Image forming device

Abstract

To provide an image forming apparatus that can convey a recording material without causing a loop of the recording material even when a variation in torque occurs in a cooler due to a change in cooling conveyance speed during the conveyance of the recording material.SOLUTION: When cooling drive torque reaches a torque threshold in a state where a recording material is sandwiched between a fixing nip part and a cooling nip part (YES in S2), a control unit changes a cooling conveyance speed to a second nominal speed slower than a fixing conveyance speed (S3). This prevents the occurrence of a loop of the recording material between a cooler and a rear conveyance roller part when a rear end of the recording material passes through the fixing nip part. The control unit increases or decreases the cooling conveyance speed so that the cooling drive torque varying with a change in cooling conveyance speed does not exceed the torque threshold (S4-S9). If the cooling drive torque does not exceed the torque threshold, the cooling conveyance speed does not temporarily become faster than a rear conveyance speed when the rear end of the recording material passes through the fixing nip part, which prevents the occurrence of the loop of the recording material.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine that uses an electrophotographic system. [Background technology]

[0002] In electrophotographic image forming apparatuses, a toner image formed on a recording material such as paper is fixed to the recording material by heating and pressurizing it in a fixing unit. The toner image is fixed in the fixing unit using a fixing roller heated by a heater or the like and a pressure roller that contacts the fixing roller to form a fixing nip that sandwiches and transports the recording material. Because the recording material is heated as it passes through the fixing nip, the temperature of the recording material increases after passing through the fixing nip. If a large number of recording materials that have been transported while still at a high temperature after the toner image is fixed are stacked in a stacking section, there is a risk that the toner will stick to each other.

[0003] To prevent this, a cooler is provided to cool the recording material conveyed from the fixing unit. The cooler has a conveying belt (called a cooling belt) cooled by a heat sink or the like, and reduces the temperature of the recording material through a cooling nip formed by the cooling belt. The recording material, on which the toner image has been fixed by the fixing unit, is nipped and conveyed with its leading edge reaching the cooling nip before its trailing edge passes through the fixing nip. The recording material, cooled by the cooler, is nipped and conveyed with its leading edge reaching a rear conveying roller before its trailing edge passes through the cooling nip.

[0004] Incidentally, the outer diameter of a fixing roller heated by a heater or the like can change due to thermal expansion, which can easily cause variations in the speed at which the recording material is conveyed by the fixing device (hereinafter referred to as the fixing conveyance speed). This can cause the recording material to bend (loop) between the transfer nip where the toner image is transferred and the fixing nip, resulting in image defects such as gloss unevenness, which causes the gloss of the toner image to be disturbed. Therefore, devices have been proposed that perform speed control to accelerate or decelerate the fixing conveyance speed, thereby preventing loops from occurring in the recording material after fixing (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-86754 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-207648 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the past, the fixing conveying speed was slowed down, and the conveying speed of the recording material by the cooler (hereinafter referred to as the cooling conveying speed) became faster relative to the fixing conveying speed, which sometimes resulted in a large speed difference between the fixing conveying speed and the cooling conveying speed. In this case, the recording material is conveyed while being pulled from the fixing unit by the cooling belt, so the torque of the cooling belt increases. Then, when the trailing edge of the recording material passes through the fixing nip while the torque of the cooling belt remains high, the cooling conveying speed can temporarily become faster than the conveying speed of the recording material by the rear conveying roller unit (hereinafter referred to as the rear conveying speed). In this case, a loop occurs in the recording material between the cooler and the rear conveying roller unit, which can cause image defects due to the loop.

[0007] The present invention has been made in consideration of the above problems, and aims to provide an image forming apparatus that can transport recording material without causing the recording material to loop, even if torque fluctuations occur in the cooler in response to changes in the cooling transport speed when transporting the recording material. [Means for solving the problem]

[0008] An image forming apparatus according to one embodiment of the present invention includes image forming means for forming a toner image on a recording material, fixing means having a fixing nip portion for applying heat and pressure to fix the toner image to the recording material while nipping and conveying the recording material on which the toner image has been formed by the image forming means, cooling means arranged to be able to nip the recording material while being held by the fixing means and having a cooling nip portion for cooling the recording material on which the toner image has been fixed by the fixing means while being nip and conveyed, post-conveying means arranged to be able to nip the recording material while being held by the cooling means and having a conveying nip portion for nip and conveying the recording material cooled by the cooling means, and a driving means for driving the stages, an acquisition means for acquiring information relating to the torque of the driving means, and a control means for controlling the driving means based on the information relating to the torque and for controlling a cooling conveying speed at which the cooling means conveys the recording material, wherein the control means sets the cooling conveying speed to a first speed that is faster than a fixing conveying speed at which the recording material is conveyed by the fixing means before the recording material reaches the fixing nip portion, and then, when the torque exceeds a threshold value while the recording material is sandwiched between the fixing nip portion and the cooling nip portion, sets the cooling conveying speed to a second speed that is slower than the fixing conveying speed. [Effects of the Invention]

