JP2010276766A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a secondary transfer roller from being soiled without causing deterioration in image forming efficiency and useless power consumption, regarding an image forming apparatus wherein the secondary transfer roller is always brought in press contact with an intermediate transfer belt. <P>SOLUTION: When the value of an image forming operation counter reaches a predetermined value, a first cleaning operation of cleaning a secondary transfer member is performed by alternately applying a voltage whose polarity is the same as that of the charged toner and a voltage whose polarity is opposite to that of the charged toner to the secondary transfer roller. Further, when a change in internal temperature of the apparatus is detected by a detection sensor, an image stabilizing operation is performed by forming a reference pattern image on a photoreceptor drum, transferring the reference pattern image to the intermediate transfer body, determining an image forming performance, and then, adjusting an image forming condition. When the image stabilization operation is performed, the image forming operation counter is initialized, accordingly, the first cleaning operation is prevented from being performed in a short time period after finishing the image stabilizing operation. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus in which a secondary transfer member is always pressed against an intermediate transfer member.

  In a so-called tandem type image forming apparatus in which a plurality of image forming units are arranged side by side, toner images of different colors formed in the respective image forming units are transferred onto an intermediate transfer belt to form a full color toner image. The image is conveyed to a nip portion between the intermediate transfer belt and the secondary transfer roller. On the other hand, the paper is also transported to the nip portion at the timing when the toner image is transported to the nip portion. Then, a voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller, and the toner image on the intermediate transfer belt is drawn toward the secondary transfer roller to be collectively transferred onto the sheet.

  In such a conventional image forming apparatus, in order to prevent the secondary transfer roller from being soiled, the secondary transfer roller is provided so as to be detachable with respect to the intermediate transfer belt, and the secondary transfer roller is disposed at the intermediate transfer belt except during image formation. (For example, Patent Document 1).

  Further, in a normal image forming apparatus, when the temperature or humidity in the apparatus changes, an image stabilization operation is performed in order to stabilize the image quality. The image stabilization operation forms a reference pattern image at each image forming unit, transfers it to the intermediate transfer belt, measures the density and transfer position of the reference pattern image, and determines the image formation performance from the measurement results. Thus, the image forming conditions such as the charge amount of the photosensitive drum are adjusted.

  In the conventional image forming apparatus in which the secondary transfer roller is separated from the intermediate transfer belt, there is no possibility that the secondary transfer roller is soiled by the reference pattern image even if such an image stabilization operation is performed.

  However, even if the secondary transfer roller is separated from the intermediate transfer belt except during image formation, for example, when a plurality of continuous image formations are performed, the non-image forming area of the secondary transfer roller gradually becomes dirty, If the next sheet to be transported is larger in the width direction than the previous sheet, a problem arises in that the back surface of the next transported sheet becomes dirty. For this reason, when the number of formed images reaches a predetermined number, a voltage having the same polarity as the toner charging polarity is applied to the secondary transfer roller, or a voltage having the same polarity and the opposite polarity to the toner charging polarity is alternately applied. The next transfer roller was regularly cleaned (for example, Patent Document 2).

  By the way, in recent years, attention has been paid to a system in which the secondary transfer roller is always pressed against the intermediate transfer belt without the secondary transfer roller separation / contact mechanism from the viewpoint of reducing the size and weight of the apparatus.

  In the case of this method, when the above-described image stabilization operation is performed, the reference pattern image comes into contact with the secondary transfer roller and the secondary transfer roller becomes dirty.

  Therefore, for example, a technique has been proposed in which a voltage having the same polarity as the toner charging polarity is applied to the secondary transfer roller during the image stabilization operation so that the reference pattern image does not adhere to the secondary transfer roller (for example, patents). Reference 3).

JP 2001-312154 Japanese Unexamined Patent Publication No. 9-6146 JP 2006-47779 A

  In order to prevent the reference pattern image from adhering to the secondary transfer roller, applying a voltage having the same polarity as the toner charging polarity to the secondary transfer roller during the image stabilization operation is substantially effective for cleaning the secondary transfer roller. Although applicable, on the other hand, when the number of formed images reaches a predetermined number, the secondary transfer roller is also periodically cleaned.

  Since there is no correlation between the timing of periodic cleaning of the secondary transfer roller and the timing of image stabilization operation, the secondary transfer roller may be periodically cleaned immediately after the image stabilization operation is performed. It can happen. Such operation control causes a reduction in image forming efficiency and wasteful power consumption.

