Image forming device

Abstract

To perform image formation while avoiding an image from protruding from a sheet when performing printing on a non-standard size sheet.SOLUTION: An image forming apparatus comprises: a controller unit 201 that outputs an image signal with reference to a timing signal; notification means that notifies an image size; an image control unit 206 that forms an image on a photoconductor drum 1 based on the image signal from the controller unit 201; a sheet conveying unit 208 that feeds sheets on an MP tray 50; a transfer unit that transfers the image formed on the photoconductor drum 1 to a sheet; a registration sensor 35 that is arranged between the MP tray 50 and the transfer unit and detects a sheet; and an MP tray conveyance sensor 52 that is arranged at a position separated from the registration sensor 35 on the upstream side of a conveyance path by a distance longer than a sheet that is fed from the sheet conveying unit 208 and has the maximum length in a conveyance direction, and detects a sheet. The image control unit 206 outputs the timing signal to the controller unit 201 according to the timing when the MP tray conveyance sensor 52 detects a first recording material (S620-S625).SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus utilizing an electrophotographic system. [Background technology]

[0002] Conventionally, an image forming apparatus having an intermediate transfer body has been known as an electrophotographic image forming apparatus. In a primary transfer process, a toner image formed on a photosensitive drum, which is an image carrier, is transferred to an intermediate transfer body (hereinafter referred to as an intermediate transfer belt). After that, this primary transfer process is repeatedly performed on the toner images formed in each of the image forming stations of yellow (Y), magenta (M), cyan (C), and black (Bk), thereby forming a multi-color toner image on the intermediate transfer belt.

[0003] Paper loaded in the paper feed section is fed into the machine at any timing. When the leading edge of the fed paper is detected by a transport sensor installed downstream of the paper feed section, the transport is controlled so that the toner image formed on the intermediate transfer belt is transferred to the appropriate position of the fed paper in the secondary transfer process. The toner image transferred to the paper is then fixed to the paper by a fixing device, forming a color image.

[0004] In such an image forming apparatus, the controller receives print data from an external device such as a host computer and develops bitmap data based on the received print data. After the controller finishes developing the bitmap data, it outputs the developed bitmap data as video data to the engine section that controls image formation. The controller section has a development circuit corresponding to each image forming station in order to transmit video data to each image forming station controlled by the engine section. The controller section transmits the video data to each image forming station via the development circuit in accordance with an image write signal (hereinafter referred to as a / TOP signal) output from the engine section, thereby forming an image.

[0005] On the other hand, image forming devices assume that users use non-standard size paper and often have a multipurpose tray (hereinafter referred to as MP tray) for non-standard size paper. When printing on non-standard size paper transported from the MP tray, the engine unit is required to perform appropriate printing according to the size of the paper without causing transport problems such as paper jams, regardless of the size of the paper (length of the paper in the transport direction).

[0006] For example, in Patent Document 1, when the size of the paper placed on the MP tray is unknown, image formation control and transport control are performed based on the maximum size of paper that can be placed on the paper feed section.The paper size is then measured by a transport sensor, and when the paper size is determined, the image formation control and transport control are changed to match the determined paper size.This makes it possible to perform printing operations without causing transport failures, thereby improving throughput and suppressing declines in productivity. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-143795 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the image forming device proposed in Patent Document 1, when printing on non-standard size paper, the size of the paper is measured while the paper is being transported by a registration sensor (hereinafter referred to as the registration sensor) located upstream of the transport path near the secondary transfer unit. The registration sensor not only corrects misalignment of the paper, but is also used as a sensor for changing the paper transport speed or, in some cases, stopping the paper transport temporarily so that the toner image formed on the intermediate transfer belt and the transfer position of the paper coincide with each other at the secondary transfer unit.

[0009] In the image forming apparatus having the above-mentioned configuration, when printing on paper of a non-standard size, if the size of the image formed by the controller unit (image length in the transport direction) is larger than the size of the paper loaded in the paper feed unit (paper length in the transport direction), the following situation occurs. That is, until the registration sensor completes measuring the size of the paper, image formation is performed according to the image sent from the controller unit, so that the formed image is transferred to the secondary transfer unit so as to extend beyond the paper. When such a printing operation is performed, the amount of waste toner increases due to an increase in waste toner consumption, and as a result, there is a risk that the waste toner may overflow from the waste toner container that contains the waste toner. In addition, the secondary transfer roller is stained by the image that extends beyond the paper being transferred by the secondary transfer roller, and as a result, the stain on the secondary transfer roller is transferred to the subsequent paper, causing problems such as image defects.

[0010] The present invention has been made under such circumstances, and has an object to form an image without the image extending beyond the edge of the paper when printing on paper of a non-standard size. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0012] (1) An output means for converting image information into an image signal and outputting the image signal based on a timing signal; a notification means for notifying an image size, which is the length of an output section of the image signal; an image forming means for forming an image on an image carrier based on the image signal output from the output means; a feeding means for feeding a recording material loaded in a paper feed section; a transfer means for transferring the image formed on the image carrier to the recording material fed by the feeding means; a first detection means disposed on a recording material transport path between the paper feed section and the transfer means for detecting the recording material; The upper limit size determined in the control when forming an image on a recording material of unknown sizeand a second detection means that is arranged at a position farther away from the first detection means than the length of the recording material in the transport direction, and detects the recording material, wherein the image forming means outputs the timing signal to the output means in accordance with the timing at which the second detection means detects the first sheet of recording material in a print job. Effect of the Invention

[0013] According to the present invention, when printing on paper of a non-standard size, an image can be formed without the image extending beyond the edge of the paper. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus according to first and second embodiments. [Diagram 2] A control block diagram illustrating a system configuration of an image forming apparatus according to first and second embodiments. [Diagram 3] 1 is a timing chart of a conventional printing operation for comparison with an embodiment of the present invention. [Figure 4] 1 is a diagram showing a configuration of a sheet conveying path of an MP tray in an image forming apparatus according to the first and second embodiments; [Diagram 5] Timing chart for printing operation in the first embodiment [Figure 6] A flowchart showing a control sequence of an image control unit and a paper transport unit according to the first embodiment. [Figure 7] Timing chart of printing operation in the second embodiment [Figure 8] A flowchart showing a control sequence of an image control unit and a paper transport unit according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. EXAMPLES

[0016] [Configuration of image forming device] FIG. 1 is a cross-sectional view showing the overall configuration of a laser printer as an example of an image forming apparatus according to the first embodiment. The image forming apparatus shown in FIG. 1 has four image forming stations, which are image forming stations having yellow (Y), magenta (M), cyan (C), and black (Bk) toners from the left in the figure. The suffixes a, b, c, and d in the reference numerals in the figure indicate the components of the image forming stations of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. The image forming stations have the same configuration, and in the following description, the reference numerals a to d will not be used unless otherwise necessary.

