JP2007233276A - Image recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: a bias adjusting mode is performed at every process speed in cleaning a second image carrier, so that it takes a long time to start the following image forming operation, regarding an image forming apparatus using a plurality of process speeds. <P>SOLUTION: A cleaning process is performed after adjusting the process speed for cleaning the second image carrier 81 to a normal image forming process speed, thereby eliminating need of a bias adjusting operation related to each process speed, consequently, the adjusting time required before the start of a copying operation is shortened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which a visible image is formed on an image carrier and the toner image is electrostatically transferred onto a recording material. It can be suitably applied to a forming apparatus or the like.

  As a conventional electrophotographic multi-color or full-color image forming apparatus, in recent years, each color toner image formed on a photosensitive drum is sequentially superimposed on an intermediate transfer member (intermediate transfer belt) to form a color image, There has been proposed an intermediate transfer type image forming apparatus that transfers images onto recording paper in a lump.

  In this intermediate transfer method, a toner image is formed on the photosensitive drum by charging means, exposure means, and developing means arranged around the photosensitive drum, and electrostatically transferred to the intermediate transfer belt by the transfer means in the primary transfer portion. In the case of forming a color image, a full color image can be formed on the intermediate transfer belt by sequentially transferring the toner images to the intermediate transfer belt. The toner image transferred to the intermediate transfer belt is conveyed to the secondary transfer portion by the rotation of the intermediate transfer belt, and is electrostatically transferred to the recording medium. At this time, the toner remaining on the intermediate transfer belt without being transferred onto the recording paper can be removed by pressing the cleaning blade against the intermediate transfer belt to remove the residual toner, or by applying a bias to the fur brush cleaning means. A method for electrostatically removing residual toner has been proposed. The fur brush cleaning is advantageous for the influence on the life of the intermediate transfer belt, which is a problem in the blade cleaning means, or for problems such as load fluctuation due to frictional resistance fluctuation. The polarity is charged to (+) by the secondary transfer bias and charged to (-), so all the residual toner can be collected with a single fur brush and with a single polarity bias applied. No problems occur. In order to solve this problem, a method described in Japanese Patent Laid-Open No. 2002-207403 is proposed that collects transfer residual toner after secondary transfer by applying (+) and (-) biases of different polarities to a plurality of fur brushes, respectively. Has been.

  As a method for controlling the voltage applied to the transfer means, as disclosed in Japanese Patent Application Laid-Open No. 05-006112, the current required for transfer during non-image formation in which the potential of the photosensitive drum is constant is set to a constant current circuit. The ATVC method that uses the generated voltage for the resistance value of the transfer means at that time as the transfer voltage during image formation.

  Furthermore, the transfer voltage applied to the transfer means is digitally increased / decreased, the current value at that time is detected, the voltage value for the current required for transfer is calculated based on the current value, and the transfer voltage at the time of image formation is calculated. A PTVC method has been proposed.

  In the above-described full-color image forming apparatus, the heat capacity varies depending on the basis weight of the transfer material. Therefore, with respect to recording paper having a large heat capacity such as cardboard, the speed when passing through the fixing device 110 is set to a normal process. Take a method that decelerates rather than speed.

  Specifically, when the image forming apparatus receives an instruction from the user or an instruction to use the thick paper by the recording material detection unit, the toner image of four colors is transferred to the surface of the intermediate transfer belt 105 during a series of image forming processes. After the primary transfer, the rotational speed (peripheral speed) of the photosensitive drum 101, the intermediate transfer belt 105, and the fixing device 101 is decelerated from the normal process speed before the leading edge of the toner image reaches the second transfer portion 109. Switch to mode. The degree of deceleration is generally 1/2, 1/3, 1/4, etc. of the normal process speed, although it depends on the capacity of the recording paper and the fixing means of the image forming apparatus.

  In this deceleration state, the four-color toner images on the intermediate transfer belt 105 are secondarily transferred onto the surface of the transfer material P (OHT or thick paper), and the transfer material P is conveyed to the fixing device 110 and decelerated until the fixing is completed. Continue to maintain state.

  As described above, by fixing the process speed, it is possible to ensure toner fixability on recording sheets having different heat capacities.

