JP5409574B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In general, an image forming apparatus that forms an image of a color document on a recording sheet as shown in Patent Document 1, a plurality of developing devices arranged along a moving direction of a transfer belt, Transfer is performed on the moving transfer belt surface (primary transfer).

  Thereby, toner images of different colors are superimposed on the surface of the transfer belt, and a color image is formed on the surface of the transfer belt.

  Then, the image forming apparatus transfers the toner image transferred onto the surface of the transfer belt to the recording paper conveyed through the conveyance path by the secondary transfer unit disposed at a predetermined position of the transfer belt (secondary transfer). ). As a result, a color image is formed on the recording paper.

  This type of image forming apparatus, when forming an image of a color document on a plurality of recording sheets, feeds the recording sheet to the conveyance path and transfers the toner image to the surface of the transfer belt at a timing based on the recording sheet size. Start transcription.

  By the way, when setting a recording paper of an irregular size in a paper storage unit such as a paper cassette or a manual feed tray, especially when setting a recording paper in the manual feed tray, the user can set the size of the recording paper to an operation button or the like. Set by operation.

  If the size of the recording paper set in the paper storage unit is set to a size different from the actual size, or if the size of the recording paper is not set, the image forming apparatus At a timing based on the actual size, it is not possible to start feeding the recording paper to the transport path and transferring the toner image onto the transfer belt surface.

  For example, when a size smaller than the actual size is set as the size of the set recording paper, the recording paper feeding and the toner image transfer belt are performed at a timing based on the smaller size than the actual size. Initiate transfer to the surface. In this case, an image defect occurs in which a plurality of pages of color images are formed on one sheet of recording paper.

JP 2004-155522 A JP-A-6-234440

  Incidentally, the image forming apparatus described in Patent Document 1 changes the paper feeding interval of the recording paper when the size of the set recording paper is set to a size different from the actual size. In this case, if the recording paper feed interval becomes larger than the paper feed interval before the change, the productivity of image formation decreases.

  Further, the image forming apparatus described in Patent Document 2 stops the image forming process when the size of the set recording paper is set to a size different from the actual size, prompts the correct size setting, and corrects the correct size. When the size is set, the image forming process is resumed. In this case, the productivity of image formation decreases.

  The present invention has been made to solve the above-described problems, and provides an image forming apparatus that eliminates the possibility of image defects on recording paper and suppresses a decrease in image formation productivity. With the goal.

An image forming apparatus according to an aspect of the present invention includes an image carrier on which a toner image of a document image is transferred to a surface of the image forming apparatus while the surface moves in a predetermined direction. A primary transfer portion that transfers the toner image onto the surface by applying a preset transfer voltage between the carrier and the carrier, and is disposed to face the image carrier. A toner image removing unit that removes the toner image transferred to the surface, and a secondary transfer unit that transfers the toner image transferred to the surface by the primary transfer unit onto a recording sheet conveyed through a conveyance path. And a predetermined detection of the transport path after the toner image is transferred to the surface by the primary transfer unit and before the toner image passes a position facing the toner image removal unit. in position, the toner image A determination unit for determining whether the recording sheet is fed immediately before the recording paper to be transferred is present, by the determination unit, to the detection position, the recording sheet to be transferred the toner image A control unit that causes the toner image removing unit to remove the toner image on the surface when it is determined that the recording sheet fed immediately before the image is present (claim). Item 1).

  Here, the detection position is the toner image when the toner image on the surface of the image carrier passes the position facing the toner image removal unit when the recording paper conveyed through the conveyance path exists at the detection position. Represents the position where is transferred to the recording paper.

  According to this configuration, the conveyance path is determined in advance between the time when the toner image is transferred to the surface of the image carrier by the primary transfer unit and the time when the toner image passes through the position facing the toner image removing unit. When the recording paper is present at the detected position, the toner image removal unit removes the toner image on the surface of the image carrier.

  Thus, after the color original image of the page on the recording paper is transferred, the color original image of the next page is not transferred to the recording paper even if the recording paper exists at the detection position. An image defect in which a color image of a page is formed on one sheet of recording paper does not occur.

  As a result, there is no risk of image defects on the recording paper, and there is no need to widen the recording paper feed interval, which reduces the reduction in image formation productivity compared to changing the recording paper feed interval. can do. Further, since it is not necessary to interrupt the image forming process and reset the recording paper size, it is possible to suppress a decrease in image forming productivity as compared with the case where the image forming process is interrupted.

