JP2004026353A - Sheet conveying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet conveying device which achieves both stabilization in conveying various sheets of paper, especially heavy paper print, high image quality and high printing accuracy. <P>SOLUTION: A torque limiter 12 is provided for controlling a loop amount of a sheet 11 formed between a pair of register rollers 1, 2 and a pair of conveying rollers 4, 5 so that more than a predetermined amount of conveying torque is not applied on the register front roller 5 against a reaction force of a loop of the sheet 11. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is, for example, in an image recording apparatus such as a printer, a facsimile, a copying machine, etc. employing an appropriate transfer type or a direct type image forming process such as an electrophotographic method, an ink jet method, an office machine, and various other sheet-using devices, Sheets (transfer paper, photosensitive paper, thermal paper, electrostatic recording paper, printing paper, originals, label paper, cards, The present invention relates to a sheet transport device that regulates the leading edge of a sheet such as an envelope or a postcard, and the material is not limited to paper, and feeds a sheet to a next stroke unit such as an image forming unit, an information reading unit, and a processing unit at a predetermined timing. .
[0002]
[Prior art]
A conventional image forming apparatus will be described with reference to FIG. FIG. 13 is a schematic sectional view of a laser beam printer which is an example of a conventional image forming apparatus. Hereinafter, the overall configuration and functions of the laser beam printer will be described.
[0003]
In FIG. 13, a paper feed cassette 120 for stacking and storing sheets S is mounted on the lower part of the apparatus main body of the laser beam printer. The paper cassette 120 is configured to be detachable from the main body of the laser beam printer.
[0004]
The paper feed roller 121 feeds the sheets S stacked in the paper feed cassette 120 one by one from the uppermost side. The guide member 122 guides the sheet S fed by the paper feed roller 121. The transport roller 105 transports the fed sheet S. The driven roller 104 is provided to face the pre-registration roller 105, and rotates following the conveyed sheet S.
[0005]
Pre-registration rollers 105 and driven rollers 104 form pre-registration roller pairs 104 and 105. Further, a pair of registration rollers 101 and 102 are formed by a registration upper roller 101 and a registration lower roller 102. Then, after the leading end of the sheet S abuts against the nip portion of the stopped registration roller pair 101, 102 to form a loop and correct skew, the registration roller pair 101, 102 is rotated at a predetermined timing to rotate the sheet. S is conveyed to the image forming means.
[0006]
The process cartridge 126 is detachably mounted on the apparatus main body. Inside the process cartridge 126, a photosensitive drum 127 and an image forming means such as a primary charger and a developing device (not shown) are provided around the photosensitive drum 127.
[0007]
The laser scanner 128 scans a laser beam in accordance with image information and writes (latent image formation) on the photosensitive drum 127.
[0008]
The transfer roller 129 is in pressure contact with the photosensitive drum 127, and a developed image (toner image) is transferred from the photosensitive drum 127 when the sheet S passes between the transfer roller 129 and the photosensitive drum 127. .
[0009]
The transport guide 130 guides the sheet S after the image transfer to the fixing device. The fixing device fixes the image (toner image) transferred to the sheet S, and includes a fixing roller 131, a pressure roller 132, a fixing discharge roller pair 133, and the like.
[0010]
The sheet S is sent to the sheet discharge roller pair 135 by the conveying roller pair 134, and is discharged out of the apparatus with the surface of the image forming unit of the sheet S after image fixing down. The paper discharge tray 136 is formed on the upper surface of the apparatus main body, and stacks and holds the sheets S discharged out of the apparatus after the image is fixed.
[0011]
Next, the image forming operation of the laser beam printer configured as described above will be described. When an image formation is instructed by a host computer (not shown), first, the sheet feeding roller 121 is rotated, and the uppermost sheet in the sheet feeding cassette 120 is rotated. The sheet S is fed one by one from the sheet S on the side, and guided by a guide member 122 to be guided to a pair of pre-registration rollers 104 and 105 composed of a pre-registration roller 105 and a driven roller 104 and a pair of registration rollers 101 and 102.
