Image formation device

Abstract

To provide an image formation device that can efficiently adjust an excess amount without generating a margin relative to a medium upon implementing frameless printing.SOLUTION: An image formation device of the present invention has: an image formation unit that includes an image carrier, and forms a developer image on the image carrier; a transfer unit that transfers the developer image the image formation unit forms to a medium; a detection unit that detects a residual developer image sticking out from the medium on the transfer unit; and a control unit that calculates an inclination amount of the medium on the basis of a detection result of the detection unit, and controls a size of the developer image the image formation unit forms on the basis of the inclination amount.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus, and can be applied to, for example, an image forming apparatus that performs printing without creating margins on a medium (borderless printing).

Background Art

[0002] In borderless printing, printing is performed to print an image that protrudes from the four sides of the medium so that no margin portions are generated at the four sides (top, bottom, left, and right) of the medium. For example, in Patent Document 1, a method is disclosed in which the top and bottom protrusion amounts and the left and right protrusion amounts are measured by dedicated sensors from the protruding toner remaining on the transfer belt, and the writing position is adjusted based on the difference from the target value of the protrusion amount to perform borderless printing.

[0003] Generally, the protrusion amount is determined based on the specifications (performance as an apparatus) of the positional deviation amounts and the skew amount in the up, down, left, and right directions so that no margin is generated on the medium even when there is variation in conveyance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when the protrusion amount is large, the amount of protruding toner (waste toner) remaining on the transfer belt after printing inevitably increases. The increase in waste toner leads to a shortened life due to the capacity limit of the waste toner box for collecting waste toner. Therefore, in an apparatus with small positional deviation and skew amount, it is desirable to reduce the protrusion amount.

[0006] Therefore, there is a demand for an image forming apparatus that can efficiently adjust the protrusion amount without creating margins on the medium when performing borderless printing.

Means for Solving the Problem

[0007] The image forming apparatus of the present invention includes: (1) an image forming unit that includes an image carrier and forms a developer image on the image carrier; (2) a transfer unit that transfers the developer image formed by the image forming unit to a medium; (3) a detection unit that detects a residual developer image protruding from the medium on the transfer unit; and (4) a control unit that calculates an inclination amount of the medium based on a detection result of the detection unit and controls a size of the developer image formed by the image forming unit based on the inclination amount.

Effect of the Invention

[0008] According to the present disclosure, when performing borderless printing, the amount of protrusion can be efficiently adjusted without causing a margin on the medium.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0010] (A) First Embodiment Hereinafter, a first embodiment of an image forming apparatus according to the present disclosure will be described in detail with reference to the drawings. In the first embodiment, an example in which the image forming apparatus of the present disclosure is applied to a printer will be described.

[0011] (A-1) Configuration of the First Embodiment FIG. 2 is a configuration diagram showing an outline of the overall configuration of a printer according to the first embodiment.

[0012] In FIG. 2, the printer 1 includes a paper feed tray 10 as a medium storage unit, conveyance rollers 14 and 15, a discharge roller 16, a writing sensor 17, an image forming unit 20 (20C, 20M, 20Y, 20K), a transfer unit 30 as a transfer unit, a fixing unit 50, and a stacker 60.

[0013] The paper feed tray 10 is disposed at the lower part of the printer 1 and stores sheets P of a predetermined size (standard size). The paper feed tray 10 is detachably (openably and closably) disposed with respect to the apparatus main body so that the user can set the sheet P, and is pulled out from the apparatus main body and opened, or pushed into the apparatus main body and closed. The paper feed tray 10 includes a mounting table 11 for stacking and placing the sheet P, a pickup roller 12 as a feeding member for feeding the sheet P placed on the mounting table 11, a spring 13 as a biasing member for biasing the mounting table 11 upward and pressing the uppermost sheet P against the pickup roller 12, and the like.

[0014] The paper P fed out from the paper feed tray 10 is fed into the paper feed path T connected to the paper feed tray 10, and further fed into the paper conveyance path Rt for image formation. Hereinafter, regarding the conveyance direction of the paper P, the side where the conveyance source is located is also referred to as the "upstream side", and the side where the conveyance destination of the paper P is located is also referred to as the "downstream side".

[0015] In the paper feed path T, a conveyance roller 14 for sending the paper P fed out from the paper feed tray 10 to the downstream side in the printer 1 for image formation is disposed.

