JP2007101755A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which a toner image, obtained by superimposing at least different kinds of toner of two colors, can be transferred properly. <P>SOLUTION: When a multiple toner image, provided with first, second and third toner images comprising the different kinds of first toner, second toner and third toner (for example, toner of YMC), is formed on transfer material P on a transfer body 40, the second toner image is transferred later than the first toner image, and the third toner image is transferred later than the second toner image in the image forming apparatus 100. The apparatus 100 is constituted so that the value of bias output by a transfer bias output means, when the third toner image of the multiple toner image is transferred to the transfer material P on the transfer body 40 is decided, based on a result obtained by detecting the transfer characteristics of the first toner and the second toner. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 or an electrostatic recording system. More specifically, the present invention relates to an image forming apparatus that forms a multiple toner image by transferring a plurality of types of toners on a transfer target in an overlapping manner.

  In recent years, for example, 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.

  As an electrophotographic color image forming apparatus, for example, the following tandem (inline) type is available. The tandem image forming apparatus includes a plurality of image forming units that form different types (colors) of toner images. The image forming unit has an electrophotographic photosensitive member (photosensitive member) as an image carrier, and forms a toner image on the photosensitive member by an electrophotographic image forming process. The plurality of image forming units are arranged in parallel along the moving direction of the transfer target body onto which the toner image is transferred from the photoconductor.

  The tandem image forming apparatus is promising as a mainstay of future color printers because it can form color images at high speed.

  Electrophotographic color image forming apparatuses include a direct transfer method and an intermediate transfer method. Further description will be given in connection with the above-described tandem image forming apparatus. These direct transfer type and intermediate transfer type image forming apparatuses are as follows.

  The direct transfer type image forming apparatus includes a transfer material conveying unit. Generally, a belt member that moves endlessly, that is, a transfer belt, is used as the transfer material conveying means. The transfer belt carries a transfer material such as recording paper and sequentially conveys it toward each image forming unit. Then, different types (colors) of toner images formed in the respective image forming units are sequentially superimposed and transferred onto a transfer material on the transfer belt. At this time, a transfer bias is applied to the transfer member disposed so as to face the photoconductor of each image forming unit via the transfer belt, and the toner image on the photoconductor is electrostatically transferred onto the transfer material. .

  An intermediate transfer type image forming apparatus includes an intermediate transfer member. As the intermediate transfer member, a belt member that moves endlessly, that is, an intermediate transfer belt is generally used. Then, different types (colors) of toner images formed in the respective image forming units are sequentially superimposed on the intermediate transfer belt and transferred (primary transfer). At this time, the primary transfer bias is applied to the primary transfer means disposed so as to face the photoconductor of each image forming unit via the intermediate transfer belt, and the toner image on the photoconductor is electrostatically transferred to the intermediate transfer belt. Transferred onto the belt. Thereafter, the toner image on the intermediate transfer belt is collectively transferred (secondary transfer) onto a transfer material such as recording paper. At this time, the secondary transfer bias is applied to one or both of the members opposed to each other so as to sandwich the intermediate transfer belt as the secondary transfer unit, and the toner image on the intermediate transfer belt is electrostatically transferred to the transfer material. Transcribed above.

  In recent years, a variety of paper (media) that can be handled in terms of size, thickness (basis weight), surface properties (for example, rough paper with a rough surface), etc., from the viewpoint of enhancing the functionality of image forming apparatuses. Furthermore, there is an increasing demand for compatibility with double-sided printing. Also, the environment in which the image forming apparatus is used is not limited to offices equipped with air conditioning equipment as in the past. It is desired that a good output image can be obtained even in various environments such as a personal office and a home by the flow of making a SOHO (small office home office).

  As described above, image forming apparatuses are required to have higher performance from the viewpoint of media flexibility, usage environment, and the like.

  However, for example, in the above-described direct transfer type color image forming apparatus, the transfer material is transferred four times to form a full color image. The transfer material and the transfer belt have elements that are unstable in resistance value due to changes in the environment (temperature, humidity). For this reason, an image defect may occur depending on the environmental change in which the apparatus is placed and the type of transfer material.

  As the transfer belt, for example, a film-like member in which an electronic conductive agent such as carbon black or an ionic conductive agent for adjusting electric resistance is added to a resin is used. In a transfer belt to which an electronic conductive agent is added, the electrical resistance value may become non-uniform due to poor dispersion during manufacture. In addition, in a transfer belt to which an ionic conductive agent is added, the amount of water contained may fluctuate due to environmental fluctuations, resulting in environmental variations in electrical resistance values.

On the other hand, as a transfer material, for example, the main component of paper is cellulose having a high hygroscopic property, and the electric resistance value greatly varies depending on the moisture absorption state. For example, in a high-temperature and high-humidity environment where paper absorbs moisture (H / H environment (30 ° C./80% RH)), its electrical resistance decreases to about 10 ⁶ Ωcm, and the applied charge is likely to leak. . On the other hand, in a low-temperature and low-humidity environment (L / L environment (15 ° C./10% RH)), the electrical resistance of the paper rises to about 10 ¹² Ωcm, making it difficult to inject charges into the paper and making charge difficult Become.

  When a toner image is transferred to a transfer belt or transfer material having a variation factor of electric resistance as described above, if the electric resistance is high, transfer failure occurs due to the fact that the transfer current hardly flows. On the other hand, when the electrical resistance is low, the transfer current flows too much, and the toner image transferred from the photoconductor to the transfer material is reversely charged by the discharge and the polarity is easily reversed. Then, the toner whose charging polarity is reversed is retransferred to the photoreceptor, and the transfer efficiency is lowered.

  In addition, the optimum transfer bias is originally different depending on the state of the transferred toner. The main toner state includes a charge amount (tribo) per unit weight of toner. For example, when the toner tribo is 25 μC / g and the optimum transfer current value at the time of passing the paper is about 10 μA, the optimum transfer current value is reduced when the toner tribo is lowered to about 15 μC / g due to environmental fluctuation or durability deterioration. It becomes about 6 μA.

In view of such a problem, Patent Document 1 discloses a method of changing the setting of the transfer bias according to the toner tribo of the toner image formed on the image carrier. That is, the image forming apparatus described in Patent Document 1 transfers a predetermined toner image formed on an image carrier to a transfer target while sequentially changing a transfer bias applied from a power source to a transfer unit during non-image formation. . Then, the transfer voltage and the transfer current at this time are read, and the setting of the transfer bias applied from the power source to the transfer unit at the time of transfer is changed based on the read transfer voltage or transfer current information.
JP 2003-29551 A

  However, the reduction in transfer efficiency and the deterioration in retransfer as described above are generally more remarkable in a secondary color toner image in which at least two colors of toner are superimposed. In addition, the deterioration of the secondary transfer efficiency in the intermediate transfer body method is more remarkable in the secondary color toner image.

  According to the study by the present inventors, the transfer efficiency and retransfer of the secondary color toner image vary greatly depending on the combination of the upper layer / lower layer toner tribo.

  For example, retransfer occurs most significantly when the toner tribo of the lower layer (transfer member side) is high and the toner tribo of the upper layer (photoreceptor side) is low. For example, the secondary transfer efficiency is most deteriorated when the toner tribo of the lower layer (transfer member side) is high and the toner tribo of the upper layer (intermediate transfer member side) is low.

  Further, according to the study by the present inventors, for retransfer, it is possible to optimally control the bias applied in the transfer section that first passes after the toner image is superimposed on the transfer medium in two layers. I found it important.

  Here, in the above-described conventional transfer bias control method, the transfer bias is controlled so as to be optimal for transferring one color toner. Therefore, the transfer bias control is not optimal for the secondary color.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of satisfactorily transferring a toner image in which toners of at least two colors are superimposed.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention includes an image forming unit including an image carrier on which a toner image is formed, a transfer body that receives and conveys a toner image from the image forming unit, and the image forming unit. Transfer means for transferring the toner image to the transfer body or a transfer material on the transfer body, and transfer bias output means for outputting a bias for the transfer to the transfer means, When forming a multiple toner image comprising first, second, and third toner images composed of different types of first, second, and third toners on the transfer body or a transfer material on the transfer body, In the image forming apparatus that transfers the second toner image after the first toner image and transfers the third toner image after the second toner image, the third toner of the multiple toner image The image is transferred to the transfer body or the transfer material on the transfer body. Bias values the transfer bias output means outputs when transfer is an image forming apparatus characterized by being determined based on a result of detecting a transfer characteristic of said first and second toners.

  According to the second aspect of the present invention, an image forming unit including an image carrier on which a toner image is formed, a transfer body onto which a toner image from the image forming unit is transferred, and a toner image from the image forming unit A transfer means for transferring to the transfer body; a transfer bias output means for outputting a bias for the transfer to the transfer means; and a second for transferring a toner image from the transfer body to a transfer material. A multi-toner comprising: a transfer unit; and a second transfer bias output unit that outputs a bias for the transfer to the second transfer unit, each of which includes a plurality of toner images made of different types of toner. In the image forming apparatus for forming an image on the transfer member and transferring the multiple toner image to a transfer material, the second transfer bias output means outputs when transferring the multiple toner image from the transfer member to the transfer material. You The value of the bias, the image forming apparatus is provided, characterized in that is determined based on the result of detecting the transfer characteristic of at least two toners of different toner constituting the multiple toner image.

  According to the third aspect of the present invention, the image forming apparatus starts from the first toner while sequentially changing the constant current controlled or constant voltage controlled bias value output from the transfer bias output means during non-image formation. A first step of transferring the predetermined toner image to the transfer body or a transfer material on the transfer body, and a constant current control or constant voltage controlled bias output from the transfer bias output means during non-image formation. A second step of transferring a predetermined toner image made of the second toner to the transfer member or a transfer material on the transfer member while sequentially changing the value, and the first and second steps. When the voltage value or current value when the relationship between the output voltage value and the output current value of the transfer bias output means at the inflection point becomes an inflection point is α1 and α2, respectively, the third toner image of the multiple toner image is Transcript or front The bias value output by the transfer bias output means when transferring to the transfer material on the transfer body is expressed as | α1 | <| α2 | and | α1 |> | α2 | The configuration is characterized in that it differs depending on the case where the expressed relationship is established.

  According to the fourth aspect of the present invention, the image forming apparatus receives a predetermined toner image composed of at least two types of toners constituting the multiple toners from the transfer bias output unit during non-image formation. And having at least two steps of sequentially transferring the bias value controlled by the constant current control or the constant voltage control to be transferred to the transfer body, and of the toners of the multiple toner image among the at least two steps. In the step of transferring the predetermined toner image composed of the toner of the toner image previously transferred to the transfer body, and the step of transferring the predetermined toner image composed of the toner of the toner image transferred later to the transfer body. When the voltage value or current value when the relationship between the output voltage value and the output current value of the transfer bias output means becomes an inflection point is αA and αB, respectively, The absolute value of the bias output from the second transfer bias output means when the multiple toner image is transferred from the transfer member to the transfer material is expressed by | αA | <| αB | The configuration is characterized in that the case where it does not hold between toners is different from the case where it holds between any two types of toners.

