Fixing device

Abstract

To prevent an excessive increase in temperature of a fixing device to prevent damage to a member.SOLUTION: A fixing device comprises: a heating rotating body; a pressure rotating body, the heating rotating body and the pressure rotating body applying heat and pressure to a recording material at a nip part to fix a toner image to the recording material, and the heating rotating body having a plurality of heat sources; a safety element that stops the heat sources generating heat at a predetermined temperature, the heating rotating body capable of rotating at a plurality of speeds including a first speed and a second speed; and a speed detection member that detects the rotation speed of the heating rotating body. The heat quantity per unit time of the heat sources is set based on the rotation speed of the heating rotating body detected by the speed detection member. The first speed is smaller than the second speed. The heat quantity per unit time of the heat sources is smaller in a case where the heating rotating body rotates at the first speed than in a case where the heating rotating body rotates at the second speed.SELECTED DRAWING: Figure 5

Description

Technical Field

[0005]

[0001] The present invention relates to a fixing device for fixing a toner image on a recording material.

Background Art

[0002] In image forming apparatuses such as copiers, printers, and multifunction peripherals using an electrophotographic method, a heating type fixing device that fixes an image on a recording material by heating the recording material carrying the image is widely used. The heating type fixing device includes a heating rotating body having a heat source and a control unit that controls the amount of heat of the heating rotating body. Further, the fixing device includes a temperature detecting member (thermistor) that detects the temperature of the heating rotating body. The control unit controls the amount of heat of the heating rotating body according to the detection result of the thermistor to adjust the temperature of the fixing device.

[0003] If any one of the heating rotating body, the temperature detecting member, and the control unit does not function properly, the heating rotating body may be overheated. For example, when an abnormality occurs in the control unit that controls the amount of heat of the heating rotating body, an excessive amount of heat is supplied to the heating rotating body. As a result, the heating rotating body may be overheated and the fixing device may be damaged. Therefore, generally, the fixing device is configured to include a safety element such as a thermostat to avoid damage due to overheating of the heating rotating body.

[0004] The fixing device described in Patent Document 1 includes a safety element. Thereby, damage to the fixing device due to overheating of the heating rotating body is suppressed. Further, the fixing device described in Patent Document 1 has a speed detecting member that detects the rotation speed of the rotating body. When the speed detecting member detects that the rotating body is not rotating, a technique for suppressing damage to the fixing device by preventing the heat source from generating heat without depending on the instruction of the control unit is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In a fixing device equipped with a safety element and a speed detection member for detecting the speed of a heating rotating body, when the rotation speed of the heating rotating body is low, the rate at which the temperature of the heating rotating body rises increases. Consequently, if the heating rotating body becomes excessively hot, there is a risk that the temperature of the heating rotating body will have risen even further by the time the safety element is activated. This could potentially damage the fixing device.

[0007] Therefore, the fixing device according to the present invention aims to suppress excessive temperature rise in the fixing device and prevent damage to the components. [Means for solving the problem]

[0008] From the above problems, the fixing device of the present invention comprises a belt that is rotatably mounted and applies heat to the recording material, A fixing device comprising: a pressurizing rotating body that contacts the outer surface of the belt and forms a nip portion for nipping the recording material between itself and the belt to fix a toner image on the recording material; a heating roller that contacts the inner surface of the belt and heats the belt by tensioning it; a plurality of heaters disposed inside the heating roller and heating the heating roller; a power supply unit that supplies power to the plurality of heaters; a temperature sensing member that detects the temperature of the heating roller; a speed sensing member that detects the rotational speed of the belt; a control unit that controls the power supply unit based on the detection result of the temperature sensing member and the detection result of the speed sensing member; and a safety element configured to cut off power to the plurality of heaters at a predetermined temperature, wherein the plurality of heaters are a first heater and are in the direction of transport of the recording material and In a fixing device in which a belt can rotate at multiple speeds including a first speed and a second speed greater than the first speed, the control unit, based on the detection result of the speed detection member, controls the first and second heaters if the belt is rotating at or below the first speed. Power is supplied to both. The power supply unit is controlled to prevent the power supply from being supplied to the third heater, and if the belt is rotating at a speed greater than the first speed but less than or equal to the second speed, the power supply unit is controlled to prevent the power supply from being supplied to the first heater and the second heater simultaneously, and the power supply unit is controlled to allow the power supply to the third heater. [Effects of the Invention]

[0009] The fixing device of the present invention makes it possible to suppress excessive temperature rise in the fixing device, thereby preventing damage to the fixing device. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the image forming apparatus in this embodiment. [Figure 2] This is a schematic diagram of the fixing device in this embodiment. [Figure 3] This is a schematic diagram illustrating the heat source in this embodiment. [Figure 4] This is a block diagram of this embodiment. [Figure 5] This is a schematic diagram of a fixing device including a speed detection member in this embodiment. [Figure 6] This is a flowchart of Example 1. [Figure 7(A)] This figure shows the relationship between belt speed and temperature. [Figure 7(B)] This diagram shows the relationship between belt speed and power. [Figure 8] This is a flowchart of Example 2. [Figure 9] This figure shows the relationship between belt speed and power in Example 2. [Modes for carrying out the invention]

[0011] <Example 1> <Image forming apparatus> Figure 1 is an explanatory diagram of the configuration of the image forming apparatus of this embodiment. The image forming apparatus 100 is a color image forming apparatus and comprises an image output unit 100P, a reader unit 104 and an operation unit 105 located above the image output unit 100P. The operation unit 105 is a user interface that includes an input interface and an output interface. The input interface is, for example, a touch panel or various key buttons. The output interface is a display unit that displays information or a speaker.

