Image forming apparatus

Abstract

To maintain print quality in double-sided printing and rimless printing.SOLUTION: An image forming apparatus 1 comprises: an image forming unit 12 that forms an image based on print data on a medium P; and an apparatus control section 30 that, when double-sided printing is performed and rimless printing is performed on at least a second surface of the medium P, conveys the medium P in such a manner that a side with print pixel occupancy at least lower than a side with the highest print pixel occupancy in an image on the second surface formed in print pixel number sum-up areas at the edges of the sides, of the sides of the medium P, is placed on a leading end side in a conveyance direction G.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, and is suitable for use in, for example, an electrophotographic printer capable of double-sided printing and borderless printing. [Background technology]

[0002] Conventionally, image forming devices (also called printers) have been widely used that perform printing by forming a developer image (also called a toner image) using an image forming unit based on an image supplied from a computer device or the like, transferring the developer image (also called a toner image) to a medium such as paper, and fixing the image by applying heat and pressure. Some of these image forming devices perform double-sided printing and borderless printing (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-81607 A Summary of the Invention [Problem to be solved by the invention]

[0004] In such image forming apparatuses, it is desirable to maintain print quality even in double-sided printing and borderless printing.

[0005] SUMMARY OF THE PRESENT EMBODIMENT The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus that can maintain print quality in both double-sided printing and borderless printing. [Means for solving the problem]

[0006] In order to solve this problem, the image forming device of the present invention is provided with an image forming unit that forms an image based on print data on a medium, and a control unit that, when double-sided printing is performed and at least the second side of the medium is printed borderless, transports the medium so that the side of the medium that is at least lower than the side with the highest print pixel occupancy rate in the image on the second side formed within a specified area on the edge of each side is at the leading edge in the transport direction.

[0007] Even if the leading edge of the medium in the transport direction floats and comes into contact with the photosensitive drum when printing on the back side of the medium, the present invention makes it possible to reduce the possibility of destroying the toner image on the photosensitive drum around the contact position by making the number of printed pixels on the toner image on the photosensitive drum around the contact position small. Effect of the Invention

[0008] According to the present invention, even if the leading edge of the medium in the transport direction floats and comes into contact with the photosensitive drum when printing on the back side of the medium, the toner image on the photosensitive drum around the contact position can be made to have a low number of printed pixels, reducing the possibility of destroying the toner image on the photosensitive drum around the contact position, thereby realizing an image forming device that can maintain print quality in double-sided printing and borderless printing. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a left side view showing the overall configuration of the image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Diagram 3] 11A and 11B are diagrams illustrating transfer positions on a normal medium and defective positions on a curled medium. [Figure 4] 4 is a flowchart showing a printing process procedure according to the first embodiment. [Diagram 5] FIG. 2 is a diagram showing a configuration of image data according to the first embodiment. [Figure 6] 10A and 10B are diagrams illustrating cutouts of a print pixel count region according to the first embodiment; [Figure 7] FIG. [Figure 8] FIG. 13 is a diagram showing a media storage direction change guidance screen. [Figure 9] 10 is a flowchart showing a printing process procedure according to a second embodiment. [Figure 10] FIG. 11 is a diagram showing a configuration of image data according to the second embodiment. [Figure 11] FIG. 11 is a diagram showing the extraction of a print pixel count region according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0011] 1. First embodiment [1-1. Overall configuration of image forming apparatus] As shown in Fig. 1, the image forming apparatus 1 is, for example, a printer using an electrophotographic method, and performs an image forming operation using a developer such as toner to form a black-and-white image or a color image on a medium P such as paper or film. In the following, a position close to the medium storage tray 2 as viewed from an arbitrary position on the transport path along which the medium P is transported, or a direction toward the medium storage tray 2, is referred to as upstream. Also, a position close to the medium accumulation tray 18 onto which the medium P is discharged and loaded, or a direction toward the medium accumulation tray 18, as viewed from an arbitrary position on the transport path, is referred to as downstream. Furthermore, the direction from upstream to downstream is referred to as transport direction G.

[0012] The medium storage tray 2 is detachably attached to the lower part of the housing of the image forming apparatus 1, and stores the media P in a stacked state. The pickup roller 4 separates and removes the media P stored in the medium storage tray 2 one by one from the top, and pays it out along the medium transport path 3 toward a pair of transport rollers 5a located downstream. The pair of transport rollers 5a and 5b sandwich and transport the medium P paid out from the pickup roller 4, and transport it along the transport direction G toward the transfer unit 6.

[0013] The transfer section 6 has a transfer belt 7, a belt support roller 8, a belt drive roller 9, and transfer rollers 10 corresponding to each image forming unit 12. The transfer belt 7 is an endless belt, and is stretched by the belt drive roller 9 and the belt support roller 8. The belt drive roller 9 is rotated by a motor (not shown), and rotates the transfer belt 7 counterclockwise in FIG. 1. The belt support roller 8 is a driven roller, and rotates together with the transfer belt 7. As a result, while the toner image is transferred to the medium P by the image forming units 12 (12K, 12C, 12M, and 12Y), the transfer section 6 rotates the transfer belt 7, and transports the medium P, which has been transported along the medium transport path 3, along the medium transport path 3 to the fixing unit 17.

[0014] The image forming units 12K, 12C, 12M, and 12Y are arranged in order from the upstream side to the downstream side along the transport direction G, and form developer images (toner images) on the medium P using toners (developers) of different colors. Specifically, the image forming units 12K, 12C, 12M, and 12Y form black, cyan, magenta, and yellow toner images using black (K), cyan (C), magenta (M), and yellow (Y) toners, respectively. The image forming units 12K, 12C, 12M, and 12Y have the same configuration except that they form toner images using toners of different colors, black, cyan, magenta, and yellow, respectively. Hereinafter, the image forming units 12K, 12C, 12M, and 12Y are also collectively referred to as image forming units 12.

[0015] Toner cartridges 13K, 13C, 13M, and 13Y are provided above the image forming units 12K, 12C, 12M, and 12Y, respectively. The toner cartridges 13K, 13C, 13M, and 13Y have the same configuration except that they contain toner of different colors, black, yellow, magenta, and cyan, respectively. Hereinafter, the toner cartridges 13K, 13C, 13M, and 13Y are also collectively referred to as toner cartridges 13. The toner cartridges 13 (13K, 13C, 13M, and 13Y) contain toner of each color, discharge the toner from a discharge port, and supply the toner to the image forming unit 12 via a toner supply duct 14 (14K, 14C, 14M, and 14Y).

