Fixing device, image forming apparatus, and heater power control method

Abstract

A fixing device capable of maintaining a heater and a fixing belt at a predetermined temperature. [Solution] The fixing device 7 includes a heater 22 in contact with the inner surface of the fixing belt 20, a belt temperature detection unit 35 that detects the temperature of the fixing belt 20, and a heater temperature detection unit 36 ​​that detects the temperature of the heater 22. The control device that controls the supply power performs a first power supply control in a first control period in which the heater temperature detection unit 36 ​​detects a target temperature and supplies power to the heater 22 until the belt temperature detection unit 35 detects a temperature outside the target range. When the belt temperature detection unit 35 detects a temperature outside the target range, the control device 8 performs a correction control in which the target temperature is corrected so that the belt temperature detection unit 35 detects a temperature within the target range, and a second power supply control in which power is supplied to the heater 22 so that the heater temperature detection unit 36 ​​detects the corrected target temperature, in a second control period that is at least 10 times the first control period.

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium, an image forming apparatus, and a heater power control method. [Background technology]

[0002] An electrophotographic image forming apparatus includes a fixing device that fixes a toner image on a sheet of paper. The fixing device described in Patent Document 1 includes a fixing belt heated by a resistance heating element, a pressure member that forms a nip between the fixing belt and the pressure member, a temperature detection unit that detects the temperature of the fixing belt, and a position detection unit that detects the circumferential position of the fixing belt. The fixing device has a characteristics storage mode that supplies power to the resistance heating element during non-fixing operations and stores the temperature associated with the circumferential position of the fixing belt, and a fixing execution mode that corrects the power supplied to the resistance heating element based on the stored position and temperature during fixing operations to control the temperature of the nip to a target temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-186094 Summary of the Invention [Problem to be solved by the invention]

[0004] In the fixing device described above, the resistance heating element generates heat when power is supplied, and the fixing belt receives heat from the resistance heating element and is heated. In other words, the temperature of the fixing belt begins to rise with a delay from the temperature of the resistance heating element. In the fixing device described above, the power supplied to the resistance heating element is controlled based on the temperature of the fixing belt, so there is a risk that the temperature of the resistance heating element will have risen excessively by the time the nip portion (fixing belt) reaches the target temperature. This has led to problems such as the resistance heating element itself and surrounding components (such as sensors) breaking down in high-temperature environments.

[0005] Furthermore, when the power supplied to the resistance heating element is controlled based on the temperature of the fixing belt, the following problems arise. For example, even if the power supply to the resistance heating element is stopped when the nip portion (fixing belt) exceeds the target temperature, the fixing belt continues to receive heat from the overheated resistance heating element, causing the temperature of the fixing belt to continue to rise. Furthermore, since the resistance heating element disposed within the fixing belt cools down more slowly than the fixing belt itself, restarting the power supply to the resistance heating element when the nip portion falls below the target temperature could cause the insufficiently cooled resistance heating element to overheat again. This causes the temperature of the nip portion to become unstable, making it impossible to perform proper fixing, resulting in problems such as a deterioration in the quality of the fixed image.

[0006] In consideration of the above circumstances, the present invention provides a fixing device, an image forming apparatus, and a heater power control method that can maintain the heater and fixing belt at predetermined temperatures. [Means for solving the problem]

[0007] The fixing device of the present invention includes a fixing belt formed in a cylindrical shape and rotating around its axis to heat toner on a medium, a pressure member forming a pressure region between the fixing belt and the pressure member and rotating around its axis to pressurize the toner on the medium passing through the pressure region, a heater in contact with the inner surface of the fixing belt facing the pressure region, generating heat upon receiving power supply and heating the fixing belt, a belt temperature detection unit that detects the temperature of the fixing belt, a heater temperature detection unit that detects the temperature of the heater, and a power control unit that controls the power supplied to the heater, a first power supply control that supplies power to the heater until the heater temperature detection unit detects a target temperature and the belt temperature detection unit detects a temperature outside the target range, and when the belt temperature detection unit detects a temperature outside the target range, the power control unit executes correction control that corrects the target temperature so that the belt temperature detection unit detects a temperature within the target range and second power supply control that supplies power to the heater so that the heater temperature detection unit detects the corrected target temperature, in a second control period set to a time interval of at least 10 times the first control period.

[0008] In this case, if the belt temperature detection unit detects a temperature above the target range, the power control unit sets the corrected target temperature to a value obtained by subtracting a predetermined correction amount from the target temperature, and if the belt temperature detection unit detects a temperature below the target range, the power control unit sets the corrected target temperature to a value obtained by adding the predetermined correction amount to the target temperature.

[0009] In this case, the second control period is preferably set to a time interval that is 10 times or more and 50 times or less than the first control period.

