JP4763988B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by an electrophotographic system or an electrostatic recording system.

  Conventionally, as an electrophotographic image forming apparatus, toner images formed on a plurality of photosensitive drums are conveyed by an electrostatic transportation belt (hereinafter referred to as “ETB”) as a transfer material conveying means. A tandem type direct transfer multicolor image forming apparatus that forms a multicolor image by transferring onto a transfer material such as recording paper has been put into practical use.

  In this multicolor image forming apparatus, a plurality of photosensitive drums are individually charged by a charging unit, and an electrostatic latent image is formed on each of the plurality of photosensitive drums by an exposure unit. Then, toner that is triboelectrically charged to a predetermined polarity (for example, negative polarity) is supplied as a developer by the developing unit, so that toner images are formed on the plurality of photosensitive drums. This toner image is directly transferred to a transfer material conveyed by the ETB.

  In the tandem type direct transfer multicolor image device, since the toner image can be transferred only once, for example, the tandem type direct transfer multicolor image device is essentially superior in character scattering, etc., as compared with a method of performing transfer twice using an intermediate transfer member. There is an advantage that a clear image can be obtained.

  By the way, in the combination of the negatively charged OPC and the reversal development method generally used in the tandem type direct transfer multicolor image device, the distribution of the toner tribo (the charge amount per unit mass of the toner) of the toner image is spread to some extent. have. For this reason, in addition to the toner charged to the original charged polarity (for example, negative polarity), there is toner (hereinafter referred to as “reversal toner”) charged to the opposite polarity (for example, positive polarity). However, since the reversal toner is developed in the non-latent image portion on the photosensitive drum, the reversal toner is transferred to the non-image area of the transfer material, causing a phenomenon that the image quality is deteriorated. Hereinafter, this phenomenon is referred to as “fogging”. Further, the reversal toner that appears in the non-image area in the fog is referred to as “fog reversal toner”.

  In the prior art, it is considered impossible to prevent the fog reversal toner generated on the photosensitive drum from being transferred to the non-image area of the transfer material in the transfer process. Therefore, in order to reduce “fogging”, various methods have been proposed in terms of how much fog reversal toner on the photosensitive drum can be reduced. Examples of the techniques disclosed in Patent Document 1 and Patent Document 2 are given.

In the present invention, instead of reducing the fog reversal toner on the photosensitive drum, in the transfer process from the photosensitive drum to the transfer material, the fog reversal toner is reduced, the “fog” on the transfer material is reduced, and a high-quality print is achieved. Suggest to get.
Japanese Patent Laid-Open No. 10-123743 Japanese Patent Laid-Open No. 10-161353

  An object of the present invention is to provide an image forming apparatus capable of suppressing fog reversal toner from being transferred to a transfer material in a transfer process.

  Another object of the present invention is to provide an image forming apparatus capable of effectively suppressing fogging in a transfer process according to image forming conditions.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of the above-mentioned transfer media via the transfer material conveyance belt. Each of the image carrier and a plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveying belt at the nip portion. In the image forming apparatus capable of changing the difference between the moving speed of the image carrier and the moving speed of the transfer material conveying belt in the image forming apparatus, the type of transfer material conveyed to the nip portion is smooth paper The absolute value of the difference between the moving speed of the image carrier and the moving speed of the transfer material transport belt when it is determined that the type of transfer material transported to the nip is smoother than the smooth paper. It is a kind of rough transfer material An image forming apparatus which being greater than the absolute value of the difference between the determined moving speed of the transfer material conveyance belt and the moving speed of the image bearing member when.
According to another aspect of the present invention, a plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of transfer material conveyance belts via the transfer material conveyance belt. A plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion. In the image forming apparatus capable of changing the difference between the moving speed of the image carrier and the moving speed of the transfer material transport belt in the section, the environment detection for detecting the temperature and humidity environment around the image forming apparatus The image carrier is moved when the detection result of the environment detection means is a high humidity and high temperature environment when it is determined that the type of transfer material conveyed to the nip portion is smooth paper. And transfer material The absolute value of the difference between the moving speed of the belt is the difference between the moving speed of the image carrier and the moving speed of the transfer material conveying belt when the detection result of the environment detecting means is a low humidity and low temperature environment. There is provided an image forming apparatus characterized by being larger than the absolute value of.
According to another aspect of the present invention, a plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of transfer material conveyance belts via the transfer material conveyance belt. A plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion. In the image forming apparatus capable of changing the difference between the moving speed of the image carrier and the moving speed of the transfer material conveying belt in the section, the image forming apparatus has a current detecting means for detecting a current value flowing through the transferring means. When the transfer material conveyed to the nip portion is determined to be smooth paper, the image bearing when the current value detected by the current detection unit is greater than or equal to a reference current value. body Absolute value of the difference between the moving speed and the moving speed of the transfer material conveyance belt, of the image bearing member when a current value flowing through the transfer unit is detected by said current detecting means is less than the reference current value An image forming apparatus is provided in which the absolute value of the difference between the moving speed and the moving speed of the transfer material conveying belt is larger.
According to another aspect of the present invention, a plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of transfer material conveyance belts via the transfer material conveyance belt. A plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion. In the image forming apparatus capable of changing the difference between the moving speed of the image carrier and the moving speed of the transfer material transport belt in the section, the type of transfer material transported to the nip section is smooth paper When it is determined that there is an absolute value of the difference between the moving speed of the image carrier and the moving speed of the transfer material conveying belt when the integrated value of the used amount of the image forming apparatus is equal to or greater than a reference used amount value Of the image forming apparatus Image forming apparatus integrated value of dose being larger than the absolute value of the difference between the moving speed of the transfer material conveyance belt and the moving speed of the image bearing member is less than the reference usage value is Provided.

  According to the present invention, it is possible to suppress the fog reversal toner from being transferred to the transfer material in the transfer step. Further, according to the present invention, it is possible to effectively suppress fogging in the transfer process according to image forming conditions.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. Embodiments of the present invention are not limited to the following.

Example 1
[Entire configuration of image forming apparatus]
FIG. 1 shows a schematic cross section of a main part of a color image forming apparatus (laser printer or copying machine) using an electrophotographic process.

The image forming apparatus 100 includes an image carrier, a charging unit, an exposing unit, a developing unit, and a cleaning unit as image forming units for yellow (Y), magenta (M), cyan (C), and black (K), respectively. Have four independent image forming stations (first, second, third and fourth image forming stations) P1, P2, P3 and P4. The image forming stations P1, P2, P3, and P4 are arranged in a vertical row. Then, the transfer material S adsorbed by an ETB (electrostatic transport belt) 8 serving as a transfer material transport belt as a transfer material transport means is transported to each of the image forming stations P1, P2, P3, and P4, and a toner image is obtained. A full-color image is obtained by performing the transfer.

  More specifically, each of the image forming stations P1, P2, P3, and P4 is a rotating drum type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 11, 12, 13, and 14 that is repeatedly used as an image carrier. Have The photosensitive drums 11, 12, 13, and 14 have a predetermined peripheral speed (moving speed on the surface of the image carrier: hereinafter, simply referred to as “moving speed”) v1 [mm / s] (process speed) indicated by an arrow in the drawing. ).

  In this embodiment, each of the photosensitive drums 11, 12, 13, and 14 is a negatively charged OPC photosensitive member having a diameter of 30 mm, and corresponds to the process speed of the image forming apparatus 100 of this embodiment (in this embodiment, it corresponds to the speed of ETB8). ) Is 180 mm / sec.

  Each of the photosensitive drums 11, 12, 13, and 14 is uniformly charged to a predetermined polarity and potential by primary charging rollers 21, 22, 23, and 24 as charging means during the rotation process.

