of each position in the main scanning direction. The analog image signals of all the pixels represent the luminance value of one line in the main scanning direction of the original image.

The reading unit 105A generates image data, which is a digital signal representing one line of the original image, based on the analog image signal. The reading unit 105A stands by at the home position when the reading process is not performed. The home position is, for example, directly below the scanning glass 207 (reading position A). Since the configuration and reading process of the reading unit 105B are the same as those of the reading unit 105A, the description thereof will be omitted.

As described above, a white reference plate is provided inside the reading device 100 between the scanning glass 207 and the platen glass 102. The white reference plate is a reference member for acquiring shading data used for shading correction.

(Image forming device)
In the present embodiment, an image forming device 401 that forms an image on a recording medium based on the image read by the image reading device 1 is provided below the image reading device 1. The image forming apparatus 401 used in the present embodiment is a monochrome electrophotographic copying machine, but the image forming apparatus is not limited to the copying machine, and may be, for example, a facsimile machine, a printing machine, a printer, or the like. Further, the recording method is not limited to the electrophotographic method, and may be, for example, an inkjet or the like. Further, the format of the image forming apparatus may be either monochrome or color.

Sheet storage trays 402 and 404 are provided inside the image forming apparatus 401. Different types of recording media can be stored in the sheet storage trays 402 and 404. For example, the sheet storage tray 402 stores A4 size plain paper, and the sheet storage tray 404 stores A4 size thick paper. The recording medium is one in which an image is formed by an image forming apparatus, and for example, paper, a resin sheet, a cloth, an OHP sheet, a label, and the like are included in the recording medium.

The recording medium stored in the sheet storage tray 402 is fed by the pickup roller 403 and sent out to the registration roller 408 by the transport roller 406. Further, the recording medium stored in the sheet storage tray 404 is fed by the pickup roller 405 and sent out to the registration roller 408 by the transport rollers 407 and 406.

The image data output from the image reading device 1 is input to the optical scanning device 411 including the semiconductor laser and the polygon mirror. Further, the outer peripheral surface of the photosensitive drum 409 is charged by the charger 410. After the outer peripheral surface of the photosensitive drum 409 is charged, the laser beam corresponding to the image signal input from the image reading device 1 to the optical scanning device 411 passes from the polygon mirror of the optical scanning device 411 via the mirrors 412 and 413. The outer peripheral surface of the photosensitive drum 409 is irradiated. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 409.

Subsequently, the electrostatic latent image is developed by the toner in the developer 414, and the toner image is formed on the outer peripheral surface of the photosensitive drum 409. The toner image formed on the photosensitive drum 409 is transferred to the recording medium by a transfer charger 415 provided at a position (transfer position) facing the photosensitive drum 409. The registration roller 408 feeds the recording medium to the transfer position at the transfer timing at which the image is transferred to the recording medium by the transfer charger 415.

As described above, the recording medium on which the toner image is transferred is sent to the fixing device 418 by the transport belt 417 and heated and pressed by the fixing device 418 to fix the toner image on the recording medium. In this way, the image forming apparatus 401 forms an image on the recording medium.

When image formation is performed in the single-sided printing mode, the recording medium that has passed through the fixing device 418 is ejected to an output tray (not shown) by the output rollers 419 and 424. When image formation is performed in the double-sided printing mode, after the first surface of the recording medium is fixed by the fixing device 418, the recording medium is a paper ejection roller 419, a transport roller 420, and an inversion roller 421. Is transported to the reverse path 425. After that, the recording medium is conveyed to the registration roller 408 again by the conveying rollers 422 and 423, and an image is formed on the second surface of the recording medium by the method described above. After that, the recording medium is ejected to an output tray (not shown) by the output rollers 419 and 424.

Further, when the recording medium on which the image is formed on the first surface is discharged face-down to the outside of the image forming apparatus 401, the recording medium that has passed through the fixing device 418 passes through the paper ejection roller 419 and is conveyed to the transport roller 420. It is transported in the direction toward. After that, just before the rear end of the recording medium passes through the nip portion of the transfer roller 420, the rotation of the transfer roller 420 is reversed, so that the recording medium is a paper ejection roller with the first surface of the recording medium facing downward. It is discharged to the outside of the image forming apparatus 401 via the 424.

The above is a description of the configuration and function of the image forming apparatus 401.

