JP2008139864A - Fixing device and control method of fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-quality fixed image even at the time of continuous image formation at a high speed by solving an insufficiency of heat capacity of a heat generating member accompanying an increase in warm-up time with an induction heating type fixing device, Improve productivity during image formation.
SOLUTION: A heat capacity of a heat roller 20 is reduced, and a belt 33 facing the heat roller 20 is heated by a metal roller 32 that is induction-heated. An auxiliary pressure member 42 for pressing the belt 33 against the heat roller 20 is provided at the position of the nip 37 between the heat roller 20 and the belt 33. Further, the distance around the heat roller 20 from the first and second thermistors 56a, 56b to the center of the first and second induced current generating coils 50a, 50b and further to the nip 37, and around the belt 33 The distances from the third and fourth thermistors 61a and 61b to the center of the central coil 60a and the side coil 60b and the distance to the nip 37 are the same.
[Selection] Figure 2

Description

  The present invention relates to a fixing device mounted on an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to a fixing device and a control method for the fixing device using an induction heating method.

In recent years, there are induction heating type fixing devices used in image forming apparatuses such as electrophotographic copying machines and printers. In this induction heating type fixing device, it is desired to further increase the fixing speed by shortening the warm-up time of the fixing device. For this reason, there is an image heating apparatus in which an exciting coil is arranged around a heat generating roller having a small heat capacity to shorten the warm-up time (for example, Patent Document 1).
US Pat. No. 6,819,904

  However, in Patent Document 1, although the heat generating roller on the side in contact with the toner image is heated by the exciting coil to increase the speed, there is no heat source on the pressure member side. For this reason, when a large amount of heat is continuously consumed during fixing, such as when a color image is continuously formed at a high speed, the amount of heat on the pressing member side is particularly insufficient, and fixing failure may occur.

  Accordingly, the present invention solves the above-mentioned problems, and in a fixing device that achieves high speed by an induction heating method, the shortage of heat on the pressure member side is resolved, and fixing is performed even during continuous color image formation at high speed. It is an object of the present invention to provide a fixing device and a fixing device control method capable of obtaining a high-quality fixed image without causing defects.

  As a means for solving the above-mentioned problems, the present invention provides a heat generating member having a metal layer that is induction-heated, a first induced current generator disposed in proximity to the heat generating member, and the heat generating member. A belt that is rotatably supported by a plurality of rollers and forms a nip with the heat generating member, and a second induction current generator that is disposed around the belt and that heats the belt by induction heating. And a pressing member that presses the belt against the heat generating member at the nip position.

  According to the present invention, the warm-up time can be shortened, the shortage of heat capacity during continuous image formation can be compensated, and the image productivity can be improved. Furthermore, the load applied to the nip between the heat generating member and the belt at the time of fixing can be reduced, and the life of the heat generating member and the belt can be extended. In addition, the productivity of the image can be improved by increasing the speed of the control of the heat generating member and the belt.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic configuration diagram showing an image forming apparatus 1 according to a first embodiment of the present invention. The image forming apparatus 1 includes a scanner unit 6 that reads a document, and a paper feeding unit 3 that supplies sheet paper P as a fixing medium to a printer unit 2 that forms an image. The scanner unit 6 converts image information read from a document supplied by the automatic document feeder 4 provided on the upper surface into an analog signal.

  The printer unit 2 performs image forming stations 18Y, 18M, 18C for each color of yellow (Y), magenta (M), cyan (C), and black (K) along the transfer belt 10a rotated in the direction of the arrow q. The image forming unit 10 is arranged in 18K in tandem. Further, the image forming unit 10 includes a laser exposure device 19 that irradiates the photosensitive drums 12Y, 12M, 12C, and 12K of the image forming stations 18Y, 18M, 18C, and 18K of the respective colors with laser beams according to image information. Further, the printer unit 2 includes a fixing device 11 and a paper discharge roller 52, and includes a paper discharge conveyance path 53 that conveys the fixed sheet paper P to the paper discharge unit 5.

  In the yellow (Y) image forming station 18Y of the image forming unit 10, a charger 13Y, a developing device 14Y, a transfer roller 15Y, a cleaner 16Y, and a static eliminator 17Y are arranged around the photosensitive drum 12Y rotating in the direction of arrow r. It has become. The magenta (M), cyan (C), and black (K) image forming stations 18M, 18C, and 18K have the same configuration as the yellow (Y) image forming station 18Y.

  The paper feed unit 3 includes first and second paper feed cassettes 3a and 3b. In the conveyance path 7 of the sheet paper P from the paper feed cassettes 3a and 3b to the image forming unit 10, pickup rollers 7a and 7b for taking out the sheet paper P from the paper feed cassettes 3a and 3b, separation conveyance rollers 7c and 7d, conveyance A roller 7e and a registration roller 8 are provided.

