Image forming device

Abstract

To prevent the occurrence of a failure in conveyance of a sheet due to mismatch between sheet sizes.SOLUTION: Based on an image formation interval according to the length of an image signal output from a controller unit 201 and the feeding interval between recording materials fed by an MP tray pickup roller 51 from an MP tray 50 in correspondence with the length of the image signal, an engine unit 202 determines the timing at which the image signal is output and the timing at which the recording materials are fed, and when an MP conveyance sensor 52 does not detect a rear end of a first recording material fed by the MP tray pickup roller 51 from when the MP conveyance sensor detects a leading end of the first recording material until when the feeding interval elapses (S504-S506), determines the timing at which an image signal for a second recording material is output from the controller unit 201 and the timing at which the second recording material loaded on the MP tray 50 is fed by the MP tray pickup roller 51 based on the length of the first recording material (S507, S508).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that utilizes an electrophotographic process or the like. [Background technology]

[0002] Conventionally, electrophotographic image forming apparatuses having an intermediate transfer member have been known. When performing continuous printing operations, such image forming apparatuses typically calculate the image formation intervals and paper feed intervals based on the paper size specified by an external device such as a host computer. The image forming apparatus then controls the image formation timing and paper feed timing to always be consistent, thereby reducing the possibility of paper jams and other transport problems and ensuring normal printing operations. Furthermore, such image forming apparatuses often have a multipurpose tray (hereinafter referred to as an MP tray) as a paper feed unit to allow users to easily use paper of any size.

[0003] In image forming devices that use an intermediate transfer belt as an intermediate transfer body, the distance from the image formation start position on the photosensitive drum to the secondary transfer unit is generally longer than the distance from the paper feed unit where the paper is placed to the secondary transfer unit where the image is transferred to the paper. Therefore, image formation often begins before the paper feed operation, which feeds paper from the paper feed unit. However, when image formation begins, the size (length of paper in the transport direction) of the paper loaded in the paper feed unit is unknown. Therefore, the image formation interval is set based on the paper size (hereinafter referred to as the specified size) specified by an external device such as a host computer. However, if the size of paper loaded in the MP tray (hereinafter referred to as the loaded size) is larger than the specified size, the mismatch between the specified size and the loaded size can cause a timing mismatch between the image formation operation and the feeding operation, potentially resulting in a paper jam or other transport failure. The "timing mismatch" here refers to a discrepancy in control timing that occurs when "image formation is based on the specified size" and "feed control is based on the loaded size."

[0004] For example, the image forming apparatus proposed in Patent Document 1 performs the following control. That is, when the loaded size is unknown, image formation control and feed control are performed based on the maximum size of paper that can be loaded in the paper feed unit. Then, the size of the loaded paper is measured by a transport sensor, and once the paper size is determined, the image formation control and feed control are changed to match the loaded paper size. This allows printing operations to be performed without transport problems and while suppressing a decrease in productivity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-143795 Summary of the Invention [Problem to be solved by the invention]

[0006] In the image forming apparatus described above, when printing on irregular-sized paper, the size of the paper is measured while the paper is being transported by a transport sensor located upstream of the transport path near the secondary transfer unit. Therefore, in the print control of the image forming apparatus, if paper exceeding the maximum size is used or if paper of different sizes is loaded and fed in the same paper feed unit, there is a risk of transport problems such as jams occurring.

[0007] The present invention has been made under these circumstances, and has as its object to prevent paper transport failures caused by mismatched paper sizes. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0009] (1) A feeding means for sequentially feeding a plurality of recording materials placed on a paper feeding section to an image forming position, an image forming means for forming an image on the recording materials fed by the feeding means in accordance with an image signal output from an output means at the image forming position, a detecting means for detecting the recording materials fed by the feeding means, and an image signal output from the output means. No. Image formation according to Image formation start timing , and By the feeding means The recording material Delivered Salary sending start and a control unit that determines the timing of the feeding after the detection unit detects the leading edge of the first recording material in the conveying direction fed by the feeding unit. Start timing If the trailing edge of the first recording material in the conveying direction is not detected by ,before For the second recording material fed next to the first recording material The aforementioned image Start of formation Timing Gu and and the feeding start The timing, The timing at which the detecting means detects that the trailing edge of the first recording material in the conveying direction has passed is shifted by a time that is delayed from the feeding start timing. An image forming apparatus characterized by: (2) A recording apparatus including: a feeding means for sequentially feeding a plurality of recording materials placed on a paper feeding section to an image forming position; an image forming means for forming an image on the recording material fed by the feeding means at the image forming position in response to an image signal output from an output means; a detection means for detecting the recording material fed by the feeding means; and a control means for determining an image formation start timing for starting image formation in response to the image signal output from the output means and a feed start timing for feeding the recording material by the feeding means, wherein if the detection means does not detect the trailing end of the first recording material in the transport direction between the time when it detects the leading end of the first recording material fed by the feeding means in the transport direction and the feed start timing, the control means determines the image formation start timing and the feed start timing for a second recording material fed after the first recording material based on the length of the first recording material in the transport direction, An image forming apparatus characterized in that the image formation start timing is determined based on the length of an image signal corresponding to the first recording material and the length of a section in which no image signal is output, which is provided between the image signal corresponding to the first recording material and the image signal corresponding to the second recording material. (3) A feeding means for sequentially feeding a plurality of recording materials placed on a paper feeding section to an image forming position, an image forming means for forming an image on the recording material fed by the feeding means at the image forming position in response to an image signal output from an output means, a detection means for detecting the recording material fed by the feeding means, and a control means for determining an image formation start timing for starting image formation in response to the image signal output from the output means and a feed start timing for feeding the recording material by the feeding means, wherein the control means is configured to determine whether the detection means detects the recording material fed by the feeding means. and a detection means for detecting a trailing edge of the first recording material in the transport direction from the detection of the leading edge of the first recording material in the transport direction to the detection of the feed start timing, the image formation start timing and the feed start timing for a second recording material fed next to the first recording material are determined based on the length of the first recording material in the transport direction, and the feed start timing is determined based on the length of the first recording material, the inter-sheet gap between the first recording material and the second recording material, and the distance of the transport path from the paper feed unit to the detection means. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent paper transport failures caused by mismatched paper sizes. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the configuration of an image forming apparatus according to first to third embodiments; [Figure 2] FIG. 1 is a block diagram illustrating a system configuration of an image forming apparatus according to first to third embodiments. [Figure 3] 1 is a timing chart illustrating conventional image formation control and feed control for comparison with the embodiment. [Figure 4] Timing chart for explaining image formation control and feeding control in the first embodiment [Figure 5] Flowchart showing a control sequence of image formation control and feeding control in the first embodiment [Figure 6] Timing chart for explaining image formation control and feeding control in the second embodiment [Figure 7] Flowchart showing a control sequence of image formation control and feeding control in the second embodiment [Figure 8] Timing chart for explaining image formation control and feeding control in the third embodiment [Figure 9] Flowchart showing a control sequence of image formation control and feeding control in the third embodiment DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0013] [Configuration of image forming device] FIG. 1 illustrates the overall configuration of a laser beam printer as an example of an image forming apparatus according to the first embodiment. The image forming apparatus shown in FIG. 1 includes four image forming stations, which, from the left in the drawing, are image forming stations having yellow (Y), magenta (M), cyan (C), and black (Bk) toner. The suffixes a, b, c, and d in the drawing indicate the components of the yellow (Y), magenta (M), cyan (C), and black (Bk) image forming stations, respectively. Each image forming station has the same configuration, and in the following description, the symbols a to d will not be used unless otherwise necessary.

[0014] (Image forming section) In each image forming station, a photosensitive drum 1, which serves as an image carrier, is driven by a drive motor (not shown) to rotate in the direction of the arrow (counterclockwise) in the figure. A charging roller 2, which serves as 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 consisting of a DC voltage or a superimposed AC voltage is applied to the charging roller 2, and the photosensitive drum 1 is charged via the contact nip between the charging roller 2 and the surface of the photosensitive drum 1. A scanning unit 11, which serves as an exposure means, is composed of a scanner unit or an LED array that deflects laser light with a rotating polygonal mirror and scans the photosensitive drum 1 with the deflected laser light. The scanning unit 11 irradiates the photosensitive drum 1 with a scanning beam 12 modulated based on a video signal (image signal), forming an electrostatic latent image. The developing unit 8, which serves as a developing means, is composed of a developing roller 4 in contact with the photosensitive drum 1, a developer (toner) 5, and a developer application blade 7. The developing unit 8 develops the electrostatic latent image formed on the photosensitive drum 1 with toner to form a toner image. A waste toner container 3 collects toner that remains on the photosensitive drum 1 and is not transferred to an intermediate transfer belt 80 (described later). The process cartridge 9 incorporates the photosensitive drum 1, charging roller 2, waste toner container 3, and developing unit 8, and is an integrated cartridge that is detachable from the image forming apparatus. The charging roller 2 and developing roller 4 are connected to a charging voltage power supply 20, which supplies voltage to the charging roller 2, and a developing voltage power supply 21, which supplies voltage to the developing roller 4, respectively. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1, and a charging voltage is applied to the charging roller 2 from the charging voltage power supply 20, thereby uniformly charging the surface of the photosensitive drum 1.

