JP2009282335A - Fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which can perform temperature control with a favorable fast-response and high accuracy by preventing delay time due to overshoot for control temperature, and which can achieve uniform fixability by suppressing occurrence of unevenness in heating, as a belt fixing device using a planar heating element. <P>SOLUTION: A control means 90 controls power supply to resistance heating elements 22, 25 and 28 forming a plurality of heating patterns divided in a longitudinal direction of the planar heating element 20. In the control means 90, a detection unit 92 detects a current value flowing though each resistace heating element and an applied voltage value. Then, an electric power calculation section 93 calculates an electric power value from the current value and the voltage value detected by the detection section 92. Furthermore, a power supply control section 33 controls power supply to each resistance heating element so that the surface of the fixing belt 64 is heated by each resistance heating element to a prescribed temperature range based on the calculated electric power value calculated by the electric power calculating section 93. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device including a heating member having a planar heating element and an image forming apparatus including the fixing device.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a heat roller fixing type fixing device is frequently used. A heat roller fixing type fixing device includes a pair of rollers (fixing roller and pressure roller) that are in pressure contact with each other, and the roller is heated by a heating unit including a halogen lamp or the like disposed inside or both of the roller pair. After the pair is heated to a predetermined temperature (fixing temperature), a recording medium such as a recording sheet on which a fixed toner image is formed is fed to the pressure contact portion (fixing nip portion) of the roller pair and passed through the pressure contact portion. The toner image is fixed on the recording paper by heat and pressure.

  By the way, in a fixing device provided in a color image forming apparatus, it is common to use an elastic roller provided with an elastic layer made of silicon rubber or the like on the surface of the fixing roller. By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed corresponding to the unevenness of the unfixed toner image, and comes into contact so as to cover the toner image surface. It is possible to perform heat fixing on an unfixed toner image satisfactorily. In addition, due to the strain relief effect of the elastic layer at the fixing nip, it is possible to improve the releasability for color toners that are more likely to be offset than in monochrome. Further, since the nip shape of the fixing nip is convex upward (on the fixing roller side) (so-called reverse nip shape), it is possible to improve the recording paper peeling performance without using a peeling means such as a peeling claw. The recording paper can be peeled off (self-stripping), and image defects caused by the peeling means can be eliminated.

  Incidentally, in the fixing device provided in such a color image forming apparatus, it is necessary to widen the nip width of the fixing nip portion in order to cope with the high speed. As a method for widening the nip width, there are methods such as increasing the thickness of the elastic layer of the fixing roller and increasing the diameter of the fixing roller. However, in a fixing roller having an elastic layer, since the thermal conductivity of the elastic layer is very low, there is a problem that the temperature of the fixing roller does not follow when the process speed is increased when there is a heating means inside the fixing roller. is there. On the other hand, when the diameter of the fixing roller is increased, there are problems that the warm-up time becomes longer and the power consumption increases.

  As a fixing device provided in a color image forming apparatus that solves such a problem, Patent Document 1 discloses that a fixing belt is stretched between a fixing roller and a heating roller, and the fixing roller and the pressure roller are interposed via the fixing belt. A belt-fixing type fixing device having a configuration in which the two are in pressure contact with each other is disclosed. In this belt fixing type fixing device, since the fixing belt having a small heat capacity is heated, the warm-up time is short, and it is not necessary to incorporate a heat source such as a halogen lamp in the fixing roller. A thick elastic layer can be provided, and a wide nip width can be secured.

  Further, Patent Document 2 discloses a fixing device using a sheet heating belt fixing method in which a heating unit is a sheet heating element in a belt fixing method fixing device. In this surface heating belt fixing type fixing device, the heat capacity of the heating means is reduced, and at the same time, the surface heating element as the heating means directly generates heat, so the heating roller is indirectly heated using a halogen lamp or the like. Compared with the method, the thermal response speed is improved, and the warm-up time can be further shortened and further energy saving can be achieved.

  Various image forming devices such as printers using the belt fixing type fixing device with a small heat capacity as described above eliminates the need for preheating during standby and eliminates waiting time due to high heating efficiency and rising speed. It is expected to be introduced not only to small and low speed machines but also to large and high speed machines.

  Further, in Patent Document 3, in a fixing roller type fixing device using a planar heating element, the temperature state of the planar heating element is read from a change in electric resistance value of the planar heating element itself, and the set temperature of the fixing roller is read. A technique for controlling the temperature by comparing with the reference temperature of the planar heating element is disclosed.

  However, since the electrical resistance value of the planar heating element itself has a certain tolerance, and the applied voltage also has a tolerance, the amount of power supplied to the planar heating element varies. Therefore, variation occurs in the temperature of the planar heating element. Further, when the planar heating element is a heating element made of a ceramic heater, the heat capacity is large, so that the rate of temperature rise is slow and the immediate heat property cannot be achieved. Therefore, there is a problem in controlling the temperature only from the electric resistance value of the ceramic heater.

  Further, when the fixing device is adapted to high-speed recording while supporting recording papers of various sizes, a problem called non-sheet passing portion temperature rise occurs. This is because the temperature of the fixing nip portion in a non-passing area (non-passing area) of the recording paper when continuously passing a small-sized recording paper having a small width with respect to the longitudinal direction of the heating member of the fixing device. If the temperature rises excessively and exceeds the heat resistance temperature of the peripheral members, damage to the fixing device may be caused by heat deformation or local expansion of the pressure roller, and then the normal size recording paper is passed. Further, fixing unevenness occurs in the longitudinal direction, and wrinkles are caused due to uneven conveyance of the recording paper. In particular, when the heat capacity of the fixing roller is reduced in order to shorten the warm-up time, the thermal conductivity in the paper width direction is lowered, and this problem becomes more remarkable.

  Such a non-sheet passing portion temperature rise can be dealt with by reducing the fixing speed and throughput only when passing a small size recording paper, or by temporarily stopping printing and cooling. In either case, print productivity for small-size recording paper is reduced. Further, in a fixing device in which the heat source is a halogen lamp, a general method is to cope with a non-sheet passing portion temperature rise by using a plurality of lamps corresponding to the paper width.

  Even in a belt fixing type fixing device, the temperature rise in the non-sheet passing portion is a serious problem. Particularly, since a fixing belt having a low heat capacity is used, the pressure roller in the non-sheet passing portion expands and is not There is also a problem in that the belt conveying force of the paper passing portion becomes higher than that of the paper passing portion, and the fixing belt is unevenly conveyed in the longitudinal direction, causing the fixing belt to be damaged.

  As a heating device that solves such a problem of temperature rise in the non-sheet-passing portion, Patent Document 4 uses a planar heating element as a heating element, and provides a plurality of heating elements according to the size of the recording paper. A technique for controlling the temperature of a heating body based on a temperature detected by a contact thermistor attached to a part is disclosed.

JP-A-10-30796 JP 2002-333788 A JP 58-192065 A JP 2002-151232 A

  However, when the heating device disclosed in Patent Document 4 is applied to a device for heating a fixing belt of a belt fixing device, there are the following problems.

  That is, in the configuration in which the temperature of each heat generating part is detected by a contact thermistor as in the heating device disclosed in Patent Document 4, the response time until detection usually takes 2 to 3 seconds or more. In a fixing device having a slow rise time of 30 to 40 seconds, even the above response time does not cause a problem. In particular, in a fixing device provided in a high-speed image forming apparatus, the response time is low in the above response time. Therefore, when the rate of temperature rise is fast, there is a problem that overshoot and undershoot with respect to the control temperature become prominent, and heating unevenness may occur.

  Further, as described above, since the electrical resistance value of the planar heating element itself has a certain tolerance, and the applied voltage also has a tolerance, the amount of power supplied to the planar heating element varies. When the applied voltage is low, the temperature rise in the planar heating element is fast, and conversely, when the applied voltage is high, the temperature rise is slow. The tolerance of the electric resistance value and the applied voltage tolerance of the planar heating element itself increase the variation of the temporal variation of the temperature of the planar heating element such as overshoot, resulting in uneven heating.

  Further, in the configuration in which the contact type thermistor is disposed in contact with the surface of the fixing member, the contact type thermistor may wear the surface release layer of the fixing belt at the interface where the fixing member contacts the fixing belt. In this way, when the surface release layer of the fixing belt is damaged or deteriorated, the influence is exerted on the image, resulting in a poor image.

  Accordingly, an object of the present invention is to avoid a delay time due to an overshoot with respect to a control temperature in a belt fixing device using a planar heating element, and to enable highly accurate temperature control with good responsiveness and uneven heating. It is an object of the present invention to provide a fixing device that can suppress occurrence and achieve uniform fixing properties. Another object of the present invention is to provide an image forming apparatus provided with the fixing device.

The present invention includes an endless fixing belt stretched between a fixing member and a heating member, and a pressure member facing the fixing member via the fixing belt, the heating member including the fixing belt A fixing device that heats and fixes a toner image carried on a recording medium on a recording medium at a fixing nip formed by the fixing belt and the pressure member by contacting and heating the fixing belt. There,
In the heating member that heats the fixing belt in contact with the fixing belt in the heating member, a resistance heating element that generates heat when energized forms a heat generating pattern by forming a surface having a certain shape as a whole. A planar heating element formed on one surface in the thickness direction is formed,
The heat generation pattern is divided into a plurality in the longitudinal direction of the insulating layer, and a plurality of the heat generation patterns are formed, and in a state of being distinguished from each other, energization is controlled by a control unit,
The control means includes
A detection unit for detecting a current value and a voltage value applied to each resistance heating element constituting the plurality of heat generation patterns;
A power calculator that calculates a power value from the current value and the voltage value detected by the detector;
Based on the calculated power value calculated by the power calculation unit, power supply control for controlling power supply to the resistance heating element such that each resistance heating element constituting the plurality of heating patterns generates heat within a predetermined temperature range. A fixing device.