  When the printing operation is started, in the yellow (Y) image forming station 18Y of the printer unit 2, the photosensitive drum 12Y is rotated in the direction of the arrow r and is uniformly charged by the charger 13Y. Next, the photosensitive drum 12Y is irradiated with exposure corresponding to the yellow image information read by the scanner unit 6 by the laser exposure device 19 to form an electrostatic latent image. Thereafter, toner is supplied to the photosensitive drum 12Y by the developing device 14Y, and a yellow (Y) toner image is formed on the photosensitive drum 12Y. This yellow (Y) toner image is transferred to the sheet paper P conveyed in the direction of arrow q on the transfer belt 10a at the position of the transfer roller 15Y. After the transfer of the toner image, the photosensitive drum 12Y is cleaned of residual toner by the cleaner 16Y, the surface of the photosensitive drum 12Y is discharged by the charge eliminator 17Y, and the next printing can be performed.

  In the magenta (M), cyan (C), and black (K) image forming stations 18M, 18C, and 18K, toner images are formed in the same manner as the yellow (Y) image forming station 18Y. The toner images of the respective colors formed by the image forming stations 18M, 18C, and 18K are sequentially transferred to the sheet paper P on which the yellow toner image is formed at the positions of the transfer rollers 15M, 15C, and 15K. The sheet paper P on which the color toner image has been formed in this way is heated and pressed and fixed by the fixing device 11 to complete the print image and discharged to the paper discharge unit 5.

  Next, the fixing device 11 will be described. FIG. 2 is a schematic configuration diagram of the fixing device 11 viewed from the axial direction. The fixing device 11 is a heat generating member and includes a heat roller 20 having an outer diameter of 50 mm. A unitized belt mechanism 30 having a belt is disposed at a position facing the heat roller 20. The belt mechanism 30 includes a plurality of opposing rollers 31 and metal rollers 32, and an endless belt 33 supported by the opposing rollers 31 and the metal rollers 32. Further, the belt mechanism 30 has an auxiliary pressure member 42 that is a pressing member for increasing the nip width. The auxiliary pressure member 42 is pressed by the spring 41 to press the belt 33 against the heat roller 20. As a result, a nip 37 having a constant width is formed between the heat roller 20 and the belt 33.

  The heat roller 20 is rotated in the arrow s direction by the first drive motor 36a. The belt 33 travels in the arrow t direction by the rotation of the metal roller 32 by the second drive motor 36b. The heat roller 20 and the belt 33 sandwich the sheet paper P at the nip 37 and convey it in the direction of the paper discharge roller 52. The sheet paper P passes through such a nip 37 between the heat roller 20 and the belt 33, whereby the toner image on the sheet paper P is fixed by heating and pressing. The drive mechanism of the heat roller 20 and the belt 33 is not limited. For example, the heat roller 20 and the belt 33 may be rotated by the same drive motor.

  The heat roller 20 has an elastic roller 21 and a surface layer 22. The elastic roller 21 includes a cored bar 20a made of, for example, iron (Fe) or aluminum, and a foamed silicon rubber layer 20b that is an elastic layer disposed around the cored bar 20a. The cored bar 20a may be either solid or hollow. The foamed silicon rubber layer 20b has heat resistance and heat insulation, and is composed of, for example, an open-cell microcellular foam having an average cell diameter of about 150 microns.

  As shown in FIG. 3, the surface layer 22 is formed, for example, on the surface of a metal conductive layer 20c, which is a metal layer having a thickness of 30 to 50 μm formed of nickel (Ni), and has a thickness of 0.1 to 0.5 mm, for example. It has a rubber layer 20d. Further, the surface layer 22 is configured by forming a release layer 20e on the surface of the silicon rubber layer 20d. The release layer 20e is made of, for example, a fluororesin (PFA or PTFE (polytetrafluoroethylene) or a mixture of PFA and PTFE). The layer thickness of the release layer 20e is, for example, 0.05 to 0.2 mm. The metal layer is not limited to nickel, but may be magnetic stainless steel, iron, or the like. Any metal layer may be used as long as it is an induction heating method and has good heating efficiency.

  The foamed silicon rubber layer 20b of the elastic roller 21 thermally insulates the metal core 20a and the metal conductive layer 20c. As a result, the heat capacity of the entire heat roller 20 can be kept low. The foamed silicon rubber layer 20b keeps the nip 37 formed with the belt 33 wide, and keeps a distance that does not affect the magnetic flux generated from the induced current generator to the core 20a. For example, the thickness is about 5 to 15 mm. If the foamed silicon rubber layer 20b is too thick, the stress at the interface with the cored bar 20a increases due to the torque (load) accompanying the rotation of the heat roller 20. Since the foamed silicon rubber layer 20b may be damaged at the boundary surface with the core metal 20a due to this stress, the thickness of the foamed silicon rubber layer 20b is desirably about 15 mm or less. The rubber hardness of the foamed silicon rubber layer 20b is preferably about ASKER C 20 to 40 °.

  The cored bar 20a and the foamed silicon rubber layer 20b of the elastic roller 21 are fixed to each other. The metal conductive layer 20c and the silicon rubber layer 20d, and the silicon rubber layer 20d and the release layer 20e of the surface layer 22 are also fixed to each other. However, the foamed silicon rubber layer 20b and the metal conductive layer 20c are not bonded.