[0016] Toner supply ducts 14K, 14C, 14M, and 14Y are connected to the toner cartridges 13K, 13C, 13M, and 13Y, respectively. The toner supply ducts 14K, 14C, 14M, and 14Y have the same configuration, except that they transport toner of different colors, black, cyan, magenta, and yellow, respectively. Hereinafter, the toner supply ducts 14K, 14C, 14M, and 14Y are collectively referred to as toner supply duct 14. The toner supply duct 14 transports the toner discharged from the toner cartridge 13 to the image forming unit 12.

[0017] The transfer rollers 10 are provided for each of the image forming units 12K, 12C, 12M, and 12Y, and are arranged so as to face the photosensitive drums 19 of the image forming units 12K, 12C, 12M, and 12Y with the transfer belt 7 interposed therebetween. The transfer rollers 10 have substantially the same configuration. The transfer rollers 10 electrostatically transfer the toner images of each color formed in the image forming units 12K, 12C, 12M, and 12Y onto the medium P. In addition, the image forming units 12C, 12M, and 12Y including the respective photosensitive drums 19, other than the image forming unit 12K, are spaced apart from the respective transfer rollers 10 by a certain distance upward from the respective transfer rollers 10 by moving upward from the transfer section 6 during monochrome printing.

[0018] The toner image formed on the photosensitive drum 19 is transferred to the medium P transported by the transfer belt 7 on the medium transport path 3. The fixing unit 17 applies heat and pressure to the toner image on the medium P transported from the transfer belt 7, fixing the toner image to the medium P, and feeds it along the medium transport path 3 toward the transport roller pair 5c.

[0019] After passing through the fuser unit 17, the medium transport path 3 branches into a discharge path 20 that transports the medium P to a medium accumulation tray 18, and a medium inversion path 21 that inverts the medium P to perform double-sided printing. A path switching mechanism 22 switches the destination of the medium P that has passed through the fuser unit 17 to the discharge path 20 or the medium inversion path 21. When the medium P is transported to the medium accumulation tray 18, the pairs of transport rollers 5c, 5d, and 5e hold the medium P and transport it through the discharge path 20, and the medium P is discharged and accumulated in the medium accumulation tray 18 formed on the top surface of the housing.

[0020] On the other hand, when the medium P is to be inverted, the conveying roller pairs 5f, 5g, 5h, and 5i hold the medium P and convey it along the medium inversion path 21, inverting the medium P having, for example, a first-side toner image fixed on its front surface, and conveying it upstream of the conveying roller 5b in the medium conveying path 3. As a result, the image forming device 1 conveys the medium P in an inverted state to the image forming unit 12, and forms, for example, a second-side toner image on the back surface of the medium P opposite to the front surface.

[0021] The operation display unit 26 is an operation panel composed of an input unit such as operation buttons that accept input operations from an operator and a display unit such as a display, and displays the operating status of the image forming apparatus 1 and provides the operator with an interface for menu operations.

[0022] [1-2. Control configuration of image forming apparatus] 2, the image forming apparatus 1 has a device control unit 30. The device control unit 30 is configured with a CPU (Central Processing Unit), and centrally controls the image forming apparatus 1 by reading and executing a predetermined program from a storage unit 36. The device control unit 30 has a print control unit 32, a menu control unit 34, a storage unit 36, an image forming unit 38, and a communication unit 40.

[0023] The print control means 32 controls the image forming unit 12, the fuser unit 17, the motor control unit 42, the toner supply duct 14, and the path switching mechanism 22 to execute the printing operation. The motor control unit 42 operates the motors that drive the belt drive roller 9, the fuser unit 17, and the image forming unit 12.

[0024] The menu control means 34 uses the operation display unit 26 to display to the operator guides and options for changing the orientation of the medium P in the medium storage tray 2, and acquires the results of the operation from the operator. The storage means 36 is composed of storage devices such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and stores the print data received by the communication means 40.

[0025] The image forming means 38 converts the print data stored in the storage means 36 into image data to be used by the image forming unit 12 for image formation, and rotates the image data in any direction in response to a request from the print control means 32. The communication means 40 controls a communication interface 44 such as a USB (Universal Serial Bus) I / F, and receives print data from an external device such as a client PC 46.

[0026] [1-3. About curling] Here, the manner in which a curl-free medium P1 and a curled medium P2 pass through the photosensitive drum 19 will be described with reference to FIG. 3. Hereinafter, the media P1 and P2 will be collectively referred to as the medium P. In an image forming apparatus 1 that uses heat and pressure to fix a toner image formed on the medium P to the medium P, curling (warping) may occur in the medium P during the fixing process. As shown in FIG. 3A, the manner in which the curl-free medium P1 passes through the photosensitive drum 19 when the second side is printed during double-sided printing is shown. The curl-free medium P1 comes into contact with the photosensitive drum 19 at a toner transfer position Pt, and the toner image TI is transferred from the photosensitive drum 19.

[0027] 3B, when medium P2 has curled so that its leading edge in the transport direction floats, medium P2 is more likely to come into contact with the photosensitive drum 19 at contact position Pd, which is a position upstream of toner transfer position Pt in the rotation direction of the photosensitive drum 19. In this case, when medium P2 comes into contact with toner image TI on the photosensitive drum 19, the toner image TI is destroyed, and the destroyed toner image TI is then transferred from the photosensitive drum 19 to medium P2 at toner transfer position Pt. This causes poor image quality, such as blurring, at the leading edge of medium P2 in the transport direction.

[0028] In the case of double-sided printing with margins, a margin area that is not printed is provided at the leading and trailing ends of the medium P2 in the transport direction. Therefore, a toner image TI is not formed in the vicinity of the contact position Pd on the photosensitive drum 19 in correspondence with this margin area. Therefore, even if the medium P2 comes into contact with the photosensitive drum 19 near the contact position Pd due to curling, the toner image TI on the photosensitive drum 19 is not destroyed, and no problems with image quality occur on the medium P2.

[0029] However, in the case of double-sided printing and borderless printing, there may be printing on the leading and trailing ends of the medium P2 in the transport direction. Therefore, a toner image TI corresponding to this printing is formed near the contact position Pd on the photosensitive drum 19. For this reason, if the medium P2 comes into contact with the photosensitive drum 19 near the contact position Pd due to curling, the toner image TI on the photosensitive drum 19 will be destroyed, causing problems in image quality on the medium P2.

[0030] Here, borderless printing refers to printing having an image that is arranged from the inner edge of the smallest margin that can be set for printing with margins in the image forming apparatus 1 to the edge of the medium P. When attempting to perform double-sided printing and borderless printing in this way, if a slight curl occurs when fixing the toner image TI to the first side of the medium P, and the leading edge of the medium P in the transport direction contacts the photosensitive drum 19 before the toner transfer position Pt, poor image quality such as smudges is likely to occur at the leading edge of the second side of the medium P.

