Image forming apparatus

Abstract

To provide an image forming apparatus that can transport recording material without creating loops in the recording material, even when torque fluctuations occur in the cooler in response to changes in the cooling transport speed during the transport of the recording material. [Solution] When the cooling drive torque reaches a torque threshold while the recording material is held between the fixing nip and the cooling nip (YES in S2), the cooling transport speed is changed to a second nominal speed that is slower than the fixing transport speed (S3). This makes it less likely for a loop to form in the recording material between the cooler and the rear transport roller when the rear end of the recording material passes through the fixing nip. The cooling transport speed is then increased or decreased (S4-S9) so that the cooling drive torque, which fluctuates with the change in the cooling transport speed, does not exceed the torque threshold. If the cooling drive torque does not exceed the torque threshold, the cooling transport speed will not temporarily become faster than the rear transport speed when the rear end of the recording material passes through the fixing nip, and therefore no loop will form in the recording material.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction peripheral using an electrophotographic method.

Background Art

[0002] In an electrophotographic image forming apparatus, a toner image formed on a recording material such as paper is fixed to the recording material by heating and pressurizing it with a fuser. In the fuser, the fixing of the toner image is performed by a fixing roller heated by a heater or the like and a pressure roller that forms a fixing nip portion that abuts on the fixing roller and sandwiches and conveys the recording material. Since the recording material is heated when passing through the fixing nip portion, the temperature of the recording material after passing through the fixing nip portion becomes high. When a large number of the recording materials conveyed at a high temperature after the fixing of the toner image are stacked on the stacking portion, there is a risk that the stacked recording materials will stick to each other due to the toner.

[0003] To suppress this, a cooler for cooling the recording material conveyed from the fuser is provided. The cooler has a conveyance belt (referred to as a cooling belt) cooled by a heat sink or the like, and lowers the temperature of the recording material through a cooling nip portion formed by the cooling belt. The recording material on which the toner image is fixed by the fuser is sandwiched and conveyed in a state where the leading end reaches the cooling nip portion before the trailing end passes through the fixing nip portion. Further, the recording material cooled by the cooler is sandwiched and conveyed in a state where the leading end reaches the post-conveyance roller portion before the trailing end passes through the cooling nip portion.

[0004] By the way, since the outer diameter of the fixing roller heated by a heater or the like may change due to thermal expansion, the conveyance speed of the recording material by the fuser (hereinafter referred to as the fixing conveyance speed) is likely to vary. Then, the recording material being conveyed curves between the transfer nip portion where the toner image is transferred and the fixing nip portion (so-called loop), and image defects such as gloss unevenness where the gloss of the toner image is disturbed occur. Therefore, a device has been proposed that performs speed control to increase or decrease the fixing conveyance speed to suppress the occurrence of a loop 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 Publication No. 2017-207648 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, conventionally, the fixing and transport speed is reduced, and the transport speed of the recording material by the cooler (hereinafter referred to as the cooling transport speed) becomes faster than the fixing and transport speed, resulting in a large speed difference between the two. In this case, the recording material is transported while being pulled away from the fixer by the cooling belt, so the torque of the cooling belt increases. If the torque of the cooling belt remains high and the trailing end of the recording material passes the fixing nip, the cooling transport speed may temporarily become faster than the transport speed of the recording material by the rear transport roller (hereinafter referred to as the rear transport speed). If this happens, a loop may form in the recording material between the cooler and the rear transport roller, potentially causing image defects due to the loop.

[0007] The present invention has been made in view of the above problems, and aims to provide an image forming apparatus that can transport recording material without creating loops in the recording material, even when torque fluctuations occur in the cooler in accordance with changes in the cooling transport speed during the transport of the recording material. [Means for solving the problem]

[0008] An image forming apparatus according to one embodiment of the present invention includes: an image forming means for forming a toner image on a recording material; a fixing means having a fixing nip section for fixing the toner image on the recording material by applying heat and pressure while clamping and transporting the recording material on which the toner image has been formed by the image forming means; a cooling means having a cooling nip section that is positioned to clamp the recording material while it is clamped by the fixing means, and for cooling the recording material while clamping and transporting the recording material on which the toner image has been fixed by the fixing means; a rear transport means having a transport nip section that is positioned to clamp the recording material while it is clamped by the cooling means, and for clamping and transporting the recording material that has been cooled by the cooling means; and a drive for the cooling means. The device comprises a driving means, 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 torque information and controlling the cooling transport speed for transporting the recording material by the cooling means, wherein, when the recording material is held between the fixing nip and the cooling nip, the control means, based on the torque information, sets the cooling transport speed to a first speed that is faster than the fixing transport speed for transporting the recording material by the fixing means if the torque is below a threshold, and sets the cooling transport speed to a second speed that is slower than the first speed if the torque exceeds the threshold. [Effects of the Invention]