[0015] The intermediate transfer belt 80 is supported by three rollers, namely, a secondary transfer counter roller 86, a drive roller 14, and a tension roller 15, which serve as tensioning members, and is configured to maintain an appropriate tension. Driven by the drive roller 14, the intermediate transfer belt 80 moves at approximately the same speed in the direction indicated by the arrow (clockwise) in the figure. Furthermore, a primary transfer roller 81 is disposed on the opposite side of the intermediate transfer belt 80 from the photosensitive drum 1 and is connected to a primary transfer voltage power supply 84, which supplies voltage to the primary transfer roller 81. By applying a primary transfer voltage to the primary transfer roller 81, the toner image on the photosensitive drum 1 (image carrier) is sequentially transferred onto the intermediate transfer belt 80, which is in contact with the photosensitive drum 1, forming a multicolor image on the intermediate transfer belt 80. Furthermore, a charge removal member 23 is disposed downstream of each primary transfer roller 81 in the direction of movement of the intermediate transfer belt 80. The drive roller 14, tension roller 15, charge removal member 23a, and a secondary transfer counter roller 86, which will be described later, are electrically grounded.

[0016] (Cassette feeding section) Paper P1, which is a recording material, is placed in paper feed cassette 16. When paper P1 (hereinafter simply referred to as paper), a stepping motor (not shown) (hereinafter referred to as paper feed motor) drives cassette pickup roller 17 to raise paper feed cassette bottom plate 29 and push up paper P1 placed in paper feed cassette 16. The topmost sheet of paper P1 thus pushed up comes into contact with cassette pickup roller 17, and as cassette pickup roller 17 rotates, paper P1 is separated and fed one sheet at a time. The fed paper P1 is transported to registration roller 18 (hereinafter referred to as registration roller 18), which is a transport means. When registration sensor 35 (hereinafter referred to as registration sensor 35), which is a recording material detection means that detects the recording material, detects the leading edge of paper P1 in the transport direction, the paper feed motor (not shown) stops driving, and transport of paper P1 is temporarily halted. The paper P1, which has been temporarily stopped by the registration rollers 18, is resumed in conveyance (also referred to as re-feeding) at a timing when the toner image formed on the intermediate transfer belt 80 and the position (image forming position) where the toner image on the paper P1 is transferred coincide with each other at the secondary transfer section. The size of the paper P1 (length in the conveying direction; hereinafter referred to as paper size) is determined based on the elapsed time from the time (point) when the paper P1 is re-fed to the time (point) when the registration sensor 35 detects the trailing edge of the paper P1 in the conveying direction.

[0017] (MP tray feeding section) Sheets of paper P2, which are recording materials, are placed on the MP tray 50 (paper feed section). When feeding sheets of paper P2 (hereinafter also simply referred to as paper), the above-mentioned paper feed motor (not shown) drives the MP tray pickup rollers 51 (feeding means), and the topmost sheet of paper P2 abuts against the MP tray pickup rollers 51 and is fed into the apparatus. The fed sheet of paper P2 passes through an MP transport sensor 52, which is a detection means in the transport path (transport path), and is transported to the registration rollers 18. After being transported to the registration rollers 18, printing is performed in the above-mentioned operation. Furthermore, when sheets of paper (recording materials) are continuously fed from the MP tray 50, the feeding of the subsequent sheet is performed after the MP transport sensor 52 detects that the trailing edge of the preceding sheet has passed in the transport direction.

[0018] (Secondary transfer section) The intermediate transfer belt 80, onto which the toner images formed on the photosensitive drums 1 of each image forming station have been transferred, is moved in the direction of the arrow in the figure (clockwise direction) by a drive roller 14. The toner images transferred onto the intermediate transfer belt 80 are transported to a secondary transfer section, which is the contact point between a secondary transfer roller 82 and the intermediate transfer belt 80. The secondary transfer roller 82 and a secondary transfer opposing roller 86, which is installed opposite the secondary transfer roller 82, then sandwich and transport the paper P and the intermediate transfer belt 80, and a voltage is applied to the secondary transfer roller 82 from a secondary transfer voltage power supply 85. As a result, the toner image on the intermediate transfer belt 80 is transferred to the paper P.

[0019] (fixing part) Fixing unit 19, which serves as a fixing means, applies heat and pressure to the toner image transferred onto paper P, thereby fixing the toner image to paper P. Fixing unit 19 has a fixing belt 19a and a pressure roller 19b, and pressure roller 19b and a belt guide member (not shown) sandwich the fixing belt 19a with a predetermined pressure, forming a fixing nip. With the fixing nip adjusted to a predetermined temperature, paper P with an unfixed toner image transferred thereto is introduced between fixing belt 19a and pressure roller 19b in the fixing nip with the image side facing upward, i.e., facing the surface of fixing belt 19a. Then, in the fixing nip, the image side of paper P is in close contact with the outer surface of fixing belt 19a, and paper P is conveyed through the fixing nip. As the paper P is sandwiched and transported by the fixing belt 19a through the fixing nip, the toner image on the paper P is heated by the fixing belt 19a and fixed onto the paper P, and the paper P with the fixed toner image is discharged onto the discharge tray 36.

[0020] [System configuration of image forming device] FIG. 2 is a block diagram illustrating the overall system configuration of the image forming apparatus of this embodiment. In FIG. 2, the image forming apparatus includes a controller unit 201 and an engine unit 202. The controller unit 201 is capable of communicating with an external host computer 200 and the engine unit 202. The controller unit 201, which outputs image signals, receives print commands including image information (print data) and printing conditions from the host computer 200 and generates bitmap data (image data) based on the received print data. After the controller unit 201 has finished generating the bitmap data, it transmits image size information and a print reservation command to the CPU 204 via the video interface unit 203 in accordance with the print command from the host computer 200. When the engine unit 202 becomes ready to print (ready to form an image), the controller unit 201 transmits a print start command to the CPU 204.

[0021] The engine unit 202, which is a control means, 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 (commands, / TOP signals, video signals) between the engine unit 202 and the controller unit 201. The image control unit 206 controls each image forming station, which is 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 feeding unit and MP tray feeding unit described above.

[0022] The CPU 204, which transmits and receives data such as commands to and from the controller unit 201, prepares to execute a print job when it receives a paper size specification command or a print reservation command from the controller unit 201. The CPU 204 then waits for a print start command to be sent from the controller unit 201. Upon receiving the print start command, the CPU 204 instructs each control unit (image control unit 206, fixing control unit 207, and paper transport unit 208) to start a printing operation (hereinafter also referred to as a print operation) based on information in the print reservation command, such as the specified paper size. The CPU 204 includes a ROM and a RAM. The ROM stores control programs and data executed by the CPU 204, and the RAM is memory used by the control programs executed by the CPU 204 to temporarily store information. The image control unit 206, paper transport unit 208, etc. also include a CPU, ROM, and RAM (not shown). Like the CPU 204, the ROM stores control programs and data, and the RAM is used by the control programs to temporarily store information.

[0023] Upon receiving an instruction to start a printing operation from the CPU 204, the image control unit 206 begins preparation for image formation. Upon receiving a notification from the image control unit 206 that preparation for image formation is complete, the CPU 204 outputs a / TOP signal, which is a timing signal that serves as a reference timing for outputting a video signal, to the controller unit 201 via the video interface unit 203. Upon receiving the / TOP signal from the CPU 204, the controller unit 201 outputs a video signal (image signal) generated from bitmap data for a specified paper size to the image processing GA 205, based on the timing at which the / TOP signal was received. Upon receiving the video signal from the controller unit 201, the image processing GA 205 converts the received video signal into image formation data and transmits it to the image control unit 206. The image control unit 206 forms images based on the image formation data received from the image processing GA 205. Note that, in image formation during continuous printing, the image control unit 206 determines the image formation interval, which is the time interval (period) at which the / TOP signal is output, based on the paper size specified in the print reservation command received from the controller unit 201. Then, the image control unit 206 instructs the CPU 204 to transmit a / TOP signal in accordance with the determined image formation interval.

