JP2013007960A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that, when forming images on both sides of a recording member, transporting recording members in such an overlapped manner will possibly give rise to an image defect resulting from rubbing an image formed on the recording member.SOLUTION: Based on a zone where a recording member S1 being a preceding sheet and a recording sheet S2 being a following sheet can be passed by each other, a pass-by timing for the recording members S1 and S2 is calculated. This enables prevention of the occurrence of an image defect on images formed on the passing-by surfaces of the recording sheets S1 and S2 due to passing by. Further, transporting the preceding and following sheets in such an overlapped manner shortens a transporting interval, thereby making it possible to improve the productivity of a two-sided printing.

Description

  The present invention relates to an image forming apparatus for forming an image on a recording material.

  2. Description of the Related Art Conventionally, in an image forming apparatus, a method for shortening a sheet interval as a recording material conveyance interval as much as possible is known in order to improve printing productivity. In such an image forming apparatus, for example, Patent Document 1 discloses a method for improving productivity by transporting a preceding sheet and a succeeding sheet in an overlapped manner in order to further shorten the sheet interval.

JP 2002-160860

  However, in an image forming apparatus that forms an image only on one side of a recording material, the conveyance control as in Patent Document 1 is effective, but in the case where image formation is performed on both sides of the recording material, the recording material However, there is a problem that an image formed on the recording material may be rubbed to cause an image defect when the images are conveyed in a superimposed manner.

  The invention according to the present application has been made in view of the above situation, and in an image forming apparatus that forms images on both sides of a recording material, the recording material is stacked and conveyed when performing double-sided printing. However, the object is to prevent the occurrence of image defects and to improve the productivity during double-sided printing.

  In order to achieve the above object, an image forming unit that forms an image on a recording material, and a recording material on which an image is formed by the image forming unit is conveyed toward a paper discharge unit, or an image is formed by the image forming unit. A double-sided conveyance unit that conveys the formed recording material toward the image forming unit, and a control that controls whether the recording material on which an image is formed by the image forming unit is discharged or conveyed to the image forming unit An image forming apparatus including: a control unit, wherein the control unit transports a preceding sheet, which is a recording material transported first, toward the image forming unit by the double-sided transport unit; When the succeeding sheet, which is a recording material, is transported by the double-sided transport unit toward the paper discharge unit, the timing of passing between the preceding sheet and the succeeding sheet is controlled.

  According to the configuration of the present invention, in an image forming apparatus that forms an image on both sides of a recording material, even when the recording material is conveyed while being double-sided printed, the occurrence of an image defect is prevented and double-sided printing is performed. It becomes possible to improve productivity at the time.

Schematic configuration diagram of an image forming apparatus Block diagram showing control operation of image forming apparatus Schematic configuration diagram of the double-sided reversing unit The figure shown about the conveyance method of the recording material S at the time of duplex printing Diagram showing the minimum paper space of the recording material when performing double-sided reversal in the double-sided conveyance path Flow chart showing transport control when performing duplex printing Timing chart showing the feeding timing of the recording material S1 and the recording material S2 The figure which showed the determination method of the feed timing of recording material S1 and recording material S2 in 1st Embodiment The figure which showed the determination method of the feed timing of recording material S1 and recording material S2 in 2nd Embodiment The figure which showed the determination method of the feed timing of recording material S1 and recording material S2 in 3rd Embodiment The figure which showed the determination method of the feed timing of recording material S1 and recording material S2 in 4th Embodiment

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

(First embodiment)
FIG. 1 is a schematic configuration diagram of an image forming apparatus. Here, a laser beam printer will be described as an example of the image forming apparatus. When receiving a print instruction from the video controller, the laser beam printer 101 feeds the recording material S as paper from the paper feed cassette 102. When the recording material S is fed from the paper feed cassette 102, the recording roller S is driven to transport the recording material S to the transport path. The recording material S fed from the paper feed cassette 102 is transported by transport rollers 106 and 107 and reaches the top sensor 108. When the top sensor 108 detects the leading edge of the recording material S, the recording material S is conveyed to the image forming unit 120. During continuous printing, the top sensor 108 controls to maintain the throughput by feeding the next recording material S a predetermined time after detecting the leading or trailing edge of the recording material S.

