JP2016170283A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing the occurrence of inconvenience such as an end fixability failure by uniformizing a temperature distribution in a longitudinal direction, when a large-size sheet is fed, while preventing end temperature rise when a small-size sheet is fed and to provide an image forming apparatus.SOLUTION: The fixing device includes a heating unit 17, a heating source 3, a temperature detection sensor which detects the temperature of a paper passing area Ar1 through which a predetermined size sheet P passes, a temperature detection sensor which detects the temperatures of non-paper passing areas Ar2 and Ar3, a power supply part 31 which supplies power to the heat source 3 from a position corresponding to the paper passing area Ar1, and power supply parts 32 and 33 which supply the power to the heat source 3 from the positions corresponding to the non-paper passing areas Ar2 and Ar3. When fixing a sheet, a control part performs control for preferentially supplying the power to the power supply part 31 corresponding to the temperature detection sensor on the basis of each detection result of the temperature detection sensors and for supplying the power from all of the power supply parts 31 to 33, when a difference between the respective detection temperatures of the temperature detection sensors becomes a predetermined value or less.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a fixing device that is used in a copying machine, a laser beam printer, a facsimile, and the like and fixes a toner image on a sheet by heating and pressing, and an image forming apparatus including the fixing device.

  In a fixing device that heats and presses a toner image on a sheet and fixes the toner image on the sheet, in recent years, a heating rotating body for heating that is pressed against a pressure roller is used as a cylindrical film (belt) in order to increase energy use efficiency. ) Is known. In such a fixing device, a film having a small heat capacity is used as a heating rotator on the outside of the heater as a heating element, thereby reducing energy (electric power) until the heating rotator is raised to a temperature at which the fixing operation can be performed. Can do.

  In the fixing device using the fixing film, since the heat capacity of the heating rotator is reduced, the thermal conductivity in the longitudinal direction of the heating rotator is impaired. As a result, in the longitudinal direction of the heating element, the degree of temperature non-uniformity between the sheet passing area through which the sheet passes and the non-sheet passing area through which the sheet does not pass increases. As a result, when the sheet is continuously fed, the temperature of the non-sheet passing region rises and the temperature rises excessively, and a high release layer (generally PFA, PTFE, etc.) formed on the surface of the heating rotator. There is a problem that the fluororesin layer or the Si rubber layer) is thermally deteriorated.

  In order to prevent this problem, when continuously forming images with a smaller width than the maximum width sheet (hereinafter referred to as “small size sheet”), the sheet passing interval is widened and the temperature is uniform to some extent. A sheet that performs a fixing operation for the next sheet after being made into practical use has been put into practical use. However, according to this, the production efficiency of the image forming operation is lowered, and the operation time of the image forming apparatus main body becomes long, so that there is a problem that extra energy is consumed accordingly.

  With respect to the above problem that the temperature of the non-sheet passing area rises, a heater composed of a heating element having a PTC characteristic (hereinafter referred to as “PTC heating element”) for the purpose of suppressing an excessive temperature rise in the non-sheet passing area. Has been proposed (see Patent Document 1). The PTC characteristic is a characteristic in which the electrical resistance value increases as the temperature increases. In other words, when the temperature rises, the electric resistance value increases and the current does not easily flow. When the temperature decreases, the electric resistance value decreases and the current easily flows.

  One example of the heater of the PTC heating element is shown in FIG. The heater in FIG. 19 has conductive portions (electrodes) at both ends in the short direction (width direction) orthogonal to the long direction of the elongated substrate. And between these electroconductive parts, the PTC heat generating body is provided along the longitudinal direction. By energizing these conductive parts, the heating element (heating source) generates heat.

  Here, in the case of a heating element having no PTC characteristic (hereinafter referred to as “NON-PTC heating element”), when a small-size sheet is passed, the heating element (heating source) in the sheet passing area is heated by passing the sheet. In contrast, the heating element in the non-sheet passing area rises in temperature because heat is not taken away by the sheet passing.

  However, in the case of a PTC heating element as shown in FIG. 19, the electrical resistance of the heating element itself increases due to the PTC characteristics as the temperature of the heating element rises, and it becomes difficult for current to flow through the heating element, thereby suppressing heat generation. As a result, the temperature rise in the non-sheet passing area can be suppressed (see Patent Document 1). In FIG. 19, the end input in the heater longitudinal direction is 228.6 ° C. at the center A, 240 ° C. at the left end B in the figure, and 205 ° C. at the right other end C in the figure. The temperature difference between the one end B and the other end C is 35 ° C.

JP 2005-234540 A

  However, according to the technique described in Patent Document 1, the two conductive portions provided along the longitudinal direction of the heater substrate have high conductivity, but the resistance value is not zero. Therefore, a voltage drop due to its own resistance also occurs in the conductive portion, and the heat generation amount of the heating element on the side close to the power supply portion (one end B) is large and the side far from the power supply portion (regardless of the state where paper is not passed) The amount of heat generated by the heating element at the other end C) is reduced. For this reason, the temperature unevenness in the longitudinal direction occurs because the temperature distribution is not uniform in the longitudinal direction. As a result, the portion on the high temperature side of the pressure roller that is in pressure contact with the heating rotator is thermally expanded, and its outer diameter becomes larger than the outer diameter on the low temperature side, so that the sheet conveying force differs in the longitudinal direction.

  For this reason, when the fixing film of the fixing device is pulled toward the side where the diameter is larger and the conveying force is stronger, the fixing film is shifted, the film end is damaged, or the end part is lowered in a low temperature environment. There is a possibility that the end fixability failure due to. Therefore, while preventing the temperature rise at the edge when passing a small-size sheet, the temperature distribution in the longitudinal direction is made uniform when passing a large-size sheet, thereby causing problems such as poor fixing at the edge and film breakage. It is desirable to prevent it.

  Therefore, the present invention prevents the temperature rise at the edge when passing a small size sheet, and makes the temperature distribution in the longitudinal direction uniform when passing a large size sheet, thereby causing inconveniences such as poor end fixability and film breakage. An object of the present invention is to provide a fixing device and an image forming apparatus capable of preventing the above-described problem.

  The present invention relates to a fixing device in which a heating rotator for heating a toner image on a sheet, a pressure rotator disposed to face the heating rotator, and an axial direction of the rotator inside the heating rotator. A heating unit that extends and forms a fixing nip portion that sandwiches the heating rotator between the pressure rotator and conveys the sheet while heating, and a control unit that controls the heating unit. The heating unit includes a heating element extending in the axial direction, first temperature detection means for detecting a temperature of a sheet passing area through which a sheet of a predetermined size passes in the longitudinal direction of the heating element, and the sheet passing area. A second temperature detecting means for detecting the temperature of the non-sheet passing region on the longitudinal end portion side of the heating element that is detached from the first heating unit, a first power feeding unit that supplies power to the heating element from a position corresponding to the sheet passing region, and The position corresponding to the non-sheet passing area And a second power feeding unit that feeds power to the heating element, and the control means is based on the detection results of the first and second temperature detection means and corresponds to the first temperature detection means. Power feeding control that feeds power preferentially to the power feeding unit and feeds power from both the first and second power feeding units when the difference between the detected temperatures of the first and second temperature detecting means becomes a predetermined value or less. It is characterized by performing.

  According to the present invention, it is possible to give priority to voltage supply to a low temperature part, and at the time when the temperature near the power supply unit becomes constant, it becomes possible to supply voltage to each power supply unit simultaneously, It becomes possible to reach the target temperature efficiently. This prevents temperature rise at the edge when passing through small-size sheets, while making the temperature distribution in the longitudinal direction uniform when passing through large-size sheets, preventing problems such as poor edge fixability and film breakage. It becomes possible to do.

