JP2018151597A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device having a plurality of heat sources with heat generation distributions different from each other in the longitudinal direction of a fixing rotating body, and reduce a rush current at turn-on of the heat sources and make the temperature of the fixing rotating body uniform during operation.SOLUTION: A fixing device comprises: a fixing rotating body; a pressure rotating body that forms a nip part with the fixing rotating body; a first heat source that heats the center part in the longitudinal direction of the fixing rotating body; a second heat source that heats the ends in the longitudinal direction of the fixing rotating body; a first temperature sensor that detects the temperature of the center part of the fixing rotating body; and a second temperature sensor that detects the temperature of the ends of the fixing rotating body. When turning on both the first and second heat sources, the fixing device selectively delays turn-on start timings of the first and second heat sources on the basis of the detected temperatures of the fixing rotating body.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device and an image forming apparatus.

  2. Description of the Related Art In an electrophotographic image forming apparatus such as a printer, a copying machine, and a facsimile, a heat fixing method that heats and fixes a toner image transferred on a sheet (recording material) is widely adopted. In a typical heat fixing method, a fixing roller having a heat source and a pressure roller are opposed to each other with a predetermined pressure in contact with each other, and a sheet having a toner image is conveyed to the contacted portion. Thus, the unfixed toner image is fixed on the paper by the heating / pressurizing action. However, the size of paper conveyed for image formation is not constant. For example, sheets of various sizes such as A3 size (297 × 420 mm) to government postcard size (100 × 148 mm) are conveyed, and fixing is performed by the fixing device.

  In order to cope with such various sizes of paper, a plurality of heater members having different heat generation distributions in the longitudinal direction of the fixing roller are provided. The heater (only the heater) is energized (in the case of center feeding), and not only the central heater but also the heater member (end heater) having a heating portion at the end portion is energized for large size paper. It has been broken.

  By the way, once the power used for heat fixing is large, if the power is supplied from the commercial power supply at 100% when the heater is turned on, the peak current is large, and this greatly affects other devices connected to the commercial power supply line. Since there was a problem, the inrush current when the heater was turned on was suppressed. For example, in Patent Document 1, a simple switching contact and a switching contact with a parallel resistor are connected in series between a halogen heater and a power source, and a desired delay is established between both switching contacts with respect to an on timing for closing these switching contacts. It is disclosed that the time is set, the simple switching contact is turned on in advance and preheating is performed, and the switching contact with parallel resistance is turned on and the original heating is performed after the delay time has elapsed. By doing so, a closed circuit is formed through the resistance of the switching contact with parallel resistance, and the presence of the resistance causes less current to flow than usual when the halogen heater alone, and the halogen heater is gradually preheated. A large inrush current is not generated.

  However, in such a configuration, it is necessary to provide an opening / closing contact with a parallel resistor, which is complicated in configuration and requires heating that is different from the original heating such as preheating, and thus wasteful power consumption is required. did.

  In the fixing device having a plurality of heat sources having different heat generation distributions in the longitudinal direction of the fixing rotator, it is possible to suppress inrush current when the heat source is turned on and to make the temperature of the fixing rotator uniform during operation. Let it be an issue.

  The problems include a fixing rotator, a pressure rotator that forms a nip portion with the fixing rotator, a first heat source that heats a longitudinal central portion of the fixing rotator, and a length of the fixing rotator. A second heat source for heating the direction end, a first temperature sensor for detecting the temperature of the center of the fixing rotator, and a second temperature sensor for detecting the temperature of the end of the fixing rotator. A fixing device having the first and second heat sources is selected based on the detected temperature of the fixing rotator when both the first and second heat sources are turned on. Can be resolved by delaying automatically.

  According to the present invention, when lighting a plurality of heat sources having different heat generation distributions in the longitudinal direction of the fixing rotator, based on the detected temperature of the fixing rotator, the lighting start timing of these heat sources is selectively selected. Thus, the inrush current when the heat source is turned on can be suppressed, and the temperature of the fixing rotator can be made uniform during operation.

1 is a schematic diagram illustrating a configuration of a color printer that is an image forming apparatus according to an exemplary embodiment of the present invention. FIG. 2 is a schematic cross-sectional configuration diagram illustrating a fixing device in the printer of FIG. 1. FIG. 2 is a schematic plan view of a fixing device. It is a conceptual diagram which shows the heat distribution of a 1st heater and a 2nd heater, and how to wind the filament of each heater. 6 is a graph showing a temperature rising state of a fixing roller from power-on to a printing state at startup. It is a flowchart which shows the lighting timing which concerns on this embodiment. FIG. 6 is a schematic cross-sectional configuration diagram showing another embodiment of a fixing device.

  Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic color printer (hereinafter simply referred to as a printer) will be described. The printer 1 is a tandem color printer.

  Four toner bottles 102Y, 102M, 102C, and 102K corresponding to each color (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 at the top of the main body casing of the printer 1. ing. An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85. Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging device 75, a developing device 76, a cleaning unit 77, and the like are provided (a black image forming unit for clarity of depiction). Signs are only given for 4K).

  Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on 5K. The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in the clockwise direction in FIG. Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging device 75 (charging process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser beam emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (Exposure process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, and the electrostatic latent image is developed at this position to form toner images of each color (developing process). ). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the primary transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photosensitive drums 5Y, 5M, The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K. Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. It is mechanically recovered by a cleaning blade 77 (cleaning process). Finally, the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed. Thus, a series of image forming processes on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

  The toner images of the respective colors formed on the respective photosensitive drums through the development process are sequentially transferred onto the intermediate transfer belt 78 of the intermediate transfer unit 85, thereby forming a full color image on the intermediate transfer belt 78. It will be. Here, in addition to the intermediate transfer belt 78, the intermediate transfer unit 85 includes four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning device. 80 etc.

  The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84, and is endlessly moved in the direction of the arrow in FIG. 1 by the rotational drive of one roller (secondary transfer backup roller 82). The four primary transfer bias rollers 79Y, 79M, 79C, and 79K respectively sandwich the intermediate transfer belt 78 between the photosensitive drums 5Y, 5M, 5C, and 5K to form a primary transfer nip. A transfer bias opposite to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K, so that each color on the photosensitive drums 5Y, 5M, 5C, and 5K can be obtained. The toner image is primary-transferred over the intermediate transfer belt 78 to form a full-color image. Then, the intermediate transfer belt 78 carrying the full color image reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The full-color image formed by superimposing the respective color toner images on the intermediate transfer belt 78 is transferred onto the paper P as a recording material conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the paper P remains on the intermediate transfer belt 78. Thereafter, the surface of the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning device 80, and untransferred toner on the intermediate transfer belt 78 is collected at this position. Thus, a series of transfer processes on the intermediate transfer belt 78 is completed.

  Here, the paper P conveyed to the position of the secondary transfer nip is fed from the paper feeding unit 12 disposed in the lower part of the main body housing of the printer 1 through the paper feeding roller 97, the registration roller pair 98, and the like. It has been transported. Specifically, a plurality of sheets P are stored in the sheet feeding unit 12 in a stacked manner. When the paper feed roller 97 is driven to rotate counterclockwise in FIG. 1, the uppermost paper P is fed toward the rollers of the registration roller pair 98. The sheet P conveyed to the registration roller pair 98 is abutted against the roller nip of the registration roller pair 98 that has stopped rotating and temporarily stops. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the paper P is conveyed toward the secondary transfer nip. Thus, a desired color image is transferred onto the paper P.

  Thereafter, the sheet P on which the color image has been transferred is conveyed to the position of the fixing device 20, and at this position, the action of heat and pressure by the fixing roller 21 that is a fixing rotating body and the pressure roller 31 that is a pressing rotating body. As a result, the color image transferred onto the surface is fixed on the paper P. After fixing, the paper P passes through the pair of paper discharge rollers 99 and is discharged outside the apparatus. The paper P discharged out of the apparatus by the paper discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image. Thus, a series of image forming processes in the image forming apparatus is completed.

  The fixing device 20 will be described with reference to FIG. The fixing device 20 includes a fixing roller 21 having a heat source 41 therein and a pressure roller 31 that presses against the fixing roller 21. The fixing roller 21 includes a base material 21b and a surface layer 21a. The base material 21b is a metal such as iron or aluminum. The surface layer 21a is configured by providing a release layer such as PFA on a thin elastic member such as silicone rubber. ing. The surface layer 21a of the fixing roller 21 may have a configuration in which a PFA release layer is directly coated on the base material 21b. The pressure roller 31 also includes a base material 31b and an elastic layer 31a. The material is a base material 31b made of metal such as iron, and the elastic layer 31a is made of silicone rubber or sponge. A release layer is provided.

