JP5963555B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a fixing unit that heats a recording material carrying a toner image and fixes the toner image on the recording material.

  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 generally has a cylindrical film, a heater that contacts the inner surface of the film, and a pressure roller that forms a nip portion 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 unit 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 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, Patent Document 1 discloses a configuration in which a resistor is connected between the pressure roller and the FG. 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.

In order to solve the above problems, the present invention provides an image forming unit that forms a toner image on a recording material,
A cylindrical film, a heater in contact with the inner surface of the film, and a pressure member that forms a nip portion together with the heater through the film, and transports a recording material carrying a toner image at the nip portion. An image forming apparatus having a fixing unit that heats and fixes a toner image to a recording material, and has a flat surface and a first sharpened portion having a sharp tip, and power is supplied to the heater. A first electrode connected to a power supply line for supply, a second surface having a flat surface, and a second sharpened portion having a sharp tip, and connected to an electrical ground; The first sharpened portion is opposed to a part of the surface of the second electrode at a predetermined distance, and the second sharpened portion is the first electrode of the first electrode. Having a lightning arrester opposed to a part of the surface at a predetermined distance. The one in which the features.

  According to the present invention, it is possible to achieve both downsizing of the apparatus and suppression of dielectric breakdown of the protective layer of the heater used in contact with the inner surface of the film at the fixing portion regardless of the polarity of the surge voltage.

(A) The figure which shows the outline | summary of the lightning arrester of Example 1. FIG. FIG. 5B is a diagram illustrating a flow of current in the power line of the fixing unit at the normal time according to the first exemplary embodiment. (C) The figure which showed the flow of the electric current of the power source line of the fixing | fixed part at the time of the surge voltage application of Example 1. FIG. The figure which shows the outline | summary of the lightning arrester of Example 2. FIG. The figure which shows the outline | summary of the lightning arrester of Example 3. FIG. 1 is a cross-sectional view illustrating a schematic overall configuration of an image forming apparatus including a fixing unit according to an embodiment. FIG. 3 is a cross-sectional view illustrating a schematic configuration of a fixing unit according to an embodiment. FIG. 3 is a diagram illustrating an electric circuit configuration from a power source to a fixing unit according to the first embodiment. The figure which shows the outline | summary of the lightning arrester of Example 4. FIG. A modification of the fourth 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, an image forming unit that forms a toner image on the recording material S will be described. In this embodiment, the image forming unit includes an optical unit 202, a cartridge 204 including a photosensitive drum 203, and a transfer roller 206.

  A latent image is formed on the photosensitive drum 203 by the optical unit 202 based on the image information. The latent image is developed on the photosensitive drum 203 by a developing unit (not shown) in the cartridge 204 to become a toner image. The recording material S is conveyed toward the transfer nip formed by the photosensitive drum 203 and the transfer roller 206 by the registration roller pair 209 so as to match the timing with the toner image. The toner image on the photosensitive drum 203 is transferred to the recording material S at the transfer nip portion, and a toner image is formed on the recording material S.

  After passing through the image forming unit, 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. Here, PEEK is polyetheretherketone, PES is polyethersulfone, and PPS is polyphenylene sulfide. PTFE is polytetrafluoroethylene, PFA is a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, and FEP is a tetrafluoroethylene / hexafluoropropylene copolymer.

  The heater 230 includes a long insulating substrate made of alumina or the like, a heating resistor formed on the substrate along the longitudinal direction of the substrate, and an insulating layer such as glass or resin as a protective layer 232 covering the heating resistor. And the film 212a is heated in contact with the inner surface of the film 212a. 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 carrying the toner image 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 arranged with a space from the film 212a 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 configuration of the lightning arrester 111 will be described with reference to 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, the lightning arrester 111 is mounted and fixed on an electric circuit board 216 as one holding member, with an electrode α1 as a first electrode and an electrode β1 as a second electrode made of a plate-like conductor. . 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 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, and therefore, the portion that passes through the protective layer 232 (an insulating layer such as glass or resin) of the heater 230. This is because the impedance increases. 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 a ground pattern provided on the electric circuit board 216, and finally connected to the electrical grounding portion of the image forming apparatus 201. The surface portion P3 of the electrode α3 and the surface portion of the electrode β3 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.

