JPH10194529A - Image forming device and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge a paper sheet to the outside of a machine without increasing the cost of a paper sheet sensor and jamming the paper sheet, even when an user mistakes the set of a paper sheet size. SOLUTION: A vertical synchronous signal from a video controller 102 is waited when a printing start indication is issued from a printing control means 108. The video controller 102 outputs the vertical synchronous signal for the main control device 101 of a laser beam printer and outputs an image signal from that signal after a prescribed timing. A resist roller control means 109 starts the count of a timer at the same time when the rotation of the resist roller is started. Thereafter, when a paper size mis-match information is received from a paper size mis-match detection means 105, the paper sheet rear end calculated based on the paper sheet rear end detection timing of a sensor 112 before resist stands by until the timing passing the resist roller and stops the resist roller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and system having a function of forming an image on a sheet of a size designated externally, and more particularly to a method for synchronizing a sheet with an image by a predetermined roller. The present invention relates to an image forming apparatus and a system having a roller for taking an image.

[0002]

2. Description of the Related Art Conventionally, a roller for synchronizing a sheet with an image as described above (hereinafter referred to as a registration roller).
Most of the printing apparatuses having the above configuration perform positioning of the sheet before printing by pressing the leading end of the sheet sent from the sheet supply unit against the registration roller in a stopped state.

Accordingly, in continuous printing, the registration roller is controlled to continue rotating until the rear end of the paper being conveyed passes through the roller, and to stop the rotation before the succeeding paper reaches the roller. For this reason, in the control of the registration roller, processing for driving the registration roller for a predetermined time set in advance for each sheet size has been conventionally performed.

[0004]

There is a printing apparatus in which the size of paper to be printed is designated from outside. Alternatively, there is a printing apparatus in which a part of a plurality of paper feeding units employs the above-described method.

In a printing apparatus of the type in which the size of paper to be printed is designated from the outside as described above, the rotation time of the registration roller is also controlled according to the designated size. In this case, if a sheet longer than the size specified by the user is set (or a size shorter than the set sheet is specified to the printer), the registration is performed for the time set for each sheet size as in the conventional example. In the control to stop after rotating the roller, the registration roller is stopped before the trailing edge of the paper passes through the registration roller, and the paper being printed is pulled by the registration roller, causing image blurring, The paper cannot be conveyed and a jam occurs.

In order to avoid such a situation, the sensor detects the trailing end of the actually conveyed sheet, and stops the registration roller based on the timing. It must be highly accurate, leading to increased costs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is capable of discharging a sheet without jamming the sheet even if a user makes a mistake in setting a sheet size without increasing the cost of a sheet sensor. It is intended to provide a forming apparatus and a system.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a sheet before image formation is positioned by pressing a leading edge of a sheet sent from a sheet supply unit during a stop. A roller that conveys a sheet during driving, a sheet sensor positioned immediately before the roller, a sheet size specifying unit that specifies the size of a sheet to be used, a signal from the sheet sensor and a drive start timing of the roller. Paper length measuring means for measuring the length of the paper based on the paper length, and the actual paper length is obtained by the paper length measuring means, and the paper length is different from the paper size specified by the paper size specifying means. When the paper size mismatch detecting means for detecting the paper size mismatch and when the paper being conveyed is not determined to be the paper size mismatch by the paper size mismatch detecting means, The driving of the roller is stopped at a preset timing based on the specified paper size, and when it is determined that the paper sizes do not match, after a predetermined time based on the paper length measured by the paper length measuring means, A roller control means for stopping the driving of the roller.

Further, the invention according to claim 2 is characterized in that, in claim 1, the roller is a registration roller for synchronizing a sheet and image data.

Further, according to a third aspect of the present invention, in the first or second aspect, the paper size designation means designates a paper size based on external information.

Further, the invention according to claim 4 is the invention according to claims 1 to 3.
Wherein the roller control means supplies the drive start timing of the roller to the paper length measuring means.