[0031] [1-4. Printing process] A specific processing procedure of the print process by the image forming apparatus 1 will be described with reference to the flowchart in Fig. 4. When the device control unit 30 receives print data DP1 from the client PC 46 by the communication means 40 via the communication interface 44, it starts the print processing procedure RT1 by reading and executing a print processing program from the storage means 36, and proceeds to step SP1. This print data DP1 includes double-sided print data for one sheet of medium P, i.e., print data for two pages.

[0032] In step SP1, the device control unit 30 stores the received print data DP1 in the storage means 36, and proceeds to step SP2. In step SP2, the device control unit 30 causes the print control means 32 to analyze the print data DP1 using the image forming means 38, generate image data DG1, and store it in the storage means 36, and proceeds to step SP3. The image data DG1 is a bitmap image in which pixels are expanded for each color of CMYK, and is in a format that allows the image forming unit 12 to form a toner image. As shown in Fig. 5, the image data DG1 is composed of first-side image data Da, which corresponds to the first side of the medium P and is printed on the front side of the medium P, and second-side image data Db, which corresponds to the second side of the medium P and is printed on the back side of the medium P.

[0033] In step SP3, the device control unit 30 determines whether the print data DP1 is data for borderless printing. If a positive result is obtained here, this indicates that the print data DP1 is not data for normal printing with margins, but data for borderless printing, and the device control unit 30 then proceeds to step SP4.

[0034] In step SP4, the device control unit 30 extracts a print pixel count area, which is an area for which the print pixel count is to be calculated, and proceeds to step SP5. The extraction of the print pixel count area according to the first embodiment will be described with reference to Fig. 6. The print pixel count is the number of dots (pixels) printed on the medium P.

[0035] The target for which the device control unit 30 counts the number of print pixels is the K-color bitmap image DbK shown in FIG. 6, which corresponds to the image forming unit 12K on the most upstream side in the second side image data Db of the image data DG1 (FIG. 5). The occurrence rate of the poor image quality state shown in FIG. 3B is high in the image forming unit 12 on the most upstream side in the transport direction G. This is because the curled medium P is transported through the medium reversing path 21 (FIG. 1) and first reaches the image forming unit 12K located on the most upstream side of the image forming units 12. When the medium P passes through the image forming unit 12K, it is pressed against the transfer belt 7 by the photosensitive drum 19 of the image forming unit 12K, and the medium P sticks to the transfer belt 7, and the curl is settled. Therefore, the poor image quality state as shown in FIG. 3B is unlikely to occur in the image forming unit 12 downstream of the image forming unit 12K in the transport direction G. For this reason, in the present embodiment, device control section 30 counts the number of print pixels on image data DG1 of image forming unit 12K among image forming units 12K, 12C, 12M, and 12Y.

[0036] The device control unit 30 also determines the leading edge region Rd (FIG. 6A), trailing edge region Ru (FIG. 6B), left side region Rl (FIG. 6C), and right side region Rr (FIG. 6D) in the K-color bitmap image DbK as regions for which the number of printed pixels is to be counted. The leading edge region Rd, trailing edge region Ru, left side region Rl, and right side region Rr (hereinafter collectively referred to as the printing pixel number counting regions) are respectively predetermined regions at the leading edge, trailing edge, left side, and right side in the K-color bitmap image DbK with respect to the transport direction G when the medium P is in a vertically placed state (hereinafter referred to as the reference state).

[0037] 6A, the leading edge region Rd has a width that is the medium width, which is the width in the medium transport width direction perpendicular to the transport direction G of the medium P in the reference state, and a length that is a distance t from the medium edge that is the end on the leading edge side of the medium P in the transport direction G to the trailing edge side. Here, the distance t is the minimum margin width that can be set in the image forming apparatus 1 when performing printing with margins. In this embodiment, the margin widths on each side of the medium P are the same distance t.

[0038] The device control unit 30 cuts out such a leading edge region Rd from the K-color bitmap image DbK. Similarly, the device control unit 30 cuts out the trailing edge region Ru, the left side region Rl, and the right side region Rr from the K-color bitmap image DbK by a distance t from the medium edge toward the opposite end.

[0039] In step SP5, the device control unit 30 counts up the number of printed pixels in each of the printing pixel count count areas of the leading edge area Rd, the trailing edge area Ru, the left edge area Rl, and the right edge area Rr, namely, the leading edge printing pixel number NDd, the trailing edge printing pixel number NDu, the left edge printing pixel number NDl, and the right edge printing pixel number NDr, and then proceeds to step SP6.

[0040] In step SP6, the device control unit 30 calculates the print pixel occupancy rate as the ratio of the leading edge side print pixel count NDd, the trailing edge side print pixel count NDu, the left edge side print pixel count NDl, and the right edge side print pixel count NDr to the area of ​​the print pixel count count area in each of the leading edge side area Rd, the trailing edge side area Ru, the left edge side area Rl, and the right edge side area Rr, and selects and determines the minimum print pixel occupancy rate area, which is the print pixel count count area with the smallest print pixel occupancy rate, from among the leading edge side area Rd, the trailing edge side area Ru, the left edge side area Rl, and the right edge side area Rr, and then proceeds to step SP7.

[0041] In step SP7, the device control unit 30 determines the transport direction G when the minimum print pixel occupancy area is located at the leading end side of the transport direction G. In step SP8, the device control unit 30 determines whether or not it is necessary to change the orientation of the original transport direction G in order to obtain the transport direction G determined in step SP7. At this time, if the minimum print pixel occupancy area is the leading end side area Rd, the transport direction G does not need to be changed from the original transport direction G (FIG. 6(A)), and the device control unit 30 obtains a negative result in step SP8. On the other hand, if the minimum print pixel occupancy area is the trailing end side area Ru, the left side side area Rl, or the right side side area Rr, it is necessary to rotate the transport direction G by 180 degrees or 90 degrees to the left or right, and the device control unit 30 obtains a positive result in step SP8. As an example, a case where the minimum print pixel occupancy area is the left side side area Rl is shown in FIG. 7. When the left side region Rl is positioned at the leading end of the conveying direction G, the conveying direction G needs to be rotated counterclockwise by 90 degrees so that the conveying direction G changes from the upward direction shown in Figure 7(A) to the leftward direction shown in Figure 7(B).

[0042] In step SP9, the device control section 30 causes the print control means 32 to use the image forming means 38 to rotate the image data DG1 in the transport direction G determined in step SP7, and then proceeds to step SP10.

