JP3262490B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an apparatus having a function of correcting an image position.

[0002]

2. Description of the Related Art As this type of apparatus, there is known an apparatus which forms a color image using a laser beam. FIG. 6 is a diagram showing a configuration of a main part of this type of apparatus.

In FIG. 1, a laser beam emitted from a laser light source, which will be described later, is bidirectionally scanned by a rotating polygon mirror 103 rotating in a direction indicated by an arrow B in the figure to obtain cyan (C),
The scanning lines 102C, 102M, and 1 pass through fθ lenses (described later) respectively corresponding to magenta (M), yellow (Y), and black (BK), and pass through the fθ lenses.
The photosensitive drums 101C, 101M, 101Y, 101BK rotate in the direction of arrow A in FIG.
Images are formed thereon, and these images are multiplex-transferred onto the transfer material 105 conveyed in the direction of the arrow X in the figure to form a multiplex image. Reference numeral 13 denotes a transfer belt, and 31 denotes a transfer belt driving roller. 6C-8C, 6M-8M, 6Y-
8Y, 6BK to 8BK are reflection mirrors (mirrors).

In an apparatus having a plurality of image forming stations as described above, images of different colors are sequentially transferred onto the same surface of the same transfer material 105. Therefore, if the transferred image position in each image forming station deviates from the ideal position. For example, in the case of a multi-color image, image intervals of different colors are shifted or overlapped, and in the case of a color image, a difference in tint appears, and when the degree is more severe, a color shift appears, and the image quality is reduced. It had significantly deteriorated.

FIG. 7 is a view for explaining the types of positional deviation of the transferred image in the image forming apparatus shown in FIG.

As shown in FIGS. 7A to 7D, the type of the positional deviation of the transferred image is the positional deviation (top direction) in the scanning line writing (sub-scanning) direction (direction A in the figure). Margin (see FIG. 7A), misalignment (left margin) in the main scanning direction (B direction perpendicular to the A direction in the figure) (see FIG. 7B), and inclination shift in the oblique direction (see FIG. 7B). 7
(C) of FIG. 7), a magnification error deviation (see (d) of FIG. 7), and the like. The cause of the above-mentioned shift will be described below.

FIG. 8 is a plan view of an exposure unit of the multiplex image forming apparatus shown in FIG. 9, and shows the photosensitive drums 101M and 101 in FIG.
The scanning lines 102M and 102Y on 01Y are developed on the same plane. The scanning lines 102C and 102BK
Are omitted because they are the same as the scanning lines 102M and 102Y on a plane.

In FIG. 8, reference numeral 401 denotes an optical table on which one optical system is arranged in two directions (a direction in which M and C drums are provided and a direction in which Y and BK drums are provided). Are mounted with cyan and magenta laser light sources 402C and 402M, an fθ lens 403, and the like. Reference numeral 404 denotes a lens base as an optical base on which the other optical system of the two directions is disposed, and yellow and black laser light sources 402Y, 402BK, fθ lens 4
05 etc. are attached. These lens mounts 40
1, 404 are held on a base 406 as a support together with a motor housing 415 made of metal such as aluminum in which the rotary polygon mirror 103 is accommodated.
06 is positioned on the apparatus main body 407 and has three screws 4.
Mounted at 10.

Then, the two-way bidirectional optical system, that is, the optical central axes 41 of the fθ lenses 403 and 405, respectively.
Reference numerals 1 and 412 are arranged so as to coincide with the respective optical centers 413 and 414 in both directions on the reflection surface of the rotary polygon mirror 103. Further, the lens mounts 401 and 404 can rotate the optical centers 413 and 414 in the same plane in the direction of the center a and adjust the one-side magnification of each of the scanning lines 422M and 422Y, and then use the three screws 409C and 409Y respectively. It is fixed to the base 406 at an arbitrary position.

When the apparatus operates in such a configuration, the rotating polygon mirror 103 in the motor housing 415 is rotated at a high speed by a motor (not shown).

