JP6601327B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes unfixed toner on a sheet, and an image forming apparatus such as a copying machine, a printer, and a facsimile including the fixing device.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as a printer or a copying machine includes a heating roller type or film heating type fixing device that fixes a toner image on a sheet. The heating roller type fixing device has a simple configuration and can realize high speed, and the film heating type fixing device can realize energy saving. The heating member and the pressure member provided in the fixing device have a surface material made of fluororesin or the like, thereby ensuring the releasability of the paper with respect to the heating member and the pressure member. Since the fluororesin is insulative and has a property that it is difficult to attenuate once charged, an electrostatic offset may occur when applied to a heating member or a pressure member. Therefore, when this insulating fluororesin is applied to a heating member or a pressure member, the heating member and the pressure member are grounded by grounding the heating member or the pressure member via a functional member such as a Zener diode. Some of them stabilize the potential difference. For example, when an image is formed with positively charged toner on a sheet, a Zener diode is provided by connecting a cathode to the heating member side and an anode to the ground side in order to suppress negative charging of the heating member.

  For example, in the fixing device disclosed in Patent Document 1, a resistor and a constant voltage diode are connected in series between a fixing roller (heating member) and a ground, and between the pressure roller (pressing member) and the ground. Also, a resistor and a constant voltage diode are connected in series. When the toner carried on the paper is charged with a negative charge, the constant voltage diode connected to the fixing roller is provided with the anode connected to the fixing roller side and connected to the pressure roller. The voltage diode is provided with the cathode connected to the pressure roller side.

Japanese Patent Laid-Open No. 2001-100578

  As described above, since the insulating layer constituting the surface material of the heating member has a property that the charged electric charge is accumulated without losing, the cored bar and the insulating layer of the heating member may behave like a capacitor. . When positively charged toner is used, the transfer roller that transfers the toner image to the paper applies a negative charge to the paper, so that the negative charge is charged from the negatively charged paper to the insulating layer of the heating member. In particular, when the paper is water-containing paper, the resistance of the paper is low, so the negative charge applied to the heating member is large. Since the negative charge is no longer applied to the paper after the trailing edge of the paper passes through the transfer roller, the electrostatic adsorption force between the toner and the paper is reduced. At this time, when the negative charge charged in the insulating layer of the heating member is discharged, the positively charged toner may adhere to the surface of the heating member and generate an electrostatic offset.

  A configuration in which a functional member such as a Zener diode is connected to a cored bar of the heating member is known in order to suppress a charge amount accumulated in the heating member and prevent electrostatic offset. However, in this configuration, when the functional member is in a floating state due to breakage or the like, charge accumulation (storage) in the heating member (insulating layer) does not stop, and eventually the discharge to the peripheral components of the heating member Will occur. When this discharge occurs in an electrical component such as a temperature sensor provided in the fixing device, there is a risk of causing malfunction or damage of the fixing device or the electrical component. Furthermore, if this electrical component is connected to the control board of the image forming apparatus main body, the above-described discharge may affect the control board via the electrical component, possibly causing damage to the image forming apparatus main body itself.

  It is an object of the present invention to prevent the influence of discharge generated by a heating member on peripheral components.

  The fixing device according to the present invention includes a heating member having a cored bar and an insulating layer provided around the cored bar, and a pressure member that presses the heating member and forms a fixing nip between the heating member and the heating member. The heating is applied from the ground when the potential difference between the core metal and the surface of the insulating layer in the heating member during paper passing does not reach a predetermined threshold voltage while being connected between the core metal and the ground. A functional member that cuts off current to the member; and a surplus charge accumulated in the insulating layer when the insulating layer accumulates more than a predetermined discharge voltage provided between the core metal and the functional member. And a discharged member to be discharged.

  According to such a configuration, the discharged member has a surplus charge accumulated in the insulating layer even when the functional member is in a floating state due to damage or the like, and the insulating layer attempts to store the electric discharge more than a predetermined discharge voltage. Can be preferentially discharged at the installation position of the member to be discharged. Therefore, it is possible to suppress excessive power storage in the insulating layer and prevent the influence of the discharge generated by the heating member on the peripheral components. Therefore, even if the peripheral component of the heating member is connected to the control board of the image forming apparatus main body provided with the fixing device, the discharge does not affect the control board via the peripheral component, and the image forming apparatus main body It can prevent its own damage.