[0010] An image forming apparatus according to the present invention includes any one of the fixing devices described above.

[0011] The present invention is a power control method for a heater provided in any of the fixing devices described above, comprising: a power supply process for executing the first power supply control in the first control cycle, which supplies power to the heater until the heater temperature detection unit detects the target temperature and the belt temperature detection unit detects a temperature outside the target range; and a corrective power supply process for executing the corrective control in the second control cycle, which corrects the target temperature so that the belt temperature detection unit detects a temperature within the target range when the belt temperature detection unit detects a temperature outside the target range; and the second power supply control, which supplies power to the heater so that the heater temperature detection unit detects the corrected target temperature. [Effects of the Invention]

[0012] According to the present invention, the heater and the fixing belt can be maintained at a predetermined temperature. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 2 is a bottom view showing a heater of a fixing device according to an embodiment of the present invention. [Figure 5] 2 is a block diagram showing the relationship between each detection unit and a control device of the fixing device according to the embodiment of the present invention; FIG. [Figure 6] 3 is a flowchart illustrating a heater power control method according to an embodiment of the present invention. [Figure 7] 1 is a graph showing the results of a test (1) of a heater power control method according to an embodiment of the present invention, illustrating changes in heater temperature and power over time. [Figure 8]10 is a graph showing the results of a test (2) of the heater power control method according to one embodiment of the present invention, illustrating the change over time in the heater temperature and power. [Figure 9] 10 is a graph showing the results of a comparative test, illustrating the change over time in the temperature and power of a heater. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that Fr, Rr, L, R, U, and D in the drawings indicate front, rear, left, right, top, and bottom. The front-to-back direction, left-to-right direction (axial direction), and top-to-bottom direction are perpendicular to one another. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Furthermore, in each drawing, the shapes, dimensions, angles, etc. of each component are not accurate and are shown schematically for explanation purposes.

[0015] An image forming apparatus 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0016] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 having a substantially rectangular parallelepiped exterior. A paper feed cassette 3 that stores, for example, paper P (medium) is removably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may also be a resin sheet or the like. Furthermore, in this specification, the terms "upstream" and "downstream" and similar terms refer to "upstream" and "downstream" in the transport direction of the paper P, and similar concepts.

[0017] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0018] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0019] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0020] The image forming apparatus 1 is provided with a control device 8 that controls the entire apparatus. The control device 8 is configured with a memory, a processor, etc. (neither of which are shown). The processor reads out programs and data stored in the memory and executes arithmetic processing. The control device 8 is electrically connected to each device, etc. that constitutes the image forming apparatus 1 via an interface unit (not shown), and controls various processes related to image formation. The control device 8 is also electrically connected to a power supply unit 18 that supplies power to each device, etc. (see FIG. 5, described later), and controls the power supply to each device, etc. The control device 8 may be configured with a logic circuit (hardware) formed in an integrated circuit, etc.

[0021] [Image formation processing] A control device 8 that controls the image forming apparatus 1 performs the following image forming process based on image data input from an external terminal.

[0022] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0023] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0024] [Fixing device] Next, the fixing device 7 will be described with reference to Figures 2 to 4. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a bottom view showing the heater 22. Figure 5 is a block diagram showing the relationship between the detection units 35, 36, etc. of the fixing device 7 and the control device 8, etc.

[0025] 2 and 3, the fixing device 7 includes a fixing belt 20, a pressure roller 21, a heater 22, a belt temperature detector 35, and a heater temperature detector 36. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), and the frame is fixed to the device body 2.

[0026] <Fixing belt> The fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see FIG. 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0027] As shown in FIG. 3, a bridge member 25 and a support member 26 are provided in the space surrounded by the fixing belt 20. The bridge member 25 is formed, for example, from a metal material such as stainless steel into a generally rectangular cylindrical shape that is elongated in the left-right direction (axial direction), and is bridged between the pair of holding members 24. The support member 26 is fixed to the lower part of the bridge member 25. The support member 26 is formed, for example, from a heat-resistant and abrasion-resistant synthetic resin into a generally semi-cylindrical shape that is elongated in the left-right direction. The support member 26 curves along the inner surface of the fixing belt 20 and contacts the lower side of the inner surface of the fixing belt 20 (the side of the pressure region N). A fitting portion 26A into which the heater 22 is fitted is recessed in the lower part of the support member 26.

[0028] <Pressure roller> As shown in FIGS. 2 and 3, pressure roller 21, an example of a pressure member, is formed in a generally cylindrical shape elongated in the left-right direction. Pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on the outer circumferential surface of the metal core 21A (see FIG. 3). A drive motor M is connected to the left end of core 21A via a gear train (not shown) (see FIG. 2). Pressure roller 21 contacts fixing belt 20 from below, forming a pressure region N between itself and fixing belt 20. A toner image is fixed onto paper P as it passes through pressure region N. The pressure region N refers to a region extending from an upstream position where the pressure is 0 Pa, through a position where pressure is applied, to a downstream position where the pressure returns to 0 Pa. Drive motor M is electrically connected to power supply 18 via a drive circuit (not shown) (see FIG. 5).

