Belt conveying device, fixing device

Abstract

To provide a belt conveying device that can suppress belt meandering through belt-alignment control, even during the period from when the belt starts moving from a stationary state until it completes one full rotation. [Solution] The meandering of the upper belt is suppressed by reducing the feedback gain of the control system for belt-alignment control from the start of the upper belt's movement until it completes one full rotation. The control unit corrects the original steering control amount, which is determined based on the position of the upper belt detected by the sensor unit (S8), according to a reduction coefficient (feedback gain) smaller than "1" (S10) from the start of the upper belt's movement until it completes one full rotation (YES in S9). Then, the steering mechanism 400 is controlled according to the corrected steering control amount, which is smaller than the original steering control amount (S12). As a result, belt-alignment control is achieved that reduces the meandering of the upper belt from the start of the upper belt's movement until it completes one full rotation, compared to conventional methods, bringing it closer to a converged state.

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, and a fixing device including the belt conveyance device.

Background Art

[0002] In image forming apparatuses of an electrophotographic system or an inkjet recording system, 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 carry 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 roller and moves toward the end side in the width direction. If the belt end moves too much toward the end side, the belt end may contact other members, and there is a risk that the belt or other members may be damaged. Therefore, a belt skew control is performed in which the position of the end of the belt in the width direction is detected by a sensor unit, and one of the plurality of stretching rollers (so-called steering roller) is tilted based on the detection result of the sensor unit to adjust the skew of the belt.

[0003] Due to manufacturing tolerances, belts may have tolerances in their width. Therefore, in a belt conveying device, the position of the belt detected by the sensor may fluctuate over one rotation period of the rotating belt due to the dimensional tolerance of the belt width. To address this, the device described in Patent Document 1 proposes a method of controlling the belt's position based on pre-created end shape data indicating the position over one rotation of the belt. In this case, a mark indicating a reference position is provided at one point on the belt, and when the belt starts, the belt is rotated once to detect the mark with a position sensor. This allows the information indicating the position of the belt in the direction of travel in the end shape data to be matched with the information indicating the position of the belt in the direction of travel currently detected by the position sensor, thereby correcting the position of the belt detected by the sensor based on the end shape data. By using end shape data, the dimensional tolerance of the belt width included in the belt position detected by the sensor can be removed. Furthermore, as in the device described in Patent Document 2, a method has been proposed to remove the dimensional tolerance of the belt width by averaging the belt position detected by the sensor over one rotation of the belt, and then performing belt position control based on the average belt position obtained by the averaging process. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-109976 [Patent Document 2] Japanese Patent Publication No. 2014-134577 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, conventionally, even with belt-guided control, it was sometimes difficult to suppress belt meandering during the period from when the belt started moving from a standstill until it completed one rotation.

[0006] In view of the above problems, the present invention aims to provide a belt conveying device that can suppress belt meandering by belt-alignment control even when the belt has started moving from a stopped state and has completed one rotation, and a fixing device equipped with the belt conveying device. [Means for solving the problem]

[0007] A belt conveying device according to one embodiment of the present invention comprises 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, a detection unit for detecting the position of the belt in the direction of the rotation axis, and a control unit that determines the tilt angle of the first roller based on the position of the belt detected by the detection unit and controls the steering mechanism according to the tilt angle of the first roller, wherein the control unit controls the steering mechanism according to a second tilt angle that is smaller than the first tilt angle, obtained by correcting the first tilt angle determined based on the position of the belt according to a control coefficient of less than 1, from the start of the belt's movement until the belt completes one rotation. [Effects of the Invention]

[0008] According to the present invention, even during the period from when the belt starts moving from a stopped state until it completes one rotation, belt meandering can be suppressed by belt-alignment control. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing an image forming apparatus. [Figure 2] A schematic diagram showing the fixing module. [Figure 3] (a) Schematic diagram showing the sensor section, (b) Cross-sectional view showing the optical sensor. [Figure 4] A graph showing the detection characteristics of an optical sensor. [Figure 5] (a) A schematic diagram showing the steering mechanism, (b) A schematic diagram showing a part of the steering mechanism. [Figure 6] A control block diagram showing the control system for belt-driven control. [Figure 7] A block diagram illustrating the control of the steering motor. [Figure 8] A flowchart illustrating the belt-side control process. [Modes for carrying out the invention]