  The present invention has been made in view of such a conventional problem, and an object of the present invention is to reduce image formation efficiency and waste in an image forming apparatus in which a secondary transfer roller is constantly pressed against an intermediate transfer belt. It is to prevent the secondary transfer roller from being soiled without causing excessive power consumption.

  An image forming apparatus according to the present invention that achieves the above object includes an image carrier on which a toner image is formed, a rotatable intermediate transfer member onto which the toner image on the image carrier is transferred, and an image carrier. A primary transfer member that transfers the toner image on the intermediate transfer member, a secondary transfer member that is always in pressure contact with the intermediate transfer member and transfers the toner image on the intermediate transfer member to the recording member, and a toner on the secondary transfer member A voltage applying unit that applies a voltage having the same polarity and a reverse polarity to the charging polarity, a control unit that controls the operation of the voltage applying unit, an image forming operation counter that counts how many image forming operations have been performed, and Detecting means for detecting temperature and / or humidity in the apparatus, and when the image forming operation counter reaches a predetermined value, a voltage having the same polarity as the toner charging polarity is applied to the secondary transfer member or the same as the toner charging polarity. Polarity and reverse polarity voltage When a first cleaning operation for cleaning the secondary transfer member by alternately applying is performed and a change in the temperature and / or humidity in the apparatus is detected by the detection means, a reference pattern image is formed on the image carrier. Then, an image stabilizing operation is performed in which the image forming performance is determined by transferring the image to an intermediate transfer member and adjusting the image forming conditions. During this image stabilizing operation, the secondary transfer member has the same polarity as the toner charging polarity. When the voltage is applied and the image stabilization operation is performed, the image forming operation counter is initialized.

  Here, from the viewpoint of further reliably cleaning the secondary transfer member, after the image stabilization operation is completed, the second pass after the rear end of the reference pattern passes through the nip portion between the intermediate transfer member and the secondary transfer member. Every time the secondary transfer member makes at least one rotation, a second cleaning operation for cleaning the secondary transfer member by alternately switching and applying a voltage having the same polarity and opposite polarity to the toner charging polarity to the secondary transfer member is performed. preferable.

  Further, when the image forming operation counter exceeds the first predetermined value during the series of image forming operations, the toner is applied to the secondary transfer member every time the secondary transfer member makes at least one rotation after the series of image forming operations. A first cleaning operation for cleaning the secondary transfer member by alternately switching and applying voltages having the same polarity and opposite polarity to the charging polarity may be performed.

  In addition, when the image forming operation counter exceeds the second predetermined value during a series of image forming operations, the image forming operation is interrupted, and the secondary transfer member is charged with toner every time the secondary transfer member makes at least one rotation. A first cleaning operation for cleaning the secondary transfer member by alternately switching and applying voltages of the same polarity and opposite polarity to the polarity may be performed.

  The image forming operation counter may count the number of recording members conveyed. At this time, when the toner image is a color image composed of two or more colors, it is preferable to increase the number of counts of the image forming operation counter per time as compared with the case of a single color image. In addition, it is preferable that the number of counts of the image forming operation counter is increased as the length of the recording member in the conveyance direction is longer.

  The image forming operation counter may count the rotation time of the secondary transfer member.

  In the image forming apparatus of the present invention, when the image stabilizing operation is performed, the image forming operation counter is initialized, so that the first cleaning operation is performed within a short time after the image stabilizing operation is completed. Is prevented. This prevents a decrease in image forming efficiency and prevents unnecessary power consumption.

1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. 1 is a schematic block diagram showing a configuration in an image forming apparatus according to the present invention. 3 is a flowchart showing overall control of the image forming apparatus according to the present invention. It is a timing chart of the cleaning operation at the time of the process startup operation and the process shutdown operation. It is a timing chart of the 1st cleaning operation performed at the time of a process fall operation. 6 is a timing chart of a first cleaning operation performed during a series of image formation. It is a timing chart at the time of image stabilization operation | movement. 5 is a flowchart showing an example of secondary transfer applied voltage control in the image forming apparatus according to the present invention. 10 is a flowchart of a cleaning operation in which minus and plus voltages are alternately applied to the secondary transfer roller.

  Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. The image forming apparatus in FIG. 1 is a tandem digital color printer (hereinafter, simply referred to as “printer”). Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. In the following, when it is necessary to clarify whether the device or member to be described is yellow (Y), magenta (M), cyan (C), or black (K), The description will be made by adding the characters “(Y)”, “(M)”, “(C)”, and “(K)” to the reference numerals, and otherwise omitting those characters.