[0029] The paper sheet P is transported with the center of its left-right width roughly aligned with the center of the pressure area N in the left-right direction (axial direction). For this reason, the fixing belt 20 (or pressure area N) has a passing area A1 in the axial center that comes into contact with the paper sheet P, and non-passing areas A2 on both sides of the axial direction that do not come into contact with the paper sheet P (see FIG. 4). The transported paper sheet P always comes into contact with the passing area A1 near the axial center, regardless of the size (left-right width) of the paper sheet P. In contrast, normal-sized paper sheets P (e.g., A4 size) come into contact with both sides of the passing area A1 in the axial direction, but small-sized paper sheets P (e.g., A5, B5 size, etc.) do not come into contact with the passing area A1.

[0030] <Heater> 3, the heater 22 is fitted into the fitting portion 26A of the support member 26. The heater 22 comes into contact with the inner surface of the fixing belt 20 facing the pressure region N, and generates heat when supplied with power (from the power supply unit 18), thereby heating the fixing belt 20. As shown in FIG. 4, the heater 22 has a substrate 30 and a heat generating portion 31.

[0031] The substrate 30 is made of an insulator (electrically insulating material) such as ceramic and is formed into a generally rectangular plate that is long in the left-right direction (axial direction). The axial dimension of the substrate 30 (heater 22) is longer than the axial dimension of the fixing belt 20. The heat generating unit 31 is provided on the lower surface (one surface) of the substrate 30, facing the pressure region N across the fixing belt 20. The heat generating unit 31 is composed of three resistance heating elements 32A to 32C that are aligned in a row with a gap G between them in the axial direction. In this specification, only Arabic numerals are used for the reference symbols in descriptions common to the three resistance heating elements 32A to 32C. The gap G is set to an insulation distance (creepage distance) that can prevent creepage discharge between adjacent resistance heating elements 32.

[0032] The resistance heating element 32 is formed in a substantially rectangular shape from a metal material with high electrical resistance. The entire heat generating section 31 is shorter than the entire length of the fixing belt 20 in the left-right direction (axial direction) and is longer in the axial direction than the passing area A1 of the fixing belt 20. In other words, both axial sides of the resistance heating elements 32B and 32C located on both outer sides in the axial direction face the non-passing area A2 of the fixing belt 20. The resistance heating element 32A located in the center in the axial direction corresponds to the left-right width of a small-size paper P, and all of the resistance heating elements 32A to 32C correspond to the left-right width of a normal-size paper P.

[0033] Three individual electrodes 33A to 33C and a common electrode 33D are formed on the lower surface of the substrate 30. The three individual electrodes 33A to 33C and the common electrode 33D are formed, for example, from a metal material having a lower electrical resistance value than the resistance heating element 32. In this specification, when describing the three individual electrodes 33A to 33C and the common electrode 33D in common, they will be simply referred to as "electrode portion 33" and will be indicated by Arabic numerals only.

[0034] The individual electrode 33A is connected to the downstream end (rear end) of the resistance heating element 32A located in the center in the axial direction. The other individual electrodes 33B and 33C are connected to the downstream ends of the resistance heating elements 32B and 32C, respectively. The common electrode 33D is connected to the upstream ends (front ends) of all of the resistance heating elements 32A to 32C. Each of the multiple electrode portions 33 extends from a portion connected to the heat generating element 31 to both outer sides of the heat generating element 31 in the axial direction. The heat generating element 31 is electrically connected to the power supply unit 18 via the multiple electrode portions 33 on both sides of the substrate 30 in the axial direction (see FIG. 5). Although not shown, the heater 22 is preferably connected to the power supply unit 18 via a power cut-off device that cuts off power in the event of abnormal heat generation.

[0035] Heat generating unit 31 and electrode unit 33 are covered with a coating layer (not shown). Heater 22 is fitted into fitting portion 26A of support member 26, with the coating layer in contact with the inner surface of fixing belt 20. Heater 22 receives fixing belt 20 pressed against pressure roller 21, thereby forming a pressure region N at the contact point between fixing belt 20 and pressure roller 21. Note that in order to equalize the temperatures of heater 22 and fixing belt 20 in the axial direction and prevent excessive temperature rise in non-passage region A2, for example, a metal heat equalizing member (not shown) may be in contact with the upper surface of substrate 30.

