JP6024381B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus that detects passage of a sheet before image transfer and controls exposure timing based on a change in presence or absence of the sheet.

  Conventionally, in an electrophotographic image forming apparatus, a sensor for detecting a change in the presence / absence of a sheet has been arranged upstream of a transfer position on a sheet conveyance path, and exposure is performed based on a change from absence to presence of a sheet. In some cases, the exposure is terminated based on the change from presence to absence of the sheet.

  As a technique for adjusting the exposure timing based on the change in the presence or absence of a sheet, for example, there is Patent Document 1. In Patent Document 1, sensors are arranged on the upstream side and the downstream side of the registration roller, respectively, the rotation start and stop of the registration roller are controlled by the upstream sensor, and the exposure start and exposure stop are controlled by the downstream sensor. In addition, a technique is disclosed in which the sheet conveyance speed of the registration roller is controlled by a downstream sensor.

JP-A-2005-352448

  However, the conventional image forming apparatus described above has the following problems. In recent years, downsizing of the apparatus is remarkable, and the conveyance distance from the registration roller to the transfer position tends to be short. Therefore, it may be difficult to control the exposure timing with a sensor downstream of the registration rollers. Therefore, it is conceivable that the exposure timing is controlled by a sensor upstream of the registration roller. However, the sheet conveyance time by the registration roller is not always stable due to wear of the roller, temperature change, and the like. For this reason, there are concerns about adverse effects on the accuracy of exposure timing.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that has little influence on the accuracy of exposure timing even if a change occurs in the sheet conveyance time.

  An image forming apparatus for solving this problem includes an image carrier, an exposure unit that exposes the image carrier and forms an electrostatic latent image on the image carrier, and the exposure unit includes: A developing unit that develops the formed electrostatic latent image with toner, a transfer unit that transfers the toner image developed by the developing unit, and a transfer position on the sheet conveyance path where the transfer unit transfers the toner image. A transport unit that is positioned upstream and transports the sheet toward the downstream side; an upstream detection unit that is positioned upstream of the transport unit and detects the presence or absence of a sheet; and a downstream side of the transport unit; A downstream detection unit that is located upstream of the transfer position and detects the presence or absence of a sheet, and the downstream detection unit detects that there is no sheet from the position where the upstream detection unit detects a change between the absence of a sheet and the presence of a sheet. Up to the position to detect the change of the seat A storage unit that stores a reference time that is a time based on a sheet conveyance time, and the reference time that is stored in the storage unit after the upstream detection unit detects a change between presence and absence of a sheet. A control unit that controls at least one of an exposure start and an exposure end by the exposure unit based on the elapsed timing, and a change unit that changes the reference time based on a result related to sheet conveyance. It is said.

  The image forming apparatus disclosed in this specification includes an upstream detection unit upstream of the conveyance unit and a downstream detection unit downstream of the conveyance unit, and the presence of the sheet and the sheet in the detection by the upstream detection unit. The reference time, which is the time based on the conveyance time of the sheet, between the detection position where the absence of the sheet changes and the detection position where the presence of the sheet and the absence of the sheet change in the detection by the downstream detection unit I remember it. Using this reference time, the control unit controls at least one of exposure start and exposure end. In other words, in the exposure start control, the upstream detection unit detects a change from the absence of the sheet to the presence of the sheet, and in the exposure end control, the upstream detection unit detects the change from the presence of the sheet to the absence of the sheet. Then, each is performed based on the timing when the reference time elapses. These controls may be based on the timing at which the reference time elapses, and may be at the time when the reference time elapses or at the time when the adjustment time is added to the reference time. Further, the reference time is changed based on the result related to sheet conveyance. As a result related to sheet conveyance, for example, an actually measured value of conveyance time, the number of sheet conveyance, and the like are applicable. As the change of the reference time, for example, it may be changed by an actual measurement value measured every time the sheet is conveyed, or may be changed by weighting according to the number of times the sheet is conveyed.

  That is, in the image forming apparatus disclosed in this specification, the reference time, which is the time based on the sheet conveyance time from the upstream detection unit to the downstream detection unit, is changed based on the result related to sheet conveyance, and the upstream detection unit The reference time is used to control the exposure timing based on the detection timing. For this reason, the exposure timing is controlled based on the change in the conveyance time between the upstream detection unit and the downstream detection unit. As a result, it is possible to suppress the influence of variations in transport time. Therefore, even if a change occurs in the sheet conveyance time, the influence on the accuracy of the exposure timing is small.

  Further, the changing unit may change the reference time based on the measured transport time. By reflecting the actual measurement value of the current sheet conveyance time in the reference time of the next sheet, it is expected that the accuracy of the reference time is improved and the exposure timing can be controlled with higher accuracy. The reference time may be updated as it is with the actual measurement value, or a plurality of actual measurement values may be stored and the average value thereof may be changed as the reference time.

  In addition, the image forming apparatus disclosed in the present specification includes a determination unit that determines whether or not the measured transport time is within a predetermined range, and the change unit includes the determination unit that determines whether the predetermined time is within the predetermined range. The reference time may be changed based on the transport time determined to be within the range. If the measured value of the transport time is significantly different from the design tolerance, the transported sheet is likely to have been transported inappropriately. It is preferable not to use the actually measured value as the reference time because it is likely to impair the accuracy of the exposure timing.

