JP2004315163A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To complete the image formation on a plurality of sheets of paper within a time substantially same as that in a case when the delay in primary paper supply does not occur, even when the delay in primary paper supply occurs because of paper slipping during the primary paper supply and the like, when the image formation is continuously performed on the plurality of sheets of paper. <P>SOLUTION: The new secondary paper supply is started every 1000 msec as shown in Fig.(a), during a time when the primary paper supply is normally performed without the paper slipping during the primary paper supply. When the primary paper supply of the certain paper is delayed and the secondary paper supply of the paper is delayed by 100 msec from 1000 msec as shown in Fig.(b), the next secondary paper supply is started at a time earlier by 100 sec with respect to the time when 1,000 msec has passed from the start of the last secondary paper supply. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a printer.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus that forms an image on a sheet using an electrophotographic method, a primary sheet feeder feeds sheets one by one from a sheet cassette (or a sheet tray), and a sheet fed to a registration roller by the primary sheet feeder. Feeding to the image forming unit is achieved by a two-stage feeding operation including secondary feeding to be supplied to the image forming unit in a timely manner by the registration roller. The image forming section is provided with a photosensitive drum, and in the image forming section, after the toner image formed on the surface of the photosensitive drum is transferred to a sheet, the sheet on which the toner image is transferred is fixed to a fixing device. The toner image is fixed on the sheet by the fixing device, thereby forming an image on the sheet (for example, see Patent Document 1).
[0003]
The processing speed (copy speed, print speed) in this type of image forming apparatus is determined by the time interval (secondary paper feed interval) from the start of the previous secondary paper feed to the start of the next secondary paper feed. For example, in a model in which the secondary paper supply interval is set to 1000 msec when image formation on a plurality of paper sheets is performed continuously, a maximum of 60 paper sheets can be sent to the image forming unit in one minute. The maximum processing speed is 60 cpm (copy per minute) for a copying machine, and 60 ppm (print per minute) for a printer.
[0004]
[Patent Document 1]
JP-A-2002-116590
[0005]
[Problems to be solved by the invention]
FIGS. 5A and 5B show, in a copying machine having a maximum processing speed of 60 cpm, (a) a case where the primary paper feeding is normally performed, and (b) a case where the primary paper feeding is delayed. It is a time chart which shows a timing.
If the primary paper is normally fed without causing a paper slip (slip of a roller for paper conveyance) during the primary paper feeding, as shown in FIG. Before the timing to start the rotation comes, the paper reaches the registration roller, and the registration switch for detecting the arrival of the paper at the registration roller is turned on. In other words, before 1000 msec elapses from the start of the previous secondary paper feeding, the paper to be subsequently subjected to the secondary paper feeding has reached the registration roller. Therefore, in this case, a new secondary paper feed can be started every 1000 msec, and copying to 60 sheets can be completed in one minute.
[0006]
However, if a paper slip or the like occurs during the primary paper feeding, a situation in which the paper to be subsequently fed secondly has not reached the registration rollers at the time when 1000 msec has elapsed from the start of the previous secondary paper feeding. Can occur. In this case, the secondary paper feed is started simultaneously with the arrival of the paper at the registration roller, and the next secondary paper feed is made in response to the lapse of 1000 msec from the start of the delayed secondary paper feed. Done. For this reason, the time required for copying to a predetermined number of sheets is longer than the time when all of the primary paper feeds are normally performed (the primary paper feed delay time). Minutes) longer.
[0007]
For example, as shown in FIG. 5B, while the copying on 60 sheets is continuously performed, the primary sheet feeding of a certain sheet is delayed, and the sheet is delayed by the second sheet feeding. 1100 msec has elapsed since the start of the process, the time required for copying to 60 sheets is 100 msec longer than the 1 minute required when all the sheets are normally primary-fed. It just gets longer.
Accordingly, an object of the present invention is to provide an image forming apparatus that can continuously perform image formation on a plurality of sheets even if a primary paper feed delay occurs due to slippage of the paper during the primary paper feed. An object of the present invention is to provide an image forming apparatus capable of completing image formation on a plurality of sheets in the same time as the case where no paper delay occurs.
