Image forming apparatus

Abstract

To prevent the occurrence of an image defect due to hot offset and faulty fixing.SOLUTION: An image forming apparatus has: a fixing device (40) that has a fixing film (41), a heater (42) provided inside the fixing film (41), a temperature detection unit (Th) detecting the temperature of the heater (41), and a pressure roller (45); a control unit (70) that controls power to be supplied to the heater (41) so as to adjust the temperature detected by the temperature detection unit (Th) to be a target temperature; and a storage unit (72) that stores information indicating the rate of temperature increase of the temperature detection unit. The control unit (70) energizes the heater (41) at a fixed energization rate, with the pressure roller (45) being stopped, to measure the rate of temperature increase of the temperature detection unit during the use of the image forming apparatus, compares the measured rate of temperature increase with the information stored in the storage unit (72) to estimate the maximum power that can be supplied to the heater (41), and corrects the power to be supplied.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a recording material. [Background technology]

[0002] An image forming apparatus has a fixing device that fixes a toner image transferred to a recording material, such as transfer paper or an OHP sheet, in an image forming unit. A known fixing device configuration is a film heating type, which is quick-start and energy-efficient. A film heating type fixing device has a ceramic heater and a pressure roller pressed against a fixing film heated by the ceramic heater. While the recording material bearing an unfixed toner image is sandwiched and conveyed between the fixing film and the pressure roller, the toner image is heated and fixed to the recording material.

[0003] A commonly used method for controlling a heater to a set temperature is to control the amount of time the heater is energized. There are two commonly used methods for controlling the energization time: wave number control, which controls the energization / de-energization of the power supply waveform at integer multiples of the frequency, and phase control, which controls the phase angle of energization for each half cycle of the power supply waveform. In wave number control, the duty rate is the ratio of the number of waves that are energized out of the total number of waves per unit time, while in phase control, the duty rate is the ratio of the time that electricity is on out of the half cycle of the power supply waveform. By controlling this duty rate, the heater can be controlled to a set temperature.

[0004] However, there is a tolerance for the resistance value of each heater, and the voltage applied to the heater also varies. It is also known that the resistance value of a heater fluctuates due to degradation of the heater. Therefore, even if the heater is energized at the same current conduction rate, variations in the resistance value and voltage and durability fluctuations will cause variations in the power, making it difficult to accurately control the heater temperature.

[0005] If the heater temperature is too high, excessive heat may be applied to the recording material or toner, resulting in image defects (hot offset). Hot offset refers to an image defect in which toner on the recording material is heated excessively (hereinafter referred to as over-fixing), causing it to adhere to the fixing film and then adhere to the recording material after one revolution of the fixing film. If the heater temperature is too low, poor fixing (cold offset) may occur due to insufficient heat. Here, cold offset refers to a defect in which part of the toner image does not adhere to the recording material and is lost due to poor fixing ability.

[0006] To prevent these image defects, Patent Document 1 discloses the provision of a correction means for correcting the duty ratio so that the same power is output even if there are variations in the heater's resistance value or the voltage applied to the heater. The image forming apparatus in Patent Document 1 is provided with a voltage detection means for detecting the input voltage and a resistance value recording means for storing the heater's resistance value measured in advance, and calculates the maximum power that can be input to the heater from the input voltage detected by the voltage detection means and the heater's resistance value. The heater temperature is then controlled by correcting the duty ratio so that the heater outputs a predetermined power from the maximum power. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-28188 Summary of the Invention [Problem to be solved by the invention]

[0008] As in Patent Document 1, incorporating a voltage detection means or current detection means to detect maximum power increases costs. On the other hand, omitting a voltage detection means or current detection means to reduce costs makes it impossible to accurately detect maximum power. In this case, the power conduction rate cannot be accurately corrected due to the influence of variations in input voltage and heater resistance value, as well as degradation of the heater resistance due to conduction. This makes it impossible to accurately control the heater temperature, which can lead to hot offset and poor fixing.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an image forming apparatus that suppresses the occurrence of image defects due to hot offset and poor fixing. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the image forming apparatus of the present invention is an image forming apparatus comprising: an image forming means for forming an image on a recording material; a rotating fixing member; a heating member that heats the fixing member when current is applied; a temperature detection unit that detects the temperature of the heating member; and a fixing device that has a pressure roller that is arranged opposite the heating member across the fixing member and forms a nip portion with the fixing member, and that fixes the image to the recording material with the fixing member. The image forming apparatus also has: a control means that controls the power supplied to the heating member so that the temperature detected by the temperature detection unit becomes a target temperature; and a memory unit that stores information regarding the temperature rise time of the temperature detection unit, and the control means measures the temperature rise time or amount of temperature rise of the temperature detection unit by applying current to the heating member at a predetermined power conduction rate while the pressure roller is stopped and in a stationary state, where the power conduction rate is the proportion of time that current is applied to the heating member per unit time, and compares this with the information stored in the memory unit to estimate the maximum power that can be supplied to the heating member, and corrects the power supplied to the heating member. [Effects of the Invention]

[0011] According to the present invention, even in an image forming apparatus that does not have a voltage detection unit, it is possible to suppress the occurrence of image defects due to hot offset and fixing defects. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing the schematic configuration of an image forming apparatus; [Figure 2] Cross-sectional view showing the schematic configuration of a heating device [Figure 3] Schematic diagram of the heater configuration used in the heating device [Figure 4] Flowchart for measuring temperature rise time during manufacturing [Figure 5] Temperature curve and power consumption during manufacturing temperature rise measurement [Figure 6] Schematic diagram of the temperature rise measurement device during manufacturing [Figure 7] Power Detection Sequence Flowchart [Figure 8] Temperature curve and power duty during temperature rise measurement at power detection [Figure 9] Detected power table [Figure 10] Graph showing temperature curves in temperature rise measurements when detecting power at different maximum power levels [Figure 11] 1 is a flowchart of start-up control according to an embodiment of the present invention; [Figure 12] Graph showing the start-up temperature curve and current duty according to a comparative example [Figure 13] Table showing whether or not image defects occurred in Examples and Comparative Examples [Figure 14] 1 is a table showing the difference between the detected power Pd and the maximum power Pw during durability testing according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes, by way of example, a mode for carrying out the present invention with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the following embodiments.

