Image forming apparatus

Abstract

To provide an image forming apparatus that can minimize damage to components during a runaway electrical current state. [Solution] The image forming apparatus comprises a fuser F that fixes an image transferred to a recording medium onto the recording medium using an endless fixing belt 310 having a plurality of halogen heaters 341 to 346 and a pressure roller 330; a plurality of switch units 411 to 416 provided corresponding to each of the plurality of halogen heaters 341 to 346; a CPU 450 that controls the connection state of the plurality of switch units 411 to 416 and controls the supply of power to the plurality of halogen heaters 341 to 346; an exclusive connection unit 420 that exclusively connects switch unit 411 and switch unit 412; and a rotation detection unit 430 that disconnects switch unit 411 and switch unit 412 based on the rotation speed of the fixing belt 310.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a recording medium by an electrophotographic method.

Background Art

[0002] An electrophotographic image forming apparatus forms an image on a recording medium using an electrophotographic process. Examples of electrophotographic image forming apparatuses include electrophotographic copiers (e.g., digital copiers), electrophotographic printers (e.g., color laser beam printers), MFPs (multifunction peripherals), facsimile apparatuses, word processors, and the like. Such image forming apparatuses are used for forming monochrome images and color images.

[0003] An electrophotographic image forming apparatus includes a plurality of process units such as a photoreceptor, a charger, an exposure device, a developing device, a transfer unit, and a fixing device. The charger uniformly charges the surface of the photoreceptor, which is an image carrier. The exposure device irradiates and scans the surface of the uniformly charged photoreceptor with a laser beam (hereinafter referred to as "light beam") modulated according to image information to form an electrostatic latent image on the surface of the photoreceptor. The developing device develops the electrostatic latent image into a developer image (toner image) using a developer (toner). The transfer unit transfers the toner image formed on the surface of the photoreceptor to a recording medium. The fixing device heats and pressurizes the recording medium onto which the toner image has been transferred to fix the toner image on the recording medium. The image forming apparatus forms an image on the recording medium in this way.

[0004] Patent Document 1 discloses a fuser that uses a halogen heater as a heat source. Such a fuser comprises a heating rotating body, such as a roller or belt, on which a halogen heater is provided so as to face its inner circumference, and a pressurizing rotating body. The halogen heater transmits radiant heat generated by the application of electricity to the heating rotating body. The fuser holds and transports a recording medium carrying an unfixed toner image at the fixing nip portion, which is the contact point between the heating rotating body and the pressurizing rotating body, and fixes the toner image to the recording medium using heat and pressure. Patent Document 2 discloses a fuser having a configuration in which multiple halogen heaters with high power are arranged on a roller with a large heat capacity. Such a fuser is suitable for increasing the speed of image forming apparatus. In this case, since the power capacity of one power supply system is insufficient, power is supplied to the multiple halogen heaters from multiple power supply systems. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-21173 [Patent Document 2] Japanese Patent Publication No. 2008-146712 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Fusers, which require high power, can experience a power surge run due to a failure in the control system, components, or power supply. A power surge run can cause abnormal overheating, potentially damaging components. To prevent this, image forming apparatuses are equipped with a damage prevention mechanism that detects abnormal overheating and stops the fuser's operation, thus preventing damage to fuser components due to overheating.

[0007] However, if the power during a power-over is high, the fuser temperature will rise significantly in the time between the damage prevention mechanism detecting abnormal overheating and stopping the fuser's operation. Therefore, it is necessary to suppress the power during a power-over. Furthermore, if heater temperature control is performed in standby mode to shorten the first print time, the rotation speed of the heating element is slower than in normal print mode, resulting in a greater temperature rise in the fuser during a power-over. For this reason, power suppression according to the rotation speed is necessary even in standby mode.

