JP2007256868A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the reduction of the number of image output sheets in a fixed time, and effectively cleaning residual toner left after secondary transfer on an intermediate transfer body. <P>SOLUTION: The image forming apparatus 100 is composed of: a bias output means 91 for outputting a bias to a recovery member 9; a detecting means 92 for detecting the output current value or the output voltage value of the bias output means 91 when the constant voltage control of the recovery member 9 is performed by the bias output means 91 or when the constant current control bias is outputted by the bias output means 91; and a control means 17 for deciding a timing to perform a discharging operation where an electrical field having a direction to move the toner electrified with a prescribed polarity from the recovery member 9 to an intermediate transfer body 7 is formed between the recovery member 9 and the intermediate transfer body 7 in accordance with the output current value or the output voltage value detected by the detecting means 92 in reply to the output of the bias by the bias output means 91 to the recovery member 9. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by developing an electrostatic image formed on an image carrier with toner using an electrophotographic system or an electrostatic recording system. More specifically, in the present invention, a toner image formed by developing an electrostatic image formed on an image carrier with toner is once transferred onto an intermediate transfer member and then transferred onto a transfer material to obtain a recorded image. The present invention relates to an intermediate transfer type image forming apparatus.

  Conventionally, an intermediate transfer method has been widely used in an image forming apparatus that can form a multicolor image such as a full-color image using an electrophotographic method. In an intermediate transfer type image forming apparatus, for example, a toner image of a plurality of colors is transferred onto an intermediate transfer member and transferred (primary transfer), and the toner image is transferred to a transfer material in a batch (secondary transfer). Get an image.

  In such an intermediate transfer type image forming apparatus, as a method of cleaning the toner (secondary transfer residual toner) remaining on the intermediate transfer body after the secondary transfer step, as disclosed in Patent Document 1, There is a method using a recovery member.

  In the image forming apparatus described in Patent Document 1, as shown in FIG. 12 of the present specification, a photosensitive drum 101 as an image carrier is charged by a charger 102 and then exposed by an exposure unit 103. As a result, electrostatic images of the respective color components of yellow, cyan, magenta, and black are sequentially formed on the photosensitive drum 101, and the electrostatic images are developed using the developing devices 104a to 104d for the respective colors. Toner images are sequentially formed on the photosensitive drum 101. Then, the toner images of the respective colors formed on the photosensitive drum 101 are sequentially superimposed and transferred onto the intermediate transfer member 105, thereby forming a full-color toner image on the intermediate transfer member 105. This full-color toner image is collectively transferred onto the transfer material 107 by the transfer roller 106 to obtain a full-color image.

  In the image forming apparatus described in Patent Document 1, the secondary transfer residual toner remaining on the intermediate transfer member 105 is statically applied to the surface of the temporary recovery member 120 to which a bias having a polarity opposite to the charging polarity of the toner is applied. Electrically collected and accumulated (electrostatic recovery operation).

Further, after the secondary transfer operation for an arbitrary page is completed, the image forming operation is interrupted, and a bias having the same polarity as the charging polarity of the toner is applied to the temporary collection member 120. As a result, the toner (collected toner) once collected by the temporary collection member 120 is electrostatically discharged from the temporary collection member 120 onto the intermediate transfer member 105 (electrostatic discharge operation). At the same time, an electric field is formed in the primary transfer portion between the photosensitive drum 101 and the intermediate transfer member 105 so that the toner is reversely transferred from the intermediate transfer member 105 to the photosensitive drum 101. For example, the surface potential of the photosensitive drum 101 is set to −100 V, the potential of the intermediate transfer member 105 in the transfer unit is set to −300 V, and negative toner is reversely transferred to the photosensitive drum 101. This toner is finally removed from the surface of the photosensitive drum 101 by the cleaning blade 108 and collected in a waste toner container 109.
JP-A-9-197750

  However, it has been found that the conventional image forming apparatus as described above has the following problems.

  In other words, even with the temporary recovery member 120 to which a bias having a polarity that forms an electric field in the direction of attracting toner is applied, the toner cannot be recovered and retained beyond a certain amount. The limit amount of toner collected and held by the temporary collection member 120 is a composite factor such as the shape of the toner, the amount of charge held by the transfer residual toner, the electrical characteristics of the temporary collection member 120, and the surface properties and hardness of the temporary collection member 120. It depends on. For this reason, it is difficult to generalize and accurately define the amount, but it is empirically known that there is always a toner collection and retention limit regardless of the type of temporary collection member 120 used. . Therefore, the frequency of the electrostatic discharge operation of toner from the temporary recovery member 120 to the intermediate transfer member 105 is appropriately set according to the toner recovery holding limit of the temporary recovery member 120.

  However, the amount of secondary transfer residual toner is not constant for each output image. For example, the higher the printing rate in the page, the larger the amount of full-color printing than mono-color printing.

  Here, for example, if the frequency of the electrostatic discharge operation is set to be low, there is a possibility that the secondary transfer residual toner appears on the image during continuous image formation of a full color image with a high printing rate. For example, when the electrostatic discharge operation is set to be frequently performed in accordance with a full-color image with a high printing rate, for example, an image associated with the electrostatic discharge operation during mono-color image continuous image formation with a low printing rate. The forming operation is frequently interrupted. Therefore, there is a possibility that the image productivity is reduced, that is, the number of output images within a certain time is reduced.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing the decrease in the number of output images within a predetermined time and effectively cleaning the secondary transfer residual toner on the intermediate transfer member. is there.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention provides an image carrier that carries toner, an intermediate transfer member to which toner is transferred from the image carrier, and a toner that transfers toner from the image carrier to the intermediate transfer member. A first transfer unit; a second transfer unit that transfers toner from the intermediate transfer member to a transfer material; and a first transfer unit that is downstream of a transfer portion of the toner by the second transfer unit in the moving direction of the intermediate transfer member and the first transfer unit. A recovery member disposed upstream of a transfer portion of toner by the transfer means, and the toner charged with a predetermined polarity between the recovery member and the intermediate transfer member is recovered from the intermediate transfer member. A collecting operation in which an electric field in a direction moving toward the member is formed, and the toner charged to the predetermined polarity moves between the collecting member and the intermediate transfer member from the collecting member toward the intermediate transfer member. The electric field in the direction And a bias output means for outputting a bias to the recovery member, and a bias in which the bias output means is subjected to constant voltage control or constant current control with respect to the recovery member. Detecting means for detecting an output current value or an output voltage value of the bias output means when the bias output means is output, and the detection means detects the bias output means by outputting a bias to the recovery member. An image forming apparatus comprising: a control unit that determines a timing at which the discharge operation is performed according to the output current value or the output voltage value.

  According to the second aspect of the present invention, bias output means for outputting a bias to the recovery member, and the bias output means outputs a bias that is subjected to constant voltage control or constant current control to the recovery member. Detecting means for detecting an output current value or an output voltage value of the bias output means when the bias output means outputs a bias to the recovery member, and the detection means detects the bias When the output current value or the output voltage value is less than the predetermined value or greater than the predetermined value, the output current value or the output voltage value is output from when the detected current value or the detected voltage value is detected until the next discharge operation is executed. There is provided an image forming apparatus characterized in that the number of images is different.