The primary charging rollers 21, 22, 23, and 24 are of a DC contact charging type. That is, in the present embodiment, the primary charging rollers 21, 22, 23, and 24 are rollers having an actual resistance of 10 ⁶ Ω to which a DC voltage of −1.2 kV is applied. Then, the primary charging rollers 21, 22, 23, and 24 are driven to come into contact with the photosensitive drums 11, 12, 13, and 14 at a total pressure of 9.8 N to perform charging. As a result, the surfaces of the photosensitive drums 11, 12, 13 and 14 are charged to −600V.

  Next, each of the photosensitive drums 11, 12, 13, and 14 is subjected to image exposure by laser scanner devices 31, 32, 33, and 34 as image exposure means. As a result, the electrostatic latent images corresponding to the color component images of the target color image (yellow, magenta, cyan, and black color component images in this embodiment) are respectively recorded on the photosensitive drums 11, 12, 13, and 14. It is formed. The laser scanner devices 31, 32, 33, and 34 are configured by a laser diode, a polygon scanner, a lens group, and the like. The laser scanner devices 31, 32, 33, and 34 image the laser beams modulated by the image signals on the photosensitive drums 11, 12, 13, and 14. As a result, electrostatic latent images are formed on the photosensitive drums 11, 12, 13, and 14.

  In the main scanning direction (direction perpendicular to the progress of the transfer material S), the laser exposure is written from a position signal in the polygon scanner called BD for each scanning line, and in the sub-scanning direction (the progress direction of the transfer material S). In this case, the image forming station of each color can always perform exposure at the same position on the transfer material S by performing a predetermined time delay from the TOP signal starting from the switch in the transfer material conveyance path.

  Next, the electrostatic latent images are developed using toner as a developer by developing devices 41, 42, 43, and 44 as developing means provided in the respective image forming stations P1, P2, P3, and P4. Each of the developing devices 41, 42, 43, and 44 supplies yellow, magenta, cyan, and black toners to the photosensitive drums 11, 12, 13, and 14, respectively. In this embodiment, a so-called non-mag toner that does not contain a magnetic material is used as the toner. Then, development is performed by a one-component contact development method. That is, each developing device 41, 42, 43, 44 has a developing roller as a developer carrying member at a position facing the photosensitive drums 11, 12, 13, 14. The surface of the developing roller is coated with toner by a developing blade, a supply roller, or the like. In this embodiment, the developing roller is rotationally driven at the same speed as the photosensitive drums 11, 12, 13, and 14. Then, a developing roller carrying toner is brought into contact with the photosensitive drums 11, 12, 13, and 14. Further, about -500 V is applied to the developing roller. Thus, according to the electrostatic latent images on the photosensitive drums 11, 12, 13, 14, the toner is transferred from the developing roller to the photosensitive drums 11, 12, 13, 14, and on the photosensitive drums 11, 12, 13, 14. The electrostatic latent image is developed.

  In this embodiment, the toner is a spherical toner having a two-layer structure manufactured by a polymerization method. This toner has a configuration in which a resin binder layer called a shell surrounds a central wax. In this embodiment, the toner is negatively charged. Then, the toner image is transferred by reversal development, that is, by transferring the toner to the portions of the photosensitive drums 11, 12, 13, and 14 that are charged to the same polarity as the charging polarity of the toner and where the charged potential is attenuated by exposure. Form.

  In each of the image forming stations P1, P2, P3, and P4, at least the photosensitive drum, the primary charging roller, and the developing device constitute image forming units U1, U2, U3, and U4 that form a transferable toner image.

  In this embodiment, the photosensitive drum, the primary transfer roller, the developing device, and the cleaning device in each of the image forming stations P1, P2, P3, and P4 are integrally formed into a cartridge by a frame body. A process cartridge that can be attached to and detached from is configured. The cartridge that is detachable from the image forming apparatus A is not limited to such an embodiment. The process cartridge may be a cartridge in which a photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit as a processing unit that acts on the photosensitive unit are integrally formed. Further, a developing cartridge in which the developing device is detachable from the image forming apparatus main body A may be used.

  The ETB 8 is wound around a plurality of rollers 101, 102, 103. The ETB 8 is driven by the drive roller 102 among the plurality of rollers. As a result, the ETB 8 moves (rotates) in the direction indicated by the arrow in the figure at a predetermined peripheral speed (moving speed on the surface of the transfer material transport means: hereinafter simply referred to as “moving speed”) v2 [mm / s].

Examples of ETB8 include polyimide, polyamide, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEEK (polyetheretherketone), PVDF having a resistance adjusted to 10 ⁸ to 10 ¹¹ Ωcm and a thickness of 60 to 150 μm. A single-layer resin belt such as (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) can be used. The ETB 8 has ribs bonded to both sides in the thrust direction (direction perpendicular to the surface movement direction) on the back surface (side in contact with the rollers 101, 102, 103). By this rib, it is possible to regulate meandering and shifting of the ETB 8.

Transfer rollers 51, 52, 53, and 54, which are transfer members as transfer means, are disposed at positions facing the respective photosensitive drums 11, 12, 13, and 14 via the ETB 8. In this embodiment, as the transfer rollers 51, 52, 53, and 54, epichlorohydrin rubber rollers adjusted to a volume resistivity of 10 ⁷ Ωcm and capable of applying a high voltage are used. Further, the transfer rollers 51, 52, 53, and 54 have a total pressure of 2.94 [N] from the back surface of the ETB 8 to the nip portions (transfer portions) T1, T2, T3, and T4 with the photosensitive drums 11, 12, 13, and 14. ] With the transfer pressure of].

  The transfer material S supplied from a transfer material cassette (not shown) passes through a registration roller (not shown) and then contacts the ETB 8 via a transfer inlet guide (not shown).

  Here, in the present exemplary embodiment, the image forming apparatus 100 is configured to minimize the installation area, or to replace the cartridge or perform jam processing by opening / closing the front door (if the transfer material is jammed in the conveyance path). The image forming stations P1, P2, P3, and P4 are arranged vertically so that a desired object such as a process for removing the image can be achieved. As a result, an image is formed between the ETB 8 and the cartridge, that is, including an ETB (including a roller on which the ETB is stretched, a transfer member, etc.) attached to the front door, a photosensitive drum, a primary charging roller, and a developing device. The image forming apparatus main body A is divided between the units U1, U2, U3, and U4.

  Since the image forming stations P1, P2, P3, and P4 are arranged in the vertical direction in this way, the transfer material S is conveyed upward against gravity. For this reason, it is necessary that the transfer material S and the ETB 8 are sufficiently adsorbed. Therefore, in this embodiment, the suction roller 7 to which a bias is applied is provided in the vicinity of the contact point between the transfer material S and the ETB 8. During image formation, a voltage of +1 KV is applied to the suction roller 7 to give a charge to the transfer material S. Thereby, the suction conveyance force of the transfer material S by the ETB 8 is generated.

In this embodiment, the suction roller 7 is a solid rubber roller having a diameter of 12 mm in which carbon black is dispersed in EPDM rubber for resistance adjustment. The suction roller 7 is configured to apply a high-pressure bias for suction to the cored bar. The resistance value of the suction roller 7 is adjusted to 10 ⁶ Ω as a resistance value when a metal foil having a width of 1 cm is wound around the outer periphery of the roller and a voltage of 500 V is applied between the core metal.

  The transfer material S, which is supplied from the transfer material cassette (not shown) as described above and has obtained an adsorption force between the transfer entrance guide (not shown) and the adsorption roller 7 and the ETB 8, is the first. Enters the color transfer portion T1. In the transfer portion T1, a transfer bias is applied to the transfer roller 51 provided on the back surface of the ETB 8, whereby the first color toner image is transferred from the photosensitive drum 11 to the transfer material S. The bias applied to the transfer roller 51 can be calculated from the ETB 8 calculated from the current flowing through the suction roller while the transfer material S passes (paper passing) or the impedance of the transfer material S. In single-sided printing in a normal environment, a DC bias of about +1.5 kV (a voltage having a polarity opposite to the normal charging polarity of toner) is applied to the transfer voltage applying means (for each of the image forming stations P1, P2, P3, and P4). Applied to transfer rollers 51, 52, 53, and 54 from transfer bias power supplies 71, 72, 73, and 74 as high-voltage power supplies).

