JP6053376B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic system.

  In recent years, image forming apparatuses employing an electrophotographic system have been increased in speed, function, and color, and various printers, copiers, and the like are on the market. One example is a tandem image forming apparatus. This is because a plurality of image forming units are arranged in parallel, different color toner images are formed on a photosensitive drum as an image carrier provided in each image forming unit, and the different color toner images are sequentially transferred to the transfer target. It is something that overlaps. Tandem image forming apparatuses are the mainstay of current color printers because they can form color images at high speed.

  Tandem type image forming apparatuses are classified into the following two types. One is a direct transfer method in which toner images of different colors are directly transferred onto a transfer material such as a recording sheet conveyed by a transfer belt. The other is an intermediate transfer method in which toner images of different colors are sequentially superimposed on an intermediate transfer member (intermediate transfer belt) and subjected to primary transfer, and then collectively transferred to a transfer material.

  As the transfer belt and the intermediate transfer belt (hereinafter, also simply referred to as “belt”), for example, an electronic conductive agent such as carbon black or an ionic conductive agent for adjusting the electric resistance value is added to the resin. A film-like member is used. In the case of using an electronic conductive agent, individual differences in electrical resistance values are likely to occur depending on the dispersion state during manufacture. On the other hand, in the case of using an ionic conductive agent, the amount of water contained varies due to variations in temperature and humidity where the image forming apparatus is used, and variations in electrical resistance values are likely to occur. Regardless of which material is used, controlling image forming conditions to absorb fluctuations in the electric resistance value of the belt is a problem in outputting a good image.

  In addition, regarding the electric resistance value of a transfer member such as a transfer roller provided to face the photosensitive drum of each image forming unit via a belt, the electric resistance value varies depending on individual differences during manufacture and the electric resistance depends on the degree of use. The resistance value may fluctuate. For this reason, controlling the image forming conditions in order to absorb the difference or fluctuation (hereinafter, also simply referred to as “fluctuation”) of the electrical resistance value is the same problem as described above.

  There is a so-called ATVC (Active Transfer Voltage Control) type transfer voltage control method in order to absorb such fluctuations in the electrical resistance value of the member in the transfer portion (Patent Document 1). In this method, a test voltage is applied to the transfer member, and a transfer voltage through which a desired current flows is set based on the voltage-current relationship.

  In recent years, not only speeding up image formation but also reducing the stress on the user, the time from when the image forming apparatus receives image data until it is printed out (First Print Out Time: hereinafter referred to as “FPOT”). ) Is being emphasized. From this viewpoint, the tandem method is advantageous. In addition, since shortening the FPOT can reduce the rotation time of various parts, shortening the FPOT is an important issue from the viewpoint of extending the service life.

  Furthermore, in recent years, even if the process cartridges that are replaceably attached to the image forming units have the same configuration, the setting of the number of printable pages can be changed by increasing the toner capacity. Are often sold. For example, a black process cartridge with a larger number of printable pages than usual is sold to users who print many monochrome documents. In such an image forming apparatus used by the user, there are few opportunities for color printing. Therefore, it is desired that the color image forming unit is not consumed unnecessarily during monochrome printing. Therefore, there is an image forming apparatus that includes a color mode in which the belt contacts all the photosensitive drums and a monochrome mode in which the belt is separated from some of the photosensitive drums (Patent Document 2).

JP 05-006112 A Japanese Patent Laying-Open No. 2005-062642

  In the conventional ATVC method, the image forming conditions are controlled by applying a test voltage to the transfer member in all image forming units, and the fluctuation of the electric resistance value of the transfer member is absorbed. However, this method is not desirable from the viewpoint of shortening the FPOT.

  Further, in the image forming apparatus having the color mode and the monochrome mode as described above, the consumption of parts for color printing is small. For this reason, there is a difference in the degree of wear between the color parts and the monochrome parts, which may cause a large difference in the characteristics. The electrical resistance value of the transfer member generally increases with an increase in usage amount. Therefore, for example, in an image forming apparatus used by a user who prints many monochrome documents as described above, the electrical resistance value of the color image transfer member and the electrical resistance value of the monochrome image transfer member are greatly different. Sometimes. In some cases, it is necessary to control the image forming conditions so as to absorb the fluctuation of the electric resistance value of the transfer member. In this case, it is conceivable to control the image forming conditions by applying a test voltage to the transfer member in all the image forming units to absorb the fluctuation of the electric resistance value of the transfer member. However, as described above, the FPOT is shortened. From the viewpoint of

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of controlling image forming conditions so as to absorb fluctuations in the electric resistance value of a member in a transfer portion while shortening the FPOT.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a movable intermediate transfer member, a first image carrier that is provided along the moving direction of the intermediate transfer member, and carries a toner image, and the moving direction of the intermediate transfer member. along provided, a second image bearing member for bearing a location toner image on the first downstream side of the image bearing member, a first developing means for supplying toner to said first image carrier A second developing means for supplying toner to the second image carrier, and a first voltage carrier applied to the first image carrier via the intermediate transfer member . A first transfer unit that transfers toner from the image carrier to the intermediate transfer member, a first voltage application unit that applies a voltage to the first transfer unit, and the second transfer unit via the intermediate transfer member. The second image carrier is arranged to face the intermediate member by applying a voltage. A second transfer means for transferring the toner to the transfer member, the second and the second voltage applying means for applying a voltage to the transfer means, the second constant current from the voltage applying means to said second transfer means Detecting means for detecting a voltage value when a controlled voltage is applied or a current value when a constant-voltage controlled voltage is applied , the first image carrier and the first When image formation for forming a toner image on both the image carrier and the second image carrier is started, toner image formation is started on the first image carrier on which toner image formation is first started. In the image forming apparatus in which a predetermined operation is performed before the detection, the detection by the detection unit is performed during a period at least partially overlapping with the predetermined operation on the first image carrier. Before the transfer by the transfer means 1 is started Based on a detection result of said detecting means, said a transfer voltage value second voltage applying means for applying, to have a control means for determining a transfer voltage value, both of which the first voltage applying means for applying An image forming apparatus characterized by the above.

According to another aspect of the present invention, a transfer material carrier that is movable while carrying a transfer material, and a first image carrier that is provided along the moving direction of the transfer material carrier and carries a toner image, A first image carrier that is provided along the moving direction of the transfer material carrier and is located downstream of the first image carrier and carries a toner image; and the first image carrier. A first developing means for supplying toner; a second developing means for supplying toner to the second image carrier; and the first image carrier facing the first image carrier via the transfer material carrier. The voltage is applied to the first transfer means for transferring the toner from the first image carrier to the transfer material carried on the transfer material carrier, and the voltage is applied to the first transfer means. first voltage applying means, disposed opposite to the second image bearing member via the transfer material carrying member A second transfer means for transferring toner from the second image carrier to a transfer material carried on the transfer material carrier by applying a pressure, and a second for applying a voltage to the second transfer means. and second voltage applying means, when the application of the voltage value or the constant-voltage-controlled voltage when the second voltage applying means applies a constant current control voltage to the second transfer means And detecting means for detecting a current value of the first and second toner images when starting image formation for forming a toner image on both the first image carrier and the second image carrier. In the image forming apparatus in which a predetermined operation is performed before the toner image formation is started with respect to the first image carrier on which the formation of the first image carrier is started. During the period when at least a part of the predetermined operation overlaps, The detection is executed, before the transfer by the first transfer means is started, based on a detection result of said detecting means, said a transfer voltage value second voltage applying means applies the first an image forming apparatus comprising: the transfer voltage value is a voltage applying means for applying, a control means for determining both is provided.

  According to the present invention, it is possible to control the image forming conditions so as to absorb the fluctuation of the electric resistance value of the member in the transfer portion while shortening the FPOT.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. It is a timing chart figure which shows the sequence of the development contact operation in one Example of this invention. FIG. 3 is a schematic diagram for explaining a contact / separation mechanism between a developing roller and a photosensitive drum in an embodiment of the present invention. It is a graph which shows the voltage sequence of ATVC control. FIG. 3 is a schematic circuit diagram of a primary transfer power source in an embodiment of the present invention. FIG. 3 is a block diagram illustrating a control mode of a main part of the image forming apparatus according to an embodiment of the present invention. (A) Timing chart for explaining the operation of each image forming apparatus when ATVC detection is performed even in the most upstream image forming unit, and (b) ATVC detection is performed only in the most downstream image forming unit. FIG. It is a graph which shows the voltage-current characteristic for every electric resistance value of a primary transfer roller. It is a schematic diagram of the measuring apparatus of the electrical resistance value of a primary transfer roller. It is a timing chart for demonstrating the operation | movement of ATVC control in one Example of this invention. FIG. 6 is a schematic cross-sectional view of an image forming apparatus for explaining an operation in a monochrome mode in an image forming apparatus according to another embodiment of the present invention. (A) It is a graph which shows the relationship between the number of printed sheets and the electrical resistance value of a primary transfer roller, and (b) the relationship between the number of printed sheets and the amount of change of an ATVC control result, respectively. It is a block diagram which shows the control aspect of the principal part of the image forming apparatus in the other Example of this invention. It is a flowchart figure of the control which selects the correction mode in the other Example of this invention. It is a graph for demonstrating the correction mode 1 in the other Example of this invention. It is a graph for demonstrating the correction mode 2 in the other Example of this invention. It is a graph for demonstrating the correction mode 3 in the other Example of this invention. FIG. 11 is a schematic cross-sectional view of a main part of an example of another image forming apparatus to which the present invention can be applied.

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

Example 1
1. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. In this embodiment, the image forming apparatus 100 is a tandem multi-color (color) image forming apparatus capable of forming a full-color image using an electrophotographic system.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (image forming stations) UY, UM, and UC that are disposed along the flat surface of the intermediate transfer belt 5 that is a transfer target. , Have UK. The first, second, third, and fourth image forming units UY, UM, UC, and UK use yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively. Thus, a toner image of each color is formed.

  In this embodiment, the configurations of the first, second, third, and fourth image forming units UY, UM, UC, and UK are substantially the same except that the color of the toner to be used is different. . Therefore, in the following, unless it is particularly necessary to distinguish, y, m, and the like at the end of the codes indicating the elements of the first, second, third, and fourth image forming units UY, UM, UC, and UK, respectively. The explanation will be made generically with c and k omitted. Further, hereinafter, when the elements of the first, second, third, and fourth image forming units UY, UM, UC, and UK are particularly distinguished and referred to, they correspond to the respective image forming units UY, UM, UC, and UK. "First", "second", "third", and "fourth" may be added.