[0043] In step SP10, the device control unit 30 judges whether or not it is necessary to rotate the storage orientation of the medium P in the medium storage tray 2 and reset it. If a positive result is obtained here, the device control unit 30 proceeds to step SP11. At this time, when the area with the smallest print pixel occupancy rate is the left side area Rl as shown in FIG. 7B, it is necessary to rotate the storage orientation of the medium P in the medium storage tray 2 by 90 degrees from portrait to landscape so that the transport direction G is the leftward direction as shown in FIG. 7B. On the other hand, when the area with the smallest print pixel occupancy rate is the right side area Rr, it is also necessary to rotate the storage orientation of the medium P in the medium storage tray 2 by 90 degrees from portrait to landscape so that the transport direction G is the rightward direction as shown in FIG. 7B.

[0044] In step SP11, the device control unit 30 causes the menu control means 34 to display on the operation display unit 26 the media storage orientation change guidance screen DIP shown in Figure 8, which prompts the user to change the storage orientation of the media P in the media storage tray 2 from portrait to landscape, and then proceeds to step SP12.

[0045] In step SP12, the device control unit 30 waits via the menu control means 34 until the operator operates the operation display unit 26 to notify the device control unit 30 that the storage orientation of the medium P in the medium storage tray 2 has been rotated and reset.When notified, the menu control means 34 notifies the printing control means 32 and the device control unit 30 proceeds to step SP13.

[0046] In step SP13, the device control unit 30 executes the printing operation of the image data DG1 using the print control means 32, proceeds to step SP14, and ends the print processing procedure RT1. In this way, the device control unit 30 changes the transport direction G of the medium P to a transport direction G that prevents poor image quality due to curling, and then performs the printing operation. Therefore, the device control unit 30 executes the printing operation under printing conditions suitable for the paper thickness of the medium P, the environmental temperature and humidity, etc., as in the case of a normal printing operation with margins.

[0047] On the other hand, if a negative result is obtained in step SP10, this indicates that the area with the minimum print pixel occupancy rate is the rear end area Ru, so the storage orientation of the medium P in the medium storage tray 2 can remain vertical and there is no need to rotate it to horizontal, and in this case the device control unit 30 skips steps SP11 and SP12 and proceeds to step SP13 to perform the printing operation.

[0048] On the other hand, if a negative result is obtained in step SP3, this indicates that the print data DP1 is data for normal printing with margins, and in this case the device control unit 30 skips steps SP4 to SP8 and proceeds to step SP13 to execute the printing operation.

[0049] [1-5. Effects, etc.] In the above configuration, when double-sided printing with no borders is performed, the image forming device 1 counts the leading edge print pixel count NDd, trailing edge print pixel count NDu, left edge print pixel count NDl, and right edge print pixel count NDr, which are the print pixel counts in each print pixel count area of ​​the leading edge side area Rd, trailing edge side area Ru, left edge side area Rl, and right edge side area Rr, in the K-color bitmap image DbK (FIG. 6), which is the image of the image forming unit 12K formed on the second side of double-sided printing. The image forming device 1 also calculates the ratio of each of the leading edge print pixel count NDd, trailing edge print pixel count NDu, left edge print pixel count NDl, and right edge print pixel count NDr to the area of ​​the print pixel count area as the print pixel occupancy. Furthermore, the image forming apparatus 1 selects and determines the minimum print pixel occupancy area, which is the area with the smallest print pixel occupancy, from the leading edge area Rd, the trailing edge area Ru, the left side area Rl, and the right side area Rr. Next, the image forming apparatus 1 determines the transport direction G when the minimum print pixel occupancy area is located on the leading edge side of the transport direction G, and rotates the image data DG1 in accordance with the transport direction G as necessary.

[0050] Furthermore, when the medium P is currently in a vertical position and the area with the minimum print pixel occupancy rate is the leading edge area Rd or the trailing edge area Ru, the image forming device 1 determines not to change the storage orientation of the medium P in the medium storage tray 2. On the other hand, when the medium P is currently in a vertical position and the area with the minimum print pixel occupancy rate is the left edge area Rl or the right edge area Rr, the image forming device 1 determines to change the storage orientation of the medium P in the medium storage tray 2 to landscape, and prompts the user to change the storage orientation of the medium P in the medium storage tray 2 from portrait to landscape by displaying a medium storage orientation change guidance screen DIP (FIG. 8) on the operation display unit 26.

[0051] In this way, when double-sided printing and borderless printing are performed, the image forming apparatus 1 is configured so that the area with the smallest print pixel occupancy in the K-color bitmap image DbK (FIG. 6), which is the image of the image forming unit 12K formed on the second side of double-sided printing, is located at the leading edge side in the transport direction G of the medium P. As a result, the image forming apparatus 1 can position the side of the medium P with the fewest number of print pixels among the four sides at the leading edge side in the transport direction G on the back side of the medium P. Therefore, as shown in FIG. 3(B), even if the leading edge of the medium P in the transport direction floats and contacts the photosensitive drum 19 at the contact position Pd when printing the second side, the toner image TI on the photosensitive drum 19 around the contact position Pd has a small number of print pixels, so the image forming apparatus 1 can reduce the possibility of destroying the toner image TI on the photosensitive drum 19 around the contact position Pd.

[0052] In this way, in image forming apparatus 1, even if medium P curls and comes into contact with photosensitive drum 19 when printing the second side, the area with the smallest print pixel occupancy, which has the smallest effect on the toner image TI transferred to medium P, is located at the leading edge side in the transport direction G of medium P. As a result, image forming apparatus 1 can prevent degradation of image quality caused by curling of medium P in double-sided printing and borderless printing.

[0053] As described in JP 2014-81607 A, an image forming device has been proposed that prevents degradation of image quality caused by curling of the medium in double-sided printing and borderless printing by prohibiting double-sided printing depending on the width of the image formed on the edge of the medium. However, while such an image forming device can prevent degradation of image quality caused by curling of the medium in double-sided printing and borderless printing, double-sided printing is prohibited in the first place.

[0054] In contrast, the image forming apparatus 1 according to the present embodiment can prevent degradation of image quality caused by curling of the medium P in double-sided printing and borderless printing, without prohibiting double-sided printing.

[0055] Meanwhile, as described in JP 2007-199534 A, an image forming apparatus has been proposed that prevents degradation of image quality caused by curling of the medium in double-sided and borderless printing by changing printing conditions such as fixing speed and fixing temperature according to the printing rate of the image formed on the edge of the medium. However, while such an image forming apparatus can prevent degradation of image quality caused by curling of the medium in double-sided and borderless printing, printing throughput may decrease due to a slowdown in printing speed and waiting time for fixing temperature adjustment.