[0009] According to the present invention, even if torque fluctuations occur in the cooling means in response to changes in the cooling transport speed during transport of the recording material, the recording material can be transported without creating loops in the recording material. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram showing an image forming system to which the image forming apparatus of this embodiment is applied. [Figure 2] (a) Cross-sectional view showing the image forming transfer apparatus, (b) Enlarged view showing the image forming section. [Figure 3] A schematic diagram showing a cooler. [Figure 4] A control block diagram illustrating the control unit. [Figure 5] A flowchart illustrating the speed control process of the first embodiment. [Figure 6] A graph showing the time variation of the cooling drive torque and cooling transport speed in the first embodiment. [Figure 7] A flowchart illustrating the speed control process of the second embodiment. [Figure 8] A graph showing the time variation of the cooling drive torque and cooling transport speed in the second embodiment. [Modes for carrying out the invention]

[0011] [First Embodiment] <Image Forming System> The following describes this embodiment. First, the schematic configuration of the image forming apparatus of this embodiment will be explained using Figures 1 and 2. The image forming system 1X shown in Figure 1 comprises an image forming apparatus 101, a large-capacity feeding device 106 having multiple recording material storage sections, and a sensing device 107. Regarding the transport direction of the recording material S by the large-capacity feeding device 106 (from right to left in Figure 1), the sensing device 107 is located downstream of the image forming apparatus 101.

[0012] In this specification, the side from which the user stands when operating the control unit 80 described later will be referred to as the "front (or front)," and the opposite side will be referred to as the "back (or rear)." Also, the left side when viewed from the front will be referred to as the "left," and the right side when viewed from the front will be referred to as the "right." Therefore, Figure 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 that the recording material S can be transported, but are also electrically connected so that electrical signals can be sent and received. 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 the 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 the shift in image density and image position based on the fed-back image signal and corrects the image data based on the detected shift in image density and image position. Then, based on the corrected image data, it controls the image forming units SY~SK to form a toner image on the recording material S.

[0014] Furthermore, 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, etc., can be selectively connected to the upstream side of the image forming apparatus 101 in the recording material transport direction. Alternatively, a large-capacity feeding device (not shown), a manual feeding device, a long-length feeding device, etc., can be selectively connected in multiple units further upstream of the large-capacity feeding device 106. In addition, one or more combinations of various post-processing devices (not shown), such as inserters, punchers, perfect binding machines, large-capacity stackers, folding machines, finishers, and trimmers, can be selectively connected to the downstream side of the image forming apparatus 101 or the sensing device 107. In this way, by selectively connecting a variety of optional devices upstream and downstream of the image forming apparatus 101, it becomes possible to output inline output of products with various post-processing treatments applied to recording materials S of various materials, thereby providing a highly productive, high-image-quality, highly stable, and highly functional image forming system 1X.

[0015] <Image forming apparatus> The image forming apparatus 101 is roughly divided into an image forming transfer apparatus 500 and a fixing conveyance apparatus 600 which are separately configured. In the case of this embodiment, the image forming transfer apparatus 500 as an image forming means has an image forming unit 200Y, 200M, 200C, 200K, an intermediate transfer belt unit 800, etc. that realize up to a transfer process of transferring a toner image onto a recording material S. On the other hand, the fixing conveyance apparatus 600 has a fixing device 8, a cooler 310, etc. that realize a fixing process of fixing a toner image onto the recording material S. These image forming transfer apparatus 500 and fixing conveyance apparatus 600 are connected so as to be able to transfer the recording material S.

[0016] The image forming transfer apparatus 500 and the fixing conveyance apparatus 600 each have independent casings 500A and 600A, and are movable by a plurality of casters provided respectively. Thereby, even if the image forming transfer apparatus 500 and the fixing conveyance apparatus 600 are large-sized apparatuses, it becomes possible to perform packing and transportation in a state where the casings 500A and 600A are separated, and the workability until installation is improved. In addition, on the casing 500A, an original reading device 160 that reads image information of an original, a display unit capable of displaying various information, an operation unit 80 having keys etc. that can input various information according to user operations, etc. are arranged.

[0017] The casings 500A and 600A are each composed of a plurality of frames such as a front side plate on the front side, a rear side plate provided on the rear side and supporting the image forming units 200Y to 200K, the intermediate transfer belt unit 800, the fixing device 8, the cooler 310, etc. together with the front side plate, and struts that connect the front side plate and the rear side plate or support the front side plate. Resin-made exterior covers that form the exterior are attached to such casings 500A and 600A. Incidentally, the image forming transfer apparatus 500 and the fixing conveyance apparatus 600 may be provided in one casing instead of separate casings (500A, 600A).

