JP5081865B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus that reads an image and an image forming apparatus including the image reading apparatus.

  In recent years, reduction of power consumption in image forming apparatuses such as copying machines has been demanded for the purpose of environmental protection. In particular, reduction of power consumption in a standby state where image formation is not particularly performed is required.

  Therefore, for example, in Patent Document 1, an energy saving mode is provided, and in this mode, supply of operation clocks to a control unit for performing drive control of the image forming apparatus and an image processing unit for performing image forming operation is minimized. I try to suppress it.

JP 2005-17870 A

  However, as described above, in Patent Document 1, the operation clock supplied to the CPU as the control unit is simultaneously reduced at the same ratio together with the operation clock supplied to the image processing unit. Accordingly, there is a problem in that when the image formation is not performed but another operation is performed, for example, when the communication state is established with the external device, the communication operation is delayed by reducing the operation clock of the CPU.

  On the other hand, there is an image forming apparatus in which a different CPU is provided for each unit such as an image reading unit and an image processing unit, in addition to the CPU that controls the driving of the image forming apparatus. Among such image forming apparatuses, for example, in the image reading unit, when the operation clock supplied to the CPU of the image reading unit together with the operation clock to the image reading unit in the standby state is reduced as described above, The following problems occur. First, since the operation clock of the CPU of the image reading unit is different from the operation clock of the CPU of the image forming apparatus, the communication speed between the two decreases. Furthermore, the reduction in the operation clock for the CPU of the image reading unit reduces the image reading processing speed of the image reading unit itself. Accordingly, when an image reading instruction is received from another part of the image forming apparatus or the like in the standby state of the image reading unit, the image reading control is delayed.

  An object of the present invention is to reduce power consumption of an image reading apparatus without reducing the processing speed of a reading control unit in a stable standby state of the image reading apparatus.

  An image reading apparatus according to a first aspect includes an image reading unit, a reading control unit, and an operation clock adjusting unit. The image reading unit includes a light source that irradiates light on a document, and an image sensor that reads an image from reflected light from the document and outputs an image signal. The reading control unit causes the image reading unit to execute an image reading operation. The operation clock adjusting unit adjusts the operation clock supplied to the image sensor and the reading control unit according to the operation mode of the image reading unit. Here, when the image reading unit is in the standby mode, the operation clock adjusting unit sets the frequency of the operation clock to the image sensor in the normal operation mode of the image reading unit while maintaining the operation clock frequency to the reading control unit. It is made lower than the operating clock frequency.

  Here, when the image reading unit is in the standby mode, the operation clock adjusting unit reduces the frequency of the operation clock to the image sensor compared to the normal operation mode of the image reading unit. Then, since the number of operations per unit time of the image sensor is smaller than that in the normal operation mode, the power consumption of the image reading apparatus in the standby mode can be reduced. On the other hand, the operation clock adjustment unit maintains the frequency of the operation clock to the reading control unit in the normal operation mode. Therefore, the operation speed of the reading control unit itself can be maintained. Accordingly, in the standby mode of the image reading apparatus, the power consumption of the image reading apparatus can be reduced without reducing the processing speed of the reading control unit.

  An image reading apparatus according to a second aspect of the present invention is the apparatus according to the first aspect of the present invention, further comprising a period adjusting unit that adjusts the period of the horizontal synchronizing signal input to the image sensor. The cycle adjusting unit makes the cycle of the horizontal synchronization signal longer than that in the normal operation mode of the image reading unit when the image reading unit is in the standby mode.

  Here, the cycle adjustment unit adjusts the cycle of the horizontal synchronization signal that determines the cycle of the signal output from the image sensor so that it is longer in the standby mode than in the normal operation mode. Therefore, even if the period of the signal output from the image sensor is increased by reducing the frequency of the operation clock to the image sensor, the period of the horizontal synchronization signal can be increased so that such a signal can be accommodated. . Therefore, the power consumption of the image reading apparatus can be reduced while obtaining a stable image signal.