[0009] According to the present invention, even if torque fluctuation occurs in the cooling means in response to a change in the cooling conveying speed when conveying the recording material, the recording material can be conveyed without causing a loop in the recording material. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an image forming system to which an image forming apparatus according to an embodiment of the present invention is applied. [Figure 2] FIG. 2A is a cross-sectional view showing an image forming and transferring device, and FIG. 2B is an enlarged view showing an image forming section. [Figure 3] FIG. [Figure 4] FIG. 3 is a control block diagram illustrating a control unit. [Figure 5] 4 is a flowchart showing a speed control process according to the first embodiment. [Figure 6] 6 is a graph showing changes over time in cooling drive torque and cooling transport speed in the first embodiment. [Figure 7] 10 is a flowchart showing a speed control process according to a second embodiment. [Figure 8] 10 is a graph showing changes over time in cooling drive torque and cooling transport speed in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] [First embodiment] <Image forming system> This embodiment will be described below. First, the schematic configuration of the image forming apparatus of this embodiment will be described with reference to Figures 1 and 2. The image forming system 1X shown in Figure 1 includes an image forming apparatus 101, a large-capacity feeding device 106 having multiple recording material storage units, and a sensing device 107. The sensing device 107 is disposed downstream of the image forming apparatus 101 in terms of the conveying direction of the recording material S by the large-capacity feeding device 106 (from right to left in Figure 1).

[0012] In this specification, the side on which a user stands when operating an operation unit 80 (described later) is referred to as the "front (or front)," and the opposite side is referred to as the "rear (or back)." Also, the left side when viewed from the front is referred to as the "left," and the right side when viewed from the front is referred to as the "right." Therefore, FIG. 1 shows the image forming system 1X as viewed from the front.

[0013] The large-capacity feeding device 106 and the sensing device 107 are not only physically connected to the image forming apparatus 101 so as to be able to convey the recording material S, but are also electrically connected so as to be able to send and receive electrical signals. The large-capacity feeding device 106 is a device that supplies the recording material S to the image forming apparatus 101. The sensing device 107 is a device that reads a fixed toner image formed on one or both sides of the recording material S discharged from the image forming apparatus 101 and feeds it back to the image forming apparatus 101 as an image signal. The image forming apparatus 101 detects deviations in image density and image position based on the fed-back image signal, and corrects image data based on the detected deviations in image density and image position. Then, the image forming units SY to SK are controlled based on the corrected image data to form a toner image on the recording material S.

[0014] Instead of the large-capacity feeding device 106, a manual feeding device (not shown), a long-length feeding device capable of accommodating long recording materials, or the like may be selectively connected upstream of the image forming apparatus 101 in the recording material transport direction. Alternatively, a large-capacity feeding device, a manual feeding device, a long-length feeding device, or the like (not shown) may be selectively connected in tandem further upstream of the large-capacity feeding device 106. Furthermore, one or more combinations of various post-processing devices (not shown), such as an inserter, puncher, case binder, large-capacity stacker, folder, finisher, trimmer, etc., may be selectively connected further downstream of the image forming apparatus 101 or the sensing device 107. In this way, by selectively connecting various optional devices upstream and downstream of the image forming apparatus 101, it becomes possible to inline output products that have undergone various post-processing processes on recording materials S of various materials, thereby providing an image forming system 1X with high productivity, high image quality, high stability, and high functionality.

[0015] <Image forming device> The image forming apparatus 101 is broadly divided into an image forming and transferring device 500 and a fixing and conveying device 600, which are configured separately. In this embodiment, the image forming and transferring device 500, which serves as an image forming means, includes image forming sections 200Y, 200M, 200C, and 200K, an intermediate transfer belt unit 800, and the like, which perform the transfer process of transferring a toner image onto a recording material S. On the other hand, the fixing and conveying device 600 includes a fixing unit 8 and a cooler 310, which perform the fixing process of fixing the toner image onto the recording material S. The image forming and transferring device 500 and the fixing and conveying device 600 are connected so that the recording material S can be passed between them.

[0016] The image forming and transferring device 500 and the fixing and conveying device 600 have independent housings 500A and 600A, respectively, and can be moved using multiple casters provided on each. This allows the image forming and transferring device 500 and the fixing and conveying device 600 to be packed and transported in separate housings 500A and 600A, even if they are large devices, improving workability up to installation. The housing 500A is also provided with a document reading device 160 that reads image information from a document, a display unit that can display various information, an operation unit 80 that has keys and the like that can input various information in response to user operation, and the like.

[0017] The housings 500A and 600A each include a front panel on the front side, a rear panel on the rear side that supports the image forming units 200Y-200K, intermediate transfer belt unit 800, fuser 8, cooler 310, etc. together with the front panel, and multiple frames such as supports that connect the front panel and the rear panel and support the front panel. A resin exterior cover that forms the exterior is attached to the housings 500A and 600A. The image forming and transferring device 500 and the fixing and conveying device 600 may be provided in a single housing rather than in separate housings (500A, 600A).

[0018] <Image forming transfer device> Next, the image forming and transferring device 500 will be described with reference to Figures 2(a) and 2(b). The image forming and transferring device 500 is an intermediate transfer type device in which image forming units 200Y, 200M, 200C, and 200K that form yellow, magenta, cyan, and black toner images are housed within a housing 500A (inside the housing) and are arranged facing an intermediate transfer belt 208. The image forming and transferring device 500 forms a toner image on a recording material S in accordance with image data from a document reading device 160 (see Figure 1) provided above the housing 500A or an external device (not shown) such as a personal computer. Examples of the recording material S include sheet materials such as paper, plastic film, and cloth.