(Reading unit)
FIG. 3 is an explanatory diagram of a controller 300 that controls the operation of the image reading device 1. The controller 300 is connected to a reading unit 105A, a scan motor 302 that moves the reading unit 105A in the sub-scanning direction, a transport motor 303 that drives various rollers in the document transport unit 107, a document tip detection sensor 211, and an operation unit 301. Will be done.
The operation unit 301 is a user interface in which an input device and an output device are combined. The input device includes an input key, a numeric keypad, a touch panel, and the like, and an instruction or the like is input to the controller 300 by a user operation. The output device includes a display, a speaker, and the like, and displays an image and outputs a sound according to an instruction from the controller 300.
A controller (not shown) that controls the reading unit 105B and the image forming apparatus 401 is also connected to the controller 300.

The controller 300 includes a CPU (Central Processing Unit) 304, a shading unit 314, and an image processing unit 315.
The CPU 304 controls the operation of the image reading device 1 by executing a predetermined computer program. When an image reading instruction is input from the operation unit 301, the CPU 304 starts controlling the image reading process by the image reading device 1.
The shading unit 314 corrects the light intensity non-uniformity of the light emitting unit 208, the sensitivity variation of each pixel of the CMOS image sensor 209, and the like based on the image data obtained by the reading unit 105A reading the white reference plate.
The image processing unit 315 performs image processing such as noise removal on the image data shaded by the shading unit 314, and outputs the processed image data to an external device such as a controller of the image forming apparatus 401, for example. To do.

In addition to the light emitting unit 208 and the CMOS image sensor 209, the reading unit 105A includes an AD converter 305 that converts an analog image signal into image data as an AFE. The configuration of the reading unit 105A will be described in detail.

The CMOS image sensor 209 includes a pixel unit 306 composed of a plurality of pixels (light receiving elements), a line buffer 307, a shift register 308, an output amplifier 309, and a thermistor 310.
The pixel unit 306 can detect light of three colors of R (red), G (green), and B (blue), and can read a color image recorded on the document 101. In the CMOS image sensor 209 of this embodiment, for example, 7,500 R, G, and B pixels are prepared. Each pixel is composed of a photoelectric conversion element that converts light into an electric charge, and as a result of receiving light, an electric charge corresponding to the intensity of the received light is accumulated.

A line buffer 307 is connected to each pixel. The line buffer 307 converts the electric charge accumulated in each pixel into a voltage and stores it.
A shift register 308 is connected to the line buffer 307. The shift register 308 reads out the voltage of each pixel stored in the line buffer 307 in order of three pixels and transmits it to the output amplifier 309.
The output amplifier 309 is an amplifier that amplifies the voltage transmitted from the shift register 308, and transmits the amplification result as an analog image signal to the AD converter 305 at a predetermined cycle.

The thermistor 310 is provided for temperature detection of the CMOS image sensor 209, and is mounted in the vicinity of the output amplifier 309 on the same substrate as the CMOS image sensor 209. The term “on the same substrate” includes, for example, a state in which the thermistor 310 is provided on the same surface as the surface on which the pixel unit 306, the line buffer 307, the shift register 308, the output amplifier 309, and the like are provided. Further, on the same substrate, for example, in a configuration in which a plurality of layers are loaded on a silicon substrate, the thermistor 310 is provided on a silicon substrate that is different from these layers and is the same as these layers. The state of being is included. The plurality of layers loaded on the silicon substrate are a layer provided with the pixel portion 306, a layer provided with the line buffer 307, a layer provided with the shift register 308, and an output amplifier 309.

The thermistor 310 transmits an output voltage corresponding to the detected temperature to the CPU 304. The details of the temperature detection will be described later, but the thermistor 310 is used for detecting the temperature of the output amplifier 309. FIG. 4 is an example diagram of the characteristics of the thermistor 310, and shows the relationship between the detected temperature and the output voltage. The output voltage has a linear relationship with the temperature, and the higher the temperature, the higher the output voltage is output. This characteristic is an example.

