JP2018146732A - Image formation apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus and method capable of accurately determining arrival timing of a sheet at an image formation part.SOLUTION: An image formation apparatus has an electrophotography system and transfers, onto a sheet, a developer image formed on a photoreceptor drum while holding the sheet at a nip area between the photoreceptor drum and a transfer roller and transferring the sheet. The image formation apparatus detects a change in a resistance value at the nip area between the photoreceptor drum and the transfer roller, and determines timing of arrival of the sheet at the nip area according to the detected change in the resistance value.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus and method for forming an image by electrophotography.

  The image forming apparatus is configured to prevent scattering of toner in the image forming apparatus due to misalignment between the sheet and the image. In Patent Document 1, the sheet conveyance is stopped and a loop is formed on the sheet after a predetermined time has elapsed after detecting that the leading edge of the sheet has contacted the nip portion of the resist roller pair in a stopped state. Then, control is performed so that sheet feeding by the registration roller pair is started at a predetermined timing, and image formation is started in accordance with the timing at which the sheet reaches the image forming unit.

  However, if the timing at which the sheet arrives at the image forming unit is shifted due to a sheet conveyance error, the image does not match the image formation timing and the image protrudes from the sheet. In Patent Document 2, the image signal is masked when the timing at which the rear end of the sheet is detected by the sensor upstream in the sheet conveyance direction from the image forming unit is used to prevent the image from protruding.

JP 2003-280485 A Japanese Patent Application Laid-Open No. 7-193693

  However, the sheet conveyance state from when the sheet is detected by the sensor until the sheet reaches the image forming unit is not considered. For example, when the sheet flutters at the position of the sensor or when the sheet conveyance roller slips, it is difficult to accurately determine the timing at which the sheet reaches the image forming unit.

  An object of the present invention is to solve such conventional problems. In view of the above points, an object of the present invention is to provide an image forming apparatus and method capable of accurately determining the arrival timing of a sheet to an image forming unit.

  In order to solve the above problems, an image forming apparatus according to the present invention includes an image forming unit that transfers an image formed on an image carrier to a recording medium that is nipped and conveyed with the transfer unit, and the image carrier. Detection means for detecting a change in the resistance value of a nip area that sandwiches and conveys the recording medium with the transfer means, and arrival of the recording medium to the nip area based on the change in the resistance value detected by the detection means And determining means for determining timing.

  According to the present invention, it is possible to accurately determine the arrival timing of the sheet to the image forming unit.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus. 1 is a diagram illustrating a block configuration of an image forming apparatus. It is a figure for demonstrating the change of the resistance value of a transfer roller. 6 is a flowchart illustrating print control processing. It is a figure which shows the unprinted area | region of a sheet | seat. It is a figure for demonstrating the magnification change of an image. FIG. 3 is an enlarged view of the vicinity of a photosensitive drum and a transfer roller.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. . The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus. In this embodiment, the image forming apparatus 100 transfers an image on a recording medium by a so-called electrophotographic method in which an electrostatic latent image formed on a photosensitive drum is transferred to a recording medium (hereinafter also referred to as a sheet) by a transfer roller. To form. The flow of conveying the sheet P will be described with reference to FIG. In the image forming apparatus 100, the sheet feeding unit 10, the image forming unit 20, the fixing unit 30, and the sheet discharge unit 40 are sequentially arranged from the lower side (upstream in the sheet conveyance direction) to the upper side (downstream in the sheet conveyance direction) in FIG. Is provided. A sheet refeeding unit 50 is provided on the right side of the image forming unit 20 and the fixing unit 30.