[0019] The conveyance process of the recording material S in the image forming and transferring device 500 will be described. The recording material S is stored in a stacked form in one or more (here, two) cassettes 212, and is supplied one sheet at a time by a supply roller 220 in accordance with the image formation timing. The recording material S supplied by the supply roller 220 is conveyed to a registration roller 213 arranged midway along a conveyance path 250. The registration roller 213 then performs skew correction and timing correction on the recording material S, and the recording material S is sent to a secondary transfer unit ST. The secondary transfer unit ST is formed by an inner secondary transfer roller 214 and an outer secondary transfer roller 215 that face each other across the intermediate transfer belt 208, and is a transfer nip portion that transfers a toner image from the intermediate transfer belt 208 onto the recording material S by applying a predetermined pressure and secondary transfer voltage.

[0020] The process of forming an image sent to the secondary transfer station ST at the same timing as the process of conveying the recording material S to the secondary transfer station ST will be described below. First, the image forming stations 200Y to 200K will be described. However, since the image forming stations 200Y to 200K for each color are basically the same except for the color of the toner, the following description will be made using the black image forming station 200K as an example.

[0021] The image forming unit 200K includes a photosensitive drum 201K, a charger 202K, a laser scanner 203K, a developing unit 204K, etc. The surface of the rotating photosensitive drum 201K is uniformly charged in advance by the charger 202K, and then an electrostatic latent image is formed on it by the laser scanner 203K, which is driven based on image data. Next, the developing unit 204K develops the electrostatic latent image formed on the photosensitive drum 201K with toner contained in the developer, forming a toner image on the photosensitive drum 201K.

[0022] Thereafter, a predetermined pressure and primary transfer voltage are applied by primary transfer roller 207K, which is disposed opposite image forming unit 200K with intermediate transfer belt 208 sandwiched therebetween, and the toner image formed on photosensitive drum 201K is primarily transferred onto intermediate transfer belt 208. Primary transfer residual toner remaining on photosensitive drum 201K after primary transfer is removed by drum cleaner 209K. The removed primary transfer residual toner is collected in recovered toner container 211 via toner recovery path 210.

[0023] The intermediate transfer belt 208 is an endless belt that is stretched by multiple tension rollers and a secondary transfer inner roller 214 and moved by a motor (not shown) at a speed corresponding to the rotation speed of the photosensitive drums 201Y-201K. The image formation processes for each color, which are performed in parallel by the image forming units 200Y-200K, are performed at a timing that sequentially superimposes the color toner images that have been primarily transferred onto the intermediate transfer belt 208 upstream in the movement direction. As a result, a full-color toner image is finally formed on the intermediate transfer belt 208 and transported to the secondary transfer unit ST. Residual toner remaining on the intermediate transfer belt 208 after passing through the secondary transfer unit ST is collected from the intermediate transfer belt 208 by a belt cleaner device 216. The primary transfer rollers 207Y-207K, the intermediate transfer belt 208, the multiple tension rollers, the secondary transfer inner roller 214, the belt cleaner device 216, and the like may be integrally provided as an intermediate transfer belt unit 800.

[0024] Through the above-described conveying process and image forming process, the timing of the recording material S and the toner image coincides at the secondary transfer section ST, and secondary transfer is performed in which the toner image is transferred from the intermediate transfer belt 208 to the recording material S. Thereafter, the recording material S is conveyed by pre-fixing conveying belts 217a and 217b to the fixing conveying device 600, which fixes the toner image onto the recording material S.

[0025] <Fixing conveyance device> Next, the fixing and conveying device 600 will be described. As shown in FIG. 1, the fixing and conveying device 600 has a fixing unit 8 and a cooler 310. The fixing unit 8 as a fixing means has a fixing roller 8a heated by a heater (not shown) and a pressure roller 8b that presses the recording material S against the fixing roller 8a. The fixing roller 8a is driven to rotate by a fixing drive motor 700 (see FIG. 4), which will be described later. The recording material S carrying a toner image and conveyed from the image forming and transferring device 500 is heated and pressurized while being nipped and conveyed through a fixing nip N1 formed by the fixing roller 8a and the pressure roller 8b. This fixes the toner image to the recording material S. In this embodiment, a fixing exit sensor 401 is disposed at the exit of the fixing nip N1 of the fixing unit 8 (downstream in the conveying direction of the recording material S) and is capable of detecting that the leading and trailing ends of the recording material S have passed through the fixing nip N1.

[0026] Although the fixing device 8 is shown here as an example consisting of a pair of rollers, a fixing roller 8a and a pressure roller 8b, the invention is not limited to this. For example, the fixing device may have a fixing belt instead of the fixing roller 8a, and heat and pressurize the recording material S while sandwiching and conveying it in a fixing nip formed by the fixing belt heated by a heater and the pressure roller 8b, thereby fixing the toner image on the recording material S.

[0027] The recording material S heated by the fixing device 8 is conveyed toward the cooler 310 and cooled by the cooler 310. The cooler 310 is arranged so as to be able to hold the recording material S while it is sandwiched in the fixing device 8 (more specifically, the fixing nip portion N1). The cooler 310 will be described later (see FIG. 3).