1 is a schematic cross-sectional view illustrating a configuration of a fixing device according to an embodiment of the present invention. (A) is a top view which shows the technique used as the foundation of this embodiment, (b) is a front view which shows the technique of (a). The figure which shows the case where electric power is supplied from the center and a heater is made to heat | fever-generate in a sheet-passing direction energization type heater. The figure which shows the technique used as the foundation of this embodiment. The figure which shows the case where it supplies electric power to a heating source equally in the technique used as the foundation of this embodiment. 1 is a diagram showing a schematic configuration of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. 1 is a block diagram showing a control system of an image forming apparatus according to an embodiment of the present invention. The figure shown about the case where a small size sheet is passed in the technique used as the foundation of this embodiment. The figure which shows the state left to stand for 1 minute after the small size sheet passed. (A) is a figure which shows the voltage supply pattern used as the foundation of this embodiment, (b) is a graph which shows the temperature change in (a). (A) is a figure which shows the voltage supply pattern which concerns on the 1st Embodiment of this invention, (b) is a graph which shows the temperature change which concerns on 1st Embodiment. FIG. 5A is a flowchart showing an operation according to the first embodiment, and FIG. 5B is a diagram showing a comparison of rise times according to the first embodiment. (A) is a temperature distribution diagram according to the second embodiment of the present invention, (b) is a diagram showing a current voltage supply pattern. (A) is a graph which shows the present temperature change, (b) is a figure which shows the voltage supply pattern which concerns on 2nd Embodiment, (c) is a graph which shows the temperature change which concerns on 2nd Embodiment. FIG. 6A is a flowchart showing an operation according to the second embodiment, and FIG. 5B is a diagram showing a comparison of rise times according to the second embodiment. (A), (b) is a figure which shows the circuit structure of the changeover switch from which the type which concerns on the 3rd Embodiment of this invention differs. (A) is a graph showing a power change according to the third embodiment, (b) is a graph showing a correlation between time and temperature change when a large size paper is passed after passing a small size sheet. . The flowchart which shows the operation | movement which concerns on 3rd Embodiment. The figure for demonstrating the prior art which electrically heated from the edge part and made the heater generate | occur | produce heat | fever in a sheet-passing direction electricity supply type heater.

<First Embodiment>
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. It should be noted that the numerical values and configuration conditions shown in the embodiments are reference numerical values and reference configurations, and do not limit the present invention.

  In the description of the present embodiment, the first stage leading to the present invention will be described first. That is, the present inventors have proposed a heating source (heater) as shown in FIGS. This heating source 3 has a large amount of heat generated by the heating source 3 on the side close to the power supply unit 31 due to the electrical resistance of the first and second conductive units 8 a and 8 b, and the heating source 3 on the side far from the power supply unit 31. The characteristic is that the amount of heat generated is small.

  That is, a plurality of power supply units that supply power to the heat source 3 are provided in the longitudinal direction (for example, three power supply units 31, 32, and 33), and a temperature detection sensor 7 a such as a thermistor and a temperature detection are provided near each of the power supply units 31 to 33. Sensors 7b and 7c are provided to perform independent control on the power feeding units 31 to 33, respectively. Thus, by controlling the heat generation in the longitudinal direction of the heating source 3, it becomes possible to control the temperature distribution in the longitudinal direction. As compared with the case, it is possible to suppress the temperature rise at the end when the small-size sheet is passed.

  However, it is difficult to eliminate all the temperature rise at the edge after passing through the small-size sheet, and the temperature at the edge is about 20 ° C. higher than that at the center. When a large-size sheet is passed after a small-size sheet is passed in a state where there is temperature unevenness, in order to make the fixing temperature distribution flat, instead of sequentially supplying a voltage from each of the power supply units 31 to 33, Efficient start-up is possible by preferentially applying a voltage to the central part having the lowest temperature and switching to temperature adjustment (temperature adjustment) to the target temperature (temperature adjustment temperature).

  FIG. 6 is a diagram schematically showing a configuration of a main part of the image forming apparatus 50 equipped with the fixing device 27 according to the present embodiment. That is, as shown in FIG. 6, as a flow of image formation, first, the photosensitive drum 20 as the image carrier is charged to a predetermined constant potential from the charging high-voltage power supply 18 by the charging roller 19. Then, a point on the photosensitive drum 20 on which an image is formed is exposed by the scanner unit (exposure means) 21 and lowered to a predetermined potential. Then, the toner in the developing container 22 is uniformly placed on the developing sleeve 23, and the difference between the lowered potential on the photosensitive drum 20 and the potential applied to the developing sleeve 23, that is, the action of the electric field is used. Then, the charged toner is adhered onto the photosensitive drum 20.

  The toner adhering to the photosensitive drum 20 is fed by a feeding roller (feeding means) (not shown), and is conveyed to a predetermined transfer area along a pre-transfer guide 24. Is transferred to. Thereafter, the sheet is conveyed along the fixing nip entrance guide 26, fixed by the fixing device 27, and discharged. The toner that adheres to the photosensitive drum 20 and cannot be transferred is scraped off by the cleaning blade 28 into the waste toner container and collected. In order to detect the sheet width, a sheet width sensor 30 for detecting the sheet width is disposed at the feeding port.

  The photosensitive drum 20, the charging roller 19, the developing sleeve 23, and the like constitute an image forming unit that forms an image. The transfer roller 25 constitutes a transfer unit that transfers the toner image formed as an image by the image forming unit to the sheet. The fixing device 27 fixes the toner image transferred to the sheet by the transfer roller 25 on the sheet. A fixing unit is configured.

  FIG. 1 is a cross-sectional view schematically showing the configuration of the fixing device 27 according to the present embodiment. As shown in FIG. 1, the fixing device 27 includes a film unit 1 configured in a cylindrical shape of, for example, Φ30, and a pressure roller 2 configured in a cylindrical shape of, for example, Φ48, in pressure contact with the film unit 1 from below. It has. The film unit 1 includes a heating source 3 such as a ceramic heater, a fixing film 4, a film guide 5, a T stay 6, and temperature detection sensors 7a, 7b, and 7c. Hereinafter, the temperature detection sensors 7a, 7b, and 7c are collectively referred to as the temperature detection sensor 7.

  The temperature detection sensor 7a constitutes first temperature detection means for detecting the temperature of the sheet passing area Ar1 (see FIG. 8) through which a sheet of a predetermined size (small size) passes in the longitudinal direction of the heating source 3. Further, the temperature detection sensors 7b and 7c constitute second temperature detection means for detecting each temperature of the non-sheet passing regions Ar2 and Ar3 (see FIG. 8) on both sides in the longitudinal direction of the heating source 3 that is out of the sheet passing region Ar1. To do.

  The pressure roller 2 constitutes a pressure rotator arranged to face the fixing film 4. Further, the temperature detection sensor 7 a is disposed at a position corresponding to the power supply unit 31 at the center in the longitudinal direction of the heating source (heating element) 3. The temperature detection sensors 7b and 7c, which are the second temperature detection means, are arranged as one end side temperature detection means and the other end side temperature detection means at both ends in the longitudinal direction of the heating source 3, respectively. That is, the temperature detection sensor 7b is disposed at a position corresponding to the power supply portion 32 at one end portion in the longitudinal direction of the heating source 3, and the temperature detection sensor 7c is disposed at a position corresponding to the power supply portion 33 at the other end portion in the longitudinal direction. Has been placed. The fixing film 4 as a heating rotator is an endless heating belt that heats the toner image on the sheet.

  The power feeding units 32 and 33 serving as the second power feeding unit include one end side power feeding unit (32) corresponding to the temperature detecting sensor 7b serving as the one end side temperature detecting unit and the temperature detecting sensor 7c serving as the other end side temperature detecting unit. Is arranged as the other end side power supply section (33) corresponding to. Further, as a relationship between the temperature detection sensor 7 and the heating source 3, the temperature detection sensor 7 may be arranged on the heating source side. In that case, the configuration of the heating source 3 is as shown in FIGS. 2 (a) and 2 (b). It is comprised similarly.

  When the heating source 3 is a ceramic heater, the heating source 3 includes a heating element obtained by printing a heating paste on a ceramic insulating substrate 38, and a glass coating layer for protecting the heating element and ensuring insulation. Is done. Then, the AC current whose power is controlled is supplied to the heating element to generate heat. As an insulating layer, about 100 μm is provided so as to cover the heating resistor with a material such as glass. The fixing film 4 is made of polyimide formed in a cylindrical shape having a thickness of about 70 μm, and efficiently transfers heat from the heating source 3 to the toner 9 on the sheet.

