JP2004099246A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify a procedure when a double feed happens by contriving so that the double feed is not detected as a double feed. <P>SOLUTION: By means of a time measuring part 20, a CPU 12 measures a third time period from when a front end part of a sheet is detected by a delivery sensor 17 till when a rear end part of the sheet is detected. If the measured third time period exceeds a prescribed and internally set time period, it is judged to be an abnormal sheet feed and an error processing operation is performed. By means of the measuring part 20, the CPU 12 measures a third comparison time period from when a front end part of a sheet is detected by a feed sensor 16 till when a rear end part of the sheet is detected for each sheet feed. By internally setting each third comparison time period as the prescribed time period, a double feed is prevented from being judged to be abnormal, thus continuing printing operation. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention measures the time from when the paper ejection sensor detects the leading edge of the paper to when it detects the trailing edge of the paper, and when the measured time exceeds a predetermined time set internally. The present invention relates to an image forming apparatus, such as a laser printer, a copying machine, and a facsimile, configured to perform an error processing operation upon determining that a sheet is abnormal.
[0002]
[Prior art]
In an image forming apparatus, an error such that a sheet is bent and jammed in a sheet conveyance path, or an error due to a double feed that is conveyed in a state where two sheets are overlapped with a slight deviation (hereinafter, these are collectively referred to as a jam error) ), Conventionally, the printing operation is immediately stopped at that time. Then, when the user removes all the stopped paper sheets during the conveyance, the printing operation is restarted again.
[0003]
However, among the jam errors described above, the error caused by double feeding does not cause a problem such that the paper is caught in the apparatus, and if the discharge is continued, the discharge is completed, and the printing operation is not necessarily performed immediately. There is no need to stop.
[0004]
In view of such circumstances, various techniques have been proposed to solve the problem caused by the double feed without immediately stopping the printing operation even when the double feed occurs.
[0005]
For example, a double feed sensor that detects double feed from a change in transmittance is provided, and when double feed is detected by the double feed sensor, print data is printed at a correct position on the second sheet of double feed. By delaying the printing timing as described above, an image forming apparatus that avoids printing over the first sheet and the second sheet and enables reuse of the first sheet (this is referred to as prior art 1) is described. (For example, see Patent Document 1).
[0006]
Further, even if a paper feeding error occurs, the printing operation is not immediately stopped, and the printing operation such as feeding, running, and discharging the paper is continued for a predetermined number of times. In this case, there is described a printing apparatus in which the printing operation is stopped at that time (this is referred to as Conventional Technique 2) (for example, see Patent Document 2).
[0007]
Also, the length of the paper is calculated from the time when the printed print paper passes through the paper ejection detection sensor, and the calculation result is compared with data relating to the length of the paper stored in the ROM in advance. A printing apparatus that determines the degree of jam or multifeed and executes reprinting or stops the printing operation according to the determination result (this is referred to as Conventional Technique 3) is described (for example, Patent Document 3).
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 7-121079 [Patent Document 2]
JP-A-3-284961 [Patent Document 3]
JP-A-5-24321
[Problems to be solved by the invention]
According to the above-described related art 1, there is an advantage that even when double feeding occurs, print data can be printed at a regular position on the second sheet and the first sheet can be reused. However, it is necessary to separately provide a double feed sensor for detecting a change in the transmittance of the multi-fed paper, and there has been a problem that member costs are increased. In addition, in the case of manual feed, for example, when printing data on a patterned stationery or the like, the density of the pattern is detected by the multi-feed sensor, and it is determined that the multi-feed is performed even though the multi-feed is not performed. Therefore, there is a possibility that a problem that the print position of the print data is deviated from the normal position on the contrary.
[0010]
In addition, according to the above-described related art 2, even when a paper feeding error occurs, the printing operation such as feeding, running, and discharging the paper is continued a predetermined number of times. In the case of a jam error, the printing operation continues unreasonably in spite of the paper being jammed, and there is a problem that the apparatus may be damaged in some cases.
