JP2005037666A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can always stabilize the surface potential of an intermediate transfer body and can prevent density unevenness. <P>SOLUTION: The image forming apparatus 10 comprises: an image carrying body 26 where an electrostatic latent image is formed by the difference in electrification potential on the surface; a charging apparatus 28 to almost uniformly charge the surface of the image carrying body 26; an exposure apparatus 24 to irradiate the image carrying body 26 having almost uniformly charged by the charging apparatus 28 with image light to form an electrostatic latent image; a developing apparatus 30 to transfer toner onto the electrostatic latent image on the image carrying body 26 to visualize; intermediate transfer bodies 34, 36, 38 where the toner image formed on the image carrying body 26 is transferred; a final transfer body 72 to transfer the toner image from the intermediate transfer bodies 34, 36, 38 onto a recording medium S; a controlling means to control the potential gradient among the image carrying body 26, the intermediate transfer bodies 34, 36, 38 and the final transfer body 72; and a current detecting means 92 to detect the potential gradient. In this apparatus, a voltage calculated based on the detection result of the current detecting means 92 is applied on the final transfer body 72 when the surface potential of the intermediate transfer body 38 changes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these, and more particularly to a technique for stabilizing transfer to a recording medium.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers using an electrophotographic system (electrostatic transfer system) are widely known. In such an image forming apparatus, a toner image is transferred onto a recording sheet by an intermediate transfer member and a final transfer member, and the toner image is fixed, whereby a toner image as a permanent image is formed on the recording sheet.

  Further, in such an image forming apparatus, before and after transferring the toner image onto the recording sheet (the recording sheet before the start of toner image transfer and after the toner image transfer is completed is conveyed, and the next recording sheet is conveyed). A difference occurs in the surface potential on the intermediate transfer member that is in contact with the final transfer member, and this potential difference has a density on the recording sheet S as shown in FIG. It may occur as a difference (density unevenness).

For this reason, the constant current control method using a constant current circuit has been used in the past, but it tends to cause transfer failure of small size paper and interference with the paper discharge voltage. It was easy for image quality defects to occur due to changes in the resistance of the members. Further, even in a constant voltage control system using a constant current circuit, the constant current circuit and the constant voltage circuit are used together, resulting in an increase in cost (for example, see Patent Document 1).
JP 2001-282012 A

  Therefore, the present invention can always stabilize the surface potential of the intermediate transfer member without increasing the cost, prevent the occurrence of density unevenness, and change the environment, the type of transfer material, and the resistance change of the transfer member. An object of the present invention is to provide an image forming apparatus capable of obtaining a good image quality even when the image is generated.

  In order to achieve the above object, an image forming apparatus according to claim 1 according to the present invention includes an image carrier on which an electrostatic latent image is formed on a surface due to a difference in charging potential, and a surface of the image carrier. A charging device that charges the image carrier substantially uniformly, an exposure device that forms an electrostatic latent image by irradiating image light onto the image carrier that is substantially uniformly charged by the charging device, and a static image on the image carrier. A developing device for transferring toner to an electrostatic latent image for visualization, an intermediate transfer member to which the toner image formed on the image carrier is transferred, and a final transfer for transferring the toner image from the intermediate transfer member to a recording medium In an image forming apparatus comprising: a body; a control unit that controls a potential gradient between the image carrier, the intermediate transfer member, and the final transfer member; and a current detection unit that detects the potential gradient. The voltage calculated based on the detection result is displayed on the surface of the intermediate transfer member. A time when the potential is displaced, is characterized in that applied to the final transfer body.

  According to the first aspect of the present invention, the voltage calculated based on the detection result of the current detecting means is applied to the final transfer body at the time when the surface potential of the intermediate transfer body is displaced. Since the final transfer member is in contact with the intermediate transfer member, the surface potential of the intermediate transfer member is stabilized by the final transfer member. Therefore, it is possible to prevent the occurrence of density unevenness on the recording medium.