  In the sheet feeding unit 10, the sheets P stacked on the feeding cassette 11 or the manual feed tray 16 are fed to the image forming unit 20. The sheet detection sensor S <b> 1 is a sensor that detects whether the sheet P is stored in the feeding cassette 11. The sheet P stored in the feeding cassette 11 is fed to the separation roller pair 13 as the pickup roller 12 rotates. When the sheet P is being fed in a multiple manner, the sheet P is separated one by one by a separation roller pair 13 composed of a normal rotation roller and a reverse roller, and is conveyed to a feeding path PS1 indicated by a solid line. The sheet P conveyed to the feeding path PS1 is further conveyed by the feeding roller pair 14, and the skew of the sheet P is corrected by following the nip of the registration roller pair 15 that has stopped rotating. The pre-registration sensor S <b> 2 detects the timing at which the leading edge of the sheet P reaches the nip of the registration roller pair 15. When the sheet P is fed from the manual feed tray 16, the sheets are separated one by one by the supply roller 17 and the separation pad 18 and pulled into the apparatus. Then, the sheet is conveyed to the feeding roller pair 14 by the supply roller pair 19, and the skew of the sheet P is corrected by the registration roller pair 15. The sheet P whose skew has been corrected is conveyed to the image forming unit 20 by the registration roller pair 15 rotating at a predetermined timing.

  In the image forming unit 20, the surface of the photosensitive drum 21 is uniformly charged by the charging roller 22. The laser beam corresponding to the image data transmitted from the outside from the laser unit 23 is irradiated. In the portion of the photosensitive drum 21 irradiated with the laser light, the charge charged by the charging roller 22 is removed, and an electrostatic latent image corresponding to the image information is formed. Here, the formed electrostatic latent image is visualized as a developer image when the developer is attached by the developing roller 24. The developer image is conveyed to the transfer nip portion N1 by the rotation of the photosensitive drum 21.

  The sheet P is conveyed from the registration roller pair 15 to the transfer nip portion N1 in accordance with the timing of the developer image on the photosensitive drum 21. While the conveyed sheet P is nipped and conveyed by the transfer roller 25 in contact with the photosensitive drum 21 in the transfer nip portion N1, the developer image formed on the photosensitive drum 21 is transferred by the transfer roller 25.

  Next, the sheet P on which the developer image is formed is conveyed to the fixing unit 30. In the fixing unit 30, a fixing nip portion N <b> 2 is formed by the fixing roller 31 and the pressure roller 32. The fixing roller 31 is composed of an aluminum roller or the like heated to a predetermined fixing temperature by a heat source such as a halogen lamp disposed therein, and the pressure roller 32 is in contact with the fixing roller 31 with a predetermined pressure. 31 is pressurized. The sheet P on which the developer image is formed is sent to the fixing nip portion N2, and is nipped and conveyed between the fixing roller 31 and the pressure roller 32, and is heated and pressed, whereby the developer image is fixed on the sheet P. Is done. The fixing sensor S3 detects that the leading edge of the sheet P has passed through the fixing nip portion N2. The fixing unit 30 may use another method instead of the heating roller method in which the fixing roller 31 heats. For example, the fixing roller nip portion N2 is formed by pressurizing a heat source such as a ceramic heater through an endless film, and the fixing nip portion N2 is formed. A scheme may be used. The sheet P on which the developer image is fixed is conveyed to the sheet discharge unit 40 and discharged to the discharge tray 42 by the discharge roller pair 41.

  When images are formed on both sides of the sheet P, the discharge roller pair 41 after the leading edge of the sheet P imaged on the first surface passes through the fixing sensor S3 and before the trailing edge of the sheet P passes through the discharge roller pair 41. Is temporarily stopped. Then, by further rotating the discharge roller pair 41 in the reverse direction, the sheet P is reversed and conveyed to the sheet refeeding unit 50.

  The sheet P conveyed to the sheet re-feeding unit 50 is conveyed along a re-feed path PS2 indicated by a broken line by re-feed roller pairs 51 and 52, and is conveyed to a registration roller pair 15 by a re-feed roller pair 53. . Thereafter, the developer image is fixed on the sheet P by being conveyed through the fixing nip N2 in the same manner as when the image is formed on the first side, and the sheet P on which the image is formed on both sides is discharged by the discharge roller pair 41. It is discharged to the tray 42.

  FIG. 2A is a diagram illustrating a block configuration of the image forming apparatus 100. In the image forming apparatus 100, image data 350 transmitted from the outside is input to the controller 300. The image data 350 may be transmitted from an external host computer or may be generated by optically reading a document by the image reading unit 308 provided in the image forming apparatus 100. The controller 300 controls the image forming apparatus 100 as a whole. For example, when performing image formation, the controller 300 controls the laser unit 23 based on the input image data 350 to irradiate the photosensitive drum 21 with laser light.

