JP2010189102A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of surely performing positioning to an image forming reference position of paper carried from a paper tray. <P>SOLUTION: When carrying the paper to a printing reference position RP from the paper tray 4, even in a state of moving to the downstream side when the paper P carried in the next place goes over a placing position of the paper tray 4, due to the moving of the paper P carried in the next place together with the paper P carried to the reference position RP since separation from the paper P carried in the next place is not skillfully performed, and even if the tip of the carrier paper P goes over the printing reference position RP by the extent of carrying the paper P from a position going over the placing position when carrying the next paper P, the paper P can be surely positioned in the reference position RP by inversely carrying the paper P going over the reference position RP to the upstream side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for forming an image on a paper sheet once positioned at a reference position for image formation.

  Conventionally, a printer as an image forming apparatus that performs printing by forming an image on a sheet conveyed from a sheet tray is known (for example, Patent Document 1). This type of printer is configured to start printing on a sheet after the sheet conveyed from the sheet tray is once positioned at a reference position for printing (image formation). Thus, once the paper is positioned at the printing reference position, printing on the paper can be performed with high positional accuracy, thereby improving the print quality.

JP 2008-36884 A (paragraph 0029, FIG. 1, etc.)

  In a conventional image forming apparatus, the leading edge of a sheet is positioned at a reference position for image formation by conveying a sheet by a predetermined amount for each printing from a sheet tray storing a plurality of sheets. It is configured as follows. That is, if the paper is transported by a predetermined amount from the placement position provided in the paper tray, the leading edge of the paper is positioned at the reference position.

  By the way, when the top sheet of the plurality of sheets stored in the sheet tray is transported from the sheet tray, separation of the transported sheet and the next sheet is not successful, and the sheet is moved to the reference position. As the paper is transported, the next paper may also move to a position beyond the paper tray placement position in the direction of the reference position. Then, when the next sheet feeding operation is performed, if the sheet moved in the direction of the reference position is transported by a predetermined amount, the sheet is transported from the position beyond the loading position. The leading end exceeds the reference position for image formation. At this time, in the conventional apparatus, printing is not performed on the sheet conveyed beyond the reference position, and after the sheet is discharged out of the apparatus, the next sheet is conveyed again from the sheet tray for printing. Was configured to do. Therefore, there is a problem that blank pages are generated during continuous printing, and the page order is not matched during double-sided printing, and improvement in technology has been demanded.

  An object of the present invention is to provide a technique capable of reliably positioning a sheet conveyed from a sheet tray to a reference position for image formation.

  In order to achieve the above object, an image forming apparatus according to the present invention forms an image on a sheet once positioned at a reference position for image formation. In the image forming apparatus, a plurality of sheets are stored in the sheet tray. The paper is transported by a predetermined amount from the placement position provided on the paper tray to the reference position one by one for each image formation, and the leading edge of the paper at that time is the reference position And a paper feed mechanism for positioning the leading edge of the paper at the reference position by reversely conveying the paper upstream.

  In the invention configured as described above, the paper feeding mechanism conveys a sheet by a predetermined amount from the placement position of the paper tray toward the reference position for image formation one by one for each image formation. If the leading edge of the paper exceeds the reference position, instead of discharging the paper out of the device as in the past, the paper that has exceeded the reference position is transported backward to the reference position. Position to. Accordingly, when the paper is transported from the paper tray to the image formation reference position, the paper transported to the reference position is not successfully separated from the paper transported to the reference position and the next transported paper. Even if the next paper to be transported moves in the direction of the reference position beyond the placement position of the paper tray due to movement of the next paper transported together, the next paper is transported. At this time, the leading edge of the conveyed paper exceeds the reference position for image formation as much as the paper is conveyed from the position beyond the loading position, but the paper exceeding the reference position is reversely conveyed upstream. As a result, the sheet can be reliably positioned at the reference position for image formation.

  At this time, the paper feed mechanism is provided downstream of the paper feed means for feeding the paper one by one from the paper tray, and detects the leading edge of the paper carried by the paper feed means. A first paper detection sensor that is configured to be capable of transporting the paper downstream and upstream of the first paper detection sensor, and further transporting the paper transported by the paper feeding unit to the reference position further downstream A transport unit that transports the paper to the reference position, a second paper detection sensor that detects a leading edge of the paper downstream of the transport unit and upstream of the reference position, and paper feed from the paper tray to the reference position For each operation, control is performed to transport the paper from the placement position to the paper feeding unit by a predetermined transport amount, and the leading edge is transported to the first paper detection sensor by being transported to the paper feeding unit. Control means for performing control to position the discharged paper at the reference position by the transport means, and the control means, when the paper transported by the transport means reaches the reference position, If the conveyance of the sheet for the conveyance amount by the sheet feeding unit is not completed, after the conveyance of the sheet by the sheet feeding unit is completed, the second sheet detection sensor puts the sheet on the conveyance unit. Control may be performed so that the sheet is conveyed backward upstream until the leading edge of the sheet is detected, and the sheet is positioned at the reference position after the leading edge of the sheet is detected by the second sheet detection sensor.