The present invention further includes an endless fixing belt stretched between the fixing member and the heating member, and a pressure member facing the fixing member via the fixing belt, and the heating member is the fixing belt. Fixing device that heats and fixes a toner image carried on a recording medium on a recording medium in a fixing nip portion formed by the fixing belt and the pressure member in contact with the fixing belt to heat the fixing belt Because
In the heating member that heats the fixing belt in contact with the fixing belt in the heating member, a resistance heating element that generates heat when energized forms a heat generating pattern by forming a surface having a certain shape as a whole. A planar heating element formed on one surface in the thickness direction is formed,
The heat generation pattern is divided into a plurality in the longitudinal direction of the insulating layer, and a plurality of the heat generation patterns are formed, and in a state of being distinguished from each other, energization is controlled by a control unit,
The control means includes
A detection unit for detecting a voltage value applied to each resistance heating element constituting the plurality of heating patterns;
A power calculation unit that calculates a power value from the voltage value detected by the detection unit and a specific electrical resistance value of the resistance heating element;
Based on the calculated power value calculated by the power calculation unit, power supply control for controlling power supply to the resistance heating element such that each resistance heating element constituting the plurality of heating patterns generates heat within a predetermined temperature range. A fixing device.

Further, in the present invention, the resistance heating element of the planar heating element has a positive resistance temperature characteristic,
The power supply control unit applies power to the resistance heating element when the calculated power value calculated by the power calculation unit is equal to or lower than a preset power value based on an electrical resistance value at a predetermined temperature of the resistance heating element. The power supply is interrupted, and the power supply to the resistance heating element is resumed when the temperature of the resistance heating element reaches a predetermined temperature.

Further, the present invention comprises a non-contact temperature detecting means for detecting the temperature of the surface of the fixing belt in a non-contact state with respect to the fixing belt,
The control means controls energization to the planar heating element based on the temperature detected by the non-contact temperature detecting means.

In the present invention, the resistance heating element
Extending in a direction substantially orthogonal to the longitudinal direction of the insulating layer, a plurality of linear portions formed on one surface of the insulating layer in a substantially parallel state,
A connecting portion formed on one surface of the insulating layer by connecting adjacent end portions of the linear portions in the longitudinal direction of the insulating layer so as to form one line. ,
The extending direction of the plurality of linear portions is inclined at a predetermined angle with respect to the longitudinal direction of the planar heating element.

  Further, in the planar heating element, the interval between a plurality of adjacent linear portions is smaller in a predetermined region at both longitudinal ends of the planar heating element as the distance from the central portion toward both ends is increased. It is set so that it may become.

Moreover, this invention is a heating part of the said heating member,
A planar heating element is formed on one surface of a base material made of a material having high thermal conductivity,
A coating layer capable of reducing the frictional force with the fixing belt is formed on the surface in contact with the fixing belt.

  In the invention, it is preferable that the coating layer is made of at least one of PTFE resin and PFA resin containing fluorine.

  According to another aspect of the present invention, there is provided an image forming apparatus comprising the fixing device.

  According to the present invention, the planar heating element is formed in the heating portion of the heating member that heats the fixing belt. The planar heating element is formed by forming a resistance heating element that forms a heating pattern by forming a surface having a certain shape as a whole on one surface in the thickness direction of the insulating layer. A plurality of heat generation patterns are formed by being divided in the longitudinal direction of the insulating layer, and energization is controlled by the control means in a state of being distinguished from each other. And in the said control means, a detection part detects the electric current value which flows into each resistance heating element which comprises a several heat_generation | fever pattern, and the applied voltage value. Then, the power calculation unit calculates a power value from the current value and the voltage value detected by the detection unit. Furthermore, the power supply control unit supplies power to the resistance heating element based on the calculated power value calculated by the power calculation unit so that each resistance heating element forming the plurality of heat generation patterns generates heat within a predetermined temperature range. To control.

  In this way, power feeding to each resistance heating element constituting a plurality of heat generation patterns is controlled, so that even if the resistance value of the resistance heating element has a tolerance and the applied voltage also has a tolerance, the resistance By accurately grasping fluctuations in the amount of electric power supplied to the heating element, it is possible to suppress an increase in variation in temporal fluctuations in the temperature of the resistance heating element such as overshoot. Therefore, it is possible to avoid a delay time due to overshoot with respect to the control temperature of the resistance heating element, and to perform highly accurate temperature control with good responsiveness. Accordingly, it is possible to provide a fixing device capable of achieving uniform fixing performance by suppressing the occurrence of uneven heating when the fixing belt is heated by heat generated by the planar heating element.

  According to the invention, in the control means, the detection unit detects a voltage value applied to each resistance heating element constituting the plurality of heat generation patterns. Then, the power calculation unit calculates a power value from the voltage value detected by the detection unit and the specific electrical resistance value of the resistance heating element. Furthermore, the power supply control unit supplies power to the resistance heating element based on the calculated power value calculated by the power calculation unit so that each resistance heating element forming the plurality of heat generation patterns generates heat within a predetermined temperature range. To control.

  In this way, power feeding to each resistance heating element constituting a plurality of heat generation patterns is controlled, so that even if the resistance value of the resistance heating element has a tolerance and the applied voltage also has a tolerance, the resistance By accurately grasping fluctuations in the amount of electric power supplied to the heating element, it is possible to suppress an increase in variation in temporal fluctuations in the temperature of the resistance heating element such as overshoot. Therefore, it is possible to avoid a delay time due to overshoot with respect to the control temperature of the resistance heating element, and to perform highly accurate temperature control with good responsiveness. Accordingly, it is possible to provide a fixing device capable of achieving uniform fixing performance by suppressing the occurrence of uneven heating when the fixing belt is heated by heat generated by the planar heating element.

  According to the present invention, the resistance heating element of the planar heating element has a positive resistance temperature characteristic. A resistance heating element having a positive resistance temperature characteristic has a larger electrical resistance value as the temperature rises. For this reason, the value of the current flowing through the heating element is reduced, and the amount of power is reduced. In the control means for controlling the energization of the resistance heating element having such a positive resistance temperature characteristic, the power supply control unit is configured such that the calculated power value calculated by the power calculation unit becomes an electric resistance value at a predetermined temperature of the resistance heating element. Based on the preset power value that is set in advance, the power supply to the resistance heating element is cut off. In this way, the power supply control unit cuts off the power supply to the resistance heating element when it becomes equal to or lower than the set power value, and avoids a delay time due to an overshoot with respect to the control temperature of the resistance heating element.

  According to the invention, the non-contact temperature detecting means for detecting the temperature of the surface of the fixing belt in a non-contact state with respect to the fixing belt is provided. As a result, the temperature of the surface of the fixing belt can be detected while preventing the surface of the fixing belt from being worn. And a control means controls electricity supply with respect to a planar heating element based on the temperature which the non-contact temperature detection means detected. As a result, the control means controls the energization to the sheet heating element including not only the calculated power value calculated by the power calculation unit but also the temperature detected by the non-contact temperature detection means. Can be performed with higher accuracy.

  According to the present invention, the resistance heating element includes a linear portion and a connection portion. The linear portion extends in a direction substantially orthogonal to the longitudinal direction of the insulating layer, and is formed on one surface of the insulating layer in a substantially parallel state. Further, the connecting portion is formed on one surface of the insulating layer by connecting the end portions in the extending direction of the adjacent linear portions so as to extend in the longitudinal direction of the insulating layer to form one line. Furthermore, the extending direction of the linear portion is inclined at a predetermined angle with respect to the longitudinal direction of the planar heating element. In this way, by forming the linear portion so that the extending direction of the linear portion is inclined with respect to the longitudinal direction of the planar heating element, the portion of the planar heating element that generates a small amount of heat and the portion that does not generate heat The temperature drop can be compensated for, and the temperature distribution of the fixing belt to which heat is transmitted from the planar heating element can be made uniform.

  Further, according to the present invention, in the planar heating element, the interval between the adjacent linear parts is within a predetermined region at both ends in the longitudinal direction of the planar heating element, as it goes from the central part to both end parts. It is set to be smaller. Thereby, the power density in the predetermined region can be increased. Therefore, it is possible to make uniform the temperature distribution in the longitudinal direction of the planar heating element by suppressing the heat dissipation loss from both ends corresponding to the predetermined region of the planar heating element. Accordingly, it is possible to realize uniform fixing properties with respect to the toner image on the recording medium.

  Moreover, according to this invention, the heating part of a heating member forms a planar heating element in the one surface of the base material which consists of material which has high heat conductivity. A coat layer capable of reducing the frictional force with the fixing belt is formed on the surface of the heating unit that contacts the fixing belt. As a result, the frictional force between the heating member and the fixing belt can be reduced, and the fixing belt can be prevented from being worn and high durability of the fixing belt can be ensured.

  Further, according to the present invention, it is possible to realize a coat layer capable of reducing the frictional force between the heating member and the fixing belt by using a material comprising at least one of PTFE resin and PFA resin containing fluorine. it can.

  According to the invention, the image forming apparatus is realized by including the fixing device.

  FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 is an apparatus that forms multicolor and single color images on recording paper based on image data of a read original document or image data transmitted via a network or the like. The image forming apparatus 100 includes an exposure unit 10, a photosensitive drum 101 (101a to 101d), a developing device 102 (102a to 102d), a charging roller 103 (103a to 103d), a cleaning unit 104 (104a to 104d), and an intermediate transfer belt. 11, a primary transfer roller 13 (13a to 13d), a secondary transfer roller 14, a fixing device 15, paper transport paths P1, P2, and P3, a paper feed cassette 16, a manual paper feed tray 17, and a paper discharge tray 18. .

  The image forming apparatus 100 corresponds to the hues of four colors of cyan (C), magenta (M), and yellow (Y), which are three subtractive primary colors obtained by color separation of black (K) and a color image. Using the image data, image formation is performed in the image forming units Pa to Pd corresponding to each hue. Each of the image forming portions Pa to Pd has the same configuration. For example, the black (K) image forming portion Pa includes a photosensitive drum 101a, a developing device 102a, a charging roller 103a, a transfer roller 13a, a cleaning unit 104a, and the like. Composed. The image forming portions Pa to Pd are arranged in a line in the moving direction (sub-scanning direction) of the intermediate transfer belt 11.

  The charging roller 103 is a contact-type charger that uniformly charges the surface of the photosensitive drum 101 to a predetermined potential. Instead of the charging roller 103, a contact type charger using a charging brush or a non-contact type charger using a charging wire may be used.