[0017] [Image forming section] In each image forming station, the photosensitive drum 1, which is an image carrier, is driven by a drive motor (not shown) and rotated in the direction of the arrow (counterclockwise direction) in the figure. The charging roller 2, which is a charging means, contacts the photosensitive drum 1 and rotates in accordance with the rotation of the photosensitive drum 1, uniformly charging the surface of the photosensitive drum 1. A voltage in which a DC voltage or an AC voltage is superimposed is applied to the charging roller 2, and the photosensitive drum 1 is charged through the contact nip portion between the charging roller 2 and the surface of the photosensitive drum 1. The scanning unit 11, which is an exposure means, is composed of a scanner unit or an LED array that deflects a laser beam by a rotating polygon mirror and scans the surface of the photosensitive drum 1 with the deflected laser beam. The scanning unit 11 irradiates the photosensitive drum 1 with a laser beam 12 modulated based on a video signal (image signal), forming an electrostatic latent image on the surface of the photosensitive drum 1. The developing unit 8, which is a developing means, is composed of a developing roller 4 that contacts the photosensitive drum 1, a developer (toner) 5, and a developer application blade 7, and develops the electrostatic latent image formed on the photosensitive drum 1 by attaching the toner to it, thereby forming a toner image. The waste toner container 3 collects the toner that remains on the photosensitive drum 1 without being transferred to the intermediate transfer belt 80 described later.

[0018] The process cartridge 9 is an integrated cartridge that incorporates the photosensitive drum 1, charging roller 2, waste toner container 3, and developing unit 8 and is detachably mountable to the image forming apparatus. The charging roller 2 and developing roller 4 are connected to a charging voltage power source 20, which is a means for supplying voltage to the charging roller 2, and a developing voltage power source 21, which is a means for supplying voltage to the developing roller 4, respectively. By bringing the charging roller 2 into contact with the photosensitive drum 1 and applying a charging voltage from the charging voltage power source 20 to the charging roller 2, the surface of the photosensitive drum 1 is charged uniformly to a uniform potential.

[0019] The intermediate transfer belt 80 is supported by three rollers, namely, a secondary transfer counter roller 86, a driving roller 14, and a tension roller 15, which are tension members, and is configured to maintain an appropriate tension. The intermediate transfer belt 80 is driven by the driving roller 14 and moves at approximately the same speed in the direction of the arrow in the figure. The primary transfer roller 81 is disposed at a position facing the photosensitive drum 1 via the intermediate transfer belt 80, and is connected to a primary transfer voltage power source 84, which is a voltage supply means to the primary transfer roller 81. By applying a primary transfer voltage to the primary transfer roller 81, the toner image formed on the photosensitive drum 1 is sequentially transferred to the intermediate transfer belt 80 in contact with the photosensitive drum 1, and a multi-color image is formed on the intermediate transfer belt 80. Furthermore, a charge removing member 23 is disposed downstream of each primary transfer roller 81 in the moving direction of the intermediate transfer belt 80. The driving roller 14, the tension roller 15, the charge removing member 23a, and the secondary transfer counter roller 86 are electrically grounded.

[0020] [Cassette feeding section] A sheet P1, which is a recording material, is placed on the paper feed cassette 16. When feeding the sheet P1 (hereinafter simply referred to as paper), a stepping motor (hereinafter referred to as a paper feed motor) (not shown) drives the cassette pickup roller 17 and raises the paper feed cassette bottom plate 29, pushing it up toward the cassette pickup roller 17. Then, the topmost sheet P1 placed on the raised paper feed cassette bottom plate 29 comes into contact with the cassette pickup roller 17, and the cassette pickup roller 17 rotates, so that the sheets P1 are separated and fed one by one. The fed sheet P1 is conveyed to the registration roller 18, and when a registration sensor (hereinafter referred to as a registration sensor) 35, which is a first detection means for detecting the recording material, detects the leading edge of the sheet P1, the driving of the paper feed motor is stopped, and the conveyance of the sheet P1 is temporarily stopped.

[0021] The position where the secondary transfer roller 82 and the intermediate transfer belt 80 come into contact is called the secondary transfer portion. The sheet P1, which is temporarily stopped by the registration roller (hereinafter referred to as the registration roller) 18, resumes being conveyed (also referred to as being re-fed) at the timing when the toner image formed on the intermediate transfer belt 80 is transferred to an appropriate position on the sheet P1 at the secondary transfer portion. The size of the sheet P1 (length in the conveying direction; hereinafter referred to as the paper size) is determined based on the elapsed time from the timing (time) when the sheet P1 is re-fed to the timing (time) when the registration sensor 35 detects the rear end of the sheet P1.

[0022] Here, the distance from the secondary transfer unit to the registration sensor 35 is defined as distance A. Image formation is started from the secondary transfer unit based on the timing when a / TOP signal, which will be described later, is output, and laser light 12a is irradiated from the scanning unit 11a to form an electrostatic latent image. The distance from the secondary transfer unit to an exposure unit (exposure position) where the laser light 12a is irradiated from the scanning unit 11a on the photosensitive drum 1a of the most upstream image forming station (yellow (Y)) is defined as distance B. Then, the registration sensor used to measure the paper size of sheet P1 is disposed at a position that satisfies the following (Equation 1). Distance A < Distance B (Equation 1)

[0023] [MP tray feeding section] A sheet P2, which is a recording material, is placed on the MP tray 50. When feeding the sheet P2 (hereinafter also simply referred to as paper), the MP tray pickup roller 51 is driven by the above-mentioned paper feed motor (not shown). The uppermost sheet P2 placed on the MP tray 50 abuts against the MP tray pickup roller 51, and is fed into the image forming apparatus by the driven MP tray pickup roller 51. The fed sheet P2 is conveyed to the registration roller 18 via a conveying path for the sheet P2 fed from the MP tray 50, which is provided in the image forming apparatus. The sheet P2 conveyed to the registration roller 18 is printed in the same manner as the sheet P1 fed from the paper feed cassette 16.

[0024] [Secondary transfer section] The intermediate transfer belt 80, onto which the toner images formed on the photosensitive drums 1 of the image stations have been transferred, is moved by the drive roller 14, and the toner images on the intermediate transfer belt 80 are transported to a secondary transfer section where a secondary transfer roller 82 and the intermediate transfer belt 80 come into contact with each other. Then, in the secondary transfer section, which is a transfer means, the sheet P (sheet P1 or sheet P2) and the intermediate transfer belt 80 are sandwiched and transported by the secondary transfer roller 82 and a secondary transfer opposing roller 86 installed opposite the secondary transfer roller 82. Then, a voltage is applied from a secondary transfer voltage power source 85 to the secondary transfer roller 82, so that the toner image on the intermediate transfer belt 80 is transferred to the sheet P.

