Belt conveying device, fixing device, image forming device

Abstract

The present invention provides a belt conveying device that controls the belt's position based on the belt's position detected by a sensor, thereby suppressing belt meandering caused by the temperature of the sensor. [Solution] The feedback gain of the control system for belt-side control is corrected by capturing the change in the output characteristics of the sensor unit 390 caused by temperature. Using the first voltage VPD1 and the second voltage VPD2 output from the sensor unit 390, which change depending on the end position of the fixing belt, the subtraction unit 33 calculates a differential value "VPD1-VPD2" indicating the end position of the fixing belt, and the addition unit 34 calculates a sum value "VPD1+VPD2" that reflects the change in the amount of light emitted by the light-emitting unit. Then, the "steering operation amount STEPn" calculated by the PID calculation unit 31 according to the differential value "VPD1-VPD2" is corrected by a gain correction coefficient determined by the gain determination unit 35 based on the sum value "VPD1+VPD2" to determine the tilt angle of the steering roller.

Description

Technical Field

[0001] The present invention relates to a belt conveyance device suitable for use in an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction peripheral, a fixing device including the belt conveyance device, and an image forming apparatus.

Background Art

[0002] In image forming apparatuses using an electrophotographic method or an inkjet recording method, a belt conveyance device including an endless belt stretched by a plurality of stretching rollers is used. The belt is used, for example, to carry a toner image or to convey a recording material on which an image is formed. Since the belt is stretched by a plurality of stretching rollers and rotationally driven, "skewing" can occur in the belt. The "skewing" of the belt is a phenomenon in which the rotating belt meanders with respect to the stretching rollers and moves toward the end side in the width direction. If the belt moves too much toward the end side, the belt end may contact other members, and there is a risk of damage to the belt or other members. Therefore, belt skew control (also called steering control) is performed to adjust the skew of the belt by detecting the position of the belt by a sensor unit and tilting one of the plurality of stretching rollers (so-called steering roller) based on the detection result of the sensor unit.

[0003] In the device described in Patent Document 1, a sensor unit having a light emitting unit and a light receiving unit is used to detect the position of the belt based on an output signal of the light receiving unit that changes in conjunction with the movement of the belt in the width direction. However, since the light emission amount of the light emitting unit is affected by temperature, an error may occur in the position of the belt detected based on the output signal of the light receiving unit depending on the temperature of the sensor unit. Therefore, in the device described in Patent Document 1, the light amount of the light emitting unit is adjusted so that the output signal of the light receiving unit becomes a predetermined value at a predetermined adjustment timing such as when the power is turned on or during image adjustment control.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, conventionally, the temperature of the sensor sometimes caused a delay in the belt's meandering due to belt-bias control, resulting in a longer delay in the belt's alignment. This is because the sensor has a characteristic where the amount of light emitted changes with temperature, and this was particularly noticeable when the belt was started at low temperatures.

[0006] In view of the above problems, the present invention aims to provide a belt conveying device that controls the belt's position based on the position of the belt detected by a sensor unit, thereby suppressing belt meandering caused by the temperature of the sensor unit, as well as a fixing device equipped with the belt conveying device and an image forming apparatus. [Means for solving the problem]

[0007] A belt conveying device according to one embodiment of the present invention includes an endless belt, a first roller for tensioning the belt, a second roller for tensioning the belt together with the first roller, a steering mechanism that tilts the rotating first roller relative to the second roller and moves the belt back and forth in the direction of the rotation axis of the first roller, and a light-emitting unit that emits light. ,before The light emitted from the light-emitting part is received. The first possible Light receiving area A second light-receiving area was provided. Light receiving section and It has the capability to output a first signal with an output level corresponding to the amount of light received in the first light-receiving region and a second signal with an output level corresponding to the amount of light received in the second light-receiving region. Detection unit and a subtraction unit that generates a third signal by subtracting the first signal and the second signal which change in conjunction with the displacement of the belt in the direction of the rotation axis, an addition unit that generates a fourth signal by adding the first signal and the second signal, The steering mechanism is controlled by a control unit, and the control unit is With the belt not fully positioned over the end of the first roller in the direction of its rotation axis, the third signal and the fourth signal are acquired from the subtraction unit and the addition unit, respectively. The tilt angle of the first roller, determined according to the third signal acquired from the subtraction unit, is corrected according to the fourth signal acquired from the addition unit, and the first roller is tilted according to the corrected tilt angle. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, the belt positioning control is performed based on the position of the belt detected by a sensor unit having a light-emitting unit and a light-receiving unit, thereby suppressing belt meandering caused by the temperature of the sensor unit. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing an image forming apparatus. [Figure 2] A schematic diagram showing the fixing device. [Figure 3] External view showing the belt position detection unit. [Figure 4] Cross-sectional view showing the sensor section. [Figure 5] A schematic diagram showing the light-receiving section and the light-shielding section. [Figure 6] A graph showing the output characteristics of the output signals output from the sensor unit and their differential values. [Figure 7] A flowchart illustrating the belt-side control process. [Figure 8] A control block diagram showing the control system for belt-side control in this embodiment. [Figure 9] A graph showing the belt behavior during belt starting in this embodiment. [Figure 10] A control block diagram showing a conventional belt-driven control system. [Figure 11] A graph showing the output characteristics of the output signal output from the sensor unit at low and high temperatures, as well as their differential values. [Figure 12] A graph showing the belt behavior during belt starting in a conventional example. [Modes for carrying out the invention]

