JP3882301B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus effective for accurately detecting a transfer timing shift.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine or a printer, generally, a process of successively supplying sheets of a predetermined size into the apparatus and sequentially forming images on the supplied sheets is performed.
[0003]
For example, in an electrophotographic high-speed laser printer apparatus, a paper feed tray and a stacker device are connected to an image forming apparatus, and an image is formed on paper continuously supplied from the paper feed tray. Are discharged and stacked on the stacker unit.
[0004]
Here, an example of image forming processing by the image forming apparatus will be described below.
[0005]
First, the image forming apparatus receives an image signal generated by a reading device such as an external device or a scanner. Then, the image signal is modulated to generate laser light, and the photoconductor is irradiated with the laser light. As a result, a latent image corresponding to the image signal is formed on the photoconductor. Thereafter, toner is attracted to the latent image and the paper is supplied at a predetermined timing, whereby the toner is transferred to the paper. Then, the paper on which the toner is transferred is pressed with a heating roller, and the image is fixed on the paper.
[0006]
Image formation by the image forming apparatus is performed as described above, and this image forming apparatus includes means for monitoring the transfer timing in addition to the above-described configuration in order to prevent displacement of the image formed on the paper. There is something.
[0007]
FIG. 10 is a conceptual diagram showing a structure of a transfer portion of a conventional image forming apparatus. The transfer unit shown in FIG. 2 exposes the photosensitive belt 5 corresponding to the above-described photosensitive body, a photosensitive belt driving roller 6 that drives the photosensitive belt 5, and an image signal. The exposure device 80, the developing device 11 for attracting toner to the latent image formed by the exposure device 80, and the supplied paper P are charged, and the toner adsorbed on the photosensitive belt 5 is transferred to the paper P. The charging roller 7, the cleaner 10 for removing excess toner remaining on the photosensitive belt 5 after the transfer of the toner, the paper detection sensor 9 for detecting the leading edge of the supplied paper P, and the exposure device 80 are output. And a comparator 81 that compares the timing of the image to be detected with the detection timing of the paper detection sensor 9 and operates as follows.
[0008]
First, the photosensitive belt driving roller 6 rotates the photosensitive belt 5 in the direction of the arrow shown in the drawing, that is, counterclockwise. The exposure device 80 sequentially exposes the surface of the rotating photoreceptor belt 5 and forms an image corresponding to the paper P on the surface as a latent image. The latent image formed by the exposure device 80 is sent to the developing unit 11 as the photosensitive belt is rotated, and toner is supplied. Then, it is sent as it is to the contact portion between the photosensitive belt driving roller 6 and the charging roller 7, that is, the transfer portion.
[0009]
On the other hand, the paper P is supplied to the transfer portion at a timing when the portion on which the toner is formed passes through the transfer portion.
[0010]
The toner and the paper P are pressed against each other by the photosensitive belt driving roller 6 and the charging roller 7, and the toner is transferred to the paper P.
[0011]
During the series of processes, the sheet detection sensor 9 outputs a detection signal to the comparison unit 81 while the sheet P passes over the sheet detection sensor 9, and the comparison unit 81 receives the detection signal from the sheet detection sensor 9. The output detection signal is compared with the image output signal output from the exposure apparatus 80.
[0012]
FIG. 11 is a time chart for explaining the comparison process executed by the paper detection sensor shown in FIG. As shown in the figure, the comparison unit 81 measures the interval “T” between the rise of the detection signal output from the paper detection sensor 9 and the rise of the image output signal output from the exposure device 80. This interval “T” means the interval between the time when the top of the image is formed on the photosensitive belt 5 and the time when the top of the paper P passes the paper detection sensor 9 as shown in FIG.
[0013]
The comparison unit 81 takes into account the time from the exposure of the photosensitive belt 5 to the transfer portion and the time until the leading edge of the paper P detected by the paper detection sensor 9 reaches the transfer portion. It is determined whether “T” is a normal interval.
