JP5779960B2 - Image forming apparatus and reverse conveying apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus and a reverse conveyance device.

  Conventionally, an image forming apparatus as a printer, a copier, or the like is known. This type of image forming apparatus can form images not only on one side (for example, the front side) of a sheet but also on both sides of the sheet. After the image is formed, the paper is turned upside down. For example, according to the image forming apparatus disclosed in Patent Document 1, the front end of the paper used for image formation on the front side of the paper and the front end of the paper used for image formation on the back side of the paper are the same end. Thus, a reversing / conveying mechanism (reversing / conveying device) that reverses the front and back of the sheet by rotating the sheet is provided. According to the front / back reversing method by paper rotation, the toner image writing start positions on the front and back surfaces can be set with reference to the same edge of the paper. Therefore, compared with a front / back reversal method using switchback (for example, refer to Patent Document 2), there is an advantage that it is possible to improve the alignment accuracy of the front / back images. Patent Document 2 discloses a technique for increasing the conveyance speed in the switchback path in order to suppress paper jams in the apparatus.

JP 2007-31041 A JP-A-63-27367

  By the way, according to the front-to-back reversing method by paper rotation, the image forming apparatus needs to include a reversing conveyance mechanism. However, when the reverse conveyance mechanism is downsized, there is a problem that the degree of bending of the conveyance path for rotating the paper increases. In this case, since the paper transport load on the transport path increases, depending on the conditions of the paper transported on the transport path, there is a problem in that paper transport failure, noise, and image rubbing may occur.

  The present invention has been made in view of such circumstances, and an object of the present invention is to eliminate the inconvenience associated with turning the paper upside down due to sheet rotation while realizing downsizing of the apparatus.

In order to solve this problem, the first invention provides an image forming apparatus capable of forming images on both sides of a sheet. The image forming apparatus transports a sheet along a reverse transport path, a main transport unit that transports the sheet along the main transport path, an image forming unit that forms an image on the sheet transported by the main transport unit, By rotating the sheet around a rotation axis parallel to the sheet conveying direction in the main conveying path, the reversing conveying unit for reversing the front and back of the sheet and the conveying state of the sheet by the main conveying unit are controlled, and the reversing conveying unit A paper feed control unit that controls a paper transport state. In this case, the sheet feed control unit, as a reverse conveying speed of the sheet by the reversal conveyance section, and the same transport speed as the transport speed of the paper by the main transfer section, and a slower transport speed than the transport speed of the sheet by the main transfer section Switchable .

Here, in the first invention, the feed control unit, based on the condition of the sheet conveyed in the reverse conveying portion, it is preferable to allow switching the reversing transport speed.

Further, in the first invention, the feed control unit can be used as a condition of the sheet conveyed in the reverse conveyance unit, one or both of the printing rate of the image in the paper type and paper surface.

In the first invention, when the paper feed control unit determines that the sheet has a high conveyance load due to the condition of the sheet conveyed in the reverse conveyance unit, the reverse conveyance speed is set to the sheet conveyance speed by the main conveyance unit. It is preferable to use a lower conveyance speed.

In addition, according to a second aspect, when a sheet conveyed in the first sheet conveyance direction is received, the first reversing unit sends out the sheet in a second sheet conveyance direction orthogonal to the first sheet conveyance direction. And a rotation guide unit that guides the conveyance of the sheet sent out from the first reversing unit and reverses the front and back of the sheet by rotating the sheet around a rotation axis parallel to the first sheet conveyance direction, When the sheet conveyed along the rotation guide unit is received, the second reversing unit that sends out the sheet along the first sheet conveying direction, and the sheet from the first reversing unit to the second reversing unit. Provided is a reversing conveyance device having a paper feed control unit for controlling a conveyance state. In this case, the paper feed control unit uses the first transport speed and the second transport speed that is lower than the first transport speed as the transport speed of the sheet from the first reversing unit to the second reversing unit. And can be switched.

Here, in the second invention, the conveyance speed of the sheet from the first reversing unit to the second reversing unit is the speed of the sheet conveyed to the first reversing unit along the first sheet conveying direction. It is preferable that the speed is slower than the slower one of the transport speed and the transport speed of the paper transported along the first paper transport direction from the second reversing unit.