  According to the third aspect of the present invention, bias output means for outputting a bias to the recovery member, and the bias output means outputs a bias that is constant voltage controlled or constant current controlled to the recovery member. Detecting means for detecting an output current value or an output voltage value of the bias output means when the bias output means outputs a bias to the recovery member at different timings. The difference between the first detection value and the second detection value, which is the output current value or the output voltage value, is less than a predetermined value and greater than or equal to the predetermined value. There is provided an image forming apparatus characterized in that the number of images output from the time of detection of the first detection value detected first among the detection values to the next execution of the discharge operation is different. The

  According to the fourth aspect of the present invention, bias output means for outputting a bias to the recovery member, and the bias output means outputs a bias that is constant voltage controlled or constant current controlled to the recovery member. Detecting means for detecting an output current value or an output voltage value of the bias output means when the bias output means outputs a bias to the recovery member at a different timing for each output image. When the integrated value for a plurality of output images of the difference between the first detection value and the second detection value, which are the output current value or the output voltage value detected by the detection means, is less than a predetermined value, and In the case where the value is equal to or greater than a predetermined value, the release is performed from the time of detection of the second detection value detected later among the first and second detection values for the last output image in the plurality of output images. Image forming apparatus is provided, wherein the number of images are different be logged in to create is executed.

  According to the fifth aspect of the present invention, bias output means for outputting a bias to the recovery member, and the bias output means outputs a bias that is subjected to constant voltage control or constant current control to the recovery member. Detecting means for detecting an output current value or an output voltage value of the bias output means when the bias output means outputs a bias to the recovery member, and the detection means detects the bias When the electrical resistance value of the recovery member obtained from the output current value or the output voltage value is less than a predetermined value and when the electrical resistance value is greater than or equal to the predetermined value, the discharge is performed next from the detection of the detected current value or the detected voltage value An image forming apparatus, wherein the number of images output before the operation is executed is different.

  According to the present invention, it is possible to suppress the decrease in the number of image outputs within a predetermined time and effectively clean the secondary transfer residual toner on the intermediate transfer member.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
First, the overall configuration and operation of an embodiment of an image forming apparatus according to the present invention will be described. FIG. 1 shows a schematic cross-sectional configuration of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 is a full-color laser beam printer that can form a full-color image on a transfer material (recording paper, OHP sheet, etc.) according to an image information signal using an electrophotographic method. In this embodiment, the image forming apparatus 100 employs a tandem method and an intermediate transfer method. The image forming apparatus 100 of this embodiment operates at a process speed (corresponding to the surface moving speed of the image carrier and the intermediate transfer member in this embodiment) 87 mm / s.

  The image forming apparatus 100 includes first, second, third, and third images for forming yellow (Y), cyan (C), magenta (M), and black (K) images as a plurality of image forming units, respectively. 4 image forming units (stations) Sa, Sb, Sc, Sd. The image forming portions Sa to Sd are arranged in a line along the moving direction of the image transfer surface of the intermediate transfer member. In this embodiment, the arrangement direction of the image forming portions Sa to Sd is a substantially vertical direction.

  In this embodiment, the configuration and operation of each of the image forming units Sa to Sd are substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular distinction, the subscripts a, b, c, and d given to the reference numerals in the drawing are omitted to indicate that they are elements provided for any color, and are summarized Explained.

  The image forming unit S includes a cylindrical electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1. Around the photosensitive drum 1, there are arranged a charging roller 2 as a charging means, a developing device 4 as a developing means for developing an electrostatic latent image, a drum cleaner 6 as a cleaning means for cleaning the photosensitive drum 1, and the like. Has been. In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4, and the drum cleaner 6 are combined into one container by a frame body, and constitute a so-called all-in-one cartridge (process cartridge).

  The first developing device 4a has yellow (Y) toner, the second developing device 4b has magenta (M) toner, the third developing device 4c has cyan (C) toner, and the second developing device 4c. 4 developer 4d is filled with black (K) toner.

  Further, an optical system 3 as an exposure unit is formed so that electrostatic images (latent images) are formed on the respective photosensitive drums 1a to 1d by exposing each of the photosensitive drums 1a to 1d in accordance with image information signals. Is arranged. In this embodiment, a laser scanning exposure optical system is used as the optical system.

  Further, an intermediate transfer belt 7 as an intermediate transfer member is disposed so as to move endlessly facing all the photosensitive drums 1a to 1d. In each of the image forming units Sa to Sd, on the inner peripheral surface side of the intermediate transfer belt 7, primary transfer as a first transfer unit (primary transfer unit) is provided at a position facing each of the photosensitive drums 1a to 1d. Rollers 1a, 1b, 1c and 1d are arranged. The intermediate transfer belt 7 is in contact with the photosensitive drum 1 at a position where the photosensitive drum 1 and the primary transfer roller 5 face each other, thereby forming a primary transfer portion (primary transfer nip) N1.

  At the time of image formation, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. The surface of the charged photosensitive drum 1 is exposed by the optical system 3 with scanning light based on image data. Thereby, an electrostatic image corresponding to the image information is formed on the surface of the photosensitive drum 1.

  The electrostatic image formed on the photosensitive drum 1 is developed by the developing device 4. The developing device 4 has a developing roller 41 as a developer carrier. During the developing operation, a developing bias is applied to the developing roller 41 from a developing bias power source (not shown) as a developing bias output unit. The developing bias is set to an appropriate value between the charging potential of the photosensitive drum 1 (negative polarity in this embodiment) and the latent image potential (potential of the exposed portion from which the negative charge has been removed). As a result, the toner charged to the normal charging polarity (negative polarity in this embodiment) selectively adheres to the electrostatic image on the photosensitive drum 1.

  The monochromatic toner image formed on the photosensitive drum 1 is transferred (primary transfer) by the primary transfer roller 5 onto the intermediate transfer belt 7 that rotates (rotates) at a substantially constant speed in synchronization with the photosensitive drum 1. The During the primary transfer process, the primary transfer roller 5 has a bias of a polarity opposite to the toner charging polarity (positive polarity in this embodiment) output from a primary transfer bias power source 51 as a primary transfer bias output means. Applied. As a result, the toner image is primarily transferred from the photosensitive drum 1 to the intermediate transfer belt 7.

  In this embodiment, the intermediate transfer belt 7 as an intermediate transfer member is stretched around a driving roller 71, a tension roller 72, and a secondary transfer counter roller 73 as a plurality of support members. The intermediate transfer belt 7 is driven by a rotational driving force transmitted to the driving roller 71. The intermediate transfer belt 7 is given a predetermined tension by a tension roller 72.

The intermediate transfer belt 7 is a resin whose base is adjusted to a volume resistivity of 1 × 10 ⁶ to 1 × 10 ¹¹ Ωcm by adding an electronic conductive filler or ion conductive additive to the resin. It can be used suitably. Examples of the resin include PI (polyimide), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and the like. The characteristics of these intermediate transfer belts 7 are determined by transfer requirements and are not critical. In this embodiment, the volume resistivity of 1 × 10 ⁸ Ωcm is obtained by dispersing carbon black. An adjusted PI belt was used.

  Toner remaining on the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is cleaned by the drum cleaner 6. That is, the primary transfer residual toner is removed from the surface of the photosensitive drum 1 by the cleaning member 61 in the drum cleaner 6 and collected in the waste toner container 62. In this embodiment, the drum cleaner 6 performs blade cleaning using a urethane blade (cleaning blade) as the cleaning member 61.

  For example, during the formation of a full-color image, the charging, exposure, development, and primary transfer processes described above are performed in the first to fourth image forming units Sa to Sd in synchronization with the rotation of the intermediate transfer belt 7. , Yellow, magenta, cyan, and black. Thus, a full color toner image is formed on the intermediate transfer belt 7 by sequentially superimposing the toner images of the respective colors and performing primary transfer.