[0016] The paper conveyance path Rt is a conveyance path for the paper P for image formation, which conveys the paper P fed out from the paper feed tray 10 to the image forming unit 20, transfer unit 30, and fixing unit 50 on the path, and discharges it outside the apparatus from the discharge port provided at the upper part of the printer 1. Also, in the paper conveyance path Rt, a conveyance roller 15 for conveying the paper P fed from the paper feed tray 10 is disposed from the upstream side, a writing sensor 17 is disposed on the downstream side of the conveyance roller 15, and a discharge roller 16 is disposed on the downstream side of the fixing unit 50.

[0017] The writing sensor 17 detects the leading edge position of the paper P and is used for the timing of image output and the like.

[0018] On the upper part of the printer 1, image forming units 20 (20K, 20Y, 20M, 20C) for different colors of black (K), yellow (Y), magenta (M), and cyan (C) are provided from the upstream. Each image forming unit 20 is composed of a toner cartridge for accommodating toner as a developer, a developing unit for forming a toner image as a developer image, and the like. The photosensitive drum as an image carrier incorporated in the developing unit has a cylindrical shape, and a toner image is formed on its circumferential side surface during printing.

[0019] Below each image forming unit 20, a transfer unit 30 is disposed. The transfer unit 30 includes a transfer belt 31, transfer rollers 32 (32K, 32Y, 32M, 32C), belt conveyance rollers 33 and 34, a cleaning blade 35, a waste toner box 36, and reflection intensity sensors 37 (37L, 37R) as detection units.

[0020] The transfer belt 31 is driven by the belt conveyance rollers 33 and 34 to rotate, and conveys the paper P with the paper placed on its upper surface.

[0021] The transfer rollers 32 (32K, 32Y, 32M, 32C) are columnar rollers rotatable in a predetermined direction, and are provided facing the four image forming units 20 inside the transfer belt 31.

[0022] During the formation of a printed image, the transfer unit 30 sandwiches the paper P conveyed by the transfer belt 31 between the upper part of the surface of the transfer roller 32 and the lower part of the surface of the corresponding four image forming units 20 (photosensitive drums) in sequence, and transfers the toner image on the surface of the four image forming units 20 (photosensitive drums) to the surface of the paper P by applying a transfer bias voltage to the transfer roller 32.

[0023] The cleaning blade 35 contacts the transfer belt 31 to scrape off and remove the waste toner conveyed by the transfer belt 31.

[0024] The waste toner box 36 is a container for collecting and storing the waste toner removed from the cleaning blade 35 by the cleaning blade 35. In this embodiment, the waste toner box 36 is integrated with the transfer unit 30. When the waste toner box 36 is full, it is necessary to replace the transfer unit 30 itself.

[0025] Further, at the lower part of the transfer unit 30, reflection intensity sensors 37 (37L, 37R) are arranged on the left and right (L, R) at intervals in the main scanning direction. The reflection intensity sensors 37 can determine the presence or absence of toner remaining on the transfer belt 31 and the toner width in the conveyance direction.

[0026] The fixing unit 50 is composed of rotatable cylindrical fixing rollers 51 and 52 having a function of applying heat and pressure to the paper P. During the printing operation, heat and pressure are applied to the paper P conveyed to the fixing unit 50 with the toner image transferred by the transfer unit 30 from above and below by the fixing rollers 51 and 52 to fix the toner image on the paper P.

[0027] The stacker 60 is provided at the top of the printer 1 and stacks the printed papers P. In addition, the printer 1 has an input unit (such as a touch panel or an operation keyboard) that receives operations from the user such as setting the printing mode (not shown), and a display unit (such as a panel) that indicates the state of the printer 1.

[0028] Next, the configuration of the control system of the printer 1 will be described. FIG. 1 is a block diagram showing the configuration of the control system of the printer according to the first embodiment.

[0029] In FIG. 1, the printer 1 includes a control unit 100 that controls the entire printer 1, a flash ROM 110 that stores programs and the like, a RAM 120 composed of a volatile memory and the like, an EEPROM 130 that is a non-volatile memory, the above-described fixing unit 50, a conveyance mechanism unit 70 that is responsible for paper conveyance such as motors, clutches, and rollers (not shown), the above-described image forming unit 20 and transfer unit 30, a writing sensor 17, a reflection intensity sensor 37, and an interface 140 with an external device such as a PC 200.

