Image forming apparatus

Abstract

To prevent a sudden increase in temperature of a belt to increase the life of a member.SOLUTION: A fixing device comprises: a heating rotating body that applies heat to a recording material; a pressure rotating body that applies pressure to the heating rotating body to form a nip part, the heating rotating body and the pressure rotating body applying heat and pressure to the recording material at the nip part to fix a toner image to the recording material, and the heating rotating body having a plurality of heat sources; and a speed detection member that detects the rotation speed of the heating rotating body. The fixing device has a first mode for performing printing when the rotation speed detected by the speed detection member is within a predetermined speed, and a second mode for performing printing when the rotation speed detected by the speed detection member is outside the predetermined speed. The heat quantity per unit time of the heat sources is smaller in the second mode than the first mode.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] [[ID=I3]] An image forming apparatus has a fixing device for fixing a toner image on a recording material. [[ID=I5]]

[0003] The fixing device includes a fixing belt as a rotating body that applies heat to unfixed toner, and a pressure rotating body that is rotationally driven and forms a nip portion between the fixing belt by pressing the fixing belt, and has a pair of rotating bodies. When a recording material with unfixed toner on the nip portion is conveyed, the heat of the fixing belt and the pressure by the pressure rotating body are applied to the recording material, and the unfixed toner is fixed to the recording material.

[0004] The above-described fixing device is a device having a belt and a heating member. The belt is heated by the heating member. The rate at which the temperature of the belt rises due to the heating member depends on the speed at which the belt rotates. Specifically, the higher the rotation speed of the belt, the lower the efficiency of the temperature rise of the belt. Conversely, the lower the rotation speed of the belt, the higher the efficiency of the temperature rise of the belt.

[0005] The fixing device of Patent Document 1 has a speed detection member for detecting the rotation speed of the rotating body. The speed detection member for detecting the speed of the rotating body can accurately grasp the speed of the rotating body and can also grasp the efficiency of the temperature rise of the rotating body.

[0006] Also, in the fixing device of Patent Document 1, a technique has been proposed to stop power supply to the heating member when the rotation speed of the rotating body detected by the speed detection member becomes a predetermined value or less. By this technique, it is possible to prevent power supply to the heating member in a state where the rotation of the rotating body has stopped.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2011-191590 [Overview of the project] [Problems that the invention aims to solve]

[0008] If the speed detected by the speed sensing element falls outside the predetermined speed range, it becomes difficult to accurately determine the belt speed. The belt is heated by a heating element. The rate at which the belt temperature rises depends on the belt's rotation speed; the slower the rotation speed, the faster the belt temperature rises. Therefore, if image formation is performed without accurately determining the belt speed, the belt temperature may rise rapidly, potentially damaging components near the belt.

[0009] Therefore, the fixing device according to the present invention aims to suppress a rapid rise in belt temperature when it is difficult to accurately determine the belt's rotation speed, thereby improving the lifespan of the components. [Means for solving the problem]

[0010] In view of the above issues, the fixing device according to the present invention is The image forming apparatus comprises an image forming unit that forms a toner image on a recording material, a fixing device that fixes the toner image formed on the recording material, and a control unit that controls the fixing device, wherein the fixing device comprises a heating rotating body that heats the recording material, a pressurizing rotating body that pressurizes the heating rotating body to form a nip, a plurality of heat sources for heating the heating rotating body, and a speed detection member that detects the rotation speed of the heating rotating body, wherein heat and pressure are applied to the recording material passing through the nip to fix a toner image on the recording material, and the control unit controls the rotation speed of the heating rotating body based on the detection result of the speed detection member, wherein when the control unit performs a job of fixing toner images on a plurality of predetermined recording materials, (i) Based on the detection result of the speed detection member, the system can perform printing by controlling the rotation speed of the heating rotating body to a predetermined target speed, and (ii) if the rotation speed detected by the speed detection member when the heating rotating body is rotated under predetermined driving conditions is lower than the predetermined speed, the system can perform printing by limiting the maximum power that can be supplied by the heat source more than in the first mode and increasing the interval at which the recording material is transported more than in the first mode, while rotating the heating rotating body under the predetermined driving conditions, or by limiting the maximum number of heat sources that can be lit more than in the first mode and changing the driving conditions to a lower speed than the predetermined driving conditions. It is characterized by the following: [Effects of the Invention]

[0011] The fixing device according to the present invention can suppress the shortening of the lifespan of components near the belt due to a rapid rise in the belt temperature. [Brief explanation of the drawing]

[0012] [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]It is a schematic diagram of the heat generation distribution of the heat source in this embodiment. [Figure 4] It is a schematic diagram including a speed detection member in this embodiment. [Figure 5] It is a view of the fixing device in this embodiment as seen from the conveyance direction. [Figure 6] It is a diagram showing an example of the detection result of the speed detection member in this embodiment. [Figure 7] It is a flowchart showing a speed correction sequence. [Figure 8] It is a diagram showing a service technician operation screen in this embodiment. [Figure 9] It is a diagram showing an alarm display on the operation unit in this embodiment. [Figure 10] It is a table when the second mode is performed in this embodiment. [Figure 11] It is a flowchart from the speed detection sequence to the degenerate operation in this embodiment. [Figure 12] The relationship between the paper basis weight and the fixing required power in this embodiment.

Mode for Carrying Out the Invention

[0013] <Example 1> Hereinafter, embodiments of the image forming apparatus in this embodiment will be described based on the drawings. In the following, an example in which the present invention is applied to a full-color electrophotographic image forming apparatus having a plurality of photosensitive drums will be described, but the present invention is not limited to this and can also be applied to a monochromatic image forming apparatus or the like.