[0025] [Fixing section] The sheet P onto which the toner image has been transferred in the secondary transfer section is conveyed to the fixing section 19, which is a fixing means, and is heated and pressurized in the fixing section 19, so that the toner image is fixed to the sheet P. The fixing section 19 has a fixing belt 19a and a pressure roller 19b, and the pressure roller 19b is in contact with the fixing belt 19a by a belt guide member (not shown) and a predetermined pressure contact force, forming a fixing nip section. In a state in which the temperature of the fixing nip section is adjusted to a predetermined temperature, the sheet P onto which the unfixed toner image has been transferred is introduced between the fixing belt 19a and the pressure roller 19b in the fixing nip section with the image surface facing upward, i.e., facing the fixing belt 19a. Then, in the fixing nip section, the sheet P is nipped and conveyed through the fixing nip section with the image surface of the sheet P in close contact with the outer surface of the fixing belt 19a. In the process in which the sheet P is nipped and conveyed through the fixing nip section by the fixing belt 19a, the toner image on the sheet P is heated by the fixing belt 19a and is thermally fixed onto the sheet P. The sheet P on which the toner image has been fixed is then discharged onto the discharge tray 36, and a series of printing operations is completed.

[0026] [System configuration of image forming device] FIG. 2 is a control block diagram for explaining the system configuration of the image forming apparatus. In FIG. 2, the image forming apparatus includes a controller unit 201 and an engine unit 202. The controller unit 201 can communicate with a host computer 200, which is an external device, and the engine unit 202. When the controller unit 201 receives a print command including image information (print data) and print conditions from the host computer 200, the controller unit 201 develops bitmap data (image data) based on the received print data. When the controller unit 201 finishes developing the bitmap data, the controller unit 201 transmits image size information and a print reservation command to a CPU 204 of the engine unit 202 via a video interface unit 203 in accordance with the print command from the host computer 200. Then, the controller unit 201 transmits a print start command to the CPU 204 at the timing when the engine unit 202 becomes ready to print (ready to form an image).

[0027] The engine unit 202 is composed of a video interface unit 203, a CPU 204, an image processing GA (gate array) 205, an image control unit 206, a fixing control unit 207, and a paper transport unit 208. The CPU 204, the image processing GA 205, the image control unit 206, the fixing control unit 207, and the paper transport unit 208 are connected via a bidirectional bus, and transmit and receive data to and from each other via the bidirectional bus. The video interface unit 203 relays signals between the engine unit 202 and the controller unit 201. The image control unit 206 controls the image forming unit described above, the fixing control unit 207 controls the fixing unit 19 described above, and the paper transport unit 208 controls the cassette feed unit and the MP tray feed unit described above. When the CPU 204 receives a print reservation command from the controller unit 201, it prepares to execute a print job and waits for a print start command to be sent from the controller unit 201. When the CPU 204 receives a print start command from the controller unit 201, it instructs each control unit (image control unit 206, fixing control unit 207, paper transport unit 208) to start a printing operation (also called a print operation) in accordance with the information of the print reservation command already received.

[0028] CPU 204 has a ROM (not shown) and a RAM (not shown), the ROM stores the control programs and data executed by CPU 204, and the RAM is used by the control programs executed by CPU 204 to temporarily store information. CPU 204 also has a timer. Image control unit 206, paper transport unit 208, etc. also have a CPU (not shown), ROM (not shown), RAM (not shown), and a timer for measuring time. Like CPU 204, the ROM stores the control programs and data, and the RAM is used by the control programs to temporarily store information.

[0029] When the image control unit 206, which is a control means, receives an instruction to start a print operation from the CPU 204, it starts preparation for image formation. When the CPU 204 receives a notification from the image control unit 206 that preparation for image formation is complete, it outputs a / TOP signal, which is a timing signal that serves as a reference for outputting a video signal, to the controller unit 201 via the video interface unit 203. When the controller unit 201, which is an output means, receives the / TOP signal from the CPU 204, it outputs a video signal generated from bitmap data based on the timing of receiving the / TOP signal to the image processing GA 205 via the video interface unit 203. When the image processing GA 205 receives a video signal from the controller unit 201, it converts the received video signal into data for image formation and transmits it to the image control unit 206. The image control unit 206 performs image formation based on the data for image formation received from the image processing GA 205. When performing continuous printing, as described below, image control unit 206 determines an image formation interval, which is a time interval (period) at which a / TOP signal is output, based on the paper size of sheet P or an image size, described below, received from controller unit 201. Then, image control unit 206 instructs CPU 204 to send a / TOP signal in accordance with the determined image formation interval.

[0030] The paper transport unit 208, which is a feeding means, starts the feeding operation when it receives an instruction to start the printing operation from the CPU 204. The paper transport unit 208 drives a paper feed motor (not shown) to transport the sheet P placed on the MP tray 50 or the paper feed cassette 16 (hereinafter also referred to as the paper feed unit) to the secondary transfer unit, and detects the paper size of the sheet P using the register sensor 35 (FIG. 1). Note that the paper size of the sheet P placed on the paper feed unit is indefinite from the start of the printing operation until the register sensor 35 detects the paper size.

[0031] The fixing control unit 207 starts preparation for fixing processing when it receives an instruction to start a printing operation from the CPU 204. The fixing control unit 207 starts temperature adjustment according to the paper type information (e.g., the thickness of the sheet P) set in the print reservation command, in accordance with the timing when the sheet P on which the secondary transfer has been performed is transported to the fixing unit 19. Then, the fixing control unit 207 fixes the image (toner image) on the sheet P, and then transports the sheet P to the discharge tray 36 outside the machine and discharges it.

[0032] [Printing behavior overview] Next, a printing operation of the image forming apparatus for a sheet P of unknown paper size (also called non-standard size) at the time when the host computer 200 instructs printing on the sheet P placed on the MP tray 50 (at the start of a print job) will be described. In this embodiment, the minimum required interval between the preceding sheet P and the succeeding sheet P (hereinafter called the paper interval) for performing the printing operation is 40 mm. In addition, in the non-standard size printing control in the image forming apparatus of this embodiment, the upper limit size of the non-standard size sheet P is A4 size. In the following description, the image size formed by the controller unit 201 is A4 size (length in the transport direction: 297 mm), and the size of the sheet P actually placed on the MP tray 50 is A5 landscape size (paper length in the transport direction: 148 mm).

[0033] [Outline of conventional printing operations] First, the printing operation of a conventional image forming apparatus that performs printing according to the paper size of sheet P detected by registration sensor 35 will be described with reference to Fig. 3. Fig. 3 is a timing chart showing the signal states related to the printing operation when continuous printing is performed and the paper size of sheet P placed on MP tray 50 is unknown at the time when the printing operation is instructed. In Fig. 3, the vertical axis indicates, from top to bottom, (a) the / TOP signal, (b) the video signal, (c) the paper feed start signal, and (d) the state of registration sensor 35, and the horizontal axis indicates time.