[0030] The control unit 100 is responsible for the main functions (such as printing operations) of the printer 1. The control unit 100 has, for example, a CPU, a timer, an input / output interface unit (not shown), etc., and the CPU executes a program stored in the flash ROM 110 to realize the functions of the printer 1.

[0031] In addition to recording the print data received from the PC 200, the RAM 120 records the bitmap data generated by editing and expanding the print data. Also, various types of information generated during the execution of the program are temporarily recorded in the RAM 120. The RAM 120 functions as a work area when the CPU performs calculations.

[0032] The EEPROM 130 records the information that needs to be retained even when the power is turned off among the various types of information generated during the execution of the program.

[0033] The above-mentioned control unit 100 includes a communication control unit 101, a print control unit 102, a fixing control unit 103, a conveyance control unit 104, and an image formation control unit 105.

[0034] The communication control unit 101 performs communication control with external devices such as the PC 200 via the interface 140, and receives print data, etc.

[0035] The print control unit 102 is responsible for overall print control, such as managing print pages and coordinating the fixing control unit 103, the conveyance control unit 104, and the image formation control unit 105.

[0036] The fixing control unit 103 performs temperature control of the fixing unit 50 suitable for the print medium (paper P) based on a temperature sensor (not shown).

[0037] The conveyance control unit 104 controls the conveyance mechanism unit 70 and performs control to convey the paper P from the paper feed tray 10 through the image forming unit 20, the transfer unit 30, and the fixing unit 50 to the stacker 60.

[0038] The image formation control unit 105 calculates the timing of image output (writing position) based on the timing when the paper leading edge is detected by the write sensor 17, and transfers the toner image formed by the image forming unit 20 onto the paper P. In the first embodiment, the image formation control unit 105 further includes an overhang amount control unit 106, and adjusts the output image area so as to have the overhang amount determined by the overhang amount control unit 106 during borderless printing.

[0039] During borderless printing, the overhang amount control unit 106 detects the overhang toner remaining on the transfer belt 31 with the reflection intensity sensor 37, and measures the overhang width. Further, the skew amount of the paper P is calculated from the overhang width measured by the left and right reflection intensity sensors 37L and 37R, and the overhang width without causing a margin on the paper P is reset.

[0040] (A-2) Operations of the First Embodiment Next, the operations of the printer 1 according to the first embodiment having the above configuration will be described.

[0041] FIG. 3 is a flowchart showing the characteristic operations (control of the overhang amount during borderless printing) of the printer according to the first embodiment. When the printer 1 receives a print request from the PC 200, it performs control according to the following processing sequence.

[0042] <Step S101> When the control unit 100 receives a print request for borderless printing, it generates image data.

[0043] Here, borderless printing for forming an image without a margin on the paper P will be described with reference to FIG. 5. First, in borderless printing, enlarged image data is generated by enlarging the original image data for printing (FIG. 5(A)) (FIG. 5(B)). The enlarged image data may be generated by enlarging the original image data based on, for example, the toner overhang amount (for example, the maximum settable overhang amount). In FIG. 5, an example in which the image data is exaggeratedly enlarged for simplicity of explanation is shown.

[0044] <Step S102> The control unit 100 sets an initial image output range for the image data (enlarged image data) generated in the above-described step S101. As shown in FIG. 5(C) above, the image output range is the range that is actually developed in the image data. For example, if the amounts of overhang at the top, bottom, left, and right are WT, WB, WL, and WR respectively, and the paper length and paper width are PL and PW respectively, the image output length is "PL + WT + WB", and the image output width is "PW + WL + WR". The initial overhang amount is not particularly limited in this embodiment and may be the maximum overhang amount or the average value of the apparatus. Also, the previously stored set value may be used.

[0045] <Step S103> The control unit 100 starts a printing operation of feeding the paper P from the paper feed tray 10 and performing image formation on the paper P.

[0046] <Step S104> The control unit 100 starts measurement control by the reflection intensity sensor 37. Thereafter, the reflection intensity sensor measurement control (FIG. 4) is executed in parallel with the main control (FIG. 3). For convenience of explanation, the reflection intensity sensor measurement control will be described here.

[0047] FIG. 4 is a flowchart showing the characteristic operation (reflection intensity sensor measurement control) of the printer according to the first embodiment.