[0008] In view of the above-mentioned problems, the primary objective of the present invention is to provide an image forming apparatus that can minimize damage to components during a runaway electrical current state. [Means for solving the problem]

[0009] The present invention provides an image forming apparatus comprising: an image forming means for forming an image; a transfer means for transferring the image formed by the image forming means to a recording medium; a fixing means for fixing the image transferred by the transfer means to the recording medium using a heating unit and a pressurized rotating body on which a plurality of heat sources are arranged and rotate; a plurality of switch means provided corresponding to each of the plurality of heat sources; a control means for controlling the connection state of the plurality of switch means and controlling the supply of power to the plurality of heat sources; an exclusion means for exclusively connecting one of the switch means with any other switch means; and a rotation detection means for disconnecting one of the switch means with any other switch means based on the rotation speed of the heating unit. [Effects of the Invention]

[0010] According to the present invention, damage to components during a runaway electrical condition can be minimized. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram illustrating the configuration of an image forming apparatus. [Figure 2] Diagram of the fuser unit configuration. [Figure 3] (a) and (b) are diagrams illustrating the heating roller. [Figure 4] A diagram illustrating the heat distribution of a halogen heater. [Figure 5] Configuration diagram of the control board. [Figure 6] A table showing the operating duty cycle of halogen heaters. [Figure 7] (a) and (b) are diagrams illustrating the temperature changes of the fixing belt. [Figure 8] A diagram illustrating the operating modes and the total power consumption of each halogen heater. [Modes for carrying out the invention]

[0012] Preferred embodiments of this invention will be described in detail below with reference to the drawings.

[0013] Figure 1 is a diagram of the configuration of the image forming apparatus according to this embodiment. The image forming apparatus 100 is a full-color image forming apparatus that forms images of multiple colors (four colors in this embodiment) and prints a full-color image onto a recording medium P. For this purpose, the image forming apparatus 100 is equipped with multiple (four in this embodiment) image forming stations (first to fourth image forming stations Y, M, C, K). The first image forming station Y forms a yellow (y) image. The second image forming station M forms a magenta (m) image. The third image forming station C forms a cyan (c) image. The fourth image forming station K forms a black (k) image. Hereafter, the configuration for forming the yellow image will be described, and the description of the configuration for forming images of other colors will be omitted.

[0014] The first image forming station Y comprises a photosensitive drum 101y, a charging roller 102y, an exposure unit 103y, a developer unit 104y, a primary transfer roller 105y, and a photoreceptor cleaner 106y, all of which are first image carriers. The exposure unit 103y emits laser light Ey. A second image carrier, an intermediate transfer belt 107, is provided between the photosensitive drum 101y and the primary transfer roller 105y. The intermediate transfer belt 107 forms a secondary transfer section with the secondary transfer roller 109. The recording medium P is housed in a paper feed cassette 111 and is transported to the secondary transfer roller 109 according to the timing of image formation by the first to fourth image forming stations Y, M, C, and K. A pickup roller 112, a paper feed roller 113, and a registration roller 114 are provided in the transport path from the paper feed cassette 111 to the secondary transfer roller 109. A fuser unit F is positioned downstream of the secondary transfer roller 109 in the transport direction of the recording medium P.

[0015] The image forming apparatus 100 is powered by commercial power via power cords 10 and 11. The image forming apparatus 100 includes a power supply board (not shown). The power supply board converts the power supplied from commercial power into power for use inside the image forming apparatus 100 and supplies it to each part of the image forming apparatus 100. The image forming apparatus 100 includes an operation unit 119, which is a user interface, and a CPU (Central Processing Unit) described later, which acts as a controller. The CPU obtains image forming commands from external devices (not shown) or the operation unit 119, and drives the photosensitive drum 101y, the developer unit 104y, the secondary transfer roller 109, and the rollers in the fuser unit F to rotate at a predetermined process speed using a drive unit (not shown).

[0016] The photosensitive drum 101y is a drum-shaped photoreceptor having a charging layer on its surface, and is uniformly charged with a predetermined polarity and potential on its surface during rotation by a charging roller 102 which is a charger. The exposure device 103y irradiates and scans a light beam on the surface of the uniformly charged photosensitive drum 101y. By changing the potential at the irradiation position of the light beam, an electrostatic latent image is formed on the surface of the photosensitive drum 101y. The developing device 104y develops the electrostatic latent image with yellow toner. Thus, a yellow toner image is formed on the surface of the photosensitive drum 101y. Similarly, a magenta toner image is formed on the surface of the photosensitive drum 101m. A cyan toner image is formed on the surface of the photosensitive drum 101c. A black toner image is formed on the surface of the photosensitive drum 101k.