As a cleaning method in the image forming apparatus in which the process speed is changed according to the type of recording paper as described above, a method as disclosed in JP-A-2001-305932 has been proposed.
JP-A-5-006112 Japanese Patent Laid-Open No. 2001-305932

  The image forming apparatus that electrostatically cleans the intermediate transfer belt with a plurality of fur brushes as described above and changes the rotational speed of the intermediate transfer belt with recording paper has the following problems.

  As described in the prior art, in fur brush cleaning in which biases of (+) and (-) having different polarities are applied, the polarity of the collected toner differs, so the amount of toner to be cleaned differs depending on the image. come. In other words, when the image density is high, the negative transfer residual toner increases, so a lot of fur brushes to which a (+) bias is applied becomes dirty, and when there are many images with low image density, the positive transfer residual toner increases ( -) Fur brush with bias applied becomes easy to get dirty. Therefore, the amount of collected toner differs depending on the image density, and the way the fur brush is soiled differs. Therefore, as the image formation proceeds, the resistance value of each fur brush varies. Furthermore, since some fur brushes themselves have resistance variations and resistance fluctuations, if the bias value set at the initial stage is used as it is, cleaning will occur due to the resistance fluctuations of the fur brush due to dirt as described above. A proper cleaning bias may not be obtained, and cleaning failure may occur.

  In order to solve this problem, an appropriate current value is obtained by bringing the cleaning fur brush into contact with the intermediate transfer belt that rotates during, for example, the pre-rotation, post-rotation, or startup operation of the image forming apparatus other than the image forming operation. There has been proposed a cleaning bias control method for executing an adjustment mode so as to obtain an obtained cleaning bias.

  However, when changing the cleaning conditions, that is, the rotational speed of the cleaning member and the intermediate transfer belt so as not to change relatively according to the process speed as in JP-A-2001-305932, the cleaning bias depends on the process speed. Therefore, the cleaning bias adjustment mode must be executed for each process speed.

  That is, when the image forming speed has 1/2, 1/3 speed in addition to the normal process speed, the proper cleaning current at the normal process speed is 20 μA, and the proper process speed at the 1/2 speed is appropriate. When the cleaning current is 10 μA and the appropriate cleaning current at the 1/3 speed process speed is 7 μA, the cleaning bias adjustment mode must be executed at each process speed and targeting each appropriate current. .

  For this reason, there arises a problem that a long adjustment mode must be performed before image formation.

The above-described problem is a primary transfer in which a first image carrier and a toner image formed on the image carrier are transferred to a second image carrier by applying a bias having a polarity opposite to the charging polarity of the toner. Means,
A secondary transfer means for transferring the toner image transferred onto the second image carrier onto the recording paper, and a secondary transfer residual toner remaining on the second image carrier, each having a different polarity bias And an image forming apparatus having a function of switching a plurality of second image carrier cleaning means and a plurality of image forming speeds different from the normal image forming speed. In
In the image forming apparatus, when cleaning is performed by the second image carrier cleaning means, if an image forming speed different from the normal image forming speed is selected, the image forming speed is returned to the normal image forming speed before the cleaning means. The image forming apparatus is characterized in that the cleaning operation is performed with the bias value adjusted by the bias value adjusting function.

  A first image carrier, and a primary transfer means for transferring the toner image formed on the image carrier to the second image carrier by applying a bias having a polarity opposite to the charging polarity of the toner; A secondary transfer means for transferring the toner image transferred on the second image carrier onto the recording paper and a secondary transfer residual toner remaining on the second image carrier are collected, and biases of different polarities are respectively applied. In an image forming apparatus having a function of switching between a plurality of second image carrier cleaning means and a plurality of image forming speeds different from the normal image forming speed, which can be applied and has a function of adjusting a bias value to be applied The image forming apparatus returns the image forming speed to the normal image forming speed when an image forming speed different from the normal image forming speed is selected when the second image carrier cleaning means performs cleaning. By performing the cleaning operation with the leaning means with the bias value adjusted by the bias value adjusting function, even when the process speed is switched, the cleaning process is performed at the normal process speed to match the cleaning conditions. The cleaning bias adjustment operation that must be performed for each process speed is performed only at the normal process speed, and cleaning performance is secured for the secondary transfer residual toner when the process speed changes. It is. In addition, since it is not necessary to perform a bias adjustment operation for each process speed when adjusting the cleaning bias, it is possible to greatly reduce the adjustment time before the copy operation starts.

