JP2017219790A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can apply an appropriate voltage to a recording medium in contact with a fixing member and prevent electrostatic offset occurring in a fixing part.SOLUTION: An image forming apparatus 1 comprises: an image forming part 12; a fixing part 13; and a fixing control part 91. The image forming part 12 forms an image on a sheet S. The fixing part 13 fixes the image to the sheet S. The fixing control part 91 controls the fixing part 13. The fixing part 13 includes a fixing member 13a, an application part 6, and a current detection part 7. The fixing member 13a applies heat and pressure to the sheet S as well as the image formed on the sheet S. The application part 6 applies a voltage to the sheet S. The current detection part 7 detects the value of a current flowing in the fixing member 13a and outputs the detected value to the fixing control part 91. The fixing control part 91 controls the application part 6 to adjust the value of the voltage so as to make the value of the current constant.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus.

  The fixing unit of the image forming apparatus described in Patent Literature 1 includes a fixing nip portion and a fixing inlet guide. The fixing nip portion heats and pressurizes the recording material passing therethrough. As a result, the image is fixed on the recording material. The fixing entrance guide protrudes into the recording material conveyance path. The fixing inlet guide is located on the upstream side of the fixing nip portion.

  In the image forming apparatus described in Patent Document 1, for example, a voltage is applied to the fixing nip portion and the fixing inlet guide is grounded. Accordingly, when the recording material is conveyed to a position straddling the fixing nip portion and the fixing inlet guide, a voltage is applied to the fixing nip portion through the recording material. As a result, the fixing nip is prevented from being charged and electrostatic offset is prevented. When electrostatic offset occurs, the toner carried on the recording material is transferred to the charged fixing nip.

  In the image forming apparatus described in Patent Document 1, when the rear end portion of the recording material comes into contact with the fixing nip portion, the recording material and the fixing inlet guide are separated from each other. Therefore, when the trailing edge of the recording material comes into contact with the fixing nip portion, the energization between the fixing nip portion and the fixing inlet guide is interrupted. As a result, an electrostatic offset may occur at the rear end of the recording material. The electrostatic offset that occurs at the rear end of the recording material is prevented, for example, by increasing the voltage applied to the fixing nip.

JP 2000-98673 A

  However, when the applied voltage is high, a discharge occurs between the recording medium (recording material) and the fixing member (fixing nip portion). The discharge may cause the toner to peel from the recording medium in contact with the fixing member. If the voltage applied to the fixing member is low, the electrostatic offset may not be eliminated.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of applying an appropriate voltage to a recording medium in contact with a fixing member and preventing electrostatic offset generated in a fixing unit. It is in.

  An image forming apparatus according to the present invention includes an image forming unit, a fixing unit, and a fixing control unit. The image forming unit forms an image on a recording medium. The fixing unit fixes the image on the recording medium. The fixing control unit controls the fixing unit. The fixing unit includes a fixing member, an application unit, and a current detection unit. The fixing member heats and pressurizes an image formed on the recording medium together with the recording medium. The application unit applies a voltage to the recording medium. The current detection unit detects a value of a current flowing through the fixing member and outputs the detected value to the fixing control unit. The fixing control unit controls the application unit to adjust the voltage value so that the current value becomes constant.

  According to the image forming apparatus of the present invention, an appropriate voltage can be applied to the recording medium in contact with the fixing member, and electrostatic offset that occurs in the fixing unit can be prevented.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of a fixing unit in FIG. 1. It is sectional drawing which shows the roller part of the heating member of FIG. It is a figure which shows the electric circuit of the fixing | fixed part of FIG. FIG. 2 is a block diagram illustrating a configuration of a control unit of the image forming apparatus in FIG. 1. FIG. 6 is a diagram illustrating an electric circuit of a fixing unit of an image forming apparatus according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is a multifunction machine. The image forming apparatus 1 may be a copy, a printer, or a facsimile. The multi-function peripheral has, for example, at least two functions among a copy function, a printer function, and a facsimile function.

  The image forming apparatus 1 forms an image on the paper S. The paper S is an example of the recording medium of the present invention. The paper S is, for example, plain paper, copy paper, recycled paper, thin paper, thick paper, glossy paper, or OHP (Overhead Projector) paper.

  The image forming apparatus 1 includes a control unit 9, a housing 10, a storage unit 11, an image forming unit 12, a fixing unit 13, a discharge tray 14, and an operation panel 15. The sheet S is transported from the storage unit 11 to the discharge tray 14 along the sheet transport path.