[0012]
The registration roller pairs 101 and 102 convey the sheet S between the photosensitive drum 127 and the transfer roller 129 which are the next process unit, in synchronization with the image formed on the photosensitive drum 127, and the sheet S is exposed to light. When passing between the body drum 127 and the transfer roller 129, an image (toner image) is transferred.
[0013]
Further, the sheet S after the image transfer is conveyed to the fixing device along the conveyance guide 130, and when passing between the fixing roller 131 and the pressing roller 132, heat and pressure are applied to fix the transferred image. Is done. The sheet S on which the image has been fixed is conveyed by a fixing discharge roller 133, and further discharged and stacked on a discharge tray 136 by a discharge roller pair 135.
[0014]
Next, the sheet conveying device will be described in detail with reference to FIGS. FIG. 14 is a schematic sectional view of a resist portion of a conventional laser beam printer.
[0015]
13 and 14, the pair of registration rollers includes an upper registration roller 101 and a lower registration roller 102, the pair of registration rollers includes a pre-registration roller 105 and a driven roller 104, and the registration upper roller 101 includes an elastic member 103. As a result, the pair of rollers forms a nip portion by being pressed by the lower resist roller 102 and the driven roller 104 being pressed by the pre-registration roller 105 by the elastic member 106.
[0016]
The sheet S sent from the sheet cassette 120 by the sheet feeding roller 121 passes through the pair of conveying rollers 104 and 105 and is sent to the nip portion of the pair of registration rollers 101 and 102. The transport guides 107, 108, and 109 are for guiding the sheet, and are arranged at positions where a space in which the sheet S can form a loop is provided.
[0017]
The registration roller pair 101, 102 is stopped when the sheet S is conveyed, and the conveyance of the front end portion of the sheet S is temporarily performed when the front end of the sheet S hits the entrance of the nip portion of the registration roller pair 101, 102. Stopped.
[0018]
The pre-registration roller pairs 104 and 105 further convey the sheet S to the registration roller pairs 101 and 102, thereby forming a loop and correcting the skew of the sheet and controlling the image writing position.
[0019]
A sheet 110 such as thin paper or plain paper and a sheet 111 such as thick paper or label paper represent a state in which a loop is formed.
[0020]
The loop amount of the sheet S is defined by the feed amount of the pair of pre-registration rollers 104 and 105 irrespective of the paper type. When the pair of registration rollers 101 and 102 starts rotating again at a predetermined timing, the sheet S is conveyed by the conveyance guide 107 and the conveyance guide 107. The paper is passed through 108 and 109 to a nip formed by the photosensitive drum 127 and the transfer roller 129.
[0021]
[Problems to be solved by the invention]
However, in the case of the above-described conventional technology, the following problems have occurred.
[0022]
In other words, in recent years, with the speeding up, high image quality, high printing accuracy, etc. of laser beam printers, the sheets to be printed by users have become extremely diverse, and sheets with different characteristics such as thin paper, thick paper, postcards, OHT, etc. It is also common to print directly.
[0023]
14, while being guided by conveyance guides 107, 108, and 109, sheets 110 and 111 are fed by a pair of pre-registration rollers 104 and 105 into a nip portion of a pair of registration rollers 101 and 102 that have stopped rotating.
[0024]
Even after the leading ends of the sheets 110 and 111 abut the nip portions of the pair of registration rollers 101 and 102, the pair of pre-registration rollers 104 and 105 continue to rotate for a certain period of time to form a loop in the sheets 110 and 111.
[0025]
Since the amount of loop is controlled by the rotation time of the pair of pre-registration rollers 104 and 105 regardless of the type of the sheets 110 and 111, all the sheets 110 and 111 can form the same amount of loops.
[0026]
In particular, when a loop is formed on a sheet 111 having a strong reaction force, such as thick paper or label paper, large reaction forces F1 and F2 are generated on the sheet 111.
