Heating device and image forming apparatus having the same mounted therein

Abstract

To achieve both the productivity of a heating device and protection of a component of the heating device.SOLUTION: A heating device has a first rotating body, a second rotating body, and heat generation means. First switch means adjusts power supplied from an AC power supply to the heat generation means. Second switch means is provided on a power supply route for supplying the power from the AC power supply to the heat generation means. The first switch means has a lower noise resistance against foreign noise arriving from the AC power supply than the noise resistance of the second switch means. When a detected temperature exceeds a first threshold in a period during which the first rotating body and the second rotating body are in a non-rotation state, the second switch means is controlled to be in a non-conduction state without a notification of an error from notification means. When the detected temperature falls below a second threshold equal to or less than the first threshold, the second switch means is controlled to be in a conduction state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heating device and an image forming apparatus equipped with the same. [Background technology]

[0002] An image forming apparatus that forms an image with toner uses a heating device that receives power from an AC power source to generate heat and fixes the toner image onto a sheet. An electromagnetic relay is disposed in the power supply route from the AC power source to the heating device. Patent Document 1 describes that the contacts of the electromagnetic relay are controlled to a conductive state during image formation and to a non-conductive state during non-image formation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3150760 Summary of the Invention [Problem to be solved by the invention]

[0004] The operating time (state transition time) of an electromagnetic relay is longer than that of a semiconductor switching element such as a triac. This reduces the productivity of the heating device. Meanwhile, the noise immunity of a semiconductor switching element is lower than that of an electromagnetic relay. For example, a semiconductor switching element may unintentionally conduct due to external noise from an AC power source, causing the heating device to generate heat and shortening the lifespan of its components. Therefore, an object of the present invention is to achieve both increased productivity of the heating device and protection of the heating device's components. [Means for solving the problem]

[0005] The present invention is, for example, A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a heat generating means for heating at least one of the first rotating body and the second rotating body; a temperature detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a first switch means for adjusting the power supplied from an AC power source to the heat generating means; a second switch means provided in a power supply route for supplying the power from the AC power source to the heat generating means, the noise resistance of the first switch means to external noise coming from the AC power supply is lower than the noise resistance of the second switch means; The second switch means During a period in which the first rotating body and the second rotating body are in a non-rotating state, When the temperature detected by the temperature detection means exceeds a first threshold value, the temperature error is not notified by the notification means, and the temperature detection means is controlled to a non-conductive state. The heating device is controlled to be in a conductive state when the temperature detected by the temperature detection means becomes lower than a second threshold value which is equal to or lower than the first threshold value. [Effects of the Invention]

[0006] According to the present invention, it is possible to achieve both productivity of the heating device and protection of the components of the heating device. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram illustrating an image forming apparatus and a heating device. [Figure 2] FIG. [Figure 3] FIG. [Figure 4A] FIG. [Figure 4B] FIG. [Figure 4C] FIG. [Figure 5] FIG. 4 is a diagram illustrating the start-up times of a plurality of process devices involved in image formation. [Figure 6]10 is a flowchart showing a control method. [Figure 7A] FIG. [Figure 7B] FIG. [Figure 7C] FIG. [Figure 8] 10 is a flowchart showing a control method. [Figure 9] FIG. [Figure 10] 10 is a flowchart showing a control method. [Figure 11A] FIG. [Figure 11B] FIG. [Figure 11C] FIG. [Figure 12] 10 is a flowchart showing a control method. [Figure 13] FIG. [Figure 14] 10 is a flowchart showing a control method. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the claimed invention. Although the embodiments describe multiple features, 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) Image forming device FIG. 1A shows an electrophotographic image forming apparatus 10. The image forming apparatus 10 includes an image forming unit 11 that forms an unfixed toner image on a sheet R, and a heating device 100 that fixes the unfixed toner image on the sheet R to the sheet R. The image forming unit 11 includes a photosensitive drum 12, a charger 13, an exposure unit 14, a developing unit 15, a transfer unit 16, and a cleaning unit 17. The photosensitive drum 12 is an image carrier that is rotated in the direction of the arrow. The charger 13 includes a charging member (e.g., a charging roller or a charging wire) that charges the surface of the photosensitive drum 12. The exposure unit 14 includes a light source (e.g., a semiconductor laser or a light-emitting diode) that irradiates the surface of the photosensitive drum 12 with light corresponding to image data to form an electrostatic latent image. The developing unit 15 develops the electrostatic latent image using toner contained in a toner container to form a toner image. The transfer device 16 has a transfer member (e.g., a transfer roller, a transfer blade, or an intermediate transfer belt) that transfers the toner image from the photosensitive drum 12 to the sheet R. The cleaning device 17 has a cleaning member (e.g., a cleaning blade) that cleans the photosensitive drum 12.

[0010] The sheet R carrying the unfixed toner image is transported to the heating device 100. The heating device 100 is a fixing device that fixes the toner image onto the sheet R by applying heat and pressure to the unfixed toner image and the sheet R. After passing through the heating device 100, the sheet R is discharged from the image forming apparatus 10.

[0011] (2)Heating device FIG. 1B shows details of the heating device 100 mounted on the image forming apparatus 10. The heating device 100 has a film guide unit 106 and a pressure roller 107. In particular, the fixing film 102 and the pressure roller 107 are each rotating bodies. The film guide unit 106 has a holding member 101, the fixing film 102, a heater 103, a metal stay 104, and a temperature sensor 105. The holding member 101 is made of heat-resistant resin and holds the heater 103. Furthermore, the holding member 101 guides the rotation of the flexible, cylindrical fixing film 102. The heater 103 is held by the holding member 101 so as to contact the inner surface of the fixing film 102. The metal stay 104 prevents the holding member 101 from bending.

[0012] The pressure roller 107 has a core 108 and an elastic layer 109. The core 108 is made of a metal such as iron or aluminum. The elastic layer 109 is made of a material such as silicone rubber.

[0013] The temperature sensor 105 is disposed close to the heater 103 and is a temperature detection unit that detects the temperature of the heater 103. The temperature sensor 105 may be disposed so as to detect the temperature of the fixing film 102 or the pressure roller 107.

[0014] The film guide unit 106 is pressed against the pressure roller 107 by a spring or the like (not shown). As a result, a fixing nip portion N is formed between the fixing film 102 and the pressure roller 107. The pressure roller 107 is driven to rotate at a predetermined peripheral speed by a motor M1 (described later). As the pressure roller 107 rotates, a frictional force is generated between the pressure roller 107 and the fixing film 102 in the fixing nip portion N. This frictional force applies a rotational force to the fixing film 102, causing the fixing film 102 to rotate while sliding against the heater 103.

[0015] (3) Controller FIG. 2 shows a power supply circuit for supplying power from an AC power supply 201 to the heater 103. The AC power supply 201 is, for example, a commercial AC power supply. An electromagnetic relay 202 is arranged in a power supply route 200 connecting the AC power supply 201 and the heater 103. When there is no need to supply power from the AC power supply 201 to the heater 103 (for example, when the AC power supply 201 is in sleep mode) or when the temperature of the heater 103 is abnormally high, the contacts of the electromagnetic relay 202 are switched from a conductive state to a non-conductive state. The supply of power from the AC power supply 201 to the heater 103 is controlled by a triac 204 and a controller 205. The controller 205 controls the power supplied from the AC power supply 201 to the heater 103 via the triac 204 so that the temperature of the heater 103 tracks the target temperature. Specifically, the temperature of the heater 103 detected by the temperature sensor 105 is input to the controller 205, and a predetermined calculation (such as a PID control calculation) is performed within the controller 205. PID is an abbreviation for Proportional-Integral-Differential. After that, a control signal is sent from the controller 205 to the triac 204. The control signal controls whether the triac 204 is conductive or non-conductive.

[0016] (4) Controller details Fig. 3 shows the details of the controller 205. The CPU 301 is a processor that realizes various functions by executing a control program stored in the memory 302. Note that one or more of the functions described below may be realized by an integrated circuit different from the CPU 301. None of the functions shown in Fig. 3 are essential; the functions required differ depending on the embodiment.

[0017] When a predetermined acquisition condition is satisfied, the acquisition unit 311 acquires the temperature T based on the detection signal output from the temperature sensor 105. The acquisition unit 311 may sample a plurality of measurement results to obtain a statistical value.

[0018] The determination unit 313 outputs the comparison result (determination result) between the temperature T and the threshold value Tth1 to the relay control unit 325. The threshold value Tth1 is a threshold value for forcibly turning off the electromagnetic relay 202 when the temperature T is on an upward trend. In particular, the threshold value Tth1 functions to cut off power to the heater 103 when the triac 204 becomes uncontrollable due to external noise. In the first embodiment, the threshold value Tth1 is set to, for example, 100°C.

[0019] Here, exogenous noise refers to electrical noise that arrives at the image forming apparatus 10 from the AC power supply 201 via the power cable. Noise tolerance is the upper limit of the exogenous noise level from the AC power supply that the switch element can withstand without erroneous firing. In other words, if the level of the exogenous noise is below the upper limit, the switch element will not erroneously fire. On the other hand, if the level of the exogenous noise exceeds the upper limit, the switch element will erroneously fire. The noise tolerance of the electromagnetic relay 202 against exogenous noise is higher than that of semiconductor switch elements such as the triac 204. Therefore, the electromagnetic relay 202 is less likely to be erroneously turned on by exogenous noise than the triac 204.

[0020] The determination unit 314 outputs the comparison result (determination result) between the temperature T and the threshold value Tth2 to the relay control unit 325. The threshold value Tth2 is a threshold value for forcibly turning on the electromagnetic relay 202 when the temperature T is on a downward trend. The threshold value Tth2 is useful for shortening the start-up time of the heating device 100. In the first embodiment, the threshold value Tth2 is set to 100°C. In the first embodiment, the threshold value Tth1 and the threshold value Tth2 are equal, so the threshold value Tth1 also functions as the threshold value Tth2.

[0021] The determination unit 315 is used in the second and subsequent embodiments, and outputs the comparison result (determination result) between the temperature T and the threshold value Tth3 to the relay control unit 325. The threshold value Tth3 is higher than the threshold value Tth1, and is useful for protecting the heating device 100 from external noise. The setting unit 312 may determine the threshold value Tth3 based on the temperature T over a predetermined period measured based on the timer 323, and set the threshold value Tth3 in the determination unit 315.