Further, the invention of claim 5 provides the invention according to claims 1-4.
In any one of the above (1) to (4), a manual sheet feeding means for feeding the sheet is provided.

Further, the invention of claim 6 provides the invention according to claims 1 to 5
In any one of the above, when the paper size mismatch is detected by the paper size mismatch detecting means as the paper on which an image is being formed, a paper feed control means for stopping the feeding operation of the subsequent paper is provided.

According to a seventh aspect of the present invention, in the sixth aspect, the mechanism for stopping the feeding operation of the subsequent sheet is
It is characterized by being independent of other paper transport systems.

Further, the invention of claim 8 provides the invention according to claims 1 to 7
Is characterized in that the image forming apparatus is a laser beam printer.

Further, the invention of claim 9 comprises an image forming apparatus main body and a system controller for supplying image data to the image forming apparatus main body and controlling the image forming apparatus main body to perform an image forming process. In the image forming system, the image forming apparatus main body performs positioning of the sheet before image formation by pressing the leading end of the sheet sent from the sheet supply unit during stoppage, and a roller that conveys the sheet during driving, A paper sensor positioned immediately before the roller, a paper size specifying unit for specifying the size of the paper to be used based on information from the system controller, and a signal from the paper sensor and a drive start timing of the roller based on a signal from the paper sensor. Paper length measuring means for measuring the length of the paper, the actual paper length is determined by the paper length measuring means, And paper size mismatch detecting means for detecting the paper size mismatch when the paper length was different with the designated paper size by the paper size specifying unit,
When a paper size mismatch is detected by the paper size mismatch detection unit, a paper size mismatch notification unit that notifies the system controller of the paper size mismatch, and a paper transport system is stopped in response to an emergency stop instruction from the system controller. An emergency stop means for stopping an image forming operation, and an automatic paper discharge means for driving a paper transport system in response to an automatic paper discharge instruction from the system controller and discharging paper remaining in the apparatus. The controller has means for outputting an emergency stop instruction to the image forming apparatus main body and then outputting an automatic paper ejection instruction when the paper size mismatch notification unit notifies the image forming apparatus main body of a paper size mismatch. It is characterized by the following.

Further, the invention of claim 10 is characterized in that, in claim 9, the roller is a registration roller for synchronizing a sheet and image data.

Furthermore, the invention of claim 11 is characterized in that the image forming apparatus of claim 9 or 10 is a laser beam printer.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 2 is a sectional view of a laser beam printer 201 having a paper trailing edge detecting means of the present invention.

As shown in FIG. 2, the laser beam printer 201 has a cassette 202 for storing the recording paper S, a pickup roller 203 for picking up the recording paper from the cassette 202, and a paper feed for feeding out the picked-up recording paper. A roller 204 is provided. A transport roller 206 that transports the fed recording paper to a registration roller described below is provided downstream of the paper feed roller 204.

On the other hand, the laser beam printer 201 has another multipurpose tray (hereinafter referred to as MPT) 207 which can manually feed irregular-shaped paper.
MPT paper feed roller 209 for drawing out recording paper from MPT 207 and MPT lifter 2 for pressing recording paper set in MPT 207 against roller 209
08 is provided.

The recording paper transport path 205 from the cassette and the transport path 210 from the MPT 207 join at a junction C to reach a registration roller described later.

A registration roller 211 for synchronously transporting the recording paper S is provided downstream of the junction C. A registration sensor 112 as a paper sensor is provided immediately before the registration roller 211. I have. The sensor detects the presence of a sheet at the position by the light shielding plate shielding the photo-interrupter by the contact of the sheet. Downstream of the registration roller 211, a laser scanner unit 213 is provided.
Forming unit 212 that forms an image using laser light from
Are arranged. Further, a fixing unit 214 is disposed downstream of the image forming unit 212, and sheet discharge conveyance rollers 215, 216, and 217 are disposed downstream of the fixing unit 214, and a recording sheet reaches a sheet discharge tray 219. Is transported. The M
The PT 217 prints on non-standard paper, so that the MPT 207 is used.
At the time of printing from the printer, information relating to the paper size is set in advance in the laser beam printer 201 from a video controller described later.