  In addition, an image forming apparatus disclosed in this specification includes an acquisition unit that acquires a temperature in the apparatus, and a temperature storage that stores a reference temperature that is associated with the reference time and that is acquired from the acquisition unit. And a temperature correction unit that corrects the reference time stored in the storage unit based on a difference between the reference temperature stored in the temperature storage unit and the current temperature acquired by the acquisition unit The control unit may control at least one of the exposure start and the exposure end by the exposure unit based on a timing at which a reference time after correction by the temperature correction unit has elapsed. By correcting the reference time based on the temperature difference between the temperature stored in association with the reference time and the current temperature, it is possible to suppress the influence of variations in transport time due to the temperature difference.

  Further, the image forming apparatus disclosed in the present specification reversely transfers the sheet that has passed through the transfer position to a position upstream of the upstream detection unit on the transport path by inverting the transfer surface. A correction value storage unit that stores a reversal correction value used for correcting the reference time when a toner image is transferred to a sheet that has passed the anti-transfer path, and a sheet that has passed the anti-transfer path An inversion correction unit that corrects the reference time used when transferring the toner image onto the first surface of the sheet based on the inversion correction value stored in the correction value storage unit when transported to the transfer position; The control unit includes a timing at which a reference time after correction by the reversal correction unit has elapsed since the upstream detection unit detected a change between presence and absence of a sheet that passed through the anti-transfer path. Based on the exposure unit Exposure start and may be controlled at least one of the end of exposure. Sheets that have passed through the anti-transfer path are often curled due to the effects of thermal fixing, etc., and the timing for detecting whether the sheet is curled or not curled. May be different, which causes variations in transport time. By correcting the reference time for the curl portion, it is possible to suppress the influence of the variation in the conveyance time peculiar to the transfer of the toner image onto the second surface.

  Further, the image forming apparatus disclosed in the present specification is configured such that the inversion stored in the correction value storage unit is based on the transport time measured at the time of transport of the sheet in the transfer of the toner image to the first surface. A correction value changing unit for changing the correction value may be provided. By reflecting the actually measured value at the time of transfer in transferring the toner image on the first surface in the reverse correction value, the accuracy of the reference time is increased, and it can be expected that the exposure timing is controlled with higher accuracy.

  The storage unit may store the reference time for each sheet type, and the changing unit may change the reference time according to the sheet type. The sheet conveyance speed varies depending on the sheet type. Therefore, by setting the reference time for each sheet type, the accuracy of the reference time is increased, and it can be expected to control the exposure timing with higher accuracy.

  The storage unit also stores an adjustment time that is a difference time between a timing at which the reference time elapses and a timing for instructing start or end of exposure by the exposure unit, and the changing unit is configured to store the reference time. The adjustment time may be changed when the change occurs. It is expected that the exposure timing can be controlled with higher accuracy by changing the difference time for determining the exposure start or the exposure end.

  Further, the downstream detection unit is configured to detect the conveyance distance of the sheet from the position where the change from the presence of the sheet to the absence of the sheet to the transfer position and the position from the position where the change from the absence of the sheet to the presence of the sheet is detected. It is preferable that at least one of the transport distance of the sheet to the transfer position is at a position shorter than the transport distance of the electrostatic latent image from the exposure position of the exposure unit to the transfer position. In the image forming apparatus having this configuration, exposure control by the downstream detection unit is difficult. Since the image forming apparatus disclosed in this specification can measure the exposure timing at the upstream detection unit, it can be expected that the exposure timing can be controlled with high accuracy even in such a configuration.

  According to the present invention, an image forming apparatus is realized which has little influence on the accuracy of exposure timing even if a change occurs in the sheet conveyance time.

1 is a perspective view illustrating a schematic configuration of a printer according to an embodiment. FIG. 2 is a conceptual diagram illustrating an internal configuration of a printer. FIG. 2 is a block diagram illustrating an electrical configuration of a printer. It is explanatory drawing which shows the conveyance distance between each point on a regular conveyance path. It is explanatory drawing which shows reference | standard data. It is a flowchart which shows the procedure of an exposure control process. It is a flowchart which shows the procedure of a conveyance process. It is a flowchart which shows the procedure of a reference | standard data change process.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an electrophotographic color printer.

[Entire printer configuration]
As shown in FIG. 1, the printer 100 according to the embodiment includes an image forming unit 10 that forms an image on a sheet, and an operation panel 40 that is positioned on the upper surface of the image forming unit 10. The operation panel 40 includes a display unit 41 including a liquid crystal display and a button group 42 including a start key, a stop key, a numeric keypad, and the like. With this operation panel 40, the printer 100 can display an operation status and can be input by a user. The printer 100 is an example of an image forming apparatus.

[Internal configuration of printer]
FIG. 2 shows the internal configuration of the printer 100. As shown in FIG. 2, the printer 100 includes a process unit 50 that forms a toner image by a known electrophotographic method, a belt 7 that conveys a sheet, and a fixing unit 8 that fixes the toner image on the sheet. Yes. Further, an upper sheet feeding tray 91 and a lower sheet feeding tray 92 for placing sheets before printing, a sheet discharge tray 96 for placing sheets after printing, and various rollers for conveying the sheets are provided. Examples of the various rollers include a paper feed roller 71 provided on the upper paper feed tray 91, a paper feed roller 72 provided on the lower paper feed tray 92, a transport roller 73, and a registration roller 74.