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

[0019] The transport process for the recording material S in the image forming transfer apparatus 500 will now be described. The recording material S is housed in one or more (two in this case) cassettes 212 and is supplied one sheet at a time by the supply roller 220 in accordance with the image forming timing. The recording material S supplied by the supply roller 220 is transported to the registration roller 213 located in the middle of the transport path 250. There, the registration roller 213 corrects the skewness and timing of the recording material S and sends the recording material S to the secondary transfer section ST. The secondary transfer section ST is formed by the secondary transfer inner roller 214 and the secondary transfer outer roller 215 facing each other on either side of the intermediate transfer belt 208, and is a transfer nip section 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] Next, we will explain the image formation process that takes place at the same timing as the transport process of the recording material S to the secondary transfer unit ST described above. First, we will explain the image forming units 200Y to 200K. However, since the image forming units 200Y to 200K for each color are basically the same except for the toner color, we will use the black image forming unit 200K as an example below.

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

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

[0023] The intermediate transfer belt 208 is an endless belt that is tensioned by multiple tension rollers and secondary transfer internal rollers 214, and is moved by a motor (not shown) or the like at a speed corresponding to the rotation speed of the photosensitive drums 201Y to 201K. The image formation process for each color, which is processed in parallel by the image forming units 200Y to 200K for each color as described above, is performed at the timing when the toner images of the colors that were primary transferred upstream in the direction of movement are sequentially superimposed on the intermediate transfer belt 208. As a result, a full-color toner image is ultimately formed on the intermediate transfer belt 208 and transported to the secondary transfer unit ST. The secondary transfer residue toner remaining on the intermediate transfer belt 208 after passing through the secondary transfer unit ST is recovered from the intermediate transfer belt 208 by a belt cleaner device 216. The primary transfer rollers 207Y to 207K, the intermediate transfer belt 208, multiple tension rollers, secondary transfer internal rollers 214, belt cleaner device 216, etc. may be provided integrally as an intermediate transfer belt unit 800.

[0024] Through the above transport and image formation processes, the timing of the recording material S and the toner image are synchronized in the secondary transfer section ST, and a secondary transfer is performed in which the toner image is transferred from the intermediate transfer belt 208 to the recording material S. Subsequently, the recording material S is transported to the fixing transport device 600 by the pre-fixing transport belts 217a and 217b, and the fixing transport device 600 fixes the toner image to the recording material S.

[0025] <Fusing and conveying device> Next, the fixing and transport device 600 will be described. As shown in Figure 1, the fixing and transport device 600 has a fuser 8 and a cooler 310. The fuser 8, as a fixing means, has a fixing roller 8a that is heated by a heater (not shown) and a pressure roller 8b that pressurizes the recording material S against the fixing roller 8a. The fixing roller 8a is rotationally driven by a fixing drive motor 700 (see Figure 4), which will be described later. The recording material S, on which a toner image has been formed, is transported from the image forming transfer device 500 and heated and pressurized while being held and transported in a fixing nip section N1 formed by the fixing roller 8a and the pressure roller 8b. As a result, the toner image is fixed to the recording material S. In this embodiment, a fixing outlet sensor 401 capable of detecting when the leading and trailing ends of the recording material S have passed through the fixing nip section N1 is positioned at the outlet of the fixing nip section N1 of the fuser 8 (downstream in the transport direction of the recording material S).

[0026] Here, a fuser 8 consisting of a pair of rollers, a fuser roller 8a and a pressure roller 8b, is shown as an example, but the example is not limited to this. For example, a fuser may have a fuser belt instead of a fuser roller 8a, and the recording material S may be heated and pressurized while being held and transported by a fuser nip formed by the fuser belt, which is heated by a heater, and the pressure roller 8b, thereby fixing a toner image to the recording material S.

[0027] The recording material S, heated by the fuser 8, is transported to the cooler 310, where it is cooled. The cooler 310 is positioned to hold the recording material S while it is held in place by the fuser 8 (specifically, the fuser nip section N1). The cooler 310 will be described later (see Figure 3).

[0028] The recording material S, cooled by the cooler 310, is gripped and transported by the rear transport roller section 601, which is located at the outlet of the cooling nip section N2 (downstream in the transport direction of the recording material S). The rear transport roller section 601, which serves as a rear transport means, has a pair of rollers that form a transport nip section N3 for gripping and transporting the recording material S, and is rotationally driven by a rear transport drive motor 701 (see Figure 4). The rear transport roller section 601 is positioned to grip the recording material S while it is being held by the cooler 310 (more specifically, the cooling nip section N2).