  The transfer material P set in a cassette 10 as a transfer material supply unit is fed by a feed roller 11. Thereafter, the leading edge of the transfer material P is detected by a top sensor 13 provided immediately after the registration roller 12 in the conveyance direction of the transfer material P. The transfer material P is conveyed to the secondary transfer portion (secondary transfer nip) N2 by the registration roller 12 after the timing of the image on the intermediate transfer belt 7 is matched. The secondary transfer portion N2 is formed by contacting the intermediate transfer belt 7 and a secondary transfer roller 8 as a second transfer unit (secondary transfer unit). The secondary transfer roller 8 is provided at a position facing the secondary transfer counter roller 73 around which the intermediate transfer belt 7 is wound.

  The toner image formed on the intermediate transfer belt 7 is collectively transferred (secondary transfer) onto the transfer material P by the secondary transfer roller 8. During the secondary transfer process, the secondary transfer roller 8 is supplied with a secondary transfer bias power supply 81 serving as a secondary transfer bias output means and has a secondary polarity (positive in this embodiment) opposite to the toner charging polarity. A transfer bias is applied.

  The transfer material P onto which the toner image has been secondarily transferred passes through a fixing device 14 as fixing means. As a result, the toner image is melted and fixed on the transfer material P and becomes an output image of the image forming apparatus 100. Thereafter, the transfer material P is discharged out of the image forming apparatus main body.

[Cleaning of intermediate transfer belt]
Next, a cleaning method for toner (secondary transfer residual toner) remaining on the intermediate transfer belt 7 after the secondary transfer process will be described.

  The image forming apparatus 100 according to the present exemplary embodiment is downstream of the secondary transfer unit N2 and upstream of the primary transfer unit N1a of the first image forming unit Sa in the surface movement direction of the intermediate transfer belt 7. A recovery roller 9 is provided as a recovery member facing the intermediate transfer belt 7. In this embodiment, the collection roller 9 is disposed so as to contact the intermediate transfer belt 7 at a position facing the secondary transfer counter roller 9 to form a nip (collection nip) N3. In this embodiment, the collection roller 9 is always in contact with the intermediate transfer belt 7. In this embodiment, the collection roller 9 rotates following the intermediate transfer belt 7. That is, in this embodiment, the surface of the collection roller 9 moves in the same direction as the surface movement direction of the intermediate transfer belt 7 at the contact portion with the intermediate transfer belt 7 at a substantially constant speed.

  In this embodiment, the secondary transfer residual toner that is not transferred during the secondary transfer and remains on the intermediate transfer belt 7 is temporarily electrostatically recovered by the recovery roller 9 (electrostatic recovery). Operation). The collected toner temporarily collected and held by the collection roller 9 is electrostatically discharged and returned onto the intermediate transfer belt 7 during non-image formation (electrostatic discharge operation). Further, in this embodiment, this toner is electrostatically reversely transferred from the intermediate transfer belt 7 onto the photosensitive drum 1a in the primary transfer portion N1a of the first image forming portion Sa. The toner is removed from the surface of the photosensitive drum 1a by the cleaning blade 61a of the drum cleaner 6 and collected in the waste toner container 41a.

  In this embodiment, the secondary transfer residual toner is finally collected by the drum cleaner 6 of the first image forming unit Sa immediately after the collection roller 9 in the surface movement direction of the intermediate transfer belt 7. However, in the case of having a plurality of image forming units, the final collection position of the secondary transfer residual toner is not necessarily limited to the first image forming unit Sa, and arbitrarily, at least one or a plurality of images. It can be collected at the forming section.

In this embodiment, the collection roller 9 is configured as a roller having an outer diameter of 20 mm in which a sponge-like elastic body is provided in a roll shape around the shaft. This sponge-like elastic body is made of conductive NBR (nitrile-butadiene rubber) whose electric resistance is adjusted to a volume resistance value of 1 × 10 ⁷ Ωcm. The recovery roller 9 is pressed against the secondary transfer counter roller 73 via the intermediate transfer belt 7 and has a nip width of about 2 to 3 mm between the recovery roller 9 and the intermediate transfer belt 7 when pressed with a predetermined pressing force. It is formed.

  The collection roller 9 is not limited to the configuration in which the collection roller 9 is in contact with the secondary transfer counter roller 73. In this embodiment, in order to form an electric field with the intermediate transfer belt 7, it is brought into contact with a counter member that is included in the intermediate transfer belt 7 and is electrically grounded.

The collection roller 9 may be rotated with a difference in peripheral speed from the intermediate transfer belt 7. Further, the rotation direction of the collection roller 9 may be the forward direction with respect to the intermediate transfer belt 7 as in this embodiment, or may be the counter direction opposite to the intermediate transfer belt 7. In addition to the elastic material such as conductive NBR as in this embodiment, the material of the collection roller 9 is a conductive elastic material such as urethane, EPDM (ethylene-propylene-diene), silicone rubber, or the like. A foam can also be used suitably. Also in this case, the electrical resistance of the conductive elastic body or the foamed body is preferably adjusted to a volume resistivity of 10 ¹⁰ Ωcm or less. Furthermore, a conductive brush roller can also be used. The conductive brush roller can be formed by implanting conductive fibers around an elastic conductive substrate made of a highly rigid conductive substrate such as metal or conductive rubber. It is preferable that the electrical resistance of the conductive fiber is adjusted to about 10 ¹⁰ Ωcm or less. As the conductive fiber, a fiber made of rayon, polyamide, acrylic, polytetrafluoroethylene or the like and subjected to a conductive treatment such as carbon dispersion can be suitably used.

  FIG. 2 is a schematic diagram showing the vicinity of the secondary transfer residual toner recovery nip N3 by the recovery roller 9 and the energization circuit of the recovery roller 9.

  In this embodiment, the secondary transfer opposing roller 73 is electrically grounded. On the other hand, the collection roller 9 is connected in series to an energization loop for applying a bias thereto. The energization loop includes a recovery bias power source (voltage power source) 91 as a recovery bias output unit and a current detection circuit 92 as a detection unit that detects a current in the energization loop. The recovery bias power supply 91 and the current detection circuit 92 are connected to a control unit 15 provided in the image forming apparatus main body. The control unit 15 comprehensively controls the operation of the image forming apparatus main body. The control unit 15 includes a memory 16 as a storage unit and a CPU (Central Processing Unit) 17 as a control device (control unit). In particular, in connection with the present embodiment, the memory 16 stores the current value detected by the current detection circuit 92. The CPU 17 controls the bias output operation from the recovery bias power supply 91 to the recovery roller 9 using the current value stored in the memory 16.

  In this embodiment, the current detection circuit 92 outputs the second bias corresponding to the first bias when the first bias under constant voltage control is output from the recovery bias power supply 91 to the recovery roller 9. A bias is applied. The current detection circuit 92 detects the output current value of the recovery bias power supply 91 from the applied second bias. Then, an electric signal indicating the detection result is input to the control unit 15. The CPU 17 can store information corresponding to the electric signal indicating the detection result of the input current detection circuit 92 in the memory 16. The CPU 17 can read out information stored in the memory 16 at any time and use it for control.

  In this embodiment, as will be described in detail later, the recovery bias power supply 91 is configured to switch the bias so that the bias output to the recovery roller 9 can be switched between the electrostatic recovery operation and the electrostatic discharge operation. Means 93 are provided. In other words, in this embodiment, the collection bias power supply 91 outputs a bias (collection bias) output unit to the collection roller 9 during the electrostatic collection operation, and outputs to the collection roller 9 during the electrostatic discharge operation. And an output section for bias (emission bias). In this embodiment, the polarities of the recovery bias and the discharge bias are different.