[0014] <Image Forming Apparatus>​​​​​FIG. 1 is a diagram showing a full-color image forming apparatus according to the present embodiment. The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads a document placed on the document table glass 21. The light irradiated from the light source 22 is reflected by the document and imaged on the CCD sensor 24 through an optical system member 23 such as a lens. Such an optical unit scans in the direction of the white arrow in FIG. 1 to convert the document into an electric signal data string for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and image processing is performed by the control unit 30 according to each image forming unit described later. Further, the control unit 30 also receives an external input from an external host device such as a print server as an image signal.

[0016] In the image forming apparatus main body 3, four types of image forming units, namely yellow Pa, magenta Pb, cyan Pc, and black Pd, are arranged along the moving direction of the intermediate transfer belt 204. First, the process of forming a toner image on the intermediate transfer belt 204 will be described taking the yellow image forming unit Pa as an example.

[0017] In FIG. 1, the surface of the photosensitive drum 200a driven to rotate is uniformly charged by the charger 201a (charging). Then, the photosensitive drum 200a surface is irradiated with a laser according to the image data input by the exposure device 31, and an electrostatic latent image is formed on the photosensitive drum 200a surface (exposure). Then, a yellow toner image is formed on the photosensitive drum 200a by the developing device 202a. The primary transfer roller 203a applies a voltage of a polarity opposite to the potential polarity of the yellow toner image to the intermediate transfer belt 204. As a result, the yellow toner on the photosensitive drum 200a is transferred to the intermediate transfer belt 204 (primary transfer). Incidentally, the yellow toner remaining on the surface of the photosensitive drum 200a without being transferred is scraped off by the toner cleaner 207a and removed from the surface of the photosensitive drum 200a. This series of processes is similarly performed for magenta Pb, cyan Pc, and black Pd. As a result, a full-color toner image is formed on the intermediate transfer belt. [[ID=?]]

[0018] [[ID=?]] The toner image on the intermediate transfer belt 204 is transported to the secondary transfer section N2, which is formed by the secondary transfer roller pair 205, 206. In accordance with the timing of the toner image transport, one sheet of recording material S is taken out from the recording material cassettes 8, 9 and fed to the secondary transfer section N2. Then, the toner image on the intermediate transfer belt 204 is transferred to the recording material S (secondary transfer).

[0019] The recording material S onto which the toner image has been transferred is transported to the fuser unit F, where it is fixed by heat and pressure (fixing). The recording material S with the fixed toner image is then discharged into the output tray 7.

[0020] The image forming apparatus 1 can also perform monochrome image formation. When forming a monochrome image, only the black image forming unit Pd among the multiple image forming units is driven.

[0021] When image formation is performed on both sides of the recording material S, once the transfer and fixing of the toner on the first image-forming surface (1st surface) is complete, the recording material S is reversed by passing through a reversal section located inside the image forming apparatus after fixing. Next, the toner on the second image-forming surface (2nd surface) is transferred and fixed, and the material is ejected from the machine and stacked on the output tray 7.

[0022] The process from charging to the discharge of the recording material S, on which the toner image has been fixed, into the output tray 7 is called the image forming process (print job). The period during which image forming is taking place is referred to as the image forming process (print job in progress).

[0023] Figure 2 shows a schematic diagram of the overall configuration of a belt-heating type fixing device F according to an embodiment of the present invention. In Figure 2, the recording material P is conveyed from right to left. The fixing device F includes a belt 310 as an endless, rotatable heating rotating body, a pressure pad (hereinafter referred to as pad) 320, a heating roller 351, and a pressure roller 330 as a pressure rotating body that forms a nip portion N together with the belt.

[0024] The belt 310 has thermal conductivity and heat resistance, and is a thin-walled cylindrical shape with an inner diameter of 150 mm. In this embodiment, it has a three-layer structure with 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 is 60 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 310 is stretched by a pad 320, a heating roller 351, and a steer roller 340.

[0025] <Fusing device> Figure 2 shows a schematic diagram of the overall configuration of the belt heating type fixing device F according to this embodiment. In Figure 2, the recording material P is conveyed from right to left. The fixing device F has a fixing belt (hereinafter referred to as the belt) 310 as an endless, rotatable heating rotating body and a pressure pad (hereinafter referred to as the pad) 320 as members that form the nip portion N. The fixing device F also has a heating unit 300 including a heating roller 351 and a steer roller 340, and a pressure roller 330 as a pressure rotating body that faces the belt and forms the nip portion N together with the belt.

[0026] In this embodiment, the pad 320 is pressed against the pressure roller 330 with the belt 310 in between. The pad 320 is made of LCP (liquid crystal polymer) resin. The belt 310 rotates, and the inner surface of the belt 310 slides against the pad. Therefore, to improve the durability of the belt 310, a lubricant is applied to the inner surface of the belt 310. This allows the belt 310 to slide smoothly against the pad 320. Silicone oil with a viscosity of 100 cSt is used as the lubricant.

[0027] In this embodiment, the fixing device F uses a pad 320 as a means of forming a nip, but a rotating body such as a roller may also be used.