In the above configuration, the image forming apparatus includes a storage unit that stores the document image as image data, and the control unit, when the determination unit determines that the recording sheet is present at the detection position, the toner image removal unit To remove the toner image on the surface, acquire the original image for transferring the toner image from the storage unit, transfer the toner image to the surface by the primary transfer unit, and perform the secondary transfer. It is preferable that the toner image on the surface is transferred onto the recording paper conveyed through the conveyance path after the recording paper by the unit.

  According to this configuration, the detection position is detected by the determination unit after the toner image is transferred to the surface of the image carrier by the primary transfer unit and before the toner image passes the position facing the toner image removal unit. When the recording paper is determined to be present, the toner image removing unit removes the toner image on the surface of the image carrier, and the toner image is recorded on the conveyance path after the recording paper. Transfer to paper.

  According to this configuration, the toner image removed by the toner image removing unit when the recording paper is present at the detection position is transferred to the recording paper conveyed on the conveyance path after the recording paper.

  As a result, after the color original image of the page on the recording paper is transferred, the color original image of the next page is not transferred to the recording paper even if the recording paper exists at the detection position. Then, the image of the next page that has not been transferred to the recording paper is transferred to the recording paper that is transported through the transport path after the recording paper.

  As a result, even when there is an error in setting the recording paper size, it is possible to prevent a plurality of pages of color original images from being transferred to one recording paper without interrupting image formation.

  In this way, it is possible to eliminate the possibility of image defects on the recording paper. As a result, a decrease in image formation productivity can be suppressed.

  In the above configuration, when the time elapsed after the toner image is transferred to the surface by the primary transfer unit becomes a preset set time, the determination unit detects the recording paper at the detection position. It is preferable to determine whether or not it exists (claim 3).

  Here, the preset set time is a time within a range from when the toner image is transferred to the image carrier by the primary transfer unit until the toner image passes through the toner image removing unit.

  According to this configuration, when the time elapsed after the toner image is transferred to the surface of the image carrier by the primary transfer unit reaches the set time, it is determined whether or not a recording sheet exists at the detection position. It becomes possible to judge.

  In the above configuration, a plurality of the primary transfer units are arranged along the movement direction of the surface, and the toner image removal unit is arranged closest to the movement direction of the surface among the primary transfer units. Further, the control unit is configured to apply a voltage having a polarity opposite to that of the transfer voltage between the control unit and the image carrier by the primary transfer unit constituting the toner image removing unit. It is preferable to remove the toner image on the surface from the image carrier by applying (claim 4).

  According to this configuration, the toner image removing unit is arranged along the moving direction of the surface of the image carrier, and is arranged closest to the moving direction of the surface of the image carrier among the plurality of primary transfer units. It consists of a primary transfer part. Then, a voltage having a polarity opposite to the transfer voltage is applied to the image carrier by the primary transfer unit, thereby removing the toner image on the surface of the image carrier from the image carrier.

  Thus, since the primary transfer portion closest to the moving direction of the surface of the image carrier among the primary transfer portions is used as the toner image removal portion, the toner image removal portion can be added without adding a new component. Can be configured.

  In the above configuration, the moving speed of the surface is equal to the transport speed of the recording paper transported along the transport path, and the detection position is in a direction from the secondary transfer unit toward the upstream side of the transport path. It is preferable that the distance is equal to the distance from the secondary transfer portion to the toner image removing portion.

  According to this configuration, the moving speed of the surface of the image carrier is equal to the transport speed of the recording paper transported along the transport path, the distance from the toner image removal unit to the secondary transfer unit, the detection position, and the secondary transfer unit. The distance to the transfer portion is equal, the time until the toner image on the surface of the image carrier reaches the secondary transfer portion from the toner image removing portion, and the recording paper passes through the detection position to the secondary transfer portion. The time to reach is equal.

  In this case, the toner image on the surface of the image carrier, on which the recording paper transported along the transport path has passed the position facing the toner image removing unit while passing through the detection position from the front end to the rear end of the recording paper. Is transferred to the recording paper.

  As a result, if the toner image on the surface of the image carrier passes the position facing the toner image removal unit when the recording paper is present at the detection position, the toner image is transferred to the recording paper. Can be expressed as a position.

  In the above-described configuration, a recording paper sensor that detects the recording paper is disposed at the detection position, and the determination unit is located at the detection position when the recording paper is detected by the recording paper sensor. It is preferable to determine that recording paper is present (claim 6).