[0027]
Here, the reaction force refers to a force for restoring the original shape when a flat sheet usually forms a loop or the like, and depends on the material and thickness of the sheet, the amount of the loop, and the like. .
[0028]
When the reaction force F1 is larger than the nip force f1 of the pair of registration rollers 101 and 102, the sheet 111 may pass through the nip of the pair of registration rollers 101 and 102. That is, if printing is performed in that state, the leading end registration becomes large.
[0029]
When the reaction force F2 is larger than the nip force f2 of the pair of pre-registration rollers 104 and 105, there is a possibility that the loop once formed is reduced or the loop cannot be formed.
[0030]
Alternatively, the sheet 111, which has abutted the nip of the pair of registration rollers 101 and 102, is returned to the upstream side as the distance from the nip is increased. Disorder can also occur.
[0031]
Furthermore, the higher the number of high-end printers, the greater the variety of sheets that can be conveyed, and the faster the conveyance speed, making it more difficult to optimally control the loop amount. I have.
[0032]
Further, recent printers have a high resolution of 1200 dpi, 2400 dpi, etc. in order to achieve high image quality. If the resolution becomes higher, the influence on the image caused by friction, slip, and the like at the time of conveyance becomes remarkable. In addition, there is a possibility that an image may be affected even if it is not thick paper.
[0033]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and aims at achieving both high image quality and high printing accuracy while stabilizing the paper conveyance of printing on various sheets, especially thick paper. It is an object of the present invention to provide a sheet conveying device which is made to operate.
[0034]
[Means for Solving the Problems]
In order to achieve the above object, in the sheet conveying device according to the present invention,
First conveying means for temporarily stopping the conveyed sheet and conveying the sheet to a next stroke portion at a predetermined timing;
A second conveying unit that is provided upstream of the first conveying unit in the sheet conveying direction and conveys a sheet to the first conveying unit and forms a loop in the sheet;
The reaction force of the sheet loop formed between the first conveyance means and the second conveyance means is caused by the reaction force of the first conveyance means or the second conveyance means due to the reaction force of the sheet loop. It is characterized in that a part is operated and adjusted.
[0035]
The second transport means is a transport roller pair composed of two rotating bodies, and a constant or more transport torque is applied to at least one of the rotating bodies against the reaction force of the sheet loop. It is preferable to provide a torque control means for controlling the control so as not to occur.
[0036]
Further, the second transporting means includes a transport roller pair composed of two rotating bodies, and when at least one of the rotating bodies of the transport roller pair is in a predetermined position when a reaction force of the sheet loop is equal to or more than a predetermined value. And a rotating body retracting mechanism that retracts from the body.
[0037]
The rotating body retracting mechanism includes an urging means for urging at least one of the rotating bodies of the transport roller pair toward a sheet,
It is preferable to have a guide portion for retracting the rotating body in a predetermined direction when a reaction force due to the loop of the sheet is larger than an urging force of the urging means.
[0038]
The first transporting means includes two rotating bodies, and a sheet leading edge detecting means for detecting a leading edge position of a sheet that has protruded from the nip of the pair of rotating bodies to a downstream side in the transporting direction from the first transporting means. Preferably, it is provided.
[0039]
It is preferable that the first transport unit includes two rotating bodies, and a pulse encoder that detects a rotation speed fluctuation of at least one of the rotating bodies in the rotating body pair.
[0040]
It is preferable that the second transport unit includes a transport roller pair including two rotating bodies, and a regulating unit that regulates a rotation direction of at least one of the rotating bodies of the transport roller pair only in a sheet transport direction. is there.
[0041]
According to the above configuration, the reaction force due to the loop of the sheet is automatically and optimally adjusted by the reaction force of the loop of the sheet. , And the stability of sheet conveyance can be prevented from deteriorating, and a good image without defective printing accuracy or image disturbance can always be obtained regardless of the type of sheet.
[0042]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto unless otherwise specified. Absent. The materials, shapes, and the like of the members once described in the following description are the same as those in the first description unless otherwise specified.