When printing, the cassette 202 or the MPT
The sheet fed from 207 is positioned by being pressed against the registration roller 211 by the upstream roller 206 or 209 while the rotation of the registration roller 211 is stopped. And
By starting rotation of the registration roller 211 in synchronization with a vertical synchronization signal of an image output from a video controller described later, the image data sent from the video controller is synchronized with the sheet, and a predetermined position on the sheet is set. Print the image on Since the above control is publicly known, detailed description is omitted.

FIG. 1 is a block diagram showing the configuration of the present invention.

The laser beam printer 201 has a main controller 101 for controlling the entire laser beam printer 201. The main controller 101 includes a CPU, a ROM, a RAM, a gate element, and the like, and a main part of control executed by the CPU is realized by a software program written in the ROM. Further, the control procedure of the CPU as shown in FIG. 3 is also written in the ROM.

Main controller 101 is connected to video controller 102 via controller interface 103.

Main controller 101 includes controller communication means 104, paper size mismatch detection means 105, sensor reading means 106, paper size information storage means 107, print control means 108, registration roller control means 109, cassette paper feed control means 110 , MPT paper feed control means 111 and the like, and these
This is realized by a program written in. By these various functions, the cassette 202, the pickup roller 203, the sheet feeding roller 204, the conveying roller 206, the cassette sheet feeding mechanism 113 including the driving mechanism thereof, the MPT 207, the MPT lifter 208, the MP
An MPT paper feed mechanism 114 composed of a T paper feed roller 209 and a drive mechanism thereof;
1 and a registration roller mechanism 115 composed of a driving mechanism thereof.

Further, the paper size mismatch detecting means 10
5 is a paper size measuring means 116, a paper size comparing means 1
17.

Next, the function of each section will be described.

The controller communication means 104 controls communication with the video controller 102 via the controller interface 103. Controller communication means 1
04 performs clock-synchronized serial communication with the video controller 102, various commands from the video controller 102 to the laser beam printer 201,
Further, various state information is exchanged from the laser beam printer 201 to the video controller 102.
It also exchanges various timing signals related to the printing operation.

As described above, when printing the recording paper from the MPT 207, the paper size information set in the laser beam printer 201 from the video controller 102 is performed through this clock synchronous serial communication. Then, the controller communication unit 104 stores the received sheet size information in the sheet size information storage unit 107. Also,
Video controller 1 from laser beam printer 201
The information of the paper size mismatch described later, which is notified to 02, is also performed through the clock synchronous serial communication.

The paper size mismatch detecting means 105 comprises the paper size measuring means 116 and the paper size comparing means 117 as described above.

The paper size measuring means 116 measures the length of the paper being conveyed based on the information from the pre-registration sensor 112 received via the sensor reading means 106 and the registration roller drive start timing received from the registration roller control means 109. I do.

The paper size comparing means 117 compares the paper size information obtained by the paper size measuring means 116 with the information on the paper size designated by the video controller stored in the paper size information storage means 107,
As a result, when it is determined that the specified paper size is different from the actual paper size, information on paper size mismatch is reported to the print control means 108 and also to the video controller via the controller communication means 104. When checking the paper size, the sensor 11
A predetermined range is set before and after the designated sheet length in consideration of the detection error of 2, and it is determined whether or not the measured sheet length falls within the range. Since these controls are publicly known, detailed descriptions thereof will be omitted.

The print control means 108 is provided in the cassette sheet feeding mechanism 1.
13, MPT paper feed mechanism 114, registration roller mechanism 11
5 and the like to control the conveyance of the sheet, the image forming unit 212, the laser scanner unit 213, and the fixing unit 2.
14 to control the video controller 102
The image is printed on paper in accordance with the image data from.