  The controller 300 outputs a transfer bias application signal to the high voltage power source 400 to apply a transfer bias to the transfer roller 25. The high-voltage power supply 400 includes a resistance detection unit 410 that detects the output load resistance of the transfer bias and transmits it to the controller 300. Controller 300 causes main motor drive circuit 310 to drive main motor 315 by transmitting a main motor drive command to main motor drive circuit 310. The rotation of the main motor 315 is transmitted to the photosensitive drum 21, the feeding roller pair 14, and the registration clutch 325.

  The controller 300 controls to connect the registration clutch 325 by transmitting a clutch connection command to the clutch drive circuit 320 and transmit the rotation from the main motor 315 to the registration roller pair 15. The controller 300 controls the clutch drive circuit 320 to release the registration clutch 325 by transmitting a clutch release command and not to transmit the rotation from the main motor 315 to the registration roller pair 15. The pre-registration sensor S2 detects the timing at which the leading edge of the sheet P reaches the nip portion of the registration roller pair 15, and transmits the detection signal to the controller 300.

  FIG. 2B is a diagram illustrating the configuration of the controller 300. The CPU 301 controls each block connected to the system bus 310. A RAM 302 is a general-purpose RAM, and is used as a work area for the CPU 301 and a temporary storage area for data. A ROM 303 is a general-purpose ROM, stores a firmware program for driving the image forming apparatus 100 and a boot program for controlling the firmware program, and is read by the CPU 301 into the RAM 302 and executed.

  A communication interface (I / F) 304 is connected to an external host computer or the like via a wired or wireless network medium, and enables transmission / reception of image data and control information. The operation unit I / F 305 is connected to an operation unit 309 having a panel, input keys, and the like, and enables transmission / reception of display data such as a user interface screen displayed on the panel and operation information using the input keys.

  The print control unit I / F 306 is connected to the print control unit 110 including each block in FIG. 2, and can transmit / receive data converted so that the print control unit 110 can process and information from the print control unit 110. To do. The image reading unit I / F 307 is connected to an image reading unit 308 that optically reads a document placed on a document table or a document fed from an automatic document feeder (ADF).

  In addition to the blocks shown in FIG. 2B, blocks for realizing the functions of the image forming apparatus 100 are configured. For example, the controller 300 may be configured as an image processing unit for performing various image processing such as correction, conversion, rotation, enlargement / reduction, and the like on the image data acquired from the image reading unit 308.

  Next, a change in the transfer bias resistance value detected by the resistance detection unit 410 will be described with reference to a schematic diagram showing a change in the resistance value of the transfer roller 25 in FIG.

  FIG. 3A is a schematic diagram showing a state where the sheet P is not in close contact between the photosensitive drum 21 and the transfer roller 25, and FIG. 3B is a diagram between the photosensitive drum 21 and the transfer roller 25. It is the schematic diagram which showed the state with which the sheet | seat P was closely_contact | adhered. FIG. 3C is a timing chart showing whether or not the sheet P is in close contact between the photosensitive drum 21 and the transfer roller 25, and is measured by the resistance detector 410 in a state corresponding to the timing chart. It is the graph which showed the change of resistance value.

  As the transfer bias, a constant voltage (or current) is applied to the transfer roller 25 by the high-voltage power supply 400. The resistance detector 410 measures the resistance value according to Ohm's law by measuring the output current (voltage in the case of constant current control) of the transfer bias.

  The transfer bias applied to the transfer roller 25 flows from the transfer roller 25 to the photosensitive drum 21 as shown in FIG. As shown in FIG. 3B, when the sheet P is in close contact between the transfer roller 25 and the photosensitive drum 21, the flow of the transfer bias is restricted by the sheet P, and as a result, the output resistance of the transfer bias changes. Get higher. Further, when the sheet P passes between the transfer roller 25 and the photosensitive drum 21 due to the rotation of the photosensitive drum 21, the transfer bias flow is not limited, and the output resistance of the transfer bias returns to the original value.