[0043]
The description of each embodiment of the image forming apparatus according to the present invention described below also serves as the description of each embodiment of the sheet conveying apparatus according to the present invention.
[0044]
(First Embodiment)
First, a first embodiment of the sheet conveying device according to the present invention will be described. FIG. 1 is a schematic cross-sectional view of a part of the sheet conveying device according to the first embodiment.
[0045]
In FIG. 1, a resist upper roller 1 is a metal roller, a resist lower roller 2 is a rubber roller, and the resist upper roller 1 and the resist lower roller 2 constitute a resist roller, which is a component of a first conveying unit. Pairs 1 and 2 are formed.
[0046]
The elastic member 3 urges the upper resist roller 1 against the lower resist roller 2 to form a registration nip. The registration roller pairs 1 and 2 temporarily stop the sheet conveyed from the sheet cassette at the registration nip, and convey the sheet to the next process unit on the downstream side at a predetermined timing.
[0047]
Reference numeral 4 denotes a pre-registration roller as a driven roller, and 5 denotes a pre-registration roller. Is formed.
[0048]
The elastic member 6 urges the pre-registration roller 4 against the pre-registration roller 5 to form a pre-registration nip.
[0049]
The pair of pre-registration rollers 4 and 5 convey the sheet conveyed from the paper feed cassette to the pair of registration rollers 1 and 2, and even after the leading edge of the sheet strikes the nip of the pair of registration rollers 1 and 2, The time sheet is fed to form a loop in the sheet.
[0050]
The torque limiter 12 is a torque control member, and controls the transport torque of the pre-registration roller 5. The transport guides 7, 8, and 9 are arranged at positions where a space where a sheet can form a loop is secured. The sheet 10 shows a state in which a sheet having weak reaction force such as thin paper or plain paper forms a loop, and the sheet 11 shows a state in which a sheet having strong reaction force such as thick paper or label paper forms a loop.
[0051]
In the case of the sheet 10 such as thin paper or plain paper, the sheet 10 conveyed from the paper feed cassette is sent to the registration roller pairs 1 and 2 whose rotation operation has been stopped by the registration front roller pairs 4 and 5. Although the conveyance of the sheet 10 is temporarily stopped when the leading end of the sheet abuts on the registration nip, the sheet 10 forms a loop by conveying the sheet 10 further downstream by the pre-registration roller pair.
[0052]
After the sheet 10 forms a loop, the rotation of the pair of pre-registration rollers 4 and 5 is temporarily stopped, and the pair of registration rollers 1 and 2 and the pair of pre-registration rollers 4 and 5 start rotating again at a predetermined timing. 10 is transported downstream.
[0053]
In the case of a sheet 11 such as cardboard or label paper, the pre-registration rollers 4 and 5 further convey the sheet 11 which has hit the registration nip, so that a reaction force F of the sheet 11 is generated when a loop is formed. Since the reaction force F is very large as compared with the reaction force of the sheet 10, a sufficient loop cannot be formed unless the sheet 11 is fed in with a conveyance torque higher than that.
[0054]
At this time, if the sheet 11 is fed by driving the pre-registration roller 5 with an excessive conveyance torque in order to forcibly form a loop, roller marks may be left on the surface of the sheet 11 or an abnormal image due to triboelectric charging may be caused. There is.
[0055]
FIG. 2 is a schematic perspective view showing a torque control mechanism of the torque limiter 12.
[0056]
In FIG. 2, the torque limiter 12 includes a shaft 12a and a case 12b, and the shaft 12a is provided with a slit 12c.
[0057]
The torque limiter 12 is configured so that the shaft portion 12a and the case 12b rotate together with each other when the torque is equal to or less than a certain fixed torque, but the case 12b starts to slide with respect to the shaft portion 12a when a certain torque or more is applied. (The detailed internal configuration of the torque limiter is omitted here).
[0058]
The pre-registration rollers 5 each include a metal shaft 5b and a rubber roller 5a, which are separate components, and the rubber roller 5a is configured to pass through the metal shaft 5b and not to rotate.