  The image forming unit 120 includes a photosensitive drum 109, a transfer roller 110, a charging roller 111, and a developing device 112. First, the photosensitive drum 109 is uniformly charged by the charging roller 111. Thereafter, laser light L corresponding to the image signal is emitted from the laser exposure device 113, and an electrostatic latent image is formed on the surface of the photosensitive drum 109. The formed electrostatic latent image is visualized as a toner image by attaching toner to the developing device 112. Then, the photosensitive drum 109 rotates to carry the toner image to the transfer position. In synchronization with the rotation of the photosensitive drum 109, the recording material S is also conveyed to the transfer position. At the transfer position, a voltage having a reverse polarity to the toner image is applied to the transfer roller 110, and the toner image on the photosensitive drum 109 is transferred to the recording material S. The recording material S to which the toner image has been transferred is conveyed to the fixing device 114. The toner image is fixed on the recording material S by being heated and pressurized by the fixing device 114. The recording material S on which the toner image has been fixed is conveyed through the triple roller 116, the intermediate discharge roller 117, and the discharge roller 118, and is discharged onto the discharge tray 121 to complete a series of printing operations.

When images are formed on both sides of the recording material S, the recording material S is transported when the fixing paper discharge sensor 115 is transported a predetermined distance from the timing at which the rear end of the recording material S is removed after the image formation on the first surface. Stop. Then, the intermediate paper discharge roller 117 and the paper discharge roller 118 are driven reversely to reverse the recording material S and are drawn into the double-sided conveyance path 125. The recording material S drawn into the double-sided conveyance path 125 is conveyed by the double-sided conveyance roller 122, and the double-sided drawing is completed after a predetermined time from the detection of the recording material leading edge by the double-sided sensor 123. If printing is possible on the back surface as it is, the recording material S is conveyed to the image forming unit 120. If printing is not possible yet, the duplex conveying roller 122 is stopped and the conveyance is stopped. When printing is possible, the double-sided conveyance roller 122 is driven again to convey the recording material S to the image forming unit 120. The recording material S conveyed to the image forming unit 120 forms an image on the back surface as well as the front surface. Then, the image is fixed by the fixing device 114, conveyed by the triple roller 116, the intermediate paper discharge roller 117, and the paper discharge roller 118, and discharged to the paper discharge tray 121 to complete a series of printing operations. The series of processes is controlled by a CPU described later.
FIG. 2 shows an example of a block diagram showing the control operation of the image forming apparatus. The CPU 201 includes an arithmetic processing circuit, a ROM, a RAM, and the like, and an operation is realized based on a program written in advance in the ROM. Then, it operates by receiving a print instruction or image data transmitted from the video controller 300. The CPU 201 has functions of a print area determination unit 202, a print area storage unit 203, a recording material interval calculation unit 204, a paper feed control unit 205, a conveyance control unit 206, and a reverse control unit 207. The CPU 201 also receives signals from the top sensor 108, the fixing paper discharge sensor 115, and the double-side sensor 123. Further, the CPU 201 controls the rotation of the conveyance rollers 105, 106, 107, the transfer roller 110, and the photosensitive drum 109 by controlling the conveyance motor 211. Further, the rotation of the fixing device 114 and the triple roller 116 is controlled by controlling the fixing motor 210, and the rotation of the paper discharge roller 118 and the intermediate paper discharge roller 117 is controlled by controlling the reverse motor 209. Further, the rotation of the duplex conveying roller 122 is controlled by controlling the refeed motor 208.

