Image forming apparatus

Abstract

To achieve both fixability of a toner image and the productivity of an image forming apparatus.SOLUTION: An image forming apparatus has image forming means that forms a toner image, fixing means, and detection means that detects temperature. The image forming apparatus determines a temperature parameter from a first temperature detected by the detection means and a second temperature detected by the detection means after the first temperature is detected. The temperature parameter is, for example, the gradient of temperature or the difference in temperature. The image forming apparatus controls the timing for feeding means to feed a sheet or the timing for the image forming means to form an image on the basis of a result of determination as to whether the temperature parameter exceeds a threshold.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Fixing a toner image onto a sheet requires precise control of the temperature of the heating device to a target temperature. The time required for the temperature of the heating device to reach the target temperature varies depending on the voltage supplied from the commercial AC power source. Patent Document 1 proposes detecting the temperature gradient to estimate the change in power supplied to the fixing device due to a change in power supply voltage, thereby reducing temperature overshoot. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-333944 Summary of the Invention [Problem to be solved by the invention]

[0004] To improve the productivity of an image forming apparatus, it is effective to start sheet transport or toner image formation before the temperature of the heating device reaches a target temperature. However, if a sheet arrives at the heating device when the temperature is lower than the target temperature, poor toner image fixation occurs. Therefore, determining the timing to start sheet feed based on the temperature gradient would improve the productivity of the image forming apparatus. However, because the temperature gradient changes depending on the initial temperature of the temperature sensor, there is room for improvement in the accuracy of determining the start timing based on the temperature gradient. Therefore, an object of the present invention is to achieve both toner image fixability and the productivity of the image forming apparatus. [Means for solving the problem]

[0005] The present invention is, for example, a feeding means for feeding a sheet; an image forming means for forming an image on the sheet; A fixing means for fixing the image to the sheet, A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a fixing unit having a heat generating unit for heating at least one of the first rotating body and the second rotating body; a detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a control means for determining a temperature parameter, which is a gradient or a temperature difference, from a first temperature detected by the detection means and a second temperature detected by the detection means after the first temperature is detected, and for controlling a timing for feeding the sheet by the feeding means or a timing for forming the image by the image forming means based on a result of determining whether the temperature parameter is a threshold value; The image forming apparatus is provided, wherein the threshold value is determined in response to the first temperature. [Effects of the Invention]

[0006] According to the present invention, it is possible to achieve both the fixability of the toner image and the productivity of the image forming apparatus. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating an image forming apparatus. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 4 is a diagram illustrating the relationship between the initial temperature and the temperature difference. [Figure 5] FIG. [Figure 6] 10 is a flowchart showing a control method. [Figure 7] FIG. 10 is a diagram illustrating a temperature transition according to a combination of heat capacity and voltage. [Figure 8] 10A and 10B are diagrams illustrating a method for correcting a threshold value or a mathematical expression. [Figure 9] FIG. [Figure 10] 10 is a flowchart showing a control method. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0009] Example 1 (1) Structure of the image forming device As shown in FIG. 1, the image forming apparatus 1 is a printer that uses electrophotographic recording technology. A sheet cassette 11 is a storage container that stores a plurality of sheets P. The sheets P may also be called recording paper, recording materials, or transfer materials. A pickup roller 12 sends out sheets S from the sheet cassette 11 one by one to a conveyance path. A feed roller 13 is a conveyance roller that is disposed downstream of the pickup roller 12 in the conveyance direction of the sheets P. A registration roller 15 is a conveyance roller that corrects skew of the sheets P and adjusts the timing of conveyance further downstream.

[0010] The process cartridge 20 is an image forming unit that forms a toner image and transfers it to a sheet P. The process cartridge 20 has a charger 16, a developing roller 17, and a photosensitive drum 19. The charger 16 is a charging roller or charging wire that charges the surface of the photosensitive drum 19. The exposure device 22 is an exposure light source that irradiates the surface of the photosensitive drum 19 with laser light to form an electrostatic latent image. The developing roller 17 develops the electrostatic latent image using toner contained in a toner container to form a toner image. The photosensitive drum 19 rotates to transport the toner image to the transfer nip. The transfer nip is formed when the photosensitive drum 19 and a transfer roller 21 come into contact with each other. The toner image is transferred from the photosensitive drum 19 to the sheet P as the sheet P passes through the transfer nip.

[0011] The exposure device 22 has a laser diode 23, a polygon mirror 24, and a reflecting mirror 25. The laser diode 23 is a light source that outputs laser light corresponding to an image signal. The laser diode 23 may be a light-emitting diode. The polygon mirror 24 rotates to scan the laser light over the surface of the photosensitive drum 19. The reflecting mirror 25 is an optical component that further guides the light from the polygon mirror 24 to the surface of the photosensitive drum 19.