  According to this configuration, when the recording sheet is detected by the recording sheet sensor, it is determined that the recording sheet exists at the detection position. This makes it possible to make the determination using a conventional recording paper sensor.

  According to the present invention, if the recording paper is present at the detection position when the toner image transferred to the surface of the image carrier by the primary transfer unit passes the position facing the toner image removing unit, the image carrier The toner image transferred to the surface of the toner is removed by the toner image removing unit.

  As a result, it is possible to eliminate the possibility of image defects on the recording paper and to suppress a decrease in image formation productivity.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. It is a figure for demonstrating the arrangement | positioning location of a recording paper sensor. 2 is a block diagram illustrating an example of a functional module of the image forming apparatus according to the present exemplary embodiment. FIG. 5 is a flowchart showing an outline of processing for forming a document image. 5 is a flowchart showing an outline of processing for forming a document image. 5 is a flowchart showing an outline of processing for forming a document image.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the location of the recording paper sensor.

  In the present embodiment, a color printer is illustrated as the image forming apparatus 1, but the present invention is not limited to this example. The image forming apparatus 1 may be an apparatus that forms a color image, such as a multifunction machine, a copier, and a facsimile machine.

  An image forming apparatus 1 shown in FIG. 1 includes an apparatus main body 200 connected to a personal computer (not shown) or the like directly or via a LAN.

  As shown in FIG. 1, the apparatus main body 200 includes an intermediate transfer unit 92, an image forming unit 93, an exposure unit 94, a fixing unit 97, and a paper discharge unit 96. Further, the apparatus main body 200 includes a front cover 23, and a manual feed tray 50 for manually feeding recording paper is attached to the front surface of the front cover 23 so that it can be pulled out forward.

  The image forming unit 93 is a developing device (primary transfer unit) 10Y for developing a yellow toner image, a developing device (primary transfer unit) 10M for developing a magenta toner image, and develops a cyan toner image. A developing device (primary transfer portion) 10C for developing the toner image, and a developing device (primary transfer portion) 10K for developing a black toner image.

  Each of the developing devices 10Y, 10M, 10C, and 10K includes a photosensitive drum 17, a developing device 15, a charger 16, a cleaner 18, and a transfer roller 19. As the photosensitive drum 17, a photosensitive drum using an amorphous silicon (a-Si) material can be used.

  Around each photosensitive drum 17, a developing device 15, a charger 16, a cleaner 18, and a transfer roller 19 are arranged. The developing device 15 receives toner from a toner cartridge (not shown) and supplies the toner to the photosensitive drum 17.

  The charger 16 uniformly charges the surface of the photosensitive drum 17. The cleaner 18 cleans the surface of the photosensitive drum 17. The transfer roller 19 is disposed to face the corresponding photosensitive drum 17 with an intermediate transfer belt 921 described later interposed therebetween, and forms a nip portion with the photosensitive drum 17.

  An exposure unit 94 is disposed below the image forming unit 93. The exposure unit 94 has various optical system elements such as a light source, a polygon mirror, a reflection mirror, and a deflection mirror, and irradiates the surface of the photosensitive drum 17 with light based on image data.

  The intermediate transfer unit 92 includes a conductive intermediate transfer belt (image carrier) 921, a driving roller 922, and a driven roller 923. The intermediate transfer belt 921 is stretched between the driving roller 922 and the driven roller 923 in contact with the surface of the photosensitive drum 17, and is circulated in the direction of the arrow AR1. As the intermediate transfer belt 921 is circulated, the toner images are primarily transferred from the respective photosensitive drums 17 in the nip portion in a state of being overcoated.

  The primary transfer of the toner image is performed as follows.

  Each of the developing devices 10Y, 10M, 10C, and 10K charges the surface of the photosensitive drum 17 by the charger 16. Each of the developing devices 10Y, 10M, 10C, and 10K is exposed to the developing unit 15 when an electrostatic latent image is formed on the surface by the exposure unit 94 based on the image data of the document image. The electrostatic latent image is developed. As a result, toner images of different colors are formed on the surfaces of the photosensitive drums 17 of the developing devices 10Y, 10M, 10C, and 10K.

  Each toner image is sequentially transferred onto the surface of the intermediate transfer belt 921 according to the rotation of the intermediate transfer belt 921. As a result, a color toner image is formed on the intermediate transfer belt 921.