[0048] The control unit 100 determines whether the monitoring start position of the reflection intensity sensor 37 has been reached (S104-1). Specifically, when the control unit 100 measures the amount of overhang of the paper leading edge with the reflection intensity sensor 37, it starts sensor monitoring immediately before the overhang toner on the transfer belt 31 reaches the reflection intensity sensor 37 (before a distance α). For example, the control unit 100 determines based on whether the conveyance time of "(distance between the writing sensor 17 and the reflection intensity sensor 37) - α" has elapsed after the writing sensor 17 detects the leading edge of the paper P. If this determination result is affirmative (Yes), the control unit 100 executes the following processing.

[0049] As shown in FIG. 6, the control unit 100 measures the leading-edge protrusion amounts (WT_L, WT_R) of the paper at the positions of the left and right reflection intensity sensors 37L and 37R (S104-2). When the protruding toner (protruding toner 300) remaining on the transfer belt 31 passes through the left and right reflection intensity sensors 37L and 37R, the control unit 100 discriminates between the transfer belt 31 and the toner based on the reflection intensity, and measures the toner section.

[0050] The control unit 100 calculates a writing position correction amount ΔX (S104-3). The writing position correction amount ΔX can be calculated from the following formula (1). ΔX = WT - (WT_L + WT_R) / 2 …(1)

[0051] The control unit 100 stores the calculated writing position correction amount ΔX (S104-4). The data to be stored is for the most recent N_X times, and the previous data is overwritten from the oldest. N_X corresponds to the population when taking an average in step S106 described later, and is a parameter appropriately determined in consideration of the variation in the writing position.

[0052] For example, FIGS. 7(A) and (B) show an example of storing the writing position correction amount ΔX in a ring buffer format. In FIG. 7, the latest pointer indicates the location (number) where the latest position correction amount ΔX is stored. For example, in FIG. 7(A), since the latest pointer is 1, ΔX[1] (1.0 mm) is the latest data. After that, as shown in FIG. 7(B), when a new position correction amount ΔX is calculated (1.0 mm), the calculated 1.0 mm is stored in ΔX[2], which is the next data storage location, and the latest pointer is updated to "2".

[0053] The control unit 100 calculates a skew amount Skew indicating the inclination of the conveyed paper P (S104-5). As shown in FIG. 6, when the distance between the left and right reflection intensity sensors 37L and 37R is LS, the skew amount Skew can be calculated from the left and right leading-edge protrusion amounts WT_L and WT_R by the following formula (2). Skew = (WT_L - WT_R) / LS …(2)

[0054] The control unit 100 stores the calculated skew amount Skew (S104-6). The data to be stored is for the most recent N_Skew times, and the older data before that is overwritten from the oldest. N_Skew corresponds to the population when taking the average in step S109 described later, and is a parameter appropriately determined considering the variation in the skew amount.

[0055] For example, FIGS. 7(C) and (D) show an example of storing the skew amount Skew in a ring buffer format. For example, in FIG. 7(C), since the latest pointer is N_Skew, Skew[N_Skew] (0.70%) is the latest data. After that, as shown in FIG. 7(D), when a new skew amount Skew is calculated (0.55%), the calculated 0.55% is stored in Skew[1] which is the next data storage location, and the latest pointer is updated to "1".

[0056] The control unit 100 determines whether the paper leading edge overhang amount measured by the reflection intensity sensor 37 is that of the last page (S104-7). If the determination result is affirmative (Yes), the control unit 100 ends the reflection intensity sensor measurement control. On the other hand, if it is negative (No), it transitions to the above-described step S104-1).

[0057] <Step S105> The control unit 100 determines whether the leading edge of the paper P has been detected by the write sensor 17. If the determination result is affirmative (Yes), the control unit 100 executes the next step S106.

[0058] <Step S106> The control unit 100 calculates the average value ΔX_ave of the write position correction amounts for the most recent N_X times by the following formula (3). ΔX_ave = (ΔX[1] + ΔX[2] + … + ΔX[N_X]) / N_X …(3)

[0059] <Step S107> The control unit 100 determines whether the application of the write position correction is possible. The control unit 100 may determine, as an average value calculation condition, for example, whether the number of printed sheets is equal to or more than N_X sheets. Further, the control unit 100 may determine, as a countermeasure against false detection or statistical error, whether conditions such as (1) a certain number of sheets or more have been printed since the previous change in the write position correction amount and (2) there is a difference of a certain amount or more from the previous write position correction amount are satisfied.