[0028] A heating roller 351, which has a heat source, is positioned on the inner circumference of the belt 310. The heating roller 351 is a hollow roller with a diameter of Φ100 mm and uses aluminum as its core metal. The length of the heating roller 351 in the width direction is 385 mm. Inside the heating roller 351, a total of six halogen heaters 200 are arranged, each with a heating area width of 360 mm in the width direction. The belt 310 is heated by the heat from the halogen heaters 200. A thermistor 352 is also positioned to detect the temperature of the heating roller 351. Based on the temperature detection result from the thermistor 352, the halogen heaters 200 are controlled to a predetermined target temperature according to the type of paper. Three thermistors 352 are installed in contact with the heating roller 351 in the width direction. Thermistors 352a, 352b, and 352c are installed at positions 30 mm, 100 mm, and 150 mm from the center in the width direction, respectively (see Figure 3). Therefore, in the width direction of the belt 310, with respect to the center of the heating roller 351, thermistor a is positioned closest to the center compared to thermistors 352b and 352c. On the other hand, thermistor 352c is positioned closest to the edge in the width direction of the belt 310 compared to thermistors 352a and 352b.

[0029] In this embodiment, the thermistor 352 is in contact with the heating roller 351, but it is not limited to this configuration, and may be configured to be positioned without contact with the heating roller 351. Furthermore, the thermistor 352 in this embodiment detects the surface temperature of the heating roller 351. However, it is not limited to this. It may be a thermistor that detects the surface temperature of the belt 310, or a separate thermistor for detecting the surface temperature of the belt 310 may be provided.

[0030] Next, Figure 3 shows the heat generation distribution of the six halogen heaters in the width direction (hereinafter referred to as the width direction) of the belt 310. There are six halogen heaters 200, which are the heat sources in this embodiment. Let's call the six halogen heaters 2001, 2002, 2003, 2004, 2005, and 2006. Of the six halogen heaters 200, 2001 to 2004 change their heat generation distribution in the width direction, starting from 110 mm from the center of the heating roller 351, with the center of the heating roller 351 as the reference point. Heaters 2001 and 2003 are heaters in which the amount of heat generated in the region from the center to 110 mm (the region of this heating roller 351 is considered the center side) is greater than the amount of heat generated in the region outside of 110 mm (the region of this heating roller 351 is considered the end side). Halogen heaters 2002 and 2004 are heaters in which the amount of heat generated in the end side region is greater than the amount of heat generated in the center side region.

[0031] The positional relationship between the three thermistors 352 and the heating roller 351 used in this embodiment will be explained. Thermistors 352a and 352b are positioned on the central side and detect the temperature on the central side. Thermistor 352b detects the temperature in the outer region compared to thermistor 352a. On the other hand, thermistor 352c detects the temperature on the edge side of the heating roller 351. In this embodiment, the control unit 30 controls which of the six heaters has its current supplied to the greater extent according to the edge temperature detected by thermistor 352c. The halogen heaters 200 2005 and 2006 have a uniform heat distribution in the width direction. The amount of heat per unit time of the halogen heater 200 is changed according to the paper weight. In this embodiment, the number of lit heaters is changed.

[0032] The heating roller 351 has a gear fixed to one end in the width direction, and is connected to a drive motor (not shown) via the gear to be rotationally driven. The rotation of the heating roller 351 imparts conveying force to the belt 310. The rotation of the heating roller 351 may be driven by a pressure roller drive source (not shown) that rotates the pressure roller 330, or it may be driven by a drive source other than the pressure roller drive source, and the means of providing the driving force, including drive transmission means other than gears, is not limited.

[0033] The pressure roller 330 is a roller with an elastic layer formed on the outer circumference of the shaft, and a release layer formed on the outer circumference of the elastic layer. The shaft is made of stainless steel, the elastic layer is made of conductive silicone rubber with a thickness of 5 mm, and the release layer is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 50 μm. The width of the elastic part is 355 mm, and the outer diameter is Φ80 mm. The pressure roller 330 is supported by the fixing frame (not shown) of the fixing device F. A gear is fixed to one end of the pressure roller 330 in the width direction, and is connected to the pressure roller drive motor via the gear to rotate it.

[0034] The belt 310 is pressurized by the pressure roller 330 and the pad 320. Furthermore, since the pressure roller 330 is rotationally driven, the belt 310 rotates in a manner driven by the pressure roller 330.

[0035] The stay 360 is fixed to the fixing frame by fixing means (not shown) of the fixing frame, and the pressure roller 330 is pressed against the pad 320 via the belt 310 by a drive source (not shown) and a cam.

[0036] In this embodiment, the rotational speed of the belt 310 is 630 mm / s, and the pressure in the nip formed when the belt is pressed against the pressure roller via the pad is 1000 N.

[0037] A steer roller 340 is positioned upstream of the nip section N as a means for maintaining the conveying posture of the belt 310. The steer roller 340 is biased by a spring supported by a fixing frame and is a tension roller that applies a predetermined tension to the belt 310, rotating in a driven manner relative to the belt 310. The tension from the spring is 50N, applying tension to the belt 310 from within.

[0038] The steer roller 340 has a pivot point at one end or near the center in the width direction, and rotates relative to the belt 310 to generate a tension difference in the front and rear directions, thereby controlling the position of the belt 310 in the main scanning direction. In this embodiment, the pivot point is located in the center in the width direction, but a configuration with the pivot point at one end in the width direction may also be used. This steer roller 340 is biased by a spring supported by the fixing frame and also acts as a tension roller that applies a predetermined tension to the belt 310. The tension from the spring is 50N, and the belt position in the main scanning direction is controlled by applying tension to the belt 310.

[0039] As described above, the mop section N is formed by the rotationally driven pressure roller 330 and belt 310. The recording material carrying the toner image is then transported to the nip section N, applying heat and pressure to the recording material. This fixes the toner image to the recording material.