[0012] The photosensitive drum 19 and transfer roller 21 rotate to transport the sheet P further downstream. A heating device (fixer 27) is disposed downstream of the transfer nip. The fixer 27 applies heat and pressure to the sheet P and the toner image, thereby fixing the toner image onto the sheet P.

[0013] Conveying rollers 29 disposed downstream of the fixing unit 27 convey the sheet P to discharge rollers 31. The discharge rollers 31 convey the sheet P and discharge the sheet P onto a discharge tray 32 provided on the top surface of the image forming apparatus 1.

[0014] Motor 33 provides driving force to multiple rotating bodies such as pickup roller 12, fuser 27, and photosensitive drum 19. Power supply 34 has a power supply circuit that converts voltage supplied from AC power supply 10 into DC voltage for image forming apparatus 1. AC power supply 10 is, for example, a commercial AC power supply. Controller 35 operates by receiving power from power supply 34 and controls each part of image forming apparatus 1 (e.g., motor 33, exposure unit 22, fuser 27). Although only one motor 33 is shown here, multiple motors may be used. Also, an actuator such as a solenoid may be used to lower pickup roller 12 to contact sheet P.

[0015] The fixing unit 27 may have a non-volatile memory 99. The non-volatile memory 99 may store individual information for each product obtained during the manufacturing process of the fixing unit 27. As will be described in a second embodiment, the individual information may be information regarding the heat capacity of the fixing unit 27, for example.

[0016] (2) Structure of the fixing unit As shown in FIG. 2, the fixing unit 27 includes a fixing film 50, a pressure roller 51, a heater 52, a heater holder 53, a pressure stay 54, and a temperature sensor (hereinafter referred to as a thermistor 55). The fixing film 50 is a flexible, cylindrical (endless) film-like member. Reducing the thermal capacity of the fixing film 50 is advantageous for shortening the FPOT. To achieve this, the thickness of the fixing film 50 is made thin. The pressure roller 51 is a pressure member that rotates in contact with the fixing film 50. The pressure roller 51 is disposed opposite the heater 52 across the fixing film 50. The heater 52 is a heating member (heat generating element) that heats the fixing film 50. The heater 52 is a plate-shaped heat generating member that contacts the inner circumferential surface of the fixing film 50 and rapidly heats the fixing film 50. The heater 52 is a heater having an insulating ceramic substrate made of, for example, alumina or aluminum nitride. The heater 52 may be a halogen heater or an induction heater. The temperature of the heater 52 is detected by a thermistor 55 in contact with the back surface of the ceramic substrate. The thermistor 55 may be disposed adjacent to any of the fixing film 50, the pressure roller 51, or the heater 52. In this embodiment, a contact-type thermistor is used as the thermistor 55. A non-contact-type thermistor may also be used as the thermistor 55. The heater holder 53 is disposed in the internal space of the fixing film 50 and holds the heater 52. The pressure stay 54 is made of a rigid member such as metal. The pressure stay 54 receives pressure from a pressure member such as a spring (not shown). As a result, the pressure stay 54 applies pressure to the pressure roller 51 via the heater holder 53. The pressure roller 51 is driven to rotate by the motor 33 in the direction indicated by arrow R1 (clockwise). The fixing film 50 rotates in conjunction with the pressure roller 51. As a result, the sheet P is conveyed in the direction of the arrow. The portion where the heater 52 and the pressure roller 51 contact each other is called a nip portion N.

[0017] (3) Temperature transition FIG. 3 shows the temperature transition (hereinafter referred to as the start-up temperature curve) detected by the thermistor 55 when the AC voltage supplied from the AC power supply 10 is AC 100V. The vertical axis represents the temperature difference ΔT. The horizontal axis represents time. The temperature difference ΔT is the difference between the initial temperature and the temperature at a second timing a predetermined time after the first timing at which the initial temperature was measured. The temperature difference ΔT is a temperature parameter that indicates the rate of temperature rise or the rate of temperature rise over a predetermined time.

[0018] For example, the time from time t1 to time t3 and the time from time t2 to time t4 are each 2.0 seconds. Two cases are assumed in which the initial temperature of thermistor 55 is 25°C and another case is where the initial temperature is 40°C.

[0019] When the initial temperature detected by thermistor 55 is 25°C (time t1), power supply to heater 52 begins. Thereafter, the temperature T detected by thermistor 55 rises. At time t3, the temperature T detected by thermistor 55 becomes 95°C. The temperature difference ΔT1 at this time is the difference between the detected temperature T at time t3 and the detected temperature T at time t1 (ΔT1 = 95°C - 25°C = 70°C).

[0020] In the case where power supply to the heater 52 begins when the initial temperature of the thermistor 55 is 40°C (time t2), the temperature T detected by the thermistor 55 becomes 100°C at time t4. The temperature difference ΔT2 is 60°C. In this embodiment, the thermistor 55 is an NTC type with a negative temperature coefficient. Generally, when power is supplied to the heater 52, the heater 52 itself generates heat and also radiates heat. When a constant amount of power is supplied to the heater 52, a constant amount of heat is generated. On the other hand, the higher the temperature, the greater the amount of heat radiated. Therefore, the temperature transition follows a curve.