  According to the fifth aspect of the present invention, the image forming apparatus outputs a predetermined bias from the developing bias output unit to the developing unit that forms a toner image on the image carrier with the first toner. The electric resistance value of the developing means obtained from the output current value of the developing bias output means is β1, and the developing bias output means has a predetermined value for the developing means for forming a toner image on the image carrier with the second toner. When the electrical resistance value of the developing means obtained from the output current value of the developing bias output means when β2 is output is β2, the third toner image of the multiple toner image is the transfer body or the The absolute value of the bias output by the transfer bias output means when transferring to the transfer material on the transfer body is the case where the relationship represented by | β1 |> | β2 | is satisfied, and | β1 | <| β | Relationship represented by is configured, wherein a different thing as if satisfied.

  According to the sixth aspect of the present invention, the image forming apparatus includes at least two developing means for forming a toner image on the image carrier with at least two types of different toners constituting the multiple toner. The development bias output when a predetermined bias is output from the development bias output means to the development means for forming a toner image on the image carrier with the toner of the toner image previously transferred to the transfer body. The development bias obtained with respect to the developing means for forming a toner image on the image carrier by the toner of the toner image subsequently transferred to the transfer body is βA. When the electrical resistance value of the developing unit obtained from the output current value of the developing bias output unit when a predetermined bias is output from the output unit is βB, The absolute value of the bias output from the second transfer bias output means when the multiple toner image is transferred from the transfer member to the transfer material is expressed by | βA |> | βB | The configuration is characterized in that there is a difference between the case where it is not established between the two and the case where it is established between any two developing means.

  According to the present invention, it is possible to satisfactorily transfer a toner image in which toners of at least two colors are superimposed.

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

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
FIG. 1 shows a schematic sectional configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to this embodiment is a tandem laser printer that can form a full-color image on a transfer material P, for example, a recording sheet, an OHP sheet, or the like, using an electrophotographic system. In this embodiment, the image forming apparatus 100 employs a direct transfer method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (process devices) 60a, 60b, 60c, and 60d. The first, second, third, and fourth image forming units 60a, 60b, 60c, and 60d form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. To do. These four image forming units 60a, 60b, 60c, and 60d are arranged in a line at regular intervals.

  In this embodiment, the basic configuration and operation of each of the image forming units 60a to 60d are substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular need for distinction, the subscripts given to the reference numerals to indicate that the element is provided for one of the colors will be omitted, and a general description will be given.

  FIG. 2 shows the image forming unit 60 in more detail. The image forming unit 60 includes a drum-type electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 rotates in the direction of arrow R1 (clockwise) in the figure. Around the photosensitive drum 1, a charging roller 2 as a charging unit, a developing device 3 having a developing unit, a transfer roller 4 as a transfer unit, a cleaning device 5 as a cleaning unit, and the like are installed. An exposure device (scanner unit) 6 serving as exposure means is installed above the charging roller 2 and the developing device 3. In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 3, the scanner unit 6 and the like of each of the image forming units 60a to 60d constitute an image forming unit that forms a toner image.

  Then, a transfer belt (transfer body) 40 serving as a transfer material transporting unit 40 moves in contact with the photosensitive drums 1a to 1d of the image forming units 60a to 60d at the transfer units Na, Nb, Nc, and Nd. Is arranged. The transfer belt 40 is in contact with the photosensitive drums 1a to 1d at the transfer portions Na to Nd by pressing of the transfer rollers 4a to 4d. The transfer belt 40 is stretched by a driving roller 41 and a driven roller 42, and rotates (rotates) in the direction of arrow R3 (counterclockwise) in the figure as the driving roller 41 rotates.

  An adsorption roller 47 that electrostatically adsorbs the transfer material P onto the transfer belt 40 is installed upstream of the first image forming unit 60a in the transport direction of the transfer material P.

  In the vicinity of the driven roller 42, a belt cleaning device 49 that removes and collects toner adhering to the surface of the transfer belt 40 is installed.

  Further, a separation charger 48 for separating the transfer material P from the transfer belt 40 is installed on the downstream side of the transfer direction of the transfer material P from the fourth image forming unit 60d.

  Further, a fixing device 50 having a fixing roller 51 incorporating a heating unit 53 and a pressure roller 52 is installed on the downstream side in the conveyance direction of the transfer material P from the separation charger 48.

  As will be described below, the toner images of the respective colors formed on the photosensitive drums 1a to 1d of the image forming units 60a to 60d are sequentially superimposed on the transfer material P that is adsorbed and carried on the transfer belt 40. Is transcribed.

  The photosensitive drum 1 is configured by forming a photosensitive layer (organic photoconductive layer) 8 on the peripheral surface of a conductive drum base 7 made of, for example, aluminum. The photosensitive drum 1 is rotationally driven at a predetermined process speed (circumferential speed) in the direction of arrow R1 (clockwise) in the figure by a driving device (not shown).

  The charging roller 2 is in contact with the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is applied with a charging bias from a charging high voltage power source 12 as a charging bias output means. Thus, in this embodiment, the charging roller 2 charges the photosensitive drum 1 to a predetermined negative potential.

  The charging roller 2 includes a conductive metal core 9 disposed at the center, and a low-resistance conductive layer 10 and a medium-resistance conductive layer 11 formed on the outer periphery thereof. The charging roller 2 is disposed in parallel to the photosensitive drum 1 while both ends of the cored bar 9 are rotatably supported by bearing members (not shown). The bearing members at both ends of the charging roller 2 are urged toward the photosensitive drum 1 by pressing members (not shown). As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is driven to rotate in the direction of the arrow R2 (counterclockwise) in the figure as the photosensitive drum 1 rotates in the direction of the arrow R1 in the figure.

  In the present embodiment, the developing device 3 employs a two-component developing system. The developing device 3 has a developing container 14 containing a two-component developer mainly composed of a mixture of non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. A developing sleeve 15 as a developer carrier (developing means) is rotatably installed in the opening of the developing container 14 facing the photosensitive drum 1. In the developing sleeve 15, a magnet roller 16 as a magnetic field generating unit is fixedly disposed so as not to rotate with respect to the rotation of the developing sleeve 15. The developer is carried on the developing sleeve 15 by the magnetic field generated by the magnet roller 16. The developing sleeve 15 is connected to a developing high voltage power source 17 as a developing bias output means.

  In the developing container 14, a partitioned developing chamber 20 and a stirring chamber 21 are provided. Further, a replenishment chamber 22 containing replenishment toner is provided above the developing container 14. Further, a regulating blade 18 as a developer regulating member is installed at a position below the developing sleeve 15 of the developing container 14 to regulate the developer carried on the developing sleeve 15 to form a thin developer layer. Has been.

The transfer belt 40 can be made of a dielectric resin such as PC, PET, PVDF, and PI. In this embodiment, the transfer belt 40 has a volume resistivity of 10 ¹⁴ Ω · cm (using a probe conforming to JIS-K6911 method, applied voltage 1000 V, applied time 60 sec, 23 ° C., 50% RH), thickness t = 80 μm, It was formed of PI resin in which carbon was dispersed. Of course, the transfer belt 40 is not limited to that of the present embodiment, and other materials, volume resistivity, and thickness may be used.

  The transfer roller 4 includes a cored bar 23, a conductive layer 24 formed in a cylindrical shape on the outer peripheral surface thereof, and a surface layer 25 that covers the surface of the conductive layer 24. A transfer bias is applied to the cored bar 23 from a transfer high-voltage power supply 26 as transfer bias output means. The transfer high-voltage power supply 26 is connected to a control device (CPU) 28 as control means, and performs transfer bias setting control and the like. A more detailed configuration of the transfer roller 4 and transfer bias setting control will be described later.

  Both ends of the transfer roller 4 are urged toward the photosensitive drum 1 by a pressing member (not shown) such as a spring. As a result, the surface layer 25 of the transfer roller 4 comes into contact with the inner peripheral surface of the transfer belt 40, and the outer peripheral surface of the transfer belt 40 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. A transfer nip portion (transfer portion) N is formed between the photosensitive drum 1 and the transfer belt 40.

  The cleaning device 5 includes a cleaning blade 29 and a conveying screw 30. The cleaning blade 29 is in contact with the photosensitive drum 1 by a pressure member (not shown) at a predetermined angle and pressure, and collects toner and the like remaining on the surface of the photosensitive drum 1.

  The exposure device 6 forms an electrostatic latent image corresponding to the image information on the photosensitive drum 1 charged by the charging roller 2 by the image exposure L. In this embodiment, the image exposure L is composed of laser light obtained by modulating a time-series electric digital signal of input image information in accordance with a pixel signal. The exposure devices 6a to 6d of the first to fourth image forming units 60a to 60d convert color-separated image signals input from a host computer (not shown), respectively, into optical signals.

  Next, an image forming operation will be described.

  At the time of image formation, the photosensitive drum 1 is rotationally driven by a driving device (not shown) in the direction of arrow R1 in the drawing at a predetermined process speed. The surface of the rotating photosensitive drum 1 is charged to a predetermined negative potential by a charging roller 2 to which a charging bias is applied from a charging high voltage power source 12.

  Then, the photosensitive drum 1 is irradiated with an image exposure L by a laser beam corresponding to the image signal from the exposure device 6. As a result, the potential of the image exposed portion L on the photosensitive drum 1 is lowered, and an electrostatic image (latent image) is formed. Then, toner adheres to the electrostatic image on the photosensitive drum 1 from the developing sleeve 15 of the developing device 3 to which a developing bias is applied from the developing high-voltage power supply 17. As a result, the electrostatic image on the photosensitive drum 1 is reversely developed (visualized) as a toner image. In the present embodiment, the development high-voltage power supply 17 outputs a development bias in which a DC voltage and an AC voltage are superimposed during a development operation, and applies the development bias to the development sleeve 15.

  At the time of development, a thin layer of developer on the developing sleeve 15 is conveyed to a developing area facing the photosensitive drum 1. Then, the developer on the developing sleeve 15 rises due to the magnetic force of the developing main pole located in the developing region of the magnet roller 16 to form a developer magnetic brush. This magnetic brush is brought close to or in contact with the surface of the photosensitive drum 1. At this time, a developing bias having a DC component having the same polarity as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 1 is applied to the developing sleeve 15 from the developing high-voltage power supply 17. As a result, toner adheres to the exposed portion of the electrostatic image from the magnetic brush, and a toner image is formed on the photosensitive drum 1.

  For example, at the time of full-color image formation, the toner image is formed on the photosensitive drum 1 as described above in the first to fourth image forming units 60a to 60d.

  On the other hand, the transfer material P is transferred between the suction roller 47 and the transfer belt 40 by the conveying roller pair 45 and the registration roller pair 46 in accordance with the timing at which the toner image is formed on the photosensitive drum 1 in the first image forming unit 60a. Conveyed in between. The transfer material P is stored in the cassette 43 and is sent out one by one by the supply roller 44. Then, the transfer material P is electrostatically attracted to the surface of the transfer belt 40 that circulates in the direction of the arrow R3 in the drawing by the suction roller 47 to which the suction bias is applied. The transfer material P adsorbed on the transfer belt 40 is sequentially conveyed to the transfer units Na to Nd of the first to fourth image forming units 60 a to 60 d by the movement of the transfer belt 40.