[0017] The toner image formed on the photosensitive drum 101y is transferred to the intermediate transfer belt 107 by the corresponding primary transfer roller 105y. The toner remaining on the photosensitive drum 101y after transfer is recovered by the photoreceptor cleaner 106y. The toner images formed on the photosensitive drums 101m, 101c, 101k are similarly transferred to the intermediate transfer belt 107. At this time, the toner images of the respective photosensitive drums 101y, 101m, 101c, 101k are transferred so as to overlap on the intermediate transfer belt 107. Thereby, a full-color toner image is formed on the intermediate transfer belt 107. The intermediate transfer belt 107 conveys the transferred toner image to the secondary transfer roller 109 by rotating.

[0018] The recording medium P is fed from the paper feed cassette 111 by the pickup roller 112 at a predetermined timing. The paper feed roller 113 separates the recording medium P fed by the pickup roller 112 one by one and conveys it to the registration roller 114. The registration roller 114 corrects the skew of the recording medium P conveyed by the paper feed roller 113. The registration roller 114 conveys the recording medium P after skew correction to the secondary transfer roller 109 in accordance with the timing when the toner image carried by the intermediate transfer belt 107 is conveyed to the secondary transfer roller 109.

[0019] The full-color toner image carried on the intermediate transfer belt 107 is collectively transferred onto the surface of the recording medium P by the secondary transfer roller 109. The secondary transfer roller 109 transfers the toner image from the intermediate transfer belt 107 to the recording medium P when a high voltage is applied from a high-voltage substrate (not shown). The toner remaining on the intermediate transfer belt 107 after transfer is recovered by the intermediate transfer belt cleaner 110.

[0020] The recording medium P onto which the toner image has been transferred is conveyed to the fixing device F by the secondary transfer roller 109. The fixing device F fixes the toner image onto the recording medium P by heating and pressing the recording medium P onto which the toner image has been transferred. The recording medium P onto which the toner image has been fixed is conveyed to the discharge roller 118 by the conveying rollers 115, 116, and 117 provided in the conveying path. The discharge roller 118 discharges the recording medium P conveyed by the conveying rollers 115, 116, and 117 outside the machine. In this way, the recording medium P (printed matter) on which the color image has been formed is obtained.

[0021] Figure 2 is a configuration diagram of the fixing device F. The fixing device F of the present embodiment is of the belt heating type. The fixing device F includes a heating unit 300 and a pressure roller 330. The heating unit 300 includes an endless and rotatable fixing belt 310 (rotating body), a pressure pad 320 as a fixing member, a stay 360, a heating roller 340 as a heating rotating body, and a tension roller 350. The pressure roller 330 is biased toward the fixing belt 310 and is a pressure rotating body that forms a nip portion N with the fixing belt 310.

[0022] The fixing belt 310 has thermal conductivity and heat resistance, and for example, it is a thin-walled cylindrical shape with an inner diameter of 120 mm. In this embodiment, the fixing belt 310 has a three-layer structure consisting of a base layer, an elastic layer on the outer circumference of the base layer, and a release layer on the outer circumference of the elastic layer. The base layer has a thickness of 60 μm and is made of polyimide resin (PI). The elastic layer has a thickness of 300 μm and is made of silicone rubber. The release layer has a thickness of 30 μm and is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 310 is stretched by a pressure pad 320, a heating roller 340, and a tensioning roller 350.

[0023] A sensor unit 370 is positioned near the fixing belt 310 to detect the rotational speed of the fixing belt 310. The sensor unit 370 outputs a pulse signal corresponding to the rotational speed of the fixing belt 310. The faster the rotational speed, the higher the frequency of the pulse signal, and the slower the rotational speed, the lower the frequency of the pulse signal.

[0024] The pressure pad 320 is pressed against the pressure roller 330 via the fixing belt 310. The material of the pressure pad 320 is, for example, LCP (liquid crystal polymer) resin. The heating roller 340 is, for example, a stainless steel pipe with an outer diameter of 40 mm and a thickness of 1 mm, and has multiple (six in this embodiment) halogen heaters 341 to 346 arranged inside as a heat source. The halogen heaters 341 to 346 are controlled by a control board (not shown) to generate heat up to a predetermined temperature.