[0012] The image output unit 100P operates in accordance with instructions received via the operation unit 105. For example, the image output unit 100P performs a copy operation of an original image by printing the original image read by the reader unit 104 onto the recording material P. The image output unit 100P also performs a print operation by printing an image onto the recording material P based on image data stored in a storage device (not shown). The image output unit 100P comprises an image forming unit 10, a paper feeding unit 20, an intermediate transfer unit 30, a fixing device 40, a reversal transport unit 50, a double-sided transport unit 60, and a paper discharge transport unit 70.

[0013] The image forming unit 10 comprises four image forming stations a to d arranged side by side along the horizontal direction. The four image forming stations a to d have the same configuration. Each image forming station a to d is equipped with a photosensitive drum 11a to 11d, which is a photoreceptor. Each photosensitive drum 11a to 11d is pivotally supported by a drum axis and rotated in the direction of the arrow. Facing the outer surface of each photosensitive drum 11a to 11d, along the direction of rotation, are arranged primary chargers 12a to 12d, optical systems 13a to 13d, developers 14a to 14d, and cleaners 15a to 15d. The photosensitive drums 11a to 11d, primary chargers 12a to 12d, optical systems 13a to 13d, developers 14a to 14d, and cleaners 15a to 15d are components of image forming stations a to d, respectively.

[0014] The primary chargers 12a to 12d apply charges with a uniform charge amount to the surfaces of the corresponding photosensitive drums 11a to 11d. As a result, the surfaces of the photosensitive drums 11a to 11d are uniformly charged. The optical systems 13a to 13d irradiate light rays such as laser beams modulated according to image data onto the uniformly charged surfaces of the corresponding photosensitive drums 11a to 11d. Thereby, an electrostatic latent image is formed on the surface of each of the photosensitive drums 11a to 11d. The developing devices 14a to 14d store toners of black (k), cyan (c), magenta (m), and yellow (y), respectively. The developing devices 14a to 14d supply toner to the electrostatic latent images formed on the corresponding photosensitive drums 11a to 11d to form a toner image and visualize it. The toner images of each color formed on the photosensitive drums 11a to 11d are superimposed and transferred onto the intermediate transfer belt 31 described later by applying a predetermined transfer voltage to the primary transfer rollers 35a to 35d as the primary transfer portions of the intermediate transfer unit 30 described later. The cleaners 15a to 15d scrape off the residual toner remaining on the photosensitive drums 11a to 11d without being transferred to the intermediate transfer belt 31 to clean the surfaces of the photosensitive drums 11a to 11d.

[0015] The paper feed unit 20 includes a cassette 21 for storing the sheet-like recording material P. The paper feed unit 20 includes a plurality of rollers. The pickup roller 22 feeds the recording material P from the cassette 21. The fed recording material P is conveyed to the registration roller 26 by a plurality of conveyance roller pairs 23. The registration roller 26 conveys the recording material P toward the secondary transfer area Te of the intermediate transfer unit 30 described later in accordance with the timing of forming an image. The cassette 21, the pickup roller 22, the registration roller 26, the pre-registration roller pair 27, etc. are constituent members of the paper feed unit 20.

[0016] The intermediate transfer unit 30 includes an intermediate transfer belt 31. The intermediate transfer belt 31 is rotatably stretched by a driving roller 33, a tension roller 32, and a secondary transfer inner roller 34. The driving roller 33 transmits a driving force to the intermediate transfer belt 31. The tension roller 32 applies an appropriate tension to the intermediate transfer belt 31. A secondary transfer outer roller 36 is disposed so as to face the secondary transfer inner roller 34 with the intermediate transfer belt 31 interposed therebetween.

[0017] Primary transfer rollers 35a to 35d are disposed so as to face each of the photosensitive drums 11a to 11d via the intermediate transfer belt 31. The contact portions between the photosensitive drums 11a to 11d and the primary transfer rollers 35a to 35d become primary transfer regions Ta to Td, respectively. The toner images formed on the photosensitive drums 11a to 11d are transferred and superimposed on the image forming surface of the intermediate transfer belt 31 in the primary transfer regions Ta to Td. The contact portion between the secondary transfer inner roller 34 and the secondary transfer outer roller 36 becomes a secondary transfer region Te. The toner images of respective colors transferred to the intermediate transfer belt 31 are transferred to a recording material P conveyed by a registration roller 26 in the secondary transfer region Te.

[0018] A cleaner 37 is disposed so as to face the tension roller 32 via the intermediate transfer belt 31. The cleaner 37 cleans the image forming surface of the intermediate transfer belt 31 after the toner image has been transferred to the recording material P. The intermediate transfer belt 31, the driving roller 33, the tension roller 32, the secondary transfer inner roller 34, the secondary transfer outer roller 36, the cleaner 37, the primary transfer rollers 35a to 35d, etc. are constituent members of the intermediate transfer unit 30.

[0019] The fixing device 40 receives the recording material P from the secondary transfer region Te via a pre-fixing guide 47. The fixing device 40 thermally fixes the toner transferred to the recording material P in the secondary transfer region Te to the recording material P at a nip portion. A detailed description of the fixing device 40 will be given later.