[0021] FIG. 4 is a graph showing the initial temperature of the thermistor 55 and the temperature difference ΔT. The vertical axis represents the temperature difference ΔT. The horizontal axis represents the initial temperature. As described above, the temperature difference ΔT represents the temperature difference over a certain period of time (2.0 seconds). Open circles and open triangles indicate locations where no image defects occurred (OK). Black circles and black triangles indicate locations where image defects occurred (NG).

[0022] Generally, the cause of image defects is that the temperature of the nip portion N in the fixing device 27 does not reach a temperature suitable for the fixation of the sheet P. In other words, image defects occur when the power required for the fixation of the sheet P is not supplied.

[0023] In this embodiment, it is assumed that the initial temperature IT1 of the thermistor 55 is 25° C. and the initial temperature IT2 is 40° C. The voltage of the AC power supply 10 is AC 100V.

[0024] When the supply of power to heater 52 started when the initial temperature of thermistor 55 was 25°C, the temperature difference ΔT was 70°C (white circle). When the supply of power to heater 52 started when the initial temperature of thermistor 55 was 40°C, the temperature difference ΔT was 60°C (white triangle).

[0025] On the other hand, when the voltage of AC power supply 10 was set to AC85V and the initial temperature of thermistor 55 was 25°C, the temperature difference ΔT was 55°C (black circle).When the initial temperature of thermistor 55 was 40°C, the temperature difference ΔT was 45°C (black triangle).

[0026] 4, Δth is a threshold value for determining whether or not an image defect has occurred. In other words, Δth can be used as a threshold value for determining whether or not the fixing device 27 is ready for fixing. Δth may be calculated, for example, from the following equation:

[0027] Δth=c1×IT+c2 (1) Here, IT is the initial temperature. c1 and c2 are coefficients that depend on the structure of the fixing unit 27, etc. For example, c1 is -0.67, and c2 is 85. Thus, equation (1) is an example of a mathematical formula in which the temperature is the input value and the threshold value is the output value.

[0028] 4 corresponds to formula (1). By using formula (1), the threshold value Δth according to the initial temperature IT is determined in the case where the voltage of the AC power supply 10 is AC 100V.

[0029] (4) Controller FIG. 5 shows functions implemented in the controller 35 that controls the timing of sheet feeding or the timing of image formation. The CPU 501 is a processor that realizes various functions by executing a control program 523 stored in the memory 502. One or more of the functions may be realized by an integrated circuit (IC) separate from the CPU 501. The memory 502 is a storage device that includes a non-volatile memory (ROM area) and a volatile memory (RAM area). The non-volatile memory 99 may be part of the memory 502.

[0030] The acquiring unit 512 acquires the temperature T (e.g., the initial temperature IT) of the heater 52 based on the detection signal output from the thermistor 55. The determining unit 514 determines the threshold value Δth corresponding to the initial temperature IT by referring to an arithmetic expression 521 or an arithmetic table 522 based on the initial temperature IT. The arithmetic expression 521 is, for example, Equation (1). The arithmetic table 522 stores threshold values ​​Δth determined in advance for each of a plurality of initial temperatures. In other words, a plurality of initial temperatures correspond one-to-one to a plurality of threshold values ​​Δth. The acquiring unit 512 may read out Δth corresponding to the initial temperature IT acquired by the thermistor 55 from the arithmetic table 522. The non-volatile memory 99 may store the arithmetic expression 521 or the arithmetic table 522. The arithmetic expression 521 or the arithmetic table 522 may be part of the control program 523. In this way, the arithmetic table 522 may hold a plurality of pairs of the initial temperature IT and the threshold value Δth.

[0031] The timer 511 is used to determine a second timing when a predetermined time (e.g., 2.0 seconds) has elapsed since the first timing when the initial temperature IT was acquired. The acquisition unit 512 acquires the temperature T based on the timer 511 and outputs it to the calculation unit 513. The calculation unit 513 calculates a temperature difference ΔT based on the temperature T and the initial temperature IT. The determination unit 515 determines whether the temperature difference ΔT exceeds a threshold value Δth. The determination unit 515 may also determine whether the temperature difference ΔT is equal to or greater than the threshold value Δth. In this specification, the determination of whether a certain value exceeds a threshold value may be replaced with the determination of whether a certain value is equal to or greater than the threshold value. Furthermore, the determination of whether a certain value is less than a threshold value may be replaced with the determination of whether a certain value is equal to or less than the threshold value. If the temperature difference ΔT exceeds the threshold value Δth, the fixing device 27 is ready (fixing ready state). Here, being ready for the fixing device 27 means that the temperature T of the heater 52 will have reached the target temperature Ttg by the time the sheet P arrives at the fixing device 27. Therefore, when the feeding of the sheet P starts, the temperature T of the heater 52 does not have to reach the target temperature Ttg.