[0014] <Explanation of image forming device> The configuration of an image forming apparatus according to this embodiment will be described with reference to FIG. 1. The image forming apparatus shown in FIG. 1 is a monochrome laser printer that forms an image on a recording material using an electrophotographic system. An image forming unit 20 forms an electrostatic latent image using a laser beam L that is turned on, develops the electrostatic latent image to form a toner image, and then transfers the toner image to the recording material. The image forming apparatus includes a paper feed tray 12, a paper feed roller 13, a pair of registration rollers 14, a registration sensor 15, a paper discharge roller 61, and the like. The image forming unit 20 also includes a photosensitive drum 22 as an image carrier, a charger 23 as primary charging means, a scanner unit 24 as exposure means, a toner container 25, a developing means 26, and a transfer roller 34, the operation of which is controlled by a control unit 70. The control unit 70 also controls the operation of a heating device 40, which will be described later.

[0015] The photosensitive drum 22 is constructed by applying an organic photoconductive layer to the outer periphery of an aluminum cylinder, and is rotated by the driving force of a drive motor (not shown). The drive motor rotates the photosensitive drum 22 clockwise in response to image formation operations. The photosensitive drum 22 is constructed by applying an organic photoconductive layer (60 μm thick) to the outer periphery of a hollow aluminum cylinder (φ30, thickness 1.0 mm).

[0016] The charger 23 uniformly charges the surface of the photosensitive drum 22. Exposure light to the photosensitive drum 22 is sent from a scanner unit 24, and the surface of the photosensitive drum 22 is selectively exposed to light, thereby forming an electrostatic latent image.

[0017] The developing means includes a developing sleeve 26 for visualizing the electrostatic latent image, and is disposed in a toner container 25. A developing bias is applied from a power source (not shown) between the developing sleeve 26 and the corresponding photosensitive drum 22. The photosensitive drum 22 rotates clockwise during image formation, and the developing sleeve 26 in the toner container 25 develops a toner image onto the electrostatic latent image formed on the photosensitive drum 22.

[0018] The recording material 11 stored in the paper feed tray 12 is conveyed by the paper feed roller 13 to reach the pair of registration rollers 14 and is detected by the registration sensor 15. During image formation, the recording material 11 is conveyed in accordance with the timing of detection by the registration sensor 15 and the timing at which the toner image on the photosensitive drum 22 reaches the transfer roller 34.

[0019] The transfer roller 34 is an opposing member that contacts the photosensitive drum 22. The transfer roller 34 has a core (φ6) and an elastic layer made of NBR hydrin rubber with a thickness of 4 mm on top. The surface length (axial direction) of the elastic layer is 220 mm. The transfer roller 34 contacts the photosensitive drum 22 by a contact mechanism (not shown). The contact pressure at that time is 13 N. The contact width between the transfer roller 34 and the photosensitive drum 22 is 2.0 mm. While the recording material 11 is sandwiched and transported between the transfer roller 34 and the photosensitive drum 22, the toner image on the photosensitive drum 22 is transferred to the recording material 11 by a transfer bias applied from a power source (not shown).

[0020] The conveying guide 32 is a guide member for conveying the recording material 11 from the transfer portion to the heating device 40 .

[0021] Heating device 40, an example of a fixing device, heats, melts, and fixes the toner image on recording material 11 by sandwiching and transporting it. After the fixing process by heating device 40, recording material 11 passes through transport rollers 31 and is discharged by discharge rollers 61 onto a paper discharge tray 62 outside the image forming apparatus, thereby completing the image forming operation. In the case of double-sided printing, after the fixing process by heating device 40, recording material 11 is conveyed by transport rollers 31 to discharge rollers 61. Then, discharge rollers 61 switch to reverse rotation, and recording material 11 is conveyed toward double-sided rollers 64 and 65 in the double-sided conveyance path. From double-sided rollers 64 and 65, recording material 11 is conveyed to double-sided re-feed rollers 66 and reaches registration roller pair 14 again. Here, the unprinted side of the recording material undergoes the transfer process and fixing process described above, thereby forming an image, and the recording material is discharged onto paper discharge tray 62 by transport rollers 31 and discharge rollers, thereby completing the image forming operation.

[0022] The control unit 70 has a CPU 71, a ROM 72, and a RAM 73. The CPU 71 executes various programs stored in the ROM 72, and controls various operations related to image formation while using the RAM 73, which is a volatile memory, as a work area. The ROM 72 and RAM 73 are examples of storage units that store information used to control the image forming apparatus. The ROM 72 is an example of a non-volatile memory that stores a control program for the image forming apparatus.

[0023] <Explanation of the heating device configuration> A heating device 40, which is an example of a fixing device, will be described with reference to Fig. 2. The heating device 40 has a fixing film 41 as a fixing member and a heater 42 as a heating member that contacts the inner surface of the fixing film 41.

[0024] The heater 42 is an example of a heating element disposed within the internal space of the fixing film 41 and heats the fixing film 41 when energized. The heater 42 is held by a holding member 43. The holding member 43 functions as a guide for guiding the rotation of the fixing film 41. The stay 44 applies pressure from a pressure spring (not shown) to the holding member 43 in the direction of a pressure roller 45, which serves as a pressure member, to form a fixing nip N in which the toner on the recording material 11 is heated and fixed. The stay 44 is made of a highly rigid metal. The total pressure of the pressure spring is 250 N, and the width of the fixing nip N in the recording material conveyance direction is 9.0 mm. A drive gear (not shown) is attached to the end of the pressure roller 45 and receives power from a motor (not shown) to rotate counterclockwise. The fixing film 41 is rotated clockwise by the rotation of the pressure roller 45. The recording material 11 on which the toner image has been formed is heated and fixed while being sandwiched and conveyed in the direction indicated by the arrow in the nip N.

