JP2001151383A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of accurately determining a jam when an image is copied and printed to a recording sheet. SOLUTION: Cassettes 2-4 for storing sheets are disposed in a body case 1a of this image forming device 1, and respective cassettes are provided with sheet detecting sensors 5a-5c for detecting existence of the sheets. A manual paper feeding portion 7 also includes a sheet detecting sensor. A paper feeding roller 10 has a paper feeding sensor 11, and a paper discharging roller 16 has a paper discharging sensor 17. When paper is fed by each cassette or the manual paper feeding, the size of the sheet is set, and time from ON to OFF of the paper feeding sensor 11 is measured, and length of the sheet is measured based on a peripheral velocity of the paper feeding roller 10. When the size of an actually fed sheet is different from the size of a set sheet, timer value of a timer for detecting the jam is charged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to accurately determine a jam even when the set paper size is different from the actually fed paper size when copy-printing on recording paper. The present invention relates to an image forming apparatus having a configuration capable of performing the following.

[0002]

2. Description of the Related Art When copying an original in an image forming apparatus such as a facsimile machine (hereinafter abbreviated as a multifunction peripheral) or a digital copying machine having a copy function, the number of copies and the type of the original (normally After specifying the reading mode (resolution) according to the image information of the character or figure (photo or image), press the start button to start reading the original,
Copy printing is performed on the specified number of copies of recording paper.

[0003] A plurality of cassettes are arranged in a main body case of the image forming apparatus. These cassettes are provided with a switch for setting the paper size. Each cassette is loaded with recording paper of fixed size paper having different sizes. Further, it is configured such that recording paper of a predetermined size can be loaded in the manual paper feed unit.

When performing copy print on recording paper,
When feeding paper from a cassette, the size of the paper is set by specifying the cassette to be used from an operation panel provided on the main body case. Also, when paper is fed from the manual paper feed unit, the paper size is set on the operation panel.

[0005] A sensor for detecting a sheet is provided in a conveyance path of the sheet from the cassette and the manual sheet feeding unit. When the paper is detected by this sensor during copy printing,
When a timer provided in the control device is operated and the sheet is not discharged from the conveyance path even after a lapse of a predetermined time, it is notified that a defective sheet feed (jam) has occurred, and the fact is notified.
The operation of the image forming apparatus is stopped.

[0006]

When the copy print is performed, the size of the paper actually loaded in the cassette may be different from the paper size set by the switch due to an operation error or the like. is there. Also, the size of the paper fed from the manual paper feed unit may be different from the paper size set on the operation panel.

As described above, when the set paper size is different from the size of the paper actually fed from the cassette or the manual paper feed unit, and the length of the fed paper is longer than the set value. However, there is a problem in that the control device determines that a paper jam has occurred because the paper discharge time is longer than the reference time, and cannot print on the recording paper. That is, there is a problem that the jam cannot be accurately determined because the timer value for the jam determination is fixed.

[0008] The present invention has been made in view of the above situation, and even when the set paper size is different from the actually fed paper size during copy printing, the present invention is not limited thereto. It is another object of the present invention to provide an image forming apparatus having a configuration capable of judging a paper jam.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus comprising: a display unit; a recording unit for recording data; a control unit; Means for setting the size of a sheet, a sensor for detecting the size of the sheet actually conveyed in the conveyance path, and a timer for setting a timer value for judging a jam when the sheet conveyance time exceeds a predetermined time, This is achieved by changing the timer value for judging the jam according to the size of the sheet detected by the sensor.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the size of the sheet detected by the sensor is smaller than the set sheet size, an error is displayed. It is characterized by:

Further, according to a third aspect of the present invention, in the image forming apparatus according to the first aspect, when the size of the sheet detected by the sensor is longer than the set size of the sheet, the jam is determined. It is characterized in that the timer value to be changed is changed.

According to the first aspect of the invention, the timer value for judging a jam is changed according to the size of the sheet actually conveyed on the conveyance path. For this reason, a paper jam can be detected accurately.

According to the second aspect of the present invention, the operator is notified that the size of the paper actually conveyed on the conveyance path is smaller than the size of the paper to be copied. Therefore, the operator can save paper without continuing useless copy printing.