[0025] The fixing belt 310 is heated by the heating roller 340. The fuser unit F is equipped with a thermistor, described later, for detecting the temperature of the heating roller 340. Based on the temperature detection result by the thermistor, the fixing belt 310 is controlled to a predetermined target temperature according to the paper type of the recording medium P. The tension roller 350 is, for example, a stainless steel pipe with an outer diameter of 40 [mm] and a thickness of 1 [mm], and its end is rotatably supported by a bearing (not shown). The tension roller 350 is biased by a spring supported by a frame (not shown) of the heating unit 300, and is a tension roller that applies a predetermined tension to the fixing belt 310. The tension roller 350 rotates in a driven motion relative to the fixing belt 310. The tension from the spring is 50 [N]. By applying tension to the fixing belt 310, the fixing belt 310 follows the pressure pad 320. A sensor unit 370 for detecting the rotational speed of the fixing belt 310 is positioned near the tension roller 350.

[0026] The pressure roller 330 is a roller having an elastic layer on the outer circumference of its shaft, with a release layer formed on the outer circumference of the elastic layer. The shaft material is, for example, stainless steel. The elastic layer is made of, for example, conductive silicone rubber with a thickness of 5 mm. The release layer is made of, for example, PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 50 μm.

[0027] The fuser unit F heats the toner image by gripping and transporting the recording medium P, which carries the toner image, in the nip section N formed between the fuser belt 310 and the pressure roller 330. The toner image melts when heated and is fixed to the recording medium P when pressurized. In this way, the fuser unit F fixes the toner image to the recording medium P while gripping and transporting it.

[0028] Figure 3 is an explanatory diagram of the heating roller 340. Figure 3(a) is a schematic diagram of the cross-section of the heating roller 340 in the direction of the rotation axis. Halogen heaters 341 to 346 are supported by holders (not shown) inside the heating roller 340. Thermistors 401 and 402 are positioned in contact with the heating roller 340. Thermistor 401 detects the surface temperature of the axial central part of the heating roller 340. Thermistor 402 detects the surface temperature of the axial end of the heating roller 340.

[0029] Figure 3(b) is an external view of the axial end of the heating roller 340. The halogen heaters 341 to 346 consist of a glass tube through which a filament passes, and bases 347 to 349 connected to both ends thereof. Lead wires 341a to 346a are connected to bases 347 to 349, corresponding to the halogen heaters 341 to 346. Halogen heaters 341 and 342 are connected to base 347. Lead wires 341a and 342a are connected to base 347. Halogen heater 343 is connected to base 348. Lead wire 343a is connected to base 348. Halogen heaters 344 to 346 are connected to base 349. Lead wires 344a to 346a are connected to base 349. Power is supplied to the corresponding halogen heaters 341 to 346 via lead wires 341a to 346a.

[0030] Figure 4 is an explanatory diagram of the heat generation distribution of the six halogen heaters 341 to 346 in this embodiment. The horizontal axis represents the position of the halogen heaters 341 to 346 in the longitudinal direction (front-to-back direction in Figure 2), and the vertical axis represents the heat generation performance. The recording medium P is passed through in a direction perpendicular to the longitudinal direction of the halogen heaters 341 to 346.

[0031] The six halogen heaters 341-346 each have different heat distributions. With positions D1 and D2 as the boundary, halogen heaters 341 and 346 mainly generate heat in the central region. With positions D1 and D2 as the boundary, halogen heaters 342, 344, and 345 mainly generate heat in the end regions. Halogen heater 343 generates heat throughout its entire region. Halogen heaters 341-343 and 346 are supplied with 1000[W] of power. Halogen heaters 344 and 345 are supplied with 500[W] of power.

[0032] In this configuration, by reducing the illumination ratio of halogen heaters 342, 344, and 345, which mainly generate heat in their end regions, it is possible to suppress heat accumulation at both ends of the heating roller 340. As a result, even when recording media P with a short width dimension in the front-to-back direction are continuously fed through, it is possible to prevent both ends of the heating roller 340 from becoming hot.

[0033] Thermistor 401 is positioned between positions D1 and D2 and detects the temperature of the central region of the heating roller 340. Thermistor 402 is positioned outside position D1 and detects the temperature of the end region of the heating roller 340. Thermistors 401 and 402 are positioned so as not to overlap positions D1 and D2. This arrangement allows for the detection of temperatures in both the central and end regions of the heating roller 340.