  An image reading apparatus according to a third aspect of the present invention is the apparatus of the second aspect, further comprising a light amount adjustment unit that adjusts the amount of light incident from the light source to the image sensor. The light amount adjusting unit reduces the incident light amount when the image reading unit is in the standby mode as compared with the normal operation mode of the image reading unit.

  Here, when the image reading unit is in the standby mode, the light amount adjusting unit reduces the amount of light incident on the image sensor as compared to the normal operation mode of the image reading unit. Therefore, even if the period of the horizontal synchronizing signal is adjusted to be longer by the period adjusting unit, the amount of incident light from the light source is decreased by the light amount adjusting unit, so that the amount of incident light received by the image sensor in one period of the horizontal synchronizing signal increases. Can be avoided. Therefore, the power consumption of the image reading apparatus can be reduced while obtaining a stable image signal in the standby mode.

  An image reading apparatus according to a fourth invention is the apparatus according to any one of the first to third inventions, wherein a document table on which a document is placed and a document size for detecting a size of the document on the document table. And a detector. Here, when the image reading unit is in the standby mode, the operation clock adjustment unit sets the operation clock so as to supply the reduced frequency to the image sensor until the document size detection unit detects the size of the document. adjust.

  Here, the operation clock adjustment unit maintains the reduced frequency of the operation clock with respect to the image sensor until the size of the document is detected by the document size detection unit. Therefore, based on the operation clock whose frequency is reduced, the document size is detected in a state where the number of operations per unit time of the image sensor is small. However, since the amount of data read is small in the document size detection, the power consumption of the image reading apparatus can be further reduced without substantially delaying the operation speed of the document size detection.

  An image forming apparatus according to a fifth aspect of the invention includes an image reading apparatus according to any one of the first to fourth aspects of the invention, an image forming unit that forms an image read by the image reading apparatus on a recording medium, Is provided.

  According to the present invention as described above, it is possible to reduce power consumption in the image reading apparatus without reducing the processing speed of the reading control unit in the standby mode of the image reading apparatus.

1 is a perspective view showing an appearance of a copying machine according to an embodiment. FIG. 2 is an enlarged cross-sectional view of a part of a copying machine. FIG. 2 is a block diagram illustrating a main configuration of a copying machine. It is an enlarged view of an image reading apparatus. It is a block part which shows the flow of the signal in the principal part of an image reading apparatus. It is a figure which shows the operation clock and horizontal synchronizing signal which are supplied to CCD.

1. First Embodiment A digital copying machine as an image forming apparatus including an image reading apparatus according to an embodiment of the present invention will be described. Hereinafter, description will be given with reference to the drawings.
[Entire copier]
The configuration of the entire copying machine will be described with reference to FIGS. FIG. 1 is a perspective view showing an appearance of a copying machine. FIG. 2 is an enlarged cross-sectional view of a part of the copying machine. FIG. 3 is a block diagram showing a main configuration of the copying machine.

  As shown in FIGS. 1, 2, and 3, the copying machine 1 is read by a document conveying device 2 that conveys a document M, an image reading device 4 that reads an image from one side of the document M, and an image reading device 4. A main body 3 having an image forming unit 5 that prints an image or the like on a sheet, a control unit 6 that controls the operation of each unit, and a communication unit 7.

  The document conveying device 2 is a device for moving the document M with respect to the image reading device 4, and is disposed above the main body 3. The document conveying device 2 includes a housing 20, a document placing tray 21 for placing a document, and a document discharge tray 23 for receiving a document that has been read, and is provided inside the housing 20. 21 has a document conveying section 22 for conveying the document on the document 21 to the document discharge tray 23. The document transport unit 22 includes a document transport roller group 22a composed of a plurality of rollers, and a document pressing unit 22b. The document transport roller group 22 a pulls out the documents M one by one from the document placement tray 21 and discharges them to the document discharge tray 23 through the second platen glass 44. The document pressing unit 22b is configured to feed the document M conveyed by the document transport roller group 22a so that the image reading device 4 can read an image from one surface (hereinafter referred to as a surface) of the document M through the second platen glass 44. Is pressed against the second platen glass 44. The document feeder 2 further includes a CIS (Contact Image Sensor) 24. The CIS 24 is a sensor that reads an image formed on the back side of the document M.