[0022] The determination unit 316 is used in the second and subsequent embodiments, and outputs the comparison result (determination result) between the temperature T and the threshold value Tth4 to the relay control unit 325. The threshold value Tth4 may be used instead of the threshold value Tth1 when cleaning the heating device 100.

[0023] The gradient calculation unit 321 calculates the gradient G of the temperature T and outputs the gradient G to the determination unit 317. The determination unit 317 is used in the second and subsequent embodiments, compares the gradient G with a threshold Gth, and outputs the comparison result (determination result) to the relay control unit 325. The gradient G indicates whether the temperature T is on an upward or downward trend.

[0024] The counter 322 counts the number of occurrences of a predetermined event and outputs the count result (count value C) to the determination unit 318. The predetermined event may be, for example, a transition of the temperature T from an increase to a decrease, or from a decrease to an increase, in the standby state. The determination unit 318 is used in the second and subsequent embodiments, compares the count value C with a threshold value Cth, and outputs the comparison result (determination result) to the relay control unit 325. The threshold value Cth may also be set by the setting unit 312. The threshold value Cth is useful for protecting the contacts of the electromagnetic relay 202 and reducing operating noise.

[0025] The timer 323 starts timing when a predetermined event occurs. The determination unit 319 is used in the second and subsequent embodiments, and compares the timer value M with a threshold value Mth and outputs the comparison result (determination result) to the relay control unit 325. The threshold value Mth may also be set by the setting unit 312.

[0026] The relay control unit 325 controls the electromagnetic relay 202 to be on (conductive state) or off (non-conductive state) based on the determination results of the determination units 313 to 319 and 331. The determination unit 331 determines whether the temperature T exceeds an error threshold Te (e.g., 250°C) and outputs the determination result to the notification unit 332 and the relay control unit 325. Te is a specified value. The notification unit 332 outputs warning information indicating that the temperature T of the heater 103 is abnormally high. The warning information may be visual information displayed on a display device, or acoustic information output from a speaker or an audio device.

[0027] Motor control unit 327 controls motors M1 and M2. Motor M1 is a drive source that rotates pressure roller 107. Motor M2 is a drive source that brings pressure roller 107 and film 102 into contact with and separates them. If pressure roller 107 and film 102 are constantly in contact with each other, pressure roller 107 or film 102 may become deformed. Keeping them separated is an effective way to prevent deformation.

[0028] (5) Control method As shown in FIG. 2, the electromagnetic relay 202 and the triac 204 are connected in series to the heater 103. When both the electromagnetic relay 202 and the triac 204 are turned on, power is supplied from the AC power supply 201 to the heater 103. When at least one of the electromagnetic relay 202 and the triac 204 is turned off, power is not supplied from the AC power supply 201 to the heater 103. The operating time for the electromagnetic relay 202 to change from off to on is relatively long. Therefore, the triac 204, which has a shorter operating time, is required for power supply control (temperature adjustment during image formation). On the other hand, the noise resistance of the triac 204 is relatively low. The triac 204 may be unintentionally turned on due to external noise. Therefore, the electromagnetic relay 202 is required to safely cut off power.

[0029] 4A to 4C show the image forming apparatus 10 switching from a print state to a standby state. The image forming apparatus 10 is in either a print state or a standby state. The pressure roller 107 and the film 102 are either rotating or stopped (non-rotating). The external noise state is either "present" or "absent." "Absent" means that the level of external noise is low enough to prevent the triac 204 from accidentally firing, but does not mean that external noise is completely absent. The electromagnetic relay 202 is either on (conducting) or off (non-conducting). The heater 103 is either on (generating heat) or off (stopped). In particular, FIG. 4A shows the case where the triac 204 is not exposed to external noise in the standby state. The vertical axis represents the temperature T detected by the temperature sensor 105. The horizontal axis represents the elapsed time.

[0030] Ttg is a target temperature set when the image forming apparatus 10 performs printing. Ttg is, for example, 230° C. The CPU 301 may change the target temperature Ttg depending on the type of sheet R (e.g., thickness, basis weight, whether or not it is coated), etc.

[0031] Te is a threshold value for notifying an error and stopping the operation of the image forming apparatus 10 when some abnormality occurs in the heating device 100 and the temperature of the heater 103 becomes excessively high. Te is, for example, 250° C. When the determination unit 331 determines that the temperature T exceeds the threshold Te, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a non-conductive state. This cuts off the power supply from the AC power supply 201 to the heater 103. The notification unit 332 outputs an error message (warning information) to an operation panel of the image forming apparatus 10 or the like.

[0032] Tx is the temperature at which damage occurs to the film 102 and the pressure roller 107. Tx is, for example, 280°C. If the temperature T exceeds Tx, the surface layers of the film 102 and the pressure roller 107 may melt, resulting in a deterioration in fixing quality. If the temperature T significantly exceeds Tx, the film 102 and the pressure roller 107 may adhere to each other, making the heating device 100 unusable.

[0033] Tth1 and Tth2 are temperature thresholds used to determine whether to place the contacts of the electromagnetic relay 202 in a conductive state or a non-conductive state in the standby state. In the standby state, the heater 103 stops generating heat, and the temperature T is expected to gradually decrease. When the temperature T falls below Tth2 in the standby state, the controller 205 controls the contacts of the electromagnetic relay 202 to a conductive state. This improves the productivity of the heating device 100. On the other hand, if the triac 204 erroneously fires while the contacts of the electromagnetic relay 202 are in a conductive state, the heater 103 may unintentionally start generating heat. When the temperature T exceeds Tth1 during standby, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a non-conductive state. In the first embodiment, Tth1 and Tth2 are equal, for example, 100°C.

[0034] ●How to calculate Tth1 and Tth2 Tth1 is a temperature threshold for forcibly turning off the electromagnetic relay 202 to protect the heating device 100. Tth2 is a temperature threshold for forcibly turning on the electromagnetic relay 202 to increase the productivity of the heating device 100.

[0035] Tth1 and Tth2 are set, for example, between 50°C and 200°C. First, the reason why Tth2 is set to 50°C or higher will be explained. In the image forming apparatus 10, importance is placed on the first printout time (FPOT), which is the time from when a print job is received from a host computer or the like until the first printed page is output. The lower the temperature of the heating device 100, the longer the time (start-up time) required to raise the temperature T of the heating device 100 to the target temperature Ttg at which printing is possible. Therefore, the lower the temperature T, the longer the FPOT. For example, when the temperature T is below 50°C, the start-up time required for the temperature T of the heating device 100 to reach the target temperature Ttg becomes a bottleneck for FPOT. In other words, when the temperature T is below 50°C, the start-up time of the heating device 100 becomes longer than the start-up times of other devices (e.g., the charger 13, the exposure device 14) within the image forming apparatus 10. When the contacts of the electromagnetic relay 202 are in a non-conductive state in the standby state, time is also required for the contacts of the electromagnetic relay 202 to transition from a non-conductive state to a conductive state. This transition time is also added to the startup time of the heating device 100.

[0036] FIG. 5(A) shows an example of the activation time of multiple process devices (e.g., charger 13, exposure device 14, and heating device 100) when temperature T is 50°C or higher. The process devices are devices involved in the electrophotographic process. FIG. 5(B) shows an example of the activation time of charger 13, exposure device 14, and heating device 100 when temperature T is less than 50°C. tp0 is the operating time of electromagnetic relay 202. tp1 is the activation time of heater 103 when temperature T is 50°C or higher. tp2 is the activation time of heater 103 when temperature T is less than 50°C.

[0037] 5(A) and 5(B), when the temperature T is 50° C. or higher, the heating time (start-up time tp1) required to raise the temperature T of the heating device 100 to a target temperature or higher is shorter than the start-up time tp2 when the temperature T is less than 50° C. Therefore, the start-up time of the heating device 100 (the sum of tp0 and tp1), including the operating time tp0 of the electromagnetic relay 202, is shorter than the start-up time of the exposure unit 14.

[0038] As shown in FIG. 5B, the start-up time tp2 of the heating device 100 when the temperature T is below 50°C is longer than the start-up time tp1 when the temperature T is 50°C or higher. Therefore, the start-up time (tp0 + tp2) of the heating device 100, including the activation time tp0 of the electromagnetic relay 202, is longer than the start-up time of the exposure unit 14. In other words, in FIG. 5B, the heating device 100 is a bottleneck in the FPOT of the image forming apparatus 10. To prevent the heating device 100 from becoming a bottleneck, the contacts of the electromagnetic relay 202 may be pre-controlled to a conductive state when the temperature T is below 50°C. This eliminates the need for the activation time tp0 of the electromagnetic relay 202, and the start-up time of the heating device 100 is shorter than the start-up time of the exposure unit 14. In this way, by controlling the contacts of the electromagnetic relay 202 to a conductive state when the temperature T is below 50°C, the FPOT is reduced.

[0039] Next, the reason why Tth1 is set to 200°C or less will be explained. In the standby state, the film 102 and the pressure roller 107 are not rotating. If external noise is input to the triac 204 from the AC power supply 201 in the standby state, the triac 204 will erroneously ignite, causing the heater 103 to generate heat. If the contacts of the electromagnetic relay 202 were controlled to a non-conductive state before the temperature T exceeded 200°C, the temperature T would not exceed the threshold Te (=250°C), even taking into account temperature overshoot. In other words, when the temperature T is 200°C or higher, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state. This will prevent the image forming apparatus 10 from frequently stopping when the triac 204 is exposed to external noise.

[0040] In this way, when the temperature T is less than 50°C, the contacts of the electromagnetic relay 202 are controlled to a conductive state. When the temperature T is 200°C or higher, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state. In the first embodiment, the thresholds Tth1 and Tth2 are each set to 100°C as a temperature that satisfies both of these conditions. In the first embodiment, the thresholds Tth2 and Tth1 are the same (e.g., 100°C), but they may be different values. Cases in which the thresholds Tth2 and Tth1 are different will be described in detail in the second and subsequent embodiments.

[0041] 4A, the behavior of image forming apparatus 10 over time will be described. The period from time 0 to time t1 is the period during which image forming apparatus 10 is printing (printing state). During this period, film 102 and pressure roller 107 rotate, and the contacts of electromagnetic relay 202 are controlled to be in a conductive state.

[0042] At time t1, image forming apparatus 10 finishes printing and transitions to a standby state. During the period from time t1 to time t2, film 102 and pressure roller 107 are not rotating, and temperature T exceeds Tth1. Therefore, relay control unit 325 controls the contacts of electromagnetic relay 202 to a non-conductive state.