  The printer 1 includes an intermediate transfer belt (intermediate transfer member) 11 at a substantially central portion inside thereof. The intermediate transfer belt 11 is wound around the outer periphery of the roller 12, the tension roller 13, and the guide rollers 14 and 15, and is driven to rotate counterclockwise. The tension roller 13 is slidably attached to the outside and is urged by the pressing spring S from the inside to the outside of the intermediate transfer belt 11. Thus, the intermediate transfer belt 11 is always in a tensioned state.

  Below the lower horizontal portion of the intermediate transfer belt 11, four image forming portions 2Y, 2M, 2C, and 2K respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors. Are arranged in this order along the intermediate transfer belt 11. Each of the image forming units 2Y, 2M, 2C, 2K has a photosensitive drum (image carrier) 21Y, 21M, 21C, 21K, respectively. Around each of the photosensitive drums 21Y, 21M, 21C, and 21K, the chargers 22Y, 22M, 22C, and 22K, the print head portions 23Y, 23M, 23C, and 23K, and the developing device (in the order along the rotation direction). Developing means) 24Y, 24M, 24C, 24K and cleaners (cleaning means) 25Y, 25M, 25C, 25K are arranged, respectively. The print head portions 23Y, 23M, 23C, and 23K are configured by a large number of LEDs arranged in the main scanning direction parallel to the axial direction of the photosensitive drum.

  In addition, primary transfer rollers (primary transfer members) 30Y, 30M, 30C, and 30K are provided at positions facing the photosensitive drums 21Y, 21M, 21C, and 21K with the intermediate transfer belt 11 interposed therebetween. A secondary transfer roller 16 is pressed against the portion of the intermediate transfer belt 11 supported by the roller 12. A nip portion between the secondary transfer roller 16 and the intermediate transfer belt 11 becomes a secondary transfer region 17. The toner image formed on the intermediate transfer belt 11 in the secondary transfer region 17 is transferred to the conveyed paper (recording member) P.

  A paper feed cassette 91 is detachably disposed at the bottom of the printer 1. The sheets P stacked and housed in the sheet feeding cassette 91 are pulled out one by one from the uppermost one by the rotation of the sheet feeding roller 92 and sent out to the transport path 93. The conveyance path 93 extends from the paper feed cassette 91 to the paper discharge tray 98 through the nip portion of the timing roller pair 94, the secondary transfer region 17, and the fixing unit 95. The paper P sent out from the paper feed cassette 91 is conveyed to the timing roller pair 94 and is sent out to the secondary transfer area 17 at a predetermined timing.

  The fixing unit 95 has a hollow cylindrical shape, and includes a fixing roller 96 having a halogen heater H therein, and a pressure roller 97 that is pressed against the fixing roller 96 and rotates. A nip portion between the fixing roller 96 and the pressure roller 97 through which the sheet P on which the toner image is secondarily transferred passes is a fixing region.

  A schematic operation of the printer 1 having such a configuration will be described. First, in the full color mode for outputting a color image, when an image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the printer 1, the image signal processing unit converts the image signal to yellow, A digital image signal color-converted to cyan, magenta, and black is created, and this signal is transmitted to the LED drive circuit for the print head. This drive circuit performs exposure by causing the print head portions 23Y, 23M, 23C, and 23K of the image forming portions 2Y, 2M, 2C, and 2K to emit light based on the input digital signals. This exposure is performed with a time difference in the order of the print head units 23Y, 23M, 23C, and 23K. Thereby, electrostatic latent images for the respective colors are formed on the surfaces of the respective photosensitive drums 21Y, 21M, 21C, and 21K.

  The electrostatic latent images formed on the photosensitive drums 21Y, 21M, 21C, and 21K are developed by the developing devices 24Y, 24M, 24C, and 24K, respectively, and become toner images of the respective colors. The toner images of the respective colors are sequentially primary-transferred and superimposed on the intermediate transfer belt 11 that rotates counterclockwise in the drawing by the action of the primary transfer rollers 30Y, 30M, 30C, and 30K.

