JP2008122433A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high-accuracy density measurement to reflect the measured result in optimum image density or gradation density by preventing patch toner from being deteriorated because of a retransfer phenomenon in a color image forming apparatus having intermediate transfer type tandem structure. <P>SOLUTION: The image forming apparatus has the intermediate transfer type tandem structure where photoreceptor drums 1A and 1B for forming Y, M, C and K color component toner images are arrayed and an intermediate transfer body 16 coming into contact with the respective photoreceptor drums circularly turns. When a patch toner image 69A moves and reaches a density sensor 68 arranged on a more downstream side in a turning direction than the photoreceptor drum 1B while transferring the toner images formed on the photoreceptor drums 1A for Y, M and C colors, the intermediate transfer body belt 16 is separated from the photoreceptor drum 1B for K color which does not participate in image output by a cam 9 under control based on a signal obtained by detecting the density of the patch toner image 69A. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus (hereinafter simply referred to as “image forming apparatus”) such as a copying machine, a facsimile machine, a printer, and a multifunction machine (multifunction copying machine).

  In general, an image forming apparatus forms an electrostatic latent image on the surface of a drum-shaped or belt-shaped electrophotographic photosensitive member, which is an image carrier, based on an image signal read from a document, and this electrostatic latent image is developed with a developer ( Hereinafter, the toner is developed using “toner” to form a visible image. The developed toner image is transferred onto a sheet such as recording paper or a plastic material by a transfer unit, and after the transfer, the toner image is permanently fixed on the sheet by sending to a fixing device and heating and pressing.

  For example, in a color image forming apparatus using four basic colors of Y (yellow), M (magenta), C (cyan), and K (black), a plurality of developing devices are provided for each of these Y, M, C, and K colors. There are tandem structures arranged on a straight line or curve.

  As the tandem structure, there are a direct transfer method and an intermediate transfer method when classified by the process until a final image is obtained on a sheet. In the former direct transfer tandem structure, a developing device is arranged adjacent to a first image carrier, for example, a photosensitive drum, and a toner image is developed from a latent image on the photosensitive drum using toner to form a sheet. Transcript to. The latter intermediate transfer type tandem structure develops a toner image from a latent image on a photosensitive drum as a first image carrier, and once, for example, an endless intermediate transfer belt as a second image carrier. The toner images of all the colors are transferred and held on the top (primary transfer). Thereafter, each color component toner image on the intermediate transfer belt is transferred onto the sheet and transferred (secondary transfer).

  By the way, from the viewpoint of the stability of the formed image, the intermediate transfer tandem structure is more advantageous than the direct transfer tandem structure. A color image forming apparatus requires a process of superimposing toner images of Y, M, C, and K color components. In the case of the direct transfer method, since the toner image is directly transferred from the image carrier to the sheet, the image becomes unstable upon overlaying due to the physical properties, thickness, waist strength, and the like of the sheet. On the other hand, in the intermediate transfer method, the transfer object in the overlaying process is always the same object, so that a stable color image can be obtained.

  As described above, the intermediate transfer type tandem structure is more advantageous than the direct transfer type tandem structure in image stability, but there are problems in the following points.

  Regardless of the direct transfer type or intermediate transfer type tandem color image forming apparatus, the image density and gradation density are generally adjusted, and the amount of toner supplied to the developing device is adjusted. Is called.

  In the case of the intermediate transfer tandem structure, it is well known to form a density measurement sample toner image (hereinafter referred to as “patch toner image”) on the intermediate transfer belt in order to adjust the image density and gradation density. The optimum density of the toner image transferred onto the sheet is obtained from the result of detecting and measuring the density of the patch toner image. The present applicant has previously proposed a technique for adjusting to such an optimum concentration (see, for example, Patent Document 1).