[0034] In this embodiment, the length of the heating portion of halogen heaters 341 to 346 is 500 [mm], the distance from the base end of halogen heaters 341 to 346 to position D1 is 125 [mm], and the distance from the base end of halogen heaters 341 to 346 to position D2 is 375 [mm]. Differences in the supplied power are provided between the base end and position D1, between position D1 and position D2, and between position D2 and the other end. For example, for halogen heater 341, the power is 25% between the base end and position D1 (end region), 100% between position D1 and position D2 (central region), and 25% between position D2 and the other end (end region). Therefore, the power supplied to halogen heater 341 is 100 [W] at both end regions and 800 [W] at the central region.

[0035] Figure 5 is a diagram of the configuration of the control board that drives and controls the halogen heaters 341 to 346. Here, the configuration of the control board 15 for driving and controlling the halogen heaters 341 to 346 is described, but the control board 15 may also have a configuration that controls the overall operation of the image forming apparatus 100.

[0036] The control board 15 includes a CPU 450 and switch units 411 to 416. The switch units 411 to 416 are provided between the power cords 10 and 11 and the halogen heaters 341 to 346. The switch units 411 to 416 are connected to the corresponding halogen heaters 341 to 346 via corresponding lead wires 341a to 346a. The switch units 411 to 416 are switching elements for controlling the power supply from the power cords 10 and 11 to the corresponding halogen heaters 341 to 346. The switch units 411 to 416 are composed of, for example, triacs, transistors, IGBTs (Insulated Gate Bipolar Transistors), etc.

[0037] Power cord 10 is connected to switch units 411-413. Power cord 11 is connected to switch units 414-416. Switch units 411-413 are connected to halogen heaters 341-343. Switch units 414-416 are connected to halogen heaters 344-346.

[0038] The configuration of power cord 10, switch units 411-413, lead wires 341a-343a, and halogen heaters 341-343 constitutes the first power supply system. Halogen heaters 341-343 constitute the first heater group. The configuration of power cord 11, switch units 414-416, lead wires 344a-346a, and halogen heaters 344-346 constitutes the second power supply system. Halogen heaters 344-346 constitute the second heater group. The maximum power of each system is determined by the rating of the power cord; for example, the total power of the halogen heaters in each system is 2000[W] or less. Since the halogen heaters 341-343 of the first heater group would reach 3000[W] if lit simultaneously, they need to be controlled so that they do not light up at the same time.

[0039] Thermistors 401 and 402 detect the temperature of the center and edge of the heating roller 340, respectively, and transmit the detected temperature information to the CPU 450. The CPU 450 detects the temperature of the heating roller 340 based on the temperature information obtained from thermistors 401 and 402, and determines the lighting duty cycle of the halogen heaters 341 to 346 based on the detected temperature. Based on the determined lighting duty cycle, the CPU 450 outputs switching signals 451 to 456 to control the connection state of the switch units 411 to 416. The switch units 411 to 416 are switched between connected and disconnected by the switching signals 451 to 456.

[0040] The CPU 450 determines the lighting duty cycle based on temperature information obtained from thermistors 401 and 402 at predetermined time intervals, in this case, a 10-millisecond cycle. Switching of the second power supply system, switch units 414 to 416, is performed in units of two half-wave cycles of the AC power supply. The CPU 450 transmits switching signals 451 to 456 to control halogen heaters 341 to 346 independently.

[0041] The control board 15 includes an overheating unit 380, an exclusion unit 420, and a rotation detection unit 430. The overheating unit 380 transmits stop signals 381 to 386 to the switch units 411 to 416 when it detects that at least one of the thermistors 401 and 402 is above a predetermined temperature. The stop signals 381 to 386 shut off the switch units 411 to 416. The exclusion unit 420 exclusively connects one switch unit to any one other switch unit. In this embodiment, the exclusion unit 420 exclusively connects switch unit 411 and switch unit 412. To this end, when the switching signal 451 is a signal that controls switch unit 411 to connect, the exclusion unit 420 outputs a signal 421 that causes the switching signal 452 to stop switch unit 412. The mutual exclusion unit 420 outputs a signal 421 to connect the switch unit 412 when the switching signal 451 is a signal that controls the switch unit 411 to shut off, and the switching signal 452 to connect the switch unit 412. The mutual exclusion unit 420 prevents the halogen heaters 341 and 342 from lighting up at the same time, and only one of them lights up at a time.