According to the third aspect of the present invention, even when the size of the paper actually conveyed on the conveyance path is longer than the set paper size, the paper is not determined to be a jam and printed on the recording paper. can do.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic side view of an image forming apparatus to which the present invention is applied. This image forming apparatus is configured as a multifunction peripheral having both a copying function and a facsimile function as described above, and records an image on a recording sheet by an electrophotographic method.

In FIG. 1, reference numeral 1a denotes a main body case of the image forming apparatus 1, which includes a main body cassette 2, a second (second) cassette 3, and a third (third) in which sheets of different sizes are loaded.
Cassette 4 is arranged. 5a to 5c are sheet detection sensors for detecting the presence or absence of sheets in each of the cassettes 2 to 4. Each cassette is provided with switches 5x, 5y, and 5z for setting the size of the loaded paper.

Reference numerals 6a to 6c denote feed rollers, which convey sheets fed along a vertical conveying path 6x. Reference numerals 2a to 2c denote individual transport paths formed between the cassettes 2 to 4 and the vertical transport path 6x. Reference numeral 7 denotes a manual paper feed unit connected to the main body case 1a; 8, a paper detection sensor for detecting the presence or absence of paper (recording paper) in the manual paper feed unit; 9, a transport roller; and 10, a paper feed roller. Reference numerals 10a and 10a are lateral transport paths. A paper feed sensor 11 detects paper (recording paper) fed from each of the cassettes 2 to 4 and the manual paper feed unit.

Reference numeral 12 denotes a toner cartridge, 13 denotes a developing roller, 14 denotes a photosensitive drum, 14a denotes a transfer roller, and 15 denotes a fixing device using a roller. The paper fed from each of the cassettes 2 to 4 and the manual paper feed unit is transported in the horizontal transport path while the toner cartridge 12 to the fixing device 1
A predetermined image is printed by a member such as 5. Since the principle of printing an image on recording paper by the electrophotographic method is well known, detailed description thereof will be omitted.

Reference numeral 16 denotes a paper discharge roller for discharging the paper on which the image is printed, 17 a paper discharge sensor installed near the end of the horizontal transport path 10a, and 18 a link to the main body case 1a. The recording paper on which the image has been printed is accumulated on the discharged paper tray.

Here, the paper feed roller 10, the photosensitive drum 1
4. The roller of the fixing unit 16 and the discharge roller 16 are the same roller.
Driven by the Since the diameters of these members are different, the rotational speeds are different, but the peripheral speeds are the same. Therefore, the paper is conveyed at a constant speed (process speed) along the horizontal conveyance path.

FIG. 2 shows sensors 5a to 5c for detecting the presence or absence of paper in each of the cassettes 2 to 4, the sensor 8 for detecting the presence or absence of paper in the manual paper feed unit 7, a paper feed sensor 11, as shown in FIG.
FIG. 4 is an explanatory diagram showing a length between the respective sensors when a paper ejection sensor 17 is arranged. In FIG. 2, the paper detection sensor for detecting the presence or absence of paper in each cassette is PES, and the paper detection sensor for detecting the presence or absence of paper in the manual paper feed unit is HPE.
S, the paper feed sensor is represented by PSS, and the paper discharge sensor is represented by PDS.

A position having a length Sx from the PES is defined as a recording paper edge serving as a reference for detecting the length of the recording paper. The length from the end of the recording sheet to the PSS is Sa for the main body cassette, Sb for the second cassette, and Sc for the third cassette. In the manual paper feed unit, the length Sy
Is set as the recording paper edge, and the length from the recording paper edge to the PSS is Sd. The length from the PSS to the PDS is set to Se.

FIG. 3 is an explanatory diagram showing an example of a table referred to when detecting a paper feeding failure (jam). When the sheet is fed, the length between the sensors is set as shown in FIG. 2, and the reference time required for the sheet to move between these sensors is measured and set. Paper transport time is
If the time exceeds the reference time, it is determined that a paper feed failure (jam) has occurred.

In FIG. 3, the jam pattern is shown in the column (a).
1 to 3 are set. In the field (b), where the paper is to be fed from the jam 1 is set. In the jam 3, the size of the standard paper is set. In the column (c), the length (m
m) is set. In the column (d), a timer value (sec) is set.