  The film guide 5 has a plurality of ribs (not shown) in the longitudinal direction (front to back in FIG. 1), and assists the rotation of the fixing film 4 in the circumferential direction while suppressing resistance to the fixing film 4 by the ribs. ing. The T stay 6 is made of a steel plate and is configured to apply a pressure force uniformly. Further, the temperature detection sensors 7 a, 7 b, and 7 c arranged on the back surface of the ceramic insulating substrate 38 respectively detect temperature changes in the longitudinal direction of the heating source 3.

The pressure roller 2 is made of, for example, a core metal 10 made of aluminum having a diameter of Φ20, for example, coated with a conductive silicone rubber having a volumetric efficiency of about 1 × 10 ⁵ Ω · cm, and further coated with an insulating tube of about 60 μm. Has been. The pressure roller 2 is pressed against the heating source 3 with a predetermined pressure (nip pressure) with a fixing film 4 sandwiched between them by a spring, and a fixing of, for example, 5 to 8 mm is performed between the film unit 1 and the pressure roller 2. A nip portion N is formed.

  The pressure roller 2 is rotationally driven by a pressure roller driving unit (pressure roller driving unit) 300 (see FIG. 7) to rotate the fixing film 4 and fix the sheet P introduced into the fixing nip N. The film 4 is conveyed while being in close contact with the film 4. In this way, the sheet P is conveyed to the fixing nip portion N, whereby the unfixed toner image formed and carried on the sheet is fixed by the heat of the heating source 3 and the fixing nip pressure.

  2A and 2B are cross-sectional views of a heating source 3 such as a ceramic heater, and an arrangement of a temperature detection sensor 7 such as a thermistor. As shown in FIG. 2, the ceramic insulating substrate 38 is made of a material such as aluminum oxide (alumina) or aluminum nitride, and has a thickness of about 1.5 mm, a length of about 300 mm, and a length of the short side. Is formed to be approximately 15 mm. The first conductive portion 8a and the second conductive portion 8b formed on the insulating substrate 38 are mainly formed of a material such as silver, and are formed with a width of 2 mm, for example, in parallel with each other along the longitudinal direction of the insulating substrate 38. Yes.

  The material of the heating source 3 is, for example, a ruthenium oxide material having a relatively high resistance value, and is formed between the two first conductive portions 8 a and 8 b along the longitudinal direction of the insulating substrate 38. The heating resistor paste is screen-printed with a width of about 7 mm and then baked at a high temperature to have a predetermined resistance value (for example, 20Ω). The electrodes 11, 12, 13, and 14 are mainly made of a silver-based material, and the power feeding units 31, 32, and 33 are about 2 mm wide and upstream of the sheet feeding direction (arrow E direction) from the heating source 3. A plurality are provided on the side (here, three examples are shown). The electrode 14 is grounded. The second conductive portion 8 b is grounded from the central portion A in the longitudinal direction via the ground-side power feeding portion 34 and the electrode 14.

  The power supply unit 31 is disposed at a central position in the longitudinal direction of the heating source 3, and the voltage supply position is one on each of the left and right targets with respect to the central position and a position that is a non-sheet passing area when a small size sheet is passed. The 2nd, 3rd electric power feeding parts 32 and 33 are arrange | positioned. A voltage is applied to the heating source 3 from the electrodes 11, 12, and 13 corresponding to the power feeding units 31, 32, and 33, respectively. A closed loop circuit is formed by the electrodes 11, 12, 13 and the electrode 14.

  Since the image forming apparatus 50 having the fixing device 27 is a center reference in which the sheet conveyance is performed with reference to the center of the sheet, the central portion in the longitudinal direction of the heating source 3 is a sheet passing area when a small size sheet is passed. Ar1 and both end portions in the longitudinal direction become non-sheet passing regions Ar2 and Ar3 at that time. In the present embodiment, the configuration based on the central reference is described. However, the present invention is not limited to this, and can be similarly applied to a one-side reference sheet conveyance method in which a sheet is passed on the basis of, for example, one end side of the heating source 3. Of course there is.

  Here, FIG. 19 described above is a diagram in the case where the heater (heater) is heated by supplying power from one end portion in the longitudinal direction in the sheet-passing direction energization type heater. In FIG. 19, for example, when the central portion A of the heating source is controlled to be 228.6 ° C., the amount of heat generated on the side close to the power feeding portion (one end portion B) is large due to the electrical resistance of the conductive portion, Due to the characteristic that the amount of heat generated on the side far from the power feeding part (the other end C) is reduced, the heat source temperature at one end B is about 240 ° C., and the heat source temperature at the other end C is about 205 ° C. It can be seen that the amount of heat generated at one end B close to the power feeding portion is large. As described above, when a temperature difference of about 35 ° C. occurs at both longitudinal ends of the heat source 3, the higher temperature side of the pressure roller 2 expands to increase the outer diameter, and the sheet conveying force increases, thereby fixing. There is a possibility that the film 4 is moved and the fixing film 4 is finally damaged.

  Here, FIG. 3 shows the case where power is supplied from the central portion of the heating source 3 of the sheet passing direction energization type to generate heat. Reference numeral 15 denotes an electrode for supplying power to the central portion of the first conductive portion 8a. In addition, a power feeding unit connected to the electrode 16 is provided in the central portion in the longitudinal direction of the heating source 3 in the second conductive unit 8b, and the electrode 15 and the electrode 16 form a closed loop circuit.

  For example, when the central part of the heating source is controlled to be 228.3 ° C., the heat generation of the heating source 3 on the side close to the central part A to be fed is caused by the electric resistance of the first conductive part 8a and the second conductive part 8b. The amount of heat generated at the one end B and the other end C on the side far from the center A to be fed is small, and the center A is about 228 ° C. because the temperature is controlled. Both ends B and C are about 205 ° C., respectively.

  This phenomenon is that when power is supplied from the central part A, the voltage drops from the central part A to the one end part B and the other end part C are equal to each other, so that the heat generation on the left and right sides becomes equal to the central part A. to cause. It can be seen that the temperature at the one end B and the other end C is 23.3 ° C. lower than the center A, and the temperature difference between the one end B and the other end C is eliminated. Thereby, it is possible to suppress the temperature rise of the non-sheet passing area of the small size sheet. However, as a feature of the heating type fixing device 27, the end portion tends to dissipate heat and the temperature tends to decrease. In addition, the heat generation amount of the one end portion B and the other end portion C is reduced by providing the power feeding portion in the central portion A in the sheet passing direction energization type heating source 3. Therefore, when a temperature difference of about 23 ° C. occurs between the central part A, the one end part B, and the other end part C, if a large size paper is continuously passed under a low temperature environment, the one end part B and the other end part C There is a risk that the fixing property may be deteriorated.

  Therefore, here, due to the electrical resistance of the first conductive portion 8a and the second conductive portion 8b, the heat generation amount of the heating source 3 near the power feeding portion 31 to be fed is large, and the heating source 3 far from the power feeding portion 31 is used. It is configured to reduce harmful effects while taking advantage of the characteristic that the amount of heat generated becomes small. To realize this, the first and second conductive portions 8a and 8b are formed in parallel with each other along the longitudinal direction of the insulating substrate 38, and the heating source 3 is disposed between the conductive portions 8a and 8b. The first conductive part 8a is provided with power supply parts 31 to 33 so that the second conductive part 8b can be energized from the power supply parts 31 to 33 via the heating source 3.

  Here, FIG. 4 is a diagram illustrating a case where power is supplied from the central portion A with the heating source 3. That is, as shown in FIG. 4, by adopting a pattern in which the heating source 3 is energized through the electrode 11 that feeds power to the central part A by controlling the temperature to 228.3 ° C., heating in the sheet feeding direction energization type Similarly to the case where the power supply unit is provided in the central part A with the source 3 (FIG. 3), the central part A changes at about 228 ° C. under temperature control. And the one end part B and the other end part C change at about 205 degreeC, the temperature difference of about 23 degreeC arises in the center part A, the one end part B, and the other end part C, and edge part temperature rising is suppressed. I understand that.