  Hereinafter, the present invention will be described more specifically with reference to examples. These examples are examples of the best mode of the present invention, but the present invention is not limited to these examples.

  FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 1 of the present invention. This image forming apparatus is an electrophotographic image forming apparatus using an intermediate transfer member. Hereinafter, the image forming apparatus of the present invention will be described in detail.

An endless intermediate transfer member 81 that runs in the direction of arrow X is disposed in the image forming apparatus main body. The intermediate transfer member 81 is made of a dielectric resin such as polycarbonate, polyethylene terephthalate resin film, polyvinylidene fluoride resin film, polyimide, ethylene tetrafluoroethylene copolymer, or the like. In this example, a conductive polyimide seamless belt having a volume resistivity of 1 × 10 ⁹ Ω · cm (using a probe conforming to the JIS-K6911 method, an applied voltage of 500 V, an applied time of 60 seconds) and a thickness of t = 80 μm was used. Other materials, volume resistivity, and thickness may be used. Furthermore, in an intermediate transfer body having an elastic layer as a surface layer, blade cleaning may not be employed as a cleaning means for the intermediate transfer body, which is more optimal for implementation.

  The recording paper P taken out from the paper feed cassette 60 is supplied to the above-described transport roller 28 through the pickup roller 30 and further transported to the left in the figure.

  Next, the image forming unit will be described with reference to FIG. The image forming unit includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 that is rotatably arranged. The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member that basically includes a conductive substrate 1b such as aluminum and a photoconductive layer 1a formed on the outer periphery thereof. The center has a support shaft 1c, and is driven to rotate in the direction of arrow R1 about the support shaft 1c by a driving means (not shown). Around the photosensitive drum 1a, process devices such as a primary charger 2 and a developing device 4 are arranged. The primary charging device 2 is in contact with the surface of the photosensitive drum 1 and uniformly charges the surface to a predetermined polarity and potential, and is configured in a roller shape as a whole (hereinafter referred to as “charging roller 2”). ). The charging roller 2 includes a conductive roller (core metal) 2c disposed in the center and a conductive layer 2b formed on the outer periphery thereof, and both ends of the core metal 2c are rotatably supported by a bearing member (not shown). In addition, they are arranged in parallel to the photosensitive drum 1. The bearing members at both ends are urged toward the photosensitive drum 1 by pressing means (not shown), whereby the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is driven to rotate in the direction of arrow R2 as the photosensitive drum 1 rotates in the direction of arrow R1. The cored bar 2 c of the charging roller 2 is in contact with an electrical contact connected to the power supply 10. A bias voltage is applied to the charging roller 2 by the power supply 10, whereby the surface of the photosensitive drum 1 is uniformly and uniformly charged.

  The developing device 4 disposed on the downstream side of the exposure unit 3 rotates the developing device 4 by 45 ° in the R4 direction around the rotation shaft 119, so that the developing device faces the photosensitive drum 1 in the order of 4a, 4b, 4c, and 4d. It can be moved to a position. By this operation, toner images are sequentially formed on the photosensitive drum.