[0059]
The spring pin 37 is provided on the metal shaft 5b of the pre-registration roller 5, is coupled to a slit 12c provided in the torque limiter 12, and is assembled so that the torque limiter 12 rotates with the rotation of the metal shaft 5b. I have.
[0060]
The rubber roller 5a is coupled to the case 12b of the torque limiter 12, and is assembled so as to rotate with the rotation of the case 12b.
[0061]
At the time of forming the loop, the metal shaft 5b rotates so that the torque limiter 12 is also held by the metal shaft 5b when the sheet is being conveyed with a conveying torque of a certain fixed value or less so as not to apply a great load or deformation to the sheet. The rubber roller 5a that rotates around and rotates with the torque limiter 12 also rotates.
[0062]
However, when the sheet has to be conveyed with a certain conveying torque or more, the metal shaft 5b and the shaft portion 12a rotate together, but the case 12b is made of metal due to slippage at the joint portion 12d between the shaft portion 12a and the case 12b. Since the rubber roller 5a does not rotate along with the shaft 5b and the shaft portion 12a, the rubber roller 5a does not rotate.
[0063]
That is, when a certain or more conveying torque is applied to the pre-registration roller 5, only the metal shaft 5b of the pre-registration roller 5 is rotated to cause the rubber roller 5a to slip, thereby preventing the sheet from being forcibly fed. Thus, an optimal loop can be formed without damaging the sheet, and the sheet can be transported to the next step.
[0064]
In addition, since the reaction force can be automatically adjusted optimally with a simple configuration by using the reaction force due to the loop of the sheet, it is possible to avoid an increase in size, complexity, and cost of the apparatus.
[0065]
In addition, by optimally adjusting the reaction force according to the type of sheet, the sheet can be conveyed without affecting the deformation and excessive friction. And a good image free of defects.
[0066]
(Second embodiment)
Next, a second embodiment of the sheet conveying apparatus according to the present invention will be described. However, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. FIG. 3 is a partial schematic cross-sectional view of the sheet conveying device according to the second embodiment.
[0067]
In FIG. 3, the slit 39 is a guide portion for inserting the shaft portion 4 a of the pre-registration roller 4, and the pre-registration roller 4 is movably assembled along the shape of the slit 39. The pre-registration roller 4 is urged and pressed against the pre-registration roller 5 by an elastic member 6 serving as urging means. f2 is a pressurizing force, and when a certain reaction force F determined by study, which may give a great load / deformation to the sheet forming the loop, occurs, the pre-resist rollers 4 The pressure is set so that it can be retracted upward.
[0068]
FIG. 4 is a schematic cross-sectional view when the pre-registration roller 4 is temporarily retracted upward to release the nip between the pre-registration roller pairs 4 and 5.
[0069]
In FIG. 4, when the reaction force F due to the loop of the sheet exceeds a certain level, the sheet itself lifts the pre-registration roller 4 upward along the slit 39 against the pressing force f2 of the elastic member 6. The sheet lifts the pre-registration roller 4 upward to release the nip before registration, and returns the rear end of the sheet to the upstream side to reduce the loop amount.
[0070]
As the sheet reduces the loop amount, the reaction force F also weakens, and when the pressure f2 and the reaction force F are balanced, the pre-registration roller 4 is urged again by the pre-registration roller 5 by the elastic member 6 to form a nip. I do. The sheet whose loop has been optimally corrected by the balance between the reaction force F and the pressing force f2 is nipped by the pair of pre-registration rollers 4, 5 and conveyed to the next step.
[0071]
With this configuration, the thick paper is conveyed by the registration rollers 1 and 2 and the pre-registration rollers 4 and 5 in a state where the reaction force F is reduced to some extent, so that the optimum loop can be formed without damaging the sheet. The sheet can be formed and conveyed to the next step.
[0072]
(Third embodiment)
Next, a third embodiment of the sheet conveying apparatus according to the present invention will be described. However, the same components as those in the first embodiment and the second embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 5 is a schematic cross-sectional view of a part of the sheet conveying device according to the third embodiment.