  The elastic roller 21 has an outer diameter that is, for example, about 0.2 to 0.7 mm smaller than the inner diameter of the surface layer 22 at room temperature (25 ° C.). Therefore, since the surface layer 22 is not bonded and fixed to the elastic roller 21, the surface layer 22 can be slid with respect to the elastic roller 21, and can be replaced when the surface layer 22 reaches the end of its life. The elastic roller 21 is thermally expanded by heating. For example, if the surface of the heat roller 20 is left at a fixing temperature of 170 ° C., the foamed silicon rubber layer 20b gradually expands. In this state, the outer diameter of the elastic roller 21 is about 0.2 to 0.5 mm larger than the inner diameter of the surface layer 22 in a state where the foamed silicon rubber layer 20b is expanded. As a result, the surface layer 22 is fitted to the elastic roller 21 in a state where the elastic roller 21 is tightened. The structure of the heat roller 20 is not limited, and the foamed silicon rubber layer 20b and the metal conductive layer 20c may be bonded and formed integrally.

  In the belt mechanism 30, the opposing roller 31 is brought into contact with the heat roller 20. As a result, the belt 33 is brought into pressure contact with the heat roller at the position of the opposing roller 31. Further, the belt 33 is pressed against the heat roller 20 by the auxiliary pressure member 42. Accordingly, a nip 37 having a constant width of, for example, 14 mm is formed between the heat roller 20 and the belt 33 and extends from the opposing roller 31 to the auxiliary pressure member 42. On the other hand, the metal roller 32 is made of magnetic stainless steel. However, the metal roller is not limited to this, and may be iron, nickel, or the like as long as it has an induction heating method and good heating efficiency.

  As shown in FIG. 4, the belt 33 includes, for example, a base material 33a made of heat-resistant resin such as polyimide resin, an elastic layer 33b made of heat-resistant rubber such as silicon rubber, and a release layer 33c made of fluorine resin such as PFA. Is formed. The base material 33a has a thickness of 0.1 to 0.5 mm, for example. The belt used in the belt mechanism 30 is not limited to resin, and metal powder may be dispersed in the base material. As a result, the belt itself can generate heat by induction heating.

  The auxiliary pressure member 42 of the belt mechanism 30 is made of silicon rubber having a rectangular cross section, and the rectangular corner is formed in a rounded R shape. The auxiliary pressure member 42 forms a nip 37 between the heat roller 20 and the belt 33 together with the opposing roller 31 to widen the width of the nip 37. By widening the width of the nip 37 in this way, the load of the auxiliary pressure member 42 on the heat roller 20 when the sheet paper P is nipped and fixed at the nip 37 can be reduced. In this embodiment, the load of the auxiliary pressure member 42 on the heat roller 20 at the time of fixing is 400 N, for example.

  On the outer periphery of the heat roller 20, there are a peeling claw 54, first and second induced current generating coils 50 a and 50 b that are first induced current generators, and a heat generating member temperature sensor, which are in non-contact with the heat roller 20. First and second thermistors 56a and 56b and first and second thermostats 57a and 57b are provided. The peeling claw 54 prevents the sheet paper P after fixing from being wrapped around the heat roller 20. The peeling claw 54 may be either a contact type or a non-contact type.

  The first and second induced current generating coils 50a and 50b are provided on the outer periphery of the heat roller 20 via a predetermined gap, and cause the metal layer 20c of the heat roller 20 to generate heat. The first induced current generating coil 50 a generates heat in the central area of the heat roller 20, and the second induced current generating coil 50 b generates heat in areas on both sides of the heat roller 20. Therefore, when fixing small-sized sheet paper P, electric power is supplied to the first induced current generating coil 50a to generate heat in the central region of the heat roller 20, while the second induced current generating coil 50b. The power supply to is stopped.

  Further, when the heat roller 20 generates heat over the entire length, the first and second induction current generating coils 50a and 50b are alternately switched and output, and both can be adjusted to, for example, 200W to 1500W. Has been. The first and second induced current generating coils 50a and 50b may be capable of outputting simultaneously. In the case of simultaneous output, the output values of the first induced current generating coil 50a and the second induced current generating coil 50b can be changed. For example, when there is more sheet paper P passing through the central region of the heat roller 20 than on both sides, the output of the first induced current generating coil 50a may be made larger than the output of the second induced current generating coil 50b. Is possible.

  The first and second induced current generating coils 50 a and 50 b are formed by winding a wire around a magnetic core for concentrating the magnetic flux on the heat roller 20. As the wire, for example, a litz wire formed by bundling a plurality of copper wires covered with heat-resistant polyamideimide and insulated from each other is used. By using a litz wire as the wire, the diameter of the wire can be made smaller than the penetration depth of the magnetic field. Thereby, it becomes possible to flow a high-frequency current through the wire effectively. In this embodiment, 40 copper wires having a diameter of 0.3 mm are bundled to form a litz wire.

  When a predetermined high-frequency current is supplied to such a litz wire, the first and second induced current generating coils 50a and 50b generate magnetic flux. Due to this magnetic flux, an eddy current is generated in the metal layer 20c so as to prevent a change in the magnetic field. Joule heat is generated by the eddy current and the resistance value of the metal layer 20c, and the heat roller 20 is instantaneously heated.

  As the first and second thermistors 56a and 56b that are not in contact with the heat roller 20, for example, thermopile type infrared temperature sensors are used. The thermopile type infrared temperature sensor receives infrared rays, calculates infrared energy, and detects the temperature change of the hot junction generated in the thermopile as the starting power of the thermocouple. The first thermistor 56a detects the surface temperature at the center of the heat roller 20 and converts it into a voltage. The second thermistor 56b detects the surface temperature of the side portion of the heat roller 20 and converts it into a voltage.