Further, laser light sources 402C, 402M,
Laser drivers 408C, 408M, 408Y, 4 which are electric boards for blinking 402Y, 402BK
A current flows through 08BK. These motors and laser drivers are heat sources, and are provided with lens bases 401 and 404, base 4
06 will be heated and each will be heated.

However, the exposed portion does not extend uniformly due to a temperature gradient between a place close to and a place far from the heat source. Therefore, vertical displacements, that is, warpage, are generated on the lens mounts 401, 404 and the base 406. . When such a warp occurs, the scanning position of the scanning line on the photosensitive drum changes, and the scanning accuracy decreases. Hereinafter, the process of the reduction will be described with reference to FIG.

FIG. 9 is a cross-sectional view of a principal part for explaining the configuration around the rotary polygon mirror 103 shown in FIG.

It should be noted that a base 406 is provided to simplify the description.
Does not change, and only the lens mount 401 changes.

In FIG. 9A, as described above, in the lens mount 401, the position fixed by the screw 409 does not move and the vicinity of the center is curved in the vertical direction, that is, the Z direction. Lens stand 4
When the laser beam 01 is curved, the surrounding laser mounting portion is also deformed, and the irradiation direction of the laser beam is changed.
The reflection position of the laser beam at the position changes from the position (1) to the position (2). The reflection position on the rotating polygon mirror 103 is the position (2)
, The scanning position changes from position (3) to position (4) as shown in FIG. 9B.

When the scanning position changes as described above, the image writing position changes, and the scanning line curvature also increases. In a color printer that obtains a color image by repeatedly scanning a plurality of laser beams to obtain a color image, these changes appear in the image as color misregistration and color change, which significantly degrades image quality.

FIG. 10 is a schematic sectional view for explaining the laser scanning system of the image forming apparatus shown in FIG. 6, and FIG. 11 is a sectional view showing the photosensitive drums 101C, 101M, 101 shown in FIG.
FIG. 9 is a cross-sectional view of a main part showing a Y, 101BK and image transfer position shift.

In the image forming apparatus constructed as shown in FIG. 10, when the temperature of each part in the apparatus rises with the use of the apparatus, the transfer belt driving roller 31 moves the transfer belt driving roller 31 in accordance with the coefficient of linear expansion, the diameter and the amount of temperature rise of the material. The diameter increases. Since the transfer belt driving roller 31 rotates at a constant angular speed, the moving speed v of the transfer belt 13 increases by Δv. That is, the transfer belt 13 moves by v + Δv. Then, the top margin changes as shown in FIG.

As shown in FIG. 11, the photosensitive drum 101
C, 101M, 101Y, and 101BK are arranged at regular intervals. In this case, the transfer belt 1
If the moving speed of the photosensitive drum 3 is the regular moving speed, the photosensitive drum 1
Position C where image is transferred to transfer material 105 at 01C
Although the images of the other stations should overlap each other, since the speed of the transfer belt 13 is high, the image is transferred to the position M which is later than the position C on the photosensitive drum 101M.

Similarly, the photosensitive drums 101Y and 101BK
Are also transferred to the delayed positions Y and BK as shown in FIG. That is, a top margin shift of the delay level (plus level) occurs. Next, when the temperature of each part rises as the apparatus is used, the position of the side plate supporting the photosensitive drum shaft changes as shown in FIG. 11 according to the linear expansion coefficient and the size of the material and the amount of temperature rise.

FIG. 12 shows the photosensitive drum 10 shown in FIG.
FIG. 3 is a cross-sectional view of main parts showing image transfer position deviations from 1C, 101M, 101Y, and 101BK.