  The image forming apparatus according to claim 2 is characterized in that, in the image forming apparatus according to claim 1, the time is before recording medium transfer, and the image forming apparatus according to claim 3, The image forming apparatus according to claim 2, wherein an application time to the final transfer member is equal to or longer than one turn of the intermediate transfer member.

  According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the time is between pages. The image forming apparatus according to claim 5 is characterized in that, in the image forming apparatus according to claim 1, the current detecting means detects a current flowing through the final transfer member.

  The image forming apparatus according to claim 6 is the image forming apparatus according to claim 1, comprising four image carriers for yellow, magenta, black, and cyan as the image carrier. Among the four image carriers, the intermediate transfer device includes a first upstream intermediate transfer member and a first downstream intermediate transfer member that are in contact with two image carriers, respectively, and the first upstream intermediate member. After the toner image is transferred from the first upstream intermediate transfer body after contacting the transfer body and the first downstream intermediate transfer body, the toner image is transferred from the first downstream intermediate transfer body. An intermediate transfer member, and the final transfer member is in contact with the second intermediate transfer member.

  The image forming apparatus according to claim 7 is the image forming apparatus according to claim 6, wherein the time is before transfer of the recording medium, and the image forming apparatus according to claim 8, The image forming apparatus according to claim 7, wherein an application time to the final transfer member is equal to or longer than one turn of the second intermediate transfer member.

  An image forming apparatus according to claim 9 is the image forming apparatus according to claim 6, wherein the time is between pages. An image forming apparatus according to a tenth aspect is the image forming apparatus according to the sixth aspect, wherein the current detection unit detects a current flowing through the final transfer member.

  According to the present invention, the surface potential of the intermediate transfer member is stabilized by the final transfer member. Therefore, it is possible to prevent the occurrence of density unevenness on the recording medium.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is a schematic side view showing a tandem type full color printer as an image forming apparatus according to the present invention, and FIG. 2 is a schematic side view showing a main part of the full color printer shown in FIG. The full color printer 10 is roughly composed of an image forming unit 12, an intermediate transfer device 14, a final transfer unit 16, a fixing device 18, and a paper feeding unit 20.

  The image forming unit 12 includes four image forming units 22Y, 22M, 22K, and 22C for yellow (Y), magenta (M), black (K), and cyan (C), and an exposure device 24. Has been. Each of the image forming units 22Y to 22C includes four photosensitive drums (image bearing members) 26Y, 26M, 26K, and 26C, and charging rolls (contact type charging members) 28Y and 28M that respectively contact the photosensitive drums 26Y to 26C. 28K, 28C, developing devices 30Y, 30M, 30K, 30C facing the photosensitive drums 26Y-26C, respectively, and photosensitive brush rolls 32Y, 32M, 32K, 32C contacting the photosensitive drums 26Y-26C, respectively. It is configured.

  Here, with respect to the arrangement of each member around the photosensitive drum 26, the charging roll 28, the developing device 30, and the first to be described later are arranged around the photosensitive drum 26 from the upstream side to the downstream side in the rotation direction of the photosensitive drum 26. Upstream or downstream intermediate transfer rolls 34, 36 and a photosensitive brush roll 32 are arranged in this order.

  The photosensitive drums 26Y to 26C are applied with a DC voltage of about −900 V by the charging rolls 28Y to 28C, and are thereby uniformly charged to about −420V. When the electrostatic latent image is written by the exposure device 24, the surface potential is neutralized to about -70V.

The developing devices 30Y to 30C are magnetic brush contact type two-component developing type developing devices including a developing roll, a developer amount regulating member, a developer conveying member, and an auger for conveying and stirring the developer. Incidentally, amount of the developer conveyed to the developing portion is regulated by the developer amount regulating member is about ^{30g / m 2 ~45g / m 2} , the charge amount of the toner present on the developing roll to the lever is approximately - It is about 40 μC / g to −50 μC / g. The developing devices 30Y to 30C are developed by applying an AC + DC developing voltage. The developing voltage is 4 kHz for AC, 1.3 kVpp, and about −350 V for DC.