  The cleaner 18 cleans the surface of the photosensitive drum 17 after the toner image is primarily transferred.

  A secondary transfer roller 20 disposed in contact with the drive roller 922 is disposed at a position facing the drive roller 922. The secondary transfer roller 20 and the driving roller 922 function as the secondary transfer unit 98. The color toner image on the intermediate transfer belt 921 is secondarily transferred onto the recording paper P conveyed from the recording paper cassette 41 described later or the recording paper P conveyed from the manual feed tray 50 in the secondary transfer unit 98. Is done. The recording paper P that has been subjected to the secondary transfer is conveyed to the fixing unit 97.

  The fixing unit 97 performs a fixing process on the toner image on the recording paper P. The fixing unit 97 is disposed in contact with the fixing roller 97a having a built-in heat source in contact with the fixing roller 97a. And a pressure roller 97b that forms a fixing nip portion therebetween. The recording paper P for which the fixing process has been completed is conveyed toward a discharge unit 96 formed on the upper portion of the apparatus main body 200 by a discharge roller pair 44 disposed on the downstream side of the fixing roller 97a and the pressure roller 97b. The discharge unit 96 discharges the recording paper P conveyed from the fixing unit 97 onto a paper discharge tray 96 a formed on the upper surface of the apparatus main body 200.

  The recording paper P on which the secondary transfer is performed in the secondary transfer unit 98 is conveyed to the secondary transfer unit 98 by the first paper feeding device 30. Further, the recording paper P on which the secondary transfer is performed in the secondary transfer unit 98 is conveyed to the secondary transfer unit 98 by the second paper feeding device 32.

  The first paper feeding device 30 includes a recording paper cassette 41 on which the recording paper P is placed on the recording paper placement surface 43, and a first pickup that takes out the recording paper P placed on the recording paper cassette 41 one by one. A roller 37 and a first transport roller pair 33 that transports the recording paper P taken out by the first pickup roller 37 toward a second transport roller pair 34 described later are provided.

  The second paper feeding device 32 takes out the recording paper P placed on the manual feed tray 50 one by one, and transports the recording paper P toward the second transport roller pair 34. Is provided.

  A recording paper transport path (transport path) 27 is formed from the second transport roller pair 34 toward the discharge unit 96. The recording paper P fed by the first paper feeding device 30 and the recording paper P fed by the second paper feeding device 32 are transported along the recording paper transport path 27 in the direction of the arrow AR2. Passes through the secondary transfer section 98.

  A second conveyance roller pair 34 and a registration roller pair 40 are arranged in the recording paper conveyance path 27. The second transport roller pair 34 transports the recording paper P transported from the first transport roller pair 33 toward the registration roller pair 40. The registration roller pair 40 conveys the recording paper P toward the secondary transfer unit 98 at an appropriate timing and corrects the oblique feeding of the recording paper P.

  In the first paper feeding device 30, the second paper feeding device 32, and the recording paper conveyance unit 27, the first pickup roller 37, the second pickup roller 38, the first conveyance roller pair 33, and the second conveyance roller pair 34. The registration roller pair 40 and the driving roller 922 rotate so that the conveyance speed of the recording paper P in the recording paper conveyance path 27 is equal to the rotation speed of the intermediate transfer belt 921.

  A recording paper sensor S is disposed at a detection position PO in the recording paper conveyance path 27. The detection position PO is a position shown below.

  As shown in FIG. 2, the secondary transfer portion 98 is formed by a drive roller 922 and a secondary transfer roller 20. A nip portion PO <b> 2 is configured between the driving roller 922 and the secondary transfer roller 20. The detection position PO is a position away from the nip portion PO2 by a distance D2 in the upstream direction in the conveyance direction of the recording paper P.

  The distance D2 is equal to the distance D1 between the nip portion PO1 and the nip portion PO2 between the photosensitive drum 17 of the developing device 10K and the transfer roller 19 in the intermediate transfer belt 921.

  Here, the detection position PO is detected at the nip portion PO2 when the toner image on the surface of the intermediate transfer belt 921 passes through the nip portion PO1 in the developing device 10K when the recording paper P exists at the detection position PO. This is a position where the toner image is transferred to the recording paper P conveyed from the position PO.

