JP2020071325A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a temperature distribution suitable for fixing by a simple configuration. When the inside of the fuser 22 is in a cold state at the end of the warm-up process, the image forming apparatus 1 sets the temperature correction values β1 and β2 to the increase correction values by the fixing control unit 38. Then, the fixing control unit 38 controls the temperature of the side 1 heater 42B and the side 2 heater 42C by calculating the side 1 duty value DS1 and the side 2 duty value DS2 using the set temperature correction values β1 and β2. .. As a result, the image forming apparatus 1 can adjust the temperature near the end of the fixing belt 41 with respect to the main scanning direction in the fixing device 22 to a temperature range suitable for fixing, and prevents the occurrence of fixing defects and is of high quality. It is possible to perform various printing processes. [Selection diagram] FIG. 9

Description

  The present invention relates to a fixing device and an image forming apparatus, and is suitable for application to, for example, an electrophotographic printer.

  In recent years, as an image forming apparatus, for example, a toner (also referred to as a developer) is used by an image forming unit to generate a toner image based on image data, and the toner image is transferred to a sheet (also referred to as a medium). Some print an image by applying pressure or fixing to fix the image.

  As this fixing device, for example, a fixing device in which a fixing member that generates heat and a pressing member that is pressed against the fixing member are arranged to face each other on both sides of a conveyance path along which a sheet is conveyed are known. Of these, the fixing member includes, for example, a heater that is arranged along the main scanning direction and that generates heat according to the supplied power, and an endless belt that is formed into a hollow cylindrical shape, and runs so as to circulate around the heater. And a fixing belt for The pressure member is formed in a columnar shape along the main scanning direction, for example, and is configured as a rotatable pressure roller.

  In some cases, the image forming apparatus prints an image on a sheet having various widths, that is, a sheet having a different length in the main scanning direction according to a user's instruction. Therefore, as a fixing device, there has been proposed a device that divides the area where the heater generates heat into a plurality along the main scanning direction and generates heat only in the area where the paper passes, thereby minimizing the power consumption (for example, See Patent Document 1).

JP, 2014-98783, A (Fig. 2a etc.).

  In the fixing device described above, for example, a temperature sensor such as a thermistor is attached to each heating area of the heater, and feedback control is performed based on the detection result of the temperature sensor to adjust the heater itself to a desired temperature in each heating area. You can

  Further, in the fixing device, a heat diffusion member may be provided between the heater and the fixing belt for the purpose of, for example, dispersing heat of the heater to reduce temperature unevenness. As a result, in the fixing device, the temperature on the surface of the fixing belt, that is, the temperature of the portion that directly transfers heat to the sheet may differ from the temperature of the heater.

  Particularly in the fixing device, the temperature around the fixing belt may be relatively low, for example, when the printing process is started after the standby state continues for a while. In such a case, in the fixing device, even if the heater itself rises to a desired temperature, the fixing belt does not rise to a temperature suitable for fixing, especially near the end portion in the main scanning direction, and the toner is not applied to the sheet. However, there is a problem in that there is a possibility of causing a fixing failure that does not fix sufficiently.

  The present invention has been made in consideration of the above points, and an object thereof is to propose a fixing device and an image forming apparatus that can obtain a temperature distribution suitable for fixing with a simple configuration.

  In order to solve such a problem, a fixing device of the present invention is a fixing device for applying heat and pressure to a medium onto which a developer is transferred according to an image to fix the medium, and a cylindrical fixing belt and a main scanning direction. A plurality of heat generating regions are arranged along the heat generating region, and a heater that heats the fixing belt by generating heat when electric power is supplied to the heat generating region, a pressure unit that applies pressure to the fixing belt, and a heat generating region of the fixing belt. , A main temperature detection unit that detects a main temperature that is a temperature of a place corresponding to the main heat generation region, and another temperature detection unit that detects a temperature of another place that is a temperature of a place different from the fixing belt. And a control unit that controls the power supplied to the heat generation region of the power generation unit, and the control unit controls the power supplied to the sub-heat generation region of the heat generation region that is different from the main heat generation region when the temperature of the other place is lower than the predetermined boundary temperature. Increase the amount of Cormorants were to be corrected.

  Further, in the image forming apparatus of the present invention, a carrying section for carrying the medium, an image forming section for transferring the developer to the medium, and the fixing device according to any one of claims 1 to 10 are provided. did.

  The present invention can increase the temperature of the sub-heating region by increasing the amount of electric power supplied to the sub-heating region when the temperature of the other place is lower than the boundary temperature. With this, it is possible to perform temperature control based on the temperature detected by the main temperature detection unit so that the main heat generation region is adjusted to a temperature suitable for the fixing process, and the sub-heat generation region whose temperature is not detected by the main temperature detection unit is detected. It is possible to prevent the temperature from becoming too low to be suitable for the fixing process.

  According to the present invention, it is possible to realize a fixing device and an image forming apparatus capable of obtaining a temperature distribution suitable for fixing with a simple configuration.

FIG. 1 is a schematic diagram showing an overall configuration of an image forming apparatus. FIG. 3 is a schematic diagram showing a block configuration of an image forming apparatus. FIG. 3 is a schematic diagram illustrating a configuration of a fixing device according to the first embodiment. FIG. 3 is a schematic diagram illustrating a circuit configuration of a fixing device according to the first embodiment. It is an approximate line figure showing composition of an infrared temperature sensor and an infrared temperature detection circuit. It is an approximate line figure showing a heater on table. FIG. 3 is a schematic diagram showing a sheet width correction value table and a relationship between a sheet width and a sheet width correction value. 6 is a flowchart showing a temperature correction value setting processing procedure according to the first embodiment. FIG. 6 is a schematic diagram showing how the temperature changes according to the first embodiment. It is an approximate line figure showing distribution of belt surface temperature. FIG. 10 is a schematic diagram illustrating adjustment of output distribution in a conventional fixing device. It is a schematic diagram which shows the structure of the fixing device by 2nd Embodiment. FIG. 6 is a schematic diagram showing a circuit configuration of a fixing device according to a second embodiment. 9 is a flowchart showing a procedure for setting a temperature correction value β1 according to the second embodiment. 11 is a flowchart showing a procedure for setting a temperature correction value β2 according to the second embodiment. It is an approximate line figure showing signs of temperature change by a 2nd embodiment. It is a flowchart which shows the target temperature setting process procedure by 3rd Embodiment. It is an approximate line figure showing the mode of temperature change by a 3rd embodiment.

  Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[1. First Embodiment]
[1-1. Configuration of image forming apparatus]
As shown in FIG. 1, the image forming apparatus 1 is an electrophotographic printer, and can form (that is, print) a color image on a sheet P as a medium. Incidentally, the image forming apparatus 1 does not have an image scanner function for reading an original document, a communication function using a telephone line, or the like, but is a single-function SFP (Single Function Printer) having only a printer function.

  The image forming apparatus 1 includes various components arranged inside a printer housing 2 formed in a substantially box shape. Hereinafter, the right end portion in FIG. 1 will be referred to as the front surface of the image forming apparatus 1, and the vertical direction, the horizontal direction, and the front-rear direction when viewed facing the front surface will be respectively defined and described.

  The image forming apparatus 1 is configured to be integrally controlled by the print control unit 3. The print control unit 3 has a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown), and performs various processes by reading and executing a predetermined program. To execute. The print control unit 3 is connected to a higher-level device (not shown) such as a computer device by wireless or wire, and receives image data representing an image to be printed from the higher-level device and prints the image data. When instructed, a print process for forming a print image on the surface of the paper P is executed.

  At the bottom of the printer housing 2, a paper feed cassette 4 that holds the paper P is provided. A paper feed section 5 is provided above and in front of the paper feed cassette 4. The paper feeding unit 5 separates a plurality of sheets P and feeds only one sheet, a hopping roller 6, a conveyance guide 7 that guides the sheets P upward along the conveyance path U, and opposes each other across the conveyance path U. The registration roller 8 and the like are arranged at positions.

  The paper feeding section 5 appropriately rotates the hopping roller 6 and the like under the control of the print control section 3 to pick up the paper P stored in the paper feeding cassette 4 while separating them one by one. To do. Subsequently, the sheet feeding unit 5 guides the sheet P by the conveyance guide 7, and advances the sheet P along the conveyance path U while appropriately correcting the inclination by the registration rollers 8. As a result, the sheet feeding unit 5 advances the sheet P forward and upward, and then, returns the sheet P obliquely backward and upward and sends it out.

  On the upper rear side of the sheet feeding section 5, the conveyance path U is formed along a straight line that is inclined so as to slightly rise rearward when viewed from the left-right direction, and the middle conveyance section 10 is formed on the lower side thereof. It is arranged. The middle conveyance unit 10 has a configuration in which a conveyance belt 13 made of an endless belt is stretched around a driven roller 11 arranged on the front side and a belt driving roller 12 arranged on the rear side.

  When the driving force is transmitted from the belt motor to be described later to the belt drive roller 12, the middle conveyance unit 10 rotates the belt drive roller 12 in the direction of arrow R2, and the conveyance belt 13 travels accordingly. At this time, the transport belt 13 advances the upper portion along the transport path U, that is, the portion stretched between the driven roller 11 and the belt driving roller 12, in the upper rear direction. Further, at this time, when the paper P is delivered from the paper feeding unit 5, the middle conveyance unit 10 holds the paper P on the upper side of the conveyance belt 13 and moves the paper P along with the traveling of the conveyance belt 13. Move backward and upward.

  Four image forming units 15K, 15Y, 15M and 15C are arranged in order from the front side to the rear side on the upper side of the middle conveyance section 10 and on the opposite side of the middle conveyance section 10 with the conveyance path U interposed therebetween. ing. The image forming units 15K, 15Y, 15M and 15C (hereinafter collectively referred to as the image forming unit 15) respectively correspond to black (K), yellow (Y), magenta (M) and cyan (C). However, only the colors are different, and both are configured similarly. Therefore, the image forming unit 15K corresponding to black (K) will be described below as an example. The image forming unit 15 is also called an image drum (ID) unit.

  The image forming unit 15 as an image forming unit includes an image forming transfer unit 16, a toner cartridge 17, and an LED (Light Emitting Diode) head 18. Incidentally, the image forming unit 15 and each of the components forming the image forming unit 15 have a sufficient length in the left-right direction according to the length of the paper P in the left-right direction. For this reason, many parts are relatively long in the left-right direction with respect to the lengths in the front-rear direction and the up-down direction, and are formed in an elongated shape along the left-right direction.

  The toner cartridge 17 contains toner as a developer, is attached above the image forming transfer section 16, and supplies the contained toner to the image forming transfer section 16. The image forming transfer section 16 is provided with a plurality of rollers and a photosensitive drum 19. Each of the rollers and the photoconductor drum 19 is formed in a cylindrical shape having a central axis along the left-right direction, and is rotatably supported. Further, the photosensitive drum 19 is configured so that the peripheral side surface thereof can be charged. A transfer roller 20 is arranged on the opposite side of the photosensitive drum 19 with the conveyance path U and the conveyance belt 13 interposed therebetween. In the LED head 18, a plurality of light emitting elements made of LEDs are linearly arranged along the left-right direction which is the main scanning direction.

  The image forming transfer unit 16 is supplied with a driving force from an ID motor, which will be described later, to rotate each roller as appropriate and rotate the photosensitive drum 19 in the direction of arrow R1. Further, the image forming transfer section 16 applies a predetermined high voltage to each roller and the like. The LED head 18 emits light in a light emission pattern based on an image data signal supplied from the print control unit 3 (FIG. 1), sequentially exposes the peripheral side surface of the photoconductor drum 19, and the photoirradiated light causes the photoconductor drum 19 to be exposed. Electrostatic latent image is formed on the peripheral side surface of the. Subsequently, the image forming transfer section 16 forms a toner image according to the electrostatic latent image by adhering toner (developer) to the peripheral surface of the photosensitive drum 19, and the toner is rotated by rotating the photosensitive drum 19. The part where the image is formed is made to reach the vicinity of the lower end.

  When the paper P is being conveyed by the conveyor belt 13 along the conveyor path U, the image forming unit 15 sandwiches the conveyor belt 13 and the paper P between the photosensitive drum 19 and the transfer roller 20 to form a toner image. Is transferred to the paper P from the peripheral side surface of the photosensitive drum 19. In this manner, each image forming unit 15 sequentially transfers the toner images of the respective colors onto the paper P conveyed from the front along the conveyance path U and superimposes it, and advances the toner images to the rear.

  A fixing device 22 is provided near the rear end of the middle conveyance unit 10. The fixing device 22 applies heat and pressure to the paper P by two rollers arranged so as to face each other across the transport path U to fix the toner image on the paper P (details will be described later), and further rearward. Hand over to.

  A paper discharge unit 25 is disposed behind the fixing device 22. The paper discharge unit 25 has a configuration similar to that of a part of the paper supply unit 5, and includes a conveyance guide 26 that guides the paper P, a plurality of discharge rollers 27, and the like. The paper ejecting unit 25 conveys the paper P delivered from the fixing device 22 rearward and upward and then folds the paper P forward by appropriately rotating the respective conveying rollers according to the control of the print controller 3, and the printer casing 2 The paper is discharged to the discharge tray 28 formed on the upper surface of the.

  Incidentally, in the image forming apparatus 1, the size of the paper, such as the A4 size, the A5 size, the B5 size, etc., particularly, the length in the left-right direction as the main scanning direction (hereinafter referred to as the paper width or the medium width) is determined. Images can be printed on different types of paper P.

  Further, in the image forming apparatus 1, as shown in FIG. 2, each motor such as a paper feed motor 31, a belt motor 32, an ID motor 33, and a fixing motor 34 is connected to the print control unit 3. Of these, the paper feed motor 31 supplies a driving force to the hopping roller 6 (FIG. 1) and the like. The belt motor 32 supplies a driving force to the belt driving roller 12 (FIG. 1). The ID motor 33 supplies a driving force to each roller of the image forming transfer unit 16. The fixing motor 34 supplies a driving force to a roller or the like (details will be described later) provided in the fixing device 22.

  Further, the LED head 18 (FIG. 1) described above, the high voltage circuit 36, and the fixing control unit 38 are also connected to the print control unit 3. The high voltage circuit 36 supplies a predetermined high voltage to each roller of the image forming transfer unit 16, the transfer roller 20, and the like. The fixing control unit 38 is provided in the fixing device 22, has a CPU, a ROM, a RAM, and the like like the printing control unit 3, and controls the fixing device 22 by executing a predetermined program.

[1-2. Fixer configuration]
[1-2-1. Overall configuration of fixing device]
Next, the configuration of the fixing device 22 as a fixing device will be described. As shown in the schematic left side view and front view in FIGS. 3 (A) and 3 (B), the fixing device 22 is roughly divided into a heating unit 23 disposed above the transport path U and the transport path U. The pressure unit 24 is disposed below the U. Incidentally, the fixing device 22 is substantially surrounded by a casing (not shown). In this case, holes and the like for passing the paper P along the transport path U are appropriately formed.

  The heating unit 23 has a configuration in which a planar heater 42 and a heat diffusion member 43 are arranged inside a fixing belt 41 formed in a cylindrical shape. The fixing belt 41 is an endless belt made of a material having flexibility and heat resistance, and is formed in a cylindrical shape with its central axis along the left-right direction.

  The planar heater 42 is generally formed in a plate shape that is long in the left-right direction, short in the front-rear direction, and thin in the up-down direction, and has a predetermined wiring pattern, a heating element, and the like arranged on the lower surface thereof. That is, in the planar heater 42, the front surface that is a surface that generates heat faces downward, and the back surface that is the opposite surface faces upward.

  Further, in the planar heater 42, a heat generating portion is divided into five regions (that is, heat generating regions) in the left-right direction (also referred to as a main scanning direction). For convenience of explanation, in the following, the central region of the planar heater 42 is referred to as the main heater 42A, the regions on the left and right sides thereof are referred to as side 1 heaters 42B (42B1 and 42B2), and the outermost region is the side 2 heater. 42C (42C1 and 42C2). Further, hereinafter, the main heater 42A is also referred to as a main heat generation area, the side 1 heater 42B and the side 2 heater 42C are also referred to as sub heat generation areas, and the main heater 42A, the side 1 heater 42B, and the side 2 heater 42C are collectively referred to as a heater group. Call.

  Incidentally, the length of the planar heater 42 in the left-right direction is 138 [mm] for the main heater 42A alone, 230 [mm] when the side 1 heater 42B is added thereto, and 306 when the side 2 heater 42C is further added. [Mm].

  The heat diffusion member 43 is a steel plate formed in a rectangular thin plate shape that is long in the left-right direction and short in the front-rear direction, and its upper surface is in contact with the lower surface of the planar heater 42. The heat diffusion member 43 can efficiently transfer, that is, diffuse heat, due to the property of the metal material.

  Further, in the heating unit 23, the heater back main thermistor 44, the heater back side 1 thermistor 45, and the heater back side 2 thermistor are provided at positions contacting the upper side (back side) of the main heater 42A, side 1 heater 42B1, and side 2 heater 42C1. 46 (hereinafter collectively referred to as a heater backside thermistor group) is provided. Since the resistance value of each heater back thermistor changes according to the temperature of the contact position of the planar heater 42, an electric signal corresponding to this temperature is generated and the fixing controller 38 (see FIG. Supply to 2) respectively. In other words, each heater thermistor on the back side of the heater detects the temperature of the planar heater 42 itself and generates an electric signal representing the temperature.

  Further, the heating unit 23 is provided with an infrared temperature sensor 48 at a position slightly away from the front of the fixing belt 41. The infrared temperature sensor 48 receives the infrared light emitted from the fixing belt 41, generates an electric signal according to the temperature of the fixing belt 41 based on the amount of the received infrared light, etc., and outputs the electric signal. (Fig. 2).

  On the other hand, the pressure unit 24 has a pressure roller 51. The pressure roller 51 is formed in a columnar shape having a central axis extending in the left-right direction, is rotatably supported by a support member (not shown), and is biased toward the heating unit 23. Therefore, in the fixing device 22, the pressure roller 51 is pressed against the fixing belt 41, and a nip portion NP for sandwiching the paper P is formed between them.

[1-2-2. Circuit configuration of fixing device]
As shown in the circuit diagram of FIG. 4, the sheet heater 42 is supplied with the commercial power source 61 and the fixing controller 38 controls the supplied power.

  Specifically, the main heater 42A, the side 1 heater 42B, and the side 2 heater 42C of the planar heater 42 are connected to one end of a commercial power source 61, and the other end of the commercial power source 61 is connected to the triacs 62, 63, and 64. Are respectively connected via. Each of the triacs 62, 63, and 64 is a phototriac that insulates the primary side and the secondary side from each other. Does the triac 62, 63, and 64 conduct the primary side and the secondary side depending on the voltage supplied to the gate terminal? Switch whether or not.

  Further, the heater back main thermistor 44, the heater back side 1 thermistor 45, and the heater back side 2 thermistor 46 attached to the main heater 42A, the side 1 heater 42B, and the side 2 heater 42C respectively fix the electric signals representing the detected temperatures. It is supplied to the control unit 38.

  The infrared temperature sensor 48 supplies an electric signal according to the detected temperature to the infrared temperature detection circuit 65. The infrared temperature detection circuit 65 generates a new signal based on the supplied electric signal and supplies the new signal to the fixing controller 38.

  Specifically, as shown in FIG. 5, the infrared temperature sensor 48 includes two thermistors such as a detection thermistor 71 that detects the temperature of a detection target (that is, the fixing belt 41) and a compensation thermistor 72 that detects the ambient temperature. It is composed by. The temperature of the detection thermistor 71 rises due to infrared rays from the object to be detected, and the resistance value changes according to this temperature. The resistance value of the compensation thermistor 72 changes according to the temperature around the infrared temperature sensor 48.

  One end of each of the detection thermistor 71 and the compensation thermistor 72 is connected to a voltage source of 3.3 [V], and the other end is 0 [V via the voltage dividing resistors 73 and 74 of the infrared temperature detection circuit 65. ] To (i.e., grounded). The detection thermistor signal S11 obtained by dividing 3.3 [V] of the voltage source by the detection thermistor 71 and the voltage dividing resistor 73 is input to the voltage follower circuit by the operational amplifier 75. A compensating thermistor signal S12 obtained by dividing 3.3 [V] of the voltage source by the compensating thermistor 72 and the voltage dividing resistor 74 is input to the voltage follower circuit by the operational amplifier 76. For convenience of description, the detection thermistor signal S11 is also referred to as a detection signal and the compensation thermistor signal S12 is also referred to as a compensation signal below.

  The infrared temperature detection circuit 65 includes resistors 77, 78, 79 and 80 and an operational amplifier 81 to form a differential amplifier circuit 82 as an arithmetic circuit. The gain of the differential amplifier circuit 82 is set to 10 times by the resistance values of the resistors 77, 78, 79 and 80. When the detection thermistor signal S11 is input to the non-inverting input terminal and the compensating thermistor signal S12 is input to the inverting input terminal, the differential amplifier circuit 82 is a differential amplifier that amplifies the difference value between the two by 10 times. The amplified signal S13 is generated and supplied to the fixing controller 38. The infrared temperature detection circuit 65 also supplies the compensation thermistor signal S12 to the fixing controller 38.

  The fixing control unit 38 refers to a predetermined temperature table (not shown) stored in advance, and based on the differential amplified signal S13 and the compensation thermistor signal S12, the fixing target of the infrared temperature sensor 48 is fixed. The surface temperature of the belt 41 (FIG. 2) (hereinafter also referred to as the belt surface temperature) is calculated.

  Subsequently, the fixing control unit 38 (FIG. 4), based on the surface temperature of the fixing belt 41 calculated based on the electric signal supplied from the heater backside thermistor group and the signal supplied from the infrared temperature detection circuit 65, The heater control signals S1, S2 and S3 are generated and supplied to the triac drive circuit 66.

  The heater control signals S1, S2, and S3 correspond to the triacs 62, 63, and 64, respectively, and are signals for controlling the main heater 42A, the side 1 heater 42B, and the side 2 heater 42C, respectively. The heater control signals S1, S2, and S3 are pulse signals in which high level and low level are alternately repeated, and the duty ratio, which is the ratio of the high level period, is determined by the fixing control unit 38 (details will be described later). ).

  The triac drive circuit 66 is connected to the gate terminals of the triacs 62, 63 and 64, respectively. The triac drive circuit 66 changes the voltage supplied to the gate terminals of the triacs 62, 63 and 64 based on the duty ratios of the heater control signals S1, S2 and S3. As a result, the triac drive circuit 66 can change the time during which the triacs 62, 63, and 64 are conducted, and control the power supplied to each heater.

  In this manner, the fixing device 22 detects the temperature by the infrared temperature sensor 48 and the heater backside thermistor group, respectively, and controls the electric power supplied to the heater group by the fixing control unit 38 to bring the heater groups to desired temperatures. It is designed to be controlled.

[1-3. Temperature control in fixing device]
By the way, in the fixing device 22 (FIG. 2), when performing the fixing process, the toner can be stably melted by raising the surface temperature of the fixing belt 41 to a relatively high temperature such as 160 [° C.]. .. On the other hand, in the fixing device 22, when the power is off or the sleep state is sufficiently long, the temperature of the fixing belt 41 or the like may decrease to the same level as the ambient temperature.

  Therefore, the print control unit 3 (FIG. 2) of the image forming apparatus 1 raises the fixing belt 41 of the fixing device 22 (FIG. 3) to a temperature suitable for the fixing process by the control of the fixing control unit 38 as a part of the warm-up process. After that, the printing process is performed. Below, the temperature control of the fixing controller 38 will be described separately for the warm-up process and the printing process.

[1-3-1. Temperature control in warm-up process]
First, the fixing control unit 38 sets a target temperature (for example, 160 [° C.]) according to a printing condition or the like designated by the user, and a temperature to be reached in this warm-up process (hereinafter, referred to as warm-up temperature). ) Is set to a value 15 [° C.] lower than the target temperature (for example, 145 [° C.]). Then, the fixing controller 38 performs temperature control so that the surface temperature of the fixing belt 41 detected by the infrared temperature sensor 48 (FIGS. 3, 4, and 5) reaches the warm-up temperature.

  Specifically, the fixing control unit 38 sets the temperature control cycle to 100 [ms], calculates the duty value D [%] representing the duty ratio in the heater control signal S1 (FIG. 4) for each temperature control cycle, and According to the above, the heater control signal S1 is generated to control the electric power supplied to the main heater 42A. At this time, the fixing controller 38 calculates a deviation ε between the target temperature and the surface temperature of the fixing belt 41 detected by the infrared temperature sensor 48 (hereinafter referred to as the present temperature), and the PID (Proportional) based on this deviation ε. Integral Differential) control is performed. That is, the fixing controller 38 calculates the duty value D (n) according to the equation (1) which is a function of the deviation ε in the nth temperature control cycle.

  However, the deviation ε is a value obtained by subtracting the current temperature from the target temperature. The constants Kp, Ki, and Kd are a proportional gain, an integral gain, and a differential gain, respectively, and are set so that the duty value D is a value from 0 to 100. Further, the variable Dmod (n-1) is the fraction (that is, the remainder) rounded down in the previous temperature control cycle.

  The fixing control unit 38 cuts off the digit of 1 [%] in the duty value D calculated by the expression (1) to obtain a value in 10 [%] increments (hereinafter, referred to as a control duty value DC). For example, when the duty value D calculated by the equation (1) is 98 [%], the fixing control unit 38 sets the control duty value DC to 90 [%] and sets the remainder 8 [%] to the next temperature. The variable Dmod (n-1) used in the control cycle is used.

  Next, the fixing controller 38 determines the pulse waveform of the heater control signal S1 according to the obtained control duty value DC. Specifically, the fixing control unit 38 generates the heater control signal S1 for one temperature control cycle according to the heater on table TBL1 shown in FIG. Incidentally, the heater on table TBL1 is stored in advance by the fixing controller 38.

  In the heater-on table TBL1, each row in the vertical direction represents a control duty value DC, and each column in the horizontal direction represents a signal value every 10 [ms] by a value of "0" or "1". For example, when the duty value D is 25 [%], the fixing control unit 38 sets the control duty value DC to 20 [%]. At this time, the fixing control unit 38 sets the heater control signal S1 to a high level from 0 [ms] to 10 [ms], a low level to the following 50 [ms], and further to 60 [ms]. Is set to the high level again, and the remaining period is set to the low level again.

  In parallel with this, the fixing control unit 38 controls the electric power supplied to the side 1 heater 42B and the side 2 heater 42C by generating heater control signals S2 and S3 (FIG. 4) whose duty ratios are appropriately set. ..

  Specifically, with respect to the side 1 heater 42B, the fixing controller 38 sets the temperature of the main heater 42A as a target temperature, and matches the temperature detected by the heater back side 1 thermistor 45 with the temperature detected by the heater back main thermistor 44. Perform temperature control. Further, the fixing controller 38 adjusts the temperature of the side 2 heater 42C so that the temperature detected by the heater back side 2 thermistor 46 matches the temperature detected by the heater back main thermistor 44, that is, the temperature of the main heater 42A is set as the target temperature. Take control. Below, temperature control that matches the temperature of the heater back main thermistor 44 is called heater back temperature control.

  As described above, the fixing control unit 38 raises the temperature of the main heater 42A by repeating the calculation of the duty value D and the control duty value DC and the generation and output of the heater control signal S1 in each temperature control cycle in the warm-up process. Let In addition to this, the fixing control unit 38 raises the temperatures of the side 1 heater 42B and the side 2 heater 42C so as to follow the temperature of the main heater 42A, that is, by the heater backside temperature control.

  When the temperature of the fixing belt 41 detected by the infrared temperature sensor 48 reaches the warm-up temperature (that is, a temperature lower than the target temperature by 15 [° C.]), the fixing control unit 38 ends the warm-up process.

[1-3-2. Temperature control in printing process]
When the print processing is started, the print control unit 3 of the image forming apparatus 1 (FIG. 1) starts conveying the paper P, causes the image forming unit 15 to generate a toner image, and eventually transfers the toner image to the paper P. Then, the sheet P is conveyed to the fixing device 22. On the other hand, when the printing process is started, the fixing control unit 38 controls the temperature of the main heater 42A, the side 1 heater 42B, and the side 2 heater 42C by a method different from the warm-up process.

  Specifically, with respect to the main heater 42A, the fixing controller 38 adjusts the surface temperature of the fixing belt 41 detected by the infrared temperature sensor 48 to a target temperature (for example, 160 [° C.]) in accordance with the PID control described above at every temperature control cycle. Then, the duty value D is calculated to control the temperature. As a result, the surface temperature of the fixing belt 41 approaches the target temperature.

  On the other hand, the fixing controller 38 relates to the side 1 heater 42B and the side 2 heater 42C, the size of the paper P to be printed, particularly the paper width which is the length in the width direction (that is, the main scanning direction), and the temperature of the fixing device 22. In accordance with the above, the control for correcting the duty ratio of the heater control signals S2 and S3 (FIG. 4) (hereinafter, referred to as duty ratio correction control) is performed.

  Specifically, the fixing controller 38 calculates the side 1 duty value DS1 which is the duty value for the side 1 heater 42B in the n-th temperature control cycle by the following equation (2), and at the same time, for the side 2 heater 42C. The side 2 duty value DS2, which is a duty value, is calculated by the following equation (3).

  However, the duty value D (n) is a duty value for the main heater 42A calculated by the above-mentioned equation (1). The value DS1mod (n-1) is a fraction (remainder) of the side 1 duty value DS1 in the immediately preceding (that is, n-1th) temperature control cycle. Similarly, the value DS2mod (n-1) is a fraction (remainder) of the side 2 duty value DS2 in the immediately preceding temperature control cycle. The temperature correction values β1 and β2 are values determined according to the temperature inside the fixing device 22 (details will be described later).

  The sheet width correction values α1 and α2 are values determined according to the sheet width L of the sheet P. Specifically, the sheet width correction values α1 and α2 are calculated according to equations (4) and (5) that are cubic functions relating to the sheet width L.

  However, the coefficients a1, b1, c1, d1, a2, b2, c2 and d2 are values appropriately set in advance based on the paper width L, the length of each heater (FIG. 3) and the like.

  The paper width correction values α1 and α2 calculated according to the expressions (4) and (5) are calculated in advance for some typical paper widths L, and the paper width correction value table TBL2 shown in FIG. It is stored in. Incidentally, the sheet width correction value table TBL2 is stored in advance by the fixing controller 38.

  For example, when the size and orientation of the paper P is set to A4 landscape (A4LEF), the fixing control unit 38 sets the paper width L to 297 [mm], the paper width correction value α1 to 100 [%], and the paper. The width correction value α2 becomes 95 [%]. Incidentally, a graph of the relationship between the paper width L and the paper width correction values α1 and α2 is expressed as shown in FIG. 7B. That is, the fixing controller 38 reduces the amount of electric power supplied to the side 1 heater 42B and the side 2 heater 42C according to the sheet width L.

  As described above, in the printing process, the fixing control unit 38 uses the paper width correction values α1 and α2 determined according to the paper width L for the side 1 heater 42B and the side 2 heater 42C, and uses the side 1 duty value DS1 and the side 2 By calculating the duty value DS2, temperature control suitable for the paper width L is performed.

[1-3-3. Temperature compensation value setting]
Next, the setting of the temperature correction values β1 and β2 used when calculating the side 1 duty value DS1 and the side 2 duty value DS2 will be described. The fixing controller 38 sets the temperature correction values β1 and β2 in accordance with the temperature correction value setting processing procedure RT1 shown in FIG. 8 when the warm-up processing ends and the printing processing starts.

  That is, the fixing control unit 38, when starting the temperature correction value setting processing procedure RT1, moves to the first step SP1 and determines whether or not the temperature of the fixing device 22 is in a relatively low cold state. Specifically, the fixing controller 38 determines that the temperature detected by the compensating thermistor 72 (FIG. 5) of the infrared temperature sensor 48, that is, the compensating thermistor temperature obtained based on the compensating thermistor signal S12 is a predetermined first cold boundary temperature ( For example, it is determined whether the temperature is less than 40 [° C.]).

  If an affirmative result is obtained here, this means that the temperature of the fixing device 22 is relatively low, so that even if the target temperature is reached in the vicinity of the center of the fixing belt 41, the target temperature is increased in the vicinity of the outer side in the left-right direction. It means that the temperature may be sufficiently lower than the above. At this time, the fixing controller 38 moves to next step SP2. In step SP2, the fixing controller 38 sets the temperature correction values β1 and β2 to relatively high increment correction values (for example, 120 [%] in both cases), and proceeds to the next step SP3.

  As a result, the side 1 duty value DS1 and the side 2 duty value DS2 calculated for each temperature control cycle (that is, 100 [ms]) become the paper width correction values α1 and α2 in the equations (2) and (3). It is about 20% larger than the value based on the above. That is, the side 1 heater 42B and the side 2 heater 42C are temperature-controlled so as to be slightly higher than the temperature of the main heater 42A and the temperature based on the sheet width L.

  In step SP3, the fixing control unit 38 determines whether or not a predetermined increase time (for example, 15 [s]) has elapsed from the time when the temperature correction values β1 and β2 were set to the increase correction values. If a negative result is obtained here, this means that the temperatures of the side 1 heater 42B and the side 2 heater 42C are excessive because the period in which the temperature correction values β1 and β2 are set to the increase correction value is still relatively short. It is unlikely to be increasing. At this time, the fixing controller 38 returns to step SP1 again and repeats a series of processes.

  On the other hand, if an affirmative result is obtained in step SP3, this means that a sufficiently long time has elapsed since the temperature correction values β1 and β2 were set to the increase correction values, and therefore the side 1 heater 42B and the side 2 are left as they are. This indicates that the temperature of the heater 42C may rise excessively. At this time, the fixing controller 38 moves to next step SP4.

  If a negative result is obtained in step SP1, this means that the temperature inside the fixing device 22 is relatively high, and thus when the center of the fixing belt 41 reaches the target temperature, even in the vicinity of the outer side in the left-right direction. This indicates that the temperature may be sufficiently close to the target temperature. At this time, the fixing controller 38 moves to next step SP4.

  In step SP4, the fixing controller 38 sets the temperature correction values β1 and β2 to the normal correction values (both are 100%), and then proceeds to the next step SP5. That is, when the inside of the fixing device 22 is in the cold state, the fixing control unit 38 sets the temperature correction values β1 and β2 to the increase correction values, and when the increase time elapses thereafter, or the inside of the fixing device 22 is the first correction value. The normal correction value is set when the cold boundary temperature is exceeded. The fixing control unit 38 also sets the normal correction value even when the printing process is not started in the cold state.

  As a result, the side 1 duty value DS1 and the side 2 duty value DS2 calculated for each temperature control cycle (that is, 100 [ms]) become the paper width correction values α1 and α2 in the equations (2) and (3). It becomes the value which followed. That is, the side 1 heater 42B and the side 2 heater 42C are temperature-controlled based on the temperature of the main heater 42A and the paper width L.

  In step SP5, the fixing control unit 38 determines whether or not the printing process is completed. If a negative result is obtained here, the fixing control unit 38 waits for the end of the printing process by repeating this step SP5. On the other hand, when a positive result is obtained in step SP5, the fixing control unit 38 moves to the next step SP6 and ends the temperature correction value setting processing procedure RT1.

[1-3-4. Temperature change in fixing device]
Next, when the image forming apparatus 1 performs the printing process after the warm-up process, the state of the temperature change in each part of the fixing device 22 is graphed, and the temperature control method and the set value are also described. Can be expressed as

  In FIG. 9, the horizontal axis represents the passage of time. Specifically, the start time of the warm-up process is time T1, the start time of the printing process is time T2, and the time when the leading edge of the paper P reaches the nip portion NP (FIG. 3) of the fixing device 22 is time T3. The time when the inside of the fixing device 22 is not in the cold state is time T4. That is, in FIG. 9, it is assumed that the inside of the fixing device 22 is in a cold state at the time when the warm-up process is finished and the printing process is started, but thereafter the cold state is lost.

  On the upper side of FIG. 9, the operating state of the image forming apparatus 1, the temperature control method of the side 1 heater 42B and the side 2 heater 42C, and the set values of the temperature correction values β1 and β2 are shown in a table format. ..

  Further, on the lower side in FIG. 9, a graph showing the temperature change of each part is shown. The main temperature TM is the temperature of the main heater 42A, that is, the temperature detected by the heater back main thermistor 44. The side temperature TS is the temperature of the side 1 heater 42B and the side 2 heater 42C, that is, the temperature detected by the heater back side 1 thermistor 45 and the heater back side 2 thermistor 46. The belt surface temperature TB is the surface temperature of the fixing belt 41 detected by the infrared temperature sensor 48. The fixing device temperature TE is the temperature inside the fixing device 22 detected by the compensating thermistor 72 of the infrared temperature sensor 48.

  The image forming apparatus 1 starts the warm-up process at a time T1 when a print instruction is received from a host device (not shown) in the sleep state. At this time, both the main temperature TM and the side temperature TS are relatively low. The belt surface temperature TB is also sufficiently low. Further, the fixing device temperature TE is lower than the first cold boundary temperature (that is, 40 [° C.]).

  Eventually, the image forming apparatus 1 ends the warm-up process and starts the print process at the time T2 when the belt surface temperature TB reaches the warm-up temperature (that is, 145 [° C.]). At this time, the main temperature TM is slightly higher than the belt surface temperature TB. The side temperature TS has a value almost equal to the main temperature TM. Although the fixing device temperature TE is higher than the time point T1, it is still lower than the first cold boundary temperature.

  At this time T2, the fixing controller 38 switches the temperature control of the side 1 heater 42B and the side 2 heater 42C from the heater backside temperature control to the duty ratio correction control. Further, since the fixing device temperature TE is lower than the first cold boundary temperature, the fixing control unit 38 sets the temperature correction values β1 and β2 to the increase correction values (120 [%]). As a result, in the image forming apparatus 1, the side temperature TS becomes higher than the main temperature TM after the time T2. Further, the belt surface temperature TB approaches the target temperature (that is, 160 [° C]).

  Further, in the image forming apparatus 1, heat is transferred from the fixing belt 41 to the paper P at the time T3 when the leading end of the paper P reaches the nip portion NP of the fixing device 22. Along with this, the belt surface temperature TB temporarily greatly decreases. Further, the main temperature TM and the side temperature TS also temporarily decrease slightly.

  After this time T3, the fixing control unit 38 raises the main temperature TM in order to recover the temporarily lowered belt surface temperature TB to the target temperature, and also raises the side temperature TS accordingly. At this time, the side temperature TS becomes higher than the main temperature TM because the temperature correction values β1 and β2 continue to be increase correction values.

  In the image forming apparatus 1, the heat generated in the planar heater 42 raises the temperature of the entire fixing device 22, and at time T4, the fixing device temperature TE detected by the compensating thermistor 72 of the infrared temperature sensor 48 becomes the first value. Exceeds 1 cold boundary temperature (40 [℃]). At this time T4, the fixing controller 38 switches the temperature correction values β1 and β2 from the increase correction value (120 [%]) to the normal correction value (100 [%]). As a result, the side temperature TS gradually decreases after time T4 and approaches the main temperature TM. After that, the fixing control unit 38 continues the temperature control until the printing process is completed.

[1-4. Effect, etc.]
In the above-described configuration, when the image forming apparatus 1 according to the first embodiment receives a print instruction from a higher-level device (not shown), the warm-up process is performed and the belt surface temperature of the fixing belt 41 changes to the warm-up temperature. When the temperature reaches (for example, 145 [° C.]), the warm-up process is ended and the printing process is started.

  The fixing controller 38 repeatedly calculates the duty value D by the above-described formula (1) in the main heater 42A so that the belt surface temperature of the fixing belt 41 approaches the target temperature (for example, 160 [° C.]). Take control.

  On the other hand, the fixing controller 38 appropriately corrects the side 1 heater 42B and the side 2 heater 42C by the paper width correction values α1 and α2 and the temperature correction values β1 and β2 in accordance with the above-described equations (2) and (3). The temperature control is performed while calculating the side 1 duty value DS1 and the side 2 duty value DS2.

  Here, it is assumed that the inside of the fixing device 22 is in a cold state and the temperature correction is not performed, that is, the temperature correction values β1 and β2 are omitted in the expressions (2) and (3). In this case, the surface temperature of the fixing belt 41 in the left-right direction (main scanning direction) (hereinafter referred to as the non-temperature correction belt surface temperature NTB) is distributed like the characteristic curve shown by the broken line in FIG.

  FIG. 10 shows a schematic view of the fixing device 22 seen from the front side on the upper side, and shows the distribution characteristic of the surface temperature of the fixing belt 41 on the lower side. Further, in FIG. 10, regarding the temperature, the upper limit and the lower limit of the temperature range in which the toner can be satisfactorily fixed to the paper P in the fixing device 22, that is, the upper limit and the lower limit of the fixing temperature range suitable for the fixing process, respectively, are defined as the upper fixing temperature TUL and the lower fixing temperature TLL. It is expressed as.

  Incidentally, in FIG. 10, the size and direction of the paper P are set to A4 landscape (A4LEF), and the paper width correction values α1 and α2 are set to 100% and 95 [%] according to the paper width correction value table TBL2 (FIG. 7A), respectively. %], That is, the print area covers almost the entire range of the planar heater 42.

  In FIG. 10, the non-temperature correction belt surface temperature NTB is distributed between the fixing upper limit temperature TUL and the fixing lower limit temperature TLL in the vicinity of the center and is a substantially constant temperature. On the other hand, the non-temperature correction belt surface temperature NTB decreases near the left and right ends as it moves outward in the left and right directions, and is lower than the fixing lower limit temperature TLL in the print area. There are places. In such a case, in the fixing device 22, in the vicinity of the left and right ends of the paper P, there is a possibility that the toner may not be sufficiently fixed to the paper P and a fixing failure may occur.

  On the other hand, in the present embodiment, when the inside of the fixing device 22 is in the cold state, the fixing control unit 38 relatively sets the temperature correction values β1 and β2 in the temperature control of the side 1 heater 42B and the side 2 heater 42C. A high increase correction value (120 [%]) is set (FIG. 8, step SP2).

  As a result, in the fixing device 22, the belt surface temperature TB, which is the surface temperature of the fixing belt 41, is distributed as shown by the solid line in FIG. That is, the belt surface temperature TB is distributed between the fixing upper limit temperature TUL and the fixing lower limit temperature TLL in the entire range including the vicinity of the end of the printing area, and is within the fixing temperature range. As a result, the fixing device 22 can satisfactorily fix the toner on the paper P in the entire printing area without causing fixing failure.

  In addition, the fixing control unit 38 determines the temperature correction value based on an experiment or the like on the condition that the fixing device 22 is in the cold state and the elapsed time after the setting is within the increasing time (15 [s]). β1 and β2 are set to increase correction values, and the temperature correction values β1 and β2 are returned to the normal correction values when this condition is not satisfied (FIG. 8). In addition to this, the fixing control unit 38 also sets the increase correction value to 120 [%] by suppressing the increase width from the normal correction value (100 [%]) to 20 [%] based on the previous experiment. .. As a result, the fixing device 22 can prevent the temperature of the side 1 heater 42B and the side 2 heater 42C from excessively increasing, that is, prevent the belt surface temperature TB from exceeding the fixing upper limit temperature TUL, and can perform the fixing process well. The state can be maintained.

  Further, the fixing control unit 38 detects the temperature inside the fixing device 22 by the compensating thermistor 72 incorporated in the infrared temperature sensor 48 that detects the surface temperature of the fixing belt 41 (FIG. 5). That is, in the fixing device 22, since the existing compensation thermistor 72 can be used as it is, it is possible to suppress an increase in cost without separately providing a temperature sensor for detecting whether or not it is in a cold state.

  Further, in the temperature control of the side 1 heater 42B and the side 2 heater 42C, the fixing control unit 38 maintains the control method of calculating the side 1 duty value DS1 and the side 2 duty value DS2 for each temperature control cycle (100 [ms]). As it is, the temperature correction values β1 and β2 are switched to the normal correction value or the increase correction value. For this reason, in the fixing device 22, when the temperature correction values β1 and β2 are switched, the temperature control can be smoothly continued without causing a sharp change in temperature or the like and without performing complicated control.

  By the way, as a conventional fixing device, one having two heaters (a main heater and a sub heater) whose outputs are distributed so as to cover the entire range in the main scanning direction (hereinafter referred to as a full-range distribution fixing device) is known. Are known. In this full-range distribution fixing device, the output distributions of the main heater and the sub-heater are different from each other, as shown in the characteristic curve of the output distribution in FIG.

  Of these, the main heater has a relatively high output in the central region (hereinafter referred to as the inner region) in the main scanning direction, and the output of both outer regions (hereinafter referred to as the outer region) goes to the outermost end. It is getting lower gradually as we go. Specifically, the output of the main heater is 800 [W] in the inner region and 720 [W] at the outermost end, as shown by the main heater output QM in FIG.

  On the other hand, in the sub-heater, the output in the inner region is relatively low, and the output in the outer region gradually increases toward the outermost end. Specifically, the output of the sub-heater is 400 [W] in the inner region and 560 [W] at the outermost end, as shown by the sub-heater output distribution QS in FIG.

  Further, in the full-range distribution fixing device, both main heaters and sub-heaters are caused to generate heat so that the outputs of both are summed and distributed as a total output distribution QG. The output in this total output distribution QG is 1200 [W] in the inner region and 1280 [W] at the outermost end. Here, the ratio of the outermost end to the inner region in the total output distribution QG (hereinafter referred to as the outermost end output ratio) is 1.07.

  In this full-range distribution fixing device, it is assumed that the output ratio of the outer region to the inner region is increased in order to avoid insufficient rise in temperature at the outer end in the cold state. In this full-range distribution fixing device, since the output distribution in the main scanning direction is fixed in each of the main heater and the sub-heater, it is possible to reduce the contribution of the main heater and increase the contribution of the sub-heater, for example. Be done.

  For example, in the full-range distribution fixing device, as shown in FIG. 11B, when the output of the main heater is reduced to 70% while the output of the sub-heater is 100%, the output in the total output distribution QG is , 960 [W] in the inner region and 1064 [W] in the outermost end. In this case, the outermost end output ratio in the total output distribution QG is 1.11. Therefore, compared with the case of FIG. 11A in which the output of both heaters is 100%, the outer region with respect to the inner region is It can be expected to increase the relative temperature of.

  However, in this case, in the full-range distribution fixing device, the increase in the outermost end output ratio is as small as 0.04 (that is, about 4%), and thus the temperature in the outer region may not be sufficiently increased. Further, in this case, in the total range distribution fixing device, the output in the inner area is reduced from 1200 [W] to 960 [W] in the total output distribution QG, so that fixing failure due to insufficient temperature in the inner area and warm-up processing are performed. There may be a problem such as an increase in required time.

  On the other hand, in the fixing device 22 according to the present embodiment, as shown in FIG. 4, the temperature of the main heater 42A, the side 1 heater 42B, and the side 2 heater 42C can be controlled independently. Further, in the fixing control unit 38, when the fixing device 22 is in the cold state, the increase width is set to about 20% by setting the temperature correction values β1 and β2 to the increase correction value (120%), and thus the side 1 heater 42B. Also, the temperature of the side 2 heater 42C can be sufficiently increased in a short time.

  According to the above configuration, in the image forming apparatus 1 according to the first embodiment, when the inside of the fixing device 22 is in the cold state at the end of the warm-up process, the fixing control unit 38 causes the temperature correction values β1 and β2. Is set to the increment correction value. Then, the fixing control unit 38 controls the temperatures of the side 1 heater 42B and the side 2 heater 42C by calculating the side 1 duty value DS1 and the side 2 duty value DS2 using the set temperature correction values β1 and β2. .. As a result, the image forming apparatus 1 can adjust the temperature in the fixing device 22 in the vicinity of the end portion of the fixing belt 41 in the main scanning direction to a temperature range suitable for fixing, thereby preventing occurrence of fixing failure and achieving high quality. It is possible to perform various printing processes.

[2. Second Embodiment]
The image forming apparatus 101 (FIG. 1) according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in that it has a fixing device 122 instead of the fixing device 22, but is different. The point is similarly configured.

  The fixing device 122 has a fixing control unit 138 (FIG. 2 and the like) that replaces the fixing control unit 38 in the first embodiment. Further, as shown in FIG. 12 corresponding to FIG. 3, the fixing unit 122 has a heating unit 23 configured similarly to the fixing unit 22 according to the first embodiment, but replaces the pressing unit 24. The difference is that the pressure unit 124 is provided. The pressing unit 124 includes the lower main thermistor 154, the lower side 1 thermistor 155, and the lower side 2 thermistor 156 (hereinafter collectively referred to as a lower thermistor group) in addition to the pressing roller 51 similar to that of the first embodiment. have.

  The lower main thermistor 154 is provided at a position that is in contact with or extremely close to the front side of the pressure roller 51 and that is near the left end of the main heater 42A in the left-right direction. The lower side 1 thermistor 155 is provided in a position that is in contact with or extremely close to the front side of the pressure roller 51, and is near the left end of the side 1 heater 42B1 in the left-right direction. The lower side 2 thermistor 156 is provided at a position that is in contact with or extremely close to the front side of the pressure roller 51, and is near the left end of the side 2 heater 42C1 in the left-right direction.

  The lower main thermistor 154, the lower side 1 thermistor 155, and the lower side 2 thermistor 156 detect the temperature of the pressure roller 51 at each position as shown in FIG. 13 corresponding to FIG. 4, and the detected temperature is determined by the fixing controller 138. To notify. In particular, the lower side 2 thermistor 156 (FIG. 12) can detect the temperature of the end portion of the fixing belt 41 that is separated from the main heater 42A in the left-right direction or the vicinity thereof.

[2-1. Temperature control in fixing device]
When performing print processing, the image forming apparatus 101 is configured to perform warm-up processing to sufficiently raise the temperature of the fixing belt 41 and then perform print processing, as in the first embodiment.

  At this time, the fixing controller 138 of the fixing device 122 controls the temperature of the main heater 42A and the temperatures of the side 1 heater 42B and the side 2 heater 42C during the warm-up process by the fixing controller 38 according to the first embodiment. Do the same as. After the start of the printing process, the fixing control unit 138 also controls the temperature of the main heater 42A in the same manner as the fixing control unit 38.

  On the other hand, the fixing control unit 138 sets the temperature correction values β1 and β2 individually, unlike the fixing control unit 38, when performing the temperature control of the side 1 heater 42B and the side 2 heater 42C after the start of the printing process. The temperatures detected by the lower side 1 thermistor 155 and the lower side 2 thermistor 156 are used.

  Specifically, the fixing control unit 138 sets the temperature correction value β1 according to the procedure RT2 for setting the temperature correction value β1 shown in FIG. This temperature correction value β1 setting processing procedure RT2 is similar to the temperature correction value setting processing procedure RT1 (FIG. 8) in the first embodiment, but part of the processing is different.

  Specifically, when the warm-up process ends and the print process starts, the fixing control unit 138 starts the temperature correction value β1 setting process procedure RT2 and proceeds to step SP11. In step SP11, the fixing controller 138 detects the temperature (hereinafter referred to as the lower thermistor temperature) by the lower side 1 thermistor 155, and proceeds to the next step SP12.

  In step SP12, the fixing controller 138 determines whether the fixing device 122 is in the cold state. Specifically, the fixing controller 138 determines whether or not the lower thermistor temperature is lower than a predetermined second cold boundary temperature (for example, 50 [° C.]). If a positive result is obtained here, the fixing control unit 138 moves to the next step SP13, sets the temperature correction value β1 to a relatively high increase correction value (for example, 120 [%]), and moves to the next step SP14. ..

  In step SP14, the fixing controller 138 waits until a predetermined increase time (for example, 15 [s]) elapses from the time when the temperature correction value β1 is set to the increase correction value, and when the increase time elapses, the next step SP15. Move on to. That is, unlike the temperature correction value setting processing procedure RT1 (FIG. 8), when the temperature correction value β1 is set to the increase correction value, the fixing control unit 138 sets the increase correction until the increase time elapses regardless of the lower thermistor temperature. The value will be maintained. The fixing control unit 138 also proceeds to the next step SP15 even when a negative result is obtained in step SP12.

  In step SP15, the fixing controller 138 sets the temperature correction value β1 to the normal correction value (100 [%]), waits until the end of the printing process in the next step SP16, and then moves to step SP17 to correct the temperature. The procedure RT2 for setting the value β1 is ended.

  Further, the fixing control unit 138 sets the temperature correction value β2 according to the temperature correction value β2 setting processing procedure RT3 shown in FIG. In this case, the fixing controller 138 performs a process similar to the temperature correction value β1 setting process procedure RT2 (FIG. 14), but instead of the temperature of the lower side 1 thermistor 155, the temperature of the lower side 2 thermistor 156 is used as the lower thermistor temperature. Further, the value of the temperature correction value β2 is set instead of the temperature correction value β1.

  In this way, the fixing controller 138 determines whether or not the fixing device 122 is in the cold state by comparing the temperatures of the lower side 1 thermistor 155 and the lower side 2 thermistor 156 with the second cold boundary temperature. Further, if the fixing device 122 is in the cold state, the fixing control unit 138 sets the temperature correction value β1 and the temperature correction value β2 to the increase correction values, controls the temperatures of the side 1 heater 42B and the side 2 heater 42C, and increases them. It is designed to return to the normal correction value after the passage of time.

[2-2. Temperature change in fixing device]
Next, FIG. 16 corresponding to FIG. 9 shows how the temperature of each part of the fixing device 122 changes when the image forming apparatus 101 performs the printing process after the warm-up process. In FIG. 16, as in FIG. 9, the horizontal axis represents the passage of time. Specifically, the start time of the warm-up process is time T11, the start time of the printing process is time T12, and the time when the leading edge of the paper P reaches the nip portion NP of the fixing device 122 is time T13. However, in FIG. 16, unlike FIG. 9, the time point when the increase time has elapsed from the time point T13 is set as the time point T14.

  In FIG. 16, in the upper part, the operation state and the like are shown in a table format as in the upper part of FIG. 9. A graph similar to FIG. 9 is shown in the lower portion regarding the belt surface temperature TB, the main temperature TM, and the side temperature TS, but a graph of the lower thermistor temperature TL is displayed instead of the graph of the fixing device temperature TE. Has been done.

The lower thermistor temperature TL is gradually listed from the time T11 when the warm-up process is started, but is lower than the second cold boundary temperature (50 [° C.]) at the time T12 when the warm-up process is finished and the printing process is started. Has become. Therefore, the fixing controller 138 sets both the temperature correction values β1 and β2 to the increase correction value.

  Although the lower thermistor temperature TL continues to increase even after this time T12, the heat of the fixing device 122 is transferred to the paper P after the time T13 when the paper P reaches the fixing device 122, and therefore starts decreasing. After that, the fixing control unit 138 sets both the temperature correction values β1 and β2 to the normal correction values at time T14 when the increase time has elapsed from time T12. At this time, the lower thermistor temperature TL continues to decrease because heat is transferred to the paper P by performing the fixing process of the paper P subsequently.

[2-3. Effect, etc.]
With the above configuration, in the image forming apparatus 101 according to the second embodiment, the fixing controller 138 causes the fixing device 122 to be in the cold state in the printing process after the warm-up process, as in the first embodiment. For example, the temperature correction values β1 and β2 are set to the increase correction values only during the increase time.

  As a result, the fixing device 122 can prevent the surface temperature of the fixing belt 41 from being lower than the fixing lower limit temperature TLL (FIG. 10) in the vicinity of the end portion in the main scanning direction, as in the first embodiment. The fixing process can be executed well.

  In particular, the fixing controller 138 compares the temperature obtained by the lower side 1 thermistor 155 and the lower side 2 thermistor 156 in the pressure roller 51 with the second cold boundary temperature to determine whether or not it is in the cold state. did. The lower side 1 thermistor 155 and the lower side 2 thermistor 156 are provided at positions near the left ends of the side 1 heater 42B1 and the side 2 heater 42C, respectively. It can detect the temperature of a nearby location.

  Therefore, the fixing control unit 138 is based on a value close to the actual temperature of the fixing belt 41, as compared with the case where the infrared temperature sensor 48 detects and compares the temperature of the fixing device as in the first embodiment. Whether or not it is in the cold state, that is, whether or not the temperature correction values β1 and β2 should be set to the increase correction values can be appropriately determined.

  Further, since the fixing control unit 138 sets the temperature correction values β1 and β2 individually, for example, the temperature correction value β1 is set to the normal correction value while the temperature correction value β2 is set to the increase correction value. The temperatures of 42B and the side 2 heater 42C can be precisely controlled.

  In other respects, the image forming apparatus 101 according to the second embodiment can have the same effects as the image forming apparatus 1 according to the first embodiment.

  According to the above configuration, when the image forming apparatus 101 according to the second embodiment determines that the inside of the fixing device 122 is in the cold state based on the temperature obtained by the lower thermistor group at the end of the warm-up process. The fixing control unit 138 individually sets the temperature correction values β1 and β2 to the increase correction value. Then, the fixing controller 138 controls the temperatures of the side 1 heater 42B and the side 2 heater 42C by calculating the side 1 duty value DS1 and the side 2 duty value DS2 using the set temperature correction values β1 and β2. .. As a result, the image forming apparatus 101 can adjust the temperature in the fixing device 122 near the end portion of the fixing belt 41 in the main scanning direction to a temperature range suitable for fixing, thereby preventing occurrence of defective fixing and achieving high quality. It is possible to perform various printing processes.

[3. Third Embodiment]
The image forming apparatus 201 (FIG. 1) according to the third embodiment is different from the image forming apparatus 1 according to the first embodiment in that it has a fixing device 222 instead of the fixing device 22. The point is similarly configured. The fixing device 222 is different from the fixing device 22 according to the first embodiment in that it has a fixing control unit 238 (FIG. 2 and the like) instead of the fixing control unit 38, but is different in other points. Are similarly configured.

  When performing print processing, the image forming apparatus 201 is configured to perform warm-up processing to sufficiently raise the temperature of the fixing belt 41 and then perform print processing, as in the first embodiment. .. At this time, the fixing control unit 238 of the fixing device 222 controls the temperature of the main heater 42A during the warm-up process in the same manner as the fixing control unit 38 according to the first embodiment. On the other hand, the fixing controller 238 controls the temperatures of the side 1 heater 42B and the side 2 heater 42C by a method partially different from that of the first embodiment. Specifically, the fixing controller 238 is configured to execute a process in accordance with the target temperature setting process procedure RT4 shown in FIG. 17 corresponding to FIG.

[3-1. Temperature control in fixing device]
When the warm-up process is started in the image forming apparatus 201, the fixing controller 238 starts the target temperature setting process procedure RT4 and proceeds to the first step SP31. In step SP31, the fixing controller 238 determines whether or not the fixing device 222 is in the cold state based on the fixing device temperature obtained by the infrared temperature sensor 48, as in step SP1 (FIG. 8). If an affirmative result is obtained here, the fixing controller 238 moves to the next step SP32.

  In step SP32, the fixing controller 238 sets the target temperature when the side 1 heater 42B and the side 2 heater 42C are temperature-controlled to the temperature of the main heater 42A detected by the heater back main thermistor 44 (hereinafter referred to as a normal target value). ) Is added to 5 [° C.] (hereinafter referred to as an increase target value), and the process proceeds to the next step SP33. As a result, the temperature of the side 1 heater 42B and the side 2 heater 42C is controlled so that the temperature becomes higher than the main heater 42A by about 5 [° C.].

  In step SP33, the fixing controller 238 determines whether or not a predetermined increase time (for example, 15 [s]) has elapsed after setting the target temperature to the increase target value, as in step SP3 (FIG. 8). .. If a negative result is obtained here, this means that the temperature of the side 1 heater 42B and the side 2 heater 42C is excessively increased because the period in which the target temperature is set to the increase target value is still relatively short. It shows that the sex is low. At this time, the fixing controller 238 returns to step SP31 again and repeats a series of processes.

  On the other hand, if an affirmative result is obtained in step SP33, this means that the target temperature has been set to the increase target value and a sufficiently long time has elapsed. Therefore, the temperature of the side 1 heater 42B and the side 2 heater 42C is kept as it is. Is likely to increase excessively. At this time, the fixing controller 238 moves to the next step SP34.

  If a negative result is obtained in step SP31, this means that the temperature inside the fixing device 222 is relatively high, so that when the temperature near the center of the fixing belt 41 reaches the target temperature, even near the outside in the left-right direction. This indicates that the temperature may be sufficiently close to the target temperature. At this time, the fixing controller 238 moves to the next step SP34.

  In step SP34, the fixing controller 238 sets the target temperature to the normal target value, that is, the temperature of the main heater 42A detected by the heater back main thermistor 44, and then proceeds to the next step SP35. That is, when the inside of the fixing device 222 is in the cold state, the fixing control unit 238 sets the target temperature to the increase target value, and when the increase time elapses thereafter, or inside the fixing device 222, the first cold boundary temperature. When the value exceeds, the normal target value is set. Further, the fixing control unit 238 sets the normal target value even when the cold state is not present at the start of the warm-up process. As a result, the side 1 heater 42B and the side 2 heater 42C are temperature-controlled to match the temperature of the main heater 42A.

  In step SP35, the fixing control unit 238 determines whether or not the warm-up process is completed. If a negative result is obtained here, the fixing controller 238 waits for the end of the warm-up process by repeating this step SP35. On the other hand, if a positive result is obtained in step SP35, the fixing control section 238 moves to the next step SP6 and ends the target temperature setting processing procedure RT4.

[3-2. Temperature change in fixing device]
Next, FIG. 18 corresponding to FIGS. 9 and 16 shows how the temperature of each part of the fixing device 222 changes when the image forming apparatus 201 performs the warm-up process. In FIG. 18, as in FIG. 9, the horizontal axis represents the passage of time. Specifically, the start time of the warm-up process is time T21, the time when the increase time (15 [s]) has elapsed from the time T21 is time T22, and the end time of the warm-up process is time T23. Note that, in FIG. 18, the ratio of the horizontal axis representing time is different from that in FIG. 9 for the convenience of drawing, and the portion corresponding to the warm-up period is shown longer than in FIG.

  In FIG. 18, in the upper portion, the operating state and the like are shown in a table format as in the upper portion of FIG. Although a graph of the belt surface temperature TB, the main temperature TM, the side temperature TS, and the fixing device temperature TE is shown in the lower portion, some waveforms are different from those in FIG.

  That is, in FIG. 18, the belt surface temperature TB, the main temperature TM, and the fixing device temperature TE fluctuate according to the same tendency as in FIG. On the other hand, since the target temperature is set to the increase target value at the time point T21, the side temperature TS increases while drawing a steeper slope than the main temperature TM from the time point T21, and at the time point T22 when the increase time elapses. The value is higher than the main temperature TM. Subsequently, since the target temperature is set to the normal target value at the time point T22, the side temperature TS has a small increase width, and eventually follows the main temperature TM.

[3-3. Effect, etc.]
In the above-described configuration, the image forming apparatus 201 according to the third embodiment differs from the first and second embodiments in that the fixing controller 222 causes the fixing device 222 to be in the cold state during the warm-up process. For example, the target temperature of the side 1 heater 42B and the side 2 heater 42C is set to the increase correction value only during the increase time. That is, the side 1 heater 42B and the side 2 heater 42C are subjected to temperature control with the target temperature being 5 [° C.] higher than the temperature of the main heater 42A detected by the heater back main thermistor 44 during the increasing time.

  As a result, the fixing device 222 can sufficiently raise the surface temperature of the fixing belt 41 near the end portion in the main scanning direction at the time of performing the printing process after the warm-up process is completed, so that the sheet P reaches and is fixed. When the processing is performed, the fixing can be stably performed at a temperature higher than the fixing lower limit temperature TLL (FIG. 10).

  Particularly, when the fixing device 222 is in the cold state, the target temperature of the side 1 heater 42B and the side 2 heater 42C is increased by 5 [° C.] and then the temperature control is performed. The value of 5 [° C.] is set in consideration of the temperature range suitable for fixing which is determined by the fixing upper limit temperature TUL and the fixing lower limit temperature TLL (FIG. 10). Therefore, the fixing device 222 is extremely unlikely to excessively raise the temperatures of the side 1 heater 42B and the side 2 heater 42C, and can perform good fixing processing.

  In other respects as well, the image forming apparatus 201 according to the third embodiment can achieve the same effects as the image forming apparatus 1 according to the first embodiment.

  According to the above configuration, in the image forming apparatus 201 according to the third exemplary embodiment, in the warm-up process, when it is determined that the fixing device 222 is in the cold state, the fixing control unit 238 causes the side 1 heater 42B and the side heater 42B. The target temperature of the two heaters 42C is set to the increase correction value to control the temperature. As a result, the image forming apparatus 201 can adjust the temperature in the fixing device 222 in the vicinity of the end portion of the fixing belt 41 in the main scanning direction to a temperature range suitable for fixing, prevent the occurrence of defective fixing, and improve the quality. It is possible to perform various printing processes.

[4. Other Embodiments]
In the first embodiment described above, based on the temperature detected by the compensating thermistor 72 (FIG. 5) of the infrared temperature sensor 48 (FIG. 3) provided at a position slightly distant to the front of the fixing belt 41. The case has been described where it is determined whether the fixing device 22 is in the cold state. In the second embodiment, based on the temperature detected by the lower thermistor (lower main thermistor 154, lower side 1 thermistor 155 and lower side 2 thermistor 156) provided so as to contact the front side of the pressure roller 51, The case of determining whether or not the fixing device 122 is in the cold state has been described. However, the present invention is not limited to these, and it is determined whether or not the fixing device 22 or the like is in a cold state based on the temperature detected by various temperature sensors provided inside or near the fixing device 22 or the like. You may. The same applies to the third embodiment.

  In the above-described first embodiment, the infrared temperature sensor 48 (FIG. 5) provided mainly for detecting the surface temperature of the fixing belt 41 has the compensation thermistor 72 in addition to the detection thermistor 71. In the above, the case where it is determined whether or not the fixing device 22 is in the cold state based on the temperature detected by the compensating thermistor 72 has been described. However, the present invention is not limited to this, for example, a temperature sensor for detecting the temperature inside the fixing device 22 is separately provided in addition to the infrared temperature sensor 48, and the fixing device 22 or the like is cold based on the temperature detected by the temperature sensor. You may determine whether it is in a state. The same applies to the third embodiment.

  Further, in the above-described first embodiment, the temperature of the fixing belt 41 is detected by the infrared temperature sensor 48 provided in the front of the fixing belt 41 and distant from the infrared belt. If you want to. However, the present invention is not limited to this, and the temperature of the fixing belt 41 may be detected by various other temperature sensors. The same applies to the second and third embodiments.

  Further, in the above-described first embodiment, the temperature correction value β1 to be multiplied by the duty value D (n) for the main heater 42A is set to the increase correction value in the side 1 duty value DS1 calculated by the equation (2). Thus, the case where the temperature of the side 1 heater 42B is increased has been described. However, the present invention is not limited to this, and the value of the side 1 duty value DS1 may be increased by various other arithmetic processing, such as adding a predetermined value to the side 1 duty value DS1. The same applies to the side 2 duty value DS2 calculated by the equation (3), and the same applies to the second embodiment.

  Further, in the above-described first embodiment, in the side 1 duty value DS1 calculated by the equation (2), the paper width correction obtained by the equation (4) is applied to the duty value D (n) for the main heater 42A. The case where the temperature control for each heater is adjusted according to the sheet width L of the sheet P by multiplying by the value α1 has been described. However, the present invention is not limited to this, and for example, the paper width correction value α1 may be calculated by various other functions related to the paper width L, or a value according to the paper width L may be added or subtracted. May increase or decrease the value of the side 1 duty value DS1 by other various arithmetic processing. The same applies to the side 2 duty value DS2 calculated by the equation (3), and the same applies to the second embodiment.

  Further, in the above-described first embodiment, in the temperature correction value setting processing procedure RT1 (FIG. 8), the first cold boundary temperature is 40 [° C.], the increase correction value is 120 [%], and the increase time is The case of 15 [s] has been described. However, the present invention is not limited to this, and the first cold boundary temperature, the increase correction value, and the increase time may be various other values determined based on experiments and the like. Further, different increase correction values may be set for the temperature correction value β1 and the temperature correction value β2. In short, a value that can be used to appropriately determine whether the fixing device 22 is in a cold state or a value that allows the belt temperature of the fixing belt 41 to fall between the fixing upper limit temperature TUL and the fixing lower limit temperature TLL (FIG. 10). I wish I had it. The same applies to the second and third embodiments.

  Further, in the above-described first embodiment, when the fixing device 22 is no longer in the cold state after the temperature correction values β1 and β2 are set to the increase correction values, the temperature correction values β1 and β2 are set to the normal correction values. The case has been described (FIG. 8). However, the present invention is not limited to this, and for example, similarly to the second embodiment (FIGS. 14 and 15), the temperature is increased when the increase time elapses regardless of whether the fixing device 22 is in the cold state. The correction values β1 and β2 may be set to normal correction values. The same applies to the third embodiment.

  Further, in the above-described first embodiment, the case where the temperature correction values β1 and β2 are set to the normal correction values when the increase time elapses after the temperature correction values β1 and β2 are set to the increase correction values has been described. (FIG. 8). However, the present invention is not limited to this, and for example, regardless of the passage of time, the temperature correction values β1 and β2 may be set to the normal correction values when the fixing device 22 is no longer in the cold state. The same applies to the third embodiment.

  Further, in the above-described second embodiment, the case where the position of the lower side 1 thermistor 155 (FIG. 12) in the left-right direction is near the left end of the side 1 heater 42B1 has been described. However, the present invention is not limited to this, and may be various other positions such as the vicinity of the center of the side 1 heater 42B1. The point is that it is only necessary to be able to detect a temperature as close as possible to the temperature of the side 1 heater 42B1. The same applies to the lower main thermistor 154 and the lower side 2 thermistor 156.

  Further, in the third embodiment described above, in the warm-up process, when the fixing device 222 is in the cold state, the temperature of the side 1 heater 42B and the side 2 heater 42C is controlled to be higher than usual. However, the present invention is not limited to this, and for example, when the print processing performed after the warm-up processing is in a cold state again, the same temperature control as in the first embodiment may be performed.

  Further, in the above-described third embodiment, similarly to the first embodiment, it is determined whether or not the fixing device 222 is in the cold state based on the compensation thermistor temperature obtained from the infrared temperature sensor 48. Described the case. However, the present invention is not limited to this, for example, as in the second embodiment, a lower thermistor is provided in the pressurizing unit 124, and whether or not the fixing device 222 is in the cold state based on the temperature obtained from the lower thermistor. May be determined. Further, in this case, similarly to the second embodiment, the target temperature of the side 1 heater 42B and the target temperature of the side 2 heater 42C may be set individually.

  Further, in the above-described first embodiment, the planar heater 42 is divided into five heat generating regions, that is, the main heater 42A, the side 1 heaters 42B1 and 42B2, and the side 2 heaters 42C1 and 42C2 along the main scanning direction (horizontal direction). The case of splitting is described. However, the present invention is not limited to this, and the number of divisions of the planar heater 42 may be any number such as three or seven. Further, the position of the main heater 42A is not limited to the center in the main scanning direction, and may be arranged, for example, on the right side or the left side. The position of the main heater 42A in the left-right direction may be determined according to the position in the left-right direction at which the sheet P is conveyed in the middle conveyance section 10 or the like when the printing process is performed on the sheet P having a relatively small sheet width. .. The same applies to the second and third embodiments.

  Further, in the above-described first embodiment, when the fixing controller 38 controls the temperatures of the side 1 heater 42B and the side 2 heater 42C, the heater back control is performed in the warm-up process, and the duty ratio correction control is performed in the print process. When doing. However, the present invention is not limited to this, and for example, the fixing control unit 38 may adopt another temperature control method such as duty ratio correction control in the warm-up process, or another temperature control such as heater back control in the print process. The method may work. The same applies to the second and third embodiments.

  Further, in the above-described first embodiment, the case where the fixing control unit 38 is provided in the fixing device 22 has been described. However, the present invention is not limited to this, and the fixing controller 38 may be provided at various other locations. Alternatively, for example, the print control unit 3 may execute a predetermined program to realize a function corresponding to the fixing control unit 38 inside the print control unit 3 to control the temperature of each heater. Further, the temperature control may be performed by the fixing control unit 38 alone, or may be performed in cooperation with another control unit such as the print control unit 3. The same applies to the second and third embodiments.

  Further, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 which is a single-function printer (that is, SFP) has been described. However, the present invention is not limited to this, for example, a multifunction machine having an image scanner function, a communication function, and the like in addition to the printer function and capable of operating as a copier (copier) or a facsimile device, that is, a so-called MFP (Multi Function Peripheral). / Printer). Further, the present invention may be applied to various apparatuses having an electrophotographic printing function, such as a facsimile machine and a copying machine.

  Further, in the above-described embodiment, the case where the present invention is applied to the fixing device 22 incorporated in the image forming apparatus 1 has been described. However, the present invention is not limited to this, and the present invention may be applied to a fixing device mounted in various other devices.

  Furthermore, the present invention is not limited to the above-described embodiments and other embodiments. That is, the present invention is applicable to an embodiment in which a part or all of the above-described embodiments and a part or all of the above-described other embodiments are arbitrarily combined, or an embodiment in which a part is extracted Is.

  Further, in the above-described first embodiment, the fixing belt 41, the planar heater 42 as a heater, the pressure roller 51 as a pressure unit, the infrared temperature sensor 48 as a main temperature detection unit, and others. The case has been described in which the fixing thermistor 72 as the spot temperature detection unit and the fixing control unit 38 as the control unit constitute the fixing device 22 as the fixing device. However, the present invention is not limited to this, and the fixing device is configured by a fixing belt having various other configurations, a heater, a pressurizing unit, a main temperature detecting unit, another temperature detecting unit, and a control unit. Is also good.

  INDUSTRIAL APPLICABILITY The present invention can be used in, for example, a fixing unit of an image forming apparatus having an electrophotographic printing function.

  1, 101, 201 ... Image forming apparatus, 3 ... Print control section, 10 ... Medium transport section, 15 ... Image forming unit, 22, 122, 222 ... Fixing device, 23 ... Heating section, 24, 124 ... Pressurizing unit, 38, 138, 238 ... Fixing control unit, 41 ... Fixing belt, 42 ... Sheet heater, 42A ... Main heater, 42B, 42B1, 42B2 ... Side 1 heater, 42C, 42C1, 42C2 ... Side 2 heater, 43 ... Heat diffusion member, 44 ... Heater back main thermistor, 45 ... Heater back side 1 thermistor, 46 ... Heater back side 2 thermistor, 48 ... Infrared temperature sensor, 51 ...... Pressure roller, 71 ...... Detection thermistor, 72 …… Compensation thermistor, 82 …… Differential amplifier circuit, 154 …… Lower main thermistor, 155 …… Lower side 1 thermistor 156 ... Lower side 2 thermistor, D ... Duty value, DS1 ... Side 1 duty value, DS2 ... Side 2 duty value, L ... Paper width, NP ... Nip location, P ... Paper, S11 ... ... detection thermistor signal, S12 ... compensation thermistor signal, S13 ... differential amplification signal, TLL ... lower fixing temperature, TUL ... upper fixing temperature.

Claims (11)

A fixing device for applying heat and pressure to a medium onto which a developer is transferred according to an image to fix the medium.
A tubular fixing belt,
A plurality of heat generating areas are arranged along the main scanning direction, and a heater that heats the fixing belt by generating heat when electric power is supplied to the heat generating areas,
A pressure unit for applying pressure to the fixing belt,
A main temperature detection unit that detects a main temperature that is a temperature of a portion of the fixing belt that corresponds to a main heat generation area that is one of the heat generation areas;
Another location temperature detection unit that detects another location temperature that is a temperature of a location different from the fixing belt,
A control unit for controlling electric power supplied to each of the plurality of heat generation regions,
When the temperature of the other portion is lower than a predetermined boundary temperature, the control unit corrects the amount of electric power supplied to a sub-heating region different from the main heating region in the heating region so as to be increased. Fixing device. The fixing device according to claim 1, wherein the other-spot temperature detection unit detects a temperature at a position apart from the fixing belt as the other-spot temperature. The main temperature detection unit,
A detection thermistor which is provided at a position distant from the fixing belt and which generates a detection signal indicating a temperature rise by infrared rays emitted from the fixing belt;
A compensating thermistor for generating a compensating signal representing the temperature around the sensing thermistor;
An arithmetic circuit for performing arithmetic processing based on the detection signal and the compensation signal,
The fixing device according to claim 1, wherein the other-spot temperature detection unit sets the temperature represented by the compensation signal as the other-spot temperature. The fixing device according to claim 1, wherein the other-spot temperature detection unit detects a temperature of a portion of the pressing unit corresponding to the sub-heating region in the main scanning direction as the other-spot temperature. .. In the range corresponding to the sub-heating area in the main scanning direction of the pressurizing section, the temperature of the other portion is the temperature of the end portion on the side away from the main heating area or the vicinity thereof, The fixing device according to claim 4, wherein: The fixing device according to claim 1, wherein the control unit returns the amount of electric power supplied to the auxiliary heat generation region to a normal amount when the temperature of the other place exceeds the boundary temperature. The control unit returns the amount of power supplied to the sub-heating region to a normal amount when a predetermined increase time has elapsed after increasing the amount of power supplied to the sub-heating region. The fixing device according to 1. After the warm-up process of raising the fixing belt to a predetermined warm-up temperature is completed, the control unit controls the amount of electric power supplied to the sub-heating region when the temperature of the other place is lower than the boundary temperature. The fixing device according to claim 1, wherein the fixing device is corrected so as to increase. In the warm-up process of raising the fixing belt to a predetermined warm-up temperature, the control unit increases the amount of electric power supplied to the sub-heating region when the temperature of the other place is lower than the boundary temperature. The fixing device according to claim 1, wherein correction is performed. The fixing unit according to claim 1, wherein the control unit corrects the amount of power supplied to the sub-heating region according to a medium width that is a length of the medium in the main scanning direction. apparatus. A transport unit for transporting the medium,
An image forming unit that transfers the developer to the medium,
An image forming apparatus comprising: the fixing device according to any one of claims 1 to 10.

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