  The intermediate transfer device 14 includes a first upstream intermediate transfer roll (first upstream intermediate transfer member) 34 that contacts the photosensitive drums 26Y and 26M, and a first downstream side that contacts the photosensitive drums 26K and 26C. An intermediate transfer roll (first downstream intermediate transfer body) 36, a second intermediate transfer roll 38 (second intermediate transfer body) in contact with the two first intermediate transfer rolls 34, 36, and a second The toner sensor 40 is provided for optically detecting the presence and density of the toner image on the intermediate transfer roll 38 in a non-contact manner. Based on the detection result of the toner sensor 40, each charging bias, each developing bias, the amount of toner replenished in each developing device 30, and the like are controlled.

  Further, the first upstream intermediate transfer roll 34 includes a first upstream cleaning device 42. The first upstream cleaning device 42 includes a metal (stainless) cleaning roll 44 (cleaning body) that contacts the first upstream intermediate transfer roll 34, a cleaning blade 46 that contacts the cleaning roll 44, In the vicinity of the upstream side in the rotation direction of the first upstream intermediate transfer roll 34 relative to the cleaning roll 44, the brush roll 48 that contacts the intermediate transfer roll 34, and these cleaning roll 44, cleaning blade 46, and brush roll 48 are accommodated. A cleaner housing (container) 50 is provided.

  Similarly, the first downstream intermediate transfer roll 36 includes a first downstream cleaning device 52. The first downstream cleaning device 52 includes a metal (stainless) cleaning roll (cleaning body) 54 that contacts the first downstream intermediate transfer roll 36, a cleaning blade 56 that contacts the cleaning roll 54, In the vicinity of the upstream side in the rotational direction of the first downstream intermediate transfer roll 36 relative to the cleaning roll 54, the brush roll 58 that contacts the intermediate transfer roll 36, the cleaning roll 54, the cleaning blade 56, and the brush roll 58 are accommodated. A cleaner housing (container) 60 is provided.

  Further, the second intermediate transfer roll 38 includes a second cleaning device 62. This second cleaning device 62 includes a metal (stainless) cleaning roll (cleaning body) 64 that contacts the second intermediate transfer roll 38, a cleaning blade 66 that contacts the cleaning roll 64, and a cleaning roll 64. Also, in the vicinity of the downstream side in the rotation direction of the second intermediate transfer roll 38, the brush roll 68 that contacts the intermediate transfer roll 38, and the cleaner housing (container) that houses the cleaning roll 64, the cleaning blade 66, and the brush roll 68. 70.

  Here, the arrangement of the peripheral members in the first upstream intermediate transfer roll 34 is centered on the first upstream intermediate transfer roll 34 and the upstream side in the rotation direction of the first upstream intermediate transfer roll 34 from the upstream side. The photosensitive drum 26M, the photosensitive drum 26Y, the second intermediate transfer roll 38, the brush roll 48, and the cleaning roll 44 are sequentially arranged.

  The arrangement of the peripheral members in the first downstream intermediate transfer roll 36 is centered on the first downstream intermediate transfer roll 36 from the upstream side to the downstream side in the rotation direction of the first downstream intermediate transfer roll 36. The photosensitive drum 26C, the photosensitive drum 26K, the second intermediate transfer roll 38, the brush roll 58, and the cleaning roll 54 are disposed in this order.

  Further, the arrangement of the peripheral members in the second intermediate transfer roll 38 is such that the first upstream side is centered on the second intermediate transfer roll 38 from the upstream side to the downstream side in the rotation direction of the second intermediate transfer roll 38. An intermediate transfer roll 34, a first downstream intermediate transfer roll 36, a toner sensor 40, a final transfer roll 72, a cleaning roll 64, and a brush roll 68, which will be described later, are arranged in this order.

  The first intermediate transfer rolls 34 and 36 are formed by providing a silicon rubber layer on a metal pipe and further coating a high release layer thereon. The optimum value of the surface potential required to transfer the toner image from the photoreceptors 26Y to 26C to the first intermediate transfer rolls 34 and 36 is determined by the type and conveyance speed of the recording paper S, the charged state of the toner, It is set by the ambient temperature, humidity, etc. Here, the constant voltage control method is employed, and when the recording paper S is plain paper and the conveyance speed is full speed, the optimum value is set to +400 V in a normal temperature and normal humidity environment (see FIG. 3).