[0043] At time t2, temperature T becomes less than Tth2. Relay control unit 325 controls the contacts of electromagnetic relay 202 to a conductive state. After time t2, relay control unit 325 maintains the state (conductive state) of electromagnetic relay 202.

[0044] 4B illustrates a case where external noise occurs in the standby state. The solid line shows the temperature transition when the contacts of the electromagnetic relay 202 are controlled to the non-conductive state when the temperature T exceeds the threshold value Tth1. The dashed line shows the temperature transition when the first embodiment, which controls the contacts of the electromagnetic relay 202 to the non-conductive state using the threshold value Tth1, is not adopted.

[0045] When Example 1 is applied The period from time 0 to time t10 is the period during which image forming apparatus 10 is printing (printing state). During this period, film 102 and pressure roller 107 rotate, and the contacts of electromagnetic relay 202 are controlled to a conductive state. At time t10, image forming apparatus 10 finishes printing and transitions to a standby state, with film 102 and pressure roller 107 stopped. During the period from time t10 to time t11, temperature T exceeds threshold value Tth1. Therefore, relay control unit 325 controls the contacts of electromagnetic relay 202 to a non-conductive state.

[0046] At time t11, the image forming apparatus 10 begins to be exposed to external noise from the AC power supply 201. At this time, the contacts of the electromagnetic relay 202 are controlled to be in a non-conductive state. Therefore, the triac 204 does not unintentionally enter a conductive state. Therefore, unintentional power supply from the AC power supply 201 to the heater 103 does not occur, and the temperature T does not begin to rise at time t11. The contacts of the electromagnetic relay 202 remain in a non-conductive state until time t13, which is the time when the temperature T becomes less than Tth2. Therefore, unintentional power supply from the AC power supply 201 to the heater 103 is suppressed throughout the entire period from time t11 to time t12, when the image forming apparatus 10 is exposed to external noise.

[0047] At time t13, when the temperature T becomes less than the threshold value Tth2, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a conductive state. After time t13, the state of the electromagnetic relay 202 is maintained.

[0048] When Example 1 is not applied If the first embodiment, in which the contacts of the electromagnetic relay 202 are controlled to a non-conductive state when the temperature T exceeds the threshold value Tth1, were not adopted, the temperature transition would be as shown by the dashed line. If the image forming apparatus 10 is exposed to external noise at time t11 and the triac 204 is unintentionally conductive, power is unintentionally supplied from the AC power supply 201 to the heater 103, causing the temperature T to rise. When the temperature T reaches the threshold value Te, the alarm unit 332 issues an error alarm, and the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a non-conductive state. This stops the unintentional supply of power to the heater 103. Even if the temperature T reaches Te and the contacts of the electromagnetic relay 202 are controlled to a non-conductive state, the temperature T reaches Tx (e.g., 280°C) due to a temperature overshoot. As a result, damage to the film 102 and the pressure roller 107 may occur. If the temperature overshoot were small, the film 102 and the pressure roller 107 would not be damaged. However, the image forming apparatus 10 frequently stops due to external noise, which reduces the productivity of the image forming apparatus 10. Therefore, adopting the first embodiment, in which the contacts of the electromagnetic relay 202 are controlled to be in a non-conductive state when the temperature T exceeds the threshold value Tth1, brings about many advantages.

[0049] 4C will be used to explain a case where image forming apparatus 10 is exposed to external noise when in standby mode and temperature T is less than threshold value Tth2. The solid line in FIG. 4C shows the temperature transition in the case where the contacts of electromagnetic relay 202 are controlled to the non-conductive state when temperature T exceeds Tth1 based on embodiment 1. The dashed line in FIG. 4C shows the temperature transition in the case where embodiment 1 is not adopted.

[0050] When Example 1 is applied The solid line in Figure 4C will now be explained. The period from time 0 to time t21 is the period during which the image forming apparatus 10 is printing. During this period, the film 102 and pressure roller 107 rotate, and the contacts of the electromagnetic relay 202 are controlled to be in a conductive state. At time t21, the image forming apparatus 10 finishes printing and transitions to a standby state. During the period from time t21 to time t22, the temperature T exceeds Tth1 (e.g., 100°C). Therefore, the contacts of the electromagnetic relay 202 are controlled to be in a non-conductive state.

[0051] At time t22, the temperature T becomes less than Tth2 (for example, 100° C.), and the relay control unit 325 controls the contacts of the electromagnetic relay 202 to be in a conductive state.

[0052] At time t23, the image forming apparatus 10 begins to be exposed to external noise. This unintentionally places the triac 204 in a conductive state, causing the AC power supply 201 to unintentionally supply power to the heater 103. This unintentional power supply causes the temperature T to rise during the period from time t23 to time t24. When the temperature T exceeds Tth1 at time t24, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to be non-conductive again. Although the power supply from the AC power supply 201 to the heater 103 is cut off at time t24, a temperature overshoot occurs during the period from time t24 to time t25. After the temperature overshoot ends at time t25, the temperature T drops. The external noise continues until time t26. The contacts of the electromagnetic relay 202 remain non-conductive until time t27. Therefore, the temperature T does not rise again during the period from time t25 to time t26. At time t27, temperature T becomes less than 100°C, and the contacts of electromagnetic relay 202 are again controlled to the conductive state. In this way, the contacts of electromagnetic relay 202 are controlled to the conductive state during the period from time t24 to time t26, and the contacts of electromagnetic relay 202 are controlled to the non-conductive state during the period from time t22 to time t23 and after time t27. This makes it possible to protect heating device 100 from external noise while also improving the productivity of heating device 100.

[0053] When Example 1 is not applied Next, a case will be described in which the contacts of the electromagnetic relay 202 are always controlled to be conductive in the standby state because the first embodiment is not adopted. The dashed line in Fig. 4C shows the temperature transition in this case.

[0054] At time t23, external noise causes the triac 204 to unintentionally conduct. Unintentional power supply from the AC power supply 201 to the heater 103 occurs, causing the temperature T to rise. When the temperature T exceeds Te (e.g., 250°C), the alarm unit 332 issues an error alarm, and the relay control unit 325 controls the contacts of the electromagnetic relay 202 to be non-conductive. This stops the unintentional power supply from the AC power supply 201 to the heater 103. However, a temperature overshoot may cause the temperature T to reach Tx (e.g., 280°C), damaging the film 102 and the pressure roller 107. If the temperature overshoot were small, the film 102 and the pressure roller 107 would not be damaged. However, frequent shutdowns of the image forming apparatus 10 due to external noise would reduce the productivity of the image forming apparatus 10. Therefore, many advantages can be obtained by adopting the first embodiment, in which the contacts of the electromagnetic relay 202 are controlled to be non-conductive when the temperature T exceeds the threshold value Tth1.

[0055] In this way, in a standby state where the film 102 and pressure roller 107 are not rotating, the contact state of the electromagnetic relay 202 is switched based on thresholds Tth1 and Tth2 that are set separately from threshold Te. This prevents frequent shutdowns of the image forming apparatus 10 due to external noise and reduces damage to the heating device 100. Furthermore, the FPOT is also shortened.

[0056] In the first embodiment, the contact state of the electromagnetic relay 202 is switched by comparing the temperature T with the threshold value Tth1, but this is merely an example. In practice, a noise removal process may be applied to the temperature T using a digital filter or the like provided in the controller 205. The digital filter may, for example, acquire the temperature T every predetermined time (e.g., 10 msec), compare the temperature T with the threshold value Tth1, and determine the comparison result if the comparison result is the same N times in a row.

[0057] In the first embodiment, the standby state is used as an example of a state in which the film 102 and the pressure roller 107 are not rotating, but this is merely an example. The first embodiment is applicable to any state in which the film 102 and the pressure roller 107 are not rotating. Therefore, the first embodiment may be applied to a state other than the standby state, such as a sleep state.

[0058] In the first embodiment, when the temperature T exceeds Tth1 (e.g., 100°C), the CPU 301 (relay control unit 325) controls the contacts of the electromagnetic relay 202 to a non-conductive state, but this is also just one example. The electromagnetic relay 202 does not have to be controlled by the CPU 301. For example, the determination unit 313 and the relay control unit 325 may be implemented by a comparison circuit such as a comparator. When the output of the comparator indicates that the temperature T exceeds the threshold value Tth1, the contacts of the electromagnetic relay 202 may be controlled to a non-conductive state.

[0059] (6) Flowchart 6 shows a control method executed in accordance with a control program by the CPU 301. Here, it is assumed that printing has finished.

[0060] In step S601, the CPU 301 (motor control unit 327) stops the motor M1, thereby stopping the rotation of the pressure roller 107.

[0061] In S602, the CPU 301 (relay control unit 325) turns off the electromagnetic relay 202. At this point, the temperature T is the target temperature Ttg for printing.

[0062] In S603, the CPU 301 (acquisition unit 311) detects the temperature T using the temperature sensor 105. The temperature T may be stored in a RAM (random access memory) area of ​​the memory 302.

[0063] In S604, the CPU 301 (determination unit 314) determines whether the temperature T is less than a threshold value Tth2 (e.g., 100°C). If the temperature T is not less than the threshold value Tth2, the CPU 301 advances the process from S604 to S603. If the temperature T is less than the threshold value Tth2, the CPU 301 advances the process from S604 to S605. Note that the temperature T may be measured at regular intervals.

[0064] In S605, the CPU 301 (relay control unit 325) turns on the electromagnetic relay 202. This reduces the startup time of the heater 103.

[0065] In S606, the CPU 301 (acquisition unit 311) detects the temperature T using the temperature sensor 105. The temperature T may be stored in a RAM (random access memory) area of ​​the memory 302.

[0066] In S607, the CPU 301 (determination unit 313) determines whether the temperature T exceeds a threshold value Tth1 (e.g., 100°C). If the temperature T exceeds the threshold value Tth1, the CPU 301 advances the process from S607 to S608. Note that the temperature T exceeds the threshold value Tth1 at this timing due to unintended conduction of the triac 204 caused by external noise. If the temperature T does not exceed the threshold value Tth1, the CPU 301 advances the process from S607 to S606. Note that the temperature T may be measured at regular intervals.