  FIG. 5 is a diagram illustrating a state where power is evenly supplied by the heating source 3. That is, as shown in FIG. 5, the temperature is controlled to 228.3 ° C., for example, and power is supplied uniformly from the power feeding units 31, 32, and 33. For this purpose, an electrode 11 that feeds power to the central portion A of the heating source 3, an electrode 12 that feeds power to one end B of the heating source 3, and an electrode 13 that feeds power to the other end C of the heating source 3, respectively Energize evenly every 10 msec (apply voltage). In the energization pattern for controlling energization, nine half waves are set as one block pattern, and at 50 Hz, since one half wave is 10 msec (= 1/100 sec), the electrodes are switched every 10 msec. In FIGS. 4 and 5, in the half waves supplied to the electrodes 11 to 13, black portions (mesh portions) indicate an energized state, and white portions (open portions) indicate a non-energized state. The notation of the energized state and the non-energized state is the same in other drawings.

  As a result, the temperature at the center A is 228.3 ° C., the temperatures at the one end B and the other end C are 230.2 ° C., respectively, and the temperature difference between the center A and both ends B and C is 1.9. The temperature unevenness in the longitudinal direction can be satisfactorily suppressed. In addition, the control methods, such as an electricity supply pattern, are not limited to these.

  As described above, the temperature distribution in the longitudinal direction can be controlled by individually energizing the divided power feeding units and controlling them independently.

  Next, with reference to FIG. 7, the block configuration in the present embodiment will be described. FIG. 7 is a block diagram showing a control system of the image forming apparatus 50 according to the present embodiment.

  That is, as shown in FIG. 7, the image forming apparatus 50 includes a control unit 700 as a control unit. The control unit 700 includes a CPU (Central Processing Unit) 701, an I / F (interface) 702 connected to the CPU 701, a RAM (Random Access Memory) 703, and a ROM (Read Only Memory) 704. Yes.

  Further, the CPU 701 includes an operation unit 100 provided on an upper surface portion of an apparatus main body (not shown) of the image forming apparatus 50, an image process unit 200, a fixing device 27, and an optical unit 600 provided in the apparatus main body. Is connected.

  The I / F 702 is a device for connecting the CPU 701 and a network such as a LAN, and is specifically realized by a LAN card LAN board or the like. The I / F 702 receives an image formation execution instruction transmitted from the outside and outputs the instruction to the CPU 701.

  The RAM 703 holds data required when the CPU 701 executes a program, data written from the CPU 701, and the like. Specifically, the RAM 703 holds the durability specification number of sheets of the fixing device 27 (the number of repetition specifications of the fixing operation), the temperature transition based on the detected temperatures of the temperature detection sensors 7a, 7b, and 7c, and the like. The ROM 704 holds a temperature control program 704 a and a supply power control program 704 b that are executed by the CPU 701 to control the image forming apparatus 50.

  The operation unit 100 outputs an operation instruction from the outside to the CPU 701 of the control unit 700. Further, the image processing unit 200 forms a toner image based on the image data output from the scanner unit (exposure unit) 21 under the control of the CPU 701, and the formed toner image is supplied from a sheet deck (not shown). Transfer on top.

  The fixing device 27 includes a heater control unit 118 having a changeover switch 37 for switching the electrodes 11 to 13, a pressure roller driving unit 300 that drives the pressure roller 2 (FIG. 1) according to the control of the CPU 701, and a heating source (heating element). ) 3, a power source 35 for supplying a voltage from any of the electrodes 11 to 13 to the heating source 3, and a temperature detection sensor 7.

  In this embodiment, the fixing film 4 is extended in the width direction (rotating body axial direction) orthogonal to the film circumferential direction (rotating body circumferential direction) inside the fixing film 4, and the fixing film 4 is sandwiched between the pressure roller 2. Then, a heating unit 17 is provided which forms a fixing nip portion N that conveys the sheet P while heating. The heating unit 17 includes a heating source 3 extending in the width direction, and first and second conductive portions 8 a and 8 b provided along both edges in the longitudinal direction of the heating source 3. In addition, the heating unit 17 includes a power feeding unit 31 that feeds power to the central portion in the longitudinal direction of the first conductive portion 8a, a power feeding portion 32 that feeds power to one longitudinal end of the first conductive portion 8a, and the longitudinal length of the first conductive portion 8a. The power supply unit 33 supplies power to the other end in the direction. Furthermore, the heating unit 17 includes a ground-side power feeding unit 34 that is grounded via the electrode 14 from the longitudinal central portion of the second conductive portion 8b, a longitudinal central portion, a longitudinal end portion, and a longitudinal direction of the heating source 3. It has temperature detection sensors 7a, 7b, 7c arranged at the other end respectively.

  The temperature detection sensor 7a constitutes a first temperature detection unit that detects the temperature of the sheet passing area Ar1 through which a sheet P of a predetermined size (small size) passes in the longitudinal direction of the heating source 3. The temperature detection sensors 7b and 7c constitute second temperature detection means for detecting the temperatures of the non-sheet passing regions Ar2 and Ar3 on the longitudinal direction end side of the heating source 3 that is out of the sheet passing region Ar1. The power feeding unit 31 constitutes a first power feeding unit that feeds power to the heating source 3 from a position corresponding to the paper passing area Ar1, and the power feeding parts 32 and 33 are heated from a position corresponding to the non-paper passing area Ar2 and Ar3. A second power feeding unit that feeds power to the source 3 is configured.

  The control unit 700 constitutes a control unit that controls the heating unit 17. When the sheet P passed through the fixing nip N is fixed, the control unit 700 supplies power corresponding to the temperature detection sensor 7a having the lowest temperature in the longitudinal direction based on the detection results of the temperature detection sensors 7a, 7b, and 7c. Power is supplied to the unit 31 with priority. Then, when the difference between the detected temperatures of the temperature detection sensors 7a, 7b, and 7c becomes equal to or less than a predetermined value (α), power is supplied from all of the power supply units 31, 32, and 33 (of the first and second power supply units). (Power is supplied from both sides).

  That is, the control unit 700 determines the target temperature of the heating source 3 based on the detection result of the temperature change by the temperature detection sensors 7a to 7c, controls the heater control unit 118 to control the power to the heating source 3, Control is performed so that the temperature of the heating source 3 is maintained at a target temperature (printing temperature). When there is no difference between the detected temperatures of the temperature detection sensor 7b as the one end side temperature detection means and the temperature detection sensor 7c as the other end side temperature detection means, the control unit 700 controls as follows.

  That is, power is supplied only from the power supply unit 31 when the temperature detected by the temperature detection sensor 7a is lower than the detection temperature of any of the temperature detection sensors 7b and 7c. When a sheet having a size larger than the size of the sheet that has been passed through the fixing nip N is passed, the difference between the temperature detected by the temperature detection sensor 7a and the temperature detected by the temperature detection sensors 7b and 7c is less than a predetermined value. At that time, the power supply is controlled from all of the power supply units 31 to 33 so that the temperature distribution in the longitudinal direction of the heating source 3 becomes uniform.

  The control unit 700 supplies a voltage of the AC voltage to the heating source 3 by the CPU 701 and the voltage among the electrodes 11, 12, and 13 based on print information received from the operation unit 100 or a host computer (not shown). Select the electrode. The control unit 700 applies the AC voltage of the power source 35 only to the power supply unit selected from the power supply units 31, 32, and 33 provided in the first conductive unit 8a by the changeover switch 37, thereby individually energizing. To control the heating source 3 to generate heat. As the energization pattern for individually controlling energization, there is a method of switching the electrodes every 10 msec since 9 half waves are made into one block pattern, and at 50 Hz, 1 half wave is 10 msec. In addition, the method of individually controlling is not limited to this.

  Here, the changeover switch 37 is disposed on a path for supplying a voltage to the heating source 3, and can be constituted by a semiconductor switch such as Triac (registered trademark) that can turn on and off the power supply to the heating source 3, and is output from the CPU 701. ON / OFF control is performed according to the control signal. When the temperature rise of the heating source 3 is detected by the temperature detection sensors 7a to 7c, electrical analog information of each detection temperature is A / D converted and input to the control unit 700 having the CPU 701 as a digital signal. A power source (AC power source) 35 is connected to the heating source 3 via a changeover switch 37.