  In addition to the above-described members, the main body 3 includes a manual feed tray 31 for placing paper used in the image forming unit 5, a paper cassette 32 for storing paper, a paper discharge tray 33 for discharging paper after image formation, It has an operation panel 34 for receiving instructions from the user and presenting various information to the user. The housing 20 of the document feeder 2 described above also functions as a document presser that presses the document onto the first platen glass 43.

  The image reading device 4 reads an image of a document and generates digital data of the image. Details of the image reading device 4 will be described later.

  As the image forming unit 5, a printing mechanism such as an electrophotographic system or an inkjet system can be appropriately employed.

  The control unit 6 transmits and receives data signals and control signals to and from each unit of the copying machine 1 in accordance with instructions received from the user via the operation panel 34 and the detection results of various sensors, and image forming operations and the like. Is to control the overall. Specifically, the control unit 6 can be configured by a CPU 61 (Central Processing Unit), a ROM 62 (Read Only Memory), and a RAM 63 (Random Access Memory). The CPU 61 can perform various calculations and execute a program. The ROM 62 stores a program related to the control performed by the CPU 61, a program related to the operation of each unit in the copying machine 1, and the like. In addition to functioning as a work area for the CPU, the RAM 63 has an area for holding user input contents and the like. The control unit 6 further includes a crystal oscillator 64 that generates a reference clock signal and outputs the reference clock signal to each unit.

  The communication unit 7 communicates with an external device via a communication line. The communication unit 7 receives image data transmitted from, for example, an external personal computer or a FAX machine.

[Image reading device]
The image reading device 4 will be described again with reference to FIGS. 2 and 3 and FIG. FIG. 4 is an enlarged view of the image reading apparatus.

  As shown in FIG. 2, the image reading apparatus 4 moves in the direction of the arrow on the first platen glass 43 and the second platen glass 44 as a document table, a rail 41 arranged in parallel to the first platen glass 43, and on the rail 41. A possible carriage 42 is provided. Hereinafter, a direction perpendicular to the rail 41 and parallel to the longitudinal direction of the first platen glass 43 is referred to as a main scanning direction, and a direction parallel to the rail 41 is referred to as a sub-scanning direction.

  As shown in FIG. 4, the image reading device 4 includes a light source 45 as an image reading unit, a mirror group 46, a condenser lens 47, a CCD (CCD image sensor) 48, and the like in the carriage 42.

  The light source 45 is disposed close to the lower surface of the first platen glass 43 and at a position shifted upstream from the center of the first platen glass 43 in the paper transport direction. The light source 45 irradiates the surface of the document M with light through the first platen glass 43 and the second platen glass 44.

  The mirror group 46 guides the reflected light, which is the light from the light source 45 reflected from the original M by a plurality of mirrors, to the condenser lens 47. The reflected light is collected on the CCD 48 by the condenser lens 47.

  The CCD 48 is an image sensor that reads an image from reflected light from a document and outputs an image signal. The CCD 48 receives the light image and converts it into an analog electrical signal. The CCD 48 is an example of an image sensor, and can be appropriately replaced with another image sensor such as a CMOS image sensor.

  In addition to the above-described members, the image reading device 4 includes an A / D converter 401, an image processing unit 402, a reading control unit 403, a clock generation unit 404, an operation clock adjustment unit 405, a cycle adjustment, as shown in FIG. A unit 406, a light amount adjustment unit 407, and a document size detection unit 408. In the copying machine 1, the image reading device 4 and other units are connected to each other via a bus 8 such as a data bus.

  The A / D converter 401 converts an analog image signal from the CCD 48 into a digital signal, and includes an analog front end (AFE) circuit. The image processing unit 402 performs image processing such as recombining images based on the digital signal from the A / D converter 401.