[0025] The fixing film 41 is an example of a rotatable, cylindrical fixing member. The fixing film 41 has an outer diameter of 24 mm. The fixing film 41 has a base layer made of polyimide resin with a thickness of 70 μm, an elastic layer made of a 300 μm heat-conducting rubber layer on the outside of the base layer, and a release layer made of a 20 μm PFA tube as the outermost layer. In this embodiment, an example in which an elastic layer is provided to improve fixability is shown, but if there are no problems with fixability, the elastic layer may not be provided. The pressure roller 45 has an outer diameter of 25 mm. It has an iron core with an outer diameter of 17 mm, an elastic layer made of silicone rubber with a thickness of 4 mm, and a release layer made of a 40 μm PFA tube as the outermost layer.

[0026] The configuration of the heater 42 will be described using Figures 3(a) and 3(b). Figure 3(a) is a cross-sectional view of the heater 42. The substrate 401 of the heater 42 is an alumina substrate that is a ceramic substrate that is long in the longitudinal direction and has a plate thickness of 1.0 mm. The longitudinal width of the substrate 401 is 260 mm, and the lateral width (in the paper feed direction) is 7.78 mm. The surface side of the heater 42 that comes into contact with the fixing film 41 has a resistance heating layer 402 that is an example of a resistance heating element and has a thickness of 10 µm, and a protective glass 403 that is 60 µm thick. The resistance heating layer 402 is formed by applying a conductive paste containing a silver-palladium (Ag / Pd) alloy to the alumina substrate 401 by screen printing and then baking it.

[0027] The protective glass layer 403 comes into contact with the fixing film 41 via fluorine grease (not shown), providing excellent sliding properties. FIG. 3(b) is a schematic diagram of the heater as seen from the heater surface side. The resistive heating layer 402 is formed in a strip shape along the longitudinal direction. The protective glass 403 (dotted line) covers the resistive heating layer 402 and the conductor portion 406, thereby ensuring insulation. The heating area A in the longitudinal direction heated by the resistive heating layer 402 is 220 mm, and the resistance value of the resistive heating layer 402 is 9.22 Ω. In this embodiment, the substrate 401 of the heater 42 is described as being ceramic, but metal may also be used.

[0028] The fixing thermistor Th is disposed on the rear surface of the heater 42 and is an example of a temperature detection unit that detects the surface temperature of the heater 42. The fixing thermistor Th is disposed in the center of the heater 42 in a direction perpendicular to the recording material conveyance direction.

[0029] In the heating device 40, power is supplied to the electrodes 405a, 405b of the heater 42 from a control unit 70 connected to an AC power source 80 (outlet). This causes the resistance heating layer 402 of the heater 42 to heat up. The control unit 70 controls the supply of power to the heater 42 using a triac (not shown) provided in the control unit 70 based on a detection signal corresponding to the temperature of the heater 42 output from the thermistor Th. This controls the temperature of the heater 42. When the temperature information acquired based on the detection signal from the thermistor Th is lower than the control target temperature, the control unit 70 increases the power supplied to the heater 42. Conversely, when the temperature information acquired based on the detection signal from the thermistor Th is higher than the control target temperature, the control unit 70 reduces the power supplied to the heater 42. Power control is performed by controlling the power duty (power ratio), which will be described later. In this way, the control unit 70 controls the power supply to the heater 42 based on the detection signal from the thermistor Th to bring the temperature of the heater 42 closer to the control target temperature. In this embodiment, the AC voltage of the AC power supply 80 is 100 V. The voltage drop due to power consumption other than by the heater 42 within the image forming apparatus is 4 V, so the voltage applied to the electrode portion of the heater 42 is 96 V. Therefore, the resistance value of the heater 42 is 9.22 Ω, and the maximum power Pw that can be supplied is 1000 W, as W = V / R.

[0030] When the heating device 40 is installed in the image forming apparatus, the contact connector 74 inside the image forming apparatus electrically connects to the memory chip 36, an example of a storage unit, located on a portion of the surface of the heating device. This connection enables communication with the memory chip 36. By reading the information in the memory chip 36 into the RAM 73 of the control unit 70, image quality and maintenance of the heating device are further improved.

[0031] <Power detection> Next, a method for detecting power will be described. In this embodiment, a method for estimating the power input to the heater 42 will be described by comparing the temperature rise time during the manufacturing process with the measurement results of the temperature rise time in the power detection sequence at the installation site.

[0032] (1) Measurement of temperature rise time during manufacturing processMeasurement of the temperature rise time during the manufacturing process will be described using Figures 4 and 5. Figure 4 shows a flowchart of measuring the temperature rise time during the manufacturing process. Figure 5(a) shows the temperature rise curve of thermistor Th during the manufacturing process. Figure 5(b) shows the power supplied to heater 42 corresponding to the temperature rise curve of Figure 5(a). This temperature rise time measurement is performed during the assembly process of heating device 40. The temperature rise time measurement is performed by connecting heating device 40 to temperature rise measuring device 50 shown in Figure 6. Temperature rise measuring device 50 starts applying a predetermined power W1 [W] to heater 42 of heating device 40 (1001). At this time, power is supplied to heater 42 while pressure roller 45 is stopped (referred to as stop heating). When power is applied to heater 42, heater 42 starts to rise in temperature. The temperature rise measurement device 50 stores in the memory 51 the time t1 required from the start of power application until the temperature reaches the temperature rise measurement first temperature T1 [°C] based on the detection signal from thermistor Th (1002). The temperature rise measurement device 50 also stores in the memory 51 the time t2 required until the temperature reaches the temperature rise measurement second temperature T2 [°C], which is a second temperature higher than T1 [°C], based on the detection signal from thermistor Th (1003). The supply of power to the heater 42 is stopped after the temperature of thermistor Th reaches the temperature rise measurement second temperature T2 [°C] (1004). The temperature rise measurement device 50 calculates the manufacturing temperature rise time tm (= t1 - t2) using the calculation device 52 from t1 and t2 stored in the memory 51 (1005). The manufacturing temperature rise time tm is information indicating the time elapsed from when the thermistor Th detected T1 [°C] to when it detected T2 [°C] at the time of manufacturing the fixing device. The temperature rise measurement device 50 is provided with an electrical contact 53. The temperature rise measurement device 50 is electrically connected to a writing unit 54 within the temperature rise measurement device and a memory chip 36 provided on the surface of the heating device 40. The temperature rise measurement device 50 writes a value obtained by multiplying the manufacturing temperature rise time tm by 100 into the memory chip 36 (1006) and ends the temperature rise time measurement (1007). As described above, during the manufacturing process, the memory chip 36 stores the unique manufacturing temperature rise time tm for each heating device 40 at the preset power W1 [W]. In this embodiment, the preset power W1 is set to 500 [W], the first temperature rise measurement temperature T1 is set to 45 [°C], and the second temperature rise measurement temperature T2 is set to 65 [°C].At this time, the temperature rise time tm during manufacturing was 0.66 [s], so the memory chip 36 was made to hold a value of 66.