[0011]
Further, according to the above-described prior art 3, the length of the sheet is calculated from the time when the sheet passes through the sheet ejection detection sensor, and the calculation result is compared with the data regarding the length of the sheet stored in the ROM. The degree of jam or double feed is determined. However, paper of a fixed size is not always used. For example, printing may be performed on paper made by oneself or on commercially available stationery. In such a case, the length of the paper calculated from the time required to pass through the paper ejection detection sensor and the paper stored in the RAM are used. Since the length is different, the apparatus determines that the paper is jammed or multi-fed even though the user is using the intended paper, and there is a problem that printing cannot be performed as intended by the user. .
[0012]
The problems of the above-mentioned prior arts 1 and 3 are all problems caused by trying to detect a double feed as a double feed. As described above, in the double feed, if the discharge is continued, the discharge is completed without causing a paper jam. From this point, there is a problem that the printing is not performed at the regular position on the paper, but except for this point, there is no need to treat it as an error. In other words, conversely, unless the double feed is detected as a double feed, the problems of the above-described related arts 1 and 3 do not occur.
[0013]
Further, the problem of the above-described related art 2 is a problem that occurs because errors are collectively determined without discrimination between a double feed and a paper jam. In other words, this is a problem that can be solved if errors due to double feeding and errors due to other causes can be detected separately.
[0014]
The present invention has been made to solve such a problem, and its purpose is to devise not to detect a double feed as a double feed and to detect an error such as a paper jam as usual. Accordingly, an object of the present invention is to provide an image forming apparatus which simplifies the processing particularly when double feeding occurs. Another purpose is that even if the double feed is not detected as a double feed, the printing for that page is actually a defective page with a misaligned printing position. An object of the present invention is to provide an image forming apparatus capable of automatically reprinting a page.
[0015]
[Means for Solving the Problems]
An image forming apparatus according to an aspect of the invention includes a paper feed sensor provided in a paper feed traveling unit for detecting a leading edge and a trailing edge of a sheet before printing, and a leading edge of a printed paper provided in a paper ejection traveling unit. And a paper ejection sensor for detecting the trailing edge, a time measuring means for measuring various times, and a standard time from when the paper feed sensor detects the leading edge of the paper to when the trailing edge of the paper is detected. A storage unit that stores in advance for each type of usable paper, a paper supply based on a detection signal from the paper supply sensor, a detection signal from the paper discharge sensor, and a time measured by the time measurement unit. Control means for controlling the paper operation.
[0016]
The control means measures, by the time measuring means, a first time from the start of paper supply to the paper feed sensor detecting the leading end of the paper, and the first time is set internally. If the first comparison time is exceeded, it is determined that the paper is abnormal and an error handling operation is performed. After the paper feed sensor detects the leading edge of the paper, the paper ejection sensor detects the leading edge of the paper. Is measured by the time measuring means, and if the second time exceeds a second comparison time set internally, it is determined that there is a sheet feeding error and error processing is performed. The operation is performed, and a third time from when the paper ejection sensor detects the leading edge of the paper to when the trailing edge of the paper is detected is measured by the time measuring means, and the third time is internally stored. If the set third comparison time is exceeded, a paper feed error Decision to have so as to perform the error processing operation.
[0017]
Here, according to the image forming apparatus of the present invention, the third comparison time is not a fixed value, and the setting is changed as needed each time paper is fed one by one according to the length of the paper. I have.
[0018]
In other words, during the printing operation, the control means detects the leading edge of the paper by the time measuring means and detects the trailing edge of the paper every time the paper is fed one by one. By setting the measured time as the third comparison time internally in each case, the printing operation is continued while avoiding the determination of the multi-feed as a sheet feeding abnormality. .