  According to the present invention, when the sheet is conveyed by the reversing conveyance unit, the sheet conveyance speed is slower than the sheet conveyance speed by the main conveyance unit. This reduces the paper conveyance load when the paper is rotated by reversing the front and back, so that the occurrence of poor conveyance, noise, image rubbing, and the like can be suppressed. As a result, it is possible to eliminate the inconvenience associated with reversing the front and back due to the rotation of the sheet, while realizing the downsizing of the reversing conveyance unit, and thus the image forming apparatus.

Configuration diagram schematically showing an image forming apparatus FIG. 1 is a side view showing a main part of the reverse conveying unit 50 when the image forming apparatus is viewed from the A1 direction shown in FIG. The perspective view which shows typically the structure of the reverse conveyance part 50, and the reverse conveyance path | route of the paper P. FIG. Block diagram showing control system of image forming apparatus The flowchart which shows the setting process of the conveyance speed in the reverse conveyance part 50 concerning 1st Embodiment. The flowchart which shows the setting process of the conveyance speed in the reverse conveyance part 50 concerning 2nd Embodiment.

(First embodiment)
FIG. 1 is a configuration diagram schematically illustrating an image forming apparatus according to the first embodiment. The image forming apparatus is an electrophotographic image forming apparatus such as a copying machine, for example, and forms a full-color image by arranging a plurality of photoconductors facing one intermediate transfer belt in a vertical direction. A tandem color image forming apparatus.

  The image forming apparatus mainly includes a document reading device 1, an image forming unit 10, a fixing device 30, a main transport unit 40, and a reverse transport unit 50.

  The document reading apparatus 1 has an automatic document feeder (not shown) provided at the upper part of the apparatus housing, and reads an image signal while conveying a document by the automatic document feeder, thereby outputting an image signal. obtain. Specifically, the document reading device 1 irradiates an image of the document with a lamp and forms an image of the reflected light on the light receiving surface of the image sensor. The image sensor photoelectrically converts the incident light and outputs a predetermined image signal to the image reading control unit 2. The image reading control unit 2 performs processing such as A / D conversion, shading correction, and compression on the image signal, and outputs the image signal to the main control unit 70 (see FIG. 4). Note that the image data input to the main control unit 70 is not limited to the data read by the document reading device 1, but is, for example, data received from a personal computer connected to the image forming device or another image forming device. May be.

  The image forming unit 10 creates a toner image based on the image data, and transfers the created toner image onto the paper P. The image forming unit 10 is mainly composed of exposure units 15Y, 15M, 15C, and 15K, charging / developing units 20Y, 20M, 20C, and 20K, an intermediate transfer unit 23, and a secondary transfer roller 26.

  Each of the exposure units 15Y to 15K includes a laser light source, a polygon mirror, a plurality of lenses, and the like. Each of the exposure units 15Y to 15K scans and exposes the surfaces of photosensitive drums 21Y, 21M, 21C, and 21K, which will be described later, with a laser beam in accordance with output information output from the main control unit 70 based on the image data. . By this scanning exposure, latent images are formed on the photosensitive drums 21Y to 12K, respectively.

  The charging / developing unit 20Y mainly includes a photosensitive drum 21Y that rotates about a rotation axis and a charging / developing unit 22Y that is disposed around the photosensitive drum 21Y. The toner image corresponding to yellow is transferred to the photosensitive drum. It is formed on 21Y. The remaining charging / developing units 20M, 20C, and 20K have the same configuration as that of the charging / developing unit 20Y, and charging / developing units 22M, 22C, and 22K are provided around the photosensitive drums 21M, 21C, and 21K, respectively. The toner images corresponding to magenta, cyan, and black are formed on the photosensitive drums 21M, 21C, and 21K, respectively.

  Specifically, the surfaces of the photosensitive drums 21Y to 21K are uniformly charged by the charging / developing units 22Y to 22K, and as described above, latent images are formed on the surfaces of the exposing units 15Y to 15K. Is done. The charging / developing units 22Y to 22K develop latent images on the photosensitive drums 21Y to 21K by developing with toner. As a result, toner images are formed on the respective photosensitive drums 21Y to 21K. The toner images formed on the individual photosensitive drums 21 </ b> Y to 21 </ b> K are sequentially transferred to predetermined positions on the intermediate transfer belt 24 constituting the intermediate transfer unit 23.

  The secondary transfer roller 26 transfers the toner image transferred onto the intermediate transfer belt 24 onto the paper P conveyed at a predetermined timing by the main conveyance unit 40.