[0067] In S608, the CPU 301 (relay control unit 325) turns off the electromagnetic relay 202. As a result, even if the triac 204 is turned on by external noise, the supply of power to the heater 103 is cut off. Thereafter, the CPU 301 advances the process from S608 to S603.

[0068] In the standby state, the CPU 301 monitors whether a print job has been submitted. When a print job is submitted, the CPU 301 immediately transitions from the standby state to the print state. This causes the pressure roller 107 to start rotating, the electromagnetic relay 202 to turn on, and the triac 204 to start controlling the temperature of the heater 103. As a result, the temperature T is controlled to the target temperature Ttg.

[0069] In this specification, a determination as to whether a value exceeds a corresponding threshold value may be replaced with a determination as to whether a value is equal to or greater than the threshold value, and a determination as to whether a value is less than the threshold value may be replaced with a determination as to whether a value is equal to or less than the threshold value.

[0070] <Example 2> In the first embodiment, the threshold value Tth1 and the threshold value Tth2 are equal, and therefore the contact state of the electromagnetic relay 202 in the standby state is essentially switched by a single temperature threshold value. In the second embodiment, the first threshold value Tth1 that controls the contacts of the electromagnetic relay 202 to a non-conductive state and the second threshold value Tth2 that controls the contacts of the electromagnetic relay 202 to a conductive state are different. That is, two temperature threshold values ​​are used in the second embodiment. Note that the threshold value Tth1 is greater than the threshold value Tth2. In the second embodiment, a description of matters common to the first embodiment will be omitted.

[0071] 7A to 7C show temperature transitions in Example 2. FIG. 7A shows a case where the triac 204 is not exposed to external noise in the standby state. The threshold value Tth1 is, for example, 150°C. The threshold value Tth2 is, for example, 70°C. Here, the threshold values ​​Tth1 and Tth2 are set within a range from 50°C to 200°C. The threshold value Tth1 may be set to 150°C, taking into account a margin (e.g., 50°C) relative to 200°C. The threshold value Tth2 may also be set to 70°C, taking into account a margin (e.g., 20°C) relative to 50°C. The threshold values ​​Tth1 and Tth2 may be optimized for each configuration of the heating device 100.

[0072] When there is no external noise 7A, the period from time 0 to time t31 is a period during which image forming apparatus 10 is performing printing (image forming operation). During this period, film 102 and pressure roller 107 rotate, and the contacts of electromagnetic relay 202 are controlled to be in a conductive state.

[0073] At time t31, the image forming apparatus 10 finishes printing and transitions to a standby state. From time t31 to time t32, the temperature T exceeds the threshold value Tth1. Therefore, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state. From time t32 to t33, the temperature T is equal to or greater than the threshold value Tth2 and equal to or less than the threshold value Tth1. During this period, the relay control unit 325 maintains the contact state of the electromagnetic relay 202 in the previous state. In other words, the contact state of the electromagnetic relay 202 is maintained in a non-conductive state.

[0074] At time t33, the temperature T becomes less than the threshold value Tth2. Therefore, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to be in a conductive state. Even after time t33, the temperature T remains less than the threshold value Tth2, so the contacts of the electromagnetic relay 202 are maintained in a conductive state.

[0075] When there is external noise during the period when the temperature T exceeds the threshold Tth2 7B shows a case where the image forming apparatus 10 is exposed to external noise in a standby state. The solid line shows the temperature transition when the contact state of the electromagnetic relay 202 is controlled using thresholds Tth1 and Tth2. The dashed line shows the temperature transition when the second embodiment is not adopted.

[0076] (1) When Example 2 is applied The period from time 0 to time t41 is a period during which image forming apparatus 10 is printing. During this period, film 102 and pressure roller 107 rotate, and the contacts of electromagnetic relay 202 are controlled to be in a conductive state. At time t41, image forming apparatus 10 finishes printing and transitions to a standby state, and film 102 and pressure roller 107 stop.

[0077] During the period from time t41 to time t42, the temperature T exceeds the threshold value Tth1, so the relay control unit 325 controls the contacts of the electromagnetic relay 202 to be in a non-conductive state.

[0078] At time t42, external noise occurs. Because the contacts of the electromagnetic relay 202 are controlled to a non-conductive state, even if the triac 204 is unintentionally conductive, power is not supplied to the heater 103. In other words, the temperature T does not begin to rise at time t42. At time t43, the temperature T becomes equal to or lower than the threshold value Tth1.

[0079] The external noise continues until time t44. However, when the temperature T is equal to or lower than the threshold value Tth1 and equal to or higher than the threshold value Tth2, the contacts of the electromagnetic relay 202 are maintained in the previous state (non-conducting state). Thus, although external noise is present during the period from time t42 to t44, an unintended supply of power from the AC power supply 201 to the heater 103 does not occur.

[0080] At time t45, the temperature T becomes less than the threshold value Tth2. The relay control unit 325 switches the contact of the electromagnetic relay 202 from a non-conductive state to a conductive state. This reduces the start-up time of the heater 103.

[0081] (2) When Example 2 is not applied 7B shows the temperature transition when Example 2 is not applied, that is, the turning off of the electromagnetic relay 202 based on the threshold value Tth1 and the turning on of the electromagnetic relay based on the threshold value Tth2 are not executed.

[0082] At time t42, the triac 204 is exposed to external noise and unintentionally conducts. This causes an unintentional supply of power from the AC power supply 201 to the heater 103, raising the temperature T. When the temperature T reaches the threshold value Te, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state. This stops the unintentional supply of power from the AC power supply 201 to the heater 103. However, a temperature overshoot can cause the temperature T to reach Tx, potentially damaging the film 102 and the pressure roller 107. Even if the temperature overshoot is small, the image forming apparatus 10 will frequently stop due to external noise. This will reduce the productivity of the image forming apparatus 10. Therefore, many advantages can be obtained by adopting the second embodiment. Specifically, the life of the heating device 100 is extended, and productivity is improved.

[0083] When there is external noise during the period when the temperature T is below the threshold Tth2 7C shows a case where external noise occurs in the standby state when the temperature T is less than the threshold value Tth2. The solid line shows the temperature transition when Example 2 is applied. The dashed line shows the temperature transition when Example 2 is not applied.

[0084] (1) When Example 2 is applied The period from time 0 to time t51 is a period during which the image forming apparatus 10 is performing printing. During this period, the film 102 and pressure roller 107 rotate, and the contacts of the electromagnetic relay 202 are controlled to be in a conductive state.

[0085] At time t51, the image forming apparatus 10 finishes printing and transitions to a standby state, with the film 102 and pressure roller 107 being stopped. From time t51 to time t52, the temperature T exceeds the threshold value Tth1. Therefore, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state. From time t52 to t53, the temperature T is below the threshold value Tth1 and above the threshold value Tth2. During this period, the contact state of the electromagnetic relay 202 is maintained in the previous state. In other words, the contact state of the electromagnetic relay 202 is maintained in a non-conductive state.

[0086] At time t53, the temperature T becomes less than the threshold value Tth2. The relay control unit 325 controls the contacts of the electromagnetic relay 202 to be in a conductive state. At time t54, the image forming apparatus 10 begins to be exposed to external noise, and the triac 204 unintentionally becomes in a conductive state. As a result, power is unintentionally supplied from the AC power supply 201 to the heater 103. After time t54, this unintentional supply of power causes the temperature T to rise.

[0087] At time t55, the temperature T becomes equal to or higher than the threshold value Tth2. During the period in which the temperature T is equal to or lower than the threshold value Tth1 and equal to or higher than the threshold value Tth2, the contacts of the electromagnetic relay 202 are maintained in their previous state. Therefore, the electromagnetic relay 202 is maintained in the on state. Therefore, the temperature T continues to rise.

[0088] At time t56, the temperature T exceeds the threshold value Tth1. The relay control unit 325 controls the contacts of the electromagnetic relay 202 to a non-conductive state. This stops the unintended supply of power to the heater 103. However, due to a temperature overshoot, the temperature T continues to rise temporarily. Eventually, the temperature T drops.

[0089] At time t57, the temperature T becomes equal to or lower than the threshold value Tth1. The state of the electromagnetic relay 202 is maintained in the previous state. The operation from time t57 to t59 is the same as the operation from time t52 to t57.

[0090] (2) Hysteresis function Here, we will explain why the contacts of the electromagnetic relay 202 are maintained in the state they were in immediately before the temperature T falls within the threshold value range Tth1 to Tth2. In other words, the state of the contacts of the electromagnetic relay 202 is maintained in either the conductive state or the non-conductive state that was in effect when the temperature T fell within a predetermined range. This mechanism has two main purposes.

[0091] The first purpose is to prevent the contacts of electromagnetic relay 202 from reacting more sensitively than necessary when noise is added to temperature T detected by temperature sensor 105. Suppose that when temperature T is 69°C, noise is added to temperature T, causing it to be erroneously detected as 71°C. In this case, temperature T will quickly return to its original value of 69°C. In such a case, switching the contact state of electromagnetic relay 202 is not the expected behavior. This mechanism will prevent the electromagnetic relay 202 from operating too sensitively.

[0092] The second purpose is to reduce the number of times the electromagnetic relay 202 operates even if the temperature T of the heater 103 unintentionally rises due to external noise. In the first place, the condition for placing the contacts of the electromagnetic relay 202 in a non-conductive state is that the temperature T exceeds the threshold value Tth1. Therefore, in a situation where the temperature T is on a downward trend and the temperature T is equal to or lower than the threshold value Tth1, there is little benefit in controlling the contacts of the electromagnetic relay 202 to a non-conductive state. In a situation where the temperature T is on an upward trend and the temperature T is equal to or higher than the threshold value Tth2, there is little benefit in controlling the contacts of the electromagnetic relay 202 to a conductive state.

[0093] Therefore, when the temperature T is within the range from the threshold value Tth2 to the threshold value Tth1, the contacts of the electromagnetic relay 202 are maintained in the immediately preceding state. This reduces the number of times the electromagnetic relay 202 operates, lengthening the time until the end of its life. It also reduces the number of times that the electromagnetic relay 202 generates operating noise. The function of maintaining the contacts of the electromagnetic relay 202 in the immediately preceding state between the threshold value Tth1 and the threshold value Tth2 may be called a hysteresis function.