As shown in this figure, when the temperature of each part rises with the use of the apparatus, the position of the side plate supporting the photosensitive drum shaft also changes according to the linear expansion coefficient and size of the material and the amount of temperature rise. For example, considering the photosensitive drum 101C as a reference,
Photosensitive drums 101C, 101M, 101Y, 101BK
In this order, the positional change amounts (△ L, 2 △ L, 3 順 に L) increase. Then, since the transfer material 105 moves at a constant speed v, the transfer position of the image to be transferred is advanced with respect to the position C by each of the transfer positions M, Y, and BK. As a result, the top margin deviation of the advanced level (minus level) is obtained. Occurs.

On the other hand, when the side plate of the housing thermally expands in the same manner as described above, the position of the reflection mirror supported by the side plate also changes as shown in FIG.
Changes as shown in FIG.

FIGS. 13 and 14 are cross-sectional views of the main parts showing the image transfer position deviation from the photosensitive drums 101C, 101M, 101Y and 101BK shown in FIG.

As shown in this figure, when the side plate of the apparatus housing thermally expands in the same manner as described above, for example, in the x direction (paper transport direction), for example, with reference to the photosensitive drum 101C,
Since the mirror positions of all stations change, the optical path length changes. The amount of change depends on the photosensitive drum 10
It is determined by the distance from 1C and is not constant.

Further, if the side plate of the apparatus housing thermally expands in the same manner as described above, for example, if the position changes in the y direction (the direction orthogonal to the sheet conveying direction), the position of the mirror changes. Drums 101C, 101M, 101
The laser beam irradiation position on Y, 101BK changes,
As a result, a magnification shift and a top margin shift occur. In addition, since the amount of displacement of the top margin is not equal between the front side and the back side of the apparatus, inclination displacement and left margin displacement also occur.

The following methods have been considered to correct the above-described four types of deviations.

FIG. 15 is a schematic perspective view of a main part for explaining a registration correcting mechanism of this type of image forming apparatus, and FIG.
FIG. 16 is a schematic diagram illustrating a registration correction state corrected by the registration correction mechanism illustrated in FIG. 15.

With respect to the top margin and the left margin, the shift timing is corrected by electrically adjusting the scanning timing of the scanning lines 102C, 102M, 102Y, and 102BK.
For a magnification error shift and a tilt shift, the mirrors 6 and 7 are paired at right angles, and a pair of mirrors having a substantially C-shape is shown in FIG.
As shown in FIG.
The shift amount can be corrected by independently adjusting the directions.

As adjustment means for performing these adjustments, actuators 27 to 29 such as linear step actuators having a step motor as a drive source that moves linearly stepwise are provided. Here, the actuator 27 is moved substantially parallel to the direction of the arrow E1 in FIG. 10, the optical path length is reduced to above the photosensitive drums 101C, 101M, 101Y, and 101BK, and the actuator 27 is driven in the direction of the arrow E2 in FIG. The optical path length can be adjusted to be long.

As described above, by adjusting the optical path length, the scanning lines 102C, 102C having a predetermined spread angle are provided.
M, 102Y, 102BK photosensitive drums 101C, 10
The length on the surface of 1M, 101Y, 101BK can be changed from the scanning line m0 to the scanning line m1, for example, as shown in FIG.

Further, by simultaneously driving the actuators 28 and 29 in the same direction, for example, in the direction of arrow F2 in FIG. 16, the pair of mirrors 6 and 7 are parallel to the direction F which is a direction substantially perpendicular to the direction E. 16 which has been moved.
(B) can be moved to the position of the scanning line m2.

When one of the actuators 28 and 29 is moved, or when the actuators 28 are driven in opposite directions to move the actuator 28 in the direction of arrow F1 and the actuator 29 in the direction of arrow F2, The inclination angle of the scanning line m0 in FIG. 16C can be changed like the scanning line m3.

As described above, the mirrors 6, 7 in which a pair of mirrors are assembled at a substantially right angle are provided in the optical path of the scanning lines 102C, 102M, 102Y, 102BK from the scanning optical device to the photosensitive drums 101C, 101M, 101Y, 101BK. And by adjusting the positions of the pair of mirrors 6 and 7 by the actuator 27 or the actuators 28 and 29, the optical path length or the scanning lines 102C and 102C are adjusted.
The scanning positions of M, 102Y, and 102BK can be independently adjusted.

