JPS6216959A - Image forming device - Google Patents

Abstract

PURPOSE:To correct the position of image forming with respect to a sheet by moving a magnification changing block in the direction right across the moving direction of No.1 carriage in accordance with output signal from a sensor. CONSTITUTION:Sheets P are fed from a sheet feed cassette selected, and the amount of dislocation 1X of each fed sheet P is sensed on the basis of the output signal from a photo-sensitive unit 130. Then a motor 67 is operated according to the second dislocation 1X, and a magnification changing lens block 8 is moved in the direction along the dislocation of the sheet P. In this condition, copying actions are carried out and when finished, it shall be judged whether multifolded or two-sided transcription is being specified. If the case is such, a two-side and multi-copying unit is operated, and if not, the copied sheet P is directly discharged to a tray.

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 the 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 fix it.

Generally, the paper fed from the paper cassette has ±3I
A positional deviation of about llIl may occur. However, in conventional copying machines, even if there is a misalignment in the supplied paper, it cannot be detected or corrected. There were times when the quality deteriorated.

[Purpose of the invention]

This invention was made based on the above circumstances,
The purpose is to provide an image forming apparatus that can prevent misalignment of a transfer material and can form high-quality images.

[Summary of the invention]

In the present invention, for example, in front of the registration roller, an optical detector is provided that is movable in a direction perpendicular to the paper moving direction and detects a positional shift of the supplied paper, and according to the output signal of this detector, The variable magnification lens block is moved in a direction perpendicular to the moving direction of the first carriage to correct the image forming position on the paper.

[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, such as a copying machine, according to the present invention. That is, 1 is a main body of a copying machine, and a document table (transparent glass) 2 is fixed to the upper surface of the main body 1 to support a document. 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 table 2 is exposed to an exposure lamp 4 and a mirror 5.
．． By reciprocating the optical system 6.7 in the direction of arrow a along the lower surface of the document table 2, exposure scanning is performed during the reciprocation. In this case, mirror 6.7 moves at half the speed of mirror 5 so as to maintain the optical exposure length. 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 mirrors 5, 6.7, passes through the variable magnification lens block 8, and then passes through the mirror 9. 92 and 93 and is 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 rotates in the direction of arrow C in the figure, and the surface is first charged by the charging device 11, and then the image is exposed to slit light to form an electrostatic latent image on the surface. This electrostatic latent image is made into a visible image by being deposited by image carriers 121 and 122 each containing, for example, red or black toner and selectively operated as required. ing.

On the other hand, the paper (transfer material) P is delivered from the selected upper paper feed cassette 131, middle paper feed cassette 132, or lower paper feed cassette 133 to the feed rollers 14+, 142.1.
43 and roller pairs 151, 152, 153, the paper guide paths 16+, 162, 163 take out the sheets one by one.
The image is guided through the image to a pair of registration rollers 17, and guided to a transfer section by the pair of registration rollers 17. Here, the paper feed cassettes 131, 132.1
33 is removably provided at the lower right end of the main body 1, and either one can be selected on the operation panel described later. In addition, each of the above paper feed cassettes 13r
, 132 and 133 are configured such that the cassette size is detected by cassette size detection switches 60t and 602 and 603, respectively. The cassette size detection switches 60r, 602, and 603 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 comes into close contact with the surface of the photoreceptor drum 10 at the transfer charger 18, so that the toner image on the photoreceptor drum 10 is transferred by the action of the charger 18. . This transferred paper P is transferred to the peeling charger 1
The transferred image is electrostatically separated from the photoreceptor drum 10 by the action of step 9, is conveyed by a conveyor belt 20, and is sent to a fixing roller 21 as a fixing device provided at the end of the conveyor belt. It will be established. Then, paper P after fixing
The sheet is placed on a tray 25 outside the main body 1 by a pair of delivery rollers 22, a partial gate 23 operated as shown by the solid line, and a pair of discharge rollers 24. After the transfer, the photosensitive drum 10 is returned to its initial state by removing residual toner on the surface with a cleaner 26 and erasing any afterimages with a static elimination lamp 27. Furthermore, 2
9 is a cooling fan for preventing the temperature inside the main body 1 from rising.