[0034] In (a), / TOP signals 301, 302, and 303 are signals transmitted from the engine unit 202 to the controller unit 201. Timage 304, Timage 305, and Tpaper 306 indicate image formation intervals, which are intervals at which the CPU 204 outputs the / TOP signal. In (b), hatched outputs 311, 313, and 315 indicate sections (output sections) in which image formation is performed based on a video signal from the controller unit 201, and non-outputs 312, 314, and 316 indicate sections in which image formation is not performed based on a video signal. In (c), feed start signals 321, 322, and 323 are signals indicating the feed start timing of a sheet P placed on the MP tray 50. In (d), ON and OFF indicate a state in which the register sensor 35 detects a sheet P and a state in which the register sensor 35 does not detect a sheet P, respectively. Timings 331 and 333 at which the registration sensor 35 changes from an OFF state to an ON state indicate the timing at which the registration sensor 35 detects the leading edge of the transported sheet P. Meanwhile, timings 332 and 334 at which the registration sensor 35 changes from an ON state to an OFF state indicate the timing at which the registration sensor 35 detects the trailing edge of the transported sheet P. Also, a hatched feed motor stop section 335 indicates a section (period) during which the drive of the feed motor is stopped until transport of the sheet P is resumed (timings 337 and 338) in accordance with the position at which the toner image formed on the intermediate transfer belt 80 is transferred to the sheet P.

[0035] When the engine unit 202 receives a print start command from the controller unit 201, it performs a preparation operation for the print operation. Then, when the print preparation operation is completed, the engine unit 202 outputs a / TOP signal 301 for the first sheet P to the controller unit 201, and thereafter outputs / TOP signals 302 and 303 for the subsequent sheets P so that the distance between the sheets P becomes a desired interval. When the engine unit 202 receives a print start command from the controller unit 201, it starts an operation of feeding the sheet P from the MP tray 50 at a predetermined timing (feed start signals 321, 322, 323). The engine unit 202 temporarily stops the conveyance of the sheet P (feed motor stop section 335) when the sheet P reaches the register sensor 35 (timings 331 and 333). Then, the engine unit 202 resumes transporting the sheet P at the timing when the toner image formed on the intermediate transfer belt 80 is transferred to an appropriate position on the sheet P at the secondary transfer unit (timings 337 and 338), and the toner image is transferred to the sheet P.

[0036] In this embodiment, before transmitting a print start command to the CPU 204 of the engine unit 202, the controller unit 201 notifies the CPU 204 of the engine unit 202 of the image size of the image that the controller unit 201 will output to the engine unit 202. The CPU 204 notifies the image control unit 206 of the notified image size. Thereafter, the controller unit 201 transmits a print start command to the CPU 204 of the engine unit 202.

[0037] The timing chart shown in FIG. 3 will be described in detail. When the CPU 204 of the engine unit 202 receives a notification from the image control unit 206 that image formation preparation is complete, it outputs a / TOP signal 301 for the first sheet P to the controller unit 201. At this point, the paper size of the sheet P placed on the MP tray 50 is unknown. Therefore, the image control unit 206 sets the paper size of the sheet P to A4 size, which is the upper limit size of non-standard size control, and sets the output interval T, which is the time interval for outputting a / TOP signal for the subsequent sheet P, to Timage 304. In addition, since the image formation size notified from the host computer 200 is A4 size as described above, the controller unit 201 outputs a video signal 311 equivalent to A4 size to the engine unit 202. The image control unit 206 performs image formation based on the video signal 311 output from the controller unit 201.

[0038] The output interval Timage304 shown in (a) is specifically the time required for an A4 size sheet P (paper length in the transport direction is 297 mm) to be transported on the transport path at a predetermined transport speed while maintaining the paper interval (40 mm) with the succeeding sheet P. For convenience of explanation, the output interval T will be expressed as a length rather than a time. For example, the output interval Timage, when expressed as a length, is 337 mm, which is the sum of the A4 size (length in the transport direction: 297 mm) and the paper interval (40 mm). The image control unit 206 determines the output interval T of the / TOP signal, and instructs the CPU 204 to send a / TOP signal every time the output interval T has elapsed, and the CPU 204 outputs the / TOP signal to the controller unit 201.

[0039] The paper transport unit 208 feeds the first sheet P from the MP tray 50 in response to a paper feed start signal 321. When the fed sheet P reaches the register sensor 35 (timing 331), the paper transport unit 208 stops the paper feed motor (paper feed motor stop section 335) and temporarily stops the transport of the sheet P. Thereafter, the paper transport unit 208 resumes the transport of the sheet P at a timing (timing 337) when the toner image formed on the intermediate transfer belt 80 is transferred to an appropriate position on the sheet P by the secondary transfer unit, and transfers the toner image on the intermediate transfer belt 80 to the sheet P by the secondary transfer unit. Then, the paper transport unit 208 determines the paper size of the first sheet P at a timing (timing 332) when the register sensor 35 detects the rear end of the sheet P (paper size detection timing 336) and notifies the image control unit 206 of the paper size of the sheet P.

[0040] The paper transport unit 208 can determine (detect) the paper size, which is the length in the transport direction of the sheet P, by multiplying the time from when the transport of the sheet P is resumed until the registration sensor 35 detects the rear end of the sheet P by the transport speed of the sheet P. The time from when the transport of the sheet P is resumed until the registration sensor 35 detects the rear end of the sheet P is also the time obtained by subtracting the time of the feed motor stop section 335 from the time 331 to the time 332 shown in Fig. 3. Also, while the paper size of the sheets P stacked on the MP tray 50 is unknown, the feeding of the sheets P is controlled based on the A4 size so that the sheets P can be transported normally even if A4 size sheets P, which are the maximum size in the non-standard size print control described above, are stacked.

[0041] Based on the paper size of the first sheet P (A5 landscape in this embodiment) notified from the paper transport unit 208, the image control unit 206 sets the output interval T of the / TOP signal for the subsequent sheet P to Tpaper306. Specifically, the output interval Tpaper306 is the time required for a sheet P with a paper size of A5 landscape (paper length in the transport direction 148 mm) to be transported on the transport path at a predetermined transport speed while maintaining the paper interval (40 mm) with the subsequent sheet P. Note that hereinafter, the output interval Tpaper is indicated not as time but as the length of A5 landscape size (paper length 148 mm) + paper interval (40 mm).

[0042] In an image forming apparatus configured to satisfy the above-mentioned condition (Formula 1), when the size of the image to be formed is the same as the size of the sheets P stacked in the paper feed section, image formation on the first sheet P is always completed at the time 336 when the size of the sheets P is determined. In an image forming apparatus having such a configuration, an image is first formed based on a video signal, and then the sheet P is fed from the paper feed section. Therefore, as can be seen from FIG. 3, during non-standard size print control, at the time 336 when the paper size of the first sheet P stacked on the MP tray 50 is determined by the registration sensor 35, image formation on the third sheet P is already being performed. Therefore, the output interval T when the / TOP signals 302 and 303 are output is the above-mentioned time interval Timage 304 and Timage 305 because the paper size of the first sheet P is unknown. In addition, the video signal outputs 311 and 313 are also performed in the A4 size specified by the controller unit 201.