  Similarly, in the case of an intermediate transfer tandem structure in which the photosensitive drum is always in contact with the intermediate transfer belt, an image on the intermediate transfer belt may be rubbed due to sliding friction, resulting in an image defect. In order to prevent this, when outputting an image in the monochrome monochrome mode, other Y, M, and C photosensitive drums are not used in addition to the K toner, so that sliding friction with an unnecessary intermediate transfer belt is avoided. A technique for separating them is proposed (for example, see Patent Document 2). Further, a structure has also been proposed in which the rotation of the photosensitive drum separated from the intermediate transfer belt is stopped during the separation, and at the same time, the operation of the charging device is also stopped (see, for example, Patent Document 3).

Japanese Patent Laying-Open No. 2005-062244 Japanese Patent Laying-Open No. 2005-156776 Japanese Patent Laid-Open No. 2004-117813

  In the case of Patent Document 1, the density of the patch toner image is detected by a density sensor, and the toner image transferred on the sheet is adjusted to the optimum density from the measured density obtained based on the detection to obtain a good image density and gradation density. Obtaining techniques are disclosed. At that time, while the patch toner image formed on the intermediate transfer body belt moves and reaches the detection point by the density sensor, it sequentially contacts the primary transfer area with the photosensitive drums of other unrelated colors. Will pass. Due to such unnecessary contact, the patch toner image is deteriorated due to a phenomenon generally called “retransfer”, and there is a disadvantage that the density measurement accuracy of the patch toner image is lowered.

  In Patent Document 2, when outputting an image in the single monochrome mode, all other Y, M, and C photoconductor drums that are not used for colors other than K are separated from the intermediate transfer belt, and the intermediate transfer belt is used. The durability life is increased by avoiding unnecessary contact friction. The frequency of use of the photosensitive drum for K color is much higher than that for other Y, M, and C photosensitive drums. Accordingly, it is necessary to frequently adjust the charging unit corresponding to the K color and the control of the surface potential as often as the usage frequency is high. While the potential control and the image forming operation relating to the K color are performed as described above, the image forming units having the photosensitive drums for other Y, M, and C colors that are separated from each other are not adjusted. It will be left as it is. Therefore, the adjustment mode in which the Y, M, C color image forming units other than the K color are operated to form the toner image on the intermediate transfer belt cannot be executed.

  In particular, as seen in Patent Document 3, the image forming unit having the K-color photosensitive drum is being adjusted in potential, or the charging operation is stopped, and is positioned upstream from the K color. The toner image is formed by the image forming unit corresponding to the Y, M, and C colors. Thereafter, since the primary transfer portion (transfer nip portion) of the K-color image forming unit is allowed to pass, complicated control is required, productivity is lowered, and downtime is increased.

  The main object of the present invention is to prevent the deterioration of the patch toner image due to the retransfer phenomenon in the middle of the movement of the patch toner image until it reaches the density detection point in the color image forming apparatus having the intermediate transfer type tandem structure. Is reflected in the optimum image density and gradation density.

  Another object of the present invention is to use the timing of adjustment for cleaning the charging means of the image forming unit that is separated from the intermediate transfer member belt and is not involved in image output and separated from the intermediate transfer member, and for controlling the surface potential. Then, a toner image is formed on the intermediate transfer member by another image forming unit during image output. Accordingly, an object of the present invention is to provide an image forming apparatus that can reduce downtime.

  Another object of the present invention is to form a patch density on an intermediate transfer member and measure the density in order to control the mixing ratio of the toner and the carrier using a two-component developing unit as an image forming device, An image forming means that requires adjustment of the toner replenishment amount for controlling the mixing ratio, and an image forming means that does not require patch density measurement to adjust the toner replenishment amount using one-component development. Another object of the present invention is to provide an image forming apparatus provided with different image forming means and capable of reducing downtime by reducing the influence of “retransfer”.

  In order to achieve the above object, an image forming apparatus of the present invention includes an image carrier, a toner image forming unit that forms a toner image on the image carrier, and a transfer unit that transfers the toner image to an intermediate transfer member. A detecting means for detecting a control toner image formed by the image forming unit at a position downstream of the plurality of image forming units on the intermediate transfer member; And an image forming apparatus that adjusts an image forming condition of the image forming unit based on a detection result of the detecting means. An image on the upstream side in the moving direction of the intermediate transfer member in the plurality of image forming units. The image carrier of the downstream image forming unit and the intermediate transfer member are separated when the control toner image formed by the forming unit passes through the downstream image forming unit. It is an feature.