  FIG. 3 is a schematic configuration diagram of the double-side reversing unit. The recording material S fixed by the fixing device 114 is conveyed to the paper discharge conveyance path 301 by the triple roller 116. At the timing when the rear end of the recording material S reaches the recording material reversal position RP, the intermediate paper discharge roller 117 is reversed to reverse the recording material S. The reversed recording material S is sent to the duplex conveying path 125 by the triple roller 116. At this time, the timing at which the trailing edge of the recording material S reaches the recording material reversal position RP can be determined in a predetermined time after the fixing paper discharge sensor 115 detects the trailing edge of the recording material S.

  FIG. 4 is a diagram illustrating a method for conveying the recording material S during double-sided printing. 4A to 4F have the same configuration of the rollers, sensors, and the like on the conveyance path, the reference numerals are given only to FIG. 4A, and the description is omitted in the following drawings. Here, the recording material conveyed to the first sheet is defined as S1, the recording material conveyed to the second sheet is defined as S2, and the recording material conveyed to the third sheet is defined as S3.

  4A, in order to form an image on the first recording material S1, the sheet feeding roller 103 is driven, the recording material S1 fed from the sheet feeding cassette 102 is fed, and the conveying roller 105 is fed. , 106, 107. Then, the top sensor 108 detects the leading edge of the recording material S1. In FIG. 4B, the recording material S1 is conveyed to the image forming unit, and an image is formed on the recording material S1. Thereafter, the recording material S1 fixed by the fixing device 114 is conveyed by the intermediate discharge roller 117 and the discharge roller 118. When the trailing edge of the recording material S1 is conveyed to the recording material reversal position RP, the intermediate paper discharge roller 117 and the paper discharge roller 118 are driven in reverse to convey the recording material S1 to the double-sided conveyance path. Simultaneously with the conveyance of the recording material S1, the feeding of the second recording material S2 is started.

  In FIG. 4C, the recording material S1 is conveyed by the double-sided conveyance roller 122. Then, after the front end of the recording material S1 is detected by the double-sided sensor 123, the double-sided conveyance roller 122 is stopped at a predetermined timing. Then, it waits until the timing at which image formation is possible on the recording material S1. On the other hand, the recording material S2 is transported to the recording material reversal position RP by the intermediate paper discharge roller 117 and the paper discharge roller 118 after image formation by the image forming unit in the same manner as the recording material S1. In FIG. 4D, when it is time to form an image on the recording material S1, driving by the double-sided conveyance roller 122 is resumed to form an image on the second surface of the recording material S1, and the recording material S1 is used as an image forming unit. Transport. When conveyance of the recording material S1 is started, conveyance of the recording material S2 that has been waiting at the recording material reversal position RP is also started.

  In FIG. 4E, the recording material S1 is image-formed on the second surface in the image forming portion. After the leading edge of the recording material S2 is detected by the double-sided sensor 123, the driving of the double-sided conveyance roller 122 is stopped at a predetermined timing, and the recording material S2 is put on standby until a timing at which an image can be formed on the recording material S2. In addition, in order to perform image formation following the recording material S1, a pause of the third recording material S3 is started. In FIG. 4F, the recording material S 1 on which the image is formed on the second surface is discharged by the intermediate discharge roller 117 and the discharge roller 118. Following the recording material S1, the recording material S3 is subjected to image formation in the image forming unit, and then conveyed to the recording material reversal position RP by the intermediate paper discharge roller 117 and the paper discharge roller 118. After image formation on the recording material S3, conveyance of the recording material S2 is started in order to form an image on the second surface of the recording material S2. In this way, double-sided printing is performed by alternately feeding recording materials.

  FIG. 5 shows the minimum sheet spacing of the recording material when performing both-side reversal in the duplex conveyance path. In order to pass the recording material S1 that has been reversed on both sides and the recording material S2 that is subsequently conveyed in the duplex conveyance path, the recording material S1 is reversed at the recording material reversal position RP, and then the recording roller tip is moved to the triple roller 116. It is necessary to carry until it reaches. Therefore, the minimum sheet interval Lmin between the recording material S1 and the recording material S2 reaches the reversal position RP after the rear end of the recording material S1 passes through the branch point JP with the double-sided conveyance path, and starts reversal. This is the distance until the recording material reaches the triple roller 116. Therefore, the minimum paper interval Lmin = LR + LJ between the recording material S1 and the recording material S2 when performing the passing conveyance.