[0010] <Image forming apparatus> This embodiment will be described. First, the image forming apparatus of this embodiment will be described with reference to FIG. 1. The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd provided corresponding to four colors of yellow, magenta, cyan, and black. This embodiment is a tandem type image forming apparatus 1 in which the image forming units Pa, Pb, Pc, and Pd are arranged along the rotation direction of the intermediate transfer belt 204. The image forming apparatus 1 forms a toner image (image) on a recording material according to an image signal from a document reading apparatus 2 connected to the apparatus main body 3 of the image forming apparatus 1 or an external host device such as a print server communicably connected to the apparatus main body 3. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0011] As shown in FIG. 1, the image forming apparatus 1 includes a document reading apparatus 2 and an apparatus main body 3. The document reading apparatus 2 reads a document placed on the document table glass 21, and 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. When such an optical system unit is scanned in the direction of the arrow under the control of the reader control unit, the document is read line by line and converted into an electric signal data series. The image signal obtained by the CCD sensor 24 is sent to the apparatus main body 3, and image processing adapted to each image forming unit described later is performed by the control unit 30. Further, the control unit 30 also receives an external input from an external host device such as a print server as an image signal.

[0012] The apparatus main body 3 includes a plurality of image forming units Pa, Pb, Pc, and Pd, and in each image forming unit, image formation is performed based on the above-described image signal. That is, the image signal is converted into a laser beam PWM (pulse width modulation controlled) by the control unit 30. The polygon scanner 61 scans a laser beam corresponding to the image signal. Then, the photosensitive drums 200a to 200d of the respective image forming units Pa to Pd are irradiated with the laser beam.

[0013] Note that the image forming unit Pa forms a toner image of the corresponding color of yellow (Y), the image forming unit Pb forms a toner image of magenta (M), the image forming unit Pc forms a toner image of cyan (C), and the image forming unit Pd forms a toner image of black (Bk). Since these image forming units Pa to Pd have substantially the same configuration, the image forming unit Pa that forms a yellow (Y) toner image will be described as an example below, and the description of the other image forming units Pb to Pd will be omitted. In the image forming unit Pa, the photosensitive drum 200a as a photoreceptor rotates while carrying a toner image formed based on an image signal.

[0014] The charging roller 201a charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for forming an electrostatic latent image. An electrostatic latent image is formed on the surface of the photosensitive drum 200a charged to a predetermined potential by a laser beam from the polygon scanner 61. The developing device 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204 and applies a primary transfer bias of the opposite polarity to the toner, and primary transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. The surface of the photosensitive drum 200a after transfer is cleaned by the cleaner 207a.

[0015] Also, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming unit, and the toner images of each color formed in the respective image forming units Pa to Pd in the order of yellow (Y), magenta (M), cyan (C), and black (Bk) are sequentially transferred, and a four-color image is formed on its surface. Then, the toner image that has passed through the image forming unit Pd at the most downstream in the rotation direction of the intermediate transfer belt 204 is conveyed to the secondary transfer unit T2 composed of the secondary transfer roller pair 205 and 206 as a transfer unit. Then, in the secondary transfer unit T2, a secondary transfer electric field of the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, and the toner image is secondarily transferred from the intermediate transfer belt 204 to the recording material.

[0016] The recording material is housed in a cassette 9. The recording material fed from the cassette 9 is transported to a registration unit 208, which consists of, for example, a pair of registration rollers, and waits in the registration unit 208. Subsequently, the registration unit 208 is controlled in timing to align the toner image on the intermediate transfer belt 204 with the position of the paper, and then transports the recording material to the secondary transfer unit T2.

[0017] The recording material onto which the toner image has been transferred in the secondary transfer unit T2 is transported to the fuser unit 8, where heat and pressure are applied to fix the toner image to the recording material. The recording material that has passed through the fuser unit 8 is discharged to the discharge tray 7. When image formation is performed on both sides of the recording material, once the transfer and fixing of the toner image to the first side (front) of the recording material is complete, the front and back sides of the recording material are reversed via the inversion transport unit 10, and the transfer and fixing of the toner image to the second side (back) of the recording material is performed before it is discharged to the discharge tray 7.

[0018] The control unit 30 controls the entire image forming apparatus 1 described above. The control unit 30 can perform various settings based on input from the operation unit 4 of the image forming apparatus 1. The operation unit 4 may be, for example, a touch panel with a liquid crystal display, and accepts input for starting various programs such as "image forming jobs" and various data inputs in response to user touch operations. Although not shown in the figures, such a control unit 30 has a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each part while reading programs corresponding to control procedures stored in ROM. Working data and input data are stored in RAM, and the CPU performs control by referring to the data stored in RAM based on the aforementioned programs, etc. In this embodiment, the control unit 30 (more specifically the CPU) can execute the "belt-alignment control processing (program)" (see Figure 7) described later, which is stored in ROM.

[0019] <Fusing device> Next, the fixing device 8 to which the belt conveying device of this embodiment is applied will be described with reference to Figure 2. As shown in Figure 2, the fixing device 8 of this embodiment can be broadly divided into a belt unit 300 and a pressure roller 330. The pressure roller 330, as a rotating body, has its rotation axis supported by the frame 385 of the fixing device 8 and is rotated via gears by a drive source (not shown). The pressure roller 330 is in contact with the outer circumferential surface of the fixing belt 310 of the belt unit 300 and can pressurize the fixing belt 310. That is, the pressure roller 330 is movable between a pressurized position in contact with the fixing belt 310 and a non-pressurized position away from the fixing belt 310 and not pressurizing. In order for the pressure roller 330 to move between the pressurized and non-pressurized positions, the pressure roller 330 is supported by a pressure lever 332 which is oscillated by a pressure motor (not shown). Furthermore, in this embodiment, a halogen heater 331 is placed inside the pressure roller 330, and the temperature of the pressure roller 330 can be adjusted using this halogen heater 331.