Example 4
Next, FIG. 7 shows a configuration of the lightning arrester 141 of the fourth embodiment. The fourth embodiment is different from the first embodiment only in the shape of the electrodes, and the other configurations are the same, so the description thereof is omitted. The lightning arrester 141 includes an electrode α4 as a first electrode formed of a conductive plate, an electrode β4 as a second electrode also formed of a conductive plate, an insulator γ41, an insulating sheet γ42, γ43.

  The electrode α4 and the electrode β4 are mounted and fixed to the electric circuit board 216. The electrode α4 and the electrode β4 are disposed so that the surface of the electrode α4 and the surface of the electrode β4 are parallel to each other with the insulating sheet γ43, the insulator γ41, and the insulating sheet γ42 interposed therebetween.

  The electrode α4 and the electrode β4 are connected on the back surface of the electric circuit board 216 to terminals which will be described below with patterns and solder, respectively. The electrode α4 is connected to a pattern (power supply line) for supplying power from the power source to the heating resistor 230. The electrode β4 is connected to the electrical grounding portion of the image forming apparatus 201 through a grounding pattern provided on the electrical circuit board 216.

  The electrode α4 and the electrode β4 each have a first sharpened portion and a second sharpened portion having a sharpened tip. The first sharpened portion of the electrode α is formed at the end portion of the electrode α, and the second sharpened portion of the electrode β is also formed at the end portion of the electrode β.

  The first sharpened portion of the electrode α4 is opposed to a part (flat surface) of the surface of the electrode β4 with a predetermined distance, and the second sharpened portion of the electrode β4 is one of the surfaces of the electrode α. It is opposed to the portion (flat surface) with the predetermined distance described above.

  The reason why the electrodes α and β have such a shape is to make it difficult for variations in the voltage at which discharge is started as a lightning arrester even if the discharge direction is switched depending on the polarity of the surge voltage. Ease of discharge between the electrodes is related not only to the distance between the electrodes but also to the shape of the electrodes. Even if the distance between the electrodes is the same, the discharge from the sharp part to the surface is the discharge from the surface to the sharp part. More likely to occur.

  For example, when the surge voltage is positive, discharge is likely to occur from the first sharpened portion of the electrode α4 to a part of the surface of the electrode β4. In addition, when the surge voltage is negative, discharge is likely to occur from the second sharpened portion of the electrode β4 to a part of the surface of the electrode α4. Therefore, the configuration of the fourth embodiment can reduce the change in the discharge voltage even when the discharge direction is switched depending on the polarity of the surge voltage.

  The interelectrode distance between the sharpened portion of the electrode α4 and a part of the surface of the electrode β4 depends on the dimensional accuracy of the insulator γ41, the insulating sheets γ42, and γ43. Therefore, by increasing the accuracy of these components, the tolerance of the distance between the electrodes can be reduced, and the discharge voltage between the electrodes can be easily stabilized.

  In addition, as a modification of Example 4, it shows to Fig.8 (a) and (b). In the configuration of FIG. 8A, the electrode α and the electrode β are such that the surface of the electrode α and the surface of the electrode β are the same surface of the insulator so that the side surface of the electrode α and the side surface of the electrode β are parallel and face each other Is held on. Further, the sharpened portion of the electrode α is formed at a part of the end portion of the electrode α, and is opposed to a part of the side surface of the electrode β with a predetermined distance. Further, the sharpened portion of the electrode β is formed at a part of the end portion of the electrode β, and is opposed to a part of the side surface of the electrode α with a predetermined distance as described above.

  The configuration of FIG. 8B will be described. In the electrodes α4 and β4, the surface of the electrode α and the surface of the electrode β are held with an insulator therebetween so that the surface of the electrode α and the surface of the electrode β are parallel and face each other. The sharpened portion of the electrode α is formed at the tip of a bent portion obtained by bending the end portion of the electrode α in a direction perpendicular to the surface of the electrode α and in a direction approaching the electrode β, and is predetermined with respect to a part of the surface of the electrode β Are facing each other with a distance of. Further, the sharpened portion of the electrode β is formed at the tip of a bent portion obtained by bending the end of the electrode β in a direction perpendicular to the surface of the electrode β and in a direction approaching the electrode α, and with respect to a part of the surface of the electrode α. Facing each other with a predetermined distance. These modified examples of the fourth embodiment have the same effects as the configuration of the fourth embodiment.

