JP2005089009A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device for improving a continuous recording speed while eliminating image failure due to inclination and torsion of paper sheets, and improving image recording productivity as a recording speed at a double-faced printing time identical to that at a single face printing time. <P>SOLUTION: This image formation device has a paper feeding part 11a feeding paper sheets P, an image formation part 13 forming an image on the paper sheets P, and a registration roller 25 delivering the paper sheets P to the image formation part 13 while abutting a tip of the paper sheet P and positioning/aligning the tip. The device has pressure-contact releasing means 24a, 24b, 33, 34 and 35 releasing a pressure-contact condition of a pair of relay rollers 24, 24a. A predetermined time after the registration roller 25 starts delivering the preceding paper sheets P to the image formation part 13, the pressure-contact releasing means 24a, 24b, 33, 34 and 35 release pressure contact of a pair of the relay rollers 24, 24a, and the registration roller 25 switches a speed from a first delivery speed for delivering the paper sheets P to a second delivery speed faster than the first delivery speed, so as to deliver the next paper sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer provided with a sheet reversing device for forming an image on both sides of a sheet.

In order to solve the influence on image transfer due to the twist of the paper before the registration roller in the image forming apparatus, an apparatus that releases the upstream conveying roller before the registration roller is known (for example, see Patent Document 1).
However, in conventional copying machines, printers, and the like, a plurality of transport roller mechanisms such as registration rollers and relay rollers are generally used as means for transporting paper from a paper feed unit to a recording unit.
FIG. 6 is a schematic view showing conveyance of the sheet from the grip roller to the registration roller. The sheet P passes through the nip portion of the grip roller pair (relay roller) 24, hits the registration roller 25, and is conveyed in accordance with the conveyance timing.
In general, as a method of correcting the skew of the paper, the paper is transported by the upstream relay roller 24 until the paper is abutted against the nip portion of the registration roller pair 25 to form a slack, and then temporarily waits. A sheet is conveyed to a recording unit by a roller.
However, even when the skew is corrected in this way, the relay roller upstream of the registration roller holds the sheet while being skewed, and the sheet is twisted between the registration roller and the relay roller. When an image is transferred onto a sheet in the recording unit, there is a problem that the twist of the sheet affects and a transfer position shift or transfer unevenness occurs.
Japanese Patent Application Laid-Open No. 07-261572

On the other hand, in order to increase the image recording speed of the first sheet, the paper conveying speed (paper feeding speed) in the path from the paper feeding unit to the registration roller is set to be higher than the conveying speed (recording speed) at the time of image recording. There are many.
In this case, when images are continuously recorded on a plurality of sheets, the next sheet cannot be sent out at the sheet feeding speed while the preceding sheet is nipped and conveyed by the registration roller and the relay roller.
For this reason, the paper feeding unit continuously feeds the paper at a predetermined timing at a recording speed, and after the trailing edge of the preceding paper passes through the relay roller, the paper feeding speed is increased to carry the paper to the registration roller. Sometimes the recording speed is increased. However, even at this time, there is a problem that the speed cannot be increased unless the trailing edge of the preceding sheet has passed through the relay roller.
In addition, when the double-sided printing function that reverses the paper on which the image is recorded on one side and records the image on the other side is performed, the recording speed for continuous double-sided printing on multiple sheets of paper is reduced. I try not to be late.
Therefore, instead of recording an image on the front and back surfaces of the next sheet after recording an image on the front and back surfaces of one sheet, the image is recorded on the first side of the first sheet and then the second sheet of the second sheet. An image is recorded on one side, then the second side of the first paper, then the first side of the third paper, the second side of the second paper, the first side of the fourth paper, the first side of the third paper. In many cases, an interleaf method is used in which images are repeatedly recorded on the second side and the first side of the fifth sheet.
However, in general, the conveyance distance from the paper standby position to the registration roller when recording an image on the second side during duplex printing is greater than the conveyance distance from the paper feed tray to the registration roller, which is the paper standby position during single-sided printing. It is getting longer. For this reason, there is a problem that the continuous recording speed is slower in double-sided printing than in single-sided printing.
Accordingly, an object of the present invention is to eliminate the image defects due to skewing and twisting of the paper and to improve the continuous recording speed in order to solve the above-mentioned problems, and the image can be recorded at a recording speed equivalent to that for single-sided printing at the time of double-sided printing. An object of the present invention is to provide an image forming apparatus that improves recording productivity.