  With such a configuration, every time a sheet is fed from the sheet tray to the image formation reference position, the sheet is transported from the sheet tray mounting position to the sheet feeding unit by a predetermined transport amount. The paper, which has been transported to the paper feed means and whose leading edge is detected by the first paper detection sensor, is positioned at the reference position by the transport means, so that the paper is transported by a predetermined amount from the paper tray placement position. Thus, it can be easily positioned at the reference position. At this time, the conveyance amount of the sheet by the sheet feeding unit is configured to be shorter than a predetermined amount from the sheet tray placement position to the image formation reference position.

  In addition, when the paper feeding unit transports the paper that has been moved in the direction of the image formation reference position beyond the placement position of the paper tray, this paper conveyed to the paper feeding unit is the first paper detection sensor. Even if the paper reaches the reference position by being transported by the transporting unit after the detection, the transporting of the paper for the transporting amount by the paper feeding unit may not be completed. In such a case, the conveyance of the sheet by the sheet feeding unit is completed, and after the sheet has once passed the reference position, the sheet that has passed the reference position is moved to the conveying unit by the second sheet detection sensor. It is transported upstream until it is detected. Then, after the leading edge of the sheet is detected by the second sheet detection sensor, the sheet is conveyed to the reference position for image formation by the conveying unit, so that the sheet conveyed from the sheet tray can be reliably positioned at the reference position. .

  In addition, the paper feeding unit includes a loading roller that has a peripheral surface including a flat surface and an arc surface, and conveys the paper by slidingly contacting the paper on the paper tray while the arc surface rotates. The control means may perform control for transporting the paper from the placement position by the transport amount by rotating the loading roller once in a state where the plane faces the paper for each paper feeding operation. Good.

  With such a configuration, the loading roller having a circumferential surface composed of a flat surface and an arc surface is rotated once from the state where the plane faces the paper, so that the arc surface rotates and slides on the paper on the paper tray. Transport the paper. That is, the paper can be transported by the transport amount from the loading position of the paper tray until the rotating arc surface starts sliding contact with the paper and finishes sliding. And practical.

1 is a perspective view illustrating an ink jet printer that is an embodiment of the present invention. FIG. The principal part enlarged view of an inkjet printer. The figure which shows the outline of the internal structure of an inkjet printer. The figure which shows the structure of a paper edge detection sensor. FIG. 4 is a diagram illustrating a sheet feeding operation from a sheet tray. FIG. 6 is a diagram illustrating a positioning operation of a sheet to a reference position. The flowchart which shows a cueing process.

  FIG. 1 is a perspective view showing an ink jet printer 1 according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the ink jet printer 1. FIG. 3 is a diagram showing an outline of the internal configuration of the ink jet printer 1. FIG. 4 is a diagram showing the configuration of the paper edge detection sensor 57. FIG. 5 is a diagram showing a paper feeding operation of the paper P from the paper tray 4. FIG. 6 is a diagram showing the positioning operation of the paper P to the reference position RP. FIG. 6A shows the paper P from the paper tray 4 to the printing position PP of the inkjet printer 1 for printing on the paper P for printing. FIG. 6B is a diagram illustrating a state in which the automatic paper feeding apparatus 3 has started feeding, and (b) illustrates a state in which the conveyance of the paper P by the loading roller 10 is not completed when the leading edge of the paper P reaches the reference position RP. (C) is a diagram showing a state in which the leading end of the paper P exceeds the reference position RP when the conveyance of the paper P by the loading roller 10 is completed, and (d) is a diagram showing the paper P being paper. FIG. 6 is a diagram illustrating a state in which the leading edge of the paper P that once exceeds the reference position RP is positioned at the reference position RP by being reversely conveyed by the feed roller 13.

  In an inkjet printer 1 as an “image forming apparatus” of the present invention, a printing mechanism 50 is built in the printer body 2. The print mechanism 50 includes a carriage 53 that reciprocates in the width direction (main scanning direction) substantially perpendicular to the feeding direction (sub-scanning direction) of the paper P conveyed from the tray 4. A head 55 is provided. Then, in response to an operation command from a controller 20 (see FIG. 3) that controls the entire inkjet printer 1, the paper P is imaged from the paper tray 4 by the loading (LD) roller 10 and the paper feed roller 13. After the ink is transported to and positioned once, printing is performed on the paper P by ejecting ink from the print head 55 that reciprocates integrally with the carriage 53 to form an image on the paper P at the printing position PP. . The paper P printed in this way is discharged from the discharge port 2 a opened at the lower front side of the printer body 2 by the transport roller 56. Next, the ink jet printer 1 will be described in detail.

  As shown in FIG. 3, the inkjet printer 1 of the present embodiment is configured to be communicably connected to a host computer PC via an interface 24 configured by a USB interface, a parallel interface, or the like. In the host computer PC, a process of converting image data and document data into print data is executed by a printer driver configured by a program and a CPU. These print data and print commands are sent from the host computer PC to the inkjet printer 1. Sent. Further, as shown in FIG. 1, a display unit 9 constituted by, for example, an LCD for displaying characters, figures, symbols, and the like is provided on the upper surface of the printer main body 2 so that various messages for the user can be displayed. Has been.