  The toner image formed on the intermediate transfer belt 11 in this way reaches the secondary transfer region 17 as the intermediate transfer belt 11 moves. On the other hand, the paper P sent out from the paper feed cassette 91 to the transport path 93 is transported to the secondary transfer region 17 by the timing roller pair 94 at the timing when the toner image reaches the secondary transfer region 17. A voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 16. As a result, in the secondary transfer region 17, the superimposed color toner images are secondarily transferred collectively from the intermediate transfer belt 11 to the paper P. The toner remaining on the intermediate transfer belt 11 after the secondary transfer is collected by a belt cleaner (not shown).

  The sheet P onto which the toner image has been secondarily transferred is sent to the fixing unit 95 through the conveyance path 93, where the toner image is fixed on the sheet P by passing through the fixing region. Then, the paper P is discharged to the paper discharge tray 98.

  FIG. 2 is a block diagram showing a part of the control circuit of the printer 1. This control circuit includes a control unit 30 that controls the entire operation of the printer 1. The control unit 30 includes an operation panel 31, a detection sensor 32 that detects temperature and humidity in the apparatus, an image forming operation counter 33, image forming units 2 for Y, M, C, and K, an intermediate transfer belt drive unit 34, A voltage application unit 35 to the secondary transfer roller and a ROM and a RAM in which data necessary for image forming operation control are stored are connected. In addition to the above, various information / signals necessary for image forming operation control are input to the control unit 30 from an unillustrated portion, and various information / signals necessary for image forming operation control are output to an unillustrated portion. .

  The control unit 30 performs an image forming operation by driving the image forming unit 2, the intermediate transfer belt driving unit 34, and the voltage applying unit 35 to the secondary transfer roller by an input from the operation panel 31, and an image forming operation counter 33. In response to a signal from the detection sensor 32, the intermediate transfer belt drive unit 34 and the voltage application unit 35 to the secondary transfer roller are driven to perform the first cleaning operation and the image stabilization operation.

  FIG. 3 is a flowchart showing the overall control of the printer 1. When the control of the printer 1 is started, first, an image reading control 41 is performed, and electronic image data is input. Next, image processing control 42 of the electronic data of the input image is performed. Then, the image formation control 43 is performed by a known electrophotographic process. In parallel with the image formation control, the applied voltage control 44 to the secondary transfer roller is also performed.

  Specifically, the image formation control 43 is performed as follows. First, at the same time as the photosensitive drum 21 is rotated, charging (charging voltage is applied to the charging charger) 22 and discharging (lighting the eraser) are started. In order to uniformly charge the surface potential of the photosensitive drum 21, charging and discharging are performed by idling the photosensitive drum 21 for two or more rotations for a color image and for one or more rotations for a monochrome image (this operation). Is called "process startup operation"). Next, exposure is started, a developing bias is applied to the developing roller, an electrostatic latent image is formed on the photosensitive drum 21, and the electrostatic latent image is developed with toner. Before the developed toner image reaches the intermediate transfer belt 11, a transfer voltage is applied to the primary transfer member 30 to transfer the toner image on the photosensitive drum 21 to the intermediate transfer belt 11. When the above-described series of operations are performed in each image forming unit 2 and the toner images of the respective colors are transferred onto the intermediate transfer belt 11, the operation proceeds to a stop operation of the image forming process 43. That is, first, exposure and development are stopped, the photosensitive drum 21 is idled one or more times, and then charging and discharging are stopped (this operation is referred to as “process fall-down operation”).

  Next, an example of the cleaning operation of the secondary transfer roller 16 in such an image forming process will be described. The cleaning operation of the secondary transfer roller 16 includes, for example, a process startup operation and a process shutdown operation during normal image formation, a predetermined number of sheets or a predetermined time, and an image stabilization operation. Done when done. First, an example of the cleaning operation performed during the process startup operation and the process shutdown operation will be described based on the timing chart of FIG.

  FIG. 4 is a timing chart of voltage application to the secondary transfer roller 16 in a normal image forming process. First, a motor for rotating the photosensitive drum 21 is driven, and the photosensitive drum 21 starts to rotate. At this time, the drive motor for the intermediate transfer belt 11 is also started simultaneously, and the intermediate transfer belt 11 also starts to rotate. This is to prevent the photosensitive drum 21 from being rubbed by the intermediate transfer belt 11. The photosensitive drum 21 is rotated idly by two or more rotations when forming a full-color image, and idling by one or more rotations when forming a monochrome image. Next, the surface of the photosensitive drum 21 is charged, and then exposure is started. Although not shown in this timing chart, development and primary transfer are sequentially started, and the toner image formed on the photosensitive drum 21 is transferred to the intermediate transfer belt 11. Then, the toner image is conveyed to the secondary transfer region 17 between the intermediate transfer belt 11 and the secondary transfer roller 16 by the rotation of the intermediate transfer belt 11. The cleaning of the secondary transfer roller 16 during the process start-up operation is performed after the rotation of the intermediate transfer belt 11 until the toner image is conveyed to the secondary transfer region 17.