In order to solve the above-described problems, in the invention described in claim 1, the leading edge is positioned and aligned by abutting the sheet feeding section for feeding the sheet, the image forming section for forming an image on the sheet, and the leading edge of the sheet. In the image forming apparatus having a registration roller that conveys the paper to the image forming unit, the image forming unit includes a pressure release unit that releases the pressure contact state of the relay roller pair, and the registration roller leads to the image forming unit of the preceding paper. After a predetermined time from the start of the conveyance, the pressure release unit releases the pressure contact of the relay roller pair, and the registration roller transfers the first sheet from the first conveyance speed at which the sheet is conveyed to the image forming unit. The image forming apparatus is characterized by switching to a second transport speed that is faster than the transport speed and transporting the next sheet.
According to a second aspect of the present invention, a paper feeding unit that feeds out a paper, an image forming unit that forms an image on the paper, and a leading end of the paper are abutted and positioned and aligned to the image forming unit. A registration roller that conveys the sheet and a first relay roller pair that is upstream of the registration roller and that conveys the sheet to the registration roller, and a second relay that is between the first relay roller pair and the sheet feeding unit In the image forming apparatus, the image forming apparatus further includes a double-sided conveying unit that forms an image on one side of the roller and the sheet and then reverses the sheet and sends the other side as an image forming surface to the second relay roller. The double-sided conveying means after a predetermined time from the start of conveyance of the preceding sheet by the registration roller to the image forming unit at a first conveyance speed. But The paper is sent out at a second transport speed that is faster than the first transport speed, and after a predetermined time, the press-contact release means releases the press-contact of the first relay roller pair, and the second transport speed starts from the first transport speed. The image forming apparatus is switched to the conveyance speed.

The image forming apparatus has a pressure release means for the relay roller upstream of the registration roller, and releases the pressure of the relay roller before the trailing edge of the preceding paper passes through the relay roller, so that the next paper is transported faster than the recording speed. Thus, the paper is conveyed toward the registration roller, so that the effect of paper twist between the registration roller and the relay roller on image transfer can be prevented, and the paper interval can be shortened to increase productivity during continuous printing.
In addition, the image forming apparatus has a double-sided conveyance printing function, and at the time of second-side printing, the paper is fed from the double-sided conveyance device at a paper feeding speed faster than the recording speed, and the trailing edge of the preceding paper is a relay roller upstream of the registration roller Before exiting, the relay roller is released from pressure contact, and the feed speed of the main body feed system is increased from the recording speed to the feed speed to feed the paper toward the registration roller. A printing speed equivalent to that of the time can be achieved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing an embodiment of an image forming apparatus according to the present invention. The apparatus main body 10 is detachably mounted with an image forming unit 13 that can form a monochrome or color image on the paper P and a fixing unit 14 that fixes the formed image on the paper P.
FIG. 2 is a schematic diagram showing the image forming unit and the fixing unit in more detail. As shown in FIG. 2, the image forming unit 13 forms a transport path R <b> 1 so that the image carrying belt 15 transports the paper P obliquely upward (transverse direction) toward the fixing unit.
At the same time, the writing unit 16 scans the laser beam on the peripheral surface of the photosensitive drums 17Y, 17M, 17C, and 17B arranged in parallel in the order of yellow, magenta, cyan, and black along the image carrying belt 15 to statically. An electrostatic latent image is written and formed.
The developing units 18Y, 18M, 18C, and 18B develop the toner on the electrostatic latent image and transfer the toner image onto one side of the paper P conveyed by the image carrier belt 15, while the fixing unit 14 is heated by a built-in heater. The pressure roller 19 is pressed against the endless belt 20 and rotates.
The toner image on the paper P received from the carrier belt 15 is fixed by this pressure rotation, and the image is formed on the paper P. Note that the writing unit 16 writes an electrostatic latent image based on the received image data for yellow, magenta, cyan, and black.
The electrostatic latent image is written by irradiating a laser beam emitted from a laser diode (not shown) to the two-stage polygon scanner 16a and polarizing it on the mirror group 16b, whereby the photosensitive drums 17Y, 17M, 17C, and 17B are written on the photosensitive drums 17Y, 17M, 17C, and 17B. This is done by scanning.