[0024] When the paper transport unit 208 receives an instruction to start a printing operation from the CPU 204, it starts a feeding operation to feed paper. The paper transport unit 208 drives a paper feed motor (not shown) to transport paper placed on the MP tray 50 or paper feed cassette 16 (hereinafter also referred to as the paper feed unit) to the secondary transfer unit, and detects the size of the paper being transported using a register sensor 35 (FIG. 1). In feeding control when performing continuous printing using paper placed on the MP tray 50, the paper transport unit 208 feeds a subsequent paper when the following two conditions are satisfied. That is, the paper transport unit 208 controls so that the subsequent paper can be fed when a predetermined time has elapsed since the MP transport sensor 52 detected the leading edge of the preceding paper in the transport direction, and when the MP transport sensor 52 detects that the trailing edge of the preceding paper in the transport direction has passed. In the following, a paper fed following the preceding paper is referred to as a subsequent paper.

[0025] When the fixing control unit 207 receives an instruction to start the printing operation from the CPU 204, it starts preparation for the fixing process. Then, the fixing control unit 207 starts adjusting the temperature of the fixing unit 19 in accordance with the paper type information (e.g., the thickness of the paper) set in the print reservation command, in accordance with the timing when the paper onto which the toner image has been transferred is transported to the fixing unit 19. After fixing the image (toner image) on the paper, the fixing control unit 207 transports (discharges) the paper outside the machine.

[0026] [Printing Operation Overview] Next, we will explain the printing operation when printing on paper fed from the MP tray 50 and the paper size (specified size) specified by the host computer 200 differs from the paper size (loaded size) actually placed on the MP tray 50.

[0027] The print control in the image forming apparatus of this embodiment is based on the following parameters: the image interval (the interval between one image signal and the next) is 220 mm, and the paper interval (the interval between the preceding and succeeding sheets) is 140 mm. The transport speed (the speed at which the paper is transported, which is also the speed at which the image formed on the photosensitive drum 1 moves) is 150 mm / s (150 mm per second). The MP tray pickup roller 51 is driven by a paper feed motor (not shown), and the distance the MP tray pickup roller 51 rotates from the time the paper placed on the MP tray 50 begins to move is 60 mm. The distance from the leading edge of the paper placed on the MP tray 50 in the transport direction to the location where the MP transport sensor 52 is installed is 50 mm.

[0028] In the image forming apparatus of this embodiment, the distance from the secondary transfer unit to the MP transport sensor 52 is defined as A, and the distance that an image formed at the image formation start position (laser exposure position on the photosensitive drum 1 of the yellow station) moves to the secondary transfer unit is defined as B. The magnitude relationship between distance A and distance B is distance A≦distance B (distance A is equal to or less than distance B (distance or less)).

[0029] [Outline of conventional printing behavior] First, conventional image formation control and feeding control in an image forming apparatus will be described with reference to the timing charts shown in Fig. 3.

[0030] (When the specified paper size and the loaded size match) FIG. 3A is a timing chart illustrating image formation control and feed control when the specified and loaded paper sizes are both A5 landscape paper (210 mm paper width × 148 mm length in the transport direction), and the specified and loaded paper sizes match. In FIG. 3A, (a) / TOP signal indicates a signal sent from engine unit 202 to controller unit 201 upon receiving notification from image control unit 206 that image formation preparation is complete. Timage indicates the image formation interval (Timage) at which the / TOP signal is output. (b) Timage timer indicates changes in the timer value of the timer that measures the image formation interval (Timage). (c) feed start signal indicates the timing to drive MP tray pickup roller 51 to feed paper loaded on MP tray 50. (d) MP transport sensor indicates the detection state of MP transport sensor 52, which detects paper transported from MP tray 50. An ON state indicates a state in which paper is detected, and an OFF state indicates a state in which paper is not detected. (e) Tpaper timer indicates the change in the timer value of the timer that measures the feeding interval (Tpaper) of paper fed from the MP tray 50. Note that the feeding interval (Tpaper) in this embodiment is the time from when the MP transport sensor 52 detects the leading edge of paper fed from the MP tray 50 until when a feeding start signal is generated. Also, in Figure 3[A], the horizontal axis indicates time.

[0031] When the engine unit 202 receives a print start command from the controller unit 201, it instructs the image control unit 206, paper conveyance unit 208, etc. to start the print operation in order to perform image formation preparation operations for the print operation. Then, when it receives a notification from the image control unit 206 that image formation preparation is complete, the engine unit 202 outputs a / TOP signal (301) for the first sheet of paper (first recording material) to the controller unit 201 (FIG. 3[A](a)). Then, the Timage timer starts at timing (311) when the / TOP signal (301) is output (FIG. 3[A](b)). When the timer value of the Timage timer reaches the image formation interval (Timage) (FIG. 3[A](b)), the engine unit 202 outputs a / TOP signal (302) for the second sheet of paper (second recording material) to the controller unit 201 (FIG. 3[A](a)). Similarly, the Timage timer starts at the timing (312) when the / TOP signal (302) is output. When the timer value of the Timage timer reaches the image formation interval (Timage), the engine unit 202 outputs a / TOP signal (303) for the third sheet to the controller unit 201.

[0032] The image formation interval Timage in FIG. 3[A] is expressed by the following (Equation 1). Image formation interval Timage = (length of specified paper size in the transport direction + image interval) / Transport speed (Equation 1) In this embodiment, the image formation interval Timage is (length of the designated size of paper in the conveying direction (148 mm)+image interval (220 mm)) / 150 mm / s=368 mm / 150 mm / s≈2.453 seconds.

[0033] On the other hand, when the feeding preparation operation is completed, the engine unit 202 drives the MP tray pickup roller 51 at the timing of a feeding start signal (321) (Fig. 3[A](c)) to feed one sheet of paper from the MP tray 50. When the MP transport sensor 52 detects the leading edge in the transport direction of the paper fed from the MP tray 50 at timing (331) (Fig. 3[A](d)), the engine unit 202 starts the Tpaper timer at timing (341) (Fig. 3[A](e)). When the timer value of the Tpaper timer reaches the feeding interval (Tpaper) (Fig. 3[A](e)), the engine unit 202 detects at timing (332) that the MP transport sensor 52 has passed the trailing edge in the transport direction of the preceding paper (Fig. 3[A](d)). Then, the engine unit 202 drives the MP tray pickup roller 51 at the timing of the feeding start signal (322) (FIG. 3[A](c)), causing the subsequent sheet (second sheet) to be fed from the MP tray 50. Similarly, when the MP transport sensor 52 detects the leading edge of the subsequent sheet fed from the MP tray 50 at timing (333), the Tpaper timer starts at timing (342). Then, the engine unit 202 detects at timing (334) that the timer value of the Tpaper timer has reached the feeding interval (Tpaper) and the MP transport sensor 52 has passed the trailing edge of the preceding sheet. Then, the engine unit 202 drives the MP tray pickup roller 51 at the timing of the feeding start signal (323), causing the subsequent sheet (third sheet) to be fed from the MP tray 50.

[0034] The feeding interval Tpaper in FIG. 3[A] is expressed by the following (Equation 2) based on FIG. 3[A](c) and (d). Feeding interval Tpaper = (Placement size + Paper interval - MP tray pickup roller 51 is driven) Distance the paper rotates before it starts moving - from the leading edge of the paper placed on the MP tray 50 Distance to MP transport sensor 52) / Transport speed (Equation 2) In this embodiment, the loading size (the length of the loaded paper in the transport direction) is 148 mm, and the paper interval is 140 mm. Also, as described above, the distance the MP tray pickup roller 51 rotates from when it is driven until the paper starts moving is 60 mm, and the distance from the leading edge of the paper loaded on the MP tray 50 to the position where the MP transport sensor 52 is installed is 50 mm. Therefore, from (Equation 2), the feeding interval Tpaper is (148 mm + 140 mm - 60 mm - 50 mm) / 150 mm / s = 178 mm / 150 mm / s ≈ 1.187 s.