  Hereinafter, the developing device will be described using the developing device 4a. The developing device 4 a has a developing container 116 containing a two-component developer 119, and a developing sleeve 111 is rotatably installed in an opening of the container 116 facing the photosensitive drum 1, and the developing sleeve 111 has a developing sleeve in the developing sleeve 111. A magnet roller 112 that carries developer on 111 is fixedly disposed so as not to rotate with respect to the rotation of the developing sleeve 111. A regulating blade 115 that regulates the developer carried on the developing sleeve 111 to form a thin developer layer is installed above the developing sleeve 111 of the developing container 116. In the developing container 116, a developing chamber R1 and a stirring chamber R2 defined by a partition wall 117 are provided in a substantially lower half portion thereof. The developer 119 is mainly composed of toner and a magnetic carrier, and the toner is negatively charged and the carrier is positively charged. First, with the rotation of the developing sleeve 111, the developer in the developing chamber R 1 is pumped up by the magnetic pole of the magnet roller 112 and is carried on the developing sleeve 111. The developer is conveyed by the rotation of the magnet roller 112, and the toner is negatively charged in the process of conveyance up to that time, and the developer is regulated by a regulating blade 115 arranged perpendicular to the developing sleeve 111, and is thin Formed on the developer layer. When the developer formed on the thin developer layer is transported to the development area facing the photosensitive drum 1, the developer is sprinkled by the magnetic force of the development main pole located in the development area of the magnet roller 112. A magnetic brush of agent is formed. By rubbing the surface of the photosensitive drum 1 with this magnetic brush and applying a developing bias voltage to the developing sleeve 111 by a bias power source 121, the toner attached to the carrier constituting the ears of the magnetic brush is electrostatic latent image. A toner image is formed on the photosensitive drum 1 by being attached to the visible portion (exposed portion by laser light) and developing. Below the photosensitive drum 1, a roller-shaped transfer device 6 (hereinafter referred to as "transfer roller 6") is disposed.

The transfer roller 6 includes a conductive roller shaft 6a connected to a power source 11 and a conductive layer 6b formed in a cylindrical shape on the outer peripheral surface thereof. The conductive layer 6b of the transfer roller 6 has a resistance value of about 10 ⁵ to 10 ⁸ Ω · cm, and single-bubble or continuous-cell EPDM, SBR, BR, and the like are preferable. Both ends of the transfer roller 6 are urged toward the photosensitive drum 1 by a pressing member such as a spring (not shown), whereby the conductive layer 6b of the transfer roller 6 is moved toward the photosensitive drum 1 with a predetermined pressing force. A transfer nip portion N is formed by pressure contact so as to sandwich the intermediate transfer belt.

  The other developing devices 4b, 4c, and 4d have the same configuration as the developing device 4a. The difference between the developing devices 4a, 4b, 4c, and 4d is that each color is yellow, magenta, cyan, and black. The toner image is formed.

  It is assumed that yellow toner, magenta toner, cyan toner, and black toner are stored in the developing devices 4a, 4b, 4c, and 4d, respectively.

  An image signal based on the yellow component color of the document is projected onto the photosensitive drum 1 through a polygon mirror (not shown) or the like to form an electrostatic latent image, and yellow toner is supplied from the developing device 4a to the electrostatic latent image. The image becomes a yellow toner image. When this toner image arrives at the transfer nip N where the photosensitive drum 1 and the intermediate transfer belt 81 come into contact with the rotation of the photosensitive drum 1, the yellow toner image is intermediated by the transfer bias applied to the transfer roller 6. Transferred to the transfer body 81. When the intermediate transfer member 81 carrying the yellow toner image is rotated once and conveyed again to the transfer nip portion N, by this time, the developing device 4 has rotated 45 ° about the rotation shaft 119 in the R4 direction. Then, the developing unit 4b is moved to the position opposite the photosensitive drum, and the magenta toner image formed on the photosensitive drum 1 is transferred onto the yellow toner image by the same method as described above.

  Similarly, a cyan toner image and a black toner image are superimposed and transferred onto the above-described toner image, and the recording paper P taken out from the paper feed cassette 60 by this time reaches the transfer portion and is applied to the secondary transfer member 40. The four color toner images are transferred onto the recording paper P by the transfer bias.

FIG. 3 shows a detailed configuration of the secondary transfer unit. The secondary transfer member 40 includes a secondary transfer inner roller 41 positioned inside the intermediate transfer belt 81 and a secondary transfer outer roller 42 positioned outside. The secondary transfer outer roller 42 is formed of a conductive shaft 42a having a diameter of 24 mm and a conductive layer 42b covering the surface thereof. The conductive layer 42b of the secondary transfer outer roller 42 has a resistance value of about 10 ⁵ to 10 ⁷ Ω · cm, and is preferably solid or foaming EPDM, SBR, BR or the like. The secondary transfer inner roller 41 is a conductive roller, preferably 21 mm in diameter and made of SUS, Al or the like. The toner on the intermediate transfer belt is transferred to the recording paper P passing through the secondary transfer portion by applying a transfer bias to either the secondary transfer inner roller or the secondary transfer outer roller. By applying a positive bias to the secondary transfer outer roller, the toner charged to (−) is transferred from the intermediate transfer belt to the recording paper P.