  The image forming unit U is provided with a photosensitive drum 1 which is a cylindrical electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (100 mm / sec in this embodiment) in the direction of arrow a (clockwise) in the drawing.

  A charging roller (charging device) 2 that is a roller-shaped charging member as charging means is pressed against the surface of the photosensitive drum 1. The charging roller 2 rotates following the rotation of the photosensitive drum 1. The charging roller 2 is applied with a DC voltage or a vibration voltage obtained by superimposing the DC voltage and the AC voltage as a charging voltage (charging bias) from a charging power source (not shown) as a charging voltage applying unit. Thereby, the surface of the photosensitive drum 1 is charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment).

  The surface of the photosensitive drum 1 uniformly charged by the charging roller 2 is exposed in accordance with recorded image information by an image exposure unit 3 as an exposure unit (latent image forming unit). As a result, an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. Examples of the image exposure unit 3 include a laser beam scanner and an LED. In this embodiment, a laser beam scanner is used.

  The electrostatic latent image formed on the photosensitive drum 1 is developed by a developing device 4 as developing means. In this embodiment, the developing device 4 is a one-component nonmagnetic contact developing device. The developing device 4 transports toner, which is a non-magnetic one-component developer, and supplies the toner onto the surface of the photosensitive drum 1. The developing roller 41 serves as a developer carrying member, and development that supplies (applies) toner to the surface of the developing roller 41. A supply roller 42 as agent supply means is provided. In this embodiment, the intended charging polarity (normal charging polarity) of the toner for developing the electrostatic latent image on the photosensitive drum 1 is negative. In this embodiment, the toner is a polymerized toner produced by a polymerization method.

  The developing roller 41 whose surface is uniformly coated with toner is lightly pressed against the photosensitive drum 1. The developing roller 41 is rotationally driven with a speed difference with respect to the photosensitive drum 1 so that the moving direction of the photosensitive drum 1 and the developing roller 41 is the forward direction at the contact portion. A predetermined DC voltage is applied to the developing roller 41 as a developing voltage (developing bias) from a developing power source 43 as a developing voltage applying unit. Thereby, the electrostatic latent image on the photosensitive drum 1 is developed (visualized) as a toner image. The supply roller 42 is disposed in contact with the developing roller 41, and is rotationally driven so that the moving direction of the supply roller 42 and the developing roller 41 is opposite in the contact portion. The supply roller 42 supplies toner onto the developing roller 41 and removes toner that has not been used for development from the developing roller 41. In this embodiment, a toner image is formed by a combination of image exposure and reversal development. That is, the exposed portion on the photosensitive drum 1 where the absolute value of the potential is lowered by being exposed after being uniformly charged is charged to the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1. By attaching the toner, the electrostatic latent image is developed to form a toner image.

  In this embodiment, the one-component non-magnetic contact development method is adopted, but a non-contact one-component development method or a contact or non-contact two-component development method may be used.

  In this embodiment, the photosensitive drum 1 and the developing roller 41 can be separated from each other, and the developing roller 41 is brought into contact with the photosensitive drum 1 when necessary. Abutting / separating operation (hereinafter referred to as “developing contact operation”) of the developing roller 41 with the photosensitive drum 1 and a separating operation of the developing roller 41 from the photosensitive drum 1 (hereinafter referred to as “developing separation operation”). The mechanism will be further described later.

  In this embodiment, the photosensitive drum 1 and the developing roller 41 are adapted to the image formation of each of the image forming units UY, UM, UC, UK according to the operation sequence schematically shown in FIG. 2 in order to suppress toner deterioration as much as possible. A development contact operation and a development separation operation are sequentially performed. That is, for example, when forming a full-color image, first, a development contact operation is performed in the first image forming unit UY, and exposure and development are performed when the first development roller 41y is in contact with the first photosensitive drum 1y. Then, an image forming operation such as transfer is started. In the second image forming unit UM, the developing contact operation is performed with a distance between the image forming units delayed by a predetermined time corresponding to the time during which the transfer target moves, and the second developing roller 41m is moved to the second photosensitive member. When in contact with the drum 1m, image forming operations such as exposure, development and transfer are started. Similarly, in the third and fourth image forming units UC and UK, the image forming operation is started after the developing contact operation is sequentially performed with a delay of the predetermined time. The development separation operation after the end of image formation is also performed in order from the first image forming unit UY, similarly to the above-described development contact operation. The timing of the development contact operation and the like will be described in more detail later with reference to the transfer voltage control method.

  An endless belt-like intermediate transfer belt 5 as an intermediate transfer member is disposed so as to face the photosensitive drums 1y, 1m, 1c, and 1k of the image forming units UY, UM, UC, and UK. The intermediate transfer belt 5 is stretched around a drive roller 8, a support roller 9, and a secondary transfer counter roller 10 as support members. The drive roller 8 is rotationally driven in the direction of arrow b (counterclockwise) in the figure by being rotationally driven. On the inner peripheral surface side of the intermediate transfer belt 5, primary transfer rollers 6y, 6m, and 6c, which are roller-shaped transfer members serving as primary transfer means, are disposed at positions facing the photosensitive drums 1y, 1m, 1c, and 1k. , 6k are arranged. Each primary transfer roller 6 is pressed against each photosensitive drum 1 via the intermediate transfer belt 5 to form a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 5 and each photosensitive drum 1 abut. ing. The primary transfer roller 6 rotates following the rotation of the intermediate transfer belt 5. Further, on the outer peripheral surface side of the intermediate transfer belt 5, a secondary transfer roller 11 that is a roller-shaped transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 10. The secondary transfer roller 11 is pressed against the secondary transfer counter roller 10 via the intermediate transfer belt 5 and enters a secondary transfer portion (secondary transfer nip) N2 where the secondary transfer roller 11 and the intermediate transfer belt 5 come into contact. Forming.

  The toner image on the photosensitive drum 1 formed by the developing device 4 is conveyed to the primary transfer portion N1 by the rotation of the photosensitive drum 1 in the direction of arrow a in the figure. The intermediate transfer belt 5 is in contact with the photosensitive drum 1 and is driven to rotate in the direction of arrow b in the figure. The toner image that has reached the primary transfer portion N1 is transferred (primary transfer) to the surface of the intermediate transfer belt 5 by the primary transfer roller 6 that is pressed against the photosensitive drum 1 via the intermediate transfer belt 5. At this time, the primary transfer roller 6 is supplied with a DC having a polarity opposite to the normal charging polarity of the toner as a primary transfer voltage (primary transfer bias) from a primary transfer power source 7 as a primary transfer voltage application unit. A voltage is applied.

  The charged state of the photosensitive drum 1 after the primary transfer process is unstable due to the presence of a toner image and the influence of the primary transfer voltage. In this embodiment, the charged state of the photosensitive drum 1 is stabilized by irradiating the photosensitive drum 1y with light after the primary transfer process by a pre-charging exposure apparatus (not shown) using an LED or the like, and the subsequent charging. Uniform charging can be performed in the process.

  For example, at the time of forming a full-color image, toner images are formed on the photosensitive drum 1 sequentially in the first, second, third, and fourth image forming units UY, UM, UC, and UK. Then, the toner images formed on the photosensitive drums 1y, 1m, 1c, and 1k of the image forming units UY, UM, UC, and UK are sequentially superimposed on the intermediate transfer belt 5 and transferred (primary transfer). . As a result, a multiple toner image for a full color image is formed on the intermediate transfer belt 5.

  When the toner image on the intermediate transfer belt 5 reaches the secondary transfer portion N2, the toner image is transferred to the transfer material P fed from the paper feeding portion 12 to the secondary transfer portion N2 in time (secondary transfer). ) At this time, the secondary transfer roller 11 is supplied with a secondary transfer voltage (secondary transfer bias) from a secondary transfer power supply 13 as a secondary transfer voltage application unit, and has a polarity opposite to the normal charging polarity of the toner. A voltage is applied. The secondary transfer current generated when the secondary transfer voltage is applied from the secondary transfer power source 13 to the secondary transfer roller 11 is the secondary transfer roller 11, the transfer material P, the intermediate transfer belt 5, and the secondary transfer counter roller. The electric field necessary for the secondary transfer is formed by flowing through the 10 paths.

  The transfer material P onto which the toner image has been transferred is separated from the intermediate transfer belt 5 by the curvature of the secondary transfer counter roller 10, and is conveyed to a fixing device 14 as a fixing unit with the toner image placed thereon. The fixing device 14 includes a fixing sleeve 141 and a pressure roller 142. The fixing device 14 fixes the toner image on the transfer paper P by the action of heat and pressure by sandwiching and transporting the recording material P by the fixing sleeve 141 and the pressure roller 142.

  On the other hand, toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is cleaned by a cleaning device 15 as a photosensitive member cleaning unit. The cleaning device 15 has a cleaning blade 151 as a cleaning member and a waste toner container 152, removes primary transfer residual toner from the surface of the rotating photosensitive drum 1 by the cleaning blade 151, and collects it in the waste toner container 152. To do. Further, the toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 5 after the secondary transfer process is cleaned by a belt cleaning device 16 as an intermediate transfer member cleaning unit. The belt cleaning device 16 includes a cleaning blade 161 as a cleaning member and a waste toner container 162, removes secondary transfer residual toner from the surface of the rotating intermediate transfer belt 5 by the cleaning blade 161, and waste toner container 162. To recover.

  Here, in this embodiment, the primary transfer roller 6 is formed in a roller shape by forming an elastic layer in which carbon is dispersed in EPDM rubber to be conductive and foamed on a core metal. The electric resistance value of the primary transfer roller 6 will be described later.

  In this embodiment, a roller-shaped member is used as the primary transfer member, but a sheet-shaped member, a blade-shaped member, or a brush-shaped member can also be used.

In this embodiment, the drive roller 8, the support roller 9, and the secondary transfer counter roller 10 are electrically grounded. The electrical resistance value of the secondary transfer counter roller 10 is adjusted to 1 × 10 ⁶ [Ω] or less.