  Next, the operation (electrostatic recovery operation) of recovering the secondary transfer residual toner from the intermediate transfer belt 7 by the recovery roller 9 will be described with reference to FIG. FIG. 3 is a schematic diagram illustrating a method for controlling the secondary transfer residual toner collection operation by the collection roller 9.

  In FIG. 3, a region D is a region where a toner image is transferred onto the intermediate transfer belt 7 during the continuous image formation of n sheets (n is a natural number, the same applies hereinafter), and a region (image) that contacts the transfer material P. Area). Therefore, this area D is an area where the secondary transfer residual toner remains on the intermediate transfer belt 7. In FIG. 3, an area N is an area other than the image area D on the intermediate transfer body 7 when n sheets of continuous images are formed, that is, a non-image area on the intermediate transfer belt 7 corresponding to a space between sheets. In the following, regions D and N shown in other drawings also indicate the same region on the intermediate transfer belt 7 as described above.

  As shown in FIG. 3, the following electric field (potential difference) is formed in the region E including the region D where the secondary transfer toner exists on the intermediate transfer belt 7 where the secondary transfer process has been started. That is, an electric field (potential difference) is formed between the collection roller 9 and the intermediate transfer belt 7 to direct the secondary transfer residual toner charged to the first polarity (negative polarity in this embodiment) to the collection roller 9. . The area E is preferably larger than the area D on the downstream side and the upstream side in the moving direction of the intermediate transfer belt 7. In this embodiment, at this time, a DC bias (collection bias) of the second polarity (positive polarity in this embodiment) output from the collection bias power supply 91 to the collection roller 9 and having the opposite polarity to the first polarity. VC) is applied. In this embodiment, a constant-voltage controlled bias is output from the recovery bias power supply 91 to the recovery roller 9 as the recovery bias VC.

  That is, in this embodiment, since the negatively charged toner is used, the recovery bias VC has a positive polarity. In this embodiment, since the potential of the intermediate transfer belt 7 after the secondary transfer process is about 0 V to +300 V, the potential of the recovery bias VC is influenced by the potential of the intermediate transfer belt 7 after the secondary transfer process. The potential within the range not received was +1.6 kV. As a result, the secondary transfer residual toner on the intermediate transfer belt 7 is electrostatically transferred to the recovery roller 9 and recovered.

  In the area N, substantially no secondary transfer residual toner is present on the intermediate transfer belt 7, and the area N is an inter-sheet area (non-image area). Therefore, as shown by a broken line in FIG. In this case, the bias applied to the collecting roller 9 may be set to 0V. However, in this embodiment, the collection roller 9 is always in contact with the intermediate transfer belt 7. Accordingly, the potential difference between the intermediate transfer belt 7 and the collection roller 9 is reduced, so that the toner collected on the collection roller 9 is prevented from being discharged to the intermediate transfer belt 7. It is preferable to apply a recovery bias VC to 9. In the present embodiment, as shown by the solid line in FIG. 3, in the region N, the recovery bias VC = + 1.6 kV having the same value as that in the region E is continuously applied to the recovery roller 9.

  Next, an operation (electrostatic discharge operation) for discharging the collected toner once collected by the collection roller 9 to the intermediate transfer belt 7 will be described with reference to FIG. FIG. 4 is a schematic diagram illustrating a method for controlling the operation of discharging the collected toner from the collection roller 9 to the intermediate transfer belt 7.

  As shown in FIG. 4, when an instruction to execute an electrostatic discharge operation is issued from the CPU 17 of the control unit 15, a first polarity (a negative electrode in this embodiment) is set between the collection roller 9 and the intermediate transfer belt 7. An electric field (potential difference) is formed to direct the collected toner charged to the intermediate transfer belt 7 toward the intermediate transfer belt 7. In this embodiment, at this time, a DC bias (discharge bias VE) having the same polarity as the first polarity (negative polarity in this embodiment) output from the recovery bias power supply 91 is applied to the recovery roller 9. In this embodiment, a constant voltage controlled bias is output from the recovery bias power supply 91 to the recovery roller 9 as the discharge bias VE.

  That is, in this embodiment, since the negatively charged toner is used, the discharge bias VE has a negative polarity. In this embodiment, since the potential of the intermediate transfer belt 7 after the secondary transfer process is about 0 V to +300 V, the potential of the discharge bias VE is influenced by the potential of the intermediate transfer belt 7 after the secondary transfer process. The potential in a range not affected was -1.6 kV. Thereby, the collected toner on the collection roller 9 is electrostatically discharged from the collection roller 9 to the intermediate transfer belt 7 side due to a potential difference, and the collection roller 9 is cleaned.

  The electrostatic discharge time t [second] of the collection roller 9 is such that t ≧ l / v where the circumferential length of the collection roller 9 is 1 [mm] and the circumferential speed v [mm / second] of the collection roller 9. It is preferable to set to. Thus, the toner on the entire peripheral surface of the collection roller 9 is discharged, and a good cleaning effect is always obtained.

  In the present embodiment, the discharge bias VE is applied to the collection roller 9 while the collection roller 9 rotates approximately twice (electrostatic discharge time t), which is indicated by a region F in FIG. Thereafter, when the image forming operation is not continuously performed, the bias applied to the collection roller 9 is set to 0V. The rotation speed of the collection roller 9 corresponding to the electrostatic discharge time is not limited to that in the present embodiment, and can be set as appropriate according to the characteristics of the collection roller 9 and the toner.

  In this embodiment, the toner (region F in FIG. 4) returned to the intermediate transfer belt 7 is transferred to the primary transfer portion N1a between the photosensitive drum 1a of the first image forming portion Sa and the intermediate transfer belt 7. And transferred to the photosensitive drum 1a. That is, at this time, an electric field (potential difference) is formed between the photosensitive drum 1a and the intermediate transfer belt 7 to direct the toner charged to the first polarity (negative polarity in this embodiment) toward the photosensitive drum 1a. . In this embodiment, at this time, the surface potential of the photosensitive drum 1a is set to -100V, while the primary transfer roller 5a is supplied with the same polarity as the first polarity (this embodiment) from the primary transfer bias power source 51a. In this case, a negative (-1 kV) bias is applied. As a result, the toner on the intermediate transfer belt 7 is exposed to a potential difference (900 V) between the surface potential (−100 V) of the photosensitive drum 1 a and the potential (−1 kV) of the intermediate transfer belt 7 at the primary transfer portion Na. Reverse transfer is performed on the drum 1a. The toner reversely transferred onto the photosensitive drum 1a is removed from the surface of the photosensitive drum 1a by the cleaning blade 61a in contact with the photosensitive drum 1a, and is collected in the waste toner container 62a.

  The electrostatic discharge operation of the toner from the collection roller 9 and the reverse transfer of the toner to the photosensitive drum 1a in the primary transfer unit N1a are the transfer of the toner using the image forming unit. For this reason, it is difficult to carry out simultaneously with the image forming operation, and it is desirable to interrupt the image forming operation during continuous image formation.

[Electrostatic discharge timing control]
Next, a method of controlling the execution frequency of the electrostatic discharge operation of the collected toner from the collection roller 9 to the intermediate transfer belt 7 which is the most characteristic feature of this embodiment will be described. FIG. 5 shows an outline of a control flow of the execution frequency of the electrostatic discharge operation in the present embodiment.