  The secondary transfer outer roller 42 can be attached to and detached from the intermediate transfer belt 81. When the yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt, the secondary transfer outer roller 42 is in a detached state. When the full-color toner image on the transfer belt is transferred onto the recording paper P, it is in a wearing state.

  The recording paper P onto which the toner image has been transferred is conveyed to a fixing device and fixed on the recording paper by the fixing device.

  Here, the image forming apparatus of the present embodiment passes through the fixing device 14, that is, the sheet passing speed of the recording paper onto which the toner image has been transferred, that is, the fixing material 14 so that the image can be sufficiently fixed when the transfer material P is thick paper. The speed at this time is configured to be lower than the normal process speed (first process speed), and the speed of the photosensitive drum 1 and the intermediate transfer belt 5 is also reduced accordingly.

  At this time, all processes from charging to the photosensitive drum by the charger, developing by the developing unit, transfer from the photosensitive drum to the intermediate transfer belt, transfer from the intermediate transfer belt to the recording paper, and fixing operation are performed at a reduced process speed. The process from charging to the photosensitive drum, charging with the charger, development with the developer, transfer from the photosensitive drum to the intermediate transfer belt is performed at the normal process speed, and the process is performed immediately before the transfer from the intermediate transfer belt to the recording paper. In the latter case, it is not necessary to change the process from charging, development, and transfer of the toner image onto the intermediate transfer belt to the normal process speed conditions as the process speed is reduced. There are benefits.

  Residual toner remaining on the intermediate transfer belt 81 without being transferred to the recording paper in the secondary transfer portion is conveyed to the cleaning portion 8 by the rotation of the belt. The cleaning unit is arranged to face the belt stretching roller, and two fur brushes are arranged upstream and downstream in the belt conveyance direction.

  The cleaning unit 8 can also be attached to and detached from the intermediate transfer belt in the same manner as the secondary transfer outer roller 42, and is put on when the remaining toner on the intermediate transfer belt is conveyed to the cleaning unit 8.

  The fur brush used in this example is obtained by implanting conductive and fibrous hair on a φ8 conductive shaft, outer diameter: φ20, pile length: 6 mm, material: nylon, density: 100 kF, resistance: 5E + Two 6Ω ones were used.

  FIG. 4 is a diagram showing the fur brush cleaning unit 5 used in this embodiment. Metal bias rollers 52a and 52b are disposed downstream of the points of the fur brushes 51a and 51b that contact the belt stretching roller 50 so as to enter the fur brushes 51a and 51b. Further, scrapers 53 a and 53 b are pressed on the downstream side of the point of contact of the metal bias roller with the fur brush, the toner collected by the fur brush 51 is transferred to the metal roller 52, and the scraper 53 scrapes off the toner. Is dropped into a waste toner box (not shown). The fur brush rotates in the opposite direction (in the direction of arrow R5) at the position facing the belt, and the bias roller rotates in the same direction (in the direction of arrow R′5) at the position facing the fur brush. In the transfer of toner from the intermediate transfer belt to the fur brush, when +700 V is applied to the bias roller 52, a voltage of +600 V is induced in the fur brush 51, and a potential difference is generated between the grounded stretching roller 50 and the intermediate transfer. The toner on the belt 81 is transferred to the fur brush 51. Further, the toner collected by the fur brush 52 is transferred to the bias roller 52 due to a potential difference between the fur brush 51 and the bias roller 52.

  In the present embodiment, during normal image formation, a bias (−) is applied to the upstream bias roller 52a and a bias (+) is applied to the downstream bias roller 52b in the rotational direction of the intermediate transfer belt 81. That is, −700 V is applied to the upstream bias roller 52a.

  This is because the toner remaining on the intermediate transfer belt 81 after the completion of the secondary transfer may have both positive (+) polarity and negative (−) polarity, so the two fur brushes have different polarities. The bias is applied.