[0035] (When the specified paper size and the loaded size do not match) Figure 3[B] is a timing chart that explains image formation control and feed control when the specified paper size and the loaded paper size do not match. In Figure 3[B], the specified paper size is A5 size landscape paper (paper width 210 mm x length in the transport direction 148 mm), and the loaded paper size is A5 size portrait paper (paper width 148 mm x length in the transport direction 210 mm). Because the A5 size paper loaded on the MP tray 50 is loaded portrait, the length in the transport direction of the paper is longer than the specified size. The configuration of Figure 3[B] is the same as Figure 3[A] described above, and an explanation of how to read the figure will be omitted.

[0036] In FIG. 3[B], when performing continuous image formation, the engine unit 202 outputs a / TOP signal (306) to the controller unit 201, as in FIG. 3[A], and then outputs a / TOP signal (307) for the second sheet of paper after the image formation interval Timage has elapsed.

[0037] On the other hand, with regard to the feeding operation, as explained in FIG. 3[A], the engine unit 202 feeds one sheet of paper from the MP tray 50 at the timing of the feeding start signal (326) (FIG. 3[B](c)) prior to the image forming operation. When the MP transport sensor 52 detects the leading edge of the paper in the transport direction fed from the MP tray 50 at timing (335) (FIG. 3[B](d)), the engine unit 202 starts the Tpaper timer at timing (343) (FIG. 3[B](e)). Although the timer value of the Tpaper timer reaches the feeding interval (Tpaper) (FIG. 3[B](e)), the MP transport sensor 52 has not detected the passage of the trailing edge of the preceding paper (FIG. 3[A](d)), so the feeding start signal (327) is not generated (FIG. 3[B](c)). Thereafter, when the MP transport sensor 52 detects that the trailing edge of the preceding paper in the transport direction has passed (FIG. 3[B](d)), a feeding start signal (328) is generated (FIG. 3[B](c)) with a time Tgap (329) later than normal.

[0038] The shortest distance between the preceding and succeeding sheets when a feeding operation for a succeeding sheet is performed immediately after the rear end of the preceding sheet has passed the MP transport sensor 52 is expressed by the following equation (3). Shortest paper spacing = The number of rotations between the time the MP tray pickup roller 51 is driven and the time the paper starts moving + the distance from the leading edge of the paper in the MP tray 50 to the MP transport sensor 52 ...(Formula 3) In this embodiment, the shortest paper interval is 60 mm + 50 mm = 110 mm.

[0039] Therefore, the time Tgap (319) shown in FIG. 3[B](d) is expressed by the following (Equation 4). Time Tgap = (Feeding interval in Figure 3[B] - Feeding interval in Figure 3[A]) / Conveying speed ...(Formula 4) In this embodiment, the feed interval in FIG. 3[B] is the length of the loaded paper size in the transport direction (210 mm) plus the shortest paper interval (110 mm). On the other hand, the feed interval in FIG. 3[A] is the length of the specified paper size in the transport direction (148 mm) plus the paper interval (140 mm). As a result, the time Tgap is ((210 mm + 110 mm) - (148 mm + 140 mm)) / 150 mm / s = 32 mm / 150 mm / s ≈ 0.213 seconds. While the image formation interval Timage remains the same in FIGS. 3[A] and 3[B], the feed interval in FIG. 3[B] is 0.213 seconds slower than in FIG. 3[A], which shows the normal state. That is, in the case of Figure 3[B], in response to the / TOP signal (307), the paper fed from the MP tray 50 is transported 0.213 seconds later than in the normal state of Figure 3[A].

[0040] As described above, if the length of paper in the transport direction between the specified size and the loaded size does not match, and the loaded size is longer than the specified size, the transport margin for the paper transport interval relative to the image formation interval is reduced, increasing the likelihood of transport problems such as jams. If a jam occurs, the toner image formed in the image forming unit is wasted, and the used toner becomes waste toner and is collected in a waste toner container. As the number of jams increases, the risk of the waste toner container overflowing increases. The "transport margin" refers to the time allowance for normal printing without causing transport problems such as jams, even if the paper being fed is delayed for some reason.

[0041] [Outline of printing operation in this embodiment] In this embodiment, as described in FIG. 3B, the following control is performed to prevent a situation in which the transport margin is reduced when a mismatch between the specified size and the loaded size occurs. That is, in the paper feeding operation during continuous printing, if the feeding interval between the preceding and succeeding sheets is greater than the feeding interval calculated by substituting the loaded size for the specified size in the above-described (Equation 2), the feeding interval and image formation interval are extended to a predetermined interval. Note that in this embodiment, the "predetermined interval" is set to the same interval as when A4-size paper is used. A4-size paper is frequently used by users and is the largest size of paper that is likely to be loaded on the MP tray 50. Therefore, in this embodiment, the paper size used as the predetermined interval was determined to be A4, taking into consideration the need to prevent a significant decrease in productivity due to the occurrence of jams, etc.

[0042] Figure 4 is a timing chart illustrating image formation control and feed control in this embodiment. In Figure 4, as with Figure 3[B] described above, the specified paper size is A5 size landscape paper (paper width 210 mm x length in the conveying direction 148 mm). The size of the paper placed on the MP tray 50 is A5 size portrait paper (paper width 148 mm x length in the conveying direction 210 mm). The configuration of Figure 4 is the same as Figures 3[A] and [B] described above, so an explanation of how to read the figure will be omitted.

[0043] When the engine unit 202 receives a print start command from the controller unit 201, it instructs the image control unit 206, paper transport unit 208, etc. to start the print operation in order to perform image formation preparation operations for the print operation. Then, when it receives a notification from the image control unit 206 that image formation preparation is complete, the engine unit 202 outputs a / TOP signal (401) for the first sheet of paper to the controller unit 201 (FIG. 4(a)). The Timage timer starts at timing (411) when the reference / TOP signal (401) is output (FIG. 4(b)). The engine unit 202 controls the image formation interval so that it becomes the image formation interval Timage (404) corresponding to the specified paper size. Then, when the timer value of the Timage timer reaches Timage (404) (FIG. 4(b)), if the loaded paper size is the same as the specified size, the engine unit 202 outputs a / TOP signal (402) for the second sheet of paper to the controller unit 201 (FIG. 4(a)). The image formation interval Timage in FIG. 4 can be calculated using (Equation 1) explained in FIG.

[0044] Meanwhile, when the feeding preparation operation is completed, the engine unit 202 drives the MP tray pickup roller 51 at the timing of the feeding start signal (421) (FIG. 4(c)) to feed one sheet of paper from the MP tray 50. The engine unit 202 controls the feeding of the subsequent sheets while setting the desired feeding interval to the feeding interval Tpaper (424) corresponding to the same loading size as the specified size of the paper. As explained in FIG. 3, the feeding interval Tpaper is controlled based on the timing at which the MP transport sensor 52 detects the leading edge of the preceding sheet. When the MP transport sensor 52 detects the leading edge of the paper fed from the MP tray 50 at timing (431) (FIG. 4(d)), the engine unit 202 starts the Tpaper timer at timing (441) (FIG. 4(e)). The feeding interval Tpaper (424) in Figure 4 is the feeding interval when landscape paper of A5 size, the same size as the specified size, is fed from the MP tray 50, and can be calculated using (Equation 2) described in Figure 3.

[0045] The engine unit 202 checks the state of the MP transport sensor 52 when the timer value of the Tpaper timer reaches the feeding interval Tpaper(424) (FIG. 4(e)). In this embodiment, feeding control (setting of the feeding interval Tpaper(424)) is performed assuming that A5-sized paper is placed landscape-oriented on the MP tray 50. However, because the A5-sized paper actually placed on the MP tray 50 is placed portrait-oriented, the length of the paper being fed from the MP tray in the transport direction is 210 mm. Meanwhile, the numerator of the above-described (Equation 2) used to calculate the feeding interval Tpaper(424) is 178 mm (= 148 mm + 140 mm - 60 mm - 50 mm), which is shorter than the length of an A5 sheet in portrait orientation, 210 mm. Therefore, when the timer value of the Tpaper timer reaches the feeding interval Tpaper(424), the trailing edge of the preceding paper in the transport direction has not yet passed the MP transport sensor 52.