  When the transfer of the first color toner image is completed, each time the transfer material S passes through the second, third, and fourth color transfer portions T2, T3, and T4, the image forming stations P2, P3, The toner images of the respective colors are transferred onto the transfer material S from the P4 photosensitive drums 12, 13, and 14. In this way, an unfixed toner image composed of a plurality of colors of toner is formed on the transfer body S.

  After all colors have been transferred, the transfer material S separated by the curvature from the rear end of the ETB 8 is conveyed to a fixing device 9 as fixing means. The fixing device 9 includes a fixing roller 91 including a heating unit, and a pressure roller 92 that is in pressure contact with the fixing roller, and heats the transfer material S while nipping and conveying it. The unfixed toner image on the transfer material S is fixed to the transfer material S by the fixing device 9, and a full-color recorded image is formed on the transfer material S. Thereafter, the transfer material S is discharged out of the apparatus via a transport unit (not shown). A final print is thus obtained.

  The photosensitive drums 11, 12, 13, and 14 after the toner image is transferred to the transfer material S are adhered to the surface (toner, paper dust, and the like) by cleaning devices 61, 62, 63, and 64 as cleaning means. Etc.) are cleaned. The surface of the ETB 8 is also cleaned of deposits (toner, paper dust, etc.) on the surface by an ETB cleaning device 104 as a transfer material conveying means cleaning means.

  In this embodiment, the optical sensor 10 is provided on the downstream side of the driving roller 102 (and in the upstream side of the roller 101 in this embodiment) in the surface movement direction of the ETB 8. The optical sensor 10 includes a light projecting unit having a light source and a light receiving unit including a photoelectric conversion element (light receiving element), and irradiates the surface of the ETB 8 with detection light to detect the amount of light reflected on the surface. Can do. In this embodiment, a pair (two) of registration (position displacement) detection sensors (hereinafter referred to as “registration detection sensors”) 10 are arranged as optical sensors in the thrust direction of the ETB 8.

  The registration detection sensor 10 detects the toner pattern of each color transferred onto the ETB 8 and the amount of reflected light on the surface of the ETB 8. Based on the detection result of the edge position of each color toner pattern, the CPU 111 performs calculation, and corrects the writing position and magnification of each color. The registration detection sensor 10 can also be used as a toner adhesion amount detection means. That is, for example, for each color, toner patterns (patch images, reference images) having different densities are formed on the ETB 8. Then, the amount of reflected light of the toner pattern is detected, and the CPU 111 calculates based on the result, so that process conditions such as the development voltage can be set.

[Anti-fogging mechanism]
Next, means for reducing “fogging” in the transfer process will be described.

  As described above, “fogging” is mainly caused by a reversal toner (in this embodiment, a positively charged toner). Accordingly, in a system in which a transfer bias having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied, the reversal toner should not be easily transferred to the transfer material S.

  In the present invention, paying attention to the essence, as a means for causing the reversal toner to move faithfully to the transfer electric field, the speed between the moving speed of the photosensitive drums 11, 12, 13, 14 and the moving speed of the ETB 8 is used. A difference (moving speed difference (circumferential speed difference)) is provided.

  By providing a speed difference between the moving speed of the photosensitive drums 11, 12, 13, and 14 and the moving speed of the ETB 8, the toner receives a dynamic stimulus and becomes physically easy to move. It becomes easy. As a result, the reversal toner remains on the photosensitive drums 11, 12, 13, and 14 without being transferred to the transfer material S, and only the toner charged to the normal polarity (negative polarity in this embodiment) of the image portion is transferred to the transfer material S. It becomes easy to be transferred to. For this reason, "fogging" can be suppressed.

  Further, since it is essentially important to give dynamic stimulation to the reversal toner on the photosensitive drums 11, 12, 13, and 14, the moving speed of the photosensitive drums 11, 12, 13, and 14 where the reversal toner exists is present. On the other hand, increasing the moving speed of the ETB 8 has an effect of suppressing “fogging”.

  A conceptual diagram of the mechanism is shown in FIG. FIG. 2 shows the relationship between the fog amount (%) and the difference (%) in the moving speed of the photosensitive drums 11, 12, 13, and 14 with respect to the moving speed of the ETB 8.

  Here, the fog amount (%) is calculated based on the difference in the amount of reflected light between a portion where fog does not occur and a portion where fog occurs. The portion where fog does not occur indicates a portion where the printing surface side of the transfer material S is masked with a tape or the like and the masking portion is removed after printing. If the amount of reflected light in a portion where fog is not generated is 100% and the amount of reflected light in a portion where fog is generated is 95% of that, the amount of fog is 5%. As a measuring device for the amount of reflected light, DENSOMETER TC-6DS (manufactured by Tokyo Denshoku Technical Center) was used.

  As can be seen from FIG. 2, when the difference between the moving speed of the photosensitive drums 11, 12, 13, 14 and the moving speed of the ETB 8 is 0%, the fog amount (%) on the transfer material S is about 4%. is there. On the other hand, if a moving speed difference is made between the photosensitive drums 11, 12, 13, 14 and the ETB 8, the reversal toner receives a dynamic stimulus and moves faithfully to the transfer electric field. Is reduced. As described above, the transfer speed of the ETB 8 is faster than the transfer speed of the photosensitive drums 11, 12, 13, and 14 (in FIG. 2, the sign of% on the horizontal axis is in the negative direction). This is effective in reducing “fogging” on the material S.

  Note that FIG. 2 is created based on experimental results when smooth paper is used as the transfer material S. Here, the plain paper, smooth paper, and rough paper were distinguished by measuring the surface smoothness of each transfer material based on the JIS-P8119 method. The following table shows the measurement results and the distinction between the transfer material S types.

  Next, the difference in moving speed between the moving speed v1 [mm / s] of the photosensitive drums 11, 12, 13, and 14 and the moving speed v2 [mm / s] of the ETB 8 in this embodiment will be described. Here, the moving speed difference between the photosensitive drums 11, 12, 13, 14 and the ETB 8 is defined as Δv12 [%] calculated by the following equation. That is, it is the difference in the moving speed of the photosensitive drums 11, 12, 13, and 14 with respect to the moving speed of the ETB 8.

Δv12 [%] = (v1−v2) / v2 * 100 (1)
However, if a moving speed difference is provided between the photosensitive drums 11, 12, 13, and 14 and the ETB 8, the speed difference is generated when the transfer material S conveyed by the ETB 8 contacts the photosensitive drums 11, 12, 13, and 14. A frictional force is generated. For this reason, the ETB 8 is affected by the moving speed of the photosensitive drums 11, 12, 13, and 14 via the transfer material S. As a result, the movement speed fluctuation (circumferential speed fluctuation) of the ETB 8 occurs. As a result, the toner image is transferred to a position shifted from the position where the toner image should be transferred. Then, a shift amount of the transfer position for each color image forming station P1, P2, P3, P4 occurs. Hereinafter, this phenomenon is referred to as “color shift”.

  Therefore, it is necessary to set a moving speed difference that can reduce “fogging” within a range in which “color misregistration” does not deteriorate.

  FIG. 3 shows the relationship between the color misregistration amount (μm) and the difference (%) in the moving speed of the ETB 8 with respect to the moving speed of the photosensitive drums 11, 12, 13, 14 when rough paper is used as the transfer material S. Show.

  Also, the color misregistration amount (μm) in this embodiment is the distance in the sub-scanning direction from the leading edge of the transfer material S of each color line printed on the transfer material S, and cyan relative to the black position. , Magenta and yellow. The value of the color misregistration value is + when the positions of cyan, magenta, and yellow from the leading edge of the transfer material S are far from black, and when the positions of cyan, magenta, and yellow from the leading edge of the transfer material S are closer than black. In the following, unless otherwise specified, the magnitude of the color misregistration amount (μm) is discussed in terms of its absolute value.