[0020] The paper discharge and transport unit 70 includes an internal paper discharge roller 71, an external paper discharge roller 72, and a flapper 73. The internal paper discharge roller 71 transports the recording material P on which the image has been heat-fixed by the fixing device 40. The external paper discharge roller 72 discharges the recording material P to the outside of the machine. The flapper 73 distributes the destination of the recording material P to either the direction of the reversing transport unit 50, which acts as a reversing unit, or the direction of the external paper discharge roller 72. The internal paper discharge roller 71, external paper discharge roller 72, flapper 73, etc., are components of the paper discharge and transport unit 70.

[0021] The reversing transport unit 50, which serves as a reversing / duplex transport path, includes a plurality of reversing rollers 51, a reversing guide 52, a paper discharge flapper 53, and a reversing / duplex flapper 54. The reversing rollers 51 are driven by a reversing / duplex drive motor (not shown) and are configured to rotate in both forward and reverse directions. The paper discharge flapper 53 guides the recording material P, which has been reversed by the reversing guide 52, toward the outer paper discharge roller 72 of the paper discharge transport unit 70 during reversing and paper discharge. The reversing / duplex flapper 54 is driven by a reversing / duplex flapper solenoid or motor (not shown) and guides the recording material P toward the duplex transport unit 60 (described later) when executing a duplex printing job. The plurality of reversing rollers 51, the reversing guide 52, the paper discharge flapper 53, the reversing / duplex flapper 54, etc., are components of the reversing transport unit 50.

[0022] The double-sided transport unit 60 is equipped with multiple double-sided transport rollers 61 and a double-sided transport guide 62 that guides the recording material P to the transport guide 24 of the paper feed unit 20. During double-sided printing, the recording material P, on which an image has been formed on one side, is transported to the transport guide 24 by the inversion transport unit 50 and the double-sided transport unit 60 with the side on which the image is formed inverted, and an image is formed on the inverted side. The multiple double-sided transport rollers 61, the double-sided transport guide 62, etc., are components of the double-sided transport unit 60.

[0023] <Fusing device> Figure 2 is an explanatory diagram of the configuration of the fixing device 40. In Figure 2, the recording material P onto which the toner image has been transferred is transported from right to left. The fixing device 40 includes an endless, rotatable fixing belt 41 (hereinafter referred to as the belt) as a heating rotating body, and a pressure roller 48 as a pressurizing rotating body that faces the belt 41 and forms a nip portion N between itself and the belt 41. The pressure roller 48 has an elastic layer on the outer circumference of its rotating shaft, and a release layer is formed on the outer circumference of the elastic layer. The pressure roller 48 is connected to a motor M2, which is a drive source, and is rotationally driven by the motor M2.

[0024] The belt 41 has thermal conductivity and heat resistance, and is a thin-walled cylindrical shape. The inner circumferential surface of the belt 41 is equipped with a pressure pad 42 as a fixing member, a heating roller 43, a thermistor 44, a thermostat 45 as a safety element, and a tension roller 46. The thermistor 44 is a temperature detector that detects the temperature of the heating roller 43. The thermostat 45 is a safety element to prevent overheating. The belt 41 is tensioned by the pressure pad 42, the heating roller 43, and the tension roller 46. The pressure pad 42 is pressed by the pressure roller 48 via the belt 41.

[0025] The heating roller 43 incorporates multiple (three in this embodiment) heaters 49a, 49b, and 49c as heating elements. In this embodiment, heaters 49a, 49b, and 49c are halogen heaters. The heating roller 43 generates heat when electric current is supplied to heaters 49a, 49b, and 49c. The belt 41 is heated by the heating roller 43. The temperature of the heating roller 43 is controlled according to the temperature detected by the thermistor 44, and the temperature of the belt 41 is controlled to a predetermined target temperature according to the type of paper of the recording material P. The heating roller 43 is connected to a motor M1, which is a drive source, and is rotationally driven by the motor M1. The rotation of the heating roller 43 provides auxiliary driving force to the belt 41. Motors M1 and M2 may be the same or separate. That is, the drive source for rotating the heating roller 43 may be either motor M2 or motor M1, which is separate from motor M2, and the mechanism for providing driving force, including drive transmission mechanisms other than gears, is not limited.

[0026] The tension roller 46 is a tension roller that is biased by a spring (not shown) to impart a predetermined tension to the belt 41. The tension roller 46 rotates in a driven manner relative to the belt 41. The ends of the tension roller 46 are rotatably supported by bearings (not shown).

[0027] In this configuration, the fixing device 40 applies heat and pressure to the toner image while gripping and transporting the recording material P, which is carrying the toner image, at the nip section N formed between the belt 41 and the pressure roller 48. As a result, the fixing device 40 fixes the toner image to the recording material P while gripping and transporting it.

[0028] <Heater> Figure 3 is an explanatory diagram of heaters 49a, 49b, and 49c as heat sources. Figure 3(a) is an explanatory diagram of the heater configuration. The heater has an elongated cylindrical glass tube (valve) 491. A filament (tungsten wire) 492 is provided inside the glass tube 491. Furthermore, the inside of the glass tube 491 is filled with a gas containing halogen elements. A pair of linear lead wires 493 protruding outward are provided at each of the longitudinal ends of the glass tube 491. A metal foil (molybdenum foil), which is a metal body not shown, is provided at the base end of the lead wires 493 and is electrically connected to the filament 492. Furthermore, the heater has an insulator 494 for supporting the heater. A heater with this configuration generates heat when power is supplied via the lead wires 493.

