JPH06178054A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To suppress tip dislocation and the lowering of picture quality such a cut of focus, etc., when an original is read by stopping an original reader at a position with the highest reading efficiency finally with high accuracy. CONSTITUTION:After the original reader 43 is moved and stopped at, for example, a set position by a motor 85, light is emitted from a light source 41 to a carrier roller 91, and reflected light quantity is detected by a light quantity detecting means 42, and a detection value is stored in a storage means. Thence, after a control means stops by moving the original reader 43 by a little distance by rotating the motor 85 in the forward or backward direction, the light is emitted from the light source 41 to the carrier roller 91 again, and the reflected light quantity is detected by the light quantity detecting means 42, and the detection value is stored in the storage means, then, it is compared with the detection value last time. The control means repeats an operation to compare the detection value this time and that last time, and rotates the motor in the forward or backward direction so as to maximize the detection value, and stops by moving the original reader 43.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a document feeder,
When forming an image, the document reading device is moved by a motor and then stopped, and light is emitted from a light source to scan the document moving on the conveyance roller of the document conveying device by the document reading device to form an image. The present invention relates to an electrophotographic apparatus.

[0002]

2. Description of the Related Art Conventionally, in digital copying machines,
As shown in FIG. 2, which is an explanatory diagram of the present invention, a document feeder such as a double-sided automatic document feeder (hereinafter referred to as ADF (Auto D
ocument Feeder) 36).

When a document in the ADF 36 is copied by a digital copying machine equipped with this kind of ADF 36, a reading device 43 provided below the ADF 36 as shown in FIG. 7 which is an explanatory view of the present invention. After being moved to a set position by the motor 85, that is, almost immediately below the platen roller 91 in the ADF 36 and stopped, light is emitted from the lamp unit 41 and the original 93 is read between the platen roller 91 and the glass plate 92. The original is scanned while being conveyed, and the reflected light is detected by the reader 43.

Then, based on the detected data,
A copied image can be obtained by processing in the laser printer unit 32 shown in FIG.

[0005]

However, in the above-described conventional configuration, when the reading device 43 provided below the ADF 36 is moved to the set position by the motor 85, the second position is set as shown in FIG. The motor 85 is turned off when a predetermined pulse count has elapsed since the sensor 88 detected the reading device 43 (motor 8
5), the stop accuracy of the reading device 43 deteriorates (about ± 1 mm) due to variations in the mounting position of the ADF 36 and variations in the relative position between the reading position of the ADF 36 and the reading device 43. There is a problem that the image quality is deteriorated due to misalignment of the leading edge and out-of-focus when the document is read.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to improve the stopping accuracy of the reading device to suppress the leading edge deviation at the time of reading a document and to prevent the focus blurring. An object of the present invention is to provide an electrophotographic apparatus capable of suppressing deterioration of image quality.

[0007]

In order to achieve the above-mentioned object, an electrophotographic apparatus of the present invention has a document feeding device,
At the time of image formation, a document reading device provided below the document feeding device is stopped by being moved by a motor and then stopped, and a light source emits light to scan a document moving on a feeding roller of the document feeding device. In an electrophotographic apparatus which detects the reflected light by a document reading device and forms an image of a document, a light amount detecting means for detecting the reflected light amount when the light is emitted from the light source to the conveying roller, and the light amount detecting means. The detection means for storing the detection value of, and the previous detection value stored in the storage means, and the operation of comparing the detection value of this time stored in the same manner by further moving the document reading device are repeated to detect. A control means for rotating the motor in the normal direction or in the reverse direction so as to maximize the value and moving and stopping the document reading device is provided.

[0008]

According to the structure of the present invention, first, after the document reading device is moved to a set position by a motor and stopped,
Light is emitted from the light source to the conveying roller, the amount of reflected light is detected by the light amount detecting means, and the detected value is stored in the storage means. Next, after the control means rotates the motor forward or reverse to slightly move the document reading device to stop it, light is again emitted from the light source to the conveyance roller, and the reflected light amount is detected by the light amount detection means. The detected value is stored in the storage means. Then, the previous detected value and the present detected value are compared.

Here, since the conveying roller is formed in a columnar shape, when the light is emitted from the light source to the conveying roller and the reflected light amount thereof is detected, the original reading device is moved to maximize the reflected light amount. There is a position to do.