[0010] <Image forming apparatus> Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing an image forming apparatus of this embodiment. In Figure 1, the image forming apparatus 1 is shown as an example of a so-called sheet-fed inkjet recording apparatus that forms an ink image on a recording material using two liquids, a reaction solution and ink. An external device 2, such as a personal computer, is connected to the image forming apparatus 1 via an input / output interface such as a LAN. The image forming apparatus 1 forms an image on the recording material according to the image signal sent from the external device 2. The image forming apparatus 1 is also equipped with an operation unit 3 having a display unit capable of displaying various information and keys that allow various information to be input according to user operation. Various instructions such as starting and stopping an image forming job and opening and closing the tray of the paper feed module 5 are input by the user from the operation unit 3. The recording material can be any sheet material that can accept ink, such as paper such as plain paper or cardboard, plastic film such as an overhead projector sheet, specially shaped sheets such as envelopes or index paper, and cloth.

[0011] As shown in Figure 1, the image forming apparatus 1 comprises a paper feeding module 5, a print module 4, a drying module 6, a fixing module 7, a cooling module 8, and a loading module 9. The paper feeding module 5 contains a large number of recording materials, and the recording materials supplied one by one from the paper feeding module 5 undergo various processing as they are transported along the transport path within each module, and are finally discharged into the loading module 9. Note that the paper feeding module 5, print module 4, drying module 6, fixing module 7, cooling module 8, and loading module 9 each have separate housings, and these housings may be connected to constitute the image forming apparatus 1. Alternatively, all of the above modules may be arranged in a single housing.

[0012] The print module 4 has a recording unit that ejects ink onto recording material transported from the paper feed module 5 to form an image on the recording material. The recording unit has a total of five recording heads, for example, four colors: yellow, magenta, cyan, and black, in addition to a corresponding reaction solution. The method for ejecting ink from the recording head may include a method using a heating element, a method using a piezoelectric element, a method using an electrostatic element, a method using a MEMS element, etc.

[0013] The recording material with the image formed in the print module 4 is transported to the drying module 6. The drying module 6 blows hot air onto the recording material to dry the image formed by the ink, in order to improve the ink fixation to the recording material by the subsequent fixing module 7. After the image has been dried by the drying module 6, the ink is fixed to the recording material by the fixing module 7. The fixing module 7 is a fixing device that fixes the ink to the recording material by passing the recording material transported from the drying module 6 between a heated upper belt unit and a heated lower belt unit. The fixing module 7 will be described later (see Figure 2). The cooling module 8 cools the recording material heated by the fixing module 7 by blowing cold air from a cooling fan (not shown) onto the recording material transported from the fixing module 7. The cooling fans are positioned on both sides of the recording material transport path to cool both sides of the recording material. The cooled recording material is transported to the loading module 9 and loaded into the loading module 9.

[0014] <Fuser Module> Next, the fixing module 7 will be explained using Figure 2. As shown in Figure 2, the fixing module 7 comprises an upper belt unit 71 and a lower belt unit 72. The recording material S is held and conveyed by the fixing nip section formed by the upper belt 10 of the upper belt unit 71 and the lower belt 30 of the lower belt unit 72, and pressure and heat are applied at this time to fix the image formed by the ink to the recording material S. In the fixing module 7, the belt circumferences of the upper belt 10 and the lower belt 30 are made long in order to reliably fix the image formed by the ink to the recording material S.

[0015] The upper belt unit 71, as a belt conveying device, includes an upper belt 10, a plurality of rollers (11, 12, 13, 14) that rotatably tension the upper belt 10, upper belt heaters 15, 16, 17, an upper temperature control sensor 24, and upper heater temperature sensors 21, 22, 23. The plurality of rollers that tension the upper belt 10 include a drive roller 14 that rotates the upper belt 10, driven rollers 12 (second roller) and 13 that move in accordance with the rotation of the upper belt 10, and a steering roller 11, which will be described later.

[0016] Inside the endless upper belt 10, upper belt heaters 15, 16, and 17 for heating the upper belt 10 are arranged. The upper belt heaters 15, 16, and 17 as heating parts heat the upper belt 10 by emitting, for example, infrared rays. The upper belt heaters 15, 16, and 17 are covered with reflectors 18, 19, and 20 formed of members having a high heat reflectance such as aluminum. The reflectors 18, 19, and 20 can efficiently heat the upper belt 10 by reflecting the infrared rays emitted from the upper belt heaters 15, 16, and 17.