[0029] Figure 3(b) is a diagram illustrating the heat generation characteristics of heaters 49a, 49b, and 49c. The horizontal axis represents the position in the front-to-back direction, and the vertical axis represents the heat generation characteristics at that position. The front-to-back direction is perpendicular to the transport direction of the recording material P, and in Figures 1 and 2, it corresponds to the depth direction. As is clear from Figure 3(b), heaters 49a, 49b, and 49c each have different heat generation characteristics. Heater 49a mainly generates heat in its central region. Heater 49b mainly generates heat in its end regions. Heater 49c generates heat in its paper-feeding region almost flatly. The heat generation characteristics are controlled by the power supply ratio supplied to each heater 49a, 49b, and 49c. In such a fixing device 40, when recording material P with a small length (width) in the direction perpendicular to the transport direction is continuously fed, the conductivity ratio of heater 49b, which mainly generates heat at its ends, is reduced. This makes it possible to suppress heat accumulation at both ends of the heating roller 43 in the front-to-back direction.

[0030] For the sake of simplicity, the power supplied to heaters 49a, 49b, and 49c in this embodiment is assumed to be 1000 W each. However, the present invention is not limited to this and can be applied to any configuration in which multiple heaters are provided, and the power that can be supplied to heaters 49a, 49b, and 49c may also be different.

[0031] <Controller> Figure 4(A) is a diagram illustrating the configuration of a controller that controls the operation of a fixing device 40 with the above configuration. In this embodiment, the controller is implemented by a control circuit 300 having a CPU (Central Processing Unit) 301. The control circuit 300 is connected to the driver circuit 200, motors M1 and M2, and the fixing device 40. The driver circuit 200 is connected to a commercial power supply 500, and the AC power supplied from the commercial power supply 500 is supplied to the heaters 49a, 49b, and 49c of the fixing device 40 under the control of the control circuit 300.

[0032] The CPU 301 of the control circuit 300 controls the image forming operation, including temperature adjustment of the fixing device 40. The CPU 301 controls the image forming operation of each component in the image forming apparatus 100 by executing a computer program stored in a memory (not shown).

[0033] The driver circuit 200 includes a relay 201, a voltage detection unit 202, a current detection unit 203, a zero-crossing detection unit 204, and a plurality of triacs 205a, 205b, and 205c. The number of triacs 205a, 205b, and 205c is provided in a number corresponding to the number of heaters 49a, 49b, and 49c of the fixing device 40. In this embodiment, it will be described as if three triacs 205a, 205b, and 205c are provided.

[0034] Relay 201 is connected to commercial power supply 500. Relay 201 can be switched on or off by the relay control signal RL-ON obtained from CPU 301. When connected, relay 201 supplies power from commercial power supply 500 to the downstream stage, and when disconnected, it cuts off the supply of power from commercial power supply 500 to the downstream stage.

[0035] The voltage detection unit 202 detects the voltage value of the power supplied from the commercial power supply 500. The voltage detection unit 202 transmits a voltage detection signal V-DTC, which represents the voltage value detection result, to the control circuit 300. The control circuit 300 converts the voltage detection signal V-DTC into a digital signal using a built-in A / D converter (not shown) and inputs it to the CPU 301. The CPU 301 obtains the voltage value of the power supplied from the commercial power supply 500 by converting the digital signal of the voltage detection signal V-DTC back into a voltage value.

[0036] The current detection unit 203 detects the current value flowing through the fuser 40. The voltage detection unit 202 transmits a current detection signal C-DTC, which represents the current value detection result, to the control circuit 300. The control circuit 300 converts the current detection signal C-DTC into a digital signal using a built-in A / D converter (not shown) and inputs it to the CPU 301. The CPU 301 obtains the current value flowing through the fuser 40 by converting the digital signal of the current detection signal C-DTC back into a current value.

[0037] The CPU 301 can determine the power consumed by the fixing device 40 from the voltage detection signal V-DTC and the current detection signal C-DTC. In other words, the CPU 301 can calculate the power consumed by the fixing device 40 using the voltage value detected by the voltage detection unit 202 and the current value detected by the current detection unit 203.

[0038] The zero-cross detection unit 204 detects the zero-cross of the power supply from the commercial power supply 500. As a result of detecting the zero-cross, the zero-cross detection unit 204 transmits a zero-cross timing signal ZC-DTC to the control circuit 300. The CPU 301 of the control circuit 300 controls the timing of the power supply control of the fixing device 40 based on the zero-cross timing signal.

[0039] Triacs 205a, 205b, and 205c are connected to their respective heaters 49a, 49b, and 49c. The conduction of triacs 205a, 205b, and 205c is controlled by a triac drive circuit (not shown) in accordance with the heater control signal HTR*-ON (*=1~3) obtained from the CPU 301. The CPU 301 controls the amount of power supplied to heaters 49a, 49b, and 49c based on the conduction ratio of triacs 205a, 205b, and 205c. By controlling the conduction ratio of triacs 205a, 205b, and 205c, the CPU 301 can control the amount of heat generated by heaters 49a, 49b, and 49c.

[0040] The thermostat 45 of the fixing device 40 is connected to the heaters 49a, 49b, and 49c. When the temperature exceeds a predetermined level, the thermostat 45 opens an internal contact (not shown) and becomes non-conductive. The thermostat 45 prevents damage to the fixing device 40 by opening the contact in the event of a runaway current.

