JPH04322279A - Image forming device - Google Patents

Abstract

PURPOSE:To enhance the fixation of a cover paper whose heat capacity is large without giving an adverse effect to fixing performance and jam performance at a normal paper passing time. CONSTITUTION:In an image forming device which forms an electrostatic latent image corresponding to an original by irradiating a photosensitive body which is previously electrostatically charged with exposure light corresponding to the original, transfers an image obtained by developing the concerned latent image by a developing means on a transfer paper which is specified by a specification means and supplied by a paper supply means and forms the image by fixing it by a fixing device besides, a paper supply pitch change means 400 which sets a time to the supply start of the later transfer paper from the supply start of the previous transfer paper by the paper supply means longer than the interval of the supply time of the thin transfer paper when the thick transfer paper is specified by the specification means 400 is provided.

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 more particularly to an image forming apparatus having a cover mode for forming an image on cover paper forming a cover.

0002

2. Description of the Related Art In an image forming apparatus, for example, a copying machine, an electrostatic latent image corresponding to the original is formed by irradiating exposure light corresponding to an original onto a pre-charged photoreceptor, and the latent image is developed using a developing device. The converted image is transferred to transfer paper and further fixed by a fixing device to form an image. FIG. 7 schematically shows the mechanism of a general fixing device of a conventional copying machine. Referring to FIG. 7, the fixing device 12C includes a fixing roller 12CA and a pressure roller 12CB that are arranged to face each other. These rollers are rotatably supported by shafts arranged at their centers, and when performing fixing processing, the fixing roller 12CA and roller 12CB are rotated clockwise and counterclockwise, respectively. Rotationally driven. The sheet undergoing the fixing process is subjected to the fixing process when passing between the fixing roller 12CA and the pressure roller 12CB. Fixing roller 12CA
A heater HT is provided at the center of the fixing roller 12CA, and the fixing roller 12CA is heated to a high temperature. The pressure roller 12CB is movable in the vertical direction, and is supported so as to be pushed up by a pressure cam 12CF disposed below it. A pressure adjustment mechanism 50 is provided at the tip of the pressure cam 12CF.
is located. Note that 12CC is the fixing roller 12C.
Application felt for applying silicone oil to A, 1
2CD is a thermistor for detecting the temperature of the fixing roller, 12CE is a fixing claw, and 12CI is a paper discharge sensor.

By the way, there is a limit to the power that can be distributed to the fixing device of a copying machine, which requires power saving.
Even a 20A machine is around 1000W. In a copying machine having a general fixing device as shown in FIG. 7, heater control is normally performed so that the fixing roller surface temperature, which decreases with each copy, remains constant. However, when approximately 200 copies are made continuously, the heating of the heater cannot follow the decrease in the surface temperature of the fixing roller, and the surface temperature of the fixing roller falls below the low temperature limit. If fixing is performed in this state, the quality of the formed image will deteriorate, so the copying operation is temporarily stopped and the copying operation is suspended until the surface temperature of the fixing roller rises to a predetermined temperature.

0004

[Problems to be Solved by the Invention] Recently, as copying machines have become more multi-functional, a cover mode is introduced in which cover paper is fed as transfer paper to form a front or back cover at the beginning or end of a document set and an image is formed thereon. There is a copying machine that has . However, the transfer paper (cover paper) used for the front or back cover is thicker than the copy paper normally used (for example, the average weight of copy paper is 64 g/m2, whereas the cover paper is 209 g/m2).
4g/m2), and the heat capacity is large, resulting in poor fixing performance. In addition, the cover paper is fed during continuous copying, and even if the surface temperature of the fixing roller has not reached the low temperature limit, the surface temperature of the fixing roller is often lower than normal.
Can't get good quality images.

[0005] As a countermeasure to this problem, there is a method of increasing the nip (the area where the fixing roller and the heating roller engage), but this method leads to the generation of wrinkles and jams in the transfer paper, and has a large risk. In addition, in copying machines with sufficient power, the roller surface temperature may be initially set to a high temperature to suppress a drop in fixing temperature during continuous copying, but hot offset development occurs when plain paper is passed through. Also, JP-A-60-25
Japanese Patent No. 2380 discloses a copying machine that improves fixing performance, but since the copying process speed and fixing temperature are changed, a constant image and homogeneous fixing performance cannot be obtained.

An object of the present invention is to improve the fixing performance of cover paper having a large heat capacity without adversely affecting the fixing performance and jam performance when passing general paper.