  Then, in each of the transfer portions Na to Nd, yellow, magenta, cyan, and black toner images are sequentially superimposed and transferred onto the transfer material P. At this time, a transfer bias having a polarity opposite to the normal charging polarity (negative polarity in this embodiment) of the toner is applied to each of the transfer rollers 4a to 4d. As a result, a full-color toner image (a multiple toner image including a plurality of toner images composed of a plurality of types of toners) is formed on the transfer material P carried on the transfer belt 40. As will be described in detail later, in this embodiment, a constant-voltage controlled transfer bias output from the transfer high-voltage power supply 26 is applied to each transfer roller 4 during the transfer process. That is, in this embodiment, the image forming means has a plurality of photosensitive drums 1 for carrying toner images composed of different types of toners. The toner images formed on the plurality of photosensitive drums 1 are transferred to the transfer material P at different transfer portions N in the moving direction of the transfer material P as a transfer target.

  The transfer material P on which the full-color toner image is formed is separated from the surface of the transfer belt 40 by the separation charger 48 and conveyed to the fixing device 50. The transfer material P is heated and pressed at a fixing nip portion between the fixing roller 51 and the pressure roller 52 of the fixing device 50. As a result, a full-color toner image is thermally fixed on the surface of the transfer material P. Thereafter, the transfer material P is discharged to the outside of the image forming apparatus 100, and a series of image forming operations ends.

  Incidentally, the toner remaining on the surface of the photosensitive drum 1 after the toner image transfer (transfer residual toner) and other adhering matters are removed by the cleaning blade 29 of the cleaning device 5. The removed toner and the like are conveyed by the conveying screw 30 and collected in a collecting container (not shown). In addition, toner and other deposits adhered to the transfer belt 40 are removed and collected by the belt cleaning device 49.

  Next, a detailed configuration of the transfer roller 4 will be described.

In this embodiment, the transfer roller 4 has a cored bar 23 with a diameter of 8 mm, and a conductive layer 24 formed with a thickness of 4 mm around it. The conductive layer 24 of the transfer roller 4 can have an electric resistance of about 10 ⁵ to 10 ¹² Ω · cm. Moreover, as the conductive layer 24, NBR, SBR, BR, EPDM or the like having a single foam property or a continuous foam property can be preferably used. In this embodiment, the conductive layer 24 is formed of EPDM sponge, and carbon is used as the conductive material. In this embodiment, the electric resistance value of the transfer roller 4 was about 10 ⁸ Ω. The electric resistance value of the transfer roller 4 is measured by rotating the transfer roller 4 at a peripheral speed of 50 mm / sec with respect to the ground under a load of 500 g and applying a voltage of 1 kV to the core 23. It is obtained from the relationship of the measured current.

  Further, the surface layer 25 of the transfer roller 4 is made of a conductive resin having high releasability. As the surface layer 25, it is possible to preferably use a coated or coated fluororesin in which carbon is dispersed in PTFE, FEP, PVDF, PFA or the like to provide conductivity. In this example, the surface layer 25 was coated with 50 μm of PFA.

[Transfer bias setting control]
Next, transfer bias setting control in this example will be described.

  One of the objects of the present invention is to set an optimal transfer bias for a secondary color image in which image quality deterioration is remarkable, even when the toner tribo changes due to environmental fluctuations, durability deterioration, etc. It is possible to do.

  Therefore, in the present embodiment, the image forming apparatus 100 is configured as follows. That is, the image forming apparatus 100 forms on the transfer material P a multi-toner image including first, second, and third toner images made of different types of first, second, and third toners. At that time, the second toner image is transferred to the transfer material after the first toner image, and the third toner image is transferred to the transfer material P after the second toner image. In the image forming apparatus 100 having such a configuration, when the third toner image of the multiple toner image is transferred onto the transfer material P, the bias value output by the transfer bias output means (transfer high voltage power supply) 26 is the first and second values. It is determined based on the result of detecting the toner transfer characteristics. In this embodiment, the first, second, and third toners may be yellow, magenta, and cyan toners, respectively. The first, second, and third toners can also be viewed as magenta, cyan, and black toners, respectively, or yellow, cyan, and black toners, respectively.

  Here, the amount of charge per unit weight of the first toner indicated by the detection result of the transfer characteristic of the first toner is Q1, and the amount of charge per unit weight of the second toner indicated by the detection result of the transfer characteristic of the second toner is shown. Let the charge amount be Q2. At this time, in this embodiment, the absolute value of the bias output by the transfer bias output means (transfer high-voltage power supply) 26 when the third toner image of the multiple toner image is transferred to the transfer material P is set as follows. . That is, the value is smaller when the relationship represented by | Q1 |> | Q2 | is established than when the relationship represented by | Q1 | <| Q2 | is established. This will be described in more detail below.

・ ATVC
In the present embodiment, first, a transfer voltage serving as a reference to be applied to the transfer rollers 4a to 4d of the image forming units 60a to 60d is obtained in the same manner as the conventionally known ATVC (Auto Transfer Voltage Control) control.

  The ATVC control is a transfer bias control method in which a current is passed through the transfer portion N during non-image formation and the transfer bias is set based on the voltage value detected at this time. In order to determine the transfer bias, it is only necessary to obtain information on the electrical resistance of the transfer portion N. Therefore, a predetermined voltage is applied to the transfer portion N, and the transfer bias is set based on the current value flowing at that time. May be.

  In this embodiment, the transfer high-voltage power supply 26 includes a constant current bias output unit 26A that outputs a constant current controlled bias and a constant voltage bias output unit 26B that outputs a constant voltage controlled bias. Further, the transfer high-voltage power supply 26 serves as a detection means, such as a voltage detection unit 26C that detects an output voltage when outputting a constant current controlled bias or an output current when a constant voltage controlled bias is output. Has a current detection unit 26D. Then, during non-image formation, the transfer bias is controlled at a constant current during the pre-rotation of image formation, and the optimum transfer voltage for the charged potential of the photosensitive drum 1 and the electric resistance value of the transfer roller 4 at this time is detected. When the image is transferred, constant voltage control of the transfer bias value determined based on the transfer voltage obtained here is performed.

  More specifically, in this embodiment, the control device (CPU) 28 applies a constant current controlled bias from the constant current bias output unit 26A of the transfer high voltage power supply 26 to each of the image forming units 60a to 60d during non-image formation. Output. As a result, a constant current of 8 μA is applied to each transfer roller 4 from the transfer high-voltage power supply 26. The transfer voltage generated at this time is detected by the voltage detector 26C. The CPU 28 stores the voltage value detected at this time as basic transfer voltages Vy, Vm, Vc, and Vk in a storage unit built in or connected to the CPU 28.

  The CPU 28 obtains a voltage obtained by adding the shared voltage Vp applied to the transfer material P at the time of transfer, that is, Vy + Vp, Vm + Vp, Vc + Vp, Vk + Vp to this value. In this way, a value serving as a reference for the transfer bias applied at each of the transfer portions Na to Nd at the time of paper passing (at the time of image formation) is obtained. In the configuration of the present embodiment, Vy + Vp, Vm + Vp, Vc + Vp, and Vk + Vp are usually about 500 to 3500V.

  In this embodiment, at the time of image formation, the transfer high-voltage power supply 26 outputs the reference transfer bias or the transfer bias corrected as described later from the constant voltage bias output unit 26B.

Detection of toner tribo Next, in this embodiment, toner tribo on the photosensitive drum 1 is detected in the following manner for the first to third image forming units 60a to 60d.

  That is, a predetermined toner image is formed on the photosensitive drum 1 by the above-described image forming process. Thereafter, the toner image is directly transferred from the photosensitive drum 1 to the surface of the transfer belt 40 with a predetermined transfer bias (transfer voltage). At this time, the transfer material P such as recording paper is not conveyed.

  At this time, the relationship between the applied transfer voltage V and the transfer current I when the toner image is being transferred is determined while varying the transfer voltage in multiple stages. This relationship is shown in FIG. FIG. 3 also shows the relationship of the transfer efficiency from the photosensitive drum 1 to the transfer belt 40 with respect to the transfer voltage V.

  As shown in FIG. 3, when the transfer voltage V is increased, a transfer current I starts to flow from a certain voltage Va, and at the same time, transfer starts. Further, as the transfer voltage V is increased, the transfer efficiency from the photosensitive drum 1 to the transfer belt 40 is increased. The maximum transfer efficiency is obtained in the vicinity of a certain voltage Vb. When the transfer bias exceeds Vb, discharge occurs between the photosensitive drum 1 and the transfer belt 40, and the transfer current I flows more.

  That is, the slope of the line V-I becomes steep with the voltage Vb as a boundary. Thus, there is an inflection point in the relationship between the transfer voltage V and the transfer current I during toner image transfer. The transfer voltage Vb serving as an inflection point varies depending on the state of the toner (temperature / humidity of the ambient environment, durability of the developer). However, it has been confirmed by experiments by the present inventors that the transfer efficiency in the vicinity of the transfer voltage, which is the inflection point, is maximized regardless of the state of the toner.

  The transfer current Ib when the transfer voltage is Vb is a current value corresponding to the amount of toner movement because no discharge is generated between the photosensitive drum 1 and the transfer belt 40. Therefore, it can be considered that the current value Ib is substantially equivalent to the toner tribo.

  In the present embodiment, such an operation is individually performed in each transfer unit N for the first to third image forming units 60a to 60c. As a result, current values Iby, Ibm, and Ibc for toner movement are obtained for yellow, magenta, and cyan toners.

  Here, since the toner image formed on the photosensitive drum 1 detects a transfer current that flows when the toner is transferred, it is preferably as large as possible in the longitudinal direction of the photosensitive drum 1. . For example, consider a case where a toner image t having a width smaller than the maximum image forming width is formed on the photosensitive drum 1 as shown in FIG. In this case, in the transfer portion N between the photosensitive drum 1 and the transfer belt 40, a current also flows through the non-image portions on both sides of the toner image t. Since the relationship between the transfer voltage V and the transfer current I is different between the image portion and the non-image portion, it is difficult to obtain a clear inflection point as described above. That is, it is preferable that the predetermined toner image for detecting toner tribo on the photosensitive drum 1 is formed in the entire area of the image forming area in the direction intersecting the surface moving direction of the photosensitive drum 1.

  Further, the length of the toner image formed on the photosensitive drum 1 (paper passing direction) is related to the number of times the transfer current value is detected. As the length of the toner image (paper passing direction) is increased, the transfer current can be detected over a longer period of time, so the accuracy increases, but there is a problem that the toner consumption increases.

  Further, with respect to the density of the toner image formed on the photosensitive drum 1, the image density is about 1.2 to 1.6 in order to improve the detection accuracy of the current value by flowing more transfer current. It is preferable. However, the present invention is not limited to this, and may be a solid image (image with the highest density level) or a halftone image as long as information on toner tribo on the photosensitive drum 1 can be obtained.

  More specifically, in this embodiment, the CPU 28 obtains information related to toner tribo as follows. First, a toner image pattern is formed on the photosensitive drum 1 by the above-described image forming process procedure. Here, with respect to the longitudinal direction of the photosensitive drum 1, the width of the maximum image forming area is 290 mm, the length of the photosensitive drum 1 in the rotation direction (paper passing direction) is 240 mm, and the image density is 1.4. A toner image is formed.