That is, by moving a pair of mirrors 6, 7 arranged in a C-shape in the direction E, the photosensitive drum 1 is moved.
The scan lines 102C, 102M, 1Y, and 102BK imaged on 01C, 101M, 101Y, and 101BK are not changed and the scan lines 102C, 102M, 1
02Y and 102BK can be corrected, and by moving the pair of mirrors 6 and 7 in the F direction, the scanning lines 102C, 102M, 102Y and 102
Without changing the optical path length of the BK, the photosensitive drum 101C,
It is possible to correct the imaging positions (top margins) and angles on 101M, 101Y, and 101BK.

[0036]

As described above, this type of image forming apparatus has a function of correcting an image position shift due to a shift of a scanning line.
Normally, a registration mark is formed on the transfer belt 13 and read by a CCD image sensor, the amount of deviation of each registration mark from a specified position is calculated, and the positional deviation of the image is corrected based on the calculated amount of deviation. .

Therefore, while the correction operation is being performed, the normal image forming sequence must be stopped, and the deviation characteristics caused by the above-described expansion of the heat source including the scanner system and its surroundings are ignored. When the registration correction is performed, the number of corrections is rather increased, giving a wasteful waiting time to the user, and there is a problem that an image without color shift cannot be continuously formed.

In view of the above problems, an object of the present invention is to make it possible to execute an operation for correcting a positional shift of an image at an optimal timing.

Another object of the present invention is to make it possible to continuously form an image without a position shift by minimizing the number of times of execution of the position shift correction operation.

[0040]

In order to solve the above problems and achieve the object, the present invention provides an image forming means for forming an image on a recording medium and a position of the image formed on the recording medium. Correcting means for correcting, and the image forming means
Exposure unit for exposing the image carrier, and a temperature near the exposure unit
First detecting means for detecting the
A second mode for detecting the internal temperature of the device, a first mode in which the correcting unit performs the correcting operation at predetermined intervals that sequentially change, and a second mode in which the correcting operation is performed at regular intervals. And an output of the first and second detection means.
And control means for determining the mode in accordance with

[0041]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic perspective view illustrating the structure of an image forming apparatus according to an embodiment of the present invention, and FIG.
FIG. 3 is a sectional view of a main part of the exposure unit shown in FIG. The same components as those in FIG. 6 are denoted by the same reference numerals.

In these figures, SEN1 and SEN2
Is a temperature sensor composed of a thermistor or the like. The temperature sensor SEN1 is installed near the rotary polygon mirror driving motor, which is the maximum heat source, and detects the exposure unit temperature (temperature) T1. Specifically, in this embodiment, the temperature of the housing 415 is measured. Then, the temperature data is fetched via an A / D converter (not shown) of the controller CONT. The controller unit CONT includes a CPU, RAM, and RO (not shown).
M is provided to control each part comprehensively. That is, the control signals L1 to L4 control the transmission timing of the enable signal for determining the scanning area of the laser beam in each image forming station, and the actuators 27 to 29 shown in FIG. Control.

On the other hand, the temperature sensor SEN2 is installed in a place where a heat source is relatively small inside the apparatus (for example, FIG. 10).
Above the registration roller R), the internal temperature (temperature) T
2 is detected. Then, the temperature data is fetched via an A / D conversion unit (not shown) of the controller unit CONT.

In this embodiment, as described above,
The positional deviation of the image is corrected using the mechanism shown in FIG.

Further, as described above, a registration mark is formed on the transfer belt, and the registration mark is read and read.
With respect to the method of calculating the amount of displacement of each image, the method disclosed in Japanese Patent Application Nos. Hei 4-23348 and Hei 4-203971 can be applied.