The paper P is called by the calling roller 21 on the front end side (the right side of the apparatus main body 10 in the drawing) of the paper cassettes 11a to 11c for loading and storing papers of different sizes, and the separation paper feed roller pair 22 is separated and fed one by one. By feeding paper, the sheet is transferred to a registration roller pair 25 in front of the image forming unit 13 via a conveyance path R1 by a conveyance roller pair (relay roller pair) 23 and a grip roller pair (relay roller pair) 24. .
After the image is formed through the image forming unit 13 and the fixing unit 14, as shown in FIG. 1, the paper discharge roller on the upper portion of the apparatus main body 10 through the conveyance path R <b> 1 by the branch roller pair 26 and the conveyance roller pair 27. By passing to the pair 28, the front and back are reversed so that the image plane formed immediately before is in the page order, and the paper is discharged and stacked on the discharge tray 12.
Note that the paper P from the paper cassette 11c is transferred from the grip roller pair 24 to the registration roller pair 25 in common with a later-described transport roller pair (relay roller pair) 29. The apparatus main body 10 is provided with an openable / closable manual feed tray on the right side surface in the drawing, from which paper P can be directly supplied to the registration roller pair 25, and the open / closed tray is opened below the manual feed tray. A door is provided so that the jammed paper P can be removed when calling.
The registration roller 25 is driven from the same drive motor as the image forming unit 13 via an electromagnetic clutch. Further, the calling roller 21, the separation paper feed roller pair 22, the transport roller 23, the grip roller 24, and the transport roller 29 are driven by independent paper feed motors.
FIG. 3 is a schematic view showing a pressure contact release mechanism (pressure contact release means) provided in the grip roller pair in the pressure contact state. FIG. 4 is a schematic view showing the pressure release mechanism of FIG. 3 in its released state. The driven roller 24a facing the grip roller 24 is arranged so as to constantly apply pressure in the direction of the grip roller 24 by a spring (not shown).
A shaft portion (shaft portion) 24b of the driven roller 24a is disposed in a state where one end of a substantially letter-shaped pressure release arm 33 is in contact therewith, and a central portion is rotatably supported by a fulcrum 33a. The end is connected to the solenoid 34. When a release signal from the control means is input, the solenoid 34 pulls down the plunger 35 in the A direction, the pressure contact release arm 33 rotates in the B direction around the fulcrum 33a and moves in the B direction, and the shaft portion 24b of the driven roller 24a is moved. The pressure contact with the grip roller 24 is released by lifting.

Next, the paper feeding operation of the printer apparatus will be described. Referring again to FIG. 1, the paper P separated and fed one by one from the paper cassettes 11a to 11c passes through the transport roller 23 or the transport roller 29, and is then registered by the grip roller 24 to which the driven roller 24a is pressed. Sent to. The sheet conveyance speed at this time is set as a sheet feeding speed.
After the leading edge of the paper P is detected by a registration sensor 37 (see FIG. 3) disposed in front of the registration roller 25, the paper P is abutted against the nip portion of the registration roller 25 that is stopped, and a predetermined amount of bending is caused. Then, the skew correction of the paper P is performed, the state is maintained, and the paper feed drive motor is stopped.
In response to a paper conveyance command from the drive control unit to the image recording unit, the electromagnetic clutch is turned on and the registration roller 25 starts to rotate, and the paper feed drive motor is driven to feed the paper P into the image forming unit 13. The sheet conveyance speed at this time is defined as a recording speed.
For large size paper such as A3 and B4, image defects such as transfer deviation and transfer unevenness due to twisting of the paper P caused by skew correction at the registration roller 25 when the image is transferred to the paper P in the image forming unit 13 May occur.
For this reason, after the sheet P is conveyed for a predetermined time from the start of the registration roller driving, the driven roller 24a of the grip roller 24 is released from the pressure contact to widen the bending space of the sheet P and absorb the twist of the sheet P and the like.
After the rear end of the paper P passes through the nip portion, the grip roller 24 returns to the pressure contact state again in preparation for the next paper entry. It should be noted that for the paper having a short paper length in the feeding direction, such as A5 and A4 sizes, the transfer roller is not affected by the paper twisting, so that the pressure contact of the grip roller 24 need not be released.