[0020] As the pressure roller 330, for example, one may have an elastic layer made of silicone rubber, fluororubber, or fluororesin on the outer circumference of a metal rotating shaft (core), or one may have a release layer made of fluororesin such as PTFE, PFA, or FEP on the outer circumference of the elastic layer. In this embodiment, a pressure roller 330 having an elastic layer made of silicone rubber with a thickness of "300 μm" and a release layer made of PFA with a thickness of "30 μm" was used.

[0021] <Belt Unit> The belt unit 300, as a belt conveying device, includes an endless (cylindrical) fixed belt 310, a heating roller 340, a steering roller 350, a pressing member 380, a sensor unit 390, and a steering mechanism 400. In this embodiment, the fixed belt 310 is stretched by the heating roller 340, the steering roller 350, and the pressing member 380.

[0022] As the fixing belt 310, a resin belt made of resin, for example, has an elastic layer with high thermal conductivity and low heat capacity, or a composite layer structure belt with a metal belt such as stainless steel (SUS) as the base layer and an elastic layer, a release layer, etc. on its outer circumference may be used. In this embodiment, a fixing belt 310 was used that had a SUS base layer, an elastic layer made of silicone rubber with a thickness of "250 μm", and a release layer made of PFA tubing with a thickness of "30 μm". The release layer is preferably a sheet or coating layer with high release properties, and for example, fluororesins such as PFA or PTFE can be used. Alternatively, a sheet-like member with high heat resistance, such as polyester, polyethylene terephthalate, or polyimideamide, may be used as the base layer, with a conductive layer laminated on top of it, and a surface release layer laminated on top of that.

[0023] The heating roller 340, which acts as the second roller, is, for example, a stainless steel pipe with a thickness of 1 mm, and a halogen heater 341 is disposed inside it. The heating roller 340 is rotationally driven by the drive motor M1 via gears, and the fixing belt 310 rotates in accordance with the rotation of the heating roller 340. As the heating roller 340 is heated by the halogen heater 341, which acts as the heating element, the temperature of the fixing belt 310 rises via the heating roller 340. The temperature of the fixing belt 310 is adjusted to a predetermined target temperature, for example, depending on the type of recording material to be image-formed, based on the detection result of a temperature sensor 370 such as a thermistor sensor.

[0024] The steering roller 350, acting as the first roller, presses the anchoring belt 310 from the inside outwards in order to tension it with a predetermined force. To do this, the steering roller 350 is biased by a spring 351. In this way, the steering roller 350 has the function of applying a predetermined tension to the anchoring belt 310. In addition, in this embodiment, the steering roller 350 controls the meandering of the anchoring belt 310 in the width direction (the direction of the steering roller 350's rotation axis) by turning a steering angle with its center or one end in the direction of its rotation axis as the pivot point. That is, the steering roller 350 also has the function of adjusting the alignment of the anchoring belt 310.

[0025] To control the angle of the anchor belt 310 using the steering roller 350 described above, a sensor unit 390 is provided to detect the widthwise position of the end of the anchor belt 310 (hereinafter referred to as the end position). Based on the output signal of the sensor unit 390, the end position of the rotating anchor belt 310 is detected. The sensor unit 390 will be described later. Then, based on the detected end position of the anchor belt 310, the steering mechanism 400 is controlled to adjust the steering angle of the steering roller 350, thereby performing belt angle control.

[0026] The pressing member 380 has a stay 360 and a pressure pad 320. The stay 360 is a rigid metal member, such as stainless steel, that extends in the width direction of the fixing belt 310 and supports the pressure pad 320 so that it can be attached on the pressure roller 330 side. In this embodiment, the pressure pad 320 supported by the stay 360 contacts the inner circumferential surface of the fixing belt 310 and presses the fixing belt 310 from the inner circumferential surface side toward the fixing nip portion N. As a result, in cooperation with the heating roller 340, the fixing nip portion N for gripping, transporting, pressurizing, and heating the recording material on which the toner image has been formed is more reliably formed. Furthermore, by supporting the pressure pad 320 on the highly rigid stay 360, the deflection generated in the pressure pad 320 by the pressure from the pressure roller 330 is reduced, so that a uniform nip width can be obtained in the direction of the rotation axis of the pressure roller 330. Furthermore, it is preferable to interpose a lubricant, such as a lubricating sheet containing silicone oil or silicone oil, between the pressure pad 320 and the fixing belt 310 so that the fixing belt 310 and the pressure pad 320 can slide smoothly against each other.

[0027] The pressure pad 320 is a resin component formed to extend in a width direction intersecting the rotational direction of the fixing belt 310 along the stay 360. Such a pressure pad 320 is formed from a material with good insulating and heat-resistant properties, such as phenolic resin, polyimide resin, polyamide resin, polyamide-imide resin, PEEK resin, PES resin, PPS resin, PFA resin, PTFE resin, or LCP resin.

[0028] In Figure 2, the fixing device 8 is shown as a combination of an endless belt-shaped fixing belt 310 and a roller-shaped pressure roller 330, but it is not limited to this configuration. For example, an endless belt-shaped pressure belt may be used instead of the pressure roller 330. In this case, the endless belt-shaped fixing belt 310 may be combined with the pressure belt as is, or a roller-shaped fixing roller may be combined instead of the fixing belt 310. That is, the fixing device 8 may be configured to form the fixing nip portion N with a roller and a belt, or it may be configured to form the fixing nip portion N with a pair of belts.