[0032] The conveyance control unit 516 activates the motor 33 in accordance with the determination result of the determination unit 515 to start feeding the sheet P. For example, if the temperature difference ΔT exceeds the threshold value Δth, the conveyance control unit 516 immediately starts feeding the sheet P. If the temperature difference ΔT does not exceed the threshold value Δth, the conveyance control unit 516 waits until the temperature T becomes equal to or higher than the target temperature Ttg, and then starts feeding the sheet P. In this way, the conveyance control unit 516 may start feeding the sheet P after waiting until the detected temperature T becomes equal to or higher than a predetermined value.

[0033] The exposure control unit 517 starts the output of laser light by the exposing unit 22 in accordance with the determination result of the determining unit 515. For example, if the temperature difference ΔT exceeds the threshold value Δth, the exposure control unit 517 immediately causes the exposing unit 22 to start outputting laser light. If the temperature difference ΔT does not exceed the threshold value Δth, the exposure control unit 517 waits until the temperature T becomes equal to or higher than the target temperature Ttg, and then causes the exposing unit 22 to start outputting laser light. In this way, the exposure control unit 517 may start forming an image after waiting until the detected temperature T becomes equal to or higher than a predetermined value.

[0034] The heater control unit 518 controls the power supplied from the AC power supply 10 to the heater 52. For example, the heater control unit 518 turns on / off the triac 519 so that the temperature T becomes the target temperature Ttg. The triac 519 is a semiconductor switch element that can switch between supplying and cutting off the AC voltage.

[0035] (6) Flowchart 6 is a flowchart showing the control method of embodiment 1. The CPU 501 executes the following processes according to the control program 523.

[0036] In S601, the CPU 501 (acquisition unit 512) acquires the initial temperature IT of the heater 52 using the thermistor 55. The initial temperature IT may be stored in the RAM area of ​​the memory 502.

[0037] In S602, the CPU 501 (determining unit 514) determines the threshold value Δth based on the initial temperature IT. For example, the determining unit 514 determines the threshold value Δth according to the initial temperature IT using the arithmetic expression 521 or the arithmetic table 522.

[0038] In S603, the CPU 501 (heater control unit 518) starts supplying power to the heater 52. The heater control unit 518 turns on the triac 519 (to a conductive state).

[0039] In S604, the CPU 501 starts the timer 511. In S605, the CPU 501 determines whether a predetermined time has elapsed since the initial temperature IT was measured, based on the time value of the timer 511. If the predetermined time has elapsed, the CPU 501 advances the process from S605 to S606.

[0040] In S606, the CPU 501 (acquisition unit 512) acquires the temperature T from the thermistor 55. The temperature T may also be temporarily stored in the memory 502.

[0041] In S607, the CPU 501 (calculation unit 513) calculates the temperature difference ΔT based on the temperature T and the initial temperature IT. In S608, the CPU 501 (determination unit 515) determines whether the temperature difference ΔT exceeds the threshold value Δth. If the temperature difference ΔT exceeds the threshold value Δth, the CPU 501 advances the process from S608 to S609. In S609, the CPU 501 (conveyance control unit 516) starts feeding the sheet P by rotating the pickup roller 12 using the motor 33. Note that the conveyance control unit 516 may start feeding the sheet P by lowering the already rotating pickup roller 12 using a solenoid (not shown). If it is determined in S608 that the temperature difference ΔT does not exceed the threshold value Δth, the CPU 501 advances the process from S608 to S610.

[0042] In S610, the CPU 501 (acquisition unit 512) acquires the temperature T from the thermistor 55. In S611, the CPU 501 (determination unit 515) determines whether the temperature T is equal to or higher than the target temperature Ttg. If the temperature T is equal to or higher than the target temperature Ttg, the CPU 501 advances the process from S611 to S609. In S609, the CPU 501 (conveyance control unit 516) rotates the pickup roller 12 using the motor 33 to start feeding the sheet P.

[0043] According to the first embodiment, by determining the threshold value Δth based on the initial temperature IT, it is possible to achieve both the fixability of the toner image on the sheet P and the productivity of the image forming apparatus 1. In FIG. 6, the feeding timing of the sheet P is controlled by the temperature T, but this is merely an example. There are also image forming apparatuses 1 in which the exposure start timing of the exposing device 22 is earlier than the feeding start timing of the sheet P. In this case, exposure starts in S609, and feeding starts thereafter.