  The functional member is formed of a Zener diode, the anode of the Zener diode is connected to the core metal side, the cathode of the Zener diode is connected to the ground side, and the discharged member includes the core metal It is preferable to provide a predetermined distance away from the connection circuit with the Zener diode.

  By adopting such a configuration, it is possible to configure a discharged member suitable for a functional member formed of a Zener diode.

  A housing for accommodating the heating member and the pressure member may be further provided, and the discharged member may be configured using a part of the housing that is made of a conductive material and connected to the ground.

  By adopting such a configuration, the member to be discharged can be realized with a simple configuration.

  The member to be discharged may be formed in a sharp shape protruding toward the connection circuit.

  By adopting such a configuration, even when the connection circuit cannot be provided in the vicinity of the metal frame of the image forming apparatus main body including the fixing device or the housing of the fixing device, the sharply-shaped discharged member is used. , Can induce discharge.

  The image forming apparatus of the present invention includes any one of the fixing devices described above.

  According to the present invention, it is possible to prevent the discharge generated by the heating member from affecting the peripheral components.

1 is a cross-sectional view illustrating a printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. In the fixing device according to an embodiment of the present invention, it is a schematic diagram showing the relationship between the potential stored in the insulating layer of the heating member and the effect of this potential on the surroundings. It is sectional drawing which shows the fixing device which concerns on other embodiment of this invention.

  First, the overall configuration of a printer 1 (image forming apparatus) according to an embodiment of the present invention will be described with reference to FIG. Hereinafter, for convenience of explanation, the front side of the sheet in FIG.

  The printer 1 includes a box-shaped printer main body 2. A paper feed cassette 3 for storing paper is accommodated in the lower part of the printer main body 2, and a paper discharge tray 4 is provided on the upper surface of the printer main body 2.

  An exposure unit 5 composed of a laser scanning unit or the like is provided above the printer body 2, and an image forming unit 6 is provided below the exposure unit 5. The image forming unit 6 is rotatably provided with a photosensitive drum 10 that is an image carrier. Around the photosensitive drum 10, a charger 11, a developing device 12, a transfer roller 13, and a cleaning device 14 are provided. Are arranged along the rotation direction of the photosensitive drum 10 (see arrow X in FIG. 1).

  A paper transport path 15 is provided inside the printer body 2. A paper feed unit 16 is provided at the upstream end of the transport path 15. A transfer unit 17 including the photosensitive drum 10 and the transfer roller 13 is provided in the middle portion of the conveyance path 15. A fixing device 18 is provided downstream of the conveyance path 15. Note that the transfer unit 17 is configured to apply a negative bias from the print back side of the sheet by the transfer roller 13 to electrically transfer the positively charged toner onto the sheet when passing through the sheet.

  Next, an image forming operation of the printer 1 having such a configuration will be described. In the printer 1, image data is input from another computer or the like, and an instruction to start printing is given. Then, the charger 11 charges the surface of the photosensitive drum 10, and the exposure device 5 exposes the photosensitive drum 10 based on the image data, so that an electrostatic latent image is formed on the surface of the photosensitive drum 10. Next, the developing device 12 develops the electrostatic latent image into a toner image with toner.

  On the other hand, the paper in the paper feed cassette 3 is taken out by the paper feed unit 16 and is transported through the transport path 15. The sheet is conveyed to the transfer unit 17 in synchronization with the position of the toner image on the photosensitive drum 10, and the toner image is transferred to the sheet by the transfer unit 17. Next, the sheet on which the toner image has been transferred is conveyed to the fixing device 18, and the toner image is fixed on the sheet by the fixing device 18. The paper on which the toner image is fixed is discharged to the paper discharge tray 4. The toner remaining on the photosensitive drum 10 is collected by the cleaning device 14.

  Next, the fixing device 18 will be described with reference to FIG. As shown in FIG. 2, the fixing device 18 includes a housing 20, a heating member 21, a pressing member 22, a heat source 23, a functional member 24, a discharged member 25, and a temperature sensor 26.