[0029] Generally, when an endless belt, such as a fixing belt 310, is supported and rotated by multiple rollers, a meandering phenomenon can occur where the endless belt moves in the width direction while rotating. This can be caused by shape errors in the rollers supporting the endless belt or the endless belt itself, such as variations in the surface shape of the rollers or the precision of the endless belt in the width and circumferential directions, or by misalignment of the rollers' positions. In the case of the fixing device 8 shown in Figure 2, if the fixing belt 310 bends, it may come into contact with other parts and break, causing damage. Therefore, in the case of the fixing device 8 shown in Figure 2, it is necessary to suppress the meandering phenomenon of the fixing belt 310.

[0030] One of the representative technologies for correcting the meandering of an endless belt, such as the anchor belt 310, is the steering method. In the steering method, one of the multiple rollers supporting the endless belt is used as a steering roller and is oscillated to move the endless belt in the width direction, thereby suppressing the meandering phenomenon of the endless belt. Compared to methods that physically restrain and correct the meandering of the endless belt using ribs or guides, this steering method applies less force to the endless belt, resulting in the advantages of high reliability and long lifespan.

[0031] <Sensor section> Next, the sensor unit 390 for detecting the end position of the belt will be described with reference to Figures 3 to 5. As shown in Figure 3, the sensor unit 390 as a detection unit has a contact portion 391, an arm member 392, a shielding member 393, a support shaft portion 394, and an optical sensor 395. The support shaft portion 394 and the optical sensor 395 are each supported by a frame 385. The contact portion 391 is provided on one end of the arm member 392 so as to contact the end of the fixing belt 310. The arm member 392 is rotatable around the support shaft portion 394 so as to follow the movement of the fixing belt 310 in the width direction via the contact portion 391. A shielding member 393, which is formed in a planar shape, is provided on the other end of the arm member 392. When the arm member 392 rotates around the support shaft portion 394, the shielding member 393 also rotates so as to follow the trajectory of its tip, which traces an arc. The shielding member 393 is displaced relative to the sensor unit 390 in accordance with the movement of the fixing belt 310 when the fixing belt 310 moves from one end to the other in the width direction.

[0032] The optical sensor 395 is a light-transmitting sensor. As shown in Figure 4, the optical sensor 395 has a light-emitting part 396 (e.g., an LED) that emits light and a light-receiving part 397 that receives the light emitted from the light-emitting part 396. The shielding member 393 is inserted between the opposing light-emitting part 396 and the light-receiving part 397 and is positioned to block a portion of the light emitted from the light-emitting part 396 and received by the light-receiving part 397. In other words, the amount of light received by the light-receiving part 397 (amount of light received) changes depending on the position of the shielding member 393 relative to the optical sensor 395. Based on the magnitude of this amount of light received by the light-receiving part 397, the end position of the fixing belt 310 is detected.

[0033] As shown in Figure 5, the light receiving unit 397 is provided with a first light receiving area PD1 and a second light receiving area PD2. Depending on the rotational displacement of the shielding member 393, the area in each region of the first light receiving area PD1 and the second light receiving area PD2 that is blocked from light from the light emitting unit 369 changes, which can cause a difference in the amount of light received in the first light receiving area PD1 and the amount of light received in the second light receiving area PD2. The optical sensor 395 outputs a first voltage corresponding to the amount of light received in the first light receiving area PD1 and a second voltage corresponding to the amount of light received in the second light receiving area PD2. For example, in the example shown in Figure 5, the first range Q1 in the first light receiving area PD1 where light from the light emitting unit 369 is blocked by the shielding member 393 and the second range Q2 in the second light receiving area PD2 where light from the light emitting unit 369 is blocked by the shielding member 393 are the same area. In this case, the first voltage and the second voltage are approximately the same voltage value.

[0034] Figure 6 shows the output characteristics of the output signals output from the sensor unit 390 and their differential values. In the upper graph of Figure 6, the horizontal axis represents the belt end position, and the vertical axis represents the first voltage VPD1 and the second voltage VPD2 of the first light-receiving area PD1 and the second light-receiving area PD2, respectively. In the lower graph of Figure 6, the horizontal axis represents the belt end position, and the vertical axis represents the differential value "VPD1-VPD2" between the first voltage VPD1 and the second voltage VPD2. In Figure 6, the belt end position "0" is the position where the first voltage VPD1 and the second voltage VPD2 have the same voltage value and the differential value "VPD1-VPD2" is "0", for example, as shown in Figure 5, when the first range Q1 of the first light-receiving area PD1 and the second range Q2 of the second light-receiving area PD2 have the same area. The differential value "VPD1-VPD2" represents the end position of the fixing belt 310. For example, when the differential value "VPD1-VPD2" is "0", the end position of the belt is indicated when the center of the fixing belt 310, which moves in the width direction along the steering roller 350 between the front and rear plates of the device body 3, approximately coincides with the center of the frame 385 that pivotally supports the steering roller 350 (for example, between the front plate and the rear plate).

[0035] In the graph shown in Figure 6, a belt end position in the "+ direction" means that in Figure 3 the fixing belt 310 is shifted towards the "+ direction" and in Figure 5 the shielding member 393 is displaced in the "+ direction". When the shielding member 393 is displaced in the "+ direction", the amount of light received in the second light-receiving area PD2 decreases, and the amount of light received in the first light-receiving area PD1 increases. Since the first voltage VPD1 and the second voltage VPD2 change according to the amount of light received, when the shielding member 393 moves in the "+ direction", the first voltage VPD1 in the first light-receiving area PD1 increases, and the second voltage VPD2 in the second light-receiving area PD2 decreases.