[0008]
Means for Solving the Problems and Effects of the Invention
According to a first aspect of the present invention, there is provided an image forming section for forming an image on a sheet, and a conveying path (51) for conveying a sheet set at a sheet setting position (4). A primary paper feeding means (52, 54) for feeding and transporting the paper one by one to the image forming unit, and a secondary paper feeding means for feeding the paper fed through the transport path by the primary paper feeding means to the image forming unit. A registration roller (53), and a sheet detection means (55) provided near the registration roller and at a position upstream of the registration roller in the sheet transport direction and configured to detect the presence or absence of a sheet at that position. A storage means (TMR_BUF) for storing a time to be secured from the previous secondary sheet feeding by the registration roller to the next secondary sheet feeding, and in response to the start of the secondary sheet feeding by the registration roller. Start timing operation A first timing unit (TMR1) for terminating the timing operation in response to the lapse of the time stored in the storage unit, and a next secondary sheet feeding from the start of the previous secondary sheet feeding by the registration roller Time measuring means (TMR2) for measuring an elapsed time until the start of the second sheet feeding, and the sheet detecting means detecting the next sheet to be secondarily fed after the start of the previous secondary sheet feeding by the registration roller. Means (6, S3) for starting the next secondary sheet feeding by the registration roller, on condition that the timekeeping operation by the first time counting means is completed, and the next secondary sheet feeding by the registration roller. At the start of the paper, a difference between the elapsed time measured by the second timer and the time stored in the storage is obtained, and the difference is subtracted from a processing speed limit time determined according to the paper size. can get During the an image forming apparatus which comprises a means (6, S9) to be stored in the storage means.
[0009]
It should be noted that the alphanumeric characters in parentheses indicate corresponding components and the like in embodiments described later. Hereinafter, the same applies in this section.
According to the above configuration, if a paper slip occurs during the primary paper feeding and the paper arrives at the registration roller later than the end (time-up) of the timing operation of the first timing unit, the delay is caused. At the start of the secondary sheet feeding of the arrived sheet, a time obtained by subtracting the delay time from the processing speed limit time determined according to the sheet size is stored in the storage means. Therefore, the first timing unit starts the timing operation in response to the start of the secondary sheet feeding of the delayed sheet, and the first timing unit performs a time shorter than the processing speed limit time by the delay time (stored in the storage unit). When the elapsed time has elapsed, the timing operation ends. Therefore, if the next sheet has arrived at the registration roller when a time shorter than the processing speed limit time by the delay time has elapsed from the start of the secondary sheet feeding, the sheet reaching the registration roller is The secondary paper is immediately fed. In other words, when the primary paper feed is delayed and the secondary paper feed is delayed by a predetermined time, the next secondary paper feed is limited to the processing speed from the start of the previous secondary paper feed. This is performed earlier by the delay time than when the time has elapsed. As a result, it is possible to recover the delay of the secondary paper feed, and as a result, to complete the image formation on a plurality of papers in the same time as when the primary paper feed is not delayed. Can be.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an illustrative sectional view showing the internal configuration of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus is, for example, a digital copying machine that forms an image on paper by an electrophotographic method, and includes a laser scan unit 1 that emits laser light corresponding to image data input from a scanner (not shown), An image forming unit 2 for transferring an image to a sheet to form an image; a fixing unit 3 for fixing the toner image transferred to the sheet by the image forming unit 2 to the sheet; and a plurality of sheets (for example, 100 to 200 sheets) 1), and a paper feed unit 5 for feeding out the sheets one by one from the paper cassette 4 and supplying the fed sheets to the image forming unit 2.
[0011]
The image forming section 2 includes a photosensitive drum 21, a main charger 22, a developing device 23, and a transfer charger 24 arranged around the photosensitive drum 21. Laser light emitted from the laser scan unit 1 passes between the main charger 22 and the developing device 23 and is incident on the surface of the photosensitive drum 21.
During image formation, the photosensitive drum 21 is driven to rotate at a constant speed in a predetermined direction. When the surface of the photosensitive drum 21 faces the main charger 22, the surface of the photoconductor drum 21 is charged to a constant potential by the discharge from the main charger 22, and subsequently, the portion charged to the constant potential is irradiated with the laser beam from the laser scan unit 1. Is done. The charged charge is removed from the portion irradiated with the laser beam, whereby an electrostatic latent image corresponding to the image to be formed on the paper is formed on the surface of the photosensitive drum 21. This electrostatic latent image is then opposed to the developing device 23, and is supplied with toner from the developing device 23 to be visualized as a toner image. The toner image formed on the surface of the photosensitive drum 21 in this manner, when the photosensitive drum 21 is further rotated and faces the transfer charger 24, the discharge from the transfer charger 24 causes the transfer of the toner image between the photosensitive drum 21 and the transfer charger 24. It is transferred to the paper that has entered between.