[0036] <Belt temperature detector, heater temperature detector> As shown in FIG. 3 , the belt temperature detection unit 35 is attached to the lower end of the hanging member 26B, which extends downward from the upper front end of the support member 26, in the internal space of the fixing belt 20. The belt temperature detection unit 35 is a temperature sensor, such as a thermistor, that contacts the inner surface of the fixing belt 20 upstream of the pressure region N and detects the temperature of the fixing belt 20. The heater temperature detection unit 36 ​​is fixed to the top surface of the fitting portion 26A of the support member 26 and is provided between the heater 22 and the support member 26. The heater temperature detection unit 36 ​​is a temperature sensor, such as a thermistor, that contacts the upper surface of the substrate 30 of the heater 22 and detects the temperature of the heater 22. Note that the belt temperature detection unit 35 and the heater temperature detection unit 36 ​​are provided near the center in the axial direction (passing region A1); however, instead of or in addition to the passing region A1, they may be provided on either side in the axial direction (non-passing region A2) (not shown).

[0037] 5, the belt temperature detection unit 35 and the heater temperature detection unit 36 ​​are each electrically connected to the control device 8 via an A / D conversion (Analog to Digital Conversion) circuit or the like (not shown). The belt temperature detection unit 35 and the heater temperature detection unit 36 ​​each transmit their detection results (detection signals) to the control device 8. The control device 8 receives the detection signals from both detection units 35 and 36 at time intervals (sampling rates) of, for example, several ms to several tens of ms.

[0038] The power supply unit 18 is, for example, a DC stabilized power supply, and supplies power to the control device 8, the drive motor M, the heater 22, and other devices constituting the image forming apparatus 1 (not shown). The power supply unit 18 is a component of the image forming apparatus 1, but may also be considered as a component of the fixing device 7. A dedicated power supply unit that supplies power to the fixing device 7 (heater 22) may also be provided separately from the power supply unit 18 of the image forming apparatus 1 (not shown).

[0039] Furthermore, the control device 8 includes a function as a power control unit that controls the power supplied to the heater 22. The control device 8 is a component of the image forming apparatus 1, but may also be regarded as a component of the fixing device 7. Furthermore, a dedicated power control unit that controls the power supplied to the heater 22 may be provided separately from the control device 8 of the image forming apparatus 1 (not shown).

[0040] [Fixing process] Here, the operation (fixing process) of the fixing device 7 will be described. The control device 8 controls the drive motor M to rotate the pressure roller 21 around its axis. The fixing belt 20 rotates following the pressure roller 21 (see the arrow in FIG. 3). The control device 8 controls the power supply unit 18 based on detection signals from the heater temperature detection unit 36 ​​and the belt temperature detection unit 35 (details will be described later). The heater 22 (heat generating unit 31) generates heat using the power supplied from the power supply unit 18, and heats the fixing belt 20 (pressure region N).

[0041] At this time, the control device 8 changes the resistance heating elements 32 to be heated (energized) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure region N, the control device 8 executes control to cause all of the resistance heating elements 32 to generate heat. On the other hand, when a small-sized paper P passes through the pressure region N, the control device 8 executes control to cause only the resistance heating element 32A located in the center in the axial direction to generate heat. This makes it possible to heat only the necessary portions of the fixing belt 20 (pressure region N) in accordance with the size of the paper P. As a result, it is possible to minimize the amount of power used. It is also possible to prevent excessive (abnormal) temperature rise (overheating) at both ends of the fixing belt 20 in the axial direction.

[0042] When the fixing belt 20 (heater 22) reaches a predetermined temperature, the control device 8 starts the image formation process already described. The paper P onto which the toner image has been transferred enters the pressure area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressure area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressure area N while rotating around its axis. The toner image is then fixed to the paper P, forming a fixed image on the paper P. The paper P with the fixed image is then discharged to the paper output tray 4.

[0043] To perform a proper fixing process, it is necessary to maintain the fixing belt 20 at a predetermined temperature. In this fixing device 7, the heater 22 generates heat, and the heat is transferred to the fixing belt 20, thereby heating the fixing belt 20. Therefore, the temperature of the fixing belt 20 begins to rise after the heater 22 begins to rise. In other words, there is a time lag between the timing at which the heater 22 begins to heat up and the timing at which the fixing belt 20 begins to heat up. Considering this fact, the heater 22 may be overheating when the fixing belt 20 reaches the predetermined temperature. Furthermore, even if the power supply to the heater 22 is stopped when the fixing belt 20 exceeds the predetermined temperature, the fixing belt 20 continues to receive heat from the overheated heater 22, so the temperature of the fixing belt 20 continues to rise. In addition, the heater 22 disposed within the fixing belt 20 cools down more slowly than the fixing belt 20 itself. Therefore, if the power supply to the heater 22 is started again when the fixing belt 20 falls below the predetermined temperature, the heater 22, which has not yet cooled down sufficiently, may overheat again. Therefore, in the fixing device 7 according to this embodiment, the control device 8 (power control section) executes control (power control method) to maintain the heater 22 and the fixing belt 20 at a predetermined temperature.