[0028] The recording material S cooled by the cooler 310 is nipped and conveyed by a rear conveying roller unit 601 arranged at the exit of the cooling nip portion N2 (downstream in the conveying direction of the recording material S). The rear conveying roller unit 601 as a rear conveying means has a pair of rollers that form a conveying nip portion N3 that nip and conveys the recording material S, and is driven to rotate by a rear conveying drive motor 701 (see FIG. 4). The rear conveying roller unit 601 is arranged so as to be able to nip the recording material S while it is nipped by the cooler 310 (more specifically, the cooling nip portion N2).

[0029] In the single-sided mode, in which a toner image is formed on only one side of the recording material S, the cooled recording material S is guided from the rear conveying roller unit 601 to the discharge conveying path 304 and discharged from the housing 600A toward the sensing device 107. On the other hand, in the double-sided mode, in which a toner image is formed on both sides of the recording material S, the cooled recording material S is guided from the rear conveying roller unit 601 to the reversing conveying path 305, and after being inverted by the reversing conveying path 305, is returned to the image forming and transferring device 500 through the double-sided conveying path 306. Thereafter, the recording material S undergoes the same process as in the single-sided mode, and the toner image is fixed on the other side by the fixing device 8. Then, after being cooled by the cooler 310, the recording material S is guided to the discharge conveying path 304 and discharged from the housing 600A toward the sensing device 107.

[0030] <Cooler> Next, the cooler 310 will be described with reference to Fig. 3. As shown in Fig. 3, the cooler 310 as a cooling means has an endless first belt 21 and an endless second belt 25 that forms a cooling nip portion N2 where the recording material S is nipped and conveyed together with the first belt 21. For example, the first belt 21 and the second belt 25 are made of high-strength polyimide, and are set to a thickness of 100 µm and a circumferential length of 942 mm. The cooler 20 also has a heat sink 30 that cools the first belt 21.

[0031] The first belt 21 is wound around a drive roller 22a and a plurality of tension rollers 22b to 22e, and the second belt 25 is wound around a drive roller 26a and a plurality of belt tension rollers 26b to 26e. These drive rollers 22a and 26a are connected to a single belt drive motor 702 (see FIG. 4) via a drive gear (not shown), and are driven to rotate by the belt drive motor 702. In this embodiment, a direct-current motor with a wide speed range is used as the belt drive motor 702 serving as a drive means.

[0032] Pressure rollers 26f and 26g are provided on the inner circumferential side of the second belt 25 to pressurize the second belt 25 toward the heat sink 30. The pressure rollers 26f and 26g pressurize the second belt 25 with a pressure of, for example, 9.8 N (1 kgf), thereby reliably bringing the first belt 21 into contact with the heat sink 30 via the second belt 25.

[0033] The recording material S with the fixed toner image is sandwiched between the first belt 21 and the second belt 25 and transported in the transport direction (arrow C direction) as they rotate. During this process, the recording material S passes through a cooling nip N2 formed by the contact between the first belt 21 and the second belt 25. In this embodiment, the first belt 21 is cooled by a heat sink 30. The heat sink 30 is disposed so as to contact the inner surface of the first belt 21 at a location that forms the cooling nip N2 in order to efficiently cool the recording material S. As the recording material S passes through the cooling nip N2, the recording material S is cooled by the first belt 21. Even if the toner on the recording material S was in a molten state before contacting the first belt 21, the toner is cooled and fixed to the recording material S. For example, the temperature of the recording material S is raised to 90°C by the fixing device 8 and then cooled to 60°C by the cooler 310. During this process, the temperature of the toner image fixed to the recording material S also drops from 90°C to 60°C.

[0034] The heat sink 30 is a heat dissipation plate made of metal such as aluminum. The heat sink 30 has a heat receiving portion 30a that comes into contact with the first belt 21 to absorb heat from the first belt 21, a heat dissipation portion 30b that dissipates heat, and a fin base 30c that conducts heat from the heat receiving portion 30a to the heat dissipation portion 30b. The heat dissipation portion 30b is formed of a large number of heat dissipation fins to increase the contact area with the air and promote efficient heat dissipation. A cooling fan 40 that blows air toward the heat sink 30 is provided to forcibly cool the heat sink 30 itself.

[0035] <Control unit> As shown in Fig. 2, the image forming and transferring device 500 includes a control unit 300. The control unit 300, which serves as a control means, performs various controls of the image forming apparatus 101, such as the image forming operation. The control unit 300 will be described using Fig. 4 with reference to Figs. 1 to 3. However, although various devices such as motors and power supplies that operate the image forming apparatus 101 are connected to the control unit 300 in addition to those shown in the figure, illustration and description of these devices will be omitted here as they are not the main focus of the invention.

[0036] As shown in Fig. 4, the control unit 300 has a CPU 301 (Central Processing Unit) and a memory 302 such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The memory 302 stores various programs, such as image formation jobs and speed control processes (see Fig. 5 described later), various data, etc. The control unit 300 can execute the various programs stored in the memory 302 and can operate the image forming apparatus 101 by executing the various programs. The memory 302 can also temporarily store the results of arithmetic processing associated with the execution of the various programs.

[0037] An image forming job is a series of operations from the start of an image forming operation to the completion of the image forming operation based on a print signal for forming an image on a recording material S. That is, it is a series of operations from the start of a preparatory operation (so-called pre-rotation) required for image formation, through the image forming process, to the completion of a preparatory operation (so-called post-rotation) required for completing image formation. Specifically, it refers to the period from the pre-rotation (preparatory operation before image formation) after receiving a print signal (receiving an image forming job) to the post-rotation (operation after image formation), and includes the image formation period and the paper interval.