[0012]
The sheet on which the toner image has been transferred is guided to the fixing unit 3 by the transport belt 25. The fixing unit 3 includes a heat roller 31 and a press roller 32. The sheet guided to the fixing device 3 enters between the heat roller 31 and the press roller 32. Then, the toner image is conveyed while being held by the heat roller 31 and the press roller 32, and is heated and pressed at this time, so that the toner image transferred in the image forming unit 2 is fixed on the sheet. The sheet after the fixing process is discharged by a discharge roller 33 to a discharge tray (not shown) provided outside the apparatus.
[0013]
The paper supply unit 5 includes a paper supply path 51 extending from the paper cassette 4 to the image forming unit 2, a pickup roller 52 for separating sheets contained in the paper cassette 4 one by one and sending out the paper to the paper supply path 51. A registration roller 53 for performing secondary paper feeding at a timing of paper feeding to the image forming unit 2, and a transport roller 54 for transporting the paper sent out by the pickup roller 52 to the registration roller 53. I have.
A registration switch 55 for detecting the presence or absence of a sheet at the position near the registration roller 53 and upstream of the registration roller 53 in the sheet conveyance direction is provided. The registration switch 55 is turned on when detecting the leading end of the sheet sent through the sheet feeding path 51, the sheet is sent from the registration roller 53 toward the image forming unit 2, and the trailing end of the sheet has passed. A switch that is turned off at times.
[0014]
Instead of the registration switch 55, a registration sensor that detects the presence or absence of a sheet near the upstream side of the registration roller 53 in a non-contact manner and outputs a signal (Hi / Low signal) at a level corresponding to the presence or absence of the sheet is provided. May be provided.
FIG. 2 is a block diagram showing an electrical configuration relating to the secondary paper feed control of the image forming apparatus. This image forming apparatus includes a microcomputer 6 including a CPU, a RAM, and a ROM. In the RAM of the microcomputer 6, a timer buffer TMR_BUF for storing a time value to be secured from the previous secondary paper feeding to the next secondary paper feeding and a time value stored in the timer buffer TMR_BUF are set. A first timer TMR1 for measuring the set time value, and a time for measuring the time from the start of the previous secondary paper feed to the state where the next secondary paper feed can be started. And a second timer TMR2. An on / off signal of the registration switch 55 is input to the microcomputer 6.
[0015]
A driving force from the motor M is applied to the registration roller 53 via a registration clutch (CL) 56. The microcomputer 6 switches the on / off state of the registration clutch 56 based on the on / off signal from the registration switch 55 and the states of the first timer TMR1 and the second timer TMR2, so that the secondary Controls paper feeding.
FIG. 3 is a flowchart illustrating a flow of processing performed by the microcomputer 6. When a user of the image forming apparatus inputs an instruction to form an image on a sheet (for example, when a copy start key is pressed to start copying after the number of copies is set), first, the image is printed. A processing speed limit time Amsec is set according to the size of the sheet on which the image is to be formed (step S1). The processing speed limit time Amsec is, for example, when a copy (image formation) is continuously performed on a plurality of sheets, the interval (distance) between the rear end of the preceding sheet and the front end of the subsequent sheet is a predetermined interval. (For example, 100 mm). The processing speed limit time Amsec set in this way is stored in the timer buffer TMR_BUF (step S2).
[0016]
In the meantime, the pickup roller 52 and the transport roller 54 are driven to perform so-called primary paper feeding. That is, one sheet of paper is sent from the paper cassette 4 to the paper feed path 51 by the action of the pickup roller 52, and the paper is transported to the registration roller 53 by the transport roller 54. At this time, the registration roller 53 is stopped, and the sheet conveyed to the registration roller 53 stops with its leading end nipped between a pair of rollers constituting the registration roller 53. The primary feeding of the second and subsequent sheets is performed, for example, in synchronization with the start of the secondary feeding by the registration rollers 53 of the preceding sheet.