  Hereinafter, when the recording paper P is present at the detection position PO and the toner image on the surface of the intermediate transfer belt 921 passes through the nip portion PO1 in the developing device 10K, the toner image has been conveyed from the detection position PO at the nip portion PO2. The reason why the toner image is transferred to the recording paper P will be described.

  As described above, the conveyance speed of the recording paper P in the recording paper conveyance path 27 is equal to the rotational speed of the intermediate transfer belt 921 and extends upstream from the nip portion PO2 in the secondary transfer portion 98 in the conveyance direction of the recording paper P. A detection position PO that is a distance D2 that is equal to the distance D1 is set.

  Thus, the time until the toner image on the surface of the intermediate transfer belt 921 reaches the nip portion PO2 from the nip portion PO1 in the developing device 10K and the recording paper P reaches the nip portion PO2 after passing the detection position PO. The time until is equal.

  In this case, the intermediate transfer belt that has passed through the nip portion PO1 in the developing device 10K while the recording paper P transported through the recording paper transport path 27 passes through the detection position PO from the front end to the rear end of the recording paper. The toner image on the surface of 921 is transferred to the recording paper P.

  As a result, when the recording paper P exists at the detection position PO and the toner image on the surface of the intermediate transfer belt 921 passes through the nip portion PO1 in the developing device 10K, the toner image is transferred to the recording paper P. become.

  FIG. 3 is a block diagram illustrating an example of functional modules of the image forming apparatus 1 according to the present embodiment.

  The image forming apparatus 1 includes a control unit 100 configured by a CPU (Central Processing Unit), an image memory (storage unit) 101, a recording paper sensor S, a timer 102 for measuring time, a determination unit 103, developing devices 10Y and 10M, 10C and 10K, and an exposure unit 92. Since the functions of the developing devices 10Y, 10M, 10C, and 10K and the exposure unit 92 are as described above, the description thereof is omitted.

  The image memory 101 stores image data received from a personal computer (not shown). The recording paper sensor S detects the presence of the recording paper P at the detection position PO, and outputs a detection signal to the determination unit 103. The timer 102 measures time under the control of the control unit 100.

  The determination unit 103 determines whether a detection signal is output by the recording paper sensor S when the time measured by the timer 102 reaches a preset time T.

  When the detection signal is output, the determination unit 103 determines that the recording paper P is present at the detection position PO. On the other hand, when the detection signal is not output, the determination unit 103 determines that the recording paper P is present at the detection position PO. It is determined that it does not exist, and the control unit 100 is notified of the result of the determination.

  Here, the set time T is a time within a range from when the toner image is transferred to the surface of the intermediate transfer belt 921 by the primary transfer portion until the toner image passes a toner image removing portion described later.

  The set time T is, for example, after the cyan toner image is transferred to the surface of the intermediate transfer belt 921 by the developing device 10C that is a developing device that is one upstream of the developing device 10K that is a toner removing unit described later. , And the time until the toner image is positioned at the nip portion PO1.

  Strictly speaking, the set time T is defined as the time T0 from when the cyan toner image is transferred to the surface of the intermediate transfer belt 921 by the developing device 10C until the toner image is positioned at the nip portion PO1. In this case, the margin time Td such as the time from when the developing device 10K is controlled by the control unit 100 to when the toner image is actually removed is subtracted from the time T0.

  The set time T may be a time from when the yellow toner image is transferred to the surface of the intermediate transfer belt 921 by the developing device 10Y until the toner image is positioned at the position PO1.

  In this case, strictly speaking, the set time T is a time T0 from when the yellow toner image is transferred to the surface of the intermediate transfer belt 921 by the developing device 10Y until the toner image is positioned at the position PO1. In this case, the margin time Td such as the time from when the developing device 10K is controlled by the control unit 100 until the toner image is actually removed is subtracted from the time T0.

  The set time T may be a time from when the magenta toner image is transferred to the surface of the intermediate transfer belt 921 by the developing device 10M until the toner image is positioned at the position PO1.

  In this case, strictly speaking, the set time T is the time T0 from when the magenta toner image is transferred to the surface of the intermediate transfer belt 921 by the developing device 10M until the toner image is positioned at the position PO1. In this case, the margin time Td such as the time from when the developing device 10K is controlled by the control unit 100 until the toner image is actually removed is subtracted from the time T0.

  The control unit 100 comprehensively controls the image forming apparatus 1. In addition, the control unit 100 activates the timer 102 at the transfer timing by the developing device 10 </ b> C, and causes the determination unit 103 to execute the determination when the time measured by the timer 102 reaches the set time T.