In this embodiment, the secondary transfer roller 11 is an elastic rubber roller similar to the primary transfer roller 6, but has an electric resistance value of 1 × 10 ⁷ to 1 × 10 ^{13 in} an environment of 23 ° C. and 50% RH. [Ω] is adjusted.

In this embodiment, the intermediate transfer belt 5 is of an ion conductive type. Specifically, PEN (polyethylene naphthalate) was used. In this embodiment, the intermediate transfer belt 5 is adjusted so that the volume resistivity is always 1 × 10 ¹⁰ [Ωcm] or more even when manufacturing tolerance / environmental variation is taken into consideration. In this embodiment, the thickness of the intermediate transfer belt 5 is 65 [μm].

  In addition, volume resistivity is the value measured by the method based on JIS-K6911 using Mitsubishi Chemical Corporation HirestaUP in the environment of 23 degreeC50% RH.

  As the intermediate transfer belt 5, a single-layer belt in which conductive particles are dispersed in resin or rubber and the electric resistance value is adjusted can be used. The intermediate transfer belt 5 may be a multi-layer belt in which a surface layer of a resin or rubber belt is coated with a fluororesin such as PTFE, PFA, or ETFE for improving releasability. Good.

  In this embodiment, in each image forming unit U, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the cleaning device 15 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge by a frame. Thus, the process cartridge 200 is configured. The process cartridge 200 is detachable from the main body (apparatus main body) of the image forming apparatus 100. For example, when the toner in the developing device 4 runs out, the process cartridge 200 is removed from the apparatus main body and replaced. In this embodiment, the intermediate transfer belt 5 is stretched around a driving roller 8, a support roller 9, and a secondary transfer counter roller 10 to constitute an intermediate transfer unit.

2. FIG. 3 shows an example of a contact / separation mechanism for changing the relative distance between the development roller 41 and the photosensitive drum 1 so that the development roller 41 contacts or separates from the photosensitive drum 1. Indicates.

  As shown in FIG. 3, in this embodiment, the process cartridge 200 includes a first frame 201 that supports the developing device 4, a second frame that supports the photosensitive drum 1, the charging roller 2, the cleaning device 15, and the like. And a body 202. The first frame 201 is coupled to the second frame 202 so as to be rotatable about a rotation shaft 203.

  As shown in FIG. 3A, the first frame 201 is moved by the biasing force of the compression coil spring 204 as the biasing means provided between the first frame 201 and the second frame 202. The developing roller 41 is brought into contact with the photosensitive drum 1 by rotating in the direction indicated by the arrow R1. In addition, the first frame body 201 is provided with a protrusion 205 as a drive receiving portion constituting a contact / separation mechanism, and the apparatus main body of the image forming apparatus 100 is provided with a cam 101 as a drive portion constituting a contact / separation mechanism. The cam 101 is driven by a cam drive motor 103 (FIG. 6) as a drive source constituting a contact / separation mechanism.

  Then, as shown in FIG. 3B, the protrusion 205 is pressed to the left in the drawing by the cam 101, thereby rotating the first frame 201 in the direction of the arrow R2 in the drawing, and the developing roller 41 is moved to the photosensitive drum. Separated from 1. The developing contact operation is an operation for changing the separated state shown in FIG. 3B to the contact state shown in FIG. On the other hand, the development separation operation is an operation for changing the contact state shown in FIG. 3A to the separation state shown in FIG.

  The contact / separation mechanism is not limited to the one in this embodiment, and for example, the relative distance from the photosensitive drum 1 may be changed by the movement of the developing roller 41 itself.

3. ATVC Control Next, a method for controlling the primary transfer voltage in this embodiment will be described.

  In this embodiment, the control of the primary transfer voltage is controlled by the ATVC so that the optimum voltage can be stably applied by correcting environmental fluctuations and uneven electrical resistance values of the intermediate transfer belt 5 and the primary transfer roller 6. Is adopted.

  ATVC control is a method of determining a primary transfer voltage during image formation according to a voltage sequence schematically shown in FIG. That is, when a non-image portion on the photosensitive drum 1 passes through the primary transfer portion N1 during a pre-rotation operation before image formation, the voltage applied to the primary transfer roller 6 is set to a preset value. Constant current control with. The fluctuation of the electric resistance value of the intermediate transfer belt 5 and / or the primary transfer roller 6 in the primary transfer portion N1 can be detected by the fluctuation of the generated voltage value at this time. Then, at the time of image formation, constant voltage control of the voltage applied to the primary transfer roller 6 is performed with the voltage value determined by calculating the previous generated voltage value. As the calculation processing, an average value of the generated voltage values is obtained, and further, the average value is multiplied by a predetermined coefficient. Hereinafter, the operation of detecting the generated voltage value in the ATVC control (that is, the operation of detecting information related to the electrical resistance value of the member in the transfer portion) is also simply referred to as “ATVC detection”.

  By such control, an overcurrent flowing to the photosensitive drum 1 in the primary transfer portion N1 is prevented, charging abnormality of the photosensitive drum 1 is suppressed, and an appropriate voltage can be applied during image formation. Therefore, it is possible to output a stable and good image.

  In this embodiment, a constant current control of 10 μA is performed over the time for which the primary transfer roller 6 makes one rotation at the time of the pre-rotation operation, the average value of the generated voltage values at this time is obtained, and the primary transfer voltage applied at the time of image formation. To decide.

  In this embodiment, development is performed so that the measurement of the generated voltage value is not affected by a change in the current value flowing through the photosensitive drum 1 at the primary transfer portion N1 due to toner adhering to the photosensitive drum 1. ATVC detection is performed in a state where the roller 41 and the photosensitive drum 1 are separated from each other.

  In addition, the following can be cited as non-image formation that can perform ATVC detection. There is a pre-multi-rotation operation before a predetermined preparatory operation is performed for raising the fixing temperature, such as when the image forming apparatus is turned on or returned from the sleep mode. In addition, there is a pre-rotation operation in which a predetermined preparation operation is executed from when an image forming signal is input to when an image corresponding to image information is actually written. In addition, there is a corresponding paper interval between recording materials during continuous image formation. Further, there is a post-rotation operation in which a predetermined organizing operation (preparation operation) is executed after the image formation is completed. In the present embodiment, ATVC detection is performed during the pre-rotation operation as during non-image formation.

4. Primary Transfer Power Supply Next, control of the primary transfer power supply (high voltage power supply) 7 in this embodiment will be described. In this embodiment, constant voltage control is adopted as control of the primary transfer voltage. FIG. 5 shows the primary transfer power source 7 and the high voltage control unit 17 for controlling it in the present embodiment.

  The primary transfer power source 7 includes a high-voltage primary-side output circuit 7a and a high-voltage secondary-side output circuit 7b including a current detection circuit as output current detection means.

  A positive voltage is applied to the primary transfer roller 6, and the voltage is output from the inverter transformer 71. The inverter transformer 71 is driven through the transistor 72 of the high-voltage primary side output circuit 7a by a pulse signal OSC from a high-voltage control unit (CPU) 17 as voltage control means driven by the power supply voltage V [V]. . The pulse signal OSC is rectified by the diode 73 and the capacitor 74 by the high-voltage secondary circuit 7 b of the inverter transformer 71 and applied to the primary transfer roller 6.

  In the high voltage controller 17, HVT IN is a D / A output of a DC level signal, and HVT OUT is an A / D input of a high voltage output. The DC level of the primary transfer output is proportional to the emitter voltage of the transistor 75. The output HVT IN from the high voltage controller 17 is amplified by the operational amplifier 78 and input to the base of the transistor 75. Accordingly, the transfer output voltage increases as HVT IN increases.

The output current at this time can be detected by the operational amplifier 76 based on a voltage drop caused by the electric resistance 77 (r [Ω]). The high voltage control unit 17 calculates the output current It from the output (HVT OUT) of the operational amplifier 76 by the following equation:
It [A] = (V−HVT OUT) [V] / r [Ω]
Calculate as By controlling the value of HVT IN (D / A) by the high voltage controller 17 based on the value of It [A], the constant voltage control of the primary transfer voltage in the ATVC control can be performed.

  That is, the high voltage control unit 17 controls the voltage applied to the primary transfer roller 6 by constant current control by controlling the value of HVT IN (D / A) so as to keep the value of It [A] constant. Can do. Further, the high voltage controller 17 can perform constant voltage control on the voltage applied to the primary transfer roller 6 by keeping the value of HVT IN (D / A) constant. That is, the high-voltage control unit 17 has a function as a current detection unit that detects It and a function as a voltage detection unit that detects a generated voltage value from HVT IN. In other words, the high voltage control unit 17 functions as a resistance detection unit that detects information related to the electrical resistance value of the member in the primary transfer unit N1 by detecting a voltage generated when a constant current is flowing. obtain. The CPU 121 of the control unit 102 described later determines the value of the primary transfer voltage to be applied to the primary transfer roller 6 by the high voltage control unit 17 during image formation from the generated voltage value detected by the high voltage control unit 17.

5. Next, a method of controlling the primary transfer voltage of each image forming unit UY, UM, UC, UK in the present embodiment will be described.

  One of the objects of this embodiment is to control the image forming conditions so as to absorb the fluctuation of the electrical resistance value of the member in the primary transfer portion N1 while shortening the FPOT so that a good image can be output. It is to be. More specifically, all primary image transfer units perform appropriate primary transfer with an appropriate primary transfer voltage while shortening FPOT as much as possible without performing ATVC detection in all of the multiple image formation units. It is possible to do.

  As described above, it is desirable that the photosensitive drum 1 and the developing roller 41 be separated from each other when the ATVC detection is performed in order to prevent the influence on the measurement due to the influence of the transfer current fluctuation due to the toner adhesion. In this case, the development contact operation cannot be started until the ATVC detection is completed, and image formation cannot be started.

  With reference to FIG. 7, an operation sequence at the start of image formation when performing ATVC detection and developing contact operation will be described.

  First, as a comparison with the present embodiment, when ATVC detection is performed in all the image forming units UY, UM, UC, and UK, image formation is started in a sequence schematically shown in FIG.