  The paper P onto which the toner image has been transferred, that is, the paper P having an unfixed toner image is sent to the fixing device 30. The fixing device 30 presses and heats the paper P to fix the toner image on the paper P. The fixing device 30 is mainly composed of an upper fixing roller 31 and a lower fixing roller 32, for example. The upper fixing roller 31 and the lower fixing roller 32 are arranged in pressure contact with each other, and a fixing nip portion is formed between the upper fixing roller 31 and the lower fixing roller 32. The upper fixing roller 31 includes a heater (not shown) as a heating unit that performs thermal fixing, and the upper fixing roller 31 is heated by radiant heat from the heater.

  In the fixing device 30, the sheet P is conveyed in such a manner that the surface to be fixed (the surface including the unfixed toner image) faces the fixing upper roller 31, and passes through the fixing nip portion in the conveyance process. As a result, the toner image is fixed onto the paper P through the pressure applied by the upper fixing roller 31 and the lower fixing roller 32 and the heat action of the upper fixing roller 31.

  Here, in the present embodiment, the image forming unit 10 and the fixing device 30 function as an image forming unit. That is, the image forming unit (1) charges the photosensitive drums 21Y to 21K. (2) The exposure units 15Y to 15K form electrostatic latent images on the photosensitive drums 21Y to 21K. (4) The toner image on the photoconductive drums 21Y to 21K is primarily transferred to the intermediate transfer belt 24. (5) The toner image on the intermediate transfer belt 24 is transferred to the sheet P two times. An image (toner image) is formed on a sheet P conveyed by a main conveyance unit 40 to be described later through a series of processes of (6) fixing the toner image on the sheet P.

  The main transport unit 40 includes a guide member and a plurality of rollers, and is disposed along a predetermined transport path (hereinafter referred to as “main transport path”) defined for forming an image on the paper P. . When the paper P is supplied from the paper supply unit 35 (any one of the plurality of paper storage trays Tr1 and Tr2), the main transport unit 40 transports the paper P along the main transport path. The sheet conveyance direction FD1 by the main conveyance unit 40 corresponds to a direction (sub-scanning direction) orthogonal to the main scanning direction of the toner image on the sheet P.

  The main transport unit 40 supplies the paper P to the image forming position by the image forming unit in the process of transporting the paper P along the main transport path. Specifically, the paper P is supplied to the transfer position where the toner image is transferred onto the paper P by the transport rollers 42 and 42 and the registration roller 44, and then to the fixing position where the toner image is fixed on the paper P by the transport belt. Supplied with. The paper P that has passed through the image forming position (transfer position and fixing position) is guided by a guide member and discharged by a discharge roller 45 to a discharge tray 46 attached to the outer side surface of the apparatus housing.

  In contrast, when the toner image is formed not only on the front side of the paper but also on the back side of the paper, the main transport unit 40 transports the paper P that has undergone the image forming process on the front side of the paper to the reverse transport unit 50. Specifically, the paper P that has passed through the fixing position is guided to a transport roller 43 below by a guide member (not shown), and is transported to the reverse transport unit 50 by the transport roller 43.

  The reverse conveyance unit 50 includes a guide member and a plurality of rollers, and is arranged along a predetermined conveyance path (hereinafter referred to as “reverse conveyance path”) defined for performing the reverse of the paper P. . When the reverse conveyance unit 50 receives the paper P from the main conveyance unit 40 on the downstream side of the fixing device 30 (fixing position), the reverse conveyance unit 50 conveys the paper P along the reverse conveyance path. Along with this conveyance, the sheet P is rotated around a rotation axis parallel to the sheet conveyance direction FD1 in the main conveyance path, whereby image formation is performed during image formation on the sheet surface and image formation on the sheet back surface. The front and back of the paper P is reversed without the front and rear ends of the paper P reaching the position being exchanged. Then, the reverse conveyance unit 50 sends the paper P after the front and back are reversed to the main conveyance unit 40 on the upstream side of the image forming unit 10 (transfer position). In this way, the reversal transport unit 50 reverses the front and back of the paper P without changing the leading edge and the trailing edge of the paper P, and therefore forms an image with reference to the same edge of the paper P when forming the front and back images. Therefore, the alignment accuracy of the front and back images can be increased.

  In the present specification, the leading edge of the paper P refers to the front end of the paper P in the paper transport direction, and the trailing edge of the paper P refers to the rear edge. That is, the leading edge and the trailing edge of the sheet P conveyed along the main conveying path correspond to the front edge and the trailing edge of the sheet P with respect to the sheet conveying direction FD1, and are conveyed along the reverse conveying path. The leading edge and the trailing edge of the sheet P correspond to the front edge and the trailing edge of the sheet P with reference to a sheet conveyance direction FD2 described later.