  According to the image forming apparatus of the present invention, the image forming units that form toner images of a plurality of colors are each provided with an image carrier, and the toner images are sequentially transferred to the intermediate transfer member by these image carriers. While one of the image carriers forms a toner image and transfers the toner image to the intermediate transfer body, the density of the control toner image (patch toner image) on the intermediate transfer body is detected. The other image carrier that does not require toner image formation or transfer is separated from the intermediate transfer member. As a result, the influence of the retransfer phenomenon on the patch toner image can be suppressed, the density of the toner image requiring control can be measured with high accuracy, and reflected in the optimum density and gradation density of the image transferred on the sheet. Can do.

  Hereinafter, a preferred embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows a color in a tandem structure in which four image forming units for forming a four-color component toner image by, for example, Y (yellow), M (magenta), C (cyan), and K (black) are arranged by electrophotography. 1 shows an image forming apparatus. Each image forming unit corresponding to the three colors Y, M, and C is provided with a photosensitive drum 1A (image carrier), and an image forming unit corresponding to only one color of K color is a photosensitive drum 1B (image). Support). The photosensitive drum 1B is larger than the drum diameter of the photosensitive drum 1A. OPC is used for the photosensitive drum 1A, and the K-color photosensitive drum 1B used for monochrome images is frequently used, and an amorphous silicon drum having excellent wear resistance is used.

  Further, an endless intermediate transfer belt 16 (intermediate transfer body) to which the Y, M, C, and K color component toner images are sequentially transferred from the photosensitive drums 1A and 1B is provided between the rotating rollers. . The toner images formed on the photosensitive drums 1A and 1B are once transferred to the intermediate transfer belt 16 (primary transfer). The primary transferred toner image is sent to a secondary transfer portion constituted by inner and outer rollers 14 and 15 for secondary transfer, and is collectively transferred onto a sheet such as recording paper (secondary transfer). Therefore, since the intermediate transfer belt 16 is interposed while the toner images on the photosensitive drums 1A and 1B are transferred onto the sheet, a color image forming apparatus having an intermediate transfer type tandem structure is shown.

  The intermediate transfer belt 16 is wound between a plurality of belt rollers 6, 7, 11, and 14, and the belt roller 6 of the intermediate transfer belt 16 receives rotational power from a rotational drive source as a driving roller and rotates the intermediate transfer belt 16. Make it run. The belt rollers 7 and 11 that rotate along with the intermediate transfer belt 16 are driven rollers. The belt roller 14 is a backup roller that functions as the secondary transfer inner roller 14 constituting the secondary transfer portion. Power supply means (not shown) is provided that contacts the secondary transfer inner roller 14 and applies a secondary transfer bias having the same polarity as the charging polarity of the toner. As a material of the secondary transfer inner roller 14, EPDM rubber having a two-layer structure in which a foamed elastic body layer is coated on the outer periphery of the metal core material and a conductive layer is coated on the outer surface can be used. The outer conductive layer is formed of semiconductive EPDM foam rubber in which carbon black is dispersed, for example, 15 to 35% by weight, the thickness of the conductive layer is set to 0.5 to 1.5 mm, for example, and the surface resistivity is 7 Control is performed in a resistance region of -10Ω / □. Further, as the secondary transfer outer roller 15, a fluororesin having a thickness of, for example, 5 to 20 μm is interposed between a metal core material and a core layer made of carbon black dispersed foamed EPDM material fixed around the metal core material through a skin layer. A coating layer made of a system material can be formed and configured. The volume resistivity between the metal core and the coating layer is 4-5 log Ωcm.