  A nip portion N is formed between the fixing roller 21 and the pressure roller 31. By passing the paper on which the toner image is formed through the nip portion N, the toner adhering to the paper is melted by heat. It is made to adhere to a paper by pressurization.

  Inside the fixing roller 21, a plurality of halogen heaters (in this embodiment, two as shown in FIG. 3) are arranged as the heat source 41. In the case of the present embodiment in which the center paper is passed, one is a heater (first heater 41a) that mainly heats the central portion (the central portion in the longitudinal direction of the fixing roller) of the paper passing region, and the other is the paper passing. This is a heater (second heater 41b) that mainly heats the end of the region (the end in the longitudinal direction of the fixing roller). The heating state of the fixing roller 21 by the first heater 41a is detected by the first temperature sensor 51a, and the heating state of the fixing roller 21 by the second heater 41b is detected by the second temperature sensor 51b. The fixing roller 21 is controlled to a constant temperature by PID control or the like. For detecting the temperature of the roller surface, a contact type thermistor is generally used. However, toner or paper dust adheres to the element portion and causes deterioration of responsiveness. The one temperature sensor 51a is preferably a non-contact temperature sensor (for example, thermopile). In addition, a contact type thermistor is used for the second temperature sensor 51b arranged outside the maximum sheet passing width (outside the sheet passing area) so that the temperature can be reliably detected even when the sheet is wound around the fixing roller 21 due to a jam or the like. Thus, overshoot due to a detection delay in a fixing device (for example, 20 ° C./sec or more) whose temperature rises quickly is suppressed, and temperature ripples during sheet passing are suppressed.

  FIG. 4 shows the heat distribution of the first heater 41a, which is the central heater, and the second heater 41b, which is the end heater, and how to wind the filament of each heater. The first heater 41a is configured such that the central portion has a heat distribution peak with respect to the maximum sheet width. The width of this peak corresponds to, for example, the width of A5 size paper, and the winding of the filament is adjusted. The second heater 41b is configured such that both ends thereof have a heat distribution peak with respect to the maximum sheet width. In addition, the winding of the filament is adjusted so that the electric power of about 20% of the rating is applied to the central portion.

  FIG. 5 shows a temperature rising state of the fixing roller 21 from the power-on to the printing state at the start-up at the beginning of the morning in the present embodiment, for example. Normally, the temperature rise of the fixing roller 21 when the power is turned on is faster at the center and slower at the end due to external heat dissipation at the end. In particular, when the power is turned on in the morning, the main body housing of the printer 1 is cooled, and heat radiation from the end of the fixing roller is large. In particular, printers with small and compact machine sizes are designed to be as short as possible by reducing the length of the fixing roller and halogen heater close to the maximum sheet passing width in order to reduce the size in the paper width direction and the installation area. The difference between the center temperature and the edge temperature at the start-up in the first morning tends to be large, and the problem that the temperature in the edge area covering the paper passing area is greatly different from the center temperature is the image quality. It has a strong influence.

  If the central heater (first heater 41a) and the end heater (second heater 41b) are turned on at the same time, a flicker problem is likely to occur due to voltage fluctuations. In this embodiment, the size of the first heater 41a exceeds the cover area. When passing the paper, control is performed to delay one of the two heaters.

  When the power is turned on, the temperature rise at the end is slow. Therefore, when energization is started from the power-on or sleep state, the second heater 41b, which is an end heater, is energized first to heat the fixing roller end. Control to prevent delays. On the other hand, once the fixing roller 21 is warmed, the central heater (first heater 41a) on the side where the response of the temperature sensor is fast is turned on first, so that temperature control with higher accuracy becomes possible. Temperature is easy to stabilize. Incidentally, the thermopile constituting the first heater 41a has a time constant of about 100 msec, and the contact type thermistor constituting the second heater 41b is about 1 to 2 msec.