  Next, the print control process in this embodiment will be described. FIG. 4 is a flowchart illustrating the print control process, and FIG. 7 is a diagram illustrating a detailed configuration of the image forming unit. The processing in FIG. 4 is realized, for example, by the CPU 301 reading a program stored in the ROM 303 to the RAM 302 and executing it. When the controller 300 receives, for example, an instruction to execute a print job for printing an image to be recorded on the user interface screen displayed on the operation unit 309, the process in FIG. 4 starts.

  In step S <b> 401, the CPU 301 acquires the length LA in the conveyance direction of the sheet to be printed from the setting contents of the print job. In step S <b> 402, the CPU 301 obtains the length LF in the transport direction of the front end unprinted area, the length LP in the transport direction of the print area, and the length LB in the transport direction of the rear end unprinted area from the print job settings. get. Here, the front non-printing area LF indicates a blank area on the upper side of the printing area of the image as shown in FIG. The rear end unprinted area LB indicates a blank area below the image print area as shown in FIG. Note that the variables LF, LP, and LB are secured in the RAM 302, for example.

  In step S <b> 403, the CPU 301 separates the sheet P from the sheet bundle of the feeding cassette 11 and starts conveyance by the feeding roller pair 14. In S404, the CPU 301 monitors whether the detection signal of the pre-registration sensor S2 is ON. If it is determined that the detection signal of the pre-registration sensor S2 is ON, the process proceeds to S405.

  In step S <b> 405, the CPU 301 stops the driving of the pair of feed rollers 14 and waits for a predetermined time after abutting the sheet P on the nip of the registration roller pair 15 in order to correct the skew of the sheet P. In step S406, the CPU 301 turns on and connects the registration clutch 325 at a predetermined timing, transmits rotation to the registration roller pair 15 to resume conveyance of the sheet P, and conveys the sheet P to the transfer nip portion N1. In step S407, the CPU 301 starts measuring the resistance value by the resistance detection unit 410 and starts counting time T until the resistance value changes. In step S <b> 408, the CPU 301 controls the laser unit 23 to start forming an electrostatic latent image on the photosensitive drum 21.

  In S409, the CPU 301 monitors the change in the resistance value. As shown in FIG. 3C, the time when the resistance value has increased is the time when the sheet P actually reaches the transfer nip portion N1, and the processing proceeds to S410. Proceed to, and the amount of deviation L of the sheet P is calculated.

  Here, as shown in FIG. 7, the distance from the registration roller pair 15 to the transfer nip portion N1 is RN. Further, when the distance on the photosensitive drum 21 from the exposed portion of the laser scanner of the photosensitive drum 21 to the transfer nip portion N1 is LN, the shift amount L of the sheet P is calculated by the equation (1).

L = (T− (RN ÷ conveying speed)) × conveying speed (1)
According to the equation (1), when the sheet P reaches the transfer nip portion N1 in the design time (that is, RN / conveying speed), the deviation amount L = 0 (the state of FIG. 6A). Further, when the sheet P reaches the transfer nip portion N1 earlier than the design time, the shift amount L is a negative value, and the leading edge of the image is shifted by the shift amount L toward the sheet rear end direction (FIG. 6). (C) state). On the other hand, when the sheet P reaches the transfer nip portion N1 later than the design time, the shift amount L is a positive value, and the leading edge of the image is shifted by the shift amount L in the sheet leading direction direction (FIG. 6 ( b)).

  Here, when the absolute value of the shift amount L is smaller than both the leading end unprinted area LF and the trailing end unprinted area LB, the image protrudes from the sheet P even if the sheet transfer position of the printed area LP shifts. Therefore, in step S411, the CPU 301 determines whether or not the condition “| L | <LF and | L | <LB” is satisfied. If it is determined that the condition is satisfied, the process proceeds to S412 and the CPU 301 continues image formation (laser exposure and image transfer) for the distance LN and beyond.