  The reading control unit 403 controls the operation of each unit of the image reading device 4 such as the execution of the reading operation of the image reading unit including the light source 45 and the CCD 48. For example, the reading control unit 403 reads an image from a document on the first platen glass 43, when the housing 20 of the document feeder 2 is closed on the first platen glass 43, or a start button on the operation panel 34. Is turned on and the carriage 42 is moved in the sub-scanning direction. Then, while moving the light source 45, the original placed on the first platen glass 43 is irradiated with light, and the CCD 48 is controlled to image the reflected light from the original. On the other hand, when reading the image on the surface of the document conveyed by the document conveying device 2, the carriage 42 is stopped at a position facing the second platen glass 44 in response to pressing of the start button of the operation panel 34, and similarly. Control to the light source 45 and the CCD 48 is performed.

  The reading control unit 403 includes a mode monitoring unit 403a, and monitors the operation status of the image reading unit including the light source 45, the CCD 48, and the like. For example, when the image reading unit is in a normal image reading operation state, it is determined that the normal operation mode is set. Further, when the operation of the image reading unit is not performed for a certain period of time, or when there is an instruction to shift to the standby mode from the user, it is determined that the standby mode is set. If the mode monitoring unit 403a determines that the image reading unit in the normal operation mode has changed to the standby mode, the mode monitoring unit 403a generates a standby mode signal and outputs the standby mode signal to the operation clock adjustment unit 405 described later. In the present embodiment, the mode monitoring unit 403a similarly outputs a standby mode signal to a period adjusting unit 406 and a light amount adjusting unit 407, which will be described later.

  The clock generation unit 404 generates an operation clock supplied to each unit of the image reading device 4 based on the reference clock output from the crystal oscillator 64 of the control unit 6, and outputs the operation clock to the operation clock adjustment unit 405.

  The operation clock adjustment unit 405 adjusts the operation clock generated by the clock generation unit 404. Then, the adjusted operation clock is output to each unit of the image reading device 4. The period adjustment unit 406 adjusts the period of the horizontal synchronization signal supplied to the CCD 48. The light amount adjustment unit 407 adjusts the amount of incident light that is irradiated from the light source 45 and incident on the CCD 48. The operation clock adjustment unit 405, the cycle adjustment unit 406, and the light amount adjustment unit 407 will be described in detail later.

  The document size detection unit 408 detects the size of the document on the first platen glass 43. The size detection is performed when the housing 20 of the document feeder 2 is closed with respect to the first platen glass 43 or when the start button is pressed. When detecting the size of the document, for example, the reading control unit 403 turns on the light source of the light source 45. The document size detection unit 408 determines the size of the document based on a threshold value stored in advance in a storage unit (not shown). More specifically, since the reflected light from the original enters the area of the line sensor corresponding to the placement position of the original, the area becomes bright and the other areas become dark. Therefore, the size of the document is determined by comparing a predetermined threshold value with the reflected light received from the document by the CCD 48.

  When the document size detection unit 408 determines the size of the document, the document size detection unit 408 outputs a signal corresponding to the detected size to the reading control unit 403 and also detects the document size detection to the operation clock control unit 405 described above. Output a signal. The document size detection unit 408 further outputs a document detection signal to the period adjustment unit 406 and the light amount adjustment unit 407 in the same manner.

[Operation clock adjustment]
Next, the operation of the operation clock adjustment unit 405 will be described with reference to FIG. FIG. 5 is a diagram illustrating a signal flow in a main part of the image reading apparatus. In FIG. 5, the flow of the clock signal is indicated by a solid line, the flow of the original detection signal is indicated by a dotted line, the flow of the standby mode signal is indicated by a one-dot chain line, and the flow of image data is indicated by a double arrow. In FIG. 5, the flow of control data is omitted.

