JP2005145576A - Sheet carrying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To weaken power generated when rear edge of a sheet passed through a post-fixation roller and a driven roller 18 hit on a paper delivery path. <P>SOLUTION: A paper delivery portion 5 comprises the post-fixation rear roller 16 and the driven roller 18 arranged on an upstream side of the curved paper delivery path 21 carrying a sheet, a delivery roller 22 and a delivery driven roller 32 arranged on a downstream side, and a stepped portion S formed by the paper delivery path 21 and the post-fixation roller 16 by these roller. The sheet carried by the delivery roller 22 and the delivery driven roller 32, and the post-fixation roller 16 and the driven roller 18 is made to be a loop immediately before rear edge of the sheet passes through the post-fixation roller 16 and the driven roller 18. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus that guides and conveys a sheet, and in particular, at a portion where the sheet conveying path is curved, the trailing edge of the sheet immediately after passing through the sheet conveying means conveys the sheet from the sheet conveying means. The present invention relates to a sheet conveying apparatus that reduces the sheet splash sound generated by abutting on a sheet conveying path so as to be repelled, and an image forming apparatus including the sheet conveying apparatus.

  Sheet conveyance for guiding and conveying a sheet is often incorporated in an image forming apparatus that forms an image on a sheet. Examples of the image forming apparatus include a printer, a facsimile machine, a copying machine, and a complex machine of these.

  FIG. 9 is a cross-sectional view taken along the sheet conveying direction of a conventional sheet conveying apparatus incorporated in a laser beam printer which is an example of an image forming apparatus. The fixing device 214 fixes the image to the sheet semipermanently by heat-pressing the unfixed image at the nip N1. The post-fixing roller 216 and the post-fixing driven roller 218 serving as the upstream conveying unit are opposed to each other on the downstream side of the fixing device 214 to form a nip N2. The discharge roller 222 and the discharge driven roller 231, which are downstream conveying means, face each other downstream of the post-fixing roller 216 to form a discharge roller nip N 3, and discharge the sheet to the discharge tray 217. A curved sheet discharge path 221 is disposed between the post-fixing roller 216 and the discharge roller 222. A paper discharge path 221 that is a conveyance path is configured by an outer paper discharge guide member 221a and an inner paper discharge guide 221b (for example, see Patent Document 1).

  Further, a step S is provided between the post-fixing roller 216 and the outer paper discharge guide member 221a so that the front end (downstream end) of the sheet is not caught.

JP-A-6-1514

  However, the conventional sheet conveying apparatus has a problem that the sheet bounces when the trailing end (upstream end) of the sheet passes through the post-fixing roller 216. That is, when the sheet passes through the curved sheet discharge path 221, the sheet is curved along the sheet discharge path 221, and when the rear end of the sheet passes through the post-fixing roller nip N 2 of the post-fixing roller 216, the sheet itself is bent. A sheet splash sound is generated when the rear end portion strongly hits the outer paper discharge guide member 221a. In recent years, as the speed of laser beam printers increases, such sheet splashing noises are continuously generated and are no longer negligible as noise.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying apparatus in which the trailing edge of a sheet that has passed through an upstream conveying unit weakens the momentum of hitting a conveying path and suppresses sheet splashing to a minimum.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that includes a sheet conveying device with low sheet splashing noise and that has low noise.

  In order to achieve the above object, a sheet conveying apparatus of the present invention includes a sheet conveying path through which a sheet is conveyed, an upstream conveying unit that is provided on the upstream side of the sheet conveying path and conveys the sheet, and the upstream side A downstream side conveying unit that conveys a sheet conveyed by the conveying unit on a downstream side of the upstream side conveying unit, and a step formed by the sheet conveying path and the upstream side conveying unit, and the downstream side The sheet conveyed by the conveying means and the upstream conveying means is looped immediately before the trailing edge of the sheet exits the upstream conveying means.

  In order to achieve the above object, a sheet conveying apparatus according to the present invention includes a curved sheet conveying path through which a sheet is conveyed, an upstream conveying unit that is provided upstream of the sheet conveying path and conveys the sheet, A downstream conveyance unit that conveys a sheet conveyed by the upstream conveyance unit downstream of the upstream conveyance unit; a step formed by the sheet conveyance path and the upstream conveyance unit; and a rear side of the sheet. A passage detection unit that detects immediately before the end passes through the upstream conveyance unit; and a sheet conveyance operation of the downstream conveyance unit is temporarily stopped based on a detection operation of the passage detection unit; and the upstream conveyance unit Control means for sagging the rear end of the sheet positioned at the step by continuing the conveying operation.

  In order to achieve the above object, a sheet conveying apparatus according to the present invention includes a curved sheet conveying path through which a sheet is conveyed, an upstream conveying unit that is provided upstream of the sheet conveying path and conveys the sheet, A downstream conveyance unit that conveys a sheet conveyed by the upstream conveyance unit downstream of the upstream conveyance unit; a step formed by the sheet conveyance path and the upstream conveyance unit; and a rear side of the sheet. A passage detection unit that detects immediately before the end passes through the upstream side conveyance unit; and a sheet conveyance speed of the downstream side conveyance unit based on a detection operation of the passage detection unit is temporarily greater than a sheet conveyance speed of the upstream side conveyance unit. Control means for causing the trailing edge of the sheet positioned at the step to sag by slowing down and continuing the conveying operation of the upstream conveying means.