[0040] Next, we will explain the details of the heating control during the fixing operation. We will explain the case where the longer side of 80gsm high-quality paper A4 size (297mm x 210mm) is in the width direction of the belt 310. The target temperature of the belt 310 during printing is 180°C. The paper is transported to the nip section at a productivity of 130 ppm (130 sheets per minute). Productivity refers to the number of sheets printed per unit time, and ppm is a unit representing the number of sheets printed per minute. When fixing 80gsm high-quality paper A4 size (297mm x 210mm), the control unit 30 controls the power to be supplied to 2002, 2004, and 2005 of the six halogen heaters 200. At this time, the control unit 30 sets the heat distribution to be 7 w / mm in the center in the width direction and 11 w / mm at the edges in the width direction. This maintains the thermistor 352's detected temperature at 200°C, and the temperature between the heating roller 351 and the belt 310 at 180°C. The halogen heaters 2002, 2004, and 2005 are not always powered. They repeatedly switch on and off according to the temperature detected by thermistor 352, maintaining the belt temperature at 180°C. In the case of A4 size, a temperature drop occurs due to heat dissipation at the edges in the width direction, so the amount of heat generated at the edges is increased. Therefore, the frequency of lighting up halogen heaters 2002 and 2004 is increased.

[0041] This section describes the case where double-sided coated paper with a basis weight of 350gsm, printed in A4R size (210mm x 297mm), is transported with the longer side aligned with the transport direction of the recording material. The target temperature of the belt 310 during printing is 195°C, and the recording material is transported to the nip section N with a productivity of 100 ppm. Note that 100 ppm for A4R size is the productivity when transported at a speed of 630 mm / s with the same paper spacing as A4 at 130 ppm. Since the longer side of the recording material coincides with the transport direction of the recording material, the productivity is lower compared to the case where the longer side coincides with the width direction. At this time, power is supplied to 2001, 2003, 2005, and 2006 in Figure 3 of the halogen heater 200, resulting in a heat distribution of 14 w / mm towards the center in the width direction and 10 w / mm towards the edges in the width direction. This maintains the detection temperature of the thermistor 352 at 225°C, and the temperature of the belt 310 at 195°C. Furthermore, halogen heaters 2001, 2003, 2005, and 2006 are not always powered. They repeatedly switch on and off according to the temperature detected by thermistor 352, maintaining the belt temperature at 195°C. In the case of A4R size, significant edge heating occurs because heat is not absorbed by the paper at the edges in the width direction. Therefore, the amount of heat generated at the edges in the width direction is reduced compared to the center, and halogen heaters 2001 and 2003 are turned on more frequently.

[0042] In this embodiment, in the first mode, halogen heaters 200 2001 and 2002 alternately turn on and off. When fixing recording material with a small width, halogen heater 2001, which has a larger heat distribution towards the center, is used to generate heat. When fixing recording material with a large width, halogen heater 2002, which has a larger heat distribution towards the edges, is used to generate heat.

[0043] In this embodiment, if the halogen heaters 6 are lit simultaneously during paper feeding, there is a risk that the heat resistance temperature of the sensors around the fuser unit F and thermistor 352 may be exceeded due to overshoot during heating. Therefore, the hardware circuit is designed so that halogen heaters 2001 and 2002 are not lit at the same time.

[0044] This section explains the standby phase. Standby phase is the period when the image forming apparatus 1 is powered on and waits until a job is sent. Therefore, the fixing device F prepares itself so that it can perform fixing operations immediately once a job is sent. This preparation mainly involves the temperature of the heating roller 351 and the rotation speed of the belt 310. During standby, the temperature of the heating roller 351 is controlled to a predetermined temperature so that it can quickly reach the target temperature for fixing. For example, the temperature of the heating roller 351 during standby is set to 180°C. The rotation speed of the belt 310 is set to, for example, 80 mm / s. By rotating the belt 310 during standby, it is possible to raise the temperature of the belt 310 uniformly. As shown in the example, the rotation speed of the belt 310 during standby is lower than during paper feeding. In the low-speed rotation state, the contact time between the belt 310 and the heating roller 351 is longer than in the high-speed rotation state. Therefore, the belt 310 is more susceptible to heat transfer from the heating roller 351, causing the temperature of the belt 310 to rise easily. For this reason, in this embodiment, when the belt 310 is rotating at a low speed during standby, two of the six halogen heaters 200 (2001 and 2002 in this embodiment) are not lit. During standby, the belt 310 is heated by lit four of the six halogen heaters 200 (2003 to 2006 in this embodiment).

[0045] <Speed ​​detection component> Here, we will explain the details of the speed sensing member 400b.

[0046] Figure 4 is a detailed view of the speed detection member in the fixing device F. The speed detection member 400 has a rotating part 401, a rotating blade 402, and a photosensor 403. The rotating part 401 has an outer diameter of Φ20 mm and is in contact with the outer surface of the belt 310, and rotates in response to the rotation of the belt 310. Figure 5 is a front view of the fixing device F of Figure 2, viewed from the direction of the arrow. As shown in Figure 5, the central axes of the rotating blade 402 and the rotating part 401 are coaxial, and the rotating blade 402 rotates in conjunction with the rotation of the rotating part 401. The rotating blade 402 has four blades per rotation, and the photosensor 403 detects the number of times the blade portion of the rotating blade 402 crosses the photosensor 403. In this embodiment, the rotational speed of the belt 310 is detected from the time when the number of times the blade portion of the rotating blade 402 crosses the photosensor 403 reaches 16 (when the rotating part 401 completes 4 rotations). An example of the detection result is shown in Figure 6. The graph in Figure 6 shows the rotation period of the rotating blade 402 as detected by the photosensor 403 of the speed detection member 400. It takes 393 ms for the blades of the rotating blade 402 to pass the photosensor 16 times. Since the outer diameter of the rotating part 401 is Φ20 mm, the distance for four rotations is 251 mm. 251 mm / 393 ms = 640 mm / s. Therefore, the speed of the belt 310 detected by the speed detection member 400 at this time is 640 mm / s. In this embodiment, a contact-type speed detection member 400 using the rotating part 401 is used, but a non-contact type speed detection member that detects the rotation period by detecting a mark on the belt with the photosensor 403 may also be used, and the means are not limited to this.