  When the changeover switch 37 is controlled by the CPU 701 of the control unit 700 and electric power is supplied via the changeover switch 37, the heating source 3 generates heat in the longitudinal direction and the temperature rises. The temperature detection sensor 7a, 7b, 7c detects the temperature every time the temperature rises, and the control unit 700 takes in the output of these temperature detection sensors 7a, 7b, 7c by A / D conversion. The control unit 700 controls the changeover switch 37 based on the detection temperatures of the temperature detection sensors 7a, 7b, and 7c, and performs phase control (or wave number) on the electric power supplied to the heating source 3 so that the detection temperature converges to a predetermined temperature. Control).

  FIG. 8 is a diagram illustrating a case where a small-size sheet is passed by the heating source 3. As shown in FIG. 8, when a small-size sheet is fed by controlling the temperature to 200 ° C., a pattern in which the heating source 3 is energized through the electrode 11 that supplies power to the power supply unit 31 in the center A is adopted. To do. For this reason, as in the case where the power feeding unit is provided in the central portion using the heating source 3 of the paper passing direction energization type (FIG. 4), the central portion A changes at about 200 ° C. under temperature control, and both end portions B , C change at 176.7 ° C., and a temperature difference of 23.3 ° C. occurs between the central portion A and both end portions B, C, and the temperature rise at the end portion is suppressed. According to the control shown in FIG. 8, by applying (supplying) a voltage only to the central portion A of the heating source 3, it is possible to effectively suppress the temperature rise at the end when a small-size sheet is passed as compared to the conventional case. .

  However, according to the countermeasure shown in FIG. 8, although it is possible to effectively suppress the edge temperature increase than before, it is difficult to eliminate all the edge temperature increase after passing through the small-size sheet, as shown in FIG. Each temperature of both end parts B and C will be about 20 degreeC higher than the center part A. FIG. 9 shows a state in which 60 seconds have elapsed after continuous copying of 80 small sizes in the state of FIG.

  That is, when a small size sheet is continuously copied, both ends B and C are heated and adjusted at 220 ° C. immediately after 80 sheets are passed, and the center A is adjusted at 200 ° C. ing. For example, after 60 seconds have passed after passing 80 sheets, the whole is cooled, and both ends B and C are 180 ° C., and the center A is 160 ° C. In this way, when the large-size sheet is passed after the small-size sheet is passed in a state where the temperature is uneven, in order to flatten the fixing temperature distribution in the fixing device 27, the central portion A having a low temperature is used. It is efficient to apply a voltage preferentially to switch to the target temperature (temperature control temperature). However, when the voltage is supplied in the order of electrode 11 → electrode 12 → electrode 13 as shown in FIG. 10A, the voltage is supplied to the central portion A only at a constant period, and the voltages are supplied to both ends B and C. There is a timing (OFF portion) that is not performed, and it is difficult to start up efficiently.

  Here, FIG. 10B shows the temperature change when the voltage supply pattern of FIG. 10A is implemented. When the voltage supply to each of the electrodes 11 to 13 is periodically performed as in the voltage supply pattern of FIG. 10A, the temperatures at both ends B and C are increased as shown in FIG. After reaching the temperature, the standby state is maintained until the central portion A having the lowest temperature reaches the target temperature. Since the voltage is supplied to the central part A only at a constant period, the rise is delayed as compared with the case where the voltage is supplied only to the central part A. In this state, the target temperature was reached in 10 seconds.

  Therefore, in this embodiment, as shown in FIG. 11A, voltage supply to the central portion A (the lowest point) is performed with priority through the electrode 11. When the temperature in the vicinity of the electrode 11 in the central part A becomes constant, a voltage is supplied from all the electrodes 11 to 13 including the electrodes 12 and 13 (that is, the power supply units 32 and 33 including the power supply unit 31). Thereby, it is possible to efficiently reach the target temperature (temperature control temperature).

  FIG. 11B shows the temperature change when the voltage supply shown in FIG. 11A is performed. In FIG. 11 (b), the vertical axis represents the detected temperature (thermistor temperature (° C.)) of the temperature detection sensors 7a, 7b, 7c, and the horizontal axis represents time (sec).

  That is, as shown in FIG. 11A, the control unit 700 is based on the detection results of the temperature detection sensors 7a to 7c so that the temperature distribution in the longitudinal direction in the heating source 3 is uniform. When control is performed to switch the power supply timing to the target temperature by preferentially applying a voltage to the central part A which is the lowest temperature part, the result shown in FIG. 11B is obtained.

  That is, as shown in FIG. 11 (b), a voltage is supplied only from the electrode 11 to the central portion A via the power feeding portion 31 from 160 ° C. to 170 ° C. At that time, the temperatures of both ends B and C are naturally cooled and fall from 180 ° C to 170 ° C. Therefore, each electrode temperature is the same at the time of 170 ° C., and the voltage is supplied to all of the power feeding units 31, 32, 33 simultaneously from this time. Thereby, the temperature of the heating source 3 can be raised efficiently, and the target temperature (temperature control temperature) can be reached in 8 seconds. As a result, the Δ2 sec rise time can be shortened compared to the periodic rise as shown in FIGS. 10 (a) and 10 (b).

  Next, the operation of the image forming apparatus 50 including the fixing device 27 according to the present embodiment will be described in detail with reference to the control flowchart shown in FIG.

  That is, in step S10, the control unit 700 having the CPU 701 receives print information (first print information) of the first job (JOB) from the operation unit 100 or a host computer (not shown) (obtain first print information). . In addition, the control unit 700 obtains temperature detection information of each of the power feeding units 31, 32, and 33, selects a pattern in which an AC voltage is applied, and an electrode to be supplied among the electrodes 11 to 13, and selects the selected electrode. The energization from is started (S11, S12).

  Thereafter, in step S13, the control unit 700 starts an image forming operation based on the print information (first print information) of the first job, and then ends the image forming operation based on the print information of the first job in step S14. To do.

  Subsequently, in step S15, the control unit 700 receives print information (second print information) of the second job from the operation unit 100 or the host computer (not shown) (obtain second print information). Then, the control unit 700 compares the sheet size of the second print information with the sheet size of the first print information (S16), and when the sheet size of the second print information is equal to or smaller than the sheet size of the first print information. Then, an energization pattern suitable for the sheet size is selected (adopted) (S17). In step S18, energization from the selected electrode is started.

  Thereafter, in step S19, the control unit 700 starts an image forming operation based on the print information (second print information) of the second job, and then ends the image forming operation based on the print information of the second job in step S20. To do.

  On the other hand, as a result of comparing the sheet size of the second print information with the sheet size of the first print information in step S16, the control unit 700 finds that the sheet size of the second print information is larger than the sheet size of the first print information. In the case, first, the detection temperatures by the temperature detection sensors 7a to 7c of the power feeding units 31 to 33 are obtained (S30).

  In step S31, control unit 700 determines whether or not a value (temperature difference) obtained by subtracting the detected temperature at center portion A from the detected temperatures at both ends B and C is equal to or lower than a predetermined temperature α ° C. As a result, when the temperature difference is equal to or lower than the predetermined temperature α ° C., the control unit 700 starts voltage application from the electrodes 11, 12, and 13 (S32). Thereafter, in step S33, the control unit 700 starts an image forming operation based on the printing information (second printing information) of the second job, and then ends the image forming operation based on the printing information of the second job in step S34. To do. The predetermined value (α) is a value in the tolerance range of the temperature detection sensors 7a, 7b, 7c.

  On the other hand, as a result of the comparison in step S31, when the temperature difference exceeds the predetermined temperature α ° C., the control unit 700 starts voltage application only from the electrode 11 corresponding to the central part A (S41). Then, the control unit 700 determines whether or not a value (temperature difference) obtained by subtracting the detected temperature at the central portion A from the detected temperatures at both ends B and C is equal to or lower than a predetermined temperature α ° C. (S41). Further, the control unit 700 repeats step S41 until the temperature difference becomes equal to or lower than the predetermined temperature α ° C., and when the temperature difference becomes lower than the predetermined temperature α ° C., voltage application from the electrodes 11, 12, and 13 is started. (S32). Thereafter, in step S33, the control unit 700 starts an image forming operation based on the printing information (second printing information) of the second job, and then ends the image forming operation based on the printing information of the second job in step S34. To do.