[0017] [[ID=⑦]]The upper temperature control sensor 24 is a temperature sensor for detecting the temperature of the upper belt 10. The temperature control of the above-described upper belt heaters 15, 16, and 17 is performed so that the temperature of the upper belt 10 detected by the upper temperature control sensor 24 becomes the target temperature. The upper heater temperature sensors 21, 22, and 23 are non-contact temperature sensors for detecting the temperature of the upper belt 10 for each irradiation region irradiated with infrared rays from the upper belt heaters 15, 16, and 17. The upper heater temperature sensors 21, 22, and 23 monitor the temperature of the irradiation region heated by the upper belt heaters 15, 16, and 17 so that when any abnormality occurs and the temperature of the upper belt 10 exceeds the target temperature, the power supply to the upper belt heaters 15, 16, and 17 can be cut off to stop the heating.

[0018] The steering roller 11 as the first roller presses the upper belt 10 from the inside to the outside in order to stretch the upper belt 10 with a predetermined tension. Also, in the case of this embodiment, the steering roller 11 controls the meandering of the upper belt 10 in the width direction (the rotation axis direction of the steering roller 11) by turning the rudder angle with the central part or one end part in the rotation axis direction of the steering roller 11 as the rotation fulcrum. That is, the steering roller 11 has a function of adjusting the deviation of the upper belt 10.

[0019] It should be noted that in the translation of the above text, the "⑦" in the original text is likely a mislabeled ID. It is translated as "⑦" here for the sake of consistency with the original text's format. If it is a specific ID that should be translated according to certain rules, please provide more information for a more accurate translation.The shift of the upper belt 10 is a phenomenon in which the rotating upper belt 10 meanders and shifts towards the end in the width direction. If the upper belt 10 shifts too far towards the end, the belt end may come into contact with other components, potentially damaging the upper belt 10 or other components. Therefore, belt shift control (also called steering control) is performed to adjust the shift of the upper belt 10 by tilting the steering roller 11 based on the position of the upper belt 10 in the width direction. The fixing module 7 has a sensor unit 25 and a steering mechanism 400 to perform belt shift control of the upper belt 10 using the steering roller 11. The sensor unit 25 is provided to detect the position of the end of the upper belt 10 in the width direction. The steering mechanism 400 tilts the steering roller 11 so that the position of the upper belt 10 detected by the sensor unit 25 substantially coincides with the target position. As the steering angle of the steering roller 11 is adjusted, the rotating upper belt 10 reciprocates in the width direction and is positioned within a predetermined range in the width direction. The sensor unit 25 and the steering mechanism 400 will be described later.

[0020] <Lower belt unit> The lower belt unit 72 may have the same configuration as the upper belt unit 71. The lower belt unit 72 shown here includes a lower belt 30 as a rotating body, a plurality of rollers (31, 32, 33, 34) that rotatably tension the endless lower belt 30, lower belt heaters 35, 36, a lower temperature control sensor 41, and lower heater temperature sensors 39, 40. The lower belt heaters 35, 36 are covered with reflectors 37, 38 that reflect infrared rays.

[0021] The lower temperature control sensor 41 is a temperature sensor for detecting the temperature of the lower belt 30. The temperature control of the lower belt heaters 35 and 36 is performed so that the temperature of the lower belt 30 detected by the lower temperature control sensor 41 reaches the target temperature. The lower heater temperature sensors 39 and 40 are non-contact temperature sensors for detecting the temperature of the lower belt 30 in each irradiation area where infrared rays are emitted from the lower belt heaters 35 and 36. The lower heater temperature sensors 39 and 40 are provided to monitor the temperature of the irradiation area heated by the lower belt heaters 35 and 36 so that if the temperature of the lower belt 30 exceeds the target temperature, power to the lower belt heaters 35 and 36 can be cut off to stop heating.

[0022] One of the multiple rollers (31, 32, 33, 34) that tension the lower belt 30 is a steering roller 31. The fixing module 7 has a sensor unit 42 and a steering mechanism 401 to control the belt-alignment of the lower belt 30 using the steering roller 31. The sensor unit 42 is provided to detect the position of the lower belt 30. The steering mechanism 401 tilts the steering roller 31 so that the position of the lower belt 30 detected by the sensor unit 42 substantially coincides with the target position.

[0023] <Sensor section> Next, the sensor unit 25 for detecting the position of the upper belt 10 will be explained using Figures 3(a) to 4. Note that the sensor unit 42 for detecting the position of the lower belt 30 has the same configuration as the sensor unit 25, so its explanation will be omitted.