On the other hand, a double-sided multiple copying unit 28 is provided below the copying machine main body 1, which enables double-sided copying on one sheet of paper or multiple copies on the same side. This unit 28 includes a gate 23 for the above-mentioned sorting, a pair of paper ejection rollers 2
4, the scraper includes a plurality of roller pairs 28b that guide the sheets taken in by the gate 23 to the stacking section 28a.
, 28C128d are provided. Further, the stacking section 28a is provided with a delivery roller 28e that sends out the paper temporarily stored in the stacking section 28a. This delivery roller 28e can move up and down as shown by the arrow in the figure, depending on the thickness (number of sheets) of the stored paper. The paper sent out by the delivery roller 28ei passes through a separation roller pair 28f that separates the paper sheets one by one and sends them out to the control gate 28.
Guided by Q. When performing multiple copying, the control gate 28Q is rotated in the direction of the arrow M shown in the figure to guide the paper to the registration roller pair 17 via the paper guide path 281 of the transport roller pair 28h1.

Further, when double-sided copying is to be performed, the state shown in the figure is first set, and the paper is guided to the reversing section 28 via a pair of conveying rollers 28j. When the paper is stored in the reversing section 28k, the control gate 28G is rotated in the direction of arrow T in the figure, and the paper sent by the pair of transport rollers 28j is transferred to the pair of transport rollers 28.
The registration roller pair 1 via the h1 paper guide path 281
7.

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 section and paper jams; 304 is a cassette selection key for selecting upper, middle, and lower paper feed cassettes 131, 132, and 13B; 30s is a cassette selection key A cassette display section for displaying the selected cassette; 306 a magnification setting key for setting the magnification and reduction magnification of copies in a predetermined relationship; 307 a zoom key for steplessly setting the magnification and reduction magnification; 30a;
3 is a display section for displaying the set magnification; 30e is a density setting section for setting copy density; 30a is a multiple copy setting key; 3
0b is a double-sided copy setting key, 30C is a red designation key that specifies, for example, the developing device 121 containing red toner, and 30d
is a black designation key that designates, for example, the developing device 122 containing black toner.

FIG. 7 shows an example of the configuration of the drive source for each drive section of the copying machine configured as described above, and is composed of the following motors. That is, 31 is a lens motor, which is a motor for moving the position of the lens block 8 for changing the magnification.

32 is a mirror motor, which is a motor for changing the distance (optical path length) between the mirror 5 and the mirror 6.7 for changing the magnification. 33 is a scanning motor, which connects the exposure lamp 4, the mirror 5, and the mirror 6.
．． This is a motor for moving 7 for document scanning. 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. 351 and 352 are developing motors, respectively, and are motors for driving the developing rollers of the developing devices 121 and 122. 36 is a drum motor, which is a motor for driving the photosensitive drum 10. A fixing motor 37 is a motor for driving the paper conveying path 20 and the pair of fixing rollers 21. 38 is a paper feed motor, which is a motor for driving the delivery rollers 141 to 143. Reference numeral 39 denotes a paper feed motor, which is a motor for driving the registration roller pair 17. 40 is a fan motor, which is a motor for driving the cooling fan 29; 401 is a roller pair 24.28b;
, 28c, 28d, etc.

FIG. 8 shows a drive mechanism for reciprocating the optical system. That is, the mirror 5 and the exposure lamp 4 are connected to the first carriage 41! The mirrors 6, 7 are each supported by a second carriage 422, and these carriages 411, 412 are guided by guide rails 421, 422 and are movable in parallel in the direction of arrow a. That is, the four-phase pulse motor 33 drives the pulley 43. An endless belt 45 is stretched between the pulley 43 and the idle pulley 44, and a first carriage 41 that supports the mirror 5 is placed in the middle of the belt 45! - end is fixed. On the other hand, a second carriage 422 supporting the mirror 6.7
The guide portion 46 includes two grooves spaced apart in the axial direction of the rail 422.
Two pulleys 47.47 are rotatably provided, 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 50. Further, one end of a first carriage 411 is fixed to a midway portion of the wire 48. therefore,
As the pulse motor 33 rotates, the belt 45 rotates and the first carriage 41! moves, and the second carriage 422 also moves accordingly. At this time, since the pulleys 47, 47 serve as movable pulleys, the second carriage 422 moves in the same direction as the first carriage 411 at 1/2 the speed. Note that the first and second carriages 4
The direction of movement of the motors 11 and 412 is controlled by switching the direction of rotation of the pulse motor 33.