  In order to achieve the above object, a sheet conveying apparatus according to the present invention includes a curved sheet conveying path through which a sheet is conveyed, an upstream conveying unit that is provided upstream of the sheet conveying path and conveys the sheet, A downstream conveying means for conveying the sheet conveyed by the upstream conveying means on the downstream side of the upstream conveying means, and a step formed by the sheet conveying path and the upstream conveying means, A receiving receiving portion for receiving the trailing edge of the sheet is provided in the upstream conveying means.

  The sheet conveying apparatus of the present invention temporarily stops the sheet conveying operation of the downstream conveying unit based on the detection operation of the passage detecting unit that detects immediately before the sheet passes the upstream conveying unit, and the detection operation of the passage detecting unit. And a control means for sagging the trailing edge of the sheet positioned at the step by continuing the conveying operation of the upstream conveying means in a state where the trailing edge of the sheet is received by the receiving part. And.

  The sheet conveying apparatus of the present invention includes a passage detecting unit that detects immediately before the sheet passes through the upstream conveying unit, and a sheet conveying speed of the downstream conveying unit based on a detection operation of the passage detecting unit. The sheet is positioned at the level difference by continuing the conveying operation of the upstream conveying unit in a state where the sheet conveying speed of the side conveying unit is temporarily delayed and the trailing end of the sheet is received by the received receiving unit. Control means for sagging the rear end of the sheet.

  The sheet conveying apparatus of the present invention includes a thickness detecting unit that detects a sheet having a thickness greater than or equal to a predetermined thickness, and the control unit is configured to detect the downstream conveying unit based on a detection operation of the passage detecting unit and the thickness detecting unit. The sheet conveying operation is temporarily stopped, and the trailing end portion of the sheet positioned at the step is slackened by continuing the conveying operation of the upstream conveying unit.

  The sheet conveying apparatus of the present invention includes a thickness detecting unit that detects a sheet having a thickness greater than or equal to a predetermined thickness, and the control unit is configured to detect the downstream conveying unit based on a detection operation of the passage detecting unit and the thickness detecting unit. The sheet conveying speed is temporarily made slower than the sheet conveying speed of the upstream conveying means, and the trailing edge of the sheet positioned at the step is slackened by continuing the conveying operation of the upstream conveying means.

  In the sheet conveying apparatus of the present invention, the upstream driving means for driving the upstream conveying means and the downstream driving means for driving the downstream conveying means are separate.

  In the sheet conveying apparatus of the present invention, the upstream driving means for driving the upstream conveying means and the downstream driving means for driving the downstream conveying means are common driving means, and the downstream conveying means includes A clutch for cutting off the driving force of the driving means is provided.

  In the sheet conveying apparatus of the present invention, the upstream side conveying unit and the downstream side conveying unit are each a roller pair.

  In order to achieve the above object, an image forming apparatus of the present invention includes: an image forming unit that forms an image on a sheet; and a sheet conveying device that conveys a sheet on which an image is formed by the image forming unit. The conveying device is any one of the above sheet conveying devices.

  In the image forming apparatus according to the aspect of the invention, the image forming unit includes a photosensitive drum and a transfer unit that form a toner image on the sheet, and a fixing unit that fixes the toner image on the sheet. Upstream conveying means is disposed downstream of the fixing device.

  In the sheet conveying apparatus of the present invention, the sheet conveyed by the downstream conveying means and the upstream conveying means is formed in a loop shape immediately before the sheet trailing end exits the upstream conveying means. The noise can be minimized and the noise can be reduced.

  The sheet conveying apparatus according to the present invention is configured to temporarily stop the sheet conveying operation of the downstream conveying unit based on the detection operation of the passage detecting unit and to continue the conveying operation of the upstream conveying unit, so that the rear end of the sheet positioned at the level difference Since the part is slackened, the sheet splashing noise can be minimized and the noise can be reduced.

  The sheet conveying apparatus of the present invention temporarily lowers the sheet conveying speed of the downstream conveying means based on the detection operation of the passage detecting means, and continues the conveying operation of the upstream conveying means. As a result, the trailing edge of the sheet positioned at the level difference is slackened, so that the sheet splashing noise can be suppressed to a minimum, and the noise can be reduced.

  In the sheet conveying apparatus according to the present invention, the upstream conveying means is provided with a receiving portion for receiving the trailing edge of the sheet, so that the sheet splashing noise can be suppressed to a minimum and the noise can be reduced.