  The housing 20 is made of a conductive material such as metal and has a substantially box shape that is long in the front-rear direction. The housing 20 has a paper feed opening 20a that is opened at the approximate center of the right surface in the vertical direction, and a paper discharge port 20b that is opened at the approximate center of the left face in the vertical direction. The transport path 15 passes through the housing 20 through the paper feed port 20a and the paper discharge port 20b, and the paper introduced into the housing 20 through the paper feed port 20a along the transport path 15 is discharged. It is discharged from the housing 20 through the paper mouth 20b. In the housing 20, the heating member 21 and the pressure member 22 are respectively arranged on the upper side and the lower side across the conveyance path 15, and a fixing nip N is formed between the heating member 21 and the pressure member 22. The

  The heating member 21 is a heating roller that is formed in a cylindrical shape that is long in the front-rear direction and is rotatably supported in the housing 20. The rotation axis direction of the heating member 21 is the front-rear direction. The heating member 21 slides and rotates as the pressure member 22 rotates.

  The heating member 21 includes, for example, a cylindrical cored bar 21a and an insulating layer 21b provided around the cored bar 21a. The cored bar 21a is formed of a metal such as aluminum or iron. The cored bar 21 a is connected to the ground G (ground) via the functional member 24. The insulating layer 21b is formed of a fluororesin such as PFA having an insulating property. The surface of the insulating layer 21b accumulates negative charge due to contact with the paper on which negative charge is accumulated, and the insulating layer 21b has a core metal 21a side that is positive with respect to the surface of the insulating layer 21b. Thereby, the heating member 21 behaves like a capacitor that accumulates charges by having a potential difference between the cored bar 21a and the surface of the insulating layer 21b. The insulating layer 21b may be made of only a fluororesin, but it is made of an insulating silicon rubber or the like and is formed around the core metal 21a and an insulating PFA or the like. The release layer may be composed of a fluororesin and cover the elastic layer.

  The pressure member 22 is a pressure roller that is formed in a cylindrical shape that is long in the front-rear direction and is rotatably supported in the housing 20. The rotation axis direction of the pressure member 22 is the front-rear direction. The pressure member 22 is pressed against the outer peripheral surface of the heating member 21, whereby a fixing nip N is formed between the heating member 21 and the pressure member 22. A driving gear (not shown) is attached to the rear end portion of the pressing member 22. The pressure member 22 is connected to a drive source (not shown) such as a motor via a drive gear, and is rotationally driven by this drive source.

  The pressure member 22 includes, for example, a cylindrical cored bar 22a, an elastic layer 22b provided around the cored bar 22a, and a release layer 22c that covers the elastic layer 22b. The metal core 22 a of the pressure member 22 is formed of, for example, a metal such as SUS or aluminum, and the metal core 22 a serves as the rotation shaft of the pressure member 22. The elastic layer 22b of the pressure member 22 is made of, for example, silicon rubber, and the release layer 22c of the pressure member 22 is made of, for example, a fluororesin such as PFA.

  The heat source 23 is composed of, for example, a halogen heater or a ceramic heater, and is provided in the internal space of the heating member 21. The heat source 23 is configured to generate heat by power supplied from a power source (not shown) and to heat the heating member 21.

  The functional member 24 is connected between the cored bar 21 a of the heating member 21 and the ground G. The functional member 24 basically allows a current from the heating member 21 to the ground G. In addition, the functional member 24 blocks the current from the ground G to the heating member 21 when the potential difference between the cored bar 21a of the heating member 21 and the surface of the insulating layer 21b is less than a predetermined threshold voltage. On the other hand, the functional member 24 allows a current from the ground G to the heating member 21 when the potential difference between the cored bar 21a of the heating member 21 and the surface of the insulating layer 21b during the sheet passing is equal to or higher than a predetermined threshold voltage.

  By the way, the insulating layer 21b of the heating member 21 has a property that the charged electric charge is accumulated without being lost. When using positively charged toner, the transfer roller 13 applies a negative charge to the paper in order to attract the toner image to the paper. When the sheet onto which the toner image has been transferred is conveyed from the transfer roller 13 (transfer unit 17) to the fixing device 18 along the conveyance path 15, the leading edge of the sheet has a positive charge on the toner side and a negative charge on the sheet side. Enters between the heating member 21 and the pressurizing member 22 in a state of being balanced. When the trailing edge of the sheet passes through the transfer roller 13 (transfer unit 17), the negative charge is no longer applied to the sheet, and the specific gravity is biased to the positive charge on the toner side. At this time, in the insulating layer 21b on the surface of the heating member 21 facing the toner image, negative charges are accumulated by being charged with the positive charges on the toner side on the paper. Here, since the functional member 24 interrupts the current from the ground G to the heating member 21, the amount of charge accumulated in the insulating layer 21b of the heating member 21 is suppressed to a predetermined threshold voltage.