[0033] In this embodiment, the measurement of the temperature rise time during the manufacturing process has been described above using the example of heating device 40 that is removable from the image forming apparatus, and therefore memory chip 36 is provided on the surface of heating device 40. However, if heating device 40 cannot be removed from the image forming apparatus, the image forming apparatus may be connected to temperature rise measuring device 50, and the temperature rise time tm during manufacturing may be stored in RAM 73 of control unit 70.

[0034] (2) Power detection sequence Next, we will explain the power detection sequence, including measuring the temperature rise time at the user's installation site. Figure 7 shows a flowchart of the power detection sequence. Figure 8(a) shows the temperature rise curve of the thermistor Th during the power detection sequence, and Figure 8(b) shows the power duty (duty factor) corresponding to the temperature rise curve in Figure 8(a). The power duty is the proportion of time per unit time during which current is applied to the heater 42 using AC voltage from the AC power supply 80. The power duty indicates the percentage of the effective voltage (average voltage) of the voltage waveform applied to the heater 42 relative to the voltage of the AC power supply 80. When phase control is performed, the duty factor represents the proportion of time during which the triac is turned on and current is applied to the heater 42 relative to the half cycle of the voltage waveform of the AC power supply 80. When the triac is turned on / off for each half cycle of the voltage waveform of the AC power supply 80 (wave number control), the duty factor is the ratio of the number of half cycles during which the triac is on to the number of half cycles corresponding to the periodic ON / OFF pattern.

[0035] First, the controller 70 electrically connects to the memory chip 36 mounted on the surface of the heating device 40 via a contact connector 74 provided within the image forming apparatus, and reads the manufacturing temperature rise time tm stored in the memory chip 36 into the RAM 73 of the controller 70 (2001). Next, with the pressure roller 45 stopped from rotating, power W2 is applied to the heater 42 with a duty cycle of 50% (2002). When power is applied to the heater 42, the heater 42 begins to heat up. Using the thermistor Th, the CPU 71 stores in the RAM 73 the time t3 when the first temperature T1 [°C] is reached after the start of power application, and the time t4 when the second temperature T2 [°C], which is higher than the first temperature T1 [°C], is reached (2003, 2004). The supply of power to the heater 42 is stopped after the temperature of the thermistor Th reaches the second temperature T2 [°C] (2005). The control unit 70 calculates the temperature rise time td (= t4 - t3) at the time of power detection from t3 and t4 stored in RAM 73 and stores the calculated value in RAM 73. The control unit 70 calculates the temperature rise time difference Δt (= tm - td) and determines the detected power Pd by referencing the temperature rise time difference Δt with a detected power Pd table stored in ROM 72. The detected power Pd is stored in RAM 73. In this embodiment, the detected power Pd is an example of the maximum power that can be supplied to the heater 42. FIG. 9 shows an example of a detected power Pd table that shows the relationship between the maximum power Pw and the value obtained by multiplying the temperature rise time difference Δt by 100. The detected power Pd table was created by measuring the temperature rise time difference Δt in advance by varying the maximum power Pw using the central heating device 40, and then tabulating the relationship between the temperature rise time difference Δt and the maximum power Pw and storing it in ROM 72 of the control unit 70.

[0036] In this embodiment, the AC voltage is 100 [V] and the resistance value of the heater 42 is 9.22 Ω, so the maximum power Pw is 1000 [W] as described above. The power W2 supplied to the heater 42 when measuring the temperature rise time T2 at installation has a power ratio of 50%, so the power W2 at this time is set to 500 [W]. The power W1 supplied to the heater 42 when measuring the temperature rise time T1 at manufacturing is also set to 500 [W]. The temperature rise measurement first temperature T1 [°C] and second temperature T2 [°C] used to measure the temperature rise time during power detection are the same as those used during the temperature rise time at manufacturing, and are set to 45 [°C] and 65 [°C], respectively.

[0037] The power W2 input to measure the temperature rise time at installation is set to a duty ratio of 50%, so if the heater resistance is 9.22 [Ω] and the AC voltage is 100 [V], the power W2 input to measure the temperature rise time at installation will be 500 [W]. Because the input power is the same at the time of manufacture and installation, the temperature rise time at manufacture tm and the temperature rise time at power detection ts will be the same, and the temperature rise time difference Δt = 0.

[0038] Factors that affect the temperature rise time difference Δt include variations in AC voltage and changes in resistance value due to heater degradation. Variations in AC voltage cause variations in maximum power Pw, which in turn causes variations in the power W2 input to measure the temperature rise time during power detection. This results in a difference between the temperature rise time tm at the time of manufacture and the temperature rise time td during power detection, and the temperature rise time difference Δt does not become zero. Similarly, even if the AC voltage is constant, if the heater resistance changes due to durability, the temperature rise time difference Δt will not become zero. Figure 10 shows the temperature rise curves for measurements of the temperature rise time at installation when the maximum power Pw is 1000 W, 1100 W, and 900 W. In these cases, the power W2 input to measure the temperature rise time during power detection is 500 W, 550 W, and 450 W, respectively. If the heater resistance value decreases below the initial value of 9.22 Ω or if the AC power supply voltage increases above 100 V, the maximum power Pw will exceed 1000 W. For example, if the maximum power Pw is 1100 W, the power W2 measured during the temperature rise time during power detection is 550 W. In this case, the temperature rise time during power detection, td, is 0.58 s, and the temperature rise time during manufacturing, tm, is 0.66 s, so Δt (= tm - td) is 0.08 s. If the heater resistance value increases above the initial value of 9.22 Ω or if the AC power supply voltage decreases below 100 V, the maximum power Pw will fall below 1000 W. For example, if the maximum power Pw is 900 W, the power W2 measured during the temperature rise time during power detection is 450 W. In this case, the temperature rise time at the time of power detection, td, is 0.72 [s], so Δt (= tm - td) = -0.08 [s]. By referencing these Δt values ​​in the detected power Pd table, the maximum power that can be supplied to the heater 42 can be estimated.