  The sheet conveying apparatus of the present invention temporarily stops the sheet conveying operation of the downstream conveying unit based on the detection operation of the passage detecting unit, and the upstream conveying unit in a state where the rear end of the sheet is received by the receiving receiving unit. By continuing the conveying operation of the means, the trailing edge of the sheet positioned at the step is slackened, so that the sheet splashing noise can be suppressed to a minimum and the noise can be reduced.

  In the sheet conveying apparatus of the present invention, the sheet conveying speed of the downstream conveying means is temporarily delayed from the sheet conveying speed of the upstream conveying means based on the detection operation of the passage detecting means, and the upstream end of the sheet is received by the receiving portion. In this state, by continuing the conveying operation of the upstream conveying means, the sheet upstream rear portion located at the step is slackened, so that the sheet splashing noise can be suppressed to a minimum and the noise can be reduced. can do.

  The sheet conveying apparatus of the present invention temporarily stops the sheet conveying operation of the downstream conveying means based on the detection operation of the passage detecting means and the thickness detecting means, and is positioned at a step by continuing the conveying operation of the upstream conveying means. Since the upper part of the seat is slackened, if the sheet is thick and firm, and the sheet is relatively loud, the tip is paused and the sheet is relatively thin and the sheet is relatively splashed. In the case of a small sheet, since the leading end is not temporarily stopped, it is not necessary to cause the downstream conveying means to perform a useless operation, and the apparatus can be used for a long time with less failure of the apparatus.

  According to the sheet conveying apparatus of the present invention, the sheet conveying speed of the downstream conveying means is temporarily delayed from the sheet conveying speed of the upstream conveying means based on the detection operation of the passage detecting means and the thickness detecting means, and the upstream conveying means Since the sheet upstream and rear part located in the step is slackened by continuing the conveyance operation, in the case of a sheet that is thick and firm, and has a relatively large sheet splashing sound, the leading edge is decelerated and the thickness is reduced. In the case of a thin sheet having a relatively low sheet splash sound, the leading end portion is not decelerated, so that it is not necessary to cause the downstream conveying means to perform a useless operation, and the apparatus can be used for a long period of time with less failure of the apparatus.

  In order to achieve the above object, the image forming apparatus of the present invention includes a sheet conveying apparatus that suppresses sheet splashing to a minimum. Therefore, an image forming apparatus with low noise can be provided.

  Hereinafter, a sheet conveying apparatus according to an embodiment of the present invention and an image forming apparatus including the sheet conveying apparatus will be described with reference to the drawings. Examples of the image forming apparatus include a copying machine, a printer, a facsimile, and a complex machine of these. The image forming apparatus of the present embodiment is a laser beam printer, but the present invention is not limited to this.

(Laser beam printer of the first embodiment)
(Description of configuration)
FIG. 1 is a main cross-sectional view of a laser beam printer 51 of the first embodiment. The laser beam printer 51, which is an image forming apparatus according to this embodiment, is a printer that can print on both sides of a sheet. Further, the laser beam printer 51 of the present embodiment mainly includes a paper feed / conveying unit 2, an image forming unit 3, a controller board 4, a paper discharge unit 5, a refeed unit 6, and the like.

  The sheet feeding / conveying unit 2 is mainly composed of a sheet feeding tray 7 and a feeding unit 8. A plurality of sheets P are stacked on the sheet feed tray 7. The feeding unit 8 is a unit that separates and feeds the sheets P on the sheet feeding tray 7 one by one by a sheet feeding roller 8a, a friction piece 8b, and the like. The conveyance rollers 9 and 10 are rubber rollers that convey the fed sheet to the image forming unit 3. A top sensor 11 for detecting the leading edge and the trailing edge of the sheet is provided in the vicinity of the conveying roller 10 in order to detect a paper feed failure and determine image writing timing.

  The image forming unit 3 includes a process cartridge 12, a transfer roller 13, a fixing unit 14, and the like. The process cartridge 12 is integrally provided with a photosensitive drum 12a and process means (charging means, developing means, cleaning means not shown) acting on the photosensitive drum 12a, and is detachable from the printer main body 51A. The laser scanner unit 15 irradiates the photosensitive drum 12a with image information as laser bit information.

  The transfer roller 13 is configured to transfer the toner image formed on the photosensitive drum 12a to the sheet P that passes between the transfer roller 13 and the opposing photosensitive drum 12a. The fixing unit 14 fixes the toner image semi-permanently on the sheet onto which the toner image has been transferred. The controller board 4 having the CPU 40 as control means is a control unit that controls all of the image formation and sheet conveyance of the laser beam printer 51.

  The sheet discharge unit 5 that is the sheet conveying apparatus shown in FIG. 1 includes a post-fixing roller 16, a discharge tray 17, and the like. The post-fixing roller 16 and the driven roller 18 which are upstream conveying means provided at a position of about 20 to 50 mm immediately downstream of the fixing nip N1 of the fixing unit 14 are brought into pressure contact with each other to form the post-fixing roller nip N2, and the fixing nip. The sheet discharged from N1 is nipped and conveyed.