[0019]
When double feeding occurs, the length of the double feeding paper is longer than the normal paper length, so the length of the double feeding paper is first measured by the paper feed sensor, and the measurement time is used as a comparison standard. Therefore, it is set internally as the third comparison time. After that, the length of the multi-feed sheet after printing is measured again by the sheet discharge sensor, and the third time, which is the measurement result, is compared with the third comparison time set earlier.
[0020]
As a result, when printing is completed with the double feed, the relationship of third time ≦ third comparison time is satisfied (strictly speaking, third time ≒ third comparison time). Printing is continued as it is without judging.
[0021]
On the other hand, if the third time is longer than the third comparison time, there is a possibility that two sheets are shifted or one of the sheets is jammed after the sheet is fed and before the sheet is discharged. Therefore, in this case, an error processing operation is performed. For example, processing such as immediately stopping the printing operation is performed.
[0022]
Further, in the case where the printing operation is continued as described above when the double feed occurs, the control unit stores the third comparison time measured by the time measurement unit and set therein and the storage unit. The standard time of each sheet is compared with the standard time, and if there is no standard time corresponding to the third comparison time, the same print data as the print data printed on the sheet is printed again on the next sheet to be fed. It has become.
[0023]
In other words, when double feed occurs, the print data of the page is not likely to be correctly printed on the paper. In this case, the same print data is printed again on the next paper to be fed. I do. This saves the user from having to set only the multi-feed page again after printing is completed and perform additional printing.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
FIG. 2 is a schematic configuration diagram of a mechanical part of the laser printer.
Since the mechanical configuration of the laser printer 1 is a conventionally known configuration, it will be briefly described here. However, when roughly classified, the scanner unit 81, the electronic process unit 82, the photosensitive drum 83, the transfer unit 64, the heat roller 85a And a fan 86 for releasing heat inside the apparatus to the outside.
[0026]
That is, based on the image data read by the scanner unit 81, a toner image corresponding to the image is formed on the surface of the photosensitive drum 83 by the electronic processing unit 2, and the toner on the photosensitive drum 83 is supplied by the transfer unit 84. The image is transferred from the paper tray 88 to the paper fed by the transport roller 90. Then, the transferred toner is pressed and heated by the fixing device 85 and fixed on the sheet, thereby forming an image on the surface of the sheet. Thereafter, the sheet on which the image is formed is discharged to a discharge tray 89 provided in the apparatus 87 by a transport mechanism (not shown) including a discharge roller 91.
[0027]
In such a configuration, the paper feed sensor 16 is provided in the vicinity of the registration roller 90 serving as a paper feed travel unit, and the paper discharge sensor 17 is provided in the vicinity of the paper discharge roller 91 serving as a paper discharge travel unit. Reference numeral 92 in the drawing denotes a transport roller for feeding sheets one by one from the sheet feed tray 89.
[0028]
FIG. 1 is a functional block diagram showing a configuration of a main part of the laser printer having the above configuration.
The laser printer 1 having the above-described mechanism is a system that performs a printing operation based on print data supplied from the personal computer 2, for example. For this reason, the personal computer 2 and the laser printer 1 are connected via a communication cable 3 capable of bidirectional communication, for example, compatible with USB.
[0029]
The laser printer 1 is a logic circuit IC configured exclusively for the printer, and includes an ASIC 11 having a USB port (not shown) and a CPU 12 for controlling the ASIC 11. The CPU 12 includes a ROM 13 in which a program for executing a printing operation, a program for executing a paper feed abnormality determination process described later, and the like, and a RAM 14 which stores various data and serves as a work area during the printing operation are respectively provided. It is connected.