As for the paper conveyance speed, the recording speed is determined by the image forming speed of the image forming unit 13, and therefore the paper feeding speed is set to a speed higher than the recording speed in order to increase the printing speed as the printer apparatus. . Therefore, the paper feed drive motor has two drive speeds, a paper feed speed and a recording speed.
When printing continuously, it is necessary to shorten the sheet interval in order to increase the continuous printing speed. In the case where the pressure contact of the grip roller 24 is not released, the trailing edge of the preceding sheet passes through the grip roller 24, and then the sheet interval is determined by driving the sheet feeding drive motor at the sheet feeding speed and feeding the sheet from the sheet feeding cassette. Cannot be narrowed sufficiently.
Although it is possible to solve the problem by increasing the sheet feeding speed, the sheet feeding speed cannot be extremely increased from the viewpoint of noise accompanying the sheet conveyance and conveyance quality. For this reason, a pre-feed method is adopted in which the next sheet is fed out from the sheet feeding cassette by a predetermined distance in advance while the grip roller 24 conveys the preceding sheet at the recording speed.
After the trailing edge of the preceding paper passes through the grip roller 24, the paper feed drive motor is increased from the recording speed to the paper feed speed and switched from pre-feed to main paper feed to shorten the paper interval.
Next, double-sided printing will be described. The apparatus main body 10 is transferred to the conveying roller pair 29, the grip roller pair 24 and the registration roller pair 25 in the conveying path R1 through the double-sided conveying apparatus 50 arranged in parallel below the image bearing belt 15. Thus, the paper P can be conveyed again to the image forming unit 13 to form an image.
The double-sided conveyance device 50 switches the conveyance direction of the paper P on which an image is formed on one side by the image forming unit 13 with a branching claw (not shown) arranged on the downstream side of the branching roller pair 26.
As a result, the pair of carry-out rollers 30 carries out the paper P from the carry-out port 31 opened on the left side surface of the apparatus main body 10 to the paper reversing device 40 which is an external device, and the paper reversing device 40 reverses the front and back. P is fed by being carried in from a carry-in port 32 that opens below the carry-out port 31.
Further, the sheet reversing device 40 has, on the side of the apparatus, an upper discharge tray 41 that stacks with the image surface facing upward, and a lower discharge tray 42 that stacks the sheets with the image surface turned down by reversing the sheets. .

FIG. 5 is an enlarged schematic view of the sheet reversing device of FIG. In FIG. 5, the sheet reversing device 40 has a branch claw 48 for switching the sheet P carried out from the carry-out port 31 of the printer apparatus main body 10 to an upper face-up conveying path R4 and a lower reversing path R3. Not driven by solenoid.
In the default state, the branching claw 48 is positioned upward as shown in FIG. 3, and guides the paper P to the reversing path R3.
The reversing path R3 includes a path R3-1 that leads from the branching claw 48 to the upper reversing roller 43, a path R3-2 that performs switching back by the upper reversing roller 43, a path R3-3 that performs switching back by the lower reversing roller 44, and the printer main body. Path R3-4 leading to the unloading roller pair 46 to 10, and path R3-5 leading to the unloading roller pair 47 to the lower discharge tray 42.
A sheet-like paper branching member 5 is provided at a route branch point where the routes R3-2, R3-3, and R3-4 are joined, and an elastic member is provided at a route branch point where the routes R3-1, R3-2, and R3-5 are joined. A sheet-like paper branching member 6 is provided. These branch members 5 and 6 are elastically deformed to allow passage when the paper advances, but block the path after the rear end of the paper has passed, and do not allow reverse return.