[0017]
After the processing speed limit time Amsec is stored in the timer buffer TMR_BUF, when the timing of the secondary paper feed comes, the registration clutch 56 is turned on and the registration roller 53 is driven, so that the registration roller 53 is nipped by the registration roller 53. The stopped paper is secondarily fed (step S3). Then, the processing speed limit time Amsec stored in the timer buffer TMR_BUF is set in the first timer TMR1, and time measurement by the first timer TMR1 is started (step S4). At the same time as the first timer TMR1 starts counting time, the second timer TMR2 starts counting time (step S5).
[0018]
After the start of the secondary paper feeding, it is repeatedly determined whether or not all the conditions for starting the secondary paper feeding of the subsequent sheet (secondary paper feeding conditions) are satisfied (step S6). For example, whether both the condition that the clocking by the first timer TMR1 has been typed up and the condition that the registration switch 55 has been turned on have been satisfied after the processing speed limit time Amsec has elapsed since the start of the secondary paper feeding. It is determined whether or not. When both of the secondary paper feeding conditions are satisfied (YES in step S6), the time counting by the second timer TMR2 is stopped, and the time measured by the second timer TMR2 until then is stored in the timer buffer TMR_BUF. It is checked whether it is longer than the speed limit time Amsec (step S7). That is, the time from the start of the previous secondary paper supply to the satisfaction of all the secondary paper supply conditions for starting the next secondary paper supply is longer than the processing speed limit time Amsec stored in the timer buffer TMR_BUF. Is also long.
[0019]
The sheet is normally performed without causing a paper slip (slip of the transport roller 54 or the like) during the primary paper supply, and when the time counting by the first timer TMR1 has timed out, the paper to be subsequently subjected to the secondary paper supply. Has reached the registration roller 53 (NO in step S7), the processing speed limit time Amsec set in step S1 is stored in the timer buffer TMR_BUF (step S8). That is, in this case, the processing speed limit time Amsec stored in the timer buffer TMR_BUF is stored and held as it is. Then, while the next secondary paper feed is started (step S3), the processing speed limit time Amsec stored in the timer buffer TMR_BUF is set in the first timer TMR1, and time counting by the first timer TMR1 is started. Is performed (step S4). In addition, time measurement by the second timer TMR2 is started (step S5). Thereafter, it is repeatedly determined whether or not all the conditions for starting the secondary paper feeding of the succeeding paper have been satisfied (step S6). If this determination is affirmed, the second timer TMR2 has until then. It is checked again whether the measured time is longer than the processing speed limit time Amsec stored in the timer buffer TMR_BUF (step S7).
[0020]
As described above, while the primary paper feeding is normally performed, the processes of steps S3 to S8 are repeatedly performed, and the secondary paper feeding is performed every time the processing speed limit time Amsec elapses. Therefore, an image can be continuously formed on a plurality of sheets at a processing speed as specified by the image forming apparatus.
On the other hand, if a paper slip or the like occurs during the primary paper feeding, the next paper feeding starts until the processing speed limit time Amsec elapses (until the time measurement by the first timer TMR1 times out). The paper to be secondarily fed may not reach the registration roller 53 in some cases. In this case, even if the processing speed limit time Amsec has elapsed, the next secondary sheet feeding is not performed until the registration switch 55 is turned on. Then, the next secondary sheet feeding is performed in response to the sheet reaching the registration roller 53 and the registration switch 55 being turned on. Therefore, when the next secondary paper feed is started, the elapsed time from the start of the previous secondary paper feed exceeds the processing speed limit time Amsec stored in the timer buffer TMR_BUF. The determination as to whether the time measured by the two timer TMR2 is longer than the processing speed limit time Amsec stored in the timer buffer TMR_BUF is affirmed (YES in step S7). In this case, a difference between the time measured by the second timer TMR2 and the processing speed limit time Amsec stored in the timer buffer TMR_BUF is obtained, and the difference is calculated as the processing speed limit time calculated in step S1. The time "Amsec- (TMR2-TMR_BUF)" obtained by subtracting from Amsec is stored in the timer buffer TMR_BUF (step S9).
