JPS6240470A - Image forming device - Google Patents

Abstract

PURPOSE:To make the correction of positional deviation possible irrespective of the size of a transferred material and to form an image having high quality by providing an optical detecting unit that can move in the direction intersecting orthogonally with the direction of movement of paper and detects the positional deviation of fed paper, and setting the unit at a reference position according to the size of the paper. CONSTITUTION:Copying operation is made by detecting the amount of positional deviation in (x) direction and (y) direction of fed paper and controlling a lens block 8 for variable power the first carriage and an exposure lamp 4 according to the amount of positional deviation. Even when the positional deviation occurred on the fed paper, the original image can be copied in the specified position of the paper, and the quality of the copied image can be improved. When a cassette selector key is operated for selection at the optical detecting unit 130, the specified part of an optical sensor 133 is moved so as to coincide with the reference position Re of selected paper. Accordingly, the positional deviation of the paper can be detected surely even when the size of the paper is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image forming apparatus applied to, for example, an electronic copying machine.

[Technical background of invention and its problems]

As is well known, in conventional copying machines, there is a means for detecting the positional deviation of the paper supplied to the transfer section (positional deviation with respect to the moving direction of the paper or positional deviation in the direction perpendicular to the moving direction); There was no way to correct it.

Generally, the paper fed from the paper cassette has a length of ±3 m.
A positional shift of about m may occur. however,
Conventional copying machines are unable to detect and correct misalignment of paper that has been supplied, and in some cases, the image is formed on one side of the paper, resulting in a misalignment of the formed image. There were times when the quality deteriorated. Therefore, it is desired to develop a means that can detect and correct the positional deviation of the supplied paper. Moreover, it would be convenient in practice if this paper positional shift detection and correction could be performed even when the paper size changes.

[Object of the invention] This invention was made based on the above circumstances,
The purpose is to
It is an object of the present invention to provide an image forming apparatus that is capable of correcting positional deviations and forming high-quality images.

[Summary of the invention]

This invention provides, for example, an optical detection unit that is movable in a direction perpendicular to the paper movement direction in front of the registration roller and detects a positional shift of the supplied paper, and detects the position of the paper according to the output signal of the optical detection unit. , the lens block for variable magnification is moved in a direction perpendicular to the moving direction of the first carriage to correct the image forming position on the paper, and in particular, the optical detection unit 1 is moved in a direction perpendicular to the moving direction of the first carriage to correct the image forming position on the paper. The reference position is set at the reference position.

[Embodiments of the invention]

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

FIGS. 4 and 5 schematically show an image forming apparatus of the present invention, such as a copying machine. A document table (transparent glass) 2 for supporting a document is fixed to the top surface of the copying machine main body 1. The document table 2 is provided with a fixed scale 21 that serves as a reference for setting the document, and furthermore, a document cover 11 and a work table 12, which can be opened and closed, are provided near the document table 2. The original placed on the original platen 2 is processed by an optical system consisting of an exposure lamp 4 and mirrors 5, 6, and 7.
Exposure scanning is performed by reciprocating in the direction of arrow a along the lower surface of document table 2. in this case,
Mirror 6.7 is connected to one of mirrors 5 to maintain the light exposure length.
,,' is moved at a speed of 2.

The light reflected from the original by the scanning of the optical system, that is, the light reflected from the original by the light irradiation of the exposure lamp 4, is reflected by the mirror 5, 6, 7, passes through the variable magnification lens block 8, and is further reflected by the mirror. 9 and guided to the photoreceptor drum 10, so that an image of the document is formed on the surface of the photoreceptor drum 10.

The photosensitive drum 10 is rotated in the direction of arrow C in the figure, and first, the surface thereof is charged by the charging device 11. Thereafter, the image is exposed to slit light to form an electrostatic latent image on the surface. This electrostatic latent image is made visible by applying toner by the developing device 12.

On the other hand, the paper (transfer material) P is taken out one by one from the selected upper paper feed cassette 13 or lower paper feed cassette 14 by the delivery roller 15 or 16, and the taken out paper is taken out from the paper guide path 17 or 18 and is guided to a pair of registration rollers 19, and guided to a transfer section by this pair of registration rollers 19. Here, the paper feed cassettes 13 and 14 are removably provided at the lower right end of the main body 1, and one of them can be selected from an operation panel to be described later. The cassette size of each of the paper feed cassettes 13 and 14 is detected by a cassette size detection switch 601 and 602, respectively. The cassette size detection switches 601 and 602 are composed of a plurality of microswitches that are turned on and off according to the insertion of cassettes of different sizes.