  Normally, the time from when the intermediate transfer belt 11 starts to rotate until the toner image is conveyed to the secondary transfer region 17 is much longer than the time when the secondary transfer roller 16 rotates once. Therefore, cleaning during the process start-up operation is performed by alternately applying a voltage having the same polarity and opposite polarity to the charging polarity of the toner to the secondary transfer roller 16 a plurality of times. For example, voltages of +500 V and −500 V are alternately applied to the secondary transfer roller. If the charging polarity of the toner is negative, a voltage of −500 V is applied to the secondary transfer roller 16 so that the toner adhering to the secondary transfer roller 16 moves to the intermediate transfer belt 11 by electric repulsion. To do. Further, by applying a voltage of +500 V to the secondary transfer roller, the reverse polarity toner adhering to the secondary transfer roller 16 also moves to the intermediate transfer belt 11 by electric repulsion. In this way, the toner is removed from the secondary transfer roller 16. The number of times the negative and positive potentials are alternately applied depends on the time from when the intermediate transfer belt 11 starts to rotate until the toner image is conveyed to the secondary transfer region 17. As described above, since the idling speed of the photosensitive drum 21 is normally different between the full-color image and the monochrome image, the number of times of applying negative and positive voltages alternately is also different.

  Next, when the toner image and the sheet are conveyed to the secondary transfer region 17, a voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller. In the case of toner charged to positive polarity, a negative voltage is applied to the secondary transfer roller. As a result, the toner image on the intermediate transfer belt is attracted to the secondary transfer roller side and transferred onto the paper conveyed to the secondary transfer region 17. This operation is repeated.

  Next, when the transfer of a series of toner images from the photosensitive drum 21 to the intermediate transfer belt 11 is completed, as described above, the photosensitive drum 21 stops after being idled one or more times. At this time, the intermediate transfer belt 11 is also stopped simultaneously with the stop of the photosensitive drum 21 so that the photosensitive drum 21 is not rubbed. On the other hand, since a predetermined time is required for the trailing edge of the toner image on the intermediate transfer belt 11 to pass through the secondary transfer area 17, the photosensitive drum 21 is reached after the trailing edge of the toner image reaches the secondary transfer area 17. In addition, the time until the intermediate transfer belt 11 stops is very short. Therefore, there is no time to apply negative and positive voltages alternately to the secondary transfer roller as in the process start-up operation, and the cleaning operation during the process start-up operation has the same polarity ( This is performed by applying a minus voltage to the secondary transfer roller. Of course, as in the process start-up operation, cleaning may be performed by alternately applying negative and positive voltages to the secondary transfer roller 16, but the intermediate transfer belt 11 and the secondary transfer may be performed only for cleaning. The transfer roller 16 and the photosensitive drum 21 need to be rotated, which causes an increase in power consumption, which is not preferable.

  Next, the first cleaning operation of the secondary transfer roller 16 performed when the image formation exceeds a predetermined number or a predetermined time will be described. For example, when several hundreds of images are formed, there is a problem that the back surface of the paper P is soiled by the toner that has gradually adhered to the secondary transfer roller 16. Therefore, when the number of images formed exceeds a predetermined number or a predetermined time, a voltage having the same polarity as the toner charging polarity is applied to the secondary transfer roller 16 or a voltage having the same polarity and the opposite polarity to the toner charging polarity is alternately applied. To periodically clean the secondary transfer roller 16.

  5 and 6 show timing charts of the first cleaning operation of the secondary transfer roller 16. FIG. 5 is a timing chart in the case where the first cleaning operation is performed during the process start-up operation after a series of image forming processes when the number of image formed sheets exceeds a predetermined number or a predetermined time, and FIG. 10 is a timing chart when a first cleaning operation of the secondary transfer roller is performed during the forming process. First, in the timing chart shown in FIG. 5, when the secondary transfer of a series of toner images from the intermediate transfer belt 11 to the paper P is completed, a voltage having the same polarity and opposite polarity to the toner charging polarity is alternately applied a plurality of times. 1 Cleaning is performed. The mechanism for cleaning the secondary transfer roller 16 by alternately applying voltages having the same polarity and the opposite polarity to the charging polarity of the toner is the same as that in the cleaning operation at the time of starting the process. When the first cleaning operation is completed, the rotation and charging of the intermediate transfer belt are stopped.