[0021]
Subsequently, the next secondary sheet feeding is started (step S3), and the time "Amsec- (TMR2-TMR_BUF)" stored in the timer buffer TMR_BUF is set in the first timer TMR1, and the first timer TMR1 is set. Timing by TMR1 is started (step S4). In addition, time measurement by the second timer TMR2 is started (step S5). Thereafter, it is repeatedly determined whether or not all the conditions for starting the secondary paper feeding of the succeeding paper are satisfied (step S6). That is, the condition that the time “Amsec− (TMR2−TMR_BUF)” has elapsed since the start of the secondary sheet feeding, the time measurement by the first timer TMR1 has been typed up, and the condition that the registration switch 55 has been turned on. It is determined whether both have been satisfied. When both the secondary sheet feeding conditions are satisfied (YES in step S6), the time measured by the second timer TMR2 until then is calculated from the time "Amsec- (TMR2-TMR_BUF)" stored in the timer buffer TMR_BUF. It is checked whether or not is also long (step S7).
[0022]
As described above, when a paper slip or the like occurs during the primary paper supply and the paper arrives at the registration roller 53 after being delayed by the time-up of the first timer TMR1, processing is performed for the delayed time “TMR2-TMR_BUF”. Since the time “Amsec− (TMR2−TMR_BUF)” shorter than the speed limit time Amsec is set in the first timer TMR1, one of the conditions for starting the next secondary paper feed is the previous secondary paper feed. It is satisfied when a time “Amsec− (TMR2−TMR_BUF)” which is shorter than the processing speed limit time Amsec from the start of the paper has elapsed. Therefore, when image formation is continuously performed on a plurality of sheets, even if a primary paper feed delay occurs due to slippage of the paper during the primary paper feed, the primary paper feed delay is eventually ended. Image formation on a plurality of sheets can be completed in the same time as in the case where the image does not occur.
[0023]
FIG. 4 is a time chart showing the timing of secondary paper feeding in this image forming apparatus when (a) primary paper feeding is normally performed and (b) when primary paper feeding is delayed. It is.
The maximum processing speed of the image forming apparatus is set to a speed at which a maximum of 60 copies per minute can be performed on paper of row A (A4) of Japanese Industrial Standards, that is, 60 cpm (copy per minute). If there is, the processing speed limit time Amsec is calculated as 1000 msec.
[0024]
In this case, while the primary paper feeding is normally performed without causing a paper slip or the like during the primary paper feeding, the next paper feeding is performed before 1000 msec elapses from the start of the previous secondary paper feeding. The sheet to be secondarily fed reaches the registration roller 53, and the registration switch 55 is turned on. Therefore, in this case, as shown in FIG. 4A, a new secondary paper feed can be started every 1000 msec. Therefore, copying to 60 sheets of paper can be completed in one minute, and copying at a maximum processing speed (processing speed as specified) of this image forming apparatus of 60 cpm can be achieved.
[0025]
On the other hand, while copying to a plurality of sheets is being performed continuously, as shown in FIG. 4B, the primary sheet feeding of a sheet is delayed, and the sheet is When the sheet reaches the registration roller 53 when 1100 msec elapses from the start of the process, the secondary sheet feeding of the delayed sheet is started, and the time is shorter by 100 msec than the processing speed limit time Amsec of 1000 msec. 900 msec is set in the first timer TMR1, and time counting by the first timer TMR1 is started. Therefore, at the time when the time counting by the first timer TMR1 has timed out (at the time when 900 msec has elapsed from the start of the secondary feeding of the sheet that arrived with a delay to the registration roller 53), the next sheet arrived at the registration roller 53. If so, the secondary feeding of the sheet is immediately started. In other words, if the primary paper feed is delayed and the secondary paper feed is delayed by 100 msec from the 1000 msec, the next secondary paper feed is performed 1000 msec from the start of the previous secondary paper feed. This is performed at a time point 100 seconds earlier than the time point at which the time elapses. As a result, it is possible to recover the delay of the secondary paper feed, and as a result, to complete the image formation on a plurality of papers in the same time as when the primary paper feed is not delayed. Can be.
[0026]
Note that the delay of the primary paper feeding of a certain sheet is large, and when a time shorter than the processing speed limit time Amsec by a delay time has elapsed from the start of the secondary paper feeding of the delayed sheet, the next sheet is delayed. If the sheet has not reached the registration roller 53, the difference between the time measured by the second timer TMR2 until the next sheet reaches the registration roller 53 and the time stored in the timer buffer TMR_BUF at that time is calculated. The time obtained by subtracting the difference from the processing speed limit time Amsec is stored in the timer buffer TMR_BUF. Then, secondary feeding of the next sheet is started, and the time stored in the timer buffer TMR_BUF is stored in the first timer TMR1.