  The above lighting timing is summarized in the flow as shown in FIG. When the paper having a size exceeding the cover area of the first heater 41a is passed and fixed, it is determined whether or not the temperature detected by the temperature sensor is equal to or lower than a predetermined temperature (S1). If any temperature detected by each of the first temperature sensor 51a and the second temperature sensor 51b is equal to or lower than a predetermined temperature, “yes” corresponds to this step. If the temperature is equal to or lower than the predetermined temperature, it is determined that the fixing roller 21 is in a cold state when the power is turned on or the sleep state is continued to some extent, and heating is started from the end side of the fixing roller 21. First, the second heater 41b is turned on (S2), and it is determined whether the time t1 has elapsed (S3). When the time t1 has elapsed, the first heater 41a is turned on (S4). On the other hand, if it is determined in step 1 that the predetermined temperature has been exceeded, it is determined that the fixing roller 21 is in a warm standby state, and heating is started from the center in the longitudinal direction of the fixing roller 21. One heater 41a is turned on (S5), and it is determined whether time t2 has elapsed (S6). When the time t2 has elapsed, the second heater 41b is turned on (S7). After that, normal control at the time of printing is performed. In this case, the lighting timing according to the present embodiment is substantially applied, and the lighting of the second heater 41b is slightly delayed without simultaneously lighting both heaters. (T3) Avoid the flicker problem due to voltage fluctuation. That is, the lighting start timing of the first heater 41a and the second heater 41b is selectively delayed according to the surface temperature of the fixing roller.

  FIG. 7 shows a fixing device having a belt configuration as a fixing device according to another embodiment to which the above lighting timing is applied. The fixing device 20 includes an endless fixing belt 22 that is a thin and flexible cylindrical fixing rotating body, and a pressure roller 31 that is a pressure rotating body that is in contact with the outer periphery of the fixing belt 22. have. The fixing belt 22 is heated by radiant heat from halogen heaters (hereinafter also referred to as a first heater 41a and a second heater 41b) as a plurality of heat sources arranged inside (in the loop).

  Further, a nip forming member 24 that forms a nip portion N with the pressure roller 31 via the fixing belt 22 and a stay member 25 (support member) that supports the nip forming member 24 are arranged inside the fixing belt 22. Has been. The nip forming member 24 arranged across the width direction of the fixing belt 22 is fixedly supported by the stay member 25, thereby preventing the nip forming member 24 from being bent due to the pressure from the pressure roller 31, A uniform nip width is obtained over the longitudinal direction (axial direction) of the pressure roller 31.

  Further, a heat transfer assisting member 27, which is also referred to as a soaking member, for relaxing the temperature gradient in the width direction (longitudinal direction) of the fixing belt is disposed so as to cover the surface of the nip forming member 24 that faces the inner peripheral surface of the belt. Therefore, heat is prevented from staying in the end region of the fixing belt 22 when passing small-size paper, and the heat is positively moved in the width direction of the fixing belt 22, that is, in the longitudinal direction of the heat transfer auxiliary member 27. Thus, temperature non-uniformity in the longitudinal direction is eliminated. Therefore, the heat transfer auxiliary member 27 is formed of a material having high thermal conductivity that enables heat transfer in a short time, such as copper or aluminum.

  A first temperature sensor 51a for detecting the temperature at the center of the belt and a second temperature sensor 51b for detecting the temperature at the end of the belt are disposed at appropriate positions on the outer peripheral side of the fixing belt 22, and the first temperature sensor 51a. Is a non-contact type thermopile, and the second temperature sensor 51b is a contact type thermistor.

DESCRIPTION OF SYMBOLS 20 Fixing device 21 Fixing roller 22 Fixing belt 23 Pressure roller 41 Heater 51 Temperature sensor

JP 7-36234 A

Claims (5)

  A fixing rotator, a pressure rotator that forms a nip portion with the fixing rotator, a first heat source that heats a longitudinal central portion of the fixing rotator, and a longitudinal end of the fixing rotator. A fixing device having a second heat source for heating, a first temperature sensor for detecting a temperature of a central portion of the fixing rotator, and a second temperature sensor for detecting a temperature of an end portion of the fixing rotator; Then, when both the first and second heat sources are turned on, the lighting start timing of the first and second heat sources is selectively delayed based on the detected temperature of the fixing rotator. A fixing device.   The fixing device according to claim 1, wherein when the temperature of the fixing rotator is equal to or lower than a predetermined temperature, the lighting start timing of the first heat source is delayed.   The fixing device according to claim 1, wherein when the temperature of the fixing rotator is higher than a predetermined temperature, the lighting start timing of the second heat source is delayed.   The fixing device according to claim 1, wherein the first and second heat sources are halogen heaters.   5. The fixing device according to claim 1, and a control unit that performs lighting control of the first and second heat sources based on temperatures detected by the first and second temperature sensors. , Image forming apparatus.

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