[0014]
In this way, the conventional image forming apparatus monitors the timing of transferring the image onto the paper.
[0015]
[Problems to be solved by the invention]
However, since the monitoring means described above is based on the interval from the position at which the photosensitive belt 5 is exposed to the position at which toner is transferred to the paper P, the rotational fluctuation of the photosensitive belt driving roller 6 and the photosensitive body. The slippage between the belt driving roller 6 and the photosensitive belt 5 may cause a determination error. As a result, there arises a problem that even if an image shift actually occurs, it is handled as a result of normal image formation.
[0016]
In particular, since the distance from the exposure position to the transfer position becomes longer in a large image forming apparatus, detection accuracy is required in a high-speed image forming apparatus, and thus the above problem appears remarkably.
[0017]
For example, in an apparatus that forms an image on 150 sheets per minute, the photosensitive belt 5 is conveyed at a speed of 550 mm per second. When an image shift within 1 mm is detected with this apparatus, it is necessary to detect a time difference within 1.8 ms with respect to “T”. Such a time difference of about 1.8 ms can be sufficiently affected by the rotational fluctuation of the photosensitive belt driving roller 6 described above.
[0018]
Furthermore, since it is necessary to detect a time difference of about 0.1 ms to 1.0 ms in a large image forming apparatus, the image forming apparatus is easily influenced by rotational fluctuations and the like.
[0019]
As a technique for solving such a problem, a technique disclosed in Japanese Patent Application Laid-Open No. 4-261877 can be considered. However, in the technique disclosed in the publication, a detection mark is printed on a sheet at a constant cycle. By detecting the printed mark, it is determined whether or not the image formation is normally performed, so that an unnecessary mark is formed on the sheet.
[0020]
In addition, this technique has a drawback in that it is not possible to determine image shift before image formation, and wasteful printing is performed on paper.
[0021]
As described above, problems to be solved still remain in the conventional technology.
[0022]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus effective for accurately detecting a shift in transfer timing.
[0023]
[Means for Solving the Problems]
To achieve the above object, according to the invention of claim 1, wherein the image signal output means for outputting the image to be formed on the sheet as an image signal, the image signal output means on a photosensitive member based on an image signal outputted by latent image forming means for forming a latent image corresponding to the image signal, a developing unit for developing a latent image formed on said photosensitive member by said latent image forming means, the image developed by said developing means wherein a transfer means for transferring the sheet an image corresponding to the latent image on the photosensitive member at a predetermined transfer timing, comprising a sheet supply means for supplying sheets to the transfer means in accordance with the said transfer timing corresponding to the signal an image forming apparatus that forms an image corresponding to the image signal to a predetermined position of the sheet, on the photoreceptor in synchronism with the formation of the latent image corresponding to the image signal by said latent image forming means Serial mark forming means for forming a mark by said latent image forming means outside the area in which a latent image corresponding to the image signal is formed, the mark detecting means for detecting a mark formed on said photosensitive member by said mark forming means When the paper detection means for detecting a sheet that will be supplied by the sheet supply means, the paper by the paper feed unit based on the detection interval between the detection of the paper by detecting said paper detecting means of the marks by the mark detecting means Image deviation predicting means for predicting a deviation between the supply timing of the image and the transfer timing, and an allowable range of the detection interval from the position where the mark detecting means is disposed to the transfer portion of the transfer means and the sheet detection storage means for means for the distance set based on and stores from disposed position to said transfer sites, pre-by the image displacement prediction means It has been if the deviation is out of the allowable range stored in the storage means, characterized by comprising the interrupting control means of the image forming processing to notify the abnormality.