  FIG. 12B summarizes the effects of this embodiment. In the initial stage of starting up the fixing device 27, voltage is supplied only to the central part A having the lowest temperature, and the central part A is raised to a temperature at which fixing can be performed. Also, since there is no timing to turn off the voltage until both ends B and C reach the target temperature earlier than the central part A and the central part A reaches the target temperature, it is about 2 seconds faster than the conventional technique that took about 2 seconds. The target temperature can be reached.

  In the present embodiment, when there is no difference in the detection temperatures of the temperature detection sensors 7b and 7c, the control unit 700 only controls the power supply unit 31 when the detection temperature of the temperature detection sensor 7a is lower than the detection temperature of the temperature detection sensors 7b and 7c. Power is supplied from When a sheet having a size larger than the size of the sheet that has been passed through the fixing nip N is passed, the difference between the detected temperature of the temperature detecting sensor 7a and the detected temperature of the temperature detecting sensors 7b and 7c is a predetermined value (α ) When it becomes the following, control is performed to supply power from all of the power supply units 31 to 33.

  That is, the control unit 700 is the case where the sheet size in the print information of the second job input this time is larger than the sheet size in the print information of the first job input last time, and the print information of the first job is passed. When the temperature of the temperature detection sensor 7a in the paper area is lower than the temperature of the temperature detection sensors 7b and 7c outside the paper passing area of the print information of the first job, power is supplied only from the power supply unit 31. The result obtained by subtracting the temperature of the temperature detection sensors 7b and 7c outside the sheet passing area of the print information of the first job from the temperature detected by the temperature detection sensor 7a in the sheet passing area of the print information of the first job is a predetermined value ( α) When below (substantially equivalent), the power supply units 31 to 33 are switched to voltage supply from all the power supply units 31 to 33 including the power supply unit having the lowest detected temperature.

  As described above, priority is given to voltage supply to the central portion A having the lowest detected temperature, and when the temperature in the vicinity of the central portion A becomes constant, the electrodes 11 to 13 including the electrode 11 to the central portion A. By supplying voltages to each of them simultaneously, it becomes possible to efficiently reach the target temperature.

  That is, according to the present embodiment, in the initial stage of starting up the fixing device 27, voltage is supplied only to the central part A having the lowest temperature, the central part A is started, and both end parts B and C are from the central part A. There is no timing to turn off the voltage until the target temperature is reached quickly and the central part A reaches the target temperature. Therefore, it becomes possible to reach the target temperature several seconds earlier than in the prior art. Therefore, the temperature distribution in the longitudinal direction is made uniform at the time of passing the large size sheet after passing the small size sheet while preventing the temperature rise at the end when passing the small size sheet, and the fixing property at both ends B and C is fixed. It is possible to prevent inconveniences such as defects and film breakage.

<Second Embodiment>
Next, a fixing device 27 according to a second embodiment of the present invention will be described with reference to FIGS. 13 (a) and 13 (b) to FIGS. 15 (a) and 15 (b). In the present embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and descriptions of components having the same configuration and function are omitted.

  FIG. 13A shows a state in which 60 seconds have passed since the small-size sheet is passed in the configuration example shown in FIG. 8, and the temperature distribution of the heating source 3 is uneven in the longitudinal direction or the sheet is conveyed. This is a case in which the temperature of both ends B and C is not uniform. Immediately after 80 small-size sheets are continuously fed in a state in which the temperature distribution of the heating source 3 is uneven within the tolerance in the longitudinal direction or the conveyance of the sheet is deviated within the tolerance, both ends B , C will heat up. As a result, the temperature at one end B is 220 ° C., the temperature at the other end C is 240 ° C., and the temperature at the center A is 200 ° C. Further, when 1 minute and 30 seconds elapse after passing 60 sheets, the whole is cooled, the one end B becomes 160 ° C., the other end C becomes 180 ° C., and the center A becomes 140 ° C.

  When the large-size sheet is fed after the small-size sheet is passed in the state where the temperature is uneven as described above, in order to flatten the temperature distribution of the fixing device 27, the voltage is preferentially applied to the lowest temperature portion. Is effectively switched to the target temperature. However, when the voltage is supplied in the order of electrode 11 → electrode 12 → electrode 13 as shown in FIG. 13 (b), it is supplied only at a constant period even in a portion where the temperature is low. Since there is a timing when voltage is not supplied, it is difficult to efficiently start up.

  FIG. 14A is a graph showing a temperature change when the voltage supply pattern shown in FIG. 13B is implemented.

  That is, when the voltage supply to each electrode is periodically performed as in the voltage supply pattern shown in FIG. 13B, the other end C first reaches the target temperature, and then the one end B reaches the target. The temperature reaches the temperature, and the standby state is maintained until the central portion A reaches the target temperature. On the other hand, since the voltage is supplied to the central part A having the lowest temperature only at a constant cycle every two half-waves, the rise is delayed compared to when the voltage is supplied only to the central part A. In this state, the central part A reaches the target temperature in 16 seconds.

  Therefore, in the present embodiment, as shown in FIG. 14B, voltage supply to the central portion A, which is the lowest point, is performed with priority, and the power supply portions 31 and 32 near the central portion A and one end B are disposed. When the temperature reaches a predetermined temperature α ° C. or lower, voltage supply to the power feeding unit 32 is performed. Then, when the temperature in the vicinity of the power feeding units 31 and 32 in the central part A and the one end B becomes equal to or lower than a predetermined temperature α ° C., voltage supply to the other end C is started, and the central part A and the one end B And voltage supply to all of the other end C.

  FIG. 14C is a graph showing a temperature change when voltage supply is performed with the voltage supply pattern of FIG. As shown in FIG. 14C, voltage is supplied only to the central portion A at 140 ° C. to 150 ° C., and at that time, the one end portion B is naturally cooled from 160 ° C. to 150 ° C. Therefore, the temperature difference between the central portion A and the one end B is 150 ° C. or less at a predetermined temperature α ° C. or less (substantially equivalent), and voltage supply to the central portion A and the one end B is started from this point. To do.

  And in 150 to 160 degreeC, the voltage supply to the center part A and the one end part B is performed, and the other end part C is naturally cooled from 180 degreeC to 160 degreeC at that time. Accordingly, at 160 ° C., the temperature difference between the central portion A and the one end portion B and the other end portion C is equal to or lower than a predetermined temperature α ° C. From this time point, the central portion A, the one end portion B, and the other end portion C. The voltage supply from all the electrodes 11, 12, 13 is started. Thereby, efficient start-up can be realized and the target temperature can be reached in 12 seconds. For this reason, it is possible to shorten the start-up time by Δ4 sec compared to the periodic start-up as in the voltage supply pattern shown in FIG.

  Next, the operation of the image forming apparatus 50 including the fixing device 27 according to the present embodiment will be described in detail with reference to the control flowchart of FIG.

  That is, in step S50, the control unit 700 receives print information (first print information) of the first job from the operation unit 100 or a host computer (not shown) (obtain first print information). The control unit 700 determines the sheet passing size from the print information, and starts energization from the electrode 11 having the lowest detected temperature based on the temperature detection information obtained from each of the power supply units 31, 32, and 33 (S51, S52). .

  After that, in step S53, the control unit 700 subtracts the temperature of the power supply unit having the second lowest temperature from the temperature of the power supply unit having the lowest temperature while starting the image forming operation. It is determined whether or not: If the predetermined temperature α ° C. or lower, the process proceeds to step S54. If the predetermined temperature α ° C. is exceeded, step S52 is repeated until the predetermined temperature α ° C. or lower.

  In step S54, energization is started from the electrode corresponding to the power supply unit having the lowest temperature and the electrode corresponding to the power supply unit having the second lowest temperature in the print area.