  Similar to the first intermediate transfer rolls 34 and 36, the second intermediate transfer roll 38 is formed by providing a silicon rubber layer on a metal pipe and further coating a high release layer thereon. The optimum value of the surface potential necessary for transferring the toner image from the first intermediate transfer rolls 34 and 36 to the second intermediate transfer roll 38 is determined based on the type, transport speed, and toner charge of the recording paper S. It is set according to the state, ambient temperature, humidity, and the like. Here, the constant voltage control method is employed, and when the recording paper S is plain paper and the transport speed is full speed, the optimum value is +850 V in a normal temperature and normal humidity environment (see FIG. 3).

  The final transfer roll 72 constituting the final transfer portion 16 is formed by providing a urethane rubber layer on a metal pipe and further applying a resin coating thereon. In order to transfer the toner image from the second intermediate transfer roll 38 onto the recording paper S, the optimum value of the transfer voltage applied to the final transfer roll 72 is determined based on the type of the recording paper S, the conveyance speed, and the toner. It is set according to the charging state, ambient temperature, humidity and the like. Usually, the transfer voltage applied to the final transfer roll 72 is in the range of about +1200 V to +4200 V. Here, the constant voltage control method is adopted, and the optimum value is about +2000 V in a normal temperature and normal humidity environment (FIG. 3). reference).

  Unlike the first intermediate transfer rolls 34 and 36 and the second intermediate transfer roll 38, the final transfer roll 72 is configured such that a cleaning roll (cleaning body) is not in contact therewith. Further, the optimum value of the cleaning voltage to be applied to the cleaning rolls 44, 54, 64 and the brush rolls 48, 58, 68 of the cleaning devices 42, 52, 62 also depends on the type and conveyance speed of the recording paper S, the charged state of the toner, It is set by the ambient temperature, humidity, etc. For example, the brush rolls 48 and 58 of the first cleaning devices 42 and 52 have an optimum value of +600 V in a normal temperature and normal humidity environment (see FIG. 3).

  In the fixing device 18, a heating roll 74 and a pressure roll 76 are pressed to form a fixing nip. A halogen lamp (not shown) as a heat source is disposed in the heating roll 74, and is configured to heat the surface of the heating roll 74 to a predetermined fixing temperature during fixing. A fixing discharge roll pair 78 is disposed downstream of the fixing nip in the conveyance direction of the recording paper S.

  The paper feed unit 20 is formed along a conveyance path (indicated by a dotted line) P of the recording paper S from the paper feed tray 80 to the discharge tray 82. A plurality of recording sheets S are accommodated in the paper feed tray 80, and from the paper feed tray 80 to the downstream side of the transport path P, a roll pair 84 and a transport roll pair 86 including a pickup roll 84 </ b> A and a retard roll 84 </ b> B. A resist roll pair 88 and a discharge roll pair 90 (via the final transfer roll 72 and the fixing device 18) are arranged in this order.

  The full color printer 10 having such a configuration operates as follows. First, yellow, magenta, black, and cyan toner images are formed on the photosensitive drums 26Y to 26C by the image forming units 22Y to 22C, respectively. That is, the surface of each photosensitive drum 26 is uniformly charged by the charging roll 28, and a laser beam L corresponding to an output image is irradiated from the exposure device 24 onto the surface of the photosensitive drum 26 after charging, and the exposed portion. An electrostatic latent image is formed on the photosensitive drum 26 due to the potential difference from the unexposed portion. The developing device 30 selectively applies toner to the electrostatic latent image, and a toner image is formed on the photosensitive drum 26.

  First, the magenta toner image is primarily transferred from the magenta photosensitive drum 26M to the first upstream intermediate transfer roll 34. Next, the yellow toner image is primarily transferred from the yellow photosensitive drum 26 </ b> Y to the first upstream intermediate transfer roll 34 and is superimposed on the magenta toner image. On the other hand, similarly, a cyan toner image is primarily transferred from the cyan photosensitive drum 26C to the first downstream intermediate transfer roll 36. Next, the black toner image is primarily transferred from the black photosensitive drum 26 </ b> K to the first downstream intermediate transfer roll 36.