[0056] In contrast, the image forming apparatus 1 of this embodiment can prevent degradation of image quality caused by curling of the medium P in double-sided printing and borderless printing without changing the printing conditions from the optimal conditions for the medium P in order to suppress degradation of image quality caused by curling of the medium P.

[0057] In this way, the image forming apparatus 1 can prevent degradation of image quality due to curl, which is a particular problem in borderless double-sided printing, without prohibiting double-sided printing or reducing printing throughput.

[0058] According to the above configuration, the image forming device 1 is provided with an image forming unit 12 that forms an image based on print data on the medium P, and a device control unit 30 that, when double-sided printing is performed and at least the second side of the medium P is printed borderless, transports the medium P with at least one side of the medium P that is lower than the side with the highest print pixel occupancy rate in the image on the second side formed within a print pixel count area as a predetermined area on the edge of each side at the leading edge in the transport direction G. As a result, even if the leading edge of the medium P in the transport direction G floats and comes into contact with the photosensitive drum 19 during printing on the back side of the medium P, the image forming device 1 can make the toner image TI on the photosensitive drum 19 around the contact position Pd have a low number of print pixels, thereby reducing the possibility of destroying the toner image TI on the photosensitive drum 19 around the contact position Pd.

[0059] 2. Second embodiment [2-1. Control configuration of image forming apparatus] As shown in Figures 1 and 2, image forming apparatus 101 according to the second embodiment differs from image forming apparatus 1 according to the first embodiment in that it has device control unit 130 instead of device control unit 30, but is otherwise configured in the same manner.

[0060] [2-2. Printing process] A specific processing procedure of the print process by the image forming apparatus 101 will be described with reference to the flowchart of Fig. 9, in which steps corresponding to those in Fig. 4 are given the same reference numerals. When the device control unit 130 receives print data DP2 from the client PC 46 by the communication means 40 via the communication interface 44, it starts the print processing procedure RT101 by reading and executing a print processing program from the storage means 36, and proceeds to step SP21. This print data DP2 includes double-sided print data for N sheets of medium P, i.e., print data for N*2 pages.

[0061] In step SP21, the device control unit 130 stores the received print data DP2 in the storage unit 36, and proceeds to step SP22. In step SP22, the device control unit 130 causes the print control unit 32 to analyze the print data DP2 using the image forming unit 38, generate image data DG2, and store it in the storage unit 36, and proceeds to step SP23. The image data DG2 is a bitmap image in which pixels are expanded for each color of CMYK, and is in a format for the image forming unit 12 to form a toner image. As shown in FIG. 10, the image data DG2 is composed of N sheets of bitmap images D1, D2, ..., and DN, and each bitmap image DX is composed of first-side image data DXa corresponding to the first side of the medium P and printed on the front side of the medium P, and second-side image data DXb corresponding to the second side of the medium P and printed on the back side of the medium P. Here, X is 1, 2, ..., and N, and so on.

[0062] In step SP23, the device control unit 130 determines whether the print data DP2 is data for borderless printing. If a positive result is obtained here, this indicates that the print data DP2 is not data for normal printing with margins, but data for borderless printing, and the device control unit 130 then proceeds to step SP24.

[0063] In step SP24, the device control section 130 extracts a print pixel count region, and the process proceeds to step SP25. The extraction of the print pixel count region according to the second embodiment will be described with reference to FIG. 11. The object for which the device control section 130 extracts the print pixel count is the K-color bitmap image DXbK shown in FIG. 11, which corresponds to the image forming unit 12K on the most upstream side in the second side image data DXb, among the bitmap images DX (i.e., D1 to DN) (FIG. 10). As described in the first embodiment, the image quality defect state shown in FIG. 3(B) occurs frequently in the image forming unit 12 on the most upstream side in the transport direction G, so in this embodiment, the device control section 130 extracts the image data DG2 of the image forming unit 12K as the object for the print pixel count.

[0064] The device control unit 130 also counts the number of print pixels for the leading edge region Rd1-RdN (FIG. 9A), trailing edge region Ru1-RuN (FIG. 9B), left edge region Rl1-RlN (FIG. 9C), and right edge region Rr1-RrN (FIG. 9D) in the K-color bitmap image DXbK (i.e., the K-color bitmap images D1bK-DNbK) for N pages. The leading edge region Rd1-RdN, trailing edge region Ru1-RuN, left edge region Rl1-RlN, and right edge region Rr1-RrN are predetermined regions at the leading edge, trailing edge, left edge, and right edge of the K-color bitmap image DXbK (i.e., the K-color bitmap images D1bK-DNbK) in the transport direction G in the reference state, respectively.

[0065] 11A, the leading edge regions Rd1-RdN have a width that is the medium width, which is the width in the medium transport width direction perpendicular to the transport direction G of the medium P in the reference state, and a length that is the distance t from the medium edge that is the end on the leading edge side in the transport direction G of the medium P toward the trailing edge. Here, the distance t is the minimum margin width that can be set in the image forming apparatus 101 when performing printing with margins.

[0066] The device control unit 130 cuts out such leading edge region RdX (i.e. leading edge regions Rd1-RdN) from the K-color bitmap image DXbK (i.e. K-color bitmap image D1bK-DNbK). Similarly, the device control unit 130 cuts out the trailing edge region RuX (i.e. trailing edge regions Ru1-RuN), left edge region RlX (i.e. left edge regions Rl1-RlN), and right edge region RrX (i.e. right edge regions Rr1-RrN) from the K-color bitmap image DXbK (i.e. K-color bitmap image D1bK-DNbK) by a distance t from the medium edge toward the opposite edge.

[0067] In step SP25, the device control unit 130 counts the leading edge print pixel count NDdX, trailing edge print pixel count NDuX, left edge print pixel count NDlX, and right edge print pixel count NDrX, which are the print pixel counts in each of the leading edge area RdX, trailing edge area RuX, left edge area RlX, and right edge area RrX, for all pages, and proceeds to step SP26. That is, the device control unit 130 counts the leading edge print pixel counts NDd1 to NDdN for each of the leading edge areas Rd1 to RdN. Similarly, the device control unit 130 counts the trailing edge print pixel counts NDu1 to NDuN for each of the trailing edge areas Ru1 to RuN, the left edge print pixel counts NDl1 to NDlN for each of the left edge areas Rl1 to RlN, and the right edge print pixel counts NDr1 to NDrN for each of the right edge areas Rr1 to RrN.