Therefore, the control means repeats the operation of comparing the detected value of the previous time and the detected value of this time, and the motor is rotated in the normal direction or the reverse direction so that the detected value becomes the maximum, and the document reading device is moved and stopped. By doing so, the document reading device can finally be stopped accurately at the position where the reading efficiency is highest. Further, at this time, even if the mounting position of the document conveying device varies, or the relative position between the reading position of the document conveying device and the document reading device varies, the stop accuracy does not change. As a result, it is possible to suppress the misalignment of the leading edge when reading the document, and to suppress the deterioration of image quality such as out-of-focus.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

As shown in FIG. 2, a digital copying machine as an electrophotographic apparatus according to the present embodiment has a copying machine main body 30 including a scanner section 31, a laser printer section 32, a multi-stage sheet feeding unit 33, a sorter 34, and the like. Is equipped with.

The scanner unit 31 includes a document placing table 35 made of transparent glass, an automatic document feeder (hereinafter referred to as an ADF (Auto Document Feeder)) 36 such as a double-sided automatic document feeder, and a scanner unit 40. ing.

The ADF 36 automatically feeds a plurality of set originals one by one between a platen roller 91 and a glass plate 92, which will be described later, and scans one side or both sides of the original according to the operator's selection. Reader 4
It is designed to be read by 3.

The reading device 43 described above includes a plurality of reflecting mirrors, a lens 44, and a photoelectric conversion element (hereinafter referred to as CCD).
42, and forms an image of the reflected light from the document on the CCD 42 via a reflection mirror and a lens 44.

That is, when scanning an original placed on the original placing table 35, the reading device 43 is moved along the lower surface of the original placing table 35, and at this time, the light source provided above the reading device 43. The light is emitted from the lamp unit 41 as a document to the document and the reflected light from the document is read by the reading device 43
The original image is read by receiving light. On the other hand, when using the ADF 36, AD
While the reading device 43 is stopped at a predetermined position below F36, while the document is being conveyed, light is emitted from the lamp unit 41 to the document to read the document image.
A method of stopping the reading device 43 at a predetermined position in this case will be described in detail later.

In this way, the image data obtained by reading the original image with the reading device 43 of the scanner unit 40 is sent to an image processing system, which will be described later, and subjected to various processing, and then the memory 73 of the image processing system. Image data in the memory 73 is output to the laser printer unit 32 in response to an output instruction.

The laser printer unit 32 includes a manual document tray 45, a laser writing unit 46, and an electrophotographic process unit 47 for forming an image. The laser writing unit 46 emits a laser beam in accordance with the image data from the memory 73, a polygon mirror that deflects the laser beam at an equal angular velocity, and a laser beam that is deflected at an equal angular velocity in the electrophotographic process section 47. It has an f-θ lens and the like for correcting so that the light is deflected at a constant angular velocity on the photosensitive drum 48.

In the electrophotographic process section 47, a charging device, a developing device, a peeling device, a cleaning device and a charge eliminator, and an image from the photoconductor drum 48 are transferred around the photoconductor drum 48 in a known manner. And a fixing device 49 for fixing the image on the sheet. Further, in order to supply a sheet to an image forming position formed between the photoconductor drum 48 and the transfer device at a predetermined timing, a registration roller 63 is provided near the image forming position.

A transport path 50 is provided on the downstream side in the transport direction of the sheet on which the image is fixed by the fixing device 49. The transport path 50 is a transport path 57 leading to the sorter 34, and a transport path 57 below the transport path 57. It branches into a conveyance path 58 leading to the multi-stage paper feeding unit 33. The conveyance path 58 is branched in the multi-stage sheet feeding unit 33, and is provided with a reversal conveyance path 54a and a double-sided / composite conveyance path 54b as the conveyance paths after branching.

The reverse conveyance path 54a is a conveyance path for reversing the front and back sides of a sheet on which an image has been transferred and fixed in a double-sided copy mode for copying both sides of a document. On the other hand, both sides /
In the double-sided copy mode, the composite conveyance path 54b conveys the sheet whose front and back sides are reversed by the reversal conveyance path 54a to the image forming position of the photoconductor drum 48, and also images of different originals and toners of different colors on one side of the sheet. In a single-sided composite copy mode in which a composite copy for forming an image is performed, the transport path is for transporting the sheet to the above-mentioned image forming position without inverting the sheet.