  In the graph shown in FIG. 3, only the color shift due to the difference in the moving speed of the photosensitive drums 11, 12, 13, and 14 with respect to the moving speed of the ETB 8 is extracted and displayed. Further, the graph shown in FIG. 3 shows the result of the color misregistration amount (μm) between the first image forming station P1 and the fourth image forming station P4 in which the influence of the movement speed fluctuation of the ETB 8 appears most noticeably. .

  As can be seen from the graph shown in FIG. 3, when the moving speed of the ETB 8 is faster than the moving speed of the photosensitive drums 11, 12, 13, and 14 (in FIG. 3, the sign of% on the horizontal axis is in the negative direction) When the difference (%) in the moving speed of the ETB 8 relative to the moving speed of the photosensitive drums 11, 12, 13, and 14 is 1% or more, the color misregistration amount (μm) does not change much. On the other hand, when the moving speed of the ETB 8 is slower than the moving speed of the photosensitive drums 11, 12, 13, and 14 (in FIG. 3,% on the horizontal axis is a positive sign), the color shift occurs according to the moving speed difference. The amount (μm) increases linearly.

  This is considered due to the following reasons. That is, when the moving speed of the ETB 8 is slower than the moving speed of the photosensitive drums 11, 12, 13, 14, the DC motor (not shown) that drives the ETB 8 moves the moving speed of the photosensitive drums 11, 12, 13, 14. It is affected by and is turned quickly. On the other hand, if the moving speed of the ETB 8 is faster than the moving speed of the photosensitive drums 11, 12, 13, and 14, the DC motor driving the ETB 8 is controlled to rotate at a desired number of rotations. , 12, 13 and 14 are not affected by the moving speed. Therefore, with regard to “color misregistration”, it is desirable that the moving speed of the ETB 8 is faster than the moving speed of the photosensitive drums 11, 12, 13, and 14.

In this embodiment, the image forming apparatus 100 is a tandem type direct transfer multicolor image apparatus for transferring a toner image is directly to the transfer material S on ETB8. For this reason, as a factor affecting the transport speed of the transfer material S on the ETB 8, the supply speed (paper feed speed) of the transfer material S in addition to the difference in movement speed between the ETB 8 and the photosensitive drums 11, 12, 13, and 14 described above. And the influence of the fixing speed (conveying speed of the transfer material S by the fixing device 9).

  In the case of a tandem type direct multicolor image apparatus, the level of “color shift” varies depending on the type of the transfer material S. The “color shift” level when smooth paper is used as the transfer material S is better than when rough paper is used (that is, the color shift amount (μm) is small). This is because the area of contact between the ETB 8 and the transfer material S is larger on smooth paper than on rough paper, and as a result, the adsorption force between the transfer material S and ETB is increased. That is, if the attracting force between the transfer material S and the ETB 8 is weak, there is a speed difference between the supply speed of the transfer material S and the moving speed of the ETB 8 and a speed difference between the fixing speed and the moving speed of the ETB 8. This is because the transfer material S is misaligned, thereby causing a color shift. For these reasons, when smooth paper and rough paper are compared, smooth paper has less influence on “color shift” with respect to the absolute value of the movement speed difference Δv12.

  The level of “fogging” varies depending on the type of the transfer material S. In the case of smooth paper, the “fog” level becomes worse (that is, the fog amount (%) becomes larger). This is because when the fog reversal toner is fixed by the fixing device 9, the paper surface is smooth, so that the toner does not enter the paper fibers and is crushed and fixed, and as a result, the fog reversal toner is noticeable. . Rough paper (paper with a rough surface) is fixed with toner entering the paper fiber, making it less noticeable and therefore the level of “fogging” is improved (that is, the amount of fog (%)). Becomes smaller).

  The dependency of the “fogging” and “color shift” levels on the movement speed difference Δv12 for the two types of transfer materials S was confirmed. The examination results are shown in Table 2. Table 2 shows data in a high-temperature and high-humidity environment (30 ° C., 80%) so that the difference between “fogging” and “color shift” can be easily understood.

The determination criteria for the “fogging” and “color shift” levels in Table 2 are as follows.
1: Level in which generation is not observed 3: Level that does not cause a problem in practical use 5: Conspicuous level

  According to this examination result, it can be seen that the moving speed difference Δv12 that satisfies both “fogging” and “color shift” varies depending on the type of the transfer material S. With rough paper, both “fogging” and “color shift” can be suppressed to a satisfactory level when Δv12 = 0 to −1%. On the other hand, in the smooth paper, both “fogging” and “color shift” can be suppressed to a satisfactory level when Δv12 = −1 to −3%.

  Therefore, in this embodiment, the moving speed Δv12 is changed according to the type of the transfer material S as specific image forming conditions (printing conditions, printing conditions). That is, in this embodiment, the specific image forming conditions are defined by the type of transfer material. As described above, the moving speed v2 of the ETB 8 is preferably set to be equal to or higher than the moving speed v1 of the photosensitive drums 11, 12, 13, and 14.

  More specifically, in this embodiment, when printing on smooth paper as the transfer material S, the CPU 111 selects the moving speed difference Δv12 for smooth paper. More specifically, in this embodiment, when the transfer material S is smooth paper, the moving speed difference Δv12 is set to −2%. On the other hand, when a material other than smooth paper (rough paper or the like) is used as the transfer material S, the moving speed difference Δv12 is set to 0%.

  According to the study by the present inventor, even when smooth paper advantageous for the problem of color misregistration is used, the absolute value of the moving speed difference Δv12 is preferably within 3%. If the moving speed difference Δv12 exceeds 3%, color misregistration deteriorates and an image defect may occur.

  In this embodiment, the moving speed difference Δv12 is changed by changing the moving speed v1 of the photosensitive drums 11, 12, 13, and 14. The movement speed v1 of the photosensitive drums 11, 12, 13, and 14 is controlled by the CPU 111 controlling the rotational driving of the DC motor 80 (FIG. 4) that is the driving source of the photosensitive drums 11, 12, 13, and 14. Is called. The drive source may be common to all or some of the plurality of photosensitive drums 11, 12, 13, and 14, or may be provided individually for each.

  As described above, the CPU 111 changes the control speed of the DC motor 80 (FIG. 4), which is the drive source of the photosensitive drums 11, 12, 13, and 14, thereby moving the moving speed v1 of the photosensitive drums 11, 12, 13, and 14. And the moving speed difference Δv12 is changed. In this embodiment, in a personal computer (external device) 140 (FIG. 4) that is communicably connected to the image forming apparatus 100, the CPU 111 moves based on the type of the transfer material S set on the printer driver by the operator. The speed difference Δv12 is controlled.

  This will be further described with reference to FIG. FIG. 4 is a schematic control block diagram of the image forming apparatus 100 according to the present embodiment. In FIG. 4, only the first image forming station P1 is shown for the image forming station, but the control mode is the same for the other image forming stations.

  The image forming apparatus 100 includes an image forming control unit 110 that performs overall control of apparatus operation. The control unit 50 includes a CPU 111 as a central element (control means) for control, and a main memory 112 such as a ROM is connected to the CPU 111 as a storage means. The main memory 112 stores programs executed by the CPU 111 and various data. Further, the CPU 111 is connected with a memory 113 such as a RAM or a nonvolatile memory used as a working memory or the like as a storage means. The CPU 111 causes the image forming apparatus 100 to perform a sequence operation according to data, programs, and the like stored in the main memory 112.

  An image processing unit (video controller) 120 is connected to the image formation control unit 110. The image processing unit 120 receives an image signal from an external device 140 such as a personal computer that is communicably connected to the image forming apparatus main body A, and uses this signal as a signal related to image formation in the image forming apparatus 100. The image is converted and transmitted to the CPU 111 of the image formation control unit 110. The CPU 111 controls the operation of each unit of the image forming apparatus 100 in accordance with such an image forming signal.