[0038] The control unit 300 is connected to an operation unit 80, a fixing exit sensor 401, a fixing drive motor 700, a post-conveyance drive motor 701, a belt drive motor 702, and an ammeter 501 via an input / output interface. The operation unit 80 is, for example, an operation panel or an external terminal, which accepts various data inputs such as instructions from the user to execute various programs and information about the recording material S (e.g., size such as A3 or B4).

[0039] Based on the detection result of the fixing exit sensor 401, the control unit 300 can detect that the leading edge of the recording material S has passed through the fixing nip portion N1 and that the trailing edge of the recording material S has passed through the fixing nip portion N1 in the conveying direction of the recording material S in the fixing unit 8. The control unit 300 can also detect that the trailing edge of the recording material S has passed through the cooling nip portion N2 according to the elapsed time since it was detected that the trailing edge of the recording material S has passed through the fixing nip portion N1.

[0040] The control unit 300 controls the fixing drive motor 700 to start and stop the drive of the fixing roller 8a and the fixing conveyance speed. The control unit 300 also controls the rear conveyance drive motor 701 to control the drive start and stop of the rear conveyance roller unit 601 and the rear conveyance speed. The control unit 300 also controls the belt drive motor 702 to control the drive start and stop of the first belt 21 and the cooling conveyance speed. In this embodiment, when starting an image formation job, the control unit 300 sets the cooling conveyance speed of the first belt 21 and the rear conveyance speed of the rear conveyance roller unit 601 to a speed (referred to as a first nominal speed) that is 1.5% faster than the fixing conveyance speed of the fixing roller 8a. This makes it less likely that the recording material S will loop between the fixing unit 8 and the cooler 310, even if the recording material S is conveyed while sandwiched between the fixing nip N1 and the cooling nip N2.

[0041] An ammeter 501 that detects the current flowing through the belt drive motor 702 is connected to the belt drive motor 702. The control unit 300 has a belt torque detection unit 303 as an acquisition unit that acquires information about the torque of the belt drive motor 702, and the belt torque detection unit 303 receives the current value detected by the ammeter 501 as information about the torque. In this embodiment, the control unit 300 has the belt torque detection unit 303, and the belt torque detection unit 303 can detect the drive torque of the first belt 21 (hereinafter referred to as cooling drive torque) based on the current value of the ammeter 501. The control unit 300 controls the belt drive motor 702 based on the information about the torque, and controls the cooling conveying speed at which the cooler 310 conveys the recording material S.

[0042] During the execution of an image forming job, depending on the length of the recording material S in the conveying direction, there may be cases where the recording material S is conveyed while being held in the fixing nip portion N1 and also held in the cooling nip portion N2. In such a case, if the cooling conveying speed is faster than the fixing conveying speed (first nominal speed), as described above, the recording material S is conveyed while being pulled from the fixing device 8 by the first belt 21, and the cooling drive torque increases.

[0043] When the trailing edge of the recording material S passes through the fixing nip N1 while the cooling drive torque remains increased, the tension on the recording material S is released. At this time, the first belt 21 temporarily rotates faster, causing the cooling conveying speed to become faster than the first nominal speed and then returning to the first nominal speed. When the cooling conveying speed temporarily becomes faster than the first nominal speed in this manner, a loop occurs in the recording material S between the rear conveying roller unit 601, which is rotating at the first nominal speed, and the loop may cause loop marks or image scratches on the recording material S. To prevent this, the cooling drive torque must be prevented from increasing to the extent that the cooling conveying speed temporarily becomes faster than the first nominal speed at the time when the trailing edge of the recording material S passes through the fixing nip N1, in other words, before the tension on the recording material S is released.

[0044] <Speed ​​control processing> In view of the above, in this embodiment, the cooling drive torque is detected and the cooling conveying speed is adjusted based on the detected cooling drive torque. The speed control process for achieving this will be described below with reference to FIGS. 5 and 6 along with FIGS. 1, 3, and 4. FIG. 5 is a flowchart showing the speed control process of the first embodiment. FIG. 6 is a graph showing the change in cooling drive torque over time for one sheet of recording material S, with the upper graph showing the change in cooling conveying speed over time, and the lower graph showing the change in cooling conveying speed over time. The speed control process of this embodiment is executed by the control unit 300, for example, when an image forming job is started.

[0045] During the execution of an image forming job, when the control unit 300 determines based on the detection result of the fixing exit sensor 401 that the leading edge of the recording material S has passed through the fixing nip N1 (time t0), it starts detecting the cooling drive torque (S1). As described above, the control unit 300 detects the cooling drive torque based on the current value of the ammeter 501. During the idling of the cooler 310 (until time t1), the cooling conveying speed and the post-conveying speed are set to a first nominal speed (first speed: e.g., 450 mm / s) that is 1.5% faster than the fixing conveying speed (e.g., 443 mm / s). Then, when the leading edge of the recording material S reaches the cooling nip N2 (time t1), the recording material S begins to be conveyed while being pulled from the fixing unit 8 by the first belt 21 while being nipped between the fixing nip N1 and the cooling nip N2, and the cooling drive torque increases thereafter. The cooling drive torque during idling is, for example, 200 mA. In this specification, the torque value is indicated by the current value of the belt drive motor 702.