[0030]
The output of the key sensor 15 for detecting key operations such as a power key and a print start key, the output of the paper feed sensor 16, and the output of the paper ejection sensor 17 are guided to the ASIC 11. Further, the ASIC 11 includes a temperature control unit 18 for controlling the heating temperature of the heat roller, a fan drive unit 19 for controlling on / off of a fan 86 for releasing heat inside the apparatus to the outside, and various times (described later). Time measurement units 20 for measuring the first time, the second time, the third time, the third comparison time, etc.) are connected bidirectionally. In FIG. 1, the means for measuring various times are collectively illustrated as a time measuring unit 20, but in actuality, the number of timer units and the like corresponding to the various times to be measured are provided. Various times can be measured individually. In the present embodiment, the “control unit” is realized by the CPU 12 and the ASIC 11.
[0031]
In addition, in addition to the above, a control unit that actually controls the thermal drum and the transfer unit, a control unit that controls the paper feeding operation and the paper discharging operation, and the like are provided, but these are the essential parts of the present invention. Since it is not provided, it is omitted.
[0032]
The ROM 13 can use a standard time from when the paper feed sensor 16 detects the leading edge of the paper to when it detects the trailing edge of the paper (that is, from ON to OFF of the paper feed sensor 16). Is stored in advance for each kind of paper.
FIG. 3 shows a configuration example of the standard time table stored in the ROM 13.
[0033]
In the present embodiment, five types of paper, Legal, A4, Letter, A6, and B5, are prepared. In addition, the standard time of these papers was actually measured with an actual machine, and as a result, legal was 5.08 seconds, A4 was 4.24 seconds, letter was 3.99 seconds, A6 was 2.11 seconds, and B5 was 3.67. Seconds. In the present embodiment, in consideration of measurement errors, a time obtained by giving a margin of +0.05 seconds to these measurement results is set as a standard time.
[0034]
The ROM 13 stores a first comparison time Tst-on and a second comparison time Ton-on, which will be described later, in addition to the standard time.
[0035]
The first comparison time Tst-on is a time from when the paper is started to be fed from the paper feed tray 88 (Start) to when the paper feed sensor 16 detects (ON) the leading end of the paper, which is an error determination reference time. That is, the second comparison time Ton-on is between the time when the paper feed sensor 16 detects the leading edge of the sheet (ON) and the time when the paper discharge sensor 17 detects (ON) the leading edge of the same paper. Times that serve as error determination criteria, and these times are fixed values in advance. That is, the time is set in advance by experiment or the like to a time at which a jam error such as a paper jam can be reliably detected.
[0036]
On the other hand, during the third comparison time Tlen, which is a criterion for determining the length of the sheet, the paper feed sensor 16 detects the leading end of the sheet (ON) and then detects (OFF) the trailing end of the same sheet. The time until is set internally each time. In other words, when sheets are fed one by one, the third comparison time Tlen is a time unique to the type of the sheet. For example, if the type of paper is legal, the third comparison time Tlen should be 5.08 seconds with reference to the standard time shown in FIG. 3, and if the type of paper is A4, the third comparison time Tleng Should be 4.24 seconds.
[0037]
At the time of the printing operation, the CPU 12 sets the first comparison time Tst-on and the second comparison time Ton-on stored in the ROM 13 and the third comparison time Tleng set internally each time paper is fed one by one. Based on various times (first time, second time, and third time) measured by the time measuring unit 20, it is determined whether there is an abnormality in the sheet feeding operation.
[0038]
Next, in the laser printer 1 having the above-described configuration, a process of determining whether there is an abnormality in a sheet feeding operation during a printing operation and a printing operation when a double feed occurs will be described with reference to flowcharts shown in FIGS. .
[0039]
When the paper feed is started by the start of the printing operation (step S1), the CPU 12 causes the time sensor 20 to detect the leading edge of the paper from the start of the paper feed from the paper feed tray 88 by the time measuring unit 20 (step S1). The measurement of the first time T1 until it turns ON) is started (step S2). Then, before the paper feed sensor 16 is turned ON, it is determined whether or not the measured first time T1 has exceeded the first comparison time Tst-on stored in the ROM 13 (steps S3 and S4). . As a result, if the first time T1 measured up to that time exceeds the first comparison time Tst-on before the paper feed sensor 16 is turned on (when it is determined Yes in step S3). Then, the CPU 12 determines that the sheet feeding is abnormal and performs an error processing operation (step S19). That is, it is determined that a jam error has occurred, and the printing operation is immediately stopped at that time.