Further, on the document table 2, a copyable range corresponding to the specified paper is displayed. That is, if the paper size specified by the paper selection key 304 is (Px, Py) and the copy magnification specified by the magnification setting keys 30s and 307 is K, then the copyable range (x, y), rx=Px/
KJ, ry-Py/KJ. This copyable range (x
. It has become.

As shown in FIG. 9, the above-mentioned pointers 51 and 52
．． 55 via a spring 56. The pulley 55 is a motor 58
This motor 58
The distance between the hands 51 and 52 can be changed by rotating the hands according to the paper size and magnification.

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. Then, when the copy key 301 is pressed, the first
The carriage 411 is first moved toward the second carriage 412, and then the lamp 4 is turned on and the carriage 411 is moved away from the second carriage 412. When scanning of the original is completed, the lamp 4 is turned off and the first carriage 411
is returned to the home position.

FIG. 10 shows a driving PiM structure of the variable magnification lens block 8. The motor 31 is connected to the first carriage 4
A lead screw 61 disposed along the moving direction (X direction) of 11 is rotated. Bushes 631 and 632 provided at one end of the substrate 62 are screwed into this lead screw 61, and when the lead screw 61 is rotated, the substrate 62 is moved in the X direction.

A guide member 621 is provided at the other end of the substrate 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 is provided, and this support 65z, 652
are guided and held by guide members 66r and 662 provided on the substrate 62. Further, a rack 653 is provided on the longitudinal side surface of the support body 65, and a pinion 68 rotated by a pulse motor 67 provided on the base plate 62 is meshed with this rack 653. Therefore, the lens block 8 for variable magnification is controlled by the motor 6.
7 is driven, it is moved in the X direction. Note that the microswitches 691 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 variable magnification lens block 8 and the image formed will be explained. In FIG. 11(a), the focal length of the variable magnification lens block 8 is f, and the optical path length from the document table 2 to the variable magnification lens block 8 is ya1. Assuming that the optical path length is yb and the total optical path length from the document table 2 to the photosensitive drum 1o is yc, the optical formula is expressed as follows.

1/f=1/ya+1/yb Also, the magnification is expressed as yb/ya. Since the focal length of the variable power lens block 8 is constant, it can be seen that in order to focus during variable power, it is necessary not only to change the total optical path length yc 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 x 2 expressed by the following equation.

X2 = Xt xyb/ya Furthermore, in the case of a same-size copy, it becomes x2"2Xt. 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, in which the main processor group 71 and the first . 2nd subprocessor group 72.73
It is mainly composed of. The main processor group 71 includes an operation panel 30 and various switches and sensors such as the cassette size detection switches 60r and 602.60.
A high-voltage transformer 76 that detects input from an input device 75 such as a, and drives the various chargers, and the static elimination lamp 27.
, the blade solenoid 26a of the cleaner 26, the heater 21a1 of the fixing roller pair 21, the exposure lamp 4,
In addition to controlling the motors 31 to 40, 58, and 67 to perform the copying operation described above, the light emitting element 132, the light receiving element 133, and the pulse motor 138 of the optical detection unit 130 are used to detect paper misalignment. is detected, and an operation is performed to adjust the image forming position on the paper according to the detected state. Note that details of the optical detection unit 130 and the like will be described later.

Among the above motors 31 to 40,58,67, motor 35
1.352.37, 40.401 and phenomenon device 121.
Toner motor 77.771 that supplies toner to 122
is connected to the main processor group 7 via the motor driver 78.
1, the motors 31 to 34.67 are controlled by the first sub-processor group 72 via a pulse motor driver 79, and the motors 36, 39 and 38.58 are controlled by the second sub-processor group via a pulse motor driver 80. It is controlled by a processor group 73. In addition, the exposure lamp 4 is connected to a lamp regulator 8.
The heater 21a is controlled by the main processor group 71 via the heater control section 82. Then, from the main processor group 71, the first. Commands to drive and stop each motor are sent to the second sub-processor group 72, 73, and the first. A status signal indicating the drive/stop state of each motor is sent from the second sub-processor group 72, 73 to the main processor group 71. The first sub-processor group 72 also includes motors 31 to 34.
．． Position information from a position sensor 83 that detects each initial position of 67 is input.