The AD converter 305 includes a sampling unit 311, a conversion unit 312, and a pulse generation unit 313.
The analog image signal output from the output amplifier 309 is input to the sampling unit 311.
The pulse generation unit 313 transmits a timing signal, which is a pulse signal for controlling the sampling timing by the sampling unit 311, to the sampling unit 311. The timing signal has a predetermined period. In the present embodiment, the period of the timing signal is, for example, substantially the same period as the period in which the output amplifier 309 transmits the analog image signal to the AD converter 305. In the present embodiment, substantially the same period means that the difference between the period of the timing signal and the period of the output amplifier 309 transmitting the analog image signal to the AD converter 305 is within ± 10% of the period of the timing signal. ..
The sampling unit 311 samples the analog image signal according to the timing signal and transmits it to the conversion unit 312.
The conversion unit 312 AD-converts the value of the analog image signal sampled by the sampling unit 311 into image data which is a digital value.

FIG. 5 is an explanatory diagram of sampling timing of an analog image signal. In the present embodiment, the analog image signal is sampled at the timing when the timing signal transitions to High. In the present embodiment, the timing at which the timing signal first becomes high after the CMOS image sensor 209 is driven (hereinafter referred to as the start timing) is set as follows. Specifically, the start timing is set in advance at a timing at which a predetermined time has elapsed since the CMOS image sensor 209 was driven. The predetermined time is a time obtained in advance by an experiment. For example, the predetermined time is preset to the time required for the analog image signal first output from the output amplifier 309 to stabilize after the CMOS image sensor 209 is driven in a state where the output of the thermistor 310 indicates 25 ° C. Has been done.

FIG. 6 is a diagram showing the correlation between the analog image signal and the timing signal. The output amplifier 309 has a characteristic that the timing of outputting the analog image signal is delayed as the temperature rises.
For example, in a state where the temperature of the output amplifier 309 is 25 ° C., if the analog image signal is sampled at a predetermined cycle from a preset start timing, the analog image signal is sampled in a stable state. Will be done.

On the other hand, for example, when the temperature of the output amplifier 309 is 40 ° C., if the analog image signal is sampled at a predetermined cycle from a preset start timing, the analog image signal is in an unstable state. Is sampled. As a result, the reading accuracy of the original image is lowered.
Therefore, in the present embodiment, it is possible to prevent the reading accuracy of the image of the original from being lowered by applying the following configuration.

FIG. 7 is a correlation diagram between the delay time of the analog image signal and the temperature of the output amplifier 309. FIG. 7 shows the characteristic that the delay time of the analog image signal increases as the temperature of the output amplifier 309 rises. Specifically, FIG. 7 shows a characteristic that the output delay time becomes a positive value when the temperature detected by the thermistor 310 is higher than 25 ° C., and the output delay time becomes a negative value when the temperature is lower than 25 ° C. Represent.

The relationship between the temperature of the output amplifier 309 and the delay time of the analog image signal is pre-programmed (stored) in the CPU 304. The CPU 304 outputs a delay time corresponding to the output voltage of the thermistor 310 to the pulse generation unit 313.

The pulse generation unit 313 adjusts the sampling timing by the delay time. That is, the pulse generation unit 313 generates a timing signal so that the sampling timing is delayed when the delay time is a positive value. Further, the pulse generation unit 313 generates a timing signal so that the sampling timing is advanced when the delay time is a negative value. As a result, even if the timing at which the analog image signal is output fluctuates due to the fluctuation in the temperature of the output amplifier 309, the sampling timing can be optimized. That is, the voltage of the analog image signal is sampled at a stable timing. As a result, it is possible to prevent the reading accuracy of the original image from being lowered. When adjusting the sampling timing, the pulse generation unit 313 adjusts the timing at which the timing signal becomes high. That is, the period of the timing signal is not changed.

FIG. 8 is a flowchart showing an image reading process performed by the image reading device 1 having such a configuration. The processing of this flowchart is executed by the CPU 304 when an image reading instruction is input from the operation unit 301 to the CPU 304.

When the CPU 304 receives the image reading instruction, the CPU 304 starts driving the CMOS image sensor 209 (S601). When the CMOS image sensor 209 starts driving under the control of the CPU 304, the CMOS image sensor 209 starts inputting an analog image signal from the output amplifier 309 to the AD converter 305. As a result, the temperature of the output amplifier 309 begins to rise.

Next, the CPU 304 waits in this state for a predetermined time for 200 milliseconds in this embodiment (S602). This standby time is set to a time sufficient for the temperature of the output amplifier 309 to stabilize.
When the standby time elapses, the CPU 304 acquires the output voltage output from the thermistor 310 (S603). The CPU 304 converts the acquired output voltage into a digital signal.

