JP6173509B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a lightning arrester for discharging a surge voltage to an electrical ground in an image forming apparatus having a fixing means for fixing a toner image.

  In recent years, a film heating type fixing unit has been proposed as a fixing unit mounted in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer.

  The fixing unit includes a cylindrical film, a heater that contacts the inner surface of the film, and a pressure roller that forms a nip portion together with the heater via the film. In the heater, a heating resistor that generates heat when power is supplied to the substrate and a glass protective layer that protects the heating resistor are formed. The recording material is heated while being conveyed at the nip portion, and the toner image is fixed on the recording material.

  However, when the film heating type fixing means is grounded from the heater to the frame ground (hereinafter referred to as FG) of the apparatus via the film and the pressure roller, there are the following problems.

  When a surge voltage due to lightning or the like is applied between the power supply line connected to the heater of the fixing unit and the FG, a high potential surge voltage is applied to the heater, and the protective layer of the heater may break down. is there.

  In order to solve the above problem, a configuration in which a resistor is connected between the pressure roller and the FG has been proposed. As a result, when a surge voltage is applied between the power supply line and the FG, the voltage applied to the protective layer of the heater can be divided and lowered, so that dielectric breakdown is suppressed. (Patent Document 1)

JP-A-6-051659

  However, in the configuration as in Patent Document 1, the creepage / space distance from the film to the FG such as the metal frame, or the creepage / space distance from the pressure roller to the FG such as the metal frame, even if a surge voltage is applied. It must be large enough not to discharge.

  In other words, the creepage / surface distance between the film and the metal frame is increased so that the impedance of the route leading to the FG by discharging over the spatial distance is larger than the impedance of the route leading to the FG from the pressure roller through the resistance. It is necessary to set the spatial distance.

  The reason for this is that if a discharge is generated between the film and the metal frame, the voltage dividing effect due to the resistance provided between the pressure roller and the FG cannot be obtained, and a high potential surge voltage is applied to the protective layer of the heater, resulting in dielectric breakdown. Because there is a case to do.

  Therefore, the configuration of Patent Document 1 has a problem that the size of the apparatus is increased in order to avoid the dielectric breakdown of the protective layer.

A first preferred embodiment of the present invention for solving the above-described problem includes an image forming unit that forms a toner image on a recording material, and a heater that generates heat when power is supplied from a power source. In an image forming apparatus, comprising: a fixing unit that fixes the toner image to a recording material by heat from; and a power supply line that connects the heater and the power supply; a first electrode connected to the power supply line; A second electrode connected to an electrical ground and not electrically connected to the first electrode; a holding member holding the first electrode and the second electrode and having an opening; wherein the one of the first electrode and the second electrode has a sharpened tip, other has a surface which faces apart the sharpened tip a predetermined distance, the sharpened tip is the it is provided to float in space by the opening It is an feature.
A second preferred embodiment of the present invention for solving the above problems includes an image forming unit for forming a toner image on a recording material, and a heater that generates heat when power is supplied from a power source. In an image forming apparatus, comprising: a fixing unit that fixes the toner image to a recording material by heat from; and a power supply line that connects the heater and the power supply; a first electrode connected to the power supply line; A second electrode connected to an electrical ground and not electrically connected to the first electrode; a holding member holding the first electrode and the second electrode and having an opening; With
Either one of the first electrode and the second electrode has a sharpened portion, and the other has a surface portion facing the sharpened portion at a predetermined interval, and is viewed from the opening direction of the opening. In this case, the sharpened portion overlaps with the opening.

  According to the present invention, it is possible to reduce the size of the apparatus and suppress the dielectric breakdown of the protective layer of the heater.

(A) The figure which shows the outline | summary of the lightning arrester of Example 1, (B) The figure which showed the flow of the electric current of the power supply line of the fixing means in the normal time of Example 1, (C) At the time of the surge voltage application of Example 1 A diagram showing the current flow in the power line of the fixing means The figure which shows the outline | summary of the lightning arrester of Example 2. The figure which shows the outline | summary of the lightning arrester of Example 3. Sectional drawing which shows the schematic whole structure of the image forming apparatus provided with the fixing means based on an Example. Sectional drawing which shows schematic structure of the fixing means which concerns on an Example. FIG. 3 is a diagram illustrating an electric circuit configuration from a power source to a fixing unit according to the first embodiment.