  In this embodiment, the CPU 111 receives a signal indicating the type of the transfer material S transmitted from the personal computer 140 in accordance with an input from the operator. Then, the CPU 111 changes the moving speed difference Δv12 according to the type of the instructed transfer material S. That is, the CPU 111 selects an appropriate moving speed difference Δv12 from the moving speed difference Δv12 data stored in the main memory 112 in association with the type of the transfer material S. The CPU 111 generates a signal for changing the drive speed of the DC motor 80 that is the drive source of the photosensitive drums 11, 12, 13, and 14 in accordance with the movement speed difference Δv 12 selected in this way. The DC motor 80 rotationally drives the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal.

  Next, the correlation between the pressure at which the transfer rollers 51, 52, 53, and 54 contact the photosensitive drums 11, 12, 13, and 14 (hereinafter referred to as “transfer pressure”) and the “fogging” and “color shift” levels will be described. To do. In the present embodiment, the transfer pressure is preferably set as described below.

In order to make it difficult to transfer the fog reversal toner to the transfer material S, it is more effective to lower the transfer pressure. However, if the transfer pressure is too low, “transfer omission” occurs, and the original transfer property is impaired. Therefore, it is necessary to select a transfer pressure that achieves both “fogging” and “transfer omission”. Table 3 shows the transfer pressure dependency of the “fogging” and “ transfer omission ” levels when the moving speed difference Δv12 is 2%. Table 3 shows the result when smooth paper is used as the transfer material S as a representative example, but the following discussion is significant regardless of the type of the transfer material S.

The criteria for determining “fogging” and “ transfer missing ” levels in Table 3 are as follows.
1: Level in which generation is not observed 3: Level that does not cause a problem in practical use 5: Conspicuous level

From Table 3, it can be seen that the level of “fogging” and “ transfer missing ” varies depending on the transfer pressure, and the transfer pressure that achieves both is 1.96 to 3.92 [N]. For this reason, in this embodiment, the total transfer pressure is set to 2.94 [N]. Here, the total transfer pressure refers to the transfer pressure of the transfer roller to the photosensitive drum in one image forming station.

  As described above, according to the present embodiment, the moving speed difference Δv12 is changed according to the type of the transfer material S. Thereby, regardless of the type of the transfer material S, “fogging” and “color shift” can be suppressed to a good level. That is, by providing the moving speed difference Δv12 for each type of the transfer material S, both “fogging” and “color misregistration” can be satisfied, and high-quality printing is possible.

  In the above-described embodiment, the type of the transfer material S is determined from the setting on the printer driver by the operator. However, the present invention is not limited to this. A transfer material type detection unit that automatically detects the smoothness of the surface of the transfer material S can be installed in the image forming apparatus main body A. As the transfer material type detection means, for example, there can be used a method in which light is applied to a transfer material to make a determination based on the amount of reflected light, or a method in which a transfer material surface state is determined by an image sensor such as a CCD. In this case, the detection signal of the transfer material type detection unit is input to the CPU 111, and the CPU 111 determines whether the paper is smooth paper from the detection result of the transfer material type detection unit. Thus, the moving speed difference Δv12 between the photosensitive drums 11, 12, 13, 14 and the ETB 8 can be changed in the same manner as described above. Therefore, the same effect as in the present embodiment can be obtained.

  In the above-described embodiment, the movement speed difference Δv12 is changed by changing the movement speed v1 of the photosensitive drums 11, 12, 13, and 14. However, the present invention is not limited to this. Even if the moving speed difference Δv12 is changed by changing the moving speed v2 of the ETB 8, the same effect as in the present embodiment can be obtained. However, in this case, it is necessary to change the writing timing of each color in accordance with the speed change of the ETB 8.

Example 2
Next, a second embodiment of the present invention will be described. Elements having functions and configurations that are substantially the same as or equivalent to those of the image forming apparatus of the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  This embodiment is characterized in that the moving speed difference Δv12 is changed depending on the print mode as a specific image forming condition. In other words, in this embodiment, the specific image forming conditions are defined by the print mode.

  “Fog” correlates with the process speed. When the process speed is slow, the time during which the developing roller and the photosensitive drums 11, 12, 13, and 14 are in contact with each other becomes longer, so that “fog” is deteriorated.

  Therefore, the absolute value of the moving speed difference Δv12 is increased within a range where the “color shift” level described in the first embodiment does not deteriorate at a low process speed at which “fogging” deteriorates. Thereby, “fogging” on the transfer material S can be suppressed. Particularly, since the high image quality is required in the low speed mode, the effect is great.

  Table 4 shows the setting of the moving speed difference Δv12 [%] depending on the print mode in this embodiment.

  More specifically with reference to FIG. 4, the CPU 111 receives a signal indicating a print mode transmitted from the personal computer 140 in accordance with an input from the operator. Then, the CPU 111 changes the movement speed difference Δv12 according to the instructed print mode. That is, the CPU 111 selects an appropriate moving speed difference Δv12 from the data (Table 4) of the moving speed difference Δv12 stored in the main memory 112 in association with the print mode. The CPU 111 generates a signal for changing the driving speed of the DC motor 80 that is the driving source of the photosensitive drums 11, 12, 13, and 14 in accordance with the movement speed difference Δv 12 selected in this way. The DC motor 80 rotationally drives the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal.

  As described above, according to the present embodiment, the moving speed difference Δv12 [%] is appropriately changed according to the print mode. Thereby, the “fogging” level in each mode can be appropriately reduced without deteriorating “color misregistration”.

  In the present embodiment described above, the moving speed difference Δv12 is changed by changing the moving speed v1 of the photosensitive drums 11, 12, 13, and 14. However, as described in the first embodiment, the movement of the ETB 8 is changed. Even if the speed v2 is changed, the same effect as in the present embodiment can be obtained. However, in this case, it is necessary to change the writing timing of each color in accordance with the speed change of the ETB 8.

  Of course, it may be combined with the moving speed difference Δv12 corresponding to the type of the transfer material S described in the first embodiment. Thereby, further high-quality printing is possible.

Example 3
Next, a third embodiment of the present invention will be described. Elements having functions and configurations that are substantially the same as or equivalent to those of the image forming apparatuses of the above embodiments are given the same reference numerals, and detailed descriptions thereof are omitted.

  The present embodiment is characterized in that the moving speed difference Δv12 is changed as a specific image forming condition depending on the detection result of the atmosphere environment detection means. That is, in this embodiment, the specific image forming condition is defined by the atmosphere environment detected by the atmosphere environment detection unit.

  The level of “fogging” varies depending on the atmospheric environment inside and outside the image forming apparatus. For example, when the ambient temperature inside and outside the image forming apparatus is a high-temperature and high-humidity environment (for example, 30 ° C./80% [RH: relative humidity]), the normal environment (for example, 23 ° C./60% R.H. H.) and low-temperature and low-humidity environments (for example, 15 ° C./10% [RH: relative humidity]), the toner tribo is attenuated by the humidity in the air. The level of “fog” gets worse.

  Therefore, in this embodiment, the temperature / humidity sensor 130 (FIG. 4) is installed in the image forming apparatus 100 as an atmospheric environment detection unit. Then, the moving speed v <b> 1 of the photosensitive drums 11, 12, 13, 14 is changed according to the detection result by the temperature / humidity sensor 130.

  In a high-temperature and high-humidity environment where the level of “fogging” is low, the absolute value of the movement speed difference Δv12 is increased within a range where the “color shift” level described in the first embodiment is not deteriorated. Thereby, deterioration of the “fogging” level can be suppressed.

  Table 5 shows the setting of the movement speed difference Δv12 [%] depending on the atmospheric environment (temperature [° C.], humidity [RH: relative humidity]) in this example. In this embodiment, the moving speed difference Δv12 is changed according to the temperature and humidity as the atmospheric environment, but the moving speed difference Δv12 may be changed according to either the temperature or the humidity.