The multi-stage paper feeding unit 33 is provided with a first cassette 51, a second cassette 52, a third cassette 53, and a large-capacity cassette 55 which can be optionally added, and the first cassette 51, the second cassette Cassette 52 and third
A common conveyance path 56 that conveys the paper from the cassette 53 toward the laser printer unit 32 is provided. The common conveyance path 56 joins with the conveyance path 59 to which the paper from the large-capacity cassette 55 is fed on the way to the laser printer unit 32, and communicates with the conveyance path 60.

The conveyance path 60 merges as a conveyance path 61 from the double-sided / composite conveyance path 54b and the manual document tray 45 at a confluence point 62 in the laser printer section 32, and the image forming position described above via the registration roller 63. To these three transport paths 60.6
The confluence point 62 of 1 · 54b is provided close to the registration roller 63. Therefore, in such a multi-stage paper feeding unit 33, the cassettes 51, 52, 53.5 of each stage are
The sheets accommodated in the sheet 5 are taken out one by one from the top, and are conveyed to the laser printer section 32 through each conveying path.

In the above structure, the image data read by the scanning unit 31 is stored in the memory 73, and the image data read out from the memory 73 corresponds to the image data by the laser writing unit 46. By scanning the surface of the photosensitive drum 48 with the laser beam, an electrostatic latent image is formed on the surface of the photosensitive drum 48. After that, the toner image obtained by visualizing the electrostatic latent image with toner is electrostatically transferred onto the sheet conveyed from the multi-stage sheet feeding unit 33.

The sheet on which the image is transferred is fixed by the fixing device 4.
9 is sent to the sorter 34 via the transport path 50 and the transport path 57 and is discharged to the outside, or is transported to the reverse transport path 54a and the double-sided / composite transport path 54b via the transport path 50 and the transport path 58. Then, both sides are copied and synthetically copied.

Next, the structure and function of the image processing system provided in such a digital copying machine will be described.

As shown in FIG. 3, the image processing system includes an image data input section 70, an image processing section 71, and an image data output section 7.
2. Memory 7 consisting of RAM (Randam Access Memory) etc.
3, and a CPU (Central Processing Unit) 74.

The image data input section 70 is a CCD section 70.
a, histogram processing unit 70b, and error diffusion processing unit 7
0c, the image data of the original read from the CCD 42 is binarized and converted, and while taking a histogram as a binary digital amount, the image data is processed by the error diffusion method and temporarily stored in the memory 73. It is supposed to do.

The image data processing in the image data input section 70 will be described in more detail. First, C
In the CD unit 70a, the analog electric signal corresponding to each pixel density of the image data from the CCD 42 is A / D converted, and then MTF correction, black-and-white correction or gamma correction is performed.
It is output to the histogram processing unit 70b as a digital signal of 56 gradations (8 bits). Next, in the histogram processing unit 70b, the digital signal output from the CCD unit 70a is added for each pixel density of 256 gradations to obtain density information (histogram data), and the obtained density information is used as necessary. While being sent to the CPU 74, it is sent to the error diffusion processing unit 70c as pixel data. Further, the error diffusion processing unit 70c uses the error diffusion processing method, which is a kind of pseudo halftone processing, that is, the method of reflecting the binarization error in the binarization determination of the adjacent pixels.
The 8-bit / pixel digital signal output from a is converted into 1-bit (binary), and a redistribution operation for faithfully reproducing the local area density in the original is performed.

The image processing unit 71 is a multi-valued processing unit 7.
1a / 71b, combination processing unit 71c, density conversion processing unit 71
d, a scaling processing unit 71e, an image processing unit 71f, an error diffusion processing unit 71g, and a compression processing unit 71h.
That is, the image processing unit 71 is a processing unit that converts the input image data into the image data desired by the operator, and finally outputs the converted output image data to the memory 7.
It is designed to be processed by this processing unit until it is stored in 3. However, each of the above-described processing units included in the image processing unit 71 functions as necessary and may not function.