[0044] The temperature difference ΔT depends on the initial temperature IT and the level of the AC voltage supplied from the AC power source 10 (the power supply capacity of the AC power source 10). There are regions where the supply capacity of the AC power source 10 is not necessarily constant. In an image forming apparatus 1 installed in such a region, the power supply capacity of the AC power source 10 can be estimated from the temperature transition of the thermistor 55. In other words, the power supply capacity of the AC power source 10 can be estimated without detecting the voltage of the AC power source 10. If the AC power source 10 has sufficient power supply capacity, the feeding of the sheet P can be started early. If the AC power source 10 does not have sufficient power supply capacity, the start of feeding of the sheet P is delayed to ensure sufficient fixation. In this way, the temperature difference ΔT may be understood as a temperature parameter indicating the power supply capacity of the AC power source 10.

[0045] <Example 2> The second embodiment relates to a method for determining the threshold value Δth in consideration of individual product differences (product variations) of the fixing unit 27. In the second embodiment, the description of the first embodiment is cited for the explanation of matters common to the first embodiment.

[0046] FIG. 7 shows the temperature transition of the fixing device 27 depending on the voltage difference of the AC power supply 10 and the heat capacity difference. The vertical axis represents temperature, and the horizontal axis represents time. The area of ​​the nip portion N varies depending on the variations in the hardness and thickness of the pressure roller 51. Furthermore, the heat capacity of the fixing device 27 varies depending on the area of ​​the nip portion N. Therefore, the individual differences in the fixing device 27 result in variations in the heat capacity.

[0047] The time from time t1 to time t2 is, for example, 2.0 seconds. The initial temperature IT of thermistor 55 is assumed to be 25°C.

[0048] L1 indicates a case where the voltage of the AC power supply 10 is AC 100V and the heat capacity of the fuser 27 is HC1. L2 indicates a case where the voltage of the AC power supply 10 is AC 90V and the heat capacity of the fuser 27 is HC1. L3 indicates a case where the voltage of the AC power supply 10 is AC 100V and the heat capacity of the fuser 27 is HC2. HC2 is larger than HC1. L4 indicates a case where the voltage of the AC power supply 10 is AC 90V and the heat capacity of the fuser 27 is HC2. The larger the heat capacity of an object, the more difficult it is for the temperature of that object to increase.

[0049] As shown by L1, 2.0 seconds after a voltage of 100 V AC was applied to heater 52, the temperature T detected by thermistor 55 reached 95°C. As shown by L2, 2.0 seconds after a voltage of 90 V AC was applied to heater 52, the temperature T detected by thermistor 55 reached 89°C. Thus, for a given thermal capacity, the higher the voltage of AC power supply 10, i.e., the more power it supplies, the faster temperature T can reach the specified temperature.

[0050] As shown by L3, 2.0 seconds after a voltage of 100 V AC was applied to heater 52, the temperature T detected by thermistor 55 reached 86°C. As shown by L4, 2.0 seconds after a voltage of 90 V AC was applied to heater 52, the temperature T detected by thermistor 55 reached 80°C. Thus, for a given thermal capacity, the higher the voltage of AC power supply 10, i.e., the more power it supplies, the faster temperature T can reach the predetermined temperature.

[0051] Comparing L1 and L3, if the power is the same, the smaller the heat capacity, the faster the temperature T can rise. Comparing L2 and L4 suggests the same phenomenon.

[0052] Comparing L2 and L3, L2 reaches the predetermined temperature before L3. In other words, the contribution of heat capacity to the gradient of temperature T can exceed the contribution of voltage to the gradient of temperature T. In a product group of fixing units 27 with large variations in heat capacity, the variations in heat capacity have a significant impact on the determination of the start of feeding. Therefore, if the threshold value Δth is determined taking heat capacity into consideration, the accuracy of the determination of the start of feeding will be improved. As described above, the determination of the start of feeding is a concept that can be substituted for the determination of the start of exposure.

[0053] Therefore, in the second embodiment, in order to distinguish between L2 and L3, data for correcting the variation in heat capacity for each product is acquired in the inspection process of the fixing unit 27 and stored in the nonvolatile memory 99. The CPU 501 reads the data from the nonvolatile memory 99 and corrects the formula (1) for calculating the threshold value Δth.

[0054] (1) Acquisition of individual information (correction data) The fixing unit 27 is mass-produced in a factory. In the inspection process of the fixing unit 27, the fixing unit 27 is set in an inspection device and an AC voltage is supplied from an AC power supply (not shown) external to the fixing unit 27. The AC voltage supplied to the fixing unit 27 is, for example, AC 100 V (reference voltage). The reference voltage is usually the nominal voltage of the commercial AC power supply in the destination country of the fixing unit 27.

[0055] When the initial temperature IT of the thermistor 55 is 25°C, power supply to the fixing unit 27 begins. 2.0 seconds after the start of power supply, the temperature T is acquired by the thermistor 55. The individual temperature difference ΔTF is calculated as the difference between the temperature T and the initial temperature IT. The individual temperature difference ΔTF is written to the non-volatile memory 99 by the ROM writer.