After that, the CPU 304 outputs the delay time corresponding to the output voltage of the thermistor 310 to the pulse generation unit 313 (S604). As a result, the sampling timing is set according to the temperature indicated by the output voltage of the thermistor 310.

After setting the sampling timing, the CPU 304 lights the light emitting unit 208 (S605).
Next, the CPU 304 causes the shading unit 314 to perform shading correction (S606). Therefore, the CPU 304 moves the reading unit 105A directly under the white reference plate by the scan motor 302, and causes the reading unit 105A to read the white reference plate. The reading unit 105A reads the white reference plate and transmits the image data generated to the shading unit 314. The shading unit 314 performs shading correction based on the image data generated from the reading result of the white reference plate.

When the shading correction is completed, the CPU 304 executes the scanning process of the document 101 (S607). This completes the image reading process.

As described above, the CPU 304 of the present embodiment detects the temperature of the output amplifier 309 provided inside the CMOS image sensor 209, and determines the delay time of the analog image signal based on the detection result. The pulse generation unit 313 adjusts the sampling timing according to the determined delay time. As a result, even if the timing at which the analog image signal is output fluctuates due to the fluctuation in the temperature of the output amplifier 309, the sampling timing can be optimized. That is, the voltage of the analog image signal is sampled at a stable timing. As a result, it is possible to prevent the reading accuracy of the original image from being lowered.

The image scanning process of FIG. 8 is a process for scanning one document 101 (one page of the document). When scanning a plurality of original documents 101 continuously, it is necessary to adjust the sampling timing between the original documents. This is because the temperature of the output amplifier 309 of the CMOS image sensor 209 rises due to the continuous image reading process. FIG. 9 is a flowchart showing an image reading process when a plurality of original documents 101 are continuously read. The processing of this flowchart is executed by the CPU 304 when an image reading instruction is input from the operation unit 301 to the CPU 304.

The processes (S701 to S706) from the start of driving the CMOS image sensor 209 to the shading correction are the same as the processes from S601 to S606 in FIG. 6, and thus the description thereof will be omitted.
When the shading correction is completed, the CPU 304 drives the transfer motor 303 to start the document transfer by the document transfer unit 107 (S707).
Next, when the document tip detection sensor 211 detects the document 101 after the start of transporting the document 101, the CPU 304 causes the reading units 105A and 105B to read the document image from the document 101 (S708).

After that, the CPU 304 determines whether or not the scanning of one original document 101 is completed based on the image data acquired from the reading units 105A and 105B (S709).
When it is determined that the reading of one document 101 is completed (S709: Y), the CPU 304 determines whether or not the next document is placed on the document tray 201 (S710). The document tray 201 is provided with a sensor that detects the presence or absence of a document to be placed. The CPU 304 can determine the presence or absence of a document on the document tray 201 based on the detection result of the sensor. If there is no next document (S710: N), the CPU 304 ends the image reading process.

When there is the next document (S710: Y), the CPU 304 acquires the output voltage according to the detection temperature from the thermistor 310 (S711). The CPU 304 converts the acquired output voltage into a digital signal.
The CPU 304 outputs the delay time corresponding to the output voltage of the thermistor 310 to the pulse generation unit 313 (S712). As a result, the sampling timing is set according to the temperature indicated by the output voltage of the thermistor 310.
After that, the CPU 304 repeats the processes after S707 until there are no more documents on the document tray 201. This completes the image reading process.

In this way, the CPU 304 controls the sequential sampling timing between the documents that are continuously conveyed. As a result, even if the temperature detected by the thermistor 310 fluctuates when reading a plurality of original documents 101 continuously, the sampling timing can be optimized. That is, the voltage of the analog image signal is sampled at a stable timing. As a result, it is possible to prevent the reading accuracy of the original image from being lowered.

The image reading device 1 of the present embodiment as described above can perform sampling at a timing when the output level of the analog image signal is stable by setting the sampling timing according to the temperature of the CMOS image sensor 209. As a result, the image reading device 1 can accurately perform AD conversion of the analog image signal to generate image data. That is, it is possible to prevent the reading accuracy of the original image from being lowered.

In the present embodiment, the CPU 304 controls the sequential sampling timing between the documents to be continuously conveyed, but this is not the case. For example, the CPU 304 may control the sampling timing every time a predetermined number of documents (for example, 10 sheets) are conveyed.