  If it further demonstrates with reference to FIG. 4, the detection signal of the temperature / humidity sensor 130 is input into CPU111. The CPU 111 determines the atmospheric environment (temperature, humidity) from the detection signal input from the temperature / humidity sensor 130. Then, the CPU 111 changes the movement speed difference Δv12 according to the atmospheric environment (temperature, humidity). That is, the CPU 111 selects an appropriate moving speed difference Δv12 from the data (Table 5) of the moving speed difference Δv12 stored in the main memory 112 in association with the atmospheric environment (temperature, humidity). The CPU 111 generates a signal for changing the driving speed of the DC motor 80 that is the driving source of the photosensitive drums 11, 12, 13, and 14 in accordance with the movement speed difference Δv 12 selected in this way. The DC motor 80 rotationally drives the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal.

  As described above, according to the present exemplary embodiment, the detection unit for the atmospheric temperature and / or the atmospheric humidity inside and outside the image forming apparatus is provided, and the moving speed difference Δv12 [%] is changed according to the detection result. Thereby, the “fogging” level can be suppressed to a good level according to the atmosphere environment without deteriorating the “color shift” level.

  In the above-described embodiment, the moving speed difference Δv12 is changed by changing the moving speed v1 of the photosensitive drums 11, 12, 13, and 14. However, as described in the first embodiment, the ETB8 Even if the moving speed v2 is changed, the same effect as in the present embodiment can be obtained. However, in this case, it is necessary to change the writing timing of each color in accordance with the speed change of the ETB 8.

  Of course, it may be combined with the moving speed difference Δv12 corresponding to the type of the transfer material S described in the first embodiment. Thereby, further high-quality printing is possible. Table 5 shows the setting of the movement speed difference Δv12 [%] depending on the atmosphere environment (temperature, humidity) for each type of transfer material (rough paper, smooth paper).

Example 4
Next, a fourth embodiment of the present invention will be described. Elements having functions and configurations that are substantially the same as or equivalent to those of the image forming apparatuses of the above embodiments are given the same reference numerals, and detailed descriptions thereof are omitted.

  In this embodiment, as a specific image forming condition, the moving speed difference Δv12 is changed based on the result of detecting the electrical resistance of a member related to transfer, that is, the transfer portion. That is, in this embodiment, the specific image forming condition is defined by the result of detecting the electrical resistance of the transfer portion. In other words, in this embodiment, instead of the temperature / humidity sensor 130 described in the third embodiment, as a means for detecting the atmospheric environment, the difference in movement speed is based on the result of detecting the electrical resistance of the transfer portion. Δv12 is changed.

  In the image forming apparatus 100 according to the present exemplary embodiment, the transfer bias is controlled by ATVC (Active Transfer Voltage Control). The ATVC detects the impedance of the entire transfer portion by applying a predetermined current or voltage bias before the transfer material S reaches the transfer portion (when paper is not passed) (ie, detects the generated voltage or generated current). The transfer bias applied to the transfer member in order to transfer the toner image to the transfer material S when the transfer material S enters the transfer portion (when paper is passed) is determined based on the detection result. . According to ATVC, since the transfer bias is selected according to the impedance of the actual transfer portion, a good transfer bias can be selected according to the environment and the size of the transfer material S.

  In the present embodiment, the atmospheric environment is detected by using the result of this ATVC. That is, in this embodiment, a transfer bias of 1 kV is applied to the transfer roller 51 of the first image forming station P1 when no paper is passed, and the current flowing at this time is detected. Since the detected current changes according to the atmospheric environment, the atmospheric environment can be determined from the detected current value. Then, the moving speed difference Δv12 is changed according to the determined atmosphere environment.

  Here, the detection of the electrical resistance of the transfer portion means that the generated voltage changes substantially in accordance with the change in the electrical resistance of the transfer portion when a predetermined current or voltage bias is applied to the transfer member. Detecting the generated current.

  Under a high temperature and high humidity with a large detection current, the moving speed difference Δv12 is increased within a range in which the “color shift” level described in the first embodiment is not deteriorated. Thereby, deterioration of the “fogging” level can be suppressed.

  Table 6 shows the setting of the movement speed difference Δv12 [%] according to the ATVC detection current in this example.

More specifically with reference to FIG. 4, in the image forming apparatus 100 of the present embodiment, the transfer bias power supply 71 as the transfer bias applying means includes a current detector as a current detecting means , and the detection signal is , Input to the CPU 111. The CPU 111 changes the movement speed difference Δv12 according to the detection signal (that is, the atmospheric environment (temperature, humidity)) input from the transfer bias power source 71. That is, the CPU 111 selects an appropriate moving speed difference Δv12 from the data (Table 6) of the moving speed difference Δv12 stored in the main memory 112 in association with the ATVC detection current. The CPU 111 generates a signal for changing the driving speed of the DC motor 80 that is the driving source of the photosensitive drums 11, 12, 13, and 14 in accordance with the movement speed difference Δv 12 selected in this way. The DC motor 80 rotationally drives the photosensitive drum 11 so as to move the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal.

  As described above, according to this embodiment, the ambient temperature and humidity inside and outside the image forming apparatus are determined by the electrical resistance detection unit of the transfer unit, and the moving speed difference Δv12 is changed. Thereby, the “fogging” level can be suppressed to a good level according to the atmosphere environment without deteriorating the “color shift” level. In addition, according to the present embodiment, since it is not necessary to install a temperature / humidity sensor, the apparatus configuration can be simplified as compared with the third embodiment, and there is an advantage that the cost can be reduced.

  In the above-described example, the movement speed difference Δv12 is changed by changing the movement speed v1 of the photosensitive drums 11, 12, 13, and 14. However, as described in the first embodiment, the movement of the ETB 8 is changed. Even if the speed v2 is changed, the same effect as in the present embodiment can be obtained. However, in this case, it is necessary to change the writing timing of each color in accordance with the speed change of the ETB 8.

  Of course, it may be combined with the moving speed difference Δv12 corresponding to the type of the transfer material S described in the first embodiment. Thereby, further high-quality printing is possible. Table 6 shows the setting of the moving speed difference Δv12 [%] depending on the ATVC detection current for each type of transfer material (rough paper, smooth paper).

Example 5
Next, a fifth embodiment of the present invention will be described. Elements having functions and configurations that are substantially the same as or equivalent to those of the image forming apparatuses of the above embodiments are given the same reference numerals, and detailed descriptions thereof are omitted.

  The present embodiment is characterized in that the moving speed difference Δv12 is changed according to the detection result of the usage (life) of the image forming apparatus 100 as a specific image forming condition. That is, in this embodiment, the specific image forming condition is defined by the usage amount of the image forming apparatus.

  As the number of image formations of the image forming apparatus 100 increases and the life of the image forming apparatus 100 increases, the deterioration of the toner proceeds. As a result, the toner tribo is attenuated, the reversal toner is increased, and the “fogging” level is deteriorated.

  Therefore, in this embodiment, the CPU 111 of the image forming apparatus 100 counts the number of times of image formation (the number of sheets to be passed) on the transfer material S, and the number of sheets to be passed is recorded by a recording unit (memory such as a nonvolatile memory in the image forming apparatus 100. ) 113. Then, the CPU 111 further refers to the number of passing sheets recorded in the recording means (memory) 113, and changes the moving speed v1 of the photosensitive drums 11, 12, 13, and 14 as the number of passing sheets increases. Thus, the moving speed difference Δv12 is changed to be higher. As a result, it is possible to prevent the “fogging” level from deteriorating while keeping the “color shift” to a certain extent.

  Table 7 shows the setting of the movement speed difference Δv12 [%] according to the cumulative number of sheets passed in the normal environment in this embodiment.

  If further described with reference to FIG. 4, as described above, the CPU 111 counts the number of sheets passed and records it in the memory 113. Then, the CPU 111 changes the moving speed difference Δv12 according to the accumulated sheet passing number Cp read from the memory 113. That is, the CPU 111 selects an appropriate moving speed Δv12 from the data (Table 7) of the moving speed difference Δv12 stored in the main memory 112 in association with the accumulated sheet passing number Cp. The CPU 111 generates a signal for changing the driving speed of the DC motor 80 that is the driving source of the photosensitive drums 11, 12, 13, and 14 in accordance with the movement speed difference Δv 12 selected in this way. The DC motor 80 rotationally drives the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal.