[0041] The thermistor 44 is a temperature detection unit that detects the temperature of the heating roller 43 in the fixing device 40. The thermistor 44 has the characteristic that its resistance decreases as the temperature increases. The CPU 301 can detect the temperature by the voltage division value (voltage Vt) between the thermistor 44 and a resistor (not shown) in the control circuit 300, which is a reference voltage (5[V] in this embodiment) in the control circuit 300. In this embodiment, for the sake of simplicity, there is only one thermistor 44, but there may be multiple thermistors 44, such as one or more placed in the center and at the ends of the heaters 49a, 49b, and 49c.

[0042] The CPU 301 monitors the temperature of the fixing device 40 using the voltage Vt described above and controls the conduction ratio of the triacs 205a, 205b, and 205c so that the heating roller 43 reaches a target temperature (e.g., 180°C). To control the conduction ratio of the triacs 205a, 205b, and 205c, the CPU 301 adjusts the timing of transmitting the heater control signal HTR*-ON (*=1~3) to the triac drive circuit (not shown) based on the zero-cross timing signal ZC-DTC. In this way, the temperature of the fixing device 40 is adjusted.

[0043] The rotational speed of motors M1 and M2 is controlled according to the drive signals M1-CLK / M2-CLK input from the CPU 301. Motors M1 and M2 output a predetermined pulse per rotation and transmit FG signals M1-FG / M2-FG, whose pulse period (frequency) changes according to the rotational speed, to the CPU 301 of the control circuit 300. The CPU 301 can detect the rotational speed of motors M1 and M2 from the pulse period (frequency) of the input FG signals M1-FG / M2-FG. In this embodiment, since the FG signals M1-FG represent the rotational speed of the heating roller 43, the FG signals M1-FG can be detected as the rotational speed of the driven belt 41. In this embodiment, the rotational speed of the belt 41 is detected from the motor's FG signal, but the rotational speed may also be detected by a fixed belt rotation sensor (encoder) (not shown) that detects the rotation of the belt 41.

[0044] The power supply limiting means 302 consists of a rotation speed detection means and a heater OFF means. It calculates the rotation speed from the input FG signal (M1-FG) and, if it is below a predetermined speed, turns off the heater ON signal separately from the CPU 301.

[0045] <Speed ​​detection component> Here, we will explain the details of the speed sensing member 401.

[0046] Figure 5 is a detailed view of the speed detection member in the fixing device F. The speed detection member 401 has a rotating part 402, a rotating blade 403, and a photosensor 404. The rotating part 402 has an outer diameter of Φ20 mm and is in contact with the outer surface of the belt 41, and rotates in response to the rotation of the belt 41. The central axes of the rotating part 402 and the rotating blade 403 are coaxial, and the rotating blade 403 rotates in conjunction with the rotation of the rotating part 402. The rotating blade 403 has four blades per revolution, and the photosensor 404 detects the number of times the blade portion of the rotating blade 403 crosses the photosensor 404. In this embodiment, a contact-type speed detection member 401 using the rotating part 402 is used, but a non-contact type speed detection member that detects a mark on the belt with the photosensor 404 and detects the rotation period may also be used, and the means are not limited to this.

[0047] The heating roller 43 in this embodiment can rotate at multiple speeds, including a first speed, a second speed, and a third speed. The first speed is, for example, 100 mm / s, the second speed is, for example, 200 mm / s, and the third speed is, for example, 300 mm / s. Further speeds may also be set.

[0048] The first speed is the speed at which the heating roller 43 rotates in the standby state. The standby state is the period after the power of the image forming apparatus 100 is turned ON and waiting until a job is sent. Therefore, the fixing device 40 prepares itself so that it can perform the fixing operation immediately once a job is sent. This preparation mainly refers to the temperature of the heating roller 43 and the rotation speed of the belt 41. In the standby state, the temperature of the heating roller 43 is controlled to a predetermined temperature so that it can reach the target temperature for fixing in a short time. For example, the temperature of the heating roller 43 in the standby state is set to 170°C. As the belt 41 rotates at the first speed, the temperature is uniformly adjusted in the circumferential direction of the belt 41.

[0049] The second speed is the speed at which image formation is performed at a low speed. For example, when fixing a recording material with a large basis weight, a large amount of heat is required. In order to provide the required amount of heat to the recording material, the time it takes for the recording material to pass through the nip is increased. This ensures that the amount of heat necessary to fix the toner image to the recording material P is secured. Note that for recording material P with a low basis weight, the target temperature is low (e.g., 170°C), and for recording material P with a high basis weight, the target temperature is high (e.g., 200°C).

[0050] The third speed is the maximum speed in the fixing device of this embodiment. For example, when fixing a recording material with a small basis weight, less heat is required. Therefore, the time it takes for the recording material to pass through the nip is short, making it possible to rotate the heating rotating body at a speed greater than the second speed.

[0051] To make the explanation easier to understand, the speed control of the fixing device 40 in this embodiment is set to three speeds, from the first to the third, but there may be more speeds.

[0052] Slight speed fluctuations can occur due to factors such as the condition of the lubricant applied to the inner surface of the belt 41 and the roughness of the inner surface of the belt 41. As a result, the rotational speed of the heating roller 43 and the rotational speed of the belt 41 may be out of sync. Therefore, the belt 41 is corrected to reach the target speed based on the actual speed of the belt 41 detected by the speed detection member 401. Specifically, if the target rotational speed of the belt 41 is the first speed, and the speed of the belt 41 detected by the speed detection member 401 is less than the first speed, the actual rotational speed of the belt 41 is less than the target rotational speed. Therefore, the rotational speed of the heating roller 43 is controlled to increase. In this way, in this embodiment, the belt 41 is controlled to reach the target speed by using the speed detection member 401.