  When the set time T is the elapsed time since the yellow toner image is transferred to the intermediate transfer belt 921, the control unit 100 activates the timer 102 at the transfer timing by the developing device 10Y, and sets the set time. When T is the elapsed time after the magenta toner image is transferred to the intermediate transfer belt 921, the timer 102 is started at the transfer timing by the developing device 10M.

  Each of the developing devices 10Y, 10M, 10C, and 10K includes, in addition to the transfer roller 19 described above, a voltage application unit 11 that applies a transfer voltage having a polarity opposite to that of the toner to the transfer roller 19. .

  In each developing device, when the toner image on the surface of the photosensitive drum 17 is transferred to the intermediate transfer belt 921, the voltage applying unit 11 applies the transfer voltage to the transfer roller 19 corresponding to the photosensitive drum 17. Then, the transfer roller 19 applies the transfer voltage to the intermediate transfer belt 921.

  As a result, the toner forming the toner image on the surface of the photosensitive drum 17 is attracted toward the intermediate transfer belt 921, and the toner image is transferred to the surface of the intermediate transfer belt 921.

  Further, among the developing devices 10Y, 10M, 10C, and 10K, the developing device 10K that is disposed on the most downstream side in the circumferential direction of the intermediate transfer belt 921 is configured as a toner image removing unit.

  The developing device 10K constituting the toner image removing unit has a voltage having a polarity opposite to the transfer voltage when the voltage applying unit 11 transfers the toner image on the surface of the photosensitive drum 17 of the developing device 10K to the surface of the intermediate transfer belt 921. That is, a voltage having the same polarity as that of the toner is applied to the transfer roller 19. At this time, the voltage is applied to the intermediate transfer belt 921 by the transfer roller 19.

  As a result, when the toner image on the surface of the intermediate transfer belt 921 arrives at the nip portion of the developing device 10K, a Coulomb force is generated in a direction in which the toner forming the toner image is removed from the surface of the intermediate transfer belt 921. As a result, the toner image on the surface of the intermediate transfer belt 921 is removed from the intermediate transfer belt 921.

  When removing the toner image on the surface of the intermediate transfer belt 921, the voltage application unit 11 applies a voltage having a voltage value corresponding to the amount of toner forming the toner image, thereby increasing the toner image removal efficiency. Can do.

  In the image forming apparatus 1 having such a configuration, the size of the recording paper P placed on the recording paper cassette 41 is often set in advance according to the recording paper cassette 41, but is set on the manual feed tray 50. The size of the recording paper P to be recorded is not predetermined as in the recording paper cassette 41. The size is often an irregular size.

  Therefore, the image forming apparatus 1 is configured such that the size of the recording paper P set on the manual feed tray 50 is set by an input from a user operation button or the like.

  In this case, a size setting error often occurs. When the setting error occurs, a document image for one page may be formed on a plurality of recording papers P.

  Therefore, when the image forming apparatus 1 forms a document image on the recording paper P placed on the manual feed tray 50, the image forming apparatus 1 can suppress the formation of one page of the document image on the plurality of recording papers P. I have to. This will be described with reference to FIGS.

  The document image formed by the image forming apparatus 1 is an image including a color image and a black image, and the color image is developed by developing devices 10Y, 10M, and 10C corresponding to yellow, magenta, and cyan colors. The black image is developed by the developing device 10K corresponding to black.

  4 to 6 are flowcharts showing an outline of processing in which the image forming apparatus 1 forms a document image.

  The control unit 100 acquires the document image stored in the image memory 101 (step S10). Then, the control unit 100 transfers the toner image to the intermediate transfer belt 921 by the developing devices 10Y, 10M, 10C, and 10K (Step S11).

  In step S11, for example, the control unit 100 circulates the intermediate transfer belt 921 and causes the developing device 10Y to transfer a yellow toner image to the intermediate transfer belt 921. The developing device 10M causes the magenta toner image to be superimposed on the toner image transferred by the developing device 10Y, and the developing device 10C transfers the cyan toner image to the toner images transferred by the developing devices 10Y and 10M. And transfer it to the top.

  Further, the control unit 100 feeds the recording paper P by the paper feeding device 32 (step S12).

  Then, the control unit 100 performs the following processing at the transfer timing by the developing device 10C (YES in step S13).