  The primary-transferred magenta and yellow toner images are secondarily transferred to the second intermediate transfer roll 38. On the other hand, the primary transferred cyan and black toner images are also secondarily transferred to the second intermediate transfer roll 38, where the magenta and yellow toner images, the cyan toner image previously transferred, Are superimposed on each other to form a full-color toner image on the second intermediate transfer roll 38.

  The secondary transfer full color toner image and black toner image reach the nip portion between the second intermediate transfer roll 38 and the final transfer roll 72. In synchronization with the timing, the recording sheet S as a recording sheet is conveyed from the registration roll pair 88 (see FIG. 1) to the nip portion, and the full-color toner image and the black toner image are tertiary-transferred onto the recording sheet S (final transfer). )

  The recording sheet S then passes through the nip portion between the heating roll 74 and the pressure roll 76 of the fixing device 18 (see FIG. 1). At that time, the full color toner image and the black toner image are fixed on the recording paper S by the action of heat and pressure applied from both rolls 74 and 76 to form a permanent image. Further, thereafter, the recording paper S is discharged to the discharge tray 82 by the discharge roll pair 90, and the full color image formation is completed.

  In this way, a desired image is printed on the recording paper S. However, in order to prevent density unevenness in the printed image, that is, the voltage applied to the second intermediate transfer roll 38 and the second intermediate transfer roll 38. The timing for applying a predetermined voltage to the final transfer roll 72 in contact with the second intermediate transfer roll 38 is set so that no difference occurs between the surface transfer potential and the surface transfer potential.

  As shown in FIG. 3, a current detector 92 is connected to the final transfer roll 72, and after the initial voltage is applied, the final current is set so that the desired current value range is about 19.0 μA to 26.0 μA. The voltage of the transfer roll 72 is controlled. That is, the voltage applied to the final transfer roll 72 is controlled by the CPU and controller so that the current detected by the current detection device 92 falls within a desired range.

  FIG. 4 is a graph showing the relationship between the current value and the voltage value. As shown in FIG. 4, for example, when the conveyance speed of the recording paper S as a recording sheet is full speed, the range of the desired current value is about 19.0 μA to 26.0 μA (the range sandwiched between the dotted lines in the figure). It is. That is, the voltage is controlled so that a current in this range flows to the final transfer roll 72 at a predetermined time. The standard of the applied voltage is about 1400V to 1550V. In the case of the half speed, it is about 11.0 μA to 18.0 μA (the range sandwiched by the dashed line in the figure), and the standard of the applied voltage in this case is about 1250 V to 1450 V.

  Here, the predetermined time is when the current value in the final transfer roll 72 is out of the above range, and when the surface potential of the second intermediate transfer roll 38 is displaced. Specifically, before the start of the toner image transfer, and after the transfer of the toner image to the recording paper S is completed, the recording paper S is removed from the nip portion between the final transfer roll 72 and the second intermediate transfer roll 38, and the next recording paper This is a period until S is conveyed to the nip portion (hereinafter referred to as between pages).

  As shown in FIG. 5, before starting the toner image transfer, +1500 V is applied as an initial voltage in a normal temperature and humidity environment. As shown in FIG. 6, when a voltage of +1500 V or more is applied, there is a difference between the surface potential of the second intermediate transfer roll 38 (referred to as “intermediate transfer body 2” in FIG. 6) and the applied voltage. This is because it will not occur. Further, the application time at this time is set to be equal to or longer than one turn of the second intermediate transfer roll 38. As a result, the density unevenness of the recording sheet S printed on the first sheet as shown in FIG.