  In FIG. 1, the direction in which the operation panel 15 faces is defined as the front, and the front-rear direction is defined. Further, the left-hand side is defined as the left side toward the front of the image forming apparatus 1, and the left-right direction is defined. Further, the front-rear direction and the direction orthogonal to the left-right direction are defined as the up-down direction.

  The operation panel 15 includes a display unit 15a and an input unit 15b. The display unit 15a includes a display. The display includes an LCD (Liquid Crystal Display) having a touch panel function, or an organic ELD (Electro Luminescence Display). The display unit 15 a displays various setting screens of the image forming apparatus 1. The input unit 15b includes a hard key. The input unit 15b outputs an operation signal corresponding to a user operation to the control unit 9. User operations include, for example, operations for performing various settings of the image forming apparatus 1.

  The housing 10 houses the control unit 9, the storage unit 11, the image forming unit 12, and the fixing unit 13. The storage unit 11 includes a plurality of cassettes 11a. The cassette 11 a is disposed at the lower part of the housing 10. Each cassette 11a is detachable from the housing 10. Each cassette 11a can accommodate a plurality of sheets S.

  The image forming unit 12 is disposed on the downstream side of the storage unit 11 in the paper transport path. The image forming unit 12 forms a toner image on the paper S. The image forming unit 12 includes a photosensitive drum 21, a charging unit 22, an exposure unit 23, a developing unit 24, and a transfer unit 25. The photosensitive drum 21 includes, for example, a conductive substrate and a photosensitive layer. The conductive substrate has conductivity. The photosensitive layer is formed on the outer peripheral surface of the conductive substrate.

  The charging unit 22 charges the photosensitive drum 21 to a predetermined potential. The exposure unit 23 forms an electrostatic latent image by irradiating the outer peripheral surface of the charged photosensitive drum 21 with a laser. The developing unit 24 develops the electrostatic latent image as a toner image. As a result, a toner image is formed on the outer peripheral surface of the photosensitive drum 21.

  The transfer unit 25 transfers the toner image onto the paper S. The transfer unit 25 has a transfer roller. The transfer roller forms a nip portion together with the photosensitive drum 21. The nip portion transfers the toner image onto the sheet S passing between the transfer roller and the photosensitive drum 21.

  The fixing unit 13 is disposed on the downstream side of the image forming unit 12 in the paper conveyance path. The fixing unit 13 includes a fixing member 13a and a casing 13b. The fixing member 13a heats and pressurizes the toner image transferred to the paper S together with the paper S. As a result, the toner image is fixed on the paper S. A sheet S on which the toner image is fixed is stacked on the discharge tray 14.

  The casing 13b accommodates the fixing member 13a inside the casing 13b. Further, the casing 13b functions as a part of a guide unit that guides the paper S along the paper transport path.

  FIG. 2 is a diagram illustrating a configuration of the fixing unit 13. A part of the fixing unit 13 in FIG. 2 is shown in cross section. As shown in FIG. 2, the fixing member 13 a includes a heating member 4 and a pressure member 5. The heating member 4 is a member formed in a long shape along the front-rear direction of the fixing unit 13. The heating member 4 of this embodiment is a heating roller. The heating member 4 includes a roller part 41 and a heat source 43.

  The heat source 43 is accommodated inside the roller unit 41. The heat source 43 is a heater such as a halogen heater or a ceramic heater. When energized, the heat source 43 radiates heat to the surroundings. As a result, the roller unit 41 is heated. Moreover, the heating member 4 further has a gear part. The gear portion is pivotally supported on the casing 13b. The gear portion has rotating shafts provided at both ends of the heating member 4. The gear unit drives the roller unit 41 to rotate. Power is transmitted from the drive source to the gear unit. The drive source is, for example, a motor.

  The pressure member 5 is a member formed in a long shape along the front-rear direction of the fixing unit 13. The pressure member 5 of this embodiment is a pressure roller. The pressure member 5 includes a roller part 51 and a shaft part 52. The shaft portion 52 is rotatably supported by the casing 13b. The roller part 51 can rotate together with the shaft part 52.

  The roller part 51 of the pressing member 5 is arranged in parallel with the roller part 41 of the heating member 4. The roller part 51 is pressed against the roller part 41 by an elastic member such as a spring. As a result, a nip portion 13 c is formed between the roller portion 51 and the roller portion 41. The roller unit 51 of the present embodiment follows the rotation of the roller unit 41.

  In the fixing unit 13 of the present embodiment, the sheet S is transported from below to above. The sheet S has a first main surface S1 on which a toner image is formed, and a second main surface S2 facing the first main surface S1. The first main surface S1 contacts the roller portion 41 at the nip portion 13c. The second main surface S2 contacts the roller portion 51 at the nip portion 13c. The sheet S is conveyed while being heated and pressurized between the roller unit 41 and the roller unit 51. As a result, the toner on the paper S is melted and the toner image is fixed on the paper S.