[0042] Switch units 411 and 412 (halogen heater 341 and halogen heater 342) connected to the exclusion unit 420 are on the same first power supply system and are supplied with power from the power cord 10. Because the exclusion unit 420 causes halogen heater 341 and halogen heater 342 to light up exclusively, the maximum power of the first power supply system is 2000[W] or less. In other words, even when halogen heater 341 and halogen heater 343 are lit simultaneously, or when halogen heater 342 and halogen heater 343 are lit simultaneously, the maximum power of the first power supply system is 200[W] or less.

[0043] The rotation detection unit 430 acquires the detection result from the sensor unit 370 provided on the fuser unit F. The sensor unit 370 detects the rotational speed of the fuser belt 310. The rotation detection unit 430 converts the frequency of the signal representing the detection result of the sensor unit 370. If the frequency representing the detection result of the sensor unit 370 is above a predetermined frequency, the rotation detection unit 430 controls the switch units 411 and 412 to an off state, preventing the halogen heaters 341 and 342 from being lit. The frequency of the signal representing the detection result of the sensor unit 370 represents the rotational speed of the fuser belt 310.

[0044] For example, the rotation detection unit 430 controls the switch units 411 and 412 to the off state when the frequency representing the detection result of the sensor unit 370 is 1 kHz or higher, which corresponds to the rotation speed of the fixing belt 310 at 100 mm / s. To this end, the rotation detection unit 430 transmits switching signals 431 and 432 to the switch units 411 and 412. In this way, the rotation detection unit 430 suppresses the illumination of halogen heaters 341 and 342 when the fixing belt 310 is rotating at a predetermined speed or lower (100 mm / s or less).

[0045] Figure 6 is a table showing the lighting duty cycles of halogen heaters 341-346 in relation to the width dimension of the recording medium P (hereinafter referred to as "paper width"). When printing starts, the CPU 450 determines the lighting duty cycle based on the paper width of the recording medium P.

[0046] For example, in the case of a recording medium P with a paper width of 148 mm or less, it is not necessary to raise the temperature all the way to the edge region of the fuser belt 310 because the paper width is narrow. Therefore, the lighting duty cycle of halogen heaters 341 and 346, which mainly generate heat in the central region, is set to be high. In the case of a recording medium P with a paper width of 297 mm or more, it is necessary to raise the temperature all the way to the edge region of the fuser belt 310. Therefore, the lighting duty cycle of halogen heaters 342, 344, and 345, which mainly generate heat in the edge region, is set to be high.

[0047] In this way, the halogen heaters that are lit are switched depending on the paper width. The halogen heater 341 mainly generates heat in the central region, and the halogen heater 342 mainly generates heat in the edge region. Since the halogen heaters 341 and 342 have different uses, the required temperature can be maintained by lit exclusively by the mutual exclusion section 420.

[0048] Figure 7 is an explanatory diagram of the temperature change of the fixing belt 310 during a runaway power-on state. Figure 8 is an explanatory diagram of the operating modes of the image forming apparatus 100 and the total power of each halogen heater 341 to 346.

[0049] Figure 7(a) shows the temperature transition during a power-over runaway state in print mode. In print mode, an image is formed on the recording medium P. Waveform A shows the temperature transition when the mutual exclusion unit 420 operates and exclusively supplies power to halogen heaters 341 and 342. Waveform B shows the temperature transition when the mutual exclusion unit 420 does not operate and power is supplied simultaneously to halogen heaters 341 and 342.

[0050] In waveform A, the CPU 450 outputs switching signals 451 to 456 to connect switch units 411 to 416 with a 100% lighting duty cycle during a power-on runaway condition. In waveform A, because the operating mode is print mode, the fuser belt 310 rotates at a predetermined rotational speed (e.g., 300 [mm / s]). The rotation detection unit 430 compares the rotational speed of the fuser belt 310 with a threshold (e.g., 100 [mm / s]). If the rotational speed of the fuser belt 310 is greater than the threshold, the power supply to halogen heaters 341 and 342 will not stop.

