Patent Application
20230266700
The present invention relates to an image forming apparatus such as a printer, a copier, and the like that uses an electrophotographic method. The present invention also relates to a fixing device mounted on an image forming apparatus, or an image heating device such as a gloss imparting device that improves a gloss value of a toner image by reheating the toner image fixed to a recording material.
A fixing device of a film heating type is known as a fixing device used in an electrophotographic image forming apparatus. In the fixing device of a film heating type, the temperature rise in a non-paper-passing portion described below is known to be a problem. The temperature rise in the non-paper-passing area is a phenomenon in which where small-size paper is continuously printed in an image forming apparatus using such a fixing device, the temperature of the area where the paper does not pass in the longitudinal direction of a nip portion gradually rises. Where the temperature of the non-paper-passing portion becomes too high, each part in the apparatus, such as a heater, a fixing film, and a pressure roller, will be damaged. Also, when large-size paper is printed while the temperature of the non-paper-passing area is rising, a phenomenon such as high-temperature offset of toner may occur in the area corresponding to the non-paper-passing portion of small-size paper.
As one means for suppressing the temperature rise in the non-paper-passing portion, a fixing device having the configuration shown in Japanese Patent Application Publication No. 2017-54071 has been proposed. That is, the fixing device includes a heater (hereinafter referred to as a split heater) in which a heating resistor (heating element) is arranged on a substrate while being divided in the longitudinal direction of the heater. By using this configuration, the heating element on the heater can be split into a plurality of heating areas (hereinafter referred to as heating blocks FIB) in the longitudinal direction of the heater, and the heat generation distribution of the heater can be switched according to the size of the recording material. By doing so, it is possible to suppress the temperature rise in the non-paper-passing portion even when small-size paper is passed.
Furthermore, Japanese Patent Application Publication No. 2017-54071 proposes a configuration in which a circuit for supplying power to a plurality of heating elements is shared. That is, a configuration in which a common drive is used to supply power to a plurality of heating blocks installed left-right symmetrically with respect to the center of the paper. By adopting this configuration, it is possible to reduce the size and cost of the device and save energy.
When using a fixing device using a split heater, it is desirable to provide a safety element for each drive circuit in consideration of failure of the device. That is, it is desirable to install a safety element in at least one of a plurality of heating blocks to which power is supplied by a common drive circuit. Where one of the drive circuits becomes uncontrollable and generates abnormal heat, a safety element installed in each drive circuit will detect the high temperature and the power supply can be quickly stopped. Here, as a safety element, a small thermostat (hereinafter referred to as a thermoswitch) is widely used from the viewpoint of function and cost.
In particular, thermoswitches that are to be arranged in narrow spaces such as the internal space of a fixing film often have to be shaped to be elongated in the longitudinal direction of the fixing film in order to function as a safety element. Since such a thermoswitch has connector terminals at both longitudinal ends of the thermoswitch, a certain margin is required as an installation space in the longitudinal direction of the fixing film. Meanwhile, depending on the number of divisions of the heating blocks of the heater, the longitudinal width of each heating block may become narrower. Therefore, when a thermoswitch is to be arranged in each of the adjacent heating blocks, the space in the longitudinal direction of the thermoswitches becomes cramped, making it difficult to arrange the thermoswitches.
An object of the present invention is to provide a technique that can ensure safety without being restricted by the device layout.
In order to achieve the above object, the image heating device of the present invention has the following:
a heater having a plurality of heating elements arranged in a width direction of a recording material perpendicular to a conveyance direction of the recording material;
a nip forming portion that forms a nip where the recording material is nipped; and
a control portion that controls power supplied to the plurality of heating elements;
wherein the image heating device heats an image formed on the recording material, which is nipped in the nip, by heat of the heater;
wherein the plurality of heating elements include a first heating element group and a second heating element group, the first heating element group being arranged symmetrically with respect to a conveyance reference position of the recording material in the width direction and the second heating element group being arranged symmetrically with respect to the conveyance reference position so as to be adjacent to the first heating element group in the width direction;
wherein the control portion supplies power to the first heating element group through a first common circuit, and supplies power to the second heating element group through a second common circuit;
wherein in the image heating device,
wherein the first safety element is arranged on one side with respect to the conveyance reference position in the width direction, and wherein the second safety element is arranged on the other side with respect to the conveyance reference position in the width direction.
In order to achieve the above object, the image forming apparatus of the present invention has the following:
an image forming portion that forms an image on a recording material; and
a fixing portion that fixes the image formed on the recording material to the recording material;
wherein the fixing portion is the image heating device of the present invention.