[0024] As shown in Figure 3(a), the sensor unit 25, which acts as a detection unit, comprises a flag 251, an optical sensor 252, and a support member 253. The support member 253 is a member that supports the flag 251 and the optical sensor 252. The support member 253 is attached to the frame (not shown) of the fixing module 7 so that the sensor unit 25 is positioned in a predetermined location relative to the upper belt 10. The flag 251 abuts against the end of the upper belt 10 and rotates around the support shaft 254 to follow the movement of the upper belt 10 in the width direction. A shielding member 255, which is formed in a planar shape, is provided on the other end of the flag 251. The shielding member 255 is displaced relative to the optical sensor 252 as the flag 251 rotates around the support shaft 254 due to the movement of the upper belt 10 in the width direction.

[0025] The optical sensor 252 is a light-transmitting sensor, also known as a photointerrupter. As shown in Figure 3(b), the optical sensor 252 has a light-emitting unit 2521 (e.g., an LED) that emits light and a light-receiving unit 2522 that receives the light emitted from the light-emitting unit 2521. The shielding member 255 is inserted between the opposing light-emitting unit 2521 and the light-receiving unit 2522 and is positioned to block a portion of the light emitted from the light-emitting unit 2521 and received by the light-receiving unit 2522. In other words, the amount of light received by the light-receiving unit 2522 (amount of light received) changes depending on the position of the shielding member 255 relative to the optical sensor 252. Based on the magnitude of this amount of light received by the light-receiving unit 2522, the position of the upper belt 10 is detected.

[0026] Figure 4 shows the detection characteristics of the optical sensor 252. In Figure 4, the horizontal axis represents the amount X (mm) of the upper belt 10 shifting, and the vertical axis represents the detected value Vo (V) of the optical sensor 252. The "+X direction" represents the direction in which the upper belt 10 shifts to one end in the width direction, and the "-X direction" represents the direction in which the upper belt 10 shifts to the other end in the width direction.

[0027] As shown in Figure 4, the detected value Vo (V) of the optical sensor 252 changes linearly in proportion to the shift amount X (mm). This is because the amount of movement of the flag 251 is proportional to the shift amount of the upper belt 10, and the amount of light received by the light receiving unit 2522 changes linearly with respect to the amount of movement of the flag 251. In belt shift control, the steering roller 11 is tilted so that the upper belt 10 is moved in the width direction to a position where the detected value Vo of the optical sensor 252 corresponds to a detected value (Vtar) that corresponds to a shift amount of "0". The shift amount of the upper belt 10 referred to here is the amount of deviation between the position of the upper belt 10 detected by the sensor unit 25 and the target position, and a shift amount of "0" is the state in which the position of the upper belt 10 detected by the sensor unit 25 and the target position are approximately coincident. The target position is the average value (belt average position) of the end positions over one circumference of the belt, obtained by averaging the positions of the upper belt 10 detected by the sensor unit 25.

[0028] As described above, if the upper belt 10 shifts too far towards the end, the belt end may come into contact with other components, potentially damaging the upper belt 10 or other components. Therefore, if the amount of shift of the upper belt 10 exceeds a threshold, the upper belt 10 is stopped to prevent further shifting. In Figure 4, the threshold on one end in the width direction is represented by "X1," and the threshold on the other end in the width direction is represented by "X2." Furthermore, the detected value of the optical sensor 252 corresponding to the threshold "X1" on one end is represented by "Vth1," and the detected value of the optical sensor 252 corresponding to the threshold "X2" on the other end is represented by "Vth2." The upper belt 10 is stopped when the detected value Vo of the optical sensor 252 becomes greater than "Vth1," or when the detected value Vo of the optical sensor 252 becomes less than "Vth2." In this way, the upper belt 10 is prevented from shifting too far towards the end.

[0029] <Steering mechanism> Next, the steering mechanism 400 for controlling the upper belt 10 towards the belt will be explained using Figures 5(a) and 5(b). Note that the steering mechanism 401 for controlling the lower belt 30 towards the belt has the same configuration as the steering mechanism 400, so its explanation will be omitted.

[0030] As shown in Figure 5(a), the steering mechanism 400 includes a steering motor 50, a flag member 51, an HP (home position) sensor 52, a cam member 53, a bearing section 54, and a frame member 55. The steering roller 11 has one end of its shaft 11a supported by a bearing (not shown) provided on the frame member 55. The bearing section 54 is attached to the frame member 55, and the cam member 53 is in contact with the outer circumferential surface of the bearing section 54 by a spring (not shown). The cam member 53 is attached to the rotation shaft 50a of the steering motor 50 and rotates in both forward and reverse directions around the rotation shaft 50a as the steering motor 50 rotates. The steering motor 50 is a stepping motor that provides high positioning accuracy for the rotational position of the cam member 53. A stepping motor is a motor that can rotate at a desired rotational speed in any direction, forward or reverse.