  Further, when the transfer of the toner image is started and the toner image is transferred onto the first recording paper S, before the toner image is transferred onto the second recording paper S, that is, at a time corresponding to the interval between the pages. A predetermined voltage is applied. As described above, the voltage applied at this time is such that the full speed is in the range of about 19.0 μA to 26.0 μA and the half speed is in the range of about 11.0 μA to 18.0 μA. As a result, the difference between the applied voltage and the surface potential of the intermediate transfer roll 38 between pages becomes equal to the difference between the applied voltage and the surface potential of the intermediate transfer roll 38 during toner image transfer, which is shown in FIG. The density unevenness of the second and subsequent recording sheets S during continuous printing is eliminated.

  As described above, the second intermediate transfer roll 38 comes into contact with the final transfer roll 72, and a predetermined voltage is applied to the final transfer roll 72 at each time period. The surface potential can always be stabilized (adjusted). Therefore, the occurrence of density unevenness in the recording paper S can be prevented. In addition, with such constant voltage control, voltage control of the final transfer roll 72 during each of the above times and during toner transfer can be easily performed. Therefore, the second intermediate transfer roll 38 can perform each time and during toner transfer. The surface potential can be easily adjusted. Also, good image quality can be obtained even if the environment changes, the type of transfer material, and the resistance of the transfer member change.

Schematic side view of a full-color printer according to the present invention Schematic side view of essential parts of a full-color printer according to the present invention Operation explanatory diagram of a full-color printer according to the present invention Graph showing the voltage-current characteristics of the final transfer member Graph showing when to apply voltage to the final transfer body Graph showing the applied voltage of the final transfer member vs. the surface potential of the intermediate transfer member (room temperature and humidity environment) Explanatory drawing showing density unevenness

Explanation of symbols

10 Printer (image forming device)
22 Image forming unit 26 Photosensitive drum (image carrier)
28 Charging roll (charging device)
30 Developing device 34 First upstream intermediate transfer roll (intermediate transfer member)
36 First downstream intermediate transfer roll (intermediate transfer member)
38 Second intermediate transfer roll (intermediate transfer member)
72 Final transfer roll (Final transfer body)
92 Current detection device (current detection means)

Claims (10)

An image carrier on which an electrostatic latent image is formed on the surface due to a difference in charging potential, a charging device that charges the surface of the image carrier substantially uniformly, and an image carrier that is substantially uniformly charged by the charging device An exposure device that forms an electrostatic latent image by irradiating a body with image light, a developing device that transfers toner to the electrostatic latent image on the image carrier and visualizes the image, and an image formed on the image carrier. An intermediate transfer member to which a toner image is transferred, a final transfer member that transfers the toner image from the intermediate transfer member to a recording medium, and a control unit that controls a potential gradient between the image carrier, the intermediate transfer member, and the final transfer member. And an image forming apparatus comprising: a current detection unit that detects the potential gradient;
An image forming apparatus, wherein a voltage calculated based on a detection result of the current detection unit is applied to the final transfer body when the surface potential of the intermediate transfer body is displaced.   The image forming apparatus according to claim 1, wherein the time is before recording medium transfer.   The image forming apparatus according to claim 2, wherein the application time to the final transfer member is equal to or longer than one turn of the intermediate transfer member.   The image forming apparatus according to claim 1, wherein the time is between pages.   The image forming apparatus according to claim 1, wherein the current detection unit detects a current flowing through the final transfer member.   The image carrier includes four image carriers for yellow, magenta, black, and cyan, and the intermediate transfer device is in contact with two of the four image carriers. The first upstream intermediate transfer member and the first downstream intermediate transfer member, and the first upstream intermediate transfer member and the first upstream intermediate transfer member that are in contact with the first upstream intermediate transfer member and the first downstream intermediate transfer member. A second intermediate transfer member to which the toner image is transferred from the first downstream intermediate transfer member after the toner image is transferred, and the final transfer member is in contact with the second intermediate transfer member. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 6, wherein the time is before recording medium transfer.   The image forming apparatus according to claim 7, wherein the application time to the final transfer member is equal to or longer than one turn of the second intermediate transfer member.   The image forming apparatus according to claim 6, wherein the time is between pages.   The image forming apparatus according to claim 6, wherein the current detection unit detects a current flowing through the final transfer member.

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