  FIG. 2 is a side view showing a main part of the reversing conveyance unit 50 when the image forming apparatus is viewed from the A1 direction shown in FIG. 1, and FIG. 3 shows the configuration of the reversing conveyance unit 50 and the reversal conveyance path of the paper P. FIG. Specifically, the reverse conveyance unit 50 conveys the paper P along the reverse conveyance path, thereby returning the paper P that has passed the image formation position to the image formation position, and the paper conveyance direction in the main conveyance path. The sheet P is rotated around a rotation axis parallel to the FD 1, and thereby has a function of inverting the front and back of the sheet P. The sheet conveyance direction FD2 by the reverse conveyance unit 50 corresponds to a direction orthogonal to the sheet conveyance direction FD1 in the main conveyance path, that is, the main scanning direction of the toner image on the sheet P.

  The reversing conveyance unit 50 includes a first reversing unit 50A, a second reversing unit 50B, and a rotation guide unit 50C.

  The first reversing unit 50 </ b> A includes conveying rollers 52 and 53 and reversing rollers 56 and 57. The conveyance roller 52 includes a rotation roller and a driven roller, and can be switched between a pressure contact state (nip state) and a separation state (nip release state) by being driven by a driving mechanism (not shown). The rotating roller is composed of a rotating shaft and a pair of rollers attached to both ends thereof, and the driven roller is composed of a rotating shaft and a pair of rollers attached to both ends thereof. The configuration of the conveying roller 52 is the same for the conveying rollers 53 to 55 and the reversing rollers 56 to 59 described later.

  Each of the transport rollers 52 and 53 is arranged such that the rotation axis of the roller is parallel to the sheet transport direction FD2 in the reverse transport path, and the transport rollers 52 and 53 face each other with a predetermined distance therebetween. Are arranged as follows. The reversing rollers 56 and 57 are arranged such that the rotation axis of the rollers is parallel to the paper conveyance direction FD1 in the main conveyance path, and both the reversing rollers 56 and 57 face each other with a predetermined distance therebetween. Are arranged as follows.

  The transport rollers 52 and 53 receive the paper P from the main transport unit 40 at a first switching position that is a downstream position from the fixing device 30. The first switching position is a position for switching the transport direction from the paper transport direction FD1 by the main transport unit 40 to the paper transport direction FD2 by the reverse transport unit 50.

  The reversing rollers 56 and 57 nip the paper P received by the transport rollers 52 and 53 and send it out in the paper transport direction FD2. In this case, the reversing rollers 56 and 57 send the paper P so that the reversing roller 57 is on the upstream side and the reversing roller 56 is on the downstream side, whereby the second reversing unit 50B is provided via the rotation guide unit 50C. The paper P is conveyed to the top.

  The second reversing unit 50 </ b> B includes reversing rollers 58 and 59, conveying rollers 54 and 55, and a side reference plate 60. The reversing rollers 58 and 59 are configured in the same manner as the reversing rollers 56 and 57 of the first reversing unit 50A, and the conveying rollers 54 and 55 are composed of the conveying rollers of the first reversing unit 50A. Since it is the same structure as 52 and 53, description about the overlapping part is abbreviate | omitted.

  The reversing rollers 58 and 59 receive the sheet P conveyed along the rotation guide portion 50C at the second switching position. The second switching position is a position for switching the transport direction from the paper transport direction FD2 by the reverse transport unit 50 to the paper transport direction FD1 by the main transport unit 40.

  The transport rollers 54 and 55 nip the paper P received by the reversing rollers 58 and 59 and send the paper P along the paper transport direction FD1 by the main transport unit 40. In this case, the transport rollers 54 and 55 send out the paper P such that the transport roller 54 is on the upstream side and the transport roller 55 is on the downstream side, whereby the paper P is positioned upstream of the image forming unit 10. To the main transport unit 40.

  The side reference plate 60 corrects the deviation of the sheet P conveyed to the second reversing unit 50B and the bending of the sheet, and is provided at a position slightly away from the reversing roller 59. Further, the side reference plate 60 has an elongated rectangular parallelepiped shape, and is provided such that its longitudinal direction is parallel to the transport direction FD1. The side surface reference plate 60 is brought into contact with the side surface portion of the paper P conveyed via the rotation guide portion 50C (the front end portion of the paper when the paper conveyance direction FD2 is used as a reference). The paper curl can be corrected.