[0051] Because the mutual exclusion unit 420 is in operation, it outputs a signal 421 to stop the switching signal 452. As a result, halogen heaters 341, 343-346 are supplied with power at a 100% duty cycle. In this state, the total power of the heating roller 340 becomes 4000[W].

[0052] The overheating unit 380 outputs stop signals 381 to 386 to shut off the switch units 411 to 416 when the temperature of thermistor 401 or thermistor 402 exceeds a predetermined threshold temperature. In this embodiment, the threshold temperature is 200°C. In waveform A, 60 seconds after the runaway current condition occurs, the temperature of thermistor 401 or thermistor 402 exceeds 200°C, and the switch units 411 to 416 stop. However, due to the responsiveness of the overheating unit 380 and the overshoot of the fixing belt 310, the temperature of the fuser F continues to rise. The fuser F reaches its maximum temperature 90 seconds after the runaway current condition begins. At this time, the temperature of the fixing belt 310 is 290°C. The temperature at which the surrounding components of the fixing belt 310 are damaged is 300°C. Therefore, in waveform A, operation can be stopped without damaging any components even in a runaway current condition.

[0053] In waveform B, CPU 450 outputs switching signals 451-456 to connect switch units 411-416 with a 100% duty cycle. Since the mutual exclusion unit 420 is not operating, halogen heaters 341-346 are supplied with power with a 100% duty cycle. In this state, the total power of the heating roller 340 becomes 5000[W].

[0054] The overheating section 380 outputs stop signals 381-386 to shut off the switch sections 411-416 when the temperature of thermistor 401 or thermistor 402 exceeds the threshold temperature. In waveform B, the power is greater than in waveform A, resulting in a steeper slope of temperature rise. Therefore, in waveform B, 55 seconds after the runaway current condition occurs, the temperature of thermistor 401 or thermistor 402 exceeds 200°C, causing the switch sections 411-416 to shut off.

[0055] However, due to the responsiveness of the overheating section 380 and the overshoot of the fixing belt 310 temperature, the temperature of the fixing unit F continues to rise. The fixing unit F reaches its maximum temperature 95 seconds after the runaway energization condition begins. At this time, the temperature of the fixing belt 310 is 330°C. Since the temperature at which the surrounding components of the fixing belt 310 are damaged is 300°C, waveform B indicates that the surrounding components of the fixing belt 310 may be damaged during the runaway energization condition.

[0056] Figure 7(b) shows the temperature transition during a power-on runaway state in standby mode. In standby mode, no image is formed on the recording medium P, and the image forming apparatus 100 waits for job input. Normally, there is no need to transport the recording medium P in standby mode. For this reason, the rotation speed of the fixing belt 310 is set slower than in print mode, taking into account the lifespan due to wear of the rotating body and surrounding components. Waveform C shows the temperature transition when the rotation detection unit 430 is operating. Waveform D shows the temperature transition when the rotation detection unit 430 is not operating and the exclusion unit 420 is operating, exclusively supplying power to the halogen heater 341 and halogen heater 342.

[0057] In waveform C, the CPU 450 outputs switching signals 451 to 456 to connect the switch units 411 to 416 with a 100% duty cycle when the power is overloaded. In waveform C, because the operating mode is standby mode, the fuser belt 310 rotates at a predetermined rotational speed (e.g., 50 mm / s) that is slower than in print mode. The rotation detection unit 430 compares the rotational speed of the fuser belt 310 with a threshold (e.g., 100 mm / s). If the rotational speed of the fuser belt 310 is below the threshold, the rotation detection unit 430 outputs switching signals 431 and 432 to stop the switching signals 451 and 452. For this reason, the halogen heaters 343 to 346 are supplied with power with a 100% duty cycle. In this state, the total power of the heating roller 340 becomes 3000 W.

[0058] The overheating unit 380 outputs stop signals 381 to 386 to shut off the switch units 411 to 416 when the temperature of thermistor 401 or thermistor 402 exceeds a predetermined threshold temperature (200°C). In waveform C, 70 seconds after the runaway current condition occurs, the temperature of thermistor 401 or thermistor 402 exceeds 200°C, and the switch units 411 to 416 shut off. However, due to the responsiveness of the overheating unit 380 and the overshoot of the fixing belt 310, the temperature of the fuser unit F continues to rise. The fuser unit F reaches its maximum temperature 100 seconds after the runaway current condition begins. At this time, the temperature of the fixing belt 310 is 280°C. Since the temperature at which the surrounding components of the fixing belt 310 are damaged is 300°C, in waveform C, operation can be stopped without damaging any components even in a runaway current condition.