  When the image forming apparatus 100 receives a print signal, driving of the first to fourth photosensitive drums 1y, 1m, 1c, 1k and the intermediate transfer belt 5 is started. When the speeds of the first to fourth photosensitive drums 1y, 1m, 1c, and 1k and the intermediate transfer belt 5 reach predetermined values, ATVC detection is executed in each of the image forming units UY, UM, UC, and UK. When the ATVC detection is completed, the image is transferred from the first image forming unit UY arranged at the most upstream in the moving direction of the intermediate transfer belt 5 to the fourth image forming unit UK arranged at the most downstream in the moving direction. The developing contact operation is started with a predetermined time delay sequentially in accordance with the distance between the forming portions. When the development contact operation is completed in each of the image forming units UY, UM, UC, and UK, preparation for image formation is completed, and the image exposure unit 3 starts forming an electrostatic latent image.

  On the other hand, in this embodiment, image formation is started in the sequence schematically shown in FIG.

  In the present embodiment, ATVC detection is performed using only the fourth image forming unit UK which is an image forming unit whose development contact operation is started at the latest timing, and all image forming units UY are used using the detection result. , UM, UC, and UK, the primary transfer voltage is determined. In this embodiment, the developing contact operation is performed in the first image forming unit UY in parallel with the ATVC detection in the fourth image forming unit UK, that is, in a period in which at least a part of them overlaps.

  When the image forming apparatus 100 receives a print signal, driving of the first to fourth photosensitive drums 1y, 1m, 1c, 1k and the intermediate transfer belt 5 is started. When the speeds of the first to fourth photosensitive drums 1y, 1m, 1c, and 1k and the intermediate transfer belt 5 reach predetermined values, ATVC detection is executed in the fourth image forming unit UK. Further, in parallel with the ATVC detection in the fourth image forming unit UK, the developing contact operation is performed in the first image forming unit UY. When the development contact operation of the first image forming unit UY is completed, preparation for image formation is completed, and formation of an electrostatic latent image is started by the image exposure unit 3 in the first image forming unit UY. Also in the second and third image forming units UM and UC, the development contact operation is started with a predetermined time delay sequentially in accordance with the distance between the image forming units. In the present embodiment, the developing contact operation is also performed in the second and third image forming units UM and UC in parallel with the ATVC detection in the fourth image forming unit UK. In the second and third image forming units UM and UC, when the development contact operation is completed in each of the image forming units UM and UC, image formation preparation is completed, and the image exposure unit 3 performs the electrostatic latent image. The formation of is started. Further, in the fourth image forming unit UK, the ATVC detection is completed by a predetermined time delay according to the distance between the image forming units from the start of the development contact operation in the third image forming unit UC. Thereafter, the development contact operation is started. In the fourth image forming unit UK, when the development contact operation is completed, the image formation preparation is completed, and the image exposure unit 3 starts forming an electrostatic latent image.

  Thus, in this embodiment, there is no need to delay the start of image formation in order to execute ATVC detection. In addition, since the ATVC detection can be executed in a state where the developing roller 41 is separated from the photosensitive drum 1, the influence on the measurement due to the influence of the transfer current fluctuation due to the toner adhesion can be prevented.

  Comparing FIGS. 7A and 7B, it can be seen that the present embodiment can advance the image formation start timing earlier and is advantageous in shortening the FPOT.

  As described above, the primary transfer voltage applied to the fourth primary transfer roller 6k can be determined.

  Next, a method for determining the primary transfer voltage to be applied to the first, second, and third primary transfer rollers 6y, 6m, and 6c in which ATVC detection is not performed will be described.

FIG. 8 shows the voltage-current characteristics in the primary transfer portion N1 for each electrical resistance value of the primary transfer roller 6. Here, the voltage-current characteristics shown in FIG. 8 are obtained when an intermediate transfer belt 5 having a volume resistivity of 1 × 10 ¹⁰ [Ωcm] in an environment of 23 ° C. and 50% RH is used.

The electrical resistance value of the primary transfer roller 6 is a value measured in an environment of 23 ° C. and 50% RH using a measuring apparatus as shown in FIG. The measurement conditions of the primary transfer roller 6 are as follows.
Load applied to both ends of the primary transfer roller: 4.9 [N] × 2
Counter electrode outer diameter: Φ30 [mm]
Counter electrode rotation speed: 30 [rpm]
Input voltage: 10 [V]
Detection resistance: 1 [kΩ]

The electric resistance value of the primary transfer roller 6 is obtained by the following equation from the potential difference v [V] generated at both ends of the input voltage and the detection resistor.
Electrical resistance value of primary transfer roller [Ω] = 10 [V] / (v [V] / 1 [kΩ])

  Note that the electrical resistance value of the secondary transfer roller 11 is also measured under the same conditions using the measuring device.

As can be seen from FIG. 8, if the electrical resistance value R1 of the primary transfer roller 6 is lower than 1 × 10 ⁶ [Ω], the voltage-current characteristics are substantially the same regardless of the electrical resistance value R1 of the primary transfer roller 6. is there.

  This is because when the electrical resistance value R1 of the primary transfer roller 6 is sufficiently lower than the electrical resistance value R2 of the intermediate transfer belt 5, the electrical resistance value R2 of the intermediate transfer belt 5 becomes dominant. This is because the electrical resistance value R1 does not affect the voltage-current characteristics. That is, when the electrical resistance value R1 of the primary transfer roller 6 is sufficiently lower than the electrical resistance value R2 of the intermediate transfer belt 5, it is necessary to change the primary transfer voltage according to the electrical resistance value R1 of the primary transfer roller 6. It shows no.

  Here, the electrical resistance value R1 of the primary transfer roller and the electrical resistance value R2 of the intermediate transfer belt 5 will be compared.

In this embodiment, the volume resistivity of the intermediate transfer belt 5 is 1 × 10 ¹⁰ [Ωcm] or more and the thickness is 65 [μm]. In this embodiment, the width (contact width) of the region where the intermediate transfer belt 5 and the primary transfer roller 6 are in contact with each other in the direction orthogonal to the moving direction of the intermediate transfer belt 5 is 216 [mm]. . In this embodiment, the width (nip width) of the region where the intermediate transfer belt 5 and the primary transfer roller 6 are in contact with each other in the moving direction of the intermediate transfer belt 5 is 0.3 [mm].

From the above conditions, the electric resistance value (actual resistance) R2 of the intermediate transfer belt 5 is 1 × 10 ⁸ [Ω] or more.

The electric resistance value (actual resistance) of the intermediate transfer belt 5 is obtained using the following equation.
Electrical resistance of the intermediate transfer belt [Ω]
= (Volume resistivity [Ωcm] × Thickness [μm]) ÷ (Contact width [mm] × Nip width [mm])
= (Volume resistivity [Ωcm] × Thickness [μm]) ÷ (Contact area with primary transfer member [mm ² ])

  The electric resistance R1 of the primary transfer roller 6 and the electric resistance R2 of the intermediate transfer belt 5 are applied to the primary transfer voltage, and the primary transfer is related to the current flowing through the photosensitive drum 1 in the primary transfer portion N1. This represents the electrical resistance of the portion N1.

  From the above, if the ratio (R2 ÷ R1) between the electric resistance value R2 of the intermediate transfer belt 5 and the electric resistance value R1 of the primary transfer roller 6 is 100 or more, it corresponds to the electric resistance value of the primary transfer roller 6. It can be said that there is no need to change the primary transfer voltage.

In this embodiment, the intermediate transfer belt 5 having a volume resistivity of 1 × 10 ¹⁰ [Ωcm] or more is used. However, an intermediate transfer belt 5 having a different volume resistivity may be used. Even in this case, as long as the ratio (R2 ÷ R1) between the electrical resistance value R2 of the intermediate transfer belt 5 and the electrical resistance value R1 of the primary transfer roller 6 is 100 or more, the electrical resistance of the primary transfer roller 6 is the same as described above. It can be said that there is no need to change the primary transfer voltage in accordance with the value R1. For example, when an intermediate transfer belt 5 having a volume resistivity of 1 × 10 ⁸ [Ωcm] or more (thickness, contact area with the primary transfer member is the same as in this embodiment), the primary transfer roller is used. 6 may have an electrical resistance value lower than 1 × 10 ⁴ [Ω].

  Conversely, when the electrical resistance value R1 of the primary transfer roller 6 is high, it is necessary to determine the primary transfer voltage in consideration of variations in the electrical resistance value R1 of the primary transfer roller 6 due to manufacturing tolerances. It is necessary to execute ATVC for the primary transfer roller 6. In this case, as a matter of course, since it is necessary to execute ATVC detection also for the image forming unit located at the uppermost stream, the start of image formation is delayed as described above, and the FPOT becomes long.

  On the other hand, the electrical resistance value R2 of the intermediate transfer belt 5 is easily affected by the atmospheric environment and the temperature rise in the apparatus, particularly when the conductive form is ionic conductivity as in the present embodiment, and depending on the situation. It is necessary to correct the primary transfer voltage.

Therefore, in this embodiment, the electric resistance value R1 of the first to fourth primary transfer rollers 6y, 6m, 6c, and 6k is set to 1 × 10 ⁶ [Ω] or less, and the electric resistance value R2 of the intermediate transfer belt 5 is The ratio (R2 ÷ R1) with the electric resistance value R1 of the primary transfer roller 6 is 100 or more.

  This eliminates the need to change the primary transfer voltage in accordance with the electrical resistance value R1 of the primary transfer roller 6. Therefore, the primary transfer voltage having the same value as the primary transfer voltage applied to the fourth primary transfer roller 6k determined by the ATVC detection is also applied to the first to third primary transfer rollers 6y, 6m, and 6c. Can be applied.

  The ATVC control result in this case, that is, the determined value of the primary transfer voltage applied to the fourth primary transfer roller 6k is not affected by the electric resistance value of the fourth primary transfer roller 6k. However, it reflects the electric resistance value of the intermediate transfer belt 5 and absorbs the fluctuation.

  As described above, even if ATVC detection is performed by only one image forming unit, it is possible to control the primary transfer voltage in all the image forming units with high accuracy.

6). Control Mode FIG. 6 shows a schematic control mode of the main part of the image forming apparatus 100 of this embodiment. The operation of the image forming apparatus 100 is comprehensively controlled by a CPU 121 as a control unit provided in a control unit (control circuit) 102 provided in the image forming apparatus 100. The CPU 121 controls the operation of each unit of the image forming apparatus 100 in accordance with a program or data stored in the ROM 122 as a storage unit and read out to the RAM 123 as necessary.