  On the other hand, in the timing chart of FIG. 6, when the number of image formations exceeds a predetermined number or a predetermined time during a series of image forming processes, the secondary edge is passed when the trailing edge of the final fed paper has passed the secondary transfer region 17. The voltage applied to the transfer roller is a positive voltage having a polarity opposite to the toner charging polarity, and a voltage having the same polarity and the opposite polarity to the toner charging polarity is alternately applied, whereby the first cleaning operation of the secondary transfer roller 16 is performed. When the first cleaning operation is completed, the exposure of the next sheet is resumed and the normal image forming process is resumed.

  In the first cleaning operation described above, a voltage having the same polarity and the opposite polarity as the toner charging polarity is alternately applied to the secondary transfer roller 16 a plurality of times. You may make it apply for a fixed time. However, in this case, since the reverse polarity toner cannot be removed from the secondary transfer roller 16, it is preferable to alternately apply voltages having the same polarity and reverse polarity as the charging polarity of the toner as the first cleaning operation.

  Next, the image stabilization operation will be described. In the printer 1 in which the plurality of image forming units 2 shown in FIG. 1 are juxtaposed, the image forming ability changes depending on changes in temperature and humidity. Therefore, when the temperature or humidity in the apparatus changes, a reference pattern image is formed to determine the image forming performance, and image forming conditions such as the charge amount of the photosensitive drum 21 are adjusted to stabilize the image quality. I am trying. Specifically, first, a reference pattern image is formed in a non-image forming area on the photosensitive drum 21 under predetermined image forming conditions, and the reference pattern image of each color is transferred onto the intermediate transfer belt 11. The toner adhesion amount and transfer position of the transferred reference pattern image on the intermediate transfer belt 11 are measured by an image density sensor, and the image formation performance is judged based on the measured image density and formation position, and image formation is performed based on the result. The conditions are changed so that the image density and the transfer position are controlled to be predetermined values.

  In a conventional image forming apparatus in which the secondary transfer roller 16 can be separated from and contacted with the intermediate transfer belt 11, when the reference pattern image transferred onto the intermediate transfer belt 11 passes through the secondary transfer region 17, the intermediate transfer belt is used. Since the secondary transfer roller 16 was separated from the secondary transfer roller 16, the secondary transfer roller 16 was not soiled by the reference pattern image. However, in the image forming apparatus according to the present invention, since the secondary transfer roller 16 is always pressed against the intermediate transfer belt 11, when the reference pattern image passes through the secondary transfer region 17, the reference pattern image is subjected to the secondary transfer. Contact the roller 16. At this time, in order to prevent the secondary transfer roller 16 from being soiled by the reference pattern image, the printer 1 applies at least a voltage having the same polarity as the charged polarity of the toner while the reference pattern image passes through the secondary transfer region 17. It is applied to the transfer roller 16 to prevent the secondary transfer roller 16 from being soiled by the reference pattern image.

  FIG. 7 shows a timing chart showing an example of the image stabilization operation. When the image stabilization operation is started, first, a process start-up operation is performed as in normal image formation, and at this time, a cleaning operation is performed. Since the cleaning operation at the start of the process is the same as the operation described with reference to FIG. 4, the description thereof is omitted here. Next, the photosensitive drum 21 is charged, exposed and developed to form a reference pattern image, which is primarily transferred from the photosensitive drum 21 onto the intermediate transfer belt 11. A negative voltage having the same polarity as the charging polarity of the toner is applied to the secondary transfer roller 16 immediately before the reference pattern image is conveyed to the secondary transfer region 17 by the rotation of the intermediate transfer belt 11. As a result, the secondary transfer roller 16 is prevented from being soiled by the reference pattern image. In the timing chart of FIG. 7, after the reference pattern image passes through the secondary transfer region 17, every time the secondary transfer roller 16 makes at least one rotation, a voltage having the same polarity and the opposite polarity to the toner charging polarity is alternately alternated. Switching is applied (second cleaning operation). As a result, the reversely charged toner is also removed from the secondary transfer roller 16, and a more complete cleaning is achieved. When the second cleaning operation is completed, the rotation and charging of the intermediate transfer belt 11 are stopped.