[0073]
In FIG. 5, slits 40 and 41 are arranged in parallel with each other, and determine the nip pressure between the pre-registration roller 4 and the pre-registration roller 5 and between the pre-registration roller pairs 4 and 5. The shaft portion 4a of the pre-registration roller 4 is inserted into the slit 40, and the metal shaft 5b of the pre-registration roller 5 is inserted into the slit 41. The pre-registration roller 4 follows the shape of the slit 41 and the pre-registration roller 5 follows the shape of the slit 41. It is movably assembled.
[0074]
The elastic members 13 and 16 press the pre-registration rollers 4 and the pre-registration roller 5 so as to abut against the slits, respectively, to determine predetermined positions of the two. f3 and f4 are pressurizing forces, and when a certain reaction force F determined by study, which may give a great load and deformation to the sheet forming the loop, f3 is a roller 4 before the resist. Is set to a pressure at which the pre-registration roller 5 can retract to the upstream side of the slit 41.
[0075]
FIG. 6 is a schematic view when the pre-registration roller 4 and the pre-registration roller 5 are retracted from predetermined positions.
[0076]
In FIG. 6, when the reaction force F of the sheet exceeds a certain value, the sheet itself pushes the pre-registration roller 4 and the pre-registration roller 5 upstream along the slits 40 and 41 against the pressing forces f3 and f4. . The sheet temporarily retracts the pair of pre-registration rollers 4 and 5 until the reaction force F and the applied pressures f3 and f4 are balanced, and the loop is optimally corrected. The corrected sheet is conveyed to the next process at a predetermined timing.
[0077]
With this configuration, the thick paper is conveyed by the registration rollers 1 and 2 and the pre-registration rollers 4 and 5 in a state where the reaction force F is reduced to some extent, so that the optimum loop can be formed without damaging the sheet. The sheet can be formed and conveyed to the next step.
[0078]
(Fourth embodiment)
Next, a fourth embodiment of the sheet conveying apparatus according to the present invention will be described. However, the same components as those in the first, second, and third embodiments are denoted by the same reference numerals, and description thereof is omitted. FIG. 7 is a schematic cross-sectional view of a part of the sheet conveying device according to the fourth embodiment.
[0079]
In FIG. 7, the top sensor 14 is a sheet leading end position detecting member, and is disposed downstream of the pair of registration rollers 1 and 2. The elastic member 3 presses the resist upper roller 1 with a pressing force f1.
[0080]
FIG. 8 is a schematic diagram when a sheet 11 such as a thick paper or a label paper has penetrated the registration nip.
[0081]
In FIG. 8, for a sheet having a strong reaction force such as a thick sheet or a label sheet such as the sheet 11, not only the direction of the pair of downstream pre-registration rollers 4 and 5 where the loop is formed but also the upstream direction which is the conveyance direction. A large reaction force F is also generated in the direction of the pair of registration rollers 1 and 2 on the side. The leading edge of the sheet penetrates through the registration nip due to a weak pressing force f1 with respect to the reaction force F, a low idling torque of the pair of registration rollers 1 and 2, a sheet being extremely skewed and conveyed, and the like. There are cases.
[0082]
If printing is performed in a state in which the leading edge of the sheet has penetrated the registration nip, problems such as a large leading edge registration and skew correction will not occur.
[0083]
The top sensor 14 detects the position of the leading edge of the sheet that has penetrated the registration nip, and feeds back to the controller how fast or slow the writing starts, so that printing can be started from the normal writing position. Therefore, high image quality and high printing accuracy can be achieved.
[0084]
(Fifth embodiment)
Next, a fifth embodiment of the sheet conveying apparatus according to the present invention will be described. However, the same components as those in the first, second, third, and fourth embodiments are denoted by the same reference numerals, and description thereof is omitted. FIG. 9 is a schematic cross-sectional view of a part of the sheet conveying device according to the fifth embodiment.