FIG. 13 shows an example of the configuration of the main processor group 71. That is, 91 is a one-chip microcomputer (hereinafter simply referred to as microcomputer), which detects human input of keys on an operation panel (not shown) and controls various displays via an input/output board 92. Furthermore, the microcomputer 91 is expanded by input/output ports 93-96. A high voltage transformer 76, a motor driver 78, a lamp regulator 81, and other outputs are connected to the input/output boat 93. A size switch for detecting paper size and other human power are connected to the input/output boat 94. 95 is connected to a copy condition setting switch and other human power.

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. That is, 101 is a microcomputer, which is connected to the main processor group 71. 102 is a programmable interval timer for controlling the phase switching interval time of the pulse motor, and when a set value is set from the microcomputer 101, it counts based on it, and when it has counted out, it sends an end pulse to the interrupt line of the microcomputer 101. Output. A reference clock pulse is input to the timer 102. Further, the microcomputer 101 receives position information from the position sensor 83, and input/output board 103.1.
04 is connected. And the input/output boat 10
4 are 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 group 71.

FIG. 15 shows the configuration of the second sub-processor group 73. That is, 111 is a microcomputer, which is connected to the main processor group 71. Numeral 112 is a programmable interval timer for controlling the phase switching interval time of the pulse motor, and when a set value is set by the microcomputer 111, it counts based on the set value, and outputs an end pulse when the count is out. This termination pulse is latched by the latch circuit 113, and its output is
11 interrupt lines and I/O port input lines. Further, an input/output boat 114 is connected to the microcomputer 111, and a motor 36, 38, 39 is connected to this input/output boat 114 via the pulse motor driver 80.
．． 58 are connected.

Figure 16 shows the control circuit of the pulse motor, and shows the input/output boat 121 (input/output boat 1 in Figures 14 and 15).
04.114) has a pulse motor driver 122
(Equivalent to pulse motor driver 79.80 in Figure 12)
A pulse motor 123 (the pulse motors 31 to 34, 36, 3) is connected to this pulse motor driver 122.
8.39.58.67.138) windings A and B
, A, and B are connected.

Figure 17 shows a method for controlling the speed of a pulse motor.

Figure (a) shows the speed curve of the pulse motor, and Figure (b) shows the speed curve of the pulse motor.
) indicates the phase switching interval. As is clear from this figure, the phase switching interval is initially long, gradually shortens, eventually becomes equal, becomes gradually longer 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. Furthermore, tl, t2...
-tx indicates the phase switching interval time.

Next, main parts of the present invention will be explained. In this embodiment, it is possible to correct paper misalignment. That is,
As shown in FIG. 1, the optical detection unit 130 is provided between the pair of registration rollers 17 described above and the photosensitive drum 10 (not shown) for detecting a lateral positional deviation of the sheet P.

This optical detection unit 130 has a substantially U-shaped case 1.
31, and inside this case 131, for example, paper P
It is composed of a light emitting element 732 and a light receiving element 133, which are arranged at a predetermined interval M in a direction perpendicular to the front and back sides of the screen. The case 131 is movably provided on a guide shaft 134 disposed along the registration roller pair 17, and the case 131 is fixed to a timing belt 135 disposed along the guide shaft 134. . This timing belt 135 is connected to the pulley 136.1
37 pulleys, of which 13 pulleys
7 is adapted to be driven by a pulse motor 138. Therefore, when the motor 138 is driven, the optical detection unit 130 is moved along the guide shaft 134.

In FIG. 1, the pair of registration rollers 17 and the guide shaft 134 are shown separated, but the mutual distance yp
is extremely narrow.

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

As shown in FIG. 2(a), when the cassette selection keys 131, 132, and 133 of the operation panel 30 are operated, the light receiving element 133 of the optical detection unit 130 detects It is moved to the inner position, and that position lxQ is used as the reference. In this case, IXO>maximum paper misalignment amount.

In this state, first, the paper P is moved to the registration roller pair 1.
7 and when the leading edge of the paper P is detected by the light receiving element 133, the motor 138 is driven under the control of the main processor group 71, and the optical detection unit 13
0 is moved in the direction of the force shown by the arrow xd. And the same figure (b
), the side edge of the paper P is detected by the light receiving element 133. The paper P may be stopped when its leading edge is detected, but it may be necessary to continue feeding the paper P as it is, or to
), as shown by yl, it is more convenient to advance the paper a little to detect the side edges of the paper. The positional deviation amount IX detected in this way in the direction orthogonal to the moving direction of the paper P is lx-lxlo-lxa, where lxa is the distance from the reference position IXO to the side edge of the paper.