  In step S55, the control unit 700 subtracts the temperature of the power supply unit having the third lowest temperature from the temperature of the power supply unit having the second lowest temperature, and the result is equal to or lower than the predetermined temperature α ° C. (substantially equivalent). Judge whether there is. If the predetermined temperature α ° C. or lower, the process proceeds to step S56. If the predetermined temperature α ° C. is exceeded, step S54 is repeated until the predetermined temperature α ° C. or lower.

  In step S <b> 56, the control unit 700 starts voltage application from all of the electrodes 11, 12, and 13. After that, in step S57, the control unit 700 starts an image forming operation based on the print information (first print information) of the first job, and then ends the image forming operation based on the print information of the first job in step S58. To do. Also in this embodiment, the predetermined temperature α ° C. is a temperature within the tolerance of the temperature detection sensors 7a, 7b, and 7c.

  FIG. 15B summarizes the effects of the present embodiment. That is, as shown in FIG. 15B, in the initial stage of starting up the fixing device 27, only the central part A having the lowest temperature is supplied with voltage, and the central part A is started up. The second end portion B having the lowest temperature, the third end portion C having the lowest temperature, the temperature of the center portion A having the lowest temperature, and the temperature of the other end portion B and the other end portion C are constant. At this point, voltage supply is started. For this reason, there is no timing to turn off the voltage of each part until the central part A reaches the target temperature, so that the target temperature can be reached about 4 seconds earlier than in the prior art.

  In the present embodiment, when the temperature detected by the temperature detection sensor 7c is higher than the temperature detection sensor 7b, the control unit 700 is when the temperature detected by the temperature detection sensor 7a is lower than any of the temperature detection sensors 7b and 7c. The power is fed only from the power feeding unit 31. When a sheet having a size larger than the size of the sheet that has been passed through the fixing nip N is passed, the difference between the detected temperature of the temperature detecting sensor 7a and the detected temperature of the temperature detecting sensor 7b is equal to or less than a predetermined value (α). The power is supplied from the power supply unit 31 and the power supply unit 32 at the point of time (substantially equivalent). Furthermore, when the difference between the detected temperature of the temperature detection sensor 7b and the detected temperature of the temperature detection sensor 7c becomes equal to or less than a predetermined value, control is performed to supply power from all of the power supply units 31 to 33.

  According to the present embodiment described above, as in the first embodiment, the voltage supply to the part having the lowest temperature is given priority, and when the temperature in the vicinity of the electrodes becomes constant, each electrode is simultaneously advanced. It becomes possible to supply voltage. For this reason, it is possible to achieve an efficient startup target and efficiently reach the target temperature. This prevents temperature rise at the edge when passing through small-size sheets, while making the temperature distribution in the longitudinal direction uniform when passing through large-size sheets, preventing problems such as poor edge fixability and film breakage. It becomes possible to do.

<Third Embodiment>
Next, a fixing device 27 according to a third embodiment of the present invention will be described with reference to FIGS. 16 (a), 16 (b), 17 and 18. FIG. Also in this embodiment, the control block diagram of FIG. 7 and FIG. 8 showing the heating source 3 having the power feeding units 31 to 33 are also referred to. In the present embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and descriptions of components having the same configuration and function are omitted.

  When passing a large-size sheet after passing a small-size sheet in a state where there is temperature unevenness, in order to flatten the fixing temperature distribution, a voltage is preferentially supplied to the central portion A where the temperature is low, It is efficient to switch to the target temperature. However, for example, when the voltage is supplied in the order of the electrode 11 → the electrode 12 → the electrode 13, the time when the one end B and the other end C having the high temperature reach the target temperature quickly and are turned off for a certain time. Occurs (see FIG. 13B). Therefore, when voltage is supplied in the order of electrode 11 → electrode 12 → electrode 13, there is a possibility that power unevenness occurs between the electrode 11 that requires voltage supply and the electrodes 12 and 13 that do not require voltage supply and flicker occurs. .

  Therefore, in this embodiment, in order to solve this problem, in the heating source 3 having the power feeding units 31 to 33, when switching the power feeding unit by switching, the total power (total power) input from the power feeding unit before switching. And the difference between the total power (total power) from the power feeding unit after switching is controlled to be within a predetermined value. For example, the predetermined power difference is within 25% of the power before switching, or the PST value (10 minute flicker value) is 1 or less in measurement using a flicker meter (not shown). Can do.

  For example, there are two heaters (heating elements), and each heater may be used when passing a small size sheet and when passing a large size sheet. It is difficult to remove, and it is necessary to wait until the temperature of the end portion is lowered due to heat radiation and the temperature difference between the central portion A and the one end portion B and the other end portion C disappears. On the other hand, in this embodiment, it is possible to control even in a state where there is a temperature difference, it is possible to shorten the time, and it is possible to suppress voltage unevenness during switching (FIG. 17A). , (B)). In FIG. 17B, a broken line indicates a temperature change in the improvement 1 when the control according to the present embodiment is not performed, and ◇ indicates a temperature change at the one end B in the improvement 2 when the control according to the present embodiment is performed. Show. Further, □ indicates the temperature change of the central portion A in the improvement 2 when the control of the present embodiment is performed, and Δ indicates the temperature change of the other end portion C in the improvement 2 when the control of the present embodiment is performed.

  In the present embodiment, the control unit 700 applies a voltage to the power supply unit corresponding to the detection sensor having the lowest detection temperature among the temperature detection sensors 7a to 7c, and the temperature of the power supply unit corresponding to the detection sensor having the lowest detection temperature. When the temperature other than the power supply unit matches, control is performed so that the same voltage is applied simultaneously from all the power supply units having the same temperature. The control unit 700 controls the power from the power feeding unit before switching to be reduced so that the power difference before and after switching of the power feeding units 31 to 33 is equal to or less than a predetermined power difference. In the present embodiment, as described above, the predetermined power difference is a value within 25% of the power before switching, or the PST value (flicker value for 10 minutes) is 1 in the measurement using the flicker meter. Control to be the following values.

  That is, in the power supply control, the control unit 700 according to the present embodiment supplies the power from all of the power supply units 31 to 33, and supplies the total power supplied from the power supply unit before switching among the power supply units 31 to 33, and after the switching. Control is performed such that the difference from the total amount of power supplied from the power supply unit is equal to or less than a predetermined power difference. That is, the control unit 700 performs control so as to reduce the power from the power supply unit before switching through the heater control unit 118 so that the power difference before and after switching of the power supply units 31 to 33 is equal to or less than a predetermined power difference. To do. As a result, control can be performed even in the presence of a temperature difference, time can be shortened, and voltage unevenness during switching does not occur.

  Here, FIGS. 16A and 16B show heaters that apply a voltage from a power source (AC power source) 35 to any one of the central portion A, one end portion B, and the other end portion C in the longitudinal direction of the heating source 3. It is a figure which shows the specific structure of the changeover switch 37 (refer FIG. 7) of the control part 118. FIG.

  In FIG. 16 (a), one power source 35 is connected in series to each change-over switch 37 connected to the electrodes 11, 12, 13 corresponding to the center A, one end B, and the other end C, respectively. Yes. In FIG. 16B, one power source 35 is connected in parallel to each changeover switch 37 connected to the electrodes 11, 12, 13 corresponding to the central portion A, one end portion B, and the other end portion C. ing. In these cases, the changeover switch 37 can be a mechanical switch or a semiconductor switch such as Triac (registered trademark).

  Next, the operation of the image forming apparatus 50 including the fixing device 27 according to the present embodiment will be described in detail with reference to a control flowchart shown in FIG.

  That is, in step S70, the control unit 700 having the CPU 701 receives print information (first print information) of the first job from the operation unit 100 or a host computer (not shown) (obtain first print information). In addition, the control unit 700 obtains temperature detection information of each of the power feeding units 31, 32, and 33, selects a pattern in which an AC voltage is applied, and an electrode to be supplied among the electrodes 11 to 13, and selects the selected electrode. The energization from is started (S71, S72).

  Thereafter, in step S73, the control unit 700 starts an image forming operation based on the print information (first print information) of the first job, and then ends the image forming operation based on the print information of the first job in step S74. To do.