  Then, the CPU 28 first outputs a transfer bias (transfer voltage) V <b> 1 under constant voltage control from the constant voltage bias output unit 26 </ b> B of the transfer high-voltage power supply 26 and applies it to the transfer roller 4. Then, while transferring the toner image to the transfer belt 40 with the transfer bias V1, the transfer current for one rotation of the transfer roller 4 is detected by the current detection unit (ammeter) 26D. The CPU 28 stores the average value of the current value detected at this time as I1, and stores it in a storage means built in or connected to the CPU 28. The reason why the circumference of the transfer roller 4 is detected is to average the resistance unevenness of the transfer roller 4.

  Subsequently, I2 is obtained while performing constant voltage control similarly at the transfer voltage V2 (> V1). Similarly, I3 for V3 (> V2) and I4 for V4 (> V3) are obtained.

  Then, as shown in FIG. 5, the CPU 28 obtains the intersection of the VI straight line obtained from V1 · I1 and V2 · I2 and the VI straight line obtained from V3 · I3 and V4 · I4. Thus, the CPU 28 can obtain the transfer voltage Vb at this intersection and the transfer current Ib at that time.

  In this embodiment, when a toner image for detecting toner tribo on the photosensitive drum 1 is transferred, the bias value under constant voltage control is sequentially changed and outputted from the transfer high voltage power supply 26. However, the present invention is not limited to this. It is only necessary to detect the relationship between the transfer voltage and the transfer current when the toner image is transferred, and the constant current controlled bias value is sequentially changed and output. The output voltage value at that time may be measured.

-Correction of Transfer Bias Next, a method of correcting the transfer bias at the transfer portion through which the secondary color toner image passes will be described.

  Here, the toner retransfer in the secondary color toner image will be described.

  The retransfer is a problem that the toner image transferred from the photosensitive drum 1 to the transfer material P is reversely charged by the discharge, the toner charge polarity is reversed, and the toner image is retransferred to the photosensitive drum 1 to reduce transfer efficiency. It is. This phenomenon is further exacerbated when the transfer voltage of the transfer portion that passes after the two color toner images are superimposed is high.

  In the case of a secondary color toner image, if the toner tribo on the upper layer (photoreceptor side) of the superimposed toner image is low, reversal of the polarity of the toner tribo due to discharge becomes significant, and retransfer deteriorates. On the contrary, when the toner tribo of the upper layer (photoreceptor side) of the toner image is high, the polarity of the toner tribo is difficult to reverse even when discharged, so retransfer does not deteriorate.

  Therefore, in this embodiment, the current values Iby, Ibm, and Ibc for the amount of toner movement detected as described above are compared, and the upper layer (photoconductor side) and lower layer (transfer material) of the secondary color toner image are compared. Side) toner tribo relationship is compared. When it is determined that the toner tribo of the upper layer (photoreceptor side) of the secondary color toner image is low, the transfer bias is corrected as follows so that the retransfer is not deteriorated. In this embodiment, the correction voltage Vcomp is subtracted from the reference voltage as the transfer voltage of the transfer portion that first passes after the two color toner images are superimposed. That is, correction is performed to reduce the absolute value of the voltage value of the transfer bias. In this embodiment, Vcomp = 240V.

  More specifically, the CPU 28 first compares the magnitude relationship between Iby and Ibm. When Iby> Ibm, the toner tribo of the lower layer (transfer material side) is high and the toner tribo of the upper layer (photoreceptor side) is low, so it is determined that the retransfer is worsened. Then, correction is applied to the transfer bias applied to the transfer roller 4c of the third image forming unit 60c during image formation. That is, the transfer bias applied to the transfer roller 4c of the third image forming unit 60c at the time of image formation is Vc + Vp−Vcomp.

  On the contrary, when Iby <Ibm, since the toner tribo of the upper layer (photoreceptor side) is high, it is determined that the retransfer does not deteriorate. The transfer bias applied to the transfer roller 4c of the third image forming unit 60c is not corrected. That is, the transfer bias applied to the transfer roller 4c of the third image forming unit 60c at the time of image formation is Vc + Vp.

  The same correction is performed for the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d. That is, when Ibm> Ibc or Iby> Ibc, the CPU 28 sets the transfer bias to be applied to the transfer roller 4d of the fourth image forming unit 40d at the time of image formation as Vk + Vp−Vcomp. When Ibm <Ibc and Iby <Ibc, the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d at the time of image formation is set to Vk + Vp.

  In this embodiment, correction is not performed on the transfer bias applied to the transfer rollers 4a and 4b of the first and second image forming units 60a and 60b during image formation. That is, Vy + Vp and Vm + Vp determined as described above are applied to these transfer rollers 4a and 4b during image formation. However, as described in Patent Document 1, for example, the transfer rollers 4a of the first and second image forming units 60a and 60b are based on the transfer current detection results Iby and Ibm for yellow and magenta toners. The transfer bias applied to 4b may be controlled.

  The above-described control for obtaining the transfer voltage can be performed at a timing other than the time of image formation for forming an image to be recorded and output on the transfer material P, that is, at the time of non-image formation. Examples of non-image formation include preparatory operations other than image formation, pre-multi-rotation after power-on, pre-rotation of image formation, environmental change, and arrival of a predetermined number of printed sheets.

  That is, as described above, the image forming apparatus 100 according to the present exemplary embodiment performs the following first step and second step during non-image formation. That is, in the first step, during non-image formation, a predetermined toner image composed of the first toner is transferred to the transfer belt while the constant current controlled or constant voltage controlled bias value output from the transfer high voltage power supply 26 is sequentially changed. 40 is transferred. In the second step, during non-image formation, a predetermined toner image made of the second toner is applied to the transfer belt 40 while sequentially changing the value of the constant current controlled or constant voltage controlled bias output from the transfer high-voltage power supply 26. Transcript. Here, the voltage value or the current value when the relationship between the output voltage value and the output current value of the transfer high-voltage power supply 26 in the first and second steps becomes an inflection point are α1 and α2, respectively. At this time, the value of the bias output from the transfer high-voltage power supply 26 when the third toner image of the multiple toner image is transferred to the transfer material P satisfies the relationship represented by | α1 | <| α2 | This is different from the case where the relationship represented by | α1 |> | α2 | is satisfied. Typically, the absolute value of the bias output from the transfer high-voltage power supply 26 when the third toner image is transferred is greater than the case where the relationship represented by | α1 | <| α2 | is satisfied. The case where the relationship represented by | α2 | is satisfied is smaller.

  In this embodiment, when detecting toner transfer characteristics (transfer current, toner tribo), Vb and Ib are obtained by varying the constant voltage control in four stages. When the transfer roller 4 is ion-conductive or the like and the resistance unevenness is small, it is not necessary to detect the current for one rotation of the transfer roller 4. Therefore, accurate V-I characteristics and inflection points can be obtained by performing constant voltage control in more stages even within the same time, and more accurate Vb and Ib can be obtained.

  Also, toner tribo on the photosensitive drum 1 can be detected as follows. A change amount ΔI of the transfer current with respect to a predetermined change amount ΔV of the transfer voltage when the constant voltage control is applied in multiple stages is obtained. For example, when the absolute value of the transfer voltage is sequentially increased, the transfer voltage when the change amount ΔI of the transfer current exceeds a predetermined value can be obtained as Vb, and the transfer current at that time can be obtained as Ib. Further, for example, when the absolute value of the transfer voltage is sequentially decreased, the transfer voltage when the transfer current change amount ΔI becomes a predetermined value or less can be obtained as Vb, and the transfer current at that time can be obtained as Ib.

  Incidentally, in this embodiment, the transfer current value at that time was detected while directly transferring the toner image from the photosensitive drum 1 to the transfer belt 40. On the other hand, it is also possible to detect the transfer current while actually transferring to the transfer material P on the transfer belt 40, and to perform the transfer bias setting control as described above.

  As described above, in this embodiment, the transfer characteristics when the toner image on the photosensitive drum 1 is transferred to the transfer target are detected with respect to the toner of at least two colors. In particular, in this embodiment, the transfer current is detected while changing a transfer voltage when a predetermined toner image formed on the photosensitive drum 1 is transferred to the transfer belt 40. Then, toner tribo is detected based on the voltage value or current value at the inflection point obtained from the characteristics of the transfer voltage and transfer current at this time. Accordingly, it is possible to know the combination of the toner tribo of each color toner and the toner tribo in the secondary color toner image. As a result, even when the toner tribo changes due to environmental fluctuations, durability deterioration, or the like, good transfer can be performed without causing toner retransfer or transfer efficiency deterioration in the secondary color toner image. That is, according to this embodiment, even when the toner state (tribo, etc.) changes due to environmental fluctuations and durability, good transfer can be performed without causing retransfer.

Example 2
Next, another embodiment of the present invention will be described. FIG. 6 shows a schematic cross-sectional configuration of the image forming apparatus 200 of this embodiment. In the image forming apparatus 200 of the present embodiment, elements having the same or corresponding functions as those of the image forming apparatus 100 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

[Overall Configuration and Operation of Image Forming Apparatus]
The image forming apparatus 200 of this embodiment is a tandem laser printer that can form a full-color image using an electrophotographic system. In this embodiment, the image forming apparatus 200 employs an intermediate transfer method.

  That is, in the image forming apparatus 200 of this example, the toner images formed on the photosensitive drums 1a to 1d of the image forming units 60a to 60d are intermediate transfer as intermediate transfer members in the primary transfer units N1a to N1d. On the belt (transfer body) 54, they are sequentially superimposed and transferred (primary transfer). Thereafter, the toner image on the intermediate transfer belt 54 is transferred (secondary transfer) to a transfer material P such as a recording sheet at the secondary transfer portion N2.

  The intermediate transfer belt 54 is in contact with the photosensitive drums 1a to 1d at the primary transfer portions N1a to N1d by pressing of the transfer rollers (primary transfer rollers) 4a to 4d. The intermediate transfer belt 54 is stretched around a driving roller 55, a driven roller 56, and a secondary transfer counter roller 57. Then, the drive roller 55 rotates and rotates (rotates) in the direction of arrow R4 (clockwise) in the figure.

The intermediate transfer belt 54 can be made of a dielectric resin such as PC, PET, and PVDF. In this embodiment, the intermediate transfer belt 54 has a volume resistivity of 10 ⁹ Ω · cm (using a probe conforming to the JIS-K6911 method, applied voltage 100 V, applied time 60 sec, 23 ° C., 50% RH) and thickness t = 100 μm. And made of PTFE resin. Of course, the intermediate transfer belt 54 is not limited to that of the present embodiment, and may be made of other materials, volume resistivity, and thickness.

In this embodiment, the transfer roller 4 is composed of a core metal having a diameter of 8 mm and a conductive urethane sponge layer having a thickness of 5 mm. The electric resistance value of the transfer roller 4 was about 10 ^6.5 Ω (23 ° C., 50% RH). The electrical resistance value of the transfer roller 4 is measured by rotating the transfer roller 4 at a peripheral speed of 50 mm / sec with respect to the ground under a load of 500 g and applying a voltage of 500 V to the cored bar. It was obtained from the relationship of the current.