  A post-fixing guide member 19 is disposed between the fixing nip N1 and the post-fixing roller nip N2. The post-fixing guide member 19 guides the sheet discharged from the fixing nip N1 to the post-fixing roller nip N2. Further, a paper discharge sensor 20 serving as a passage detection unit is provided between the fixing nip N1 and the post-fixing roller nip N2. The paper discharge sensor 20 accurately notifies the CPU of the controller board 4 in the main body 51A of the timing at which the rear end (upstream end) of the sheet passes through the post-fixing roller 16. A sheet discharge path 21 that is a sheet conveyance path is configured by sheet discharge guide members 21 a and 21 b, and guides the sheet that has passed through the post-fixing roller 16 to the discharge roller 22 while being reversely guided. The discharge roller 22 and the discharge driven roller 32 which are downstream conveying means are opposed to each other to form a post-fixing roller nip N3 and discharge the sheet to the discharge tray 17. The discharge roller 22 is driven by a discharge roller drive motor 23 which is a downstream drive unit independent of the post-fixing roller 16, and can rotate forward and backward and stop.

  The refeed unit 6 is a part that conveys the sheet to the image forming unit 3 again to perform double-sided printing. The post-fixing roller 16 is in contact with a re-feed conveyance path introduction roller 24 in addition to the driven roller 18 so that the sheet can be fed into the re-feed unit 6.

  The CPU 40 shown in FIG. 4 controls the discharge roller driving motor 23, the main motor 41, and the like via the drivers D1, D2 based on the detection engagement from the top sensor 11, the discharge sensor 20, the paper thickness detection sensor 31, and the like. The operation is controlled. The main motor 41 is a motor of a driving source such as the image forming unit 3 or the paper feeding / conveying unit 2.

(Description of operation)
Upon receiving a print command, the sheets P stacked on the sheet feed tray 7 are separated and fed one by one by the feeding unit 8 and further passed through the top sensor 11 by the transport roller 10 and then the process cartridge. 12 between the photosensitive drum 12a and the transfer roller 13 (nip). When the top sensor 11 detects the leading edge of the fed sheet P, the laser scanner unit 15 irradiates the photosensitive drum 12a with a bit image of the image information (laser light), and in accordance with the bit image, the photosensitive drum. A toner image is formed on 12a. The toner image formed on the photosensitive drum 12 a is transferred to the sheet P by the nip between the photosensitive drum 12 a and the transfer roller 13. Then, the sheet P on which the toner image is transferred is sent to the fixing unit 14 and heated and pressed by the fixing unit 14 to fix the toner image.

  The sheet that has passed through the fixing unit 14 passes through a post-fixing roller nip N2 between the post-fixing roller 16 and the driven roller 18, and is conveyed to the discharge roller 22. Here, as described based on the conventional example of FIG. 6, when the rear end of the sheet is released from the state where it is pressed against the post-fixing roller 16 due to the elasticity of the sheet, a sheet splash sound is generated. Moreover, since the sheet discharge path 21 is curved with a small radius of curvature, when the sheet passes through the roller 16 after fixing, the sheet is strongly hit against the sheet discharge guide member 21a by the waist of the sheet, and the impact sound is a sheet splash sound. Become. Further, in the laser scanner unit 1 of the present embodiment, a refeed conveyance path introduction roller 24 is provided immediately after the post-fixing roller 16 so that images can be printed on both sides of the sheet. For this reason, the laser scanner unit 1 has a step S formed between the post-fixing roller 16 and the paper discharge guide member 21a, so that the sheet splashing sound tends to be further increased. The step S is formed so that the leading edge of the sheet that has passed the post-fixing roller 16 is not caught by the paper discharge guide 21a.

  In the present embodiment, the discharge roller drive motor 23 is stopped and the discharge roller 22 is stopped at a timing immediately before the trailing edge of the sheet P passes through the post-fixing roller 16. The timing at which the trailing edge of the sheet passes through the post-fixing roller 16 is based on a detection operation of a paper discharge sensor 20 provided between the fixing nip N1 of the fixing unit 14 and the post-fixing roller 16.

  As a result, the front end (downstream end) of the sheet stops, and the rear end side of the sheet is pushed out from the post-fixing roller 16 that continues to rotate, and as shown in FIG. Pa is generated. This slack Pa disperses energy even if the trailing edge of the sheet passes through the post-fixing roller 16, and does not cause a large sheet splash sound.

  Note that if the trailing edge of the sheet is allowed to sag, the sheet splashing sound is reduced. Therefore, the sheet discharge roller drive motor 23 may be decelerated without being stopped. That is, in the laser beam printer 51 of the present embodiment, the sheet conveyance speed due to the rotation of the discharge roller 22 is slower than the sheet conveyance speed due to the rotation of the post-fixing roller 16 or the discharge roller 22 is stopped. It is only necessary that the CPU of the controller board 4 controls the rotation of the paper discharge roller drive motor 23.