  Next, the configuration of the controller 20 of the inkjet printer 1 will be described with reference to FIG. A CPU 25, ROM 26, RAM 27, print controller 28, nonvolatile memory 29, LCD controller 30, etc. are connected to the system bus 21 of the controller 20 connected to the interface 24.

  The CPU 25 performs arithmetic processing for executing operation control of the print mechanism 50. Further, the CPU 25 executes a program stored in the ROM 26 to give an instruction necessary for print control to the print controller 28, paper feed processing of the paper P from the paper tray 4, and sending of the paper P to the printing position PP. A command for processing and discharging the paper P to the outside of the printer main body 2 is output. The ROM 26 stores a program (firmware) necessary for the control of the CPU 25. The RAM 27 temporarily stores data such as print data input from the outside, and the nonvolatile memory 29 stores various data and tables necessary for the control of the CPU 25.

  The LCD controller 30 is provided with an image processing module 30 a for performing processing necessary for displaying the print data given through the interface 24 on the display unit 9. In addition, the image processing module 30a generates image data to be displayed on the display unit 9 such as image data corresponding to a printer-specific image such as a menu screen to be displayed on the display unit 9, icons, a message to the user, and the like. It has a function. Then, the image data generated by the image processing module 30 a is displayed on the display unit 9 by the LCD controller 30.

  Detailed configurations and operations of the CPU 25 and the print controller 28 will be described later in detail. In addition, the skew in the present embodiment refers to the structure of the automatic paper feeder 3 to be described later, the usage environment of the ink jet printer 1, the habit of a user who adjusts the guide width of the edge guide 6 by himself, etc. This is an inclination generated in the paper P conveyed by the conveyance mechanism 8 due to various events.

  Next, an automatic paper feeder (corresponding to the “paper feed mechanism” of the present invention) 3 disposed on the back side of the printer main body 2 will be described. An automatic sheet feeder (Auto Sheet Feeder) 3 is provided with a sheet tray 4 in which a plurality of sheets P are stored, and a sheet guide 7 having a placement plate 5 and an edge guide 6. Further, as shown in FIG. 5, the paper tray 4 is provided with a placement position WP for the paper P, and the plurality of paper P is placed on the paper tray 4 so that the leading ends thereof are placed at the placement position WP. Stored.

  The edge guide 6 includes a fixed edge guide 6 a and a movable edge guide 6 b that can slide in the width direction of the paper P substantially perpendicular to the feeding direction of the paper P by the automatic paper feeder 3. The guide width, that is, the edge guide position of the movable edge guide 6b can be adjusted in accordance with the sheet width, and the sheet P conveyed from the sheet tray 4 by the automatic sheet feeder 3 is guided. Then, as shown in FIG. 2, by adjusting the position of the movable edge guide 6b of the edge guide 6 included in the paper guide 7 and adjusting the guide width, the paper tray 4 has a plurality of sizes from L size to A3 size. The sheet P can be stored. As shown in FIG. 5 (b), the loading plate 5 includes an arcuate surface of the rotating loading roller 10 and a sheet when a sheet P is fed from a sheet tray 4 to a printing position PP, which will be described later. The uppermost sheet P among the sheets P stored in the tray 4 is configured to swing in the direction of the arrow UP by a hopper mechanism (not shown).

  As shown in FIG. 5, the automatic paper feeder 3 prints the printing paper P stored in the paper tray 4 one by one along the paper guide 7, that is, the position of the print head 55 in the printer body 2, that is, printing. A transport mechanism 8 for feeding to the position PP is provided. The transport mechanism 8 is a loading roller that is disposed near the lower end of the mounting plate 5 on the back surface of the printer main body 2 so as to face the mounting plate 5 and has a circumferential surface composed of a flat surface and an arc surface (the “paper feeding” of the present invention). 10 ”, a paper feed roller (corresponding to“ conveying means ”of the present invention) 13 disposed downstream of the loading roller 10 and upstream of the print carriage 53, and downstream of the carriage 53. It has the conveyance roller 56 arrange | positioned. Further, a guide 12 is disposed on the downstream side of the loading roller 10 in the paper feeding direction.

  As shown in FIG. 5A, the loading roller 10 slides in contact with the paper P on the paper tray 4 while the circular arc surface rotates for each paper feeding operation from the paper tray 4 to the printing position PP. 4 conveys the paper P one by one. Further, the paper feed roller 13 is provided so that the paper P can be conveyed upstream and downstream, and the paper P conveyed from the paper tray 4 by the loading roller 10 is used for further downstream image formation, that is, a printing reference position RP. Transport to. Then, during the paper feeding operation from the paper tray 4 to the printing position PP (reference position RP), the mounting plate 5 is moved from the standby state shown in FIG. 5A to the arrow UP as shown in FIG. 5B. The loading roller 10 rotates clockwise while abutting on the arc surface of the top sheet P of the paper tray 4 and the loading plate 5 while swinging in the direction of The uppermost paper P is fed to the paper feed roller 13. Note that a separation pad (not shown) is provided at the placement position WP of the paper tray 4, and the uppermost paper P on the paper tray 4 that is conveyed when the arc surface of the loading roller 10 is slidably contacted. Then, the sheet P to be conveyed next is separated, and only the uppermost sheet P is conveyed by the loading roller 10 toward the printing position PP.