  The rotation guide part 50C is provided between the carry-out side of the reverse roller 56 of the first reverse part 50A and the carry-in side of the reverse roller 58 of the second reverse part 50B. The rotation guide portion 50C is constituted by a pair of guide plates 61 made of, for example, a metal member, and is curved in an arc shape outward. The paper P sent out from the first reversing unit 50A passes between the pair of guide plates 61 and reaches the second reversing unit 50B. That is, the rotation guide unit 50C guides the conveyance of the sheet P sent out from the first reversing unit 50A, and rotates the sheet P by 180 degrees around the rotation axis parallel to the sheet conveyance direction FD1. Invert the front and back.

  FIG. 4 is a block diagram illustrating a control system of the image forming apparatus according to the present embodiment. The image forming apparatus includes a main control unit 70 and a paper feed control unit 80 as a control system for controlling the apparatus.

The main control unit 70 has a function of integrally controlling operations related to image formation. The main control unit 70 is mainly composed of, for example, a CPU 71, performs various calculations according to a control program stored in a memory (not shown), and controls an image forming operation based on the calculation results. Specifically, the main control unit 70 executes the following series of processes by controlling the image forming unit 10 and the fixing device 30, thereby forming a toner image on the paper P.
(1) The photosensitive drums 21Y to 21K are charged. (2) The electrostatic latent images are formed on the photosensitive drums 21Y to 21K by the exposure units 15Y to 15K. (3) The toner is attached to the formed electrostatic latent images. (4) The toner images on the photosensitive drums 21Y to 21K are primarily transferred to the intermediate transfer belt 24. (5) The toner images on the intermediate transfer belt 24 are secondarily transferred to the paper P. (6) The toner images are transferred. Fix the paper P

  Further, the main control unit 70 can acquire various settings, printing conditions (number of copies, paper type (paper size, paper weight, paper quality, etc.), magnification, etc.), a print start instruction, and the like through the operation unit 5. . The operation unit 5 includes buttons and switches, but may be a touch panel integrated with a display unit that displays predetermined information. Further, the main control unit 70 can communicate with the paper feed control unit 80.

  The paper feed control unit 80 has a function of controlling operations related to paper conveyance. The paper feed control unit 80 is mainly composed of, for example, a CPU 81 and various drive circuits 82 and 83, and performs various calculations according to a control program stored in a memory (not shown). Controls the conveyance state. Specifically, the paper feed control unit 80 controls the conveyance state of the paper P by the main conveyance unit 40 through a drive signal output from the CPU 81 via the drive circuit 82. Further, the paper feed control unit 80 controls the conveyance state of the paper P by the reverse conveyance unit 50 through a drive signal output from the CPU 81 via the drive circuit 83.

  As one of the features of the present embodiment, the paper feed control unit 80 sends a paper P conveyance speed command commanded to the reverse conveyance unit 50 at a speed slower than the paper P conveyance speed command commanded to the main conveyance unit 40. A certain reverse reference speed is set. Accordingly, the conveyance speed of the paper P by the reverse conveyance unit 50 is set to the reverse reference speed that is slower than the conveyance speed of the paper P by the main conveyance unit 40. Further, the paper feed controller 80 variably sets the reversal reference speed based on the printing conditions for the paper P.

  Note that a detection signal from the paper detection sensor 85 is input to the paper feed control unit 80. The paper detection sensor 85 is disposed in the main transport path leading to the reverse transport unit 50 and detects the paper P that reaches the entrance side of the reverse transport unit 50. The paper detection sensor 85 includes, for example, a light emitting element and a light receiving element. The detection signal is turned off when the paper P does not pass through the sensor position, and is detected when the paper P passes through the sensor position. The signal turns on.

  FIG. 5 is a flowchart illustrating a conveyance speed setting process in the reverse conveyance unit 50 according to the present embodiment. The processing shown in this flowchart is called at a predetermined cycle and executed by the paper feed control unit 80.

  First, in step 10 (S10), the paper feed control unit 80 determines whether printing is started. When the user performs printing using the image forming apparatus, a print start command is input to the main control unit 70 from the operation unit 5 or from a personal computer or other image forming apparatus together with printing conditions and image data. These pieces of information are also input to the paper feed control unit 80 via the main control unit 70. Accordingly, in step 10, the paper feed control unit 80 determines whether or not a print start command has been input. If an affirmative determination is made in step 10, that is, if printing is started, the process proceeds to step 11 (S11). On the other hand, if a negative determination is made in step 10, that is, if printing is not started, this routine is exited.