[0094] (3) Latch function Incidentally, external noise may continue for a long period of time. During the period from time t54 to time t58, the number of times that the temperature T transitions from below the threshold value Tth1 to above the threshold value Tth1, i.e., the number of times that the contacts of the electromagnetic relay 202 transition from a conductive state to a non-conductive state, may exceed a predetermined number. In this case, the relay control unit 325 does not control the contacts of the electromagnetic relay 202 to a conductive state even when the temperature T next falls below the threshold value Tth2. The counter 322 counts the number of times that the contacts of the electromagnetic relay 202 transition from a conductive state to a non-conductive state (count value C). At time t58, the determination unit 319 determines that the count value C exceeds the threshold value Cth and outputs the determination result to the relay control unit 325. Based on the determination result, the relay control unit 325 maintains the contacts of the electromagnetic relay 202 in a non-conductive state even after time t60.

[0095] If external noise continues for a long period of time, the contact state of the electromagnetic relay 202 will repeatedly switch, shortening the time when the electromagnetic relay 202 will reach the end of its life, and the electromagnetic relay 202 will repeatedly make operating noise. Therefore, when the number of times the contact state of the electromagnetic relay 202 switches (count value C) reaches or exceeds a threshold value Cth, the relay control unit 325 fixes the contact of the electromagnetic relay 202 in a non-conductive state. This may also be called a latch function.

[0096] Even if the temperature T is less than the threshold value Tth2, the contacts of the electromagnetic relay 202 are maintained in a non-conductive state by the latch function. In this case, there is a possibility that the FPOT will not be reduced. However, in a situation where the image forming apparatus 10 is exposed to external noise for a long period of time, protecting the electromagnetic relay 202 and reducing operating noise may be prioritized over reducing the FPOT. From this perspective, the latch function is effective. The CPU 301 may measure the effective period of the latch function using the timer 323. When the determination unit 319 detects a timeout of the timer 323, the CPU 301 may cancel the latch function. As a result, the latch function may be automatically canceled when a predetermined time has elapsed since the latch function was enabled.

[0097] The release condition may be based on the temperature T. For example, when the temperature T falls below a lower limit, the CPU 301 may release the latch function. Here, the lower limit is a threshold Tth5. The threshold Tth5 is smaller than the threshold Tth2.

[0098] (4) Flowchart of Example 2 8 shows a control method executed by the CPU 301 in accordance with the control program. Here, it is assumed that printing has finished. The initial value of the number of times C is 0.

[0099] In S801, the CPU 301 (motor control unit 327) stops the motor M1, and the pressure roller 107 stops rotating.

[0100] In S802, the CPU 301 (relay control unit 325) turns off the electromagnetic relay 202. At this point, the temperature T is the target temperature for printing Ttg.

[0101] In S803, the CPU 301 (acquisition unit 311) detects the temperature T using the temperature sensor 105. The temperature T may be stored in a RAM (random access memory) area of ​​the memory 302.

[0102] In S804, the CPU 301 (determination unit 314) determines whether the temperature T is less than a threshold value Tth2 (e.g., 70°C). If the temperature T is not less than the threshold value Tth2, the CPU 301 advances the process from S804 to S803. If the temperature T is less than the threshold value Tth2, the CPU 301 advances the process from S804 to S805.

[0103] In S805, the CPU 301 (determination unit 319) acquires the count value C from the counter 322 and determines whether the count value C is less than the threshold value Cth. If the count value C is less than the threshold value Cth, the CPU 301 advances the process from S805 to S806.

[0104] In S806, the CPU 301 (relay control unit 325) turns on the electromagnetic relay 202. This reduces the startup time of the heater 103.

[0105] In S807, the CPU 301 (acquisition unit 311) detects the temperature T using the temperature sensor 105. The temperature T may be stored in a RAM (random access memory) area of ​​the memory 302.

[0106] In S808, the CPU 301 (determination unit 313) determines whether the temperature T exceeds a threshold value Tth1 (e.g., 105°C). If the temperature T exceeds the threshold value Tth1, the CPU 301 advances the process from S808 to S809. Note that the reason the temperature T exceeds the threshold value Tth1 at this timing is because the triac 204 is unintentionally turned on due to external noise. If the temperature T does not exceed the threshold value Tth1, the CPU 301 advances the process from S808 to S807.

[0107] In S809, the CPU 301 (relay control unit 325) turns off the electromagnetic relay 202. As a result, even if the triac 204 is turned on by external noise, the supply of power to the heater 103 is cut off.

[0108] In S809, the CPU 301 (counter 322) adds 1 to the count value C. This means that the contact of the electromagnetic relay 202 has transitioned from a conductive state to a non-conductive state. Thereafter, the CPU 301 advances the process from S810 to S803.

[0109] Incidentally, if the determination unit 319 determines in S805 that the count value C is equal to or greater than the threshold value Cth, the CPU 301 advances the process from S805 to S811.

[0110] In S811, the CPU 301 (relay control unit 325) starts latching the contact state of the electromagnetic relay 202. This keeps the electromagnetic relay 202 OFF. The CPU 301 sets a predetermined time in the timer 323 and starts the timer 323.

[0111] In S812, the CPU 301 (determination unit 319) determines whether a release condition for the latch function has been met. For example, the determination unit 319 determines whether the timer 323 has timed out. When the time measured by the timer 323 reaches a predetermined time, the determination unit 319 determines that the release condition has been met, and advances the process from S812 to S803. The start and release of the latch function may be controlled in this manner.

[0112] According to the second embodiment, thresholds Tth1 and Tth2 other than the threshold Te are used in the standby state. This suppresses frequent shutdowns of the image forming apparatus 10 and wear on the heating device 100 due to external noise. Furthermore, the FPOT is shortened. This is the same effect as that of the first embodiment. According to the second embodiment, the CPU 301 has a hysteresis function. This makes it possible to reduce the number of times the electromagnetic relay 202 operates in an environment where external noise occurs. Furthermore, according to the second embodiment, the CPU 301 has a latch function. This makes it possible to reduce the number of times the electromagnetic relay 202 operates in an environment where external noise continues for a long period of time.

[0113] Example 3 The third embodiment is a control method that takes into consideration the copy operation. As shown in Fig. 9, a process different from those in the first and second embodiments is executed until a predetermined time P0 (e.g., 60 seconds) has elapsed since printing ended. For example, when the temperature T is equal to or higher than a threshold value Tth1 (e.g., 150°C), the relay control unit 325 controls the electromagnetic relay 202 using a third threshold value Tth3 instead of the threshold value Tth1.

[0114] At time t31, printing ends and rotation of film 102 and pressure roller 107 stops. Setting unit 312 adds a predetermined temperature (e.g., 5°C) to the current temperature T detected by temperature sensor 105 to obtain threshold value Tth3. Threshold value Tth3 is set in determination unit 315.

[0115] During the period from time t31 to time t32, the temperature T exceeds the threshold value Tth1. Therefore, the setting unit 312 also updates the threshold value Tth3 sequentially (for example, every 500 msec) as the temperature T decreases.

[0116] The determination unit 315 determines whether the temperature T exceeds the threshold value Tth3. If the temperature T exceeds the threshold value Tth3, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a non-conductive state.

[0117] The period in which threshold value Tth3 is used instead of threshold value Tth1 is the period from time t31 when printing ends until a predetermined time P0 (e.g., 60 seconds) has elapsed, and the period in which temperature T exceeds threshold value Tth1. In FIG. 9, threshold value Tth3 is used from time t31 to time t32. In FIG. 9, temperature T does not exceed threshold value Tth3. Therefore, the contacts of the electromagnetic relay 202 are controlled to be conductive from time t31 to time t32. When temperature T becomes less than threshold value Tth1 at time t32, setting unit 312 stops calculating threshold value Tth3. Relay control unit 325 controls the contacts of the electromagnetic relay 202 using the comparison result between temperature T and threshold value Tth1 by determination unit 313.

[0118] During the period from time t32 to time t34, the hysteresis function described above is enabled, and the contacts of the electromagnetic relay 202 are therefore maintained in their previous state (conducting state).

[0119] After time t34, the temperature T is less than the threshold value Tth2, so the contacts of the electromagnetic relay 202 are maintained in a conductive state.

[0120] 9, the contacts of electromagnetic relay 202 are controlled to be in a conductive state throughout the entire period. Note that in FIG. 9, time t32, when temperature T first falls below threshold value Tth1, occurs before time t33, when predetermined time P0 ends. However, time t32, when temperature T first falls below threshold value Tth1, may occur after time t33. In this case, at time t33, relay control unit 325 switches from control using the comparison result between temperature T and threshold value Tth3 to control using the comparison result between temperature T and threshold value Tth1.

[0121] 9, the predetermined time P0 is a fixed time (e.g., 60 seconds), but this is just an example. The threshold value Tth3 may be used until the temperature T becomes equal to or lower than the threshold value Tth1 for the first time after printing is completed.

[0122] The purpose of using the threshold value Tth3 during the predetermined time P0 is to handle copy operations. The image forming apparatus 10 may resume printing a short time (e.g., several seconds to several tens of seconds) after printing has finished. This is called intermittent printing. Some image forming apparatuses 10 are equipped with a copy function. In copy operations, a first image is read by a document scanner, and the first image is formed on a sheet R. Then, a second image is read, and the second image is formed on a sheet R. In such operations, printing is repeatedly stopped and restarted, resulting in so-called intermittent printing.

[0123] Now, let's assume that the contacts of the electromagnetic relay 202 are controlled to be in a non-conductive state immediately after printing ends, as shown in Figures 7A to 7C. In this case, the contact state of the electromagnetic relay 202 is frequently switched due to intermittent printing. As a result, the electromagnetic relay 202 reaches the end of its life sooner. In addition, the electromagnetic relay 202 frequently produces operating noise.

[0124] Therefore, in intermittent printing, such as copying, the contacts of the electromagnetic relay 202 should be maintained in a conductive state until the predetermined time P0 has elapsed, even after printing has finished. Furthermore, during the predetermined time P0, the threshold value Tth3 also suppresses excessive temperature rise of the heater 103 due to external noise.

[0125] 10 is a flowchart showing the third embodiment. When printing is completed, the CPU 301 executes the following processing in accordance with the control program stored in the ROM (read only memory) area of ​​the memory 302.

[0126] In S1001 (setting unit 312), CPU 301 sets timer 323. For example, a predetermined time P0 is set in timer 323. In S1002, CPU 301 (motor control unit 327) stops the rotation of pressure roller 107.