  A mechanical paper detection sensor (corresponding to the “first paper detection sensor” of the present invention) 15 is disposed downstream of the loading roller 10 and upstream of the paper feed roller 13. As shown in FIG. 5B, the paper detection sensor 15 detects the leading edge of the paper P that is conveyed and contacted by the conveyance mechanism 8 (loading roller 10) at a predetermined first paper edge detection position SP1. It is configured to be able to. Then, by detecting the leading edge of the paper P by the paper detection sensor 15, it can be detected that the paper P has been fed by the loading roller 10.

  The transport mechanism 8 is controlled by a control command from the print controller 28, and is configured to transport the paper P by a predetermined feed amount preset for each paper feed control step output from the print controller 28. Yes. That is, the loading roller 10, the paper feed roller 13, and the transport roller 56 are configured to be rotated by a paper feed motor (not shown) that is driven by the roller drive circuit 33 based on a control step from the print controller 28. (See FIG. 3). Further, the loading roller 10 and the paper feed motor are connected via a clutch that switches power transmission and disconnection. Therefore, when the paper P is fed from the paper tray 4 to the paper feed roller 13, the clutch is switched to the connected state, thereby driving the loading roller 10.

  In the present embodiment, the paper feed motor generates a driving force in the rotation direction according to the drive amount commanded from the roller drive circuit 33 based on the control step from the print controller 28. The paper feed motor rotates the loading roller 10, the paper feed roller 13, and the transport roller 56 using this driving force. That is, when the paper feed motor generates a predetermined drive amount, the loading roller 10, the paper feed roller 13, and the transport roller 56 rotate by a predetermined rotation amount. When the loading roller 10, the paper feed roller 13, and the transport roller 56 are rotated by a predetermined rotation amount, the paper P is transported by a predetermined feed amount.

  Accordingly, the feed amount of the paper P is determined according to the rotation amounts of the loading roller 10, the paper feed roller 13, and the transport roller 56. Accordingly, if the rotation amounts of the loading roller 10, the paper feed roller 13, and the transport roller 56 can be detected, the feed amount of the paper P can also be detected. Therefore, the rotation amounts of the loading roller 10, the paper feed roller 13, and the transport roller 56 are detected. For this purpose, a rotary encoder (not shown) is provided.

  The rotary encoder includes a scale having a large number of slits provided at predetermined intervals, and a detection unit provided to face the scale and fixed to the printer main body 2 side. This scale is provided on each of the loading roller 10, the paper feed roller 13, and the transport roller 56, and is configured such that when the loading roller 10, the paper feed roller 13 and the transport roller 56 rotate, the scale also rotates together. . When the loading roller 10, the paper feed roller 13, and the transport roller 56 are rotated, each slit of the scale sequentially passes through the detection unit. The rotary encoder is configured to output a pulse signal every time a slit provided in the scale passes the detection unit.

  Therefore, since the slits provided in the scale sequentially pass through the detection unit according to the rotation amounts of the loading roller 10, the paper feed roller 13, and the transport roller 56, the loading roller 10, the paper feed is based on the output of the rotary encoder. The rotation amounts of the roller 13 and the conveyance roller 56 can be detected. For example, when the paper P is transported at a feed amount of 1 inch for each control step, the rotary encoder indicates that the loading roller 10, the paper feed roller 13, or the transport roller 56 has been rotated by an amount corresponding to each circumference. Until it is detected, the roller drive circuit 33 drives the paper feed motor. In this way, the roller drive circuit 33 drives the paper feed motor until the rotary encoder detects that the loading roller 10, the paper feed roller 13 or the transport roller 56 has a rotation amount corresponding to the target feed amount. Then, the conveyance of the paper P is repeated based on the number of control steps from the print controller 28, thereby conveying the paper P from upstream to downstream.

  The paper feed motor may be a stepping motor. Even in such a configuration, the print controller 28 includes a counter as a measuring unit that counts the number of steps of the paper feed motor, so that the print controller 28 can detect the position of the paper P from the count value of the counter. . When changing the feed amount of the paper P according to the control step from the print controller 28, the paper feed motor rotates at a rotation angle according to the feed amount to be changed from the control map for controlling the stepping motor. The control command may be selected as follows.

