JP3332799B2 - Image reading device and image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device in a CCD (photoelectric conversion element) for reading an image of a document and an image forming apparatus such as an electronic copying machine for forming an image using the image reading device. .

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus such as a scanner, the output of an analog image signal level by a CCD (photoelectric conversion element) is manually and electrically adjusted in the initial state for variations in a light source and variations in an optical system. I was going. Further, when the light source deteriorates due to aging or the like, the image quality deteriorates remarkably, and adjustment by a service person or the like is required.

However, in such a method, the CCD output is manually adjusted one by one due to variations in the brightness of the light source and individual variations in the optical system at the time of adjustment at the manufacturing stage of the apparatus. Therefore, the number of man-hours was extra. Further, the output level of the CCD, that is, the level of the analog image signal gradually decreases due to aging, particularly the deterioration of the light source, and the S / N, which is the original design standard, cannot be obtained. Even in the shading correction, the S / N ratio cannot be sufficiently obtained as compared with the initial level due to the deterioration of the S / N, and the image quality is deteriorated.

[0004]

As described above, in the CCD (photoelectric conversion element) of the image reading apparatus, the output level of the CCD gradually decreases due to aging, especially deterioration of the light source.
That is, the level of the analog image signal drops, so that the S / N, which is the original design standard, cannot be obtained. There has been a problem that the ratio cannot be sufficiently obtained and image quality deteriorates.

Accordingly, an object of the present invention is to provide an image reading apparatus and an image forming apparatus capable of improving the image quality deterioration due to the deterioration of the S / N ratio when the amount of light falls due to deterioration of the light source due to aging or the like. And

[0006]

According to the present invention, there is provided an image reading apparatus comprising: a base provided in advance in one line scanning time initialized;
Expose the reference surface, receive the reflected light from this reference surface, and
Determining a photoelectric conversion element for converting a conversion means for converting the image signal of the analog from the photoelectric conversion elements into a digital value, the lowest level of the converted digital value in the conversion means whether less than a predetermined threshold value Determining means, and control means for controlling a one-line scanning time of the photoelectric conversion element such that a minimum level of a digital signal converted by the converting means is equal to or more than a predetermined threshold when the value is equal to or less than a threshold value in the determining means. It is composed of

[0007] The image reading apparatus of the present invention, per line
First control means for initializing the exposure time to a predetermined time;
The exposure per line initialized by the first control means
Expose the reference surface provided in advance for the light time, and
A photoelectric conversion element for receiving the reflected light and photoelectrically converting the reflected light;
An AD converter for converting the image signal of the analog from the photoelectric conversion elements into a digital value, the lowest level of the converted digital value in the AD converter or 1/2 or less der Luca whether the dynamic range of the AD converter Judge
And that determining means, when it is determined that the Ru der 1/2 or less of the dynamic range of the AD converter in the determination means,
The lowest level of the digital value converted by the AD converter is ダ イ ナ ミ ッ ク of the dynamic range of the AD converter.
Calculating means for calculating the exposure time per line of the photoelectric conversion element so as to exceed the above range, and controlling the exposure time per line of the photoelectric conversion element by the exposure time per line calculated by the calculating means. And second control means.

The image forming apparatus according to the present invention is capable of opening an image forming operation.
When a start instruction is given, the initialization is performed for one line scanning time.
Exposure of a reference surface provided in advance, and reflection from this reference surface
A photoelectric conversion element for receiving and photoelectrically converting the light, converting means for converting the image signal of the analog from the photoelectric conversion elements into a digital value, the lowest level is a predetermined threshold value of the converted digital value in the conversion means less Determining means for determining whether or not the image forming operation is performed when the determination means determines that the value is equal to or less than a threshold.
And a control means for controlling the work.