[0031] As shown in Figure 5(b), the cam member 53 is a plate cam, and when the cam member 53 is rotated by the steering motor 50, the frame member 55 rotates around the pivot axis 56 via the bearing portion 54. The other end of the shaft portion 11a of the steering roller 11 is fixed to the frame (not shown) of the fixing module 7. Therefore, as the frame member 55 rotates, the one end of the steering roller 11 supported by the frame member 55 moves in the opposite direction to the movement of the bearing portion 54. In other words, the steering roller 11 tilts. In this way, the steering mechanism 400 controls the belt-to-belt position of the upper belt 10 by rotating the cam member 53 with the steering motor 50 and tilting the steering roller 11.

[0032] As shown in Figure 5(a), a flag member 51 is fixed to the rotating shaft 50a of the steering motor 50. The flag member 51 is formed in the shape of a disc with a protrusion, and an HP sensor 52 is positioned to detect the protrusion of the flag member 51. The HP sensor 52 is an optical sensor called a photointerrupter. The rotational position of the cam member 53 and the tilt angle of the steering roller 11 when the protrusion is detected by the HP sensor 52 are predetermined by design. Therefore, the position of the steering roller 11 when the HP sensor 52 detects the protrusion of the flag member 51 is used as the home position, and the tilt angle of the steering roller 11 can be adjusted starting from the home position.

[0033] <Belt-based control> Next, the belt alignment control of this embodiment will be explained using Figures 6 to 8. In the following explanation, the belt alignment control of the upper belt 10 will be used as an example. The belt alignment control of the lower belt 30 may be the same as that of the upper belt 10, so its explanation will be omitted.

[0034] As shown in Figure 6, the control unit 100 controls the upper belt unit 71 as a belt conveying device. In this embodiment, the control unit 100 controls at least the upper belt unit 71 in response to the input of a "image forming job" start instruction from an external device 2 or an operation unit 3. The control unit 100 has a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). In this embodiment, the control unit 100 (specifically the CPU) controls each part of the fixing module 7 by executing the "belt positioning control process (program)" (see Figure 8) stored in the ROM, which will be described later. Working data and input data are stored in the RAM, and the CPU controls by referring to the data stored in the RAM based on the aforementioned program, etc.

[0035] When the "belt-alignment control process" is executed, the control unit 100 acquires the detected values ​​from the HP sensor 52 and the sensor unit 25, respectively, and controls the drive motor 141, which rotates the drive roller 14, and the steering motor 50, which tilts the steering roller 11, according to these detected values. The drive motor 141 and the steering motor 50 are controlled by a driver IC (not shown), and a control signal corresponding to the type of driver IC is output from the CPU.

[0036] Figure 7 is a block diagram illustrating the control of the steering motor 50. The control unit 100 performs PI control, which is feedback control, based on the detected value of the sensor unit 25, calculates the steering control amount necessary to operate the steering motor 50, and controls the belt position of the upper belt 10 accordingly. As shown in Figure 7, the control unit 100 (specifically the CPU) has a proportional control unit 101 and an integral control unit 102 that perform PI control, an averaging processing unit 110, and a subtraction unit 130.

[0037] The detected value "Vsns" from the sensor unit 25 is input to the subtraction unit 130 via the averaging processing unit 110. The averaging processing unit 110 averages the detected value "Vsns" sampled by the sensor unit 25 according to the detection period "Ts (sec)". However, in this embodiment, averaging is not performed from the start of the upper belt 10's movement until sampling for one full rotation of the belt is completed, and averaging is performed only after sampling for one full rotation of the belt is completed.

[0038] The detected value input from the averaging processing unit 110 to the subtraction unit 130 is subtracted by the subtraction unit 130 using a difference calculation with the target position "Vtar". The belt position difference value "Verr" obtained by the difference calculation is the amount of deviation between the end position of the upper belt 10 detected by the sensor unit 25 and the target position "Vtar". The proportional control unit 101 performs a proportional calculation by multiplying the belt position difference value "Verr" by the proportional gain Kp and outputs the belt proportional control amount "ΔPls_p" as the calculation result. The integral control unit 102 performs an integral calculation by multiplying the belt position difference value "Verr" by the integral gain Ki and outputs the belt integral control amount "ΔPls_i" as the calculation result. The proportional gain Kp and integral gain Ki used here have been pre-adjusted using simulations and actual equipment.