According to the present invention, it is possible to ensure safety without being restricted by the device layout.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Referring to the drawings, forms for carrying out the present invention will be described in detail by way of example on the basis of an embodiment example. Note that dimensions, materials, shapes, relative positioning, and the like of components described in each of embodiments are to be appropriately changed in accordance with configurations of an apparatus and a device to which the invention is applied and various conditions, and are therefore not intended to limit the scope of the invention to the following embodiments.
Schematic Configuration of Image Forming Apparatus
The image forming apparatus of Embodiment 1 has a control portion (not shown) that controls the image forming portion A, the recording material feeding portion B, the fixing device C, and the like. The control portion is composed of a CPU and a memory such as ROM and RAM, and various programs required for image formation are stored in the memory. This control portion receives a print signal from an external device such as a host computer and executes a predetermined image formation control sequence on the basis of the print signal. As a result, the drum motor is driven to rotate, and the photosensitive drum 1 rotates in the direction of the arrow at a predetermined peripheral speed (process speed). The surface of the rotated photosensitive drum 1 is uniformly charged to a predetermined potential having the same polarity as the toner (negative polarity in this case) by the charging roller 2. The laser scanner 3 scans the charged surface of the photosensitive drum 1 with a laser beam L on the basis of image information to expose the surface of the photosensitive drum 1. As a result of the exposure, the charge is removed from the exposed portion and an electrostatic latent image is formed on the surface of the photosensitive drum 1.
The developing device 4 has a developing roller 41 and a toner container 42 accommodating the toner. The toner is rubbed by a member such as a urethane blade (not shown) and charged to a predetermined polarity (negative polarity in Embodiment 1). When a negative voltage is applied to the developing roller 41 from a developing voltage power source (not shown) in the developing device 4, the toner is caused to adhere to the electrostatic latent image on the surface of the photosensitive drum 1 by using a potential difference, and the latent image is developed as a toner image T. The toner image T formed on the surface of the photosensitive drum 1 is transferred to the recording material P by applying a positive voltage having a polarity opposite to that of the toner to the transfer roller 5 and utilizing the potential difference created by the transfer voltage. Further, the conveyance drive motor provided in the recording material feeding portion B is rotationally driven, and the delivery roller 11 delivers the recording material P from the cassette 7 to the conveyance roller 8. The recording material P is conveyed by the conveyance roller 8, passes a top sensor 9, and is conveyed to a transfer nip portion between the surface of the photosensitive drum 1 and the outer peripheral surface of the transfer roller 5. The recording material P onto which the toner image formed on the surface of the photosensitive drum 1 has been transferred is conveyed along a conveyance guide 10 to the fixing device C, where the toner image on the recording material P is heated and pressed to be thermally fixed on the recording material P. The recording material P on which the toner image T has been thermally fixed is conveyed by the conveyance roller 12 and a discharge roller 13 in this order and is discharged to a discharge tray 14 on the upper surface of the apparatus main body M. Untransferred toner remaining on the surface of the photosensitive drum 1 after the toner image has been transferred onto the recording material P is removed by a cleaning blade 64 of the cleaning device 6 and accumulated in the cleaning device 6. By repeating the above operations, sequential printing is performed. The image forming apparatus of Embodiment 1 can print at a printing speed of 70 sheets/min for A4 size. Although the details are omitted, the image forming apparatus of Embodiment 1 is provided with a reversing conveyance path that enables double-sided image formation, and the apparatus is configured so that the recording material P having an image formed on one side is returned to the upstream side of the image forming portion A by switchback caused by reverse rotation of the discharge roller 13.
Configuration of Fixing Device
Pressure Roller
The pressure roller 26 has an elastic layer 262 on the outer circumference of a core shaft portion 261 and has a surface layer 263 on the outer circumference of the elastic layer 262. The pressure roller 26 has an outer diameter of about 25 mm. A solid or hollow metal material such as aluminum or iron is used for the core shaft portion 261. In Embodiment 1, solid aluminum is used as the core metal material. The elastic layer 262 is composed of heat-resistant silicone rubber and made conductive by adding an electrically conductive material such as carbon. The surface layer 263 in contact with the outer surface of the fixing film 25 is a releasing tube having a thickness of 10 μm to 80 μm and made of a fluorine resin such as PFA, PTFE, FEP, and the like. Here, PFA stands for a tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, PTFE for polytetrafluoroethylene (tetrafluoro), and FEP for fluoroethylene/hexafluoropropylene copolymer (tetrafluoro/hexafluoro). The surface layer 263 is desirably made conductive from the viewpoint of preventing charge-up associated with the passage of paper. In Embodiment 1, the surface layer 263 of the pressure roller 26 was configured by adding carbon as a conductive material to a PFA tube having a thickness of 30 μm.