  A belt cleaner (not shown) for removing residues remaining on the intermediate transfer belt 16 after the secondary transfer is disposed at a position facing the drive roller 6 across the intermediate transfer belt 16. . As the material of the belt body of the intermediate transfer belt 16, a resin such as polyimide, polyamide, polyester, polypropylene, polyethylene terephthalate can be used. Alternatively, the intermediate transfer belt 16 can be configured by containing an appropriate amount of a conductive agent such as carbon black in various rubbers, forming a volume resistivity of, for example, 5 to 15 log Ωcm, and setting the thickness to 0.1 mm. .

  Further, the sheet after the secondary transfer is conveyed to a fixing device (not shown), heat is applied to the image transferred onto the sheet, and the sheet is permanently fixed by applying pressure, and the sheet is discharged outside the apparatus. Yes.

  The difference between the Y, M, and C image forming means and the BK image forming means will be described. First, the configuration differences between the photoconductor and the charging unit will be described. In the image forming unit corresponding to each of the colors Y, M, C, and K, a charging roller disposed in close proximity or in contact with each other as a means for charging the drum surface around the photosensitive drums 1A and 1B carrying the latent image. It is used for charging operation. The charging roller is provided with charging devices 2A and 2B that apply a DC bias voltage and an AC high voltage to charge to a predetermined potential. Here, the DC high voltage is regulated and controlled to the target VD potential in the range of 500 V to 900 V, and the high voltage of the AC component is marked with a high voltage in the range of 1000 to 2000 V, with the frequency being 1000 to 2000 Hz and Vpp. The At this time, since the VD potential of YMC converges to the DC bias, VD potential control is not required. The charging device 2A has charging rollers corresponding to Y, M, and C colors.

  The charging device 2B corresponding to the K color uses a scorotron type corona charger. As shown in FIG. 2, in the charging device 2B, shield cases 50a and 50b having a substantially U-shaped cross section are provided in the axial direction of the photosensitive drum 1B at a portion facing the photosensitive drum 1B.

  Inside the shield cases 50a and 50b, the discharge wire 20 is supported by support members (not shown) at both ends thereof. A grid 52 is disposed on the front opening side of the shield case 50 so as to face the photosensitive drum 1B. The grid 52 is made of a number of SUS wires. On the back side of the shield cases 50a and 50b, a back opening is formed along the longitudinal direction.

  The shield cases 50a and 50b have a height dimension of, for example, 30 mm and a width (inner surface) of, for example, 44 mm. The discharge wire 20 is connected to a high voltage power supply (not shown) for applying a DC high voltage, and the shield cases 50a and 50b and the grid 52 are provided with a constant voltage element such as a varistor for the purpose of holding them at a constant potential. It is connected.

  Further, the BK color photoconductor used in the present invention is an amorphous sircon drum capable of long life, and uses a corona charging device. For this reason, since the dark decay from the charging position to the development position is large, the surface potential sensor 17 is mounted to improve the pair of the K-color photosensitive drums 1B. The potential sensor 17 is arranged after exposure, and the VD potential is measured according to the grid high voltage applied by the corona charging and adjusted to the target charging potential.

  Next, FIG. 8 shows the state of control during potential control in the BK image forming unit of the present invention. FIG. 8 is a diagram showing the state of the potential control flow using the measurement example with the potential sensor 17 during the potential control.

  First, change the grid high voltage (Vg1,2,3 in Fig. 8) of the corona charging device, measure the VD potential obtained at that time, and adjust the grid high voltage to obtain the eye potential VD = 500V . Subsequently, using the image exposure apparatus, the target light potential is adjusted to VL = 200 V, for example, based on the potential measurement result obtained by changing the light intensity by two-step modulation and changing the exposure portion potential by two steps. Here, the target values of Vd and VL are not always fixed, and there is no problem in the present invention even if they are changed according to conditions.

  Referring again to FIG. 1, a laser exposure device 8A corresponding to Y, M, and C colors and a laser exposure device 8B corresponding to K color for writing electrostatic latent images on the charged photosensitive drums 1A and 1B are arranged. . In addition, developing rollers 3A and 3B are arranged as developing devices that store Y, M, C, and K color component toners and develop electrostatic latent images on the photosensitive drums 1A and 1B. Further, primary transfer rollers 5A and 5B which are transfer means for transferring the toner images carried on the photosensitive drums 1A and 1B to the intermediate transfer belt 16 are disposed, and on the photosensitive drums 1A and 1B after the primary transfer. An electrophotographic device such as a drum cleaner 12 as a cleaner for removing the residue is sequentially arranged.