[0040]
On the other hand, if the first time T1 measured up to that point is within the first comparison time Tst-on when the paper feed sensor 16 is turned on (No in step S3 and Yes in step S4). In this case, since the sheet feeding to the registration rollers 90 has been performed normally, the operation proceeds to the next step S5, the flag is set to IN, and the subsequent processing branches (step S6). ). That is, the measurement of the second time T2 (step S11) and the measurement of the third comparison time Tleng (step S7) are individually started.
[0041]
First, the CPU 12 causes the time measurement unit 20 to perform a period of time from when the paper feed sensor 16 detects (ON) the leading edge of the paper to when it detects (OFF) the trailing edge of the paper (third comparison time Tleng). Is measured (Step S7, Step S8). Then, when the paper feed sensor 16 is turned off (Yes in step S8), the measurement is terminated, the measurement time is determined as the third comparison time Tleng, and is set internally. However, the third comparison time Tlen actually has a margin of about +0.05 seconds as in the standard time shown in FIG. Thereafter, the flag set to IN is set to OUT, and the measurement and setting of the first comparison time Tlen is completed. That is, the actually measured value (time converted value) of the length of the actually fed paper becomes the reference value for the subsequent length of the paper.
[0042]
On the other hand, in parallel with the processing of steps S7 to S10, the CPU 12 detects the leading edge of the sheet (ON) with the time measuring unit 20 and then sets the discharging sensor 17 to the leading edge of the sheet. The measurement of the second time T2 until the unit is detected (ON) is started (steps S11 to S13). Then, before the paper discharge sensor 17 is turned on, it is determined whether or not the measured second time T2 has exceeded the second comparison time Ton-on stored in the ROM 13 (step S12). As a result, before the paper discharge sensor 17 is turned on, if the second time T2 measured so far exceeds the second comparison time Ton-on (if Yes is determined in step S12). Then, the CPU 12 determines that the sheet feeding is abnormal and performs an error processing operation (step S19). That is, it is determined that a jam error has occurred, and the printing operation is immediately stopped at that time.
[0043]
On the other hand, if the second time T2 measured up to that point is within the second comparison time Ton-on when the paper discharge sensor 17 is turned on (No in step S12, Yes is determined in step S13). In this case, since the sheet feeding to the sheet discharge roller 91 is normally performed, the operation proceeds to the next step S14, and the measurement of the third time T3 is started.
[0044]
In other words, the CPU 12 starts measuring the third time T3 from when the paper discharge sensor 17 detects the leading edge of the paper (ON) to when it detects (OFF) the trailing edge of the paper (steps S14 to S14). Step S17). Then, during the measurement, the CPU 12 checks whether the flag is set to OUT (step S15). Then, when it is confirmed in step S10 that the flag has been set to OUT (Yes in step S15), the measured third time T3 is internally stored before the paper discharge sensor 17 is turned off. It is determined whether or not the set third comparison time Tlen has been exceeded (step S16). As a result, before the paper discharge sensor 17 is turned off, if the third time T3 measured up to that time exceeds the third comparison time Tleng (if Yes is determined in step S16), the CPU 12 Determines that the sheet is abnormal, and performs an error processing operation (step S19). That is, it is determined that a jam error has occurred, and the printing operation is immediately stopped at that time.
[0045]
On the other hand, if the third time T3 measured up to that point is within the third comparison time Tleng when the paper discharge sensor 17 is turned off (No in step S16, and Yes in step S17) In step S18), it is determined that the sheet has been normally discharged, and the sheet discharging operation of the sheet is completed (step S18).