The registration roller control means 109 controls the stop of the driving of the registration rollers 211 so as to synchronize the paper and the image data by driving the registration rollers at a predetermined timing in accordance with an instruction from the printing control means 108. I do.

As described above, the leading end of the fed sheet is pressed against the stopped registration roller to set the sheet position before printing. Therefore, in continuous printing, the registration roller 211 is being conveyed by the same roller. It is necessary to continue the rotation until the trailing edge of the sheet passes through the roller, and to stop before the succeeding sheet reaches the roller. For this reason, conventionally, in the control of the registration roller, a process of driving the registration roller for a predetermined time set in advance for each sheet size is performed.

On the other hand, when the sheet is fed from the MPT 207, the registration roller control means 109 performs control according to the sheet size specified from the outside.
Due to the structure of the MPT 207, the user may erroneously set a sheet having a size different from the sheet designated in advance. If a sheet longer than the size specified by the user is set (or a size shorter than the set sheet is specified for the printer), the registration rollers are set for the time set for each sheet size as in the above-described conventional example. In the control to stop after rotating, the registration roller is stopped before the trailing edge of the paper passes the registration roller,
When the paper being printed is pulled by the registration roller, the image is blurred, or the paper cannot be transported, and a jam occurs. In order to avoid such a situation, the rear end of the sheet actually conveyed is detected by a sensor (for example, the pre-registration sensor 112 in this example),
If the control for stopping the registration roller is performed based on the timing, the paper sensor must have high detection accuracy, which leads to an increase in cost.

Therefore, the registration roller control means 109 of this embodiment performs control as described below without increasing the cost of the paper sensor and without jamming the paper even if the user sets the paper size incorrectly. It can be discharged outside the machine.

FIG. 3 shows a flowchart of the control of the registration roller control means 109 in this embodiment. First, in step S001 (hereinafter simply referred to as S001), the process waits until a print start instruction is received from the print control unit 108. When a print start instruction is issued from the print control unit 108, the process proceeds to S002 and waits for a vertical synchronization signal from the video controller 102. Between S001 and S002, the print control unit 108 issues a paper feed instruction to either the cassette paper feed control unit 110 or the MPT paper feed control unit 111 according to the paper feed port designated by the video controller 102.
When receiving the information of the completion of the paper supply from the paper supply control unit that has issued the instruction, the video controller 102 issues a request for outputting a vertical synchronization signal to the video controller 102. Video controller 10
2 outputs a vertical synchronizing signal to the main controller 101 of the laser beam printer 201 and outputs an image signal after a predetermined timing from the signal. Registration roller control means 1
In step S003, when a vertical synchronization signal is received from the video controller 102 in step S002, the flow advances to step S003, and after a predetermined time has passed to synchronize the sheet and the image, the registration roller starts rotating in step S004 and starts counting by a timer (not shown). Thereafter, in S005, the process stands by until the information of the trailing edge detection of the sheet is received from the sheet size measuring unit 116 of the sheet size mismatch detecting unit 105. During standby, it is checked in step S007 whether the paper size mismatch detection unit 105 outputs information on paper size mismatch detection. If it is confirmed in S007 that the trailing edge of the paper is detected by the before-registration sensor 112 before the mismatch of the paper size is detected, the process proceeds to S006 and waits until the count value of the timer reaches a preset time according to the paper size. Then, at a preset registration roller stop timing, S0
In step 09, the registration rollers are stopped. On the other hand, S007
If the information of paper size mismatch is received, the process proceeds to S008 and waits until the trailing edge of the sheet calculated based on the trailing edge detection timing of the sensor 112 before registration passes the registration roller. At this timing, the trailing edge of the sheet is sufficiently adjusted by the registration roller 2 in consideration of the detection error of the sensor 112 before registration.
11 is set. When the predetermined timing has been reached, the process proceeds to S009 to stop the registration roller.