[0060] If the determination result is affirmative (Yes), the control unit 100 executes the next step S108. On the other hand, if the result is negative (No), the control unit 100 transitions to step S109 described later.

[0061] <Step S108> The control unit 100 sets the write position correction amount ΔX’ (= ΔX_ave).

[0062] <Step S109> The control unit 100 calculates the average value Skew_ave of the skew amounts for the most recent N_Skew times by the following formula (4). Skew_ave = (Skew[1] + Skew[2] + … + Skew[N_Skew]) / N_Skew …(4)

[0063] <Step S110> The control unit 100 determines whether the reset of the overhang amount is possible. The control unit 100 may determine, as an average value calculation condition, for example, whether the number of printed sheets is equal to or more than N_Skew sheets. Further, the control unit 100 may determine, as a countermeasure against false detection or statistical error, whether conditions such as (1) a certain number of sheets or more have been printed since the previous change in the overhang amount and (2) there is a difference of a certain amount or more from the skew amount at the time of the previous change in the overhang amount are satisfied.

[0064] If the determination result is affirmative (Yes), the control unit 100 executes the next step S111. On the other hand, if the result is negative (No), the control unit 100 transitions to step S113 described later.

[0065] <Step S111> The control unit 100 calculates the top, bottom, left, and right overhang amounts WT’, WB’, WL’, and WR’ to be reset according to the following equations (5) to (8). WT_min, WB_min, WL_min, and WR_min in the following equations (5) to (8) are the overhang amounts (minimum fixed values) when there is no skew. WT’ = WT_min + |Skew_ave| * PW / 2 …(5) WB’ = WB_min + |Skew_ave| * PW / 2 …(6) WL’ = WL_min + |Skew_ave| * PL / 2 …(7) WR’ = WR_min + |Skew_ave| * PL / 2 …(8)

[0066] <Step S112> The control unit 100 sets the top, bottom, left, and right overhang amounts WT’, WB’, WL’, and WR’ to be reset within the image output range.

[0067] <Step S113> The control unit 100 performs image output according to the settings of the top, bottom, left, and right overhang amounts WT’, WB’, WL’, and WR’ and the write position correction amount ΔX.

[0068] <Step S114> The control unit 100 determines whether the sheet P that has passed through the write sensor 17 is the last page. If the determination result is affirmative (Yes), a series of controls is terminated, and if it is negative (No), the process transitions to step S105 described above.

[0069] (A-3) Effects of the First Embodiment According to the first embodiment, the following effects are achieved.

[0070] When the printer 1 tends to have little skew during borderless printing, it resets to reduce the amount of overhang toner, so that the waste toner on the transfer belt 31 can be reduced, and the life due to the capacity limit of the waste toner box 36 can be increased.

[0071] In addition, when the skew tends to be large, the printer 1 can reduce the risk of leaving margins on the paper P in order to reset it to increase the amount of protruding toner.

[0072] (B) Second Embodiment Hereinafter, a second embodiment of the image forming apparatus according to the present disclosure will be described in detail with reference to the drawings. In the second embodiment, an example in which the image forming apparatus of the present disclosure is applied to a printer will be described.

[0073] (B-1) Configuration of the Second Embodiment FIG. 8 is a configuration diagram showing an outline of the overall configuration of the printer according to the second embodiment.

[0074] In FIG. 8, the printer 1A includes the above-described paper feed tray 10 (10-1 to 10-3), the above-described conveyance rollers 14 (14-1 to 14-3), the above-described conveyance roller 15, the above-described discharge roller 16, the above-described writing sensor 17, the above-described image forming unit 20 (20C, 20M, 20Y, 20K), the above-described transfer unit 30, the above-described fixing unit 50, and the above-described stacker 60.

[0075] The difference between the printer 1A of the second embodiment and the printer 1 of the first embodiment is that the paper feed tray 10 has multiple stages (three stages). In the second embodiment, the paper feed tray 10 has three stages, but this is an example, and the number of paper feed trays 10 is not particularly limited.

[0076] Sheets of paper P fed out from each paper feed tray 10 (10-1 to 10-3) to each pickup roller 12 (12-1 to 12-3) are sent to the paper conveyance path Rt via each conveyance roller 14 (14-1 to 14-3). Since the other configurations in FIG. 8 are the same as those shown in FIG. 2 described above, the description thereof will be omitted. In addition, the configuration of the control system of the printer 1A can basically apply the configuration of FIG. 1. The control content of the printer 1A specific to the second embodiment will be described in the operation section.