[0039] As described above, the power detection sequence of this embodiment is characterized by comparing the temperature rise time td measured during power detection for the same fixing device (heating device) with the temperature rise time tm measured in advance at a predetermined power during the manufacturing process. The components that make up the heating device 40 have variations in their characteristics and dimensions, which affect the temperature rise time. However, comparing the same fixing devices is not affected by variations in the components, making it possible to accurately estimate the detected power Pd.

[0040] Furthermore, when the temperature rise measurement in the power detection sequence is performed while the pressure roller 45 is in operation, the influence of heat dissipation to the surrounding atmosphere due to the rotation of the pressure roller 45 becomes significant. When the thickness of the fixing film 41 is thin or the nip portion N is thick, the heat from the heater 42 is more likely to escape to the pressure roller, slowing the temperature rise of the heater 42. Therefore, if the thickness of the fixing film 41 becomes thin or the nip portion N becomes thicker due to a decrease in the hardness of the pressure roller over time, the temperature rise slows, affecting the accuracy of the power detection. In this embodiment, the temperature rise time is measured while the pressure roller 45 is stopped, i.e., in a stopped heating state. In a stopped heating state, the heat from the heater 42 is trapped in the nip portion N via the fixing film 41 and is almost unaffected by heat dissipation to the outside. Therefore, the temperature rise curve of the heater 42 is determined by the power supplied to the heater 42 and is less affected by variations in the thickness of the fixing film 41 or the thickness of the nip portion N, resulting in stable power detection accuracy over time.

[0041] To improve the accuracy of the power detection sequence, it is preferable for the temperature rise time td during power detection to fluctuate widely depending on the maximum power. To achieve this, either increase the power supply duty cycle to increase the power W2 supplied during power detection, or increase the temperature difference between the first temperature T1 (°C) and the second temperature T2 (°C) during temperature rise measurement to increase the temperature rise time td during power detection. When temperature rise measurement is performed using stop heating, only the nip N between the fixing film 41 and the pressure roller 45 rises in temperature. Increasing the power supply duty cycle increases the temperature rise in the nip N between the fixing film 41 and the pressure roller 45, resulting in a larger temperature difference with other areas. When this power detection sequence is performed when the heater is turned on at the start of printing, only the areas of the fixing film 41 and the pressure roller 45 that are stopped and heated rise in temperature. This manifests as a temperature ripple when the thermistor Th controls the heater temperature. Large temperature ripples can lead to unstable fixing temperature control or uneven heat output, resulting in uneven gloss in the image quality after fixing. Furthermore, if the temperature difference between the first temperature T1 and the second temperature T2 is wide, the power detection sequence time will be longer. If the power detection sequence is executed during printing, it will affect the FPOT (First Print Out Time), the time from the start of printing to the output of the first page. Therefore, to improve the accuracy of the power detection sequence of this embodiment without affecting image quality or FPOT, it is preferable to execute the power detection sequence at the following times: That is, it is preferable to execute the power detection sequence when the image forming apparatus is turned on or when the image forming apparatus returns from power saving mode.

[0042] In this embodiment, the detected power Pd was estimated by measuring and comparing the temperature rise time from the first temperature T1 to the second temperature T2 during the temperature rise time measurement during manufacturing and the temperature rise time measurement during power detection. However, as long as a comparison can be made between the time during manufacturing and the time during power detection, it is not necessary to measure the temperature rise time; for example, the amount of temperature rise over a certain period from the first timing to the second timing after power supply to the heater 42 is started may be compared.

[0043] <Power supply correction> Next, a method for correcting the power supply duty after determining the detected power Pd in ​​the power detection sequence will be described. The operation related to the correction of the heater supply power in this embodiment will be described using the flowchart in FIG.

[0044] When a print signal is input to the image forming apparatus, the image forming apparatus starts a heating device start-up sequence (3000). The fixing device start-up sequence (3000) is a sequence for heating the heating device 40 to a temperature suitable for the fixing operation.

[0045] In the fixing device startup sequence 3000, first, the detected power Pd determined in the power detection sequence is read from the RAM 73. Next, a reference value of the energization duty correction amount that is set in advance and stored in the ROM 72 is read. In this embodiment, the reference value of the energization duty correction amount is set to 1.00.

[0046] The control unit 70 sets a correction to this reference value according to the detected power Pd (3002). The correction according to the detected power Pd determined by the power detection sequence will be described in detail later.

[0047] Next, the control target temperature in the fixing device startup sequence is set (3003). In setting the control target temperature, the control unit 70 reads out a reference value of the control target temperature that is preset for each print mode and stored in the ROM 72. The control unit 70 determines the control target temperature in the fixing device startup sequence by correcting this reference value according to the temperature information (ambient temperature) of the installation location of the image forming apparatus. When the ambient temperature is low, the temperature of the recording material P is also low, so more heat is required to fix the unfixed toner image on the recording material P. Therefore, the control target temperature is corrected so that it becomes higher as the ambient temperature becomes lower. In this embodiment, a temperature sensor (not shown) is installed inside the image forming apparatus, and the ambient temperature is predicted based on the value of the temperature sensor.

[0048] After the setting of the control target temperature (3003) is completed, the rotation of the pressure roller 45 is started, and at the same time, power supply to the heater 42 is started (3004), and the heating device 40 starts to warm up. After that, when the temperature detected by the thermistor Th reaches the paper feed permission temperature or higher (3005), the conveyance of the first sheet of recording material 11 from the feed tray 12 is started (3006), and the fixing device start-up sequence (3000) is completed.