111 Lightning Arrester in Example 1 121 Lightning Arrester in Example 2 131 Lightning Arrester in Example 3 141 Lightning Arrester in Example 4 α1, α2, α3, α4 Electrodes Connected to Power Lines β1, β2, β3, β4 Connected to Electrical Ground Electrode γ2, γ3, γ41, γ42, γ43 Insulator P1, P4 Sharpened portion or surface portion of electrode α Q1, Q4 Sharpened portion or surface portion of electrode β 201 Image forming apparatus 210 Fixing portion 211 Pressure roller 211a Rubber layer 212 Fixing member 212a Film 216 Electric circuit board 230 Heater 232 Protective layer 235 Heating resistor X1, X2 Distance between electrodes S Recording material

Claims (7)

An image forming unit for forming a toner image on a recording material;
A cylindrical film, a heater in contact with the inner surface of the film, and a pressure member that forms a nip portion together with the heater through the film, and transports a recording material carrying a toner image at the nip portion. An image forming apparatus having a fixing unit that heats the toner image while fixing the toner image on the recording material,
A first electrode connected to a power line for supplying power to the heater, a flat surface, and a tip, A lightning arrester comprising: a second sharpened portion having a pointed shape; and a second electrode connected to an electrical ground, wherein the first sharpened portion is a surface of the second electrode. It has a lightning arrester opposed to a part with a predetermined distance, and the second sharpened part is opposed to a part of the surface of the first electrode with a predetermined distance. Image forming apparatus.   The first electrode and the second electrode are each formed of a conductive plate, and are arranged so that the surface of the first electrode and the surface of the second electrode are parallel and face each other. The first sharpened portion is formed at a part of the end of the first electrode, and is opposed to a part of the surface of the second electrode at a predetermined distance, The second sharpened portion is formed at a part of the end of the second electrode, and is opposed to a part of the surface of the first electrode with the predetermined distance therebetween. The image forming apparatus according to claim 1. The first electrode and the second electrode are each formed of a conductive plate, and are arranged so that the surface of the first electrode and the surface of the second electrode are parallel and face each other. And
The first sharpened portion is formed at the tip of a bent portion obtained by bending the end portion of the first electrode in a direction orthogonal to the surface of the first electrode and in a direction approaching the second electrode, A part of the surface of the second electrode is opposed to the surface of the second electrode at a predetermined distance, and the second sharpened portion has a direction in which an end of the second electrode is orthogonal to the surface of the second electrode And formed at the tip of a bent portion bent in a direction approaching the first electrode, and opposed to a part of the surface of the first electrode with a predetermined distance therebetween. The image forming apparatus according to claim 1. The first electrode and the second electrode are each formed of a conductive plate, and are arranged so that the side surface of the first electrode and the side surface of the second electrode are parallel to and face each other. And
The first sharpened portion is formed at a part of the end portion of the first electrode, and is opposed to a part of the side surface of the second electrode with a predetermined distance therebetween, and the second sharpened portion. The portion is formed at a part of an end of the second electrode, and is opposed to a part of a side surface of the first electrode with a predetermined distance therebetween. Image forming apparatus.   The surface of the first electrode and the surface of the second electrode are held by the insulator so as to sandwich the insulator, and the first electrode and the second electrode are opposed to each other. The image forming apparatus according to claim 2 or 3.   The surface of the first electrode and the surface of the second electrode are held on the same surface of the insulator, and the side surface of the first electrode and the side surface of the second electrode are opposed to each other. The image forming apparatus according to claim 4.   7. The heater according to claim 1, comprising: a long thin substrate; a heating resistor formed on the substrate along a longitudinal direction of the substrate; and an insulating layer covering the heating resistor. The image forming apparatus described.

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