In the vicinity of the paper discharge roller pair 49 and the carry-out roller pair 47, there are paper discharge sensors 1 and 7, which detect the leading and trailing edges of the paper P discharged from the paper reversing device 40. The paper P carried into the printer apparatus main body 10 from the paper reversing device 40 is detected by the double-sided conveyance sensor 3 (FIG. 1) of the double-sided conveyance apparatus 50 installed in the printer apparatus main body 10.
There is a reversing sensor 4 in the vicinity of the pair of lower reversing rollers 44. The reversing sensor 4 detects the leading edge of the paper P that is transported down the reversing path R3. 47) The switchback timing is determined for each.
The paper discharge sensors 1 and 7 and the double-sided conveyance sensor 3 use a transmissive photo interrupter having an actuator. However, the reversing sensor 4 involved in the control of the switchback of the paper P requires a higher accuracy, so that the reflection type photo interrupter is required. An interrupter is used.
The sheet reversing device 40 is driven by a separate driving motor with the upper reversing roller pair 43 together with the carry-out roller pair 47 and the lower reversing roller pair 44 together with the carry-out roller pair 46, so Before the carry-in to 32 is completed, the carry-out of the next paper P from the carry-out port 31 can be started.
Further, by incorporating a one-way clutch in the carry-out roller pair 46, the conveyance inlet roller pair 51 of the double-sided conveyance device 50 holds the paper P that has come out of the reverse roller pair 44, and then the driving direction of the reverse roller pair 44 is changed to the paper direction. The paper P can be continuously carried out and carried in by being driven in a direction opposite to the carrying direction of P.
Further, a sheet reversing device 40 is further provided so that a difference can be made between the conveyance speed when carrying out the paper P from the carry-out port 31 of the apparatus body 10 and the conveyance speed when carrying the paper P through the carry-in port 32. Is set faster than the carry-out speed from the carry-out port 31 of the apparatus main body 10.
By setting the speed equal to or slower than the carry-in speed to the carry-in entrance 32, a large interval (inter-paper) can be generated between the preceding and following sheets P without increasing the stop time of the sheet P, and the switchback. The leading and trailing edges of the sheet P can be reliably detected without causing a collision between the completed sheet and the succeeding sheet, and switching of the conveyance path can be realized.

The operation of the paper P in the paper reversing device 40 is as follows. When paper is fed again from the paper reversing device 40 to the printer apparatus main body 10 for printing on both sides of the paper P, the paper P that has entered the transport path R3-1 to R3-2 is transported by the upper reversing roller 43 to the transport path R3-. 3 is sent.
After the reversing sensor 4 detects the leading edge of the paper P, the lower reversing roller 44 lowers and conveys the paper until the trailing edge of the paper falls below the free end position of the paper branching member 5. The rear end of the paper P reaches below the free end position of the paper branching member 5, and the paper P completely enters the transport path R3-3.
Thereafter, the lower reverse roller 44 is stopped and reversely rotated at a predetermined position where the rear end of the sheet is intermediate between the free end of the sheet branching member 5 and the lower reverse roller 44 to switch back the paper P. The switched-back paper P is sent to the transport path R3-4 by the lower reverse roller 44 and transported to the transport roller 46.
When paper P printed on one or both sides is discharged and stacked from the paper reversing device 40 onto the lower paper discharge tray 42, the leading edge of the paper P transported downward along the transport paths R3-1, R3-2, and R3-3. Is detected by the reversing sensor 4, and is conveyed by the reversing rollers 43 and 44 until the rear end of the sheet is lowered below the free end position of the upper sheet branching member 6.
After the rear end of the paper P reaches below the free end position of the paper branching member 6, the reverse roller 43 at a predetermined position between the free end of the paper branching member 6 and the upper reverse roller 43. 44 is stopped and reversely rotated to switch back the paper P.
The switched-back paper P is sent to the transport path R3-5 by the upper reversing roller 43 and transported to the transport roller 47, and the page on which the image is formed on the lower paper discharge tray 42 is faced down to the page order. Loaded.