[0007]

[Means for Solving the Problems] The image forming apparatus of the present invention includes means (110) for forming an electrostatic latent image corresponding to the original by irradiating exposure light corresponding to the original onto a pre-charged photoreceptor (121).
, 120); developing means (124) for developing the latent image on the photoreceptor (121); transfer means (126) for transferring the developed image on the photoreceptor (121) onto transfer paper;
Specifying means (400) for specifying one type of transfer paper of multiple types having different thicknesses;
); and a transfer means (
126) that performs a fixing process on the transfer paper on which transfer has been completed, and a fixing device (12C) having a fixing roller (12CA) and a heater (HT) that heats the fixing roller (12CA); When the means (400) specifies thick transfer paper, the paper feeding means (130)
) for setting the time from the start of feeding of a previous transfer paper to the start of feeding of a subsequent transfer paper to be longer than the feeding time interval of thin transfer paper. Note that the symbols in parentheses are corresponding elements in the embodiment described later.

[0008]

[Operation] According to this, the paper feeding pitch changing means (400)
However, when the specifying means (400) specifies thick transfer paper, the time from the start of feeding of the first transfer paper to the start of feeding of the next transfer paper by the paper feeding means (130) is Set longer than the feeding time interval. Therefore, when thick transfer paper (cover paper) is fed, the paper feeding interval from the previous paper feeding increases. During this time, the amount of heat is accumulated on the surface of the fixing roller, so that when the cover paper is subsequently fixed, a more sufficient amount of heat is used than in the past, and the fixing performance is improved. Further, when plain paper is fed, the same processing as in the past is normally performed, so that fixing performance, jam performance, etc. are not adversely affected.

In a preferred embodiment of the present invention, means (110, 12) are provided for forming an electrostatic latent image corresponding to the document by irradiating exposure light corresponding to the document onto a pre-charged photoreceptor (121).
0); Developing means (
124); Transfer means (126) for transferring the developed image on the photoreceptor (121) onto transfer paper;
6); and a fixing roller (12CA) for fixing the transfer paper that has been transferred by the transfer unit (126); and a heater (HT) for heating the fixing roller (12CA). In an image forming apparatus including a fixing device (12C) having a cover mode instruction means (7, 8) for inputting a cover mode instruction; and transfer paper selection means (130) for instructing the paper feeding means (130) to feed thick transfer paper for at least one of the documents at the bottom, and for instructing thin transfer paper for the other documents; 40
0); and when the transfer paper selection means (400) specifies a thick transfer paper, the paper feeding means (130) will be The paper feeding pitch changing means (400) is provided for setting the time to be longer than the feeding time interval of thin transfer paper.

Therefore, thick transfer paper or thin transfer paper is fed at a predetermined timing according to an instruction from the cover mode instruction means, and when feeding thick transfer paper (cover paper), the paper feeding interval is changed from the previous paper feeding time. spreads. During this time, the amount of heat is accumulated on the surface of the fixing roller, so that when the cover paper is subsequently fixed, a more sufficient amount of heat is used than in the past, and the fixing performance is improved. Further, when plain paper is fed, the same processing as in the past is normally performed, so that fixing performance, jam performance, etc. are not adversely affected. Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0011]

[Embodiment] A copying apparatus according to an embodiment of the present invention includes a copying machine main body 100 shown in FIG. 1 and an automatic document feeder 200 shown in FIG.
It is composed of The main body 100 of the copying machine is an electrostatic transfer type copying device that fixes originals, and includes an optical system 110, an image forming system 120, a paper feeding system 130, a paper refeeding system 140, and the like. The optical system 110 includes a contact glass 111, an exposure lamp 112 disposed below the contact glass 111, and a first mirror 11.
3A, second mirror 113B, third mirror 113C, fourth
Mirror 113D, fifth mirror 113E, sixth mirror 11
3F, a lens 114, a dust-proof glass 115, etc., and the image forming system 120 includes a photoconductor drum 121 and a charger 122 disposed around it, an eraser 123, a developing device 124, a pre-transfer charger 126, a separation charger 127, and a separation system. It consists of a claw 128, a pre-cleaning static elimination charger 129, a cleaner 12A, a conveyor belt 12B disposed downstream of the photosensitive drum 121, a fixing device 12C, and the like. The paper feed system 130 has five stages, including a manual paper feed table 131, a first tray 131A, and a second tray 131.
B, third tray 131C, fourth tray 131D, and each tray (however, manual paper feed tray 131 is
Call rollers 132A, 13 provided in (shared with A)
2B, 132C, 132D, paper feed roller 133A, 133
B, 133C, 133D, and reverse roller 134A,
134B, 134C, 134D, a registration roller 135, a guide mylar 136, and various guides and intermediate rollers. The paper refeeding system 140 includes a switching claw 14
1, approaching/separating roller 142, reversing guide 143, reversing roller 144, gate pawl 145, intermediate tray 146, leading edge second roller 147, paper stopper 148, calling roller 149
, paper feed roller 14A, reverse rotation roller 14B, and paper discharge roller 14
Consists of C etc.