  The exposure unit 10 includes a semiconductor laser (not shown), a polygon mirror 4, a first reflection mirror 7, a second reflection mirror 8, and the like. Black (K), cyan (C), magenta (M), and yellow (Y). Each of the photosensitive drums 101a to 101d is irradiated with a light beam such as a laser beam modulated by the image data of each hue. Each of the photosensitive drums 101a to 101d forms an electrostatic latent image based on image data of each hue of black (K), cyan (C), magenta (M), and yellow (Y).

  The developing device 102 supplies toner as a developer to the surface of the photosensitive drum 101 on which the electrostatic latent image is formed, and develops the electrostatic latent image into a toner image. Each of the developing devices 102a to 102d contains toner of each hue of black (K), cyan (C), magenta (M), and yellow (Y), and is formed on each of the photosensitive drums 101a to 101d. The electrostatic latent image of each hue is visualized into a toner image of each hue. The cleaning unit 104 removes and collects toner remaining on the surface of the photosensitive drum 101 after development and image transfer.

  The intermediate transfer belt 11 is disposed above the photosensitive drum 101, and is stretched between the driving roller 11a and the driven roller 11b to form a loop-shaped moving path. The outer peripheral surface of the intermediate transfer belt 11 faces the photosensitive drum 101d, the photosensitive drum 101c, the photosensitive drum 101b, and the photosensitive drum 101a in this order. Primary transfer rollers 13a to 13d are arranged at positions facing the respective photosensitive drums 101a to 101d with the intermediate transfer belt 11 interposed therebetween. Each of the positions where the intermediate transfer belt 11 faces the photosensitive drums 101a to 101d is a primary transfer position. The intermediate transfer belt 11 is formed of a film having a thickness of about 100 to 150 μm.

  The primary transfer rollers 13a to 13d have constant voltage control of a primary transfer bias opposite to the charging polarity of the toner in order to transfer the toner images carried on the surfaces of the photosensitive drums 101a to 101d onto the intermediate transfer belt 11. Applied. As a result, the toner images of the respective colors formed on the photosensitive drums 101a to 101d are sequentially transferred onto the outer peripheral surface of the intermediate transfer belt 11, and a full-color toner image is formed on the outer peripheral surface of the intermediate transfer belt 11. .

  However, when image data of only a part of the hues of yellow (Y), magenta (M), cyan (C), and black (K) is input, input is performed among the four photosensitive drums 101a to 101d. The electrostatic latent image and the toner image are formed only on a part of the photoconductors 101 corresponding to the hue of the image data. For example, when forming a monochrome image, an electrostatic latent image and a toner image are formed only on the photosensitive drum 101a corresponding to the black hue, and only the black toner image is transferred to the outer peripheral surface of the intermediate transfer belt 11. Is done.

  Each of the primary transfer rollers 13a to 13d is configured by covering the surface of a shaft whose base is a metal such as stainless steel having a diameter of 8 to 10 mm with a conductive elastic material (for example, EPDM, urethane foam, etc.). A high voltage is uniformly applied to the intermediate transfer belt 11 by the elastic material.

  The toner image transferred to the outer peripheral surface of the intermediate transfer belt 11 at each primary transfer position is conveyed to a secondary transfer position that is a position facing the secondary transfer roller 14 by the rotation of the intermediate transfer belt 11. The secondary transfer roller 14 is pressed against the outer peripheral surface of the intermediate transfer belt 11 whose inner peripheral surface is in contact with the peripheral surface of the driving roller 11a at a predetermined nip pressure during image formation. When the recording paper fed from the paper feed cassette 16 or the manual paper feed tray 17 passes between the secondary transfer roller 14 and the intermediate transfer belt 11, what is the charging polarity of the toner on the secondary transfer roller 14? A high voltage of reverse polarity is applied. As a result, the toner image is transferred from the outer peripheral surface of the intermediate transfer belt 11 to the surface of the recording paper.

  Of the toner adhering to the intermediate transfer belt 11 from the photosensitive drum 101, the toner remaining on the intermediate transfer belt 11 without being transferred onto the recording paper is used for the transfer cleaning unit in order to prevent color mixing in the next process. 12 is collected.

  The recording paper onto which the toner image has been transferred is guided to fixing devices 15 and 80 of the present invention, which will be described later, and a fixing belt 64 stretched between the fixing roller 15a and the heating members 60 and 70, and a pressure roller 15b. Heat and pressure are passed through the fixing nip formed between the two. As a result, the toner image is firmly fixed on the surface of the recording paper. The recording paper on which the toner image is fixed is discharged onto the paper discharge tray 18 by the paper discharge roller 18a.

  In the image forming apparatus 100, the recording paper stored in the paper cassette 16 is transferred to the paper discharge tray 18 between the secondary transfer roller 14 and the intermediate transfer belt 11 and the fixing devices 15 and 80. A paper transport path P1 extending in a substantially vertical direction for feeding is provided. In the paper transport path P1, a pickup roller 16a that feeds the recording paper in the paper cassette 16 one by one into the paper transport path P1, a transport roller 16b that transports the fed recording paper upward, and the recording that has been transported. A registration roller 19 that guides the paper between the secondary transfer roller 14 and the intermediate transfer belt 11 at a predetermined timing, and a paper discharge roller 18 a that discharges the recording paper to the paper discharge tray 18 are disposed.

  Further, inside the image forming apparatus 100, a paper conveyance path P2 in which a pickup roller 17a and a conveyance roller 16b are arranged is formed between the manual paper feed tray 17 and the registration rollers 19. Further, a paper transport path P3 is formed between the paper discharge roller 18a and the upstream side of the registration roller 19 in the paper transport path P1.

  The paper discharge roller 18a is rotatable in both forward and reverse directions, and is used to form a second side image when forming a single-sided image for forming an image on one side of the recording paper and for forming a double-sided image for forming an image on both sides of the recording paper. At the time of formation, the recording paper is driven in the normal rotation direction and discharged to the paper discharge tray 18. On the other hand, when the first side image is formed in the double-sided image formation, the discharge roller 18a is driven in the normal direction until the rear end of the paper passes through the fixing devices 15 and 70, and then sandwiches the rear end of the recording paper. In this state, the recording paper is driven in the reverse direction to guide the recording paper into the paper conveyance path P3. As a result, the recording paper on which the image is formed only on one side at the time of double-sided image formation is guided to the paper conveyance path P1 with the front and back sides and the front and rear ends reversed.

  The registration roller 19 performs the secondary transfer of the recording paper fed from the paper cassette 16 or the manual paper feed tray 17 or conveyed via the paper conveyance path P3 at a timing synchronized with the rotation of the intermediate transfer belt 11. Guided between the roller 14 and the intermediate transfer belt 11. For this reason, the registration roller 19 stops rotating when the operation of the photosensitive drum 101 and the intermediate transfer belt 11 is started, and the recording paper fed or conveyed prior to the rotation of the intermediate transfer belt 11 is registered at the front end. The movement in the paper transport path P1 is stopped in a state where it is in contact with the roller 19. Thereafter, the registration roller 19 is a position at which the secondary transfer roller 14 and the intermediate transfer belt 11 are in pressure contact with each other, and the front end portion of the recording paper and the front end portion of the toner image formed on the intermediate transfer belt 11 face each other. To start rotation.

  At the time of full color image formation in which image formation is performed in all of the image forming portions Pa to Pd, the primary transfer rollers 13a to 13d press the intermediate transfer belt 11 against all of the photosensitive drums 101a to 101d. On the other hand, at the time of monochrome image formation in which image formation is performed only in the image forming portion Pa, only the primary transfer roller 13a is brought into pressure contact with the photosensitive drum 101a.

  FIG. 2 is a diagram illustrating a configuration of the fixing device 15 according to the first embodiment of the present invention. The fixing device 15 includes a fixing roller 15a, a pressure roller 15b, a fixing belt 64, and a heating member 60. In the fixing device 15, the fixing belt 64 is stretched between the fixing roller 15 a and the heating member 50, and the pressure roller 15 b is disposed so as to face the fixing roller 15 a through the fixing belt 64. The fixing roller 15a and the heating member 60 are disposed so as to be substantially parallel in the axial direction of the fixing roller 15a. Therefore, when the fixing belt 64 stretched between the fixing roller 15a and the heating member 60 slides, it can be prevented from meandering and the durability of the fixing belt 64 can be maintained high.

  In the fixing device 15, the heating member 60 contacts the fixing belt 64 to heat the fixing belt 64, and the fixing nip portion 15c formed by the fixing belt 64 and the pressure roller 15b is recorded at a predetermined fixing speed and copying speed. This is an apparatus for fixing an unfixed toner image 81 carried on the recording paper 82 by heating and pressing the recording paper 82 when the recording paper 82 as a medium passes.

  The unfixed toner image 81 includes, for example, a developer such as a nonmagnetic one-component developer (nonmagnetic toner), a nonmagnetic two-component developer (nonmagnetic toner and carrier), and a magnetic developer (magnetic toner). Toner). The fixing speed is a so-called process speed, and the copying speed is the number of copies per minute. Further, when the recording paper 82 passes through the fixing nip portion 15c, the fixing belt 54 comes into contact with the surface of the recording paper 82 opposite to the toner image carrying surface.

  The fixing roller 15a is pressed against the pressure roller 15b via the fixing belt 64 to form the fixing nip portion 15c. At the same time, the fixing roller 15a is opposed to and pressed against the pressure roller 15b via the fixing belt 64, and rotates around the rotation axis. It is provided rotatably. The pressure roller 15b rotates in the rotation direction Y1 following the rotation of the fixing roller 15a. The fixing roller 15a has a diameter of 30 mm and has a two-layer structure in which a core metal and an elastic layer are formed in order from the inside. The core metal includes, for example, a metal such as iron, stainless steel, aluminum, copper, or the like. An alloy or the like is used. For the elastic layer, a heat-resistant rubber material such as silicon rubber or fluorine rubber is suitable. In this embodiment, the force when the fixing roller 15a is pressed against the pressure roller 15b via the fixing belt 64 is about 216N.