The function of each processing unit in the image processing unit 71 will be described in more detail. First, the multi-value quantization processing unit 7 will be described.
In 1a and 71b, the data binarized by the error diffusion processing unit 70c is converted into 256 gradations again. In the combination processing unit 71c, a logical operation for each pixel, that is, a logical sum,
The logical product or exclusive OR operation is selectively performed.
The data to be subjected to these calculations are pixel data stored in the memory 73 and bit data from a pattern generator (PG) that stores preset words and symbols. Next, in the density conversion processing unit 71d, the relationship between the input density and the output density is arbitrarily set for the 256 gradation digital signal based on a predetermined gradation conversion table. In the scaling processing unit 71e, the pixel data (density value) for the target pixel after scaling is obtained by performing interpolation processing based on the input known data according to the instructed scaling ratio, and the sub-scanning is performed. Is scaled, the main scanning is scaled.

In the image processing section 71f, various image processes are performed on the input pixel data, and information collection such as feature extraction is performed on the data string. The error diffusion processing unit 71g performs the same processing as the error diffusion processing unit 70c of the image data input unit 70. Compression processing unit 7
At 1h, binary data is compressed by the encoding called run length. Regarding the compression of image data, the compression functions in the final processing loop when the final output image data is completed.

The image data output section 72 is the restoration section 7
The image data stored in the memory 73 in a compressed state is restored to the original 256 by including a 2a, a multi-value processing unit 72b, an error diffusion processing unit 72c, and a laser output unit 72d.
The laser output unit 7 converts the gradation into another gradation and performs error diffusion of the four-valued data that is a smoother halftone expression than the binary data.
The data is transferred to 2d.

That is, the decompression unit 72a decompresses the image data compressed by the compression processing unit 71h. The multilevel halftoning processing unit 72b performs the same processing as the multilevel halftoning processing units 71a and 71b of the image processing unit 71.
In the error diffusion processing unit 72c, the image data input unit 7 is used.
Processing similar to that of the error diffusion processing unit 70c of 0 is performed.

In the laser output section 72d, the digital pixel data is converted into a laser ON / OFF signal based on a control signal from a sequence controller (not shown), and the laser is turned on / off. The data handled by the image data input unit 70 and the image data output unit 72 is basically stored in the memory 73 in the form of binary data in order to reduce the capacity of the memory 73, but the image data is deteriorated. It is also possible to process the data in the form of four-valued data.

On the other hand, a light amount calculation section 75 and a motor control section 76 are connected to the CPU 74. In the light quantity calculation unit 75, when light is emitted from the lamp unit 41 to the white platen roller 91 inside the ADF 36,
The reflected light is received by the CCD 42 in the reading device 43, and the amount of the received light is calculated as an area, for example, and functions as a light amount detecting means.

In the motor control unit 76, the previous detection value stored in the memory 73 as a storage unit for storing the calculation result of the received light amount in the light amount calculation unit 75 and the reading device 43 are moved a little and the same. By repeating the operation of comparing the detected value stored this time with the present detected value, the motor 85 is normally or reversely rotated so as to maximize the detected value, and the reading device 43 is moved and stopped. is doing.

Next, the scanning section 31 will be described in detail.

As shown in FIG. 4, the scanner unit 40 in the scanning unit 31 is provided with a reading device 43 and an arrow S.
A guide shaft 81 for guiding the reading device 43 is provided near the side of the reading device 43 in the scanning direction for scanning in the direction, and a driving wire 82 for moving the reading device 43 is provided with a driving pulley 83 and A motor 85, which is wound between the idle pulleys 84 and drives the drive pulley 83, is provided.

In the vicinity of the idle pulley 84, positioning members 86, 86 are provided on both the front side (the front side of the paper in the figure) and the back side (the back side of the paper in the figure) of the digital copying machine. When the digital copying machine is stationary, the twisting of the reading device 43 in the scanning direction is corrected so that the reading device 43 can move accurately in parallel to the scanning direction.

The reading device 43 is usually located at the home position (HP) at the end of the scanning unit 31 on the ADF 36 side. A second position sensor (SHPS2) 88 and a first position sensor (SHPS1) 89 are sequentially provided in the direction from the home position (HP) of the reading device 43 toward the document placing table 35, and are shown in FIG. As described above, the reading device 43 starts the home position (HP) and starts the second position sensor (SHPS2) 88 and the first position sensor (SHP).
S1) After passing 89, it further moves and folds back near the idle pulley 84 to return to the home position (H
It operates so as to return to P).