[0043] If the output interval Tpaper306 has already elapsed since the / TOP signal 303 was output at the time of paper size detection timing 336, the image control unit 206 instructs the CPU 204 at that time to output a / TOP signal (not shown) for the next sheet P. On the other hand, if the output interval Tpaper306 has not elapsed since the / TOP signal 303 was output at the time of paper size detection timing 336, the image control unit 206 performs the following process. That is, when the output interval Tpaper306 has elapsed, the image control unit 206 instructs the CPU 204 to output the / TOP signal. Thereafter, when performing continuous printing, the image control unit 206 sets the output interval T of the / TOP signal to Tpaper306 and performs the printing operation.

[0044] Also, the size of the image to be formed, which is output by the video signal, is determined at timing 336 when the paper size is detected. The image control unit 206 determines whether or not a time equivalent to the paper size of the sheet P (the time required for the sheet P of the determined paper size to be conveyed) has elapsed since the / TOP signal (303) as follows. That is, the image control unit 206 makes a determination based on the paper size of the sheet P calculated at the paper size detection timing 336 and the time from the timing when the / TOP signal 303 is output to the paper size detection timing 336. If the image control unit 206 determines that a time equivalent to the paper size of the sheet P has not elapsed since the / TOP signal 303 was output, the image control unit 206 outputs 315 the video signal for the detected paper size of the sheet P. On the other hand, if the image control unit 206 determines that a time equivalent to the paper size of the sheet P has elapsed since the / TOP signal 303 was output, the image control unit 206 stops outputting the video signal at the paper size detection timing 336 and sets it to non-output 316. In this case, "masking the image" refers to not outputting the video signal output of the controller unit 201 that is attempting to form an A4 size image in accordance with the paper size of the sheet P. Also, the size of the image that is finally output after masking the image is referred to as the "masked image size."

[0045] As described above, in the example of print control of non-standard size shown in FIG. 3, the timing when the non-standard size paper size is determined (paper size detection timing 336 in the figure) is during image formation of the third sheet P. That is, for the first and second sheets P, images of a size larger than the paper size (A5 landscape) of the sheets P actually stacked on the MP tray 50 are formed. When continuous printing is performed in this situation, after the toner images of the first and second sheets P are transferred at the secondary transfer section, toner that could not be transferred to the sheet P remains on the intermediate transfer belt 80 and is collected in the waste toner container 3 of the process cartridge 9. In addition, the toner image that was not transferred to the sheet P on the intermediate transfer belt 80 adheres to the secondary transfer roller 82, and the toner image that adheres is transferred to the next sheet P, soiling the next sheet P and causing image defects.

[0046] [Configuration of the transport path from the MP tray to the register sensor in this embodiment] Next, in order to prevent the situation as shown in Figure 3 described above from occurring, the printing operation of this embodiment will be described in which image formation is performed from the first sheet onwards according to the paper size of the sheet P loaded on the MP tray 50, thereby preventing the generation of waste toner and toner stains on the secondary transfer roller 82.

[0047] 4 is a diagram showing the configuration of the transport path of the sheet P loaded on the MP tray 50 from the MP tray 50 to the registration sensor 35 in this embodiment. As shown in FIG. 4, an MP tray transport sensor 52 (second detection means) for detecting the sheet P transported from the MP tray 50 is disposed in the middle of the transport path from the MP tray 50 to the registration sensor 35. The MP tray transport sensor 52 is installed at a position away from the registration sensor 35 in the direction toward the MP tray 50 (upstream of the transport direction of the sheet P) by at least the upper limit size (length in the transport direction is D) of the non-standard size control. That is, if the distance from the registration sensor 35 to the MP tray transport sensor 52 is distance C, the length (distance) D in the transport direction and distance C satisfy the following (Equation 2). Distance C>Distance D (Formula 2)

[0048] In this embodiment, the upper limit size for non-standard size control is A4 size (paper length in the transport direction: 297 mm), and the MP tray transport sensor 52 is installed at a position more than 297 mm away from the registration sensor 35 in the direction of the MP tray 50 (upstream in the transport direction).

[0049] [Outline of the printing operation of this embodiment] Next, an outline of the printing operation of this embodiment will be described. Fig. 5 is a timing chart showing the signal states related to the printing operation when continuous printing of non-standard size sheets P is performed using the detection result of the MP tray transport sensor 52 described above. In Fig. 5, the vertical axis indicates, from the top, (a) the / TOP signal, (b) the video signal, (c) the paper feed start signal, (d) the state of the register sensor 35, and (e) the state of the MP tray transport sensor 52, and the horizontal axis indicates time.

[0050] In (e), ON and OFF respectively indicate a state in which the MP tray transport sensor 52 detects a sheet P and a state in which the MP tray transport sensor 52 does not detect a sheet P. Timings 551, 553, and 555 at which the state of the MP tray transport sensor 52 changes from the OFF state to the ON state indicate the timing at which the MP tray transport sensor 52 detects the leading edge of the sheet P being transported. Meanwhile, timings 552, 554, and 556 at which the state of the MP tray transport sensor 52 changes from the ON state to the OFF state indicate the timing at which the MP tray transport sensor 52 detects the trailing edge of the sheet P being transported. The meanings of the other signals and how to view the diagram are the same as those in FIG. 3 described above, and therefore description thereof will be omitted.

[0051] When the engine unit 202 receives a print start command from the controller unit 201, it performs a preparation operation for the print operation. The paper transport unit 208 feeds the first sheet P from the MP tray 50 in response to a paper feed start signal 521. The MP tray transport sensor 52 installed on the transport path detects the leading edge of the fed first sheet P (timing 551). The paper transport unit 208 starts measuring the size of the sheet P from the timing when the MP tray transport sensor 52 detects the leading edge of the sheet P (paper leading edge detection timing 557). The paper transport unit 208 can determine (detect) the paper size, which is the length of the sheet P in the transport direction, by multiplying the transport speed of the sheet P by the time from when the MP tray transport sensor 52 detects the leading edge of the sheet P to when it detects the rear end of the sheet P.

[0052] When the image control unit 206 confirms that the MP tray transport sensor 52 has detected the leading edge of the first sheet P and that all other image formation conditions have been prepared, it notifies the CPU 204. When the CPU 204 of the engine unit 202 receives a notification from the image control unit 206 that the leading edge of the first sheet P has been detected by the MP tray transport sensor 52 and that all other image formation conditions have been prepared, it outputs a / TOP signal 501 for the first sheet P. At this point, the paper size of the first sheet P is unknown, so the controller unit 201 forms an A4 size image.

[0053] When the MP tray transport sensor 52 detects the rear end of the first sheet P (timing 552), the paper transport unit 208 ends the size measurement of the sheet P and notifies the image control unit 206 of the detected paper size of the sheet P (paper size detection timing 558). After the paper size of the sheet P is determined, the paper transport unit 208 determines the output timing of the feed start signals 522 and 523 for the subsequent sheet P at a timing according to the determined paper size.