  The pressure roller 15b conveys the fixing belt 64 by being driven to rotate in the rotation direction Y2 around the rotation axis by a drive motor (drive means) (not shown). The pressure roller 15b has a three-layer structure in which a metal core, an elastic layer, and a release layer are formed in this order from the inside. For the metal core, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. For the elastic layer, a rubber material having heat resistance such as silicon rubber and fluorine rubber is suitable, and for the release layer, PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) is suitable. A fluororesin such as fluoroethylene) is suitable. A heater lamp 66 for heating the pressure roller 15b is disposed inside the pressure roller 15b. When a main control unit 91 described later supplies power to the heater lamp 66 from the power supply circuit (energization), the heater lamp 66 emits light, and infrared rays are emitted from the heater lamp 66. As a result, the inner peripheral surface of the pressure roller 15b is heated by absorbing infrared rays, and the entire pressure roller 15b is heated.

  The fixing belt 64 is heated to a predetermined temperature by the heating member 60, and heats the unfixed toner image 81 and the recording paper 82 that pass through the fixing nip portion 15c. The fixing belt 64 is an endless belt having a diameter of 50 mm, is suspended by the heating member 60 and the fixing roller 15a, and is wound around the fixing roller 15a at a predetermined angle. When the fixing roller 15a rotates, the fixing belt 64 follows the fixing roller 15a and rotates in the rotation direction Y1. The fixing belt 64 is formed of an elastomer material (for example, silicon rubber) excellent in heat resistance and elasticity as an elastic layer on the surface of a hollow cylindrical base material made of a heat resistant resin such as polyimide or a metal material such as stainless steel or nickel. Furthermore, a three-layer structure in which a synthetic resin material (for example, a fluororesin such as PFA or PTFE) having excellent heat resistance and releasability is formed on the surface as a release layer. Moreover, you may add a fluororesin internally to the polyimide of a base material. Thereby, the sliding load with the heating member 60 can be reduced.

  Further, in the fixing device 15, as a temperature detecting means, a heating element side thermistor 63 is disposed on the peripheral surface of the fixing belt 64, and a pressure roller side thermistor 65 is disposed on the peripheral surface of the pressure roller 15b. The surface temperature is detected. On the basis of the surface temperature of the fixing belt 64 detected by the heating element side thermistor 63, energization to the planar heating elements 20, 40 described later is controlled. The heating element side thermistor 63 in the present embodiment is a non-contact type temperature detection means, and is an infrared detection type temperature sensor. In the configuration in which the contact-type temperature detection unit is disposed in contact with the fixing belt, the contact-type temperature detection unit may wear the surface release layer of the fixing belt at the interface contacting the fixing belt. In this way, when the surface release layer of the fixing belt is damaged or deteriorated, the influence is exerted on the image, resulting in a poor image. The energization of the heater lamp 66 is controlled based on the surface temperature of the pressure roller 15b detected by the pressure roller side thermistor 65.

  FIG. 3 is a diagram illustrating a configuration of the heating member 60 included in the fixing device 15. The heating member 60 is a member for contacting the fixing belt 64 and heating the fixing belt 64 to a predetermined temperature. The heating member 60 includes a base material 62 and a planar heating element 20 or 40 described later.

  The base material 62 has a hollow roll shape composed of a body portion 60a and a journal portion 60b, and the body portion 60a has a substantially semicircular arc-shaped cross-sectional shape having a cutout portion in which the lower half is cut. The body 60 a is a portion that contacts the fixing belt 64, and a planar heating element 20 or 40 described later is fixed to the inner surface of the semicircular arc so that the longitudinal direction thereof corresponds to the axial direction of the base material 62. It is a portion that is arranged to transmit heat generated by the planar heating elements 20 and 40 to the fixing belt 64. Therefore, the base material 62 needs to be formed from a material having high thermal conductivity. Examples of the material constituting the base material 62 include metals such as aluminum.

  Further, it is preferable that a top coat layer capable of reducing a frictional force with the fixing belt 64 is formed on the body portion 60 a of the base material 62 which is a portion in contact with the fixing belt 64. Examples of the material constituting the top coat layer include at least one material of PTFE resin and PFA resin. As a result, the frictional force between the heating member 60 and the fixing belt 64 can be reduced, the wear of the fixing belt 64 can be prevented, and high durability of the fixing belt 64 can be ensured. The load on the fixing roller 15a and the pressure roller 15b for driving the belt 64 can also be reduced, and the durability of the rollers 15a and 15b can be ensured and the roller can be driven with low power.

  The journal portion 60b is a portion formed at both ends of the body portion 60a, and is fixed to the side frame 67 of the fixing device 15 so that the heating member 60 itself does not rotate due to frictional force with the fixing belt 64. Thus, since the heating member 60 itself is configured not to rotate, even when a high current is supplied to the planar heating elements 20 and 40 when the planar heating elements 20 and 40 generate heat, safety is ensured. It can be secured sufficiently.

  Further, a meandering prevention collar 66 that prevents meandering when the fixing belt 64 rotates and slides is formed in the journal portion 60 b so as to contact the end portion of the fixing belt 64. The meandering-preventing collar 66 may be a color made of polyphenylene sulfide (PPS), but is not limited to this, and any structure that can rotate independently of the heating member 60 may be used. Thus, since the meandering prevention collar 66 is freely rotatable, even if the fixing belt 64 comes into contact with the meandering prevention collar 66, no load is applied without sliding, and the fixing belt 64 is broken. The durability of the fixing belt 64 can be maintained high.

  Next, the planar heating elements 20 and 40 included in the heating member 60 will be described. FIG. 4 is a diagram illustrating a configuration of the planar heating element 20 which is a first example of the planar heating element included in the heating member 60. FIG. 5 is a diagram showing regions where the connection portions 22b, 25b, and 28b are formed in the resistance heating elements 22, 25, and 28. FIG.

  In the sheet heating element 20, a heating pattern serving as a heating area is formed on one surface in the thickness direction of the insulating layer 31. Furthermore, the planar heating element 20 is composed of a plurality of heat generation patterns and has a plurality of divided heat generation regions. In the present embodiment, the planar heating element 20 is formed so as to be divided into two heating regions, a heating region at both ends and a heating region at the center, with respect to the longitudinal direction of the insulating layer 31. The heat generation pattern 21 is formed at the longitudinal center of the insulating layer 31, and the heat generation patterns 24 and 27 are formed at both ends, respectively.

  The insulating layer 31 is a layer formed of a ceramic material such as alumina or a heat resistant polymer material such as polyimide resin, and serves as a base layer of the planar heating element 20 on which the heating patterns 21, 24, 27 are formed.

  Each of the heat generation patterns 21, 24, and 27 is formed by forming a resistance heating element that generates Joule heat when a voltage is applied and energized to form a surface having a certain shape as a whole. Here, the resistance heating element preferably has a positive resistance temperature characteristic. In a heating element having negative resistance temperature characteristics, as the temperature rises, the electric resistance value of the heating element itself decreases, so that the current flowing through the heating element increases and the amount of power increases. Therefore, a heating element having negative resistance temperature characteristics is not preferable from the viewpoint of energy saving.

  The heating pattern 21 formed on the planar heating element 20 has a resistance heating element 22 including a plurality of linear portions 22a and connecting portions 22b, and the heating pattern 24 is a resistance including a plurality of linear portions 25a and connecting portions 25b. The heating pattern 27 has a resistance heating element 28 including a plurality of linear portions 28a and connection portions 28b.

The linear portions 22a, 25a, and 28a are formed on one surface of the insulating layer 31 so as to extend in a direction substantially orthogonal to the longitudinal direction of the insulating layer 31 (longitudinal direction of the planar heating element 20). ing. The linear portions 22a, 25a, and 28a are made of a material mainly composed of nickel chrome having a volume resistivity of about 107.3 × 10 ⁻⁸ Ωcm.

  The connecting portions 22b, 25b, and 28b connect the end portions in the extending direction of the adjacent linear portions 22a, 25a, and 28a so as to extend in the longitudinal direction of the planar heating element 20 to form one line. The insulating layer 31 is formed on one surface. That is, in the resistance heating elements 22, 25, and 28 forming the heating patterns 21, 24, and 27 of the present invention, the connecting portions 22b, 25b, and 28b are bent portions in the resistance heating elements 22, 25, and 28.

  The material constituting the connecting portions 22b, 25b, and 28b may be the same material as the linear portions 22a, 25a, and 28a. However, in the present embodiment, the material that constitutes the linear portions 22a, 25a, and 28a. It is made of a low volume resistivity material having a volume resistivity of 1/10 or less with respect to the volume resistivity. As a result, the linear portions 22a, 25a, and 28a generate sufficient heat, while the connecting portions 22b, 25b, and 28b that are bent portions have a lower volume resistivity than the material that forms the linear portions 22a, 25a, and 28a. Since it is formed of the material, it is possible to prevent current from being concentrated and flowing locally in the bent portion.

As the low volume resistance material, zinc having a volume resistivity of about 5.9 × 10 ⁻⁸ Ωcm, gold having a volume resistivity of about 2.05 × 10 ⁻⁸ Ωcm, and a volume resistivity of 1.55 × 10 ^−8. Examples include copper of about Ωcm, silver having a volume resistivity of about 1.47 × 10 ⁻⁸ Ωcm, etc. Among them, silver or copper having a small volume resistivity and low cost is preferable.

  In addition, when the resistance heating elements 22, 25, and 28 are energized, they generate heat. When the connection portions 22b, 25b, and 28b are made of a material having a low volume resistivity, the amount of generated heat is as follows. It becomes smaller than 28a. Therefore, if the area ratio of the connection portions 22b, 25b, and 28b is too large, the temperature distribution on the surface of the planar heating element 20 becomes non-uniform. Accordingly, in the resistance heating elements 22, 25, 28, the area ratio of all the connecting portions 22b, 25b, 28b to the area of all the linear portions 22a, 25a, 28a is such that the temperature distribution on the surface of the planar heating element 20 is uniform. Set to.

  Here, it is sufficient that the resistance heating elements 22, 25, and 28 are bent portions, and the regions where the connection portions 22b, 25b, and 28b are formed include corners where the resistance heating elements 22, 25, and 28 are bent. A region including a portion that is bent from a corner portion of the resistance heating elements 22, 25, and 28 and extends in the longitudinal direction of the planar heating element 20 as shown in FIG. 5A, and a resistance as shown in FIG. A region including a part that is bent from a corner portion of the heating elements 22, 25, and 28 and extends in the longitudinal direction of the planar heating element 20, a corner portion of the resistance heating elements 22, 25, and 28 as shown in FIG. It is an area including only.