[0046] The control unit 300 determines whether the cooling drive torque, which increases with the setting to the first nominal speed, has reached a torque threshold (S2). The torque threshold is a lower limit of the torque at which the cooling conveying speed temporarily becomes faster than the rear conveying speed when the rear end of the recording material S, which is being pulled between the fixing unit 8 and the cooler 310, passes through the fixing nip N1, and is, for example, "500 mA." In other words, when the rear end of the recording material S passes through the fixing nip N1 with the cooling drive torque exceeding the torque threshold, a loop is likely to occur in the recording material S between the cooler 310 and the rear conveying roller unit 601.

[0047] If the cooling drive torque has not reached the torque threshold value (NO in S2), the control unit 300 jumps to the process of step S11. On the other hand, if the cooling drive torque has reached the torque threshold value (YES in S2), the control unit 300 controls the belt drive motor 702 to change the cooling conveying speed to a second nominal speed (S3). The second nominal speed (second speed) is a speed (e.g., 430 mm / s) slower than the fixing conveying speed. In this case, the tension on the recording material S by the first belt 21, which has been changed to the second nominal speed, is weakened, and the cooling drive torque is reduced. Therefore, when the trailing edge of the recording material S passes through the fixing nip portion N1, a loop is less likely to occur in the recording material S between the cooler 310 and the rear conveying roller unit 601.

[0048] However, if the second nominal speed is maintained as it is, there is a risk that a loop will occur in the recording material S between the fixing device 8 and the cooler 310, so the cooling conveying speed must be increased again. Therefore, in order to prevent a loop from occurring in the recording material S between the fixing device 8 and the cooler 310 and to prevent an increase in the cooling drive torque, it is necessary to make the recording material S be in a state where it is appropriately pulled between the fixing device 8 and the cooler 310.

[0049] After changing the cooling conveying speed to the second nominal speed, the control unit 300 monitors at predetermined time intervals (e.g., every 8 ms) whether the cooling drive torque exceeds the torque threshold (S4). If the cooling drive torque, which fluctuates with the change in the cooling conveying speed, exceeds the torque threshold (YES in S4), the control unit 300 controls the belt drive motor 702 to slow the cooling conveying speed by a predetermined speed (S7) unless the cooling conveying speed falls below a predetermined lower limit speed (NO in S5). If the cooling conveying speed falls below the predetermined lower limit speed (YES in S5), the control unit 300 sets the cooling conveying speed to the lower limit speed (S6). The predetermined speed is, for example, 4 mm / s, and the lower limit speed is 4 mm / s slower than the second nominal speed (e.g., 426 mm / s).

[0050] In the example shown in Fig. 6, after the cooling conveying speed is changed to the second nominal speed (time t2), the cooling drive torque exceeds the torque threshold value at times t3 and t4, which are 8 ms apart. Therefore, at time t3, the cooling conveying speed is slowed down from the second nominal speed by a predetermined speed. Furthermore, at time t4, when the cooling conveying speed is slowed down from the second nominal speed by the predetermined speed, the cooling conveying speed falls below the lower limit speed, so the cooling conveying speed is slowed down up to the lower limit speed. When the cooling conveying speed is slowed down in this way, the pulling state of the recording material S by the first belt 21 becomes weaker, and the cooling drive torque decreases as the cooling conveying speed is slowed down (times t3 to t5).

[0051] On the other hand, if the cooling drive torque is equal to or less than the torque threshold value (NO in S4), the control unit 300 controls the belt drive motor 702 to increase the cooling conveying speed by a predetermined speed (S8). The predetermined speed for increasing the speed may be the same as the predetermined speed for deceleration (4 mm / s). When the cooling drive torque decreases (times t3 to t5), the cooling drive torque becomes equal to or less than the torque threshold value (time t5). Therefore, at time t5, the cooling conveying speed is increased. When the cooling conveying speed is increased in this way, the pulling state of the recording material S by the first belt 21 becomes stronger, so the cooling drive torque increases as the cooling conveying speed increases (from time t5). This makes it less likely that a loop will occur in the recording material S between the fixing unit 8 and the cooler 310.

[0052] The control unit 300 determines whether the trailing edge of the recording material S has passed through the fixing nip N1 based on the detection result of the fixing exit sensor 401 (S9). If the trailing edge of the recording material S has not passed through the fixing nip N1 (NO in S9), the control unit 300 returns to step S4 and repeats the processes of steps S4 to S8. In this way, by repeating the increase and decrease of the cooling conveying speed until the trailing edge of the recording material S passes through the fixing nip N1, the cooling drive torque is maintained at a torque that does not easily cause a loop in the recording material S (times t2 to t8).

[0053] When the rear end of the recording material S has passed through the fixing nip N1 (YES in S9), the control unit 300 returns the cooling conveying speed to the first nominal speed (S10). By returning the cooling conveying speed to the first nominal speed (time t9), the next recording material S conveyed is conveyed while being pulled from the fixing device 8 by the first belt 21, making it difficult for a loop to occur in the recording material S between the fixing device 8 and the cooler 310.