Fixing Film
The fixing film 25 has a cylindrical shape with a diameter of 24 mm. The fixing film 25 is flexible and loosely fitted on the heater holder 29. The layer structure of the fixing film 25 is composed of multiple layers including a base layer 251, an elastic layer 252, and a surface layer 253 from the inside, as in the cross-sectional configuration shown in the circle in
Heater Holder
The heater 1100 is held by the heater holder 29 made of a heat-resistant resin material such as a liquid crystal polymer. The heater holder 29 also has a guide function of guiding the rotation of the fixing film 25.
Heater
The heater 1100, which is a characteristic configuration of Embodiment 1, will be described with reference to
The heater 1100 is configured of the substrate 1105, a sliding surface layer 1 provided on the first surface side of the substrate 1105 that contacts the fixing film 25, a sliding surface layer 2 that covers the sliding surface layer 1, a back surface layer 1 provided on the second surface side of the substrate 1105 opposite to the first surface side, and a back surface layer 2 that covers the back surface layer 1. The heater 1100 has a plurality of heating blocks configured of a first conductor 1101, a second conductor 1103, and a heating element 1102 on the back surface layer 1 along the longitudinal direction. In the heater 1100 of the present embodiment, a total of five heating blocks HB11 to HB15 are formed by a plurality of heating elements 1102 arranged in the width direction (longitudinal direction of the substrate 1105) perpendicular to the recording material conveyance direction.
The heater 1100 shown in
The heating elements 1102 of each heating block are arranged while being divided into a heating element 1102a on the upstream side and a heating element 1102b on the downstream side in the recording material P passage direction in relation to the widthwise direction (direction perpendicular to the longitudinal direction) of the heater 1100. Also, the first conductor 1101 is divided into a conductor 1101a connected to the heating element 1102a and a conductor 1101b connected to the heating element 1102b.
The heater 1100 is divided into five heating blocks HB11 to HB15. That is, the heating element 1102a is divided into five heating elements 1102a-1 to 1102a-5. Similarly, the heating element 1102b is divided into five heating elements 1102b-1 to 1102b-5. Further, the second conductor 1103 is also divided into five conductors 1103-1 to 1103-5.
The back surface layer 2 of the heater 1100 is provided with an insulating surface protective layer 1107 that covers the heating elements 1102, the first conductors 1101 and the second conductors 1103. In Embodiment 1, glass is used as the surface protective layer 1107. The surface protective layer 1107 does not cover the electrodes E11 to E15, E18-1 and E18-2 with which the electric contacts C11 to C15, C18-1 and C18-2 for power supply are in contact. The electrodes E11 to E15 are for supplying power to the heating blocks HB11 to HB15 via the second conductors 1103-1 to 1103-5, respectively. The electrodes E18-1 and E18-2 are for supplying electric power to the heating blocks HB11 to HB15 via the first conductors 1101a and 1101b.
Where the electrodes are thus provided on the back surface of the heater 1100, it is not necessary to provide a conductive pattern for supplying power to the second conductors 1103-1 to 1103-5 on the substrate 1105, so that the width of the substrate 1105 in the widthwise direction can be reduced. As a result, an increase in the size of the heater 1100 can be suppressed. As shown in
Although details will be described hereinbelow, various heat generation distributions can be formed in the heater 1100 of Embodiment 1 by independently controlling a plurality of heating blocks. A heat generation distribution corresponding to the size of the recording material P can thus be set. Furthermore, the heating elements 1102 are formed of a material having PTC (Positive Temperature Coefficient) properties. By doing so, even in the case where the end portion of the recording material P does not coincide with the boundary of the heating block, it is possible to suppress the temperature rise in the non-paper-passing portion.