[0077] (B-2) Operation of the Second Embodiment Next, the operation of the printer 1A according to the second embodiment having the above configuration will be described.

[0078] Skew is caused by factors such as roller alignment and tends to occur along the paper feed path. It also tends to vary depending on the type of medium (plain paper, recycled paper, thick paper, etc.). In the second embodiment, based on the above tendencies, the skew amount is measured for each paper feed tray 10 and type of paper P, the amount of overhang and the amount of correction for the writing position are calculated, and they are applied.

[0079] FIG. 9 is a flowchart showing the characteristic operation (control of the overhang amount during borderless printing) of the printer according to the second embodiment. Among the processes in FIG. 9, the processes denoted by the same reference numerals as those in the flowchart of FIG. 3 described above are basically the same or similar processes, so detailed description thereof is omitted.

[0080] Hereinafter, it is assumed that the information specifying the type of medium is included in the print request from the PC 200. When the printer 1A receives a print request from the PC 200, it performs control according to the following processing sequence.

[0081] <Step S201> After the above-described steps S101 to S103, the control unit 100 starts the measurement control by the reflection intensity sensor 37. Thereafter, the reflection intensity sensor measurement control (FIG. 10) is executed in parallel with the main control (FIG. 9). For convenience of explanation, the description will be made here starting from the reflection intensity sensor measurement control.

[0082] FIG. 10 is a flowchart showing the characteristic operation (reflection intensity sensor measurement control) of the printer according to the second embodiment. Among the processes in FIG. 10, the processes denoted by the same reference numerals as those in the flowchart of FIG. 4 described above are basically the same or similar processes, so detailed description thereof is omitted.

[0083] <Step S201-1> After the above steps S104-1 to S104-3, the control unit 100 stores the calculated writing position correction amount ΔX as the writing position correction amount ΔX[Tray][Media] corresponding to the paper feed tray 10 and the media type. Here, Tray and Media indicate the indexes of the paper feed tray 10 and the media type (the same applies hereinafter). Since the content is the same as that described in step S104-4 above except for storing for each paper feed tray 10 and media type, the details are omitted.

[0084] <Step S201-2> After the above step S104-5, the control unit 100 stores the skew amount Skew as the skew amount Skew[Tray][Media] corresponding to the paper feed tray 10 and the media type. Since it is the same as step S104-6 except for storing for each paper feed tray 10 and media type, the details are omitted.

[0085] <Step S202> After the above step S105 (the determination result is Yes), the control unit 100 calculates the average value ΔX_ave[Tray][Media] of the writing position correction amounts for the most recent N_X times with the current paper feed tray 10 and media type by the following formula (9). ΔX_ave[Tray][Media]=(ΔX[Tray][Media][1]+ΔX[Tray][Media][2]+…+ΔX[Tray][Media][N_X]) / N_X …(9)

[0086] <Step S203> The control unit 100 determines whether it is possible to apply the writing position correction with the current paper feed tray 10 and media type. The control unit 100 may determine, for example, whether the condition of having printed N_X sheets or more is satisfied with the current paper feed tray 10 and media type as the average value calculation condition. Further, as a countermeasure against false detection and statistical error, the control unit 100 may determine whether the conditions such as (1) having printed a certain number of sheets or more since the previous writing position correction amount change with the current paper feed tray 10 and media type and (2) having a certain or more difference from the previous writing position correction amount with the current paper feed tray 10 and media type are satisfied.

[0087] If the determination result is affirmative (Yes), the control unit 100 executes the above-described step S108. On the other hand, if it is negative (No), the process proceeds to step S204 described below.

[0088] <Step S204> After the above-described step S108 (or when the determination result in the above-described step S203 is No), the control unit 100 calculates the average value Skew_ave[Tray][Media] of the skew amounts for the most recent N_Skew times based on the current paper feed tray 10 and the media type by the following equation (10). Skew_ave[Tray][Media] =(Skew[Tray][Media][1]+Skew[Tray][Media][2]+…+Skew[Tray][Media][N_Skew]) / N_Skew …(10)

[0089] <Step S205> The control unit 100 determines whether it is possible to reset the amount of protrusion based on the current paper feed tray 10 and the media type. As an average value calculation condition, the control unit 100 may determine, for example, whether the condition of having printed N_Skew sheets or more is satisfied based on the current paper feed tray 10 and the media type. Further, as a countermeasure against false detection and statistical error, the control unit 100 may determine whether conditions such as (1) having printed a certain number of sheets or more since the previous change in the amount of protrusion based on the current paper feed tray 10 and the media type, and (2) having a certain difference or more from the skew amount at the time of the previous change in the amount of protrusion based on the current paper feed tray 10 and the media type are satisfied.