[0039] These belt proportional control amount "ΔPls_p" and belt integral control amount "ΔPls_i" are added together to output a steering control amount "ΔPls_c". This steering control amount "ΔPls_c" is sent to the driver IC that controls the steering motor 50. The driver IC controls the steering motor 50 according to the steering control amount "ΔPls_c". In this way, the tilt angle of the steering roller 11 is adjusted by the steering motor 50 so that the belt end is positioned as close as possible to the target position "Vtar" based on the detected value "Vsns" of the sensor unit 25. Note that any feedback control such as PID control, PD control, or P control may be used, not limited to PI control, as long as the above steering control amount "ΔPls_c" can be output.

[0040] From the start of the upper belt 10's movement until after the first rotation, the control unit 100 matches the detection period Ts (sec) of the sensor unit 25 with the control period Tc (sec) that controls the tilt angle of the steering roller 11. The detection period Ts of the sensor unit 25 is 1 / N times the belt rotation period Tb (sec) of the upper belt 10. The reason for this is explained below. The widthwise dimension of the upper belt 10 has a dimensional tolerance due to belt manufacturing. This widthwise dimensional tolerance may differ along the direction of travel of the upper belt 10. Therefore, the detection value of the sensor unit 25 that detects the position of the belt end includes a repeating fluctuation component (called the edge profile component) of one rotation of the belt. In order to remove this edge profile component, the detection period Ts of the sensor unit 25 is set to divide one rotation of the belt into equal intervals, and the detection values ​​of multiple sensor units 25 obtained by sampling one rotation of the belt are averaged by the averaging processing unit 110. In this embodiment, the number of divisions N of one rotation of the belt is set to "8", and it is divided into 8 parts. If the number of divisions N is too small, it becomes difficult to remove the edge profile component, while if the number of divisions N is too large, the CPU load increases. Therefore, the number of divisions N is set to a value that takes these factors into consideration.

[0041] The detection period Ts of the sensor unit 25 is set to "Lb÷Vb÷8" because, for example, if the rotational speed of the upper belt 10 is "Vb (mm / sec)" and the belt circumference is "Lb (mm)", the belt rotation period Tb (sec) is derived as "Lb÷Vb". When the detection value of the sensor unit 25 is sampled at the detection period Ts, the averaging processing unit 110 performs averaging based on the 8 detection values.

[0042] However, during the period from the start of the upper belt 10's movement until it completes one rotation, sampling according to the detection period Ts may not correctly acquire the detected value from the sensor unit 25. In other words, the detected value output from the averaging processing unit 110 includes an edge pro-profile component, making it difficult to accurately detect the amount of belt deviation. As a result, even with PI control, the behavior of the upper belt 10 was unstable, and there was a risk that the upper belt 10 would meander significantly and become completely deviationd.

[0043] In view of the above, in this embodiment, averaging is not performed from the start of travel of the upper belt 10 until it completes one rotation, and the behavior of the upper belt 10 is stabilized by correcting the steering control amount "ΔPls_c" obtained by PI control. This will be explained below.

[0044] As shown in Figure 7, the control unit 100 has a gain reduction coefficient generation unit 120. The gain reduction coefficient generation unit 120 outputs the "reduction coefficient" shown in Table 1 to the proportional control unit 101 and the integral control unit 102 for each of the multiple samplings for one rotation of the belt, from the start of the upper belt 10's movement until the completion of sampling for one rotation of the belt. The proportional control unit 101 and the integral control unit 102 output the belt proportional control amount "ΔPls_p" and the belt integral control amount "ΔPls_i", respectively, corrected according to the "reduction coefficient".

[0045] Table 1 shows the reduction coefficients output by the gain reduction coefficient generation unit 120. This Table 1 is stored in advance in the ROM of the control unit 100. The detection count indicates which sampling number (1st, 2nd, ...) is being used out of multiple samplings of the belt position detected by the sensor unit 25, which are performed from the start of the upper belt 10's movement until it completes one full rotation. In this embodiment, the "control period Tc" that controls the tilt angle of the steering roller 11 from the start of the upper belt 10's movement until it completes one full rotation is set at multiple timings that equally divide the length of one full rotation of the upper belt 10, and the belt position is sampled accordingly. [Table 1]

[0046] The gain reduction coefficient generation unit 120 outputs a "reduction coefficient" (control coefficient) smaller than "1" when the number of detections has not yet reached the equivalent of one full belt rotation (1st to 7th detections). Furthermore, the gain reduction coefficient generation unit 120 outputs a relatively small "reduction coefficient" when the number of detections is low, and outputs a larger "reduction coefficient" as the number of detections approaches the equivalent of one full belt rotation (8 detections). In other words, the gain reduction coefficient generation unit 120 outputs a first control coefficient at the first timing, and outputs a second control coefficient that is larger than the first control coefficient at the second timing, which is later than the first timing. This is because, by correcting the original steering control amount calculated based on the detection value of the sensor unit 25 according to the "reduction coefficient," the meandering of the upper belt 10 can be reduced and brought closer to a converged state as the number of detections (number of samples) increases.