  For example, in relation to this embodiment, the CPU 121 controls ON / OFF and output values of the primary transfer power supplies 7y, 7m, 7c, and 7k via the high-voltage control unit 17. Further, the CPU 121 controls the cam drive motors 103y, 103m, 103c, and 103k that constitute the contact / separation mechanism between the developing roller 41 and the photosensitive drum 1, and controls the ON / OFF and rotation amount of the cams 101y, 101m, 101c, Control the rotation of 101k. In addition, although not limited thereto, the CPU 121 turns on the drum drive motors 104y, 104m, 104c, and 104k as drive means for the respective photosensitive drums 1 and the belt drive motor 105 as drive means for the intermediate transfer belt 5. / OFF, drive speed, etc. are controlled.

  In this embodiment, the CPU 121 functions as an execution unit that executes ATVC detection as described above. Further, the CPU 121 determines the primary transfer voltage applied to the fourth primary transfer roller 6k and the primary transfer voltages applied to the first to third primary transfer rollers 6y, 6m, and 6c as described above. Functions as a decision means.

  Next, the operation of the ATVC control in the present embodiment will be described in more detail with reference to FIG.

  When the image forming apparatus 100 receives the print signal, the first to fourth photosensitive drums 1y, 1m, 1c, and 1k and the intermediate transfer belt 5 start to rotate. When the speeds of the first to fourth photosensitive drums 1y, 1m, 1c, and 1k reach predetermined values, the development contact operation is started. As described above, the development contact operation is sequentially delayed by a predetermined time according to the interval between the image forming units, in the order of the first, second, third, and fourth image forming units UY, UM, UC, and UK. Done in

  When the developing contact operation in the first image forming unit UY is completed, preparation for image formation is completed, and in the first image forming unit UY, formation of an electrostatic latent image is started by the image exposure unit 3y.

  On the other hand, in the primary transfer unit N1k of the fourth image forming unit UK, when the speeds of the first to fourth photosensitive drums 1y, 1m, 1c, 1k and the intermediate transfer belt 5 reach predetermined values, ATVC detection is performed. Done. Thereby, the primary transfer voltage VK to be applied to the fourth primary transfer roller 6k is determined.

  The ATVC detection in the fourth image forming unit UK and the determination of the primary transfer voltage based on the detection result are performed by developing the electrostatic latent image formed by the image exposure unit 3y in the first image forming unit UY. The process ends before reaching the primary transfer portion N1y of the image forming unit UY. In the first image forming unit UY, the primary transfer voltage is applied to the first primary transfer roller 6y in accordance with the timing. At this time, the primary transfer voltage applied to the first primary transfer roller 6y is the same value as the primary transfer voltage VK determined by the ATVC detection in the fourth image forming unit UK.

  In other words, in the present embodiment, a common predetermined operation at the time of image formation is sequentially started from the most upstream image forming unit UY to the most downstream image forming unit UK in the moving direction among the plurality of image forming units U. It has become. In this embodiment, the predetermined operation is an operation in which the developing means 4 that is separated from the image carrier 1 is brought into contact with the image carrier 1. Then, the CPU 121 as an execution unit causes the detection unit 17 to perform the ATVC detection during a period at least partially overlapping with the predetermined operation in the most upstream image forming unit UY. In this embodiment, the CPU 121 as the determining unit determines the transfer voltage value of the most upstream image forming unit UY before the transfer is started in the most upstream image forming unit UY.

  Thereafter, the primary transfer voltage is also applied to the second and third primary transfer rollers 6m and 6c with a predetermined time delay sequentially in accordance with the interval between the image forming units. The primary transfer voltage applied at this time is also the same value as the primary transfer voltage VK determined by the ATVC detection in the fourth image forming unit UK.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment includes the movable intermediate transfer member 5 and the plurality of image forming units UY, UM, UC, and UK provided along the moving direction of the intermediate transfer member 5. Have Each image forming unit U includes an image carrier 1 and a developing unit 4 that supplies toner to the image carrier 1. Each image forming unit U is arranged to face the image carrier 1 through the intermediate transfer member 5 and is applied with a voltage to transfer toner 6 from the image carrier 1 to the intermediate transfer member 5. And voltage applying means 7 for applying a voltage to the transfer means 6. The image forming apparatus 100 further applies a voltage value or a constant voltage controlled voltage when a constant current controlled voltage is applied from the voltage applying unit 7 to the transfer unit 6 in the specific image forming unit U. Detection means 17 for detecting the current value at the time. The specific image forming unit U is a detection execution image forming unit UK which is at least one image forming unit other than the most upstream image forming unit in the moving direction among the plurality of image forming units UY, UM, UC, UK. is there. In this embodiment, there is one detection execution image forming unit, but there may be two or more. When there are a plurality of detection execution image forming units, detection may be executed by any one of them, or may be executed by a plurality, as desired. When detection is performed by a plurality of detection execution image forming units, for example, the obtained detection results can be used after being subjected to statistical processing such as averaging. Further, the image forming apparatus 100 includes an execution unit that executes detection by the detection unit 17. The image forming apparatus 100 determines the transfer voltage value in the detection execution image forming unit UK and the transfer voltage value in the non-detection execution image forming units UY, UM, UC based on the detection result of the detection unit 17. A determination means for determining; Here, the transfer voltage is a voltage value applied from the voltage application unit to the transfer unit for transfer. The detection non-execution image forming units UY, UM, and UC are at least one image forming unit upstream of the detection execution image forming unit UK in the moving direction. In this embodiment, the CPU 121 functions as the execution unit and the determination unit.

  In this embodiment, both the detection execution image forming unit and the detection non-execution image formation unit provide the transfer unit 6 with an electric current that is applied to a transfer current value flowing between the transfer unit 6 and the image carrier 1 during transfer. The electric resistance value of the transfer means 6 is set sufficiently low so that the influence of the resistance value fluctuation can be ignored. Then, the determination unit 121 determines the value determined as the transfer voltage value of the detection execution image forming unit UK as the transfer voltage value of the detection non-execution image formation units UY, UM, and UC.

  As described above, the primary transfer voltage can be controlled so as to absorb the influence of the fluctuation of the electric resistance value of the intermediate transfer belt 5 while shortening the FPOT, and a good image can be output. Therefore, according to the present exemplary embodiment, it is possible to control the image forming condition so as to absorb the fluctuation of the electric resistance value of the member in the transfer portion while shortening the FPOT.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, in the image forming apparatus of the present embodiment, the same or equivalent elements as those of the image forming apparatus of Embodiment 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, an image forming apparatus 100 for a user who prints many monochrome prints will be described.

In this embodiment, as in the first embodiment, the intermediate transfer belt 5 is adjusted so that the volume resistivity is always 1 × 10 ¹⁰ [Ωcm] or more even when manufacturing tolerances / environmental fluctuations are taken into consideration. In this embodiment, the thickness of the intermediate transfer belt 5 is 65 [μm].

In this embodiment, the electric resistance values of the first to fourth primary transfer rollers 6y, 6m, 6c, and 6k are adjusted to 1 × 10 ⁵ [Ω] in the unused state.

  In this embodiment, the image forming apparatus 100 can execute a color mode (first image forming mode) and a monochrome mode (second image forming mode). In the color mode, image formation is performed in all of the first to fourth image forming units UY, UM, UC, and UK, and in the monochrome mode, image formation is performed only in the fourth image forming unit UK. That is, the number of image forming units that perform image formation among the first to fourth image forming units UY, UM, UC, and UK differs between the color mode and the monochrome mode. The first to third image forming units UY, UM, and UC form an image only in the color mode, but the fourth image forming unit UK forms an image in both the color mode and the monochrome mode.

  First, the operation in the monochrome mode will be described. In the monochrome mode, as shown in FIG. 11, the first to third primary transfer rollers 6y, 6m, 6c and the first to third photosensitive drums 1y are moved by a primary transfer roller separating means (not shown). The first primary transfer roller 6k and the fourth photosensitive drum 1k are in contact with each other. At this time, the first to third primary transfer rollers 6y, 6m, 6c, the first to third photosensitive drums 1y, 1m, 1c, and the first to third developing rollers 41y, 41m, 41c are driven. It is stationary. The first to third developing rollers 41y, 41m, and 41c are separated from the first to third photosensitive drums 1y, 1m, and 1c (FIG. 11 schematically shows the separated state. The contact / separation mechanism is the same as in the first embodiment.) Basic image forming operations such as charging, exposure, development, primary transfer, and secondary transfer of the toner image from the intermediate transfer belt 5 to the transfer material P in the fourth image forming unit UK are the same as in the first embodiment. Same as described.

  As a result, the elements for color printing in the mono color mode, that is, the elements of the first to third image forming units UY, UM, UC such as the first to third primary transfer rollers 6y, 6m, 6c are consumed. Can be prevented.

  On the other hand, in the color mode, as shown in FIG. 1, the first to fourth primary transfer rollers 6y, 6m, 6c, and 6k and the first to first primary transfer rollers 6y, 6m, 6c, and 6k are separated by a primary transfer roller separating means (not shown). The four photosensitive drums 1y, 1m, 1c, and 1k are brought into contact with each other. Basic image forming operations such as a developing contact operation in the color mode are the same as those in the first embodiment.

  FIG. 12A shows the relationship between the number of printed sheets and the electrical resistance value of the primary transfer roller 6. As can be seen from FIG. 12A, the electrical resistance value of the primary transfer roller 6 generally increases as the number of printed sheets increases.

  By the way, in the image forming apparatus in which the first to third primary transfer rollers 6y, 6m, and 6c and the first to third photosensitive drums 1y, 1m, and 1c are separated in the monochrome mode, the first to third primary transfer rollers 6y, 6m, and 6c are separated from each other. The primary transfer rollers 6y, 6m, and 6c are used only in the color mode. That is, the first to third primary transfer rollers 6y, 6m, and 6c are not used in the monochrome mode. On the other hand, the fourth primary transfer roller 6k is used in both the color mode and the monochrome mode.