[0068] In step SP26, the device control unit 130 calculates the print pixel occupancy rate of each print pixel count area of ​​all pages for all print pixel count areas, selects the page with the largest print pixel occupancy rate as the maximum print pixel occupancy page, and proceeds to step SP27. That is, the device control unit 130 calculates the ratio of the value of the leading edge print pixel counts NDd1 to NDdN to the area of ​​the print pixel count area of ​​each leading edge side area Rd1 to RdN as the print pixel occupancy rate, and selects and determines the maximum print pixel occupancy page Pdmax, which is the page with the largest print pixel occupancy rate, from among the K-color bitmap images D1bK to DNbK. Similarly, for the rear end areas Ru1 to RuN, the left side areas Rl1 to RlN, and the right side areas Rr1 to RrN, the device control unit 130 calculates the ratio of the rear end side printing pixel counts NDu1 to NDuN, the left side side printing pixel counts NDl1 to NDlN, and the right side side printing pixel counts NDr1 to NDrN to the area of ​​each printing pixel count collection area as the printing pixel occupancy rate, and selects and determines the maximum printing pixel occupancy pages Pumax, Plmax, and Prmax, which are the pages with the largest printing pixel occupancy rate, from the K-color bitmap images D1bK to DNbK.

[0069] In step SP27, the device control unit 130 compares the print pixel occupancy of each of the maximum print pixel occupancy pages Pdmax, Pumax, Plmax, and Prmax, and selects and determines the minimum print pixel occupancy area, which is the print pixel count count area with the smallest print pixel occupancy, from among the leading end area RdN, the trailing end area RuN, the left side area RlN, and the right side area RrN, and then proceeds to step SP7.

[0070] In steps SP7 to SP14, the device control section 130 performs the same processes as in the printing process procedure RT1 (FIG. 4).

[0071] [2-3. Effects, etc.] In the above configuration, when the image forming apparatus 101 performs double-sided printing and borderless printing of print data DP2 including double-sided printing data for multiple sheets, the image forming unit 12K forms an image on the second side of the double-sided printing by tallying up the leading edge print pixel count NDdX, trailing edge print pixel count NDuX, left edge print pixel count NDlX, and right edge print pixel count NDrX for all pages in the K-color bitmap image DXbK (D1bK to DNbK) which is the image of the image forming unit 12K formed on the second side of the double-sided printing. The image forming apparatus 101 also calculates the print pixel occupancy of each print pixel occupancy count area of ​​all pages for all print pixel occupancy count areas, and selects and determines the maximum print pixel occupancy page Pdmax, Pumax, Plmax, and Prmax, which is the page with the largest print pixel occupancy, from the K-color bitmap images D1bK to DNbK. Furthermore, the image forming apparatus 101 compares the print pixel occupancy of each of the maximum print pixel occupancy pages Pdmax, Pumax, Plmax, and Prmax, and selects and determines the minimum print pixel occupancy area, which is the print pixel count area with the smallest print pixel occupancy, from the leading edge side area RdN, the trailing edge side area RuN, the left side side area RlN, and the right side side area RrN. Next, the image forming apparatus 101 determines the transport direction G when the minimum print pixel occupancy area is located on the leading edge side of the transport direction G, and rotates the image data DG2 in accordance with the transport direction G as necessary.

[0072] Furthermore, when the medium P is currently in a vertical position and the area with the minimum print pixel occupancy rate is the leading edge area Rd or the trailing edge area Ru, the image forming device 101 determines not to change the storage orientation of the medium P in the medium storage tray 2. On the other hand, when the medium P is currently in a vertical position and the area with the minimum print pixel occupancy rate is the left edge area Rl or the right edge area Rr, the image forming device 101 determines to change the storage orientation of the medium P in the medium storage tray 2 to landscape, and prompts the user to change the storage orientation of the medium P in the medium storage tray 2 from portrait to landscape by displaying a medium storage orientation change guidance screen DIP (FIG. 8) on the operation display unit 26.

[0073] In this way, when performing double-sided printing and borderless printing on multiple sheets, the image forming apparatus 101 arranges that the minimum print pixel occupancy area among the maximum print pixel occupancy page Pdmax, Pumax, Plmax, and Prmax, which has the smallest print pixel occupancy, is located at the leading edge of the medium P in the transport direction G. Therefore, compared to a case where the area among the maximum print pixel occupancy page Pdmax, Pumax, Plmax, and Prmax, which has the large print pixel occupancy, is located at the leading edge of the medium P in the transport direction G, the image forming apparatus 101 can arrange the side of the medium P with the fewer number of print pixels among the four sides at the leading edge of the transport direction G on the back surface of the medium P. Therefore, as shown in FIG. 3B, even if the leading edge of the medium P in the transport direction floats and contacts the photosensitive drum 19 at the contact position Pd when printing the second side, the toner image TI on the photosensitive drum 19 around the contact position Pd has a smaller number of print pixels, so that the image forming apparatus 101 can reduce the possibility of destroying the toner image TI on the photosensitive drum 19 around the contact position Pd.

[0074] In other respects as well, image forming apparatus 101 according to the second embodiment can achieve the same effects as image forming apparatus 1 according to the first embodiment.

[0075] 3. Other embodiments In the above-described first embodiment, the image forming apparatus 1 has been described as determining, in step SP6 of the print processing procedure RT1 (FIG. 4), the region with the smallest print pixel occupancy rate as the minimum print pixel occupancy rate region by selecting from the leading edge region Rd, trailing edge region Ru, left edge region Rl, and right edge region Rr. The present invention is not limited to this, and the image forming apparatus 1 may determine, as the minimum print pixel occupancy rate region, a region with a print pixel occupancy rate that is at least smaller than the region with the largest print pixel occupancy rate (i.e., not the largest print pixel occupancy rate) from the leading edge region Rd, trailing edge region Ru, left edge region Rl, and right edge region Rr. Even in this case, by setting the print pixel count area with the largest print pixel occupancy rate to the leading edge side in the transport direction G, even if the leading edge of the medium P in the transport direction floats and contacts the photosensitive drum 19 when printing on the back side of the medium P, the toner image TI on the photosensitive drum 19 around the contact position Pd can be reduced, thereby reducing the possibility of destroying the toner image TI on the photosensitive drum 19 around the contact position Pd.