  The process unit 50 is capable of forming a color image. In parallel, the photoconductors 1Y, 1M, 1C, and 1K corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors are arranged. It is arranged. Further, the process unit 50 exposes each of the photoconductors with the charging units 2Y, 2M, 2C, and 2K for uniformly charging the surface of each photoconductor, and an electrostatic latent image is formed on the outer peripheral surface of each photoconductor. Are developed and developed by the developing units 4Y, 4M, 4C, and 4K for developing the electrostatic latent images formed by the exposure units with toner, and the developing units. Transfer portions 5Y, 5M, 5C, and 5K for transferring the toner images. Each photoconductor is an example of an image carrier.

  The belt 7 is an endless belt member wound around a driven roller 75 and a driving roller 76. The drive roller 76 is rotationally driven by a drive motor 79. The belt 7 circulates in a clockwise direction on the paper surface when the driving roller 76 is driven to rotate. Accordingly, the sheet placed on the upper surface of the belt 7 is conveyed from the registration roller 74 side toward the fixing unit 8 side. The driven roller 75 rotates following the movement of the belt 7.

  The sheet conveyed to the belt 7 and passing through the process unit 50 receives the transfer of the toner image formed on the photoconductor at a position where the photoconductor and the transfer unit face each other with the belt 7 interposed therebetween. The transfer position of each color is the position where the transfer portion of each color transfers the toner image on the sheet conveyance path. In the following description, the most upstream color transfer position on the transport path is referred to as the “most upstream transfer position”. In the printer 100 of this embodiment, the “upstream transfer position” is a yellow transfer position. Note that the color order of the process unit 50 is not limited to this.

  The printer 100 is provided with a normal conveyance path 11 indicated by a one-dot chain line in FIG. 2 and an anti-transfer path 12 indicated by a two-dot chain line in FIG. 2 as paths for conveying the sheet. For example, the normal conveyance path 11 passes the sheet pulled out from the upper sheet feeding tray 91 by the sheet feeding roller 71 through the sheet conveying roller 73, the registration roller 74, the process unit 50, and the fixing unit 8 through the sheet discharge roller 77. This is a path leading to the upper discharge tray 92. The normal conveyance path 11 also includes a path for similarly conveying the sheet drawn from the lower sheet feed tray 92 by the sheet feed roller 72.

  In the normal conveyance path 11, the registration roller 74 is positioned upstream from the most upstream transfer position on the sheet conveyance path, and conveys the sheet toward the process unit 50 on the downstream side. The registration roller 74 is an example of a transport unit. In the printer 100, different types of sheets can be placed on the upper sheet feeding tray 91 and the lower sheet feeding tray 92. There are three types of sheets, for example, thick paper, plain paper, and thin paper. The user can set the type of sheet placed on each paper feed tray by using the operation panel 40 of the printer 100 or the like.

  The reverse transfer path 12 is a conveyance path for reversing the front and back of a sheet printed on one side and re-conveying it to the process unit 50 in order to perform double-sided printing. The counter-transfer path 12 branches from the regular transport path 11 at a branch point 15 at a position downstream of the process unit 50 in the sheet transport direction and upstream of the paper discharge roller 77. A path that passes between the process unit 50 and the upper paper feed tray 91 from the branch point 15 and joins with the normal conveyance path 11 is formed at the junction 16 on the upstream side of the registration rollers 74 of the regular conveyance path 11. ing.

  The printer 100 also includes an upstream sensor 63 and a downstream sensor 64 that detect the presence or absence of a sheet. The upstream sensor 63 is located downstream of the conveyance roller 73 and upstream of the registration roller 74. The downstream sensor 64 is located downstream of the registration roller 74 and upstream of the most upstream transfer position. The upstream sensor 63 and the downstream sensor 64 can continuously detect the presence or absence of a sheet at each position on the normal conveyance path 11. The upstream sensor 63 is an example of an upstream detection unit, and the downstream sensor 64 is an example of a downstream detection unit.

  Both the upstream side sensor 63 and the downstream side sensor 64 have no sheet when the sheet is changed from a state where there is no sheet at the detection position to a state where there is a sheet, and when there is a sheet at the detection position. Each time it changes to a state, it is detected separately. In the following description, a state where the presence of a sheet is detected at the detection position is “ON”, and a state where the absence of a sheet is detected at the detection position is “OFF”. The upstream sensor 63 and the downstream sensor 64 include, for example, a light transmission sensor with a swinging piece that swings by contact with a sheet, a light transmission sensor disposed across a conveyance path, and a difference in reflectance depending on the presence or absence of a sheet. This is realized by a light reflection sensor or the like that detects

[Electrical configuration of printer]
Next, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 includes a control unit 30 including a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. The control unit 30 is electrically connected to the image forming unit 10, the operation panel 40, the network interface 37, the upstream sensor 63, the downstream sensor 64, and the like. In addition, the printer 100 includes a temperature acquisition unit 65 that acquires the temperature in the apparatus, and the temperature acquisition unit 65 is also electrically connected to the control unit 30. The temperature acquisition unit 65 is an example of an acquisition unit.