  FIG. 6 is a flowchart illustrating conveyance control when performing duplex printing in the present embodiment. In step S <b> 101, when the CPU 201 receives a print instruction from the video controller 300, the CPU 201 starts preparation for a paper feeding operation. Based on the image data received from the video controller 300, the print area is determined. The determined print area is stored in the print area storage unit 203. In step S102, the CPU 201 determines whether it is the paper feed timing for feeding the recording material S1. The paper feed timing for the first recording material S1 in the series of print jobs is the timing when preparation for the paper feed operation is completed.

  If it is determined in S102 that the paper feed timing has come, the CPU 201 starts the paper feed operation in S103. In step S <b> 104, the CPU 201 determines whether the recording material S <b> 1 has been conveyed to the top sensor 108. When the top sensor 108 detects the leading edge of the recording material S1, in step S105, the CPU 201 determines whether there is a print instruction for subsequent image formation. If there is no print instruction, the print operation is terminated. When there is a print instruction, in S106, the CPU 201 determines whether or not to perform double-sided printing on the recording material S1. If double-sided printing is not performed, the process proceeds to S108. When performing duplex printing, the process proceeds to S107.

  In step S107, the CPU 201 determines the printing area of the recording material S1 and the printing area of the recording material S2 fed after the recording material S1. In step S608, the CPU 201 determines the timing for feeding the recording material S2. When determining in S106 that the recording material S1 is not subjected to double-sided printing, the recording material S2 is determined based on the length of the recording material S1 and the timing at which the space between the sheets when performing single-sided printing is secured. This is the timing for feeding the material S2. On the other hand, when it is determined in S106 that double-sided printing is performed on the recording material S1, the feeding timing of the recording material S2 differs depending on the printing area of the recording material S1 and the printing area of the recording material S2. This paper feed timing control method will be described in detail with reference to FIGS. When the feeding timing of the recording material S2 is determined in S108, the process proceeds to S102.

FIG. 7 is a timing chart showing the feeding timing of the recording material S1 and the recording material S2. The paper feed timing determination timer T is a free-run timer, which becomes 0 when the paper feed roller 103 is driven and starts counting. The feeding timing Tth of the recording material S2 is set at the timing when the top sensor 108 detects the leading edge of the recording material S1 after the recording material S1 is fed. The sheet feeding timing Tth is set such that the length of the recording material S1 is LS1, the interval between sheets is L, and the recording material conveyance speed is V.
Tth = (LS1 + L) ÷ V (1)
Can be obtained from At the timing when the paper feed timing determination timer T exceeds Tth, the feeding of the recording material S2 is started.

  FIG. 8 is a diagram showing a method for determining the feeding timing of the recording material S1 and the recording material S2 in the present embodiment. Here, both the recording material S1 and the recording material S2 show a state where there is no image on the passing surface. In this embodiment, the passing surface of the recording material S1 is a surface on which image formation is performed on the first surface, and the passing surface of the recording material S2 is a surface on which image formation is performed on the second surface. FIG. 8A is a diagram showing how the recording material S1 and the recording material S2 pass each other in the double-sided conveyance unit. FIG. 8B shows a print area of an image formed on the passing surfaces of the recording material S1 and the recording material S2. In the figure, LS1 indicates the length of the recording material S1. LS2 indicates the length of the recording material S2.

  In the present embodiment, the sheet interval L when the recording material S1 and the recording material S2 are passed is Lmin, which is the minimum sheet interval, since no image is formed on the passing surfaces of the recording material S1 and the recording material S2. Become. Furthermore, the sheet feeding timing of the recording material S2 can be determined from the minimum sheet interval Lmin and the above equation (1). If the recording material S1 needs to pass through the intermediate paper discharge roller 117 before the recording material S2 reaches the intermediate paper discharge roller 117, LJ + (LS1- (from the reverse position RP to the intermediate paper discharge roller 117). The longer distance)) and Lmin are compared, and the longer one is set as the sheet interval L.