[0036] On the other hand, in the graph shown in Figure 6, the belt end position being in the "- direction" means that in Figure 3 the fixing belt is shifted towards the "- direction" and in Figure 5 the shielding member 393 is displaced in the "- direction". When the shielding member 393 is displaced in the "- direction", the amount of light received in the first light-receiving area PD1 decreases and the amount of light received in the second light-receiving area PD2 increases. Since the first voltage VPD1 and the second voltage VPD2 change according to the amount of light received, when the shielding member 393 is displaced in the "- direction", the first voltage VPD1 in the first light-receiving area PD1 decreases and the second voltage VPD2 in the second light-receiving area PD2 increases.

[0037] <Belt-side control processing> In this embodiment, the control unit 30 operates the steering mechanism 400 to control the belt-shifting of the fixing belt 310 based on the end position detected based on the first voltage VPD1 and second voltage VPD2 output from the sensor unit 390. Therefore, an overview of the belt-shifting control of the fixing belt 310 will be explained using Figure 7 with reference to Figures 2 and 6. The "belt-shifting control process" shown in Figure 7 is started by the control unit 30 (specifically the CPU) when the fixing belt 310 is started. The fixing belt 310 is started when the fixing belt 310 is rotated from a stopped state, for example, when the image forming apparatus 1 is started up or when it returns from sleep mode, which is a power-saving standby state.

[0038] As shown in Figure 7, when the fixing belt 310 starts to rotate, the control unit 30 acquires a first voltage VPD1 and a second voltage VPD2 output from the sensor unit 390 (S1). The control unit 30 compares each of the acquired first voltage VPD1 and second voltage VPD2 with a "threshold THerr" (S2). The "threshold THerr" is a belt shift threshold used to determine whether or not the fixing belt 310 is in a shifted state. If the first voltage VPD1 is greater than the "threshold THerr" (VPD1>THerr), or if the second voltage VPD2 is greater than the "threshold THerr" (VPD2>THerr), the control unit 30 determines that the fixing belt 310 is in a shifted state. The state in which the fixing belt 310 is shifted means that the fixing belt 310 has shifted significantly towards the end, and there is a high risk that the end of the fixing belt 310 will come into contact with other components other than the belt, causing damage to the fixing belt 310 or other components.

[0039] If at least one of the first voltage VPD1 and the second voltage VPD2 exceeds the "threshold THerr" (YES in S2), the control unit 30 determines that the fixing belt 310 is in a fully engaged state and notifies the user by displaying a "fully engaged error" on the liquid crystal display of the operation unit 4 (S6). The control unit 30 then emergency stops the fixing belt 310 before the fixing belt 310 or other components are damaged (S7) and terminates the belt engagement control process.

[0040] On the other hand, if neither the first voltage VPD1 nor the second voltage VPD2 exceeds the "threshold THerr" (NO in S2), the control unit 30 performs a "tailing control calculation process" to calculate the tilt angle of the steering roller 350 (S3). Then, the control unit 30 controls the steering mechanism 400 based on the tilt angle of the steering roller 350 obtained by the "tailing control calculation process" (S4). After that, the control unit 30 determines whether or not the anchoring belt 310 has stopped (S5). If the anchoring belt 310 has not stopped (NO in S5), the control unit 30 returns to the process in step S1 and repeats the process described above. If the anchoring belt 310 has stopped (YES in S5), the control unit 30 terminates this belt tailing control process.

[0041] Next, we will explain the calculation of the tilt angle of the steering roller 350 by the "shift control calculation process" (S3) described above, and the control of the steering mechanism 400 (S4). First, we will explain a conventional example for comparison using Figures 10 to 12, and then we will explain this embodiment using Figures 8 and 9. Figure 10 is a control block diagram showing the control system of a conventional belt shift control.

[0042] As shown in Figure 10, the steering mechanism 400 includes a stepping motor 402 that can rotate at a desired rotational speed in any direction in forward or reverse, a driver 401 for driving the stepping motor 402, and a drift correction mechanism 403. The drift correction mechanism 403 includes a steering roller 350 and various members (not shown) for tilting the steering roller 350 in accordance with the rotation of the stepping motor 402. As the steering angle of the steering roller 350 is adjusted by the drift correction mechanism 403, the rotating anchor belt 310 is positioned within a predetermined range in the width direction while reciprocating in the width direction.

[0043] In conventional systems, the control unit 30 includes a PID calculation unit (Proportional Integral Differential Controller) 31, a pulse / direction signal generation unit 32, and a subtraction unit 33. The PID calculation unit 31 performs PID control, which is a common type of feedback control. Specifically, the first voltage VPD1 and the second voltage VPD2 output from the sensor unit 390 are input to the control unit 30 via an analog / digital port and converted from analog signals to digital signals. The first voltage VPD1 and the second voltage VPD2, converted to digital signals, are differentially calculated by the subtraction unit 33 to obtain the differential value "VPD1 - VPD2". The control unit 30 sets the target position REF to "0" and inputs the deviation En, obtained by differential calculation between the differential value "VPD1 - VPD2" and the target position REF, to the PID calculation unit 31. The deviation En represents the difference between the detected end position of the fixing belt 310 and the target position REF (hereinafter referred to as the belt position difference).