  Further, as shown in FIG. 3, a post-fixing roller is formed by forming a protrusion or a groove on the post-fixing roller, and the post-fixing roller is received in a state where the rear end of the sheet is hooked on the protrusion or the groove. The trailing edge of the sheet can be temporarily held by the post-fixing roller to weaken the momentum of the trailing edge of the sheet contacting the sheet discharge guide member 21a and reduce the sheet splash noise. In this case, it is not always necessary to stop the discharge roller 22 or make the sheet conveyance speed by the discharge roller 22 slower than the sheet conveyance speed of the post-fixing roller 16.

  In the post-fixing roller 16A shown in FIG. 3A, ridges 16a along the axial direction are formed at equal intervals in a plurality of rows in the rotational direction. The post-fixing roller 16B shown in FIG. 3B is provided with a plurality of protrusions 16b arranged along the axial direction so as to protrude in a plurality of rows at equal intervals in the rotation direction. In the post-fixing roller 16C shown in FIG. 3 (c), protrusions 16c along the axial direction are formed at one end at equal intervals in the rotation direction. In the post-fixing roller 16D shown in FIG. 3 (d), grooves 16d along the axial direction are formed at equal intervals in a plurality of rows in the rotational direction. The ridges 16a, the ridges 16b, the ridges 16c, and the grooves 16d, which are the receiving portions, receive the rear end of the sheet.

  Further, the sheet splash noise increases as the thickness of the sheet increases, because the waist is stronger and the energy is higher. On the contrary, in the case of thin paper, there is a case where almost no sheet splashing sound is generated. Therefore, the thickness of the sheet is detected by the sheet thickness detection sensor 31 which is a thickness detection means, and when the sheet thickness exceeds a certain value, the sheet conveyance speed of the discharge roller 22 is decreased or stopped. Good. Note that the thickness of the sheet may be determined based on sheet thickness information input by the user.

  When an image is printed only on one side of the sheet, the sheet is quickly discharged from the discharge roller 22 to the discharge tray 17 when the stopped or decelerated discharge roller drive motor 23 returns to the original rotation speed. When printing an image on both sides of the sheet, the paper discharge roller drive motor 23 that has stopped or decelerated reverses at the timing when the trailing edge of the sheet completely exits the post-fixing roller 16 and re-feeds the sheet from the trailing edge. The sheet is fed into the nip between the paper conveyance path introduction roller 24 and the post-fixing roller 16, and the sheet is fed to the refeed conveyance unit 6. The sheet is sent to the paper discharge path 21 and passes through the post-fixing roller 16 and then turned over by a series of switchback conveyances sent to the refeed conveyance unit 6. The sheet is sent again from the re-feed conveyance unit 6 to the image forming unit 3, and an image is printed on the second side and sent to the paper discharge unit 5 in the same manner as the first side.

  As described above, the laser beam printer 51 of this embodiment stops or decelerates the discharge roller drive motor 23 immediately before the trailing edge of the sheet passes through the post-fixing roller 16 to reduce the waist energy of the sheet. Since they are dispersed, the sheet splash can be minimized and the noise can be reduced.

(Laser beam printer of the second embodiment)
A laser beam printer 52, which is the image forming apparatus of the second embodiment shown in FIG. 5, prints an image only on one side of a sheet. Therefore, in the laser beam printer 51 according to the first embodiment that prints images on both sides of a sheet, the refeed conveyance path 6 is removed so that the discharge roller 22 does not have to be functionally reversed. The laser beam printer 52 of FIG. Accordingly, the same parts are denoted by the same reference numerals, and the description thereof is omitted.

  In the laser beam printer 52 of the present embodiment, the main motor that is the driving source of the post-fixing roller 16 and the driving source of the image forming unit 3 and the paper feeding / conveying unit 2 does not have to be independent from the discharge roller 22. The discharge roller 22 is also rotated via the gear 25. That is, the post-fixing roller 16 and the discharge roller 22 are rotated by a common main motor.

  A spring clutch 26 that is a clutch is provided between the gear 22 a that drives the discharge roller 22 and the gear 25. The clutch 26 is configured to transmit or disengage the rotational force from the gear 25 to the gear 22a when the actuator 27 is operated. Also in the present embodiment, a step S is generated between the post-fixing roller 16 and the paper discharge guide member 21a. The step S is formed so that the leading edge of the sheet that has passed through the post-fixing roller 16 is not caught by the paper discharge guide member 21a.

  Next, a characteristic operation of the laser beam printer 52 of this embodiment will be described. The sheet on which the toner image has been fixed passes through the curved sheet discharge conveyance path 21 and is conveyed to the discharge tray 17 by the discharge roller 22 to which the driving force is transmitted. In the laser beam printer 52 of the present embodiment, the actuator 27 operates at the timing immediately before the trailing edge of the sheet exits the post-fixing roller 16, so that the spring clutch 26 stops transmitting the driving force to the discharge roller 22. ing. The timing at which the trailing edge of the sheet passes through the post-fixing roller 16 is detected by the paper discharge sensor 20 as in the first embodiment.