The image forming apparatus according to the present invention is capable of opening an image forming operation.
When the start instruction is given, the exposure time per line is specified.
First control means for initializing to time, and the first control means
Pre-set with the exposure time per line initialized in the stage
A photoelectric conversion element that exposes the reference plane thus formed , receives reflected light from the reference plane, and performs photoelectric conversion, an AD converter that converts an analog image signal from the photoelectric conversion element into a digital value, and the AD converter in a determination unit configured to determine ½ der Luca whether the converted minimum level dynamic range of the AD converter the digital value, this
The dynamic range of the AD converter
Image forming operation is determined
And second control means for controlling the control .

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a digital copying machine according to an image forming apparatus of the present invention.

That is, the digital copying machine is the main body 10 of the apparatus.
In the apparatus main body 10, there are provided a scanner unit 4 functioning as an image reading unit described later and a printer unit 6 functioning as an image forming unit.

On the upper surface of the apparatus main body 10, there is provided an original placing table 12 made of transparent glass on which an object to be read, that is, the original D is placed. An automatic document feeder 7 (hereinafter, referred to as an ADF) for automatically feeding a document onto the document table 12 is provided on the upper surface of the apparatus body 10.
The ADF 7 is provided so as to be openable and closable with respect to the document table 12, and also functions as a document holder for bringing the document D placed on the document table 12 into close contact with the document table 12.

The ADF 7 includes a document tray 8 on which a document D is set, an empty sensor 9 for detecting the presence or absence of a document, a pickup roller 14 for taking out documents one by one from the document tray 8, and a paper feed roller for transporting the taken out document. 1
5. A pair of aligning rollers 16 for aligning the leading edge of the document,
A transport belt 18 is provided so as to cover almost the entire document table 12. The plurality of originals set upward on the original tray 8 are taken out in order from the bottom page, that is, the last page, are aligned by the aligning roller pair 16, and are placed on the original by the transport belt 18. The sheet is transported to a predetermined position on the table 12.

In the ADF 7, a reversing roller 20, a non-reversing sensor 21, a flapper 22, and a paper discharging roller 23 are disposed at an end opposite to the aligning roller pair 16 with the transport belt 18 interposed therebetween. The document D whose image information has been read by the scanner unit 4 described later is sent out from the document table 12 by the transport belt 18,
The ADF 7 via the flapper 21 and the paper discharge roller 22
The document is discharged onto the document discharge unit 24 on the upper surface. When reading the back side of the original D, the original D transported by the transport belt 18 is inverted by the reversing roller 20 by switching the flapper 22, and is again moved to a predetermined position on the original placing table 12 by the transport belt 18. Sent. At the left end of the document table 12 in the drawing, a back plate 19 is provided as a reference for shading correction.

The scanner unit 4 provided in the apparatus main body 10
Has an exposure lamp 25 as a light source for illuminating the document D placed on the document table 12, and a first mirror 26 for deflecting the reflected light from the document D in a predetermined direction. The first mirror 25 and the first mirror 26 are attached to a first carriage 27 disposed below the document table 12.

The first carriage 27 is arranged so as to be movable in parallel with the document table 12, and is reciprocated below the document table 12 by a drive motor via a toothed belt or the like (not shown).

A second carriage 28 that can move in parallel with the document placing table 12 is provided below the document placing table 12. The second carriage 28 has a first mirror 2
Second and third mirrors 30 and 31 for sequentially deflecting the reflected light from the document D deflected by 6 are mounted at right angles to each other. The second carriage 28 is driven by the first carriage 27 by a toothed belt or the like for driving the first carriage 27, and the first carriage 2
7 is moved in parallel with the document table 12 at a half speed.

An image forming lens 32 for converging the reflected light from the third mirror 31 on the second carriage 28 and a light receiving the reflected light converged by the image forming lens are provided below the document table 12. (Photoelectric conversion element) 3 for photoelectric conversion
4 are provided. The imaging lens 32 is movably disposed via a drive mechanism in a plane including the optical axis of the light deflected by the third mirror 31, and moves the reflected light at a desired magnification by moving itself. Form an image. And CCD34
Converts the incident reflected light into a photoelectric signal and outputs an electric signal corresponding to the read original D.