  The operation clock adjustment unit 405 receives the operation clock from the clock generation unit 404 and adjusts the frequency of the operation clock for at least the CCD 48 and the reading control unit 403 according to the operation mode of the image reading unit. In this embodiment, as shown in FIG. 5, the frequency of the operation clock to the A / D converter 401 and the image processing unit 402 is also adjusted in the same manner. The A / D converter 401 may be selectively adjusted only for the analog front end (AFE) included in the A / D converter 401.

  Specifically, when the image reading unit including the light source 45 and the CCD 48 is in the normal operation mode, the CCD 48, the reading control unit 403, the A / D converter 401, and the like without adjusting the operation clock from the clock generation unit 404. The image is output to the image processing unit 402. On the other hand, when the operation clock adjustment unit 405 receives the output of the standby mode signal from the mode monitoring unit 403a of the reading control unit 403, the operation clock frequency to the reading control unit 403 maintains the frequency of the operation clock in the normal operation mode. The frequency of the operation clock supplied to the CCD 48, the A / D converter 401, and the image processing unit 402 is adjusted to be reduced.

  Thereafter, when the image reading unit is in the standby mode, the operation clock adjustment unit 405 continues the same adjustment until the document detection signal is received from the document size detection unit 408. That is, the frequency of the operation clock to the reading control unit 403 is set to the frequency of the operation clock in the normal operation mode, and the CCD 48, the A / D converter 401, and the image processing unit 402 are supplied with a reduced frequency. Adjust the clock. When the document detection signal is received, the operation clock adjustment unit 405 increases the frequency of the operation clock to the CCD 48, the A / D converter 401, and the image processing unit 402 to the frequency of the operation clock in the normal operation mode. adjust.

  By providing such an operation clock adjustment unit 405, when the image reading unit is in the standby mode, the frequency of the operation clock to the CCD 48, the A / D converter 401 and the image processing unit 402 is reduced as compared with the normal operation mode. Can be made. As a result, the number of operations per unit time of the CCD 48, the A / D converter 401, and the image processing unit 402 can be reduced. Therefore, the power consumption of the image reading device 4 can be reduced. On the other hand, the operation clock adjustment unit 405 does not change the frequency of the operation clock to the reading control unit 403 from the normal operation mode. Therefore, the operation speed of the reading control unit 403 itself can be maintained. Therefore, for example, even when the image reading unit is in the standby mode, the reading control unit 403 can operate with the operation clock in the normal operation mode. Even if it is received, the reading operation can be controlled without delay. As described above, in this embodiment, in the standby mode of the image reading unit, it is possible to reduce the power consumption of the image reading apparatus without reducing the processing speed of the reading control unit 403.

  The operation clock adjustment unit 405 reduces the frequency of the operation clock and then waits until the document size detection unit 408 detects the size of the document in the standby mode of the image reading unit, and then the CCD 48 and the A / D converter 401. The image processing unit 402 is adjusted so as to supply the reduced frequency of the operation clock. Therefore, the detection of the document size in the standby mode of the image reading unit is supplied to the CCD 48, the A / D converter 401 and the image processing unit 402 with the reduced frequency of the operation clock. This is performed in a state where the number of operations per hour is reduced. However, since the amount of data read at the time of document detection is small, the power consumption of the image reading apparatus can be further reduced without substantially delaying the document detection operation.

[Cycle adjustment operation]
Next, the operation of the cycle adjustment unit 406 will be described with reference to FIGS. FIG. 6 is a diagram showing an operation clock and a horizontal synchronization signal supplied to the CCD. 6A shows the operation clock and horizontal synchronization signal when the image reading unit is in the normal operation mode, and FIG. 6B shows the operation clock and horizontal synchronization signal when the image reading unit is in the standby mode. Indicates.

  The period adjustment unit 406 adjusts the period of the horizontal synchronization signal supplied to the CCD 48. The horizontal synchronization signal determines the period of the voltage signal (pixel signal) output from the CCD 48 and determines the resolution in the sub-scanning direction.