A plurality of thermistors (temperature detection elements) for detecting the temperature of each of the heating blocks HB11 to HB15 is formed on the sliding surface layer 1 on the sliding surface side (the surface that contacts the fixing film 25) of the heater 1100. The plurality of thermistors are indicated by T11-1C to T11-3C, T11-1E to T11-3E, T12-4C to T12-5C, and T12-3E to T12-7E, respectively, in
The thermistor arrangement for each heating block HB will be explained hereinbelow. In Embodiment 1, as shown in
The heater holder 29 will be described with reference to
Power Application Control Circuit for Heater
A zero-cross detection portion 1421 is a circuit that detects a zero-cross of an AC power supply 1401 and outputs a ZeroX signal to the CPU 420. The ZeroX signal is used as a reference signal or the like for phase-controlling the triacs 1411 to 1413.
Heater Temperature Detection Method
A method for detecting the temperature of the heater 1100 will be described hereinbelow. Signals (Th11-1C to Th11-3C, Th11-1E to Th11-3E, Th12-4C to Th12-5C, and Th12-3E to Th12-5E) obtained by dividing a voltage Vcc by the resistance value of the thermistors and the resistance values of resistors 1451 to 1461 are input to the CPU 420. In
The CPU 420 calculates the electric power to be supplied to the heater, for example, by PI control on the basis of the set temperature (control target temperature) of each heating block and the detected temperature (output) of each thermistor. Furthermore, the calculated supply power is converted into control timings such as corresponding phase angles (phase control) and fractions (fraction control), and the triacs 1411 to 1413 are controlled at these control timings. Processing of signals corresponding to other thermistors is the same, so the description thereof is omitted.
Heater Power Control
The power control of the heater 1100 (heater temperature control) will be described hereinbelow. During the fixing process, each of the heating blocks HB11 to HB15 is controlled so that the temperature detected by the thermistors is maintained at the set temperature (control target temperature). Specifically, the power supplied to the heating block HB14 is determined by controlling the driving of the triac 1414 so that the temperature detected by the thermistor T11-4C is maintained at the set temperature. Thus, each thermistor is used when performing control for keeping each heating block HB at a constant temperature.
Heater Protection
A relay 1440 is provided as a means for cutting off power to the heater 1100 when the temperature of the heater 1100 rises excessively due to factors such as device failure. Also, three thermoswitches 50-12, 50-13, and 50-15 are on the DC circuit connected to the 24 V power supply. In this configuration, where any one of the three thermoswitches 50-12, 50-13, and 50-15 is opened, the 24 V applied to the relay 1440 is cut off, the relay 1440 is opened, and the AC circuit is cut off
Thermoswitch
The safety element, which is a characteristic configuration of Embodiment 1, will be explained hereinbelow. The safety element is installed for the purpose of safely shutting off the power input to the heater 1100 without damaging the heater 1100 or the like even when the CPU 420 cannot perform control and the heater 1100 runs out of control. In the present embodiment, a case where a thermoswitch is used as a safety element will be described, but other elements such as a thermostat and a thermal fuse may be used as the element that detects abnormal heat generation of the heater and cuts off the power supply to the heater.
The operation of the thermoswitch 50 (50-12, 50-13, and 50-15) will be described with reference to
As shown in
As shown in
A heater according to a comparative example will be described with reference to
In the split heater according to Comparative Example 1 shown in
Thermoswitches 510-11, 510-12, and 510-13 have the same configuration as the thermoswitch 50 according to the present embodiment shown in
From the viewpoint of safety, it is desirable to install the thermoswitches 510-11, 510-12, and 510-13 each in one of the heating blocks HB belonging to the heating group powered by the same drive. As an example of the installation configuration, as shown in
In the heater of Comparative Example 1, which is used in a fixing device with a maximum print width of A3 size, all the thermoswitches can be installed in the heating blocks HB on one longitudinal side with respect to the conveyance reference position in order to ensure a sufficient width of the heating blocks HB. However, in a heater having a heating block HB with a small width, such as the heater according to the present embodiment, it may be difficult to install the thermoswitches due to space considerations.
As shown in
The thermoswitches 510-11, 510-12, and 510-13 have the same configuration as the thermoswitch 50 according to the present embodiment shown in
The arrangement of the thermoswitches in the heater according to Comparative Example 2 is similar to that of the heater according to Comparative Example 1 in that all the thermoswitches are installed in the heating blocks HB located on one longitudinal side with respect to the conveyance reference position which is the center of the paper width. That is, in this configuration, thermoswitches 510-11, 510-12, and 510-13 are installed in the heating block HB11, the heating block HB12, and the heating block HB13, respectively. Here, the longitudinal widths of the heating block HB11 and the heating block HB12 in the heater according to Comparative Example 2 are narrower than the longitudinal widths of the heating block HB11 and the heating block HB12 in the heater according to Comparative Example 1.