  In this embodiment, the image forming apparatus 100 detects the decrease in the current value applied to the collection roller 9 before and after collecting the secondary transfer residual toner, thereby detecting the secondary transfer residual toner of the collection roller 9. Estimate total recovery. Based on the result, the execution timing of the electrostatic discharge operation of the collected toner from the collection roller 9 to the intermediate transfer belt 7 is determined. This will be described in more detail below.

  First, the constant voltage output from the recovery bias power supply 91 to the recovery roller 9 immediately after the electrostatic discharge operation of the toner from the recovery roller 9, that is, the state in which the toner is not substantially held on the surface. A first detection voltage Va, which is a controlled first detection bias, is applied. At this time, the current value flowing in the energization loop is detected by the current detection circuit 92 and stored in the memory 16 as the reference current value Ia. The above operation is shown in S101 to S102 in FIG.

  Next, after the electrostatic recovery operation of the recovery roller 9 after the image is formed on the transfer material P, that is, with respect to the recovery roller 9 in a state where the toner is held on the surface, the constant voltage control output from the recovery bias power supply 91 is performed. The second detection voltage Vb, which is the second detection bias, is applied. At this time, the current detection circuit 92 detects the current value (evaluation current value) Ib flowing through the energization loop. The above operation is shown in S103 to S104 in FIG.

Further, the CPU 17 calculates a difference current value A between the reference current value Ia stored in the memory 16 and the evaluation current value Ib. In this embodiment, the differential current value A is expressed by the following equation:
Differential current value A = Log (Ia) −Log (Ib)
Calculated by This is because the detected current value is very small. However, the differential current value A is not limited to being calculated in this form.

  Then, the CPU 17 compares the calculated difference current value A with the determination value α. Thereby, it is determined whether or not the electrostatic discharge operation of the collected toner from the collection roller 9 should be executed.

  Here, the differential current value A is a decrease in the current value from the reference current value Ia due to an increase in the electrical resistance value accompanying the secondary transfer residual toner recovery of the recovery roller 9. Therefore, by detecting the difference current value A, the toner collection amount of the collection roller 9 can be estimated.

  The determination value α corresponds to the electrostatic recovery holding limit of the recovery roller 9 and can be set by examining the recovery capability of the recovery roller 9 in advance. The preset determination value α is stored in advance in the storage unit of the CPU 17 in this embodiment.

  As an example, FIG. 6 shows the relationship between the toner collection capability of the collection roller 9 in this embodiment and the increase in the differential current value A during toner collection.

  In FIG. 6, the differential current value A is a value obtained from the reference current value Ia and the evaluation current value Ib when Va = Vb = + 1.6 kV is applied. In FIG. 6, the reflection density is the density of the toner that has flowed back onto the intermediate transfer belt 7 even though the collection bias VC = + 1.6 kV is applied to the collection roller 9. It is a value measured by Macbeth RD918).

  FIG. 6 shows that, in the configuration of this embodiment, the reflection density rapidly increases when the toner collection amount of the collection roller 9 exceeds 20 mg, that is, exceeds the retention collection limit. The differential current value A (Log (Ia) −Log (Ib)) at this time is 0.8. Therefore, in this embodiment, the determination value α is set to 0.8 and compared with the differential current value A calculated by the CPU 17.

  Referring to FIG. 5 again, when the CPU 17 determines that the differential current value A is less than α, that is, when it is determined that the toner recovery amount of the recovery roller 9 at that time is small, the CPU 17 The electrostatic discharge operation of the collected toner is not performed, and the image forming operation is continuously performed. On the other hand, when the CPU 17 determines that the differential current value A is greater than or equal to α, that is, when it is determined that the toner recovery amount of the recovery roller 9 at that time is about to exceed the recovery holding limit, the CPU 17 The electrostatic discharge operation of the collected toner is performed. The above operation is shown in S106 to S107 in FIG.

  As described above, in this embodiment, the toner collection amount of the collection roller 9 at an arbitrary time is estimated from the decrease in the evaluation current value Ib from the reference current value Ia. Thereby, the electrostatic discharge operation of the collected toner from the collection roller 9 can be set to the minimum necessary number.

  That is, in this embodiment, the difference between the first detection value and the second detection value, which are output current values (or output voltage values as will be described later) detected by the detection means at different timings, is obtained. Then, when the difference is less than a predetermined value and greater than the predetermined value, the static value is detected next from the time of detection of the first detection value detected first among the first and second detection values. The number of images that are output before the electric discharge operation is executed is different.

  By the way, in this embodiment, as described above, when the execution timing of the electrostatic discharge operation of the collected toner from the collecting roller 9 is defined by the detected current value in the energization loop of the collecting roller 9, the current value is large. It is specified by the difference. This is preferable, for example, in order to eliminate the influence of manufacturing variations in volume resistivity of the collecting roller 9 and environmental fluctuations.

  It is desirable that the detection timing of the reference current value Ia is set immediately after the electrostatic discharge operation is performed, and the detection of the reference current value Ia is performed with a small amount of deposits on the surface of the collection roller 9. In this embodiment, as indicated by a region G in FIGS. 7 and 8, the reference current value Ia is detected immediately after the electrostatic discharge operation, and then the next image formation preparation operation or standby state is entered. I did it. However, the detection timing of the reference current value Ia is an arbitrary timing after the electrostatic discharge operation is performed and before the image area D of the next image formed on the intermediate transfer belt 7 reaches the recovery nip N3. The timing can be set.

  On the other hand, the detection timing of the evaluation current value Ib can be set after performing the electrostatic recovery operation. Typically, as shown by a region H in FIG. 7, the region N (inter-paper region, non-image region) The evaluation current value Ib can be detected at the timing in (). The evaluation current value Ib may be detected in each region N or may be detected for each of the plurality of regions N. Alternatively, at the time of organizing operation (post-rotation operation) after completion of one or more jobs (a series of image forming operations for one or more transfer materials according to one image formation start instruction), or before the start of the next job The evaluation current value Ib may be detected during the preparation operation (pre-rotation operation). If the evaluation current value Ib is detected in the region N every time, it is preferable because fluctuations in the electrical resistance of the collection roller 9 can be detected sequentially for each image formation.

  However, depending on the apparatus configuration, the region N is short and may not be enough for one revolution of the collection roller 9. In such a case, if the toner collected by the collection roller 9 is biased in the circumferential direction of the collection roller 9, accurate detection reflecting the electrical resistance of the collection roller 9 may not be performed. Therefore, it may be preferable to detect the evaluation current value Ib in the region E where the collection roller 9 collects the toner. In such a case, the recovery bias VC may also serve as the second detection bias Vb. That is, at the same time that the recovery bias VC is applied to the recovery roller 9, the current flowing in the energization loop can be detected by the current detection circuit 92. In this embodiment, as shown in FIG. 8, more specifically, each time an image is formed, the evaluation current value Ib is obtained in a region H within the region E where the collection roller 9 collects toner each time an image is formed. Was detected. In this embodiment, since the recovery bias VC having the same value as that in the region E is continuously applied in the region N, the evaluation current value Ib can be detected across the regions E and N.

  The values of the first detection bias Va and the second detection bias Vb can be set as appropriate according to the image forming apparatus. However, by making the values of the first detection bias Va and the second detection bias Vb the same as the recovery bias VC, there are the following advantages. That is, it is preferable because the recovery bias VC can also serve as the second detection bias Vb as described above, and the degree of freedom in detection timing of the evaluation current value Ib can be increased. Further, by making the values of the first detection bias Va and the second detection bias Vb the same as the actual recovery bias VC, the electrostatic recovery operation and the electrical resistance of the recovery roller 9 are being detected. The difference in electrical characteristics of the collecting roller 9 is small or preferable. In this embodiment, recovery bias VC = first detection bias Va = second detection bias Vb = + 1.6 kV.