[0127] In S1003, the CPU 301 (setting unit 312) determines whether an update condition for the threshold Tth3 is satisfied. For example, the update condition may be every predetermined period. If the update condition is not satisfied, the CPU 301 advances the process from S1003 to S1006. If the update condition is satisfied, the CPU 301 advances the process from S1003 to S1004.

[0128] In S1004, the CPU 301 (acquisition unit 311) acquires the temperature T using the temperature sensor 105. In S1005, the CPU 301 (setting unit 312) determines the threshold value Tth3 based on the temperature T. For example, the setting unit 312 may determine the threshold value Tth3 by adding a predetermined value (e.g., 5° C.) to the temperature T. The setting unit 312 sets the threshold value Tth3 in the determination unit 315.

[0129] In S1006, the CPU 301 (acquisition unit 311) acquires the temperature T using the temperature sensor 105. In S1007, the CPU 301 (determination unit 315) determines whether the temperature T exceeds the threshold value Tth3. If the temperature T does not exceed the threshold value Tth3, the CPU 301 advances the process from S1007 to S1009. If the temperature T exceeds the threshold value Tth3, the CPU 301 advances the process from S1007 to S1008.

[0130] In S1008, CPU 301 (relay control unit 325) turns off electromagnetic relay 202 based on the determination result of determination unit 315. In S1009, CPU 301 (determination unit 319) determines whether timer 323 has timed out. For example, if the time measured by timer 323 becomes equal to or greater than predetermined time P0, CPU 301 advances the process from S1009 to S603 (first embodiment) or S803 (second embodiment). If timer 323 has not timed out, CPU 301 advances the process from S1009 to S1003. Therefore, threshold value Tth3 gradually decreases over time.

[0131] According to the third embodiment, the threshold value Tth3 is used instead of the threshold value Tth1 for a certain period after printing is completed, which makes it possible to reduce the number of times the electromagnetic relay 202 operates in intermittent printing such as copying.

[0132] Example 4 In the third embodiment, a threshold value Tth3 is used instead of the threshold value Tth1 for a certain period after printing is completed. This reduces the number of times the electromagnetic relay 202 operates during intermittent printing. In the fourth embodiment, a method is adopted in which the electromagnetic relay 202 is controlled using both the temperature T and the temperature gradient G as a method for reducing the number of times the electromagnetic relay 202 operates during intermittent printing.

[0133] 11A to 11C show the transition of temperature T in the standby state for Example 4. In particular, FIG. 11A shows a case in which the triac 204 is not exposed to external noise in the standby state. In Example 4, the determination made when the temperature T exceeds a threshold value Tth1 (e.g., 150°C) differs from that made in Examples 2 and 3. In Examples 2 and 3, if the temperature T exceeds the threshold value Tth1, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state. In Example 4, if the temperature T exceeds the threshold value Tth1 and the gradient G of the temperature T exceeds a threshold value Gth, the contacts of the electromagnetic relay 202 are controlled to a non-conductive state.

[0134] For example, the acquisition unit 311 acquires and monitors the temperature T every 20 msec. Furthermore, the acquisition unit 311 calculates a moving average (10-point moving average) every 200 msec. The slope calculation unit 321 calculates the slope G [°C / msec] from the difference between the previous moving average and the current moving average. The threshold value Gth is, for example, the slope when the temperature T rises by 2°C over 400 msec. When the determination unit 317 determines that the slope G exceeds the threshold value Gth, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a non-conductive state. Even if the temperature T subsequently changes from rising to falling, the relay control unit 325 maintains the contacts of the electromagnetic relay 202 in a non-conductive state. However, when the temperature T falls below the threshold value Tth2, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a conductive state.

[0135] 11A, image forming apparatus 10 performs printing during the period from time 0 to time t61. During this period, film 102 and pressure roller 107 rotate, and the contacts of electromagnetic relay 202 are controlled to be in a conductive state.

[0136] At time t61, the image forming apparatus 10 finishes printing and transitions to a standby state. During the period from time t61 to time t62, the temperature T exceeds the threshold value Tth1. However, because the slope of the temperature T is negative, the condition that the temperature T exceeds the threshold value Tth1 and the slope G is positive is not met. Therefore, the contacts of the electromagnetic relay 202 remain conductive.

[0137] During the period from time t62 to time t63, the previous state is maintained, that is, the contacts of the electromagnetic relay 202 are maintained in a conductive state.

[0138] At time t63, the temperature T becomes less than the threshold value Tth2. The contacts of the electromagnetic relay 202 are already in a conductive state. Therefore, the contacts of the electromagnetic relay 202 remain in a conductive state even after time t63.

[0139] Cases where Example 4 is applied (external noise occurs when temperature T is equal to or higher than Tth2) 11B shows a case where external noise occurs in the standby state. The solid line shows the temperature transition in the case where the fourth embodiment is applied. The dashed line shows the temperature transition in the case where the fourth embodiment is not applied. The standby state starts at time t71.

[0140] During the period from time t71 to time t72, the temperature T exceeds the threshold value Tth1, but because the slope G is negative, the contacts of the electromagnetic relay 202 remain conductive. At time t72, external noise occurs. This causes the triac 204 to unintentionally enter a conductive state, and the heater 103 begins to generate heat. As a result, the temperature T rises after time t72.

[0141] At time t73, it is determined that the gradient G exceeds the threshold value Gth, and the contacts of the electromagnetic relay 202 are controlled to be in a non-conductive state, thereby stopping the heat generation of the heater 103. After experiencing a temperature overshoot, the temperature T begins to decrease.

[0142] During the period from time t74 to time t76, the hysteresis function is active, and the contacts of the electromagnetic relay 202 are maintained in a non-conductive state.

[0143] At time t75, the external noise disappears. At time t76, the temperature T falls below the threshold value Tth2. Therefore, the contacts of the electromagnetic relay 202 are controlled to be in a conductive state. This state is maintained from time t76 onwards.

[0144] Cases where Example 4 is not applicable (external noise occurs when temperature T is Tth2 or higher) If Example 4 is not applied, the temperature transition will be as shown by the dashed line. The behavior of the dashed line shown in Figure 11B is the same as the behavior of the dashed line in Figure 7B described in Example 2.

[0145] Cases where Example 4 is applied (external noise occurs when temperature T is less than Tth2) 11C shows a case where external noise occurs when the temperature T is less than the threshold value Tth2 in the standby state. The solid line shows the case where the fourth embodiment is applied. The dashed line shows the case where the fourth embodiment is not applied.

[0146] The period from time 0 to time t81 is a period during which printing is being performed. The standby state begins at time t81. From time t81 to time t82, the temperature T exceeds the threshold value Tth1, but the slope G is equal to or less than the threshold value Gth. Therefore, the contacts of the electromagnetic relay 202 are maintained in a conductive state. From time t82 to t83, the temperature T is equal to or greater than the threshold value Tth2 and equal to or less than the threshold value Tth1. Since the hysteresis function is enabled during this period, the contacts of the electromagnetic relay 202 are maintained in a conductive state.

[0147] At time t83, the temperature T falls below the threshold value Tth2. However, the contacts of the electromagnetic relay 202 are already in a conductive state. At time t84, external noise occurs, causing the triac 204 to unintentionally enter a conductive state. As a result, the heater 103 begins to generate heat, and the temperature T rises. At time t85, the temperature T exceeds the threshold value Tth2, but the hysteresis function maintains the contacts of the electromagnetic relay 202 in their previous state. During the period from time t85 to time t86, power is supplied to the heater 103 due to the external noise. As a result, the temperature T continues to rise.

[0148] At time t86, the temperature T exceeds the threshold value Tth1, so the hysteresis function is deactivated and monitoring of the slope G begins.

[0149] At time t87, the temperature T exceeds the threshold value Tth1 and the gradient G exceeds the threshold value Gth. Therefore, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to be in a non-conductive state.

[0150] In this example, monitoring of the slope G begins after the temperature T exceeds the threshold value Tth1, but this is merely an example. The detection of the temperature T and the detection of the slope G may be performed sequentially. Alternatively, the comparison of the temperature T with the threshold value Tth1 may be performed after the slope G exceeds the threshold value Gth.

[0151] Since the contacts of the electromagnetic relay 202 are controlled to be in a non-conductive state, the temperature T begins to decrease after experiencing a temperature overshoot. From time t87 to time t88, the contacts are maintained in a non-conductive state by the hysteresis function.

[0152] The counter 322 described in the third embodiment is applied during the period from time t88 to time t89. That is, when the number of times the contact of the electromagnetic relay 202 is switched from a conductive state to a non-conductive state (count value C) exceeds the threshold Cth1, the CPU 301 activates the latch function. After time t89, the contact of the electromagnetic relay 202 is fixed to the non-conductive state by the latch function. The latch function and the release of the latch function are as described in the third embodiment.

[0153] 12 shows a control method of the embodiment 4. When printing is completed, the CPU 301 executes the following processing in accordance with the control program stored in the ROM (read only memory) area of ​​the memory 302.

[0154] In S1201, the CPU 301 (motor control unit 327) stops the rotation of the pressure roller 107. In S1202, the CPU 301 (acquisition unit 311) acquires the temperature T using the temperature sensor 105.

[0155] In S1203, the CPU 301 (determination unit 313) determines whether the temperature T exceeds the threshold value Tth1. If the temperature T does not exceed the threshold value Tth1, the CPU 301 advances the process from S1203 to S603 or S803. On the other hand, if the temperature T exceeds the threshold value Tth1, the CPU 301 advances the process from S1203 to S1204.

[0156] In S1204, the CPU 301 (calculation unit 321) finds the slope G. In S1205, the CPU 301 (determination unit 317) determines whether the slope G exceeds a threshold Gth. For example, it may be determined whether the slope G is a positive value. If the slope G is a negative value, the CPU 301 advances the process from S1205 to S1202. On the other hand, if the slope G is a positive value, the CPU 301 advances the process from S1205 to S1206.

[0157] In S1206, the CPU 301 (relay control unit 325) turns off the electromagnetic relay 202. Thereafter, the CPU 301 advances the process from S1206 to S603 or S803.

[0158] According to the fourth embodiment, the gradient G is used instead of the variable threshold Tth3. To improve productivity of intermittent printing, the electromagnetic relay 202 may be kept on even in standby mode. At that time, the temperature T of the heater 103 may unintentionally rise due to external noise. In this case, the gradient G is monitored to turn off the heater 103. This reduces the number of times the electromagnetic relay 202 operates, suppresses frequent shutdowns of the image forming apparatus 10, and protects the heating device 100.