  Next, the difference in configuration of the image forming means for Y, M, C and BK will be described. In this embodiment, the image forming units corresponding to Y, M, and C colors are cleanerless systems, and the structure is different from that of the image forming unit corresponding to K colors.

  Further, each of the image forming units Y, M, and C is provided with a brush member 4 that erases the history of residual toner that has not been transferred. The toner is collected. The developing system using the developing roller 3A is a two-component magnetic brush system, and the developing system using the developing roller 3B is a one-component jumping developing system using magnetic toner. In the image forming means for Y, M, and C, the toner afterimage after the primary transfer is neutralized by using the history erasing brush, and a predetermined VD potential is obtained by a charging roller. In addition, the charging polarity of the toner is adjusted to the charging polarity of the toner in the developing means, and the toner is collected in the developing unit. Further, since the BK image forming apparatus is not a cleanerless system, a cleaning unit is provided on the photosensitive member, and the primary transfer residual toner is collected by the cleaning unit.

    On the intermediate transfer belt 16, as shown in FIG. 3, a patch toner image serving as a specimen for appropriately adjusting the image density of the Y, M, and C color toner images transferred onto the sheet. A (control toner image) pattern 69A is formed. In order to measure the density of the patch toner image pattern 69A, a regular reflection type density sensor 68 for toner image detection is disposed on the downstream side of the photosensitive drum 1B, and a registration sensor 61 for measuring the toner density for registration adjustment is further provided. It is installed. This toner image density measurement is carried out in order to maintain the mixing ratio of the toner of the two-component developer, which is the image forming means of Y, M, and C, and the carrier at a predetermined ratio. Further, since the BK developing means is a one-component developing device, it does not require patch toner image formation and density measurement in order to adjust the toner replenishment amount.

  In the color image forming apparatus having the intermediate transfer type tandem structure, the following image forming process is executed.

  For example, in the case of an image forming apparatus such as a digital color copying machine, a document on a platen is read by a color image reading device, and the read signal is converted into a digital image signal by a processing circuit and temporarily stored in a memory and stored. To do. A toner image of each color is formed based on the accumulated digital image signals of four colors Y, M, C, and K. That is, the image forming unit is driven according to the digital image signal of each color, and a charging bias voltage is applied by the charging devices 2A and 2B to uniformly charge the surfaces of the photosensitive drums 1A and 1B. The electrostatic latent images corresponding to the digital image signals are written on the charged photosensitive drums 1A and 1B by the laser exposure devices 8A and 8B. The electrostatic latent images formed on the photosensitive drums 1A and 1B are developed by the developing rollers 3A and 3B to form toner images of respective colors. When the image forming apparatus is a printer, each color component toner image is formed based on a digital image signal input from the outside.

  The toner images formed on the photosensitive drum 1A are sequentially transferred from the photosensitive drum 1A to the surface of the intermediate transfer belt 16 by the primary transfer roller 5 at a primary transfer portion where the photosensitive drum 1A and the intermediate transfer belt 16 are in contact with each other. Transcribed. Untransferred residual toner remaining on the photosensitive drum 1B is cleaned by the drum cleaner 12. The toner images primarily transferred to the intermediate transfer belt 16 are superposed, and the intermediate transfer belt 16 rotates and is sent to a secondary transfer portion including secondary transfer inner and outer rollers 14 and 15. In synchronization with this, the sheet is conveyed to the secondary transfer portion, and the secondary transfer outer roller 15 nips the sheet in cooperation with the secondary transfer inner roller 14 as a backup roller. In the secondary transfer portion, the toner image carried on the intermediate transfer belt 16 is transferred to the sheet by the action of the transfer electric field formed between the secondary transfer inner and outer rollers 14 and 15 (secondary transfer). The sheet onto which the toner image has been transferred is conveyed to a fixing device, where the toner image on the sheet is heated and pressurized in the fixing device for permanent fixing, and then discharged onto a discharge tray (not shown) provided outside the apparatus. The residual toner that has not been transferred to the intermediate transfer belt 16 after the transfer is cleaned and removed by the belt cleaner 30.