The paper P sent to the transfer section is brought into close contact with the surface of the photosensitive drum 1o at the transfer charger 20, and
The toner image on the photoreceptor drum 10 is transferred by the action of 0. The transferred image w1P is electrostatically peeled off from the photoreceptor drum 10 by the action of a peeling charger 21, and is sent by a conveyor belt 22 to a fixing roller 23, which serves as a fixing device, provided at the end of the conveyor belt 22. The transferred image is fixed by passing through this, and the fixed paper P is discharged to a tray 25 outside the main body 1 by a pair of paper discharge rollers 24 . After the photosensitive drum 10 has been transferred, the charge is removed by the charger 26, residual toner on the surface is removed by the cleaner 27, and the residual image is erased by the charge removal lamp 28, so that the drum 10 returns to its initial state. It is now possible to do so. Note that 29 is a cooling fan for preventing the temperature inside the main body 1 from rising.

FIG. 6 shows the operation panel 30 provided on the main body 1. 301 is a copy key for instructing the start of copying; 302
is a numeric keypad for setting the number of copies, etc., 303 is a display unit that displays the operating status of each part and paper jams, etc., 304 is a cassette selection key for selecting the upper and lower paper feed cassettes 13 and 14, and 30s is a selected key. A cassette display section for displaying the cassette, 306 a magnification setting key for setting the enlargement and reduction magnification of copies in a predetermined relationship, 307 a zoom key for steplessly setting the enlargement and reduction magnification, and 30a for displaying the set magnification. The display section 30°9 is a density setting section for setting the copy density.

FIG. 7 shows an example of the configuration of the drive sources for each drive section of the copying machine configured as described above, and is configured with the following components. That is, 31 is a lens motor, which is a motor for moving the position of the lens block 8 for performing magnification change. 32 is a mirror motor;
This is a motor for changing the distance 1 (optical path length) between the mirror 5 and the mirror 6.7 for changing the magnification.

A scanning motor 33 is a motor for moving the exposure lamp 4, the mirror 5, and the mirror 6.7 for scanning the original. A shutter motor 34 is a motor for moving a shutter (not shown) for adjusting the charging width of the photosensitive drum 10 by the charger 11 during zooming. A developing motor 35 is a motor for driving the developing roller of the developing device 12 and the like. 36 is a drum motor, which is a motor for driving the photosensitive drum 10. 37 is a fixing motor, which is a motor for driving the paper transport path 22, the pair of fixing rollers 23, and the pair of paper ejecting rollers 24.

38 is a paper feed motor, and the feed roller 15, 16
This is a motor for driving. 3 is a paper feed motor, which is a motor for driving the pair of registration rollers 19; 40 is a fan motor, which is a motor for driving the two cooling fans.

FIG. 8 shows a drive mechanism for reciprocating the optical system. That is, the mirror 5 and the exposure lamp 4 are supported by a first carriage 411, and the mirror 6.7 is supported by a second carriage 422, and these carriages 411 and 412 are guided by guide rails 421 and 422 in the direction of arrow a. It is said to be able to move in parallel. Further, the four-phase pulse motor 33 drives a pulley 43. An endless belt 45 is passed between this pulley 43 and the idle pulley 44, and this belt 45
One end of a first carriage 411 that supports the mirror 5 is fixed in the middle of the mirror. On the other hand, a rail 422 is attached to the guide portion 46 of the second carriage 422 that supports the mirror 6.7.
Two pulleys 47.47 are rotatably provided apart from each other in the axial direction, and a wire 48 is stretched between these pulleys 47.47. One end of this wire 48 is fixed to a fixed part 49, and the other end is fixed to the fixed part 49 via a coil spring 5o. In addition, the wire 4
One end of a first carriage 411 is fixed to the middle part of 8. Therefore, when the pulse motor 33 is rotated, the bell 45 is rotated and the first carriage 41 is rotated.
1 is moved, and along with this, the second carriage 422
will also be moved. At this time, since the pulleys 47 and 47 act as movable pulleys, the second carriage
Carriage 422 is moved in the same direction at 1/2 speed. Note that the moving directions of the first and second carriages 411 and 412 are controlled by switching the rotational direction of the pulse motor 33.