[0046]
As described above, according to the present embodiment, the third comparison time Tleng is not a fixed value, and the setting is changed as needed each time paper is fed one by one according to the length of the paper. . That is, when a double feed occurs, the length of the double feed paper is longer than the normal paper length, so the length of the double feed paper is first measured by the paper feed sensor 16 and the measurement time is compared. It is set internally as a reference third comparison time Tleng. After that, the length of the multi-feed sheet on which printing has been completed is measured again by the sheet discharge sensor 17, and the third time T3, which is the measurement result, is compared with the third comparison time Tleng set earlier. As a result, when the printing is completed with the double feed, the relationship of the third time T3 ≦ the third comparison time Tlength is always satisfied. In this case, the printing is continued without judging an error. Will do. That is, in the laser printer 1 of the present embodiment, even if a double feed occurs, it is not detected as a double feed, and can be handled in the same manner as a normal printing operation.
[0047]
By the way, when the double feed occurs and the printing operation is continued as described above, there is a high possibility that the print data of the page is not printed at a correct position on the paper. Therefore, in this state, the user needs to perform an operation to print only the page again. Therefore, in the present embodiment, when double feeding occurs, the same print data is printed again on the next sheet to be fed.
[0048]
Next, the printing operation at the time of occurrence of double feeding will be described with reference to the flowchart shown in FIG.
When the measured third comparison time Tlen is determined in step S9, the CPU 12 compares the measured third comparison time Tlen with the standard time of each sheet in the standard time table stored in the ROM 13 (step S21). It is confirmed whether there is a standard time that matches the third comparison time Tlen (step S22). As a result, when there is a matching standard time (when it is determined Yes in step S22), the sheet is fed one by one as usual, so that the normal printing operation is performed without performing any special processing. To continue.
[0049]
On the other hand, when there is no matching standard time (when it is determined as No in step S22), there is a high possibility that two sheets are overlapped and fed, and thus the CPU 12 The print data of the corresponding page stored in the buffer area not to be stored is stored without erasing even after printing (step S23), and the stored print data is printed again on the next paper to be fed (step S23). S24). As a result, the print data printed on the multi-feed sheet is printed again on the next sheet fed as usual, so that a missing page due to a printing defect does not occur even after the entire print is completed. This saves the user from having to set only the multi-feed page again after printing is completed and perform additional printing.
【The invention's effect】
According to the image forming apparatus of the present invention, the third comparison time is not a fixed value, and the setting is changed as needed each time paper is fed one by one according to the length of the paper. As a result, even if a double feed occurs, it is not detected as a double feed, and it is not determined that the sheet is abnormal, so that the printing operation can be continued as usual. As a result, it is possible to eliminate the user's trouble of removing the paper remaining in the apparatus and canceling the jam error when the double feed occurs.
Further, according to the image forming apparatus of the present invention, when a double feed occurs, the same print data is printed again on the next sheet to be fed, so only the double feed page is set again after the printing is completed. This saves the user the trouble of additional printing.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration of a main part of, for example, a laser printer which is an image forming apparatus of the present invention.
FIG. 2 is a schematic configuration diagram of a mechanical part of the laser printer.
FIG. 3 is an explanatory diagram showing a configuration example of a standard time table stored in a ROM.
FIG. 4 is a flowchart for explaining a processing operation of determining whether there is an abnormality in a sheet feeding operation during a printing operation in the laser printer of the present embodiment.
FIG. 5 is a flowchart for explaining a printing operation when a double feed occurs in the laser printer of the present embodiment.