  Subsequently, in step S75, the control unit 700 receives print information (second print information) of the second job from the operation unit 100 or the host computer (not shown) (obtain second print information). Then, the control unit 700 compares the sheet size of the second print information with the sheet size of the first print information (S76), and when the sheet size of the second print information is equal to or smaller than the sheet size of the first print information. Then, the energization pattern of the first print information is continued (S77). In step S78, energization from the selected electrode is started.

  After that, in step S79, the control unit 700 starts an image forming operation based on the print information (second print information) of the second job, and then ends the image forming operation based on the print information of the second job in step S80. To do.

  On the other hand, as a result of comparing the sheet size of the second print information with the sheet size of the first print information in step S76, the control unit 700 finds that the sheet size of the second print information is larger than the sheet size of the first print information. In the case, first, the detection temperatures by the temperature detection sensors 7a to 7c of the power feeding units 31 to 33 are obtained (S81).

  In step S82, the controller 700 determines whether or not a value (temperature difference) obtained by subtracting the detected temperature at the center A from the detected temperatures at both ends B and C is equal to or lower than a predetermined temperature α ° C. As a result, when the temperature difference is equal to or lower than the predetermined temperature α ° C., the control unit 700 starts voltage application from the electrodes 11, 12, and 13 (S83).

  Thereafter, in step S84, whether or not the control unit 700 subtracts the total power supplied before switching the energization pattern and the total power applied from the electrodes 11 to 13 after switching is equal to or less than a predetermined power. Judging. As a result, if the subtracted value is equal to or less than the predetermined power, the process proceeds to step S85. If the subtracted value exceeds the predetermined voltage, steps S83 and S84 are repeated while adjusting the voltage in step S87.

  In step S85, the control unit 700 starts an image forming operation based on the print information (second print information) of the second job, and then ends the image forming operation based on the print information of the second job in step S86. To do.

  On the other hand, if the temperature difference exceeds the predetermined temperature α ° C. as a result of the comparison in step S82, the control unit 700 determines an energization pattern (S87) and starts voltage application only from the electrode 11 corresponding to the central part A. (S88). Then, the control unit 700 determines whether or not a value (temperature difference) obtained by subtracting the detected temperature at the central portion A from the detected temperatures at both ends B and C is equal to or lower than a predetermined temperature α ° C. (S89). Further, the control unit 700 repeats steps S87 and S88 until the temperature difference becomes equal to or lower than the predetermined temperature α ° C. When the temperature difference becomes lower than the predetermined temperature α ° C, the control unit 700 proceeds to step S83 and performs the same processing as described above. Perform (S84, S85, S86, S87).

  According to the above embodiment, substantially the same effect as that of the first embodiment can be obtained, control can be performed even in a temperature difference state, time can be shortened, and voltage unevenness during switching can be achieved. Can also be deterred.

  In the first to third embodiments described above, the temperature detection sensor 7a is the first temperature detection means and the temperature detection sensors 7b and 7c are the second temperature detection means. However, the present invention is not limited to this configuration. Absent. That is, other temperature detection sensors including the temperature detection sensor 7a are arranged and configured as the first temperature detection means, and other temperature detection sensors including the temperature detection sensors 7b and 7c are arranged and configured as the second temperature detection means. It is also possible to do.

  2 ... Pressure roller (pressure rotator) / 3 ... Heat source (heating element) / 4 ... Fixing film (heating rotator, heating belt) / 7a ... Temperature detection sensor (first temperature detection means) / 7b ... Temperature Detection sensor, one end side temperature detection means (second temperature detection means) / 7c ... temperature detection sensor, other end side temperature detection means (second temperature detection means) / 17 ... heating unit / 19, 20, 23 ... charging roller, Photosensitive drum, developing sleeve (image forming means) / 25... Transfer roller (transfer means) / 27... Fixing device (fixing means) / 31... Power feeding section (first power feeding section) / 32. (Second power supply unit) / 33... Power supply unit, other end side power supply unit (second power supply unit) / 50... Image forming apparatus / 700... Control unit (control means) / Ar1. Paper area / N ... fixing nip / P ... sheet / α ... predetermined temperature (place Value)

Claims (10)

A heating rotator for heating the toner image on the sheet;
A pressure rotator disposed opposite to the heating rotator;
A heating unit that extends in the axial direction of the rotator inside the heating rotator and forms a fixing nip portion that conveys the sheet while heating the sheet while sandwiching the heating rotator with the pressure rotator. When,
Control means for controlling the heating unit,
The heating unit is
A heating element extending in the axial direction;
First temperature detection means for detecting a temperature of a sheet passing region through which a sheet of a predetermined size passes in the longitudinal direction of the heating element;
Second temperature detecting means for detecting the temperature of the non-sheet passing region on the longitudinal end side of the heating element that is out of the sheet passing region;
A first power feeding unit that feeds power to the heating element from a position corresponding to the paper passing area; and a second power feeding unit that feeds power to the heating element from a position corresponding to the non-paper passing area;
The control means includes
Based on the detection results of the first and second temperature detection means, power is preferentially supplied to the first power supply unit corresponding to the first temperature detection means, and the detection temperatures of the first and second temperature detection means are detected. When the difference is equal to or less than a predetermined value, power supply control is performed to supply power from both the first and second power supply units.
A fixing device. The first temperature detection means is disposed at a central portion in the longitudinal direction of the heating element,
The second temperature detecting means is arranged as one end side temperature detecting means and the other end side temperature detecting means at both ends in the longitudinal direction of the heating element, respectively.
The second power supply unit is arranged as one end side power supply unit corresponding to the one end side temperature detection unit and the other end side power supply unit corresponding to the other end side temperature detection unit,
The fixing device according to claim 1. The control means includes
When there is no difference between the detected temperatures of the one end side temperature detection means and the other end side temperature detection means, the detection temperature of the first temperature detection means is lower than the detection temperature of the one end side temperature detection means or the other end side temperature detection means When a sheet having a size larger than that of the sheet previously fed to the fixing nip portion is fed from only the first feeding portion, the detected temperature of the first temperature detecting means and the one end side and the other end are passed. When the difference from the detected temperature of the side temperature detecting means becomes equal to or less than the predetermined value, power is supplied from all of the first power supply unit, the one end side power supply unit, and the other end side power supply unit,
The fixing device according to claim 2. The control means includes
When the detected temperature of the other end side temperature detecting unit is higher than that of the one end side temperature detecting unit, the detected temperature of the first temperature detecting unit is lower than the detected temperature of either the one end side or the other end side temperature detecting unit. Sometimes when the power is fed only from the first power feeding unit, the first power feeding unit is turned on when the difference between the detected temperature of the first temperature detecting unit and the detected temperature of the one end side temperature detecting unit becomes equal to or less than the predetermined value. When the difference between the detected temperature of the one end side temperature detecting means and the detected temperature of the other end side temperature detecting means becomes equal to or less than the predetermined value, the first feeding section and Power is supplied from all of the one end side power supply unit and the other end side power supply unit,
The fixing device according to claim 2. The predetermined value is a value of a tolerance range of the first temperature detection means and the second temperature detection means.
The fixing device according to any one of claims 1 to 4, wherein the fixing device is characterized in that: In the power supply control, the control unit supplies power from all of the first, second, and third power supply units and supplies power from the power supply unit before switching among the first, second, and third power supply units. And the difference between the total power supplied from the power supply unit after switching is controlled to be equal to or less than a predetermined power difference,
The fixing device according to claim 1, wherein The control means controls the power from the power supply unit before switching to be lowered so that the power difference before and after switching of the power supply unit is equal to or less than the predetermined power difference.
The fixing device according to claim 6. The predetermined power difference is within 25% of the power before the switching, or a PST value is 1 or less in measurement using a flicker meter,
The fixing device according to claim 6 or 7, wherein: The heating rotator is an endless heating belt,
The fixing device according to claim 1, wherein Image forming means for forming an image on a sheet;
Fixing means for fixing the toner image formed on the sheet,
The fixing device is the fixing device according to any one of claims 1 to 9.
An image forming apparatus.

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