[0049] <Correction of heating device power duty> The maximum power Pw and temperature control will be described using FIG. 12 . In the heating device 40, power is supplied from a control unit 70 connected to an AC power source 80 to the electrodes 405 a and 405 b of the heater 42, causing the resistance heating layer 402 of the heater 42 to generate heat. The control unit 70 controls the temperature of the heater 42 by controlling the power supply to the heater 42 using a triac (not shown) provided in the control unit 70 based on information about the temperature of the heater 42 output from the thermistor Th. In the temperature control of this embodiment, a power supply duty is set based on a predetermined PI control in accordance with the difference between the current temperature output by the thermistor Th and the target temperature. The P and I values ​​in the PI control are set so that the temperature control is most stable when the maximum power Pw of the heating device 40 is 1000 W, which is the reference power P0.

[0050] Fig. 12(a) shows the temperature curve of thermistor Th without power supply duty correction when the maximum power Pw of heating device 40 is set to 1000 W, 1200 W, and 800 W by changing the voltage of AC power supply 80 using the same heating device 40. The solid line is the temperature curve when the maximum power Pw of heating device 40 is set to 1000 W. The dashed line is the temperature curve when the maximum power Pw is set to 1200 W, and the dashed-dotted line is the temperature curve when the maximum power Pw is set to 800 W. Fig. 12(b) shows the behavior of the power supply duty corresponding to the rise-up temperature curve of Fig. 12(a).

[0051] When the maximum power Pw is 1000 W, the same as the reference power P0, if the temperature difference between the target temperature and thermistor Th is large at the beginning of startup, the power duty is set to 100%. Then, as the temperature difference between the target temperature and thermistor Th becomes smaller, the power duty is reduced. This allows the temperature of thermistor Th to stabilize at the target temperature.

[0052] When the maximum power Pw is 1200 [W], PI control is optimized for the reference power P0 of 1000 [W], so controlling with the same current duty as when it was 1000 [W] causes the temperature of thermistor Th to significantly overshoot the target temperature. Once the overshoot becomes large, the current duty is reduced in an attempt to lower the temperature of thermistor Th, which then causes an undershoot of the target temperature. After that, the temperature of thermistor Th continues to repeatedly overshoot and undershoot the target temperature, gradually approaching the target temperature.

[0053] When the maximum power Pw is 800 [W], when the temperature difference between the target temperature and thermistor Th becomes small, control is performed using the current duty at the reference power P0 of 1000 [W]. Therefore, even though it is actually necessary to maintain a high current duty, the current duty is lowered. As a result, it takes a long time for thermistor Th to reach the target temperature.

[0054] In other words, because PI control is optimized for the reference power P0 of 1000 [W], if the maximum power Pw deviates, it is difficult to stabilize the temperature of the thermistor Th at the target temperature. In this embodiment, the current supply duty correction amount A is determined according to the following equation 1 so that the input power ratio is changed according to the detected power Pd determined in the power detection sequence.

[0055] (Number 1) A=P0 / Pd Here, P0 is the reference maximum power, which is 1000 [W] in this embodiment. Pd is the detected power estimated by the power detection sequence. The current duty X [%] in the reference state calculated by PI control is corrected using the correction amount A determined by Equation 1, as shown in Equation 2.

[0056] (Number 2) Energization Duty=X×A This correction of the current conduction duty selects a current conduction duty smaller than the reference 1000 [W] when the detected power Pd is large, and selects a current conduction duty larger than the reference 1000 [W] when the detected power Pd is small. The corrected current conduction duty makes the power during control the same as the reference power P0, 1000 [W], so it is possible to quickly stabilize the thermistor Th at the target temperature during start-up.

[0057] The following experiment was conducted to confirm the effects of the power detection sequence and current duty correction of this embodiment. The conditions of the experiment were: recording material conveyance speed: 222 mm / sec, printing speed (throughput): 38 ppm, recording material: RedLabel manufactured by Canon Oce, A4 paper with a paper basis weight of 80 g / m2. From Table 1, the fixing reference temperature Ta for RedLabel is 180°C.

[0058] Furthermore, it is desirable to carry out the comparative experiment in an environment where the temperature and humidity conditions are controlled to a certain level using air conditioning or the like, and in this example, the comparative experiment was carried out in an environment of temperature: 23°C and relative humidity: 50%.

[0059] As a comparative condition, the occurrence of poor fixing on the first to fifth sheets was confirmed when the heating device 40 was set at room temperature of 23° C. and continuous paper feed was performed.

[0060] Specifically, the AC voltage was varied between 100 [V], 110 [V], and 90 [V], and a power detection sequence was performed at each voltage when the power was turned on. Then, the current duty correction amount A was determined from the detected power Pd, and the fixability of the first to fifth sheets was confirmed when controlled with the corrected current duty. The results are shown in Figure 13.

[0061] As a comparative example, the fixability of the first to fifth sheets was also checked when the AC voltage was varied between 100 [V], 110 [V], and 90 [V] without executing the power detection sequence and without performing the power duty correction.

[0062] In the image forming apparatus according to this embodiment, when the AC power supply voltage was 100 V, the detected power Pd detected by the power detection sequence was 1000 W, and the power duty correction amount A was 1.00. The first five sheets of paper passed under these conditions showed no fixation problems, either due to insufficient heat or hot offset due to excessive fixation. Next, when the AC voltage was 110 V, the detected power Pd detected by the power detection sequence was 1225 W, and the power duty correction amount A was 0.82. The first five sheets of paper passed under these conditions also showed no particular fixation problems. When the AC power supply voltage was 90 V, the detected power Pd detected by the power detection sequence was 805 W, and the power duty correction amount A was 1.24. The first five sheets of paper passed under these conditions also showed no particular fixation problems. Although the maximum power Pw changes due to changes in AC voltage, the power during control is corrected to be equivalent to the reference power P0 of 1000 [W] through current duty correction, which allows the thermistor Th to quickly converge to the target temperature at start-up.

[0063] When the AC voltage of the comparative example is 100 [V], the maximum power at this time is the same as the reference power P0 of 1000 [W], resulting in the same behavior as the 100 [V] of the example. Therefore, neither poor fixing due to insufficient heat nor hot offset due to over-fixing occurred in the fixability of the first to fifth sheets. Next, at 110 [V], overshoot and undershoot occurred, similar to the rise curve for 1200 [W] in Figure 12(a), resulting in both hot offset and poor fixing on the first to fifth sheets. Furthermore, at 90 [V], the temperature of the thermistor Th continued to fall short of the target temperature, similar to the rise curve for 800 [W] in Figure 12(a), resulting in poor fixing.