[0056] (2) Correction method FIG. 8 shows the relationship between the initial temperature IT and the temperature difference ΔT. Δth1 indicates a threshold value obtained by supplying a reference voltage (e.g., AC 100V) to a standard unit (fixing unit 27). The standard unit may also be called a reference fixing means. The standard unit temperature difference (reference information) is denoted as ΔTB. As described above, the threshold value Δth is calculated from equation (1). In FIG. 8, the coefficient c1 of Δth1 is -0.67. The coefficient c2 is 85. All numerical values ​​appearing in this specification are merely examples.

[0057] Δth2 indicates a threshold value obtained by supplying a reference voltage (e.g., AC 100 V) to the fixing unit 27 having an individual temperature difference of ΔTF. According to the example shown in Fig. 8, the heat capacity of the fixing unit 27 corresponding to Δth2 is larger than the heat capacity of the fixing unit 27 corresponding to Δth1.

[0058] The temperature difference ΔT of the fixing unit 27 corresponding to Δth2 is lower by ΔX than the temperature difference ΔT of the fixing unit 27 corresponding to Δth1. ΔX is also the difference between ΔTB and ΔTF. Therefore, correcting equation (1) by ΔX reduces the influence of individual differences depending on differences in heat capacity on the threshold value Δth.

[0059] Δth=c1×IT+c2+ΔX (2) In this example, ΔTF is 61°C and ΔTB is 68°C. Therefore, ΔX is -7°C. The CPU 501 can obtain Δth2 by adding -7 to Δth1. This is equivalent to correcting the addition coefficient c2 in equation (1) with ΔX to obtain equation (2).

[0060] (3) Controller 35 9 shows the controller 35 of the second embodiment. The correction unit 901 of the CPU 501 reads ΔTF and ΔTB from the nonvolatile memory 99 to determine the correction value ΔX. Note that the nonvolatile memory 99 may store a correction value ΔX that has been determined in advance. The correction unit 901 corrects the calculation formula 521 (formula (1)) with the correction value ΔX to determine formula (2), and passes formula (2) to the determination unit 514. Alternatively, the correction unit 901 may correct Δth1 obtained from the calculation table 522 based on the initial temperature IT with the correction value ΔX to determine Δth2, and pass Δth2 to the determination unit 514.

[0061] (4) Flowchart 10 shows a control method of the embodiment 2. The CPU 501 executes the following processes in accordance with the control program 523 stored in the memory 502.

[0062] In step S1001 , the CPU 501 (correction unit 901 ) acquires individual information (correction data ΔX) from the nonvolatile memory 99 of the fixing unit 27 .

[0063] In S1002, the CPU 501 (correction unit 901) corrects the arithmetic expression 521 (expression (1)) for determining the threshold value Δth. As a result, expression (1) is corrected to expression (2). Thereafter, the CPU 501 executes S601 to S611. However, in S602, Δth is determined using expression (2). Note that S1001 and S1002 may be executed within S602.

[0064] The second embodiment can achieve the same effects as the first embodiment. Furthermore, the second embodiment can determine the threshold value Δth more accurately than the first embodiment. Therefore, the second embodiment will further improve the fixability of the toner image and the productivity of the image forming apparatus 1.

[0065] <Technical ideas derived from examples> (Item 1) a feeding means for feeding a sheet; an image forming means for forming an image on the sheet; A fixing means for fixing the image to the sheet, A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a fixing unit having a heat generating unit for heating at least one of the first rotating body and the second rotating body; a detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a control means for determining a temperature parameter, which is a gradient or a temperature difference, from a first temperature detected by the detection means and a second temperature detected by the detection means after the first temperature is detected, and for controlling a timing for feeding the sheet by the feeding means or a timing for forming the image by the image forming means based on a result of determining whether the temperature parameter is a threshold value; The threshold value is determined in accordance with the first temperature.

[0066] In this way, the controller 35 determines the threshold value Δth for controlling the timing of feeding the sheet P or the timing of forming an image, based on the initial temperature IT. The threshold value Δth is determined based on the rate of increase in the temperature T according to the power supply capacity of the AC power source 10. This makes it possible to achieve both the fixability of the toner image on the sheet P and the productivity of the image forming apparatus 1. (Item 2) 2. The image forming apparatus according to item 1, wherein the control unit acquires the threshold value corresponding to the first temperature using a mathematical formula in which the temperature is an input value and the threshold value is an output value.

[0067] Equations (1) and (2) are examples of mathematical expressions. (Item 3) 3. The image forming apparatus according to item 2, wherein the formula is a formula that outputs the threshold value corresponding to the first temperature by adding a second coefficient to the product of a predetermined first coefficient and the first temperature. (Item 4) further comprising a first storage means for storing the formula; 4. The image forming apparatus according to item 2 or 3, wherein the control unit acquires the formula from the first storage unit.