[0024]
According to a second aspect of the present invention, in the first aspect of the invention, the paper detection means includes a first side edge detection means for detecting a first side edge of the paper supplied by the paper supply means; And a second side edge detecting means for detecting a second side edge of the paper supplied by the paper supply means, wherein the mark forming means is on the photoconductor on the side corresponding to the first side edge. First mark forming means for forming a first mark outside a region where a latent image corresponding to the image signal is formed, and the image signal on the photoconductor on the side corresponding to the second side end. And a second mark forming means for forming a second mark outside the region where the latent image corresponding to is formed , wherein the mark detecting means detects the first mark. And second mark detecting means for detecting the second mark. Wherein the image displacement predicting means, first measuring the detection interval between the detection of the first mark by detecting said first mark detecting means of said first side edge by said first side edge detecting means Second detection for measuring a detection interval between detection interval measurement means, detection of the second side edge by the second side edge detection means, and detection of the second mark by the second mark detection means. It comprises an interval measurement means, and a skew deviation prediction means for comparing the measurement results of the first detection interval measurement means and the second detection interval measurement means and predicting the skew deviation of the image. To do.
[0025]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the mark forming unit corresponds to a leading end position of a latent image corresponding to an image signal formed by the latent image forming unit. A latent image corresponding to the mark is formed outside a region where the latent image corresponding to the image signal is formed on the photoconductor , and the mark detecting unit corresponds to the mark formed by the mark forming unit. A developed image of the latent image to be developed by the developing unit is detected, and the paper detecting unit detects a leading end position of the paper supplied by the paper supplying unit.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0027]
First, the outline of the present invention will be described with reference to FIG. FIG. 1 is a conceptual diagram showing the structure of a transfer portion provided in an image forming apparatus according to the present invention.
[0028]
In the present invention, as shown in the figure, a mark output from the mark signal output unit 2 is combined with an image signal to form a latent image on the photosensitive belt 5, and a mark detected immediately before the transfer portion is detected. The mark is detected by the sensor 8, and the detection result is output to the image shift prediction unit 12. At the same time, the leading edge of the paper P is detected by the paper detection sensor 9 disposed immediately before the transfer portion, and the detection result is output to the image shift prediction unit 12. The image shift prediction unit 12 measures the interval between the time when the mark is detected by the mark detection sensor 8 and the time when the leading edge of the paper P is detected by the paper detection sensor 9, and determines whether or not the interval is normal. By judging, the above-mentioned problems are solved.
[0029]
Hereinafter, the contents of the present invention will be described in more detail.
[0030]
The transfer unit shown in FIG. 1 is provided in an image forming apparatus such as a copying machine or a printer, and transfers a toner image onto a sheet supplied from a paper feed tray and outputs it to a fixing unit such as a heating roller. Detailed configurations of the image forming apparatus, the paper feed tray, and the like have been disclosed in conventionally known copying machines, printers, and the like, and thus description thereof will be omitted, and description will be given here with a focus on the transfer unit.
[0031]
In the transfer unit shown in FIG. 1, an image signal that is the basis of an image formed on a sheet is output from the image signal output unit 1. The image signal output unit 1 may be an external terminal such as a personal computer or an image reading device such as a scanner.
[0032]
The mark formed on the photosensitive belt 5 is output from the mark signal output unit 2 as a mark signal. The mark signal output unit 2 stores a mark having a predetermined shape such as a linear shape or a rectangular shape.
[0033]
The synchronization signal generator 13 outputs an exposure synchronization signal to the image signal output unit 1 and the mark signal output unit 2 in accordance with the printing timing. The image signal output unit 1 and the mark signal output unit 2 that have received the exposure synchronization signal output the image signal and the mark signal to the combining unit 3, respectively.
[0034]
FIG. 2 is a time chart showing timings of signals output from the synchronization signal generation unit 13, the image signal output unit 1, and the mark signal output unit 2 shown in FIG. As shown in the figure, the exposure synchronization signal is an enable signal output for each number of sheets, and the image signal is output while the exposure synchronization signal is enabled. The mark signal is output simultaneously with the image signal, and the rising edge of the mark signal corresponds to the top of the image on each sheet.