[0047] Thus, in this embodiment, at a stage where the number of detections from the start of travel of the upper belt 10 is small, the steering mechanism 400 is controlled according to a corrected steering control amount (second tilt angle) that is smaller than the original steering control amount (first tilt angle), obtained by correcting the original steering control amount calculated based on the detection value of the sensor unit 25 according to a reduction coefficient smaller than "1". As a result, the displacement of the tilt angle of the steering roller 11 is reduced, and thus, in this embodiment, meandering of the upper belt 10 is suppressed and stable travel is possible from the start of travel until the belt completes one rotation, a period from the start of travel to the end of one rotation, in which the edge profile component could not be removed in the conventional method.

[0048] <Belt-side control processing> Next, the "belt alignment control process" of this embodiment will be explained using Figure 8 with reference to Figures 6 and 7. Figure 8 shows a flowchart of the belt alignment control process. The belt alignment control process shown in Figure 8 is started by the control unit 100 (specifically the CPU) when the fixing module 7 is started up. The fixing module is started up when, for example, the image forming apparatus 1 is started up or when it recovers from sleep mode, which is a power-saving standby state.

[0049] As shown in Figure 8, the control unit 100 determines whether the detected value of the HP sensor 52 is "High" or not (S1). If the detected value of the HP sensor 52 is "High" (YES in S1), the control unit 100 rotates the steering motor 50 in the forward direction to tilt the steering roller 11 in either the up or down direction (S2). If the detected value of the HP sensor 52 is not "High" but "Low" (NO in S1), the control unit 100 rotates the steering motor 50 in the reverse direction to tilt the steering roller 11 in the opposite direction to the one direction (S3).

[0050] The control unit 100 rotates the steering motor 50 until the HP sensor 52 detects the end (edge) of the upper belt 10 (NO in S4). The control unit 100 determines that the HP sensor 52 has detected the end of the upper belt 10 when the detected value of the HP sensor 52 changes from "High" to "Low" or from "Low" to "High". When the control unit 100 detects the end of the upper belt 10 (YES in S4), it stops the steering motor 50 (S5). In this way, the steering roller 11 is positioned in the home position, which is the starting point for adjusting the tilt angle of the steering roller 11.

[0051] Next, the control unit 100 drives the steering motor 50 by a predetermined amount of rotation to tilt the steering roller 11 from the home position to a tilt angle corresponding to the neutral point where the upper belt 10 does not deviate from its design nominal value (S6). Since the steering motor 50 is a stepping motor, the predetermined amount of rotation can be controlled by the number of pulses of the clock signal output to a driver IC (not shown). After tilting the steering roller 11 to the tilt angle corresponding to the neutral point, the control unit 100 rotates the drive motor 141 to start the movement of the upper belt 10 (S7). Then, the control unit 100 acquires the detected value from the sensor unit 25 (S8).

[0052] The control unit 100 determines whether the number of times the sensor unit 25 has detected the value is less than a predetermined number (for example, 8 times) (S9). If the number of times the sensor unit 25 has detected the value is less than the predetermined number, in other words, if the number of samples of the belt position by the sensor unit 25 is less than the predetermined number (YES in S9), the control unit 100 causes the gain reduction coefficient generation unit 120 to output a "reduction coefficient" (S10). In other words, the control unit 100 corrects the original steering control amount calculated based on the detected value of the sensor unit 25 described above by the "reduction coefficient" for the period from the start of travel of the upper belt 10 until one rotation of the belt, when the number of samples of the belt position by the sensor unit 25 is less than the predetermined number, and performs belt-biased control (S12).

[0053] On the other hand, if the number of detections of the sensor unit 25 is greater than or equal to a predetermined number, in other words, if the number of samples of the belt position is greater than or equal to a predetermined number (NO in S9), the control unit 100 does not cause the gain reduction coefficient generation unit 120 to output a "reduction coefficient" (S11). In this case, the control unit 100 performs belt-bias control without correcting the original steering control amount calculated based on the sensor unit 25's detection value (S12).