  Accordingly, the paper P is fed into the paper feed roller 13 by the loading roller 10, and the front end of the paper P is detected at the first paper edge detection position SP 1 by the paper detection sensor 15 disposed on the upstream side of the paper feed roller 13. Then, the leading end of the paper P is bitten by the paper feed roller 13 by further rotating the loading roller 10 by a predetermined amount. As the paper P is further fed by the rotation of the paper feed roller 13, the leading edge of the paper P reaches the second paper edge detection position SP <b> 2, and the leading edge of the paper P is detected by the paper edge detection sensor 57. The sheet P is further conveyed downstream, and the leading end of the sheet P is positioned at a position that coincides with the print head 55, that is, the reference position RP for printing (image formation). That is, for each printing (image formation), after the sheet P fed one by one from the sheet tray 4 is detected at the first sheet edge detection position SP1 by the sheet detection sensor 15, between the sheet feed rollers 13 is detected. Is conveyed by an amount determined by the design configuration of the print mechanism 50, and is conveyed by a predetermined amount from the paper tray 4 to be printed between the print head 55 (carriage 53) and the platen 14. It is fed into PP and cueed to the reference position RP.

  Then, the printing on the paper P sent to the printing mechanism 50 is finished, and the paper P is discharged from the discharge port 2a by the transport roller 56, whereby the rear end of the paper P reaches the second paper edge detection position SP2. This is detected by the paper edge detection sensor 57 and the trailing edge of the paper P is detected. Then, the sheet P is further conveyed downstream, and the sheet P is fed from the sheet tray 4 to the printing position PP (sheet feeding) at a timing when the sheet P is discharged from the discharge port 2a by a predetermined amount. ) Is started. In the present embodiment, when the previous paper P is being discharged from the discharge port 2a and the leading edge of the succeeding paper P is fed to the cueing reference position RP, the previous paper P is transferred to the transport roller 56. The feeding of the succeeding sheet P to the printing position PP is started at the timing when the sheet P falls from the start position.

  Further, as shown in FIGS. 5B and 6A, in this embodiment, the arcuate surface of the loading roller 10 having a substantially D-shaped cross section according to the control step from the print controller 28. However, before the leading edge of the paper P reaches the cueing reference position RP, the sliding contact with the paper P by the arc surface of the loading roller 10 is completed. Cueing to the reference position RP at the tip of the paper is performed by the paper feed roller 13. Then, when the loading roller 10 rotates once, the control step for the loading roller 10 is reset and the rotation of the loading roller 10 is stopped. After the rotation of the loading roller 10 is stopped, as shown in FIG. 6D, the loading roller 10 is in a period until the control step for starting the feeding of the next sheet P is output from the print controller 28. It is configured to wait in a rotation stopped state at the initial position.

  In this embodiment, as shown in FIGS. 5B and 6A, before the feeding of the paper P due to the arc surface of the loading roller 10 being in sliding contact with the paper P, the paper P is completed. However, the transport speed of the paper P by the loading roller 10 and the transport speed of the paper P by the paper feed roller 13 are substantially the same. ing. In the example shown in FIG. 6, a case where only one sheet P is stored in the sheet tray 4 will be described in order to easily explain the sheet feeding operation of the sheet P for printing. As shown, it goes without saying that a plurality of sheets P may be stored in the sheet tray 4. The printing reference position RP may be any position as long as it is set upstream of the most downstream nozzle among the plurality of nozzles provided on the ink ejection surface 55a of the print head 55. . The configuration of the paper edge detection sensor 57 will be described in detail later.

  Next, the print mechanism 50 that performs printing on the paper P sent from the paper tray 4 will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, the print mechanism 50 is driven by a timing belt 51 that is looped in the left-right direction and reciprocates left and right (in the main scanning direction) along the guide 52. The carriage 53 is provided with a paper edge detection sensor (corresponding to the “second paper detection sensor” of the present invention) 57 and detects the left and right edges and the upper and lower edges of the paper P. In other words, the paper edge detection sensor 57 detects the paper P fed from the paper tray 4 at the second paper edge detection position SP2 downstream of the paper feed roller 13 and upstream of the reference position RP of the print head 55. Thus, when the carriage 53 scans in the left-right direction before printing, the left and right edges of the paper P are detected so that the paper width can be recognized, or the leading edge of the paper P conveyed from upstream to downstream by the conveyance mechanism 8 It is possible to recognize the length of the paper P by detecting that the trailing edge passes the second paper edge detection position SP2.

  Note that the transport amount of the paper P by the transport mechanism 8 (paper feed roller 13) from when the leading edge of the paper P is detected by the paper edge detection sensor 57 to when the leading edge of the other side is detected is It is derived based on the control step for the paper feed roller 13 by the print controller 28 and the output of the rotary encoder described above. The position of the carriage 53 in the main scanning direction can be detected by a position sensor such as a linear potentiometer or a linear encoder (not shown). Based on this, the distance between the both sides of the leading edge of the paper P detected by the paper edge detection sensor 57 as described above is derived in a direction substantially perpendicular to the paper feeding direction, and the paper P conveyed by the conveyance mechanism 8. If there is a skew, the derived distance is smaller than the paper width.