  In the sheet heating element 20, power feeding is performed so that the heating pattern 21 at the center in the longitudinal direction of the sheet heating element 20 and the heating patterns 24 and 27 at both ends can be energized in a distinguished state. Energization control is performed by the control unit 33.

  Specifically, both ends of the resistance heating element 22 of the heat generation pattern 21 are connected to power supply terminal portions 23 formed at both ends in the longitudinal direction of the planar heating element 20. The resistance heating element 22 generates heat when a voltage from the power supply 32 is applied to the power supply terminal portion 23 via the power supply control unit 33 and is energized. One end of the resistance heating element 25 of the heating pattern 24 and the resistance heating element 28 of the heating pattern 27 are electrically connected by a pattern connection portion 30 made of the same material as the connection portion, and each other end portion is a power supply terminal portion. 23 is connected to a power feeding terminal portion 29 which is a terminal different from the terminal 23. The resistance heating element 25 and the resistance heating element 28 are distinguished from the resistance heating element 22 by applying a voltage from the power supply 32 to the power supply terminal unit 29 via the power supply control unit 33 and applying current thereto. Fever.

  As described above, in the planar heating element 20, the amount of heat generated in the longitudinal direction of the planar heating element 20 can be adjusted by switching the energization state, and the temperature distribution on the surface of the planar heating element 20 is desired. The temperature distribution can be adjusted.

  Here, the power supply control unit 33 is controlled by the control unit 90 to control the supply power from the temperature detected by the heating element side thermistor 63 and the power values set in the resistance heating elements 22, 25, 28. It is configured as follows.

  FIG. 6 is a block diagram showing the configuration of the control means 90 that controls energization in the planar heating element 20. The control unit 90 includes a main control unit 91, a detection unit 92, a power calculation unit 93, and a power supply control unit 33. The main control unit 91 comprehensively controls the detection unit 92, the power calculation unit 93, and the power supply control unit 33.

  The energization control for the planar heating element 20 in the control means 90 can include the following two energization control examples.

  In the first energization control example, the detection unit 92 of the control means 90 applies the current value flowing through the resistance heating elements 22, 25, 28 constituting the heat generation patterns 21, 24, 27 and the power supply terminal units 23, 29. The detected voltage value is detected. The power calculation unit 93 calculates the power value supplied to each resistance heating element 22, 25, 28 based on the current value and the voltage value detected by the detection unit 92. Then, based on the calculated power value calculated by the power calculation unit 93, the power supply control unit 33 generates heat within each of the resistance heating elements 22, 25, and 28 within a predetermined temperature range set based on the fixing temperature. In addition, power supply to each resistance heating element 22, 25, 28 is controlled.

  In the second energization control example, the detection unit 92 of the control means 90 is applied to the power supply terminal units 23 and 29 corresponding to the resistance heating elements 22, 25 and 28 constituting the heat generation patterns 21, 24 and 27. Detect voltage value. The power calculation unit 93 calculates the power value supplied to each resistance heating element 22, 25, 28 based on the voltage value detected by the detection unit 92 and the electrical resistance value of each resistance heating element 22, 25, 28. To do. Then, based on the calculated power value calculated by the power calculation unit 93, the power supply control unit 33 generates heat within each of the resistance heating elements 22, 25, and 28 within a predetermined temperature range set based on the fixing temperature. In addition, power supply to each resistance heating element 22, 25, 28 is controlled.

  In the present embodiment, the main control unit 91 transmits the temperature information of the surface of the fixing belt 64 detected by the heating element side thermistor 63 to the power supply control unit 33, and the power supply control unit 33 to which the temperature information is transmitted In addition to the calculated power value, the temperature information is also included to control the power supply to each resistance heating element 22, 25, 28.

  Next, the energization control for the planar heating element 20 in the control means 90 will be specifically described with reference to FIGS. FIG. 7 is a graph showing the relationship between applied voltage and power in the difference in electrical resistance value of the resistance heating element. When the voltage value applied to the power supply terminal connected to both ends of the resistance heating element increases, the power value in the resistance heating element increases in proportion to the applied voltage value. At this time, three types of resistance heating elements 1 to 3 having different electrical resistance values at 25 ° C. (resistance heating element 1: electrical resistance value 9.0Ω, resistance heating element 2: electrical resistance value 10.0Ω, resistance heating element 3: (Electric resistance value 11.0Ω) is compared, the electric power value decreases as the electric resistance value of the resistance heating element increases.

  Here, generally, the electric resistance value of the resistance heating element has a tolerance due to variations in manufacturing and the like, and the applied voltage value also has a tolerance. As described above, since the electrical resistance value and the applied voltage value of the resistance heating element are closely related to the power value in the resistance heating element, the tolerance of the electrical resistance value of the resistance heating element and the tolerance of the applied voltage value are It becomes a factor which fluctuates the electric energy supplied to a resistance heating element.

  FIG. 8 is a graph showing the relationship between the temperature of the resistance heating element and the electric resistance value and the relationship between the temperature of the resistance heating element and the power value in the difference in the electric resistance value of the resistance heating element. FIG. 9 is a graph showing the relationship between the energization time and power value for the resistance heating element and the relationship between the energization time and temperature for the resistance heating element in the difference between the electrical resistance value and the applied voltage value of the resistance heating element. is there.

  As shown in FIG. 8, the resistance heating element having a positive resistance temperature characteristic has a larger electrical resistance value as the temperature rises. For this reason, the value of the current flowing through the resistance heating element is reduced, and the power value is reduced.

  For example, in the resistance heating element 2 having an electrical resistance value of 10.0Ω at 25 ° C. (T1), a predetermined set temperature (T3) set based on the fixing temperature from the electrical resistance value at the temperature T1 and the resistance temperature coefficient of the material. ) Can be calculated (R2-T3). Temperature control in a state in which overheating is prevented by applying a voltage to the resistance heating element 2 and cutting off the energization when the electrical resistance value of the resistance heating element 2 reaches a desired value (R2-T3). Is possible.

  On the other hand, in the resistance heating element 1 whose electrical resistance value at the temperature T1 is 9.0Ω and whose electrical resistance value is smaller than that of the resistance heating element 2, the electrical resistance value (R1-T3) at the temperature T3 is resistance heating. Since it is smaller than the body 2, the power value (W1-T3) at the temperature T3 is larger than the power value (W2-T3) of the resistance heating element 2. As shown in FIG. 9, the resistance heating element 1 whose power value at the predetermined set temperature T3 is larger than that of the resistance heating element 2 has a shorter energization time until the temperature reaches the temperature T3.

  Further, in the resistance heating element 3 having an electric resistance value of 11.0Ω at the temperature T1 and a larger electric resistance value than the resistance heating element 2, the electric resistance value (R3−T3) at the temperature T3 is higher than that of the resistance heating element 2. Therefore, the power value (W3-T3) at the temperature T3 is smaller than the power value (W2-T3) of the resistance heating element 2. As shown in FIG. 9, the resistance heating element 3 whose power value at the predetermined set temperature T3 is smaller than that of the resistance heating element 2 has a longer energization time until it reaches the temperature T3.

  From the above, when there is a tolerance of the electrical resistance value and a tolerance of the applied voltage value in the resistance heating element, the power value of the resistance heating element varies, and the energization time until reaching the predetermined set temperature T3 is reached. It can be seen that variations occur. Therefore, when a certain energization time is set for the resistance heating element, the resistance heating element having a small electric resistance value rises to a temperature (T4) higher than the set temperature T3, and an overshoot occurs. In a resistance heating element having a large value, the temperature reaches only a temperature (T2) lower than the set temperature T3, and undershoot occurs.

  Therefore, as described above, the control unit 90 provided in the fixing device 15 of the present invention distinguishes between the heat generation pattern 21 at the center in the longitudinal direction of the sheet heating element 20 and the heat generation patterns 24 and 27 at both ends. In the state, the energization control is performed based on the calculated power values corresponding to the respective resistance heating elements 22, 25, and 28 constituting the heating patterns 21, 24, and 27.

  The energization control of the control means 90 when the heat generation pattern 21 corresponds to the sheet passing portion on the surface of the fixing belt 64 and the heat generation patterns 24 and 27 correspond to the non-sheet passing portion will be described below with reference to FIG. FIG. 10 is a graph showing the relationship between the energization time for the resistance heating element and the calculated power value and the relationship between the energization time for the resistance heating element and the temperature in the energization control for the planar heating element 20.

  In the fixing device 15, a predetermined fixing temperature is set in advance. The set power value is set in advance based on the electrical resistance value at the fixing temperature of the resistance heating elements 22, 25, and 28.

  When the main power supply of the fixing device 15 is turned on, the main control unit 91 of the control unit 90 controls the detection unit 92, the power calculation unit 93, and the power supply control unit 33 in an integrated manner, and each resistance heating element. The energization control for 22, 25, and 28 is started.

  First, the power supply control unit 33 controls the power supply 32 to apply a voltage to the power supply terminal units 23 and 29. When a voltage is applied to the power supply terminal portions 23 and 29, a current flows through the resistance heating elements 22, 25 and 28. The detection unit 92 detects the current value flowing through each resistance heating element 22, 25, 28 and the voltage value applied to the power supply terminal units 23, 29 at predetermined time intervals, and the power calculation unit 93 detects Based on the current value and the voltage value detected by the unit 92, the power value supplied to each resistance heating element 22, 25, 28 is calculated.

  Each resistance heating element 22, 25, 28 generates heat with a positive resistance temperature characteristic when a voltage is applied to the power supply terminal portions 23, 29 and a current flows. Each of the resistance heating elements 22, 25, and 28 generates heat, and as the temperature rises, the electrical resistance value increases and the current value decreases. However, the detection unit 92 detects this change in current value, Based on this, the power calculator 93 calculates a power value.

  Based on the temperature information on the surface of the fixing belt 64 transmitted from the heating element side thermistor 63, the power supply control unit 33 determines that the temperature of each resistance heating element 22, 25, 28 has reached the fixing temperature, and also calculates the power. When the calculated power value calculated by 93 is equal to or lower than the set power value, the power supply is cut off. At this time, in the fixing device 15 in which the temperature of the surface of the fixing belt 64 has reached the fixing temperature, paper feeding is started.