  Specifically, when the cycle adjustment unit 406 receives the standby mode signal from the mode monitoring unit 403a of the above-described reading control unit 403, the cycle of the horizontal synchronization signal is set longer than that in the normal operation mode as shown in FIG. adjust. For example, the cycle adjusting unit 406 multiplies one cycle of the operation clock reduced by the above-described operation clock adjusting unit 405 by the number of pixels read by the CCD 48, and the cycle thus multiplied is used as the horizontal synchronization signal in the standby mode. Adjust to a cycle. Here, in general, the number of pixels per cycle read by the CCD is about 7500 for an A4 size original. However, since the number of pixels differs depending on the type of CCD, the horizontal synchronization signal is adjusted according to the setting of each CCD. The period of is adjusted. Note that the period of the long horizontal synchronization signal in the standby mode may be adjusted in advance by multiplying it in advance and storing it in a storage unit (not shown) and reading it out when receiving the standby mode signal. You may multiply each time.

  Thereafter, when the image reading unit is in the standby mode, the cycle adjustment unit 406 continues the same adjustment until a document detection signal is received from a document size detection unit 408 described later. That is, the horizontal synchronizing signal supplied to the CCD 48 is adjusted to have a longer period than that of the normal operation mode. When the document detection signal is received, the cycle adjustment unit 406 adjusts the cycle of the horizontal synchronization signal to the CCD 48 so as to be the cycle in the normal operation mode.

  As described above, in this embodiment, when the image reading unit is in the standby mode, the frequency of the operation clock supplied to the CCD 48 is reduced as shown in FIG. Then, there is a problem that the image signal output from the CCD 48 does not fit within a predetermined horizontal synchronizing signal, resulting in an image defect.

  However, in the present embodiment, the period adjusting unit 406 is provided to adjust the period of the horizontal synchronization signal so that it is longer in the standby mode than in the normal operation mode. Therefore, even if the period of the image signal output from the CCD 48 is increased by reducing the frequency of the operation clock to the CCD 48, the period of the horizontal synchronization signal can be increased so that such an image signal can be accommodated. . Therefore, the power consumption of the image reading apparatus can be reduced while obtaining a stable image signal.

[Light intensity adjustment operation]
Next, the operation of the light amount adjustment unit 407 will be described with reference to FIG. 5 again.

  When the light amount adjustment unit 407 receives the standby mode signal from the mode monitoring unit 403 a of the reading control unit 403 described above, the light amount adjustment unit 407 adjusts the incident light amount incident on the CCD 48 from the light source 45. For example, when the period of the horizontal synchronization signal becomes twice as long as that in the normal operation mode, the light amount in the standby mode is set to ½ times that in the normal operation mode.

  Specifically, if the relationship value between the light amount of the light source 45 and the current value is known in advance before the copying machine 1 is shipped, the relationship value is stored in a storage unit (not shown). The light amount adjustment unit 407 reads the current value for the light amount according to the adjustment of the period of the horizontal synchronization signal when receiving the standby mode signal, and adjusts the light amount by adjusting the current to the light source 45. For example, when the light source 45 is a white LED, the light amount adjusting unit 407 may adjust the light amount from the light source 45 by adjusting the lighting pulse time in conjunction with the adjustment ratio of the horizontal synchronization signal. .

  Thereafter, in the standby mode of the image reading unit, the light amount adjustment unit 407 adjusts the light amount so that the light amount reduced from the light source 45 compared with that in the normal mode is incident on the CCD 48. When a document detection signal is received from the document size detection unit 408 in the standby mode of the image reading unit, the light amount is adjusted so as to increase the light amount that is reduced to the light amount in the normal operation mode.