As described above, the pre-registration sensor 112 of this embodiment employs a mechanical mechanism in which the light-shielding plate shields the photo-interrupter upon contact with the sheet, so that chattering of the sensor particularly occurs at the rear end of the sheet. The accuracy of detecting the trailing edge of the paper is low. Therefore, if the control from S008 to S009 is performed, in the case of continuous printing, after the leading edge of the succeeding sheet has passed through the registration roller 211, the roller may be stopped. However, when a paper size mismatch occurs in the laser beam printer 201, error information is output to the video controller 102 and print control is interrupted. The control after S008 is started after the paper size mismatch is detected, and even if the leading edge of the succeeding paper is in front of the registration roller 211 as described above, the paper is removed by a known method. By automatically discharging the paper, when the paper size mismatch occurs, the paper being transported can be entirely discharged to the outside of the apparatus without jamming.

(Second Embodiment) In the first embodiment, when there is a succeeding paper feed following a paper determined to have a paper size mismatch, the succeeding paper feed is performed as described above due to a detection error of the pre-registration sensor 112. There is a case where the sheet is stopped at the registration roller portion in a state where the leading end of the paper feed advances ahead of the registration roller. Further, as shown in FIG. 4, when the actual paper length is longer than the designated paper length and the difference is larger than the paper supply interval at the time of continuous printing, the two papers are overlapped. Sensor 11
In 2, the trailing edge of the sheet can be detected when the trailing edge of the second sheet has passed the sensor. For this reason, if a paper size mismatch occurs in continuous printing using only the control of the first embodiment, another sheet may be wasted in addition to the sheet being printed.

Therefore, in the second embodiment, a control is added to stop the paper feeding operation if continuous paper is being fed at the time when the paper size mismatch is detected.

The laser beam printer of this embodiment is the first
Since the embodiment is the same as that of FIG.

FIG. 5 shows a functional configuration of the present embodiment. First
The difference from FIG. 1 of the embodiment is that the number of information transmission paths for notifying the paper size mismatch information from the paper size mismatch detection means 505 to the MPT paper feed control means 511 has been increased. The control procedure of the CPU as shown in FIG. 6 is written in the ROM. MPT paper feed control means 511
When the information of the paper size mismatch is received from the paper size mismatch detecting means 505, the paper feed control is stopped immediately.

FIG. 6 shows the MPT paper feed control means 5 of this embodiment.
11 shows a flowchart of the control of FIG. First, in step S101, a print start instruction from the print control unit 508 is waited.
To start paper feed control from the MPT. Then S
At 103, the process waits until the leading edge of the sheet is detected by the pre-registration sensor 112. When the leading edge sensor 112 detects the leading edge of the sheet, the process proceeds to the sheet registration control of S104. Above, S1
02 to S104 are the same as the conventional paper feed control, but the MPT paper feed control unit 511 of the present invention performs S
While waiting for the detection of the leading edge of the sensor paper at 103 in S103,
It is checked whether paper size mismatch information has been received from the paper size mismatch detection means 505. And S1
If the paper size mismatch information is received in 05, the flow advances to S106 to forcibly end the paper feeding operation. As a result, the drive of the MPT paper feed roller 209 is stopped when the paper size mismatch of the preceding paper is detected as shown in FIG. 4, for example, and the paper being fed stops before the registration sensor 112. Become. Then, when the trailing edge of the paper being printed, which is determined to be inconsistent with the paper size, passes the pre-registration sensor 112, the trailing edge of the paper is detected, and the registration roller control unit 509 described in the first embodiment also controls the paper being printed. After the rear end passes through the registration roller 221, the rotation of the roller is stopped. The sheet being fed is stopped before the pre-registration sensor as shown in the figure, so that it can be reused at the next sheet feeding.