  Next, an image forming operation will be described.

  For example, when an image forming operation start signal is issued during full color image formation, toner images are formed on the photosensitive drums 1a to 1d that are driven to rotate at a predetermined process speed in the image forming units 60a to 60d. The operation of forming toner images on the photosensitive drums 1a to 1d in the image forming units 60a to 60d is the same as that in the first embodiment. The toner images formed on the respective photosensitive drums 1a to 1d are sequentially superimposed and transferred (primary transfer) in the primary transfer portions N1a to N1d as the intermediate transfer belt 54 moves. At this time, each primary transfer roller 4a to 4d has a normal charging polarity (negative polarity in this embodiment) of toner from a primary transfer high-voltage power supply 26 (FIG. 7) as a primary transfer bias output means. A reverse transfer primary transfer bias is applied. Thus, a full color toner image is formed on the intermediate transfer belt 54. That is, in this embodiment, the image forming means has a plurality of photosensitive drums 1 for carrying toner images composed of different types of toners. The toner images formed on the plurality of photosensitive drums 1 are transferred to the intermediate transfer belt 54 at different primary transfer portions N1 in the moving direction of the intermediate transfer belt 54 that is a transfer target.

  On the other hand, the secondary transfer portion is synchronized with the timing at which the front end of the full-color toner image on the intermediate transfer belt 54 is moved to the secondary transfer portion N2 between the secondary transfer roller facing 57 and the secondary transfer roller 58. The recording material P is conveyed to N2. The recording material P is stored in the cassette 43, sent out one by one by the supply roller pair 44, and conveyed to the secondary transfer portion N2 by the conveyance roller pair 45 and the registration roller pair 46.

  Then, full-color toner images are collectively transferred (secondary transfer) onto the transfer material P at the secondary transfer portion N2. At this time, the secondary transfer roller 58 as the secondary transfer unit is supplied with a secondary having a polarity opposite to the normal charging polarity of the toner from the secondary transfer high-voltage power source 59 (FIG. 7) as the secondary transfer bias output unit. A transfer bias is applied. In this embodiment, a bias is applied to the secondary transfer roller 58. However, a bias is applied to one or both of the secondary transfer roller 58 and the secondary transfer counter roller 57 facing each other with the intermediate transfer belt 54 interposed therebetween. By doing so, a secondary transfer electric field can be generated. For example, when a bias is applied to the secondary transfer counter roller 57, a bias having the same polarity as the normal charging polarity (negative polarity in this embodiment) of the toner can be applied.

  The transfer material P on which the full-color toner image is formed is conveyed to the fixing device 50. In the fixing device 50, the transfer material P is heated and pressed at a fixing nip portion between the fixing roller 51 having a heater 53 and the pressure roller 52. As a result, a full-color toner image is thermally fixed on the surface of the transfer material P. Thereafter, the transfer material P is discharged to the outside of the image forming apparatus 200, and a series of image forming operations ends.

  Incidentally, the transfer residual toner remaining on the photosensitive drum 1 at the time of the primary transfer is removed and collected by the cleaning device 5. The residual toner remaining on the surface of the intermediate transfer belt 54 after the secondary transfer is removed and collected by the belt cleaning device 49.

[Transfer bias setting control]
Prevention of retransfer at the primary transfer portion In this embodiment, first, the primary transfer bias is set and controlled in substantially the same manner as in the first embodiment.

  That is, first, as in the first embodiment, reference primary transfer voltages Vy + Vp, Vm + Vp, Vc + Vp, and Vk + Vp are obtained by ATVC control. In the configuration of the present embodiment, Vy + Vp, Vm + Vp, Vc + Vp, and Vk + Vp are usually about 500 to 3500V. In this embodiment, at the time of image formation, the transfer high-voltage power supply 26 outputs the reference primary transfer bias or the primary transfer bias corrected as described later from the constant voltage bias output unit 26B.

  Next, as in the first embodiment, the first to third image forming units 60a to 60d perform an operation of detecting toner tribo on the photosensitive drum 1 independently at each primary transfer unit N1. . That is, in the same manner as in the first embodiment, a predetermined toner image formed on the photosensitive drum 1 is directly transferred onto the intermediate transfer belt 54, and the transfer voltage V and the transfer current I at this time are detected, and their relationship is determined. Ask for. In the same manner as in the first embodiment, the current values Iby, Ibm, and Ibc for toner movement are obtained for the toners of yellow, magenta, and cyan.

  Next, the CPU 28 corrects the primary transfer bias by comparing the magnitude relationship among the current values Iby, Ibm, and Ibc for the toner movement as in the first embodiment.

  That is, the CPU 28 compares the magnitude relationship between Iby and Ibm. When Iby> Ibm, correction is applied to the transfer bias applied to the transfer roller 4c of the third image forming unit 60c during image formation. That is, the transfer bias applied to the transfer roller 4c of the third image forming unit 60c at the time of image formation is Vc + Vp−Vcomp. In this embodiment, Vcomp = 250V.

  Conversely, when Iby <Ibm, no correction is applied to the transfer bias applied to the transfer roller 4c of the third image forming unit 60c during image formation. That is, the transfer bias applied to the transfer roller 4c of the third image forming unit 60c at the time of image formation is Vc + Vp.

  The same correction is performed for the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d. That is, when Ibm> Ibc or Iby> Ibc, the CPU 28 sets the transfer bias to be applied to the transfer roller 4d of the fourth image forming unit 40d at the time of image formation as Vk + Vp−Vcomp. When Ibm <Ibc and Iby <Ibc, the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d at the time of image formation is set to Vk + Vp.

  In the present embodiment, as in the first embodiment, the transfer bias applied to the transfer rollers 4a and 4b of the first and second image forming portions 60a and 60b during image formation is not corrected. That is, Vy + Vp and Vm + Vp obtained in the same manner as in the first embodiment are applied to these transfer rollers 4a and 4b at the time of image formation. However, as described in Patent Document 1, for example, the transfer rollers 4a of the first and second image forming units 60a and 60b are based on the transfer current detection results Iby and Ibm for yellow and magenta toners. The transfer bias applied to 4b may be controlled.

  By the control as described above, it is possible to prevent retransfer of the secondary color toner image in the primary transfer portion.

Transfer efficiency in the secondary transfer portion Next, control of the secondary transfer bias will be described.

  As for the secondary transfer bias, first, a reference secondary transfer voltage is obtained by ATVC control.

  In this embodiment, the control device (CPU) 28 outputs a constant current controlled bias from the constant current bias output unit 59A of the secondary transfer high voltage power source 59 during non-image formation. As a result, a constant current of 12 μA is applied to the secondary transfer roller 58 from the secondary transfer high voltage power source 59. The voltage V2 generated at this time is detected by the voltage detector 58C. The CPU 28 stores the voltage value V2 detected at this time in a storage means built in or connected to the CPU 28.

  The CPU 28 obtains a voltage obtained by adding the shared voltage V2p applied to the transfer material P during transfer to this value, that is, V2 + V2p. In this way, a value serving as a reference for the secondary transfer bias applied at the secondary transfer portion N2 at the time of paper passing (at the time of image formation) is obtained. Usually, V2 + V2p is about 500 to 3500V.

  In this embodiment, at the time of image formation, the secondary transfer high-voltage power supply 59 outputs the reference secondary transfer bias or the secondary transfer bias corrected as described later from the constant voltage bias output unit 59B.

  Here, the efficiency of the secondary transfer of the secondary color toner image depends on the toner tribo of the upper layer (intermediate transfer member side) and the lower layer (transfer material side) as in the case of retransfer. The following reasons are conceivable. That is, when the toner tribo of the upper layer (intermediate transfer member side) is low, the polarity of the tribo of the upper layer toner is reversed by the discharge in the transfer nip of the secondary transfer portion N2. As a result, the toner image on the intermediate transfer belt 54 cannot be transferred to the transfer material P and remains on the intermediate transfer belt 54.

  Therefore, in this embodiment, current values Iby, Ibm, and Ibc for the toner movements of the respective colors of yellow, magenta, and cyan detected by the primary transfer units N1a to N1c of the first to third image forming units 60a to 60c. The secondary transfer bias is corrected based on the above.

  In other words, in this embodiment, the image forming apparatus 200 forms a multiple toner image including a plurality of toner images of different types of toner on the intermediate transfer belt 54 and transfers the multiple toner image onto the transfer material P. . The bias value output from the second transfer bias output means (secondary transfer high-voltage power supply) 59 when the multiple toner image is transferred from the intermediate transfer belt 54 to the transfer material P is determined as follows. That is, the value is determined based on the result of detecting the transfer characteristics of at least two types of toners among the different types of toner constituting the multiple toner image.

  Here, among the charge amounts per unit weight of at least two types of toner indicated by the detection result of the transfer characteristics of the toner, the toner transferred to the intermediate transfer belt 54 first in the toner of the multiple toner image The amount of charge per unit weight of image toner is defined as QA. Further, the charge amount per unit weight of the toner image transferred to the intermediate transfer belt 54 later is QB. At this time, in this embodiment, the absolute value of the bias output from the secondary transfer high-voltage power supply 59 when the multiple toner image is transferred from the intermediate transfer belt 54 to the transfer material P is set as follows. That is, the value is larger when the relationship represented by | QA | <| QB | is not established between any two types of toner than when the relationship is established between any two types of toner. Like that.

  More specifically, in this embodiment, the CPU 28 compares the magnitude relationship between Iby and Ibm, Iby and Ibc, and Ibm and Ibc. When one or more of the conditions Iby <Ibm, Iby <Ibc, and Ibm <Ibc are satisfied, it is determined that the secondary transfer efficiency is likely to deteriorate. The bias applied to the secondary transfer roller 58 at the time of image formation is set to V2 + V2p + V2comp by adding the corrected transfer bias value V2comp to the reference voltage value obtained as described above. That is, correction is performed to increase the absolute value of the voltage value of the secondary transfer bias. In this embodiment, V2comp = 500V.

  On the other hand, when none of the above conditions is satisfied, no correction is made to the reference voltage obtained as described above. That is, the secondary transfer bias applied to the secondary transfer roller 58 at the time of image formation is V2 + V2p.

  In this embodiment, the configuration in which the secondary transfer bias is controlled based on the magnitude relationship between the two color toner tribos for the purpose of controlling the secondary transfer bias has been described. On the other hand, when it is determined that the tribo is high even in one of the yellow, magenta, cyan, and black toners, it is determined that the secondary transfer efficiency is deteriorated and the secondary transfer bias is corrected. good. For example, when any one or more of Iby, Ibm, Ibc, and Ibk exceeds 10 μA, the absolute value of the voltage value of the secondary transfer bias is increased.