[0046] If the loaded size of paper is the same as the specified size, the trailing edge of the preceding paper (preceding paper) in the transport direction will have passed the MP transport sensor 52 at the timing when the timer value of the Tpaper timer reaches the feed interval Tpaper (424) (FIG. 4[d]). Therefore, the engine unit 202 generates a feed start signal (422) to feed the next paper (FIG. 4(c)). On the other hand, if the engine unit 202 determines that the trailing edge of the preceding paper has not passed the MP transport sensor 52 at the timing (442) when the timer value of the Tpaper timer reaches the feed interval Tpaper (424), it switches the feed interval from Tpaper to Tpaper'. In other words, the engine unit 202 switches the feed interval for feeding the subsequent paper from the MP tray 50 from the feed interval Tpaper (424) for A5 size landscape paper to the feed interval Tpaper' (425) for A4 size portrait paper. Then, when the timer value of the Tpaper timer reaches the feeding interval Tpaper' (425), the engine unit 202 generates a feeding start signal (423), drives the MP tray pickup roller 51, and feeds the subsequent paper.

[0047] The paper interval Tpaper' in FIG. 4 is expressed by the following (Equation 5). Feeding interval Tpaper' = (A4 size + paper interval - MP tray pickup roller 51 is driven Distance the paper rotates before it starts moving - from the leading edge of the paper placed on the MP tray 50 Distance to MP transport sensor 52) / Transport speed (Equation 5) In this embodiment, the A4 size (the length of an A4 size sheet in the conveying direction) is 297 mm, and the sheet interval is 140 mm. Also, as described above, the distance the sheet rotates from when the MP tray pickup roller 51 is driven until it starts moving is 60 mm, and the distance from the leading edge of the sheet placed on the MP tray 50 to the MP conveyance sensor 52 is 50 mm. Therefore, from (Equation 5), the feeding interval Tpaper' is (297 mm + 140 mm - 60 mm - 50 mm) / 150 mm / s = 327 mm / 150 mm / s = 2.180 s (seconds).

[0048] When the engine unit 202 determines that the preceding paper has not passed the MP transport sensor 52 at the timing (442) when the timer value of the Tpaper timer reaches the feeding interval Tpaper (424), the engine unit 202 switches the feeding interval from Tpaper to Tpaper'. The engine unit 202 also switches the image formation interval from Timage (404) to Timage' (405) at the timing when the feeding interval is switched from Tpaper (424) to Tpaper' (425).

[0049] The image formation interval Timage' in FIG. 4 is expressed by the following (Equation 6). Image formation interval Timage' = (A4 size + image interval) / conveyance speed (Equation 6) In this embodiment, the A4 size (the length of an A4 size sheet in the transport direction) is 297 mm, and the image interval is 220 mm. Therefore, from (Equation 6), the image formation interval Timage' is (297 mm + 220 mm) / 150 mm / s = 517 mm / 150 mm / s ≈ 3.447 s (seconds).

[0050] [Image formation control and feed control sequence] Fig. 5 is a flowchart showing the control sequence of image formation control and feed control in this embodiment. Fig. 5(a) is a flowchart showing the control sequence of feed control for paper placed on the MP tray 50, and Fig. 5(b) is a flowchart showing the control sequence of image formation control for forming an image on fed paper. The processes shown in Figs. 5(a) and 5(b) are started when the engine unit 202 receives a print start command from the controller unit 201, and are executed by the engine unit 202. It is assumed that the engine unit 202 has received image size information, a paper size specification command, and a print reservation command from the controller unit 201 before receiving the print start command.

[0051] (Control sequence for feed control) The control sequence for controlling the feeding of paper placed on the MP tray 50 shown in Figure 5(a) will be described. In step (hereinafter referred to as S) 500, the engine unit 202 starts a feeding preparation operation when it receives a print start command from the controller unit 201. In S501, the engine unit 202 determines whether or not the preparation for feeding of paper placed on the MP tray 50 is complete. If the engine unit 202 determines that the preparation for feeding is complete, the process proceeds to S502, and if it determines that the preparation for feeding is not complete, the process returns to S501.

[0052] In S502, the engine unit 202 drives the MP tray pickup roller 51 to feed one sheet (the first sheet) of paper placed on the MP tray 50. In S503, the engine unit 202 acquires the detection status of the MP transport sensor 52 and determines, based on the acquired detection status (detection result), whether the MP transport sensor 52 has detected the leading edge of the paper in the transport direction fed from the MP tray 50 (MP transport sensor on?). If the acquired detection status of the MP transport sensor 52 is on (ON), the engine unit 202 determines that the MP transport sensor 52 has detected the leading edge of the fed paper, and proceeds to S504. On the other hand, if the acquired detection status of the MP transport sensor 52 is not on (ON) (is off (OFF)), the engine unit 202 determines that the MP transport sensor 52 has not detected the fed paper, and returns the process to S503.

[0053] In S504, the engine unit 202 calculates the feeding interval Tpaper using the above-mentioned (Equation 2) based on the paper size specified by the paper size specification command, and resets and starts the Tpaper timer that measures the feeding interval. In S505, the engine unit 202 references the Tpaper timer and determines whether the feeding interval has elapsed. If the engine unit 202 determines based on the timer value of the Tpaper timer that the feeding interval has elapsed, it proceeds to S506, and if it determines that the feeding interval has not elapsed, it returns to S505.

[0054] In S506, the engine unit 202 acquires the detection state of the MP transport sensor 52 and determines whether the trailing edge in the transport direction of the paper fed from the MP tray 50 has passed the MP transport sensor 52 (MP transport sensor OFF?). If the acquired detection state of the MP transport sensor 52 is OFF, the engine unit 202 determines that the trailing edge of the fed paper has passed the MP transport sensor 52, and proceeds to S509. On the other hand, if the acquired detection state of the MP transport sensor 52 is not OFF (ON), the engine unit 202 determines that the trailing edge of the fed paper has not passed the MP transport sensor 52, and proceeds to S507.

[0055] In S507, the engine unit 202 determines that the size of the paper fed from the MP tray 50 is larger than the size of the paper specified by the paper size specification command. Then, the engine unit 202 switches the feeding interval from the feeding interval Tpaper corresponding to the paper size specified by the paper size specification command to the feeding interval Tpaper' corresponding to A4 size paper, calculated using the above-mentioned (Equation 5). In S508, the engine unit 202 switches the image formation interval from Timage corresponding to the image size information to the image formation interval Timage' corresponding to A4 size paper, calculated using the above-mentioned (Equation 6). Then, the engine unit 202 returns the process to S505.

[0056] In S509, the engine unit 202 drives the MP tray pickup roller 51 to feed one sheet of paper (subsequent paper) placed on the MP tray 50. In S510, the engine unit 202 determines whether feeding of all sheets has been completed based on the print reservation command for the subsequent paper. If the engine unit 202 has received the print reservation command, it determines that feeding of sheets has not been completed, and returns the process to S503. On the other hand, if the engine unit 202 has not received the print reservation command, it determines that feeding of all sheets has been completed, and ends the process.

[0057] (Image formation control sequence) The control sequence of image formation control for forming an image on fed paper, shown in Fig. 5(b), will be described. In S520, when the engine unit 202 receives a print start command from the controller unit 201, it starts image formation preparation operations. In S521, the engine unit 202 determines whether image formation preparation is complete. If the engine unit 202 determines that image formation preparation is complete, it proceeds to S522, and if it determines that image formation preparation is not complete, it returns to S521. In S522, the engine unit 202 outputs a / TOP signal for the first sheet of paper to the controller unit 201 and starts image formation.

[0058] In S523, the engine unit 202 calculates the image formation interval Timage using the above-mentioned (Equation 1) based on the image size information received from the controller unit 201, and resets and starts the Timage timer that measures the image formation interval. In S524, the engine unit 202 references the Timage timer and determines whether the image formation interval has elapsed. If the engine unit 202 determines based on the timer value of the Timage timer that the image formation interval has elapsed, the process proceeds to S525, and if it determines that the image formation interval has not elapsed, the process returns to S524.

[0059] In S525, the engine unit 202 outputs a / TOP signal for the next sheet (subsequent sheet) to the controller unit 201 and starts image formation. In S526, the engine unit 202 determines whether printing on all sheets has finished based on the print reservation command for the subsequent sheets. If the engine unit 202 has received the print reservation command, it determines that printing on the sheets has not finished, and returns the process to S523. On the other hand, if the engine unit 202 has not received the print reservation command, it determines that printing on all sheets has finished, and ends the process.