When an original is set on the contact glass 111 and a start instruction is given, the paper feed clutch is turned on and the calling roller of the tray selected at that time feeds the recording paper to the paper feeding roller. Since the paper feed rollers rotate in the opposite direction, double feeding is prevented and only the topmost sheet of recording paper is sent toward the registration rollers 135. During this time, optical system 1
Reference numeral 10 scans an original on a contact glass 111, and directs the reflected light of the original illuminated by an exposure lamp 112 to a first mirror 113A, a second mirror 113B, a third mirror 113C,
Lens 114, fourth mirror 113D, fifth mirror 113
E, guided to the photosensitive surface of the photosensitive drum 121 via the sixth mirror 113F and the dustproof glass 115.

The photosensitive drum 121 is rotating clockwise in the drawing, and its photosensitive surface is uniformly charged by a charging charger 122 before receiving the reflected light from the optical system 110, and is charged by an eraser 123. A latent image area is formed by static electricity removal. Therefore, when this latent image area is irradiated with light reflected from the original, photoconduction occurs depending on the strength of the light, and an electrostatic latent image is formed. This electrostatic latent image is developed by a developing device 124, and becomes a toner image with toner attached thereto according to the density of the document. This toner image is transferred onto the recording paper fed out from the registration rollers 135, but in order to facilitate the transfer, the PTL 125 removes the charge before the transfer.

The recording paper fed out by the registration roller 135 is brought into close contact with the photosensitive surface of the photosensitive drum 121 by a guide mylar 136, and the toner image is transferred directly above the transfer charger 126. Immediately after this, the recording paper is transferred to separate charger 1.
27, but if the separation is insufficient, the separation claw 128 forcibly separates the photosensitive material. After the recording paper is separated, residual toner is removed from the photosensitive surface of the photosensitive drum 121 by a cleaner 12A, and the recording paper is sent to a fixing device 12C by a conveyor belt 12B. The fixing device 12C includes a fixing roller 12CA and a pressure roller 12C.
The recording paper onto which the toner image has been transferred is heated (approximately 185° C.) while applying pressure to fix the toner image. Note that the fixing device 12C has the same configuration as the conventional general fixing device shown in FIG.

The recording paper on which the toner image has been fixed is delivered to a paper refeed system 140. The paper refeeding system 140 guides the recording paper to the paper ejection roller 14C by the action of the switching claw 141 when copying the first side in duplex mode, but when copying the first side in duplex mode
When copying a surface, it is guided to a reversal guide 143. After this, when the trailing edge of the recording paper passes the switching claw 141, the switching claw 141
is switched, the contact/separation roller 142 is brought into contact and the recording paper is sent to the reversing roller 144, and the reversing roller 144 is connected to the gate claw 1.
Send to 45. There are four gate claws 145, and when the gate claws corresponding to the size of the recording paper are opened, the recording paper is ejected to the intermediate tray 146. The recording paper that has fallen onto the intermediate tray 146 is moved to the paper stopper 148 by the leading edge shifting roller 147.
They are brought together until they come into contact with each other, their tips are aligned, and they are stacked. When copying the second side of the recording sheets stacked on the intermediate tray 146 is started in the double-sided mode, the topmost sheet is sent to the registration rollers 135 by the paper feeding rollers 14A and the reversing rollers 14B by the calling rollers 149. Note that PSN in the figure is a P sensor that detects the toner concentration of the developing device 124.

Next, an automatic document feeder (hereinafter referred to as RDH) 200 will be explained with reference to FIG. The RDH200 automatically attaches the document to contact glass 1 before starting optical scanning.
It is a type of automatic document feeder/discharge device that feeds the document onto the document scanner 11 and discharges it after optical scanning is completed, and resets the discharged document at the end (top in this example), making it possible to repeatedly feed and discharge the same document. This facilitates copying of double-sided originals and re-copying in the event of a misfeed. This device includes a document placing table 210, a document feeding system 220, a document resetting system 230, a reversing system 240, and the like.