  In this way, the area where the preceding sheet and the succeeding sheet are overlapped is controlled according to the print area formed on the passing surface of the preceding sheet and the succeeding sheet. Thereby, even if the preceding sheet and the succeeding sheet are conveyed while being overlapped in the double-sided conveying path, it is possible to prevent the occurrence of image defects in the images formed on the recording materials. In addition, since the preceding paper and the succeeding paper are overlapped and conveyed, the conveyance interval can be shortened, and the productivity of double-sided printing can be improved.

  In this embodiment, the laser beam printer for monochrome printing has been described as an example of the image forming apparatus. However, the present invention is not limited to this, and a laser for color printing can be used as long as the image forming apparatus has a double-sided conveyance path. It is also possible to adapt to a beam printer.

(Second Embodiment)
In the present embodiment, a method for controlling the sheet feeding timing in a state where an image is formed on the passing surface of the recording material S1 and no image is formed on the passing surface of the recording material S2. The only difference from the first embodiment is the difference in the feeding timing of the recording material S2, which is the subsequent sheet. Since the configuration, control circuit, flowchart, and the like of the image forming apparatus are the same as those in the first embodiment, description thereof is omitted here.

  FIG. 9 is a diagram illustrating a method for determining the feeding timing of the recording material S1 and the recording material S2 in the present embodiment. Here, the image is formed on the passing surface of the recording material S1, and the image is not formed on the passing surface of the recording material S2. FIG. 9A is a diagram showing how the recording material S1 and the recording material S2 pass each other in the double-sided conveyance unit. FIG. 9B shows a print area of an image formed on the passing surfaces of the recording material S1 and the recording material S2. In the figure, LS1 indicates the length of the recording material S1. LS2 indicates the length of the recording material S2. L1 indicates a passable area outside the image area of the recording material S1.

  In the present embodiment, the sheet interval L when the recording material S1 and the recording material S2 are transported by passing is calculated from the minimum sheet interval Lmin and the possible region L1 of the recording material S1. The passing surface of the recording material S1 is the surface on which image formation has been performed as the first surface of the recording material S1. When the recording material S1 is reversed and conveyed to the double-sided conveyance path, the passable area L1 that can pass the recording material S2 is the leading end side in the conveyance direction of the first surface of the recording material S1. Therefore, in order to perform the passing conveyance, it is only necessary to pass the recording material S2 at a timing after the minimum sheet interval Lmin and the recording material S1 have been conveyed by an amount corresponding to the image area formed on the first surface after the start of reversal. . By passing at this timing, the recording material S1 and the recording material S2 can pass each other without causing image defects.

  In view of such conditions, the sheet interval L between the recording material S1 and the recording material S2 is L = Lmin + (LS1-L1). Further, the sheet feeding timing of the recording material S2 can be determined from the sheet interval L and the above equation (1). However, the space L is L> = Lmin. If the recording material S1 needs to pass through the intermediate paper discharge roller 117 before the recording material S2 reaches the intermediate paper discharge roller 117, LJ + (LS1- (from the reverse position RP to the intermediate paper discharge roller 117). The longer distance)) and Lmin are compared, and the longer one is set as the sheet interval L.

  In this way, the area where the preceding sheet and the succeeding sheet are overlapped is controlled according to the print area formed on the passing surface of the preceding sheet and the succeeding sheet. Thereby, even if the preceding sheet and the succeeding sheet are conveyed while being overlapped in the double-sided conveying path, it is possible to prevent the occurrence of image defects in the images formed on the recording materials. In addition, since the preceding paper and the succeeding paper are overlapped and conveyed, the conveyance interval can be shortened, and the productivity of double-sided printing can be improved.