  Accordingly, in the image forming apparatus 100 of a user who uses a lot of monochrome printing, the first to third primary transfer rollers 6y, 6m, 6c and the fourth primary transfer roller 6k are used between the number of printed sheets. Large differences can occur. That is, the electrical resistance values of the first to third primary transfer rollers 6y, 6m, and 6c may be greatly different from the electrical resistance value of the fourth primary transfer roller 6k.

In particular, when the number of printed sheets increases and the electric resistance value of the fourth primary transfer roller 6k exceeds 1 × 10 ⁶ [Ω], the primary transfer voltage control method similar to the first embodiment is as follows: An appropriate primary transfer voltage may not be applied in the first to third image forming units UY, UM, and UC. That is, the same value as the primary transfer voltage applied to the fourth primary transfer roller 6k cannot be applied to the first to third primary transfer rollers 6y, 6m, and 6c.

  In this case, it is conceivable that the ATVC detection is also executed in the first to third image forming units UY, UM, and UC. However, as described in the first embodiment, this delays the start of image formation and causes the FPOT to occur. It will be long.

  One of the purposes of this embodiment is that even if the electrical resistance values of the first to third primary transfer rollers 6y, 6m, and 6c and the electrical resistance value of the primary transfer roller 6k are greatly different, FPOT The primary transfer voltage applied to each primary transfer roller 6 is appropriately determined while shortening the above.

  Therefore, in this embodiment, the ATVC control result by the ATVC detection performed using the fourth primary transfer roller 6k, that is, the determined value of the primary transfer voltage applied to the fourth primary transfer member 6k. Add corrections. Thereby, the value of the primary transfer voltage applied to the first to third primary transfer rollers 6y, 6m, and 6c is determined. The correction is performed based on the usage history information of the first to third primary transfer rollers 6y, 6m, and 6c and the usage history information of the fourth primary transfer roller 6k.

  That is, as will be described in detail later, based on the usage history information of the fourth primary transfer roller 6k, the influence due to the increase in the electrical resistance value of the fourth primary transfer roller 6k included in the ATVC control result is calculated. Predict. Then, a value obtained by subtracting the influence is set as a value of the primary transfer voltage applied to the first to third primary transfer rollers 6y, 6m, and 6c.

  Thus, the primary transfer voltage applied to the first to third primary transfer rollers 6y, 6m, and 6c is determined without being affected by the increase in the electric resistance value of the fourth primary transfer roller 6k. Can do.

More specifically, in the image forming apparatus 100 of this embodiment, the relationship between the number of printed sheets and the electrical resistance value of the primary transfer roller 6 is as shown in FIG. As can be seen from FIG. 12A, when 50000 sheets are printed, the electrical resistance value of the primary transfer roller 6 becomes 1 × 10 ⁶ [Ω] or more.

  At this time, when the electric resistance value of the intermediate transfer belt 5 is fixed and the amount of change in the ATVC control result with the increase in the electric resistance value of the primary transfer roller 6 is measured, the result shown in FIG. 12B is obtained. It was.

The results shown in FIGS. 12A and 12B show that the voltage-current characteristics were not changed when the electrical resistance value of the primary transfer roller 6 in Example 1 was 1 × 10 ⁶ [Ω] or less. (FIG. 8).

In this embodiment, the primary transfer voltage was corrected by performing the following case classification based on the examination results of FIGS. 12 (a) and 12 (b).
(1) When the total number of printed sheets (T) is less than 50000 (correction mode 1)
(2) When the total number of printed sheets (T) is 50000 sheets or more and the number of printed sheets in color mode (F) is less than 50000 sheets (correction mode 2)
(3) When the number of printed sheets (F) in the color mode is 50000 or more (correction mode 3)

  The results shown in FIGS. 12A and 12B differ depending on the atmosphere environment in which the image forming apparatus 100 is used. Therefore, the results corresponding to FIGS. 12A and 12B are obtained in advance for each atmosphere environment, and the results shown in FIG. 12A are used based on the results of the environment sensor 106 (FIG. 13) as the atmosphere environment detection means. , (B) can be selected. In this embodiment, an example in an environment of 23 ° C. and 50% RH will be described.

  FIG. 13 shows a schematic control mode of the main part of the image forming apparatus 100 of the present embodiment. The control mode in the present embodiment is the same as that in the first embodiment shown in FIG. 6, but in this embodiment, an environmental sensor 106 is provided. Detection information of the environmental sensor 106 is input to the CPU 121. The CPU 121 can obtain information on the absolute water content and the relative humidity from the detection result of the environmental sensor 106. Further, the ROM 122 has information indicating the relationship between the number of printed sheets corresponding to FIGS. 12A and 12B and the electrical resistance value of the primary transfer roller 6 which are obtained in advance for each absolute moisture amount and relative humidity. Information indicating the relationship between the number of printed sheets and the amount of change in the ATVC detection result is stored. Then, the CPU 121 can select and use the corresponding information from the information stored in the ROM 122 according to the obtained information on the absolute water content and the relative humidity. The environmental sensor 106 may be a temperature / humidity sensor that detects temperature and humidity, or a humidity sensor that detects humidity.

  In this embodiment, a counter 107 serving as a storage device is provided as a counting unit that counts the number of printed sheets in each of the color mode and the monochrome mode. The CPU 121 can read the count result of the counter 107. Thereby, the CPU 121 can detect the number of printed sheets as information (usage history information) correlated with the usage amounts of the first to fourth primary transfer rollers 6y, 6m, 6c, and 6k.

  Next, the operation of ATVC control in the present embodiment will be described in more detail.

  Since basic operations such as the developing contact operation and the ATVC detection timing in this embodiment are the same as those in the first embodiment, detailed description thereof will be omitted.

  In the present embodiment, the following information is sequentially stored in the counter 107 in order to obtain a difference in usage amount between the first to third primary transfer rollers 6y, 6m, 6c and the fourth primary transfer roller 6k. First, information on the number of sheets printed in the color mode (color printing number) F [sheets]. Further, it is information on the number of printed sheets (total number of printed sheets) T [sheets] in the color mode and the monochrome mode. The CPU 121 uses the information stored in the counter 107 to correct the primary transfer voltage.

  Note that the number of sheets printed in the monochrome mode (number of monochrome prints) is TF [sheets]. The CPU 121 obtains the number of printed sheets from the information stored in the counter 107 in the monochrome mode.

  First, the CPU 121 determines the primary transfer voltage VK to be applied to the fourth primary transfer roller 6k by performing ATVC detection in the same procedure as in the first embodiment.

  Next, the CPU 121 calls up information on the color print number F [sheets] and the total print number T [sheets] from the counter 107.

  Based on this information, the CPU 121 selects a correction mode according to the flowchart shown in FIG. 14 and determines primary transfer voltages to be applied to the first to third primary transfer rollers 6y, 6m, and 6c.

  The relationship between the number of printed sheets and the electrical resistance value of the primary transfer roller 6 shown in FIGS. 15, 16 and 17 used in the following description, and the relationship between the number of printed sheets and the amount of change in the ATVC detection result are shown in FIG. It is the same as shown in.

-Correction mode 1 (when the total number of printed sheets (T) is less than 50000)
The correction mode 1 will be described with reference to FIG. In this case, the electrical resistance values of both the first to third primary transfer rollers 6y, 6m, 6c and the fourth primary transfer roller 6k are 1 × 10 ⁶ [Ω] or less. Therefore, as described in the first embodiment, the primary transfer voltage having the same value can be used in both of them. Accordingly, in this case, the CPU 121 does not correct the value of the primary transfer voltage applied to the determined fourth primary transfer roller 6k, but applies to the first to third primary transfer rollers 6y, 6m, and 6c. The value is determined as the value of the primary transfer voltage to be applied. That is, in this case, the same primary transfer voltage VK as the primary transfer voltage applied to the fourth primary transfer roller 6k is applied to the first to third primary transfer rollers 6y, 6m, and 6c. (The correction amount is zero).

Correction mode 2 (when the total number of printed sheets (T) is 50000 sheets or more and the number of printed sheets (F) in the color mode is less than 50000 sheets)
The correction mode 2 will be described with reference to FIG. In this case, the first to third primary transfer roller 6y, 6 m, the electric resistance value of 6c is 1 × 10 ⁶ [Ω] or less, the electric resistance value of the fourth primary transfer roller 6k is 1 × 10 ⁶ [ Ω] or more. Therefore, the ATVC control result by the ATVC detection performed using the fourth primary transfer roller 6k, that is, the determined value of the primary transfer voltage applied to the fourth primary transfer member 6k is the fourth 1 This is influenced by the increase in the electric resistance value of the next transfer roller 6k. Accordingly, the ATVC control result in this case becomes the value of the primary transfer voltage to which the change amount A in FIG. 16 is added.

  On the other hand, the primary transfer voltage applied to the first to third primary transfer rollers 6y, 6m, and 6c does not need to be affected by the increase in the electric resistance value of the fourth primary transfer roller 6k. Therefore, in this case, the CPU 121 obtains a value obtained by subtracting the influence A from the ATVC control result VK affected by the increase in the electric resistance value of the fourth primary transfer roller 6k. The value is determined as the value of the primary transfer voltage applied to the next transfer rollers 6y, 6m, and 6c. That is, in this case, the primary transfer voltages obtained by subtracting the correction amount A from the primary transfer voltage applied to the fourth primary transfer roller 6k are applied to the first to third primary transfer rollers 6y, 6m, and 6c. VK-A is applied.

-Correction mode 3 (when the number of prints in color mode (F) is 50000 or more)
The correction mode 3 will be described with reference to FIG. In this case, the electrical resistance values of both the first to third primary transfer rollers 6y, 6m, 6c and the fourth primary transfer roller 6k are 1 × 10 ⁶ [Ω] or more. Therefore, the first transfer voltage in consideration of the effect of the increase in the electrical resistance value of the primary transfer roller 6 is applied to both the first to third primary transfer rollers 6y, 6m, 6c and the fourth primary transfer roller 6k. Must be applied. However, the degree of increase in the electric resistance value is the difference in the number of sheets used for printing each of the first to third primary transfer rollers 6y, 6m, 6c and the fourth primary transfer roller 6k, that is, monochrome. It differs depending on the number of printed sheets TF [sheets]. Therefore, the CPU 121 corrects the primary transfer voltage applied to the first to third primary transfer rollers 6y, 6m, and 6c based on the monochrome print number TF [sheets].