[0059] In standby mode, there is no need to fix the toner image to the recording medium P, resulting in lower power consumption than in print mode. Therefore, the fuser unit F can maintain the necessary temperature even without power being supplied to the halogen heaters 341 and 342.

[0060] In waveform D, the image forming apparatus 100 operates in the same way as in waveform A when it is in a runaway power-on state. The exclusive control unit 420 is operating and outputs a signal 421 to stop the switching signal 452. As a result, the halogen heaters 341, 343-346 are supplied with power at a 100% duty cycle. In this state, the total power of the heating roller 340 becomes 4000 [W]. Unlike waveform A, waveform D is in standby mode, so the rotation speed of the fuser belt 310 is slower than in print mode. As a result, the heat dissipation of the fuser belt 310 is poor, and the slope of the temperature rise becomes steeper.

[0061] In waveform D, 50 seconds after the runaway current condition occurs, the temperature of thermistor 401 or thermistor 402 exceeds 200°C, causing the switch units 411-416 to shut off. However, due to the responsiveness of the overheating section 380 and the overshoot of the fixing belt 310, the temperature of the fuser unit F continues to rise. The fuser unit F reaches its maximum temperature 110 seconds after the runaway current condition begins. At this time, the temperature of the fixing belt 310 is 310°C. The temperature at which the surrounding components of the fixing belt 310 are damaged is 300°C. Therefore, in waveform D, there is a possibility that the surrounding components of the fixing belt 310 may be damaged during the runaway current condition.

[0062] Thus, in this embodiment, the image forming apparatus 100 can stop the power supply to one halogen heater using the exclusion unit 420 in order to limit the power of the halogen heater during print mode. Furthermore, in standby mode, when the rotation speed of the fixing belt 310 is slow, the image forming apparatus 100 can stop the power supply to two halogen heaters using the rotation detection unit 430.

[0063] The halogen heaters 341 and 342, which are connected to the switch units 411 and 412 controllable by the mutual exclusion unit 420, are connected to the same power supply system (first power supply system). This allows the power to be controlled so as not to exceed the maximum rating of the system. Furthermore, the halogen heaters 341 and 342 connected to the switch units 411 and 412 controllable by the mutual exclusion unit 420 are the same as the halogen heaters 341 and 342 connected to the switch units 411 and 412 controllable by the rotation detection unit 430. In this configuration, even if the mutual exclusion unit 420 fails, the rotation detection unit 430 can operate in print mode to forcibly stop the power supply to up to two halogen heaters. This may prevent a drop in the temperature of the fuser unit F. This configuration minimizes equipment damage due to heat generation. As a result, the cost of replacement parts and services for the image forming apparatus 100 can be reduced.

[0064] In this embodiment, a configuration in which the rotational speed of the fixing belt 310 is detected by the sensor unit 370 has been described, but the method for detecting the rotational speed of the fixing belt 310 is not limited to this. For example, the rotational speed of the fixing belt 310 may be detected by detecting the rotational speed of a motor (not shown) that drives the fixing belt 310. Also, the fixing unit F in this embodiment employs a belt heating method, but is not limited to this. For example, the heating unit 300 may be composed of a rotating body (roller) having a plurality of heat sources (halogen heaters). The heat sources of the rotating body are controlled by the control board 15 as described above. In this case, the rotation detection unit 430 detects the rotational speed of the rotating body.

Claims

[Claim 1] Image forming means for forming an image, A transfer means for transferring the image formed by the image forming means onto a recording medium, A fixing means for fixing the image transferred by the transfer means onto the recording medium, using a heating unit and a pressurized rotating body equipped with multiple heat sources, Multiple switch means provided corresponding to each of the multiple heat sources, Control means for controlling the connection state of the plurality of switching means to control the supply of power to the plurality of heat sources, An exclusive means for exclusively connecting one of the switching means with any other switching means, The heating unit is characterized by comprising a rotation detection means that shuts off one of the switch means and the other one of the switch means based on the rotation speed of the heating unit, Image forming apparatus.

Images