  Here, as the transfer timing by the developing device 10C, for example, the toner transferred to the surface of the intermediate transfer belt 921 by the developing devices 10Y and 10M at the nip portion between the photosensitive drum 17 and the transfer roller 19 in the developing device 10C. Examples include the timing when the leading edge of the image is positioned, and the transfer of the cyan toner image to the surface of the intermediate transfer belt 921 by the developing device 10C.

  As described above, when the set time T is the elapsed time after the yellow toner image is transferred to the intermediate transfer belt 921, the timer 102 is started at the transfer timing by the developing device 10Y.

  In this case, the transfer timing by the developing device 10Y includes, for example, the timing at which the transfer of the yellow toner image to the surface of the intermediate transfer belt 921 is started by the developing device 10Y.

  Further, as described above, when the set time T is the elapsed time after the magenta toner image is transferred to the intermediate transfer belt 921, the timer 102 is started at the transfer timing by the developing device 10M.

  In this case, as the transfer timing by the developing device 10M, for example, the toner image transferred to the surface of the intermediate transfer belt 921 by the developing device 10Y at the nip portion between the photosensitive drum 17 and the transfer roller 19 in the developing device 10M. Examples thereof include the timing when the leading edge is located and the transfer of the magenta toner image to the surface of the intermediate transfer belt 921 by the developing device 10M.

  At the transfer timing by the developing device 10C (YES in step S13), the control unit 100 starts time measurement by the timer 102 (step S14), and when the time measured by the timer 102 reaches the set time T (YES in step S15). The determination unit 103 determines whether or not the recording paper P is present at the detection position PO (step S16).

  As a result of the determination, when the recording paper P is not present at the detection position PO (NO in step S16), the control unit 100 feeds the recording paper P fed immediately before the recording paper P fed in step S12. Is already passed through the detection position, and the process shown in FIG. 6 is performed.

  That is, the control unit 100 causes the developing device 10K to transfer the toner image to the intermediate transfer belt 921 (step S17).

  Then, the control unit 100 causes the registration roller pair 40 to convey the recording paper P fed in step S12 toward the nip PO2 in the secondary transfer unit 98 (step S18), and the recording paper P is niped. When reaching the portion PO2, the toner image on the surface of the intermediate transfer belt 921 is transferred onto the recording paper P by the secondary transfer roller 20 (step S19). And the control part 100 returns to the process of step S10.

  On the other hand, as a result of the determination in step S16, when the recording paper P exists at the detection position PO (YES in step S16), the control unit 100 supplies the recording paper P immediately before the recording paper P fed in step S12. Assuming that the trailing edge of the printed recording paper P has not yet passed the detection position PO, the processing shown in FIG. 7 is performed.

  That is, the control unit 100 causes the developing device 10K to remove the toner image transferred to the surface of the intermediate transfer belt 921 by the developing devices 10Y, 10M, and 10C (Step S20).

  Then, the control unit 100 starts the transfer of the toner image to the intermediate transfer belt 921 by the developing devices 10Y, 10M, 10C, and 10K (Step S21), and starts feeding a new recording paper P (Step S22). ).

  Then, the control unit 100 causes the registration roller pair 40 to convey the recording paper P fed in step S22 toward the nip part PO2 (step S23), and when the recording paper P reaches the nip part PO2, The toner image on the surface of the intermediate transfer belt 921 is transferred onto the recording paper P by the next transfer roller 20 (step S24). And the control part 100 returns to the process of step S10.

  As described above, according to the image forming apparatus 1 according to the present embodiment, for the second and subsequent document images, after the document image of a certain page is transferred to the recording paper P, the trailing edge of the recording paper P Until the document passes the detection position PO, even if the original image of the next page is transferred to the surface of the intermediate transfer belt 921, the original image is removed from the surface of the intermediate transfer belt 921.

  As a result, it is possible to prevent an image defect in which a plurality of pages of document images are formed on one recording sheet P.

  As a result, even when there is an error in the size setting of the recording paper P placed on the manual feed tray 50, it is possible to eliminate the possibility of image defects on the recording paper P.

  As described above, when the recording paper P is present at the detection position PO, the toner image transferred on the surface of the intermediate transfer belt 921 is removed by the developing device 10K which is a toner image removing unit, thereby recording paper. The possibility of image defects in P is eliminated.