[0060] In S523, the image formation interval Timage is calculated based on the image size information received from the controller unit 201. However, if the specified paper size does not match the size of the paper fed from the MP tray 50, the image formation interval is switched from Timage to Timage', an image formation interval corresponding to A4 size paper, in the processing of S508 described above. As a result, the image formation interval of the Timage timer may be switched from Timage to Timage' depending on the size of the paper fed from the MP tray 50. This prevents a decrease in the transport margin of paper fed from the MP tray 50 and suppresses the occurrence of transport problems such as jams. It also reduces the risk of the waste toner container overflowing due to the collection of waste toner caused by a jam.

[0061] In this embodiment, when the specified paper size and the loaded paper size do not match, the image formation interval and the feed interval are extended to the same as the feed interval for A4-sized paper. In this embodiment, the extended feed interval is set to the feed interval for A4-sized paper. However, this is not limiting and the extended feed interval may be determined based on, for example, the maximum paper size supported by the image forming apparatus or a paper size frequently used by users. Also, in this embodiment, the case where paper of a size different from the specified size is loaded in the MP tray 50 is described. However, this is not the only case where a paper size mismatch can occur. For example, even if paper of the specified size is actually loaded in the MP tray 50, if the fed paper is multi-fed (a state in which multiple sheets of paper are transported together (overlapping)), the MP transport sensor 52 cannot detect the leading and trailing edges of each sheet. Therefore, there are cases where a paper size mismatch is determined, and in this embodiment, the same control as for a paper size mismatch is performed.

[0062] As described above, according to this embodiment, it is possible to prevent the occurrence of paper transport failures due to mismatches in paper sizes. [Example]

[0063] In the first embodiment, when continuous printing is performed on paper fed from the MP tray, if it is determined that the feeding interval between the preceding and succeeding sheets is equal to or greater than the specified size + paper interval, the control is explained, which enables normal conveyance by widening the feeding interval and image formation interval to a predetermined interval. In the second embodiment, if a mismatch in paper size occurs, the control is explained, in which the MP conveyance sensor determines the start of feeding of the succeeding sheet and the start of image formation based on the detection of the passage of the trailing edge of the preceding sheet, thereby conveying the sheets according to the paper size. Note that the configuration and system configuration of the image forming apparatus of this embodiment are the same as those of the first embodiment, and the same devices and components are designated by the same reference numerals, and their description is omitted.

[0064] [Outline of printing operation in this embodiment] FIG. 6 is a timing chart illustrating image formation control and feed control in this embodiment. In FIG. 6, the specified paper size is A5 landscape paper (paper width 210 mm × length in the transport direction 148 mm). On the other hand, the loading size of the paper loaded on the MP tray 50 is LTR (letter) paper (paper width 215.9 mm × length in the transport direction 279.4 mm). The specified paper size and the loaded size do not match, and the paper loaded on the MP tray 50 is longer in the transport direction. Furthermore, the parameters used in the image forming apparatus and print control are the same as those in the first embodiment. Note that the configuration in FIG. 6 is the same as FIG. 4 of the first embodiment described above, and explanation of how to read the figure will be omitted.

[0065] When the engine unit 202 receives a print start command from the controller unit 201, it instructs the image control unit 206, paper transport unit 208, etc. to start the print operation in order to perform image formation preparation operations for the print operation. Then, when it receives a notification from the image control unit 206 that image formation preparation is complete, the engine unit 202 outputs a / TOP signal (601) for the first sheet of paper to the controller unit 201 (FIG. 6(a)). The Timage timer starts at timing (611) when the reference / TOP signal (601) is output (FIG. 6(b)). The engine unit 202 controls the image formation interval to be the image formation interval Timage (604) corresponding to the specified paper size. Then, when the timer value of the Timage timer reaches Timage (604) (FIG. 6(b)), if the loaded paper size is the same as the specified size, the engine unit 202 outputs a / TOP signal (602) for the second sheet of paper to the controller unit 201 (FIG. 6(a)). The image formation interval Timage in FIG. 6 can be calculated using (Equation 1) explained in FIG. 3 of the first embodiment.

[0066] Meanwhile, when the feeding preparation operation is completed, the engine unit 202 drives the MP tray pickup roller 51 at the timing of a feeding start signal (621) (FIG. 6(c)) to feed one sheet of paper from the MP tray 50. The engine unit 202 controls the feeding of subsequent sheets while setting the desired feeding interval to the feeding interval Tpaper (624) corresponding to the same loading size as the specified size of the paper. As in the first embodiment, the feeding interval Tpaper is controlled based on the timing at which the MP transport sensor 52 detects the leading edge of the preceding sheet of paper. When the MP transport sensor 52 detects the leading edge in the transport direction of the paper fed from the MP tray 50 at timing (631) (FIG. 6(d)), the engine unit 202 starts the Tpaper timer at timing (641) (FIG. 6(e)). The feeding interval Tpaper (624) in Figure 4 is the feeding interval when landscape paper of A5 size, the same size as the specified size, is fed from the MP tray 50, and can be calculated using (Equation 2) described in Figure 3 of Example 1.

[0067] The engine unit 202 checks the state of the MP transport sensor 52 when the timer value of the Tpaper timer reaches the feeding interval Tpaper (624) (FIG. 6(e)). In this embodiment, feeding control (setting of the feeding interval Tpaper (624)) is performed assuming that A5-sized paper is placed landscape-oriented on the MP tray 50. However, the paper actually placed on the MP tray 50 is LTR (letter) paper (paper width 215.9 mm × length in the transport direction 279.4 mm), which is longer than the length of A5-sized landscape-oriented paper, 148 mm. Therefore, at the timing (642) when the timer value of the Tpaper timer reaches the feeding interval Tpaper (624), the trailing edge in the transport direction of the preceding paper has not yet passed the MP transport sensor 52.

[0068] Therefore, when the engine unit 202 determines at timing (642) that the trailing edge of the preceding sheet in the transport direction has not passed the MP transport sensor 52, it prohibits image formation and feeding of the succeeding sheet. Because the engine unit 202 prohibits image formation on the succeeding sheet, even if the Timage timer reaches the image formation interval Timage (604), it does not output the / TOP signal (602) and does not start image formation on the succeeding sheet. Thereafter, when the MP transport sensor 52 detects the passage of the trailing edge of the sheet (preceding sheet) in the transport direction fed from the MP tray 50 at timing (632) (FIG. 6(d)), the engine unit 202 permits image formation and feeding of the succeeding sheet. As a result, the engine unit 202 outputs the / TOP signal (603) for the second sheet (successive sheet) to the controller unit 201 at timing (632) (FIG. 6(a)). Furthermore, the engine unit 202 drives the MP tray pickup roller 51 at the timing of the feeding start signal (623) to feed one subsequent sheet of paper (subsequent paper) from the MP tray 50.

[0069] [Image formation control and feed control sequence] FIG. 7 is a flowchart showing the control sequence of image formation control and feeding control in this embodiment. FIG. 7(a) is a flowchart showing the control sequence of feeding control for paper placed on the MP tray 50, and FIG. 7(b) is a flowchart showing the control sequence of image formation control for forming an image on fed paper. The processes shown in FIGS. 7(a) and 7(b) are started and executed by the engine unit 202 when the engine unit 202 receives a print start command from the controller unit 201. It is assumed that the engine unit 202 has received image size information, a paper size specification command, and a print reservation command from the controller unit 201 before receiving the print start command. It is also assumed that, when the processes shown in FIGS. 7(a) and 7(b) are started, image formation and feeding of subsequent paper, which will be described later, are permitted.

[0070] (Control sequence for feed control) A control sequence for controlling the feeding of sheets placed on the MP tray 50 shown in Fig. 7(a) will be described. The processes of S700 to S705 are the same as the processes of S500 to S505 shown in Fig. 5(a) of the first embodiment, and therefore the description thereof will be omitted here.

[0071] In S706, the engine unit 202 acquires the detection status of the MP transport sensor 52 and determines whether the trailing edge in the transport direction of the paper fed from the MP tray 50 has passed the MP transport sensor 52 (MP transport sensor OFF?). If the acquired detection status of the MP transport sensor 52 is OFF, the engine unit 202 determines that the trailing edge of the fed paper has passed the MP transport sensor 52 and proceeds to S708. On the other hand, if the acquired detection status of the MP transport sensor 52 is not OFF (ON), the engine unit 202 determines that the trailing edge of the fed paper has not passed the MP transport sensor 52 and proceeds to S707. In S707, because the trailing edge of the preceding paper has not passed the MP transport sensor 52, the engine unit 202 sets prohibition of image formation and feeding of the succeeding paper so that the feeding operation of the succeeding paper from the MP tray 50 and the image forming operation are not started, and returns to S706.