Further, in this example, the paper size mismatch may occur only in the paper feeding from the MPT. By performing the paper control in the same manner, the fed paper can be stopped in a reusable state.

With the above-described control, it is possible to eliminate waste of the paper when the paper size mismatch is detected.

(Third Embodiment) In the first and second embodiments, the main control units 101 and 501 of the laser beam printer 201 perform control when paper size mismatch is detected. However, it has a function of stopping paper conveyance by an instruction of an external device (a video controller or the like) to the printing apparatus main body, and a function of driving a paper conveyance mechanism and discharging residual paper in the apparatus by an instruction from the outside. As long as the device does not have the functions of the first and second embodiments, the same effects as those of the devices of the first and second embodiments can be obtained by controlling the external device.

The laser beam printer of this embodiment is the first type.
Since the embodiment is the same as that of FIG.

FIG. 7 shows a functional configuration of the present embodiment. First
1 and 2 in FIG. 1 are different from FIG. 5 in the embodiment of FIG. 1 and FIG.
There is no information transmission path for notifying the paper size mismatch information, and there is an emergency stop control unit 718 and an automatic paper discharge control unit 719. The video controller 702 includes a CPU and this CP.
It has a U work area and a memory in which the control procedure of the CPU is written as shown in FIG. Emergency stop control means 7
Numeral 18 stops all paper transport mechanisms in response to an emergency stop instruction sent from the video controller 702. Also,
The automatic sheet discharging control means 719 drives the sheet conveying mechanism in response to the emergency stop instruction sent from the video controller 702, and performs an operation of discharging the sheet remaining in the apparatus. Since these functions are publicly known, detailed description will be omitted.

FIG. 8 shows a flowchart of control of the video controller 702 in the present embodiment. First, S2
In step 01, the main controller 701 is instructed to start printing.
Next, in step S202, output of a vertical synchronization signal request from the main control device 701 is waited. If a vertical synchronization signal request is received, the process proceeds to S203, where a vertical synchronization signal is output to the main controller 701, and after a predetermined timing, output of image data is started in S204. Then, while waiting for the completion of image data output in S205, the main controller 701 in S206.
Check if the information of paper size mismatch occurrence is output from. If the output interference of the image data is normal, the process ends normally. On the other hand, if information of paper size mismatch is output from the main control device 701 in S206, the process proceeds to S207, and an emergency stop instruction is sent to the main control device 701. Then, the process proceeds to S208, in which an automatic sheet ejection instruction is sent to the main control device 701, and the process ends.

Under the control of the video controller 702 as described above, the main control unit 101 operates the emergency stop control means 718 as soon as the paper size mismatch is detected, and stops the conveyance of the paper of the paper size mismatch. If the succeeding paper is being fed, the feeding operation is also stopped. Then, in response to the automatic sheet ejection from the video controller 702, the automatic sheet ejection control means 719 operates to eject the sheet whose paper size does not match the outside of the apparatus. However, in the automatic paper discharge control, the paper feeding mechanism remains stopped, so that the paper being fed is left as it is, and can be reused in the next and subsequent printing.

According to the above-described control, even in the case of a conventional printer main body, if the paper size mismatch occurs only by changing the control of the video controller, all the paper in the apparatus can be discharged.

[0057]

As described above, according to the present invention,
Without increasing the cost of the paper sensor, even if the paper length instructed from the outside and the actually set paper length are different, the paper does not jam and can be discharged outside the machine. .

When the specified paper size is different from the actual paper size, if there is a subsequent paper being fed, the roller is stopped and the paper feeding operation is stopped. The paper can be held in a reusable state.

Therefore, even when the designated paper size differs from the actual paper size, the image forming apparatus can be kept in an image-formable state, and paper other than during image formation is not wasted. And the usability of image formation can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a functional configuration of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a laser beam printer embodying the present invention.

FIG. 3 is a flowchart illustrating control of a registration roller control unit according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a state of a sheet when a sheet size differs during continuous printing.