When the paper P is discharged to the upper paper discharge tray 41, the branch claw 48 switches the transport direction of the paper P carried out from the carry-out port 31 of the apparatus body 10 to the transport path R4 above the reverse roller pair 43. Then, the paper is transferred to the paper discharge roller pair 49 as it is, and the paper P is discharged without being reversed and discharged and stacked with the surface on which the image is formed facing up.
For example, when manually feeding application paper such as OHP or thick paper, by specifying the upper paper discharge tray 41 as the paper discharge destination, the paper P is discharged without applying a load of curving and reversing. And can be loaded.
The double-sided conveyance device 50 (see FIG. 1) includes a conveyance inlet roller 51, four conveyance relay rollers 52 and a conveyance outlet roller 53, and four conveyance rollers and a guide member. A duplex conveyance sensor 3 is installed in the vicinity of the upstream side of the conveyance outlet roller 53.
The conveyance roller group of the double-sided conveyance device 50 is driven by a single drive motor, transmits drive from the drive motor to the conveyance outlet roller 53 via the one-way clutch, and is conveyed from the conveyance outlet roller 53 to the conveyance relay roller 52 and the conveyance inlet by the timing belt. The drive is transmitted to the rollers 51 sequentially.
The double-sided conveyance device 50 receives the paper P carried into the carry-in port 32 from the paper reversing device 40, and after the double-sided conveyance sensor 3 detects the leading edge of the paper P, the drive is stopped after a predetermined time and the paper P is conveyed on both sides. Wait in the device once. The sheet conveyance speed from the sheet reversing apparatus 40 to the duplex conveying apparatus 50 at this time is set as the reversal speed.
In the paper reversing device 40, it is necessary to widen the paper interval in order to switch back the paper P, and the reversing speed must be higher than the recording speed and is set to a speed higher than the paper feeding speed.
After the paper P arrives at the standby position, the double-sided conveyance device 50 is driven at the paper feed speed, and then the paper feed drive motor starts to drive at the paper feed speed, and the paper P is conveyed from the double-sided conveyance device 50 to the relay roller 29. Then, the tip is brought into contact with the registration roller 25 through the grip roller 24 to form a bend, thereby performing skew correction.
Thereafter, an image is recorded on the second side in the same manner as single-sided printing. The drive motor of the double-sided conveyance device 50 has two drive speeds, a reverse speed and a paper feed speed.