[0076] Also, in the above-mentioned second embodiment, the image forming apparatus 101 compares the print pixel occupancy rates of the maximum print pixel occupancy pages Pdmax, Pumax, Plmax, and Prmax in step SP27 of the print processing procedure RT101 (FIG. 9), and selects and determines the print pixel count tally region with the smallest print pixel occupancy rate as the minimum print pixel occupancy rate region from among the leading edge region RdN, trailing edge region RuN, left edge region RlN, and right edge region RrN. The present invention is not limited to this, and the image forming apparatus 101 may select and determine the print pixel count tally region with a print pixel occupancy rate that is at least smaller than the print pixel occupancy rate region with the largest print pixel occupancy rate (i.e., not the largest print pixel occupancy rate) as the minimum print pixel occupancy rate region from among the leading edge region RdN, trailing edge region RuN, left edge region RlN, and right edge region RrN. Even in this case, by setting the print pixel count calculation area of ​​the page with the largest print pixel occupancy at the leading edge in the transport direction G, even if the leading edge of the medium P in the transport direction floats and comes into contact with the photosensitive drum 19 when printing on the back side of the medium P, the toner image TI on the photosensitive drum 19 around the contact position Pd can be reduced, thereby reducing the possibility of destroying the toner image TI on the photosensitive drum 19 around the contact position Pd.

[0077] Furthermore, the image forming device 101 may calculate the print pixel occupancy rate of each print pixel count area of ​​all pages for all print pixel count areas, calculate the average of these print pixel occupancy rates, and select the print pixel count count area with the smallest average rate as the minimum print pixel occupancy rate area from among the leading edge area RdN, the trailing edge area RuN, the left edge area RlN, and the right edge area RrN.

[0078] Furthermore, in the first embodiment described above, in step SP3 of the printing process procedure RT1 (FIG. 4), the image forming apparatus 1 has been described as determining whether or not to rotate the transport direction G when borderless printing is set on both sides (front and back sides (first and second sides)) of the medium P. The present invention is not limited to this, and the image forming apparatus 1 may determine whether or not to rotate the transport direction G when borderless printing is set on at least the back side (second side) of the medium P, even if printing with margins is set on the front side (first side). The same is true in the second embodiment.

[0079] Further, in the above-described first embodiment, the image forming apparatus 1 has been described as determining in step SP10 that it is necessary to rotate the storage orientation of the medium P in the medium storage tray 2 and reset it if the area with the minimum print pixel occupancy rate determined in step SP6 of the print processing procedure RT1 (FIG. 4) is the left side area Rl or the right side area Rr. The present invention is not limited to this, and the image forming apparatus 1 may determine in step SP10 that it is not necessary to rotate the storage orientation of the medium P in the medium storage tray 2 and reset it if the leading edge side print pixel count NDdX tallied in step SP5 is equal to or less than a predetermined threshold value, even if the area with the minimum print pixel occupancy rate determined in step SP6 of the print processing procedure RT1 (FIG. 4) is the left side area Rl or the right side area Rr. In this case, it is possible to prevent the user from having to go through the trouble of changing the storage orientation of the medium P in the medium storage tray 2. Even in this case, since the number of printing pixels NDdX on the leading edge side is below a predetermined threshold value, even if the leading edge of the medium P in the transport direction G curls and contacts the photosensitive drum 19 at contact position Pd before the toner transfer position Pt (Figure 3(B)), the toner image TI formed near the contact position Pd on the photosensitive drum 19 is small, so the possibility of destroying the toner image TI is low.

[0080] Furthermore, in the above-described first embodiment, the image forming apparatus 1 has been described as tallying up the number of print pixels for the K-color bitmap image DbK corresponding to the image forming unit 12K that is located at the most upstream side in the transport direction G among the multiple image forming units 12. The present invention is not limited to this, and the image forming apparatus 1 may tally up the number of print pixels for bitmap images corresponding to various image forming units 12 that are located at the most upstream side in the transport direction G among the multiple image forming units 12. The same is true in the second embodiment.

[0081] Furthermore, in the above-described first embodiment, the image forming device 1 has been described as urging the user to change the storage direction of the medium P in the medium storage tray 2 in step SP11 of the print processing procedure RT1 (FIG. 4) by displaying the medium storage direction change guidance screen DIP on the operation display unit 26. The present invention is not limited to this, and when the image forming device 1 has multiple medium storage trays, it may change the paper feed source to a medium storage tray in which media is stored in an orientation suitable for the changed transport direction G, without urging the operator to operate it.

[0082] Furthermore, in the above-described first embodiment, a case has been described in which image forming apparatus 1 waits until an operator operates operation display unit 26 in step SP12 of print processing procedure RT1 (FIG. 4) to notify that the storage orientation of medium P in medium storage tray 2 has been rotated and reset. The present invention is not limited to this, and image forming apparatus 1 may detect that the storage orientation of medium P in medium storage tray 2 has been rotated and reset using various sensors provided in image forming apparatus 1, regardless of the operator's operation. The same is true in the second embodiment.

[0083] Furthermore, in the above-described first embodiment, the image forming apparatus 1 has been described as setting the distance t to the minimum margin width that can be set in the image forming apparatus 1 when performing printing with margins. The present invention is not limited to this, and the image forming apparatus 1 may set the distance t to be longer or shorter than the minimum margin width. The same applies to the second embodiment.

[0084] Furthermore, in the above-mentioned first embodiment, the image forming apparatus 1 has been described as setting the distance t of each print pixel count t region (leading edge region Rd, trailing edge region Ru, left side region Rl, and right side region Rr) (FIG. 6) to the same value. The present invention is not limited to this, and the image forming apparatus 1 may set the distance t to different values, for example, in the print pixel count t region on the short side of the medium P (leading edge region Rd and trailing edge region Ru) and the print pixel count t region on the long side of the medium P (left side region Rl and right side region Rr). Also, the image forming apparatus 1 may set the distance t to different values, for example, in each print pixel count t region (leading edge region Rd, trailing edge region Ru, left side region Rl, and right side region Rr). The same is true in the second embodiment.

[0085] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1 or 101 of a so-called direct transfer type, in which the toner image TI is directly transferred from the photosensitive drum 19 to the medium P. However, the present invention is not limited to this, and the present invention may also be applied to an image forming apparatus of a so-called intermediate transfer type (or secondary transfer type), in which the toner images of each color are transferred from the photosensitive drum 19 to an intermediate transfer belt so as to be sequentially superimposed on top of each other, and the toner image TI is transferred from this intermediate transfer belt to the medium P.

[0086] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1 or 101 that uses a developer for a one-component development method. However, the present invention is not limited to this, and the present invention may be applied to an image forming apparatus that uses a developer for a two-component development method in which a carrier and a toner are mixed together and friction between the carrier and the toner is used to impart an appropriate amount of charge to the toner.

[0087] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1 or 101 having four image forming units 12 and forming a color image using toner of four colors. However, the present invention is not limited to this, and the present invention may be applied to an image forming apparatus having three or less image forming units 12 or five or more image forming units 12 and forming an image using toner of a predetermined number of colors.