[0047] The target belt rotation speed in this embodiment is 630 mm / s, and a drive motor gear is used such that when the drive motor connected to the heating roller 351 rotates at 4000 rpm, the rotation speed of the heating roller 351 becomes 630 mm / s. However, slight speed fluctuations occur due to the condition of the lubricant applied to the inner surface of the belt 310, the roughness of the inner surface of the belt 310, etc. Therefore, even if the rotation speeds of the pressure roller 330 and the heating roller 351 are set to 630 mm / s, the belt rotation speed may deviate from 630 mm / s. In this case, the belt 310 is corrected to reach the target speed based on the actual belt speed detected by the speed detection member 400. Specifically, in the correction, the rotation speed of at least one of the pressure roller 330 and the heating roller 351 is changed. If the target rotational speed of the belt 310 is 630 mm / s, and the speed of the belt 310 detected by the speed detection member 400 is less than 630 mm / s, then the actual rotational speed of the belt 310 is lower than the target rotational speed. Therefore, the rotational speed of at least one of the pressure roller 330 and the heating roller 351 is controlled to be higher. In this embodiment, the belt 310 is controlled to reach the target speed by using the speed detection member 400.

[0048] However, the configuration using the speed detection member 400 presents the following challenges. If the speed detected by the speed detection member 400 falls outside the predetermined speed range, it may not be possible to accurately determine the belt speed. For example, this can occur if the lubricant applied to the inner surface of the belt 310 flows around to the outer surface of the belt 310 and interposes itself between the rotating part 401 and the belt 310. In this case, the rotating part 401 may slip due to the lubricant, potentially causing it to detect a speed slower than the actual rotational speed of the belt 310. Consequently, the speed detection member 400 cannot accurately detect the rotational speed of the belt 310. The belt 310 is heated by the heating member. The rate at which the temperature of the belt 310 rises depends on the belt's rotational speed; the slower the rotational speed, the greater the rate at which the belt's temperature rises. When image formation is performed in such a state where the speed of the belt 310 cannot be accurately determined, it is difficult to accurately determine the degree of temperature rise of the belt 310. This could cause the temperature of the belt 310 to rise rapidly, potentially damaging components near the belt 310.

[0049] Therefore, the fixing device F of this embodiment prevents the belt temperature from rising rapidly when image formation is performed in a situation where it is difficult to accurately grasp the rotation speed of the belt, thereby preventing a shortened lifespan of the components.

[0050] Figure 7 is a flowchart showing how the control unit 30 controls the number of halogen heaters 200, which are heat sources, to light up according to the rotational speed of the belt 310 detected by the speed detection member 400. The speed detection member 400 and the number of halogen heaters 200 to light up will be explained in accordance with the flowchart in Figure 7. In this embodiment, the target rotational speed of the belt 310 is 630 mm / s. The fixing device F uses a drive motor gear such that when the drive motor connected to the heating roller 351 is rotated at 4000 rpm, the rotational speed of the heating roller 351 becomes 630 mm / s.

[0051] S101 When power is turned on to the image forming apparatus 1, the initial operation of the image forming apparatus 1 begins.

[0052] S102 Image forming apparatus 1 enters standby mode. In standby mode, the belt 301 of the fixing device F rotates at a standby speed of 80 mm / s (drive motor rotation speed 507 rpm).

[0053] S103 In standby mode, the halogen heaters 200, which are the heat sources, are also lit. In this embodiment, four halogen heaters 200 are lit in standby mode, and halogen heaters 2001 and 2002 are not lit.

[0054] S104 Image forming apparatus 1 receives a print job.

[0055] S105 A speed correction sequence is initiated to correct the speed of belt 310. The rotation speed of the drive motor connected to the heating roller 351 is changed to 4000 rpm.

[0056] S106 The target rotational speed of the heating roller 351 is set to 630 mm / s. The speed sensing member 400 then detects the rotational speed of the belt 310. If the detected rotational speed is within the predetermined speed range, that is, if the error between the detected rotational speed and the target rotational speed is within ±10%, the process proceeds to S107. On the other hand, if the detected rotational speed is outside the predetermined speed range, that is, if the error between the detected rotational speed and the target rotational speed is greater than ±10%, the process proceeds to S110.

[0057] S107 The ratio between the rotational speed detected by the speed sensing member 400 and the target rotational speed is calculated.

[0058] For example, if the rotational speed of the belt 310 detected by the speed sensing member 400 is 640 mm / s, the ratio of this to the target rotational speed of 630 mm / s is calculated as 630 / 640 = 0.984.

[0059] S108 Based on the calculated ratio, the rotational speed of the drive motor is corrected, and the number of halogen heaters 200 that light up is changed. In this example, the calculated ratio is 0.984. The rotational speed of the drive motor, 4000, is multiplied by the calculated ratio of 0.984 (4000 × 0.984 = 3938 rpm). As a result of the calculation, a correction value is calculated. In this case, the correction value is 3938 rpm. The rotational speed of the drive motor is corrected to 3938 rpm. As a result, the actual belt speed is prevented from deviating from the target rotational speed.