[Explanation of symbols]
1 laser printer 2 personal computer 3 communication cable 11 ASIC
12 CPU
13 ROM
14 RAM
15 Key Sensor 16 Feed Sensor 17 Discharge Sensor 18 Temperature Control Unit 19 Fan Drive Unit 20 Clock Measurement Unit 82 Electronic Processing Unit 83 Photosensitive Drum 84 Transfer Unit 85 Fixing Unit 86 Fan

Claims (4)

A paper feed sensor provided in the paper feed traveling unit for detecting the leading and trailing ends of the paper before printing, and a paper discharging sensor provided in the paper discharging traveling unit for detecting the leading and trailing ends of the printed paper. A paper sensor, a time measuring unit for measuring various times, and a paper feeding operation based on a detection signal from the paper feeding sensor, a detection signal from the paper ejection sensor, and a time measured by the time measuring unit. Control means for measuring, by the time measuring means, a first time from the start of paper feeding until the paper feed sensor detects the leading edge of the paper, and the first time If the time exceeds the first comparison time set internally, it is determined that the paper is abnormal and an error handling operation is performed. After the paper feed sensor detects the leading edge of the paper, the paper discharge sensor The second time until the leading edge of the paper is detected is When the second time exceeds the second comparison time set internally, it is determined that the sheet is abnormal and an error processing operation is performed. When a third time from when the sheet is detected to when the trailing edge of the sheet is detected is measured by the time measuring means, and the third time exceeds a third comparison time set internally. In an image forming apparatus configured to perform an error processing operation by determining that a paper feed is abnormal,
A storage unit that stores in advance a standard time from when the sheet feed sensor detects the leading end of the sheet to when the trailing end of the sheet is detected, for each type of usable sheet;
At the time of printing operation, the control means,
Each time paper is fed one by one, the time measuring means measures the time from when the paper feed sensor detects the leading edge of the paper to when it detects the trailing edge of the paper. By setting the third comparison time inside each time, it is possible to avoid determining that multi-feeding is a paper feeding abnormality and to continue the printing operation, and to set the third time measured by the time measurement unit and set inside. The third comparison time is compared with the standard time of each sheet stored in the storage means. If there is no standard time that matches the third comparison time, the same print data as the print data printed on the sheet is replaced with the next time. An image forming apparatus that prints again on a sheet fed to the printer. A paper feed sensor provided in the paper feed traveling unit for detecting the leading and trailing ends of the paper before printing, and a paper discharging sensor provided in the paper discharging traveling unit for detecting the leading and trailing ends of the printed paper. A paper sensor, a time measuring unit for measuring various times, and a paper feeding operation based on a detection signal from the paper feeding sensor, a detection signal from the paper ejection sensor, and a time measured by the time measuring unit. The control means measures the time from when the paper ejection sensor detects the leading edge of the paper to when it detects the trailing edge of the paper, by the time measuring means. When the measurement time exceeds a predetermined time set internally, in the image forming apparatus configured to perform the error processing operation by determining that the paper supply is abnormal,
At the time of a printing operation, each time the sheet is fed one sheet at a time, the control unit sets a time period from when the time sensor detects the leading edge of the sheet to when the trailing edge of the sheet is detected. An image forming apparatus that measures a time and sets the measured time as the predetermined time inside each time, thereby avoiding determining a multi-feed as an abnormal sheet feeding and continuing the printing operation. The control means measures, by the time measuring means, a first time from the start of paper supply to the paper supply sensor detecting the leading edge of the paper, and the first time is set internally. If the time exceeds the first comparison time, it is determined that the sheet is abnormal, and an error processing operation is performed. A second time until the detection is measured by the time measuring means, and if the second time exceeds a second comparison time set internally, it is determined that the sheet is abnormal and the error processing operation is performed. The image forming apparatus according to claim 2, wherein: A storage unit that stores in advance a standard time from when the sheet feed sensor detects the leading end of the sheet to when the trailing end of the sheet is detected, for each type of usable sheet,
The control means, when the time measuring means measures the time from when the paper feed sensor detects the leading end of the sheet to when it detects the trailing end of the sheet, the measured time is stored in the storage means. If the standard time does not match the measured time, print the same print data on that paper again on the next paper. The image forming apparatus according to claim 2, wherein:

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