  First, the ATVC control result by the ATVC detection performed using the fourth primary transfer roller 6k, that is, the determined value of the primary transfer voltage applied to the fourth primary transfer member 6k is the fourth 1 This is influenced by the increase in the electric resistance value of the next transfer roller 6k. Accordingly, the ATVC control result in this case becomes the value of the primary transfer voltage to which the change amount B in FIG. 17 is added.

  On the other hand, the primary transfer voltages applied to the first to third primary transfer rollers 6y, 6m, and 6c are also affected by the increase in electrical resistance value. If ATVC detection is performed using the first to third primary transfer rollers 6y, 6m, and 6c, the ATVC control result becomes the value of the primary transfer voltage to which the change C in FIG. 17 is added. Therefore, in this case, the CPU 121 affects the influence B of the increase in the electrical resistance value of the fourth primary transfer roller 6k and the effect of the increase in the electrical resistance values of the first to third primary transfer rollers 6y, 6m, and 6c. Find the difference D from the minute C. Then, the CPU 121 obtains a value obtained by subtracting the difference D from the ATVC control result VK affected by the increase in the electric resistance value of the fourth primary transfer roller 6k, as the first to third primary transfer rollers 6y. , 6m, and 6c, the primary transfer voltage value is determined. That is, in this case, the first to third primary transfer rollers 6y, 6m, and 6c receive a correction amount D (= BC) from the primary transfer voltage applied to the fourth primary transfer roller 6k. The subtracted primary transfer voltage VK-D is applied.

  Also in this embodiment, the ATVC control result, that is, the determined value of the primary transfer voltage applied to the fourth primary transfer roller 6k reflects the electric resistance value of the intermediate transfer belt 5 and its fluctuation. As a result of absorbing.

  As described above, in this embodiment, the image forming apparatus 100 can execute the following two image forming modes. That is, one is a first image formation mode (color color) in which image formation is performed using both the detection non-execution image formation units UY, UM, UC and the detection execution image formation unit UK among the plurality of image formation units U. Mode). The other is a second image formation mode (monochrome mode) in which image formation is performed using only the detection execution image formation unit UK among the plurality of image formation units U. In this embodiment, the determination unit 121 corrects the value determined as the transfer voltage value of the detection execution image forming unit UK and determines the transfer voltage value of the detection non-execution image formation units UY, UM, UC. This correction is based on the detection result of the detection unit 17, information correlating with the usage amount of the transfer unit 6 of the detection execution image forming unit UK, and the usage amount of the transfer unit 6 of the non-detection execution image forming units UY, UM, UC. And based on correlated information. In particular, in both the detection execution image forming unit and the detection non-execution image forming unit, when the transfer unit is not used, the electric resistance of the transfer unit is applied to the transfer current flowing between the transfer unit and the image carrier during transfer. The electric resistance value of the transfer means is set sufficiently low so that the influence of the value fluctuation can be ignored. In the following case, the determination unit 121 determines the value determined as the transfer voltage value of the detection execution image forming unit UK as the transfer voltage value of the detection non-execution image formation units UY, UM, and UC. That is, this is a case where the usage amount of the transfer means 6 indicated by the above information is less than a predetermined value in both the detection execution image forming unit UK and the detection non-execution image formation units UY, UM, and UC. In the following case, the transfer voltage value determined as the transfer voltage value of the detection execution image forming unit UK is corrected and determined as the transfer voltage value of the detection non-execution image formation units UY, UM, UC. That is, this is a case where the amount of use of the transfer means 6 indicated by the information in the detection execution image forming unit UK or both of the detection execution image formation unit UK and the detection non-execution image formation units UY, UM, UC is equal to or greater than the predetermined value. . The correction can be performed by subtracting the variation due to the electrical resistance value of the transfer means of the detection execution image forming unit UK from the determined transfer voltage value of the detection execution image forming unit UY.

  As described above, even when the electrical resistance values of the first to third primary transfer rollers 6y, 6m, and 6c and the electrical resistance value of the fourth primary transfer roller 6k are greatly different from each other, The same effect as 1 is obtained. That is, the primary transfer voltage can be controlled so as to absorb the influence of fluctuations in the electrical resistance value of the intermediate transfer belt 5 and / or the primary transfer roller 6 while shortening the FPOT, and a good image can be output. . Therefore, according to the present exemplary embodiment, it is possible to control the image forming condition so as to absorb the fluctuation of the electric resistance value of the member in the transfer portion while shortening the FPOT.

  In this embodiment, the correction is performed based on the information on the number of printed sheets in the color mode and the monochrome mode. However, the rotation speed or rotation time of the primary transfer roller 6 or the primary transfer voltage is applied to the primary transfer roller 6. You may correct | amend based on the applied time. That is, any information that correlates with the usage amount of the primary transfer roller 6 may be used.

  In the present embodiment, the primary transfer roller 6 has an electrical resistance value that can be ignored relative to the electrical resistance value of the intermediate transfer belt 5 until the primary transfer roller 6 reaches a predetermined usage amount from the unused time. However, a configuration is also conceivable in which the electric resistance value of the primary transfer roller 6 is not negligible with respect to the electric resistance value of the intermediate transfer belt 5 by starting use when not in use. Even in such a case, it is possible to execute the correction from the initial use of the primary transfer roller 6 by executing the same correction as in the correction mode 3 described above.

Other Embodiments Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiments, the present invention is applied to an intermediate transfer type image forming apparatus, but the present invention can also be applied to a direct transfer type image forming apparatus. FIG. 18 illustrates a schematic configuration of a main part of an example of the direct transfer type image forming apparatus 300. In FIG. 18, elements having the same or corresponding functions and configurations as those of the intermediate transfer type image forming apparatus shown in FIG. The direct transfer type image forming apparatus 300 includes, for example, an endless belt-like transfer belt 305 as a transfer material carrier instead of the intermediate transfer belt 5 in the above-described embodiment. Further, the transfer roller 6 corresponding to the primary transfer roller 6 in the above-described embodiment is pressed against the photosensitive drum 1 via the transfer belt 305. The toner images formed on the photosensitive drums 1y, 1m, 1c, and 1k in the image forming units UY, UM, UC, and UK are transferred onto the transfer belts N by the transfer belt 305 and conveyed. The images are sequentially superimposed and transferred onto P. In such a direct transfer type image forming apparatus 300, the image forming operation by each of the image forming units UY, UM, UC, UK, and the timing thereof (development contact, etc.) are the intermediate transfer type image forming apparatus in the above-described embodiment. And can be similar. In such a direct transfer type image forming apparatus 300, the transfer voltage applied to each transfer roller 6 can be controlled by the same control method as in the case of controlling the primary transfer voltage in the above-described embodiment. it can.

  In this case as well, the ratio (R2 ÷ R1) between the electric resistance value R2 of the transfer belt 305 and the electric resistance value R1 of the transfer roller 6 is set to 100 or more.

  Here, the electric resistance value R2 of the transfer belt 305 can be obtained in the same manner by replacing the intermediate transfer belt 5 with the transfer belt 305 in the calculation method of the electric resistance value of the intermediate transfer belt 5 in the above embodiment. . The electric resistance value R1 of the transfer roller 6 can be measured in the same manner as the electric resistance value of the primary transfer roller 6 in the above embodiment. Here, if the ratio (R2 / R1) between the electric resistance value R2 of the transfer belt 305 and the electric resistance value R1 of the transfer roller 6 is 100 or more, the transfer belt 305 and the transfer material P conveyed by the transfer belt 305 The ratio between the combined resistance and the resistance of the transfer roller 6 is also 100 or more. Therefore, for example, the transfer material P is conveyed to the transfer unit N of the detection execution image forming unit while starting the development contact operation in the detection non-execution image forming unit, and the transfer resistance is related to the combined resistance of the transfer belt 305 and the transfer material P. Information may be detected, and the transfer voltage may be controlled according to the result.

  In addition, it is preferable that each primary transfer roller has the same configuration from the viewpoint of cost reduction, etc., but each of the primary transfer rollers has a predetermined configuration as described above with respect to the intermediate transfer belt, the transfer belt, etc. The same effect can be obtained as long as the electrical resistance values are related.

  In the above-described embodiment, the ATVC detection is performed in the most downstream image forming unit, but the present invention is not limited to this. The ATVC detection is executed in parallel with a part of the development contact operation and the image forming operation by the timing when the application of the transfer voltage is started in the uppermost image forming unit among the image forming units used for image formation, and the transfer is performed. It is sufficient if the voltage can be determined. In that case, ATVC detection can be performed in an arbitrary image forming unit downstream of the most upstream image forming unit among the image forming units used for image formation. However, the most downstream image forming unit is preferable because of the time allowance. Further, at least when the control of the second embodiment is performed, the image forming unit that performs ATVC detection is preferably an image forming unit that is used in a monochrome mode, in particular, an image forming unit for black. That is, it can be said that the image forming unit for black is generally used more frequently than the image forming units for other colors. Accordingly, the electric resistance value of the primary transfer roller is more likely to increase in the black image forming unit than in the other color image forming units. Therefore, when the control of the second embodiment is performed, ATVC detection is performed in the black image forming unit so that the influence of the increase in the electrical resistance value of the primary transfer roller of the image forming unit can be measured. It is preferable.