Further, on the document table 2, a copyable range corresponding to the specified paper is displayed. That is, the cassette selection key 304
Let the paper size specified by (Px, Py) be,
If the copy magnification specified by the magnification setting keys 306 and 307 is K, the copyable range (x, y) is [x=
Px/Kl.

ry=Py/K". This copyable range (x.

y), the X direction is indicated by the distance between the pointers 51 and 52 provided on the back surface of the document table 2, and the y direction is indicated by the distance between the scale 53 provided on the upper surface of the first carriage 411 and the fixed point. It is displayed by the distance between the scales 21.

As shown in FIG. 9, the above-mentioned pointers 51.
55 via a spring 56. The pulley 55 is rotated by a motor 58, and by driving the motor 58 according to the determined copyable range in the X direction, the finger! 151.52 can be changed.

Further, the first carriage 411 is moved to a predetermined position (home position according to the magnification) by driving the motor 33 according to the paper size and magnification. When the copy key 301 is pressed, the first carriage 411 is first moved toward the second carriage 412, and then the lamp 4 is turned on and moved away from the second carriage 412. When scanning of the original is completed, the lamp 4 is turned off and the first carriage 41
1 is returned to the home position.

FIG. 10 shows a drive mechanism for the variable magnification lens block 8. As shown in FIG. The motor 31 is connected to a first carriage 41+
A lead screw 61 arranged along the moving direction (y direction) is rotated. Bushes 631 and 632, which are provided at one end of the substrate 62, are screwed into the lead screw 61, and when the lead screw 61 is rotated, the substrate 62 is moved in the y direction.

A guide member 621 is provided at the round end of the board 62, and the guide member 621 is slidably engaged with the guide rail 64. Further, the substrate 62 includes a substrate 62 .
A movable body 65 is provided, which is movable in a direction (X direction) orthogonal to the above, and to which the variable magnification lens block 8 is attached. That is, supports 651. are provided at both ends of the moving body 65.
652 are provided, and these supports 651 and 652 are guided and held by guide members 66+ and 662 provided on the base plate 62. Further, a rack 653 is provided on the side surface in the longitudinal direction of the support body 651, and a pinion 68 rotated by a pulse motor 67 provided on the base plate 62 is engaged with this rack 653. Therefore, the variable magnification lens block 8 is operated by the motor 67.
is moved in the X direction by being driven. The microswitches 69+ and 692 are for detecting the initial positions of the substrate 62 and the moving body 65, respectively.

Next, the relationship between the operation of the transformation lens block 8 and the image formed will be explained. In FIG. 11<a>, the focal length of the variable power lens block 8 is f, the optical path length from the document table 2 to the variable power lens block 8 is ya, and from the variable power lens block 8 to the photosensitive drum 10. When the optical path length of is yb and the total optical path length from the document table 2 to the photosensitive drum 10 is yc, the optical formula is expressed as follows.

1 / f = 1, / y a + 1 / y
b Also, the magnification is expressed as yb/ya. Since the focal length f of the variable power lens block 8 is constant, in order to focus during variable power, it is necessary not only to change the total optical path length VC but also to change ya or yb. This ya, yb
can be changed by moving the variable power lens block 8 in the y direction. Further, the total optical path length yc can be changed by moving the second carriage 412 and changing the position of the mirror 6.7.

On the other hand, as shown in FIG. 11(b), the distances between the document table 2, the variable magnification lens block 8, and the photosensitive drum 10 are kept constant, and the variable magnification lens block 8 is moved in the X direction by the motor 67, for example, by a distance x When the image on the photosensitive drum 10 is moved by 1, the image on the photosensitive drum 10 is moved by a distance Wi×2 expressed by the following equation.

X 2 = X IX yb / Va In addition, in the case of equal size copying, it becomes ×2 to 2X+. In this way, by moving the variable magnification lens block 8 in the X direction, the center of the copied image can be moved.

FIG. 12 shows the overall control circuit.