  That is, as described above, the image forming apparatus 200 according to the present exemplary embodiment forms a predetermined toner image composed of at least two kinds of toners among different kinds of toner constituting the multiple toner at the time of non-image formation. The toner image is transferred to the intermediate transfer belt 54 while sequentially changing the constant current controlled or constant voltage controlled bias value output from the transfer high-voltage power supply 26. Here, in the above-described at least two steps, the following is detected for the toner of the toner image transferred first to the intermediate transfer belt 54 and the toner of the toner image transferred later in the multiple toner image toner. . That is, the voltage value or current value when the relationship between the output voltage value and the output current value of the transfer high-voltage power supply 26 becomes an inflection point is detected. The values detected in each process are αA and αB, respectively. At this time, the absolute value of the bias output from the secondary transfer high voltage power source 59 when the multiple toner image is transferred from the intermediate transfer belt 54 to the transfer material P is set as follows. That is, the value differs depending on whether the relationship represented by | αA | <| αB | is not established between any two types of toner and when the relationship is established between any two types of toner. Typically, the value is greater when the relationship represented by | αA | <| αB | is not established between any two types of toner than when the relationship is established between any two types of toner. Is big.

  As described above, in this embodiment, the transfer characteristics when the toner image on the photosensitive drum 1 is transferred to the transfer target are detected with respect to the toner of at least two colors. In particular, in this embodiment, the transfer current is detected while changing the transfer voltage when a predetermined toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 54. Then, toner tribo is detected based on the voltage value or current value at the inflection point obtained from the characteristics of the transfer voltage and transfer current at this time. Accordingly, it is possible to know the combination of the toner tribo of each color toner and the toner tribo in the secondary color toner image. As a result, even when the toner tribo changes due to environmental fluctuations or durability deterioration, good transfer can be performed without causing retransfer or deterioration of secondary transfer efficiency.

Example 3
Next, still another embodiment of the present invention will be described. In the image forming apparatus of the present embodiment, elements having the same or corresponding functions as those of the image forming apparatus of Embodiment 1 or 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  Here, the developing device 3 used in this embodiment will be described. FIG. 8 shows a schematic cross-sectional configuration of the image forming unit 60 in the present embodiment. In the present embodiment, the developing device 3 uses a nonmagnetic one-component developer (nonmagnetic toner) as a developer. The developing device 3 includes a developing container 31. The developing container 31 includes a developing chamber 31A that supports a developer carrying member and the like, and a developer storage portion 31B that stores toner. A developer stirring and conveying member 35 is provided in the developer storage portion 31B. The developer stirring / conveying member 35 sends the toner in the developer storage portion to the developing chamber 31A while stirring the toner.

  A developing roller 32 is rotatably installed as a developer carrying member (developing means) in an opening facing the photosensitive drum 1 in the developing chamber 31A. The developing roller 32 rotates in contact with or close to the photosensitive drum 1 during a developing operation. As indicated by the arrows in the figure, the photosensitive drum 1 and the developing roller 32 rotate so that their surface movement directions are the same at the contact portion. In this embodiment, the developing roller 32 is a urethane rubber single layer elastic body roller.

  The developing roller 32 is connected to a developing high voltage power source 17 as a developing bias output means. In the present embodiment, the development high-voltage power supply 17 outputs a development bias in which a DC voltage and an AC voltage are superimposed during a development operation, and applies the development bias to the development sleeve 15.

  Further, a supply roller 33 as a developer supply member is disposed in the developing chamber 31A. The supply roller 33 rotates in contact with the developing roller 1. As indicated by the arrows in the figure, the developing roller 32 and the supply roller 33 rotate so that their surface movement directions are in the opposite directions (counter directions) at the contact portion. The supply roller 33 is formed of an elastic member such as a foam. As a result, the toner is applied onto the developing roller 32 by the supply roller 33.

  Further, a developing blade 34 as a developer layer thickness regulating member is in contact with the developing roller 32. The toner carried on the developing roller 32 and transported is regulated in layer thickness by the developing blade 34 and given triboelectric charge. Thereafter, the toner is conveyed to a contact portion with the photosensitive drum 1 and used for developing the electrostatic image on the photosensitive drum 1. On the other hand, the supply roller 33 removes the toner (development residual toner) remaining on the development roller 32 after passing through the development position.

  In this embodiment, the photosensitive drum 1, the charging roller 2 as the process means acting on the photosensitive drum 1, the developing device 3, and the cleaning device 5 integrally form a process cartridge 70 by the frame body 72. Yes. The process cartridge 70 can be attached to and detached from the image forming apparatus main body (apparatus main body). In this embodiment, the process cartridge 70 is provided with a storage means 71 for storing information related to the process cartridge 70. As the storage means 71, an electronic storage medium such as a nonvolatile memory can be suitably used.

  The process cartridge 70 is detachably mounted on the apparatus main body via mounting means 80 provided on the apparatus main body. The mounting means 80 is a positioning member for positioning the process cartridge 70 within the apparatus main body, a guide member for guiding the process cartridge 70 into the apparatus main body, or the like.

  In this embodiment, the developing device 3 uses a non-magnetic one-component developer (non-magnetic toner), but is not limited to this. A magnetic one-component developer (magnetic toner) may be used. Further, a two-component developer may be used as in the first and second embodiments.

  In this embodiment, the current values Iby, Ibm, and Ibc for the toner movement described in the first and second embodiments are not detected, and the toner image on the photosensitive drum 1 is detected based on the electric resistance value of the developing roller 31. Predict toner tribo.

  First, the case where the present embodiment is applied to an image forming apparatus of the direct transfer type similar to that of the first embodiment will be described.

  In this embodiment, the transfer characteristic of the toner on the photosensitive drum 1 is detected based on the characteristics of the developing unit that forms a toner image on the photosensitive drum 1 with the toner. In particular, in this embodiment, a predetermined bias is output from the development high-voltage power supply 17 to the developing roller 32 as developing means. Then, the characteristics of the developing roller 32 are detected based on the result of detecting the output current value of the developing high-voltage power supply 17 at that time. That is, the electrical resistance value of the developing roller 32 can be detected from the detection result. From the detection result of the electric resistance value of the developing roller 32, toner transfer characteristics, in particular, toner tribo on the photosensitive drum 1 can be detected in this embodiment.

  In this embodiment, the resistance value information of the developing roller 32 is stored in advance in the storage means 71 mounted on the process cartridge 70. A control device (CPU) 28 provided in the apparatus main body predicts toner tribo of the toner image on the photosensitive drum 1 using information on the electrical resistance value stored in the storage means 71.

  That is, there is a correlation as shown in FIG. 9 between the electric resistance value of the developing roller 32 and the toner tribo of the toner image on the photosensitive drum 1, and the lower the electric resistance of the developing roller 32, the more sensitive The toner tribo of the toner image on the drum 1 becomes high. Therefore, in this embodiment, the toner tribos Ty, Tm, and Tc of the toner image on the photosensitive drum 1 are obtained from the correlation shown in FIG.

  More specifically, in this embodiment, the control device (CPU) 28 performs a predetermined voltage controlled by the developing high-voltage power supply 17 for the first to third image forming units 60a to 60c during non-image formation. A bias (DC-350 V in this embodiment) is output. Then, this voltage is applied to the developing roller 32. The current generated at this time is detected by the current detection unit 17A as detection means. The CPU 28 stores the current value detected at this time in a storage means built in or connected to the CPU 28. Then, the CPU 28 obtains the electric resistance value of the developing roller 32 from the detected current value and the output voltage value at that time.

  In this embodiment, when the electric resistance of the developing roller 32 is detected, the developing high voltage power supply 17 outputs a bias value controlled by constant voltage. However, the present invention is not limited to this, and it is only necessary to be able to detect the electric resistance value of the developing roller 32, and the output voltage value at that time may be measured by outputting a constant current controlled bias value. .

  Further, the CPU 28 determines the toner image on the photosensitive drum 1 based on the relationship between the electric resistance value of the developing roller 32 stored in the storage unit 71 of the process cartridge 70 and the toner tribo of the toner image on the photosensitive drum 1. The toner tribos Ty, Tm, and Tc are obtained.

  After that, the CPU 28 compares the magnitude relationships of Ty, Tm, and Tc and corrects the transfer bias as in the first embodiment.

  That is, the CPU 28 compares the magnitude relationship between Ty and Tm. When Ty> Tm, correction is applied to the transfer bias applied to the transfer roller 4c of the third image forming unit 60c during image formation. That is, the transfer bias applied to the transfer roller 4c of the third image forming unit 60c at the time of image formation is Vc + Vp−Vcomp.

  Conversely, when Ty <Tm, no correction is applied to the transfer bias applied to the transfer roller 4c of the third image forming unit 60c during image formation. That is, the transfer bias applied to the transfer roller 4c of the third image forming unit 60c at the time of image formation is Vc + Vp.

  The same correction is performed for the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d. That is, when Tm> Tc or Ty> Tc, the CPU 28 sets the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d to Vk + Vp−Vcomp when the image is formed. When Tm <Tc and Ty <Tc, the transfer bias applied to the transfer roller 4d of the fourth image forming unit 60d is set to Vk + Vp.

  In this embodiment, correction is not performed on the transfer bias applied to the transfer rollers 4a and 4b of the first and second image forming units 60a and 60b during image formation. That is, Vy + Vp and Vm + Vp obtained in the same manner as in the first embodiment are applied to these transfer rollers 4a and 4b at the time of image formation. However, as described in Patent Document 1, for example, the transfer rollers 4a of the first and second image forming units 60a and 60b are based on the transfer current detection results Iby and Ibm for yellow and magenta toners. The transfer bias applied to 4b may be controlled.

  As described above, in the image forming apparatus substantially similar to the first embodiment, instead of transferring the toner image to the transfer belt 40 and detecting the transfer current, the toner tribo is detected by detecting the electric resistance of the developing roller 32. Can be detected. Thereby, the same effect as Example 1 can be acquired.

  That is, as described above, from the output current value of the development high-voltage power supply 17 when a predetermined bias is output from the development high-voltage power supply 17 to the development roller 32 that forms a toner image on the photosensitive drum 1 with the first toner. The electric resistance value of the developing roller 32 can be obtained. Let the electrical resistance value be β1. Further, the developing roller 32 is determined from the output current value of the developing high-voltage power source 32 when a predetermined bias is output from the developing high-voltage power source 17 to the developing roller 32 that forms a toner image on the photosensitive drum 1 with the second toner. Can be obtained. Let the electrical resistance value be β2. At this time, the absolute value of the bias output from the transfer high-voltage power supply 26 when the third toner image of the multiple toner image is transferred to the transfer material P is the case where the relationship represented by | β1 |> | β2 | , | Β1 | <| β2 |. Typically, the absolute value of the bias output from the transfer high-voltage power supply 26 when the third toner image is transferred is greater than that in the case where the relationship represented by | β1 |> | β2 | is satisfied. The case where the relationship represented by | β2 | is satisfied is smaller.

  In the above description, the case where the present embodiment is applied to an image forming apparatus having the same basic configuration as that described in the first embodiment has been described as an example. Naturally, the present embodiment can also be applied to an image forming apparatus having the same basic configuration as that described in the second embodiment. In this case, in the same image forming apparatus as that of the second embodiment, instead of transferring the toner image to the intermediate transfer belt 54 and detecting the transfer current, the toner tribo is detected by detecting the electric resistance of the developing roller 32. can do. The primary transfer bias can be controlled in the same manner as the transfer bias control in the case of the above-described direct transfer type image forming apparatus.