  The predetermined threshold voltage of the functional member 24 is, for example, 1 KV or less, preferably 1 KV as the upper limit value of the surface potential of the heating member 21 that enables proper fixing processing of the toner image by the heating member 21 and the pressure member 22. (See FIG. 3). The functional member 24 is formed of, for example, a Zener diode having a predetermined threshold voltage as a Zener voltage, and the anode is connected to the cored bar 21a side and the cathode is connected to the ground G side.

  The discharged member 25 is provided between the cored bar 21 a of the heating member 21 and the functional member 24, and is connected to the ground G. For example, the member to be discharged 25 is constituted by a part of the metal frame of the printer main body 2 connected to the ground G or a part of the housing 20 electrically connected to the metal frame. The discharged member 25 is provided, for example, at a predetermined distance (for example, about 1 to 2 mm) from the connection circuit 27 between the cored bar 21a and the functional member 24 as a Zener diode. The connection circuit 27 is made of a coated wire having a diameter of 1 mm or less, includes an uncoated portion 27a in part, and the discharged member 25 is disposed corresponding to the uncoated portion 27a. FIG. 2 shows an example in which the edge of the paper discharge outlet 20b of the housing 20 is used as the member to be discharged 25, but the configuration of the member to be discharged 25 is not limited to this, and is close to the uncovered portion 27a of the connection circuit 27. If so, any part of the metal frame of the printer main body 2 or the housing 20 may be used.

  By the way, as described above, the functional member 24 suppresses the amount of charge accumulated in the insulating layer 21b of the heating member 21 to a predetermined threshold voltage, but the functional member 24 is in a float state due to damage or the like. In addition, charge accumulation (storage) in the insulating layer 21b of the heating member 21 does not stop. When the charge amount in the insulating layer 21b of the heating member 21 becomes equal to or higher than a predetermined discharge voltage (for example, 10 KV) that can be stored in the cored bar 21a and the insulating layer 21b (pseudo capacitor) of the heating member 21, the excess charge A discharge is generated (see FIG. 3). The discharged member 25 preferentially discharges surplus charges accumulated in the insulating layer 21b at the installation position of the discharged member 25 when the insulating layer 21b stores the electric charge higher than a predetermined discharge voltage. For example, the member 25 to be discharged is configured to discharge in the range of 1 KV to 10 KV, preferably about 5 KV.

  The temperature sensor 26 is provided in the vicinity of the heating member 21 inside the housing 20, for example, at a position spaced about 1 mm from the surface of the heating member 21. The temperature sensor 26 is composed of, for example, a thermistor and detects the surface temperature of the heating member 21.

  According to the present embodiment, as described above, the fixing device 18 of the printer 1 (image forming apparatus) includes the heating member 21 including the cored bar 21a and the insulating layer 21b provided around the cored bar 21a, and the heating member. A pressure member 22 that presses against the heating member 21 and forms a fixing nip N between the heating member 21 and a cored bar 21a in the heating member 21 that is connected between the cored bar 21a and the ground G. And a functional member 24 that cuts off the current from the ground G to the heating member 21 when the potential difference between the surface of the insulating layer 21b does not reach a predetermined threshold voltage, and is provided between the cored bar 21a and the functional member 24, And a member to be discharged 25 that discharges surplus charges accumulated in the insulating layer 21b when the insulating layer 21b stores a voltage higher than a predetermined discharge voltage.

  As a result, the discharged member 25 has a surplus charge accumulated in the insulating layer 21b even when the functional member 24 is in a floating state due to breakage or the like, and the insulating layer 21b attempts to store more than a predetermined discharge voltage. The discharge can be preferentially discharged at the installation position of the member 25 to be discharged. Therefore, it is possible to suppress excessive power storage in the insulating layer 21b and to prevent the discharge generated in the heating member 21 from affecting peripheral components. Therefore, even if the peripheral components are connected to the control board of the printer 1 main body, the discharge does not affect the control board via the peripheral components, and the printer 1 main body itself can be prevented from being damaged.