[0054] Then, the control unit 300 determines whether image formation on the last recording material S in the image forming job being executed has been completed (S11). If image formation on the last recording material S has not been completed (NO in S11), the control unit 300 returns to the process of step S1 and repeats the processes of steps S1 to S10 described above for the next recording material S. On the other hand, if image formation on the last recording material S has been completed (YES in S11), the control unit 300 ends this speed control process.

[0055] As described above, in this embodiment, when the cooling drive torque reaches the torque threshold while the recording material S is sandwiched between the fixing nip N1 and the cooling nip N2, the cooling conveying speed is changed to the second nominal speed, which is slower than the fixing conveying speed. This makes it less likely that a loop will occur in the recording material S between the cooler 310 and the rear conveying roller unit 601 when the trailing edge of the recording material S passes through the fixing nip N1.

[0056] Then, when the recording material S is sandwiched between the fixation device 8 and the cooler 310, the cooling conveying speed is increased or decreased so that the cooling drive torque, which fluctuates with the change in the cooling conveying speed, does not exceed the torque threshold. If the cooling drive torque does not exceed the torque threshold, the cooling conveying speed does not temporarily become faster than the rear conveying speed when the trailing edge of the recording material S passes through the fixing nip portion N1. Therefore, when the trailing edge of the recording material S passes through the fixing nip portion N1, no loop occurs in the recording material S between the cooler 310 and the rear conveying roller unit 601, so no image defects due to the loop occur. Furthermore, even when the recording material S is sandwiched between the fixation device 8 and the cooler 310, the cooling conveying speed is increased or decreased based on the torque fluctuation of the cooling drive torque, so that no loop occurs in the recording material S between the fixation device 8 and the cooler 310.

[0057] In this embodiment, the control unit 300 is configured to determine that the leading or trailing edge of the recording material S has passed through the fixing nip N1 based on the detection result of the fixing exit sensor 401, but this is not limited to this. For example, a fixing entrance sensor may be disposed upstream of the fixing nip N1, and the leading or trailing edge of the recording material S may be detected to have passed through the fixing nip N1 from the timing at which the leading or trailing edge of the recording material S passes through the fixing entrance sensor and the fixing conveyance speed. Also, the cooling drive torque is detected based on the value of the current flowing through the belt drive motor 702 detected by the ammeter 501, but this is not limited to this, and the torque value of the belt drive motor 702 may be detected using a torque sensor or the like.

[0058] [Second embodiment] Incidentally, if the length of the recording material S in the conveying direction is longer than the distance from the fixing device 8 to the rear-conveying roller unit 601, the leading edge of the recording material S will reach the rear-conveying roller unit 601 while still being sandwiched in the fixing device 8. In other words, the recording material S will be sandwiched between the fixing nip N1, the cooling nip N2, and the conveying nip N3. The clamping force of the rear-conveying roller unit 601 is set to be weaker than that of the fixing device 8 and stronger than that of the cooler 310. In this case, as described above, if the rear-conveying speed is "1.5%" faster than the fixing conveying speed, which is the same as the cooling conveying speed, the rear-conveying roller unit 601 will be more likely to slip with respect to the nipped recording material S, and this will increase the driving torque of the rear-conveying roller unit 601.

[0059] To prevent this, it is preferable that the post-conveying speed is approximately the same as the fixing conveying speed in the case of a recording material S whose length in the conveying direction is, for example, 30 inches, longer than the distance from the fixing device 8 to the post-conveying roller unit 601. Therefore, when the length in the conveying direction of the recording material S is shorter than the distance from the fixing device 8 to the post-conveying roller unit 601, the control unit 300 sets both the cooling conveying speed and the post-conveying speed to a first nominal speed (for example, 450 mm / s) that is faster than the fixing conveying speed, as described above, when starting an image forming job.

[0060] On the other hand, if the length of the recording material S in the conveying direction is longer than the distance from the fixing device 8 to the rear conveying roller unit 601, the control unit 300 sets the cooling conveying speed to the first nominal speed and the rear conveying speed to the fixing conveying speed when starting an image forming job. However, as described above, if the cooling conveying speed is changed to the first nominal speed at the timing when the rear end of the recording material S passes through the fixing nip N1 (see S10 in FIG. 5), the cooling conveying speed becomes faster than the rear conveying speed, which is undesirable because it causes a loop in the recording material S between the cooler 310 and the rear conveying roller unit 601.

[0061] 7 and 8, with reference to Figures 1, 3, and 4, a speed control process that takes into account control of the cooling conveying speed when the length of the recording material S in the conveying direction is longer than the distance from the fixing device 8 to the rear conveying roller unit 601. However, in the speed control process shown in Figure 7, the processes of steps S1 to S11 are the same as the speed control process of the first embodiment (see Figure 5), and therefore a description thereof will be omitted.

[0062] 7, when the rear end of the recording material S passes through the fixing nip portion N1 (YES in S9), the control unit 300 determines whether the length of the recording material S in the conveying direction is equal to or greater than a predetermined length (S21). The predetermined length is the distance from the fixing device 8 to the rear conveying roller unit 601. The control unit 300 determines whether the length of the recording material S in the conveying direction is equal to or greater than the predetermined length based on information about the recording material S input from the operation unit 80.