  In each resistance heating element 22, 25, 28 in which power feeding is interrupted, the calculated power value instantaneously becomes zero, but the temperature rises within a predetermined temperature range and then falls. At this time, the temperature decreasing rate of each resistance heating element 22, 25, 28 is faster in the resistance heating elements 25, 28 corresponding to the non-sheet passing portion than in the resistance heating element 22 corresponding to the sheet passing portion. This is because heat radiation occurs in the resistance heating elements 25 and 28 corresponding to the non-sheet passing portion. Based on the temperature decrease rate of the resistance heating elements 22, 25, and 28, it can be determined that the portions corresponding to the resistance heating elements 25 and 28 are non-sheet passing portions. The power supply control unit 33 does not perform power supply control on the resistance heating elements 25 and 28 corresponding to the non-sheet passing unit, and maintains the state where the power supply is cut off.

  When the power supply control unit 33 determines that the temperature of the resistance heating element 22 has decreased to the fixing temperature based on the temperature information on the surface of the fixing belt 64 transmitted from the heating element side thermistor 63, the power supply control unit 33 energizes the resistance heating element 22. Return. In the resistance heating element 22 to which the power supply has been restored, the calculated power value increases because the current value increases while the temperature continues to decrease. Thereafter, the calculated power value decreases when the temperature increases as the power supply returns. Then, when the calculated power value is equal to or lower than the set power value, the power supply is cut off. Thereafter, the power supply control unit 33 repeats power supply interruption and return as described above.

  In the fixing device 15 of the present invention, as described above, the power value is calculated by accurately grasping the fluctuations in the current value and the voltage value of the resistance heating elements 22, 25, and 28, and the control means is based on the calculated power value. Since the energization control by 90 is repeated, even if the resistance values of the resistance heating elements 22, 25, 28 have tolerances and the applied voltage also has tolerances, the resistance heating elements 22, It is possible to suppress an increase in variation in temporal fluctuations of the temperatures 25 and 28. Therefore, it is possible to avoid a delay time due to overshoot or the like with respect to the control temperature of the resistance heating elements 22, 25, 28, and to perform highly accurate temperature control with good responsiveness. Accordingly, the fixing device 15 is a device capable of achieving uniform fixing properties by suppressing the occurrence of uneven heating when the fixing belt 64 is heated by the heat generated by the resistance heating elements 22, 25, 28. Become.

  Further, in the planar heating element 20, the extending direction of the linear portions 22 a, 25 a, 28 a of the resistance heating elements constituting the heating patterns 21, 24, 27 is relative to the longitudinal direction of the planar heating element 20. It is preferable to incline by a predetermined angle θ. As a result, the temperature decrease of the portion where the heat generation amount is small and the portion where the heat generation amount does not generate is compensated, so that the temperature distribution of the fixing belt 64 to which heat is transmitted from the planar heating element 20 can be made uniform. In particular, even in the case of having a plurality of heat generation patterns 21, 24, 27, it is possible to prevent a sudden temperature change from occurring in the heat generation patterns 24, 27 formed at both ends in the longitudinal direction of the planar heating element 20. can do.

  Further, in the planar heating element 20, the interval between the linear portions in the heating patterns 24 and 27 formed on both ends in the longitudinal direction of the planar heating element 20 is directed from the inside to the outside within a predetermined region. By setting so as to become smaller, the power density in the predetermined region can be increased. Therefore, heat dissipation loss from the end portions of the heat generation patterns 24 and 27 corresponding to a predetermined region of the planar heating element 20 can be suppressed, and the temperature distribution in the longitudinal direction of the planar heating element 20 can be made uniform.

  FIG. 11 is a view showing a heat generation pattern at both ends of the sheet heating element 20. In the heat generation patterns 24 and 27 of the planar heating element 20, the intervals between the plurality of linear portions formed in the predetermined region may be changed one by one or the same.

  For example, when the intervals between the linear portions of the resistance heating elements constituting the heat generation patterns 24 and 27 are the interval A1, the interval A2, the interval A3, and the interval A4 in order from the outside to the inside, the interval between the linear portions. As a setting example, as shown in FIG. 11A, a setting example that satisfies the interval A1 = A2 <A3 = A4 can be given. Also, a setting example that satisfies the interval A1 <A2 <A3 = A4 as shown in FIG. 11B, and a setting that satisfies the interval A1 <A2 <A3 <A4 as shown in FIG. 11C. Examples can also be given.

  In the present embodiment, the range of the predetermined region in the heat generation patterns 24 and 27 formed on both ends in the longitudinal direction of the sheet heating element 20 is the two linear portions arranged on the outermost side in the heat generation pattern 24. The range including 25 a and the range including the two linear portions 28 a arranged on the outermost side in the heat generation pattern 27 are set. The interval between the two linear portions 25a in the predetermined area and the interval between the two linear portions 28a are set to the same interval (3.0 mm), and the other linear portions 25a , 28a is set to 3.5 mm, which is the same as the interval between the linear portions 22a constituting the heat generation pattern 21.

  Here, the range of the predetermined area may be set in consideration of, for example, the width of the recording paper that is passed through the fixing device 15. Specifically, the predetermined area of the sheet heating element 20 disposed facing the fixing belt 64 is not disposed outside the both ends of the sheet passing width of the recording paper. Set the range. As a result, the recording paper passed through the fixing device 15 comes into contact with the fixing belt 64 in a state where the heat generation amount is large with the passing width of the recording paper. For this reason, the recording paper is passed in a state in which the temperature distribution is uniform over the entire paper passing width region with no temperature difference between the both end portions and the central portion with the heat dissipation loss at both ends in the width direction being suppressed. Paper.

  In the planar heating element 20, a coat layer made of a material having a low friction coefficient may be formed so as to cover the heating patterns 21, 24, 27 formed on the insulating layer 31. When the sheet heating element 20 is disposed so as to be in contact with the fixing belt 64 as a member for heating the fixing belt 64 included in the fixing device 80 to be described later, the surface of the sheet heating element 20 is provided with a coat layer, thereby providing a surface. The frictional force between the heat generating member 20 and the fixing belt 64 can be reduced, the wear of the fixing belt 64 can be prevented, and high durability of the fixing belt 64 can be ensured. Examples of the material constituting the coating layer include at least one of PTFE (polytetrafluoroethylene) resin and PFA (tetrafluoroethylene and perfluoroalkyl vinyl ether) resin.

  The method of forming the resistance heating elements 22, 25, 28 having the linear portions 22a, 25a, 28a and the connecting portions 22b, 25b, 28b on the insulating layer 31 in the planar heating element 20 is commonly used in this field. For example, methods such as painting, thermal spraying, printing, and adhesion can be used.

  FIG. 12 is a diagram illustrating a configuration of a planar heating element 40 that is a second example of the planar heating element. The planar heating element 40 includes an insulating layer 50 configured in the same manner as the insulating layer 31 included in the planar heating element 20 described above, and a heating pattern serving as a heating region is formed on one surface in the thickness direction of the insulating layer 50. Has been. Furthermore, the planar heating element 40 is composed of a plurality of heating patterns and has a plurality of divided heating regions. In the present embodiment, the planar heating element 40 is divided into three, that is, a heating region at one end, a heating region at the other end, and a heating region at the center with respect to the longitudinal direction of the insulating layer 50. A heat generation pattern 41 is formed at the center in the longitudinal direction of the insulating layer 50, a heat generation pattern 44 is formed at one end, and a heat generation pattern 47 is formed at the other end so that a heat generation region is formed.

  The heat generation pattern 41 has a resistance heating element 42 including a linear portion 42a and a connection portion 42b, the heat generation pattern 44 has a resistance heating element 45 including a linear portion 45a and a connection portion 45b, and the heat generation pattern 47 has a linear shape. A resistance heating element 48 including a part 48a and a connection part 48b is provided.

  The linear portions 42a, 45a, and 48a in the planar heating element 40 are configured in the same manner as the linear portions 22a, 25a, and 28a of the planar heating element 20 described above. The connection portions 42b, 45b, and 48b in the planar heating element 40 may be formed of a material having a low volume resistivity, like the connection portions 22b, 25b, and 28b of the planar heating element 20, but this embodiment In a form, it forms with the material similar to a linear part, and it is comprised similarly to the connection parts 22b, 25b, 28b of the planar heating element 20 other than that.

  In the planar heating element 40, the heating pattern 41 at the center in the longitudinal direction of the planar heating element 40, the heating pattern 44 at one end, and the heating pattern 47 at the other end are energized in a distinguished state. Energization control is performed by the power supply control unit 52 so as to be possible. At this time, the power supply control unit 52, like the power supply control unit 33 of the planar heating element 20 described above, the temperature detected by the heating element side thermistor 63 and the calculated power value for each resistance heating element 42, 45, 48. Thus, the power supply to the heat generating area divided into three is controlled.

  Specifically, both ends of the resistance heating element 42 of the heat generation pattern 41 are connected to the power supply terminal portion 43 formed at the center in the longitudinal direction of the planar heating element 40 corresponding to the heat generation pattern 41. . The resistance heating element 42 generates heat when a voltage from the power source 51 is applied to the power supply terminal portion 43 via the power supply control unit 52 and is energized. Both ends of the resistance heating element 45 of the heating pattern 44 are connected to a power supply terminal portion 46 formed at one end in the longitudinal direction of the planar heating element 40 corresponding to the heating pattern 44. Then, the resistance heating element 45 generates heat in a state distinguished from the resistance heating element 42 when the voltage from the power source 51 is applied to the power supply terminal section 46 via the power supply control section 52 and energized. Both ends of the resistance heating element 48 of the heat generation pattern 47 are connected to a power supply terminal portion 49 formed at the other longitudinal end of the planar heating element 40 corresponding to the heat generation pattern 47. The resistance heating element 48 generates heat while being distinguished from the resistance heating elements 42 and 45 by applying a voltage from the power supply 51 to the power supply terminal section 49 via the power supply control section 52 and applying current thereto.

  As described above, in the sheet heating element 40, the amount of heat generated in the longitudinal direction of the sheet heating element 40 can be adjusted by switching the energization state, and the fixing from which heat is transmitted from the sheet heating element 40. The temperature distribution on the surface of the belt 64 can be made uniform.