  As described above, according to the present embodiment, according to the detection result of the number of image formations serving as a life index, the moving speed difference Δv12 [ %] Is changed. Thereby, the “fogging” level could be suppressed to a favorable level.

  In the present exemplary embodiment, the number of times of image formation (number of sheets to be passed) is used as an index of the usage amount of the image forming apparatus 100, but the present invention is not limited to this. In addition, for example, the total number of rotations of the developing roller and the remaining amount of toner can be used.

  In the present embodiment described above, the moving speed difference Δv12 is changed by changing the moving speed v1 of the photosensitive drums 11, 12, 13, and 14. However, as described in the first embodiment, the ETB8 Even if the moving speed v2 is changed, the same effect as in the present embodiment can be obtained. However, in this case, it is necessary to change the writing timing of each color in accordance with the speed change of the ETB 8.

  Of course, it may be combined with the moving speed difference Δv12 corresponding to the type of the transfer material S described in the first embodiment. Thereby, further high-quality printing is possible. Table 7 shows the setting of the moving speed difference Δv12 [%] according to the total number of sheets set for each type of transfer material (rough paper, smooth paper).

Example 6
Next, a sixth embodiment of the present invention will be described. Elements having functions and configurations that are substantially the same as or equivalent to those of the image forming apparatuses of the above embodiments are given the same reference numerals, and detailed descriptions thereof are omitted.

  As described in the fifth exemplary embodiment, the deterioration of the toner progresses as the number of image formations of the apparatus increases and the life of the apparatus increases. For this reason, the toner tribo is attenuated, the reversal toner is increased, and the “fogging” level is deteriorated. As described in the third and fourth embodiments, the “fogging” level varies depending on the atmosphere environment inside and outside the image forming apparatus. For example, when the ambient temperature inside and outside the image forming apparatus is a high-temperature and high-humidity environment (for example, 30 ° C./80% [R.H .: relative humidity]), the normal environment (for example, 23 ° C./60% [R.H. .: Relative humidity]) and low-temperature and low-humidity environments (for example, 15 ° C./10% [RH: relative humidity]), the toner tribo is attenuated by the humidity in the air. As a result, the “fogging” level deteriorates.

  In the present embodiment, as a specific image forming condition, the moving speed difference Δv12 is changed based on the amount of light reflected from the surface of the ETB 8 by the optical sensor 10. In other words, in the present embodiment, the specific image forming condition is defined by the amount of light reflected from the surface of the ETB 8 by the optical sensor 10.

  In other words, as described above, the image forming apparatus 100 of the present embodiment is provided with the registration detection sensor 10 as an optical sensor on the downstream side of the drive roller 102 in the surface movement direction of the ETB 8. This registration detection sensor 10 is used as detection means for detecting the amount of reflected light on the surface of the ETB 8 for controlling the movement speed difference Δv12. In this embodiment, a pair (two) of registration detection sensors 10 are arranged in the thrust direction of the ETB 8. In order to control the movement speed difference Δv12, either one of the two registration detection sensors 10 or both of them may be used.

  When “fogging” deteriorates, the amount of reflected light on the surface of the ETB 8 decreases. Therefore, the amount of reflected light on the surface of the ETB 8 detected by the registration sensor 10 at the time of pre-printing rotation (during preparatory operation before image formation) or post-rotation (during preparatory operation after image formation) is monitored. When the detected value exceeds a predetermined threshold (that is, when the amount of light reflected from the ETB 8 is lower than the predetermined value), the moving speed v1 of the photosensitive drums 11, 12, 13, and 14 is changed. . As a result, it is possible to set the movement speed difference Δv12 where “fogging” is unlikely to occur.

  The threshold value of the detection output of the registration detection sensor 10 is not particularly limited, and may be appropriately determined through experiments or the like so that “fogging” can be suppressed to a desired level and according to the configuration of the ETB 8 to be used. It can be set.

  As a result, for example, in the initial state of toner with little deterioration, or in a normal environment where the toner tribo is difficult to attenuate or in a low temperature and low humidity environment, “fogging” does not occur, so the moving speed difference Δv12 that is most advantageous for “color shift” is selected. Can be printed. In addition, since “fogging” occurs in a state where toner deterioration has progressed or in a high-temperature and high-humidity environment, a moving speed difference Δv12 for suppressing “fogging” is selected to achieve both “color shift” and “fogging”. Can be printed.

  This will be further described with reference to the block diagram of FIG. 4 and the flowchart of FIG. A detection signal of the registration detection sensor 10, that is, information (P) indicating the amount of reflected light of the ETB 8 is input to the CPU 111 at the time of pre-rotation or post-rotation (S101). The CPU 111 compares the detection signal input from the registration detection sensor 10 with a predetermined threshold value stored in the main memory 112 (S102). That is, the CPU 111 constantly monitors whether the reflected light amount (P) on the surface of the ETB 8 detected by the registration detection sensor 10 during the pre-rotation or the post-rotation is lower than the predetermined value (X). When the detection result of the registration detection sensor 10 exceeds a predetermined threshold value (that is, when the reflected light amount (P) from the ETB 8 becomes lower than the predetermined value (X)), the following image forming operation is performed in advance. The moving speed difference Δv12 is changed by an appropriate amount according to the data stored in the main memory 112 (S103). That is, the CPU 111 generates a signal for changing the drive speed of the DC motor 80 that is the drive source of the photosensitive drums 11, 12, 13, 14 in order to change the movement speed difference Δv 12 by a predetermined amount. The DC motor 80 rotationally drives the photosensitive drum 11 so as to move the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal. On the other hand, if it is determined in S102 that the amount of reflected light (P) by the registration detection sensor 10 is equal to or greater than the predetermined value (X), the moving speed difference Δv12 is not changed (S104).

  As described above, according to the present embodiment, the movement speed difference Δv12 is changed by detecting the amount of reflected light on the surface of the ETB 8 using the registration detection sensor 10 and constantly monitoring the “fogging” amount. As a result, both “color shift” and “fogging” can be satisfied according to the deterioration state of the toner and the ambient temperature inside and outside the image forming apparatus.

  In the above-described embodiment, the moving speed difference Δv12 is changed by changing the moving speed v1 of the photosensitive drums 11, 12, 13, and 14. However, as described in the first embodiment, the ETB8 Even if the moving speed v2 is changed, the same effect as in the present embodiment can be obtained. However, in this case, it is necessary to change the writing timing of each color in accordance with the speed change of the ETB 8.

  Of course, it may be combined with the moving speed difference Δv12 corresponding to the type of the transfer material S described in the first embodiment. Thereby, further high-quality printing is possible.

Example 7
Next, a seventh embodiment of the present invention will be described. Elements having functions and configurations that are substantially the same as or equivalent to those of the image forming apparatuses of the above embodiments are given the same reference numerals, and detailed descriptions thereof are omitted.

  In the present embodiment, as in the sixth embodiment, the movement speed difference Δv12 is controlled by using the registration detection sensor 10 that is an optical sensor.

  In particular, in this embodiment, the amount of reflected light on the surface of the ETB 8 by the registration detection sensor 10 after cleaning the ETB 8 by the ETB cleaning device 104 as a transfer material conveying means cleaning means is compared with the amount of reflected light on the ETB 8 after printing. Do. Then, when the compared value (typically, the difference) exceeds a predetermined threshold, the moving speed difference Δv12 is changed. That is, in this embodiment, the specific image forming condition is defined by a result of comparing the amount of reflected light on the surface of the ETB 8 immediately after cleaning the ETB 8 by the ETB cleaning device 104 and the amount of reflected light on the surface of the ETB 8 after printing. Is.