  FIG. 5 is a graph showing the voltage applied to the secondary transfer roller and the transfer efficiency at the secondary transfer portion in this embodiment. The dotted lines (1) and (2) in this graph indicate the transfer voltage when the transfer efficiency is 90%.

Transfer efficiency is << Transfer efficiency = toner amount transferred to recording paper / toner amount on intermediate transfer body before transfer × 100 (%) >>
Sought by. Although the voltages corresponding to the dotted lines (1) and (2) are different from 1.5 kV and 3.5 kV, respectively, the residual toner on the intermediate transfer member when the transfer voltage is set to 1.5 kV is mainly There are many (−) polar toners, and a large amount of (+) polar toner remains mainly at 3.5 kV. This occurs when the transfer voltage is insufficient with respect to the charge of the transferred toner when 1.5 kV is set, and when the transfer voltage is too high when the voltage is set to 3.5 kV, charge is injected into the toner, or charge jumps into the toner due to discharge. The polarity of the toner charge is reversed.

  For the above reason, two fur brushes and biases having different polarities are applied.

  Hereinafter, a method for controlling the bias applied to the cleaning fur brush of this embodiment will be described.

  As described in [Problems to be Solved by the Invention], the remaining toner cleaning means on the transfer belt used in this embodiment has different polarities of toner collected by the upstream and downstream fur brushes. For this reason, the method of smearing differs between the upstream and downstream fur brushes when there are many originals with a high original image density during image formation and when there are many thin originals. Therefore, the bias applied to the cleaning fur brush must be adjusted individually on the upstream side and the downstream side.

  Further, the cleaning bias in this embodiment is controlled by a constant voltage. The constant voltage control allows the fur brush to be partially soiled.If there is a difference in resistance in the longitudinal direction of the fur brush, or if there is residual transfer toner with a different image ratio in the longitudinal direction, the current can be set according to the resistance. Become.

  The cleaning current necessary for cleaning the transfer residual toner on the belt can be determined from the recoverability of the transfer residual toner when the cleaning current is applied as shown in FIG.

  The defective cleaning causes a problem that the transfer residual toner on the belt after the secondary transfer is not collected by the cleaning unit and slips through. Furthermore, there is a problem that the amount of toner that slips through is an amount that affects the image formation from the next time.

  Therefore, first, as shown in FIG. 6, a slip-through density (A in the figure) is set such that the toner amount that passes through the cleaning unit does not affect the image. By setting the cleaning current value to such a current value that the slip-through toner density is A or less, defective cleaning can be prevented. This appropriate current is set for each of the cleaning fur brushes as in this embodiment.

  In the bias control, when no paper is passed before image formation is performed, the cleaning bias is gradually changed for each fur brush, and the current value flowing into the opposite roller is detected. The voltage value is changed so that the detected current becomes the appropriate current obtained from the above. When a voltage value corresponding to an appropriate current is found, the voltage is used as a cleaning bias that is applied to the cleaning fur brush during image formation.

  For example, the appropriate current required for cleaning is 20 μA for the upstream fur brush, and −20 μA for the downstream fur brush. For an appropriate current of 20 μA, voltages of 300 V, 500 V, and 700 V are applied upstream as shown in FIG. When the current when these three voltages are applied is 10 μA, 14 μA, and 21 μA, several voltage is further applied between 600 to 700 V, and when the current is detected 20 μA, the voltage at that time is detected at the time of image formation. It is applied as a transfer belt cleaning voltage. After the upstream fur brush is adjusted, -300V, -500V, and -700V are sequentially applied to the downstream as well. The following control may be performed in the same manner as the upstream fur brush.

  According to the method proposed in the present embodiment, for example, even when a plurality of fur brushes cause image formation and the fur brush is unevenly stained, the cleaning bias corresponding to the appropriate current can be set. .

  The cleaning sequence of the present invention will be described (see FIG. 8).

  In this embodiment, the process speed is switched at a normal process speed for a recording paper of 105 g / cm ^ 2 or less in basis weight of the recording paper, and normally for a recording paper of 105 g / cm ^ 2 or more. It has control to switch to 1/2 of the process speed. However, since this depends on the ability of the fixing device, it is not limited to this.