In the case of the jam 1, FIG.
As shown by, a length obtained by adding a margin α to the length from the recording paper end to the paper feed sensor PSS is set. The margin α is, for example, 1 (sec) of paper at the process speed.
Set the length to move between. (D) timer value (s
ec) sets a reference time required for the paper to pass through from the end of the recording paper to which the margin α has been added to the paper feed sensor PSS.

When paper is fed from the main body cassette, the reference time required for the paper to be transported in a section having a length obtained by adding a margin α to the length Sa from the end of the recording paper to the paper feed sensor PSS is , Ta (sec). If the paper transport time exceeds the reference time, it is determined that the jam 1 has occurred.

The jam 2 is commonly determined when paper is fed from any of the cassettes or when paper is fed from the manual paper feed unit. In the column (c), the position of the paper feed sensor (PSS) and the paper discharge sensor (PD)
The length obtained by adding the margin α to the length Se to the position S) is set. In the column (d), the reference time Te required for the sheet to be transported in the section having the length of Se + α is used.
(Sec) is set.

When a sheet is fed from each cassette or a manual sheet feeding unit, the sheet is detected by a sheet feed sensor (PSS), and even if the reference time Te (sec) is exceeded, a sheet discharge sensor (PDS) is detected. ) Does not detect a sheet, it is determined that the jam 2 has occurred.

As for the jam 3, the length obtained by adding a margin α to the lengthwise size of the paper is set in the column (b) for each fixed-size sheet set in the column (a). .
In the field (d), a reference time obtained by dividing the length of the field (b) by the peripheral speed of the discharge roller is set. That is, during this reference time, the sheet ejection sensor (PDS) detects the leading edge of the sheet (PDS).
This is equivalent to the time from when the switch is turned on) to when the rear end of the sheet is detected (PDS is turned off). If the time from when the paper discharge sensor (PDS) is turned on to when it is turned off exceeds the reference time when the paper is discharged, it is determined that the jam 3 has occurred.

When the paper size set on the operation panel is different from the paper size actually fed as described above, for example, when A4 size paper is set,
Actually, when an A3-size sheet is fed, it is determined that the jam 3 has occurred because the discharge time of the sheet exceeds the reference time, and there is a possibility that an image is not printed on the sheet.

In the present invention, an image can be printed on a sheet even when the sheet size set on the operation panel and the actually fed sheet size are different. Next, the basic principle will be described.

As described above, since the peripheral speed of the paper feed roller 10 is known, when the paper is fed, the paper feed sensor 1
1 measures the time from when the leading edge of the paper is detected (the paper feed sensor 11 is turned on) to when the trailing edge of the paper is detected (the paper feed sensor 11 is turned off). The size can be determined.

Therefore, in the case of the above example, in the jam 3 table shown in FIG. 3, the jam 3 reference time Th for A4 paper is changed to the jam 3 determination reference time Tf for A3 paper. I do. In this way, by changing the reference time for judging the jam 3, printing can be performed on the paper even when the paper size set on the operation panel is different from the paper size actually conveyed on the conveyance path. .

FIG. 4 is a schematic block diagram showing a control device of the image forming apparatus of the present invention. Next, this block diagram will be described. The control device 20 includes a central processing control unit (CPU) 21, a network control unit (NCU) 22, a modem 23, an image memory 24, and a RAM.
25, a ROM 26, a codec 27, a display unit 28, an operation unit 29, a reading unit 30, a sensor 31, and a recording unit 32 are provided.

A timer operated by a program is set in the CPU 21. The timer value for jam determination can be set by this program timer. A network control unit (NCU) 22 controls closing and opening of the telephone line L, and detects transmission and reception of dial pulses corresponding to the fax number of the destination. The modem 23 modulates and demodulates transmission and reception data.
The image memory 24 temporarily stores received image data and image data (image data) read by an optical reading system.

The RAM 25 functions as a work area for storing temporary data and the like obtained by the arithmetic processing according to the control program. The ROM 26 stores various control programs necessary for controlling the operation of the apparatus.