[0035]
The combining unit 3 combines the received image signal and mark signal and outputs the combined signal to the exposure unit 4. The exposure unit 4 modulates the received signal into a laser drive signal, and irradiates the photosensitive belt 5 with laser light. As a result, a latent image of an image and a mark is formed on the surface of the photoreceptor belt 5.
[0036]
FIG. 3 is a top view showing a state in which an image and a latent image of a mark are formed on the surface of the photosensitive belt 5 shown in FIG. As shown in the figure, the image and the latent image of the mark are formed in an image forming area 50 and a mark forming area 51 provided on the surface of the photoreceptor belt 5, respectively.
[0037]
Here, the image forming area 50 is provided in accordance with the maximum width of the supplied paper P, and the mark forming area 51 is provided outside thereof. That is, the latent image formed in the mark formation area 51 does not contribute to the transfer onto the paper P.
[0038]
The photoconductor belt 5 shown in FIG. 3 moves in the direction indicated by the arrow in the drawing, and a left end mark A21a and a right end mark A22a are formed on the surface of the photoconductor belt 5 outside both ends of the image A20a. And
The photoconductor belt 5 shown in FIG. 3 moves in the direction indicated by the arrow in the drawing, and a left end mark A21a and a right end mark A22a are formed on the surface of the photoconductor belt 5 outside both ends of the image A20a. Thus, a left end mark B21b and a right end mark B22b are formed outside both ends of the image B20b. Here, the image A20a is a latent image corresponding to the image formed on the first sheet, and the image B20b is a latent image corresponding to the image formed on the second sheet.
[0039]
Further, the left end mark A21a, the right end mark A22a, the left end mark B21b, and the right end mark B22b are formed in accordance with the leading positions in the traveling direction of the images A20a and B20b, respectively.
[0040]
Thus, in the exposure process in the image forming apparatus, the photosensitive belt 5 is continuously exposed according to the number of sheets supplied.
[0041]
The latent image formed as described above is sent onto the developing unit 11 by the photosensitive belt driving roller 6. The developing device 11 supplies and adsorbs toner to the sent latent image. As a result, a toner image is formed on the photosensitive belt 5.
[0042]
The toner image is sent to the transfer site as the photosensitive belt 5 moves. A mark detection sensor 8 is provided between the transfer portion and the developing device 11, and the mark detection sensor 8 detects a mark formed on the photosensitive belt 5. The mark detection sensor 8 is configured by using a photo sensor or the like that irradiates the photosensitive belt 5 with light and detects reflected light.
[0043]
On the other hand, the paper P on which an image is formed is supplied to the transfer site in accordance with the transfer timing. A paper detection sensor 9 is provided immediately before the transfer portion, and this paper detection sensor 9 detects the top of the supplied paper.
[0044]
By providing the mark detection sensor 8 and the sheet detection sensor 9 as close as possible to the transfer site, errors due to rotational fluctuations of the photosensitive belt driving roller 6 can be reduced.
[0045]
Further, the mark detection sensor 8 and the paper detection sensor 9 are arranged at a distance where the time for the mark and the paper to reach the transfer portion is the same in consideration of the moving speed of the photosensitive belt 5 and the transport speed of the paper P. It is preferable to arrange in this way, and this makes it possible to simplify the image shift prediction process described later. Since the moving speed of the photosensitive belt 5 and the conveyance speed of the paper P are generally the same, it is preferable that the mark detection sensor 8 and the paper detection sensor are arranged at an equal distance from the transfer site.
[0046]
FIG. 4 is a perspective view showing the structure near the transfer site shown in FIG. As shown in the figure, the mark detection sensor is composed of a mark detection sensor A8a and a mark detection sensor B8b disposed corresponding to the mark formation region 51 shown in FIG. The mark detection sensor A8a detects the left end mark A21a and the left end mark B21b shown in FIG. 3, and the mark detection sensor B8b detects the right end mark A22a and the right end mark B22b shown in FIG.