The original table 210 is equipped with a recycle lever drive motor 211, a recycle lever 212 coupled to the shaft thereof, and a sensor 213 for detecting rotation of the recycle lever 212. When a document is set and a copy start instruction is given, the motor 211 rotates the recycle lever 212 to place the final document on top. Thereafter, when the last original is fed and the lever 212 rotates due to its own weight, and the tip of the original falls from the notch formed in the original placing table 210, the sensor 213 detects that the lever 212
Detect. In other words, the sensor 213 detects one cycle of a series of originals placed at the beginning. Also, if the number of original feeding/ejection cycles is two or more, the sensor 213 detects one cycle of a series of originals placed on the original. A lever 212 is mounted to detect each cycle.

The feeding system 220 includes a half-moon roller 221, a feeding belt 222, a separating belt 223, a conveying roller 224,
It includes a conveyor belt 225, a presser roller 226, a document sensor 227, a paper feed sensor 228, a paper feed registration sensor 229, and the like. When the document sensor 227 detects a document, a feed-in signal is sent from the main body 100 at a predetermined timing. This starts the document feeding operation, and first, the half-moon roller 221 separates the document. Since a plurality of these documents may overlap, only the lowest document is sent to the conveyance roller 224 by the action of the feed belt 222 and separation belt 223. Conveyance roller 224 passes this document to conveyance belt 225, which further conveys it. At this time, when the registration sensor 229 detects the trailing edge of the document, a predetermined stop timing is set and the feeding of the document is stopped. This results in
A document is positioned on contact glass 111. Note that the paper feed sensor 228 detects misfeed.

The reset system 230 includes a deflection plate 231, discharge rollers 232, 233, and 234, and the like. Resetting is performed by completing the optical scan, and after selecting the ejection guide 235 by the direction change plate 231, the conveyor belt 225 is reversed. As a result, the last part of the document on the document tray (
is discharged to the top).

The reversing system 240 includes the switchback roller 2
41, a reversal sensor 242, a reversal registration sensor 243, and part of the original feeding system 220 and original resetting system 230 are used together. Here, the original resetting system 230
During ejection, a reversal sensor 242 detects the point at which the trailing edge of the document passes the ejection guide 235, and the document is guided to the switchback roller 241 by reversing the ejection rollers 232, 233, and 234. The switchback roller 241 guides the document to the reversing guide 244 and then reverses the document and guides it to the reversing paper feed guide 245 . At this time, the reversing paper feed guide 245 is selected by the direction change plate 231 and the document is sent to the conveyor belt 225. Note that the timing of stopping the document in this case is determined by detection by the reversal registration sensor 243.

The operations of the document feeding system 220, the document resetting system 230, and the reversing system 240 described above allow the document to be fed normally and ejected normally in the "normal feed and eject mode", and the document to be reversed and fed. "Reverse feed forward/discharge mode" that feeds and discharges as is.
"Normal feed/counter-discharge mode" in which the document is normally fed, reversed and ejected, "Reverse feed/counter-discharge mode" in which the document is reversed, fed, reversed and ejected, and "Reverse" is simply reversed. mode” becomes possible.

FIG. 3 shows a part of the external appearance of the operation board 150 provided in the copying machine main body 100. Each key and display will be explained. Reference numeral 1 is a print start key for inputting copy start instructions, reference numeral 2 is a mode clear key for clearing each mode of the copying machine, reference numeral 3 is a stop/clear key for inputting instructions such as clearing the number of copies in a copy set and interrupting copying. Reference numeral 4 indicates a numeric keypad for inputting the number of copies to be set, etc., reference numeral 5 indicates a 7-segment display for the number of originals set, and reference numeral 6 indicates a 7-segment display for the number of copies to be processed. Further, reference numeral 7 is a front cover mode key for instructing the front cover mode, and reference numeral 8 is a back cover mode key for instructing the front cover mode. Note that there are various other keys and indicators on the operation board 150, such as density adjustment, variable magnification, duplex mode keys, etc., but they are omitted here.