  First, when the main body power is turned on, the intermediate transfer belt is rotated at a normal process speed. While the rotation is stable, the cleaning unit is switched from the detached state to the worn state. At that time, the cleaning unit performs the same operation as the normal cleaning operation, that is, rotates the fur brush and applies the cleaning bias. After that, as described above, the bias adjustment operation is started, 300V, 500V, and 700V voltages are applied to the upstream fur brush, and -300V, -500V, and -700V are sequentially applied to the downstream fur brush. Find the voltage value at which an appropriate current can be obtained.

  Conventionally, this operation is followed by a bias adjustment operation at a 1/2 process speed. Decrease the process speed of the intermediate transfer belt from the normal process speed to 1/2 speed. The cleaning unit is put on the belt after the rotation speed of the belt is stabilized. The fur brush rotation speed is also set to 1/2 speed with respect to the belt speed 1/2 speed, and the appropriate current at 1/2 speed is obtained by swinging the cleaning bias by 3 points in the same manner as above. Determine the voltage value to be obtained. Here, since the process speed is ½ slower than the normal process speed, the time is twice as long as the bias adjustment operation at the normal process speed. When the speed becomes 1/3 speed or 1/4 speed due to the capability of the fixing device, the time is 3 times or 4 times longer.

  Next, the user selects the type of recording paper used for the copy paper, and the copy button is pressed.

  Regardless of the type of recording paper, the process proceeds to the charging process, the developing process, and the transfer process from the photosensitive belt to the intermediate transfer belt for the photosensitive drum. When a color image is selected here, the above process is performed for four colors Y / M / C / K, and when the transfer of the final color to the intermediate transfer belt is completed, 4 steps are placed on the intermediate transfer belt. A color toner image is carried.

  Next, when the user selects a recording paper with a basis weight of 105 g / cm ^ 2 or less, the intermediate transfer belt and the recording paper can be transferred from the intermediate transfer belt to the recording paper without reducing the conveyance speed of the recording paper. Secondary transfer is performed, the recording paper is conveyed from the secondary transfer portion to the fixing portion, and the fixing process is completed. The secondary transfer residual toner remaining on the intermediate transfer belt in the secondary transfer unit is collected by a cleaning unit that is in contact with the intermediate transfer belt. As the bias to be applied, the cleaning bias determined by the bias adjustment operation is applied.

  Next, when the user selects a recording paper with a grammage of 105 g / cm ^ 2 or more by weight, when the transfer of the final color to the intermediate transfer belt is completed, the process speed of the intermediate transfer belt is increased. Decrease to 1/2 the normal process speed. After the decelerated belt speed is stabilized, the secondary transfer unit is put on the intermediate transfer belt, and the secondary transfer is performed on the recording paper at the decelerated process speed. The recording paper that has been subjected to the secondary transfer process is conveyed to the fixing unit at the same process speed, and the fixing process is completed. After that, the intermediate transfer belt, which has completed the secondary transfer process, returns to the normal process speed during the post-rotation process. The cleaning unit is attached to the intermediate transfer belt while the belt speed is stable, and the cleaning process is started. As the cleaning bias applied to the fur brush, the cleaning bias determined by the bias adjusting operation is applied as in the normal process speed.

  In the present invention, the process speed is reduced when the transfer process from the photosensitive drum to the intermediate transfer belt is completed. However, after the process is decelerated from the first charging process and the fixing process is completed, the process speed is reduced to the normal process. The same effect can be obtained when returning to speed and performing cleaning.

  According to the present invention, even when the process speed is switched, not only the cleaning conditions can be adjusted by performing the cleaning process at the normal process speed, but also the cleaning bias adjustment operation that must be performed for each process speed. Only the normal process speed is performed, and the cleaning performance is secured for the secondary transfer residual toner when the process speed changes. In addition, since it is not necessary to perform a bias adjustment operation for each process speed when adjusting the cleaning bias, it is possible to greatly reduce the adjustment time before the copy operation starts.