On the other hand, the printer section 6 includes a laser exposure device 40 which functions as a latent image forming means. The laser exposure device 40 includes a semiconductor laser 41 as a light source, a polygon mirror 36 as a scanning member that continuously deflects laser light emitted from the semiconductor laser 41, and a polygon mirror 36 that rotates at a predetermined rotation speed described later. A scanning motor to be driven also includes a polygon motor 37 and an optical system 42 that deflects laser light from the polygon mirror and guides the laser light to a photosensitive drum 44 described later. The laser exposure apparatus 40 having such a configuration is fixedly supported by a support frame (not shown) of the apparatus main body 10.

The semiconductor laser 41 is turned on / off in accordance with image information of the document D read by the scanner unit 4 or facsimile transmission / reception document information, and the like, and the laser light is transmitted through the polygon mirror 36 and the optical system 42. The electrostatic latent image is formed on the peripheral surface of the photosensitive drum 44 by scanning the peripheral surface of the photosensitive drum 44 toward the photosensitive drum 44.

The printer section 6 has a rotatable photosensitive drum 44 serving as an image carrier disposed substantially at the center of the apparatus main body 10. And a desired electrostatic latent image is formed. Around the photosensitive drum 44, a charging charger 45 for charging the drum peripheral surface to a predetermined charge,
A developing device 46 for supplying toner as a developer to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 44 to develop the electrostatic latent image at a desired image density, a transfer material fed from a paper cassette described later, A transfer charger 48 for integrally transferring a toner image formed on the photosensitive drum 44 to the paper P, and a separation charger 47 for separating the copy sheet P from the photosensitive drum 44; A peeling claw 49 for peeling off the copy paper P, a cleaning device 50 for cleaning the toner remaining on the peripheral surface of the photosensitive drum 44, and a static eliminator 51 for removing static on the peripheral surface of the photosensitive drum 44 are arranged in this order.

An upper cassette 52, a middle cassette 53, and a lower cassette 54 which can be pulled out from the apparatus main body are arranged in a lower part in the apparatus main body 10, respectively.
Copy papers of different sizes are loaded in each cassette. A large-capacity feeder 5 is located beside these cassettes.
The large-capacity feeder 55 accommodates about 3000 copy sheets P of a frequently used size, for example, A4 size copy sheets P. Above the large-capacity feeder 55, a paper feed cassette 57 also serving as a manual feed tray 56 is detachably mounted.

In the apparatus main body 10, a transport path 5 extending from each cassette and the large capacity feeder 55 through a transfer portion located between the photosensitive drum 44 and the transfer charger 48 is provided.
8 are formed, and a fixing lamp 60a is provided at the end of the conveyance path 58.
Is provided. Fixing device 60
A discharge port 61 is formed in the side wall of the apparatus main body 10 facing the printer, and the discharge port 61 has a single tray finisher 15.
0 is attached. In the vicinity of the upper cassette 52, the middle cassette 53, the lower cassette 54, the paper feed cassette 57 and the vicinity of the large capacity feeder 55, pickup rollers 63 for taking out the sheets P one by one from the cassette or the large capacity feeder are provided. . The transport path 58 is provided with a number of paper feed roller pairs 64 that transport the copy sheet P taken out by the pickup roller 63 through the transport path 58.

A pair of registration rollers 65 is provided upstream of the photosensitive drum 44 in the transport path 58. The registration roller pair 65 corrects the inclination of the copy paper P taken out, aligns the leading end of the toner image on the photosensitive drum 44 with the leading end of the copy paper P, and adjusts the moving speed of the peripheral surface of the photosensitive drum 44 to The copy paper P is fed to the transfer unit at the same speed. A pre-alignment sensor 66 for detecting the arrival of the copy sheet P is provided in front of the registration roller pair 65, that is, on the side of the feed roller 64.