The codec 27 encodes (encodes) the image data read by the reading unit 30 by MH, MR, MMR or the like when transmitting the image data to another facsimile apparatus or the like.
I do. Also, it decodes (decodes) image data received from another facsimile machine or the like. The display unit 28 includes a liquid crystal display panel and a light emitting diode (LED), and displays various information such as an operation state of the apparatus.

The operation unit 29 includes a numeric keypad 29a, a reading mode key for setting a reading mode (resolution) of a copy in accordance with whether the document is image information such as characters or photo information, and automatic reduction. A mode key 29b such as a key for setting an automatic recording paper selection mode is provided. These modes can be configured to be selected and set on the screen of the display unit 28 using a touch panel. Further, the operation unit 29 includes a copy / communication key, a start key, and a stop key for selecting which function of the copy / facsimile multifunction machine, the copy mode or the facsimile communication mode, is to be selected. And various keys necessary for operating the image forming apparatus.

The reading section 30 is constituted by an optical reading system, and inputs an image reading signal to the image processing circuit 30a.
After performing image area separation processing according to whether the original image data is image information such as characters or photographic information, that is, according to the characteristics of the original image data such as density distribution and variation. , And performs a binarization process on each image area.

As described above, the sensor 31 has a paper detection sensor (PES) for detecting the presence or absence of paper in each cassette.
And a paper detection sensor 31a including a paper detection sensor (HPES) for detecting the presence / absence of paper in a manual paper feed unit, a paper supply sensor (PSS) 31b, and a paper discharge sensor (PDS) 31c.

The recording unit 32 is composed of an electrophotographic printer and converts received image data and image data read by an optical reading system onto recording paper of a fixed size supplied from each cassette or a manual paper feed unit. Make a copy print. It is also possible to provide a clock section for counting the current time and print the time at that point on a received document using the output.

FIGS. 5 to 8 are flowcharts showing the processing procedure when copying and printing on recording paper in the image forming apparatus of the present invention. Next, this flowchart will be described.

(1) A processing program is started in step S1, and a cassette to be used is determined in step S2. At this time, the paper size length set in the selected cassette is detected. When the user selects paper feeding from the manual paper feeding unit, the user inputs a paper size from the operation unit. Next, in step S3, the feed of the sheet is started.

(2) Subsequently, in step S4,
According to the paper feeding method selected in step S2, FIG.
The timer for jam 1 determination described above is started. The jam 1 is for determining whether or not a paper feed failure (jam) has occurred before the paper that has passed the recording paper edge at the reference position reaches the paper feed sensor (PSS).
These timer values Ta to Td are fixed values.

(3) Next, in step S5, it is determined whether or not the paper feed sensor (PSS) is on. If the result of this determination is YES (hereinafter abbreviated as Y), it means that no paper jam has occurred between the recording paper edge and the paper feed sensor (PSS).
Stop the timer. If the decision result in the step S5 is NO (hereinafter abbreviated as N), the process shifts to a step S8 to decide whether or not the jam 1 timer has timed out. If the decision result in the step S8 is N, a step S is executed.
Returning to the processing of step 5, the loop processing of steps S5 and S8 is repeated until the jam 1 timer times out.

(4) If the result of the determination in step S8 is Y, the jam 1 timer has expired before the paper reaches the position of the paper feed sensor (PSS).
It is determined that a jam has occurred in the transport path between the recording sheet end of each cassette or the manual sheet feeding unit and the sheet feeding sensor (PSS). At this time, the occurrence of an error before recording on the recording paper is displayed on the display unit in the processing of step S9, and the processing program ends in step S16.

(5) After the jam 1 timer is stopped in the process of step S6, the process proceeds to step S7.
In the process of step S7, a feed sensor (PSS) off monitoring timer is started. In this case, in the case of sheet feeding from each cassette, the timer value is obtained by dividing a value obtained by adding a margin value α to the length according to the sheet size set in each cassette by the peripheral speed value of the sheet feeding roller. Value. In the case of paper feeding from the manual paper feeding unit, a value obtained by adding a margin α to the length according to the paper size set in the operation unit is divided by the peripheral speed value of the paper feeding roller. .

(6) Next, the jam 2 timer is started in the process of step S10. The jam 2 detects a jam in the transport path from the paper feed sensor (PSS) to the paper ejection sensor (PDS) as described above. The time-up time (timer value) of the jam 2 timer is fixed.