[0054] The control unit 100 determines whether or not it has received a belt stop instruction from the external device 2 or the operation unit 3 (S13). If a belt stop instruction is received (YES in S13), the control unit 100 stops the belt-shifting control by the steering motor 50 (S15), stops the rotation of the drive motor 141, and stops the upper belt 10 (S16).

[0055] On the other hand, if a belt stop instruction has not been received (NO in S13), the control unit 100 determines, based on the time counted from the start of the upper belt 10's movement, whether time has elapsed according to the control period Tc that controls the tilt angle of the steering roller 11 from the timing of sampling the belt position (S14). If time according to the control period Tc has elapsed (YES in S14), the control unit 100 returns to the process of step S8 and continues to sample the belt position using the sensor unit 25. As described above, the "control period Tc" is set to the timing when the length of the upper belt 10 is at equal intervals with respect to the direction of travel, from the start of the upper belt 10's movement until one rotation of the belt, and is set to the detection period Ts of the sensor unit 25 after one rotation from the start of the upper belt 10's movement.

[0056] As described above, in this embodiment, the meandering of the upper belt 10 can be suppressed by reducing the feedback gain of the control system for belt-alignment control from the start of the upper belt 10's movement until it completes one full rotation of the belt. The control unit 100 controls the steering mechanism 400 according to the steering control amount determined based on the position of the upper belt 10 detected by the sensor unit 25, from the start of the upper belt 10's movement until it completes one full rotation of the belt. In contrast, the control unit 100 corrects the original steering control amount determined based on the position of the upper belt 10 detected by the sensor unit 25 according to a reduction coefficient (feedback gain) smaller than "1" from the start of the upper belt 10's movement until it completes one full rotation of the belt. The control unit 100 then controls the steering mechanism 400 according to the corrected steering control amount, which is smaller than the original steering control amount. As a result, belt-alignment control can be achieved that reduces the meandering of the upper belt 10 from the start of the upper belt 10's movement until it completes one full rotation of the belt, compared to the conventional method, bringing it closer to a converged state.

[0057] <Other Embodiments> Furthermore, the belt transport device of this embodiment is not limited to applications where the upper belt 10 or lower belt 32 are controlled to be closer to the belt in the fixing module 7. For example, it may be applied to applications where the belts that transport recording material are controlled to be closer to the belt in other modules such as the print module 4, drying module 6, and cooling module 8. Alternatively, it may be applied to applications where intermediate transfer belts used in electrophotographic image forming apparatuses are controlled to be closer to the belt. [Explanation of symbols]

[0058] 7... Fixing device (fixing module), 10... Belt (upper belt), 11... First roller (steering roller), 12... Second roller (driven roller), 15, 16, 17... Heating unit (upper belt heater), 25... Detection unit (sensor unit), 30... Rotating body (lower belt), 71... Belt conveying device (upper belt unit), 100... Control unit, 400... Steering mechanism, S... Recording material

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 detection unit for detecting the position of the belt in the direction of the rotation axis, The steering mechanism comprises: a control unit which determines the tilt angle of the first roller based on the position of the belt detected by the detection unit, and controls the steering mechanism according to the tilt angle of the first roller; The control unit controls the steering mechanism according to a second tilt angle smaller than the first tilt angle, obtained by correcting the first tilt angle, which is determined based on the position of the belt, according to a control coefficient of less than 1, from the start of the belt's movement until it completes one rotation of the belt. A belt conveying device characterized by the following features.

2. The control unit determines the first tilt angle based on the position of the belt detected by the detection unit at multiple timing intervals, which are equal divisions of the length of one rotation of the belt, from the start of the belt's movement until it completes one full rotation. The belt conveying device according to feature 1.

3. The control unit corrects the first tilt angle according to a first control coefficient at a first timing, and corrects the first tilt angle according to a second control coefficient that is larger than the first control coefficient at a second timing that is later than the first timing. The belt conveying device according to feature 2.

4. The control unit performs proportional and integral calculations on the difference between the detected belt position and the target position, and determines the tilt angle of the first roller according to the sum of the calculation results of each calculation. The belt conveying device according to feature 1.

5. The control unit corrects the first tilt angle using the control coefficient when performing the proportional and integral calculations from the start of the belt's movement until it completes one rotation of the belt. The belt conveying device according to feature 4.

6. The control unit controls the steering mechanism according to the first tilt angle determined based on the position of the belt, from the start of the belt's movement through the first rotation of the belt. The belt conveying device according to feature 1.

7. A fixing device for fixing a toner image formed on a recording material to the recording material, A belt conveying device according to any one of claims 1 to 6, 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.

8. The rotating body is an endless belt. The fixing device according to feature 7.

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