The copy paper P taken out one by one from each cassette or the large-capacity feeder 55 by the pickup roller 63 is sent to the registration roller pair 65 by the paper supply roller pair 64. Then, the copy paper P is sent to the transfer section after the leading end is aligned by the registration roller pair 65.

In the transfer section, the developer image formed on the photosensitive drum 44, that is, the toner image, is transferred onto the sheet P by the transfer charger 48. The copy paper P on which the toner image has been transferred is separated from the peripheral surface of the photosensitive drum 44 by the action of the separation charger 47 and the separation claw 49,
The sheet is conveyed to the fixing device 60 via a conveyance belt 67 constituting a part of the conveyance path 52. Then, after the developer image is fused and fixed to the copy sheet P by the fixing device 60, the copy sheet P is discharged onto the finisher 150 through the discharge port 61 by the pair of paper feed rollers 68 and the pair of discharge rollers 69.

Under the transport path 58, the copy sheet P passing through the fixing device 60 is turned over,
5 is provided with an automatic double-sided device 70 for feeding. The automatic duplexing device 70 includes a temporary stacking unit 71 for temporarily stacking the copy sheets P, and a reversing path 72 that branches off from the transport path 58 and reverses the copy sheet P that has passed through the fixing device 60 and guides the copy sheet P to the temporary stacking unit 71. A pickup roller 73 for taking out the copy papers P accumulated in the temporary accumulation section one by one; and a paper feed roller 75 for feeding the taken out paper to a pair of registration rollers 65 through a transport path 74. Also, the transport path 58
The copy paper P is provided at a branch portion between the
A distribution gate 76 for selectively distributing to one or the inversion path 72 is provided.

When performing double-sided copying, the copy paper P that has passed through the fixing device 60 is guided to a reversing path 72 by a sorting gate 76, is temporarily accumulated in a reversed state in a temporary accumulation section 71, and is then picked up. The sheet is sent to a pair of registration rollers 65 through a conveyance path 74 by a roller 73 and a pair of sheet feeding rollers 75. Then, after the copy paper P is aligned by the registration roller pair 65, the copy paper P is sent to the transfer unit again, and the toner image is transferred to the back surface of the copy paper P. Thereafter, the copy sheet P is discharged to the finisher 150 via the transport path 58, the fixing device 60, and the discharge roller 69.

The finisher 150 is for stapling and storing the discharged partially structured documents in a unit. Each time the copy sheet P to be stapled is discharged from the sheet discharge port 61, the copy sheet P is brought closer to the side to be stapled by the guide bar 151 and aligned. When all the sheets have been ejected, the paper holding arm 152 suppresses the part of the ejected copy sheet P, and a stapler unit (not shown) performs stapling. Thereafter, the guide bar 151 is lowered, and the stapled copy paper P is discharged to the finisher discharge tray 154 by the finisher discharge roller 155 in a unit. Finisher discharge tray 154
The amount of decrease is determined to some extent by the number of copy sheets P to be discharged, and decreases step by step every time a part of the copy paper P is discharged. Further, the guide bar 151 for aligning the copy paper P to be discharged is at a position such that it does not hit the already stapled copy paper P placed on the finisher discharge tray 154.

Further, the finisher discharge tray 154 is
In the sort mode, it is connected to a shift mechanism (not shown) that shifts every part (for example, in four directions of front, rear, left and right).

An operation panel 80 for inputting various copy conditions, a copy start signal for starting a copy operation, and the like is provided on an upper front portion of the apparatus body 10.

FIG. 2 shows a control configuration of the digital copying machine according to the present invention. That is, the digital copying machine
A scanner unit 4 for reading a document, an image processing unit 82 for performing image processing of an image signal read by the scanner unit 4, a printer unit 6 for printing an image signal from the image processing unit 82 on recording paper, and reading from a scanner unit 4. Image memory unit 83 for temporarily storing the image signal, scanner unit 4, image processing unit 8
2, a system control unit 81 including a CPU 80 for controlling each processing unit of the printer unit 6 and the image memory unit 83.