Example 1
Hereinafter, an embodiment of an image forming apparatus according to the present invention applied to an electrophotographic laser beam printer will be described with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

  FIG. 4 shows the overall configuration of the image forming apparatus according to the first embodiment. When the recording material S in the feeding cassette 205 is fed by the feeding unit 207, it is sent to the conveying roller pair 208. Next, a latent image is formed on the photosensitive drum 203 by the optical means 202 based on the image information. The recording material S is sent by the registration roller pair 209 in time with the latent image. The toner image on the photosensitive drum 203 is transferred to the recording material S at the transfer nip portion formed by the photosensitive drum 203 and the transfer roller 206, and the toner image is formed on the recording material S. Thereafter, the recording material S is sent to the fixing unit 210, and the toner image on the recording material is fixed to the recording material. The recording material S after the fixing process is discharged onto a discharge tray 215 outside the apparatus by an inner discharge roller pair 213 and an outer discharge roller pair 214.

Next, the fixing unit 210 according to the first embodiment will be described with reference to the cross-sectional view of FIG.
212a is a cylindrical film, and is externally fitted to a stay 231 that is a guide member of the film 212a. The film 212a is composed of a composite layer film in which a release layer composed of a fluororesin such as PTFE, PFA, FEP, etc. is formed on a surface of a base layer film such as polyimide, polyamideimide, PEEK, PES, PPS or the like by coating or a tube. ing.

  In the heater 230, an electric resistance material is applied as a heating resistor on the surface of an insulating substrate made of alumina or the like, and an insulating layer such as glass or fluororesin is coated thereon as a protective layer 232.

  The control means (not shown) controls the temperature of the heater 230 by controlling the power supplied to the heater 230 based on the temperature detected by the thermistor 234 provided on the heater 230.

  211, a rubber layer 211a made of a heat-resistant and conductive silicone sponge or the like is provided on the cored bar 233, and the surface is covered with a release layer made of a PFA tube. A pressure roller, which is driven by a motor (not shown). The pressure roller 211 forms a nip portion that heats the recording material together with the heater 230 through the film 212a. The shaft of the cored bar 233 is electrically grounded to the FG via the high resistance 235.

  Reference numeral 602 denotes a metal frame of the fixing unit 210, which is electrically grounded to the FG, and is disposed with a space between the film 212 a and the pressure roller 211.

  Further, it can be considered that the film 212a, the rubber layer 211a of the pressure roller 211, and the cored bar 233 are electrically connected with low impedance as compared with the protective layer 232 of the heater 230.

  Next, the electrical circuit from the power source to the fixing means in the first embodiment is shown in FIG.

  The lightning arrester 111 has an electrode α1 as a first electrode and an electrode β1 as a second electrode. The electrode α1 is connected to a power supply line from a power source 601 to a heater (heating resistor), and the electrode β1 Is grounded to the FG of the image forming apparatus 201.

  Here, the electrode α1 is attached to only one of the two power supply lines in the first embodiment, but may be attached to each of the two power supply lines. When only one power supply line is attached as in this embodiment, it is effective to use a surge absorbing element such as a varistor between the power supply lines in order to suppress the voltage rise of the other power supply line.

  Next, the structure of the lightning arrester 111 of Example 1 is demonstrated in detail using FIG. 1 (A). In the first embodiment, in the lightning arrester 111, an electrode α1 and an electrode β1 made of a plate-like conductor are mounted and fixed on an electric circuit board 216 as one holding member. The terminals of the electrode α1 and the electrode β1 are electrically connected to each other on the back surface of the electric circuit board 216 by a pattern and solder. At this time, the electrode α1 is disposed on a pattern in which power is supplied from the power source to the heater 230. Further, the electrode β1 is connected to a ground pattern provided on the electric circuit board 216, and finally connected to an electric grounding portion of the image forming apparatus 201 (see FIG. 1B).