As described above, when the period of the horizontal synchronizing signal is adjusted to be longer by the period adjusting unit 406, the amount of incident light received by the CCD 48 is increased by the longer adjustment. However, in this embodiment, as described above, the light amount adjustment unit 407 is provided, and when the image reading unit is in the standby mode, the incident light amount to the CCD 48 is reduced as compared with the normal operation state of the image reading unit. Therefore, even if the period of the horizontal synchronization signal is adjusted to be longer by the period adjusting unit 406, the amount of incident light received by the CCD 48 can be prevented from increasing, and image degradation resulting from saturation of the image signal can be avoided. Therefore, the power consumption of the image reading apparatus can be further reduced while obtaining a stable image signal in the standby mode.
2. Other Embodiments (a) In the first embodiment, an image forming apparatus having both an image reading function and an image forming function has been described. However, the present invention is not limited to this, and can be implemented as an image reading apparatus having no image forming function.
(B) In the first embodiment, the CCD 48 in the carriage 42 is taken as an example as an image sensor to which the operation clock adjusted by the operation clock adjustment unit is supplied. However, the present invention is not limited to this example. For example, the present invention is also applicable to another image sensor such as a CIS (Contact Image Sensor) 24 (see FIG. 2) that reads an image on the other side (back side) of the document M. Is possible.
(C) In the first embodiment, the reading control unit 403 of the image reading apparatus 4 has a mode monitoring unit 403a, and the mode monitoring unit 403a monitors the operation status of the image reading unit including the light source 45, the CCD 48, and the like. The example in which the image reading operation state by the image reading unit is determined has been described.

  However, in the multifunction device 1, the control unit 6 may monitor the operation status of the image reading unit. For example, the control unit 6 may monitor the operation of the image reading unit and output a signal corresponding to the operation state (normal operation mode or standby mode) of the image reading unit to the mode monitoring unit 403a. The mode monitoring unit 403a may generate a standby mode signal when receiving a signal indicating that the image reading unit is in the standby mode from the control unit 6 and output the standby mode signal to the operation clock adjustment unit 405.

  The control unit 6 monitors the operation of the image reading unit, but does not output a signal according to the operation state of the image reading unit, and the mode monitoring unit 403a is based on the monitoring of the control unit 6 at predetermined intervals. The operating state of the image reading unit may be read.

  Embodiments obtained by combining the above-described embodiments with conventionally known techniques are also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Copying machine 2 Original conveying apparatus 3 Main body 4 Image reading apparatus 45 Light source 48CCD
401 A / D converter 402 Image processing unit 403 Reading control unit 404 Clock generation unit 405 Operation clock adjustment unit 406 Period adjustment unit 407 Light amount adjustment unit 408 Document size detection unit 5 Image forming unit 6 Control unit

Claims (4)

An image reading unit comprising: a light source for irradiating light on the document; and an image sensor that reads an image from reflected light from the document and outputs an image signal;
A reading control unit for controlling an image reading operation in the image reading unit;
An operation clock adjusting unit for adjusting an operation clock supplied to the image sensor and the reading control unit;
A document table on which the document is placed;
A document size detector for detecting the size of the document on the document table;
With
When the image reading unit is in the standby mode, the operation clock adjusting unit sets the frequency of the operation clock to the image sensor while maintaining the frequency of the operation clock to the reading control unit. The image sensor is adjusted to be lower than the operation clock frequency in the operation mode, and until the document size detection unit detects the size of the document when the image reading unit is in the standby mode, the image sensor An image reading apparatus that adjusts an operation clock so as to supply a frequency that is lower than an operation clock frequency in a normal operation mode . A cycle adjustment unit for adjusting a cycle of a horizontal synchronization signal input to the image sensor;
The image reading apparatus according to claim 1, wherein when the image reading unit is in a standby mode, the cycle adjusting unit makes the cycle of the horizontal synchronization signal longer than that in the normal operation mode of the image reading unit. A light amount adjustment unit for adjusting the amount of incident light from the light source to the image sensor;
The image reading apparatus according to claim 2, wherein when the image reading unit is in a standby mode, the light amount adjusting unit decreases the incident light amount as compared with a normal operation mode of the image reading unit. The image reading apparatus according to any one of claims 1 to 3,
An image forming unit that forms an image read by the image reading device on a recording medium;
An image forming apparatus comprising:

Images