[0064] As described above, by adjusting the power during control to the reference power through the power detection sequence and energization duty correction in this embodiment, the start-up curve can be stabilized, thereby preventing poor fixing and hot offset.

[0065] Next, we confirmed the durability of the detected power Pd detected by the power detection sequence in this example. In this experiment, we conducted a paper feed test of 200,000 sheets, which is the lifespan of the heating device, and compared the detected power Pd measured by the power detection sequence from the beginning of the test. We also measured the thickness of the release layer of the fixing film, nip width, and heater resistance. The results are shown in Figure 14. The thickness of the release layer of the fixing film was initially 20 μm, but became 15 μm at 100,000 sheets and 11 μm at 200,000 sheets, indicating gradual wear with paper feed durability. The nip width was initially 9.0 mm, but became 9.4 mm at 100,000 sheets and 9.6 mm at 200,000 sheets. The pressure roller hardness decreased with paper feed durability, and the nip width gradually widened. The heater resistance was initially 9.1 Ω, but due to power degradation, it became 9.23 Ω at 100,000 sheets and 9.35 Ω at 200,000 sheets. Furthermore, because the AC voltage was 100 V throughout the test, the maximum power Pw was initially 1013 W, but dropped to 998 W at 100,000 sheets and 986 W at 200,000 sheets. The detected power Pd by the power detection sequence was initially 1015 W, but dropped to 1000 W at 100,000 sheets and 985 W at 200,000 sheets, almost identical to the maximum power Pw. This is because the power detection sequence in this example is performed in a stopped heating state, and is therefore less affected by changes in the release layer thickness of the fixing film 41 or the nip width, and is determined by the maximum power supplied to the heater. Furthermore, the resistance of the heater increased due to degradation of electrical conductivity over time, and the power detection sequence was also able to detect the decrease in maximum power.

[0066] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0067] Summary of the Disclosure The present disclosure includes at least the following configurations.

[0068] (Item 1) an image forming means for forming an image on a recording material; a fixing device including a rotating fixing member, a heating member that heats the fixing member when energized, a temperature detection unit that detects the temperature of the heating member, and a pressure roller that is disposed opposite the heating member across the fixing member and forms a nip portion with the fixing member, and fixes the image to the recording material with the fixing member; An image forming apparatus comprising: a control means for controlling a power supply rate, which is a ratio of time during which power is supplied to the heating member per unit time, so that the temperature detected by the temperature detection unit becomes a target temperature; a storage unit that stores information about a temperature rise time of the temperature detection unit; and The control means measures the temperature rise time of the temperature detection unit by passing electricity through the heating element at a predetermined current conduction rate while stopping the rotation of the pressure roller, estimates the power that can be supplied to the heating element by comparing the measured temperature rise time information with the information stored in the memory unit, and corrects the current conduction rate based on the estimated power.

[0069] (Item 2) The image forming apparatus described in item 1, characterized in that the information regarding the temperature rise time stored in the memory unit is information indicating the time elapsed from when the temperature detection unit detected a first temperature at the time of manufacturing the fixing device until when it detected a second temperature higher than the first temperature.

[0070] (Item 3) 3. The image forming apparatus according to claim 1, wherein the control unit measures the time elapsed from when the temperature detection unit detects a first temperature until when the temperature detection unit detects a second temperature higher than the first temperature.

[0071] (Item 4) 4. The image forming apparatus according to any one of items 1 to 3, wherein the storage unit is a memory chip arranged on a part of a surface of the fixing device.

[0072] (Item 5) The image forming apparatus described in any one of items 1 to 4, characterized in that the control means measures the temperature rise time when the image forming apparatus is turned on or when it returns from a power saving mode.

[0073] (Item 6) The image forming apparatus according to any one of items 1 to 5, characterized in that when controlling the power supplied to the heating element so that the temperature detected by the temperature detection unit becomes the target temperature, the control unit uses a power rate obtained by multiplying the power rate by a value obtained by dividing the reference maximum power by the estimated maximum power.

[0074] (Item 7) the fixing member is a cylindrical film, the heating member has a resistance heating element that generates heat when electricity is applied, and is disposed in the internal space of the film; the pressure member is a pressure roller that forms the nip portion between itself and the film, The image forming apparatus described in any one of items 1 to 6, characterized in that the fixing device heats the image by the film heated by heat conduction from the heating member while sandwiching and transporting the recording material in the nip portion.

[0075] (Item 8) an image forming means for forming an image on a recording material; a fixing device including a rotating fixing member, a heating member that heats the fixing member when energized, a temperature detection unit that detects the temperature of the heating member, and a pressure roller that is disposed opposite the heating member across the fixing member and forms a nip portion with the fixing member, and fixes the image to the recording material with the fixing member; An image forming apparatus comprising: a control means for controlling a power supply rate, which is a ratio of time during which power is supplied to the heating member per unit time, so that the temperature detected by the temperature detection unit becomes a target temperature; a storage unit that stores information about the temperature rise amount of the temperature detection unit; and The control means measures the temperature rise of the temperature detection unit by passing electricity through the heating element at a predetermined current rate while stopping the rotation of the pressure roller, estimates the power that can be supplied to the heating element by comparing the measured temperature rise information with the information stored in the memory unit, and corrects the current rate based on the estimated power.

[0076] (Item 9) Item 9. The image forming apparatus according to item 8, wherein the information regarding the temperature rise amount stored in the memory unit is information indicating the temperature rise amount in the temperature detection unit from when power is first applied to the heating member to a predetermined timing at the time of manufacturing the fixing device.

[0077] (Item 10) 10. The image forming apparatus according to item 8 or 9, wherein the control unit measures the amount of temperature rise in the temperature detection unit from when power is started to be supplied to the heating member until a predetermined timing.

[0078] (Item 11) 11. The image forming apparatus according to any one of items 8 to 10, wherein the storage unit is a memory chip arranged on a part of the surface of the fixing device.