FIG. 3 shows a schematic configuration of the image signal processing in the scanner unit 4.

The scanner unit 4 includes an exposure lamp (light source) 25
The CCD 34 converts reflected light from the original D illuminated by the CCD into an electric signal, a sample-and-hold circuit 91 for extracting an image signal for each pixel output from the CCD 34, An amplifier circuit 92 for amplifying the image signal; an A / D converter 93 for quantizing the image signal from the amplifier circuit 92 from analog to digital; a shading correction circuit 94 for correcting the image signal digitized by the A / D converter 93; CCD3
4, a scanner control circuit 95 for controlling the sample-and-hold circuit 91 and the A / D converter 93, and an image signal level determination circuit 96 for determining the image signal level digitized by the A / D converter 93.

The scanner control circuit 95 receives the judgment result from the image signal level judgment circuit 96,
It is connected to and controlled by the CPU 80 of the system control unit 81. After the processing by the shading correction circuit 94, an image signal is output from the scanner unit 4 to the image processing unit 82.

FIG. 4 shows control signals for the CCD 34.

The shift pulse SH shown in FIG.
The clock pulse φ1 and the clock pulse φ2 shown in FIGS. 4B and 4C are clock signals for transferring even-numbered bits and odd-numbered bits of the light-receiving pixels of the CCD 34, respectively. 4 (d)
Is a reset pulse RS, and FIG. 4E is a clamp pulse CL.

The image signal read by the CCD 34 is output in synchronization with the transfer clocks φ1 and φ2. Image signal (data) output in synchronization with transfer clocks φ1 and φ2
There are dummy (non-effective pixel) data and valid pixel data, and both are transferred. The scanning time per line is linked to the moving speed of the first carriage 27 for reading in the sub-scanning direction of the digital copier, and the scanning time of the CCD 34 matches the moving time of the carriage in the sub-scanning direction. I do.

That is, the width (t _INT ) of the shift pulse SH
Is the moving speed of the first carriage 27 (moving speed in the sub-scanning direction).

FIG. 5 shows the principle of the present invention.
In the present invention, the t _INT time shown in FIG. 5A is variable, but the number of copies per minute which is a predetermined specification in a digital copying machine, for example, as shown in FIG. 5C. To satisfy the reading performance of 20 sheets per minute
_Let the scanning time per line be t _{INT_MAX} . This t _IN
If t _INT time than _{T_MAX} time is prolonged, because it can not ensure a predetermined number of copies per minute, the maximum value of t _INT time is this value.

The time t _INT is _calculated as shown in FIG.
As shown in (d), the time must be longer than the time t _clk during which all the dummy data and valid pixel data of the CCD 34 can be transferred (t _clk <t _INT ).

In the present invention, the initial value of the t _INT time is t
_{Set to INT_MAX} / 2 (> t _clk ).

FIG. 6 shows the setting of the dynamic range of the A / D converter 93 and the shading waveform S. That is, when the digital copying machine is shipped, adjustment of the image signal output of the A / D converter 93 is performed by the amplifier circuit 92.
As shown in FIG. 6B, the adjustment is performed so that the lowest part of the shading waveform S is higher than half the dynamic range of the A / D converter 93. The point is to make the _tINT time variable by adjusting in this way.

Next, the operation of the scanner section 4 in such a configuration will be described with reference to the flowchart of FIG.

First, initialization of the t _INT time (t _INT = t
_{INT_MAX} / 2) is performed (ST1). When the copying operation is started, the waveform (shading waveform S) of the back plate 19 as a reference is always read by the CCD 34 (ST).
2).