  The paper edge detection sensor 57 is composed of a light emitting means 57a constituted by a light emitting diode and the like, and a light receiving means 57b constituted by a light receiving sensor such as a phototransistor and receiving the reflected light L2 of the light L1 from the light emitting means by the paper P. And. That is, the light L1 emitted from the light emitting means 57a is reflected by the paper P, and the reflected light L2 is received by the light receiving means 57b and converted into an electrical signal. Then, the magnitude of the electrical signal is measured as the output value of the light receiving sensor corresponding to the intensity of the received reflected light L2.

  The paper edge detection sensor 57 converts an electrical signal corresponding to the amount of received light into an 8-bit digital value (maximum received light amount is 0 and received light amount is 255) A / D conversion (analog / digital). Converted) and output to the controller 20. That is, the sensor output (A / D value) becomes closer to 255 as the reflected light amount is smaller and the received light amount is smaller in the state where there is no sheet at the second sheet end detection position SP2, and the sheet is detected at the second sheet end detection position SP2. In a certain state, the larger the amount of reflected light and the larger the amount of received light, the closer to zero. In the present embodiment, the sensor output when there is no paper at the second paper edge detection position SP2 is the paper output sensor output, and the sensor output when there is paper at the second paper edge detection position SP2 is the paper output. Yes Sensor output.

  Then, the CPU 25 of the controller 20 is substantially in the sub-scanning direction (paper P feeding direction) or the main scanning direction (sub-scanning direction) when the sensor output output by the paper edge detection sensor 57 reaches a threshold value to be described later. The position in the orthogonal direction) is set to the edge position (paper edge) of the paper P, the sub-scanning direction and the main scanning direction of the paper P by the print head 55 are set, and printing on the paper P is executed. It is configured as follows.

  By the way, the measurement sensitivity of the received light amount (reflected light amount) of the paper edge detection sensor 57 is that the paper edge detection sensor 57 itself deteriorates over time, or the ink mist generated when ink is ejected from the print head 55 is detected by the paper edge detection sensor. It gradually decreases due to adhesion to the light receiving means 57. Thereby, the detection accuracy of the edge position of the paper P by the paper edge detection sensor 57 is lowered. Therefore, in this embodiment, each time printing is performed on the paper P, the sensor output without the paper and the sensor output with the paper are detected, and an intermediate value between the two sensor outputs is set as a threshold when detecting the edge of the paper P. Is configured to do. With such a configuration, it is possible to always detect the edge position of the paper P with high accuracy even if the measurement sensitivity of the received light amount of the paper edge detection sensor 57 changes.

  In the present embodiment, the reflection type paper edge detection sensor 57 in which the light emitting means 57a and the light receiving means 57b are integrated is configured. However, the light emitting means and the light receiving means may be configured by individual devices. . Further, the paper end detection sensor may be configured as a so-called photo interrupter by arranging the light emitting means and the light receiving means so as to face each other and the light receiving means directly receive the light from the light emitting means. With such a configuration, the sheet P is positioned between the light emitting means and the light receiving means provided at the predetermined paper edge detection position, and the light from the light emitting means to the light receiving means is blocked, thereby It can be detected that the edge of the paper P is arranged at the paper edge detection position.

  The carriage 53 is mounted with an ink cartridge 54 that individually accommodates ink of each color such as cyan, magenta, yellow, and black. Each of these ink cartridges 54 is connected to a print head 55. The print head 55 applies pressure to the ink from the ink cartridge 54 and ejects the ink from the nozzle (not shown) toward the paper P. In this embodiment, the print head 55 employs a method in which a voltage is applied to the piezoelectric element to deform the piezoelectric element and pressurize the ink. However, a voltage is applied to the heating resistor (for example, a heater) to apply the ink. You may employ | adopt the system which pressurizes ink with the bubble generated by heating. The printed paper P is sent out to the discharge port 2a by the transport roller 56.

  Next, the CPU 25 and the print controller 28 constituting the controller 20 will be described in detail with reference mainly to FIG. The CPU 25 functions as a “control unit” of the present invention that controls the automatic paper feeder 3 and the print mechanism 50, and the print controller 28 controls the automatic paper feeder 3 and the print mechanism 50 in accordance with a control command from the CPU 25. . That is, the print controller 28 is connected with a head drive circuit 31, a belt drive circuit 32, and a roller drive circuit 33. The print controller 28 ejects ink onto the paper P by controlling the print head 55 via the head drive circuit 31. Further, the print controller 28 performs a reciprocating movement of the carriage 53 by controlling a carriage motor (not shown) via the belt drive circuit 32. Further, the print controller 28 controls a paper feed motor (not shown) via the roller drive circuit 33 to rotate the transport roller 56, the paper feed roller 13, and the loading roller 10 at arbitrary timings. In the present embodiment, the print command for instructing printing on the paper P includes at least information regarding the paper type and paper size of the paper P, and the print controller 28 transports the paper P in accordance with the print command. In this way, the transport mechanism 8 is controlled.