[0063] If the length of the recording material S in the conveying direction is shorter than the predetermined length (NO in S21), the control unit 300 returns the cooling conveying speed to the first nominal speed (S10). This process is the same as in the first embodiment described above, and by returning the cooling conveying speed to the first nominal speed (see time t9 in FIG. 6), the next conveyed recording material S is conveyed while being pulled from the fixing device 8 by the first belt 21, making it difficult for a loop to occur in the recording material S between the fixing device 8 and the cooler 310.

[0064] On the other hand, if the length of the recording material S in the conveying direction is longer than the predetermined length (YES in S21), the control unit 300 changes the cooling conveying speed to the third nominal speed (S22). Then, when the trailing edge of the recording material S passes through the cooling nip N2 (S23), the control unit 300 changes the cooling conveying speed back to the first nominal speed from the third nominal speed (S10). Thus, as shown in FIG. 8, the cooling conveying speed is set to the third nominal speed from the time the trailing edge of the recording material S passes through the fixing nip N1 until it passes through the cooling nip N2 (time t9 to t10). The third nominal speed (third speed: for example, 435 mm / s) is slower than the fixing conveying speed (the same applies to the post-conveying speed) and faster than the second nominal speed.

[0065] As described above, during the period from when the trailing edge of the recording material S passes through the fixing nip portion N1 until when it passes through the cooling nip portion N2, in other words, while the recording material S is not sandwiched by the fixer 8 but is sandwiched between the cooler 310 and the rear-conveying roller unit 601, the cooling conveying speed is made slower than the rear-conveying speed. That is, when the trailing edge of the recording material S passes through the fixing nip portion N1, the cooling conveying speed does not become faster than the rear-conveying speed, but when the trailing edge of the recording material S passes through the cooling nip portion N2, the cooling conveying speed becomes faster than the rear-conveying speed. This makes it less likely that a loop will occur in the recording material S between the cooler 310 and the rear-conveying roller unit 601 when the length of the recording material S in the conveying direction is longer than the distance from the fixer 8 to the rear-conveying roller unit 601. [Explanation of symbols]

[0066] 8...fixing means (fixing device), 300...control means (control unit), 303...acquisition means (belt torque detection unit), 310...cooling means (cooler), 500...image forming means (image forming transfer device), 601...post-conveying means (post-conveying roller unit), 702...driving means (belt drive motor), N1...fixing nip portion, N2...cooling nip portion, N3...conveying nip portion, S...recording material

Claims

1. an image forming means for forming a toner image on a recording material; a fixing means having a fixing nip portion for applying heat and pressure to fix the toner image to the recording material while nipping and conveying the recording material on which the toner image has been formed by the image forming means; a cooling means having a cooling nip portion that is disposed so as to be able to hold a recording material in a state where the recording material is held between the fixing means and that cools the recording material on which a toner image has been fixed by the fixing means while nipping and conveying the recording material; a post-conveying means disposed so as to be able to hold the recording material in a state where it is held between the cooling means and having a conveying nip portion for nipping and conveying the recording material cooled by the cooling means; a driving means for driving the cooling means; an acquisition means for acquiring information about the torque of the driving means; a control unit that controls the driving unit based on information about the torque and controls a cooling conveying speed at which the recording material is conveyed by the cooling unit, the control means sets the cooling conveying speed to a first speed that is faster than a fixing conveying speed at which the recording material is conveyed by the fixing means before the recording material reaches the fixing nip portion, and thereafter, when the torque exceeds a threshold value in a state in which the recording material is held in the fixing nip portion and the cooling nip portion, sets the cooling conveying speed to a second speed that is slower than the fixing conveying speed. An image forming apparatus characterized by:

2. the control unit detects torque at predetermined time intervals while the recording material is sandwiched in the fixing nip portion and the cooling nip portion after the cooling conveyance speed is set to the second speed, and if the torque is equal to or less than a threshold value, increases the cooling conveyance speed by a predetermined speed, and if the torque exceeds the threshold value, decreases the cooling conveyance speed by the predetermined speed.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. When the control means slows the cooling conveying speed to the predetermined speed, the control means controls the cooling conveying speed so that the cooling conveying speed does not fall below a predetermined lower limit speed.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. a rear conveying speed at which the recording material is conveyed by the rear conveying means is the first speed; the control unit controls the cooling conveying speed to be the first speed after the trailing edge of the recording material has passed through the fixing nip portion; 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. when the length of the recording material in the conveying direction is equal to or longer than a predetermined length at which the recording material is sandwiched between the fixing nip portion, the cooling nip portion, and the conveying nip portion, before the recording material reaches the fixing nip portion, the control means controls the post-conveying speed at which the recording material is conveyed by the post-conveying means to be substantially the same as the fixing conveying speed, and after the trailing edge of the recording material passes through the fixing nip portion, the cooling conveying speed to be a third speed slower than the post-conveying speed.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. when the length of the recording material in the conveying direction is shorter than the predetermined length, the control means controls the rear conveying speed of the rear conveying means to be the first speed before the recording material reaches the fixing nip portion, and controls the cooling conveying speed to be the first speed after the rear end of the recording material has passed through the fixing nip portion; 6. The image forming apparatus according to claim 5,

7. the control unit controls the cooling conveying speed to be the first speed after the trailing edge of the recording material has passed through the cooling nip portion; 7. The image forming apparatus according to claim 5, wherein the image forming apparatus is a recording medium.

8. the driving means is a motor, The information about the torque is a value of a current flowing through the motor.

8. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images