The main processor group 71 includes a high-voltage transformer 76 that detects inputs from the operation panel 30 and input devices 75 such as various switches and sensors, such as the cassette size detection switches 601 and 602, and drives the various band R devices.
the static elimination lamp 28, the blade solenoid 27a1 of the cleaner 27, the heater 23a of the fixing roller pair 23,
The exposure lamp 4 and each of the motors 31 to 40.5
8.67, etc., to perform the above-mentioned copying operation, and detect the positional deviation of the paper using the light emitting element 132 of the optical detection unit 130, the optical sensor 133, and the pulse motor 138, and perform the copying operation according to the state. , an operation is performed to correct the image forming position on the paper. Note that details of the optical detection unit 130 and the like will be described later.

Among the motors 31 to 40, 58, 67, and 138, the toner motor 77 that supplies toner to the Tanabata 35, 37, and 40 and the developing device 12 is connected to the main processor group 71 via a motor driver 78. controlled, motor 31~
34, 67, 138 are controlled by the first sub-processor group 72 via a pulse motor driver 79, and the motor 36
, 39°38.58 are controlled by the second sub-processor 8\73 via the pulse motor driver 8o. Also,
The exposure lamp 4 is controlled by the main processor group 71 via the lamp regulator 81, and the heater 23a is controlled by the main processor group 71 via the heater control section 82. Then, from the main processor group 71, the first.
The second sub-processor group 72 and 73 drive each motor;
A stop command is sent to the first and second sub-processor groups 72.
73 to the main processor group 71 for driving each motor,
A status signal indicating a stopped state is sent. Also, the first
The sub-processor group 72 includes motors 31 to 34, 67 .
Position information from a position sensor 83 that detects each initial position of 138 is input.

FIG. 13 shows an example of the configuration of the main processor group 71. That is, the one-chip microcomputer 91 (
(hereinafter simply referred to as microcontroller), the input/output board 9
2, key input detection and various display controls on an operation panel (not shown) are performed. Further, the microcomputer 91 is expanded by input/output ports 93-96. and,
The input/output boat 93 is connected to the high voltage 1 to the lance 76, the motor driver 78, the lamp regulator 81, and other outputs, and the input/output boat 94 is connected to a size switch for detecting paper size and its value input, and the input/output A copy condition setting switch, its value input, etc. are connected to the boat 95. Note that the input/output port 96 is an option.

FIG. 14 shows an example of the configuration of the first sub-processor group 72. The microcomputer 101 is the main processor group 7
1 is connected. Programmable interval
The timer 102 controls the phase switching interval time of the pulse motor. When a set value is set from the microcomputer 101, the timer 102 starts counting reference clock pulses based on the setting value. When the timer 102 has counted out, the end pulse is sent to the microcomputer 101. It is configured to output to the interrupt line. The microcomputer 101 also includes the position sensor 8.
The position information from 1o3.104 is input, and the input/output boat 1o3.104 is connected. The input/output boat 104 is connected to the motors 31 to 34, 67, and 138 via the pulse motor driver 79. The input/output board 103 is used, for example, to output status signals of each pulse motor to the main processor 8$71.

FIG. 15 shows the configuration of the second sub-processor u73. The microcomputer 111 is connected to the main processor group 71
is connected to. The programmable interval timer 112 controls the phase switching interval time of the pulse motor, and when a set value is set by the microcomputer 111, the count of reference clock pulses is started based on the set value.

When the count is out, a termination pulse is output. This termination pulse is latched by the latch circuit 113, and its output is supplied to the interrupt line of the microcomputer 111 and the input line to the turnout port 1. Also, microcontroller 1
11 is connected to an input/output boat 114, and motors 36, 38, 39, and 58 are connected to this input/output boat 114 via the pulse motor driver 80.

Figure 16 shows the control circuit of the pulse motor.
A novel smoke driver 122 (corresponding to the seven pulse motor drivers 80 in Fig. 12) is connected to the input/output boat 121 (corresponding to the input/output boats 104 and 114 in Figs. 14 and 15), and this pulse motor The driver 122 includes a pulse motor 123 (the pulse motors 31 to 34 .
36.3B, 39.58.67.13B) are connected to each other.

FIG. 17 shows the pulse motor speed &1 gA method, and the same figure (aCt is the speed curve of the Yuvals motor, and the same figure (b) shows the phase switching interval.