  Further, the value of the first detection bias Va and the value of the second detection bias Vb are not limited to the same value. That is, the values of the first detection bias Va and the second detection bias Vb do not necessarily have to be the same as long as information on the electrical resistance of the collection roller 9 at each time point can be obtained. . However, when the value of the first detection bias Va and the value of the second detection bias Vb are the same, the differential current value A is calculated from the reference current value Ia and the evaluation current value Ib. Arithmetic control becomes easy. In addition, since the reference current value Ia and the evaluation current value Ib are detected, the degree of error with respect to the information relating to the detected electrical resistance of the collecting roller 9 can be made equal, so that the accuracy is higher. Good control can be performed. When the value of the first detection bias Va is different from the value of the second detection bias Vb, the differential current value A is obtained by multiplying the detected reference current value Ia or the evaluation current value Ib by a predetermined coefficient. May be calculated. Alternatively, as described later, when control is performed using information related to the electrical resistance value itself of the collection roller 9, the current values Ia and Ib detected using different values of the detection bias are respectively set to the electrical resistance values. What is necessary is just to use for control, such as calculating | requiring a difference, after converting into the information which concerns on.

  As described above, according to the present embodiment, the total recovery of the secondary transfer residual toner of the recovery roller 9 is detected by detecting the decrease in the current value supplied to the recovery roller 9 before and after the recovery of the secondary transfer residual toner. Estimate the amount. Based on the result, the execution timing of the electrostatic discharge operation of the collected toner from the collection roller 9 to the intermediate transfer belt 7 is determined. Thereby, the secondary transfer residual toner on the intermediate transfer belt 7 can be effectively cleaned without unnecessarily reducing the print productivity of the image forming apparatus 100.

Example 2
Next, another embodiment of the image forming apparatus according to the present invention will be described. The basic configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus of the first embodiment. Accordingly, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted, and characteristic points of the present embodiment will be described.

  In this embodiment, the timing for measuring information related to the electrical resistance value of the collecting roller 9 and the control method based on the detection result are different from those in the first embodiment.

  That is, in the method for determining the execution timing of the electrostatic discharge operation according to the first embodiment, when the reference current value Ia fluctuates, the decrease in the evaluation current value Ib from the reference current value Ia may not be accurately detected. . For example, when the usage environment of the image forming apparatus 100 changes after detecting the reference current value Ia, the electrical resistance of the collection roller 9 changes, and the reference current value Ia also changes accordingly. Further, for example, when the image forming apparatus is stopped for a long time after the reference current value Ia is detected in a state where the temperature inside the apparatus is raised during continuous image formation, and the inside of the apparatus is cooled, the electrical resistance of the collection roller 9 fluctuates. Accordingly, the reference current value Ia also varies.

  Therefore, in this embodiment, the decrease of the current value supplied to the collection roller 9 before and after the electrostatic collection operation for each output image is integrated, and this value is compared with the determination value.

  FIG. 9 shows an outline of a control flow of the execution frequency of the electrostatic discharge operation in the present embodiment. The reference current value Ia detected by the current detection circuit 92 when the nth image is formed after the electrostatic discharge operation is set as a reference current value Ian. Also, the evaluation current value Ibn detected by the current detection circuit 92 at the time of forming the nth image is defined as an evaluation current value Ibn. Further, the differential current value A between the reference current value Ian and the evaluation current value Ibn at the time of forming the nth image is defined as a differential current value An. The method for detecting and calculating the reference current value, the evaluation current value, and the differential current value itself is the same as in the first embodiment. The above operation is shown in S201 to S205 and S207 to S210 in FIG.

  Here, the detection of the reference current value Ian and the evaluation current value Ibn may be performed before and after electrostatic recovery for each image. Typically, as indicated by a region G in FIG. 10, the reference current value Ian for the nth image is detected in a region N (inter-paper region, non-image region) after the n−1th image. To do. Further, as indicated by a region H in FIG. 10, the evaluation current value Ibn for the nth image is detected in a region N (inter-paper region, non-image region) after the nth image.

  However, depending on the configuration of the apparatus, the region N is short, and it may not be possible to take the time for one rotation of the collection roller 9 to detect the reference current value Ian and the evaluation current value Ibn. In this case, as described in the first embodiment, if the toner collected by the collection roller 9 is biased in the circumferential direction of the collection roller 9, accurate detection reflecting the electrical resistance of the collection roller 9 is performed. There are things that cannot be done. Therefore, the recovery bias VC may serve as both the first detection bias Va and the second detection bias Vb. That is, at the same time that the recovery bias VC is applied to the recovery roller 9, the current flowing in the energization loop can be detected by the current detection circuit 92.

  That is, as indicated by a region G in FIG. 11, the first detection bias Van for detecting the reference current value Ian for the nth image is set as the recovery bias VC (Van = VCn) for the n−1th image. -1). Further, as indicated by a region H in FIG. 11, the second detection bias Vbn for detecting the evaluation current value Ibn for the nth image is the recovery bias VC (Vbn = VCn) for the nth image. I also serve. In this embodiment, the reference current value Ian and the evaluation current value Ibn are detected in this way. Also in this case, the reference current value Ia1 for the first image after the electrostatic discharge operation is detected in the non-image area before the electrostatic recovery operation for the first image. Can do.

  In this way, the first detection value (reference current value) for the nth output image is the nth image during or after the collection operation for the (n−1) th image. May have been detected before the recovery operation. The second detection value (evaluation current value) for the n-th output image is the value of the recovery operation for the n + 1-th image during or after the collection operation for the n-th image. It may have been detected before.

  In this embodiment, the CPU 17 accumulates and stores the differential current value An in the memory 16 as needed each time image formation is performed. That is, as the number of prints increases, the integrated value TA of the differential current values integrated by the following equation and stored in the memory 16 typically increases.

  Then, the CPU 17 compares the integrated value TA of the difference current value with the determination value β. Thereby, it is determined whether or not the electrostatic discharge operation of the collected toner from the collection roller 9 should be executed. The determination value β is set in the same manner as the determination value α in the first embodiment. In addition, the preset determination value β is stored in advance in the storage unit of the CPU 17 in this embodiment.

  That is, when the CPU 17 determines that the integrated value TA of the differential current value is less than β, that is, when it is determined that the toner collection amount of the collection roller 9 is still small, the electrostatic discharge of the collected toner from the collection roller 9 is performed. The image forming operation is continuously performed without performing the operation. On the other hand, when the CPU 17 determines that the integrated value TA of the differential current values is equal to or greater than β, that is, when the CPU 17 determines that the toner recovery amount of the recovery roller 9 has increased beyond the recovery retention limit, The electrostatic discharge operation of the collected toner is performed. The above operation is shown in S206 and S211 to S212 in FIG. After the electrostatic discharge operation, the accumulated value TA of the differential current value that has been accumulated and stored in the memory 16 can be reset.

  In this embodiment, the current value of the energization loop of the collection roller 9 is detected before and after the area E per image for one transfer material P. Therefore, the measurement time difference between the reference current value Ian for the nth image and the evaluation current Ibn for the nth image is small. Thereby, the influence of the fluctuation | variation by the external factor of the reference current value Ia can be avoided. Further, by detecting the decrease in the detected current value per image for one sheet of transfer material P and accumulating it, the toner recovery amount of the recovery roller 9 is detected every time an image is formed, The total amount of toner collected on the collection roller 9 can be estimated sequentially. Based on this, the electrostatic discharge timing can be determined.