[0027]
For example, a sheet reaches the registration roller 53 when 1300 msec elapses from the start of the previous secondary sheet feeding, and 700 msec (= 1000-300 msec) is set to the first timer TMR1 with the start of the sheet secondary feeding. Is set to, and the first timer TMR1 starts counting, but the next sheet arrives at the registration roller 53 800 msec after the start of the second sheet feeding of the sheet which arrived with a delay earlier. A difference 100 msec between the time 800 msec measured by the second timer TMR2 and the time 700 msec stored in the timer buffer TMR_BUF at that time is obtained, and the time 900 msec obtained by subtracting the difference 100 msec from the processing speed limit time Amsec 1000 msec is obtained. Is the timer buffer TMR_BU It is stored in. Then, secondary feeding of the next sheet is started, and the time 900 msec stored in the timer buffer TMR_BUF is stored in the first timer TMR1. That is, when a certain sheet arrives at the registration roller 53 with a large delay, the secondary sheet feeding interval of a plurality of subsequent sheets is shortened from the processing speed limit time Amsec of 1000 msec.
[0028]
As mentioned above, although one Embodiment of this invention was described, this invention can be implemented in another form. For example, in the above embodiment, the case where the present invention is applied to a digital copying machine is taken as an example, but the present invention can also be applied to a digital printer. In this case, data of an image to be formed on paper is input to the laser scan unit 1 from a personal computer (not shown) or the like via a communication cable.
[0029]
Further, the apparatus is not limited to a digital image forming apparatus, and is a so-called analog type copier that guides reflected light from a document to the surface of the photosensitive drum 21 to form an electrostatic latent image on the surface of the photosensitive drum 21. The present invention can also be applied to
In addition, various design changes can be made within the scope of the matters described in the claims.
[Brief description of the drawings]
FIG. 1 is an illustrative sectional view showing an internal configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration related to secondary paper feed control of the image forming apparatus.
FIG. 3 is a flowchart illustrating a flow of processing performed by the microcomputer.
FIG. 4 is a time chart showing timing of secondary paper feeding in the image forming apparatus when (a) primary paper feeding is normally performed and (b) when primary paper feeding is delayed; It is.
FIG. 5 is a time chart showing the timing of secondary paper feeding when (a) primary paper feeding is normally performed and (b) when primary paper feeding is delayed in the conventional image forming apparatus. It is a chart.
[Explanation of symbols]
2 Image forming unit
4 Paper cassette
5 Paper feed unit
6. Microcomputer
51 Paper feed path
52 Pickup roller
53 Registration roller
54 transport roller
55 Registration switch
56 Registration Clutch
TMR_BUF timer buffer
TMR1 first timer
TMR2 second timer

Claims (1)

An image forming unit for forming an image on paper;
A primary paper feeding means for feeding and transporting the paper set at the paper setting position one by one to a transport path,
A registration roller for secondarily feeding the sheet sent through the conveyance path by the primary sheet feeding means to the image forming unit;
A sheet detecting means provided near the registration roller and at a position on the upstream side of the registration roller in the sheet conveyance direction to detect the presence or absence of a sheet at that position;
Storage means for storing a time to be secured from the previous secondary paper feeding by the registration roller to the next secondary paper feeding;
First timing means for starting a timing operation in response to the start of secondary paper feeding by the registration roller, and terminating the timing operation in response to elapse of the time stored in the storage means;
Second timing means for measuring an elapsed time from the start of the previous secondary sheet feeding by the registration roller to the start of the next secondary sheet feeding;
After the start of the previous secondary paper feed by the registration rollers, the paper detection means detects the paper to be subsequently fed secondarily, and the timing operation by the first clock means is completed. Means for starting the next secondary sheet feeding by the registration roller;
At the start of the next secondary paper feeding by the registration roller, a difference between the elapsed time measured by the second clock means and the time stored in the storage means is determined, and the difference is determined according to the paper size. Means for storing the time obtained by subtracting from the processing speed limit time obtained in the storage means in the storage means.

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