As is clear from this figure, the phase switching interval is long at the beginning;
It gradually shortens, becomes evenly spaced, then gradually lengthens again, and then stops. In other words, this indicates the through-up and through-down of the pulse motor, starting from the self-starting region, being used in the high-speed region, and finally falling down. Note that tl, t2, . . . tx indicate the time of the phase switching interval.

Next, main parts of the present invention will be explained. In this embodiment, it is possible to correct paper misalignment with the device. That is,
As shown in FIG. 1(a), the above-mentioned registration roller pair 1
9 and the photoreceptor drum 10 (not shown), there is an optical detection unit 13 for detecting a lateral positional deviation of the MP.
0 is set. This optical detection unit 130 is
U-shaped case 131. ．． 1'j and this case 1
31, light emitting elements 13 are arranged, for example, at predetermined intervals in a direction orthogonal to the front and back sides of the paper P.
2, and an optical sensor 133 consisting of a plurality of light receiving elements 133a to 133d. The case 131 is movably provided on a guide shaft 134 disposed along the resist 0-ra pair 19.
1 is fixed to a timing belt 135 disposed on the guide shaft 134. This timing belt 1
35 is stretched between pulleys 136 and 137, and among these, a boo 9137 is driven by a pulse motor 138.

Therefore, when the pulse motor 138 is driven,
The optical detection unit 130 is moved along a guide shaft 134. Further, a microswitch 139 is provided near one end of the guide shaft 134, and the initial position of the optical detection unit 130 is detected by this microswitch 139. Furthermore, Fig. 1(a)
In (J, register l-roller pair 19 and guide shaft 134
are shown separated, but the distance yp between them is extremely narrow.

In the above configuration, a paper misalignment detection operation using the optical detection unit 130 will be described.

When the copy key 301 of the operation panel 30 is operated,
The main processor 71 performs the operations shown in the second factor. That is, first, in step STI, the upper paper feed cassette 13 and the lower paper feed cassette 14 are selected by operating the cassette selection key 304 on the operation panel 30.
It is determined which paper feed cassette is selected. As a result, if it is determined that the upper paper feed cassette 13 is being operated, the control is shifted to step ST2, and if it is determined that the lower paper feed cassette 14 is being operated, the control is shifted to step ST2. The process moves to ST3. These steps ST2. In step ST3',
The optical detection units 130 are each moved to a reference position corresponding to the selected paper size. Figure 1 (
As shown in b), if the reference position Re of a paper P is detected between the light emitting elements 133b and 1330 of the optical sensor 133, the size of the paper selected is between the light emitting elements 133b and 133C. Reference position I according to
Moved to Re. Note that the paper P is fed so that its center in the width direction is aligned with the center in the longitudinal direction of the pair of registration rollers 19. Furthermore, when the paper is changed by operating the cassette selection key 304, the amount of movement S by which the optical detection unit 130 moves from the reference position MRe of one paper to the reference position Re of the other paper is shown in FIG. 2 selected by the cassette selection key 304 as shown in C).
If the widths of the types of paper Pi and P2 are x1 and x2, respectively, then S=(xl-X2)/2.

As described above, in a state in which the optical detection unit 130 has been moved to the reference position Re of the selected paper, paper is fed from the selected paper feed cassette in step ST4, and the position of the fed paper is The amount of deviation is detected by the optical detection unit 130. Here, the paper X
The misalignment in the direction (width direction) and misalignment direction are as follows:
Light emitting elements 133a to 1 constituting the optical sensor 133
It is detected by the output signal of 33d. For example, if there is no positional shift in the fed paper, the light emitting elements 133a and 133b are blocked by the fed paper, and output signals are detected only from the light emitting elements 133 and 133d. On the other hand, if the fed paper is misaligned in the X direction, the light emitting elements 133a to 133 of the optical sensor 133
The number of outputs M obtained from d changes. Therefore, from changes in this output signal, it is possible to detect the maximum positional deviation of the paper and the direction of positional deviation.