  The print controller 28 interprets the print data command input from the host computer PC, performs data expansion, and controls the print head 55 via the head drive circuit 31 based on this data. Yes. In this manner, the print controller 28 drives the print mechanism 50 to perform print control, and performs a paper P feeding process and a discharge process based on a print command via the CPU 25.

  Further, the CPU 25 is configured to implement the functions described below by executing a program stored in the ROM 26.

  The CPU 25 causes the loading roller 10 to transport the paper P from the placement position WP of the paper tray 4 by a predetermined predetermined transport amount every time the paper P is fed from the paper tray 4 to the printing reference position RP. Take control. At this time, the CPU 25 gives a control command to the print controller 28 to rotate the loading roller 10 once from the state where the plane of the peripheral surface of the loading roller 10 faces the paper P as shown in FIG. As a result, the sheet P is transported from the placement position WP by the transport amount. As described above, the loading roller 10 having a circumferential surface composed of a plane and a circular arc surface is rotated once from the state in which the plane faces the paper P, so that the arc surface rotates and slides on the paper P on the paper tray 4. The paper P is conveyed. That is, the paper P can be transported by the transport amount from the placement position WP of the paper tray 4 between the time when the rotating arc surface starts sliding contact with the paper P and the end of sliding contact. Thus, the paper P can be conveyed and is practical.

  Next, the CPU 25 transports the paper P, which is transported to the loading roller 10 and whose leading edge is detected by the paper detection sensor 15, by the paper feed roller 13 by an amount determined by the design configuration of the print mechanism 50, thereby causing the reference position. Control to position the RP. In this way, each time the paper P is fed from the paper tray 4 to the reference position RP for printing (printing head 55), the paper P is fed from the placement position WP of the paper tray 4 by a predetermined transport amount. The paper P is transported to the loading roller 10 and transported to the loading roller 10 and the leading edge is detected by the paper detection sensor 15. The paper feed roller 13 transports the paper P by an amount determined by the design configuration of the print mechanism 50, and the reference position By positioning on the RP, the paper P can be transported from the placement position WP of the paper tray 4 by a predetermined amount and easily positioned at the reference position RP. At this time, the conveyance amount of the paper P by the loading roller 10 is configured to be shorter than a predetermined amount from the placement position WP of the paper tray 4 to the printing reference position RP.

  By the way, among the plurality of sheets P stored in the sheet tray 4, when the uppermost sheet P is conveyed from the sheet tray 4 by the loading roller 10, separation between the conveyed sheet P and the next sheet P is performed. However, as the paper P is transported to the reference position RP, the next paper P may also move from the placement position WP of the paper tray 4. When the paper P that has been moved downstream from the placement position WP is transported by the loading roller 10 during the next paper feeding operation, the paper P is transported from a position beyond the placement position WP to the downstream side. Therefore, even if the paper P transported to the loading roller 10 is detected by the paper detection sensor 15 and then transported by the paper feed roller 13, the transport amount by the loading roller 10 is reached. In some cases, the conveyance of the sheet P is not completed (see FIG. 6B).

  In this way, even when the paper P is transported by the paper feed roller 13 and reaches the reference position RP, when the transport of the paper P for the transport amount by the loading roller 10 is not completed (FIG. 6B). As shown in FIG. 6C, the automatic paper feeder 3 is configured to once complete the conveyance of the paper P by the loading roller 10. Then, the automatic paper feeder 3 does not discharge the paper P whose leading edge exceeds the reference position RP to the outside of the printer main body 2 as in the prior art, but reversely conveys the paper P to the upstream side as a reference. Positioning is performed at the position RP (see FIG. 6D).

  Specifically, as shown in FIG. 6B, when the paper P transported by the paper feed roller 13 reaches the reference position RP, the transport of the paper P for the transport amount by the loading roller 10 is completed. If not, that is, if the sliding contact with the paper P by the arc surface of the loading roller 10 continues, the CPU 25 conveys the paper P by sliding the arc surface of the loading roller 10 with the paper P. (See FIG. 6C). Then, the CPU 25 causes the paper feed roller 13 to reversely convey the paper P upstream until the paper edge detection sensor 57 detects the leading edge of the paper P, and if the paper edge detection sensor 57 detects the leading edge of the paper P, the carriage 25 The sheet P is conveyed to the reference position RP by conveying the sheet P by an amount determined by the design configuration of 53, and thereby the sheet P conveyed from the sheet tray 4 is reliably positioned at the reference position RP. (See FIG. 6D). Next, referring to FIG. 7, a cueing process executed when printing is performed on the paper P will be described.

  FIG. 7 is a flowchart showing the cueing process. The cueing process shown in FIG. 7 is a process that is performed every time the paper P is fed from the paper tray 4 to the printing position PP. As shown in FIG. 7, when a print command is given from the host computer PC, the conveyance of the sheet from the sheet tray 4 by the loading roller 10 is started (step S1). When the sheet conveyance by the loading roller 10 is started, the leading edge of the sheet P conveyed by the rotation of the loading roller 10 is detected by the sheet detection sensor 15 (NO in step S2).