[0044] The PID calculation unit 31 performs PID calculations based on the input deviation En to calculate the "steering operation amount STEPn" required to operate the steering mechanism 400. Expressing this calculation formula in the form of a transfer function, we get Equation 1 shown below. In Equation 1, the control gains (KP, Ki, Kd) are the proportional gain, integral gain, and differential gain, respectively. These proportional gain Kp, integral gain Ki, and differential gain Kd have been pre-adjusted using simulations and actual equipment. STEPn=(Kp+Ki / s+Kds)En ··· Equation 1

[0045] Specifically, the PID calculation unit 31 performs a proportional calculation by multiplying the belt position difference (deviation En) by the proportional gain Kp to obtain the belt proportional control amount (Kp × En). It also performs an integral calculation by multiplying the belt position difference (deviation En) by the integral gain Ki to obtain the belt integral control amount (Ki / s × En). At this time, in order to calculate the next belt integral control amount, the obtained belt integral control amount is replaced (updated) with the integrated value. Furthermore, a differential calculation is performed by multiplying the belt position difference (deviation En) by the differential gain Kd to obtain the belt differential control amount (Kds × En). Finally, the "steering operation amount STEPn" (see Equation 1), which is the sum of the calculated belt proportional control amount, belt integral control amount, and belt differential control amount, is output to the pulse / direction signal generation unit 32.

[0046] "Steering operation amount STEPn" is an angle command for the stepping motor 402. The pulse / direction signal generation unit 32 generates a signal regarding the number of pulses and rotation direction when operating the stepping motor 402 based on "Steering operation amount STEPn", and transmits it to the driver 401. The driver 501 drives the stepping motor 402 by receiving the signal regarding the number of pulses and rotation direction.

[0047] In this way, based on the detection result of the sensor unit 390, the tilt angle of the steering roller 350 is adjusted so that the end of the belt is positioned as close as possible to the target position REF, thereby preventing the fixed belt 310 from coming too close to the frame 38. Furthermore, if the above-mentioned "steering operation amount STEPn" can be determined, feedback control such as PI control, PD control, or P control may be employed, not limited to the PID control described above.

[0048] Here, for example, in the fixing device 8, when the temperature rises due to the halogen heater 331 and the drive motor M1 (see Figure 2), the sensor unit 390 is affected by that heat. As the temperature of the sensor unit 390 rises, the amount of light emitted by the light-emitting unit 396 decreases, so the output characteristics of the sensor unit 390 change due to temperature changes. The light-emitting unit 396 emits light at a first emission amount when the temperature of the sensor unit 390 is at a first temperature, and emits light at a second emission amount that is greater than the first emission amount when the temperature of the sensor unit 390 is at a second temperature which is lower than the first temperature.

[0049] Figure 11 shows the output characteristics and differential values ​​of the output signals output from the sensor unit 390 at low and high temperatures. In the upper graph of Figure 11, the horizontal axis represents the belt end position, and the vertical axis represents the first voltage VPD1 (solid line) and second voltage VPD2 (dashed line) of the first light-receiving area PD1 and second light-receiving area PD2, respectively. In the lower graph of Figure 11, the horizontal axis represents the belt end position, and the vertical axis represents the differential value "VPD1-VPD2" between the first voltage VPD1 and the second voltage VPD2. Furthermore, the thin line represents the characteristics at low temperatures when the temperature of the sensor unit 390 (hereinafter referred to as sensor temperature) is low, and the thick line represents the characteristics at high temperatures when the sensor temperature is high.

[0050] As can be seen from Figure 11, at high temperatures, the amount of light emitted by the light-emitting section 396 decreases compared to low temperatures. As a result, the voltage levels of both the first voltage VPD1 and the second voltage VPD2, which vary depending on the amount of light received, decrease overall. Consequently, the slope of the differential value "VPD1-VPD2" becomes smaller.

[0051] Next, Figure 12 shows the belt behavior during belt startup in a conventional example. The horizontal axis represents time, and the vertical axis represents the belt end position. In Figure 12, the solid line shows the behavior when the fixing belt 310 is started from a state where the sensor temperature is high, and the dashed line shows the behavior when the fixing belt 310 is started from a state where the sensor temperature is low. The control gains (KP, Ki, Kd) are pre-adjusted so that performance can be obtained when the device is running continuously and the temperature is high, such as during printing.

[0052] As shown in Figure 12, when the belt is started with a high sensor temperature, the belt meanders less and converges quickly, as shown by the solid line. However, when the belt is started with a low sensor temperature, the belt meanders more significantly, as shown by the dashed line, and the behavior is somewhat unstable, taking longer to converge. This is because the slope of the differential value "VPD1-VPD2" is larger at low temperatures compared to high temperatures (see Figure 11), and the gain of the control system for belt-biased control, which combines the control unit 30 and the steering mechanism 400, is higher at low temperatures.

[0053] Cases in which the fuser belt 310 is started when the sensor temperature is high include when the next image forming job is started immediately after the completion of an image forming job, or when returning from jam processing to remove recording material that has become jammed during transport. On the other hand, cases in which the fuser belt 310 is started when the sensor temperature is low include when the image forming apparatus 1 is started up or when it returns from sleep mode, or when the fuser belt 310 is started up after being stopped for a while. Furthermore, the sensor temperature shows various changes depending on the operating environment, operating time, and changes in heater control due to printing settings such as the type of recording material and the process speed for image forming. In addition to temperature, the output characteristics of the sensor unit 390 may also change due to the decrease in light intensity of the light-emitting unit 396 over time.

[0054] In conventional systems, the characteristic changes of the sensor unit 390 caused by these temperature changes hindered stable belt alignment control when the fixing belt 310 was started, resulting in a longer time for the belt's meandering to settle down, as described above. For example, when the fixing belt 310 was started with a high sensor temperature, it took approximately 5 to 10 seconds for the belt's meandering to settle down, whereas when the fixing belt 310 was started with a low sensor temperature, it took approximately 15 to 20 seconds for the belt's meandering to settle down (see Figure 12).