  Further, in the fixing device 15, the planar heating elements 20 and 40 are formed so as to extend parallel to the axial direction of the fixing roller 15a and to follow the semicircular arc-shaped inner surface of the body portion 50a. At this time, it is preferable that the insulating layers 31, 50 included in the planar heating elements 20, 40 are formed so as to be on the side in contact with the body 60 a of the base material 62. As a result, insulation between the resistance heating element of the planar heating elements 20 and 40 and the substrate 62 can be ensured, and a safer heating member 60 can be obtained.

  FIG. 13 is a diagram illustrating a configuration of a fixing device 80 according to the second embodiment of the present invention. The fixing device 80 is similar to the fixing device 15 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In the fixing device 80, the layer configuration of the body 72 of the base member 72 included in the heating member 70 is different from that of the heating member 60 of the fixing device 15. Here, the energization of the heating members 70 and 40 of the heating member 70 included in the fixing device 80 is controlled by the control unit 90 in the same manner as the fixing device 15 described above.

  In the fixing device 80, the planar heating elements 20 and 40 are formed so as to extend parallel to the axial direction of the fixing roller 15a and to follow the semicircular arc outer surface of the body portion. That is, the planar heating elements 20 and 40 come into contact with the fixing belt 64. At this time, the planar heating elements 20, 40 are formed on the base material 72 so that the coating layer of the planar heating elements 20, 40 is the outermost layer in the body portion of the heating member 70 and is a layer in contact with the fixing belt 64. It is preferable to form it on the outer surface. As a result, the frictional force between the heating member 70 and the fixing belt 64 can be reduced, the wear of the fixing belt 64 can be prevented, and high durability of the fixing belt 64 can be ensured. The load on the fixing roller 15a and the pressure roller 15b for driving the belt 64 can also be reduced, and the durability of the rollers 15a and 15b can be ensured and the roller can be driven with low power.

  Further, when the sheet heating elements 20, 40 are fixedly formed on the outer surface of the base material 72 so that the coat layer of the sheet heating elements 20, 40 becomes the outermost layer in the body portion of the heating member 70, sheet heating is performed. The insulating layers 31 and 50 of the bodies 20 and 40 are layers that come into contact with the base material 72. As a result, insulation between the resistance heating element of the planar heating elements 20 and 40 and the base material 72 can be secured, and the heating member 70 can be made safer.

[Example]
EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to these Examples.

Example 1
The fixing device used in Example 1 is the fixing device 80 described above. The fixing device 80 was mounted on a copying machine (trade name: MX-7000N, manufactured by Sharp Corporation). Detailed conditions in Example 1 were as follows.

<Fixing roller>
A stainless steel having a diameter of 30 mm, a core metal of 15 mm in diameter, and an elastic layer made of silicon sponge rubber having a thickness of 3 mm was used.

<Pressure roller>
A 30 mm diameter PFA tube having a diameter of 30 mm and a heater lamp having a rated power of 400 W was used as the release layer.

<Fixing belt>
A belt in which a polyimide having a thickness of 70 μm was formed on a belt substrate, a silicon rubber having a thickness of 150 μm was formed on an elastic layer, and a PTFE coat having a thickness of 30 μm was formed on a release layer was used.

<Color to prevent meandering>
A polyphenylene sulfide (PPS) collar having an inner diameter of 20 mm, a diameter of 32 mm, and a width of 7 mm was disposed so as to contact the end of the fixing belt.

<Heating member>
Base material: The diameter of the barrel part is 28 mm, the diameter of the journal part is 20 mm, the aluminum pipe with a thickness of 1 mm, and the belt sliding part have an arc shape with half cut.

Planar heating element: The planar heating element used in Example 1 is the planar heating element 20 described above. In the sheet heating element, the length in the longitudinal direction, which is a direction extending corresponding to the axial direction of the fixing roller, is 330 mm, and an insulating layer made of alumina is formed on the arcuate outer surface of the substrate by plasma spraying. A masking material is pasted in accordance with the heat generation patterns 21, 24, 27 of the sheet heating element 20, and a material mainly composed of nickel chromium as a resistance heating element (volume resistivity: 107.3 × 10 ⁻⁸ Ωcm) After forming the linear part using plasma and plasma spraying the connection part using copper (volume resistivity: 1.55 × 10 ⁻⁸ Ωcm) to form a pattern, the masking material is removed and the surfaces thereof are removed. A PTFE layer was coated to a thickness of 20 μm, and a lead wire was connected to the power supply terminal portion. At this time, the electric resistance of all the heating elements of the heating member was 10.10Ω at 25 ° C.

  The resistance heating element has a width of 6.6 mm, and the interval between adjacent linear portions and the inclination angle θ of the linear portions are the amount of power in the heat generation region, the applied voltage, and the volume of the resistance heating element to be used. Estimate the width, length, and film thickness of the linear part to be installed from the resistivity, adjust the surface temperature distribution of the fixing belt in the image area by measuring with a radiation thermometer and confirming the fixing property of the fixed image. Were determined. The inclination angle θ of the linear portion was 70 °.

<Thermistor>
One non-contact infrared sensor as the heating element side thermistor was installed in the center in the axial direction, and a contact thermistor was used as the pressure roller side thermistor.

<Control means>
The power supply to the divided heat generating region is controlled from the temperature detected by the heat generating body side thermistor and the calculated power value for each resistance heating element. Further, power supply to the heater lamp of the pressure roller is controlled based on the temperature detected by the pressure roller side thermistor.

<Fixing conditions>
Fixing nip length: 7 mm (the length of the fixing nip in the recording paper conveyance direction)
Fixing speed: 220mm / sec
Heating nip length: 44 mm (contact length in the recording paper conveyance direction between the fixing belt and the heating member)
Heating nip width: 330 mm (length corresponding to the axial direction of the fixing roller)

  The electrical resistance value of each resistance heating element of the sheet heating element when the surface temperature measured using a radiation thermometer was increased to 200 ° C. was measured by connecting a 100 V power source and control means to the heating member. The electric resistance value was 10.14Ω, the center portion was 16.90Ω, and both end portions were 50.7Ω.

  Next, the warm-up time in the copying machine, the temperature unevenness when 50 sheets were continuously fed, and the edge temperature rise when small-size sheets were passed were observed.

  When a voltage of 100 V was applied to the entire sheet heating element, the time required for the entire fixing belt surface temperature on the fixing roller to reach 200 ° C. (warm-up time) was 26.6 sec. 197 W was set as the set power value in the power supply control of the resistance heating element corresponding to the heat generation regions at both ends of the planar heating element. There was almost no unevenness in image density during continuous paper feeding, and a high-quality image was obtained. Furthermore, when the temperature at both ends of the sheet heating element when small-size paper was passed was measured with a heating element side thermistor, no excessive temperature increase was observed, and power consumption could be efficiently suppressed.

  Further, considering the supply voltage variation, the voltage was set to 90V and 110V, and the same evaluation was performed. The set power values for the resistance heating elements corresponding to the heating regions at both ends of the planar heating element were 159 W at 90 V and 238 W at 110 V. The warm-up time when the entire planar heating element was energized was 29.5 sec when a voltage of 90 V was applied and 24.1 sec when a voltage of 110 V was applied. A target warm-up time of 30 sec or less could be achieved regardless of variations in supply voltage.

  Even when the set voltages were 90 V and 110 V, there was almost no image density unevenness in continuous paper passing, and a high quality image was obtained. Furthermore, when the temperature at both ends of the sheet heating element when small-size paper was passed was measured with a heating element side thermistor, no excessive temperature increase was observed, and power consumption could be efficiently suppressed.

  In addition, since a coating layer made of PTFE resin is formed on the surface of the sheet heating element, the frictional force between the sheet heating element and the fixing belt is suppressed, resulting in smooth sliding without friction resistance. In addition, heat transfer efficiency to the fixing belt is good, it is possible to suppress the meandering of the fixing belt, and a non-contact thermistor is used to detect the temperature of the fixing belt surface. did it.

  In addition, the density of the resistance heating element is high at both ends of the planar heating element, so the power density at both ends is higher than the central part, temperature unevenness due to heat dissipation from both ends is suppressed, and the fixing property is uniform and high quality A good image was obtained.

  Accordingly, it has been possible to provide a copying machine equipped with an energy-saving fixing device as well as ensuring reliability and safety over a long period of time and maintaining the life of the heating member.

(Example 2)
The fixing device used in Example 2 is the fixing device 15 described above. The planar heating element used in Example 2 is the planar heating element 40 described above. Specifically, a polyimide film having a thickness of 25 μm is used as an insulating layer, and a stainless steel foil is formed as a resistance heating element in accordance with the heating patterns 41, 44, and 47 of the planar heating element 40. The polyimide film was insulatively covered with an adhesive to obtain a film heater as a planar heating element. This film heater was adhered and adhered to the inner surface of a base material made of aluminum with a heat-resistant adhesive made of polyimide resin. Furthermore, a 20 μm-thick topcoat layer made of PTFE resin and PFA resin was formed on the outer surface of the substrate and in contact with the fixing belt. Except for the above, the procedure was the same as in Example 1.

  In the evaluation, three types of planar heating elements having different electric resistance values were used by changing the thickness of the stainless steel foil in consideration of variations in the production of the stainless steel foil as the resistance heating element. The electrical resistance values of the three types of planar heating elements used in the evaluation are 9.0Ω ± 1%, 10.0Ω ± 1%, 11.0Ω ± 1% at 25 ° C., respectively. The electrical resistance values at 10 ° C. were 10.53Ω, 11.53Ω, and 12.53Ω, respectively.

  First, the voltage applied to the film heater, which is a sheet heating element, is set to 100 V, the warm-up time in the copying machine, the temperature unevenness when 50 sheets are continuously fed, and the edge rise when small-size sheets are passed. The temperature was observed.

  The time required for the entire fixing belt surface temperature on the fixing roller to reach 200 ° C. (warm-up time) is 23.7 sec in the case of a planar heating element having an electrical resistance value of 9.0Ω, and the electrical resistance value is 10.0Ω. In this case, 26.3 sec, and in the case where the electric resistance value was 11.0Ω, it was 28.9 sec. A target warm-up time of 30 sec or less could be achieved regardless of variations in the electrical resistance value of the planar heating element.