[0054] The image control unit 206 masks the image so that the video signal is not output (512) when a time corresponding to the paper size of the sheet P notified by the paper transport unit 208 has elapsed from the output timing of the / TOP signal 501 for the first sheet. Also, the image control unit 206 sets the output interval T of the / TOP signals 502, 503 for the second and subsequent sheets P as the paper size of the sheet P notified by the paper transport unit 208+paper interval, that is, the time interval Tpaper 504, 505.

[0055] 3 described above, when the fed sheet P reaches the register sensor 35 (timing 531), the paper transport unit 208 stops driving the paper feed motor (paper feed motor stop section 537) and temporarily stops transport of the sheet P. Thereafter, the paper transport unit 208 resumes transport of the sheet P at the timing when the toner image formed on the intermediate transfer belt 80 is transferred to an appropriate position on the sheet P at the secondary transfer unit (timing 538), and the toner image is transferred to the sheet P.

[0056] [Image formation control sequence] Fig. 6 is a flowchart showing a control sequence of non-standard size print control in this embodiment. Fig. 6(a) is a flowchart showing a control sequence of transport control for transporting sheets P stacked on the MP tray 50 to the registration sensor 35. Fig. 6(b) is a flowchart showing a control sequence of image formation control for non-standard size sheets P.

[0057] 6A will be described in detail first. The process shown in FIG. 6A is started when the CPU 204 receives an image size designation command, a print reservation command, or a print start command from the controller unit 201, and is executed by the paper transport unit 208.

[0058] In step (hereinafter, S) 600, the paper transport unit 208 feeds the first sheet P stacked on the MP tray 50. In S601, since the paper size of the fed sheet P is unknown, the paper transport unit 208 sets the post-mask image size to A4 size, which is the maximum size in non-standard size print control, and initializes the image mask size.

[0059] In S602, the paper transport unit 208 determines whether the MP tray transport sensor 52 has detected the leading edge of the sheet P fed from the MP tray 50 (MP tray transport sensor ON?). If the paper transport unit 208 determines that the MP tray transport sensor 52 has detected the leading edge of the sheet P fed from the MP tray 50 and has turned ON, the process proceeds to S603. On the other hand, if the paper transport unit 208 determines that the MP tray transport sensor 52 has not detected the sheet P fed from the MP tray 50 (is OFF), the process returns to S602.

[0060] In S603, the paper transport unit 208 starts measuring the size of the sheet P whose leading edge has been detected (measuring the paper length in the transport direction) (start of paper size measurement). Specifically, the paper transport unit 208 resets and starts a timer to measure the paper size of the sheet P.

[0061] In S604, the paper transport unit 208 determines whether the MP tray transport sensor 52 has detected the rear end of the sheet P fed from the MP tray 50 (MP tray transport sensor OFF?). If the paper transport unit 208 determines that the MP tray transport sensor 52 has detected the rear end of the sheet P fed from the MP tray 50 and has turned OFF, the process proceeds to S606. On the other hand, if the paper transport unit 208 determines that the MP tray transport sensor 52 has not detected the rear end of the sheet P fed from the MP tray 50 (is ON), the process proceeds to S605.

[0062] In S605, the paper transport unit 208 determines whether the registration sensor 35 has detected the leading edge of the sheet P fed from the MP tray 50 (is the registration sensor ON?). If the paper transport unit 208 determines that the registration sensor 35 has detected the leading edge of the sheet P fed from the MP tray 50 and has turned ON, the process proceeds to S608. On the other hand, if the paper transport unit 208 determines that the registration sensor 35 has not detected the leading edge of the sheet P fed from the MP tray 50 (is OFF), the process returns to S604.

[0063] In S606, the paper transport unit 208 stops the timer started in S603 to measure the paper size, ends the measurement of the paper size of the sheet P fed from the MP tray 50, and calculates the paper size of the sheet P fed from the MP tray 50. Specifically, the paper transport unit 208 stops the timer for measuring the paper size, and calculates the paper size of the sheet P (paper length in the transport direction) by multiplying the acquired timer value by the transport speed of the sheet P. In S607, the paper transport unit 208 sets the paper size of the sheet P calculated in S606 as the post-mask image size, and ends the process.

[0064] In S608, the paper transport unit 208 stops the timer for measuring the paper size that was started in S603, and ends the measurement of the paper size of the sheet P fed from the MP tray 50. In S609, the paper transport unit 208 sets the image size specified by the controller unit 201 to the post-mask image size. Note that in this embodiment, the image size specified by the controller unit 201 is A4 size.

[0065] As explained above in (Formula 2), if the registration sensor 35 detects the leading edge of the sheet P before the MP tray transport sensor 52 detects the trailing edge of the sheet P, this indicates that the sheet P being transported is longer than the upper limit size (A4 size) of non-standard size control. In this case, even if the masked image size described below is set to the upper limit size (A4 size) of non-standard size control, the formed image will not protrude from the sheet P. Therefore, in this embodiment, if the registration sensor 35 detects the leading edge of the sheet P before the MP tray transport sensor 52 detects the trailing edge of the sheet P, the A4 size designated by the controller unit 201 is set as the masked image size.

[0066] Next, Fig. 6B will be described in detail. The process shown in Fig. 6B is started when CPU 204 receives an image size designation command, a print reservation command, or a print start command from controller unit 201, and is executed by image control unit 206.

[0067] In S620, the image control unit 206 determines whether the sheet P stacked on the MP tray 50 is fed and the leading edge of the sheet P is detected by the MP tray transport sensor 52 (MP tray transport sensor ON?) as described in Fig. 6(a). If the image control unit 206 determines that the MP tray transport sensor 52 has detected the leading edge of the sheet P fed from the MP tray 50 and has turned ON, the process proceeds to S621. On the other hand, if the image control unit 206 determines that the MP tray transport sensor 52 has not detected the sheet P fed from the MP tray 50 (is in the OFF state), the process returns to S620.

[0068] In S621, image control unit 206 determines whether or not other preparations necessary for image formation have been completed (image formation preparation completed?). The preparations shown here refer to whether or not units necessary for image formation, such as each image forming station and scanning unit 11, are ready. If image control unit 206 determines that other preparations necessary for image formation have been completed, it advances the process to S622, and if it determines that other preparations necessary for image formation have not been completed, it returns the process to S621.

[0069] In S622, image control unit 206 notifies CPU 204 that preparations necessary for image formation have been completed, and upon receiving the notification of completion of image formation preparations from image control unit 206, CPU 204 transmits a / TOP signal (outputs a / TOP signal) to controller unit 201. In S623, image control unit 206 starts a mask start timer for starting image masking.