  The ROM 32 stores various control programs for controlling the printer 100, various settings, initial values, and the like. The CPU 31 controls each component of the printer 100 according to a control program read from the ROM 32 and signals sent from the upstream sensor 63, the downstream sensor 64, and the like. The RAM 33 is used as a work area from which various control programs are read or as a storage area for temporarily storing image data. The CPU 31 is an example of a control unit, a change unit, a determination unit, a temperature correction unit, an inversion correction unit, and a correction value change unit.

  The NVRAM 34 stores various setting values. The NVRAM 34 stores, for example, a reference time that is a time based on the sheet conveyance time when the sheet is conveyed from the detection position of the upstream sensor 63 to the detection position of the downstream sensor 64. The reference time will be described later. The NVRAM 34 also stores, for example, a temperature acquired by the temperature acquisition unit 65, reference data for an exposure control process described later, and the like. The NVRAM 34 is an example of a storage unit, a temperature storage unit, and a correction value storage unit.

  The network interface 37 is connected to a network such as a LAN, and enables connection to an external device in which a printer driver for the printer 100 is incorporated. The printer 100 can deliver a print job via the network interface 37.

[Image formation operation of printer]
Next, the operation of the process unit 50 at the time of image formation by the printer 100, that is, the printing operation in the image forming unit 10 will be described by taking a yellow configuration as an example. At the time of image formation, the surface of the photoreceptor 1Y is uniformly charged by the charging unit 2Y. Thereafter, exposure is performed by light emitted from the exposure unit 3Y, and an electrostatic latent image of an image to be formed on the sheet is formed on the surface of the photoreceptor 1Y. Next, toner is supplied to the photoreceptor 1Y via the developing unit 4Y. Thereby, the electrostatic latent image on the photoreceptor 1Y is visualized as a toner image. The operation of forming the other color toner images is the same as the yellow operation.

  The formed toner image is conveyed to the transfer position, that is, the most upstream transfer position by the rotation of the photoreceptor 1Y. The timing at which the toner image reaches the transfer position is determined based on the timing at which the sheet reaches the transfer position. Since the photosensitive member 1Y rotates at a substantially constant rotation speed, the exposure start timing is determined based on the timing at which the toner image reaches the transfer position.

  On the other hand, the print instruction includes designation of a paper feed tray from which the sheet is drawn. That is, the printer 100 receives an instruction from the user as to which of the upper sheet feed tray 91 and the lower sheet feed tray 92 is to be used. The sheet pulled out from the paper feed tray instructed by the user is conveyed along the normal conveyance path 11 by the conveyance roller 73, the registration roller 74, and the like. When the leading edge of the sheet reaches the detection position by the upstream sensor 63 during the conveyance, the upstream sensor 63 detects a change from the absence of the sheet to the presence of the sheet and is turned ON.

  As will be described later, the printer 100 controls exposure start by the exposure unit 3Y based on the ON detection timing of the upstream sensor 63. The yellow toner image formed on the photoreceptor 1Y is transferred to the sheet at the most upstream transfer position. Then, the sheet that has received the transfer of the yellow toner image is further conveyed to receive the transfer of the toner images of other colors. The toner image transferred to the sheet is fixed on the sheet in the fixing unit 8.

  FIG. 4 shows an example of the conveyance distance between each point on the normal conveyance path 11 of the printer 100 of this embodiment. The sheet conveyance direction is from left to right in the figure. In the drawing, “upstream sensor ON” is an ON detection position of the upstream sensor 63, which is downstream of the conveyance roller 73 and upstream of the registration roller 74. “Downstream sensor ON” is an ON detection position of the downstream sensor 64, which is downstream of the registration roller 74 and upstream of the driven roller 75. In the drawing, “Y transfer position” is a transfer position of yellow, which is the most upstream color, and is downstream of the driven roller 75.

  In the printer 100 of this embodiment, the sheet conveyance distance from the position at which the downstream sensor 64 is turned on to the most upstream transfer position is static from the exposure position of the exposure unit 3Y to the transfer position by the transfer unit 5Y in the yellow process unit. It is shorter than the transport distance of the electrostatic latent image. For example, the conveyance distance of the sheet from the position at which the downstream sensor 64 is turned on to the most upstream transfer position is shorter than the circumferential length of the photoreceptor 1Y from the yellow exposure unit 3Y to the transfer unit 5Y. The peripheral speed of the photoreceptor 1Y and the sheet conveying speed are substantially equal during image formation.

  Therefore, the conveyance time from the timing at which the downstream sensor 64 detects the passage of the leading edge of the sheet to the timing at which the leading edge of the sheet reaches the most upstream transfer position is the exposure to the yellow exposure unit 3Y that is the most upstream color. There is a possibility that it is shorter than the time from the start control timing to the timing when the leading edge of the toner image reaches the most upstream transfer position. That is, in FIG. 4, the “downstream sensor ON” is on the downstream side of the “Y exposure position”. For this reason, if the start of exposure of the most upstream color is controlled after the downstream sensor 64 is turned on, the exposure may not be in time.

  Similarly, the conveyance distance of the sheet from the position where the downstream sensor 64 detects the trailing edge of the sheet and turns OFF to the most upstream transfer position is equal to the photoreceptor 1Y from the yellow exposure unit 3Y to the most upstream transfer position. Shorter than the circumference. Therefore, the conveyance time from the timing at which the downstream sensor 64 detects the passage of the trailing edge of the sheet to the timing at which the trailing edge of the sheet reaches the most upstream transfer position is determined from the control timing of the end of exposure in the most upstream color. There is a possibility that it is shorter than the time until the rear end of the image reaches the most upstream transfer position. That is, if the end of exposure of the most upstream color is controlled after the downstream sensor 64 detects the presence or absence of the sheet, a part of the toner image may protrude from the sheet and be transferred onto the belt 7. .