[0060] At this time, the restriction on lighting halogen heaters 2001 and 2002 is lifted. However, halogen heaters 2001 and 2002 are not lit simultaneously. Therefore, the maximum number of halogen heaters 200 that can be lit in this embodiment is 5, and some halogen heaters 200 will not be lit. By lifting the restriction on lighting 2001 and 2002, the heat output of halogen heaters 200 increases, and the efficiency of heating the belt 310 increases. As a result, it becomes advantageous for continuous paper feeding and fixing of recording material with a large basis weight.

[0061] S109 Depending on the paper size and type of the recording material, halogen heaters 2001-2006 are switched on and paper is fed. The first mode is when printing is performed without any prohibited heat sources (halogen heaters).

[0062] S106 If the error between the rotational speed detected by the speed detection member 400 and the target rotational speed is greater than ±10%, the process proceeds to S110. For example, as a specific example, we will explain the case where the speed detected by the speed detection member 400 is 50 mm / s.

[0063] S110 If the speed of the belt 310 detected by the speed detection member 400 is 50 mm / s, there is a possibility that the rotational speed of the belt 310 has not reached the target temperature. Therefore, the prohibition against lighting halogen heaters 2001 and 2002 should continue. However, it is also possible that the speed detection member 400 is unable to accurately detect the rotational speed of the belt 310, and the drive mechanism of the fixing device is functioning normally. For example, lubricant that has seeped in from the inner surface of the belt may be interposed between the rotating part 401 and the belt 310, preventing the speed detection member 400 from accurately detecting the rotational speed of the belt 310. In this case, the speed detection member 400 may detect a speed lower than the target rotational speed, such as 50 mm / s. However, the actual speed of the belt 310 may be rotating with a small error (error within ±10%) from the target rotational speed. Therefore, even if the error in the belt 310 speed detected by the speed detection member 400 is large, the possibility that the speed detection member 400 is not accurately detecting the rotational speed of the belt 310 is considered, and the drive motor continues to rotate the belt at 4000 rpm. In this case, the halogen heaters 200 of 2001 and 2002 remain in a state where they are not allowed to light up.

[0064] S111 When the two halogen heaters 200 are disabled, the amount of heat generated by the halogen heaters 200 decreases. Therefore, the amount of heat that can be supplied to the belt 310 decreases. In this embodiment, even when the two halogen heaters 200 are disabled, productivity is reduced compared to when the disabling of the two halogen heaters 200 is lifted, so that the toner image can be fixed. Specifically, productivity is reduced to 50 ppm (A4 equivalent). The error range is a value calculated from the measurement experiment results of speed variation, and can be within a range of ±5%, etc., and the range is not specified. Possible factors for variation include the oil temperature, lubrication condition, and the roughness of the belt's inner surface. The mode in which printing is performed with a heat source (halogen heater) that is disabled is defined as the second mode.

[0065] For example, when printing on A4 size (210mm x 297mm) double-sided coated paper with a basis weight of 350gsm in the second mode, the surface temperature of the belt 310 becomes 195°C. The productivity is 50ppm and the target rotational speed of the heating roller 351 is 630mm / s. At this time, power is supplied to the halogen heaters 200 of 2004, 2005, and 2006, and they become lit. Specifically, by creating a heat distribution of 8w / mm towards the center in the width direction and 10w / mm towards the edges in the width direction, the temperature detected by the thermistor 352 is maintained at 210°C, and the temperature of the belt 310 is maintained at 195°C. The three halogen heaters 2004, 2005, and 2005 are not always lit, but repeatedly turn on and off according to the temperature detected by the thermistor 352, maintaining the belt temperature at 195°C. Since the productivity is 50 ppm compared to 130 ppm, the amount of heat lost per unit of time to the belt 310 due to the passage of the recording material is reduced. This allows for fixing with lower power consumption.

[0066] Furthermore, for example, when printing on 80gsm basis weight A4R size (210mm x 297mm) high-quality paper in the second mode, the surface temperature of the belt 310 becomes 180°C. The productivity is 45ppm, and the target rotational speed of the heating roller 351 is 630mm / s. Note that 45ppm for A4R size is the productivity when the paper is transported at a speed of 630mm / s with the same paper spacing as A4 50ppm. At this time, power is supplied to the halogen heaters 200 of 2003 and 2006, resulting in a heat distribution of 6w / mm towards the center in the width direction and 4w / mm towards the edges in the width direction. This maintains the temperature detected by the thermistor 352 at 190°C, and the temperature of the belt 310 at 180°C. 2003 and 2006 are not always lit, but repeatedly turn on and off according to the temperature detected by the thermistor 352, maintaining the belt temperature at 180°C. Since the productivity is 45 ppm (50 ppm in A4 equivalent) compared to 100 ppm (130 ppm in A4 equivalent), the amount of heat lost per unit of time due to the passage of the recording material through belt 310 is reduced. As a result, fixing becomes possible with low power consumption.

[0067] In this embodiment, if the speed of the belt 310 detected by the speed detection member 400 exceeds a predetermined speed (error of 10% or more), an alarm history is recorded in the memory of the image forming apparatus as a speed detection abnormality alarm. The alarm history is accessed from the operation unit 4 to a screen accessible only to service personnel, and is recorded as an alarm history as shown in Figure 8. Alarm code 0055 in Figure 8 is the speed detection abnormality alarm in this embodiment, and service personnel can check the date and time of the speed detection abnormality, the paper count counter, and other history from the operation unit 4.