  The fixing unit 13 further includes an application unit 6 and a current detection unit 7. The application unit 6 applies a voltage to the paper S. The application unit 6 of this embodiment includes a contact application unit 60. The contact application unit 60 contacts the second main surface S <b> 2 of the paper S and applies a voltage to the paper S. The contact application unit 60 includes a first contact application unit 61 and a second contact application unit 62.

  The first contact application unit 61 is located on the upstream side of the fixing member 13 a in the paper transport path of the paper S. For example, the first contact application unit 61 extends from the casing 13b and is inclined along the transport direction of the paper S. The first contact application unit 61 comes into contact with the second main surface S2 of the sheet S conveyed along the sheet conveyance path. The first contact application unit 61 functions as a part of a guide unit that guides the sheet S to the fixing member 13a. Further, the first contact application unit 61 has conductivity. The first contact application unit 61 is formed including a metal-based material. It is desirable that the first contact application unit 61 be disposed close to the upstream side of the fixing member 13a within a range that does not hinder the operation of the fixing member 13a.

  The second contact application unit 62 is located on the downstream side of the fixing member 13 a in the paper transport path of the paper S. The second contact application unit 62 includes, for example, an elastic member such as a brush. The second contact application unit 62 extends from the casing 13b and protrudes into the paper transport path. The second contact application unit 62 is in contact with the second main surface S2 of the paper S that is transported through the paper transport path. The second contact application unit 62 functions as a part of a guide unit that guides the paper S along the paper transport path. The second contact application unit 62 has conductivity. The second contact application unit 62 is formed including a metal-based material. It is desirable that the second contact application unit 62 be arranged close to the downstream side of the fixing member 13a as long as the operation of the fixing member 13a is not hindered.

  An interval along the paper conveyance path between the first contact application unit 61 and the second contact application unit 62 is smaller than the length of the smallest size paper S in the conveyance direction. Accordingly, the sheet S that contacts the fixing member 13 a contacts at least the first contact application unit 61 or the second contact application unit 62.

  The current detection unit 7 detects the value of the current flowing through the fixing member 13 a and outputs it to the control unit 9. The current detection unit 7 of the present embodiment detects the current flowing through the roller unit 41 of the heating member 4.

  The fixing unit 13 further includes a sheet separating member 13d. The sheet separating member 13 d has a leading end portion that faces the roller portion 41. The leading end of the sheet separating member 13d is disposed in the vicinity of the roller portion 41 on the downstream side of the nip portion 13c. Therefore, when the paper S is not separated from the roller unit 41, the leading end of the paper separating member 13d enters between the roller unit 41 and the paper S as the roller unit 41 rotates. As a result, even when the paper S is not separated from the roller portion, the paper S is separated from the roller portion 41 by the paper separating member 13d.

  FIG. 3 is a cross-sectional view showing the roller portion 41 of the heating member 4. As shown in FIG. 3, the roller portion 41 of the heating member 4 includes a first layer 45, a second layer 46, and a third layer 47.

  The third layer 47 is formed in a cylindrical shape. Inside the third layer 47, the heat source 43 described with reference to FIG. Therefore, the third layer 47 is heated by the heat source 43 and radiates heat to the surroundings. The third layer 47 has conductivity. The third layer 47 is formed of a metal material such as aluminum, for example. The third layer 47 is located immediately below the second layer 46.

  The second layer 46 is disposed on the surface of the third layer 47. The second layer 46 is formed in a cylindrical shape. The second layer 46 has elasticity. The second layer 46 forms the nip portion 13 c by the roller portion 41 being pressed by the roller portion 51 of the pressure member 5 and elastically deforming. The nip portion 13 c fixes the toner image on the paper S by heating and pressurizing the paper S passing therethrough. The second layer 46 has an insulating property. The second layer 46 is formed of a resin material such as silicon rubber or urethane rubber, for example. The second layer 46 is located immediately below the first layer 45.

  The first layer 45 is disposed on the surface of the second layer 46. The first layer 45 has releasability. The first layer 45 contacts the paper S that passes through the nip portion 13c. The first layer 45 is formed in a cylindrical shape. The first layer 45 is highly releasable and insulating. The first layer 45 is made of, for example, a fluorine resin such as PTFE or PFA. As a result, the heating member 4 can maintain high releasability with respect to the paper S. Note that the first layer 45, the second layer 46, and the third layer 47 are formed using a coating process such as an adhesion method, a dip coating method, or a spray coating method.