[0068] The memory 502 and the nonvolatile memory 99 are an example of a first storage means. (Item 5) 5. The image forming apparatus according to item 4, wherein the first storage unit is provided in the fixing unit. (Item 6) further comprising a second storage means for pre-storing a correction value for correcting the formula; 6. The image forming apparatus according to any one of items 2 to 5, wherein the control unit acquires the correction value from the second storage unit, determines the threshold value based on the formula corrected by the correction value, and compares the determined threshold value with the temperature parameter.

[0069] The memory 502 and the nonvolatile memory 99 are examples of a second storage unit. In this way, by correcting the formula based on the correction value due to individual differences, etc., it will be possible to determine the feeding timing or image formation timing with higher accuracy. (Item 7) The method further includes a second storage means for pre-storing a correction value for correcting the threshold value obtained using the formula, 6. The image forming apparatus according to any one of items 2 to 5, wherein the control unit acquires the correction value from the second storage unit and compares the threshold value corrected by the correction value with the temperature parameter.

[0070] In this way, the controller 35 may determine the threshold value Δth2 by correcting the threshold value Δth1 obtained by the formula (1) with the correction value ΔX. Correcting the formula and correcting the threshold value obtained by the formula are substantially the same. (Item 8) a second storage means for pre-storing individual information acquired in a manufacturing process of the fixing means; 6. The image forming apparatus according to any one of items 2 to 5, wherein the control unit determines a correction value based on reference information acquired from a reference fixing unit that serves as a reference for heat capacity and the individual information acquired from the second storage unit, corrects the formula using the correction value, and compares the temperature parameter with a threshold value determined using the corrected formula.

[0071] As described in the second embodiment, ΔTF (individual information) may be stored in the non-volatile memory 99. In this case, ΔTB (reference information) may also be used to calculate the correction value ΔX. The reference fixing unit may be the standard fixing unit 27 used to obtain ΔTB. Here, the standard fixing unit 27 may be a fixing unit 27 having a standard heat capacity among the many fixing units 27 mass-produced in a manufacturing factory. (Item 9) 9. The image forming apparatus according to any one of items 6 to 8, wherein the second storage unit is provided in the fixing unit. (Item 10) The temperature sensor further includes a first storage means for storing a plurality of pairs of temperatures and threshold values; 2. The image forming apparatus according to item 1, wherein the control unit acquires the threshold value corresponding to the first temperature from the first storage unit.

[0072] The calculation table 522 may hold a plurality of pairs of the initial temperature IT and the threshold value Δth. (Item 11) Item 11. The image forming apparatus according to item 10, wherein the first storage unit is provided in the fixing unit. (Item 12) further comprising a second storage means for pre-storing a correction value for correcting the threshold value; Item 11. The image forming apparatus according to item 10, wherein the control unit acquires the correction value from the second storage unit, and compares the threshold value corrected by the correction value with the temperature parameter.

[0073] In this way, the threshold value Δth1 obtained from the calculation table 522 may be corrected by the correction value ΔX. (Item 13) a second storage means for pre-storing individual information acquired in a manufacturing process of the fixing means; Item 11. The image forming apparatus according to item 10, wherein the control means determines a correction value based on reference information acquired from a reference fixing means that serves as a reference for heat capacity and the individual information acquired from the second storage means, and compares a threshold value corrected by the correction value with the temperature parameter.

[0074] In this way, the correction value ΔX may be calculated from ΔTB (reference information) and ΔTF (individual information). (Item 14) 14. The image forming apparatus according to item 12 or 13, wherein the second storage unit is provided in the fixing unit. (Item 15) The feeding means is If the temperature parameter exceeds the threshold value, feeding of the sheet is started at a first timing; 15. The image forming apparatus according to any one of items 1 to 14, wherein, if the temperature parameter does not exceed the threshold value, feeding of the sheet is started at a second timing that is later than the first timing.

[0075] In this way, when the power supply state of the AC power source 10 is good, feeding may be started at the first timing. This improves the productivity of the image forming apparatus 1 while maintaining fixability. When the power supply state of the AC power source 10 is not good, feeding or exposure may be started at the second timing. This maintains fixability. (Item 16) The feeding means is if the temperature parameter exceeds the threshold, starting feeding of the sheet; 15. The image forming apparatus according to any one of items 1 to 14, wherein, if the temperature parameter does not exceed the threshold value, the image forming apparatus waits until the temperature detected by the detection means becomes equal to or greater than a predetermined value before starting to feed the sheet. (Item 17) The image forming means If the temperature parameter exceeds the threshold, starting the formation of the image at a first timing; 15. The image forming apparatus according to any one of items 1 to 14, wherein, if the temperature parameter does not exceed the threshold value, the image formation is started at a second timing that is later than the first timing.