[0072] In S708, the engine unit 202 determines whether the prohibition of image formation and feeding of subsequent sheets has been set in the processing of S707 (feeding / image formation prohibited?). If the engine unit 202 determines that the prohibition of image formation and feeding of subsequent sheets has been set, the process proceeds to S709. On the other hand, if the engine unit 202 determines that the prohibition of image formation and feeding of subsequent sheets has not been set (image formation and feeding of subsequent sheets has been set to be permitted), the process proceeds to S710. In S709, the engine unit 202 sets the permission of image formation and feeding of subsequent sheets. The processing of S710 and S711 is the same as the processing of S509 and S510 shown in FIG. 5(a) of the first embodiment, and therefore a description thereof will be omitted here.

[0073] (Image formation control sequence) The control sequence of image formation control for forming an image on a fed sheet shown in Fig. 7(b) will be described. The processes of S720 to S723 are the same as the processes of S520 to S523 shown in Fig. 5(b) of the first embodiment, and therefore will not be described here.

[0074] In S724, the engine unit 202 refers to the Timage timer and determines whether the image formation interval has elapsed. If the engine unit 202 determines based on the timer value of the Timage timer that the image formation interval has elapsed, the process proceeds to S725. If the engine unit 202 determines that the image formation interval has not elapsed, the process returns to S724. In S725, the engine unit 202 determines whether the prohibition of image formation on subsequent sheets has been set in the process of S707 described above (image formation prohibited?). If the engine unit 202 determines that the prohibition of image formation on subsequent sheets has been set, the process returns to S725. On the other hand, if the engine unit 202 determines that the prohibition of image formation on subsequent sheets has not been set (image formation on subsequent sheets is permitted), the process proceeds to S726. The processes of S726 and S727 are the same as the processes of S525 and S526 shown in FIG. 5B of the first embodiment, and therefore will not be described here.

[0075] In this embodiment, an example has been described in which, if the trailing edge of the preceding sheet has not passed the MP transport sensor 52 at the feed interval Tpaper according to the specified paper size, image formation on and feeding of the succeeding sheet are prohibited until the trailing edge of the preceding sheet passes the MP transport sensor 52. As described above, when performing continuous printing on sheets placed on the MP tray, even if a mismatch in paper size causes a mismatch in the timing of the image formation operation or feeding operation, it is possible to prevent transport problems such as jams by performing control according to the timing deviation.

[0076] As described above, according to this embodiment, it is possible to prevent the occurrence of paper transport failures due to mismatches in paper sizes. [Example]

[0077] In the second embodiment, when the specified paper size (designated size) differs from the paper size (loading size) loaded on the MP tray 50, control is described for determining the start of feeding of the subsequent paper and the start of image formation at the timing when the preceding paper passes the MP transport sensor. In the third embodiment, when the specified paper size (designated size) differs from the paper size (loading size) loaded on the MP tray 50, control is described for changing the start timing of image formation of the subsequent paper depending on the amount of delay in feeding timing. Note that the configuration and system configuration of the image forming apparatus of this embodiment are the same as those of the first and second embodiments, and the same devices and members are designated by the same reference numerals, and description thereof will be omitted.

[0078] [Outline of printing operation in this embodiment] FIG. 8 is a timing chart illustrating image formation control and feed control in this embodiment. In FIG. 8, the specified paper size is A5 landscape paper (paper width 210 mm × length in the transport direction 148 mm). On the other hand, the loading size of the paper loaded on the MP tray 50 is LTR (letter) paper (paper width 215.9 mm × length in the transport direction 279.4 mm). The specified paper size and the loaded size do not match, and the paper loaded on the MP tray 50 is longer in the transport direction. The parameters used in the image forming apparatus and print control are the same as those in the first embodiment. The configuration in FIG. 6 is the same as FIG. 4 of the first embodiment and FIG. 6 of the second embodiment, and explanation of how to read the figure will be omitted.

[0079] When the engine unit 202 receives a print start command from the controller unit 201, it instructs the image control unit 206, paper transport unit 208, etc. to start the print operation in order to perform image formation preparation operations for the print operation. Then, when it receives a notification from the image control unit 206 that image formation preparation is complete, the engine unit 202 outputs a / TOP signal (801) for the first sheet of paper to the controller unit 201 (FIG. 8(a)). The Timage timer starts at timing (811) when the reference / TOP signal (801) is output (FIG. 8(b)). The engine unit 202 controls the image formation interval to be the image formation interval Timage (804) corresponding to the specified paper size. Then, when the timer value of the Timage timer reaches Timage (804) (FIG. 8(b)), if the loaded size of the paper is the same as the specified size, the engine unit 202 outputs a / TOP signal (802) for the second sheet of paper to the controller unit 201 (FIG. 8(a)). The image formation interval Timage in FIG. 8 can be calculated using (Equation 1) explained in FIG. 3 of the first embodiment.

[0080] Meanwhile, when the feeding preparation operation is completed, the engine unit 202 drives the MP tray pickup roller 51 at the timing of the feeding start signal (821) (FIG. 8(c)) to feed one sheet of paper from the MP tray 50. The engine unit 202 controls the feeding of the subsequent sheets while setting the desired feeding interval to the feeding interval Tpaper (824) corresponding to the same loading size as the specified size of the paper. As in the first and second embodiments, the feeding interval Tpaper is controlled based on the timing at which the MP transport sensor 52 detects the leading edge of the preceding sheet in the transport direction. When the MP transport sensor 52 detects the leading edge of the paper in the transport direction of the paper fed from the MP tray 50 at timing (831) (FIG. 8(d)), the engine unit 202 starts the Tpaper timer at timing (841) (FIG. 8(e)). The feeding interval Tpaper (824) in Figure 4 is the feeding interval when landscape paper of A5 size, the same size as the specified size, is fed from the MP tray 50, and can be calculated using (Equation 2) described in Figure 3 of Example 1.

[0081] The engine unit 202 checks the state of the MP transport sensor 52 when the timer value of the Tpaper timer reaches the feeding interval Tpaper (824) (FIG. 6(e)). In this embodiment, feeding control (setting of the feeding interval Tpaper (824)) is performed assuming that A5-sized paper is placed landscape-oriented on the MP tray 50. However, the paper actually placed on the MP tray 50 is LTR (letter) paper (paper width 215.9 mm × length in the transport direction 279.4 mm), which is longer than the length of A5-sized landscape-oriented paper, 148 mm. Therefore, at the timing (842) when the timer value of the Tpaper timer reaches the feeding interval Tpaper (824), the trailing edge in the transport direction of the preceding paper has not yet passed the MP transport sensor 52.

[0082] Therefore, if the engine unit 202 determines at timing (842) that the trailing edge in the transport direction of the preceding paper has not passed the MP transport sensor 52, it prohibits image formation and feeding of the succeeding paper. Because the engine unit 202 prohibits image formation on the succeeding paper, even if the Timage timer reaches the image formation interval Timage (804), it does not output the / TOP signal (802) and does not start image formation on the succeeding paper. Note that time measurement by the Tpaper timer continues as is.

[0083] Thereafter, when the MP transport sensor 52 detects the passage of the trailing edge in the transport direction of the paper (preceding paper) fed from the MP tray 50 at timing (832) (FIG. 8(d)), the engine unit 202 performs the following process. That is, the engine unit 202 calculates a difference ΔTpaper (843) from the current timer value of the Tpaper timer and the paper feed interval Tpaper. Then, using the calculated difference ΔTpaper (843), the engine unit 202 switches the image formation interval of the Timage timer from Timage to (Timage + ΔTpaper (812)). In addition, the engine unit 202 changes the prohibition setting for image formation and feeding of the subsequent paper to the permission setting.

[0084] In accordance with the setting to allow feeding of the subsequent sheet, the engine unit 202 drives the MP tray pickup roller 51 at the timing of the feeding start signal (823) to feed one subsequent sheet of paper (subsequent sheet) from the MP tray 50. Furthermore, when image formation on the subsequent sheet is permitted and the Timage timer reaches the image formation interval (Timage+△Tpaper), the engine unit 202 outputs a / TOP signal (803) for the second sheet of paper (subsequent sheet) to the controller unit 201 (FIG. 8(a)).