  If the leading edge of the paper P is detected by the paper detection sensor 15 (YES in step S2), the loading roller 10 is rotated once, the control step for the loading roller 10 by the print controller 28 is reset, and the loading roller 10 is rotated. Stop and enter a standby state (step S3).

  After the rotation of the loading roller 10 is stopped, the CPU 25 determines whether the leading edge of the paper P has already been transported beyond the cueing position (reference position RP) by the paper feed roller 13 (step S4). If it determines with YES in step S4, CPU25 will start the reverse conveyance of the paper P by the paper feed roller 13 (step S5). When the reverse conveyance of the paper P by the paper feed roller 13 is started, the leading edge of the paper P conveyed by the reverse rotation of the paper feed roller 13 is detected by the paper edge detection sensor 57 (NO in step S6).

  If the leading edge of the paper P is detected by the paper edge detection sensor 57 (YES in step S6), the CPU 25 conveys the paper P downstream by the paper feed roller 13 by an amount determined by the design configuration of the carriage 53. Thus, cueing is performed by positioning the leading edge of the paper P at the reference position RP, and the process is terminated (step S7). On the other hand, if it is determined NO in step S4, the CPU 25 conveys the paper P downstream by the paper feed roller 13 by an amount determined by the design configuration of the print mechanism 50, so that the leading edge of the paper P is at the reference position RP. The cueing by positioning is performed, and the process is terminated (step S7).

  As described above, in this embodiment, when the paper is transported from the paper tray 4 to the printing reference position RP, the separation of the paper P transported to the reference position RP and the paper P transported next is successful. Instead, the sheet P to be transported next moves together with the sheet P to be transported to the reference position RP, so that the sheet P to be transported next passes downstream of the placement position WP of the sheet tray 4. Even when the paper P is moved to the position where the paper P is transported from the position beyond the placement position WP when the next paper P is transported, the leading end of the transported paper P is the printing reference position RP. However, it is possible to reliably position the paper P at the reference position RP by reversely conveying the paper P exceeding the reference position RP upstream.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the ink jet printer 1 that performs color printing is described as an example of the image forming apparatus of the present invention. However, a printing apparatus (such as an ink jet printer that performs monochrome printing or another ink cartridge type photo printer) ( The present invention is also applied to a printing apparatus as a network printer having a wired LAN, a printing apparatus as a multifunction machine having a FAX or a scanner, and a printing apparatus other than an ink cartridge system. May be. That is, the present invention can be widely applied to an image forming apparatus that forms an image on a paper sheet that has been transported from a paper tray and once positioned at a reference position for image formation.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet printer (image forming apparatus), 3 ... Automatic paper feeder (paper feed mechanism), 4 ... Paper tray, 10 ... Loading roller (paper feed means), 13 ... Paper feed roller (conveyance means), 15 ... Paper Detection sensor (first paper detection sensor), 25 ... CPU (control means), 57 ... paper edge detection sensor (second paper detection sensor), P ... paper, RP ... reference position, WP ... loading position

Claims (3)

In an image forming apparatus for forming an image on a paper sheet once positioned at a reference position for image formation,
A paper tray for storing a plurality of the paper;
From the placement position provided on the paper tray, the paper is transported by a predetermined amount one by one toward the reference position for each image formation, and the leading edge of the paper at that time sets the reference position. An image forming apparatus, comprising: a paper feed mechanism that positions the leading edge of the paper at the reference position by reversely conveying the paper upstream if it exceeds the upper limit. The paper feeding mechanism is
Paper feeding means for conveying the paper one by one from the paper tray;
A first paper detection sensor that is provided downstream of the paper supply means and detects a leading edge of the paper conveyed by the paper supply means;
A transport unit provided downstream of the first paper detection sensor so that the paper can be transported both upstream and downstream, and transports the paper transported by the paper feed unit to the downstream reference position;
A second paper detection sensor that detects the leading edge of the paper downstream of the transport means and upstream of the reference position;
Each time the sheet is fed from the sheet tray to the reference position, control is performed to convey the sheet from the setting position to the sheet feeding unit by a predetermined conveyance amount, and the sheet feeding unit Control means for performing control to position the paper whose front edge is detected by the first paper detection sensor to the reference position by the transport means,
The control means includes
When the sheet conveyed by the conveying unit reaches the reference position, if the conveyance of the sheet by the conveyance amount by the sheet feeding unit is not completed, the sheet is conveyed by the sheet feeding unit. After completing
The conveyance means reversely conveys the sheet upstream until the second sheet detection sensor detects the leading edge of the sheet, and positions the sheet at the reference position after the leading edge of the sheet is detected by the second sheet detection sensor. The image forming apparatus according to claim 1, wherein control is performed. The paper feeding means is
A loading roller that has a peripheral surface composed of a flat surface and an arc surface, and conveys the paper by slidingly contacting the paper on the paper tray while the arc surface rotates;
The control means includes
3. A control for transporting the paper from the placement position by the transport amount by rotating the loading roller once from a state where the flat surface faces the paper is performed for each paper feeding operation. The image forming apparatus described.

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