(Third embodiment)
In the present exemplary embodiment, a method for controlling the sheet feeding timing in a state where image formation is not performed on the passing surface of the recording material S1 and image formation is performed on the passing surface of the recording material S2. Note that the difference from the first and second embodiments is only the difference in the feeding timing of the recording material S2, which is the subsequent sheet. Since the configuration, control circuit, flowchart, and the like of the image forming apparatus are the same as those in the first and second embodiments, description thereof is omitted here.

  FIG. 10 is a diagram showing a method for determining the feeding timing of the recording material S1 and the recording material S2 in the present embodiment. Here, an image is not formed on the passing surface of the recording material S1, and an image is formed on the passing surface of the recording material S2. FIG. 10A is a diagram showing how the recording material S1 and the recording material S2 pass each other in the double-sided conveyance unit. FIG. 10B shows a print area of an image formed on the passing surfaces of the recording material S1 and the recording material S2. In the figure, LS1 indicates the length of the recording material S1. LS2 indicates the length of the recording material S2. L2 indicates a passable area outside the image area of the recording material S2.

  In the present embodiment, the sheet interval L when the recording material S1 and the recording material S2 are conveyed and passed is calculated from the minimum sheet interval Lmin and the region L2 where the recording material S2 can pass. The passing surface of the recording material S2 is a surface on which image formation has been performed as the first surface of the recording material S2. The passable area L2 in which the recording material S1 is reversed and the recording material S2 can pass while being conveyed to the double-sided conveyance path is the rear end side in the conveyance direction of the first surface of the recording material S2. Therefore, in order to perform the passing conveyance, after the recording material S1 is started to be reversed, the recording material S1 is transported by a distance obtained by subtracting the passable area L2 of the recording material S2 from the minimum sheet interval Lmin and the length of the recording material S1. What is necessary is just to pass the recording material S2 at timing. By passing at this timing, the recording material S1 and the recording material S2 can pass each other without causing image defects.

  In view of such conditions, the sheet interval L between the recording material S1 and the recording material S2 is L = Lmin + (LS1-L2). Further, the sheet feeding timing of the recording material S2 can be determined from the sheet interval L and the above equation (1). However, the space L is L> = Lmin. If the recording material S1 needs to pass through the intermediate paper discharge roller 117 before the recording material S2 reaches the intermediate paper discharge roller 117, LJ + (LS1- (from the reverse position RP to the intermediate paper discharge roller 117). The longer distance)) and Lmin are compared, and the longer one is set as the sheet interval L.

  In this way, the area where the preceding sheet and the succeeding sheet are overlapped is controlled according to the print area formed on the passing surface of the preceding sheet and the succeeding sheet. Thereby, even if the preceding sheet and the succeeding sheet are conveyed while being overlapped in the double-sided conveying path, it is possible to prevent the occurrence of image defects in the images formed on the recording materials. In addition, since the preceding paper and the succeeding paper are overlapped and conveyed, the conveyance interval can be shortened, and the productivity of double-sided printing can be improved.

(Fourth embodiment)
In the present embodiment, a method for controlling the sheet feeding timing in a state where an image is formed on the passing surface of the recording material S1 and the passing surface of the recording material S2. Note that the difference from the first to third embodiments is only the difference in the feeding timing of the recording material S2, which is the subsequent sheet. Since the configuration, control circuit, flowchart, and the like of the image forming apparatus are the same as those in the first to third embodiments, description thereof is omitted here.

  FIG. 11 is a diagram illustrating a method for determining the feeding timing of the recording material S1 and the recording material S2 in the present embodiment. Here, an image is formed on the passing surfaces of the recording material S1 and the recording material S2. FIG. 11A is a diagram showing how the recording material S1 and the recording material S2 pass each other in the double-sided conveyance unit. FIG. 11B shows a print area of an image formed on the passing surfaces of the recording material S1 and the recording material S2. In the figure, LS1 indicates the length of the recording material S1. LS2 indicates the length of the recording material S2. L1 indicates a passable area outside the image area of the recording material S1. L2 indicates a passable area outside the image area of the recording material S2.