[0044] [Power control method] A method of controlling the power of the heater 22 provided in the fixing device 7 according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the method of controlling the power of the heater 22.

[0045] When the control device 8 receives an instruction to start the image forming process (fixing process), it controls the input power (supply power) to the heater 22 as described below. The power control method for the heater 22 includes a power supply step S1 and a corrective power supply step S2.

[0046] <Power supply process> In the power supply step S1, the control device 8 executes a first power supply control, which supplies power to the heater 22, in a first control period (T1) until the heater temperature detector 36 detects a target temperature (tC) and the belt temperature detector 35 detects a temperature outside the target range (tR). The target temperature (tC) is, for example, a temperature at which the fixing belt 20 can be heated to a temperature required for the fixing process and is below the heat-resistant temperature of the heater 22 and its surrounding components (such as the heater temperature detector 36). The target temperature range (tR) is the temperature range (upper and lower limits) of the fixing belt 20 that allows proper fixing. The first control period (T1) is a time interval (period) during which the power supplied to the heater 22 is monitored. The target temperature (tC), target range (tR), and first control period (T1) are experimentally determined and stored (saved) in advance in the memory of the control device 8.

[0047] The power supply step S1 includes a first heater temperature determination step S11, a first belt temperature determination step S12, and a first heater heating step S13.

[0048] In the first heater temperature determination step S11, the control device 8 compares the detection signal (temperature of the heater 22) sent from the heater temperature detection unit 36 ​​with a target temperature (tC) (e.g., 200 degrees Celsius). If the temperature of the heater 22 is below the target temperature (tC) (NO in S11), the control device 8 executes the first heater heating step S13, in which the control device 8 supplies power to the heater 22 while controlling the power supply unit 18. On the other hand, if the temperature of the heater 22 is equal to or higher than the target temperature (tC) (YES in S11), the control device 8 executes the first belt temperature determination step S12.

[0049] In the first belt temperature determination step S12, the control device 8 determines whether the detection signal (temperature of the fixing belt 20) sent from the belt temperature detection unit 35 is outside the target range (tR). If the temperature of the fixing belt 20 is within the target range (tR) (below the upper limit and above the lower limit) (NO in S12), the control device 8 executes the first heater heating step S13. On the other hand, if the temperature of the fixing belt 20 is outside the target range (tR) (above the upper limit or below the lower limit) (YES in S12), the control device 8 executes the corrective power supply step S2, which will be described later.

[0050] The first power supply control is realized by the control device 8 controlling and executing the first heater temperature determination step S11, the first belt temperature determination step S12, and the first heater heating step S13 (i.e., the entire power supply step S1). The control device 8 repeatedly executes the first power supply control (power supply step S1) at a first control cycle (T1) (for example, at intervals of 0.1 seconds).

[0051] <Corrective power supply process> In the corrective power supply step S2, the control device 8 executes the corrective control and the second power supply control in a second control cycle (T2). The corrective power supply step S2 includes a correcting step S20, a second heater temperature determination step S21, a second belt temperature determination step S22, and a second heater heating step S23.

[0052] In the correction step S20, if the belt temperature detection unit 35 detects a temperature outside the target range (tR) (YES in S12), the control device 8 corrects the target temperature (tC) so that the belt temperature detection unit 35 detects a temperature within the target range (tR). Specifically, if the belt temperature detection unit 35 detects a temperature above the target range (tR), the control device 8 subtracts a predetermined correction amount (h) from the target temperature (tC) and sets the result as the corrected target temperature (tC). On the other hand, if the belt temperature detection unit 35 detects a temperature below the target range (tR), the control device 8 adds the predetermined correction amount (h) to the target temperature (tC) and sets the result as the corrected target temperature (tC). The corrected target temperature (tC) is temporarily stored in the memory of the control device 8.

[0053] The predetermined correction amount (h) is a value that can be subtracted or added to the target temperature (tC) to bring the temperature of the fixing belt 20 that has deviated from the target range (tR) back into the target range (tR), and is experimentally determined and stored (saved) in advance in the memory of the control device 8. The correction step S20 is executed and controlled by the control device 8, thereby realizing the correction control.

[0054] In the second heater temperature determination step S21, the control device 8 compares the detection signal (temperature of the heater 22) sent from the heater temperature detection unit 36 ​​with the corrected target temperature (tC). If the temperature of the heater 22 is lower than the corrected target temperature (tC) (NO in S21), the control device 8 executes the second heater heating step S23, in which the control device 8 supplies power to the heater 22 while controlling the power supply unit 18. On the other hand, if the temperature of the heater 22 is equal to or higher than the corrected target temperature (tC) (YES in S21), the control device 8 executes the second belt temperature determination step S22.