[0053] Figure 4(B) shows that the photosensor 404 of the speed detection member 401 is connected to the control circuit 300. The rotational speed of the belt 41 detected by the speed detection member 401 is transmitted to the control circuit 300.

[0054] The rate at which the temperature of belt 41 rises depends on the rotational speed of belt 41. When belt 41 is rotating at the first speed, the contact time between belt 41 and the heating roller 43 is longer than when it is rotating at the second speed. Therefore, heat is more easily transferred from the heating roller 43 to belt 41, and the temperature of belt 41 rises more easily. Thus, assuming that the temperature of the heating roller 43 is constant, the rate at which the temperature of belt 41 rises depends on the rotational speed of belt 41.

[0055] In a fixing device 40 that includes a thermostat 45 and a speed detection member 401 for detecting the speed of a heating roller 43, when the rotation speed of the heating roller 43 is low, the rate at which the temperature of the belt 41 rises increases. Consequently, if the belt 41 becomes excessively hot, there is a risk that the temperature of the belt 41 will rise even further by the time the thermostat 45 activates. This could potentially damage the fixing device 40.

[0056] Therefore, the fixing device 40 of this embodiment aims to suppress excessive temperature rise in the fixing device 40 and prevent damage to the components.

[0057] By setting an upper limit power according to the rotation speed of the belt 41, damage to the fixing device 40 in the event of an abnormal power supply can be suppressed. Figure 6 is a flowchart showing the temperature control process, including the process of setting such an upper limit power. Figure 7 is an explanatory diagram of the relationship between the rotation speed of the belt 41 and the supplied power / upper limit power. This process starts when the power switch of the image forming apparatus 100 is turned on or when it wakes up from sleep mode. First, we will explain according to the flowchart in Figure 6.

[0058] S101 The CPU 301 determines whether or not temperature adjustment of the fuser unit 40 has started. If temperature adjustment has started, the process proceeds to S102.

[0059] S102 The CPU 301 detects the rotational speed of the belt 41 based on the rotational speed detection signal M1-FG obtained from the motor M1. Alternatively, the CPU 301 may detect the rotational speed of the heating roller 43 instead of the belt 41.

[0060] S103 The CPU 301 determines the maximum power limit according to the detected rotational speed of the belt 41.

[0061] S104 The CPU 301, having determined the upper limit power, determines the target temperature based on information such as the basis weight of the recording material P used for image formation, which is stored in the paper feed unit 20. For example, if the basis weight of the recording material P is 81 [gsm], the CPU 301 determines the target temperature to be 180 [°C].

[0062] S105 The CPU 301, having determined the target temperature, detects the temperature of the heating roller 43 based on the detection result of the thermistor 44.

[0063] S106 The CPU 301 derives the required power to be supplied to the fixing device 40 from the determined target temperature and the detected temperature of the heating roller 43. The CPU 301 determines the required power from the target temperature and the detected temperature. For example, if the target temperature is 180°C and the current detected temperature of the heating roller 43 is 100°C, the CPU 301 determines the required power to be 500W. The greater the difference between the target temperature and the detected temperature, the greater the required power.

[0064] S107 CPU301 compares the calculated required power with the upper limit power. If the required power is less than the upper limit power, proceed to S108.

[0065] S108 The CPU 301 supplies the required power derived in the S106 process to the heating roller 43. To do this, the CPU 301 controls the conductivity ratios of the triacs 205a, 205b, and 205c according to the required power. The CPU 301 controls the conductivity ratios of the triacs 205a, 205b, and 205c by sending heater control signals HTR*-ON (*=1~3) corresponding to the conductivity ratios.

[0066] S109 If the required power exceeds the upper limit power, the process proceeds to S109. The CPU 301 supplies the upper limit power determined in S103 to the heating roller 43. To do this, the CPU 301 controls the conduction ratios of the triacs 205a, 205b, and 205c according to the upper limit power. The CPU 301 controls the conduction ratios of the triacs 205a, 205b, and 205c by sending heater control signals HTR*-ON (*=1~3) according to the conduction ratio. In other words, the CPU 301 supplies the heating roller 43 with the smaller of the required power and the upper limit power.

[0067] S110 The CPU 301 determines whether or not to terminate the temperature adjustment of the fuser unit 40. If the temperature adjustment is not terminated, the CPU 301 returns to process S102 and repeats the processes from S102 onward. If the temperature adjustment is terminated, the CPU 301 terminates this temperature adjustment process.

[0068] As described above, the fixing device 40 of this embodiment can set an upper limit power of the fixing device 40 according to the rotation speed of the rotating heating members, such as the belt 41 and the heating roller 43. The power supplied to the heating roller 43 is the smaller of the required power and the upper limit power. Therefore, damage to the fixing device 40 can be suppressed in the event of an abnormal power supply.

[0069] Figure 7(A) shows the relationship between the rotational speed of the belt 41 and the power. The horizontal axis of Figure 7(A) represents the rotational speed of the belt 41, and the vertical axis represents the temperature reached by the belt 41 when the thermostat 45 is operating. The solid lines A, B, and C represent the power supplied to the heating roller 43. Solid line A represents a supplied power of 3000 [W], solid line B represents a supplied power of 2000 [W], and solid line C represents a supplied power of 1000 [W]. The dotted line D represents the threshold temperature for suppressing damage to the fixing device 40. As shown in Figure 7(A), the temperature reached by the belt 41 increases as the supplied power increases and the rotational speed of the belt 41 decreases. Also, if the temperature of the belt 41 exceeds the dotted line D, the damage to the fixing device 40 will increase.