  The first thermostat 57 a detects an abnormality in the surface temperature of the center portion of the heat roller 20. The second thermostat 57 b detects an abnormality in the surface temperature of the side portion of the heat roller 20. When the first or second thermostat 57a, 57b detects an abnormality, the power supply to the first and second induced current generating coils 50a, 50b is forcibly turned off.

  A central coil 60a and a side coil 60b, which are second induced current generators, are provided around the belt 33 and at positions facing the metal roller 32. Third and fourth thermostats 62a and 62b are provided around the belt 33 after passing through the positions of the central coil 60a and the side coil 60b. Further, around the belt 33 after passing through the nip 37, third and fourth thermistors 61a and 61b, each of which is a belt temperature sensor and is a thermopile infrared temperature sensor that is not in contact with the belt 33, are provided.

  The central coil 60 a generates heat at the center in the width direction of the metal roller 32, and the side coil 60 b generates heat at both sides in the width direction of the metal roller 32. Accordingly, when fixing the small-sized sheet paper P, power is supplied to the central coil 60a to generate heat at the center of the metal roller 32, while power supply to the side coil 60b is stopped. When the entire length of the metal roller 32 is heated, the central coil 60a and the side coil 60b are alternately switched and output, and both are set to be adjustable from 200 W to 1200 W, for example. The central coil 60a and the side coil 60b may be capable of outputting simultaneously. The central coil 60a and the side coil 60b are formed in the same manner as the first and second induced current generating coils 50a and 50b. The metal roller 32 is instantaneously heated by the magnetic flux of the central coil 60a and the side coil 60b, and heats the belt 33.

  The third thermistor 61a detects the surface temperature at the substantially center in the width direction of the belt 33 and converts it into a voltage. The fourth thermistor 61b detects the surface temperature of the side portion in the width direction of the belt 33 and converts it into a voltage. The third thermostat 62 a detects an abnormality in the surface temperature of the central portion in the width direction of the belt 33. The fourth thermostat 62 b detects an abnormality in the surface temperature of the side portion of the belt 33 in the width direction. When the third or fourth thermostat 62a, 62b detects an abnormality, the power supply to the central coil 60a and the side coil 60b is forcibly turned off.

  Next, the arrangement of the first and second induced current generating coils 50a and 50b around the heat roller 20, the central coil 60a and the side coil 60b around the belt, and the first and second thermistors 56a and 56b The arrangement of the third and fourth thermistors 61a and 61b will be described.

  In FIG. 2, the entrance position of the nip 37 is a, the central position of induction heating by the first and second induction current generating coils 50a and 50b is b, and the central position of induction heating by the central coil 60a and the side coil 60b is c. And At this time, the first and second induced current generating coils 50a and 50b, the central coil 60a and the side coil 60b around the belt have the same distance between b and a and the distance between c and a. Placed in position.

  Further, a reading position on the heat roller 20 by the first and second thermistors 56a and 56b is d, and a reading position on the belt 33 by the third and fourth thermistors 61a and 61b is e. At this time, the first and second thermistors 56a and 56b and the third and fourth thermistors 61a and 61b are arranged at positions where the distance between d and b and the distance between e and c are the same. The

  When the surface temperature of the heat roller 20 and the belt 33 is feedback controlled by making the distance between b and a the same between c and a, the first and second induced current generating coils 50a and 50b It is possible to align the phases of control and control of the central coil 60a and the side coil 60b. Further, by making the distance between d and b the same as the distance between e and c, the phase difference control of the temperature difference between the heat roller 20 side and the belt 33 side by heat transfer to the sheet paper P at the time of fixing is performed. Can be constant. Therefore, phase difference control by the control unit is facilitated.

  In particular, when the heat capacities of the heat roller 20 and the belt 33 are small, the temperature ripple due to the supply of electric power increases. For this reason, very delicate control is required when feedback controlling the temperature of the heat roller 20 and the belt 33. Therefore, by facilitating the phase difference control in the control unit as described above, it is possible to prevent the feedback control of the surface temperature of the heat roller 20 and the belt 33 from becoming complicated.

  Further, as in this embodiment, the heat roller 20 and the belt 33 are divided into two parts by the first and second induced current generating coils 50a and 50b and the third and fourth induced current generating coils 60a and 60b, respectively. In the case of temperature control, setting control of the inverter drive circuit 72 by the CPU 71 becomes more complicated than in the case of using an integral induction current generating coil. Therefore, particularly in such a case, the setting control of the inverter drive circuit 72 can be speeded up by facilitating the phase difference control in the CPU 71.

  Next, a control system 70 for controlling the temperature of the heat roller 20 and the belt 33 will be described with reference to FIG. The control system 70 has, on the secondary side, a CPU 71 that is a control unit that controls the entire image forming system, including optional devices such as a document feeder, finisher, or fax machine. On the other hand, the control system 70 includes, on the primary side, first and second induction current generating coils 50a and 50b, an inverter drive circuit 72 for supplying drive power to the central coil 60a and the side coil 60b, and a commercial AC power source 73. A noise filter 74 that rectifies the current and supplies it to the inverter drive circuit 72, a coil control circuit 76 that controls the inverter drive circuit 72, and an output of the noise filter 74 are detected so that the power from the commercial AC power source 73 becomes constant. A power supply detection circuit 77 and a fuse 78 are fed back.