Therefore, as shown in
Although a comparison between the fixing device with a maximum print width of A4 size and the fixing device with a maximum print width of A3 size is shown here, similar problems occur in other configurations as well. For example, the same problem occurs in a fixing device in which the maximum print size remains A3 and the heating block HB is split into more section to support a large number of paper sizes.
Installation Positions of Thermoswitches in Embodiment 1
In Embodiment 1, the installation positions of the thermoswitches 50 are in the three heating blocks HB12, HB13, and HB15, but configuration examples in which the thermoswitches 50 are installed so as not to be adjacent to each other in the heating group including a plurality of heating blocks HB are not limited to this. For example, the combination of heating blocks in which the thermoswitches 50 are installed may be the heating blocks HB11, HB13, and HB14.
In the present embodiment, an example of the heater 1100 in which the heating element 1102a and the heating element 1102b are separately provided in the conveyance direction of the recording material P has been described, but the shape of the heating elements does not matter as long as the heater is split into heating blocks HB in the width direction of the recording material P. In addition, the configuration in which the electrodes E11 to E15, E18-1 and E18-2 are formed on the back surface of the recording material passing area of the heater 1100 is exemplified in Embodiment 1, but a configuration in which end electrodes are formed as in the modification example shown in
Further, the heating elements 1102-1 to 1102-5 have a shape folded multiple times in the width direction of the heater 1100-1, as shown in
Thermoswitches 50-11, 50-13, and 50-14 are installed at the positions shown in
Further, in this modification example, as in Embodiment 1, the heating blocks HB12, HB13, and HB15 can be set as a combination of heating blocks in which the thermoswitches are installed.
Also, in the present embodiment, the case in which the heating group is divided into three has been described, but the same effect can be exhibited even in a fixing device in which the heating area is split into larger number of sections. An example is shown in
Furthermore, in Embodiment 1, the heat-sensitive portion 51 of the thermoswitch 50 is arranged so as to contact the heating element 1100, but such contact is not necessary, provided that the heat-sensitive portion can be arranged at a position making it possible to detect the temperature of the area of the heating block HB (to react to excessive temperature rise). For example, it is possible to insert a resin material or the like between the heater 1100 and the heat-sensitive portion 51.
The fixing device according to Embodiment 2 of the present invention is configured as a fixing device operating at a low printing speed, but capable handing a finer paper size.
In the fixing device according to Embodiment 2, the maximum recording material width that can pass is the LTR size (216 mm), and the heating block HB is split into seven heating blocks. Also, as a safety element, a thermal fuse 60 smaller than the thermoswitch 50 used in Embodiment 1 is used. The difference between Embodiment 2 and Embodiment 1 is only in the heater 1200 and the safety element (thermal fuse 60). The rest of the configuration is the same as that of Embodiment 1, and therefore the description thereof is omitted.
The configuration of the heater 1200 of Embodiment 2 will be described with reference to
As with the heater of Embodiment 1, the heater of Embodiment 2 is also divided into heating groups for each heating block HB having a common drive circuit. A heating group 1 as a reference heating element group is composed of a heating block HB14. A heating group 2 as a first heating element group is composed of heating blocks HB13 and HB15. A heating group 3 as a second heating element group is composed of heating blocks HB12 and HB16. A heating group 4 as a third heating element group is composed of heating blocks HB11 and HB17.
A thermal fuse 60, which is a safety element used in Embodiment 2, will be described with reference to
It is desirable that the thermal fuse 60 have a certain size or larger in order to stably function at a low cost. Specifically, it is desirable that the width indicated by Xb in
Also in Embodiment 2, the combination of the heating blocks HB in which the thermal fuses 60 are installed is not limited to the combination described above. That is, the above-described arrangement is not limiting as long as the thermal fuses 60 are installed between a plurality of heating groups including a plurality of heating blocks HB so as not to be adjacent to each other between the adjacent heating blocks HB. For example, the heating blocks HB in which the thermal fuses 60 are installed may be the heating blocks HB22, HB24, HB25, and HB27.
The thermoswitch 50 shown in Embodiment 1 can also be used as a safety element for the heater 1200 of Embodiment 2. Furthermore, the thermal fuse 60 and the thermoswitch 50 can be used together. Also, in Embodiment 2, as in Embodiment 1, it is possible to insert a resin material or the like between the heater 1200 and the thermal fuse 60.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2022-025647, filed on Feb. 22, 2022, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-025647 | Feb 2022 | JP | national |