  That is, in this embodiment, the first detection value and the second detection value, which are output current values (or output voltage values as will be described later) detected by the detection means at different timings for each output image. An integrated value of the difference for a plurality of output images is obtained. The number of images to be output before the next electrostatic discharge operation is different depending on whether the integrated value is less than the predetermined value or more than the predetermined value. The number of images is determined by the electrostatic discharge operation from the time of detection of the second detection value detected later among the first and second detection values for the last output image in the plurality of output images. You can compare until you do.

  As described above, according to the present embodiment, every time the secondary transfer residual toner for each image is collected, the decrease amount of the current value supplied to the collection roller 9 is detected and integrated, so that the collection roller 9 The total recovery amount of the secondary transfer residual toner is estimated. Based on the result, the execution timing of the electrostatic discharge operation of the collected toner from the collection roller 9 to the intermediate transfer belt 7 is determined. Thereby, the secondary transfer residual toner on the intermediate transfer belt 7 can be effectively cleaned without unnecessarily reducing the image productivity of the image forming apparatus 100. Further, according to the present embodiment, the electrostatic discharge timing can be determined more accurately regardless of the usage state of the image forming apparatus 100.

  As mentioned above, although this invention was demonstrated according to the specific Example, it should be understood that this invention is not limited to the above-mentioned embodiment.

  For example, in each of the above embodiments, the recovery roller 9 has been described as always in contact with the intermediate transfer belt 7. However, the recovery roller 9 may be detachable from the intermediate transfer belt 7. . In this case, it is preferable to control the collection roller 9 so as to contact the intermediate transfer belt 7 at least during the electrostatic collection operation and the electrostatic discharge operation. For example, when the collection roller 9 is separated from the intermediate transfer belt 7 in the illustrated area N (inter-paper area, non-image area), the bias applied to the collection roller 9 in this area N may be 0V.

  In each of the embodiments described above, the current detection circuit 92 responds to the first bias when the first bias under constant voltage control is output from the recovery bias power supply 91 to the recovery roller 9. A second bias is applied. The current detection circuit 92 has been described as detecting the current value flowing in the energization loop from the applied second bias. However, the present invention is not limited to this, and information regarding the electrical resistance of the collection roller 9 may be obtained in order to estimate the total amount of secondary transfer residual toner collected by the collection roller 9. Therefore, instead of or in addition to the current detection circuit 92 in each of the above embodiments, a voltage detection circuit as detection means can be provided in the energization loop. In this case, when the first bias under constant current control is output from the recovery bias circuit 91 to the recovery roller 9, the voltage detection circuit applies a second bias corresponding to the first bias. Is done. The voltage detection circuit detects the output voltage value of the recovery bias power supply 91 from the applied second bias. Then, the CPU 17 of the control unit 15 stores the detected voltage value in the memory 16 and can read it out at any time and use it for control. That is, an increase in voltage value may be used instead of the decrease in current value used for control in the above embodiments. In this case, as the determination values corresponding to the determination values α and β in each of the above embodiments, a determination value set in advance corresponding to the increment of the voltage value is used. Of course, the detection means detects the output current value or the output voltage value when the bias subjected to constant voltage control or constant current control is output from the recovery bias power supply 91 to the recovery roller 9, and this is detected. It may be converted into information indicating the electrical resistance itself. The increase in electrical resistance can be used for control. That is, in this case, the electrical resistance value of the recovery member obtained from the output current value or the output voltage value detected by the detection means is less than a predetermined value and more than the predetermined value. The number of images output before the discharge operation is executed is different.

  Further, in each of the above embodiments, when the execution timing of the electrostatic discharge operation is defined by the detected current value in the energization loop of the collection roller 9, it is defined by the difference instead of the current value. This is because, as described above, for example, it is preferable to eliminate the influence of variation in volume resistivity of the collection roller 9 in manufacturing and environmental fluctuations. However, the present invention is not limited to this, and the execution timing of the electrostatic discharge operation can be determined by comparing the detection current value itself in the energization loop of the collecting roller 9 at an arbitrary time point with the determination value. You may decide. Of course, as described above, since it is only necessary to obtain information on the electrical resistance of the collecting roller 9, the electrostatic discharge operation is performed by comparing the voltage value itself or the electrical resistance value itself with the determination value instead of the current value. May be determined. That is, in this case, when the output current value or the output voltage value detected by the detection means is less than the predetermined value or more than the predetermined value, the next time from the detection of the detection current value or the detection voltage value. The number of images that are output before the electric discharge operation is executed is different.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram illustrating an arrangement relationship in the vicinity of a collection roller and an energization loop connected to the collection roller in the image forming apparatus of FIG. 1. It is a schematic diagram showing an example of electrostatic recovery operation of secondary transfer residual toner by the recovery roller according to the present invention. It is a schematic diagram showing an example of electrostatic discharge operation of the collected toner by the collecting roller according to the present invention. It is a schematic flowchart figure which shows an example of the control method of the execution timing of the electrostatic discharge | release operation | movement according to this invention. FIG. 10 is a graph showing an example of a change in a differential current value reflecting a backflow toner concentration from the collection roller to the intermediate transfer belt and an electrical resistance of the collection roller with respect to a toner collection amount of the collection roller. It is a schematic diagram for demonstrating an example of the detection timing of the reference electric current value and evaluation electric current value according to this invention. It is a schematic diagram for demonstrating the other example of the detection timing of the reference electric current value and evaluation electric current value according to this invention. It is a schematic flowchart figure which shows the other example of the control method of the execution timing of the electrostatic discharge | release operation | movement according to this invention. It is a schematic diagram for demonstrating the other example of the detection timing of the reference electric current value and evaluation electric current value according to this invention. It is a schematic diagram for demonstrating the further another example of the detection timing of the reference electric current value and evaluation electric current value according to this invention. It is a schematic sectional drawing of an example of the conventional image forming apparatus.

Explanation of symbols

1 Photosensitive drum (image carrier)
5 Primary transfer roller (first transfer means)
7 Intermediate transfer belt (intermediate transfer member)
8 Secondary transfer roller (second transfer means)
9 Collection roller (collection member)

Claims (17)