[0055] Therefore, in this embodiment, belt lateral control is performed in real time in response to the output characteristics of the sensor unit 390 which change moment by moment due to temperature, thereby suppressing meandering of the fixing belt 310, especially when the fixing belt 310 is started. The flow of the belt lateral control process in this embodiment is the same as the flowchart shown in Figure 7, but the "lateral control calculation process" (S3 in Figure 7) differs from the conventional example. The "lateral control calculation process" in the belt lateral control process of this embodiment will be explained below using Figures 8 and 9. Figure 8 is a control block diagram showing the control system of the belt lateral control in this embodiment. In Figure 8, the same reference numerals are used for control blocks that are the same as those in the control system of the conventional belt lateral control described above (see Figure 10), and the explanation is simplified or omitted.

[0056] As shown in Figure 8, in this embodiment, the control unit 30 has an adder 34 and a gain determination unit 35 in addition to the PID calculation unit 31, pulse / direction signal generation unit 32, and subtraction unit 33. The adder 34 calculates a summation value "VPD1+VPD2" by adding the first voltage VPD1 and the second voltage VPD2 output from the sensor unit 390. The gain determination unit 35 determines a gain correction coefficient based on the summation value "VPD1+VPD2". The gain correction coefficient may be determined using table data in which the gain correction coefficient is associated with the summation value, or it may be determined using a function that takes the summation value as an input variable. Then, the "steering operation amount STEPn" (see Equation 1) calculated by the PID calculation unit 31 is multiplied by the gain correction coefficient determined by the gain determination unit 35, and the "steering operation amount STEPn" corrected by the gain correction coefficient is output to the pulse / direction signal generation unit 32.

[0057] When the light emission amount of the light-emitting unit 369 is large (at low temperatures), the slope of the differential value "VPD1-VPD2" becomes larger (see Figure 11), and the feedback gain of the control system for belt-side control increases. The sum value "VPD1+VPD2" also increases. Taking advantage of this characteristic, the gain determination unit 35 reduces the gain correction coefficient based on the sum value "VPD1+VPD2". Conversely, when the light emission amount of the light-emitting unit 369 is small (at high temperatures), the slope of the differential value "VPD1-VPD2" becomes smaller (see Figure 11), and the feedback gain of the control system for belt-side control decreases. The sum value "VPD1+VPD2" also decreases. Taking advantage of this characteristic, the gain determination unit 35 increases the gain correction coefficient based on the sum value "VPD1+VPD2".

[0058] In this embodiment, the reason for using the sum value "VPD1 + VPD2" to determine the gain correction coefficient is explained. Based solely on the changes in the first voltage VPD1 and the second voltage VPD2, it is impossible to determine whether the voltage value is changing due to a change in the amount of light emitted by the light-emitting unit 369 caused by temperature, or due to the position of the belt end. However, the sum of the first voltage VPD1 and the second voltage VPD2 is almost constant regardless of the belt end position when the fixing belt 310 is not fully shifted, that is, when neither the first voltage VPD1 nor the second voltage VPD2 exceeds the "threshold THerr". Therefore, if the sum value "VPD1 + VPD2" changes, it can be determined that the change in the first voltage VPD1 and the second voltage VPD2 is due to a change in the amount of light emitted by the light-emitting unit 369. Thus, when performing the "shift control calculation processing," the change in the amount of light emitted by the light-emitting unit 369 is detected by the change in the sum value "VPD1 + VPD2". This allows for real-time gain correction to adjust belt alignment based on the output characteristics of the sensor unit 390, which change due to temperature.

[0059] Next, Figure 9 shows the belt behavior during belt startup in this embodiment. The horizontal axis represents time, and the vertical axis represents the end position of the belt. In Figure 9, both the solid and dashed lines show the belt behavior when the fixing belt 310 is started when the sensor temperature is low. However, the dashed line shows the belt behavior when the "shift control calculation processing" of the conventional example is performed, and the solid line shows the belt behavior when the "shift control calculation processing" of this embodiment is performed.

[0060] As shown in Figure 12, in the conventional example, when the fixing belt 310 was started at a low sensor temperature, it took about 15 to 20 seconds for the belt's meandering to settle down. This is because, as mentioned above, the slope of the differential value "VPD1-VPD2" at low temperatures is larger than at high temperatures (see Figure 11), and the feedback gain of the control system for belt-oriented control, which combines the control unit 30 and the steering mechanism 400, is high at low temperatures. In contrast, in this embodiment, when the fixing belt 310 was started at a low sensor temperature, the belt's meandering settles down in a shorter time of about 10 to 15 seconds compared to the conventional example.

[0061] As described above, in this embodiment, belt meandering can be suppressed by capturing changes in the output characteristics of the sensor unit 390 due to temperature and correcting the feedback gain of the control system for belt meandering control. Specifically, similar to the differential value "VPD1-VPD2" indicating the end position of the fixed belt 310, a sum value "VPD1+VPD2" reflecting the change in the amount of light emitted by the light-emitting unit 369 is obtained using the first voltage VPD1 and the second voltage VPD2 output from the sensor unit 390, which change depending on the end position of the fixed belt 310. Then, the "steering operation amount STEPn" calculated by the PID calculation unit 31 according to the differential value "VPD1-VPD2" is corrected by a gain correction coefficient determined based on the sum value "VPD1+VPD2" to determine the tilt angle of the steering roller 350. As a result, even if the amount of light emitted by the light-emitting unit 369 changes due to the temperature of the sensor unit 390, belt meandering can be corrected in a shorter time than in the conventional method.