In the image forming apparatus configured as described above, the temperature difference ΔT between the above-mentioned temperature T1 and temperature T2 (T2-T
1) The value is small when the whole device is cold,
ΔT = Δ when the exposure unit and the entire device are thermally expanded by the heat source (mainly a polyhedron drive motor) by operating the device body.
This is a large value of Tmax (about 15 deg).

As described above, the various scanning deviation phenomena (scanning line magnification error, inclination deviation, top margin deviation, left margin deviation) increase in proportion to the temperature difference ΔT. In particular, the above-mentioned top margin shift amount becomes the largest as shown in FIG.

FIG. 3 is a characteristic diagram for explaining the top margin deviation amount based on the temperature difference by the temperature sensor shown in FIG. 1. The vertical axis indicates the top margin deviation amount, and the horizontal axis indicates the time after power-on. Show.

As shown in this figure, when the power is turned on, the exposure section is heated and the top margin shifts by shifting the scanning line as shown in FIG. The increase in the deviation is larger when the temperature difference ΔT is small, and becomes smaller immediately before the temperature difference ΔT is saturated. That is, when the temperature difference ΔT is small, the shift of the scanning line is large with the passage of time, and the image quality is significantly deteriorated with the passage of time.

Therefore, in the present embodiment, the degree of change of the image shift amount with respect to the lapse of time is considered, and
The controller unit CONT executes an operation for correcting a positional shift of an image according to the flowchart shown in FIG.

FIG. 14 is a flowchart for explaining the registration correction processing operation of the apparatus of FIG.

Hereinafter, the CP using the flowchart of FIG.
The operation of U will be described.

First, when the power is turned on (step S1)
01), time measurement by the internal timer TM of the controller unit CONT is started (step S102). Predetermined time Δ
At the time point when t1 has elapsed (step S103), the temperature difference ΔT is obtained from the detection results of the temperature sensors SEN1 and SEN2.
Is derived, and the temperature difference ΔT is equal to the reference temperature difference ΔT0 (in the present embodiment, the reference temperature difference ΔT0 is set to be about 5 deg lower than the maximum temperature difference ΔTmax, for example, about 10 deg)
It is determined whether it is below (step S104). As a result, if ΔT is equal to or smaller than ΔT0, it is determined that the scan line shift corresponds to a time zone as described above, and the above-described correction operation is performed (step S105).

In this embodiment, the reference temperature difference ΔT
0 is set lower than ΔTmax because of the temperature measurement error,
This is in consideration of variations between devices. When the predetermined time Δt1, Δt2,... Has elapsed, the above operation is repeated. In this embodiment, the predetermined time Δt1, Δt
2,..., Δt1 = 0 minutes, Δt2 = 10 minutes,
Δt3 = 30 minutes, Δt4 = 60 minutes, Δt5 = 9
0 minutes, Δt6 = 120, and thereafter S10 every 120 minutes
Steps 3 to S105 are repeated. This is because the shift operation of the scanning line is large immediately after the power is turned on, so that the correction operation is frequently performed. Further, as the elapsed time becomes longer, the degree of change of the shift amount with the elapse of time becomes smaller, so that the number of executions of the correction operation can be reduced.

On the other hand, the temperature difference ΔT is equal to the reference temperature difference ΔT0
If T> ΔT0, the scanning line deviation has already disappeared and the correction operation is not performed, so that the image forming apparatus main body is continuously usable.

Further, when the power switch is turned off and then turned on again in a state where the apparatus is sufficiently warmed (there is no displacement of the scanning line), that is, the time from when the power switch is turned off to when it is turned on. Is shorter, ΔT> ΔT0 even when the temperature in the apparatus is Δt1 = 0, and
Since there is no scanning deviation and no correction operation is performed, the image forming apparatus can be used immediately in a good state.

If the time from when the power switch is turned off to when it is turned on is long, the temperature inside the device may also decrease, and ΔT <ΔT0 may be satisfied. At this time, although the scanning lines are shifted, the above steps (S104 and S105) are repeated and the correction operation is performed, so that the scanning lines are not shifted and a good image is obtained.