[0047]
In addition, the paper detection sensor includes a paper detection sensor A9a and a paper detection sensor B9b, which are arranged corresponding to the width of the supplied paper. These paper detection sensors detect both ends of the paper P, respectively.
[0048]
As described above, by forming marks on both side edges of the photosensitive belt 5 and providing means for independently detecting the marks and means for independently detecting both side edges of the sheet, prediction of skewing of the image is provided. Is possible.
[0049]
FIG. 5 is a time chart showing an example of detection signals output from the mark detection sensor and the paper detection sensor shown in FIG. As shown in the figure, the paper detection sensor A9a outputs a detection signal while the left edge of the paper P passes, and the mark detection sensor A8a receives the left edge mark A21a or the left edge mark B21b shown in FIG. The detection signal is output while passing. Similarly, the sheet detection sensor B9b and the mark detection sensor B8b also output detection signals shown in FIG. Each detection result is output to the image shift prediction unit 12, where determination processing described later is performed.
[0050]
The sheet P supplied to the transfer portion is pressed against the photosensitive belt 5 on which the toner image is formed by the photosensitive belt driving roller 6 and the charging roller 7, and the toner image is transferred.
[0051]
After the transfer of the toner image, the toner image remaining on the photosensitive belt 5 is sent to the cleaner 10 and removed as the photosensitive belt 5 moves.
[0052]
FIG. 6 is a block diagram showing an internal configuration of the image shift prediction unit shown in FIG. As shown in the figure, the image shift prediction unit 12 includes a counter A61 that counts the detection interval between the paper detection sensor A9a and the mark detection sensor A8a, a register A62 that stores the value of the counter A61, and a paper detection sensor B9b. A counter B63 that counts the detection interval between the mark detection sensor B8b, a register B64 that stores the value of the counter B63, and a ROM 65 are connected to the CPU 60.
[0053]
The ROM 65 is provided with an allowable time difference storage area 70 for storing an allowable time difference and an allowable skew amount storage area 71 for storing an allowable skew amount.
[0054]
Here, the allowable time difference is an allowable value of a detection interval between the detection of the mark by the mark detection sensor 8 and the detection of the paper by the paper detection sensor, and the distance from the position where the mark detection sensor 8 is disposed to the transfer site. And the distance from the position where the paper detection sensor 9 is disposed to the transfer site.
[0055]
For example, when the mark detection sensor 8 and the paper detection sensor 9 are arranged so that the mark and the paper simultaneously reach the transfer site from the respective sensors, the allowable time difference is determined based on the conveyance speed of the paper. This is a value obtained by converting the allowable range of deviation into time.
[0056]
Further, the allowable skew amount is an allowable amount that regulates an oblique shift of an image formed on the paper P when the paper P is supplied in an inclined state. It is defined as the difference between the detection times of the right side sensor.
[0057]
Hereinafter, the image shift prediction processing by the image shift prediction unit 12 configured as described above will be described with reference to the flowcharts shown in FIGS.
[0058]
FIG. 7 is a flowchart showing an execution procedure of an image shift prediction process executed by the image shift prediction unit 12 shown in FIG. 6 based on the sheet detection sensor A9a and the mark detection sensor A8a. The processing shown in the figure is performed for each sheet.
[0059]
In the process shown in the figure, first, the CPU 60 resets the value of the counter A61 (step 100), and waits for detection of a sheet by the sheet detection sensor A9a or detection of a mark by the mark detection sensor A8a (step 100). No in step 101). When either a sheet or a mark is detected (Yes in step 101), the counter A61 starts incrementing (step 102).
[0060]
Here, when a sheet is detected in step 101, a mark is detected in step 103, and when a mark is detected in step 101, a sheet is detected in step 103.