  In step 11, the paper feed control unit 80 reads printing conditions. In relation to the present embodiment, the paper feed control unit 80 can recognize the type of paper on which a toner image is to be formed, specifically the amount of paper P, by reading the printing conditions.

  In step 12, the paper feed control unit 80 determines whether or not the amount of paper P satisfies the predetermined amount of paper. This weighting condition defines a weight corresponding to thick paper as the weight of the paper P, and an optimum value is set in advance through experiments and simulations. In general, since the rotation guide unit 50C is designed to have a small curvature in order to reduce the size of the reverse conveyance unit 50, the conveyance load of the paper P increases when passing through the rotation guide unit 50C, resulting in conveyance failure, noise, and image. The rubbing may occur. In particular, the larger the amount of paper P, that is, the thicker the paper, the more the tendency becomes. In the present embodiment, the occurrence of such an event is suppressed by determining the amount of paper P in Step 12 and appropriately setting the transport speed of the paper P by the reverse transport unit 50 according to the determination result. Yes. For example, in the drooping condition, the drooping amount of the paper P recognized as a thick paper is set in advance in consideration of the curvature set in the rotation guide portion 50C.

  If a negative determination is made in step 12, that is, if the amount of paper P does not correspond to thick paper, the process proceeds to step 13 (S13). On the other hand, if an affirmative determination is made in step 12, that is, if the amount of paper P is equivalent to thick paper, the process proceeds to step 14 (S14).

  In step 13, the paper feed control unit 80 sets the transport speed command for the paper P, which is commanded to the reverse transport unit 50, to the first reverse reference speed V 21. The reversal reference speed is a speed slower than the transport speed command of the paper P that the paper feed control unit 80 commands the main transport unit 40, and the first reversal reference speed V21 passes the non-thick paper through the rotation guide unit 50C. In consideration of the above, an arbitrary value is set from the inversion reference speed.

  On the other hand, in step 14, the paper feed control unit 80 sets the transport speed command for the paper P commanded to the reverse transport unit 50 to the second reverse reference speed V 22. The second reverse reference speed V22 is set to an arbitrary value from the above-described reverse reference speeds in consideration of passing thick paper through the rotation guide portion 50C. In particular, the second inversion reference speed V22 is slower than the first inversion reference speed V21.

  Thus, in the present embodiment, the paper feed control unit 80 sets the transport speed of the paper P by the reverse transport unit 50 to the reverse reference speed that is slower than the transport speed of the paper P by the main transport unit 40. .

  For example, when the conveyance speed of the paper P by the reverse conveyance unit 50 is set to be the same as the conveyance speed of the paper P by the main conveyance unit 40, the conveyance speed when passing through the rotation guide unit 50C is too high, and the paper P There is a risk that the transport load increases, resulting in transport failure, noise, image rubbing, and the like. In this regard, according to the present embodiment, when the paper is transported by the reverse transport unit 50, the transport speed of the paper P is reduced compared to the transport speed of the paper P by the main transport unit 40. As a result, the conveyance load of the paper P when passing through the rotation guide portion 50C is reduced, so that the occurrence of poor conveyance, noise, image rubbing, and the like can be suppressed. Moreover, since the conveyance speed of the whole apparatus is not slowed down, a reduction in productivity can be suppressed. As a result, it is possible to eliminate the inconvenience associated with reversing the front and back due to the rotation of the sheet, while realizing the downsizing of the reversing and conveying unit 50 and thus the image forming apparatus.

  In the present embodiment, the paper feed control unit 80 variably sets the reversal reference speed based on the conditions of the paper P that is transported through the reversal transport unit 50. In the present embodiment, the paper type, in particular, the amount of paper P, is used as the condition of the paper P that is transported through the reverse transport unit 50.

  The conveyance load of the paper P in the rotation guide unit 50C affects the amount of paper P. Therefore, by setting the reverse reference speed according to the amount of paper P such as the first reverse reference speed V21 and the second reverse reference speed V22, an appropriate transport speed in the reverse transport unit 50 is set. Can do. Thereby, it is possible to reduce the conveyance load of the paper P while suppressing a decrease in productivity.