[0070] In S624, the image control unit 206 refers to the mask start timer and judges whether or not a time equivalent to the paper size set in the masked image size has elapsed (has a time equivalent to the masked image size elapsed?). As described in FIG. 6A, the masked image size is set to the initial value A4 size set in S601 until the measurement of the paper size of the sheet P is completed. Thereafter, when the MP tray transport sensor 52 detects the rear end of the sheet P and the size detection of the sheet P is completed, in the process of S607 described above, the measurement result of the detected paper size of the sheet P is set as the masked image size. Therefore, during the process of S624 in which the mask start timer judges whether or not a time equivalent to the A4 size has elapsed, the masked image size is updated from the A4 size to the paper size based on the measurement result by the MP tray transport sensor 52 (in this embodiment, the A5 landscape size). If the image control unit 206 determines that the time equivalent to the paper size set in the masked image size has elapsed, the process proceeds to S625, and if the image control unit 206 determines that the time equivalent to the paper size set in the masked image size has not elapsed, the process returns to S624. In S625, the image control unit 206 sets an image mask, switches the video signal output to non-output, and ends the process.

[0071] As described above, in the printing control for non-standard sizes, even if the image to be formed is larger than the paper size of the fed sheet P, the image is formed so that the image does not extend beyond the paper from the printing of the first sheet P. This makes it possible to suppress the generation of waste toner and prevent the occurrence of image defects.

[0072] In this embodiment, the size of the sheet P is measured by the MP tray transport sensor 52, and the measured paper size is set as the post-mask image size. Similar control can be performed by notifying the image control unit 206 of the time from when the MP tray transport sensor 52 turns ON to when it turns OFF, and the timing when the MP tray transport sensor 52 turns ON and OFF.

[0073] In addition, in this embodiment, the custom size print control has the upper limit of custom sizes set to A4 size, but this is not necessarily synonymous with the upper limit size supported by the image forming device. For example, an image forming device whose upper limit of supported paper size is LGL (Legal) (paper size: 355.6 mm) has custom size print mode 1 with the upper limit size set to LGL size and custom size print mode 2 with the upper limit size set to A4 size. In this way, there is no particular limit to the supported upper limit size and the size upper limit of custom size print control.

[0074] As described above, according to this embodiment, when printing on paper of a non-standard size, an image can be formed without the image extending beyond the edge of the paper. EXAMPLES

[0075] In the first embodiment, in the non-standard size printing control when the paper size of the sheet placed on the MP tray is unknown, one of the conditions for starting image formation is the detection of the leading edge of the sheet by the MP tray transport sensor that detects the size of the sheet. In the second embodiment, unlike the first embodiment, one of the conditions for starting image formation in the non-standard size printing control is the determination of the paper size of the sheet. Note that the configuration of the image forming apparatus and the system configuration are the same as those in the first embodiment in Figs. 1, 2, and 4, and the same members and control units are designated by the same reference numerals, and detailed description thereof will be omitted.

[0076] [Outline of the printing operation of this embodiment] Next, as in the first embodiment, the printing operation of the image forming apparatus for a sheet P with an unknown paper size (irregular size) at the time when the host computer 200 instructs the printing operation of the sheet P placed on the MP tray 50 (at the start of the print job) will be described. The minimum paper space between sheets P required for the printing operation is 40 mm, as in the first embodiment. In addition, in the irregular size print control in the image forming apparatus of this embodiment, the upper limit size of the irregular size sheet P is A4 size, as in the first embodiment. In the following, the image size formed by the controller unit is A4 size (paper length in the transport direction: 297 mm), and the size of the sheet P actually placed on the MP tray 50 is A5 landscape size (paper length in the transport direction: 148 mm).

[0077] Fig. 7 is a timing chart showing signal states related to a printing operation in which non-standard size sheets P are continuously printed using the detection results of the MP tray transport sensor 52. As with Fig. 5 of the first embodiment, Fig. 7 shows, from the top, the vertical axis (a) indicating the / TOP signal, (b) the video signal, (c) the feeding start signal, (d) the state of the registration sensor 35, and (e) the state of the MP tray transport sensor 52, while the horizontal axis indicates time. The meaning of each signal and how to read the figure are the same as Figs. 3 and 5 of the first embodiment, and therefore description thereof will be omitted here.

[0078] When the engine unit 202 receives a print start command from the controller unit 201, it performs a preparation operation for the print operation. The paper transport unit 208 feeds the first sheet P from the MP tray 50 in response to a paper feed start signal 721. The MP tray transport sensor 52 installed on the transport path detects the leading edge of the fed first sheet P (timing 751). The paper transport unit 208 starts measuring the size of the sheet P from the timing (timing 751) when the MP tray transport sensor 52 detects the leading edge of the sheet P.

[0079] Thereafter, when the MP tray transport sensor 52 detects the rear end of the first sheet P (timing 752), the paper transport unit 208 ends the size measurement of the sheet P and notifies the image control unit 206 of the detected paper size of the sheet P (paper size detection timing 757). Note that the paper transport unit 208 can determine (detect) the paper size, which is the length of the sheet P in the transport direction, by multiplying the time from when the MP tray transport sensor 52 detects the leading end of the sheet P to when it detects the trailing end of the sheet P by the transport speed of the sheet P.

[0080] When the image control unit 206 confirms that the paper size of the first sheet P has been determined and that all other image formation conditions have been prepared, it notifies the CPU 204. When the CPU 204 of the engine unit 202 receives a notification from the image control unit 206 that the paper size of the first sheet P has been determined and that all other image formation conditions have been prepared, it outputs a / TOP signal 701 for the first sheet P. At this point, since the paper size of the first sheet P has already been determined, the engine unit 202 controls the controller unit 201 to mask the A4 size image formed by the controller unit 201 to the A5 landscape size. In other words, it controls the output 711 of the video signal for image formation to be the A5 landscape size in accordance with the paper size of the sheet P.

[0081] The paper transport unit 208 uses the paper size of the first sheet P to determine the output timing of feed start signals 722, 723 for the subsequent sheets P. The image control unit 206 sets the output interval T of / TOP signals 702, 703 for the subsequent sheets P after the first sheet P as the paper size notified by the paper transport unit 208+paper interval, that is, the time interval Tpaper 704, 705.

[0082] 3 in the first embodiment, when the fed sheet P reaches the register sensor 35 (timing 731), the paper transport unit 208 stops driving the paper feed motor (paper feed motor stop section 737) and temporarily stops transport of the sheet P. Thereafter, the paper transport unit 208 resumes transport of the sheet P at the timing when the toner image formed on the intermediate transfer belt 80 is transferred to an appropriate position on the sheet P at the secondary transfer unit (timing 738), and the toner image is transferred to the sheet P.

[0083] [Image formation control sequence] Fig. 8 is a flowchart showing a control sequence of non-standard size print control in this embodiment. Fig. 8(a) is a flowchart showing a control sequence of transport control for transporting sheets P stacked on the MP tray 50 to the registration sensor 35. Fig. 8(b) is a flowchart showing a control sequence of image formation control for non-standard size sheets P.

[0084] The process shown in Fig. 8(a) is started when the CPU 204 receives an image size designation command, a print reservation command, or a print start command from the controller unit 201, and is executed by the paper transport unit 208. The flowchart of the transport control shown in Fig. 8(a) is the same as the control explained in Fig. 6(a) of the first embodiment, and therefore the explanation here will be omitted.