FIG. 4 schematically shows the electrical control system of the copying machine 100. This electrical control system includes a main control section 400, a storage section 410, an optical control section 420, an AC control section 430,
It consists of an operation control section 440, an RDH control section 450, a sorter control section 460, and the like. The main control unit 400
Various sensors 420 provided in each part of 00 are monitored to control the loads of solenoids, motors, etc. of each part. Optical control section 4
20 controls the lens motor that drives the lens 114 and the scanner motor that performs optical scanning, and the AC control unit 430 controls the exposure lamp 112, the heater of the fixing device 12C,
Controls AC loads such as the main motor, developing motor, transport motor, and paper feed motor. The operation control section 440 performs key operation reading and display control on the operation and display board 150. Further, the RDH control section 450 controls the RDH 200, and the sorter control section 460 controls a sorter unit (not shown here) that can be attached to the outside of the copying machine.

The cover mode of the present invention will be explained below. Generally, the cover mode is a mode in which a separate transfer sheet (cover paper) is used at the beginning or end of a normal copying transfer sheet (plain paper) when copying a plurality of documents. However, if the cover paper is fed at the normal timing during continuous copying, the heat capacity required for fixing the cover paper is large and the fixing device cannot cope with this, resulting in poor fixing performance. For this reason, in this embodiment, when fixing the cover paper, the fixing interval is made wider than in normal copying so that the fixing is performed after sufficient thermal energy has been stored on the surface of the roller of the fixing device.

Normally, when conveying transfer paper, in order to match the difference in the length of the conveyance path from each tray, the transfer paper is temporarily stopped by registration rollers 135, and the transfer paper is moved at a predetermined timing synchronized with the process operation. The registration rollers 135 are driven to perform conveyance. For this reason, when the fixing interval is made wider than during normal copying, it is easier to control the timing before the transfer sheet reaches the registration rollers, rather than changing the travel time of the transfer paper from the start of driving of the registration rollers to the fixing device. Therefore, in the cover mode of this embodiment, when feeding the cover paper, the timing of feeding the paper from the tray is controlled and the fixing interval of the fixing device is controlled to improve the fixability of the cover paper.

Note that in this embodiment, the tray 113A
Plain paper is set in ~113C, and cover paper is set in tray 131D. This reduces the frequency of use by setting plain paper in a paper feed tray located near the process side where image formation is performed, and setting cover paper in a paper feed tray located far from the process side where image formation is performed. The expensive paper feeding time for plain paper can be shortened, and the copying time for one sheet in normal copying can be shortened. Further, it is convenient for controlling (delaying) the timing of feeding the cover paper.

FIG. 5 shows a control flowchart of the main control section 400. First, make input settings (Step 1:
(The word step is omitted below in parentheses.) In this setting, the number of copy sets, magnification, density, mode, etc. are set in response to key inputs from the operation board 150. Next, it is checked whether a document is set in the RDH 200 (2), and the process waits until a start instruction is given. Note that if there is an input on the operation board 150 during this time, the input setting is performed again.

When a start instruction is given (3), initial settings are performed. In this initial setting, the document number counter is cleared and the transport motor starts to be driven. After that, RDH20
0 to feed the original (5), and when the original is fed, transfer paper feeding control (S1), copying (
6), perform the process of ejecting the transfer paper (7) several times to set the transfer paper (
8), the original is ejected by the RDH 200 (9). Details of the transfer paper feeding control (S1) will be described later. Further, copying (6) and discharging the transfer paper (7) are the same processes as described with reference to FIG.

The processes of steps 5 to 9 are executed for each document in the document set (10), and similarly, if there are multiple document sets, the above-described process is performed for each document set (11). After that, post-processing is performed (12). In this post-processing, when a sorter unit (not shown) is installed externally, processing such as sorting processing and stapling processing is performed on the ejected transfer paper.

FIG. 6 shows a flowchart of transfer paper feeding control (S1). When the first original of a set of originals is fed and the front cover mode is instructed, the cover paper is fed from the tray 131D (a1, a2, a3, a
6) If it is not the first job, the timer T feeds the cover paper from the tray 131D after a predetermined time has elapsed (a4 to a
6). Additionally, if the back cover mode is instructed for the last document in the document set, the timer T feeds the cover paper from the tray 131D after a predetermined time has elapsed (a7 to a1
1). Other than the above, load plain paper into tray 1 at the specified timing.
Feed paper from 31A (a1, a2, a7, a8, a11
).