An image carrier for carrying toner, an intermediate transfer member to which toner is transferred from the image carrier, a first transfer means for transferring toner from the image carrier to the intermediate transfer member, and the intermediate transfer member A second transfer unit that transfers toner to a transfer material; and a downstream side of a toner transfer unit by the second transfer unit and an upstream side of a toner transfer unit by the first transfer unit in the moving direction of the intermediate transfer member. And an electric field in a direction in which the toner charged to a predetermined polarity moves from the intermediate transfer body toward the recovery member between the recovery member and the intermediate transfer body. And a discharge operation in which an electric field is formed between the recovery member and the intermediate transfer member in a direction in which the toner charged to the predetermined polarity moves from the recovery member toward the intermediate transfer member. ,I do In the image forming apparatus,
Bias output means for outputting a bias to the recovery member, and an output current of the bias output means when the bias output means is outputting a constant voltage controlled or constant current controlled bias to the recovery member Detection means for detecting a value or an output voltage value, and the discharge according to the output current value or the output voltage value detected by the detection means by the bias output means outputting a bias to the recovery member. And an image forming apparatus comprising: a control unit that determines a timing at which the operation is performed.   The control means includes a difference between the first detection value and the second detection value, which are the output current value or the output voltage value detected at different timings, and a determination value determined in advance corresponding to the difference. The image forming apparatus according to claim 1, wherein the timing at which the discharge operation is performed is determined by comparing the two.   The first detection value is detected before the collection operation is performed after the previous discharge operation is performed, and the second detection value is after the first detection value is detected. The image forming apparatus according to claim 2, wherein the image forming apparatus is detected during the collection operation or after the collection operation is performed.   The image forming apparatus according to claim 3, wherein the first detection value is detected immediately after the previous discharge operation is executed.   The second detection value is detected every time the collecting operation is performed, and the control unit compares the difference with the determination value every time the second detection value is detected. Item 5. The image forming apparatus according to Item 3 or 4.   6. The image forming apparatus according to claim 3, further comprising a storage unit that stores the first detection value.   The image forming apparatus according to claim 2, wherein when the difference is equal to or greater than the determination value, the discharge operation is performed during non-image formation.   The control means is an integrated value for a plurality of output images of a difference between the first detection value and the second detection value that are the output current value or the output voltage value detected at different timings for each output image. 2. The image forming apparatus according to claim 1, wherein a timing at which the discharge operation is executed is determined by comparing a predetermined determination value corresponding to the integrated value.   The collection operation is performed for each output image, and the first detection value for the n-th (n is a natural number) output image is the value at the time of the collection operation for the (n-1) -th image or the collection operation. The second detection value is detected at the time of the collecting operation for the nth image or when the collecting operation is performed. 9. The image forming apparatus according to claim 8, wherein the image forming apparatus is detected before the collecting operation for the (n + 1) th image.   The image forming apparatus according to claim 8, further comprising a storage unit that stores the integrated value.   11. The image forming apparatus according to claim 8, wherein when the integrated value is equal to or greater than the determination value, the discharge operation is performed during non-image formation.   The bias output means forms the electric field by outputting a bias having a polarity opposite to the predetermined polarity to the recovery member during the recovery operation, and has the same polarity as the predetermined polarity during the discharge operation. The image forming apparatus according to claim 1, wherein the electric field is formed by outputting a bias to the recovery member.   The bias output from the bias output means to the recovery member when the detection means detects the output current value or output voltage value is the bias output from the bias output means to the recovery member during the recovery operation. The image forming apparatus according to claim 12, wherein An image carrier for carrying toner, an intermediate transfer member to which toner is transferred from the image carrier, a first transfer means for transferring toner from the image carrier to the intermediate transfer member, and the intermediate transfer member A second transfer unit that transfers toner to a transfer material; and a downstream side of a toner transfer unit by the second transfer unit and an upstream side of a toner transfer unit by the first transfer unit in the moving direction of the intermediate transfer member. And an electric field in a direction in which the toner charged to a predetermined polarity moves from the intermediate transfer body toward the recovery member between the recovery member and the intermediate transfer body. And a discharge operation in which an electric field is formed between the recovery member and the intermediate transfer member in a direction in which the toner charged to the predetermined polarity moves from the recovery member toward the intermediate transfer member. ,I do In the image forming apparatus,
Bias output means for outputting a bias to the recovery member, and an output current of the bias output means when the bias output means is outputting a constant voltage controlled or constant current controlled bias to the recovery member Detection means for detecting a value or an output voltage value, and the output current value or the output voltage value detected by the detection means when the bias output means outputs a bias to the recovery member, The number of images output from the time when the detected current value or the detected voltage value is detected to the next time when the discharge operation is executed differs depending on whether the value is less than a predetermined value or greater than the predetermined value. Image forming apparatus. An image carrier for carrying toner, an intermediate transfer member to which toner is transferred from the image carrier, a first transfer means for transferring toner from the image carrier to the intermediate transfer member, and the intermediate transfer member A second transfer unit that transfers toner to a transfer material; and a downstream side of a toner transfer unit by the second transfer unit and an upstream side of a toner transfer unit by the first transfer unit in the moving direction of the intermediate transfer member. And an electric field in a direction in which the toner charged to a predetermined polarity moves from the intermediate transfer body toward the recovery member between the recovery member and the intermediate transfer body. And a discharge operation in which an electric field is formed between the recovery member and the intermediate transfer member in a direction in which the toner charged to the predetermined polarity moves from the recovery member toward the intermediate transfer member. ,I do In the image forming apparatus,
Bias output means for outputting a bias to the recovery member, and an output current of the bias output means when the bias output means is outputting a constant voltage controlled or constant current controlled bias to the recovery member Detection means for detecting a value or an output voltage value, and the output current value or output voltage detected by the detection means when the bias output means outputs a bias to the recovery member at different timings. When the difference between the first detection value and the second detection value, which is a value, is less than the predetermined value and greater than the predetermined value, the first detection value is detected first. An image forming apparatus, wherein the number of images output from when the first detection value is detected to when the discharge operation is next executed is different. An image carrier for carrying toner, an intermediate transfer member to which toner is transferred from the image carrier, a first transfer means for transferring toner from the image carrier to the intermediate transfer member, and the intermediate transfer member A second transfer unit that transfers toner to a transfer material; and a downstream side of a toner transfer unit by the second transfer unit and an upstream side of a toner transfer unit by the first transfer unit in the moving direction of the intermediate transfer member. And an electric field in a direction in which the toner charged to a predetermined polarity moves from the intermediate transfer body toward the recovery member between the recovery member and the intermediate transfer body. And a discharge operation in which an electric field is formed between the recovery member and the intermediate transfer member in a direction in which the toner charged to the predetermined polarity moves from the recovery member toward the intermediate transfer member. ,I do In the image forming apparatus,
Bias output means for outputting a bias to the recovery member, and an output current of the bias output means when the bias output means is outputting a constant voltage controlled or constant current controlled bias to the recovery member Detection means for detecting a value or an output voltage value, and the bias output means outputs a bias to the recovery member at a different timing for each output image, and the detection means detects the bias. The difference between the first detection value and the second detection value, which is the output current value or the output voltage value, when the integrated value for a plurality of output images is less than a predetermined value and more than the predetermined value, From the time of detection of the second detection value detected later among the first and second detection values for the last output image in a plurality of output images, until the next discharge operation is executed. An image forming apparatus wherein the number of images to be force are different. An image carrier for carrying toner, an intermediate transfer member to which toner is transferred from the image carrier, a first transfer means for transferring toner from the image carrier to the intermediate transfer member, and the intermediate transfer member A second transfer unit that transfers toner to a transfer material; and a downstream side of a toner transfer unit by the second transfer unit and an upstream side of a toner transfer unit by the first transfer unit in the moving direction of the intermediate transfer member. And an electric field in a direction in which the toner charged to a predetermined polarity moves from the intermediate transfer body toward the recovery member between the recovery member and the intermediate transfer body. And a discharge operation in which an electric field is formed between the recovery member and the intermediate transfer member in a direction in which the toner charged to the predetermined polarity moves from the recovery member toward the intermediate transfer member. ,I do In the image forming apparatus,
Bias output means for outputting a bias to the recovery member, and an output current of the bias output means when the bias output means is outputting a constant voltage controlled or constant current controlled bias to the recovery member Detecting means for detecting a value or an output voltage value, and the bias output means outputs a bias to the recovery member and is obtained from the output current value or the output voltage value detected by the detection means. When the electrical resistance value of the recovery member is less than a predetermined value and greater than or equal to the predetermined value, it is output from the time when the detected current value or the detected voltage value is detected until the next discharge operation is executed. An image forming apparatus having different numbers of images.

Images