[0085] [Image formation control and feed control sequence] FIG. 9 is a flowchart showing the control sequence of image formation control and feeding control in this embodiment. FIG. 9(a) is a flowchart showing the control sequence of feeding control for paper placed on the MP tray 50, and FIG. 9(b) is a flowchart showing the control sequence of image formation control for forming an image on fed paper. The processes shown in FIGS. 9(a) and 9(b) are started and executed by the engine unit 202 when the engine unit 202 receives a print start command from the controller unit 201. It is assumed that the engine unit 202 has received image size information, a paper size specification command, and a print reservation command from the controller unit 201 before receiving the print start command. It is also assumed that, when the processes shown in FIGS. 9(a) and 9(b) are started, image formation and feeding of subsequent paper, which will be described later, are permitted.

[0086] (Control sequence for feed control) A control sequence for controlling the feeding of sheets placed on the MP tray 50 shown in Fig. 9(a) will be described. The processing of S900 to S910 is the same as the processing of S500 to S510 shown in Fig. 7(a) of the second embodiment, and therefore the description thereof will be omitted here.

[0087] In S911, the engine unit 202 acquires the time of the Tpaper timer at the timing when the trailing edge of the preceding paper in the transport direction passes the MP transport sensor 52, and calculates the difference ΔTpaper from the feeding interval Tpaper. The difference ΔTpaper indicates how much the timing to feed the succeeding paper is delayed from the timing when the preceding paper is a paper of the specified size.

[0088] The difference ΔTpaper can also be calculated using the following (Equation 7). Difference△Tpaper = ((loading size + paper spacing) - (specified size + paper spacing)) / transport speed ...(Formula 7) In this embodiment, the loading size (length of LTR paper in the transport direction) is 279.4 mm, and the paper spacing is 140 mm. The specified size (length of A5 landscape paper in the transport direction) is 148 mm. Therefore, from Equation 7, the difference ΔTpaper is ((279.4 mm + 140 mm) - (148 mm + 140 mm)) / 150 mm / s = 131.4 mm / / 150 mm / s ≒ 0.876 seconds.

[0089] In S912, the engine unit 202 switches the image formation interval of the Timage timer from the image formation interval Timage when the paper is of the specified size to the image formation interval (Timage+ΔTpaper) to which the difference ΔTpaper has been added. The process of S913 is the same as the process of S711 shown in FIG. 7A of the second embodiment, and therefore a description thereof will be omitted here.

[0090] (Image formation control sequence) The control sequence of image formation control for forming an image on a fed sheet shown in Fig. 9(b) will be described. The processes of S920 to S923 are the same as the processes of S720 to S723 shown in Fig. 7(b) of the second embodiment, and therefore will not be described here.

[0091] In S924, the engine unit 202 refers to the Timage timer and determines whether the image formation interval has elapsed. If the engine unit 202 determines based on the timer value of the Timage timer that the image formation interval has elapsed, the process proceeds to S925. If the engine unit 202 determines that the image formation interval has not elapsed, the process returns to S924. In S925, the engine unit 202 determines whether the prohibition of image formation on subsequent sheets has been set in the process of S907 in FIG. 9A described above (image formation prohibited?). If the engine unit 202 determines that the prohibition of image formation on subsequent sheets has been set, the process returns to S924. On the other hand, if the engine unit 202 determines that the prohibition of image formation on subsequent sheets has not been set (image formation on subsequent sheets is permitted), the process proceeds to S926. The processes of S926 and S927 are the same as the processes of S726 and S727 shown in FIG. 7B of the second embodiment, and therefore will not be described here.

[0092] As described above, even if a mismatch in the timing of image formation or feeding operations occurs due to a control delay caused by a paper size mismatch, control can be performed to match the timing discrepancy, thereby preventing transport problems such as jams.

[0093] As described above, according to this embodiment, it is possible to prevent the occurrence of paper transport failures due to mismatches in paper sizes. [Explanation of symbols]

[0094] 50 MP tray 51 MP tray pickup roller 52 MP transport sensor 201 Controller 202 Engine section

Claims

1. A feeding means for sequentially feeding a plurality of recording materials placed in a paper feeding section to an image forming position; an image forming means for forming an image on the recording material fed by the feeding means at the image forming position in accordance with an image signal output from the output means; a detection means for detecting the recording material fed by the feeding means; a control means for determining an image formation start timing for starting image formation in response to the image signal output by the output means, and a feeding start timing for feeding the recording material by the feeding means; Equipped with The image forming apparatus is characterized in that, if the detection means does not detect the trailing end of the first recording material in the transport direction between the time when the detection means detects the leading end of the first recording material in the transport direction fed by the feeding means and the time when the feeding start timing begins, the control means shifts the image formation start timing and the feeding start timing for the second recording material fed after the first recording material by an amount of time that is delayed from the time when the detection means detects that the trailing end of the first recording material in the transport direction has passed.

2. A feeding means for sequentially feeding a plurality of recording materials placed in a paper feeding section to an image forming position; an image forming means for forming an image on the recording material fed by the feeding means at the image forming position in accordance with an image signal output from the output means; a detection means for detecting the recording material fed by the feeding means; a control means for determining an image formation start timing for starting image formation in response to the image signal output by the output means, and a feeding start timing for feeding the recording material by the feeding means; Equipped with when the detection means does not detect the trailing edge of the first recording material in the conveying direction until the feeding start timing after detecting the leading edge of the first recording material fed by the feeding means, the control means determines the image formation start timing and the feeding start timing for a second recording material fed next to the first recording material based on the length of the first recording material in the conveying direction, An image forming apparatus characterized in that the image formation start timing is determined based on the length of the image signal corresponding to the first recording material and the length of the section in which no image signal is output, which is provided between the image signal corresponding to the first recording material and the image signal corresponding to the second recording material.

3. A feeding means for sequentially feeding a plurality of recording materials placed on a paper feeding section to an image forming position; an image forming means for forming an image on the recording material fed by the feeding means at the image forming position in accordance with an image signal output from the output means; a detection means for detecting the recording material fed by the feeding means; a control means for determining an image formation start timing for starting image formation in response to the image signal output by the output means, and a feeding start timing for feeding the recording material by the feeding means; Equipped with when the detection means does not detect the trailing edge of the first recording material in the conveying direction until the feeding start timing after detecting the leading edge of the first recording material fed by the feeding means, the control means determines the image formation start timing and the feeding start timing for a second recording material fed next to the first recording material based on the length of the first recording material in the conveying direction, An image forming apparatus characterized in that the timing for starting feeding is determined based on the length of the first recording material, the paper-to-paper interval between the first recording material and the second recording material, and the distance of the conveying path from the paper feed unit to the detection means.

4. The image forming apparatus according to claim 2 or claim 3, characterized in that the control means determines the timing at which an image signal for the second recording material is output from the output means and the timing at which the second recording material is fed by the feeding means based on the image formation start timing and the feeding start timing corresponding to the case where the length of the first recording material in the transport direction is the maximum length in the transport direction that can be placed in the paper feed section.

5. The image forming apparatus according to claim 2 or claim 3, characterized in that the control means, when the detection means detects that the trailing edge of the first recording material in the transport direction has passed, causes the output means to output an image signal for the second recording material, and causes the feeding means to feed the second recording material.

6. 4. The image forming apparatus according to claim 2, wherein the control means shifts the timing at which an image signal for the second recording material is output from the output means and the timing at which the second recording material is fed by the feeding means by an amount equal to the time at which the timing at which the detection means detects that the trailing edge of the first recording material in the transport direction has passed is delayed from the feeding start timing.

7. 2. The image forming apparatus according to claim 1, wherein the image formation start timing is determined based on the length of the image signal corresponding to the first recording material and the length of the section in which no image signal is output between the image signal corresponding to the first recording material and the image signal corresponding to the second recording material.

8. 2. The image forming apparatus according to claim 1, wherein the timing for starting feeding is determined based on the length of the first recording material, the paper-to-paper interval between the first recording material and the second recording material, and the distance of the transport path from the paper feed unit to the detection means.

9. the image forming means includes an image carrier and a transfer section that transfers the image formed on the image carrier onto a recording material fed by the feeding means; 9. The image forming apparatus according to claim 1, wherein the distance from the transfer unit to the detection means is equal to or less than the distance the image travels from the position where the image is formed on the image carrier to the transfer unit.

10. a recording material detecting means provided between the detecting means and the transfer unit, for detecting the conveyed recording material; a conveying means provided between the detecting means and the transfer unit, for conveying a recording material; Equipped with 10. The image forming apparatus according to claim 9, wherein the control means controls the timing at which the recording material conveyed by the conveying means reaches the transfer unit based on the detection result of the recording material detection means.

Images