  Thus, since it is not necessary to widen the paper feed interval of the recording paper P in order to eliminate the possibility of image defects on the recording paper P, the productivity of image formation is higher than when the paper feed interval of the recording paper P is changed. The decrease can be suppressed. Further, since it is not necessary to interrupt the image forming process and reset the size of the recording paper P, it is possible to suppress a decrease in image forming productivity compared to the case where the image forming process is interrupted.

  In this embodiment, the image forming apparatus 1 transfers the toner images to the surface of the intermediate transfer belt 921 in the order of the developing devices 10Y, 10M, 10C, and 10K. However, the toner images are transferred in a different order. May be. In this case, the toner image removing unit is constituted by the developing device that is the most downstream in the circumferential direction of the intermediate transfer belt 921 among the developing devices.

  Further, the image forming apparatus 1 has a toner on the surface of the intermediate transfer belt 921 on the downstream side in the circumferential direction of the intermediate transfer belt 921 with respect to each developing device, independently of each developing device, in the same manner as the developing device 10K. A toner image removing unit for removing the image may be arranged.

  In this embodiment, the color printer including the developing devices 10Y, 10M, 10C, and 10K is illustrated as the plurality of primary transfer units. However, the image forming apparatus 1 transfers the black toner image onto the surface of the photosensitive drum. A monochrome printer having one developing device as a primary transfer unit may be used.

  In this case, a toner image removing unit that removes the toner image on the surface of the intermediate transfer belt 921 by a method similar to that of the developing device 10K is disposed downstream of the primary transfer unit in the circumferential direction of the photosensitive drum.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10Y, 10M, 10C, 10K Primary transfer part 27 Recording paper conveyance path 98 Secondary transfer part 100 Control part 103 Judgment part 921 Intermediate transfer belt AR1 Circumferential direction of intermediate transfer belt AR2 Conveyance direction of recording paper P, P Recording paper PO detection position S Recording paper sensor T Set time

Claims (6)

An image carrier on which a toner image of a document image is transferred to the surface while the surface moves in a predetermined direction;
A primary transfer portion that is arranged to face the surface and applies a preset transfer voltage to the image carrier to transfer the toner image to the surface;
A toner image removing unit that is disposed to face the image carrier and removes the toner image transferred to the surface by the primary transfer unit;
A secondary transfer unit that transfers the toner image transferred to the surface by the primary transfer unit onto a recording sheet conveyed through a conveyance path;
After the toner image is transferred to the surface by the primary transfer unit, the toner image passes through a position facing the toner image removal unit and then reaches a predetermined detection position on the conveyance path. A determination unit for determining whether or not the recording sheet fed immediately before the recording sheet to which the toner image is to be transferred exists;
When the determination unit determines that the recording sheet fed immediately before the recording sheet on which the toner image is to be transferred exists at the detection position, the surface of the surface is removed by the toner image removal unit. A controller for removing the toner image of
An image forming apparatus comprising: A storage unit for storing the original image as image data;
The controller is
When the determination unit determines that the recording sheet is present at the detection position, the toner image removing unit removes the toner image on the surface and transfers the original image for transferring the toner image. acquired from the storage unit, the toner image is transferred to the surface by the primary transfer portion, the toner image of the surface by the secondary transfer portion, is transported to the transport path later than the recording sheet The image forming apparatus according to claim 1, wherein the image forming apparatus is transferred to a recording sheet. The determination unit
When the time elapsed after the toner image is transferred to the surface by the primary transfer unit becomes a preset set time, it is determined whether or not the recording paper is present at the detection position. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A plurality of the primary transfer portions are arranged along the moving direction of the surface,
The toner image removing unit is composed of the primary transfer unit disposed on the most moving direction side of the surface among the primary transfer units.
The control unit applies a voltage having a polarity opposite to that of the transfer voltage to the image carrier by the primary transfer unit constituting the toner image removing unit, whereby the toner image on the surface is The image forming apparatus according to claim 1, wherein the image forming apparatus is removed from the image carrier. The movement speed of the surface is equal to the conveyance speed of the recording paper conveyed through the conveyance path,
The detection position is a position away from the secondary transfer unit in a direction toward the upstream side of the conveyance path by a distance equal to a distance from the secondary transfer unit to the toner image removing unit. The image forming apparatus according to any one of claims 1 to 4. A recording paper sensor for detecting the recording paper is disposed at the detection position,
6. The determination unit according to claim 1, wherein the determination unit determines that the recording sheet exists at the detection position when the recording sheet is detected by the recording sheet sensor. The image forming apparatus described.

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