[0085] Next, the process shown in Fig. 8(b) will be described in detail. The process shown in Fig. 8(b) is started when CPU 204 receives an image size designation command, a print reservation command, or a print start command from controller unit 201, and is executed by image control unit 206.

[0086] In S820, the image control unit 206 determines whether or not the measurement of the paper size of the sheet P has been completed (paper size measurement completed?) by the process shown in Fig. 8(a). Here, the process shown in Fig. 8(a) refers to the process of S806 in which the MP tray transport sensor 52 detects the rear end of the sheet P and ends the measurement of the paper size, or the process of S808 in which the registration sensor 35 detects the leading end of the sheet P and ends the measurement of the paper size. If the image control unit 206 determines that the measurement of the paper size of the sheet P has been completed, the process proceeds to S821, and if the image control unit 206 determines that the measurement of the paper size of the sheet P has not been completed, the process returns to S820.

[0087] The processing in S821 to S823 is similar to the processing in S621 to S623 in FIG. 6(b) of the first embodiment, and therefore the description thereof will be omitted.

[0088] In S824, the image control unit 206 refers to the mask start timer and determines whether or not a time equivalent to the paper size set in the masked image size has elapsed (has a time equivalent to the masked image size elapsed?). The masked image size is set to the initial value of A4 size set in S801 of FIG. 8A until the measurement of the paper size of the sheet P is completed. In this embodiment, after the measurement of the paper size of the sheet P shown in FIG. 8A is completed and the masked image size is set in the processing of S807 or S809, the / TOP signal is output in the processing of S822, and then S824 is started. Therefore, the masked image size is not set to the initial value, but an image size corresponding to the detected paper size of the sheet P is set. If the image control unit 206 determines that a time equivalent to the paper size set in the masked image size has elapsed, the process proceeds to S825, and if the image control unit 206 determines that a time equivalent to the paper size set in the masked image size has not elapsed, the process returns to S824. In S825, the image control unit 206 sets an image mask, switches the output of the video signal to non-output, and ends the process.

[0089] As described above, in the printing control for non-standard sizes, even if the image to be formed is larger than the paper size of the fed sheet P, the image is formed so that the image does not extend beyond the paper from the printing of the first sheet P. This makes it possible to suppress the generation of waste toner and prevent the occurrence of image defects.

[0090] In this embodiment, unlike the first embodiment, image formation is performed after the paper size (masked image size) of the sheet P is determined. Therefore, in the control of this embodiment, even if sheets P of different paper sizes are mixed in the MP tray 50, image formation is performed so that the image does not extend beyond the paper. As a result, the generation of waste toner is suppressed, and the occurrence of image defects can be prevented.

[0091] In this embodiment, the size of the sheet P is measured by the MP tray transport sensor 52, and the measured paper size is set as the post-mask image size. Similar control can be performed by notifying the image control unit 206 from the paper transport unit 208 of the time from when the MP tray transport sensor 52 turns ON to when it turns OFF, and the timing when the MP tray transport sensor 52 turns ON and OFF.

[0092] Furthermore, in the non-standard size print control in this embodiment, the upper limit of the non-standard size is A4 size, but this is not necessarily synonymous with the upper limit size supported by the image forming device. For example, an image forming device whose upper limit of supported paper size is LGL (Legal) (paper size: 355.6 mm) has non-standard size print mode 1 whose upper limit size is LGL size and non-standard size print mode 2 whose upper limit size is A4 size. In this way, there is no particular limit to the supported upper limit size and the size upper limit of the non-standard print control.

[0093] As described above, according to this embodiment, when printing on paper of a non-standard size, an image can be formed without the image extending beyond the edge of the paper. [Explanation of symbols]

[0094] 35 Registration sensor 50 MP Tray 52 MP tray transport sensor 201 Controller 206 Image control section 208 Paper transport section

Claims

1. an output means for converting image information into an image signal and outputting the image signal based on a timing signal; a notification means for notifying an image size, which is the length of an output section of the image signal; an image forming means for forming an image on an image carrier based on the image signal output from the output means; A feeding means for feeding the recording material loaded in the paper feeding section; a transfer means for transferring the image formed on the image carrier onto a recording material fed by the feeding means; a first detection unit that is disposed on a recording material conveyance path between the paper feed unit and the transfer unit and detects the recording material; a second detection means that is disposed upstream of the first detection means in the recording material conveying direction on the conveying path and at a position farther away from the first detection means than a length in the conveying direction of a recording material of an upper limit size determined in control when an image is formed on a recording material of an unknown size among the recording materials fed by the feeding means, and that detects the recording material; Equipped with The image forming apparatus according to claim 1, wherein the image forming means outputs the timing signal to the output means in response to a timing at which the second detection means detects a first sheet of recording material in a print job.

2. 2. The image forming apparatus according to claim 1, wherein said image forming means outputs said timing signal to said output means at a timing when said second detection means detects the leading edge of said recording material.

3. 3. The image forming apparatus according to claim 2, wherein when the second detection means detects the trailing end of the recording material, the image forming means forms an image of an image size according to the detected length of the recording material in the transport direction.

4. 4. An image forming apparatus according to claim 3, wherein the length of the recording material in the transport direction is calculated by multiplying the time from when the second detection means detects the leading end of the recording material to when the second detection means detects the trailing end of the recording material by the transport speed at which the recording material is transported.

5. 3. The image forming apparatus according to claim 2, wherein the image forming means performs image formation of the image size notified by the notifying means when the first detecting means detects the leading edge of the recording material before the second detecting means detects the trailing edge of the recording material.

6. 2. The image forming apparatus according to claim 1, wherein the image forming means outputs the timing signal to the output means at the earlier of either the timing when the second detection means detects the trailing end of the recording material or the timing when the first detection means detects the leading end of the recording material.

7. The image forming apparatus according to claim 6, characterized in that, when the timing at which the second detection means detects the trailing end of the recording material is earlier, the image forming means forms an image of an image size corresponding to the detected length of the recording material in the transport direction.

8. 8. An image forming apparatus according to claim 7, wherein the length of the recording material in the transport direction is calculated based on the time from when the second detection means detects the leading edge of the recording material to when the second detection means detects the trailing edge of the recording material, and the transport speed at which the recording material is transported.

9. 7. The image forming apparatus according to claim 6, wherein the image forming means forms an image of the image size notified by the notifying means when the timing at which the first detecting means detects the leading edge of the recording material is earlier than the timing at which the first detecting means detects the leading edge of the recording material.

10. The image forming apparatus according to any one of claims 3, 4, 7 and 8, characterized in that the image forming means outputs the timing signal for the second and subsequent sheets of recording material of the print job to the output means at time intervals corresponding to the detected length of the first sheet of recording material in the transport direction.

11. 11. The image forming apparatus according to claim 10, wherein the time interval is calculated by summing up a length of the recording material in a transport direction and a distance to a succeeding recording material, and dividing the sum by a transport speed of the recording material.

12. 12. The image forming apparatus according to claim 1, wherein a length in a transport direction of the recording material fed by the feeding means is indefinite at the start of the print job.

Images