On the other hand, if the determination in step (S104) is NO,
In other words, if the temperature difference ΔT is larger than the reference temperature difference ΔT0, the correction operation is performed at regular intervals ta (120 minutes in this embodiment) (step S10).
7) It is possible to correct even a slight shift of the scanning line.

As described above, in the present embodiment, the difference between the outputs of the respective sensors is detected in response to the lapse of the predetermined time, and whether or not to execute the correction operation is determined based on the difference. In addition, the number of executions of the registration correction operation can be minimized.

Accordingly, good images can be continuously formed.

Next, another embodiment of the present invention will be described.

FIG. 5 is a flowchart for explaining the operation of the controller unit in this embodiment.

First, when the power is turned on (step S2)
01), a temperature difference ΔT is calculated from the measurement data detected by each of the temperature sensors SEN1 and SEN2, and it is determined whether or not the temperature difference ΔT is equal to or smaller than a reference temperature difference ΔT0 (step S202). Note that also in the present embodiment, the reference temperature difference ΔT0 is 5 deg lower than the maximum temperature difference ΔTmax.
For example, in FIG. 3, ΔTmax = 5 deg.
It is set to about 10 deg, which is a low deg. This reference temperature difference ΔT0 can be changed as appropriate according to the internal temperature condition unique to each device.

Here, when ΔT is equal to or smaller than ΔT0, as described above, it is considered that the degree of change in the amount of displacement of the image with respect to the lapse of time thereafter is large, and ΔT is equal to ΔT0.
If it is larger, it is considered that the degree of this change is small.

Therefore, in the present embodiment, the temperature difference ΔT is measured, for example, during warm-up of the apparatus after the power is turned on, and when the temperature difference is small, the correction operation is frequently performed.

That is, when ΔT is equal to or smaller than ΔT0 in step S202, a timer operation is started (step S203), and when a predetermined time t1 has elapsed (step S204), each image forming operation is started as described above. The amount of misregistration between images formed by the stations is calculated, and a misregistration correction operation is performed (step S20).
5).

The predetermined time Δt1, Δt
The above operation is repeated at the point when 2 ... has elapsed. Also in the present embodiment, the predetermined times Δt1, Δt2,.
t1 = 0 minutes, Δt2 = 10 minutes, Δt3 = 30 minutes, Δt4 = 60 minutes, Δt5 = 90 minutes, Δt
6 = about 120 minutes, and thereafter, every 120 minutes S204,
S205 is repeated. That is, immediately after power-on, Δ
When T is equal to or less than ΔT0, the degree of change in the amount of deviation of the scanning line with the passage of time increases, and the correction operation is frequently performed. Further, as the elapsed time becomes longer, the degree of change of the shift amount with the elapse of time becomes smaller, so that the number of executions of the correction operation can be reduced.

When the temperature difference ΔT is larger than the reference temperature difference ΔT0, the scanning line shift is already eliminated by the correction operation before that and the correction operation is not performed, so that the image forming apparatus main body is continuously used. It is possible.

That is, it is possible to continuously form a good image without any positional displacement.

On the other hand, in step S202, ΔT becomes Δ
If it is greater than T0, the timer starts counting time (step S206), and after a certain time interval ta (ta = 120 minutes in this embodiment) elapses (step S2).
07), the above-described correction operation is performed.

That is, for example, in a state where the apparatus is sufficiently warmed as described above (a state where there is no shift of the scanning line),
When the power switch is turned off and then turned on again, the temperature inside the apparatus is ΔT> ΔT0 even when Δt1 = 0.
It has become.

In this case, it is considered that the degree of change in the positional deviation of the scanning line with the passage of time is small, so that steps S206 to S208 are repeated after the power is turned on, and the sequence is relatively smaller than the sequence of steps S204 and S205. By executing the correction operation at long intervals, even a slight shift of the scanning line can be corrected, and the normal image forming sequence can be prevented from being frequently interrupted by the position shift correction sequence.

Accordingly, good images can be continuously formed.