FIG. 5 is a block diagram showing a functional configuration according to a second embodiment of the present invention.

FIG. 6 is a flowchart illustrating control of an MPT paper feed control unit according to a second embodiment of the present invention.

FIG. 7 is a block diagram illustrating a functional configuration according to a third embodiment of the present invention.

FIG. 8 is a flowchart illustrating control of a video controller according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Main control part 102 Video controller 105 Paper size mismatch detection means 106 Sensor reading means 109 Registration roller control means 110 Paper supply control means 111 MPT paper supply control means 201 Laser beam printer 207 Multipurpose tray (MPT) 211 Registration roller

Claims (11)

[Claims] A roller that conveys the paper during driving; a roller that conveys the paper during driving; and a roller that is positioned immediately before the roller during driving. A paper sensor; a paper size designating unit for designating a size of the paper to be used; a paper length measuring unit for measuring a length of the paper based on a signal from the paper sensor and a drive start timing of the roller; Paper size mismatch detecting means for determining the actual paper length by the length measuring means and detecting a paper size mismatch when the paper length is different from the paper size designated by the paper size designating means; If the mismatch detecting means does not determine that the paper being conveyed does not match the paper size, a preset paper size based on the specified paper size is used. A roller control means for stopping the driving of the roller at the time of printing and stopping the driving of the roller after a predetermined time based on the paper length measured by the paper length measuring means when it is determined that the paper size does not match. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the roller is a registration roller for synchronizing a sheet and image data. 3. The image forming apparatus according to claim 1, wherein the paper size specification unit specifies a paper size based on external information. 4. The image forming apparatus according to claim 1, wherein the roller control unit supplies a driving start timing of the roller to the sheet length measuring unit. 5. The image forming apparatus according to claim 1, further comprising a manual sheet feeding unit for feeding the sheet. 6. The paper feeding device according to claim 1, wherein when the paper size mismatch detecting means determines that the paper sheet on which an image is being formed has a paper size mismatch, the paper feeding operation of the subsequent paper sheet is stopped. An image forming apparatus comprising a control unit. 7. The image forming apparatus according to claim 6, wherein the mechanism for stopping the feeding operation of the succeeding sheet is independent of another sheet transport system. 8. An image forming apparatus according to claim 1, wherein said image forming apparatus is a laser beam printer. 9. An image forming system comprising: an image forming apparatus main body; and a system controller that supplies image data to the image forming apparatus main body and controls the image forming apparatus main body to perform an image forming process. The forming apparatus main body positions the paper before image formation by pressing the leading end of the paper sent from the paper supply unit during the stop, and a roller that conveys the paper during driving, and is positioned immediately before the roller. A paper sensor, a paper size designating unit for designating the size of the paper to be used based on information from the system controller, and measuring the length of the paper based on a signal from the paper sensor and a drive start timing of the roller. Paper length measuring means, and the actual paper length is determined by the paper length measuring means,
A paper size mismatch detecting means for detecting a paper size mismatch when the paper length is different from the paper size specified by the paper size specifying means; and a paper size mismatch detected by the paper size mismatch detecting means. A paper size mismatch notifying unit for notifying the system controller of a paper size mismatch, an emergency stop unit for stopping a paper transport system and stopping an image forming operation in response to an emergency stop instruction from the system controller, the system controller And an automatic paper discharging means for driving the paper transport system in response to an automatic paper discharging instruction from the apparatus, and discharging the paper remaining in the apparatus, wherein the system controller sends the paper size mismatch notification means from the image forming apparatus main body. When the paper size mismatch is notified, an emergency stop instruction is issued to the image forming apparatus main body. An image forming system, comprising: means for outputting an output instruction and then outputting an automatic paper ejection instruction. 10. The image forming system according to claim 9, wherein the roller is a registration roller for synchronizing a sheet and image data. 11. An image forming system according to claim 9, wherein said image forming system is a laser beam printer.