  The interface 80 of the secondary side CPU 71 is transmitted to and received from the primary side coil control circuit 76 via the photocoupler 81. By using the photocoupler 81, the secondary and primary sides of the control system 70 can be insulated. The temperature detection results by the first and second thermistors 56 a and 56 b and the third and fourth thermistors 61 a and 61 b are input to the CPU 71.

  Next, temperature control of the heat roller 20 and the belt 33 by the control system 70 will be described using the flowchart of FIG. The belt mechanism 30 is separated from the heat roller 20 while the image forming apparatus 1 is powered off. In this state, when the image forming apparatus 1 is turned on, the OS of the CPU 71 is activated to control the entire image forming system. It is compared whether the OS of the CPU 71 is activated (step 101). When the OS is activated, it is compared whether the belt mechanism 30 is at the home position separated from the heat roller 20 (step 102). If the belt mechanism 30 is not at the home position, the belt mechanism 30 is moved to the home position, and a separation operation for separating from the heat roller 20 is performed (step 103).

  If the belt mechanism 30 is at the home position in step 102, the first and second drive motors 36a and 36b are turned on to rotate the heat roller 20 and the belt 33, respectively (step 105). Next, the inverter drive circuit 72 supplies power to the first and second induced current generating coils 50a and 50b, the central coil 60a and the side coil 60b around the belt (step 106), and warm-up is started. At this time, the total amount of power that can be used by the entire image forming apparatus 1 is determined. For this reason, the inverter drive circuit 72 is connected to the first and second induction current generating coils 50a and 50b, the center coil 60a, and the side coil 60b within the range of the electric energy that can be used for temperature control out of the total electric energy. Is optimally allocated and feedback controlled.

  The first and second thermistors 56a and 56b and the third and fourth thermistors 61a and 61b allow the surface temperature of the heat roller 20 and the belt 33 to contact the heat roller 20 and the belt mechanism 30. When it is detected that the pre-run temperature is reached (step 107), the heat roller 20 and the belt mechanism 30 are brought into contact with each other (step 108). At this time, the load of the auxiliary pressure member 42 is 400 N, and the width of the nip 37 between the heat roller 20 and the belt 33 is 14 mm. Thereafter, the warm-up operation is continued, and it is compared whether the surface temperature of the heat roller 20 reaches 170 ° C. and the surface temperature of the belt 33 reaches 160 ° C., for example (step 110). When the heat roller 20 and the belt 33 reach the fixing possible temperature in step 110, the warm-up is completed and the image forming apparatus 1 enters the standby mode.

  In this standby mode, the surface temperature of the heat roller 20 is detected by the first and second thermistors 56a and 56b, and the first and second induced current generating coils 50a and 50b are fed back so as to maintain the fixable temperature. Control. Similarly, the surface temperature of the belt 33 is detected by the third and fourth thermistors 61a and 61b, and the central coil 60a and the side coil 60b are feedback-controlled so as to maintain the fixable temperature.

  When a print command is instructed from the CPU 71 after the warm-up is completed, the printer unit 2 starts a print operation and forms a toner image on the sheet paper P in the image forming unit 10. Next, the sheet paper P having the toner image is inserted into a nip 37 having a width of 14 mm between the heat roller 20 and the belt 33, and the toner image is fixed by heating and pressing.

  At the time of fixing, the sheet paper P can also obtain fixing energy from the back surface of the sheet paper P by the belt 33 whose temperature is controlled by the inverter drive circuit 72. Therefore, although the heat capacity of the heat roller 20 and the belt 33 is small, the sheet paper P can obtain fixing energy from both sides, and the sheet paper P has sufficient fixing energy even if the fixing operation is performed continuously at high speed. Will be obtained.

  On the other hand, when the small-size sheet P is continuously fixed, the heat capacities of the heat roller 20 and the belt 33 are small, so that the temperature of the heat roller 20 and the belt 33 is on the side of the heat roller 20 outside the paper passing area. The rise is intense. Therefore, in order to prevent the heat roller 20 or the belt 33 from reaching the heat resistance limit, it waits for the temperature of the heat roller 20 or the belt 33 to decrease before the heat roller 20 or the belt 33 reaches the heat resistance limit. Because of this, wait time is required. However, in this embodiment, since the setting control of the inverter drive circuit 72 by the CPU 71 is speeded up, the temperature of the side portions of the heat roller 20 and the belt 33 rises, and it becomes possible to cope with it early. Therefore, it is possible to shorten the wait time for waiting for the temperature of the side portions of the heat roller 20 and the belt 33 to decrease.

  In this way, while the wait time has elapsed, the fixing operation is completed while the heat roller 20 and the belt 33 are held at the fixing possible temperature, and when there is no print command for a predetermined time after entering the standby mode, The forming apparatus 1 is in the preheating mode.