  Further, the sharpened portion P1 of the electrode α1 and the surface portion Q1 of the electrode β1 are arranged so as to face each other with a spatial distance (hereinafter referred to as an interelectrode distance X1). During normal fixing processing, current is supplied from the power source 601 to the heater (heating resistor) as shown in FIG. When a high-potential surge voltage is applied to the power supply line, as shown in FIG. 1C, it is discharged beyond the interelectrode distance X1 and flows to the electrical ground. As a result, no surge voltage is applied to the protective layer 232 of the heater 230 downstream of the electrode α1 in the power supply line, so that the dielectric breakdown of the protective layer 232 of the heater 230 shown in FIG. 5 can be avoided.

  Here, the relationship between the interelectrode distance X1 of the lightning arrester 111 and the voltage at which discharge starts will be described. The voltage at which discharge starts between the electrodes of the lightning arrester 111 changes according to the interelectrode distance X1, and the discharge starts when a higher voltage is applied as the distance increases. That is, by managing the interelectrode distance X1, the value of the voltage at which discharge is started can be managed. As a guideline, the discharge voltage increases by 1 kV every time the interelectrode distance X1 increases by 1 mm. Therefore, the accuracy of the interelectrode distance X1, that is, the positional accuracy of the electrode β1 with respect to the electrode α1 is important. Therefore, in the first embodiment, the electrode α1 and the electrode β1 are fixed to the electric circuit board 216 as one holding member, and the positional accuracy of the electrode β1 with respect to the electrode α1 is increased.

  In the test of the international standard (IEC61000-4-5), the surge voltage applied between the power supply line and the FG may be a high voltage of 4 kV or higher. In the first embodiment, a case will be described in which discharge is performed between the electrodes of the lightning arrester 111 when the surge voltage applied between the power supply line and the FG is 4 kV.

  In the configuration of Example 1, the tolerance of the interelectrode distance X1 is ± 1.0 mm. If the design value of the designation of the distance between the electrodes is 3.0 mm, the distance between the electrodes will be in the range of 2.0 to 4.0 mm (the distance between the electrodes is required to be at least 2.0 mm for safety standards). . Therefore, as a guideline, when the applied voltage of the power supply line becomes 2.0 to 4.0 kV or more, discharge occurs between the electrodes of the lightning arrester 111, so that discharge occurs when 4.0 kV is applied.

  However, the impedance of the first route from the power source 601 to the FG by discharging between the electrodes of the lightning arrester 111 (hereinafter referred to as the first impedance) must be the smallest among the plurality of routes from the power source 601 to the FG. . Here, the impedance of the second route from the power source 601 exceeding the creepage / space distance between the film 212a and the metal frame 602 (hereinafter referred to as the second creepage / space distance) and reaching the FG is defined as the second impedance. Further, the impedance of the third route from the power source 601 over the creepage / space distance (third creepage / space distance) between the pressure roller 211 and the metal frame 602 to reach the FG is defined as a third impedance. In order to discharge between the electrodes of the lightning arrester 111 when a surge voltage is applied to the power supply line, the first impedance needs to be smaller than the second impedance and the third impedance. That is, it is necessary to set the second creepage / space distance and the third creepage / space distance so as to satisfy the above-described impedance magnitude relationship. Basically, if the second creepage / space distance and the third creepage / space distance are set to be equal to the interelectrode distance X1, the above-described impedance relationship is satisfied. This is because the second route and the third route are grounded to the FG downstream of the protective layer 232 of the heater 230, so that the impedance increases by passing through the protective layer 232 of the heater 230. Therefore, in the first embodiment, the second creepage / space distance and the third creepage / space distance are set to 4 mm, respectively, so that a discharge occurs between the electrodes of the lightning arrester 111 when the surge voltage is applied, and the protective layer of the heater 230 232 insulation breakdown can be avoided.