  In the present embodiment, as shown in FIG. 3B, the paper feed control unit 80 is configured to lower the conveyance speed V2 of the paper P by the reverse conveyance unit 50 than the conveyance speed of the paper P by the main conveyance unit 40. The reverse reference speed, which is the speed, is set. By the way, the conveyance speed V1 of the paper P from the fixing device 30 to the first reversing unit 50A and the conveyance speed V3 of the paper P from the second reversing unit 50B to the image forming unit 10 may be different. . In this case, the paper feed control unit 80 may set a speed slower than the slower one of the transport speeds V1 and V3 as the reverse reference speed. As a result, the conveyance load of the paper P when passing through the rotation guide portion 50C is reduced, so that the occurrence of poor conveyance, noise, image rubbing, and the like can be suppressed.

  In this embodiment, the paper feed control unit 80 refers to the amount of paper P when setting the reversal reference speed. However, in addition to this, the type of the paper P such as the degree and size of the surface treatment of the paper P is also used. The reverse reference speed can be set according to For example, coated paper has a larger transport load than plain paper, and large-size paper P has a smaller transport load than small-size paper P. Thus, it is possible to determine the reversal reference speed in consideration of the level of the conveyance load caused by the type of the paper P.

  In the present embodiment, the reversal reference speeds V21 and V22 are set in two stages. However, the types of paper P may be subdivided and the reversal reference speeds may be set in multiple stages.

  Further, in the present embodiment, the reverse reference speed is applied to all the sheets P when the reverse conveying unit 50 is conveyed. However, the reversal reference speed is applied to the paper P having a high transport load in the rotation guide unit 50C depending on the paper type, but the other paper P may be kept at the transport speed of the paper P by the main transport unit 40. Good. That is, the paper feed control unit 80 sets the conveyance speed of the paper P by the reverse conveyance unit 50 as a conveyance speed corresponding to the conveyance speed of the paper P by the main conveyance unit 40, and the reverse reference speed that is slower than this. There may be a configuration in which two transport speeds are included, and these are used properly as necessary.

(Second Embodiment)
FIG. 5 is a flowchart illustrating a conveyance speed setting process in the reverse conveyance unit 50 according to the second embodiment. The image forming apparatus according to the second embodiment is different from that of the first embodiment in the condition for determining the reversal reference speed. Note that description of points that are the same as in the first embodiment will be omitted, and hereinafter, differences will be mainly described.

  First, in step 20 (S20), the paper feed control unit 80 determines whether printing is started, that is, whether a print start command is input. If an affirmative determination is made in step 20, that is, if printing is started, the process proceeds to step 21 (S21). On the other hand, if a negative determination is made in step 20, that is, if printing is not started, this routine is exited.

  In step 21, the paper feed control unit 80 reads the printing conditions. In relation to this embodiment, the paper feed control unit 80 can recognize the printing rate of the toner image on the paper surface through reading of the printing conditions. Here, the printing rate is the ratio of the area of the area where the toner image is actually transferred, assuming that the total area constituting the paper P is 100%. For example, the printing rate can be calculated based on the read image data.

  In step 22, the paper feed control unit 80 determines whether the printing rate of the toner image on the paper P satisfies a printing rate condition (for example, 50% or more). This printing rate condition takes into consideration the curvature set in the rotation guide portion 50C, and the printing rate that would cause image rubbing when the paper P is conveyed at the first reverse reference speed V21 in the rotation guide portion 50C. The optimum value is set in advance through experiments and simulations.

  If a negative determination is made in step 22, that is, if the printing rate of the toner image does not satisfy the printing rate condition (low printing rate), the process proceeds to step 23 (S23). On the other hand, when an affirmative determination is made in step 22, that is, when the printing rate of the toner image satisfies the printing rate condition (high printing rate), the process proceeds to step 24 (S24).

  In step 23, the paper feed control unit 80 sets the conveyance speed command of the paper P to be instructed to the reverse conveyance unit 50 to the first reverse reference speed V21. The reversal reference speed is a speed slower than the transport speed command of the paper P commanded to the main transport section 40 by the paper feed control unit 80, and the first reversal reference speed V21 is a sheet with a low printing rate in the rotation guide section 50C. In consideration of passing P, an arbitrary value is set from among the inversion reference speeds.

  On the other hand, in step 24, the paper feed control unit 80 sets the transport speed command for the paper P commanded to the reverse transport unit 50 to the second reverse reference speed V22. The second reverse reference speed V22 is set to an arbitrary value from the above-described reverse reference speeds in consideration of passing the paper P having a high printing rate through the rotation guide portion 50C. In particular, the second inversion reference speed V22 is slower than the first inversion reference speed V21.