[0061]
Thereafter, the detection signal from the sheet detection sensor A9a or the mark detection sensor A8a is again waited, and when there is a detection signal (Yes in Step 103), the value of the counter A61 is stored in the register B64 (Step 107). Thereafter, the process proceeds to the skew prediction process shown in FIG.
[0062]
On the other hand, if there is no detection signal (No in step 103), it is determined whether or not the value of the counter A61 exceeds the allowable time difference stored in the ROM 65 (step 104). When the allowable time difference is not exceeded (No in Step 104), the process returns to Step 102 again and continues incrementing the counter A61.
[0063]
In step 104, when the value of the counter A61 exceeds the allowable time difference, the occurrence of the image shift is notified (step 105), and the image forming process is interrupted (step 106).
[0064]
FIG. 8 is a flowchart showing an execution procedure of an image shift prediction process executed by the image shift prediction unit 12 shown in FIG. 6 based on the sheet detection sensor B9b and the mark detection sensor B8b. The process shown in the figure is performed in the same manner as the process shown in FIG.
[0065]
FIG. 9 is a flowchart showing the execution procedure of the skew shift prediction process executed by the image shift prediction unit 12 shown in FIG. In the process shown in the figure, first, the CPU 60 waits for both detection signals output from the paper detection sensor A9a and the paper detection sensor B9b to fall, that is, the trailing edge of the paper is detected by each sensor. (Step 300).
[0066]
When the trailing edge of the paper is detected (step 300), the CPU 60 reads the values stored in the register A62 and the register B64 (step 301), obtains the absolute value of the difference between the values (step 302), and Then, it is determined whether or not the absolute value is within the range of the allowable skew amount stored in the ROM 65 (step 303).
[0067]
If the absolute value obtained in step 302 is within the allowable skew amount range (Yes in step 303), the process is terminated. If the absolute value is not within the allowable skew amount range (No in step 303), An image skew is notified (step 304), and the image forming process is interrupted (step 305).
[0068]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an image forming apparatus effective for accurately detecting a transfer timing shift.
[0069]
Further, by forming marks on both side edges of the photosensitive belt 5 and providing means for independently detecting the marks and means for independently detecting both side edges of the paper, it is possible to predict the skew of the image. It becomes.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the structure of a transfer portion provided in an image forming apparatus according to the present invention.
FIG. 2 is a time chart showing timings of signals output from the synchronization signal generation unit 13, the image signal output unit 1 and the mark signal output unit 2 shown in FIG.
3 is a top view showing a state in which an image and a latent image of a mark are formed on the surface of the photosensitive belt 5 shown in FIG. 1. FIG.
4 is a perspective view showing a structure in the vicinity of a transfer site shown in FIG. 1. FIG.
5 is a time chart showing an example of detection signals output from the mark detection sensor and the paper detection sensor shown in FIG. 4;
6 is a block diagram showing an internal configuration of an image shift prediction unit shown in FIG.
7 is a flowchart showing an execution procedure of an image shift prediction process executed by the image shift prediction unit 12 shown in FIG. 6 based on the sheet detection sensor A9a and the mark detection sensor A8a.
8 is a flowchart showing an execution procedure of an image shift prediction process executed by the image shift prediction unit 12 shown in FIG. 6 based on the sheet detection sensor B9b and the mark detection sensor B8b.
9 is a flowchart showing an execution procedure of skew shift prediction processing executed by the image shift prediction unit 12 shown in FIG. 6;
FIG. 10 is a conceptual diagram illustrating a structure of a transfer unit of a conventional image forming apparatus.