[0076] In this way, when the power supply state of the AC power source 10 is good, exposure may be started at the first timing. This improves the productivity of the image forming apparatus 1 while maintaining fixability. When the power supply state of the AC power source 10 is not good, feeding or exposure may be started at the second timing. This maintains fixability. (Item 18) The image forming means if the temperature parameter exceeds the threshold, initiating formation of the image; 15. The image forming apparatus according to any one of items 1 to 14, wherein if the temperature parameter does not exceed the threshold, the image forming apparatus waits until the temperature detected by the detection unit becomes equal to or greater than a predetermined value before starting image formation.

[0077] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0078] 12: Feeding roller, 20: Process cartridge, 27: Fixing unit, 50: Fixing film, 51: Pressure roller, 52: Heater, 55: Thermistor, 35: Controller

Claims

1. a feeding means for feeding a sheet; an image forming means for forming an image on the sheet; A fixing means for fixing the image to the sheet, A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a fixing unit having a heat generating unit for heating at least one of the first rotating body and the second rotating body; a detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a control means for determining a temperature parameter, which is a gradient or a temperature difference, from a first temperature detected by the detection means and a second temperature detected by the detection means after the first temperature is detected, and for controlling a timing for feeding the sheet by the feeding means or a timing for forming the image by the image forming means based on a determination result between the temperature parameter and a threshold value, The threshold value is determined in accordance with the first temperature.

2. 2. The image forming apparatus according to claim 1, wherein the control unit acquires the threshold value corresponding to the first temperature using a mathematical formula in which the temperature is an input value and the threshold value is an output value.

3. 3. The image forming apparatus according to claim 2, wherein the formula is a formula that outputs the threshold value corresponding to the first temperature by adding a second coefficient to the product of a predetermined first coefficient and the first temperature.

4. further comprising a first storage means for storing the formula; 3. The image forming apparatus according to claim 2, wherein the control means acquires the formula from the first storage means.

5. 5. The image forming apparatus according to claim 4, wherein the first storage means is provided in the fixing means.

6. further comprising a second storage means for pre-storing a correction value for correcting the formula; 3. The image forming apparatus according to claim 2, wherein the control means acquires the correction value from the second storage means, determines the threshold value based on the formula corrected by the correction value, and compares the determined threshold value with the temperature parameter.

7. The method further includes a second storage means for pre-storing a correction value for correcting the threshold value obtained using the formula, 3. The image forming apparatus according to claim 2, wherein the control means acquires the correction value from the second storage means, and compares the threshold value corrected by the correction value with the temperature parameter.

8. a second storage means for pre-storing individual information acquired in a manufacturing process of the fixing means; 3. The image forming apparatus according to claim 2, wherein the control means determines a correction value based on reference information acquired from a reference fixing means serving as a standard for heat capacity and the individual information acquired from the second storage means, corrects the formula using the correction value, and compares the temperature parameter with a threshold value determined using the corrected formula.

9. 9. The image forming apparatus according to claim 6, wherein the second storage unit is provided in the fixing unit.

10. The temperature sensor further includes a first storage means for storing a plurality of pairs of temperatures and threshold values; The image forming apparatus according to claim 1 , wherein the control unit acquires the threshold value corresponding to the first temperature from the first storage unit.

11. 11. The image forming apparatus according to claim 10, wherein the first storage unit is provided in the fixing unit.

12. further comprising a second storage means for pre-storing a correction value for correcting the threshold value; 11. The image forming apparatus according to claim 10, wherein the control unit acquires the correction value from the second storage unit, and compares the threshold value corrected by the correction value with the temperature parameter.

13. a second storage means for pre-storing individual information acquired in a manufacturing process of the fixing means; The image forming apparatus according to claim 10, wherein the control means determines a correction value based on reference information acquired from a reference fixing means serving as a standard for heat capacity and the individual information acquired from the second storage means, and compares a threshold value corrected by the correction value with the temperature parameter.

14. 14. The image forming apparatus according to claim 12, wherein the second storage unit is provided in the fixing unit.

15. The feeding means is If the temperature parameter exceeds the threshold value, feeding of the sheet is started at a first timing; The image forming apparatus according to claim 1 , wherein, if the temperature parameter does not exceed the threshold value, feeding of the sheet is started at a second timing that is later than the first timing.

16. The feeding means is if the temperature parameter exceeds the threshold, starting feeding of the sheet; 2. The image forming apparatus according to claim 1, wherein, if the temperature parameter does not exceed the threshold value, feeding of the sheet is started after waiting until the temperature detected by the detecting means reaches or exceeds a predetermined value.

17. The image forming means If the temperature parameter exceeds the threshold, starting the formation of the image at a first timing; The image forming apparatus according to claim 1 , wherein, if the temperature parameter does not exceed the threshold value, the image formation is started at a second timing that is later than the first timing.

18. The image forming means if the temperature parameter exceeds the threshold, initiating formation of the image; 2. The image forming apparatus according to claim 1, wherein, if the temperature parameter does not exceed the threshold value, the image forming apparatus waits until the temperature detected by the detecting means reaches or exceeds a predetermined value, and then starts forming the image.

Images