  In the configuration of the first embodiment, the second creepage / space distance and the third creepage / space distance can be made shorter than the configuration without the conventional lightning arrester. In the first embodiment, since the electrode α is upstream of the heating resistor in the power supply line from the power source 601, the impedance of the route that reaches between the electrodes of the lightning arrester 111 and reaches the FG can be made smaller than in the conventional case.

  As described above, it can be seen that the first embodiment can reduce the size of the apparatus and suppress the dielectric breakdown of the protective layer 232 of the heater 230.

  However, the ease of discharging is not always determined according to the distance between the electrodes. The electric field distribution also changes depending on the shape of the discharge part of the electrode, and also changes depending on humidity and atmospheric pressure. Therefore, the discharge is not always performed at a short distance. Therefore, the terminal shape of the lightning arrester 111 in the first embodiment is such that the electrode α1 has a sharp portion and the electric field tends to concentrate.

  The lightning arrester 111 according to the first embodiment may be disposed between the power supply line and the heating resistor, and the same effect can be obtained even if it is not necessarily disposed on the electric circuit board 216.

  In the first embodiment, the two electrodes are plate-like conductors, but the same effect as in the first embodiment can be obtained even if a wire or a shaft-like electrode is used. Further, the same effect as in the present embodiment can be obtained by using an electric circuit (pattern) mounted on the electric circuit board 216 as an electrode.

  Regarding the two electrode shapes of Example 1, the electrode α1 has a sharpened portion P1, and the electrode β1 has a surface portion Q1. However, the electrode α1 as the first electrode may have a surface portion, and the electrode β1 as the second electrode may have a sharp portion.

(Example 2)
Next, FIG. 2 shows the configuration of the lightning arrester 121 according to the first embodiment. The difference from the first embodiment is that one holding member that holds the electrode α2 and the electrode β2 is an insulator γ2 that is easier to obtain component accuracy than the electric circuit board 216, and the insulator γ2 is fixed to the electric circuit board 216. It is a part that has been. The terminals of the electrode α2 and the electrode β2 are electrically connected to each other on the back surface of the electric circuit board 216 by a pattern and solder. At this time, the electrode α1 is connected to a pattern in which power is supplied from the power source to the fixing unit 210. In addition, the electrode β1 is connected to a ground pattern provided on the electric circuit board 216, and finally connected to an electric ground portion of the image forming apparatus 201.

  The configuration of the second embodiment has an effect that the inter-electrode distance X2 is not easily affected even when the electric circuit board 216 is made of a cheap material and warpage due to thermal expansion or bending due to insufficient rigidity is likely to occur. . This is because the electrode α1 and the electrode β1 are fixed to the insulator γ2, and the interelectrode distance X2 is determined. Therefore, in the configuration of the second embodiment, the tolerance of the interelectrode distance X2 can be ± 0.5 mm, which is smaller than that of the first embodiment. Therefore, the design value of the designation of the interelectrode distance is 2.5 mm, and the interelectrode distance is within the range of 2.0 to 3.0 mm. When the applied voltage of the power supply line becomes 2.0 to 3.0 kV or more, discharge occurs between the electrodes of the lightning arrester 111. If the creepage / space distance of the metal frame 602 from the pressure roller 211 or the film 212a is 3 mm, the dielectric breakdown of the protective layer 232 of the heater 230 can be avoided. Therefore, the metal frame 602 can be closer to the film 212a and the pressure roller 211 by 1 mm than in the first embodiment, and thus there is an effect that the apparatus can be further downsized.

(Example 3)
The structure of the lightning arrester 131 in Example 3 is demonstrated and shown in FIG. The lightning arrester 131 is configured such that an electrode β3 made of a plate-like conductor is mounted and fixed on the electric circuit board 216, and a part of the electrode α3 made of a plate-like conductor sandwiches an insulator γ3, and the electrode α The electrode β3 is disposed to face the electrode β3. The electrode α3 is also mounted and fixed on the electric circuit board 216.