  Thus, in the present embodiment, the paper feed control unit 80 variably sets the reversal reference speed based on the conditions of the paper P that is transported through the reversal transport unit 50. In this embodiment, the printing rate of the toner image on the surface of the paper is used as the condition of the paper P that is transported through the reverse transport unit 50.

  When the rotation guide portion 50C is passed, the lower the conveyance speed of the paper P, the more the image can be rubbed. Therefore, the higher the printing rate of the toner image on the paper surface, the more noticeable the effect of image rubbing. Therefore, by setting the reversal reference speed according to the printing rate of the toner image such as the first reversal reference speed V21 and the second reversal reference speed V22, an appropriate transport speed in the reversal transport unit 50 is set. be able to. Thereby, it is possible to suppress image rubbing while suppressing a decrease in productivity.

  In each of the above-described embodiments, the paper type and the image printing rate on the paper surface are independently described as the conditions of the paper conveyed by the reversing conveyance unit. The speed may be set.

  The image forming apparatus according to the embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention. . For example, an apparatus (reverse conveyance apparatus) itself as a reverse conveyance mechanism constituting the image forming apparatus also functions as a part of the present invention.

DESCRIPTION OF SYMBOLS 1 Document reader 2 Image reading control part 10 Image forming unit 15Y-15K Exposure part 20Y-20K Charging / development unit 21Y-21K Photosensitive drum 22Y-22K Charging / development part 23 Intermediate transfer part 26 Transfer roller 30 Fixing apparatus 40 Main Conveying unit 50 Reverse conveying unit 50A First reversing unit 50B Second reversing unit 50C Rotating guide unit 52 to 55 Conveying rollers 56 to 57 Reversing rollers 60 Side reference plate 70 Main control unit 80 Paper feeding control unit

Claims (6)

In an image forming apparatus capable of forming images on both sides of paper,
A main transport section for transporting paper along the main transport path;
An image forming unit that forms an image on a sheet conveyed by the main conveying unit;
A reversing conveyance unit that conveys the sheet along the reversal conveyance path and rotates the sheet around a rotation axis parallel to the sheet conveyance direction in the main conveyance path, thereby reversing the front and back of the sheet;
A paper feed control unit for controlling a paper conveyance state by the main conveyance unit and for controlling a paper conveyance state by the reverse conveyance unit,
The paper feed control unit, as a reverse conveying speed of the sheet by the reversal conveyance section, and the same transport speed as the transport speed of the paper by the main transfer section, and a slower transport speed than the transport speed of the sheet by the main transfer section An image forming apparatus characterized by being switchable . The paper feed control portion, based on the condition of the sheet conveyed in the reverse conveyance unit, an image forming apparatus according to claim 1, characterized in that to enable switching the reversing transport speed. The paper feed control unit, as a condition of the sheet conveyed in the reverse conveyance unit, according to claim 2, characterized by using one or both of the printing ratio of the image in the sheet type and sheet surface Image forming apparatus. When the paper feeding control unit determines that the paper has a high transport load due to the condition of the paper transported in the reverse transport unit, the reverse transport speed is lower than the paper transport speed by the main transport unit The image forming apparatus according to claim 2, wherein a speed is set. A first reversing unit that, upon receiving a sheet conveyed in the first sheet conveying direction, sends out the sheet in a second sheet conveying direction orthogonal to the first sheet conveying direction;
A rotation guide that reverses the front and back of the sheet by guiding the conveyance of the sheet fed from the first reversing unit and rotating the sheet about a rotation axis parallel to the first sheet conveyance direction;
A second reversing unit that receives the sheet conveyed along the rotation guide unit and sends out the sheet along the first sheet conveying direction;
A paper feed control unit that controls a conveyance state of a sheet from the first reversing unit to the second reversing unit,
The paper feed control unit includes a first transport speed and a second transport speed that is lower than the first transport speed as a transport speed of the sheet from the first reversing unit to the second reversing unit. And a reversing conveyance device characterized in that it can be switched. The conveyance speed of the sheet from the first reversing unit to the second reversing unit is the conveyance speed of the sheet conveyed to the first reversing unit along the first sheet conveyance direction and the first reversing unit. 6. The reversal according to claim 5, wherein a reversal speed is set to be slower than the slower one of the transport speeds of the paper transported along the first paper transport direction from the two reversing sections. Conveying device.

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