  When the present embodiment is applied to an intermediate transfer body type image forming apparatus similar to that of the second embodiment, the secondary transfer bias is controlled by comparing the magnitude relationships of Ty, Tm, and Tc. be able to.

  That is, the CPU 28 compares the magnitude relationship between Ty and Tm, Ty and Tc, and Tm and Tc. When any one of Ty <Tm, Ty <Tc, and Tm <Tc is satisfied, it is determined that the secondary transfer efficiency is likely to deteriorate. The bias applied to the secondary transfer roller 58 at the time of image formation is set to V2 + V2p + V2comp by adding the corrected transfer bias value V2comp to the reference voltage value obtained in the same manner as in the second embodiment. Conversely, when none of the above conditions is satisfied, the bias applied to the secondary transfer roller 58 during image formation is set to V2 + V2p.

  As described above, in the case of the intermediate transfer type image forming apparatus, the developing roller that forms the toner image on the photosensitive drum 1 with the toner of the toner image transferred to the intermediate transfer belt 54 first in the toner of the multiple toner image. A predetermined bias is output from the development high-voltage power supply 17 to 32. The electrical resistance value of the developing roller 32 obtained from the output current value at that time is βA. Further, a predetermined bias is output from the developing high-voltage power supply 17 to the developing roller 32 that forms a toner image on the photosensitive drum 1 by the toner of the toner image transferred to the intermediate transfer belt 54 later. The electrical resistance value of the developing roller 32 obtained from the output current value at that time is βB. At this time, the absolute value of the bias output from the secondary transfer high voltage power source 59 when the multiple toner image is transferred from the intermediate transfer belt 54 to the transfer material P is set as follows. That is, the value is obtained when the relationship represented by | βA |> | βB | is not established between any two developing rollers 32 and when the relationship is established between any two developing rollers 32. Different. Typically, the value is established between any two developing rollers 32 than when the relationship represented by | βA |> | βB | is not established between any two developing rollers 32. If you do it is bigger.

  In this embodiment, the transfer bias, the primary transfer bias, or the secondary transfer bias is controlled based on the resistance value information of the developing roller 32. On the other hand, the measurement may be performed based on the development current (or voltage) characteristics measured in advance and stored in the storage unit 71 of the process cartridge 70. That is, the transfer bias, primary transfer bias, or secondary transfer bias can be controlled based on the relationship between the development current (or voltage) and the toner tribo of the toner image on the photosensitive drum 1. The primary transfer bias or the secondary transfer bias can be controlled based on the developing current (or voltage) measured by actually applying a predetermined developing bias to the developing roller 32 during non-image formation.

  As described above, in this embodiment, the transfer characteristics when the toner image on the photosensitive drum 1 is transferred to the transfer target are detected with respect to the toner of at least two colors. In particular, in this embodiment, the tribo of the toner supplied onto the photosensitive drum 1 is detected from the electric resistance value of the developing roller 32. Thus, by creating a test pattern, it is possible to know the combination of the toner tribo of each color and the toner tribo in the secondary color toner image without consuming the toner. Therefore, it is possible to perform good transfer while suppressing toner consumption and without causing retransfer or deterioration of secondary transfer efficiency even when the toner tribo changes due to environmental fluctuation or durability deterioration.

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

  For example, in each of the above embodiments, the image forming apparatus is described as a tandem image forming apparatus having a plurality of image forming units, but the present invention is not limited to this. Conventionally, a plurality of developing units are provided for one image carrier, and toner images sequentially formed from different types (colors) of toner on the image carrier are sequentially transferred to a transfer material conveyed by a transfer material conveyance unit. There is an image forming apparatus for transferring the image. Alternatively, there is an image forming apparatus in which toner images sequentially formed with different types (colors) of toner on an image carrier are sequentially transferred to an intermediate transfer member and then transferred to a transfer material at a time. The present invention can also be applied to such an image forming apparatus, and the same effects as described above can be obtained.

  FIG. 10 shows a schematic sectional configuration of an example of an image forming apparatus in which a plurality of developing devices 3 a to 3 d are provided for one photosensitive drum 1. The image forming apparatus 300 in FIG. 10 employs an intermediate transfer method. In the image forming apparatus 300 of FIG. 10, elements having the same or corresponding functions as those of the image forming apparatuses 100 and 200 shown in FIG. 1 or FIG.

  An image forming apparatus 300 illustrated in FIG. 10 includes a rotary developing device 90. The rotary developing device 90 includes first, second, third, and fourth developing devices 3a, 3b, 3c, and 3d on a rotating body 90A as a developing device support. The rotary developing device 90 can place a desired developing device 3 at a developing position facing the photosensitive drum 1 by rotating the rotating body 90A. At the time of image formation, an electrostatic image that is sequentially formed on the photosensitive drum 1 according to the image information separated on the photosensitive drum 1 is developed as a toner image of a predetermined color by a predetermined developing device 3. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 54 at the primary transfer portion N1 each time it is formed. Then, the image area on the intermediate transfer belt 54 passes through the primary transfer portion N1 a plurality of times, so that the toner for the desired number of colors is transferred on the intermediate transfer belt 54 in an overlapping manner. Thereafter, the toner image formed on the intermediate transfer belt 54 is transferred to the transfer material P at the secondary transfer portion N2. That is, in this image forming apparatus 300, the image forming means has a single photosensitive drum 1 for sequentially carrying toner images composed of different types of toners. The toner images formed on the photosensitive drum 1 are sequentially transferred to the intermediate transfer belt 54 at the same transfer portion in the moving direction of the intermediate transfer belt 54 that is a transfer target.

  As described above, in the image forming apparatus 300 in which the plurality of developing devices 3 are provided for one photosensitive drum 1, the transfer bias (primary transfer bias and secondary transfer bias) can be controlled according to the present invention. . For example, the transfer current is detected in the primary transfer portion N1 for the toner of the color transferred to the first to third colors. Based on the detection result, the primary transfer bias when the third and fourth color toner images are primarily transferred can be controlled. Further, the secondary transfer bias at the time of secondary transfer can be controlled based on the detection result of the transfer current.

  It is apparent from the above description that the transfer bias can be controlled according to the present invention even when an image forming apparatus provided with a plurality of developing units for one photosensitive drum adopts the direct transfer method. is there. In this case, for example, with respect to the toner of the color transferred to the first to third colors, the transfer current is detected at the transfer portion of the toner image from the photosensitive drum to the transfer belt. Based on the detection result, the transfer bias at the time of transferring the toner images of the third color and the fourth color can be controlled.

  In the image forming apparatus in which a plurality of developing units are provided for the one photosensitive drum 1, the control itself of the transfer bias (primary transfer bias, secondary transfer bias) is substantially the same as the above embodiments. can do. However, when a predetermined toner image is transferred from the photosensitive drum 1 and toner tribo on the photosensitive drum 1 is detected, the predetermined toner image is sequentially transferred at the same transfer portion, and the transfer voltage and transfer at that time are transferred. Current relationships are detected sequentially and independently.

  In the third embodiment, the configuration in which the process element of the image forming unit is formed into a cartridge and is detachable from the apparatus main body has been described. Such a configuration is naturally applicable to other embodiments. In the above description, the cartridge that can be attached to and detached from the apparatus body has been described as a process cartridge in which the photosensitive drum, the charging roller, the developing device, and the cleaning device are integrated into a cartridge, but the present invention is not limited to this. . In the process cartridge, 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 into a cartridge and can be attached to and detached from the apparatus main body. May be. The cartridge that can be attached to and detached from the apparatus main body may be a developing cartridge in which the developing device is a cartridge that can be attached to and detached from the apparatus main body alone.

  In the above-described embodiment, the information described as being stored in the storage unit mounted on the cartridge detachable from the apparatus main body may be stored in the storage unit included in the apparatus main body. However, by storing the above information in the storage means of the cartridge and holding the information in each cartridge, it becomes possible to perform control according to each cartridge.

1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic cross-sectional configuration diagram illustrating an image forming unit of the image forming apparatus in FIG. 1 in more detail. 6 is a graph showing an example of a relationship of a transfer current I with respect to a transfer voltage V. FIG. It is a schematic diagram which shows a transcription | transfer part. FIG. 10 is a graph for explaining an example of a toner transfer characteristic detection method. FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of an image forming apparatus according to the present invention. FIG. 7 is a schematic control block diagram relating to transfer bias control in the image forming apparatus of FIG. 6. FIG. 6 is a schematic cross-sectional configuration diagram illustrating an image forming unit in another embodiment of the image forming apparatus according to the present invention. FIG. 6 is a graph showing an example of a correlation between a resistance value of a developing roller and toner tribo on a photosensitive drum. It is a schematic sectional block diagram of the other example of the image forming apparatus which can apply this invention.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 Developer (Developer)
4 Transfer roller (transfer means)
5 Cleaning device (cleaning means)
6 Exposure equipment (exposure means)
17 Development high voltage power supply (Development bias output means)
26 High-voltage transfer power supply (transfer bias output means)
28 CPU (control means)
32 Developing roller (developing means)
40 Transfer belt (transfer body)
54 Intermediate transfer belt (transfer body)
59 Secondary transfer high-voltage power supply (second transfer bias output means)
60 Image forming part P Transfer material

Claims (27)