The position sensors 88 and 89 are photoelectric sensors and are shielded from light by a sensor shading plate 90 provided above the reading device 43.
The passage of the reading device 43 is detected.

Therefore, as shown in FIG. 6, the reading device 43, when scanning the original 87 placed on the original placing table 35, reads it along the lower surface of the original placing table 35 as described above. The device 43 reads the original image while scanning.

On the other hand, when the ADF 36 is used, as shown in FIG.
As shown in FIG. 4, the reading device 43 is moved to a predetermined document reading position below the ADF 36 by the motor 85 by a method described later, and the reading device 43 is stopped.
A platen roller 91 as a conveyance roller in the ADF 36
The document image is read by the reading device 43 while the document 93 is conveyed between the sheet and the glass plate 92.

Now, the position adjustment of the reading device 43 when the ADF 36 is used in the digital copying machine of this embodiment will be described in detail.

Reader 43 when using ADF 36
To stop at a predetermined position, as shown in FIG. 8, the motor 85 is turned on and rotated normally while the reading device 43 is in the home position (HP). Next, the reading device 43 is scanned from when the first position sensor (SHPS1) 89 changes from the detection state to the non-detection state until the encoder pulse becomes 1511 PLS, for example. Next, the encoder pulse is 1511PL
At S, the rotation direction of the motor is reversed. This causes the reader 43 to start the return operation.

Then, the first position sensor (SHPS
1) When the state of 89 is changed from the non-detection state to the detection state, the motor 85 is once reversed by, for example, 24 PLS,
As a result, the reader 43 is braked (plucking brake). Then, at this time, for example, 10
When 0 μS has elapsed, the motor speed is changed from the normal speed (eg, 1072.126 rpm) to about 1/4 normal speed (256.032 rpm), and the motor clock signal is also set to the frequency of the normal speed mode (eg, 803.9).
4 Hz) to 1/4 normal speed mode frequency (20
0.985 Hz).

Then, after the lapse of 24 PLS, the motor 8 is restarted.
The forward rotation of 5 causes the reading device 43 to eventually
The light shield 90 on the upper side of the second position sensor (SHPS
2) At the position of 88, the second position sensor (SH
PS2) 88 changes from the non-detection state to the detection state. Then, from this time point, for example, after turning on the motor 85 for 10 PLS, the motor 85 is turned off once.

ADF3 in the conventional digital copying machine
The position adjustment of the reading device 43 in the case of using 6 has been completed by this, but in the present embodiment, the following adjustment is further performed.

That is, as shown in FIG.
Is again rotated normally (S1), and then the lamp unit 41
The copy lamp is turned on (S2). Then, the motor 85 is once stopped for a predetermined number of pulses, and the amount of light received by the CCD 42 in the reading device 43 is detected (S3). Next, after the motor 85 is normally rotated by several pulses, the CCD is again rotated.
The amount of received light of 42 is detected (S4). Then this CC
It is determined whether or not the received light amount of D42 has increased (S5). If there is an increase in the amount of received light, CCD4
The motor 85 is normally rotated, for example, in increments of 1 pulse until the amount of received light 2 becomes maximum (S6). And the CCD 42
The motor 85 is stopped when the amount of received light is maximized (S8).

On the other hand, when the amount of received light is reduced in S5, the motor 85 is rotated in reverse by, for example, 1 bul until the amount of received light of the CCD 42 becomes maximum (S7). Then, at S8, the motor 85 is stopped when the amount of light received by the CCD 42 becomes maximum.

That is, the digital copying machine of this embodiment is
First, after the reading device 43 is moved to the set position by the motor 85 and stopped, light is emitted from the lamp unit 41 to the white platen roller 91, and the reflected light amount is calculated as a detection value by the light amount calculation unit 75, This detected value is stored in the memory 73. Next, after the motor control unit 76 rotates the motor 85 forward or backward to slightly move the reading device 43 and stop it, light is emitted from the lamp unit 41 to the platen roller 91 again, and the reflected light amount is the light amount. The calculation value is calculated by the calculation unit 75 as a detection value, and the detection value is stored in the memory 73. Then, the previous detected value and the present detected value are compared.