(7) Subsequently, it is determined in step S11 whether the paper discharge sensor (PDS) is on. If the result of this determination is Y, the sheet has been properly discharged.
Has been conveyed to the position of
In step 12, the jam 2 timer is stopped. Step S
If the determination result in Step 11 is N, the process proceeds to Step S14. During the loop of steps S11 and S14, the sheet feed sensor (PS
S) Processing during off monitoring is performed in parallel.

(8) Next, it is determined whether or not the jam 2 timer has expired in the process of step S14. If the result of the determination is N, the process returns to step S11,
The loop processing of steps S11, S13, and S14 is repeated. If the decision result in the step S11 becomes Y, this loop processing is exited and the step S11 is executed as described above.
The process proceeds to step 12.

(9) If the determination result in step S14 is Y, it means that the jam 2 timer has expired even though the paper has not passed through the paper ejection sensor (PDS). Sensor (PSS) and paper ejection sensor (PD
It is determined that a jam has occurred on the transport path between S) and
After the error during recording is displayed in step S15, the process ends in step S16.

(10) Jam 2 in the process of step S12
After performing the process of stopping the timer, the process proceeds to step S17. In the process of step S17, the jam 3 timer is started. This timer uses a paper ejection sensor (PDS)
This is a jam monitoring timer for setting the time from ON to OFF. In the case of sheet feeding from cassettes, the timer value is a value obtained by dividing a value obtained by adding a margin value to a length according to a sheet size set in each cassette by a peripheral speed value of a sheet discharging roller. In the case of sheet feeding from the manual sheet feeding unit, the value obtained by adding a margin value to the sheet size input from the operation unit is divided by the peripheral speed value of the sheet discharging roller.

(11) Next, in the processing of step S18,
It is determined whether the discharge sensor (PDS) is off. If the result of this determination is Y, it means that the paper has been properly ejected, and subsequently the jam 3 timer is stopped in the processing of step S19. If the decision result in the step S18 is N,
The process moves to step S24a. Step S18,
During the loop of steps S24a and S27, the process of monitoring the feed sensor (PSS) off in step S24 indicated by the broken line is performed in parallel.

(12) In the process of step S20, it is determined whether or not there is a paper size length shortage error in the feed sensor (PSS) off monitoring process. This determination result is Y
If so, in the process of step S22, a message "recorded on paper less than the selected paper size length" is displayed on the display unit. By notifying the operator of such an error message, the operator can stop useless copy printing and save paper.

(13) If the decision result in the step S20 is N, then in a step S21 the paper feed sensor (P
SS) It is determined whether there is a paper size length excess error in the off monitoring process. If this determination result is N,
In step S16, the processing program ends. If the decision result in the step S21 is Y, then a step S22 is executed.
The message "Recorded on paper longer than the selected paper size" is displayed on the display unit.

(14) In the process of step S24a, it is determined whether or not the jam 3 timer is being activated for the first time. If the result of this determination is Y, then in the processing of step S27,
It is determined whether it is the first time-out of the jam 3 timer. If the determination result is N, the process returns to step S18, and it is determined whether the sheet discharge sensor (PDS) is off.

(15) If the decision result in the step S27 is Y, then in a step S28, a paper size length excess error in the feed sensor (PSS) off monitoring processing is executed.
It is determined whether or not there is. If the result of this determination is Y, then the jam 3 timer 2
A second activation is performed, and the process returns to step S18.

As described above, in the present invention, when a sheet of a size longer than the set sheet size is fed, a means for changing the timer value to the jam 3 timer corresponding to the sheet size is provided. ing. For this reason, when the size of the paper actually conveyed in the conveyance path is different from the set paper size, the jam (paper jam) is accurately determined without determining that a paper jam (paper jam) has occurred in the paper discharge unit. Clogging) can be determined.

(16) If the determination result in step S24a is N
In the case of, it is next determined whether or not the second time of the jam 3 timer has expired in the process of step S25. If the determination result is Y, the jam 3 timer has reached the second time-up even though the paper ejection sensor (PDS) has not been turned off, so the ejection error ( Is displayed on the display unit.