  If it is determined in S411 that the condition is not satisfied, the image protrudes from the leading end side or the trailing end side of the sheet P. Therefore, the process proceeds to S413, and the CPU 301 calculates the sum of the deviation amount L of the sheet P and the sheet length LA. Then, the front end unprinted area LF and the sum of the print area LP are compared to determine whether or not the condition of “L + LA> LF + LP” is satisfied. Here, the case where it is determined that the condition is satisfied is a case where the sheet P arrives later than the design time, and is a state where the image protrudes from the leading end side of the sheet P as shown in FIG. In this case, since the toner that has not been transferred to the sheet P adheres to the transfer roller 25, the process proceeds to S419, and the CPU 301 performs image formation (laser exposure and image transfer) for the distance LN and thereafter, and then proceeds to S420. Then, the transfer roller 25 is cleaned.

  On the other hand, when the condition is not satisfied in S413, that is, when “L + LA ≦ LF + LP”, the sheet P reaches the nip portion N1 earlier than the design time, and the sheet P as shown in FIG. In this state, the image protrudes from the rear end side. In this case, the image can be prevented from protruding by reducing the image in the sheet conveyance direction according to the shift amount L. Accordingly, in S414, the CPU 301 calculates a reduction ratio of the print magnification so that an image after the distance LN from the leading edge of the sheet P can be printed in the sheet P.

  The printing magnification is calculated by using the length {LA-LN} of the remaining printing area of the sheet P after the leading edge of the sheet P arrives at the nip portion N1 and the length {LP- (LN + L-LF) of the unexposed portion of the printing area LP. )} Divided by. Therefore, the printing magnification after the leading edge of the sheet P has arrived at the nip portion N1 can be expressed as in Expression (2).

Printing magnification = (LA−LN) ÷ {LP− (LN + L−LF)}
... (2)
In S415, it is determined whether or not the printing magnification obtained by Expression (2) is 1 or more. If it is 1 or more, the magnification is set to 1 in S416. That is, the magnification is not changed. Thereby, it is possible to prevent the image from protruding without adding a margin to the rear end side of the sheet P.

FIG. 6D shows an image after the print magnification is changed (reduced) according to the equation (2). As shown in FIG. 6D, the image can be stored on the sheet P by changing the printing magnification. In S415, if the printing magnification obtained by the equation (2) is less than 1, the printing magnification obtained by the equation (2) is set to reduce the image. In step S417, the CPU 301 performs image formation for the distance LN and beyond at the set print magnification, and then returns the magnification setting to 1 in step S418.

  In S412, S420, and S418, when the image formation after the distance LN is completed, in S421, the CPU 301 turns off the registration clutch 325 to separate it, and stops the rotation of the registration roller pair 15.

  In step S422, the CPU 301 determines whether the execution of the print job has ended. If it is determined that the print job has ended, the process proceeds to S423. If it is determined that the print job has not ended, the processes from S402 are repeated.

  In S423, the CPU 301 determines whether or not at least one of the transfer cleaning in S420 and the change of the printing magnification in S417 has been performed. If it is determined that any of the processes has been performed, the user is notified to confirm the print contents, and the process of FIG. 4 ends. This notification may be performed, for example, by displaying a message on the operation unit 309. On the other hand, if it is determined that no processing is performed, the processing in FIG. 4 is terminated without notification.

  As described above, according to the present embodiment, it is possible to accurately determine the arrival timing of the sheet to the nip portion between the transfer roller 25 and the photosensitive drum 21, preventing the image from protruding, Dirt can be properly cleaned. The transfer roller may be cleaned also in the case of No in S414 (when the sheet P reaches the nip portion N1 earlier than the design time).

(Other embodiments)
In the embodiment described above, whether the print region LP protrudes from the sheet in consideration of the amounts of the front unprinted region LF (front end side margin) and the rear end unprinted region LB (rear end side margin) of the image to be actually formed. Whether or not the leading edge unprinted area LF and trailing edge unprinted area LB are treated as fixed values N. When the deviation amount | L |> N, image reduction or transfer cleaning is performed, and the user confirms the print contents. You may be notified. In this case, the reduction ratio (printing magnification) of image reduction can be expressed as the following expression (2) ′.