  On the other hand, a toner image is sequentially formed on the Y, M, and C color photosensitive drums 1A and transferred to the intermediate transfer belt 16, and a K color corresponding photosensitive drum that does not require toner image formation or transfer during that time. In 1 </ b> B, the intermediate transfer belt 16 is separated while avoiding rotational contact. FIG. 4 shows a state where the intermediate transfer belt 16 at a portion facing the K-color corresponding photosensitive drum 1B is separated from the K-color corresponding photosensitive drum 1B.

  A separation mechanism for separating a part of the intermediate transfer belt 16 from the rotational contact with the K-color photosensitive drum 1B is provided, and the cam 9 constitutes the main part of the drive. When the cam 9 receives rotational power from the cam shaft and rotates in the clockwise direction indicated by an arrow in FIG. 4, the cam 9 moves backward from the position where the primary transfer roller 5 </ b> B of the primary transfer portion presses the intermediate transfer belt 16. Then, the intermediate transfer belt 16 is moved away from the photosensitive drum 1B that has been in contact with it. When the cam 9 rotates counterclockwise, the primary transfer roller 5B presses the intermediate transfer belt 16 from the inside and presses against the photosensitive drum 1B to return to the state shown in FIG. Thus, the two-component development system is obtained by setting the primary transfer roller 5B for K color transfer in a separated state. While the toner image formed on the photosensitive drum 1A for Y, M and C colors is transferred to the intermediate transfer belt 16, there is no pressing by the K primary transfer roller 5B, and the intermediate transfer belt 16 from the photosensitive drum 1B is not pressed. Since they are separated from each other, no retransfer phenomenon occurs there. That is, it is possible to avoid the patch toner image pattern 69A on the sheet being rubbed at the primary transfer nip between the photosensitive drum 1B and the intermediate transfer drum 16 and being deteriorated by being pressed by the primary transfer roller 5B that is not used. Accordingly, the density of the Y, M, and C color patch toner image patterns 69A in FIG. 3 formed on the intermediate transfer belt 16 can be detected with high accuracy by the density sensor 68.

  The density sensor 68 is a specular reflection type optical sensor that reads and detects the patch toner image pattern 69A and outputs a density detection signal. That is, the intermediate transfer belt 16 is irradiated with a predetermined exposure amount, and a regular reflection is received with respect to the received exposure amount, and the presence or absence of the patch toner image pattern 69A for each color of Y, M, C, Y, M, C Conversion to a toner density signal is performed based on the output difference of the light receiving unit obtained by the density difference between the colors. Based on this, the measured density value of the patch toner image pattern 69A is obtained, and based on this, the image density and gradation density on the sheet are reflected so as to be optimized.

  Further, when forming a full-color image using the photosensitive drum 1B corresponding to the K color, the sheet passes through the transfer area at the primary transfer portion by the primary transfer roller 5B facing the photosensitive drum 1B. The transfer high-pressure value for K color is adjusted in consideration of the retransfer amount at. Accordingly, even when the registration patterns 65 and 66 that need to form the toner image in the “wearing” state in contact with the primary transfer portion of the K color are formed, the toner image is not disturbed and an appropriate image is measured. Is possible.