  In the above-described embodiment, in the ATVC detection, a voltage value generated when a constant current controlled voltage is applied to the transfer member is detected, and the transfer voltage at the time of image formation is determined from the detection result. . However, the present invention is not limited to this. In ATVC detection, a current value that flows when a constant voltage controlled voltage is applied to the transfer member is detected, and the transfer voltage at the time of image formation is detected from the detection result. You may decide. That is, it is only necessary to obtain information related to the electrical resistance value of the member in the transfer portion. Further, the transfer voltage at the time of image formation is not limited to the constant voltage control. For example, when the current value is detected in the ATVC detection as described above, the transfer voltage at the time of image formation is controlled at a constant current. May be.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Image exposure part 4 Developer 5 Intermediate transfer belt 6 Primary transfer roller 7 Primary transfer power supply

Claims (24)

A movable intermediate transfer member;
A first image carrier that is provided along the moving direction of the intermediate transfer member and carries a toner image ;
A second image carrier which is provided along the moving direction of the intermediate transfer member and which is located downstream of the first image carrier and carries a toner image;
A first developing means for supplying toner to said first image carrier,
Second developing means for supplying toner to the second image carrier;
A first transfer means for transferring the toner to the intermediate transfer member from said first image bearing member in the said through an intermediate transfer member the first voltage is arranged to face the image holding member is applied ,
First voltage applying means for applying a voltage to the first transfer means,
A second transfer unit disposed opposite to the second image carrier through the intermediate transfer member and applying a voltage to transfer toner from the second image carrier to the intermediate transfer member; ,
Second voltage applying means for applying a voltage to the second transfer means ;
Detection that detects a voltage value when a constant current controlled voltage is applied from the second voltage applying means to the second transfer means or a current value when a constant voltage controlled voltage is applied. Means,
Have
When starting image formation for forming a toner image on both the first image carrier and the second image carrier, the first image carrier on which toner image formation is started first is started. On the other hand, in an image forming apparatus in which a predetermined operation is performed before toner image formation is started.
The detection means performs the detection during a period at least partially overlapping the predetermined operation on the first image carrier, and before the transfer by the first transfer means is started , based on the detection result, and having said a transfer voltage value second voltage applying means applies a control means for determining a transfer voltage value, both of which the first voltage applying means for applying Image forming apparatus. Predetermined operation for said first image bearing member, and wherein a first said first in a state of being separated from the image carrier of the operation of the developing unit is brought into contact with the first image bearing member The image forming apparatus according to claim 1 . When the image formation for forming a toner image on both the first image carrier and the second image carrier is started, the detection by the detection unit is completed for the second image carrier. The image forming apparatus according to claim 1, wherein a predetermined operation is performed after the toner image formation is started before the toner image formation is started. The predetermined operation with respect to the second image carrier is an operation in which the second developing unit in a state of being separated from the second image carrier is brought into contact with the second image carrier. The image forming apparatus according to claim 3. Effect of the variation of the electrical resistance value of the first transfer means for supplying a transfer current value flowing between the first transfer means and the first image carrier during the previous SL transfer, and during the transfer as the influence of the variation in the electric resistance of the second transfer means for providing a transfer current value flowing between the second transfer means and the second image bearing member can be ignored, the first, second The electric resistance value of transfer means 2 is set sufficiently low,
5. The control unit determines a value determined as a transfer voltage value applied by the second voltage application unit as a transfer voltage value applied by the first voltage application unit. The image forming apparatus according to claim 1. The control means is based on the detection result of the detection means, information correlating with the usage amount of the first transfer means, and information correlating with the usage amount of the second transfer means . 5. The transfer voltage value applied by the first voltage application unit is determined by correcting the value determined as the transfer voltage value applied by the voltage application unit. 5. The image forming apparatus described in 1. A first image forming mode in which a toner image is formed on both the first image carrier and the second image carrier to form an image; and among the first and second image carriers, The image forming apparatus according to claim 6, wherein a second image forming mode in which a toner image is formed only on the second image carrier to form an image can be executed. The first, in the unused state of the second transfer means, the first transfer means for supplying a transfer current flowing between the first transfer means and the first image bearing member during the transfer The influence of the fluctuation of the electric resistance value and the fluctuation of the electric resistance value of the second transfer means given to the transfer current flowing between the second transfer means and the second image carrier during the transfer. effect as can be ignored, the first electric resistance value of the second transfer means is set sufficiently low,
Wherein, as the case where the information is shown to use a dose of both the first transfer means and the second transfer means is less than the predetermined value, the transfer voltage value to which the second voltage applying means for applying the determined value was determined as the transfer voltage value, wherein the first voltage applying means applies the second transfer means, or the information both of said first transfer means and the second transfer means is shown If you use doses of the predetermined value or more, the corrected decision value as the transfer voltage value by the second voltage applying means applies said first voltage applying means is determined as the transfer voltage value to be applied The image forming apparatus according to claim 6, wherein the image forming apparatus is an image forming apparatus. 9. The correction according to claim 6, wherein the correction is performed by subtracting a variation due to the electric resistance value of the second transfer unit from the determined transfer voltage value applied by the second voltage application unit . The image forming apparatus according to claim 1. Rotation of the first, respectively the information to correlate with the amount of the second transfer means, the first, information of the number of prints were made by using the second transfer means, the first, second transfer means The image forming apparatus according to claim 6, wherein the image forming apparatus is information on a number or a rotation time, or information on a time when a voltage is applied to the first and second transfer units. The first, each set of electrical resistance of the second transfer means, the electrical resistance value of the first or second transfer means R1 [Omega], the resistance value of the intermediate transfer member R2 [Omega] The following formula
(R2 ÷ R1) ≧ 100
[Where R2 = (volume resistivity of the intermediate transfer member × thickness of the intermediate transfer member) / (contact area between the intermediate transfer member and the first or second transfer unit)]
The image forming apparatus according to claim 5, wherein: When the second image carrier forms a toner image on both the first image carrier and the second image carrier to form an image, the toner image formation is finally started. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image carrier . A transfer material carrier that is movable while carrying a transfer material;
A first image carrier that is provided along a moving direction of the transfer material carrier and carries a toner image ;
A first image carrier that is provided along a moving direction of the transfer material carrier and is located downstream of the first image carrier and carries a toner image;
A first developing means for supplying toner to said first image carrier,
Second developing means for supplying toner to the second image carrier;
The toner to the transfer material through said carrier first transfer material a voltage is arranged to face the image bearing member is supported from the first image bearing member to the transfer material bearing member by being applied A first transfer means for transferring;
First voltage applying means for applying a voltage to the first transfer means,
A toner is applied from the second image carrier to the transfer material carried on the transfer material carrier by applying a voltage by being arranged to face the second image carrier through the transfer material carrier. A second transfer means for transferring;
Second voltage applying means for applying a voltage to the second transfer means ;
Detection that detects a voltage value when a constant current controlled voltage is applied from the second voltage applying means to the second transfer means or a current value when a constant voltage controlled voltage is applied. Means,
Have
When starting image formation for forming a toner image on both the first image carrier and the second image carrier, the first image carrier on which toner image formation is started first is started. On the other hand, in an image forming apparatus in which a predetermined operation is performed before toner image formation is started.
The detection means performs the detection during a period at least partially overlapping the predetermined operation on the first image carrier, and before the transfer by the first transfer means is started , based on the detection result, and having said a transfer voltage value second voltage applying means applies a control means for determining a transfer voltage value, both of which the first voltage applying means for applying Image forming apparatus. Predetermined operation for said first image bearing member, and wherein a first said first in a state of being separated from the image carrier of the operation of the developing unit is brought into contact with the first image bearing member The image forming apparatus according to claim 13 . When the image formation for forming a toner image on both the first image carrier and the second image carrier is started, the detection by the detection unit is completed for the second image carrier. 15. The image forming apparatus according to claim 13, wherein a predetermined operation is performed after the toner image formation is started before the toner image formation is started. The predetermined operation with respect to the second image carrier is an operation in which the second developing unit in a state of being separated from the second image carrier is brought into contact with the second image carrier. The image forming apparatus according to claim 15. Effect of the variation of the electrical resistance value of the first transfer means for supplying a transfer current value flowing between the first transfer means and the first image carrier during the previous SL transfer, and during the transfer as the influence of the variation in the electric resistance of the second transfer means for providing a transfer current value flowing between the second transfer means and the second image bearing member can be ignored, the first, second The electric resistance value of transfer means 2 is set sufficiently low,
The control means determines a value determined as a transfer voltage value applied by the second voltage application means as a transfer voltage value applied by the first voltage application means. The image forming apparatus according to claim 1. The control means is based on the detection result of the detection means, information correlating with the usage amount of the first transfer means, and information correlating with the usage amount of the second transfer means . 17. The transfer voltage value applied by the first voltage application unit is corrected by correcting a value determined as the transfer voltage value applied by the voltage application unit. 17. The image forming apparatus described in 1. A first image forming mode in which a toner image is formed on both the first image carrier and the second image carrier to form an image; and among the first and second image carriers, The image forming apparatus according to claim 18, wherein a second image forming mode in which a toner image is formed only on the second image carrier to form an image can be executed. The first, in the unused state of the second transfer means, the first transfer means for supplying a transfer current flowing between the first transfer means and the first image bearing member during the transfer The influence of the fluctuation of the electric resistance value and the fluctuation of the electric resistance value of the second transfer means given to the transfer current flowing between the second transfer means and the second image carrier during the transfer. effect as can be ignored, the first electric resistance value of the second transfer means is set sufficiently low,
Wherein, as the case where the information is shown to use a dose of both the first transfer means and the second transfer means is less than the predetermined value, the transfer voltage value to which the second voltage applying means for applying the determined value was determined as the transfer voltage value, wherein the first voltage applying means applies the second transfer means, or the information both of said first transfer means and the second transfer means is shown If you use doses of the predetermined value or more, the corrected decision value as the transfer voltage value by the second voltage applying means applies said first voltage applying means is determined as the transfer voltage value to be applied The image forming apparatus according to claim 18, wherein the image forming apparatus is an image forming apparatus. 21. The correction according to claim 18, wherein the correction is performed by subtracting a variation due to the electric resistance value of the second transfer unit from the determined transfer voltage value applied by the second voltage application unit . The image forming apparatus according to claim 1. Rotation of the first, respectively the information to correlate with the amount of the second transfer means, the first, information of the number of prints were made by using the second transfer means, the first, second transfer means The image forming apparatus according to any one of claims 18 to 21, wherein the information is information on a number or a rotation time, or information on a time when a voltage is applied to the first and second transfer units. The first, each set of electrical resistance of the second transfer means, the electrical resistance value of the first or second transfer means R1 [Omega], the resistance value of said transfer material bearing member R2 [Omega ], The following formula:
(R2 ÷ R1) ≧ 100
[Where R2 = (volume resistivity of the transfer material carrier × thickness of the transfer material carrier) / (contact area between the transfer material carrier and the first or second transfer means)]
21. The image forming apparatus according to claim 17, wherein: When the second image carrier forms a toner image on both the first image carrier and the second image carrier to form an image, the toner image formation is finally started. The image forming apparatus according to claim 13, wherein the image forming apparatus is an image carrier .

Images