  Therefore, the printer 100 controls at least one of the exposure start and the exposure end based on the detection timing of the change in the presence / absence of the sheet by the upstream sensor 63, not the detection timing of the change in the presence / absence of the sheet by the downstream sensor 64. I do. Since the timing when the upstream sensor 63 is turned on is earlier than the timing when the downstream sensor 64 is turned on, the possibility that the exposure will not be in time is reduced. In addition, since the timing at which the upstream sensor 63 is turned off is earlier than the timing at which the downstream sensor 64 is turned off, the possibility that a part of the toner image protrudes from the sheet and is transferred onto the belt 7 is also reduced.

  However, the sheet conveyance time from the detection timing of the sheet by the upstream sensor 63 to the most upstream color transfer position varies and changes over time due to the influence of the temperature in the apparatus, the wear of the registration roller 74, the type of the sheet, and the like. there is a possibility. Therefore, the printer 100 creates reference data 81 for predicting the sheet conveyance time as shown in FIG. 5 and stores it in the NVRAM 34.

  As shown in FIG. 5, the reference data 81 includes various data related to sheet conveyance from the detection position by the upstream sensor 63 to the detection position by the downstream sensor 64. When executing printing, the CPU 31 of the printer 100 refers to the reference data 81 and predicts the sheet conveyance time from the ON timing of the upstream sensor 63 to the most upstream color transfer position. Then, the printer 100 performs yellow exposure start control based on the prediction result and the ON timing of the upstream sensor 63.

  At the time of shipment from the factory, reference data 81 determined in advance by experiment is stored in the NVRAM 34. Further, the printer 100 measures the sheet conveyance time from the detection of the upstream sensor 63 to the detection of the downstream sensor 64 every time the sheet is conveyed. Also, the temperature in the device at the time of execution of this timing is acquired. The printer 100 changes the reference data 81 based on the data acquired when printing is performed. Details of the changing method will be described later. By appropriately changing the reference data 81, the printer 100 can make the sheet conveyance time prediction closer to the current state.

  The reference data 81 of this embodiment includes “reference time A”, “reference temperature B”, “adjustment time C”, “reversal correction value D”, “previous transport time E”, “previous temperature F”, “previous transport time”. Each item includes “G” and “Temperature H”. The reference time A is a reference for the sheet conveyance time from the detection position of the upstream sensor 63 to the detection position of the downstream sensor 64 (see FIG. 4). The reference temperature B is a temperature in the apparatus corresponding to the time when the sheet conveyance time is the reference time A. The adjustment time C is a time representing the difference between the sheet detection timing by the downstream sensor 64 and the timing for instructing the start or end of exposure (see FIG. 4).

  The inversion correction value D is a correction value for correcting the reference time A when printing on the second surface during duplex printing. The previous transport time E is a transport time measured at the previous sheet transport. The previous temperature F is a temperature acquired when the previous conveyance time E is measured. The last-second conveyance time G is a conveyance time measured at the time of sheet conveyance prior to the measurement of the previous conveyance time E. The last-time temperature H is a temperature acquired when the last-time conveyance time G is measured.

  Further, the printer 100 stores data of each item of the reference data 81 for each sheet type. This is because the sheet conveyance speed in the printer 100 is different for each type of sheet. As the sheet type, for example, there is a classification based on the thickness of the sheet. For example, the reference time A is stored separately for a reference time A (thick paper) for thick paper, a reference time A (plain paper) for plain paper, and a reference time A (thin paper) for thin paper. These values may be different from each other, or may have the same value.

  Further, since the reference temperature B is a temperature associated with the reference time A, the reference temperature B is stored for each sheet type, as with the reference time A. Similarly, other items below the adjustment time C are also stored separately for each sheet type. In the following description, unless otherwise specified, the sheet type of each code is omitted.

[Exposure control processing]
Next, an exposure control process for controlling the exposure timing when printing is performed in the printer 100 will be described with reference to the flowchart of FIG. The exposure control process is executed by the CPU 31 when the image forming unit 10 starts a printing operation.

  In the exposure control process, first, the sheet type specified in the print instruction is acquired (S101). Then, the sheet feeding tray on which the designated type of sheet is placed is selected from either the upper sheet feeding tray 91 or the lower sheet feeding tray 92 and determined as the sheet feeding tray. Further, when the sheet type is not specified in the print instruction, for example, the sheet type set in the sheet feeding tray to be fed may be acquired.

  Subsequently, the temperature P in the apparatus is acquired by the temperature acquisition unit 65 (S102). S101 and S102 may be performed in reverse order or in parallel. Subsequently, the reference data 81 of the NVRAM 34 is referred to, and the reference time A, reference temperature B, and adjustment time C corresponding to the sheet type acquired in S101 are read out (S103). The reference time A is a time based on the sheet conveyance time from when the upstream sensor 63 is turned on to when the downstream sensor 64 is turned on, and is appropriately updated by reference data changing processing described later.