  In this case, the degree of influence due to the retransfer phenomenon varies depending on the amount of toner applied on the intermediate transfer belt 16. Therefore, the gradation density pattern as shown in FIG. 6 is measured in two modes in the separated state and the non-separated state at the primary transfer portion of K color. Thereby, in consideration of the influence on the re-transfer generated at each image density from the signal difference of the light receiving unit of the density sensor 68, the CPU of the control unit calculates the correction amount with the measurement data based on the density detection signal, A voltage corresponding to the correction value is applied to the primary transfer portion of K color. In addition, with the intermediate transfer drum 16 being separated, the rotational driving, development high voltage and charging high voltage of the K-color corresponding photosensitive drum 1B can be kept the same as during image formation. It is also possible to control the operation to turn off. With this configuration, in an image forming unit that does not require toner image formation or transfer on the intermediate transfer body belt 16, the patch toner image pattern 69A can be formed without being affected by the primary transfer by pressing with the primary transfer roller. The difference between the density measurement value and the image density transferred onto the sheet can be controlled to be corrected.

(Second Embodiment)
In the present embodiment, while the intermediate transfer belt 16 is separated at a position facing the photosensitive drum 1B corresponding to the K color shown in the first embodiment, it is different from the colors Y, M, and C. The adjustment mode is executed. Also in this case, the corona charger 2B shown in FIG. 2 is used to charge the drum surface of the photosensitive drum 1B for K color. In this corona charger 2B, as shown in FIG. 7, a cleaning member 21 for reciprocating the cleaning of the charging wire 20 is attached, and the charging wire is reciprocated by a driving means in the direction of the bus of the photosensitive drum 1B. 20 can be cleaned.

  Further, while the Y, M, and C color component toner images are formed, the intermediate transfer belt 16 is separated from the K photosensitive drum 1B, and the rotational driving of the photosensitive drum 1B is turned off during that time. It is possible to execute an adjustment mode in which cleaning is performed in a state where development, charging, and light neutralization are also turned off. Further, even if the charging devices 2A and 2B that charge the photosensitive drums 1A and 1B by applying a charging bias voltage are different, one is a charging roller and the other is a corona charger. Therefore, downtime can be shortened.

(Third embodiment)
As in the second embodiment, the corona charger 2B shown in FIG. 2 is used to charge the drum surface of the photosensitive drum 1B for K color. During the separation, potential control using the surface potential sensor 17 is performed on the photosensitive drum 1B for K color. In this case, during full-color image formation, it is possible to execute a plurality of image formation modes that can change the printing speed and output an image in K single-color image formation.

  In general, this is different from the one in which the potential control is performed at the time of mono-color image formation using only the image forming unit corresponding to K color with a tandem structure. In this case, the potential control can be performed with a configuration that reduces deterioration factors such as the life of the drum due to an increase in the rotational speed of the photosensitive drum 1A corresponding to Y, M, and C colors and the charging means. Further, the timing for performing the potential control can be performed simultaneously with the adjustment of the image forming unit such as the toner image formation shown in the first embodiment. Furthermore, it is possible to perform surface potential control under the condition that the rotational speed of the photosensitive drum 1B is changed irrespective of the rotational speed of the intermediate transfer belt 16. It is also possible to carry out surface potential adjustments at a plurality of rotational speeds at the timing of carrying out image stabilization adjustments involving the formation of toner images of Y, M, and C colors. Moreover, even when the K color mode and the full color image formation mode are switched as a continuous operation by performing such complex control in a timely manner, it is necessary to instantaneously adjust the power of the laser that performs charging high voltage, photostatic discharge, and image exposure. There is no switchover. Thereby, productivity can be improved and image stability can be improved.