  In the cleaning operation of the secondary transfer roller 16 described above, the first cleaning operation performed when image formation exceeds a predetermined number or a predetermined time and the image stabilization operation performed when the temperature or humidity in the apparatus changes It is done without interrelation. For this reason, the first cleaning operation may be performed immediately after the image stabilization operation is performed. In the present invention, in order to prevent such overlapping of cleaning operations, when an image stabilization operation is performed, an image forming operation counter that measures the start timing of the first cleaning operation is initialized, that is, the count is reset to zero. To.

  FIG. 8 is a flowchart showing an example of voltage control applied to the secondary transfer roller 16. Hereinafter, it is assumed that the charging polarity of the toner is negative and the image forming operation counter is a number counter. First, it waits for the intermediate transfer belt drive motor to start rotating (step S701). When the intermediate transfer belt drive motor starts rotating, it is next determined whether the formed image is a color image or a monochrome image (step S702). As a result, the number N of repetitions of the plus / minus voltage applied to the secondary transfer roller 16 in the next start-up cleaning operation is determined. If the formed image is a color image, the number of repetitions N is 4 (step S703), and if it is a monochrome image, the number of repetitions N is 2 (step S704). Then, the start-up cleaning operation is performed (step S705). Details of the startup cleaning operation will be described later with reference to FIG.

  Next, it is determined whether or not the temperature or humidity in the apparatus has changed (step S706). If there is no change in temperature or humidity in the apparatus, as a normal image forming process, a transfer voltage having a polarity opposite to the toner charging polarity is applied to the secondary transfer roller 16 at the timing when the toner image reaches the secondary transfer region 17. (Step S707). As a result, the toner image is transferred from the intermediate transfer belt 11 to the paper P conveyed to the secondary transfer region 17. When the trailing edge of the toner image passes through the secondary transfer roller 16 (step S708), it is determined whether or not there is a next image formation (step S709). If there is the next image formation, it is further determined whether or not the number of image formations accumulated by the number counter is 400 or more (step S710). If the number of image formations is less than 400, the temperature or humidity in the apparatus is again determined. The process returns to the determination of whether or not has changed (step S706). On the other hand, if the number of formed images is 400 or more (step S710), the first cleaning operation is performed (step S712) with the repetition count N set to 3 (step S711). Details of the first cleaning operation will be described later with reference to FIG. When the first cleaning operation is completed, the number counter is reset (cleared to zero) (step S713). Then, the process returns to the determination of whether the temperature or humidity in the apparatus has changed (step S706).

  On the other hand, if there is no next image formation (step S709), it is determined whether the number of image formations accumulated by the number counter is 300 or more (step S714). If the number of image forming sheets is less than 300, after a fall cleaning operation in which a negative voltage is applied to the secondary transfer roller for a predetermined time (step S725), the process waits for the intermediate transfer belt drive motor to be turned off. (Step S718) The voltage application to the secondary transfer roller is stopped (Step S719). If the number of formed images is 300 or more (step S714), the number of repetitions N is set to 5 (step S715), and the first cleaning operation is performed (step S716). Details of the first cleaning operation will be described later with reference to FIG. When the first cleaning operation is completed, the number counter is reset (zero cleared) (step S717), and then waiting for the intermediate transfer belt drive motor to be turned off (step S718), the voltage application to the secondary transfer roller is performed. Stopped (step S719).

  Returning to step S706, if there is a change in the temperature or humidity in the apparatus, an image stabilization operation is performed, and a negative voltage is applied to the secondary transfer roller (step S720). This suppresses the secondary transfer roller 16 from being soiled by the reference pattern image. When the reference pattern image passes through the secondary transfer roller 16 (step S721), the number of repetitions N is set to 5 (step S722), and the second cleaning operation is performed (step S723). Details of the second cleaning operation will be described later with reference to FIG. When the second cleaning operation is completed, the number counter is reset (zero cleared) (step S724), and then the intermediate transfer belt drive motor is turned off (step S718), as described above, and the secondary transfer roller. The voltage application to 16 is stopped (step S719).

  FIG. 9 shows a flowchart of the cleaning operation, the first cleaning operation, and the second cleaning operation at the time of starting the process. These cleaning operations are basically the same control. First, when the cleaning operation is started, a negative voltage is applied to the secondary transfer roller 16 (step S801). Then, a negative voltage is applied until the secondary transfer roller makes one rotation (step S802). Next, a positive voltage is applied to the secondary transfer roller 16 (step S803). Then, a positive voltage is applied until the secondary transfer roller rotates halfway (step S804). When the application of the plus voltage is finished, 1 is subtracted from the set number N of the minus / plus alternating voltage application (step S105), and then it is determined whether N is zero (step S106). Then, the application of the positive and negative voltages is repeated until N becomes zero, and the secondary transfer roller is cleaned.