The terminals of the electrode α3 and the electrode β3 are electrically connected to each other by a pattern and solder on the back surface of the electric circuit board 216. At this time, the electrode α3 is connected to a pattern in which power is supplied from the power source to the fixing unit 210. The electrode β3 is connected to the ground pattern provided on the electric circuit board 216, and finally the surface portion P3 of the electrode α3 and the surface portion of the electrode β3 that are to be connected to the electrical ground portion of the image forming apparatus 201. The inter-electrode distance of Q depends on the dimensional accuracy of the insulator γ1 component. Therefore, by increasing the dimensional accuracy of the insulator γ3, it is possible to reduce the tolerance of the distance between the electrodes, so that there is an effect that it is easy to realize downsizing.

111 Lightning Arrester in Example 1 121 Lightning Arrester in Example 2 131 Lightning Arrester in Example 3 α1, α2, α3 Electrodes Connected to Power Lines β1, β2, β3 Electrodes Connected to Electrical Ground γ2, γ3 Insulator P1 Electrode α sharpened portion or surface portion Q1 Sharpened portion or surface portion of electrode β 201 Image forming apparatus 202 Optical means 203 Photosensitive drum 204 Process cartridge 205 Paper feed cassette 206 Transfer roller 207 Recording material feeding device 208 Conveying roller pair 209 Registration roller Pair 210 Fixing means 211 Pressure roller 211a Rubber layer 212 Fixing member 212a Film 213 Inner discharge roller pair 214 Outer discharge roller pair 215 Discharge tray 216 Electric circuit board 230 Heater 231 Stay 232 Protective layer 233 Core metal 234 Thermistor 235 Heat resistor X1, X2 electrode distance S recording medium

Claims (7)

An image forming unit for forming a toner image on a recording material;
A heater that generates heat when power is supplied from a power source; and a fixing unit that fixes the toner image to a recording material by heat from the heater;
A power line connecting the heater and the power source;
In an image forming apparatus comprising:
A first electrode connected to the power line;
A second electrode connected to an electrical ground and not electrically connected to the first electrode; a holding member holding the first electrode and the second electrode and having an opening; With
One of the first electrode and the second electrode has a sharpened portion, the other has a surface portion facing the sharpened portion with a predetermined interval, and the sharpened portion is formed by the opening. An image forming apparatus, wherein the image forming apparatus is provided so as to float in a space. An image forming unit for forming a toner image on a recording material;
A heater that generates heat when power is supplied from a power source; and a fixing unit that fixes the toner image to a recording material by heat from the heater;
A power line connecting the heater and the power source;
In an image forming apparatus comprising:
A first electrode connected to the power line;
A second electrode connected to an electrical ground and not electrically connected to the first electrode; a holding member holding the first electrode and the second electrode and having an opening; With
Either one of the first electrode and the second electrode has a sharpened portion, and the other has a surface portion facing the sharpened portion at a predetermined interval, and is viewed from the opening direction of the opening. In this case, the sharpened portion overlaps the opening. The holding member, the image forming apparatus according to claim 1 or 2, characterized in that an electric circuit board for driving the heater. The holding member is an insulating material, the image forming apparatus according to claim 1 or 2, characterized in that the insulator is held by the electric circuit board for driving the heater. The holding member is an insulator,
The first electrode is provided on one surface of the holding member, the image forming according the second electrode to claim 1 or 2, characterized in that provided on the other surface of the holding member apparatus. The heater has a substrate, a heating resistor formed on the substrate, and a protective layer provided so as to cover the heating resistor, and the protective layer is in contact with the film,
The impedance of the path from the power source through the first electrode and the second electrode to the electrical ground portion is the path impedance from the power source through the protective layer of the heater to the electrical ground portion. the image forming apparatus according to any one of claims 1 to 5, wherein the smaller than the impedance. The fixing unit includes a cylindrical film and a roller,
The heater according to claim 1 to 6 for contact with the inner surface of the film, and forming a nip for heating while conveying the recording material on which the toner image has been formed together with the roller through said film The image forming apparatus according to any one of the above.

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