Here, since the platen roller 91 is formed in a cylindrical shape, when the light is emitted from the lamp unit 41 to the platen roller 91 and the amount of reflected light is detected,
There is a position where the amount of reflected light is maximized by moving the reader 43. On the contrary, the larger the distance from the position where the reflected light amount is maximized, the smaller the reflected light amount.

Therefore, the motor control unit 76 repeats the operation of comparing the previously detected value with the presently detected value, and the motor 85 is normally or reversely rotated to move the reading device 43 so that the detected value becomes maximum. And then stop
Finally, the reading device 43 can be accurately stopped at the position where the reading efficiency is highest.

That is, by setting the movement amount of the reading device 43 to be one pulse of the motor 85, the reading device 4
The stop accuracy of No. 3 is the accuracy of the encoder pulse built in the motor 85 to stabilize the rotation unevenness (1 pulse is about ± 0.3 mm; however, the interval can be arbitrarily reduced. ) Is possible. Even if the mounting position of the ADF 36 varies or the relative position between the reading position of the ADF 36 and the reading device 43 varies, the stop accuracy does not change. Therefore, the reading device 43 should be stopped accurately. You can As a result, it is possible to suppress the misalignment of the leading edge when reading the document, and to suppress the deterioration of image quality such as out-of-focus.

[0056]

As described above, the electrophotographic apparatus of the present invention stores the light amount detecting means for detecting the reflected light amount when the light is emitted from the light source to the conveying roller and the memory for storing the detected value of the light amount detecting means. Means and the previous detection value stored in the storage means, and the operation of comparing the detection value of this time, which is also stored by moving the document reading device further, are repeated to maximize the detection value. A control means for rotating the motor in the normal direction or in the reverse direction to move and stop the document reading device is provided.

As a result, since the carrying roller is formed in a cylindrical shape, when the light is emitted from the light source to the carrying roller and the reflected light amount is detected, the original reading device is moved little by little to change the reflected light amount. There is a position to maximize.

Therefore, the control means repeats the operation of comparing the detected value of the previous time with the detected value of this time, and the motor is rotated in the normal direction or the reverse direction so that the detected value becomes the maximum, and the document reading device is moved and stopped. By doing so, the document reading device can finally be stopped accurately at the position where the reading efficiency is highest. As a result, there is an effect that it is possible to suppress the leading edge deviation when reading the document and to suppress deterioration in image quality such as out-of-focus.

[Brief description of drawings]

FIG. 1 is a flowchart showing movement control of a reading device in a digital copying machine according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing the digital copying machine.

FIG. 3 is a block diagram showing a configuration of an image processing system of the digital copying machine.

FIG. 4 is a configuration diagram showing a scanning unit of the digital copying machine.

FIG. 5 is an explanatory diagram showing a movement path of a reading device in the scanning unit of the digital copying machine.

FIG. 6 is an explanatory diagram showing a state in which a reading device scans a document on a document mounting table in the scanning unit of the digital copying machine.

FIG. 7 is an explanatory diagram showing a state in which a reading device scans an ADF document in the scanning unit of the digital copying machine.

FIG. 8 is a time chart showing a moving operation until the reading device in the digital copying machine stops at a set position.

[Explanation of symbols]

 31 Scanner Section 36 ADF (Document Feeding Device) 41 Lamp Unit (Light Source) 42 CCD 75 Light Quantity Calculation Section (Light Quantity Detection Means) 76 Motor Control Section (Control Means) 85 Motor 88 Second Position Sensor [SHPS2] 89 First Position Sensor [SHPS1] 90 Sensor light-shielding plate 91 Platen roller (conveying roller) 93 Original

Claims (1)

[Claims] 1. A document feeder is provided, and when an image is formed,
The document reading device provided below the document feeding device is stopped after being moved by the motor, and the light source emits light to scan the document moving on the feeding roller of the document feeding device and read the reflected light. In an electrophotographic apparatus for forming an image of an original by detecting the light amount with a device, a light amount detecting means for detecting a reflected light amount when light is emitted from the light source to a conveying roller, and a memory for storing a detected value of the light amount detecting means. Means and the previous detection value stored in the storage means, and the operation of comparing the detection value of this time, which is also stored by moving the document reading device further, are repeated to maximize the detection value. An electrophotographic apparatus, comprising: a control unit that rotates a motor forward or backward to move and stop the document reading device.