  In each mode, the CPU 71 always uses the temperature detection results from the first and second thermistors 56a and 56b and the third and fourth thermistors 61a and 61b, so that the surface temperature of the heat roller 20 and the belt 33 is increased. Is controlled to maintain the temperature at various locations. Based on this setting, the CPU 71 controls the inverter drive circuit 72 via the coil control circuit 76. Thus, when setting and controlling the inverter drive circuit 72, the CPU 71 determines the positions of the first and second induced current generating coils 50a and 50b, the center coil 60a, and the side coil 60b in the heat roller 20 and the belt 33. There is no need to consider the difference and the phase difference due to the difference in position between the first and second thermistors 56a, 56b and the third and fourth thermistors 61a, 61b. Therefore, the setting control of the inverter drive circuit 72 by the CPU 71 is facilitated, and the control speed can be increased.

  Note that while the inverter drive circuit 72 performs feedback control of the surface temperature of the heat roller 20 in this way, the surface temperature of the heat roller 20 is set to a threshold value because the inverter drive circuit 72 cannot be controlled due to a malfunction. Is exceeded, the first or second thermostat 57a, 57b or the third or fourth thermostat 62a, 62b detects an abnormality and forcibly turns off the inverter drive circuit 72.

  According to the fixing device 11 of the first embodiment, the heat capacity of the heat roller 20 is reduced to increase the warm-up time. Further, the belt 33 is heated by induction heating of the metal roller 32 using the central coil 60a or the side coil 60b to compensate for the lack of heat capacity on the heat roller 20 side during continuous fixing. Therefore, during continuous fixing, fixing failure due to insufficient fixing energy can be prevented, and the wait time for waiting for the heat roller 20 to reach the fixing temperature can be shortened, thereby preventing reduction in productivity during image formation. .

  Furthermore, by providing the auxiliary pressure member 42, the width of the nip 37 can be widened without increasing the load. Therefore, the load between the nip 37 of the heat roller 20 and the belt 33 can be reduced at the time of fixing, and the life of the heat roller 20 and the belt 33 can be extended.

  Further, the distance from the detection of the surface temperature in the heat roller 20 to the nip through heating is the same as the distance from the detection of the surface temperature in the belt 33 to the nip through the heating. . Therefore, when the CPU 71 performs setting control of the inverter drive circuit 72, it is not necessary to perform phase difference interpolation control due to the dislocation of the thermistor and the coil between the heat roller 20 and the belt 33. Setting control of the drive circuit 72 is facilitated. Thereby, the setting control of the inverter drive circuit 72 by the CPU 71 can be speeded up. As a result, the inverter drive circuit 72 can be set and controlled early, such as during continuous fixing of small-size sheet paper, and the heat roller 20 and the belt 33 that have approached the heat resistance limit wait for the temperature to drop. Thus, the waiting time for saving can be saved, and the decrease in productivity can be prevented.

  Next, a second embodiment of the present invention will be described. This second embodiment is the same as the first embodiment described above except that the heating width in the axial direction of the belt is controlled differently. Accordingly, in the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the second embodiment, the heat generation width of the metal roller 32 of the belt mechanism 30 is not controlled using the central coil 60a and the side coil 60b divided into two, but a magnetic flux control member 87 provided in the metal roller 32. To do.

  As shown in FIG. 7, in the fixing device 84 of the second embodiment, a third induction current generating device, which is the second induced current generating device, is positioned around the belt 33 and facing the metal roller 32. An induced current generating coil 86 is provided. The third induced current generating coil 86 generates magnetic flux over the entire length of the metal roller 32 in the axial direction. In addition, a magnetic flux control member 87 for controlling the heat generation width of the metal roller 32 is rotatably provided in the hollow interior of the metal roller 32. The magnetic flux control member 87 is provided with a core member 87b made of a magnetic material made of a nickel-zinc (Ni-Zn) alloy on the outer peripheral surface of a cylindrical base material 87a made of a nonmagnetic member such as aluminum. The core member 87b is formed according to the width of various sheet papers P that can be fixed, for example. The metal roller 32 in a region corresponding to a region where the core member 87b of the magnetic flux control member 87 exists generates heat.

  The core member 87b of the magnetic flux control member 87 is formed in a step shape with a plurality of widths as shown in FIG. For example, the first stage 88a of the core member 87b is formed over the entire length of the cylindrical base material 87a and has a width that covers the JIS standard A3 size and the LD size. The second stage 88b of the core member 87b is formed to have a width that covers the JIS standard B4 size and the legal size. The third step 88c of the core member 87b is formed to have a width that covers the JIS standard A4R size and the letter size. Note that the cylindrical base material is not limited to aluminum, and may be any material such as a non-magnetic resin. Further, the material of the core member is not limited and may be formed of a manganese-nickel (Mn—Ni) alloy or the like.

  Even if power is supplied to the third induction current generating coil 86 at the time of fixing, the metal roller 32 does not generate heat over the entire length in the axial direction, but only the region corresponding to the core member 87b of the magnetic flux control member 87 generates heat. Is done. That is, no heat is generated in the region of the metal roller 32 corresponding to the cylindrical base material 87a. The magnetic flux control member 87 is rotated by a predetermined angle by, for example, a stepping motor 90. The magnetic flux control member 87 is rotationally moved so that the step having a predetermined width of the core member 87 b faces the third induced current generating coil 86 according to the size of the sheet paper P at the time of fixing. In this embodiment, as a belt temperature sensor for detecting the surface temperature of the belt 33, a fifth thermistor 91 for detecting the surface temperature at the substantially center in the width direction is provided.