[0079] (Item 12) Item 9. The image forming apparatus according to item 8, wherein the control unit measures the temperature rise time when the image forming apparatus is turned on or when the image forming apparatus returns from a power saving mode.

[0080] (Item 13) The image forming apparatus according to any one of items 8 to 12, characterized in that when controlling the power supplied to the heating element so that the temperature detected by the temperature detection unit becomes the target temperature, the control unit uses a power rate obtained by multiplying the power rate by a value obtained by dividing the reference maximum power by the estimated maximum power.

[0081] (Item 14) the fixing member is a cylindrical film, the heating member has a resistance heating element that generates heat when electricity is applied, and is disposed in the internal space of the film; the pressure member is a pressure roller that forms the nip portion between itself and the film, The image forming apparatus described in any one of items 8 to 13, characterized in that the fixing device heats the image by the film heated by heat conduction from the heating member while sandwiching and transporting the recording material in the nip portion. [Explanation of symbols]

[0082] 12 Paper tray 13 Paper feed roller 14 Registration roller pair 15. Cash register sensor 20 Image forming unit 22 Photosensitive drum 23 Charger 24 Scanner unit 25 Toner container 26 Developing sleeve (developing means) 34 Transfer roller 36 memory chips 40 Heating device (fixing device) 41 Fixing film 42 heater (heating element) 45 Pressure roller (pressure member) 50 Temperature rise measurement device 51 memory 53 Electrical Contacts 70 Control unit (control means) 71 CPU 72 ROM 73 RAM 401 Substrate 402 Resistive heating layer 403 Protective Glass Layer 405 Electrode section Th Thermistor (temperature detection part)

Claims

1. an image forming means for forming an image on a recording material; a fixing device including a rotating fixing member, a heating member that heats the fixing member when energized, a temperature detection unit that detects the temperature of the heating member, and a pressure roller that is disposed opposite the heating member across the fixing member and forms a nip portion with the fixing member, and fixes the image to the recording material with the fixing member; An image forming apparatus comprising: a control means for controlling a power supply rate, which is a ratio of time during which power is supplied to the heating member per unit time, so that the temperature detected by the temperature detection unit becomes a target temperature; a storage unit that stores information about a temperature rise time of the temperature detection unit; and The control means measures the temperature rise time of the temperature detection unit by passing electricity through the heating element at a predetermined current conduction rate while stopping the rotation of the pressure roller, estimates the power that can be supplied to the heating element by comparing the measured temperature rise time information with the information stored in the memory unit, and corrects the current conduction rate based on the estimated power.

2. 2. The image forming apparatus according to claim 1, wherein the information regarding the temperature rise time stored in the memory unit is information indicating the time elapsed from when the temperature detection unit detected a first temperature at the time of manufacturing the fixing device until when the temperature detection unit detected a second temperature higher than the first temperature.

3. 2. The image forming apparatus according to claim 1, wherein the control unit measures the time elapsed from when the temperature detection unit detects a first temperature until when the temperature detection unit detects a second temperature higher than the first temperature.

4. 2. The image forming apparatus according to claim 1, wherein the storage unit is a memory chip disposed on a part of a surface of the fixing device.

5. 2. The image forming apparatus according to claim 1, wherein the control unit measures the temperature rise time when the image forming apparatus is powered on or when the image forming apparatus returns from a power saving mode.

6. 2. The image forming apparatus according to claim 1, wherein the control means uses a power conduction rate obtained by multiplying the power conduction rate by a value obtained by dividing a reference maximum power by the estimated maximum power when controlling the power supplied to the heating element so that the temperature detected by the temperature detection unit becomes the target temperature.

7. the fixing member is a cylindrical film, the heating member has a resistance heating element that generates heat when electricity is applied, and is disposed in the internal space of the film; the pressure member is a pressure roller that forms the nip portion between itself and the film, 2. The image forming apparatus according to claim 1, wherein the fixing device heats the image by the film heated by heat conduction from the heating member while nipping and conveying the recording material at the nip portion.

8. an image forming means for forming an image on a recording material; a fixing device including a rotating fixing member, a heating member that heats the fixing member when energized, a temperature detection unit that detects the temperature of the heating member, and a pressure roller that is disposed opposite the heating member across the fixing member and forms a nip portion with the fixing member, and fixes the image to the recording material with the fixing member; An image forming apparatus comprising: a control means for controlling a power supply rate, which is a ratio of time during which power is supplied to the heating member per unit time, so that the temperature detected by the temperature detection unit becomes a target temperature; a storage unit that stores information about the temperature rise amount of the temperature detection unit; and The control means measures the temperature rise of the temperature detection unit by passing electricity through the heating element at a predetermined current rate while stopping the rotation of the pressure roller, estimates the power that can be supplied to the heating element by comparing the measured temperature rise information with the information stored in the memory unit, and corrects the current rate based on the estimated power.

9. 9. The image forming apparatus according to claim 8, wherein the information regarding the temperature rise amount stored in the memory unit is information indicating the temperature rise amount in the temperature detection unit from when power is first applied to the heating member to a predetermined timing at the time of manufacturing the fixing device.

10. 9. The image forming apparatus according to claim 8, wherein the control unit measures the amount of temperature rise in the temperature detection unit from when the power supply to the heating member starts until a predetermined timing.

11. 9. The image forming apparatus according to claim 8, wherein the storage unit is a memory chip disposed on a part of a surface of the fixing device.

12. 9. The image forming apparatus according to claim 8, wherein the control unit measures the temperature rise time when the image forming apparatus is turned on or when the image forming apparatus returns from a power saving mode.

13. 9. The image forming apparatus according to claim 8, wherein the control unit uses a power conduction rate obtained by multiplying the power conduction rate by a value obtained by dividing a reference maximum power by the estimated maximum power when controlling the power supplied to the heating element so that the temperature detected by the temperature detection unit becomes the target temperature.

14. the fixing member is a cylindrical film, the heating member has a resistance heating element that generates heat when electricity is applied, and is disposed in the internal space of the film; the pressure member is a pressure roller that forms the nip portion between itself and the film, 9. The image forming apparatus according to claim 8, wherein the fixing device heats the image by the film heated by heat conduction from the heating member while nipping and conveying the recording material at the nip portion.

Images