  Similarly to the laser beam printer 51 of the first embodiment, the laser beam printer 52 of the present embodiment also causes sagging at the rear end portion (rear end portion) of the sheet P when the rotation of the discharge roller 22 stops. Sheet splashing can be minimized. Further, since the discharge roller 22 is rotated by a main motor which is a drive source of the post-fixing roller 16, the image forming unit 3, and the paper feeding / conveying unit 2, no special motor is required. Therefore, the laser beam printer has a simplified configuration.

  In the present embodiment, the rotation of the discharge roller 22 is stopped by the spring clutch 26 and the actuator 27. For example, an electromagnetic clutch may be used.

  Further, the laser beam printer 52 of the present embodiment can also enhance the sheet splash noise suppression effect when the post-fixing rollers 16A, 16B, 16C, and 16D shown in FIG. 3 are used as the post-fixing rollers. In this case, the discharge roller 22 does not necessarily need to be stopped.

  Further, the laser beam printer 52 of the present embodiment may detect the thickness of the sheet by the paper thickness detection sensor 31 and stop the rotation of the discharge roller 22 when the sheet thickness exceeds a certain level. Note that the thickness of the sheet may be determined based on sheet thickness information input by the user.

  The CPU 40 shown in FIG. 6 controls the operation of the main motor 41, the actuator 27, etc. via the drivers D1, D2 based on the detection meshes from the top sensor 11, the paper discharge sensor 20, the paper thickness detection sensor 31, etc. It has become. The main motor 41 is a motor of a driving source such as the image forming unit 3, the sheet feeding / conveying unit 2, the post-fixing roller 16, and the discharge roller 22.

(Laser beam printer of the third embodiment)
The laser beam printer 53 of the embodiment shown in FIG. 7 is a laser beam printer capable of duplex printing.

  Similarly to the laser beam printer 51 of the first embodiment, the laser beam printer 53 that is the image forming apparatus of the present embodiment mainly includes a paper feed / conveying unit 102, an image forming unit 103, and a controller having a CPU that is a control unit. A board 104, a paper discharge unit 105, a refeed unit 106 that is a sheet conveying device, and the like. In the laser beam printer 53 of the present embodiment, the configuration and operation other than those relating to double-sided printing are not significantly different from those of the laser beam printer 51 of the first embodiment, and thus description thereof is omitted.

  A configuration related to double-sided printing will be described.

  A flapper 129 is provided immediately after the fixing unit 114. The flapper 129 selectively switches the conveyance path between double-sided printing and single-sided printing. The refeed unit 106 mainly includes a sheet detection sensor 120, a conveyance roller 116, a reversing path 121, a reversing roller 122, a reversing conveyance path 128, and the like.

  The conveying roller 116 and the conveying roller 118 as upstream conveying means are opposed to each other to form a post-fixing roller nip N2 to convey the sheet. A sheet detection sensor 120 serving as a passage detection unit is disposed immediately before the conveyance roller 116 to detect the timing at which the trailing edge of the sheet comes out of the conveyance roller. The sheet is sent to the reverse roller 122 via the reverse transfer path 121 by the transfer roller 116. At this time, the sheet is switched back and back so that it is reversed. A reversing path 121, which is a sheet conveying path immediately after the conveying roller 116, is formed by guide members 121a and 121b, and the entrance portion is bent into a Y-shape and curved. The reversing roller 122 can be rotated in the forward and reverse directions and stopped by a reversing roller driving motor 130 that is a downstream driving unit that is a driving source independent of other rollers such as the conveying roller 116. The reversing roller 122 and the reversing driven roller 132 which are the downstream side conveying means are opposed to each other to form a reversing roller nip N4, and the sheets are fed forward and backward. The post-reversal conveyance path 128 is a conveyance path that guides the sheet reversed by the reversing roller 122 to the image forming unit 103 that is an image forming unit.

  Next, a double-sided printing operation will be described.

  The sheet guided to the refeed unit 106 by the guidance of the flapper 129 and the curved sheet conveyance 133 is sent to the reverse path 121 by the conveyance roller 116. The reversing roller 122 rotates normally until the trailing edge of the sheet passes through the conveying roller 116 and then stops. The timing at which the trailing edge of the sheet is removed from the conveyance roller 116 is detected by the sheet detection sensor 120. Here, as in the conventional example, even if the trailing edge of the sheet comes out of the post-fixing roller nip N2 and comes off the conveying roller 116, if the reversing roller 122 continues to rotate and continue to convey the sheet, the curved sheet The guide member 121a strikes against the sheet due to the waist, and a sheet splash sound is generated.

  Therefore, similarly to the laser beam printer 51 of the first embodiment, the laser beam printer 53 of this embodiment also has the conveyance roller 116 that continues to rotate and the reverse roller 122 stops rotating or rotates at a reduced speed. Since sagging occurs at the trailing edge of the sheet and energy is dispersed, the sheet splashing noise is minimized even after the trailing edge of the sheet passes through the conveying roller 116. After the trailing edge of the sheet has completely passed through the conveyance roller 116, the reverse roller 122 reverses and feeds the sheet to the conveyance path 128 after reversal.