[0159] <Example 5> The contacts of the electromagnetic relay 202 may be controlled depending on the state of the fixing nip portion N. During printing, the film guide unit 106 is pressed against the pressure roller 107 by a spring or the like (not shown), forming the fixing nip portion N. This is called the contact state. Meanwhile, the force with which the film guide unit 106 is pressed against the pressure roller 107 is controlled by the motor M2. When the pressure force becomes relatively weak, the fixing nip portion N narrows or disappears. The state in which the fixing nip portion N narrows is called the pressure-released state. The state in which the film guide unit 106 and the pressure roller 107 separate and the fixing nip portion N disappears is called the separation state. In the sleep state, if the film 102 and the pressure roller 107 remain in contact with each other for a long period of time while stopped, both may become deformed. The pressure-released state and separation state prevent this deformation from occurring.

[0160] Incidentally, the phenomenon in which the sheet R gets stuck inside the image forming apparatus 10 is called a jam. When a jam occurs, the user needs to remove the sheet S. The pressure release state and the separated state make it easier to pull out the sheet S from the heating device 100.

[0161] Therefore, when the image forming apparatus 10 transitions to a sleep state or when a jam occurs, the motor control unit 327 controls the motor M2 to place the heating device 100 in a pressure-released state or a separation state. When the heating device 100 is in the pressure-released state or the separation state, the contacts of the electromagnetic relay 202 may be controlled to a non-conductive state regardless of the temperature T. A mechanical operating time is required for the heating device 100 to transition from the pressure-released state or the separation state to the printing state (contact state). This operating time is generally longer than the time it takes for the contacts of the electromagnetic relay 202 to transition from a non-conductive state to a conductive state. In other words, when transitioning from the pressure-released state or the separation state to the printing state, the operating time of the electromagnetic relay 202 does not become a bottleneck for the FPOT of the image forming apparatus 10.

[0162] Therefore, when the heating device 100 is in the pressure release state or the separated state, the relay control unit 325 may control the contacts of the electromagnetic relay 202 to be always in a non-conducting state. This prevents the heater 103 from generating heat even if the triac 204 is turned on by external noise. As a result, frequent shutdowns of the image forming apparatus 10 are suppressed, and the heating device 100 can also be protected.

[0163] Example 6 In Example 6, a case will be described in which power is intentionally and temporarily supplied to heater 103 in a standby state. In a standby state in which film 102 and pressure roller 107 are not rotating, power may be temporarily supplied to heater 103 for purposes such as cleaning of heating device 100. This is called rotation-stop heating or temporary heating.

[0164] FIG. 13 is a diagram illustrating temporary heating. The operation of the second embodiment is applied during the period from time 0 to time t93. At time t93, the CPU 301 starts temporary heating. At time t93, the CPU 301 changes the temperature threshold for switching the contact of the electromagnetic relay 202 to a non-conductive state from threshold Tth1 (e.g., 150°C) to a fourth threshold Tth4 (e.g., 200°C). The relay control unit 325 switches the contact of the electromagnetic relay 202 from a non-conductive state to a conductive state. Furthermore, the relay control unit 325 controls the triac 204 based on the temperature T to adjust the power supplied to the heater 103. The temperature T increases from time t93. At time t94, the temperature T reaches a predetermined temperature. During the period from time t94 to time t95, the temperature T is maintained at the predetermined temperature.

[0165] During the period from time t93 to time t95, the determination unit 316 compares the temperature T with the temperature Tth4. There may be cases where the triac 204 is fixed to a constant on state due to external noise, causing the temperature T to exceed the temperature Tth4. In this case, the relay control unit 325 may switch the electromagnetic relay 202 off.

[0166] At time t95, the temporary heating is completed, and the relay control unit 325 turns off the triac 204. This stops the supply of power to the heater 103.

[0167] Furthermore, at time t95, CPU 301 changes the temperature threshold for switching the contacts of electromagnetic relay 202 to a non-conductive state back from Tth4 to Tth1. At time t95, temperature T exceeds threshold Tth1. Therefore, relay control unit 325 controls the contacts of electromagnetic relay 202 from a conductive state to a non-conductive state.

[0168] After time t95, the temperature T decreases. The hysteresis function is enabled from time t96 to time t97. Therefore, the contacts of the electromagnetic relay 202 are maintained in a non-conductive state. When the temperature T becomes less than the threshold value Tth2 at time t97, the relay control unit 325 controls the contacts of the electromagnetic relay 202 to a conductive state.

[0169] 14 shows a control method according to the sixth embodiment. In the standby state, the CPU 301 executes the following processing in parallel with any one of the first to fifth embodiments.

[0170] In S1401, the CPU 301 determines whether a condition for starting temporary heating is satisfied. If the condition for starting temporary heating is satisfied, the CPU 301 advances the process from S1401 to S1402. The condition for starting temporary heating may be that the operating time of the heating device 100 has exceeded a predetermined time, or that the number of sheets R that have passed through the heating device 100 has exceeded a predetermined number.

[0171] In S1402, the CPU 301 (relay control unit 325) turns on the electromagnetic relay 202. In S1403, the CPU 301 switches the temperature threshold for turning off the electromagnetic relay 202 from Tth1 to Tth4. For example, the relay control unit 325 may ignore the determination result of the determination unit 313 and adopt the determination result of the determination unit 316.

[0172] In S1403, the CPU 301 (relay control unit 325) controls the triac 204 based on the temperature T to control the temperature T to a predetermined temperature. In S1405, the CPU 301 determines whether the termination condition for temporary heating is satisfied. If the termination condition is not satisfied, the CPU 301 advances the process from S1405 to S1404. If the termination condition is satisfied, the CPU 301 advances the process from S1405 to S1406.

[0173] In S1406, CPU 301 switches the temperature threshold for turning off electromagnetic relay 202 from Tth4 to Tth1. In S1407, CPU 301 (motor control unit 327) drives motor M1 for a predetermined time. Motor M1 rotates film 102 and pressure roller 107 for cleaning heating device 100.

[0174] According to the sixth embodiment, the temperature threshold for switching the contact of the electromagnetic relay 202 to non-conduction is temporarily changed. This makes it possible to perform rotation-stop heating in a standby state. That is, the effects described in the first to fifth embodiments are achieved, and rotation-stop heating during standby is also possible.

[0175] <Technical ideas derived from examples> (Item 1) A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a heat generating means for heating at least one of the first rotating body and the second rotating body; a temperature detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a first switch means for adjusting the power supplied from an AC power source to the heat generating means; a second switch means provided in a power supply route for supplying the power from the AC power source to the heat generating means, the noise resistance of the first switch means to external noise coming from the AC power supply is lower than the noise resistance of the second switch means; The second switch means During a period in which the first rotating body and the second rotating body are in a non-rotating state, When the temperature detected by the temperature detection means exceeds a first threshold value, the temperature error is not notified by the notification means, and the temperature detection means is controlled to a non-conductive state. The heating device is controlled to a conductive state when the temperature detected by the temperature detection means becomes lower than a second threshold value which is equal to or lower than the first threshold value.

[0176] According to the embodiment, it is possible to achieve both productivity of the heating device 100 and protection of the components of the heating device 100. As a result, it is possible to achieve both productivity of the image forming device 10 and protection of the components of the image forming device 10. (Item 2) Item 2. The heating device according to item 1, wherein the first threshold value and the second threshold value are equal.

[0177] A single threshold may be used as described in Example 1. The first threshold and the second threshold are different from the threshold Te for reporting an error. (Item 3) the first threshold is higher than the second threshold; 2. The heating device according to claim 1, wherein, when the temperature is within a range from the first threshold value to the second threshold value, the second switch means is maintained in one of the conductive state and the non-conductive state, whichever state is selected when the temperature enters the range.

[0178] As explained in the second and subsequent examples, multiple thresholds may be used. (Item 4) 4. The heating device according to any one of items 1 to 3, wherein the first threshold value is set to a temperature at which, when the second switch means is in a conductive state during a period in which the first rotating body and the second rotating body are in a non-rotating state and the first switch means becomes uncontrollable and power is supplied from the AC power supply to the heat generating means, the second switch means is switched from a conductive state to a non-conductive state at a timing when heat damage is unlikely to occur to any of the first rotating body, the second rotating body, the heat generating means, and the temperature detecting means.

[0179] In this way, the threshold value Tth1 may be determined so as to prevent heat damage from reaching any of the fixing film 102, the pressure roller 107, the heater 103, and the temperature sensor 105. However, the threshold value Tth1 may be determined so as to prevent heat damage from reaching at least one of the fixing film 102, the pressure roller 107, the heater 103, and the temperature sensor 105. (Item 5) The temperature sensor further includes a notification unit that notifies the user of the error when the temperature exceeds a specified value, 5. The heating device according to item 4, wherein the first threshold value is lower than a temperature at which thermal damage may occur to any of the first rotating body, the second rotating body, the heat generating means, and the temperature detecting means, and is lower than the specified value.

[0180] The threshold value Te is an example of a specified value. The temperature at which damage may occur is, for example, Tx. (Item 6) When the first rotating body and the second rotating body transition from a rotating state to a non-rotating state, the second switch means is maintained in a conductive state, 6. The heating device according to any one of items 1 to 5, wherein the second switch means switches from a conductive state to a non-conductive state when the temperature exceeds a third threshold value that is higher than the first threshold value during a predetermined period after the first rotating body and the second rotating body transition from a rotating state to a non-rotating state.

[0181] 9, P0 is an example of a predetermined period, and Tth3 is an example of a third threshold. (Item 7) 7. The heating device according to item 6, wherein the length of the predetermined period is a predetermined length. (Item 8) 7. The heating device according to claim 6, wherein the third threshold value is reduced over time. (Item 9) 7. The heating device according to claim 6, wherein the predetermined period is a period from the time when the first rotating body and the second rotating body transition from a rotating state to a non-rotating state to the time when the temperature falls below the first threshold value for the first time.

[0182] 9, the temperature T becomes equal to or lower than the threshold value Tth1 for the first time at time t32. Therefore, time t32 may be used as the end time of the predetermined period. In this case, the length of the predetermined period is variable. (Item 10) 10. The heating device according to any one of items 1 to 9, wherein the second threshold value is determined so that a start-up time of the heating device, which is the sum of an operating time of the second switch means that occurs when an image forming apparatus equipped with the heating device starts an image forming operation and a heating time required to control the temperature of the heat generating means to a target temperature or higher, is shorter than a start-up time of at least one other process device that is provided in the image forming apparatus together with the heating device.