  In the flowchart of FIG. 8, the number counter is used as the image forming operation counter, but a rotation time counter of the secondary transfer roller may be used instead. Further, with respect to the number of images formed, the amount of toner on the intermediate transfer belt 11 is larger in the color image than in the monochrome image, so in the case of color image formation, the count number is 2 to 4 times that in the case of the monochrome image. It is desirable to do. Further, it is desirable to change the count number depending on the length of the paper to be passed. For example, when the A4 size horizontal is set as the reference size, the A3 size vertical is set to double the number of counts.

  The imager apparatus according to the present invention is useful because it can efficiently clean the secondary transfer roller without causing a decrease in image forming efficiency and without wasteful power consumption.

1 Printer (image forming device)
P paper (recording member)
11 Intermediate transfer belt (intermediate transfer member)
16 Secondary transfer roller (secondary transfer member)
21 Photosensitive drum (image carrier)
30 Primary transfer member 32 Detection sensor (detection means)
33 Image forming operation counter 35 Voltage application means

Claims (8)

An image carrier on which a toner image is formed, a rotatable intermediate transfer member to which the toner image on the image carrier is transferred, and primary transfer for transferring the toner image on the image carrier to the intermediate transfer member A secondary transfer member that is in constant pressure contact with the member and the intermediate transfer member and transfers the toner image on the intermediate transfer member to the recording member, and a voltage having the same polarity and opposite polarity as the toner charging polarity is applied to the secondary transfer member. A voltage applying unit; a control unit that controls the operation of the voltage applying unit; an image forming operation counter that counts how many image forming operations have been performed; and a detecting unit that detects temperature and / or humidity in the apparatus. With
When the image forming operation counter reaches a predetermined value, a voltage having the same polarity as the toner charging polarity is applied to the secondary transfer member or a voltage having the same polarity and the opposite polarity to the toner charging polarity is alternately applied to the secondary transfer member. A first cleaning operation for cleaning is performed,
When a change in the temperature and / or humidity in the apparatus is detected by the detecting means, a reference pattern image is formed on the image carrier, and this is transferred to an intermediate transfer member to determine image forming performance and image forming conditions. An image stabilization operation is performed to adjust the voltage, and during this image stabilization operation, a voltage having the same polarity as the toner charging polarity is applied to the secondary transfer member,
An image forming apparatus, wherein the image forming operation counter is initialized when an image stabilizing operation is performed.   After the image stabilization operation is completed, the secondary transfer member is charged with toner every time the secondary transfer member makes at least one rotation after the trailing edge of the reference pattern passes through the nip portion between the intermediate transfer member and the secondary transfer member. The image forming apparatus according to claim 1, wherein a second cleaning operation for cleaning the secondary transfer member by alternately switching and applying voltages of the same polarity and opposite polarity to the polarity is performed.   When the image forming operation counter exceeds the first predetermined value during a series of image forming operations, the toner charge polarity is applied to the secondary transfer member every time the secondary transfer member makes at least one rotation after the end of the series of image forming operations. The image forming apparatus according to claim 1, wherein a first cleaning operation is performed in which the secondary transfer member is cleaned by alternately switching and applying voltages having the same polarity and reverse polarity.   If the image forming operation counter exceeds the second predetermined value during a series of image forming operations, the image forming operation is interrupted, and the secondary transfer member has the same toner charging polarity as at least one rotation. The image forming apparatus according to claim 1, wherein a first cleaning operation is performed in which the secondary transfer member is cleaned by alternately switching and applying a voltage having a polarity and a reverse polarity.   The image forming apparatus according to claim 1, wherein the image forming operation counter counts the number of recording members conveyed.   6. The image forming apparatus according to claim 5, wherein when the toner image is a color image composed of two or more colors, the number of counts of the image forming operation counter per time is larger than that in the case of a single color image.   6. The image forming apparatus according to claim 5, wherein the number of counts of the image forming operation counter per time is increased as the length of the recording member in the conveyance direction is longer.   The image forming apparatus according to claim 1, wherein the image forming operation counter counts a rotation time of the secondary transfer member.