  As described above, in the laser beam printer 53 of this embodiment, the sheet conveyance speed due to the rotation of the reverse roller 122 is slower than the sheet conveyance speed due to the rotation of the conveyance roller 116, or the rotation of the reverse roller 122. Since the rotation of the reversing roller drive motor 130 is controlled by the CPU of the controller board 4 so as to stop the sheet, slack is created at the rear end of the sheet, and the sheet splashing at the rear end of the sheet is minimized. To the limit.

  Further, the laser beam printer 53 of the present embodiment can also enhance the sheet splash noise suppression effect when the reverse roller having the same shape as the post-fixing rollers 16A, 16B, 16C, and 16D shown in FIG. 3 is used as the reverse roller. it can. In this case, the conveyance roller does not necessarily need to be stopped.

  Further, the laser beam printer 53 of the present embodiment also detects the thickness of the sheet by the paper thickness detection sensor 131 which is a thickness detection means, and when the sheet thickness exceeds a certain level, the rotation of the reversing roller 122 is stopped. Good. Note that the thickness of the sheet may be determined based on sheet thickness information input by the user.

  The CPU 40 shown in FIG. 8 controls the reverse roller drive motor 130, the main motor 41, and the like via the drivers D1, D2 based on the detection engagement from the sheet detection sensor 120, the paper thickness detection sensor 131, and the like. It has become. The main motor 41 is a motor of a drive source such as the image forming unit 3.

  The present invention is not limited to the case where the entire sheet conveyance path through which the sheet is conveyed is curved, the case where the sheet conveyance path is formed linearly, and the trailing edge of the sheet is upstream. It is possible to reduce or eliminate the generation of popping sound that occurs when the conveying means is removed. Therefore, the present invention can be applied to any case where the sheet conveyance path through which the sheet is conveyed is curved, linear, or any case.

1 is a main cross-sectional view of a laser beam printer of a first embodiment that is an example of an image forming apparatus. FIG. 2 is an enlarged view of the sheet conveying apparatus in FIG. 1. FIG. 6 is a perspective view of a post-fixing roller in which a receiving portion for receiving a sheet is formed. (A) Post-fixing roller with protrusions (b) Post-fixing roller with protrusions (c) Post-fixing roller with protrusions at the ends (d) Grooves Some post-fixing rollers It is a control block diagram of the laser beam printer of the first embodiment. It is a main sectional view of a laser beam printer of a second embodiment which is an example of an image forming apparatus. It is a control block diagram of the laser beam printer of 2nd Embodiment. It is a main sectional view of a laser beam printer of a third embodiment which is an example of an image forming apparatus. It is a control block diagram of the laser beam printer of 3rd Embodiment. It is sectional drawing along the sheet conveyance direction of the sheet conveying apparatus of a prior art example.

Explanation of symbols

P sheet N1 fixing nip N2 post-fixing roller nip N3 discharge roller nip N4 reversing roller nip P sheet Pa slack S step 2 paper feed conveyance unit 3 image forming unit (image forming unit)
4 Controller board 5 Paper discharge unit (sheet transport device)
6 Refeeding section 14 Fixing unit 16 Post-fixing roller (upstream conveying means)
16A Roller after fixing 16B Roller after fixing 16C Roller after fixing 16D Roller after fixing 16a Projection (receiving part)
16b Protrusion (receiving part)
16c ridge (receiving part)
16d groove (receiving part)
18 driven roller (upstream conveying means)
20 Paper discharge sensor (passage detection means)
21 Paper discharge path (sheet transport path)
21a Paper discharge guide member 21b Paper discharge guide member 22 Discharge roller (downstream conveying means)
23 Discharge roller drive motor (downstream drive means)
26 Spring clutch (clutch)
31 Paper thickness detection sensor (thickness detection means)
32 discharge driven roller (downstream conveying means)
40 CPU (control means)
41 Main motor 51 Laser beam printer (image forming apparatus) of the first embodiment
51A Main Body of Laser Beam Printer 52 Laser Beam Printer (Image Forming Apparatus) of Second Embodiment
53 Laser Beam Printer (Image Forming Apparatus) of Third Embodiment
102 Paper Feeding and Conveying Unit 103 Image Forming Unit (Image Forming Unit)
104 Controller board 105 Paper discharge unit 106 Refeed unit (sheet conveying device)
111 Fixing unit 116 Conveying roller (Upstream conveying means)
118 Conveyor roller (Upstream conveying means)
120 Sheet detection sensor (passage detection means)
121 Reverse path (sheet transport path)
121a guide member 121b guide member 122 reverse roller (downstream conveying means)
128 Post-reverse transport path 130 Reverse roller drive motor (downstream drive means)
131 Paper thickness detection means (thickness detection means)
132 Reverse driven roller (downstream conveying means)

Claims (13)