In the case of continuous double-sided printing, the interleaf double-sided method is adopted in order to increase the continuous printing speed. For example, in the case of A4 size paper, print in order of 2 pages, 4 pages, 6 pages, 1 page, 8 pages, 3 pages, 10 pages, 5 pages,... To load in page order.
That is, two sheets of paper P are present in the transport path in excess of single-sided continuous printing. One of the sheets P is waiting on the duplex conveying device 50.
During the continuous double-sided printing, the paper feeding unit alternately feeds paper from the paper feeding cassette 11a to the registration roller 25 and re-feeds from the double-sided conveyance device 50 to the registration roller 25, and wastes waiting time. Continuous double-sided printing can be performed without making it.
Similarly to the case of single-sided continuous printing, in the case of double-sided continuous printing, feeding of paper from the paper feeding cassette or the double-sided conveyance device 50 toward the registration roller 25 is started at the paper feeding speed after the trailing edge of the preceding paper has passed through the grip roller 24. In this case, since the paper interval becomes wide, pre-feeding is performed.
However, when the paper is fed again from the duplex conveying device 50, the paper P must be conveyed to the registration roller 25 through the conveying roller 29 and the grip roller 24 having different driving systems.
Therefore, in the case of refeeding from the duplex conveying device 50, the duplex conveying device 50 feeds the sheet P from the standby position at a predetermined timing after the preceding sheet is started to be conveyed to the image forming unit 13 by the registration roller 25. Start transporting at speed.
Before the leading edge of the sheet arrives at the relay roller 29, the pressure contact of the grip roller 24 is released, and the sheet feeding drive motor is switched from the recording speed to the sheet feeding speed. The grip roller 24 returns to the press-contact state again after the trailing edge of the preceding paper is removed.
In this way, the re-feed paper P from the double-sided transport device 50 is transported to the registration roller 25 by the relay roller 29 and the grip roller 24 at the paper feed speed. By doing so, it is possible to start feeding the next sheet at the sheet feeding speed before the trailing edge of the preceding sheet passes through the grip roller 24.
For this reason, the double-sided conveyance device 50 does not have a driving speed for paper conveyance at the recording speed, and the paper interval is the same as that for single-sided printing before the paper P reaches the registration roller 25 even when the double-sided paper is fed again. It is possible to reduce the size, and it is possible to achieve 100% print productivity of double-sided continuous printing relative to single-sided continuous printing.
In this embodiment, for the paper having a short paper length in the transport direction, the pressure roller is not released when the paper is fed from the paper cassette during single-sided continuous printing, but the trailing edge of the preceding paper P is gripped. The pressure contact may be released before passing through the roller 24, and the next sheet P may be fed from the sheet feeding cassette 11a at the sheet feeding speed.

1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram illustrating an image forming unit and a fixing unit in more detail. It is the schematic which shows the press-contact cancellation | release mechanism provided in the grip roller pair in the press-contact state. It is the schematic which shows the press-contact cancellation | release mechanism of FIG. 3 in the cancellation | release state. It is the schematic which expands and shows the paper inversion apparatus of FIG. FIG. 6 is a schematic diagram illustrating conveyance of a sheet from a grip roller to a registration roller.

Explanation of symbols

P Paper 10 Device main body 11a Paper feed unit (paper feed cassette)
13 Image forming unit (image forming unit)
24 First relay roller (grip roller)
24a driven roller 24b driven roller shaft (pressure contact release means)
33 Pressure release arm (pressure release means)
34 Solenoid (pressure contact release means)
35 Plunger (pressure release means)
25 Registration roller 29 Second relay roller (conveyance roller)
40 Paper reversing device 50 Double-sided conveying means (double-sided conveying device)

Claims (2)

  A pair of relay rollers that conveys the sheet delivered from the sheet feeding unit to the image forming unit; a registration roller that conveys the leading end of the sheet by abutting and aligning the leading end of the sheet to the image forming unit; and the relay roller In the image forming apparatus having a pressure release unit that releases the pair of pressure contact states, the pressure release unit releases the relay after a predetermined time after the registration roller starts conveying the preceding paper to the image forming unit. While releasing the pressure contact between the roller pair, the registration roller switches from the first conveyance speed at which the sheet is conveyed to the image forming unit to the second conveyance speed that is faster than the first conveyance speed, and conveys the next sheet. An image forming apparatus.   A sheet feeding unit that feeds out a sheet, an image forming unit that forms an image on the sheet, a registration roller that abuts the leading end of the sheet to position and align the leading end, and conveys the sheet to the image forming unit, and the registration roller The first relay roller pair that conveys the paper to the registration rollers, the second relay roller between the first relay roller pair and the paper feeding unit, and an image on one surface of the paper In the image forming apparatus having a double-sided conveying unit that reverses the sheet and forms the other side as an image forming surface and sends it to the second relay roller, the pressure contact state of the first relay roller pair is released. A pressure canceling unit, and after the predetermined time has elapsed after the registration roller starts transporting the sheet preceded by the registration roller to the image forming unit at a first transporting speed, the double-sided transporting unit is faster than the first transporting speed. 2 The sheet is fed at a feeding speed, and after a predetermined time, the pressure-contact releasing unit releases the pressure-contact of the first relay roller pair and switches from the first transport speed to the second transport speed. Image forming apparatus.

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