[0068] Furthermore, in this embodiment, productivity is reduced if an abnormality occurs during speed detection (if the detected speed exceeds a predetermined speed), so an alarm may be displayed on the user operation screen as shown in Figure 9. Since the speed correction sequence is performed when a job is received, the alarm message is displayed on the print operation screen when the job starts.

[0069] The effects of this embodiment are shown in Figure 10. As a comparative example, it is compared with a conventional technology that stops the power supply to the heater based on the speed detection result of the speed detection member 400.

[0070] In conventional technology, if there is a malfunction in the speed detection element 400, power to the heater is stopped even if there is no abnormality in the actual rotation speed of the belt 310. Therefore, printing does not occur. The user is unable to print.

[0071] On the other hand, in this embodiment, if there is a malfunction in the speed detection member 400 but there is no abnormality in the actual rotation speed of the belt 310, the power supply to the halogen heater 200 is not stopped, and only the power supply to the predetermined halogen heater 200 is cut off. As a result, the number of halogen heaters 200 that light up is reduced compared to when there is no malfunction in the speed detection member 400 (first mode). However, printing operations become possible even with reduced productivity of the image forming apparatus 1. An alarm is displayed on the operation unit 4, a service technician is called, and the user can perform minimal printing operations until the service technician arrives, thus reducing downtime compared to conventional technology.

[0072] In the second mode of this embodiment, productivity is reduced compared to the first mode. The method of reducing productivity is to widen the gap between sheets of paper. The gap between sheets of paper refers to the space between recording materials. The rotation speed of the heating roller 351 is the same as in the first mode, and this mode reduces productivity to 50 ppm by widening the gap between sheets of paper. However, this is not the only way to reduce productivity; any means of reducing productivity is acceptable, such as reducing the rotation speed of the heating roller 351 (for example, from 630 mm / s to 410 mm / s).

[0073] As described above, this embodiment includes a second mode. In the second mode, the actual rotational speed of the belt 310 cannot be determined, making it difficult to determine the degree of temperature rise of the belt 310. Therefore, when the control unit 30 controls the amount of heat generated by the halogen heater 200 based on the rotational speed of the belt 310, it becomes difficult to reflect the actual rotational speed of the belt 310 in the amount of heat generated. This can lead to a large temperature rise in the belt 310, potentially damaging nearby components. To suppress this, if the detected speed of the belt 310 detected by the speed detection member 400 is outside a predetermined speed, printing is performed in the second mode. In the second mode, the amount of heat supplied to the halogen heater 200 per unit time is reduced compared to the first mode. In this embodiment, the number of halogen heaters 200 that are lit is limited. This prevents the belt 310 from overheating when printing is performed in the second mode.

[0074] When printing in the second mode, productivity is lower than in the first mode. This is because, in the second mode, the number of halogen heaters 200 that can be lit is reduced compared to the first mode. Reducing the number of halogen heaters 200 that can be lit reduces the efficiency of transferring the heat necessary for fixing to the belt 310. If the productivity were the same as the first mode, there would be insufficient heat for fixing if fixing were performed continuously. Therefore, in the second mode of this embodiment, the spacing between the sheets of paper is widened to increase the time that heat is supplied from the heating roller 351 to the belt 310. This makes it possible to perform fixing even in the second mode, where the number of halogen heaters 200 that can be lit is reduced compared to the first mode.

[0075] In this embodiment, there are six halogen heaters 200, with a maximum of five heaters lit. During fixing, halogen heaters 2001 and 2002 are lit alternately. The number of halogen heaters 200 lit is also changed depending on the basis weight of the recording material. For example, when printing recording material with a high basis weight, more halogen heaters 200 are lit compared to when printing recording material with a low basis weight. As shown in Figure 12, when printing recording material with a high basis weight (350 gsm recording material) in the first mode, five heaters are lit for fixing. However, when printing recording material with a high basis weight (350 gsm recording material) in the second mode, the maximum number of halogen heaters lit is four. Therefore, when printing recording material with a predetermined basis weight or higher, fewer halogen heaters 200 are lit in the second mode than in the first mode. When printing recording material with a predetermined basis weight or lower, the number of halogen heaters 200 lit in the first mode and the second mode may be the same.

[0076] The two halogen heaters that do not light up simultaneously in the first mode and the two halogen heaters that are prohibited from lighting up in the second mode are the same halogen heaters. In this embodiment, halogen heaters 2001 and 2002 have different heat generation in the width direction. Similarly, 2003 and 2004 also have different heat generation in the width direction. The heat generation of 2001 and 2002 is greater than that of 2003 and 2004. By prohibiting the lighting of halogen heaters with high heat generation in the second mode, a rapid rise in the temperature of the belt 310 is suppressed.

[0077] Furthermore, in standby mode, the two halogen heaters 200 are not lit. Similarly, in the second mode, the two halogen heaters 200 are not lit. The halogen heaters that are not lit in both standby mode and the second mode are the same heaters.

[0078] <Example 2> This embodiment shows a speed correction sequence that provides a mode to prevent a reduction in productivity according to the basis weight, even when the detected belt speed in the speed detection sequence exceeds the range of 630 ± 10%. A detailed flowchart is shown in Figure 11.