[0070] Figure 7(B) shows the relationship between the rotational speed of the belt 41 and the upper limit power. In Figure 7(B), the horizontal axis represents the rotational speed of the belt 41, and the vertical axis represents the upper limit power. The solid line represents the upper limit power that keeps the temperature below the threshold temperature in order to suppress damage to the fixing device 40. The CPU 301 can suppress damage to the fixing device 40 even in the event of an abnormal power supply by keeping the power supplied to the heating roller 43 below the upper limit power. Based on the relationship between Figure 7(A) and Figure 7(B), the CPU 301 determines the upper limit power according to the rotational speed of the belt 41 detected in S102.

[0071] In other words, when the heating roller 43 rotates at the first speed, the rate at which the belt 41's temperature rises is greater than when the heating roller 43 rotates at the second or third speed. Therefore, when the heating roller 43 rotates at the first speed, the power supplied to the heater 49 is reduced compared to when the heating roller 43 rotates at the second or third speed. As a result, when the heating roller 43 rotates at the first speed, the amount of heat supplied to the heater 49 per unit time is smaller than when the heating roller 43 rotates at the second or third speed. This suppresses the rate at which the belt 41's temperature rises, thereby reducing damage to the fixing device 40.

[0072] If the temperature of the belt 41 rises excessively, a thermostat 45, acting as a safety element, will activate for safety. If the rate of temperature rise of the belt 41 is high, the temperature of the belt 41 will be even higher when the thermostat 45 activates. However, with the fixing device 40 of this embodiment, the amount of heat per unit time of the heater 49 can be changed based on the rotational speed of the belt 41. As a result, the temperature of the belt 41 when the thermostat 45 activates can be made lower than in the conventional method. This can suppress damage to the fixing device 40.

[0073] Furthermore, if the speed sensing member 401 cannot detect the rotational speed of the belt 41, the belt 41 is not rotating, and therefore power is not supplied to the heater 49. If the heater 49 generates heat while the belt 41 is not rotating, the temperature of the belt 41 will rise rapidly. To prevent this, power is not supplied to the heater 49.

[0074] In this embodiment, the amount of heat generated by the heater 49 per unit time when fixing the toner image to the recording material may be changed according to the basis weight of the recording material. Let us explain using recording materials of a first basis weight and a second basis weight as an example. Assume that the first basis weight is greater than the second basis weight. The larger the basis weight, the greater the amount of heat required for fixing. Therefore, when continuously feeding recording material with a large basis weight, a large amount of heat is lost, and there is a risk of insufficient heat. For this reason, when fixing recording material with a large basis weight, it is necessary to increase the power supplied to the heater 49 and increase the heat output of the heater 49. Accordingly, in this embodiment, when fixing recording material with the first basis weight, the amount of heat generated by the heater 49 per unit time is increased compared to when fixing recording material with the second basis weight.

[0075] <Example 2> The configuration of the second embodiment will now be described.

[0076] By limiting the number of heaters 49 that can be energized according to the rotation speed of the belt 41, damage to the fixing device 40 in the event of an abnormal power supply can be suppressed. Figure 8 is a flowchart illustrating the temperature control process in such a case. This process is initiated when the power switch of the image forming apparatus 100 is turned on or when it wakes up from sleep mode.

[0077] S201 The CPU 301 determines whether or not to start temperature adjustment of the fuser unit 40. If temperature adjustment has started, the process proceeds to S202.

[0078] S202 The CPU 301 determines the target temperature based on information such as the basis weight of the recording material P used for image formation, which is stored in the paper feed unit 20. For example, if the basis weight of the recording material P is 81 [gsm], the CPU 301 determines the target temperature to be 180 [°C].

[0079] S203 The CPU 301, having determined the target temperature, detects the temperature of the heating roller 43 based on the detection result of the thermistor 44.

[0080] S204 The CPU 301 derives the required power to be supplied to the fixing device 40 from the determined target temperature and the detected temperature of the heating roller 43. The CPU 301 determines the required power using a predetermined calculation formula and set values ​​based on the target temperature and the current detected temperature of the heating roller 43. For example, if the target temperature is 180°C and the current detected temperature of the heating roller 43 is 100°C, the CPU 301 determines the required power to be 500W. The greater the difference between the target temperature and the detected temperature, the greater the required power.

[0081] S205 The CPU 301 detects the rotational speed of the belt 41 based on the rotational speed detection signal M1-FG obtained from the motor M1. Here, the relationship between the rotational speed of the belt 41 and the heater 49 that limits the power supply will be explained. Note that the relationship between the rotational speed of the belt 41 and the supplied power has already been explained in Figure 7(A).

[0082] Figure 9 is an explanatory diagram illustrating the relationship between the rotational speed of the belt 41 and the heater 49 that limits the current supply. The horizontal axis represents the rotational speed of the belt 41, and the vertical axis represents the upper limit power. The solid line represents the upper limit power that keeps the temperature below the threshold temperature required to suppress damage to the fixing device 40.