  Next, the control system 170 of this embodiment is shown in FIG. The control system 170 has, on the primary side, first and second induced current generating coils 50a and 50b, and an inverter drive circuit 72 that supplies driving power to a single third induced current generating coil 86. Further, the control system 170 outputs, on the primary side, the noise filter 74 that rectifies the current from the commercial AC power supply 73 and supplies the current to the inverter drive circuit 72, the coil control circuit 76 that controls the inverter drive circuit 72, and the output of the noise filter 74. A power supply detection circuit 77 and a fuse 78 for detecting and feeding back the power from the commercial AC power supply 73 to be constant are provided. The secondary CPU 71 receives temperature detection results from the first and second thermistors 56 a and 56 b and the fifth thermistor 91. Therefore, in the control system 170 of this embodiment, the temperature control portion of the belt 33 is simplified compared to the first embodiment described above.

  Next, temperature control of the heat roller 20 and the belt 33 by the control system 170 will be described with reference to the flowchart of FIG. After the power of the image forming apparatus 1 is turned on, the belt mechanism 30 is first set to the home position through steps 101 to 103 as in the first embodiment. Next, the magnetic flux control member 87 is rotationally moved so that the first stage 88a of the core member 87b faces the third induced current generating coil 86, and the magnetic flux control member 87 is set to the initial position (step 104). Thereafter, when the warm-up is completed through steps 105 to 108 and step 110 as in the first embodiment, the image forming apparatus 1 enters the standby mode. In this standby mode, the belt 33 is heated to a fixing temperature throughout the entire axial direction.

  When the CPU 71 gives a print instruction after the warm-up is completed, the belt mechanism 30 has a core member 87b having a width corresponding to the sheet paper P size according to the sheet paper P size to be used. The magnetic flux control member 87 is rotationally moved so that the predetermined stage faces the third induced current generating coil 86. As a result, the metal roller 32 generates heat in a region corresponding to the core member 87 b, that is, a region corresponding to the sheet paper P size, and heats a region corresponding to the sheet paper P size of the belt 33.

  Next, the fixing device 84 heats and fixes the toner image formed on the sheet paper P by the printing operation. In the standby mode after the fixing operation is completed, the magnetic flux control member 87 is rotated and moved again so that the first stage 88a of the core member 87b faces the third induced current generating coil 86. If there is no print command for a predetermined time after completion of the fixing operation, the image forming apparatus 1 is in the preheat mode (the surface temperatures of the heat roller 20 and the belt 33 are kept at predetermined preheat temperatures lower than the fixable temperatures, respectively, and there is a print instruction. In this case, the surface temperature of the heat roller 20 and the belt 33 is set to a fixing temperature at which printing can be performed immediately.

  During this time, the inverter drive circuit 72 only supplies power to the single third induced current generating coil 86 according to the temperature detection result of the fifth thermistor 91 on the belt mechanism 30 side. The

  According to the fixing device 84 of the second embodiment, as in the first embodiment, it is possible to increase the warm-up time and to prevent a decrease in productivity when continuously forming images. Further, by using the auxiliary pressure member 42, the width of the nip 37 can be widened without increasing the load between the heat roller 20 and the belt 33. Therefore, the load applied between the heat roller 20 and the belt 33 at the nip 37 position can be reduced, and the life of the heat roller 20 and the belt 33 can be extended. In addition, during the setting control of the inverter drive circuit 72 by the CPU 71, it is not necessary to perform the phase difference interpolation control as in the first embodiment, and the setting control of the inverter drive circuit 72 can be speeded up. Therefore, it is possible to reduce the waiting time for waiting for the temperature of the heat roller 20 or the belt 33, which has reached the heat resistance limit, to decrease, and to prevent the productivity from being lowered during image formation. Moreover, on the belt mechanism 30 side, by using the magnetic flux control member 87, the heat generation width of the metal roller 32 can be controlled despite induction heating by the single third induction current generating coil 86. . Therefore, as compared with the case where the heat generation width of the metal roller 32 is divided into two parts, that is, the central coil and the side coil as in the first embodiment, the structure and control including the circuit are simplified and the fixing is performed. The device 84 can be downsized.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. For example, the shape or structure of the pressing member is arbitrary. Further, the width of the nip formed by the pressing member and the magnitude of the load are not limited. In order to simplify the correction of the phase difference during temperature control, either the distance from the temperature detection position to the center position of induction heating or the distance from the center position of induction heating to the nip of the heating member and belt You may make it arrange only either.

  Further, the structure of the fixing device is not limited, and the heat generating member is not limited to a roller shape, but may be a belt shape like the fixing device 120 of another modification shown in FIG. In this modified example, a second belt mechanism 121 that supports the second belt 123 rotated in the direction of the arrow v by the second metal roller 122 and the second counter roller 124 is provided. The metal roller 122 is induction-heated by the fifth and sixth induction current generating coils 126a and 126b. The surface temperature of the second belt 123 is detected by the fifth and sixth thermistors 127a and 127b. In the fixing device 120, the third belt mechanism 130 that supports the third belt 133 rotated in the direction of the arrow w by the third metal roller 132 and the fourth counter roller 134 is opposed to the second belt mechanism 121. Deploy. The metal roller 132 is induction-heated by the seventh and eighth induced current generating coils 136a and 136b. The surface temperature of the third belt 133 is detected by the seventh and eighth thermistors 137a and 137b.