[0085]
In FIG. 9, the pulse encoder 15 is assembled to the registration lower roller 2 and detects a rotation speed fluctuation of the registration lower roller 2.
[0086]
FIG. 10 is a schematic diagram when the thick paper / label paper 11 has penetrated the registration nip. In FIG. 10, when the sheet passes through the registration nip due to its own reaction force F, the registration upper roller 1 and the registration lower roller 2 are rotated to enter the registration nip.
[0087]
By detecting the amount of rotation of the sheet by rotating the registration lower roller 2 with the pulse encoder 15, the leading end position of the sheet is detected and fed back to the controller.
[0088]
By setting the write start position of the sheet based on the information fed back from the pulse encoder 15, printing can be started from the normal write start position. Therefore, high image quality and high printing accuracy can be achieved.
[0089]
(Sixth embodiment)
Next, a sixth embodiment of the sheet conveying apparatus according to the present invention will be described. However, the same components as those of the first, second, third, fourth, and fifth embodiments are denoted by the same reference numerals. The description is omitted. FIG. 11 is a schematic cross-sectional view of a part of the sheet conveying device according to the sixth embodiment.
[0090]
In FIG. 11, the one-way gear 17 is mounted on the metal shaft 5b of the pre-registration roller 5 so as to rotate the pre-registration roller 5 together. When the drive is transmitted to the one-way gear 17, the one-way gear 17 and the pre-registration roller 5 rotate, and the pre-registration roller 4, which is a driven roller pressed against the pre-registration roller 5 by the elastic member 6, accordingly. By performing the rotation operation, the pair of pre-registration rollers 4 and 5 convey the sheet to the registration nip.
[0091]
Here, the one-way gear 17 is a gear characterized in that it rotates in one direction but does not rotate at all in the other direction. It is restricted to only one transport direction.
[0092]
FIG. 12 is a schematic diagram showing a state in which the one-way gear holds an optimal loop. In FIG. 12, the sheet fed into the registration nip by the pair of pre-registration rollers waits for conveyance timing in a state where an optimal loop amount is formed according to the type of the sheet. Immediately after the loop formation, the registration rollers 1 and 2 and the pre-registration rollers 4 and 5 both stop rotating, and at a certain timing, both rollers restart the rotation and convey the sheet.
[0093]
While the pair of rollers stopped rotating, the idling torque of the pair of pre-registration rollers 4 and 5 was light, and the pre-registration roller 5 was slightly affected by the reaction force of the sheet. There is a possibility of reverse rotation with respect to the transport direction. When the pre-registration roller 5 rotates in the reverse direction, the loop amount optimally held is reduced or eliminated.
[0094]
In order to prevent this, the one-way gear 17 is assembled to the pre-registration roller 5 to prevent the pre-registration roller 5 from rotating in the reverse direction, and to stably convey the sheet while maintaining the sheet loop. Further, high image quality and high printing accuracy can be achieved.
[0095]
【The invention's effect】
As described above, according to the present invention, the reaction force can be optimally adjusted by utilizing the reaction force due to the sheet loop, so that the sheet conveyance can be stabilized. In addition, since image formation can be performed from a regular writing position, high image quality and high printing accuracy can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a part of a sheet conveying apparatus according to a first embodiment.
FIG. 2 is a schematic perspective view illustrating a torque control mechanism of the sheet conveying apparatus according to the embodiment.
FIG. 3 is a schematic cross-sectional view of a part of a sheet conveying apparatus according to a second embodiment.
FIG. 4 is a schematic cross-sectional view illustrating a retracting mechanism of a pair of conveying rollers of a sheet conveying apparatus according to a second embodiment.
FIG. 5 is a schematic cross-sectional view of a part of a sheet conveying apparatus according to a third embodiment.
FIG. 6 is a schematic cross-sectional view illustrating a retracting mechanism of a pair of conveying rollers of a sheet conveying apparatus according to a third embodiment.
FIG. 7 is a schematic cross-sectional view of a part of a sheet conveying apparatus according to a fourth embodiment.