Further, when the paper size is changed from Pa to Pb as shown in FIG. 2(C), the reference position of the light receiving element 133 is moved from lxg to lxl. The amount of movement S at this time is S - (xa-xb)/2, where Xa is the width of the paper Pa, xb is the width of the paper Pb, and assuming that these papers are fed centering on the center CT. At this position, paper misalignment is detected by the same operation as described above.

Next, a copying operation using the optical detection unit 130 and the variable magnification lens unit 8 will be explained. For example, the cassette selection keys 131 and 132 on the operation panel 30
．． 133 and then presses the copy key 301, the main processor group 71 performs operational control according to the flowchart shown in FIG. That is, in step $1, paper P is fed from the selected paper feed cassette, and in step S2, the positional deviation llx of the fed paper P is detected based on the output signal of the optical detection unit 130. Ru.

Thereafter, in step S3, the motor 67 is driven according to the detected positional deviation amount 1x, and the variable magnification lens block 8 is moved in the direction along the deviation of the paper P.

In this state, a copying operation is performed in step S4, and when the copying operation is completed, it is determined in step S5 whether multiple copying or double-sided copying is set, and if these are set, step S6 Control is transferred to In this step S6, the double-sided multiple copying unit 28 is operated, and the copied paper P is stored in the double-sided multiple copying unit 28.

After that, for example, another original is set on the original platen 2,
When the copy key 301 is pressed, the double-sided multiple copy unit is operated, and the paper P contained therein is again supplied to the transfer section. Then, control is transferred to step S2, and the above-described operations are repeated. On the other hand, the step S
If it is determined in step S5 that multiple copying or double-sided copying is not set, the control moves to step S7, the copied paper P is ejected to the tray 25, and the operation ends.

According to the above embodiment, the optical detection unit detects the lateral positional deviation Ilx of the fed paper P, moves the magnification changing lens block 8 in accordance with this positional deviation amount 1x, and performs the copying operation. I try to do this. therefore,
Even if a misalignment occurs in the fed paper, an image can be formed at a predetermined position on the paper, and the quality of the copied image can be improved.

Particularly, when multiple copies are made using this function, it is possible to prevent positional deviations between the two images, so that the quality of the copied images is good.

In the above embodiment, the positional deviation in the direction perpendicular to the sheet feeding direction has been described, but for example, after the sheet feeding rollers 141 to 143 are operated, the optical detection unit 1
The time until the leading edge of the paper is detected is measured by the light receiving element 133 of 30, the time difference between this measured time and a preset reference time is determined, and the scanning timing of the original is determined according to the determined time difference. By controlling this, it is possible to correct positional deviations corresponding to the moving direction of the paper.

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

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide an image forming apparatus that can prevent positional shift of a transfer material and can form a high-quality image.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of an image forming apparatus according to the present invention, and shows a perspective view of the main parts showing an optical detection unit;
FIG. 2 is a plan view of the main parts shown to explain the sheet misalignment detection operation, and FIG. 3 is a diagram shown to explain the operation.
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. 12 is a configuration diagram showing the overall control circuit, and FIG. 13 is a block diagram showing the main processor group, FIG. 14 is a block diagram showing the first sub-processor group, FIG. 15 is a block diagram showing the second sub-processor group,
Figure 6 is a schematic configuration diagram showing the control circuit of the pulse motor.
FIG. 17 is a diagram for explaining the speed control method of the pulse motor. DESCRIPTION OF SYMBOLS 1... Main body, 2... Original table, 8... Lens block for variable magnification, 10... Photosensitive drum, 121.122.
...Developer, 17...Register roller pair, 28...
Double-sided multiple copy unit, 30...operation panel, 71.
...Main processor group, 130... Optical detection unit, 132... Light emitting element, 133... Light receiving element. Applicant's agent Patent attorney Takehiko Suzue Figure 1■ 1-1---1 (a) Figure 2 (C) Figure 2vA Figure 3 4fJjJ Figure 7 9 Figure 10r! A

Claims (2)

[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; In an image forming apparatus comprising a moving means for changing an image forming position, the apparatus is provided near the transfer means and is movable in a direction perpendicular to the moving direction of the transferred material, and detects a positional shift of the supplied transferred material. 1. An image forming apparatus comprising: a detection means for detecting; and a control means for operating the moving means in accordance with an output signal of the detection means to correct 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 comprises a light receiving element.