If the time from when the power switch is turned off to when the power switch is turned on is long as described above, the temperature inside the device may also decrease, and ΔT <ΔT0 may be satisfied.
This is detected in step S202, and the above-mentioned steps (S204 and S205) are repeated as described above to perform the correction operation. Therefore, there is no shift in the scanning line and a good image can be obtained.

[0076]

As is apparent from the above description, the present invention has a mode for correcting the position of an image at predetermined intervals that change sequentially and a mode for correcting the position of the image at fixed intervals. Therefore, the position of the image can be corrected at an appropriate interval according to the state of the apparatus.

Therefore, for example, when the degree of image displacement relative to the lapse of time is large, the interval at which the correction is performed is shortened. Can be made longer.

Therefore, the number of times the correction operation is performed can be set optimally, and a good image can be continuously formed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus as an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an exposure unit shown in FIG.

FIG. 3 is a diagram illustrating a state of image displacement.

FIG. 4 is a flowchart illustrating a registration correction operation according to the embodiment of the present invention.

FIG. 5 is a flowchart for explaining another registration correction operation in the embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a conventional image forming apparatus.

FIG. 7 is a diagram illustrating types of image misalignment.

FIG. 8 is a view showing an exposure unit of FIG. 1;

FIG. 9 is a view for explaining a configuration of the rotary polygon mirror shown in FIG. 8;

FIG. 10 is a diagram for explaining the laser scanning system of FIG. 1;

11 is a diagram showing a deviation between each photosensitive drum and an image transfer position in FIG. 10;

12 is a diagram illustrating a deviation between each photosensitive drum and an image transfer position in FIG. 10;

FIG. 13 is a diagram illustrating a deviation between each photosensitive drum and an image transfer position in FIG. 10;

FIG. 14 is a diagram showing a deviation between each photosensitive drum and an image transfer position in FIG. 10;

FIG. 15 is a diagram illustrating a configuration of a registration correction mechanism.

FIG. 16 is a diagram showing a state of registration correction.

[Explanation of symbols]

 13 Conveyor belt 101 Photosensitive drum 103 Rotating polygon mirror

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-51607 (JP, A) JP-A-5-197244 (JP, A) JP-A-9-204087 (JP, A) JP-A-3-3 293679 (JP, A) JP-A-6-18796 (JP, A) JP-A-7-245701 (JP, A) JP-A-63-307483 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/01-15/01 117 G03G 21/00 370-502 G03G 21/14 B41J 2/44

Claims (5)

(57) [Claims] An image forming unit that forms an image on a recording medium; a correcting unit that corrects a position of an image formed on the recording medium; and an exposing unit that exposes an image carrier in the image forming unit.
And first detecting means for detecting a temperature near the exposure section
Detecting a temperature inside the apparatus other than the exposure unit
2, a first mode in which the correction means performs the correction operation at predetermined intervals that sequentially change, and a second mode in which the correction operation is performed at regular time intervals. The mode according to the output of the first and second detection means
An image forming apparatus comprising: a control unit that determines 2. The control unit according to claim 1, wherein the control unit includes a calculation unit that calculates a difference between an output of the first detection unit and an output of the second detection unit, and a comparison unit that compares the difference with a predetermined reference value. 2. The image forming apparatus according to claim 1 , wherein the mode is determined according to a comparison result of the comparison unit. 3. The image forming apparatus according to claim 2 , wherein the control unit determines a mode of the apparatus according to a comparison result of the comparing unit immediately after power-on of the apparatus. 4. The control means sets the first mode when the difference is equal to or less than the reference value, and sets the second mode when the difference is larger than the reference value. The image forming apparatus according to claim 2 , wherein: 5. The image forming unit has a plurality of image forming units for forming images of different colors on the recording medium, and the correcting unit forms the image on the recording medium by the plurality of image forming units. The image forming apparatus according to claim 1, wherein the image forming apparatus corrects a positional shift between images to be performed.