FIG. 8 is a schematic cross-sectional view illustrating a state in which a sheet has passed through a registration nip in a sheet conveying apparatus according to a fourth embodiment.
FIG. 9 is a schematic cross-sectional view of a part of a sheet conveying apparatus according to a fifth embodiment.
FIG. 10 is a schematic cross-sectional view illustrating a state in which a sheet has passed through a registration nip in a sheet conveying apparatus according to a fifth embodiment.
FIG. 11 is a schematic cross-sectional view of a part of a sheet conveying apparatus according to a sixth embodiment.
FIG. 12 is a schematic cross-sectional view illustrating a state where a loop of a sheet conveying apparatus according to a sixth embodiment is held.
FIG. 13 is a schematic sectional view of a laser beam printer as an example of a conventional image forming apparatus.
FIG. 14 is a schematic sectional view of a resist unit of the laser beam printer shown in FIG.
[Explanation of symbols]
1 Roller on resist
2 Resist lower roller
3 elastic members
4 Rollers in front of cash register (driven rollers)
4a Shaft
5 Pre-registration roller (transport roller)
5a Rubber roller
5b metal shaft
6 elastic members
7,8,9 Transport guide
10, 11 sheets
12 Torque limiter
12a Shaft
12b case
12c slit
12d joint
13,16 elastic member
14 Top sensor
15 pulse encoder
17 One Way Gear
37 Spring Pin
39, 40, 41 slit
f1, f2, f3, f4 Pressing force
F1, F2 reaction force
S sheet

Claims (8)

First conveying means for temporarily stopping the conveyed sheet and conveying the sheet to a next stroke portion at a predetermined timing;
A second conveying unit that is provided upstream of the first conveying unit in the sheet conveying direction and conveys a sheet to the first conveying unit and forms a loop in the sheet;
The reaction force due to the loop of the sheet formed between the first conveyance means and the second conveyance means is caused by the reaction force of the loop of the sheet, the reaction force of the first conveyance means or the second conveyance means. A sheet conveying device characterized in that a part thereof is operated and adjusted. The second conveying means is a pair of conveying rollers composed of two rotating bodies, and at least one of the rotating bodies is applied with a certain or more conveying torque to the rotating bodies against the reaction force of the loop of the sheet. 2. The sheet conveying apparatus according to claim 1, further comprising a torque control unit for controlling the sheet conveyance. The second transporting means includes: a transport roller pair including two rotating members; and, when a reaction force of the loop of the sheet is equal to or greater than a predetermined value, at least one of the rotating members of the transport roller pair is temporarily moved from a predetermined position. The sheet conveying apparatus according to claim 1, further comprising: a rotating body retracting mechanism that retracts the rotating body. The rotating body retracting mechanism includes an urging means for urging at least one of the rotating bodies of the transport roller pair toward a sheet,
A guide portion for retracting the rotating body in a predetermined direction, when a reaction force due to the loop of the sheet is larger than an urging force of the urging means;
The sheet conveying device according to claim 3, comprising: The first transporting unit includes two rotating bodies, and a sheet leading edge detecting unit that detects a leading edge position of a sheet that has protruded from the nip of the rotating body pair to the downstream side in the transporting direction from the first transporting unit. The sheet conveying device according to any one of claims 1 to 4, further comprising: The pulse generator according to claim 1, wherein the first transport unit includes two rotating bodies, and includes a pulse encoder that detects a rotation speed fluctuation of at least one of the rotating bodies in the rotating body pair. The sheet conveyance device according to claim 1. The second transporting unit includes a transport roller pair including two rotating bodies, and a regulating unit that regulates a rotation direction of at least one of the rotating bodies of the transport roller pair only in a sheet transport direction. The sheet conveying device according to any one of claims 1 to 6, wherein A sheet conveying device according to any one of claims 1 to 7,
Image forming means for forming an image on a sheet conveyed by the sheet conveying device,
An image forming apparatus having:

Images