Claims (16)

A light emitting part that irradiates the document with light,
A reader including a line sensor arranged in a predetermined direction and having a plurality of light receiving elements for receiving the light reflected by the document, and an amplifier for amplifying an analog signal corresponding to the light receiving result of the light receiving elements included in the line sensor. Means and
A temperature detecting means for detecting the temperature of the reading means and
A sampling means for sampling the value of the analog signal output from the amplifier, and
A conversion means for converting the value sampled by the sampling means into a digital value, and
A generation means for generating image data representing an image of the original document based on a digital value converted by the conversion means is provided.
When the temperature detected by the temperature detecting means is the first temperature, the sampling means samples the analog signal corresponding to the first light receiving element included in the plurality of light receiving elements at the first timing. When the temperature detected by the temperature detecting means is a second temperature higher than the first temperature, the analog signal corresponding to the first light receiving element is sent to a second timing later than the first timing. It is characterized by sampling at the timing,
Image reader. The amplifier outputs the analog signal in the first cycle,
The sampling means changes the timing of sampling the analog signal value before starting sampling of the analog signal value corresponding to the image for one page of the document.
The sampling means is characterized in that the value of the analog signal is sampled in the second cycle during the period for sampling the value of the analog signal corresponding to the image for one page of the document.
The image reading device according to claim 1. The first cycle is the same as the second cycle.
The image reading device according to claim 2. The first cycle is substantially the same as the second cycle.
The image reading device according to claim 2. Further equipped with a document transport section for transporting documents
The reading means reads an image of a document conveyed by the document conveying unit, and reads the image.
The sampling means changes the timing of sampling the value of the analog signal based on the temperature detected by the temperature detecting means every time a predetermined number of documents are conveyed from the document conveying unit.
The image reading device according to claim 1. The sampling means changes the timing of sampling the value of the analog signal based on the temperature detected by the temperature detecting means every time one document is conveyed from the document conveying unit.
The image reading device according to claim 5. The amplifier outputs the analog signal in the first cycle,
The sampling means changes the timing of sampling the analog signal value before starting sampling of the analog signal value corresponding to the image for one page of the document.
The sampling means is characterized in that the value of the analog signal is sampled in the second cycle during the period for sampling the value of the analog signal corresponding to the image for one page of the document.
The image reading device according to claim 5. The first cycle is the same as the second cycle.
The image reading device according to claim 7. The first cycle is substantially the same as the second cycle.
The image reading device according to claim 7. The temperature detecting means is mounted on the same substrate as the reading means.
The image reading device according to claim 1. The temperature detecting means is a temperature detecting means for detecting the temperature of the amplifier.
The image reading device according to claim 1. The period at which the amplifier outputs the analog signal is the same as the period during which the sampling means samples the analog signal.
The image reading device according to claim 1. The period at which the amplifier outputs the analog signal is substantially the same as the period during which the sampling means samples the analog signal.
The image reading device according to claim 1. The line sensor is a CMOS image sensor.
The image reading device according to claim 1. The sampling means is characterized in that the timing of sampling the value of the analog signal is changed so that the analog signal is sampled during the period when the analog signal is stable.
The image reading device according to claim 1. A light emitting part that irradiates the document with light,
A reader including a line sensor arranged in a predetermined direction and having a plurality of light receiving elements for receiving the light reflected by the document, and an amplifier for amplifying an analog signal corresponding to the light receiving result of the light receiving elements included in the line sensor. Means and
A temperature detecting means for detecting the temperature of the reading means and
A sampling means for sampling the value of the analog signal output from the amplifier, and
A conversion means for converting the value sampled by the sampling means into a digital value, and
A generation means for generating image data representing an image of the manuscript based on a digital value converted by the conversion means, and a generation means.
An image forming unit that forms an image on a recording medium based on the image data generated by the generation means is provided.
When the temperature detected by the temperature detecting means is the first temperature, the sampling means samples the analog signal corresponding to the first light receiving element included in the plurality of light receiving elements at the first timing. When the temperature detected by the temperature detecting means is a second temperature higher than the first temperature, the analog signal corresponding to the first light receiving element is sent to a second timing later than the first timing. It is characterized by sampling at the timing,
Image forming device.

Images