  The roller portion 51 of the pressure member 5 has at least a surface layer. The surface layer of the roller unit 51 is configured in the same manner as the first layer 45 of the roller unit 41 of the heating member 4. The surface layer is formed on the most surface side of the roller unit 51. The surface layer has releasability from the paper S. The surface layer can suppress the sheet S from sticking to the roller portion 51. Further, the surface layer has an insulating property. The surface layer is formed of a fluorine-based resin such as PTFE or PFA, for example.

  FIG. 4 is a diagram illustrating an electric circuit of the fixing unit 13. The electrical circuit of FIG. 4 is schematically shown. As shown in FIG. 4, the application unit 6 further includes a power source E. The first contact application unit 61 and the second contact application unit 62 are connected to the power source E. The power source E is a variable power source which is controlled by the control unit 9 and whose voltage value can be adjusted.

  The roller unit 41 of the heating member 4 is connected to the first contact application unit 61 and the second contact application unit 62 via the paper S. Specifically, after the sheet S comes into contact with the first contact application unit 61, the roller unit 41 is connected to the first contact application unit 61 through the sheet S by contacting the fixing member 13 a. Further, the sheet S that contacts the fixing member 13 a contacts the first contact application unit 61 and the second contact application unit 62, so that the roller unit 41 passes the first contact application unit 61 and the first contact application unit 61 via the sheet S. A two-contact application unit 62 is connected. Further, the sheet S that contacts the fixing member 13 a is separated from the first contact application unit 61, whereby the roller unit 41 is connected to the second contact application unit 62 through the sheet S.

  The current detection unit 7 is connected to the third layer 47 of the roller unit 41. The current detection unit 7 detects the value of the current flowing into the third layer 47 described with reference to FIG. A surface current generated in the first layer 45 and the second layer 46 flows into the third layer 47. In the first layer 45 and the second layer 46, when a voltage is applied to the paper S from the contact application unit 60, a surface current that tries to cancel the potential difference from the paper S is generated. The current detection unit 7 outputs the detected current value to the control unit 9.

  FIG. 5 is a block diagram illustrating a configuration of the control unit 9 of the image forming apparatus 1. As shown in FIG. 5, the control unit 9 functions as a fixing control unit 91 by executing a computer program stored in advance. The control part 9 is comprised from CPU (Central Processing Unit), for example.

  The fixing control unit 91 controls the fixing unit 13. The fixing control unit 91 controls the application unit 6 to adjust the value of the voltage applied from the application unit 6 so that the value of the current detected by the current detection unit 7 is constant. Specifically, the fixing control unit 91 controls the power supply E to adjust the value of the voltage applied from the first contact application unit 61 and the second contact application unit 62. Note that the fixing control unit 91 of the present embodiment can adjust the amount of heat radiated from the heat source 43 by controlling the power source connected to the heat source 43 of the heating member 4.

  As described with reference to FIGS. 1 to 5, in the image forming apparatus 1 according to the present embodiment, the sheet S conveyed to the fixing unit 13 is at least a first contact applying unit when contacting the fixing member 13 a. 61 or the second contact application unit 62. Therefore, a voltage can be applied from the application section 6 to the paper S that contacts the fixing member 13a. The voltage applied to the sheet S is adjusted so that the value of the current flowing through the heating member 4 is constant. As a result, in the image forming apparatus 1 of the present embodiment, an appropriate voltage can be applied to the paper S that is in contact with the fixing member 13a, and electrostatic offset that occurs in the fixing unit 13 can be prevented.

  The image forming apparatus 1 according to the embodiment of the present invention has been described above with reference to FIGS. However, the present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof.

  For example, in the embodiment of the present invention, the application unit 6 includes the contact application unit 60, but the present invention is not limited to this. FIG. 6 is a diagram showing an electric circuit of the fixing unit 13 of the image forming apparatus 1 according to another embodiment of the present invention. The electrical circuit of FIG. 6 is schematically shown. As shown in FIG. 6, the application unit 6 may have a non-contact application unit 65.

  As for the roller part 51 of the pressurization member 5 of the aspect shown in FIG. 6, a surface layer has electroconductivity. The surface layer having conductivity is formed, for example, by adding a filler to a fluororesin. The filler is, for example, a carbon-based filler such as carbon. The carbon-based filler has conductivity. In addition, the electroconductivity of the surface layer of the roller part 51 is proportional to the quantity of the filler added to fluororesin, for example.