An image forming unit including an image carrier on which a toner image is formed, a transfer member that receives and conveys the toner image from the image forming unit, and a toner image from the image forming unit that is transferred to the transfer member or the transfer member. A transfer means for transferring to the upper transfer material; and a transfer bias output means for outputting a bias for the transfer to the transfer means. When forming a multiple toner image comprising the first, second, and third toner images made of the toner on the transfer member or a transfer material on the transfer member, the second toner image is formed after the first toner image. An image forming apparatus for transferring the third toner image after the second toner image;
The bias value output by the transfer bias output means when transferring the third toner image of the multiple toner image to the transfer body or a transfer material on the transfer body is the transfer value of the first and second toners. An image forming apparatus that is determined based on a result of detecting a characteristic. An image forming unit including an image carrier on which a toner image is formed, a transfer body onto which the toner image from the image forming unit is transferred, and a transfer for transferring the toner image from the image forming unit onto the transfer body. A transfer bias output means for outputting a bias for the transfer to the transfer means; a second transfer means for transferring a toner image from the transfer body onto a transfer material; and the second transfer. A second transfer bias output means for outputting a bias for the transfer to the means, and forming a multi-toner image comprising a plurality of toner images each made of different types of toner on the transfer body. In the image forming apparatus for transferring the multiple toner image to a transfer material,
The bias value output by the second transfer bias output means when transferring the multiple toner image from the transfer body onto a transfer material is the value of at least two types of toners of different types constituting the multiple toner image. An image forming apparatus that is determined based on a result of detecting a transfer characteristic.   A transfer bias detection unit that detects an output voltage value or an output current value of the transfer bias output unit when a bias is output from the transfer bias output unit; 3. The image formation according to claim 1, wherein the toner image is detected based on a detection result of the transfer bias detection unit when the toner image is transferred to the transfer body or a transfer material on the transfer body. apparatus.   The transfer characteristic of the toner is such that the predetermined toner image is transferred to the transfer body or the transfer material while sequentially changing a constant current controlled or constant voltage controlled bias value output from the transfer bias output means during non-image formation. 4. The image forming apparatus according to claim 3, wherein the image is transferred to an upper transfer material and detected by detecting an output voltage value or an output current value of the transfer bias output unit at that time by the transfer bias detection unit. .   5. The toner transfer characteristic is detected based on a voltage value or a current value when a relationship between an output voltage value and an output current value of the transfer bias output unit becomes an inflection point. Image forming apparatus.   The toner transfer characteristic is detected based on a voltage value or a current value when a change amount of the output current value with respect to a predetermined change amount of the output voltage value of the transfer bias output means becomes a predetermined value or more. The image forming apparatus according to claim 4.   The toner transfer characteristic is detected based on a voltage value or a current value when a change amount of the output current value with respect to a predetermined change amount of the output voltage value of the transfer bias output means becomes a predetermined value or less. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 3, wherein the predetermined toner image is formed in the entire image forming region in a direction intersecting with a surface moving direction of the image carrier. .   The image forming means has a plurality of developing means for forming a toner image on the image carrier with different types of toner, and the transfer characteristics of the toner are characteristics of the developing means for forming a toner image with the toner. The image forming apparatus according to claim 1, wherein the detection is performed based on the image.   A developing bias output means for outputting a bias for forming the toner image to the developing means, and an output current value or an output voltage of the developing bias output means when a bias is output from the developing bias output means The image forming apparatus according to claim 9, further comprising: a developing bias detecting unit configured to detect a value, wherein the characteristic of the developing unit is detected based on a detection result of the developing bias detecting unit.   The developing unit is characterized in that an electrical resistance value of the developing unit is detected from a detection result of the developing bias detection unit, and a transfer characteristic of the toner is detected based on the detection result of the electrical resistance value. The image forming apparatus according to claim 10.   12. The image forming apparatus according to claim 9, further comprising a storage unit that stores information relating the characteristics of the developing unit and the transfer characteristics of the toner.   13. The image forming apparatus according to claim 12, wherein at least a cartridge having the developing unit is detachable from a main body of the image forming apparatus, and the storage unit is mounted on the cartridge.   The charge amount per unit weight of the first toner indicated by the detection result of the transfer characteristic of the first toner is Q1, and per unit weight of the second toner indicated by the detection result of the transfer characteristic of the second toner. When the charge amount is Q2, the absolute value of the bias output by the transfer bias output means when the third toner image of the multiple toner image is transferred to the transfer body or a transfer material on the transfer body is: 2. The case where the relationship represented by | Q1 |> | Q2 | is smaller than the case where the relationship represented by | Q1 | <| Q2 | is established. Image forming apparatus.   Of the charge amount per unit weight of each of the at least two types of toner, the multiple toner image indicated by the result of detecting the transfer characteristics of at least two types of toner among the different types of toner constituting the multiple toner image. QA is the charge amount per unit weight of the toner of the toner image transferred to the transfer body in the first toner, and QB is the charge amount per unit weight of toner of the toner image transferred to the transfer body later. The absolute value of the bias output by the second transfer bias output means when the multiple toner image is transferred from the transfer body to the transfer material is any relationship expressed by | QA | <| QB | The image forming apparatus according to claim 2, wherein a case where any two types of toner is established is larger than a case where the relationship is not established between the two types of toner.   The image forming means includes a plurality of the image carriers to carry toner images composed of different types of toner, and the toner images formed on the plurality of image carriers are stored on the transfer body. The image forming apparatus according to claim 1, wherein the image is transferred to the transfer body or a transfer material on the transfer body at different transfer portions in the moving direction.   The image forming means has a single image carrier for sequentially carrying toner images of different types of toner, and the toner image formed on the image carrier is the transfer body. The image forming apparatus according to claim 1, wherein the image forming apparatus sequentially transfers the image to the transfer body or a transfer material on the transfer body at the same transfer portion in the moving direction. An image forming unit including an image carrier on which a toner image is formed, a transfer member that receives and conveys the toner image from the image forming unit, and a toner image from the image forming unit that is transferred to the transfer member or the transfer member. A transfer means for transferring to the upper transfer material; and a transfer bias output means for outputting a bias for the transfer to the transfer means. When forming a multiple toner image comprising the first, second, and third toner images made of the toner on the transfer member or a transfer material on the transfer member, the second toner image is formed after the first toner image. An image forming apparatus for transferring the third toner image after the second toner image;
During non-image formation, a predetermined toner image composed of the first toner is transferred onto the transfer body or the transfer body while sequentially changing the constant current controlled or constant voltage controlled bias value output from the transfer bias output means. A first step of transferring to the transfer material;
At the time of non-image formation, a predetermined toner image composed of the second toner is transferred onto the transfer body or the transfer body while sequentially changing the constant current controlled or constant voltage controlled bias value output from the transfer bias output means. A second step of transferring to the transfer material;
Have
When the voltage value or current value when the relationship between the output voltage value and the output current value of the transfer bias output means in the first and second steps becomes an inflection point is α1 and α2, respectively, the multiple toner image The bias value output by the transfer bias output means when the third toner image is transferred to the transfer body or the transfer material on the transfer body has a relationship represented by | α1 | <| α2 |. And an image forming apparatus characterized in that the relationship expressed by | α1 |> | α2 | is different.   The absolute value of the bias output by the transfer bias output means when the third toner image of the multiple toner image is transferred to the transfer body or a transfer material on the transfer body is represented by | α1 | <| α2 |. 19. The image forming apparatus according to claim 18, wherein the relationship expressed by | α1 |> | α2 | is smaller than the case where the relationship expressed is satisfied. An image forming unit including an image carrier on which a toner image is formed, a transfer body onto which the toner image from the image forming unit is transferred, and a transfer for transferring the toner image from the image forming unit onto the transfer body. A transfer bias output means for outputting a bias for the transfer to the transfer means; a second transfer means for transferring a toner image from the transfer body onto a transfer material; and the second transfer. A second transfer bias output means for outputting a bias for the transfer to the means, and forming a multi-toner image comprising a plurality of toner images each made of different types of toner on the transfer body. In the image forming apparatus for transferring the multiple toner image to a transfer material,
A constant current control or constant voltage controlled bias value for outputting a predetermined toner image composed of at least two types of different toners constituting the multiple toner during non-image formation from the transfer bias output means. Each having at least two steps of transferring to the transfer body while sequentially changing
Of the at least two steps, the step of transferring the predetermined toner image made of the toner of the toner image transferred first to the transfer body in the toner of the multiple toner image, and the later transferred to the transfer body A voltage value or a current value when the relationship between the output voltage value and the output current value of the transfer bias output means becomes an inflection point in the step of transferring the predetermined toner image made of toner of the toner image, respectively, is αA, When αB, the absolute value of the bias output by the second transfer bias output means when the multiple toner image is transferred from the transfer body to the transfer material has a relationship represented by | αA | <| αB |. An image forming apparatus, characterized in that a case where no relationship is established between any two types of toner is different from a case where the relationship is established between any two types of toner.   The absolute value of the bias output by the second transfer bias output means when the multiple toner image is transferred from the transfer body to the transfer material is expressed by | αA | <| αB | 21. The image forming apparatus according to claim 20, wherein the case where the relationship is established between any two types of toner is greater than the case where the relationship is not established between toners. An image forming unit including an image carrier on which a toner image is formed and a plurality of developing units that form toner images on the image carrier using different types of toner, and for forming the toner image on the developing unit A developing bias output means for outputting the bias of the toner, a transfer body for receiving and transporting the toner image from the image forming means, and the toner image from the image forming means on the transfer body or a transfer material on the transfer body. A transfer means for transferring, and a transfer bias output means for outputting a bias for the transfer to the transfer means, each of which comprises first, second, and third toners of different types. The second toner image is transferred after the first toner image when a multiple toner image including the first, second, and third toner images is formed on the transfer body or a transfer material on the transfer body. And said In the image forming apparatus to transfer the third toner image after the toner image,
The development obtained from the output current value of the developing bias output means when a predetermined bias is output from the developing bias output means to the developing means for forming a toner image on the image carrier with the first toner. The developing bias output means when the predetermined bias is outputted from the developing bias output means to the developing means for forming a toner image on the image carrier with the second toner. When the electric resistance value of the developing means obtained from the output current value is β2, the transfer bias output is output when the third toner image of the multiple toner image is transferred to the transfer member or the transfer material on the transfer member. The absolute value of the bias output by the means differs between the case where the relationship represented by | β1 |> | β2 | is satisfied and the case where the relationship represented by | β1 | <| β2 | An image forming apparatus comprising Rukoto.   The absolute value of the bias output by the transfer bias output means when the third toner image is transferred to the transfer member or the transfer material on the transfer member has a relationship represented by | β1 |> | β2 | 23. The image forming apparatus according to claim 22, wherein the case where the relationship represented by | β1 | <| β2 | is satisfied is smaller than the case where it is performed. An image forming unit including an image carrier on which a toner image is formed and a plurality of developing units that form toner images on the image carrier using different types of toner, and for forming the toner image on the developing unit A developing bias output means for outputting the bias of the toner, a transfer body to which the toner image from the image forming means is transferred, a transfer means for transferring the toner image from the image forming means to the transfer body, and the transfer A transfer bias output means for outputting a bias for the transfer to the means, a second transfer means for transferring a toner image from the transfer body to a transfer material, and the second transfer means. A second transfer bias output means for outputting a bias for transfer, and forming a multiple toner image comprising a plurality of toner images made of different types of toner on the transfer member In the image forming apparatus for transferring to a transfer material the said multiplexing toner image,
Of the at least two developing units for forming a toner image on the image carrier with each of at least two types of different toners constituting the multiple toner, the toner of the toner image transferred to the transfer body first The electric resistance of the developing means obtained from the output current value of the developing bias output means when a predetermined bias is output from the developing bias output means to the developing means that forms a toner image on the image carrier The development when a predetermined bias is output from the development bias output means to the development means for forming a toner image on the image carrier with toner of a toner image to be subsequently transferred to the transfer body with a value of βA When the electric resistance value of the developing means obtained from the output current value of the bias output means is βB, the multiple toner image is transferred from the transfer body to the transfer material. The absolute value of the bias output from the second transfer bias output means when copying is the case where the relationship represented by | βA |> | βB | does not hold between any two developing means, An image forming apparatus, wherein the image forming apparatus differs depending on whether it is established between two developing units.   The absolute value of the bias output by the second transfer bias output means when the multiple toner image is transferred from the transfer member to the transfer material is expressed by | βA |> | βB | 25. The image forming apparatus according to claim 24, wherein a case where the relationship is established between any two developing units is greater than a case where the relationship is not established between the units.   The image forming means includes a plurality of the image carriers to carry toner images composed of different types of toner, and the toner images formed on the plurality of image carriers are stored on the transfer body. The image forming apparatus according to any one of claims 18 to 25, wherein the image is transferred to the transfer body or a transfer material on the transfer body at different transfer portions in the moving direction.   The image forming means has a single image carrier for sequentially carrying toner images of different types of toner, and the toner image formed on the image carrier is the transfer body. The image forming apparatus according to any one of claims 18 to 25, wherein the image forming apparatus is sequentially transferred to the transfer body or a transfer material on the transfer body by the same transfer portion in the moving direction of the image forming apparatus.

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