[0079] Parts of the explanation that overlap with Figure 7, which is the flowchart for Example 1, will be omitted. Steps S101 to S110 in Figure 7 correspond to S201 to S210, and the actions performed are the same, so the explanation will be omitted. Also, S111 corresponds to S213, and the actions performed are the same, so the explanation will be omitted. S211 is an item that was added from Example 1 to Example 2, so an explanation of S211 will be given.

[0080] C211 If the detected speed of the belt 310 detected by the speed detection member 400 is outside the predetermined speed, the flowchart proceeds to S211. In S211, the productivity is changed according to the basis weight of the recording material being fed through. In this embodiment, 220 gsm is used as the standard, and for recording material of 220 gsm or more, the productivity is reduced and printing is performed. Therefore, the process proceeds to S213.

[0081] On the other hand, if the basis weight of the recording material being fed is less than 220 gsm, fixing is possible at the normal productivity of 130 ppm by only illuminating the remaining four halogen heaters 200, even if halogen heaters 2001 and 2002 are prohibited from being lit. Therefore, proceed to S209.

[0082] Figure 12 is a graph showing the power required to fix toner based on paper weight. As shown in Figure 12, even when halogen heater operation is prohibited, power can be supplied to the halogen heater up to 11 w / mm. Therefore, fixing operation at 130 ppm is possible for recording materials up to 220 gsm, which corresponds to 11 w / mm.

[0083] In this embodiment, however, paper was fed at normal productivity without reducing productivity only under conditions where fixing was possible even when the halogen heater was not lit, depending on the basis weight. However, the determination of productivity reduction could also be made based on factors such as the amount of toner on the paper or the smoothness of the paper, and the means of determining productivity reduction are not limited.

[0084] In Example 1, regardless of the basis weight of the recording material, printing in the second mode results in lower productivity than in the first mode. In Example 2, when printing recording material with a predetermined basis weight or higher in the second mode, productivity is lower than in the first mode. Therefore, it is common that when printing recording material with a predetermined basis weight or higher (220 gsm in this embodiment) in the second mode, productivity is lower than in the first mode. [Explanation of symbols]

[0085] 1. Image forming apparatus 4 Control section 200 Halogen Heater 300 heating units 310 belt 320 Compression Pads 330 Pressure Roller 340 Steerola 351 Heating roller 352 Thermistor 400 Speed ​​detection member 401 Rotating part 402 Rotating blades 403 Photosensor

Claims

1. An image forming unit that forms a toner image on the recording material, A fixing device for fixing the toner image formed on the recording material, The system comprises a control unit for controlling the fixing device, The fixing device is A heating rotating body that applies heat to the recording material, A pressurized rotating body that pressurizes the heated rotating body to form a nip portion, Multiple heat sources for heating the aforementioned rotating heating body, The system includes a speed detection member for detecting the rotational speed of the heating rotating body, Heat and pressure are applied to the recording material passing through the nip section to fix the toner image onto the recording material. In an image forming apparatus, the control unit controls the rotation speed of the heating rotating body based on the detection result of the speed detection member. When the control unit performs a job to fix toner images onto a plurality of predetermined recording materials, (i) A first mode in which printing is performed by controlling the rotation speed of the heating rotating body to a predetermined target speed based on the detection result of the speed detection member, (ii) When the heating rotating body is rotated under predetermined driving conditions, if the rotation speed detected by the speed sensing member is lower than the predetermined speed, This limits the maximum power that can be supplied by the heat source more than the first mode described above, An image forming apparatus characterized by being capable of performing printing by rotating the heating rotating body under predetermined driving conditions with a longer interval for transporting the recording material than in the first mode, or by changing the driving conditions to a lower speed than the predetermined driving conditions and performing printing.

2. The heating rotating body is a rotatable, endless fixing belt. The image forming apparatus according to claim 1, characterized in that the speed detection member detects the rotational speed of the fixing belt.

3. The image forming apparatus according to claim 1 or 2, characterized in that, when the control unit executes the second mode, if the basis weight of the predetermined recording material is equal to or greater than the predetermined basis weight, the transport interval for the recording material is set to be longer than that of the first mode, and if the basis weight of the predetermined recording material is less than the predetermined basis weight, the transport interval for the recording material is set to be the same as that of the first mode.

4. The image forming apparatus according to claim 1 or 2, characterized in that when the control unit executes the second mode, if the basis weight of the predetermined recording material is equal to or greater than the predetermined basis weight, it changes the drive conditions to be lower than the predetermined drive conditions and performs printing, and if the basis weight of the predetermined recording material is less than the predetermined basis weight, it prints under the predetermined drive conditions.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the second mode has fewer heat sources that can be lit than the first mode.

6. The image forming apparatus according to any one of claims 1 to 5, characterized in that, when printing is performed in the first mode, at least one of the plurality of heat sources is not lit.

7. A standby state in which the rotation speed of the heating rotating body is lower than that of the first mode, The image forming apparatus according to any one of claims 1 to 6, characterized in that the number of heat sources that can be lit in the standby state is less than the number of heat sources that can be lit in the first mode.

8. The image forming apparatus according to claim 7, characterized in that the heat source that is not lit in the standby state is the same as the heat source that is not lit in the second mode.

9. The image forming apparatus according to any one of claims 1 to 8, characterized in that, when fixing a recording material of a predetermined basis weight or more, the number of heat sources lit in the first mode is greater than the number of heat sources lit in the second mode.

10. The image forming apparatus according to any one of claims 1 to 9, comprising an operating unit capable of displaying information, wherein when the control unit executes the second mode, it displays an alarm on the operating unit indicating that there is a possibility of a malfunction in the fuser and therefore the printing speed is reduced compared to normal.

Images