Furthermore, the positional deviation of the paper in the X direction (movement direction) affects the timing from when the paper starts being fed until an output signal is detected from any of the light emitting elements 133a to 133d forming the optical sensor 133. It can be detected by detecting. This detection method involves counting the number of pulses supplied to the motor 39 that drives the pair of registration rollers 19 until the optical sensor 133 detects the paper, and comparing this counted value with a preset reference value. This makes it possible to detect a gate that is misaligned in the X direction. When the positional deviation amount in the X direction and the 41+ or exposure lamp 4
The operation timing is controlled according to the amount of positional deviation in the X direction, and the copying operation described above is performed in step ST7. Therefore, the position at which an image is formed on the paper is changed depending on the amount of positional deviation of the paper, and the original image is formed at a predetermined position on the paper. In this way, the paper on which the original image has been copied is transferred to the paper output tray 2 in step ST8.
The paper is ejected at 5, and all processing is completed.

According to the above embodiment, the optical detection unit 130 detects the amount of positional deviation of the fed paper in the X direction and the ．． The copying operation is performed by appropriately controlling the exposure lamp 4. Therefore, even if a misalignment occurs in the fed paper, the original image can be copied at a predetermined position on the paper, and the quality of the copied image can be improved. Furthermore, when the cassette selection key 304 is selected, the optical detection unit 130 moves a predetermined portion of the optical sensor 733 to match the reference position Re of the selected paper. Therefore,
Even when the paper size is changed, it is possible to reliably detect paper misalignment.

In the above embodiment, the optical sensor 133 is composed of a plurality of light emitting elements 133a to 133d.
As shown in Figures (a) and (b), the CCD line sensor 140
You may also use With this kind of configuration,
Furthermore, it is possible to detect the amount of paper misalignment with higher accuracy.

It goes without saying that various other modifications can be made without departing from the gist of the invention.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to correct positional deviation regardless of the size of the transfer material, and image formation is possible in which a high-quality image can be formed. equipment can be provided.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of an image forming apparatus according to the present invention; FIG. FIG. 3(C) is a plan view showing the movement field of the optical detection unit; FIG. 2 is a diagram showing positional deviation detection and correction copying operations; FIG. 3(a) (b) shows another embodiment of the present invention, in which (a) is a perspective view showing an optical detection unit, (b) is a plan view showing the main part of (a), 4 and 5 show the configuration of the image forming apparatus, respectively. FIG. 4 is an external perspective view, FIG. 5 is a side sectional view, and FIG. 6 is a plan view showing the configuration of the operation panel. Fig. 7 is a perspective view showing the configuration of the drive section, Fig. 8 is a perspective view schematically showing the drive mechanism of the optical system, Fig. 9 is a perspective view schematically showing the drive mechanism of the pointer, and Fig. 10 is a perspective view schematically showing the drive mechanism of the optical system. FIG. 11 is a perspective view of the main parts showing the configuration of the magnification lens block. FIG. 11 is a diagram shown to explain the operation of the magnification lens block. FIG. Fig. 13 is a block diagram of the main processor group, Fig. 14 is a detailed block diagram of the first sub-processor, Fig. 15 is a block diagram of the second sub-processor, and Fig. 16 is a block diagram of the second sub-processor.
The figure is a schematic configuration diagram showing the control circuit of the pulse motor, No. 17.
The figure is a diagram for explaining a speed control method of a pulse motor. DESCRIPTION OF SYMBOLS 1... Main body, 2... Original table, 10... Photosensitive drum, 19... Registration roller pair, 30... Operation panel, 304... Cassette selection key, 71... Main processor Group, 130... Optical detection unit, 133
...Optical sensor, 138...Pulse motor, P...
・Paper. Applicant's representative Patent attorney Takehiko Suzue (C) Figure 1 Figure 2 (a) Figure 3 Figure 4

Claims (3)

[Claims] (1) A scanning means for optically scanning a document placed on a document table; a transfer means for transferring an image corresponding to the document image guided by the scanning means onto a transfer material; An image forming apparatus comprising a moving means for changing an image forming position, a setting means for setting the size of the transfer material, and a setting means provided near the transfer means and movable in a direction perpendicular to the moving direction of the transfer material. a detection means for detecting a positional deviation of the transferred material supplied as a transfer material; An image forming apparatus comprising: a control means for operating the moving means in accordance with an output signal and correcting a position at which an image is formed on a transfer material. (2) The image forming apparatus according to claim 1, wherein the detection means includes a plurality of light receiving elements. (3) The image forming apparatus according to claim 1, wherein the detection means comprises a CCD line sensor.