Next, using the temperature P acquired in S102 and the reference temperature B acquired in S103, the reference time A acquired in S103 is corrected to obtain a corrected reference time Q (S105). That is, the roller diameter of the registration roller 74 that conveys the sheet between the upstream sensor 63 and the downstream sensor 64 changes depending on the temperature. Therefore, the conveyance speed between these sensors also changes with temperature. Therefore, the reference time A is corrected by the following formula 1, and the corrected reference time Q is calculated. The correction coefficient σ in Equation 1 is a fixed value determined in advance regardless of the sheet type, and is, for example, a value comparable to the thermal expansion coefficient of the registration roller 74.
Q = A × (1 + σ × (P−B)) (Formula 1)

  Next, using the correction reference time Q acquired in S105 and the adjustment time C read out in S103, a conveyance process for instructing sheet conveyance and exposure start is executed (S107). The carrying process of S107 will be described with reference to the flowchart of FIG.

  In the conveyance process, first, conveyance of a sheet is started (S201). That is, the printer 100 pulls out one sheet from the paper feed tray determined in S101 of FIG. Then, it is determined whether or not ON is detected by the upstream sensor 63 (S203). If it is determined that the upstream sensor 63 is not turned on (S203: No), the sheet has not reached the detection position of the upstream sensor 63, and therefore the apparatus waits until the upstream sensor 63 is turned on.

  If it is determined that the upstream sensor 63 has been turned on (S203: Yes), a timer is started (S205). That is, the elapsed time from when the upstream sensor 63 detects the leading edge of the sheet is started. Then, it is determined whether or not the time measured by the timer has passed the correction reference time Q + the adjustment time C (S207). The correction reference time Q is a value obtained in S105 of FIG. The adjustment time C is a value read from the reference data 81. When it is determined that the time measured by the timer has not passed the correction reference time Q + adjustment time C (S207: No), the process waits until the correction reference time Q + adjustment time C elapses.

  If it is determined that the time measured by the timer has passed the correction reference time Q + the adjustment time C (S207: Yes), an exposure start signal is input to the yellow exposure unit 3Y which is the most upstream color (S209). For the other color exposure start signals, the respective input timings are determined based on the yellow exposure start instruction timing in S209.

  That is, in the printer 100, the control timing for starting the exposure of the most upstream color is after the reference time + adjustment time C has elapsed since the upstream sensor 63 was turned ON. Furthermore, since the correction reference time Q that takes into account the influence of temperature is used as the reference time, the influence of variations in transport time due to temperature is suppressed. In the printer 100, as described above, the sheet conveyance distance between the ON detection position of the downstream sensor 64 and the most upstream transfer position is short, and the exposure start timing is greater than the ON timing of the downstream sensor 64. Since it is first, the adjustment time C is a negative value. Therefore, the exposure start signal is input before the downstream sensor 64 is turned on.

  Next, the CPU 31 determines whether or not the downstream sensor 64 is ON (S211). If it is determined that the downstream sensor 64 is not ON (S211: No), the process waits until the downstream sensor 64 is turned ON. If it is determined that the downstream sensor 64 is ON (S211: Yes), the timer is stopped (S212). Thereby, the sheet conveyance time from the ON detection of the upstream sensor 63 to the ON detection of the downstream sensor 64 is counted. This measured time is acquired as the current transport time R and stored in the RAM 33 (S213). As a result, the carrying process is terminated, and the process returns to S107 in FIG. 6 to continue the exposure control process.

  After the transport process in S107, the CPU 31 compares the current transport time R acquired in the transport process in S107 with the correction reference time Q acquired in S105, and determines whether or not the difference is within an allowable range. Judgment is made (S109). When it is determined that the difference between the current transport time R and the correction reference time Q is not within the allowable range (S109: No), the set sheet type matches the actually transported sheet type. It may not be. Accordingly, a warning display for prompting confirmation of the sheet type is performed (S111), and this process is terminated. If the sheet types do not match, there is a possibility that a printed matter with good image quality cannot be obtained. For this reason, it is desirable to have the user confirm the sheet type without continuing printing even if there are continuous print pages.

  On the other hand, when it is determined that the difference between the current transport time R and the correction reference time Q is within the allowable range (S109: Yes), printing with good image quality can be expected. Therefore, a reference data changing process for changing the content of the reference data 81 is performed based on the result of the current sheet conveyance (S113). Next, the reference data changing process will be described with reference to the flowchart of FIG.

  In the reference data change process, first, the previous transfer time E, the previous temperature F, the previous transfer time G, and the previous temperature H are read from the reference data 81 (see FIG. 5) of the NVRAM 34 (S301). Note that for each value, a value suitable for the sheet type acquired in S101 is used. Then, the average value of the transport time for three times of the previous transport time E, the last transport time G, and the current transport time R is calculated. Then, the reference time A of the reference data 81 is changed to the calculated average value (S303). Further, an average value of the previous temperature F, the previous temperature H, and the current temperature P is calculated, and the reference temperature B of the reference data 81 is changed to the calculated average value (S305).

  That is, in the printer 100, the conveyance time R actually measured in the current conveyance is not used as the reference time A as it is, but the average value of the conveyance times acquired during the past three sheet conveyances is used as the reference time A. Thereby, the influence by the dispersion | variation in a measurement is suppressed. Further, the temperature in the apparatus at the time of measuring the transportation time for the past three times is averaged, and the average value is set as a reference temperature B. That is, when the reference time A is changed, the reference temperature B is also changed so that the reference temperature B is a temperature associated with the reference time A.