(Other examples)
In the first embodiment, the proposal has been described in which, even when the process speed is switched, the bias adjustment time can be shortened and the cleaning ability can be secured by performing the cleaning process at the normal process speed.

  In the second embodiment, a proposal corresponding to an image forming apparatus having a cleaning unit in which the cleaning fur brush does not have an attaching / detaching mechanism, that is, is always attached to the intermediate transfer belt will be described.

  An image forming apparatus having a cleaning fur brush that does not have an attaching / detaching mechanism, that is, a cleaning unit that is always attached to the intermediate transfer belt, mainly has a plurality of color image forming units attached to the intermediate transfer belt as shown in FIG. Used in a tandem type image forming apparatus arranged side by side. In this case, when the distance D from the secondary transfer portion to the cleaning portion is longer than the maximum image width in the belt rotation direction, and the residual secondary transfer is between the distance D even after the recording paper is fixed. After the transfer process from the photosensitive drum to the intermediate transfer belt, the process speed of the intermediate transfer belt is reduced, and after the secondary transfer is completed, that is, while the secondary transfer residual toner is between the distance D, the process speed is reduced. The same effect can be obtained if the cleaning process is performed after returning to the normal process speed.

  If the maximum image width in the belt rotation direction is longer than the distance D, the process speed is returned to the normal process speed at the end of the fixing operation, and the cleaning bias is applied with the belt rotation speed of the intermediate transfer belt being stable. Like that. In other words, since the secondary transfer residual toner immediately after the secondary transfer and the process speed is reduced cannot be cleaned with an appropriate cleaning bias, the normal process is performed by returning the belt to the normal belt speed and making another round. Cleaning can be performed at high speed and with an appropriate cleaning bias.

Simplified sectional view of the image forming apparatus of the present invention FIG. 4 is a simplified cross-sectional view showing an image forming unit of the image forming apparatus of the present invention Simplified sectional view showing the secondary transfer portion of the present invention Simplified sectional view showing the intermediate transfer belt cleaning means of the present invention The graph which showed the relationship between the transfer voltage and transfer efficiency in the secondary transfer part of the image forming apparatus of this invention The graph which showed the relationship between the cleaning current of the transfer belt cleaning used in the image forming apparatus of the present invention, and the slip-through density The figure which showed the application method of the cleaning bias of this invention Flowchart showing image forming operation of the present invention Schematic diagram of an image forming apparatus used in other embodiments

Claims (6)

A first image carrier and primary transfer means for transferring the toner image formed on the image carrier to the second image carrier by applying a bias having a polarity opposite to the charging polarity of the toner;
Secondary transfer means for transferring the toner image transferred onto the second image carrier to the recording material, and secondary transfer residual toner remaining on the second image carrier to collect the biases of different polarities. A plurality of second image carrier cleaning means having an adjustment function for adjusting the applied bias value, a normal image forming speed, and a plurality of image forming speeds different from the normal image forming speed. In the selectable image forming apparatus,
In the image forming apparatus, when cleaning is performed by the second image carrier cleaning means, if an image forming speed different from the normal image forming speed is selected, the image forming speed is returned to the normal image forming speed before the cleaning means. The image forming apparatus characterized in that the cleaning operation is performed with a bias value adjusted by the bias value adjusting function.   2. The image forming apparatus according to claim 1, wherein the bias value adjustment of the second image carrier cleaning means is performed at a normal image forming speed.   2. The image forming apparatus according to claim 1, wherein the image forming speed is selected based on a type of recording material.   2. The image forming apparatus according to claim 1, wherein the cleaning condition of the second image carrier cleaning means is a cleaning condition that is normally used at an image forming speed.   Even when an image forming speed different from the normal image forming speed is selected, the image forming apparatus is operated at the normal image forming speed at least until the operation of transferring the toner image to the second image carrier is completed. The image forming apparatus according to claim 1, wherein the image forming apparatus is operated.   In the image forming apparatus, when an image forming speed different from the normal image forming speed is selected, a part or all of the secondary transfer residual toner passes through the cleaning unit by the second cleaning unit at a different image forming speed. 2. The image forming apparatus according to claim 1, wherein the cleaning operation is performed again in a state in which at least a portion that has passed is returned to the normal image forming speed.

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