  A nip 140 is formed by a plate 128 made of silicon rubber of the second belt mechanism 121 and a second auxiliary pressure member 138 made of silicon rubber of the third belt mechanism 130 and applied with a load by a second pressing spring 138a. . The entrance position of the nip 140 of the fixing device 120 is f, the center position of induction heating of the second belt mechanism 121 is g, the center position of induction heating of the third belt mechanism 130 is h, and the position of the second belt mechanism 121 is The temperature reading position is i, and the temperature reading position of the third belt mechanism 130 is j. At this time, the distance between g and f may be the same as the distance between h and f, and the distance between i and g may be the same as the distance between j and h. In addition, by making the heat generating member into a belt shape in this way, in both the second belt mechanism 121 and the third belt mechanism 130, the magnetic flux control member is placed in the metal roller without dividing the induced current generator into two. By providing this, it becomes possible to control the heating width of the belt.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first exemplary embodiment of the present invention. 1 is a schematic configuration diagram of a fixing device according to a first exemplary embodiment of the present invention when viewed from an axial direction. It is a schematic sectional drawing which shows the surface layer of the heat roller of the 1st Example of this invention. It is a schematic sectional drawing which shows the belt of the 1st Example of this invention. It is a schematic circuit diagram which shows the control system of 1st Example of this invention. It is a flowchart which shows the warm-up of the heat roller and belt of 1st Example of this invention. FIG. 5 is a schematic configuration diagram of a fixing device according to a second exemplary embodiment of the present invention viewed from the axial direction. It is an expanded view which shows the core member of the 2nd Example of this invention. It is a schematic circuit diagram which shows the control system of the 2nd Example of this invention. It is a flowchart which shows the warm-up of the heat roller and belt of 2nd Example of this invention. FIG. 10 is a schematic configuration diagram of a fixing device according to another modified example of the present invention viewed from the axial direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... Printer part 10 ... Image forming unit 10a ... Transfer belt 11 ... Fixing device 20 ... Heat roller 20c ... Metal conductive layer 30 ... Belt mechanism 32 ... Metal roller 33 ... Belt 36a, 36b ... 1st and 1st 2 drive motor 37 ... nip 41 ... spring 42 ... auxiliary pressurizing member 50a, 50b ... first and second induction current generating coils 56a, 56b ... first and second thermistors 60a ... central coil 60b ... side coil 61a, 61b ... Third and fourth thermistors 71 ... CPU
72. Inverter drive circuit

Claims (10)

A heat generating member having a metal layer to be induction-heated;
A first induced current generator disposed in proximity to the heating member;
A belt facing the heat generating member and rotatably supported by a plurality of rollers to form a nip with the heat generating member;
A second induced current generator disposed around the belt for heating the belt by induction heating;
And a pressing member that presses the belt against the heat generating member at the nip position.   The distance from the center of induction heating by the first induction current generator on the outer periphery of the heat generating member to the nip, and the center of induction heating by the second induction current generator on the outer periphery of the belt The fixing device according to claim 1, wherein the distance to reach the nip is the same. A heating member temperature sensor for detecting the surface temperature of the heating member; and a belt temperature sensor for detecting the surface temperature of the belt;
The distance from the heat generating member temperature sensor on the outer periphery of the heat generating member to the center of induction heating by the first induced current generator, and the generation of the second induced current from the belt temperature sensor on the outer periphery of the belt 3. The fixing device according to claim 1, wherein the distance to reach the center of induction heating by the device is the same. The plurality of rollers have at least one metal roller;
4. The fixing device according to claim 1, wherein the second induction current generating device induction heats the metal roller. 5.   The fixing device according to claim 4, wherein the second induced current generator is divided into a plurality of parts in the axial direction of the metal roller. In the hollow interior of the metal roller further has a magnetic flux control member,
5. The fixing device according to claim 4, wherein the second induced current generating device is a single induced current generating coil that generates a magnetic flux over the entire length of a sheet passing region of the metal roller. The plurality of rollers have at least one facing roller facing the heat generating member,
The fixing device according to claim 1, wherein the pressing member is disposed in proximity to the counter roller and forms the nip reaching the pressing member from the counter roller. . A heating member having a metal layer that generates heat by the first induced current generator, and a belt that is rotatably supported by a plurality of rollers and that is heated by the second induced current generator;
And a step of pressing the belt against the heat generating member using a pressing member to form a nip between the heat generating member and the belt.   The timing until the heating member reaches the nip after heat generation by the first induced current generator matches the timing until the belt reaches the nip after heat generation by the second induced current generator. 9. A method for controlling a fixing device according to claim 8, wherein:   The timing until the heating member reaches the induction heating position by the first induction current generator after the surface temperature is detected by the heating member temperature sensor, and the second induction current after the belt is detected by the belt temperature sensor. 10. The fixing device control method according to claim 8, wherein the timing until the induction heating position by the generator is reached is made coincident.

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