Further, the CPU 31 acquires a change amount ΔA of the reference time before and after the change in S303 (S307). That is, the change amount ΔA is the difference between the reference time A before the change and the reference time A after the change in S303. Then, the adjustment time C is acquired using the change amount ΔA, and the adjustment time C of the reference data 81 is changed to the acquired value (S309). The adjustment time C is obtained by the following equation 2. The correction coefficient β in Equation 2 is a fixed value determined in advance regardless of the sheet type, and may be, for example, the adjustment time C / reference time A in the initial state.
C after change = C + ΔA × β before change (Formula 2)

  Subsequently, the previous transport time E and the previous temperature F are overwritten on the previous transport time G and the previous temperature H, respectively, and the current transport time R and temperature P are overwritten on the previous transport time E and the previous temperature F, respectively. Is stored in the reference data 81 of the NVRAM 34 (S311). This completes the reference data change process, returns to S113 in FIG. 6, and continues the exposure control process.

  Subsequently, it is determined whether or not double-sided printing on the sheet being printed is requested (S115). If it is determined that double-sided printing is not performed (S115: No), the exposure control process for this sheet ends. If there is an instruction to print on another sheet, the process returns to S101 and is executed from the beginning.

  On the other hand, if it is determined that double-sided printing is requested (S115: Yes), then printing on the second side is executed. For this purpose, the sheet that has been printed on the first surface is switched back by the paper discharge roller 77 and drawn from the branch point 15 to the anti-transfer path 12. Then, the sheet is reversed so that the second surface, which is a non-printed surface, faces the photoreceptor, and enters the normal conveyance path 11 from the junction 16 (see FIG. 2).

  The sheet is often curled by printing on the first surface before reversal. For this reason, the sheet conveyance status differs between the first surface and the second surface, and the conveyance time can also be different. Therefore, when printing on the second surface, the correction reference time Q obtained in S105 is further corrected for the second surface (S117). For example, the inversion correction value D is read from the reference data 81 of the NVRAM 34, and the correction reference time Q + inversion correction value D is set as the correction reference time Q for the second surface.

  Then, the above-described transport process is executed (S107). The procedures for conveying and printing the sheet in this process are the same as those for the first surface. Thereby, the actually measured transport time U at the time of transport of the second surface is acquired, and the transport time U is stored in the RAM 33.

  Subsequently, the reverse correction value D used in S117 is changed (S119). The reversal correction value D after the change is, for example, the difference between the current transport time R acquired in the first surface transport process and the transport time U acquired in the second surface transport process. Further, the changed inversion correction value D is written in the reference data 81 of the NVRAM 34. This completes the exposure control process.

  As described above in detail, the printer 100 according to the present embodiment includes the upstream sensor 63 on the upstream side of the registration roller 74 and the downstream sensor 64 on the downstream side of the registration roller 74, and the sheet conveyance therebetween. A reference time A that is a time based time is stored in the NVRAM 34. The exposure control timing is determined based on the timing at which the reference time A elapses after the upstream sensor 63 detects a change in the presence / absence of a sheet. Therefore, the exposure control timing is determined based on the arrangement of the upstream sensor 63 regardless of the arrangement of the downstream sensor 64. Further, the reference time is changed based on the result related to sheet conveyance. Therefore, even if a change occurs in the sheet conveyance time, the influence on the accuracy of the exposure timing is small.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the image forming apparatus is not limited to a printer, and can be applied to any apparatus having a printing function such as a multifunction machine, a copier, and a FAX apparatus. Further, even if a color image can be formed, it may be dedicated to a monochrome image. Further, the number of paper feed trays may be one, or three or more.

  In the above embodiment, the transport time from the ON of the upstream sensor 63 to the ON of the downstream sensor 64 is measured and the reference time A is changed based on the measured value. However, the present invention is not limited to this. For example, the degree of wear of the registration roller 74 can be predicted based on the number of times the sheet has been conveyed since the new article, the total number of rotations of the registration roller 74, etc., and the reference time A can be changed based on the predicted degree of wear. Such a predicted degree of wear is an example of a result related to sheet conveyance. However, if it is actually measured, the reference time A can be set to a more accurate and accurate reference time A.

  In the above embodiment, the correction reference time Q is calculated by adding the temperature correction to the reference time A, but the temperature correction may not be performed. However, more accurate control is possible with temperature compensation. Further, in the above embodiment, the reversal correction is performed in the printing on the second surface during the double-sided printing, but the reversal correction may not be performed. However, if reversal correction is performed, high-precision control can be performed for printing on the second side during duplex printing.

  In the above embodiment, the value of the reference data is different depending on the type of sheet. However, the type of sheet is not distinguished and may be a single value. Alternatively, instead of distinguishing three types of sheets, two types of thick paper and thin paper may be used with a predetermined thickness as a boundary. Alternatively, it may be further divided into four or more types. By controlling differently depending on the type of sheet, more accurate control is possible.

  In the above embodiment, the data of the previous time and the previous time are stored as the reference time and the reference temperature, and the average of the data for three times is calculated together with the current time. However, the present invention is not limited to this. For example, only the reference time and the reference temperature may be stored and rewritten to the newest data every time the sheet is conveyed. Or you may use the average value for twice this time and this time. Or you may use the average value for 4 times or more.