[0055] In the second belt temperature determination step S22, the control device 8 determines whether the detection signal (temperature of the fixing belt 20) sent from the belt temperature detection unit 35 is outside the target range (tR). If the temperature of the fixing belt 20 is within the target range (tR) (NO in S22), the control device 8 executes the second heater heating step S23. On the other hand, if the temperature of the fixing belt 20 is outside the target range (tR) (YES in S22), the control device 8 executes the correction step S20 again. Note that when the image formation process (fixing process) is completed, the power control method for the heater 22 (correction control, second power supply control) also ends.

[0056] The second power supply control is realized by the control device 8 controlling and executing the second heater temperature determination step S21, the second belt temperature determination step S22, and the second heater heating step S23 described above. In the second power supply control, power is supplied to the heater 22 so that the heater temperature detection unit 36 ​​detects the corrected target temperature (tC). The control device 8 repeatedly executes the correction control (correction step S20) and the second power supply control (steps S20 to S23) at a second control period (T2) (e.g., 1-second intervals) that is longer than the first control period (T1). The second control period (T2) is set to a time interval that is at least 10 times the first control period (T1). Preferably, the second control period (T2) is set to a time interval that is at least 10 times but not more than 50 times the first control period (T1).

[0057] [verification] The applicant conducted tests (verification) to confirm the effectiveness of the fixing device 7 and the power control method for the heater 22 according to this embodiment. The tests (verification) for the fixing device 7 and the power control method will be described below with reference to Figs. 7 to 9. Figs. 7 to 9 are graphs showing changes over time in the temperature and power of the heater 22, with Fig. 7 showing the test results of test (1), Fig. 8 showing the test results of test (2), and Fig. 9 showing the test results of a comparison test.

[0058] In this verification, three tests were conducted with different second control periods (T2). Specifically, tests (1) and (2) were conducted using the power control method for the heater 22 according to this embodiment, and a comparative test was conducted without using this power control method.

[0059] The following describes the conditions common to the three tests. In each of the three tests, the image forming apparatus 1 (fixing device 7) according to this embodiment was used, the image forming process (fixing process) was performed for approximately 60 seconds, and the following [1] to [3] were measured during the process, and the measurement results were graphed. [1] Temperature of the heater 22 (detection result of the heater temperature detection unit 36) [2] Temperature of the fixing belt 20 (detection result of the belt temperature detection unit 35) [3] Power supplied to heater 22 (power consumption) In each of the three tests, the initial target temperature (tC) was set to 200 degrees Celsius, and the first control period (T1) was set to 0.1 seconds.

[0060] <Comparative test> First, the comparative test will be described with reference to Fig. 9. In the comparative test, the second control period (T2) was set to 0.1 seconds, which is the same as the first control period (T1). In other words, in the comparative test, the second control period (T2) was set to a time interval less than 10 times the first control period (T1).

[0061] It is presumed that the power supply process S1 (first power supply control) was executed for approximately 10 seconds from the start of the test (start of power supply to heater 22). Approximately 10 seconds after the start of the test, the first correction process S20 (correction control) was executed, and the power supply process S1 (first power supply control) was transitioned to the corrected power supply process S2 (second power supply control). After 10 seconds had elapsed, the target temperature (tC) (temperature of heater 22) changed in stages, so it is presumed that the correction process S20 (correction control) was executed multiple times in response to changes in the temperature of the fixing belt 20.

[0062] Although the temperature of the fixing belt 20 did occasionally deviate from the target range (tR), it was confirmed that it generally remained within the target range (tR). However, at approximately 25 seconds, 37 seconds, and 49 seconds after the start of the test, the temperature of the fixing belt 20 slightly dropped below the lower limit of the target range (tR), causing a correction to rapidly increase the target temperature (tC). Because the corrected target temperature (tC) exceeded the initial target temperature (tC), the temperature of the heater 22 rose rapidly. After the target temperature (tC) rose rapidly, a correction to rapidly decrease the target temperature (tC) was made, causing the temperature of the heater 22 to also drop rapidly. This phenomenon is presumably caused by the target temperature (tC) being corrected multiple times during the period when the temperature of the fixing belt 20 was rising and falling because the time interval of the second control period (T2) was too short. It was also confirmed that a temporary surge in power consumption occurred in order to bring the temperature of the heater 22 up to the corrected target temperature (tC).

[0063] From the above, it was confirmed that in the comparative test in which the second control period (T2) was set to 0.1 seconds, which is the same as the first control period (T1), the target temperature (tC) changed excessively, causing the temperature of the heater 22 to become unstable. It was also confirmed that unnecessary power was consumed.