  In the present embodiment, the sheet interval L when the recording material S1 and the recording material S2 are conveyed and passed is calculated from the minimum sheet interval Lmin, the recording material S1 passable area L1 and the recording material S2 passable area L2. . Hereinafter, a method for calculating the sheet interval L and the sheet feeding timing of the recording material S2 in the case where L1 <= L2 and the case where L1> L2 will be described.

  When L1 <= L2, the sheet interval L and the sheet feeding timing of the recording material S2 can be calculated based on the possible region L1 of the recording material S1. The method for obtaining the sheet interval L based on the passable area L1 of the recording material S1 is the same as the method described in the second embodiment. Therefore, the sheet interval L is L = Lmin + (LS1−L1). Further, the sheet feeding timing of the recording material S2 can be determined from the sheet interval L and the above equation (1). However, the space L is L> = Lmin.

  When L1> L2, the sheet interval L and the sheet feeding timing of the recording material S2 can be calculated based on the passable area L2 of the recording material S2. The method for obtaining the paper interval L based on the passing area of the recording material S2 is the same as the method described in the third embodiment. Therefore, the sheet interval L is L = Lmin + (LS1-L2). Further, the sheet feeding timing of the recording material S2 can be determined from the sheet interval L and the above equation (1). However, the space L is L> = Lmin. If the recording material S1 needs to pass through the intermediate paper discharge roller 117 before the recording material S2 reaches the intermediate paper discharge roller 117, LJ + (LS1- (from the reverse position RP to the intermediate paper discharge roller 117). The longer distance)) and Lmin are compared, and the longer one is set as the sheet interval L.

  In this way, the area where the preceding sheet and the succeeding sheet are overlapped is controlled according to the print area formed on the passing surface of the preceding sheet and the succeeding sheet. Thereby, even if the preceding sheet and the succeeding sheet are conveyed while being overlapped in the double-sided conveying path, it is possible to prevent the occurrence of image defects in the images formed on the recording materials. In addition, since the preceding paper and the succeeding paper are overlapped and conveyed, the conveyance interval can be shortened, and the productivity of double-sided printing can be improved.

101 Laser beam printer 116 Triple roller 117 Intermediate paper discharge roller 122 Double-sided conveyance roller 201 CPU
RP Reverse position JP Branch point

Claims (5)

Image forming means for forming an image on a recording material;
A double-sided conveyance unit that conveys a recording material on which an image is formed by the image forming unit toward a paper discharge unit, or a conveyance unit that conveys a recording material on which an image is formed by the image forming unit toward the image forming unit;
An image forming apparatus comprising: a control unit that controls whether the recording material on which an image is formed by the image forming unit is discharged or conveyed to the image forming unit;
The control unit conveys the preceding sheet, which is the recording material conveyed first, toward the image forming unit by the double-sided conveyance unit, and the subsequent sheet, which is the next conveyed recording material, as the double-sided conveyance unit. An image forming apparatus that controls a timing of passing between the preceding sheet and the succeeding sheet when the sheet is conveyed toward the sheet discharge unit.   The control means controls the timing of passing between the preceding sheet and the succeeding sheet based on the image area formed on the passing surface of the preceding sheet and the image area formed on the passing surface of the succeeding sheet. The image forming apparatus according to claim 1.   The control means includes a non-imaged area at the leading edge in the conveyance direction of the preceding paper and a non-imaged area at the trailing edge in the conveyance direction of the subsequent paper on the passing surfaces of the preceding paper and the subsequent paper. 3. The image forming apparatus according to claim 2, wherein the image forming apparatus controls the timing of passing between the preceding paper and the succeeding paper by determining that the area is a passable area.   The said control means controls the said passing timing so that the image formed in the passing surface of the said preceding paper and the said following paper may not overlap, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Image forming apparatus.   2. The double-sided conveyance unit is a triple roller, and can carry out conveyance toward the paper discharge unit and conveyance toward the image forming unit at the same time. 5. The image forming apparatus according to any one of items 1 to 4.

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