(17) If the result of the determination in step S28 is N, the jam 3 timer has reached the first time-up even though the paper discharge sensor (PDS) has not been turned off. And feed sensor (PSS)
This is not an error of paper size length excess in the off monitoring process. In this case as well, a discharge error is displayed on the display unit in the process of step S26.

FIG. 9 is a flowchart showing a processing procedure during monitoring of the feed sensor (PSS) off. This processing is performed in parallel with the processing described with reference to FIGS. Next, this flowchart will be described.

(1) The processing program is started in step S30, and it is determined in step S31 whether or not the sheet feed sensor (PSS) is off. If the result of this determination is N, the process moves to step S32, and it is determined whether or not the feed sensor (PSS) off monitoring timer has expired. If the determination result in step S32 is N, the process returns to step S31, and step S3
1. The loop processing of step S32 is repeated.

(2) If the result of the determination in step S32 is Y, the feed sensor (PSS) off monitoring timer has expired, even though the feed sensor (PSS) has not been turned off. Therefore, the process proceeds to step S33 to turn on the error status that the size length is exceeded.
Subsequently, the process returns to step S31.

(3) If the decision result in the step S31 is Y, then in a step S34, it is determined whether or not an error status exceeding the paper size length is on. If the result of this determination is Y, the processing program ends in step S38.

(4) If the result of the determination in step S34 is N, the feed sensor (PSS) off monitoring timer is stopped, and the actual measurement time (from when the PSS is on to when the paper passes the feed sensor (PSS)) is stopped. Off time).

(5) In the process of step S36, in the case of paper feeding from cassettes, the length according to the paper size set in each cassette, and in the case of paper feeding from the manual paper feeding unit, operation is performed. And a time (B) obtained by subtracting a constant value α from the time required for the paper to pass through the length according to the paper size input from the unit, and the actual measurement time (B) when the paper has passed the paper feed sensor (PSS). Shall be compared).

(6) If the result of the comparison is A> B, then in step S37 the paper size shortage error status is turned on. If the comparison result is not A> B, it means that the paper has been normally fed, and the processing program ends in step S38.

[0068]

As described above, according to the first aspect of the present invention, the timer value for judging a jam is changed according to the size of the sheet actually conveyed on the conveying path. For this reason, a paper jam can be detected accurately.

According to the second aspect of the present invention, the operator is notified that the size of the paper actually conveyed on the conveyance path is smaller than the size of the paper to be copied and printed. Therefore, the operator can save paper without continuing useless copy printing.

According to the third aspect of the present invention, even when the size of the paper actually conveyed on the conveyance path is longer than the set paper size, the paper is not determined to be a jam and is printed on the recording paper. can do.

[Brief description of the drawings]

FIG. 1 is a schematic side view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a length between respective sensors shown in FIG. 1;

FIG. 3 is an explanatory diagram showing an example of a table referred to when a jam is detected.

FIG. 4 is a schematic block diagram illustrating a control device of the image forming apparatus.

FIG. 5 is a flowchart showing a processing procedure of the present invention.

FIG. 6 is a flowchart showing a processing procedure of the present invention.

FIG. 7 is a flowchart showing a processing procedure of the present invention.

FIG. 8 is a flowchart showing a processing procedure of the present invention.

FIG. 9 is a flowchart showing a processing procedure of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2-4 Cassette 5a-5c Paper detection sensor 6x Vertical conveyance path 7 Manual paper feed unit 8 Paper detection sensor 10 Paper feed roller 11 Paper feed sensor 12 Toner cartridge 13 Developing roller 14 Transfer drum 15 Fixing unit 16 Discharge roller 17 Discharge sensor

Claims (3)

[Claims] A display unit; a recording unit for recording data;
A control unit, means for setting a size of paper to be fed,
A sensor for detecting the size of the sheet actually conveyed on the conveyance path, and a timer for setting a timer value for judging a jam when the conveyance time of the sheet exceeds a predetermined time, the sheet detected by the sensor An image forming apparatus that changes a timer value for judging the jam according to the size of the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein an error is displayed when the size of the sheet detected by the sensor is smaller than the set sheet size. 3. The image forming apparatus according to claim 1, wherein when the size of the paper detected by the sensor is longer than the set paper size, a timer value for determining the jam is changed. apparatus.