  Further, according to the present embodiment, the functional member 24 is constituted by a Zener diode, and the anode of the Zener diode is connected to the cored bar 21a side, and the cathode of the Zener diode is connected to the ground G side. The discharged member 25 is provided at a predetermined distance from the connection circuit 27 between the cored bar 21a and the Zener diode.

  Thereby, the to-be-discharged member 25 suitable for the functional member 24 comprised with a Zener diode can be comprised.

  In addition, according to the present embodiment, the fixing device 18 further includes the housing 20 that houses the heating member 21 and the pressure member 22. The member to be discharged 25 is configured using a part of the housing 20 that is made of a conductive material and connected to the ground.

  Thereby, the to-be-discharged member 25 is realizable with a simple structure.

  In the present embodiment, an example in which the member to be discharged 25 is configured by a part of the metal frame of the printer main body 2 connected to the ground G or a part of the housing 20 electrically connected to the metal frame will be described. However, the configuration of the discharged member 25 is not limited to this example. For example, in another different embodiment, as shown in FIG. 4, the discharged member 25 may be formed of a conductive material and may have a sharp shape protruding toward the uncovered portion 27 a of the connection circuit 27. Good. In addition, the member 25 to be discharged is not limited to such a sharp shape, but may be any other shape as long as the discharge can be preferentially induced.

  Thereby, even when the connection circuit 27 cannot be provided in the vicinity of the metal frame or the housing 20 of the printer main body 2, the discharge can be induced by the sharply-shaped discharged member 25.

  In this embodiment, the case where the heating member 21 as a heating roller is used has been described. However, in another different embodiment, a fixing belt may be used as the heating member 21. Although the case where the pressure member 22 as the pressure roller is used has been described in the present embodiment, a pressure belt may be used as the pressure member 22 in other different embodiments.

  In the present embodiment, the configuration in which the heat source 23 such as a halogen heater or a ceramic heater is provided in the internal space of the heating member 21 has been described. However, in another different embodiment, the heat source 23 composed of an IH coil is provided outside the heating member 21. May be configured.

  In this embodiment, the case where the configuration of the present invention is applied to the printer 1 has been described. However, in another different embodiment, the configuration of the present invention is applied to other image forming apparatuses such as a copying machine, a facsimile machine, and a multifunction machine. It is also possible.

1 Printer (image forming device)
6 Image forming unit 10 Photosensitive drum 13 Transfer roller 15 Transport path 18 Fixing device 20 Housing 21 Heating member 21a Core metal 21b Insulating layer 22 Pressure member 23 Heat source 24 Functional member 25 To-be-discharged member 26 Temperature sensor 27 Connection circuit 27a Uncoated portion

Claims (3)

A heating member having a cored bar and an insulating layer provided around the cored bar;
A pressure member that presses against the heating member to form a fixing nip with the heating member;
The heating member is connected between the cored bar and the ground, and when the potential difference between the cored bar and the surface of the insulating layer in the heating member during paper passing does not reach a predetermined threshold voltage A functional member that cuts off the current to
A member to be discharged provided between the cored bar and the functional member, and discharging the surplus charge accumulated in the insulating layer when the insulating layer accumulates more than a predetermined discharge voltage ; and
The functional member is composed of a Zener diode, the anode of the Zener diode is connected to the core metal side, and the cathode of the Zener diode is connected to the ground side,
The discharged member is provided a predetermined distance away from a connection circuit between the cored bar and the Zener diode,
A housing for accommodating the heating member and the pressure member;
The fixing member, wherein the member to be discharged is made of a part of the housing made of a conductive material and connected to a ground . A heating member having a cored bar and an insulating layer provided around the cored bar;
A pressure member that presses against the heating member to form a fixing nip with the heating member;
The heating member is connected between the cored bar and the ground, and when the potential difference between the cored bar and the surface of the insulating layer in the heating member during paper passing does not reach a predetermined threshold voltage A functional member that cuts off the current to
A member to be discharged provided between the cored bar and the functional member, and discharging the surplus charge accumulated in the insulating layer when the insulating layer accumulates more than a predetermined discharge voltage; and
The functional member is composed of a Zener diode, the anode of the Zener diode is connected to the core metal side, and the cathode of the Zener diode is connected to the ground side,
The discharged member is provided a predetermined distance away from a connection circuit between the cored bar and the Zener diode,
The fixing device, wherein the member to be discharged is formed in a sharp shape protruding toward the connection circuit. An image forming apparatus comprising the fixing device according to claim 1 .

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