(Fourth embodiment)
In the present embodiment, during the transfer and separation at the K color position shown in the first embodiment, the K color developer is transferred to the toner layer holding roller 13 provided in the cleaning unit (see FIG. 1). Toner is supplied. In this case, a magnet roller is mounted on the cleaning unit for the K photosensitive drum 1B, a toner layer is formed using magnetic toner used as a developer, and the photosensitive drum and the toner layer are slid. The role of the toner layer coat has a function of supplying a stable toner to the cleaning blade 18 and maintaining the cleaning performance. However, since the toner layer is contacted and rotated with the rotating photoconductor, there is a problem that when an image with a small image ratio is output for a long time, the coating amount of the toner layer is reduced and cleaning becomes unstable. As a countermeasure, a method of supplying magnetic toner from a developing device has been conventionally employed. In an image forming apparatus using an intermediate transfer belt, in order to supply a toner image formed on a drum to a magnet roller, it is necessary to pass through a primary transfer area. Therefore, a reverse bias function of primary transfer that is not normally used at the time of image formation is provided, and when a developer is supplied, the supply is performed by applying a reverse bias voltage. However, even if a transfer prevention electric field is formed by applying a reverse bias, it is impossible to create a state in which the transfer body is not physically moved to 100%. Furthermore, back dirt due to dirt on the secondary transfer roller 15 occurs. In order to avoid this, in general, useless control for reducing productivity such as cleaning of the intermediate transfer belt 16 and cleaning mode of the secondary transfer outer roller 15 is performed. On the other hand. In this embodiment, an adjustment mode is provided in which toner is supplied to the magnet roller without staining the intermediate transfer belt 16 while the Y, M, and C color image forming units are forming the toner image. Therefore, productivity can be improved even when low duty is continuously performed and toner supply is necessary.

1 is a diagram showing an embodiment of an image forming apparatus of the present invention. The figure which shows the corona charger in 1st Embodiment. FIG. 6 is a diagram illustrating a patch toner image density measurement pattern and a reading structure thereof. FIG. 6 is a diagram illustrating a state in which an intermediate transfer belt is separated from a K-color corresponding photosensitive drum. The figure which shows a registration adjustment pattern and its reading structure. The figure which shows a gradation density pattern typically. FIG. 10 is a diagram illustrating a mechanism for cleaning a corona charger provided around a photosensitive drum for K color as a second embodiment. The figure which shows a mode that the mode of the electric potential control flow in a K image formation unit.

Explanation of symbols

1A Y, M, C color photosensitive drum (image carrier)
1B Photosensitive drum for K color (image carrier)
2A Y, M, C, K Color Charger 2B K Color Corona Charger 4 Brush 5A Y, M, C Color Primary Transfer Roller 5B K Color Primary Transfer Roller 6 Driven Roller DESCRIPTION OF SYMBOLS 7 Drive roller 8 Density sensor 9 Cam of separation mechanism 10 Cam support stand 11 Primary transfer roller 12 Cleaning blade 13 Toner layer controller 14 Secondary transfer inner roller 15 Secondary transfer outer roller 16 Intermediate transfer body belt (intermediate transfer body)
17 Potential sensor 18 Photostatic discharge 20 Charged wire 21 Cleaning member 52 Grid electrode 61 Sensor part (registration sensor)
62 Light Emitting Unit 63 Light Receiving Unit 65, 66 Registration Pattern 69 Density Pattern 80 Registration Sensor Unit (Detection Unit)

Claims (5)

A plurality of image forming units each including an image carrier, a toner image forming unit that forms a toner image on the image carrier, and a transfer unit that transfers the toner image to an intermediate transfer member;
Detecting means for detecting a control toner image formed by the image forming unit on the intermediate transfer body at a downstream position of the plurality of image forming units;
Means for adjusting an image forming condition of the image forming unit based on a detection result of the detecting means;
In an image forming apparatus having
Among the plurality of image forming units, when the control toner image formed by the image forming unit upstream in the moving direction of the intermediate transfer member passes through the downstream image forming unit, the downstream image is formed. An image forming apparatus, wherein an image carrier of a forming unit and the intermediate transfer member are separated from each other.   2. The image forming apparatus according to claim 1, wherein the adjustment of the surface potential measurement is performed on the downstream image carrier that is being separated.   The image forming apparatus according to claim 1, wherein cleaning is performed on a charging unit that charges the downstream image carrier that is being separated.   The image forming apparatus according to claim 1, wherein the rotation speed is adjusted with respect to the downstream image carrier being separated.   When the downstream image carrier is a photosensitive drum that forms a black component toner image, an intermediate transfer belt provided as the intermediate transfer member is separated from a primary transfer portion with respect to the photosensitive drum. The image forming apparatus according to any one of claims 1 to 4.

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