At the same time, the image signal level judgment circuit 96
Determines whether or not V _{IN_MIN,} which is the image signal lowest level data shown in FIG. _6A, is equal to or less than 1/2 (V _DYNAMIC / 2) of the dynamic range of the A / D converter 93 ( ST4), the image signal level determination circuit 96
The determination result data of the image signal lowest level in
0 reads.

If the judgment result data is not less than 1/2,
The CPU 80 starts copying (ST5).

If the determination result data is less than ２, the CPU 80 sets the image signal lowest level data V
_{The ratio} between _{IN_MIN} and the value of 50% of the dynamic range of the A / D converter 93 is obtained, and 1
The exposure time per line is set to _tINT = (1 + α) × _tINT .

In this case, α is defined as follows.

Α = (V _DYNAMIC / 2) / V _{IN — MIN} Therefore, the following equation is set (ST6).

T _INT = (1 + V _DYNAMIC / 2 / V _{IN — MIN} ) × t _INT This t _INT is set so that the CPU 80 increases the setting of the counter in the scanner control circuit 11 that determines the width of the shift pulse SH. , T _INT is made variable as shown in FIG.

After that, the next scanning output of the CCD 34 becomes the CCD 34 by increasing the exposure time t _INT.
, The reference data using all the bits of the A / D converter 93 is obtained as shown in FIG. 6B.

When t _INT > t _{INT_MAX} (ST7), the CPU 80 suspends copying. Incidentally, for a copy interrupted when it becomes long t _INT time than this t _{INT_MAX} time, it can not be ensure a predetermined number of copies per minute as described above.

Such an operation is performed at the start of copying, and
A stable S / N can be obtained by always obtaining a stable shading waveform S. Even if the exposure lamp (light source) 25 deteriorates due to aging, a stable image quality can be maintained.

Further, if t _INT > t _{INT_MAX} during the main operation, the main correction becomes impossible, so that it is easy to interrupt copying and change the exposure lamp (light source) 25. Understand.

When the speed of the printer unit 6 is _sufficient for t _INT , the printer unit 6 is connected to the scanner unit 4.
If the speed of the scanner unit 4 exceeds the speed of the printer unit 6,
The image signal is temporarily stored in the image memory unit 83, and is stored in the printer unit 6
By transferring the image signal from the image memory unit 83 in accordance with the speed, the speed can be adjusted to cope with the situation.

In this manner, a stable image quality can be maintained while maintaining the number of copies per minute, which is the specification of the digital copying machine.

As described above, according to the embodiment of the present invention, since the automatic gain control is automatically performed in the digital copying machine, a stable S / N ratio is always achieved.
The image signal level of the ratio can be input to the AD converter, and stable image quality can be maintained.

Further, since the actual light source level can be determined in addition to the conventional total lighting time, the light source can be used up to the actual life of the light source being used. The service life can be extended.

[0061]

As described in detail above, according to the present invention,
It is possible to provide an image reading apparatus and an image forming apparatus capable of improving image quality deterioration due to deterioration of the S / N ratio at the time of a decrease in light amount due to light source deterioration due to aging or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a digital copying machine according to an image forming apparatus of the present invention.

FIG. 2 is a block diagram illustrating a control configuration of the digital copying machine.

FIG. 3 is a diagram showing a schematic configuration of image signal processing in a scanner unit.

FIG. 4 is a diagram showing control signals of a CCD.

FIG. 5 is a diagram illustrating the principle of the present invention.

FIG. 6 is a diagram for explaining setting of a dynamic range and a shading waveform of an A / D converter.

FIG. 7 is a flowchart illustrating the operation of the scanner unit.