  For example, the non-contact application unit 65 is supported by the casing 13 b and contacts the roller unit 51 of the pressing member 5. The non-contact application unit 65 is an elastic member such as a brush, for example. The non-contact application unit 65 has conductivity. The non-contact application unit 65 is formed including a metal material. The non-contact application unit 65 is connected to the power source E. The non-contact application unit 65 applies a voltage to the pressure member 5. As a result, the non-contact application unit 65 can apply a voltage to the paper S that contacts the roller unit 51 via the roller unit 51 of the pressure member 5. The fixing control unit 91 controls the power source E and adjusts the value of the voltage applied from the non-contact application unit 65 so that the value of the current detected by the current detection unit 7 is constant.

  In the image forming apparatus 1 of the embodiment shown in FIG. 6, a voltage is applied to the paper S that is in contact with the pressure member 5 through the pressure member 5 by the non-contact application unit 65. Further, the voltage applied from the non-contact application unit 65 is adjusted by the fixing control unit 91 so that the value of the current flowing through the heating member 4 is constant. As a result, an appropriate voltage can be applied to the sheet S in contact with the fixing member 13a, and an electrostatic offset generated in the fixing unit 13 can be prevented.

  Further, for example, in the embodiment of the present invention, the heating member 4 is a heating roller, but the present invention is not limited to this. The heating member 4 may be in the form of a heating belt 48.

  The heating belt 48 includes, for example, a belt portion 48a, a pressing pad 48b, and a heat source 48c. For example, the belt portion 48a is rotatably supported by the casing 13b. The pressing pad 48b presses the inner peripheral surface of the belt portion 48a. For example, the heat source 48c is disposed inside the belt portion 48a and heats the belt portion 48a from the inside. The heat source 48c may be arranged outside the belt portion 48a to heat the belt portion 48a from the outside.

  The roller portion 51 of the pressing member 5 is pressed against the pressing pad 48b via the belt portion 48a. As a result, the roller portion 51 and the pressing pad 48b form a nip portion 13c via the belt portion 48a. The shaft portion 52 of the pressure member 5 is transmitted from a drive source such as a motor and is driven to rotate together with the roller portion 51. The belt portion 48 a is rotated following the roller portion 51.

  The belt portion 48a has a first layer, a second layer, and a third layer. The first layer and the second layer of the belt portion 48a are respectively formed to have the same physical properties as the first layer 45 and the second layer 46 of the roller portion 41 of the heating member 4 described with reference to FIG. . The third layer of the belt portion 48a is different from the roller portion 41 of the embodiment in that it is formed by adding a metal material such as nickel to a resin material. As a result, the releasability with respect to the paper S can be maintained high, and electrostatic offset can be prevented.

  In order to facilitate understanding, the drawings schematically show each component mainly, and the thickness, length, etc. of each component shown in the drawings are different from the actual for convenience of drawing. . In addition, the material, shape, dimensions, and the like of each component shown in the above embodiment are merely examples, and are not particularly limited, and various changes can be made without departing from the effects of the present invention. is there.

  The present invention relates to an image forming apparatus, and is useful for an image forming apparatus including a fixing unit that fixes an image on a recording medium by heating and pressurizing the recording medium.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Application part 7 Current detection part 12 Image formation part 13 Fixing part 13a Fixing member 91 Fixing control part S Paper

Claims (7)

An image forming unit for forming an image on a recording medium;
A fixing unit for fixing the image on the recording medium;
A fixing control unit for controlling the fixing unit,
The fixing unit is
A fixing member that heats and pressurizes an image formed on the recording medium together with the recording medium;
An application unit for applying a voltage to the recording medium;
A current detection unit that detects and outputs a value of a current flowing through the fixing member;
The image forming apparatus, wherein the fixing control unit controls the application unit to adjust the voltage value so that the current value becomes constant. The recording medium is
A first main surface on which an unfixed image is formed;
A second main surface facing the first main surface,
The image forming apparatus according to claim 1, wherein the application unit includes a contact application unit that contacts the second main surface of the recording medium and applies the voltage to the recording medium. In the conveyance path of the recording medium, the contact application unit
A first contact application unit that is located upstream of the fixing member and contacts the recording medium;
The image forming apparatus according to claim 2, further comprising: a second contact application unit that is located downstream of the fixing member and contacts the recording medium. The fixing member has a pressure member,
The image forming apparatus according to claim 1, wherein the application unit includes a non-contact application unit that applies a voltage to the pressure member and applies a voltage to the recording medium via the pressure member. The fixing member has a heating member,
The image forming apparatus according to claim 1, wherein the current detection unit detects a value of a current flowing through the heating member.   The image forming apparatus according to claim 1, wherein the fixing member includes a heating roller and a fixing roller.   The image forming apparatus according to claim 1, wherein the fixing member includes a heating belt and a fixing roller.

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