[0183] 5(A) and 5(B), the threshold value Tth2 may be determined so that the startup time of the heating device 100 does not become a bottleneck, which will further improve the productivity of the heating device 100. (Item 11) a counting means for counting the number of times the second switch means transitions from a conductive state to a non-conductive state during a period in which the first rotating body and the second rotating body are in a non-rotating state; a latch means for latching the second switch means in a non-conductive state when the number of times exceeds a predetermined number; 11. The heating device according to any one of items 1 to 10, further comprising:

[0184] Counter 322 is an example of a counting means. As described in relation to Fig. 7C, CPU 301, determination section 318 and relay control section 325 function as a latching means. (Item 12) Item 12. The heating device according to item 11, wherein the latch means releases the latch of the second switch means when a predetermined release condition is satisfied after the second switch means is latched in the non-conductive state. (Item 13) Item 13. The heating device according to item 12, wherein the predetermined release condition is that the time during which the second switch means is latched exceeds a predetermined time.

[0185] In this way, the latch may be released depending on the elapsed time, which will prevent a decrease in productivity. (Item 14) Item 13. The heating device according to item 12, wherein the predetermined release condition is that the temperature falls below a lower limit value that is lower than the second threshold value.

[0186] In this way, the latch may be released depending on the temperature, which will reduce the loss of productivity. (Item 15) A calculation means for calculating the temperature gradient; determining whether the temperature exceeds the first threshold and the slope exceeds a slope threshold; 15. The heating device according to any one of items 1 to 14, wherein the second switch means switches from a conductive state to a non-conductive state when the temperature exceeds the first threshold and the slope exceeds a slope threshold. (Item 16) The second switch means When the temperature is controlled to a predetermined target temperature higher than the first threshold value by intentionally supplying power from the AC power supply to the heat generating means during a period when the first rotating body and the second rotating body are in a non-rotating state, Even if the temperature exceeds the first threshold, the conductive state does not switch to the non-conductive state, 16. The heating device of any one of items 1 to 15, wherein the heating device switches from a conductive state to a non-conductive state when the temperature exceeds a fourth threshold value that is higher than the predetermined target temperature.

[0187] In this way, it is possible to temporarily heat the heating device 100 in the standby state. (Item 17) Item 17. The heating device according to item 16, wherein the intentional supply of power from the AC power source to the heat generating means is performed in order to clean the first rotating body and the second rotating body.

[0188] This allows the heating device 100 to be cleaned. (Item 18) The rotor further includes an adjusting means for adjusting the pressure acting between the first rotor and the second rotor, 18. The heating device according to any one of items 1 to 17, wherein the second switch means is controlled to a non-conductive state when the pressure is lower than a predetermined value, regardless of the temperature.

[0189] The motor M2 is an example of an adjusting means. The predetermined value is, for example, the pressure in the contact state. The pressure in the fixing nip N in the pressure-released state or the separated state is lower than the pressure in the fixing nip N in the contact state. (Item 19) 19. The heating device according to any one of items 1 to 18, wherein an actuation time of the first switch means is shorter than an actuation time of the second switch means.

[0190] In this way, the first switch means may be a switch that has low resistance to external noise but can operate at high speed, and the second switch means may be a switch that operates at low speed but has high resistance to external noise. (Item 20) A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a heat generating means for heating at least one of the first rotating body and the second rotating body; a temperature detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a semiconductor switch element that adjusts the power supplied from an AC power source to the heat generating means; an electromagnetic relay provided in a power supply route that supplies the power from the AC power source to the heat generating means, The electromagnetic relay is During a period in which the first rotating body and the second rotating body are in a non-rotating state, When the temperature detected by the temperature detection means exceeds a first threshold value, the temperature error is not notified by the notification means, and the temperature detection means is controlled to a non-conductive state. The heating device is controlled to a conductive state when the temperature detected by the temperature detection means becomes lower than a second threshold value which is equal to or lower than the first threshold value.

[0191] The triac 204 and the thyristor are examples of semiconductor switching elements. (Item 21) a transfer means for transferring a toner image onto a sheet; 20. The heating device according to any one of items 1 to 19, which applies heat to the image transferred to the sheet, thereby fixing the image to the sheet; An image forming apparatus having the same.

[0192] 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]

[0193] 102: film, 107: pressure roller, 103: heater, 105: temperature sensor, 202: electromagnetic relay, 204: triac

Claims

1. A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a heat generating means for heating at least one of the first rotating body and the second rotating body; a temperature detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a first switch means for adjusting the power supplied from an AC power source to the heat generating means; a second switch means provided in a power supply route for supplying the power from the AC power source to the heat generating means, the noise resistance of the first switch means to external noise coming from the AC power supply is lower than the noise resistance of the second switch means; The second switch means During a period in which the first rotating body and the second rotating body are in a non-rotating state, When the temperature detected by the temperature detection means exceeds a first threshold value, the temperature error is not notified by the notification means, and the temperature detection means is controlled to a non-conductive state. The heating device is controlled to a conductive state when the temperature detected by the temperature detection means becomes lower than a second threshold value which is equal to or lower than the first threshold value.

2. The heating device of claim 1 , wherein the first threshold value and the second threshold value are equal.

3. the first threshold is higher than the second threshold; 2. The heating device according to claim 1, wherein when the temperature is within a range from the first threshold value to the second threshold value, the second switch means is maintained in one of the conductive state and the non-conductive state, whichever state is selected when the temperature enters the range.

4. 2. The heating device according to claim 1, wherein the first threshold value is set to a temperature at which, when the second switch means is in a conductive state during a period in which the first rotating body and the second rotating body are in a non-rotating state, and when the first switch means becomes uncontrollable and power is supplied from the AC power source to the heat generating means, the second switch means is switched from a conductive state to a non-conductive state at a timing when heat damage is unlikely to occur to any of the first rotating body, the second rotating body, the heat generating means, and the temperature detection means.

5. The temperature sensor further includes a notification unit that notifies the user of the error when the temperature exceeds a specified value, The heating device of claim 4, wherein the first threshold value is lower than a temperature at which thermal damage may occur to any of the first rotating body, the second rotating body, the heat generating means, and the temperature detecting means, and is lower than the specified value.

6. When the first rotating body and the second rotating body transition from a rotating state to a non-rotating state, the second switch means is maintained in a conductive state, 2. The heating device of claim 1, wherein the second switch means switches from a conductive state to a non-conductive state when the temperature exceeds a third threshold value higher than the first threshold value during a predetermined period after the first rotating body and the second rotating body transition from a rotating state to a non-rotating state.

7. The heating device according to claim 6 , wherein the length of the predetermined period is a predetermined length.

8. The heating device of claim 6 , wherein the third threshold is reduced over time.

9. 7. The heating device according to claim 6, wherein the predetermined period is the period from the time when the first rotating body and the second rotating body transition from a rotating state to a non-rotating state to the time when the temperature falls below the first threshold value for the first time.

10. 2. The heating device according to claim 1, wherein the second threshold value is determined so that the start-up time of the heating device, which is the sum of the operation time of the second switch means that occurs when the image forming apparatus in which the heating device is installed starts an image forming operation and the heating time required to control the temperature of the heat generating means to a target temperature or higher, is shorter than the start-up time of at least one other process device that is provided in the image forming apparatus together with the heating device.

11. a counting means for counting the number of times the second switch means transitions from a conductive state to a non-conductive state during a period in which the first rotating body and the second rotating body are in a non-rotating state; a latch means for latching the second switch means in a non-conductive state when the number of times exceeds a predetermined number; The heating device of claim 1 further comprising:

12. 12. The heating device according to claim 11, wherein the latch means unlatches the second switch means when a predetermined unlatching condition is satisfied after the second switch means is latched in the non-conductive state.

13. 13. The heating device according to claim 12, wherein the predetermined release condition is that the time during which the second switch means is latched exceeds a predetermined time.

14. The heating device according to claim 12 , wherein the predetermined condition for canceling the temperature change is that the temperature has fallen below a lower limit value that is lower than the second threshold value.

15. A calculation means for calculating the temperature gradient; determining whether the temperature exceeds the first threshold and the slope exceeds a slope threshold; 2. The heating device of claim 1, wherein the second switch means switches from a conducting state to a non-conducting state when the temperature exceeds the first threshold and the slope exceeds a slope threshold.

16. The second switch means When the temperature is controlled to a predetermined target temperature higher than the first threshold value by intentionally supplying power from the AC power supply to the heat generating means during a period when the first rotating body and the second rotating body are in a non-rotating state, Even if the temperature exceeds the first threshold, the conductive state does not switch to the non-conductive state, The heating device of claim 1 , wherein the device switches from a conductive state to a non-conductive state when the temperature exceeds a fourth threshold value that is higher than the predetermined target temperature.

17. The heating device according to claim 16 , wherein the intentional supply of power from the AC power source to the heat generating means is performed in order to clean the first rotating body and the second rotating body.

18. The rotor further includes an adjusting means for adjusting the pressure acting between the first rotor and the second rotor, 2. The heating device according to claim 1, wherein said second switch means is controlled to a non-conductive state when said pressure is lower than a predetermined value, regardless of said temperature.

19. 2. The heating device of claim 1, wherein the activation time of said first switch means is shorter than the activation time of said second switch means.

20. A first rotating body; a second rotating body that contacts the first rotating body to form a nip portion; a heat generating means for heating at least one of the first rotating body and the second rotating body; a temperature detection means disposed adjacent to any one of the first rotating body, the second rotating body, or the heat generating means; a semiconductor switch element that adjusts the power supplied from an AC power source to the heat generating means; an electromagnetic relay provided in a power supply route that supplies the power from the AC power source to the heat generating means, The electromagnetic relay is During a period in which the first rotating body and the second rotating body are in a non-rotating state, When the temperature detected by the temperature detection means exceeds a first threshold value, the temperature error is not notified by the notification means, and the temperature detection means is controlled to a non-conductive state. The heating device is controlled to a conductive state when the temperature detected by the temperature detection means becomes lower than a second threshold value which is equal to or lower than the first threshold value.

21. a transfer means for transferring a toner image onto a sheet; The heating device according to claim 1 , which applies heat to the image transferred to the sheet, thereby fixing the image to the sheet; An image forming apparatus having the same.

Images