[0090] If the determination result is affirmative (Yes), the control unit 100 executes the above-described step S111. On the other hand, if it is negative (No), the process proceeds to the above-described step S113. Since the subsequent processing is the same as that of the first embodiment, the description thereof is omitted.

[0091] (B-3) Effects of the Second Embodiment According to the second embodiment, in addition to the effects described in the first embodiment, the following effects are achieved.

[0092] Since the printer 1A measures the skew amount for each type of medium in the paper feed tray 10, calculates and applies the protrusion amount, it is possible to set a more suitable protrusion amount compared to the first embodiment. Further, when using the previous set value, since the protrusion amount corresponding to the paper feed tray 10 and the type of medium can be set, printing can be performed with a suitable set value immediately after printing.

[0093] (C) Other Embodiments The present invention is not limited to the above-described embodiments, and modified embodiments as exemplified below can also be cited.

[0094] (C-1) In the above-described embodiment, an electrophotographic printer is exemplified as the image forming apparatus, but the present invention is also applicable to a copying machine, a multifunction peripheral, etc.

[0095] (C-2) In the above-described embodiment, the transfer belt 31 and the toner are discriminated by the reflection intensity sensor 37, but other sensors may be used as long as discrimination is possible.

[0096] (C-3) In the above-described embodiment, the description has been made of an apparatus having only a single-sided printing paper conveyance path, but the present invention may be applied to an apparatus having a double-sided printing paper conveyance path. In this case, in the second embodiment, the writing position correction amount and the skew amount are stored for each paper feed tray, and the writing position correction amount and the protrusion amount are calculated and applied. However, paper feeding from the double-sided printing paper conveyance paths with different skew factors will also be individually stored, calculated, and applied.

Explanation of Reference Numerals

[0097] 1, 1A... printer, 10... paper feed tray, 11... placement table, 12... pickup roller, 13... spring, 14... conveyance roller, 15... conveyance roller, 16... discharge roller, 17... writing sensor, 20... image forming unit, 30... transfer unit, 31... transfer belt, 32... transfer roller, 33, 34... belt conveyance roller, 35... cleaning blade, 36... waste toner box, 37(37L, 37R)... reflection intensity sensor, 50... fixing unit, 51... fixing roller, 60... stacker, 70... conveyance mechanism unit, 100... control unit, 101... communication control unit, 102... printing control unit, 103... fixing control unit, 104... conveyance control unit, 105... image forming control unit, 106... output amount control unit, 110... flash ROM, 120... RAM, 140... interface, 300... protruding toner, P... paper, Rt... paper conveyance path, T... paper feed path.

Claims

1. An image forming unit including an image carrier and forming a developer image on the image carrier; A transfer unit transferring the developer image formed by the image forming unit onto a medium; A detection unit detecting a residual developer image protruding from the medium on the transfer unit; A control unit calculating an inclination amount of the medium based on a detection result of the detection unit and controlling a size of the developer image formed by the image forming unit based on the inclination amount; An image forming apparatus, characterized by comprising the above components.

2. When performing borderless printing in which a developer image larger than the medium is formed and the developer image is transferred until it reaches the edge of the medium, the control unit calculates a writing position correction amount based on the detection result and a preset protrusion amount, and controls a writing position on the medium based on the writing position correction amount. The image forming apparatus according to claim 1, characterized by the above.

3. Comprising a plurality of medium storage units for storing the medium; The control unit calculates a writing position correction amount based on the detection result and a preset protrusion amount according to each medium storage unit and the type of the medium, and controls a writing position on the medium based on the writing position correction amount. The image forming apparatus according to claim 2, characterized by the above.

4. Comprising a plurality of medium storage units for storing the medium; The control unit calculates an inclination amount of the medium according to each medium storage unit and the type of the medium, and controls a size of the developer image based on the inclination amount. The image forming apparatus according to claim 1, characterized by the above.

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