Printing magnification = (LA−LN) ÷ (LA−LN + L) (2) ′
By reducing the image at such a printing magnification, it is possible to prevent the image from protruding from the sheet even if the margin amount is not acquired.

  In this embodiment, the case where an image is directly transferred from a photosensitive drum to a sheet has been described. However, when a color image is formed, a toner image is formed on a belt-like image carrier, and then the image is carried. It is also possible to apply to a method of transferring a toner image from a body to a sheet.

  15 Registration roller pair: 21 Photosensitive drum: 25 Transfer roller: 100 Image forming apparatus: 301 CPU: 302 RAM: 303 ROM

Claims (15)

An image forming means for transferring an image formed on the image carrier to a recording medium which is nipped and conveyed with the transfer means;
Detecting means for detecting a change in resistance value of a nip region in which a recording medium is nipped and conveyed by the image carrier and the transfer means;
Determination means for determining the arrival timing of the recording medium to the nip region based on the change in the resistance value detected by the detection means;
An image forming apparatus comprising:   The determination means is a timing at which the recording medium is predicted to reach the nip area after the start of image formation on the image carrier, and the arrival of the recording medium to the nip area determined from the change in the resistance value. The image forming apparatus according to claim 1, wherein a deviation amount of a timing at which the recording medium reaches the nip region is determined based on a difference from the timing.   The determination unit is further configured to determine whether the arrival of the recording medium at the nip region is earlier or later than the predicted timing based on the deviation amount determined by the determination unit. The image forming apparatus according to 2.   Reduction that reduces the length of the image formed on the image carrier after the determination when the determination means determines that the arrival of the recording medium to the nip region is a predetermined amount earlier than the predicted timing. The image forming apparatus according to claim 3, further comprising means.   The image forming apparatus according to claim 4, wherein a reduction ratio by the reduction unit is in accordance with the amount of deviation determined by the determination unit.   The apparatus further comprises a cleaning unit that cleans the transfer unit when the determination unit determines that the arrival of the recording medium to the nip region is a predetermined amount later than the predicted timing. The image forming apparatus according to 3.   The image forming apparatus according to claim 2, further comprising: a cleaning unit that cleans the transfer unit when the shift amount determined by the determination unit is greater than or equal to a predetermined amount.   The notification means for notifying that the confirmation of the image formed on the recording medium is further provided when the amount of deviation determined by the determination means is a predetermined amount or more. 2. The image forming apparatus according to item 1. An acquisition means for acquiring a margin amount of an image to be formed;
The determination unit further determines whether or not the transferred image protrudes from the recording medium based on a difference between the deviation amount determined by the determination unit and the margin amount acquired by the acquisition unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   A reduction means for reducing the length of the image formed on the image carrier after the determination when it is determined that the image transferred by the determination means protrudes from the rear end side in the conveyance direction of the recording medium; The image forming apparatus according to claim 9.   The reduction ratio by the reduction means is determined by the length of the recording medium conveyed after it is determined that the image transferred by the determination means protrudes from the rear end side in the conveyance direction of the recording medium, and the image carrier after the determination. The image forming apparatus according to claim 10, wherein the image forming apparatus conforms to a ratio with a length of an image formed on the image forming apparatus.   The image according to claim 9, further comprising: a cleaning unit that cleans the transfer unit when the determination unit determines that the transferred image protrudes from the leading end side in the conveyance direction of the recording medium. Forming equipment.   The image forming apparatus according to claim 9, further comprising a cleaning unit that cleans the transfer unit when it is determined that the image transferred by the determination unit protrudes from the recording medium.   14. A notification means for notifying that the image formed on the recording medium is confirmed when it is determined that the image transferred by the determination means protrudes from the recording medium. The image forming apparatus according to claim 1. A method executed in an image forming apparatus having an image forming unit that transfers an image formed on an image carrier to a recording medium that is nipped and conveyed with a transfer unit,
A detection step of detecting a change in resistance value of a nip region in which a recording medium is nipped and conveyed by the image carrier and the transfer unit;
A determination step of determining the arrival timing of the recording medium to the nip region based on the change in the resistance value detected in the detection step;
A method characterized by comprising:

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