  This embodiment is a tandem type direct transfer multicolor image apparatus that directly transfers to a transfer material S on the ETB 8. For this reason, as the number of image formations of the apparatus increases and the lifespan advances, paper dust adheres to the ETB 8 and the amount of reflected light of the ETB 8 decreases.

  Therefore, in this embodiment, the amount of reflected light on the surface of the ETB 8 after cleaning is recorded in recording means (memory) 113 such as a nonvolatile memory in the image forming apparatus main body A. Then, the value is compared with the amount of reflected light of the ETB 8 after printing.

  Thereby, it is possible to detect “fogging” on the ETB 8 in a state including a decrease in the amount of reflected light on the surface of the ETB 8 due to durability deterioration of the ETB 8. As a result, it is possible to reliably determine a decrease in the amount of reflected light due to “fogging”. In addition, the same effects as in the sixth embodiment can be obtained.

  This will be further described with reference to the block diagram of FIG. 4 and the flowchart of FIG. First, the amount of reflected light of the ETB 8 immediately after cleaning is measured by the registration detection sensor 10. That is, a detection signal of the registration detection sensor 10 immediately after cleaning, that is, information (Pcl) indicating the amount of reflected light of the ETB 8 immediately after cleaning is input to the CPU 111 (S201). The CPU 111 stores (stores) this Pcl in the memory 113 (S202). Next, the amount of reflected light of the ETB 8 after printing is measured by the registration detection sensor 10. That is, a detection signal of the registration detection sensor 10 after printing, that is, information (Pp) indicating the amount of reflected light of the ETB 8 after printing is input to the CPU 111 (S203). The CPU 111 compares the ratio (Pp / Pcl) between this Pp and Pcl stored in the memory 113 with a predetermined threshold (Z) stored in the main memory 112 (S204). When Pp / Pcl becomes smaller than the threshold value Z, the moving speed difference Δv12 is changed by an appropriate amount according to data stored in advance in the main memory 112 during the subsequent image forming operation (S205). That is, the CPU 111 generates a signal for changing the drive speed of the DC motor 80 that is the drive source of the photosensitive drums 11, 12, 13, 14 in order to change the movement speed difference Δv 12 by a predetermined amount. The DC motor 80 rotationally drives the photosensitive drum 11 so as to move the photosensitive drums 11, 12, 13, and 14 at a predetermined moving speed v1 according to this signal. On the other hand, if it is determined in S204 that Pp / Pcl is equal to or greater than the threshold value Z, the moving speed difference Δv12 is not changed (S206).

  As described above, according to this embodiment, the same effect as that of Embodiment 6 can be obtained, and fog on ETB 8 can be more reliably monitored to change movement speed difference Δv12.

  As a matter of course, by combining with the moving speed difference Δv12 corresponding to the type of the transfer material S described in the first embodiment, further high-quality printing can be performed.

  In the above-described embodiment, the image forming apparatus includes a plurality of image carriers (photosensitive drums) and a transfer material conveying unit that carries and conveys a transfer material onto which a toner image is transferred from the plurality of image carriers. Although the image forming apparatus provided is described, the present invention is not limited to this. The present invention is equally applicable when there is only one image carrier.

1 is a cross-sectional view of a main part of an image forming apparatus according to the present invention. FIG. 6 is a graph showing the relationship between fog on the transfer material and the moving speed difference (%) of the photosensitive drum with respect to the moving speed of the ETB. FIG. 6 is a graph showing a relationship between a difference in moving speed of the photosensitive drum and a color shift with respect to the moving speed of the ETB. It is a general | schematic control block diagram which shows the control aspect which concerns on the Example of this invention. It is a general | schematic control flowchart of the moving speed difference (DELTA) V12 in one Example of this invention. It is a general | schematic control flowchart of the moving speed difference (DELTA) V12 in the other Example of this invention.

Explanation of symbols

11-14 Photosensitive drum (image carrier)
21-24 Charging roller 31-34 Exposure device 41-44 Development device 51-54 Transfer roller (transfer member)
61-64 Photoconductor cleaning device 7 Adsorption roller 8 ETB (electrostatic transfer belt, transfer material conveying means)
9 Fixing device

Claims (8)

A plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of the image carriers via the transfer material conveyance belt, respectively. And a plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion, and a moving speed of the image carrier at the nip portion And an image forming apparatus capable of changing a difference between the moving speed of the transfer material conveying belt,
The absolute value of the difference between the moving speed of the image carrier and the moving speed of the transfer material conveyance belt when it is determined that the type of transfer material conveyed to the nip portion is smooth paper is the nip portion. Between the moving speed of the image carrier and the moving speed of the transfer material conveyance belt when it is determined that the type of transfer material conveyed to the transfer material is a transfer material whose surface smoothness is rougher than that of the smooth paper. An image forming apparatus characterized by being larger than an absolute value of a difference.   The image forming apparatus according to claim 1, wherein the type of the transfer material conveyed to the nip portion is determined to be smooth paper according to an operator's instruction.   A transfer material type detecting means for detecting the smoothness of the surface of the transfer material, and judging from the detection result of the transfer material detecting means that the type of the transfer material conveyed to the nip portion is smooth paper; The image forming apparatus according to claim 1, wherein:   When it is determined that the type of transfer material conveyed to the nip portion is smooth paper, the transfer speed of the transfer material conveyance belt when the type of transfer material conveyed to the nip portion is smoother than that of the smooth paper. 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is slower than a moving speed of the transfer material conveying belt when it is determined that the transfer material is of a rough type. 5. A plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of the image carriers via the transfer material conveyance belt, respectively. And a plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion, and a moving speed of the image carrier at the nip portion And an image forming apparatus capable of changing a difference between the moving speed of the transfer material conveying belt,
In the case of having environment detection means for detecting the temperature and humidity environment around the image forming apparatus and determining that the type of transfer material conveyed to the nip portion is smooth paper, the detection result of the environment detection means is The absolute value of the difference between the moving speed of the image carrier and the moving speed of the transfer material conveying belt in a high humidity and high temperature environment is the same as that in the case where the detection result of the environment detection means is a low humidity and low temperature environment. An image forming apparatus, wherein an absolute value of a difference between a moving speed of an image carrier and a moving speed of the transfer material conveying belt is larger. A plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of the image carriers via the transfer material conveyance belt, respectively. And a plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion, and a moving speed of the image carrier at the nip portion And an image forming apparatus capable of changing a difference between the moving speed of the transfer material conveying belt,
The transfer means having current detection means for detecting a current value flowing through the transfer means, and detected by the current detection means when it is determined that the type of the transfer material conveyed to the nip portion is smooth paper. The absolute value of the difference between the moving speed of the image carrier and the moving speed of the transfer material conveying belt when the current value flowing through the reference current value is greater than or equal to the reference current value is applied to the transfer means detected by the current detection means. An image forming apparatus, wherein an absolute value of a difference between a moving speed of the image carrier and a moving speed of the transfer material transport belt when a flowing current value is smaller than the reference current value . A plurality of movable image carriers that carry a toner image, a transfer material conveyance belt that is movable and conveys a transfer material, and a plurality of the image carriers via the transfer material conveyance belt, respectively. And a plurality of transfer means for transferring a toner image from the image carrier to a transfer material conveyed by the transfer material conveyance belt at the nip portion, and a moving speed of the image carrier at the nip portion And an image forming apparatus capable of changing a difference between the moving speed of the transfer material conveying belt,
When it is determined that the type of transfer material conveyed to the nip portion is smooth paper, the moving speed of the image carrier when the integrated value of the usage amount of the image forming apparatus is equal to or greater than a reference usage amount value, and the The absolute value of the difference between the transfer speed of the transfer material transport belt is the transfer speed of the image carrier and the transfer material transport belt when the integrated value of the use amount of the image forming apparatus is smaller than the reference use amount value. An image forming apparatus characterized by being larger than the absolute value of the difference between the moving speeds of the two.   The image forming apparatus according to claim 7, wherein the usage amount of the image forming apparatus is determined from the accumulated number of sheets to be passed.

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