[0064] <Test (1) and Test (2)> Next, tests (1) and (2) will be described with reference to Figures 7 and 8. In test (1), the second control period (T2) was set to 1 second, which is 10 times the first control period (T1), and in test (2), the second control period (T2) was set to 5 seconds, which is 50 times the first control period (T1). In other words, in tests (1) and (2), the second control period (T2) was set to a time interval that was 10 to 50 times the first control period (T1).

[0065] As in the comparative test described above (see FIG. 9), the power supply process S1 (first power supply control) was executed for approximately 10 seconds from the start of the test, and the first correction process S20 (correction control) was executed at approximately 10 seconds, resulting in a transition from the power supply process S1 (first power supply control) to the corrected power supply process S2 (second power supply control). Since the target temperature (tC) (temperature of heater 22) changed stepwise after 10 seconds had elapsed, it is assumed that the correction process S20 (correction control) was executed multiple times in response to changes in the temperature of fixing belt 20.

[0066] Although the temperature of the fixing belt 20 was outside the target range (tR) at certain times, it was confirmed that it generally remained within the target range (tR). The target temperature (tC) gradually decreased from the start of the test until approximately 30 seconds, and then gradually increased and decreased after 30 seconds. However, in Tests (1) and (2), no corrections were observed that caused the target temperature (tC) to suddenly increase or decrease, as was observed in the comparative test (see Figure 9). Furthermore, in Tests (1) and (2), no temporary sudden increases in power consumption were observed, as was observed in the comparative test (see Figure 9).

[0067] From the above, in Tests (1) and (2), in which the second control period (T2) was set to 10 times or more and 50 times or less than the first control period (T1), it was confirmed that excessive changes in the target temperature (tC) were suppressed and the temperature of the heater 22 was stabilized. It was also confirmed that unnecessary power consumption was suppressed. In other words, this verification confirmed the effectiveness of the power control method for the fixing device 7 and heater 22 according to this embodiment.

[0068] In the fixing device 7 (the method for controlling the power of the heater 22) according to the present embodiment described above, the heater 22 reaches the target temperature (tC) and the first power supply control for the heater 22 is executed in the first control period (T1) until the temperature of the fixing belt 20 falls outside the target range (tR). If the temperature of the fixing belt 20 subsequently falls outside the target range (tR), correction control is executed in the second control period (T2) to correct the target temperature (tC) to return the temperature to within the target range (tR), and second power supply control is executed in the second control period (T2) to bring the heater 22 to the corrected target temperature (tC). The second control period (T2) is set to a time interval at least 10 times longer than the first control period (T1). This configuration corrects the target temperature (tC) of the heater 22 so as to maintain the temperature of the fixing belt 20 within the target range (tR), and the heater 22 can be controlled at the corrected target temperature (tC). Furthermore, since the second control period (T2) is longer than the first control period (T1), it is possible to correct (change) the target temperature (tC) of the heater 22 after a change in the temperature of the fixing belt 20. This makes it possible to maintain the heater 22 at the target temperature (tC) while absorbing the difference (time lag) in the timing of the temperature changes between the heater 22 and the fixing belt 20, and also to maintain the fixing belt 20 at a temperature within the target range (tR).

[0069] Furthermore, according to the fixing device 7 (the method for controlling the power of the heater 22) of this embodiment, the heater 22 and the fixing belt 20 can be maintained at a predetermined temperature, and an excessive temperature rise in the heater 22 can be prevented, thereby suppressing breakdowns of components around the heater 22 (e.g., the heater temperature detection unit 36, etc.). Furthermore, because the temperature change of the fixing belt 20 is kept within a certain range, the temperature in the pressure region N is stabilized, ensuring proper fixing processing. As a result, the quality of the fixed image can be improved. Furthermore, because excessive power supply to the heater 22 is prevented, power saving can also be achieved.

[0070] Furthermore, in the fixing device 7 according to this embodiment, the control device 8 (power control unit) is configured to change (increase or decrease) the target temperature (tC) by a predetermined correction amount (h) when the belt temperature detection unit 35 detects a temperature outside the target range (tR). This configuration makes it possible to quickly calculate the target temperature (tC) for returning the temperature of the fixing belt 20 to the target range (tR) through simple calculations. This allows even an inexpensive control device 8 with a slow calculation speed to correct the target temperature (tC), thereby reducing the manufacturing cost of the fixing device 7.