  In the above embodiment, only the exposure start timing has been described. However, the exposure end timing can be similarly implemented. In the above embodiment, the correction coefficient σ and the correction coefficient β are fixed values. However, the present invention is not limited to this. The temperature may be changed according to the temperature in the apparatus, the age since the start of use, or the like. In the above embodiment, the example in which the exposure start timing of the most upstream color is earlier than the ON detection of the downstream sensor 64 has been described. However, the present invention can also be applied to an apparatus in which the exposure start timing of the most upstream color is later than the ON detection of the downstream sensor 64.

  Further, the processing disclosed in the embodiment may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the process disclosed in the embodiment can be realized in various modes such as a recording medium or a method in which a program for executing the process is recorded.

1Y, 1M, 1C, 1K Photoconductor 3Y, 3M, 3C, 3K Exposure unit 4Y, 4M, 4C, 4K Development unit 5Y, 5M, 5C, 5K Transfer unit 11 Positive transport path 12 Anti-transfer path 31 CPU
34 NVRAM
63 Upstream sensor 64 Downstream sensor 65 Temperature acquisition unit 74 Registration roller 100 Printer

Claims (9)

An image carrier;
Exposing the image carrier to form an electrostatic latent image on the image carrier;
A developing unit for developing the electrostatic latent image formed by the exposure unit with toner;
A transfer portion for transferring a toner image developed by the developing portion;
A conveying unit that is located upstream of a transfer position at which the transfer unit transfers the toner image on a conveyance path of the sheet, and conveys the sheet toward the downstream side;
An upstream detection unit that is located upstream of the conveying unit and detects the presence or absence of a sheet;
A downstream detection unit that is located downstream of the transport unit and upstream of the transfer position, and detects the presence or absence of a sheet;
The time based on the sheet conveyance time from the position where the upstream detection unit detects the change between the absence of the sheet and the presence of the sheet to the position where the downstream detection unit detects the change between the absence of the sheet and the presence of the sheet. A storage unit for storing a reference time;
Starting timing of the upstream detection unit detects the change between the non-perforated and sheets of the sheet when the elapsed time has passed a time based on the previous SL reference time, exposure and end the exposure initiation by the exposure unit A control unit that performs at least one of
A changing unit for changing the reference time based on a result relating to sheet conveyance;
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image forming apparatus, wherein the changing unit changes the reference time based on the measured transport time. The image forming apparatus according to claim 2,
A determination unit for determining whether or not the measured transport time is within a predetermined range;
The image forming apparatus according to claim 1, wherein the changing unit changes the reference time based on the transport time determined by the determining unit to be within the predetermined range. The image forming apparatus according to any one of claims 1 to 3,
An acquisition unit for acquiring the temperature in the device;
A temperature storage unit that stores a reference temperature that is associated with the reference time and is a temperature acquired from the acquisition unit;
A temperature correction unit for correcting the reference time stored in the storage unit based on a difference between the reference temperature stored in the temperature storage unit and a current temperature acquired by the acquisition unit;
With
The image forming apparatus, wherein the control unit performs at least one of an exposure start and an exposure end by the exposure unit when the elapsed time based on the reference time corrected by the temperature correction unit has elapsed. In the image forming apparatus according to any one of claims 1 to 4,
A reverse transfer path for transporting the sheet that has passed through the transfer position to a position upstream of the upstream detector on the transport path by inverting the transfer surface;
A correction value storage for storing a reversal correction value used for correcting the reference time when a toner image is transferred to a sheet that has passed through the anti-transfer path;
The reversal correction stored in the correction value storage unit is the reference time used when the toner image is transferred to the first surface of the sheet when the sheet that has passed the anti-transfer path is conveyed to the transfer position. An inversion correction unit for correcting based on the value;
With
The control unit , based on a reference time after correction by the reversal correction unit, starts from a timing at which the upstream detection unit detects a change in presence or absence of a sheet that has passed through the anti-transfer path. An image forming apparatus, wherein at least one of exposure start and exposure end by the exposure unit is performed when time elapses. The image forming apparatus according to claim 5,
And a correction value changing unit that changes the inversion correction value stored in the correction value storage unit based on the conveyance time measured at the time of conveyance of the sheet in transferring the toner image to the first surface. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 6,
The storage unit stores the reference time for each sheet type,
The image forming apparatus according to claim 1, wherein the changing unit changes the reference time according to a sheet type. In the image forming apparatus according to any one of claims 1 to 7,
The storage unit also stores an adjustment time that is a difference time between a timing at which the reference time elapses and a timing for instructing start or end of exposure by the exposure unit,
The image forming apparatus, wherein the changing unit changes the adjustment time when the reference time is changed. In the image forming apparatus according to any one of claims 1 to 8,
The downstream detection unit includes a conveyance distance of the sheet from a position where the change from the presence of the sheet to the absence of the sheet to the transfer position and a transfer position from the position where the change from the absence of the sheet to the presence of the sheet is detected. The image forming apparatus according to claim 1, wherein at least one of the sheet transport distance and the sheet transport distance is shorter than the transport distance of the electrostatic latent image from the exposure position of the exposure unit to the transfer position.

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