11 is a time chart for explaining comparison processing executed by the paper detection sensor shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image signal output part, 2 ... Mark signal output part, 3 ... Composition part, 4 ... Exposure part, 5 ... Photoconductor belt, 6 ... Photoconductor belt drive roller, 7 ... Charging roller, 8 ... Mark detection sensor, 8a ... mark detection sensor A, 8b ... mark detection sensor B, 9 ... paper detection sensor, 9a ... paper detection sensor A, 9b ... paper detection sensor B, 10 ... cleaner, 11 ... developer, 12 ... image misalignment prediction unit, 13 ... Sync signal generator 20a ... Image A, 20b ... Image B, 21a ... Left end mark A, 21b ... Left end mark B, 22a ... Right end mark A, 22b ... Right end mark B, 50 ... Image formation area, 51 ... Mark formation area, 60 ... CPU, 61 ... Counter A, 62 ... Register A, 63 ... Counter B, 64 ... Register B, 65 ... ROM, 70 ... Allowable time difference storage area, 71 ... Allowable skew amount storage area 80 ... exposure apparatus, 81 ... comparison section, P ... paper.

Claims (3)

Image signal output means for outputting an image to be formed on paper as an image signal;
Latent image forming means for forming a latent image corresponding to the image signal on the photosensitive body based on the image signal output by the image signal output means ;
A developing unit for developing a latent image formed on said photosensitive member by said latent image forming means,
A transfer unit that transfers the sheet an image corresponding to the latent image on the photosensitive member corresponding to the image signal developed by the predetermined transfer timing by said developing means,
A sheet supply means for supplying a sheet to the transfer unit in conformity to the transfer timing
In an image forming apparatus for forming an image corresponding to the image signal at a predetermined position on the paper,
In synchronization with the formation of the latent image corresponding to the image signal by the latent image forming means, a mark is formed by the latent image forming means outside the region where the latent image corresponding to the image signal is formed on the photoconductor. Mark forming means ;
Mark detection means for detecting a mark formed on the photoreceptor by the mark forming means;
A paper detecting means for detecting a sheet that will be supplied by the sheet supply means,
An image deviation prediction means for predicting a deviation between the paper supply timing by the paper supply means and the transfer timing based on a detection interval between the mark detection by the mark detection means and the paper detection by the paper detection means;
An allowable range of the detection interval is set based on the distance from the position where the mark detection means is disposed to the transfer portion of the transfer means and the distance from the position where the paper detection means is disposed to the transfer portion. Storage means for storing;
Control means for notifying the abnormality and interrupting the image forming process when the deviation predicted by the image deviation prediction means is out of the allowable range stored in the storage means;
An image forming apparatus comprising: The paper detection means includes
First side edge detection means for detecting a first side edge of the paper supplied by the paper supply means;
Second side edge detecting means for detecting a second side edge of the paper supplied by the paper supply means,
The mark forming means includes
First mark forming means for forming a first mark outside a region where a latent image corresponding to the image signal on the photoconductor on the side corresponding to the first side edge is formed ;
A second mark forming means for forming a second mark outside a region where a latent image corresponding to the image signal on the photoconductor on the side corresponding to the second side end is formed ;
The mark detection means includes
First mark detection means for detecting the first mark;
Second mark detection means for detecting the second mark, and
The image shift prediction means
First detection interval measuring means for measuring a detection interval between detection of the first side edge by the first side edge detection means and detection of the first mark by the first mark detection means;
Second detection interval measurement means for measuring a detection interval between detection of the second side edge by the second side edge detection means and detection of the second mark by the second mark detection means;
2. The skew deviation prediction means for comparing the measurement results of the first detection interval measurement means and the second detection interval measurement means and predicting the skew deviation of the image. Image forming apparatus. The mark forming means includes
The latent image corresponding to the mark corresponding to the leading end position of the latent image corresponding to the image signal formed by the latent image forming means is outside the region where the latent image corresponding to the image signal on the photoconductor is formed. formed in,
The mark detection means includes
Detecting a developed image by the developing means of a latent image corresponding to the mark formed by the mark forming means;
The paper detection means includes
The image forming apparatus according to claim 1, wherein a leading end position of a sheet supplied by the sheet supply unit is detected.

Images