[0071] Although the fixing device 7 according to the present embodiment includes one belt temperature detector 35 and one heater temperature detector 36, the present invention is not limited to this and may include two or more of each (not shown). While the belt temperature detector 35 and the heater temperature detector 36 are thermistors, the present invention is not limited to this and may include other temperature sensors, such as thermocouples or resistance temperature detectors. While the belt temperature detector 35 is in contact with the inner surface of the fixing belt 20, the present invention is not limited to this and may include other temperature sensors, such as thermocouples or resistance temperature detectors. Alternatively, the belt temperature detector 35 may be in contact with the outer surface of the fixing belt 20 in the non-passage area A2 (not shown). Alternatively, the belt temperature detector 35 may be a non-contact temperature measuring device, such as an infrared thermometer, and may be provided without contacting the inner or outer surface of the fixing belt 20 (not shown). Although the heater temperature detector 36 is in contact with the upper surface of the substrate 30 of the heater 22, the present invention is not limited to this and may include other temperature sensors, such as thermocouples or resistance temperature detectors (not shown).

[0072] In the fixing device 7 (heater 22 power control method) according to this embodiment, the second control period (T2), which is the execution period of the correction control and the second power supply control, may be set to a time interval at least 10 times the first control period (T1), which is the execution period of the first power supply control. While the lower limit of the multiplication factor for the second control period (T2) is 10, the upper limit of the multiplication factor for the second control period (T2) is not particularly limited and may be set experimentally based on, for example, the difference in heat capacity between the heater 22 and the fixing belt 20, the difference in the rate of temperature rise (time lag), and the like. The applicant has confirmed through testing (verification) that the heater 22 and the fixing belt 20 can be effectively maintained at a predetermined temperature by setting the second control period (T2) to a time interval at least 10 times but not more than 50 times the first control period (T1).

[0073] Furthermore, in the fixing device 7 according to this embodiment, the heat generating section 31 is divided into three resistance heating elements 32A to 32C, but this is not limiting and the heat generating section 31 may be divided into two, four or more, or may not be divided at all (all of which are not shown). Additionally, the heat generating section 31 may be a single resistance heating element extending from one side to the other in the axial direction, or a U-shaped resistance heating element extending from one side to the other in the axial direction and then folding back to extend from the other side to one side in the axial direction (all of which are not shown).

[0074] Furthermore, in the fixing device 7 according to this embodiment, the paper P passes through the center of the pressure region N in the axial direction, but this is not limiting, and the paper P may pass through a position closer to one side in the axial direction of the pressure region N (not shown). In this case, the non-passing region A2 is set only on one side in the axial direction of the fixing belt 20 (or the pressure region N).

[0075] Furthermore, in the fixing device 7 according to this embodiment, the pressure roller 21 is driven to rotate, and the fixing belt 20 is driven to rotate, but this is not limited to this, and the fixing belt 20 may be driven to rotate, and the pressure roller 21 may be driven to rotate.

[0076] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0077] The above-described embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0078] 1. Image forming device 7 Fixing device 8. Control device (power control unit) 20 Fixing belt 21 Pressure roller (pressure member) 22 Heater 35 Belt temperature detection unit 36 Heater temperature detection unit N pressure area P Paper (media) S1 Power supply process S2 Correction power supply process

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a heater that contacts the inner surface of the fixing belt facing the pressure area, generates heat upon receiving power, and heats the fixing belt; a belt temperature detection unit that detects the temperature of the fixing belt; a heater temperature detection unit that detects the temperature of the heater; a power control unit that controls the power supplied to the heater, the power control unit executes a first power supply control in a first control cycle to supply power to the heater until the heater temperature detection unit detects a target temperature and the belt temperature detection unit detects a temperature outside a target temperature range; a power supply control unit that supplies power to the heater so that the heater temperature detection unit detects the corrected target temperature when the belt temperature detection unit detects a temperature outside the target range, and a power supply control unit that supplies power to the heater so that the heater temperature detection unit detects the corrected target temperature when the belt temperature detection unit detects a temperature outside the target range, and the power supply control unit performs these control operations at a second control period that is set to a time interval that is 10 times or more the first control period.

2. When the belt temperature detection unit detects a temperature exceeding the target range, the power control unit sets a value obtained by subtracting a predetermined correction amount from the target temperature as the corrected target temperature, 2. The fixing device according to claim 1, wherein, when the belt temperature detection unit detects a temperature below the target range, the power control unit sets the corrected target temperature to a value obtained by adding a predetermined correction amount to the target temperature.

3. 2. The fixing device according to claim 1, wherein the second control period is set to a time interval that is 10 times or more and 50 times or less than the first control period.

4. 4. An image forming apparatus comprising the fixing device according to claim 1.

5. 4. A method for controlling power to a heater provided in the fixing device according to claim 1, comprising: a power supplying step of executing the first power supply control to supply power to the heater in the first control cycle until the heater temperature detecting unit detects the target temperature and the belt temperature detecting unit detects a temperature outside the target temperature range; a correction control for correcting the target temperature so that the belt temperature detection unit detects a temperature within the target range when the belt temperature detection unit detects a temperature outside the target range, and a second power supply control for supplying power to the heater so that the heater temperature detection unit detects the corrected target temperature, in the second control cycle.

Images