[0062] [Other embodiments] Furthermore, the belt conveying device of this embodiment can be applied not only when controlling the fixing belt 310 to the belt side, but also, for example, when controlling the intermediate transfer belt 204 to the belt side. It can also be applied when controlling the recording material conveying belt that carries and conveys the recording material to the belt side.

[0063] In the embodiment described above, an optical sensor 395 having two light-receiving units 397 was used as an example, but it is not limited to this. For example, an optical sensor having three or more light-receiving units may also be used. In that case, the change in the amount of light emitted by the light-emitting unit 369 can be detected by changing the sum of multiple voltage values ​​output from multiple light-receiving units, thereby capturing the change in the output characteristics of the sensor unit 390 and performing gain correction.

[0064] In the embodiment described above, gain correction corresponding to the change in the output characteristics of the sensor unit 390 was performed on the "steering operation amount STEPn" calculated by the PID calculation unit 31 (see Figure 8), but this is not limited to this. Gain correction may be performed on any signal in the feedback path within the control unit 30. For example, it may be performed on the deviation En input to the PID calculation unit 31, on the differential value "VPD1-VPD2", or on the first voltage VPD1 and the second voltage VPD2, respectively. In such cases as well, the feedback gain of the control system for belt-bias control will be corrected, and the belt behavior due to belt-bias control can be stabilized in the same way as in the embodiment described above.

[0065] In the above-described embodiment, an intermediate transfer type image forming apparatus 1 was explained as an example in which toner images of each color are first transferred from each color photosensitive drum 200a to 200d to an intermediate transfer belt 204, and then the toner images of each color are secondarily transferred to the recording material. However, the apparatus is not limited to this. For example, it may be a direct transfer type image forming apparatus in which the toner image on the photosensitive drum is directly transferred to the recording material being transported by the transport belt by applying voltage to transfer rollers positioned opposite each other across the photosensitive drum and the transport belt, with the recording material being transported on a transport belt having a nip portion formed between it and the photosensitive drum. [Explanation of Symbols]

[0066] 1…Image forming apparatus, 8…Fusing apparatus, 30…Control unit, 200a (200b, 200c, 200d)…Photoreceptor (photosensitive drum), 205, 206…Transfer section (secondary transfer roller pair), 300…Belt conveying device (belt unit), 310…Belt (fixing belt), 330…Rotating body (pressure roller), 340…Second roller (heating roller), 341…Heating section (halogen heater), 350…First roller (steering roller), 390…Detection section (sensor section), 393…Shielding section (shielding member), 396…Light-emitting section, 397…Light-receiving section, 400…Steering mechanism, N…Fusing nip section, PD1, PD2…Light-receiving area

Claims

1. An endless belt, A first roller that tensions the aforementioned belt, A second roller tensions the belt together with the first roller, A steering mechanism that tilts the rotating first roller relative to the second roller and moves the belt back and forth in the direction of the rotation axis of the first roller, A light-emitting unit that emits light, a light-receiving unit provided with a first light-receiving area and a second light-receiving area capable of receiving light emitted from the light-emitting unit, and a detection unit capable of outputting a first signal with an output level corresponding to the amount of light received in the first light-receiving area, and a second signal with an output level corresponding to the amount of light received in the second light-receiving area. A subtraction unit generates a third signal by subtracting the first signal and the second signal, which change in conjunction with the displacement of the belt in the direction of the rotation axis, An adder that generates a fourth signal by adding the first signal and the second signal, The steering mechanism is controlled by a control unit, The control unit acquires the third signal and the fourth signal from the subtraction unit and the addition unit, respectively, while the belt is not fully positioned over the end of the first roller in the direction of the rotation axis. The control unit corrects the tilt angle of the first roller, which is determined according to the third signal acquired from the subtraction unit, according to the fourth signal acquired from the addition unit, and tilts the first roller according to the corrected tilt angle. A belt conveying device characterized by the following features.

2. The control unit corrects the tilt angle of the first roller, which is determined according to the third signal, according to the fourth signal, when neither the first signal nor the second signal exceeds a predetermined threshold. The belt conveying device according to feature 1.

3. The steering mechanism has a stepping motor for tilting the first roller, The system further includes a gain determination unit that determines a feedback gain corresponding to the level of the fourth signal acquired from the summing unit, The control unit performs feedback control according to the feedback gain in response to the signal relating to the operation of the stepping motor to correct the tilt angle of the first roller. The belt conveying device according to feature 1.

4. The gain determination unit reduces the feedback gain as the level of the fourth signal increases. The belt conveying device according to feature 3.

5. The detection unit is positioned between the light-emitting unit and the light-receiving unit and has a shielding unit that, as the belt moves back and forth in the direction of the rotation axis, shields a portion of the light emitted from the light-emitting unit and received by the first light-receiving area and the second light-receiving area. The belt conveying device according to feature 1.

6. A fixing device for fixing a toner image formed on a recording material to a recording material, A belt conveying device according to any one of claims 1 to 5, A heating unit for heating the belt of the belt conveying device, The system includes a rotating body that contacts the outer surface of the belt and forms a fixing nip section that applies heat and pressure to fix the toner image onto the recording material while gripping and transporting the recording material. A fixing device characterized by the following features.

7. An image forming apparatus for forming an image on a recording material, A photoreceptor on which a toner image is formed on its surface, A belt conveying device according to any one of claims 1 to 5, The system includes a transfer unit that transfers a toner image from the photoreceptor to the belt of the belt transport device. An image forming apparatus characterized by the following:

Images