  In addition, as a set power value to be supplied to the resistance heating element of the sheet heating element, when the electrical resistance value is 9.0Ω, 190 W at both ends and 570 W at the center part, and when the electrical resistance value is 10.0Ω. When both ends are 173 W, the center is 520 W, and the electrical resistance is 11.0Ω, the both ends are 160 W and the center is 479 W.

  By setting the set power value to be supplied to the resistance heating element of the sheet heating element in this way, there was almost no image density unevenness in continuous paper passing, and a high quality image was obtained. Furthermore, when the temperature at both ends of the sheet heating element when small-size paper was passed was measured with a heating element side thermistor, no excessive temperature increase was observed, and power consumption could be efficiently suppressed.

  In addition, since the top coat layer made of PTFE resin and PFA resin is formed on the outer surface of the base material, the frictional force between the base material and the fixing belt is suppressed, resulting in smooth sliding with no frictional resistance. In addition, heat transfer efficiency to the fixing belt is good, and the meandering of the fixing belt can be suppressed. Further, a non-contact thermistor is used to detect the temperature of the fixing belt surface, so there is no damage to the bell and the surface, and the belt life is 200K. I was able to secure it.

  In addition, the density of the resistance heating element is high at both ends of the planar heating element, so the power density at both ends is higher than the central part, temperature unevenness due to heat dissipation from both ends is suppressed, and the fixing property is uniform and high quality A good image was obtained.

  Accordingly, it has been possible to provide a copying machine equipped with an energy-saving fixing device as well as ensuring reliability and safety over a long period of time and maintaining the life of the heating member.

(Comparative Example 1)
The heating pattern in the planar heating element used for the heating member was changed from the heating pattern 41, 44, 47 of the planar heating element 40 to the heating pattern 201 of the planar heating element 200 in the prior art. FIG. 14 is a diagram illustrating a configuration of a planar heating element 200 provided in a conventional fixing device. The planar heating element 200 has a heating pattern 201 composed of a resistance heating element 202 that forms a fixed surface as a whole. The heat generating pattern 201 made up of the resistance heating element 202 includes a plurality of substantially parallel linear portions 202a arranged to be inclined at a predetermined angle θ with respect to the axial direction X of the fixing belt. 203 is formed on the surface. At this time, in the resistance heating element 202, the connecting portions 202b are connected so that both ends in the extending direction of the adjacent linear portions 202a extend in the longitudinal direction of the planar heating element 200 to form one line. And formed on one surface of the insulating layer 203. Then, both ends of the resistance heating element 202 are connected to the power source 204 via the energization control unit 205. At this time, the planar heating element 200 is configured such that the energization control unit 205 performs energization control based only on the temperature detected by the heating element-side thermistor. Except for the above, the procedure was the same as in Example 2. The electrical resistance value of the resistance heating element of the planar heating element used for the evaluation was 10.0Ω ± 10% at 25 ° C. and 11.53Ω at 200 ° C.

  First, the voltage applied to the resistance heating element of the sheet heating element is set to 100V, the warm-up time, the temperature unevenness when 50 sheets are continuously passed, and the edge temperature rise when passing a small size sheet evaluated. The time (warm-up time) for the entire fixing belt surface temperature on the fixing roller to reach 200 ° C. was 26.3 sec.

  In Comparative Example 1, image density unevenness occurred during continuous paper passing, resulting in an image defect. Further, when the temperature at both ends of the sheet heating element when small-size paper was passed was measured with a heating element side thermistor, an excessive temperature increase occurred, and the heating member and the fixing member were damaged.

  Also in Comparative Example 1, a top coat layer made of PTFE resin and PFA resin is formed on the outer surface of the base material, but when a small size paper is passed as described above, a planar heating element Since heat dissipation was not suppressed at both ends, the balance of the sliding resistance of the fixing belt was poor, smooth sliding was not possible, and suppression of the meandering of the fixing belt could not be achieved. For this reason, the fixing belt was cracked at 10K.

1 is a diagram illustrating a configuration of an image forming apparatus 100 according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a fixing device 15 according to a first embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a heating member 60 included in the fixing device 15. It is a figure which shows the structure of the planar heating element 20 which is a 1st example of the planar heating element which the heating member 60 has. It is a figure which shows the area | region in which connection part 22b, 25b, 28b is formed in resistance heating element 22,25,28. 3 is a block diagram illustrating a configuration of a control unit 90 that controls energization in the planar heating element 20. FIG. It is a graph which shows the relationship between the applied voltage and electric power in the difference in the electrical resistance value of a resistance heating element. It is a graph which shows the relationship between the temperature of a resistance heating element, and an electrical resistance value in the difference in the electrical resistance value of a resistance heating element, and the relationship between the temperature of a resistance heating element, and an electric power value. It is a graph which shows the relationship between the energization time with respect to a resistance heating element, and a power value in the difference between the electrical resistance value and applied voltage value of a resistance heating element, and the relationship between energization time with respect to a resistance heating element and temperature. 4 is a graph showing the relationship between the energizing time for the resistance heating element and the calculated power value and the relationship between the energizing time for the resistance heating element and the temperature in energization control for the planar heating element 20. FIG. 4 is a view showing a heat generation pattern at both end portions of a planar heating element 20. It is a figure which shows the structure of the planar heating element 40 which is a 2nd example of a planar heating element. It is a figure which shows the structure of the fixing device 80 which is 2nd Embodiment of this invention. It is a figure which shows the structure of the planar heating element 200 with which the fixing device of a prior art is provided.

Explanation of symbols

15, 80 Fixing device 20, 40 Planar heating element 21, 24, 27, 41, 44, 47 Heat generation pattern 22, 25, 28, 42, 45, 48 Resistance heating element 31, 50 Insulating layer 33, 52 Feed control unit 60, 70 Heating member 62, 72 Base material 63 Heating element side thermistor 64 Fixing belt 65 Pressure roller side thermistor 90 Control means 91 Main control part 92 Detection part 93 Power calculation part 100 Image forming apparatus

Claims (9)

An endless fixing belt stretched between a fixing member and a heating member, and a pressure member facing the fixing member via the fixing belt, and the heating member comes into contact with the fixing belt for fixing A fixing device that heats and fixes a toner image carried on a recording medium on a recording medium in a fixing nip formed by heating the belt and formed by the fixing belt and the pressure member;
In the heating member that heats the fixing belt in contact with the fixing belt in the heating member, a resistance heating element that generates heat when energized forms a heat generating pattern by forming a surface having a certain shape as a whole. A planar heating element formed on one surface in the thickness direction is formed,
The heat generation pattern is divided into a plurality in the longitudinal direction of the insulating layer, and a plurality of the heat generation patterns are formed, and in a state of being distinguished from each other, energization is controlled by a control unit,
The control means includes
A detection unit for detecting a current value and a voltage value applied to each resistance heating element constituting the plurality of heat generation patterns;
A power calculator that calculates a power value from the current value and the voltage value detected by the detector;
Based on the calculated power value calculated by the power calculation unit, power supply control for controlling power supply to the resistance heating element such that each resistance heating element constituting the plurality of heating patterns generates heat within a predetermined temperature range. A fixing device. An endless fixing belt stretched between a fixing member and a heating member, and a pressure member facing the fixing member via the fixing belt, and the heating member comes into contact with the fixing belt for fixing A fixing device that heats and fixes a toner image carried on a recording medium on a recording medium in a fixing nip formed by heating the belt and formed by the fixing belt and the pressure member;
In the heating member that heats the fixing belt in contact with the fixing belt in the heating member, a resistance heating element that generates heat when energized forms a heat generating pattern by forming a surface having a certain shape as a whole. A planar heating element formed on one surface in the thickness direction is formed,
The heat generation pattern is divided into a plurality in the longitudinal direction of the insulating layer, and a plurality of the heat generation patterns are formed, and in a state of being distinguished from each other, energization is controlled by a control unit,
The control means includes
A detection unit for detecting a voltage value applied to each resistance heating element constituting the plurality of heating patterns;
A power calculation unit that calculates a power value from the voltage value detected by the detection unit and a specific electrical resistance value of the resistance heating element;
Based on the calculated power value calculated by the power calculation unit, power supply control for controlling power supply to the resistance heating element such that each resistance heating element constituting the plurality of heating patterns generates heat within a predetermined temperature range. A fixing device. The resistance heating element of the planar heating element has a positive resistance temperature characteristic,
The power supply control unit applies power to the resistance heating element when the calculated power value calculated by the power calculation unit is equal to or lower than a preset power value based on an electrical resistance value at a predetermined temperature of the resistance heating element. The fixing device according to claim 1, wherein power supply is interrupted and power supply to the resistance heating element is resumed when the temperature of the resistance heating element reaches a predetermined temperature. Non-contact temperature detecting means for detecting the temperature of the surface of the fixing belt in a non-contact state with respect to the fixing belt,
The fixing device according to claim 1, wherein the control unit controls energization of the planar heating element based on the temperature detected by the non-contact temperature detection unit. The resistance heating element is
Extending in a direction substantially orthogonal to the longitudinal direction of the insulating layer, a plurality of linear portions formed on one surface of the insulating layer in a substantially parallel state,
A connecting portion formed on one surface of the insulating layer by connecting adjacent end portions of the linear portions in the longitudinal direction of the insulating layer so as to form one line. ,
The fixing device according to claim 1, wherein an extending direction of the plurality of linear portions is inclined at a predetermined angle with respect to a longitudinal direction of the planar heating element. .   In the planar heating element, an interval between a plurality of adjacent linear parts is set so as to become smaller from the central part toward both ends in a predetermined region at both longitudinal ends of the planar heating element. The fixing device according to claim 5. The heating part of the heating member is
A planar heating element is formed on one surface of a base material made of a material having high thermal conductivity,
The fixing device according to claim 1, wherein a coating layer capable of reducing a frictional force with the fixing belt is formed on a surface on a side in contact with the fixing belt. .   The fixing device according to claim 7, wherein the coat layer is made of at least one of a PTFE resin containing fluorine and a PFA resin.   An image forming apparatus comprising the fixing device according to claim 1.

Images