As described above, in this paper feeding control, cover paper or plain paper is fed depending on the document depending on the setting of the front or back cover mode, and the cover paper is fed after feeding the plain paper. When paper is to be fed, the timing is shifted by a predetermined time using a timer T and the paper is fed. In addition, timer T
The time is the transport time from tray 131A and the time for transporting from tray 131A.
This time is determined by taking into account the difference in conveyance time from 1D and the energy accumulation time of the roller 12CA, which is determined by the size of the cover paper, the circumferential length of the roller 12CA of the fixing device 12C, and the like.

[0032]

As described above, according to the present invention, when the cover paper is fed, the paper feeding interval from the previous paper feeding is increased. During this time, heat is accumulated on the surface of the fixing roller, so
Thereafter, when fixing the cover paper, the fixing is performed with a more sufficient amount of heat than in the past, and the fixing performance is improved. Further, when plain paper is fed, the same processing as in the past is normally performed, so that fixing performance, jam performance, etc. are not adversely affected.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a schematic configuration of a copying machine main body 100 of a copying apparatus according to the present invention.

FIG. 2 is a side view showing a schematic configuration of an automatic document feeder (RDH) 200 mounted on the upper part of the copying machine main body 100.

[Fig. 3] Operation board 15 provided in the copying machine main body 100
FIG. 2 is a plan view schematically showing a part of 0.

FIG. 4 is a block diagram schematically showing the control system of the present invention.

FIG. 5 is a control flowchart of the main control unit 400.

6 is a control flowchart of paper feed control (S1) shown in FIG. 5. FIG.

FIG. 7 is a side view schematically showing a mechanism of a fixing device included in a general copying machine.

[Explanation of symbols]

100: Copying machine main body 110: Optical system
120: Image forming system (110, 120: means for forming a static image) 124: Developing device (developing means)
126: Transfer charger (transfer means) 12C: Fixing device (fixing device) 1
2CA: Fixing roller HT: Heater 130: Paper feeding system (paper feeding means) 14
0: Paper refeed system 150: Operation board 7, 8: Cover mode key (cover mode instruction means) 2
00: Automatic document feeder 400: Main control unit (specifying means, transfer paper selection means, paper feeding pitch changing means)

Claims (3)

[Claims] 1. Means for forming an electrostatic latent image corresponding to the original by irradiating exposure light corresponding to the original onto a pre-charged photoreceptor; Developing means for developing the latent image on the photoreceptor; Transfer means for transferring the image visualized by development onto transfer paper; Designation means for specifying one type of transfer paper of multiple types having different thicknesses; Paper feeding means for supplying the designated type of transfer paper to the transfer means and a fixing device having a fixing roller and a heater that heats the fixing roller, which performs a fixing process on the transfer paper on which the transfer unit has finished transferring, when the specifying unit specifies thick transfer paper. , by the paper feeding means,
An image forming apparatus comprising: a paper feeding pitch changing means for setting a time from the start of feeding of a first transfer paper to the start of feeding of a subsequent transfer paper to be longer than the feeding time interval of a thin transfer paper. Device. 2. Means for forming an electrostatic latent image corresponding to the original by irradiating exposure light corresponding to the original onto a pre-charged photoreceptor; developing means for developing the latent image on the photoreceptor; Transfer means for transferring the image visualized by development onto transfer paper; Paper feeding means for selectively supplying one type of transfer paper of different thicknesses to the transfer means; and, when the transfer means has finished the transfer. In an image forming apparatus that includes a fixing device that performs a fixing process on transfer paper and has a fixing roller and a heater that heats the fixing roller, a cover mode instruction unit that inputs a cover mode instruction; Instructs the paper feeding means to feed thick transfer paper for at least one of the top and bottom originals of a set of originals, and instructs the paper feeding means to feed thin transfer paper for the other originals. and, when the transfer paper selection means specifies thick transfer paper, the time from the start of feeding of the first transfer paper to the start of feeding of the next transfer paper by the paper feeding means; An image forming apparatus comprising: a paper feeding pitch changing unit that sets a feeding pitch longer than a feeding time interval of thin transfer paper. 3. Exposure light corresponding to the original is irradiated onto a pre-charged photoreceptor to form an electrostatic latent image corresponding to the original, the latent image is visualized by a developing device, and the image is transferred onto transfer paper. , further selectively feeding cover paper, which forms a front or back cover for the first or last document of a set of multiple documents, as transfer paper to an image forming means that fixes the image in a fixing device, and forms an image; When selectively feeding plain paper as transfer paper for other documents, when feeding cover paper consecutively after feeding plain paper, the paper feeding start timing of the paper feeding means is delayed by a predetermined amount of time. A paper feed control method in image formation, characterized in that: