Image forming device

Abstract

To control a plurality of heaters for fixation based on a temperature detected by one temperature sensor.SOLUTION: An image forming apparatus 1 has: a fixing roller 20 whose surface is heated; a pressure roller 25 that forms a fixing nip with the fixing roller 20; a main heater 21 that heats a first area R1 of the fixing roller 20; a sub heater 22 that heats a second area R2 of the fixing roller 20; a temperature sensor 26 that detects a temperature of the first area R1 of the fixing roller 20; and a fixation control unit 51 that controls the main heater 21 and the sub heater 22 based on a temperature detected by the temperature sensor 26. The fixation control unit 51 controls the sub heater 22 by using a correction value A determined in advance based on a ratio between a value of current flowing in the main heater 21 and a value of current flowing in the sub heater 22 under a predetermined condition.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus that forms an image on a medium. [Background technology]

[0002] An image forming apparatus using an electrophotographic process is equipped with a fixing device that applies heat and pressure to an image (toner image) transferred onto a medium to fix it to the medium. The fixing device has a fixing body such as a fixing roller or a fixing belt, and the fixing body is heated by a heater.

[0003] In recent years, in order to accommodate a plurality of types of media with different widths, a fixing device has been proposed in which a plurality of heaters are arranged in the width direction of the media (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-240945 (see Figures 7A and 7B) Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional fixing devices, a plurality of heaters are controlled while detecting the respective temperatures, and therefore a plurality of temperature sensors must be provided.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has as its object to control a plurality of heaters for fixing based on the temperature detected by a single temperature sensor. [Means for solving the problem]

[0007] The image forming apparatus of the present disclosure includes a fixing body having a heated surface, a pressure member that forms a fixing nip between the fixing body and the pressure member, a first heater that heats a first region of the fixing body, a second heater that heats a second region of the fixing body, a temperature sensor that detects the temperature of the first region of the fixing body, and a control unit that controls the first heater and the second heater based on the temperature detected by the temperature sensor. The control unit controls the output of the first heater by changing the duty of a heater ON signal that drives the first heater, and controls the output of the second heater by changing the duty of a heater ON signal that drives the second heater. The control unit calculates a correction value that is determined in advance based on the ratio of the current value flowing through the first heater to the current value flowing through the second heater under predetermined conditions. The duty of the heater ON signal for the second heater is corrected according to do. The image forming apparatus of the present invention also includes a fuser having a heated surface, a pressure member forming a fixing nip between the fuser and the pressure member, a first heater for heating a first region of the fuser, a second heater for heating a second region of the fuser, a temperature sensor for detecting the temperature of the first region of the fuser, and a control unit for controlling the first heater and the second heater based on the temperature detected by the temperature sensor. The control unit controls the second heater using a correction value determined in advance based on the ratio of the current value flowing through the first heater to the current value flowing through the second heater under predetermined conditions. The correction value is determined based on a value a calculated using the formula a = (IS / IS0) / (IM / IM0) where IM is a measured value of the current flowing through the first heater when a predetermined power is supplied to the first heater, IS is a measured value of the current flowing through the second heater when a predetermined power is supplied to the second heater, IM is a designed value of the current flowing through the first heater, and IS is a designed value of the current flowing through the second heater. [Effects of the Invention]

[0008] According to the present disclosure, the second heater is controlled using a correction value determined based on the ratio of the current values ​​flowing through the first heater and the second heater, so that both the first heater and the second heater can be controlled based on the temperature detected by a single temperature sensor. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a basic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the first embodiment. [Figure 3] 1A, 1B, and 1C are diagrams showing the basic configuration of a fixing device according to a first embodiment. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a main heater according to the first embodiment. [Figure 5] FIG. 3 is a diagram illustrating a configuration of a sub-heater according to the first embodiment. [Figure 6] FIG. 2 is a diagram illustrating a configuration for controlling a main heater and a sub-heater according to the first embodiment. [Figure 7] FIG. 3 is a diagram showing, in functional blocks, processing for controlling a main heater according to the first embodiment. [Figure 8] FIG. 3 is a diagram showing, in functional blocks, processing for controlling a sub-heater according to the first embodiment. [Figure 9] FIG. 3 is a diagram illustrating a configuration for determining a correction value used to control a sub-heater according to the first embodiment. [Figure 10] 1A is a graph showing temperature changes when the heater ON signals for two heaters have the same duty cycle, and FIG. 1B is a graph showing temperature changes when the heater ON signals have different duties. [Figure 11] 6A and 6B are graphs showing the output distribution of the main heater and the sub-heater and the temperature distribution on the surface of the fixing roller. [Figure 12] 10A and 10B are schematic diagrams showing the basic configuration of a fixing device according to a second embodiment. [Figure 13] FIG. 10 is a diagram illustrating a configuration for controlling a main heater and a sub-heater according to a second embodiment. [Figure 14] FIG. 10 is a diagram illustrating a configuration for determining a correction value used to control a sub-heater according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First embodiment. <Image forming device> First, a description will be given of an image forming apparatus 1 according to a first embodiment. Fig. 1 is a diagram showing the image forming apparatus 1. The image forming apparatus 1 forms an image using an electrophotographic process, and is, for example, a color printer.

[0011] The image forming apparatus 1 has a medium supply section 7 that supplies the medium P, process units 10K, 10Y, 10M, and 10C as image forming units that form toner images (developer images) of black (K), yellow (Y), magenta (M), and cyan (C), a transfer unit 8 that transfers the image onto the medium P, a fixing device 2 that fixes the image onto the medium P, and a medium discharge section 9 that discharges the medium P.

[0012] These components are housed in a housing 1A. An openable and closable top cover 1B is provided on the top of the housing 1A.

[0013] The medium supply unit 7 has a medium cassette 70 that stores medium P such as printing paper, a hopping roller 71 and a retard roller 72 that separate the medium P in the medium cassette 70 one sheet at a time and send them out onto a conveyance path, a registration roller 73 that corrects skew of the medium P sent out onto the conveyance path, and a conveyance roller 74 that conveys the medium P to the transfer unit 8. As the medium P, in addition to printing paper, transparencies, envelopes, copy paper, special paper, etc. can be used.

[0014] The process units 10K, 10Y, 10M, and 10C are arranged in this order along the transport path of the medium P from the upstream side to the downstream side (here, from the right side to the left side).

[0015] The process units 10K, 10Y, 10M, and 10C each include a photosensitive drum 11K, 11Y, 11M, and 11C as an image carrier, a charging roller 12K, 12Y, 12M, and 12C as a charging member, a developing roller 13K, 13Y, 13M, and 13C as a developer carrier, and a supply roller 14K, 14Y, 14M, and 14C as a supply member.

[0016] Furthermore, print heads 18K, 18Y, 18M, and 18C serving as exposure devices (print heads) are disposed above and facing the photosensitive drums 11K, 11Y, 11M, and 11C. The print heads 18K, 18Y, 18M, and 18C are suspended and supported by the top cover 1B.

[0017] Photoconductor drums 11K, 11Y, 11M, and 11C are cylindrical members with photosensitive layers on their surfaces, and rotate counterclockwise in FIG. 1. Charging rollers 12K, 12Y, 12M, and 12C uniformly charge the surfaces of photoconductor drums 11K, 11Y, 11M, and 11C. Print heads 18K, 18Y, 18M, and 18C have light-emitting element arrays in which light-emitting elements such as LEDs (light-emitting diodes) are arranged, and expose the surfaces of photoconductor drums 11K, 11Y, 11M, and 11C to light to form electrostatic latent images.

[0018] Developing rollers 13K, 13Y, 13M, and 13C form toner images by attaching toner (developer) to the electrostatic latent images on the surfaces of photosensitive drums 11K, 11Y, 11M, and 11C. Supply rollers 14K, 14Y, 14M, and 14C supply toner to developing rollers 13K, 13Y, 13M, and 13C.

[0019] Further, toner cartridges 15K, 15Y, 15M, and 15C serving as developer containers for accommodating unused toner are detachably attached to the process units 10K, 10Y, 10M, and 10C.

[0020] The transfer unit 8 includes a transfer belt 80 that attracts and travels on the medium P, a drive roller 81 that drives the transfer belt 80, a tension roller 82 that applies tension to the transfer belt 80, and transfer rollers 19K, 19Y, 19M, and 19C that serve as transfer members and are arranged to sandwich the transfer belt 80 between the photosensitive drums 11K, 11Y, 11M, and 11C. The transfer rollers 19K, 19Y, 19M, and 19C transfer the toner images of each color formed on the photosensitive drums 11K, 11Y, 11M, and 11C onto the medium P.

[0021] The fixing device 2 has a fixing roller 20 as a fixing body, heaters 21 and 22 as heat sources, a pressure roller 25 as a pressure body, and a temperature sensor 26 as a temperature detection unit. The heaters 21 and 22 heat the fixing roller 20 from the inner circumferential side. The pressure roller 25 is pressed against the fixing roller 20 to form a fixing nip therebetween. The temperature sensor 26 is, for example, a thermopile, and detects the surface temperature of the fixing roller 20. Details of the fixing device 2 will be described later.

[0022] The medium discharge unit 9 has two pairs of discharge rollers 91 and 92 that transport the medium P that has passed through the fixing device 2 and discharge it from a discharge port. The top cover 1B of the image forming apparatus 1 is provided with a stacker unit 93 that places the medium P discharged by the discharge rollers 91 and 92.

[0023] A write sensor S1 and a discharge sensor S2 are arranged on the transport path of the medium P to detect the passage of the medium P. The write sensor S1 is arranged downstream of the transport rollers 74, and the discharge sensor S2 is arranged downstream of the fixing device 2. The detection signal of the write sensor S1 is used to determine the exposure start timing of the print heads 18K, 18Y, 18M, and 18C and the application timing of the transfer voltage to the transfer rollers 19K, 19Y, 19M, and 19C. The detection signal of the discharge sensor S2 is used to determine the end of the image formation operation on the medium P.

[0024] When there is no particular need to distinguish between the process units 10K, 10Y, 10M, and 10C and their components, the K, Y, M, and C will be omitted in the description. When there is no particular need to distinguish between the print heads 18K, 18Y, 18M, and 18C, the K, Y, M, and C will also be omitted in the description.

[0025] In Figure 1, the axial direction of the photosensitive drum 11 and each roller of the image forming apparatus 1 is the X direction. The X direction is the width direction of the image forming apparatus 1 and also the width direction of the medium P. The direction of movement of the medium P as it passes through the process unit 10 is the Y direction. The direction perpendicular to the XY plane is the Z direction. Note that in Figure 1, the Y direction is inclined at about 10 degrees with respect to the horizontal plane, but this inclination is not necessarily required.

[0026] Regarding the Y direction, the direction of movement of the medium P as it passes through the process unit 10 is the +Y direction, and the opposite direction is the -Y direction. Regarding the X direction, the right direction as viewed from the +Y direction is the +X direction, and the left direction is the -X direction. Regarding the Z direction, the approximately upward direction in FIG. 1 is the +Z direction, and the approximately downward direction is the -Z direction. Note that these directions do not limit the orientation of the image forming apparatus 1.

[0027] <Image forming device control system> Next, we will explain the control system of the image forming apparatus 1. Fig. 2 is a block diagram showing the control system of the image forming apparatus 1. The image forming apparatus 1 includes a print control unit 100, an I / F (interface) control unit 101, a receiving memory 102, an image data editing memory 103, an operation unit 104, a sensor group 105, a power supply control unit 106, a head control unit 111, a drive control unit 112, a belt drive control unit 113, a fixing control unit 51, a fixing drive control unit 114, and a paper feed / conveyance control unit 115.

[0028] These control units and memories, except for the power supply control unit 106, can be mounted on the same control board.

[0029] The print control unit 100 includes a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, a timer, etc. The print control unit 100 receives print data and control commands from a higher-level device via an I / F control unit 101, and controls the print operation of the image forming apparatus 1.

[0030] Receiving memory 102 temporarily stores print data input from a higher-level device via I / F control unit 101. Image data editing memory 103 receives the print data stored in receiving memory 102 and records image data formed by editing the print data, i.e., image data.

[0031] The operation unit 104 includes a display unit (e.g., LED) for displaying the status of the image forming apparatus 1 and an operation unit (e.g., switch) for the operator to input instructions. The sensor group 105 includes various sensors for monitoring the operating status of the image forming apparatus 1, such as the above-mentioned write sensor S1 and discharge sensor S2, a temperature and humidity sensor, and a concentration sensor.

[0032] The power supply control unit (high voltage control unit) 106 controls a charging voltage power supply 107 that applies a charging voltage to the charging roller 12, a developing voltage power supply 108 that applies a developing voltage to the developing roller 13, a supply voltage power supply 109 that applies a supply voltage to the supply roller 14, and a transfer voltage power supply 110 that applies a transfer voltage to the transfer roller 19.

[0033] The head control unit 111 controls the light emission of the print head 18 based on the image data recorded in the image data editing memory 103 .

[0034] The drive control unit 112 controls the driving of a drive motor 116 that rotates the photosensitive drum 11 of each process unit 10. The belt drive control unit 113 controls the driving of a belt motor 117 that rotates the drive roller 81.

[0035] The fixing control unit 51 has a temperature adjustment circuit and a storage unit such as a memory, and controls the heaters 21 and 22 based on an output signal of the temperature sensor 26 of the fixing device 2. The control of the heaters 21 and 22 by the fixing control unit 51 will be described later.

[0036] The fixing drive control unit 114 controls the driving of a fixing motor 118 that rotates the fixing roller 20. The discharge rollers 91 and 92 are rotated by the rotation transmitted from the fixing motor 118.

[0037] The paper feed and transport control unit 115 controls the driving of a paper feed motor 119 that rotates the hopping roller 71 and a transport motor 120 that rotates the registration roller 73 and transport roller 74 .

[0038] <Basic operation of image forming device> Next, the basic operation of the image forming apparatus 1 will be described with reference to Figures 1 and 2. When the print control unit 100 of the image forming apparatus 1 receives a print command and print data from a host device via the I / F control unit 101, it starts the image forming operation. The print control unit 100 temporarily records the print data in the receiving memory 102, edits the recorded print data to generate image data, and records it in the image data editing memory 103.

[0039] In the medium supply unit 7, the hopping roller 71 is rotated by the paper feed motor 119, and the medium P in the medium cassette 70 is sent out one by one to the conveyance path. In addition, the conveyance motor 120 rotates the registration roller 73 and the conveyance roller 74 at predetermined timings, correcting any skew in the medium P and conveying it to the transfer unit 8.

[0040] In the transfer unit 8, the drive roller 81 is rotated by the belt motor 117, which causes the transfer belt 80 to run and attract, hold and transport the medium P. The medium P passes through the process units 10K, 10Y, 10M and 10C in this order.

[0041] In each process unit 10, a charging voltage, a developing voltage and a supply voltage are applied to the charging roller 12, the developing roller 13 and the supply roller 14 from a charging voltage power supply 107, a developing voltage power supply 108 and a supply voltage power supply 109, respectively.

[0042] In addition, the photosensitive drum 11 is rotated by the drive motor 116. As the photosensitive drum 11 rotates, the charging roller 12, the developing roller 13, and the supply roller 14 also rotate. The charging roller 12 uniformly charges the surface of the photosensitive drum 11 with its charging voltage.

[0043] The print control unit 100 also transmits the image data recorded in the image data editing memory 103 to the head control unit 111, and the head control unit 111 drives the print head 18 to expose the surface of the photosensitive drum 11 to light, thereby forming an electrostatic latent image.

[0044] The electrostatic latent image formed on the surface of the photosensitive drum 11 is developed by the toner attached to the developing roller 13, and a toner image is formed on the surface of the photosensitive drum 11. When the toner image approaches the surface of the transfer belt 80 due to the rotation of the photosensitive drum 11, a transfer voltage is applied to the transfer roller 19 from the transfer voltage power supply 110. As a result, the toner image formed on the photosensitive drum 11 is transferred to the medium P on the transfer belt 80.

[0045] In this way, the toner images of each color formed in each process unit 10K, 10Y, 10M, and 10C are sequentially transferred and superimposed onto the medium P. The medium P onto which the toner images of each color have been transferred is further transported by the transfer belt 80 and reaches the fixing device 2.

[0046] In the fixing device 2, at the start of the image forming operation, the fixing drive control unit 114 drives the fixing motor 118, which rotates the pressure roller 25. The fixing control unit 51 also heats the heaters 21 and 22 to a predetermined fixing temperature. The medium P transported from the transfer unit 8 to the fixing device 2 passes through the fixing nip between the fixing roller 20 and the pressure roller 25, and the toner image is fixed to the medium P by the application of heat and pressure.

[0047] The medium P on which the toner image has been fixed is discharged to the outside of the image forming apparatus 1 by discharge rollers 91 and 92, and is stacked on a stacker unit 93. This completes the image forming operation on the medium P.

[0048] <Configuration of fixing device> Next, the configuration of the fixing device 2 in the first embodiment will be described. Figures 3(A), (B), and (C) are diagrams showing the basic configuration of the fixing device 2. More specifically, Figures 3(A), (B), and (C) are a side view, a plan view, and a front view, respectively, showing the fixing roller 20 and the pressure roller 25.

[0049] The longitudinal direction of both the fixing roller 20 and the pressure roller 25 is the X direction. A fixing nip is formed between the fixing roller 20 and the pressure roller 25, and the medium P conveyed from the transfer unit 8 is introduced into the fixing nip. The toner image transferred to the medium P by the transfer unit 8 adheres to the medium P by weak electrostatic force, but is melted by the heat of the fixing roller 20 and fixed to the medium P by the pressure of the pressure roller 25.

[0050] The fixing roller 20 is a roller in which an elastic layer and a surface layer are laminated on the surface of a substantially cylindrical base material. The base material is made of aluminum, stainless steel, or the like. The elastic layer is made of silicone rubber. The surface layer is made of a coating layer or a tube made of a fluororesin such as PTFE (polytetrafluoroethylene) or PFA (perfluoroalkoxyalkane).

[0051] Although not shown, shaft portions are formed on both ends of the base material of the fixing roller 20 in the X direction, and are rotatably supported by bearings provided on the frame of the fixing device 2.

[0052] As shown in Figure 3(B), the end of the roller portion (the cylindrical portion excluding the shaft) of the fixing roller 20 in the +X direction is set as the reference position P1. Regardless of the size, the medium P is transported so that one end of the medium P in the X direction coincides with the reference position P1. Therefore, the reference position P1 is also referred to as the medium transport reference position.

[0053] The fixing roller 20 has a hollow structure, and inside thereof, a main heater 21 serving as a first heater and a sub-heater 22 serving as a second heater are disposed. Here, as shown in FIG. 3A, the main heater 21 is disposed in the -Y direction (i.e., upstream in the transport direction of the medium P) relative to the sub-heater 22. However, this is not the only possible arrangement, and the sub-heater 22 may also be disposed in the -Y direction (i.e., upstream in the transport direction of the medium P) relative to the main heater 21.

[0054] Both the main heater 21 and the sub-heater 22 are halogen heaters, and extend from the end of the roller portion of the fixing roller 20 in the +X direction (reference position P1) to the end in the −X direction.

[0055] The main heater 21 heats a first region R1 in the X direction of the fixing roller 20, and the sub-heater 22 heats a second region R2 in the X direction of the fixing roller 20. The first region R1 includes the reference position P1. In FIG. 3B, the first region R1 is larger than the second region R2, but the two regions may be the same size or may be reversed in size.

[0056] The width of the main heater 21 in the X direction (i.e., the width of the first region R1) is set to suit a narrow medium. The combined width of the main heater 21 and the sub-heater 22 in the X direction (i.e., the combined width of regions R1 and R2) is set to suit a wide medium.

[0057] A narrow medium is, for example, a medium with a width of 3 inches in the X direction. A wide medium is, for example, a medium with a width of 4 inches or 5 inches in the X direction. However, this is not limited to this example, and for example, the narrow medium may be B5 size (portrait feed) or the like, and the wide medium may be A4 size (landscape feed) or the like.

[0058] 3(A) and 3(C), a temperature sensor 26 is disposed on the outside of the fixing roller 20 to detect the surface temperature of the fixing roller 20. In this example, the temperature sensor 26 is configured as a thermopile. The thermopile is a non-contact temperature sensor that receives infrared rays emitted from the surface of the fixing roller 20 and converts them into an electrical signal representing the temperature.

[0059] The temperature sensor 26 is disposed in a position in the X direction corresponding to the first region R1 of the fixing roller 20 (i.e., the region heated by the main heater 21). The temperature sensor 26 faces the -Y side surface of the fixing roller 20, i.e., the surface on the upstream side in the transport direction of the medium P. The temperature sensor 26 is not limited to a thermopile, and other non-contact or contact type temperature sensors may be used. The location of the temperature sensor 26 is also not limited to the above example, and the temperature sensor 26 may be disposed so as to face the +Y side surface of the fixing roller 20, i.e., the surface on the downstream side in the transport direction of the medium P.

[0060] 4 is a diagram showing the configuration of the main heater 21. The main heater 21 has a bulb 33 made of a glass tube that is long in the X direction, and halogen gas is sealed in the bulb 33. A filament 31 and an internal bulb lead wire 32 are provided inside the bulb 33.

[0061] The filament 31 extends a length corresponding to the first region R1 from the end of the bulb 33 in the +X direction (reference position P1 shown in FIG. 3(B)). The lead wire 32 in the bulb extends from the end of the filament 31 to the end of the bulb 33 in the -X direction.

[0062] The filament 31 is connected to a lead wire 34 provided on the outside of the bulb 33. The lead wire 32 inside the bulb is connected to a lead wire 35 provided on the outside of the bulb 33.

[0063] The connection between the filament 31 and the lead wire 34, and the connection between the lead wire 32 inside the bulb and the lead wire 35 are sealed to prevent leakage of halogen gas inside the bulb 33. The lead wires 34 and 35 are connected to a commercial power supply 56 and a triac 53 (FIG. 6), which will be described later.

[0064] 4, the length of the bulb 33 may be the same as that of the filament 31. In that case, the lead wire 32 inside the bulb is not provided, and the lead wire 35 is connected to the filament 31.

[0065] 5 is a diagram showing the configuration of the sub-heater 22. The sub-heater 22 has a bulb 43 made of a glass tube that is long in the X direction, and halogen gas is sealed in the bulb 43. A filament 41 and an internal bulb lead wire 42 are provided inside the bulb 43.

[0066] Filament 41 extends a length corresponding to second region R2 from the −X-direction end of bulb 43. Lead wire 42 within bulb extends from the end of filament 41 to the +X-direction end of bulb 43.

[0067] The filament 41 is connected to a lead wire 44 provided on the outside of the bulb 43. The lead wire 42 inside the bulb is connected to a lead wire 45 provided on the outside of the bulb 43.

[0068] The connection between the filament 41 and the lead wire 45, and the connection between the lead wire 42 inside the bulb and the lead wire 44 are sealed to prevent leakage of halogen gas inside the bulb 43. The lead wires 44 and 45 are connected to a commercial power supply 56 and a triac 54 (FIG. 6), which will be described later.

[0069] 5, the length of the bulb 43 may be the same as that of the filament 41. In that case, the lead wire 42 is not provided inside the bulb, and the lead wire 44 is connected to the filament 41.

[0070] <Heater control> 6 is a diagram showing a configuration for controlling the heaters 21 and 22. Lead wires 34 and 44 of the main heater 21 and the sub-heater 22 are connected to a commercial power supply 56. Lead wire 35 of the main heater 21 is connected to one terminal of a triac 53 serving as a first switching element. Lead wire 45 of the sub-heater 22 is connected to one terminal of a triac 54 serving as a second switching element. The other terminals of each of the triacs 53 and 54 are connected to the commercial power supply 56.

[0071] The gate terminals of the triacs 53 and 54 are connected to a triac drive circuit 52, which serves as a switching drive circuit. A signal is input to the triac drive circuit 52 from the fixing control unit 51. The triac drive circuit 52 is configured to insulate the primary and secondary sides of the triacs 53 and 54 using a phototriac.

[0072] When a heater-ON signal H1 to the main heater 21 is input, the triac drive circuit 52 activates the triac 53 to supply power to the main heater 21. When a heater-ON signal H2 to the sub-heater 22 is input, the triac drive circuit 52 activates the triac 54 to supply power to the sub-heater 22.

[0073] The fixing control unit 51 outputs heater ON signals H1 and H2 to the triac driving circuit 52 based on a temperature detection signal input from the temperature sensor 26 and a control signal input from the print control unit 100.

[0074] 7 is a functional block diagram showing the process executed by the fixing control unit 51 when controlling the main heater 21. This process is executed every 100 [ms], which is a control cycle, by the fixing control unit 51 starting a predetermined control program.

[0075] First, duty calculation unit 501 calculates the duty from the difference between the temperature detected by temperature sensor 26 and a preset target temperature. The duty is calculated by, for example, PID (Proportional Integral Differential) control.

[0076] Specifically, if the duty of the main heater 21 in the nth cycle (n is an integer equal to or greater than 1) of the control cycle is represented as Duty(n), this Duty(n) can be calculated by the following formula. Duty(n) =Kp×ε+Ki×Σ(ε)+Kd×d(ε) / dt+DutyMod(n-1)

[0077] In the above equation, ε is the temperature deviation, which is the value obtained by subtracting the detected temperature from the target temperature. Kp is the proportional gain, Ki is the integral gain, and Kd is the differential gain, which are all determined in advance. DutyMod(n-1) is the remainder of the duty that was not consumed in the n-1th control cycle. This DutyMod(n-1) does not necessarily have to be used.

[0078] The limit processing unit 502 limits the duty output from the duty calculation unit 501 to a range of 0 to 100 and outputs it. Specifically, if the duty value output from the duty calculation unit 501 is 0 or less, it is converted to 0, and if it is 100 or more, it is converted to 100.

[0079] The heater ON signal generating unit 503 outputs the heater ON signal H1 with a specified time constant based on the duty output from the limit processing unit 502.

[0080] 8 is a functional block diagram showing the process executed by the fixing control unit 51 when controlling the sub-heater 22. This process is executed every 100 [ms], which is a control cycle, by the fixing control unit 51 starting a predetermined control program.

[0081] First, duty calculation unit 504 calculates the duty from the difference between the temperature detected by temperature sensor 26 and a preset target temperature. The method of calculating the duty is as described for duty calculation unit 501 in FIG.

[0082] The correction processing unit 505 corrects and outputs the duty using a correction value A stored in advance in the fixing control unit 51. The correction value A will be described later.

[0083] The limit processing unit 506 limits the corrected duty output from the correction processing unit 505 to a range of 0 to 100 and outputs it.

[0084] The heater ON signal generating unit 507 outputs a heater ON signal H2 with a specified time constant based on the duty output from the limit processing unit 506.

[0085] <Determining the correction value> Next, we will explain how to determine the correction value A. Fig. 9 is a diagram showing a system for determining the correction value A. Ideally, the main heater 21 and the sub-heater 22 should have the same heat generation amount (output) per unit length if the heater ON signals have the same duty cycle. However, output variations that occur during the manufacturing stage of the heaters 21 and 22 result in differences in the heat generation amount per unit length.

[0086] Therefore, it is conceivable to control the main heater 21 and the sub-heater 22 while detecting the temperatures of both of them. In this case, however, the same number of temperature sensors as the heaters 21 and 22 must be provided.

[0087] Therefore, in this embodiment, the ratio of the current values ​​flowing through the main heater 21 and the sub-heater 22 when the same power is supplied is measured in advance, and based on that ratio, a correction value A (FIG. 8) is determined when generating a heater-ON signal for the sub-heater 22. It is desirable to determine the correction value A after the image forming apparatus 1 is completed (for example, before the product is shipped).

[0088] The correction value A is determined using an output measurement unit 201, a triac drive circuit 202, triacs 203 and 204, a current detection unit 206, and a commercial power supply 207. These elements may be incorporated into the image forming apparatus 1 or may be separate, independent units from the image forming apparatus 1.

[0089] If the configuration (201 to 207) for determining the correction value A is an independent unit (output measurement unit), the fixing device 2 may be temporarily removed from the image forming apparatus 1 when determining the correction value A, and the output measurement unit may be connected to the fixing device 2. In this case, after determining the correction value A, the fixing device 2 is removed from the output measurement unit and then assembled into the image forming apparatus 1.

[0090] The lead wire 34 of the main heater 21 and the lead wire 44 of the sub-heater 22 are connected to a commercial power supply 207. A current detection unit 206 is connected between the lead wires 34, 44 and the commercial power supply 207. The current detection unit 206 detects the current flowing through each of the heaters 21, 22 and outputs the detection result to the output measurement unit 201.

[0091] The lead wire 35 of the main heater 21 is connected to one terminal of the triac 203. The lead wire 45 of the sub-heater 22 is connected to one terminal of the triac 204. The other terminal of each of the triacs 203 and 204 is connected to a commercial power supply 207. The gate terminal of each of the triacs 203 and 204 is connected to the triac drive circuit 202.

[0092] The triac drive circuit 202 activates a triac 203 when a heater ON signal B1 to the main heater 21 is input, and activates a triac 204 when a heater ON signal B2 to the sub-heater 22 is input.

[0093] The correction value A is obtained by the following method. First, a heater ON signal B1 to the main heater 21 is input from the output measurement unit 201 to the triac drive circuit 52. The heater ON signal B1 is not a pulse signal, but a signal that remains ON for a certain period of time. This causes a predetermined power to be supplied to the main heater 21 from the commercial power supply 207. For example, a predetermined voltage (e.g., 100 V) is applied to the main heater 21. At this time, the current I flowing through the main heater 21 is M is detected by the current detection unit 206 and output to the output measurement unit 201.

[0094] Next, the output measuring unit 201 inputs a heater ON signal B2 to the sub-heater 22 to the triac driving circuit 202. The heater ON signal B2 to the sub-heater 22 is the same signal as the heater ON signal B1 to the main heater 21. As a result, the predetermined power is supplied to the sub-heater 22 from the commercial power supply 207. For example, the predetermined voltage is applied to the sub-heater 22. At this time, the current I flowing through the sub-heater 22 is Sis detected by the current detection unit 206 and output to the output measurement unit 201.

[0095] In addition, the design current value (design value) flowing through the main heater 21 when a predetermined power is supplied to the main heater 21 from the commercial power supply 56 is defined as I M 0, and the designed current value (design value) flowing through the sub-heater 22 when a predetermined power is supplied to the sub-heater 22 from the commercial power supply 207 is I S Let's say 0. I M 0 and I S All of the values ​​0 are determined in advance by experiment and stored in the output measurement unit 201.

[0096] current I M is proportional to the output of the main heater 21, and the current I S is proportional to the output of the sub-heater 22. Therefore, the ratio a of the deviation of the output of the main heater 21 and the output of the sub-heater 22 from the design value is expressed as follows: (I S / I S 0) / (I M / I M 0). Based on this ratio a, the above correction value A is derived. The ratio a is also called the output variation ratio.

[0097] When the output measurement unit 201 calculates the correction value A, the operator reads the value and stores it in the fixing control unit 51 of the image forming apparatus 1. If the output measurement unit 201 is incorporated in the image forming apparatus 1, the correction value A may be input from the output measurement unit 201 to the fixing control unit 51 as shown by the dashed line in FIG.

[0098] Here, we will explain the relationship between the heater ON signal and the heating temperature of the fixing roller 20 by the heaters 21 and 22. Figures 10(A) and 10(B) are diagrams showing the relationship between the heater ON signal for two heaters α and β that have the same output per unit length and the temperatures (detected temperatures) of the heating parts by the heaters α and β.

[0099] As shown in Figure 10(A), when heaters α and β have the same output per unit length, if a heater ON signal with the same duty is applied, the temperatures of both heaters α and β change in the same manner. The temperature change period of both heaters α and β is equal to the period of the heater ON signal.

[0100] On the other hand, as shown in FIG. 10B, when the duty of the heater ON signal to the heater α is set higher than the duty of the heater ON signal to the heater β, the temperature of the heater α becomes higher than the temperature of the heater β.

[0101] In consideration of this, in this embodiment, the duty of the heater ON signal to the heater of which the temperature is desired to be increased, either the main heater 21 or the sub-heater 22, is increased.

[0102] 11A and 11B are graphs respectively showing the output distribution of heaters 21 and 22 and the temperature distribution on the surface of fixing roller 20. At the design stage, it is assumed that heaters 21 and 22 have the same output per unit length, and that first region R1 (portion heated by main heater 21) and second region R2 (portion heated by sub-heater 22) of fixing roller 20 are heated to the same temperature.

[0103] However, in reality, due to output variations that occur during the manufacturing process, the outputs of the heaters 21 and 22 often differ from the design values. In addition, in this embodiment, both heaters 21 and 22 are controlled based on the detected temperature of the first region R1 heated by the main heater 21 (i.e., the output of the temperature sensor 26), so that the control is in line with the output of the main heater 21. The greater the difference between the output of the sub-heater 22 and the output of the main heater 21, the more the temperature of the portion heated by the sub-heater 22 (second region R2) differs from the temperature of the portion heated by the main heater 21 (first region R1).

[0104] Here, as shown in FIG. 11(A), for example, the output W1 per unit length of the main heater 21 is set to the design output W SET The output W2 per unit length of the sub-heater 22 is higher than the design output WSET The output W1 and W2 are the upper limit W of the output tolerance range. HIGH Below, the lower limit W LOW The above is assumed.

[0105] The main heater 21 is controlled based on the detected temperature of the heated portion (ie, the output of the temperature sensor 26), and therefore the temperature of the main heater 21 is controlled within a target temperature range.

[0106] On the other hand, since the sub-heater 22 is controlled based on the detected temperature of the heated portion of the main heater 21, there occurs a heating shortage corresponding to the difference in output per unit length between the two heaters 21 and 22 due to output variations. As a result, as shown by the dashed line in FIG. 11(B), the temperature of the heated portion (second region R2) by the sub-heater 22 falls below the lower limit T of the target temperature range. LOW may fall below.

[0107] In contrast, when the sub-heater 22 is controlled by a heater ON signal whose duty is increased by the above-mentioned correction value A, the temperature of the portion heated by the sub-heater 22 is kept within the target temperature range (i.e., the upper limit T HIGH Below, the lower limit T LOW (above) can be accommodated.

[0108] As an example, in a fixing device 2 in which the upper limit of the target temperature of the fixing roller 20 is 170°C and the lower limit is 150°C, if the temperature of the part heated by the main heater 21 is approximately 160°C, by setting the duty of the heater ON signal of the sub-heater 22 to 1.1 compared to the duty of the heater ON signal of the main heater 21 to 1.0 (i.e., setting the correction value A to 1.1), the temperature of the part heated by the sub-heater 22 can be raised from approximately 140°C to approximately 150°C, and kept within the target temperature range.

[0109] Regarding the determination of the correction value A, the current I flowing through the main heater 21 M and the design current value (design value) I flowing through the main heater 21. M 0, and the current IS and the design current value (design value) I flowing through the sub-heater 22. S 0 may be the same.

[0110] <Effects of the embodiment> As described above, the image forming apparatus 1 of this embodiment includes the fixing roller 20 (fixing member), the pressure roller 25 (pressing member), the main heater 21 (first heater) for heating the first region R1 of the fixing roller 20, the sub-heater 22 (second heater) for heating the second region R2 of the fixing roller 20, the temperature sensor 26 for detecting the temperature of the first region R1 of the fixing roller 20, and the fixing control unit 51 (control unit) for controlling the heaters 21 and 22 based on the temperature detected by the temperature sensor 26. The fixing control unit 51 calculates the ratio I of the current values ​​flowing through the main heater 21 and the sub-heater 22. S / I M The sub-heater 22 is controlled using the correction value A determined based on the above. Therefore, the main heater 21 and the sub-heater 22 can be controlled with high accuracy based on the temperature detected by one temperature sensor .

[0111] In particular, since the duty of the heater ON signal to the sub-heater 22 is corrected by the correction value A, the output of the sub-heater 22 can be controlled with high precision by reflecting the output variation between the main heater 21 and the sub-heater 22.

[0112] In addition, when the same power is supplied to the main heater 21 and the sub-heater 22, the current I M and the current I flowing through the sub-heater 22 S Since the correction value A is determined based on the above, it is possible to obtain a correction value A that accurately reflects the output variation between the main heater 21 and the sub-heater 22.

[0113] Second embodiment. Next, a second embodiment will be described. In the first embodiment, two regions R1 and R2 are heated by heaters 21 and 22, which are halogen heaters. In the second embodiment, three regions R1, R2, and R3 are heated by heaters 61, 62, and 63, which are planar heaters. In addition, while the first embodiment uses a fixing roller 20, the second embodiment uses a fixing belt 60.

[0114] 12A and 12B are a side view and a front view showing the basic configuration of a fixing device 6 according to the second embodiment. The fixing device 6 includes a fixing belt 60 as a fixing body, a planar heater 6H, a pressure roller 65 as a pressure body, and a temperature sensor 66. The planar heater 6H heats the fixing belt 60 from the inner circumferential side. The pressure roller 65 is pressed against the fixing belt 60 to form a fixing nip therebetween. The temperature sensor 66 is, for example, a thermopile, and detects the surface temperature of the fixing belt 60.

[0115] The fixing belt 60 is an endless belt having a metal substrate and an elastic layer formed on the outer peripheral surface of the substrate. The substrate is made of, for example, stainless steel, which has appropriate rigidity and flexibility. The elastic layer is made of, for example, silicone rubber.

[0116] A planar heater 6H is disposed on the inner circumferential side of the fixing belt 60. Between the planar heater 6H and the fixing belt 60, a heat diffusion member 64 made of, for example, stainless steel may be disposed.

[0117] The planar heater 6H is formed by laminating an electrical insulating layer, a resistance heating element, and a protective layer in this order on a substrate made of, for example, stainless steel, and generates heat when electricity is passed through the resistance heating element. The planar heater 6H is disposed so that the protective layer is in contact with the heat diffusion member 64, and heat is transferred to the fixing belt 60 via the heat diffusion member 64.

[0118] Planar heater 6H is divided into five parts in the X direction (longitudinal direction). Planar heater 6H has a main heater 61 which is a first heat generating part located in the center in the X direction, sub-heaters 62L and 62R (first sub-heaters) which are second heat generating parts located on the -X side and +X side of main heater 61, respectively, and sub-heaters 63L and 63R (second sub-heaters) which are third heat generating parts located on the -X side of sub-heater 62L and +X side of sub-heater 62R, respectively.

[0119] The main heater 61, sub-heaters 62L, 62R, and sub-heaters 63L, 63R are arranged symmetrically on the left and right sides of the plane heater 6H with respect to the center of the plane heater 6H in the X direction. The left and right sub-heaters 62L, 62R are electrically connected and are heated simultaneously when current is applied. Similarly, the left and right sub-heaters 63L, 63R are electrically connected and are heated simultaneously when current is applied.

[0120] The main heater 61 heats a first region R1 at the center in the X direction of the fixing belt 60. The sub-heaters 62L and 62R heat second regions R2 on both sides of the first region R1 in the X direction. The sub-heaters 63L and 63R heat third regions R3 at both ends of the fixing belt 60 in the X direction. In the second embodiment, the center position of the fixing belt 60 in the X direction is the reference position P1 for medium transport.

[0121] The width in the X direction of the main heater 61 is set to suit narrow media. The combined width of the main heater 61 and the sub-heaters 62L and 62R is set to suit medium-width media. The combined width of the main heater 61, the sub-heaters 62L and 62R, and the sub-heaters 63L and 63R is set to suit wide media.

[0122] The pressure roller 65 is configured similarly to the pressure roller 25 of the first embodiment, and forms a fixing nip between itself and the fixing belt 60. The temperature sensor 66 is configured similarly to the temperature sensor 26 of the first embodiment, and detects the temperature of the first region R1 of the fixing belt 60.

[0123] 13 is a diagram showing a configuration for controlling the main heater 61 and the sub-heaters 62L, 62R, 63L, and 63R. Here, a case where the left and right sub-heaters 62L and 62R are controlled collectively will be described, but they may also be controlled separately in consideration of individual differences. The same applies to the left and right sub-heaters 63L and 63R.

[0124] One electrode of the main heater 61 is connected to the commercial power supply 56 via a lead wire 61a, and the other electrode is connected to one terminal of the triac 53 via a lead wire 61b.

[0125] One electrode of each of the sub-heaters 62L, 62R is connected to the commercial power supply 56 via a lead wire 62a, and the other electrode is connected to one terminal of the triac 54 via a lead wire 62b.

[0126] One electrode of each of the sub-heaters 63L and 63R is connected to the commercial power supply 56 via a lead wire 63a, and the other electrode is connected to one terminal of the triac 55 via a lead wire 63b.

[0127] The other terminal of each of the triacs 53, 54, and 55 is connected to a commercial power supply 56. The gate terminal of each of the triacs 53, 54, and 55 is connected to a triac drive circuit 52. The triac drive circuit 52 is configured to insulate the primary and secondary sides of each of the triacs 53, 54, and 55 using a phototriac.

[0128] When a heater-ON signal H1 is input to the main heater 61, the triac drive circuit 52 activates the triac 53 to supply power to the main heater 61. When a heater-ON signal H2 is input to the sub-heaters 62L and 62R, the triac drive circuit 52 activates the triac 54 to supply power to the sub-heaters 62L and 62R. When a heater-ON signal H3 is input to the sub-heaters 63L and 63R, the triac drive circuit 52 activates the triac 55 to supply power to the sub-heaters 63L and 63R.

[0129] The fixing control unit 51 outputs heater ON signals H1, H2, and H3 to the triac drive circuit 52 based on a temperature detection signal input from the temperature sensor 26 and a control signal input from the print control unit 100.

[0130] In the second embodiment, the temperatures of the main heater 61 and the sub-heaters 62L, 62R, 63L, and 63R are controlled based on the temperature of the first region R1 (region heated by the main heater 61) of the fixing belt 60 detected by the temperature sensor 66. Therefore, a correction value A1 is used to control the sub-heaters 62L and 62R, and a correction value A2 is used to control the sub-heaters 63L and 63R.

[0131] 14 is a diagram showing a configuration for determining the correction values ​​A1 and A2. It is desirable to determine the correction values ​​A1 and A2 after the image forming apparatus 1 is manufactured (for example, before the product is shipped).

[0132] The correction values ​​A1 and A2 are determined using an output measurement unit 301, a triac drive circuit 302, triacs 303, 304, and 305, a current detection unit 306, and a commercial power supply 307. These elements may be incorporated into the image forming apparatus 1 or may be separate, independent units from the image forming apparatus 1.

[0133] If the components (301 to 307) for determining the correction values ​​A1 and A2 are configured as an independent unit (output measurement unit), the fixing device 6 may be temporarily removed from the image forming apparatus 1 when determining the correction values ​​A1 and A2, and the output measurement unit may be connected to the fixing device 6. In this case, after determining the correction value A, the fixing device 6 is removed from the output measurement unit and then assembled into the image forming apparatus 1.

[0134] The lead wire 61a of the main heater 61, the lead wire 62a of each of the sub-heaters 62L, 62R, and the lead wire 63a of each of the sub-heaters 63L, 63R are connected to a commercial power supply 307. A current detection unit 306 is connected between the lead wires 61a, 62a, 63a and the commercial power supply 307. The current detection unit 306 measures the current flowing through each of the heaters 61, 62L, 62R, 63L, 63R, and outputs the measurement result to the output measurement unit 301.

[0135] The lead wire 61b of the main heater 61 is connected to one terminal of the triac 303. The lead wire 62b of each of the sub-heaters 62L, 62R is connected to one terminal of the triac 304. The lead wire 63b of each of the sub-heaters 63L, 63R is connected to one terminal of the triac 305. The other terminal of each of the triacs 303, 304, 305 is connected to a commercial power supply 307. The gate terminal of each of the triacs 303, 304, 305 is connected to the triac drive circuit 302.

[0136] The triac drive circuit 302 activates a triac 303 when a heater-ON signal B1 is input to the main heater 61, activates a triac 304 when a heater-ON signal B2 is input to the sub-heaters 62L and 62R, and activates a triac 305 when a heater-ON signal B3 is input to the sub-heaters 63L and 63R.

[0137] The correction values ​​A1 and A2 are obtained by the following method. First, a heater ON signal B1 to the main heater 61 is input from the output measurement unit 301 to the triac drive circuit 302. The heater ON signal B1 is not a pulse signal, but a signal that remains ON for a certain period of time. This causes a predetermined power to be supplied to the main heater 61 from the commercial power supply 307. For example, a predetermined voltage (for example, 100 V) is applied to the main heater 61. At this time, the current I flowing through the main heater 61 is M is detected by the current detection unit 306 and output to the output measurement unit 301.

[0138] Next, the output measurement unit 301 inputs a heater ON signal B2 to the sub-heaters 62L, 62R to the triac drive circuit 302. The heater ON signal B2 to the sub-heaters 62L, 62R is the same signal as the heater ON signal B1 to the main heater 61. As a result, the predetermined power is supplied from the commercial power supply 307 to the sub-heaters 62L, 62R. For example, the predetermined voltage is applied to the sub-heaters 62L, 62R. At this time, the current I flowing through the sub-heaters 62L, 62R is S1 is detected by the current detection unit 306 and output to the output measurement unit 201.

[0139] Furthermore, the output measuring unit 301 inputs a heater ON signal B3 to the sub-heaters 63L, 63R to the triac driving circuit 302. The heater ON signal B3 to the sub-heaters 63L, 63R is the same signal as the heater ON signal B1 to the main heater 61. As a result, the predetermined power is supplied from the commercial power supply 307 to the sub-heaters 63L, 63R. For example, the predetermined voltage is applied to the sub-heaters 63L, 63R. At this time, the current I flowing through the sub-heaters 63L, 63R is S2 is detected by the current detection unit 306 and output to the output measurement unit 301.