[0083] In the speed range of the belt 41's rotational speed from a stopped state to a first speed, the upper limit power is limited to 1000[W] in the first energization restriction section. In the speed range of the belt 41's rotational speed from the first speed to a second speed, the upper limit power is limited to 2000[W] in the second energization restriction section. If the belt 41's rotational speed exceeds the second speed, no upper limit power is set, and no energization restriction is performed. The CPU 301 can suppress damage to the fixing device 40 even in the event of an energization abnormality by keeping the power supplied to the heating roller 43 below the upper limit power.

[0084] In this embodiment, power supply is limited by individually controlling the energization of heaters 49a, 49b, and 49c. In the first power supply limitation, the energization of heaters 49a and 49b is limited, and only heater 49c is energized. In the second power supply limitation, simultaneous energization of heaters 49a and 49b is restricted, and heater 49c is allowed to be energized. In this embodiment, the heaters whose energization is limited are fixed, but any combination of heaters that are energized is acceptable as long as the total power remains below the upper limit.

[0085] S206 The CPU 301 determines whether the rotational speed of the belt 41 is less than or equal to the first speed. In this embodiment, the first speed is 100 [mm / s] as described above. If the rotational speed of the belt 41 is less than or equal to the first speed (S206:Y), the process proceeds to S207.

[0086] S207 The CPU 301 decides to perform a first power restriction. In this case, the CPU 301 restricts the power supply to both heater 49a and heater 49b.

[0087] S208 If the rotational speed of belt 41 is faster than the first speed (S206:N), the CPU 301 determines whether the rotational speed of belt 41 is less than or equal to the second speed. In this embodiment, the second speed is 200 [mm / s] as described above. If the rotational speed of belt 41 is less than or equal to the second speed, the process proceeds to S209.

[0088] S209 The CPU 301 decides to perform a second power restriction. In this case, the CPU 301 restricts the power supply to either heater 49a or heater 49b.

[0089] S210 If the rotational speed of belt 41 is faster than the second speed, CPU 301 decides not to limit the power supply. In this case, CPU 301 supplies the required power derived in processing S204 to the heating roller 43. To do this, CPU 301 controls the conduction ratios of triacs 205a, 205b, and 205c according to the required power. CPU 301 controls the conduction ratios of triacs 205a, 205b, and 205c by sending heater control signals HTR*-ON (*=1~3) corresponding to the conduction ratios.

[0090] In other words, the CPU 301 supplies power to the heating roller 43 in accordance with the rotation speed of the belt 41.

[0091] C211 The CPU 301 determines whether or not to terminate the temperature adjustment of the fuser unit 40. If the temperature adjustment is not terminated, the CPU 301 returns to the S202 process and repeats the processes from S202 onward. If the temperature adjustment is terminated, the CPU 301 terminates this temperature adjustment process.

[0092] As described above, in Embodiment 2, the number of heaters 49 that can be lit is limited according to the rotation speed of the belt 41, thereby reducing the amount of heat supplied to the belt 41. Based on the rotation speed of the belt 41, the number of heaters 49 that are lit is limited; if the rotation speed of the belt 41 is high, the number of heaters 49 that are lit increases, and if the rotation speed of the belt 41 is low, the number of heaters 49 that are lit decreases. This makes it possible to lower the rate at which the temperature of the belt 41 rises. [Explanation of Symbols]

[0093] 40 Fixing device 41 Fixing belt 42 Compression Pads 43 Heating roller 44 Thermistor 45 Thermostat (safety element) 48 Pressure rollers 49 Heater 100 Image forming apparatus 300 control circuits 401 Speed ​​detection member 402 Rotating part 403 Rotating blades 404 Photosensor

Claims

1. A rotatable belt that applies heat to the recording material, A pressurizing rotating body that contacts the outer surface of the belt and forms a nip portion for fixing the toner image on the recording material by nipping the recording material between itself and the belt, A heating roller that contacts the inner surface of the belt, tensions the belt, and heats the belt, A plurality of heaters are arranged inside the heating roller and heat the heating roller, A power supply unit that supplies power to the aforementioned multiple heaters, A temperature sensing member for detecting the temperature of the heating roller, A speed detection member for detecting the rotational speed of the belt, A control unit that controls the power supply unit based on the detection result of the temperature sensing member and the detection result of the speed sensing member, A fixing device comprising a safety element configured to shut off the power supply to the plurality of heaters at a predetermined temperature, The plurality of heaters include a first heater configured such that the amount of heat generated in the center is greater than that at the edges in the width direction of the recording material, which is perpendicular to the transport direction of the recording material, A second heater is disposed inside the heating roller and heats the heating roller, wherein the second heater is configured such that the amount of heat generated at the edges is greater than that at the center in the width direction. A third heater is disposed inside the heating roller and heats the heating roller, and is configured such that the amount of heat generated in the central part and the ends is substantially the same in the width direction, In a fixing device in which the belt is capable of rotating at multiple speeds including a first speed and a second speed greater than the first speed, Based on the detection result of the speed detection member, the control unit controls the power supply unit so that power is not supplied to either the first heater or the second heater if the belt is rotating at or below the first speed, and controls the power supply unit to allow power to be supplied to the third heater. A fixing device characterized in that, based on the detection result of the speed detection member, if the belt is rotating at a speed greater than the first speed but less than or equal to the second speed, the power supply unit is controlled so that power is not supplied to the first heater and the second heater simultaneously, and the power supply unit is controlled to allow power to be supplied to the third heater.

2. The fixing device according to claim 1, characterized in that the control unit does not restrict the power supply to the first heater, the second heater, and the third heater if the belt is rotating at a speed greater than the second speed based on the detection result of the speed detection member.

Images