[0088] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1 or 101, which is a single-function printer. The present invention is not limited to this, and may be applied to image forming apparatuses having various other functions, such as an MFP (Multi Function Peripheral) having the functions of a copier or facsimile machine. The present invention may also be applied to various electronic devices that form an image on a medium P, such as paper, using a developer by an electrophotographic method. For example, the present invention may be applied to a copy operation in an MFP having a scanner function, in which an original image read by a scanner unit is printed on the medium.

[0089] Furthermore, the present invention is not limited to the above-mentioned embodiments and other embodiments. That is, the scope of application of the present invention extends to embodiments in which the above-mentioned embodiments and the other embodiments are combined in part or in whole in any manner. The scope of application of the present invention also extends to embodiments in which a part of the configuration described in any of the above-mentioned embodiments and other embodiments is extracted and replaced or diverted with a part of the configuration of any of the above-mentioned embodiments and other embodiments, or an embodiment in which a part of the extracted configuration is added to any of the embodiments.

[0090] Furthermore, in the above-described embodiment, the image forming apparatus 1 or 101 is configured as an image forming apparatus by the image forming unit 12 as an image forming section and the device control section 30 or 130 as a control section. However, the present invention is not limited to this, and the image forming apparatus may be configured by an image forming section and a control section having various other configurations. [Industrial Applicability]

[0091] The present invention can be used when printing an image on a medium using an electrophotographic image forming apparatus. [Explanation of symbols]

[0092] 1, 101...image forming apparatus, P...medium, 2...medium storage tray, 3...medium transport path, 4...pickup roller, 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 5i...pair of transport rollers, 6...transfer section, 7...transfer belt, 8...belt support roller, 9...belt drive roller, 10...transfer roller, 12...image forming unit, 13...toner cartridge, 14...toner supply duct, 17...fuser unit, 18...medium accumulation tray, 19...photosensitive drum, G...transport direction, 20...discharge path, 21...medium reversal path, 22...path switching mechanism, 26...operation display section, 30...device control section, 32...print control means, 34...menu control means, 36...storage means, 38...image forming means, 40...communication means, 42...motor control section, 44...communication interface, 46...client PC, DP1, DP2...print data, DG1, DG 2...Image data, Da...Image data of first side, Db...Image data of second side, DbK...K-color bitmap image, D1~DN...Bitmap image, DXa...Image data of first side, DXb...Image data of second side, Rd...Front side area, Ru...Rear side area, Rl...Left side area, Rr...Right side area, Rd1~RdN...Front side area, Ru1~RuN...Rear side area, Rl1~RlN...Left side area, Rr1~RrN ...right side area, NDd...number of printed pixels on the leading edge side, NDu...number of printed pixels on the trailing edge side, NDl...number of printed pixels on the left side, NDr...number of printed pixels on the right side, NDdX...number of printed pixels on the leading edge side, NDuX...number of printed pixels on the trailing edge side, NDlX...number of printed pixels on the left side, NDrX...number of printed pixels on the right side, Pdmax, Pumax, Plmax, Prmax...page with maximum print pixel occupancy, Pt...toner transfer position, Pd...contact position, TI...toner image.

Claims

1. an image forming unit that forms an image on a medium based on print data; a control unit that, when double-sided printing is performed and at least a second side of the medium is printed without borders, transports the medium such that, of each side of the medium, a side that is at least lower than a side with the highest print pixel occupancy rate in an image on the second side formed within a predetermined area of ​​the edge of each side is at the leading end in the transport direction; An image forming apparatus comprising:

2. The control unit is When double-sided printing is performed and at least the second side of the medium is printed without borders, the medium is transported with the side of the medium having the lowest print pixel occupancy rate in the image on the second side formed within the predetermined area of ​​the edge of each side at the leading edge side in the transport direction. The image forming apparatus according to claim 1 .

3. The image forming unit includes a plurality of image forming units arranged along the transport direction, The control unit is When double-sided printing is performed and at least the second side of the medium is printed without borders, the medium is transported with the side of each side of the medium that has the lowest print pixel occupancy rate in the image on the second side of the image forming unit arranged on the most upstream side in the transport direction, the side being formed within the predetermined area of ​​the edge of each side, at the leading end side in the transport direction. The image forming apparatus according to claim 2 .

4. The control unit is The print pixel occupancy rate of the specified area of ​​each side is calculated, and if the side with the lowest print pixel occupancy rate is either the long side or the short side of the medium, and the leading end side of the current medium in the paper feed tray in the transport direction is either the other of the long side or the short side of the medium, a notification is given to change the storage direction of the medium in the paper feed tray. The image forming apparatus according to claim 2 .

5. The control unit is The print pixel occupancy rate of the specified area of ​​each side is calculated, and if the side with the lowest print pixel occupancy rate is either one of the long side or the short side of the medium and the leading edge side of the current medium in the paper feed tray in the transport direction is either one of the long side or the short side of the medium, printing is performed without notifying a change in the storage direction of the medium in the paper feed tray. The image forming apparatus according to claim 4 .

6. The control unit is The print pixel occupancy rate of the predetermined area of ​​each side is calculated, and if the side with the lowest print pixel occupancy rate is different from the side at the leading edge of the current medium in the paper feed tray in the transport direction, the image to be formed on the medium is rotated so as to correspond to the case where the side with the lowest print pixel occupancy rate is at the leading edge of the transport direction. The image forming apparatus according to claim 2 .

7. The control unit is When the print data includes an image of a plurality of pages, the printing is double-sided, and at least the second side of the medium is printed borderless, the print pixel occupancy rate of all pages in the specified area of ​​each side is calculated, and a maximum print pixel occupancy rate page which is the page with the maximum print pixel occupancy rate is selected for each specified area, and the medium is transported with the side of the maximum print pixel occupancy rate page in each specified area with the side with the lowest print pixel occupancy rate at the leading end side in the transport direction. The image forming apparatus according to claim 2 .

8. The control unit is The print pixel occupancy rate of the specified area on each side is calculated, and even if the side with the lowest print pixel occupancy rate is either the long side or the short side of the medium, and the leading end side of the current medium in the transport direction in the paper feed tray is the other of the long side or the short side of the medium, if the print pixel occupancy rate of the specified area on the leading end side of the current medium in the transport direction in the paper feed tray is equal to or less than a predetermined value, printing is performed without notifying that the storage direction of the medium in the paper feed tray will be changed. The image forming apparatus according to claim 4 .

9. The predetermined area is the minimum margin area that can be set in the image forming device. The image forming apparatus according to claim 1 .

Images