[Description of Signs] 4 ... Scanner unit (image reading device) 6 ... Printer unit (image forming unit) 34 ... Photoelectric conversion element (CCD) 35 ... Image processing circuit (image processing unit) 80 ... CPU 81 ... System control unit 82 ... Image processing unit 83 ... Image memory unit 91 ... Sample hold circuit 92 ... Amplification circuit 93 ... A / D converter 94 ... Shading correction circuit 95 ... Scanner control circuit 96 ... Image signal level judgment circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/04-1/207

Claims (6)

(57) [Claims] (1) A preset one line scanning time is set in advance.
The exposed reference surface is exposed, and the reflected light from this reference surface is received.
A photoelectric conversion element for photoelectrically converting light, converting means for converting the image signal of the analog from the photoelectric conversion elements into a digital value <br/>, the lowest level is the predetermined converted digital value by the conversion means determining means for determining whether the threshold or less, one line of the photoelectric conversion elements as the lowest level of the digital converted by the above conversion means when equal to or less than the threshold value in the determination means is equal to or greater than a predetermined threshold value An image reading apparatus comprising: a control unit configured to control a scanning time. 2. The method according to claim 1 , further comprising the steps of:
The exposed reference surface is exposed, and the reflected light from this reference surface is received.
A photoelectric conversion element for photoelectrically converting light, an AD converter for converting an image signal of the analog from the photoelectric conversion elements into a digital value, a minimum level of the converted digital value in the AD converter
Le is a determination unit configured to determine whether more than a predetermined threshold value, the decision means the conversion means the lowest level of the digital converted by the conversion the photoelectric so that the predetermined threshold value or more in the case was equal to or less than the threshold value in Control means for controlling a one-line scanning time of the element. 3. The exposure time per line is set to a predetermined time.
First control means for initializing, dew 1 per line is initialized with the first control means
Expose the reference surface provided in advance for the light time, and
A photoelectric conversion element for receiving and photoelectrically converting a et of the reflected light, an AD converter for converting an image signal of the analog from the photoelectric conversion elements into a digital value <br/>, the converted digital value in the AD converter The lowest level is １ ／ of the dynamic range of the AD converter
Following determination means for determining der Luke not, when it is determined that the Ru der 1/2 or less of the dynamic range of the AD converter in the determination means, the lowest level of the digital value to be converted by the AD converter Means for calculating the exposure time per line of the photoelectric conversion element so as to exceed 1/2 of the dynamic range of the AD converter; and the photoelectric conversion based on the exposure time per line calculated by the calculation means. And a second control unit for controlling an exposure time per line of the element. 4. When an instruction to start an image forming operation is issued,
A reference plane provided in advance with one line scanning time
Exposure, receive light reflected from this reference plane, and perform photoelectric conversion
That a photoelectric conversion element, a conversion means for converting the image signal of the analog from the photoelectric conversion elements into a digital value <br/>, whether the lowest level of the converted digital value in the conversion means is equal to or less than a predetermined threshold value An image forming apparatus comprising: a determination unit configured to determine the image forming apparatus; and a control unit configured to control an image forming operation when the determination result is equal to or smaller than a threshold. 5. When an instruction to start an image forming operation is given,
A reference plane provided in advance with one line scanning time
Exposure, receive light reflected from this reference plane, and perform photoelectric conversion
That the photoelectric conversion element, and an AD converter for converting an image signal of the analog from the photoelectric conversion elements into a digital value, a minimum level of the converted digital value in the AD converter
Image Le is characterized by comprising a control unit that controls the image forming operation <br/> if not below the threshold value in determining means and, the determining means for determining whether or not less than a predetermined threshold value Forming equipment. 6. When an instruction to start an image forming operation is issued, 1
First, the exposure time per line is initialized to a predetermined time.
Control means, and the exposure per line initialized by the first control means.
Expose the reference surface provided in advance for the light time, and
A photoelectric conversion element that receives the reflected light from the photoelectric conversion element and performs photoelectric conversion, an AD converter that converts an analog image signal from the photoelectric conversion element into a digital value, and a minimum level of the digital value converted by the AD converter is as described above. 1/2 of the dynamic range of the AD converter
Determination means for determining der Luke not less, dynamic range of the AD converter in this determination means
Image forming operation when it is determined that the
An image forming apparatus, comprising: a second control unit for controlling .