[0140] In addition, the design current value (design value) flowing through the main heater 21 when a predetermined power is supplied to the main heater 61 from the commercial power supply 307 is I M 0. The design current value (design value) flowing through the sub-heaters 62L and 62R when a predetermined power is supplied to the sub-heaters 62L and 62R from the commercial power supply 307 is I S1 0. The design current value (design value) flowing through the sub-heaters 63L and 63R when a predetermined power is supplied to the sub-heaters 63L and 63R from the commercial power supply 307 is I S2 Let's say 0. I M 0, I S1 0 and I S2 All of the values ​​0 are determined in advance by experiment and stored in the output measurement unit 301.

[0141] current I M and current I S1is proportional to the output of the main heater 61 and the sub-heaters 62L and 62R, respectively. Therefore, the ratio a1 of the deviation of the output of the main heater 61 and the sub-heaters 62L and 62R from the design value is a1=(I S1 / I S1 0) / (I M / I M 0). Based on this ratio a1, the correction value A1 is derived.

[0142] Similarly, the current I M and current I S2 are proportional to the outputs of the main heater 61 and the sub-heaters 63L and 63R, respectively. Therefore, the ratio a2 of the deviations of the outputs of the main heater 61 and the sub-heaters 63L and 63R from the design values ​​is expressed as a2=(I S2 / I S2 0) / (I M / I M 0). Based on this ratio a2, the correction value A2 is derived.

[0143] The heater ON signals for the sub-heaters 62L, 62R using the correction value A1 are generated as described in the first embodiment with reference to Fig. 8. That is, the fixing control unit 51 calculates the duty by PID control from the temperature detected by the temperature sensor 66 and the target temperature, corrects the duty by the correction value A1, limits the duty value to a range of 0 to 100, and generates the heater ON signals for the sub-heaters 62L, 62R.

[0144] The heater ON signals for the sub-heaters 63L and 63R are generated in the same manner using the correction value A2. That is, the fixing control unit 51 calculates the duty by PID control from the detected temperature detected by the temperature sensor 66 and the target temperature, corrects the duty by the correction value A2, limits the duty value to the range of 0 to 100, and generates the heater ON signals for the sub-heaters 63L and 63R.

[0145] As described above, in the second embodiment, even in a fixing device that heats areas R1, R2, and R3 of a fixing belt 60 (fixing body) using heaters 61, 62L, 62R, 63L, and 63R, which are planar heaters having heating resistors, the main heater 61 and sub-heaters 62L, 62R, 63L, and 63R can be controlled with high precision based on the detected temperature of one temperature sensor 66.

[0146] In the first embodiment, the heater is a halogen heater, and in the second embodiment, the heater is a planar heater (having a heating resistor), but other heaters may also be used.

[0147] In addition, in the first embodiment, the fixing body is divided into two regions R1 and R2 and heated, and in the second embodiment, the fixing body is divided into three regions R1, R2, and R3 and heated, but the number of regions to be heated is arbitrary.

[0148] Although the above embodiment has been described as an image forming apparatus for forming color images, the present invention can also be applied to an image forming apparatus for forming single-color (monochrome) images. Furthermore, the present invention can be used, for example, in an image forming apparatus (such as a copier, facsimile, printer, or multifunction device) that forms an image on a medium using an electrophotographic method, and in a fixing device thereof. [Explanation of symbols]

[0149] 1 image forming apparatus, 2,6 fixing device, 6H planar heater, 7 medium supply section, 8 transfer unit, 9 medium discharge section, 10,10K,10Y,10M,10C process unit (image forming unit), 11,11K,11Y,11M,11C photosensitive drum (image carrier), 18,18K,18Y,18M,18C print head, 20 fixing roller (fixing body), 21 main heater (first heater), 22 sub-heater (second heater), 25 pressure roller (pressure body), 26 thermopile (temperature sensor), 31,41 filament (heat generating section), 32,42 lead wire, 33,43 valve, 51 fixing control section (control section), 52 Triac drive circuit (switching drive circuit), 53, 54, 55 Triac (switching element), 60 Fixing belt (fixing body), 61 Main heater (first heater), 62L, 62R Sub-heater (second heater), 63L, 63R Sub-heater (second heater), 65 Pressure roller (pressure body), 66 Thermopile (temperature sensor), 100 Print control unit, 201, 301 Output measurement unit, 202, 302 Triac drive circuit, 203, 204, 303, 304, 305 Triac, 206, 306 Current detection unit.

Claims

1. a fixing member whose surface is heated; a pressure member that forms a fixing nip between itself and the fixing member; a first heater for heating a first region of the fuser; a second heater for heating a second region of the fuser; a temperature sensor for detecting the temperature of the first region of the fixing body; a control unit that controls the first heater and the second heater based on the temperature detected by the temperature sensor; and the control unit controls an output of the first heater by changing a duty of a heater ON signal that drives the first heater, and controls an output of the second heater by changing a duty of a heater ON signal that drives the second heater; The control unit corrects the duty of a heater ON signal for the second heater in accordance with a correction value that is determined in advance based on a ratio between a value of a current flowing through the first heater and a value of a current flowing through the second heater under a predetermined condition. An image forming apparatus characterized by:

2. A fixing body whose surface is heated; a pressure member that forms a fixing nip between itself and the fixing member; a first heater for heating a first region of the fuser; a second heater for heating a second region of the fuser; a temperature sensor for detecting the temperature of the first region of the fixing body; a control unit that controls the first heater and the second heater based on the temperature detected by the temperature sensor; and the control unit controls the second heater using a correction value that is determined in advance based on a ratio between a value of a current flowing through the first heater and a value of a current flowing through the second heater under a predetermined condition; The correction value is calculated from a measured value IM of a current flowing through the first heater when a predetermined power is supplied to the first heater, a measured value IS of a current flowing through the second heater when the predetermined power is supplied to the second heater, a design value IM0 of the current flowing through the first heater, and a design value IS0 of the current flowing through the second heater, a=(IS / IS0) / (IM / IM0) is determined based on the value a calculated by An image forming apparatus characterized by:

3. a current detection unit that detects a current flowing through the first heater and a current flowing through the second heater and obtains the measurement values ​​IM and IS; an output measurement unit that calculates the correction value from the measurement values ​​IM and IS; 3. The image forming apparatus according to claim 2, further comprising:

4. The first region includes a transport reference position of a medium passing through the fixing nip.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. two or more second heaters for heating two or more of the second regions; 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The first heater and the second heater are each constituted by a halogen heater.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. The first heater and the second heater are each constituted by a planar heater having a heating resistor.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. The fixing member is a fixing roller or a fixing belt.

8. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. a medium supply unit that supplies a medium; an image forming unit that forms an image; a transfer unit that transfers the image formed by the image forming unit onto the medium and transports the medium to the fixing nip; 9. The image forming apparatus according to claim 1, further comprising:

Images