A sheet conveyance path through which the sheet is conveyed;
An upstream conveying means provided on the upstream side of the sheet conveying path for conveying the sheet;
A downstream conveying unit that conveys the sheet conveyed by the upstream conveying unit downstream of the upstream conveying unit;
A step formed by the sheet conveying path and the upstream conveying means,
A sheet conveying apparatus characterized in that the sheet conveyed by the downstream conveying means and the upstream conveying means is looped immediately before the trailing edge of the sheet exits the upstream conveying means. A curved sheet conveyance path through which the sheet is conveyed;
An upstream conveying means provided on the upstream side of the sheet conveying path for conveying the sheet;
A downstream conveying unit that conveys the sheet conveyed by the upstream conveying unit downstream of the upstream conveying unit;
A step formed by the sheet conveying path and the upstream conveying means;
Passage detection means for detecting immediately before the trailing edge of the sheet passes through the upstream conveying means;
Based on the detection operation of the passage detection unit, the sheet conveyance operation of the downstream conveyance unit is temporarily stopped, and the conveyance operation of the upstream conveyance unit is continued to sag the sheet trailing edge located at the step. Control means;
A sheet conveying apparatus comprising: A curved sheet conveyance path through which the sheet is conveyed;
An upstream conveying means provided on the upstream side of the sheet conveying path for conveying the sheet;
A downstream conveying unit that conveys the sheet conveyed by the upstream conveying unit downstream of the upstream conveying unit;
A step formed by the sheet conveying path and the upstream conveying means;
Passage detection means for detecting immediately before the trailing edge of the sheet passes through the upstream conveying means;
Based on the detection operation of the passage detection unit, the step difference is obtained by temporarily lowering the sheet conveyance speed of the downstream conveyance unit than the sheet conveyance speed of the upstream conveyance unit and continuing the conveyance operation of the upstream conveyance unit. Control means for sagging the rear end of the sheet located at
A sheet conveying apparatus comprising: A curved sheet conveyance path through which the sheet is conveyed;
An upstream conveying means provided on the upstream side of the sheet conveying path for conveying the sheet;
A downstream conveying unit that conveys the sheet conveyed by the upstream conveying unit downstream of the upstream conveying unit;
A step formed by the sheet conveying path and the upstream conveying means,
A sheet conveying apparatus, wherein the upstream conveying means is provided with a receiving portion for receiving the trailing edge of the sheet. Passage detection means for detecting immediately before the sheet passes through the upstream conveying means;
Based on the detection operation of the passage detection unit, the sheet conveyance operation of the downstream side conveyance unit is temporarily stopped, and the conveyance of the upstream side conveyance unit is performed in a state where the rear end portion of the sheet is received by the receiving receiving unit. Control means for sagging a rear end portion of the sheet positioned at the step by continuing the operation;
The sheet conveying apparatus according to claim 4, further comprising: Passage detection means for detecting immediately before the sheet passes through the upstream conveying means;
Based on the detection operation of the passage detecting means, the sheet conveying speed of the downstream conveying means is temporarily made slower than the sheet conveying speed of the upstream conveying means, and the trailing end portion of the sheet is received by the received receiving portion. Control means for slackening the trailing edge of the sheet located at the step by continuing the conveying operation of the upstream conveying means in a state;
The sheet conveying apparatus according to claim 4, further comprising: A thickness detecting means for detecting a sheet having a predetermined thickness or more,
The control unit temporarily stops the sheet conveying operation of the downstream conveying unit based on the detection operation of the passage detecting unit and the thickness detecting unit, and the step is performed by continuing the conveying operation of the upstream conveying unit. The sheet conveying apparatus according to claim 2, wherein a rear end portion of the positioned sheet is slackened. A thickness detecting means for detecting a sheet having a predetermined thickness or more,
The control means temporarily delays the sheet conveying speed of the downstream conveying means based on the detection operation of the passage detecting means and the thickness detecting means, and the upstream conveying 7. The sheet conveying apparatus according to claim 3, wherein a trailing end portion of the sheet positioned at the step is slackened by continuing the conveying operation of the means.   The sheet according to any one of claims 1 to 8, wherein the upstream driving unit that drives the upstream conveying unit and the downstream driving unit that drives the downstream conveying unit are separate. Conveying device.   The upstream driving means for driving the upstream conveying means and the downstream driving means for driving the downstream conveying means are common driving means, and the driving force of the driving means is applied to the downstream conveying means. The sheet conveying apparatus according to any one of claims 1 to 8, wherein a clutch for disconnecting is provided.   11. The sheet conveying apparatus according to claim 1, wherein each of the upstream conveying unit and the downstream conveying unit is a roller pair. Image forming means for forming an image on a sheet;
A sheet conveying device that conveys a sheet on which an image is formed by the image forming unit,
12. The image forming apparatus according to claim 1, wherein the sheet conveying apparatus is the sheet conveying apparatus according to claim 1. The image forming unit includes a photosensitive drum and a transfer unit that form a toner image on the sheet; and a fixing unit that fixes the toner image on the sheet;
The image forming apparatus according to claim 12, wherein an upstream conveying unit of the sheet conveying apparatus is disposed on the downstream side of the fixing device.

Images