[0029] In single-sided mode, where a toner image is formed on only one side of the recording material S, the cooled recording material S is guided from the rear transport roller section 601 to the discharge transport path 304 and discharged from the housing 600A toward the sensing device 107. On the other hand, in double-sided mode, where a toner image is formed on both sides of the recording material S, the cooled recording material S is guided from the rear transport roller section 601 to the inversion transport path 305, where it is inverted, and then returned to the image forming transfer device 500 via the double-sided transport path 306. Thereafter, the recording material S undergoes the same process as in single-sided mode, and a toner image is fixed to the other side by the fuser 8. After cooling by the cooler 310, it is guided to the discharge transport path 304 and discharged from the housing 600A toward the sensing device 107.

[0030] <Cooler> Next, the cooler 310 will be described using Figure 3. As shown in Figure 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 section N2 that sandwiches and transports the recording material S between the first belt 21. For example, the first belt 21 and the second belt 25 are made of high-strength polyimide, with a thickness of "100 μm" and a circumference of "942 mm". The cooler 20 also has a heat sink 30 that cools the first belt 21.

[0031] The first belt 21 is wrapped around a drive roller 22a and several tension rollers 22b to 22e, and the second belt 25 is wrapped around a drive roller 26a and several belt tension rollers 26b to 26e. These drive rollers 22a and 26a are connected to a single belt drive motor 702 (see Figure 4) via a drive gear (not shown), and are rotationally driven 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 as the driving means.

[0032] On the inner circumference side of the second belt 25, pressure rollers 26f and 26g are provided to press the second belt 25 toward the heat sink 30. The pressure rollers 26f and 26g press the second belt 25 with a force of, for example, "9.8N (1kgf)", thereby ensuring that the first belt 21 is in firm contact with the heat sink 30 via the second belt 25.

[0033] The recording material S, on which the toner image has been fixed, is held between the first belt 21 and the second belt 25 and transported in the transport direction (direction of arrow C) as these belts circumferentially move. At this time, the recording material S passes through a cooling nip section 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 positioned to contact the inner surface of the first belt 21 at the location where the cooling nip section N2 is formed, in order to efficiently cool the recording material S. As the recording material S passes through the cooling nip section N2, it is cooled via the first belt 21, so 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 onto the recording material S. For example, the temperature of the recording material S rises to 90°C by the fuser 8 and then drops to 60°C by the cooler 310. At this time, the temperature of the toner image fixed on the recording material S also drops from 90°C to 60°C.

[0034] The heat sink 30 is a heat dissipation plate made of a metal such as aluminum. The heat sink 30 has a heat receiving section 30a that contacts the first belt 21 to absorb heat from the first belt 21, a heat dissipation section 30b for dissipating heat, and a fin base 30c for conducting heat from the heat receiving section 30a to the heat dissipation section 30b. The heat dissipation section 30b is formed of numerous heat dissipation fins to increase the contact area with air and promote efficient heat dissipation. In addition, a cooling fan 40 is provided to forcibly cool the heat sink 30 itself by blowing air toward the heat sink 30.

[0035] <Department Head> As shown in Figure 2, the image forming and transfer apparatus 500 is equipped with a control unit 300. The control unit 300, as a control means, performs various controls of the image forming apparatus 101, such as image forming operations. The control unit 300 will be explained using Figure 4 with reference to Figures 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, their illustration and explanation are omitted here as they are not the essence of the invention.

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

[0037] An image forming job is a series of operations from the start to the completion of an image forming operation based on a print signal for forming an image on a recording material S. In other words, it is a series of operations from the start of the preparatory operations necessary for image forming (so-called pre-rotation), through the image forming process, to the completion of the preparatory operations necessary for ending image forming (so-called post-rotation). Specifically, it refers to the period from the pre-rotation (preparatory operations before image forming) after receiving the print signal (receiving the image forming job) to the post-rotation (operations after image forming), including the image forming period and the time between sheets of paper.

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

[0039] Based on the detection results of the fuser exit sensor 401, the control unit 300 can detect, regarding the transport direction of the recording material S in the fuser 8, that the leading edge of the recording material S has passed the fuser nip section N1, and that the trailing edge of the recording material S has passed the fuser nip section N1. Furthermore, the control unit 300 can detect, according to the elapsed time since detecting that the trailing edge of the recording material S has passed the fuser nip section N1, that the trailing edge of the recording material S has passed the cooling nip section N2.

[0040] The control unit 300 controls the fixing drive motor 700 to start and stop the fixing roller 8a and control the fixing transport speed. The control unit 300 also controls the rear transport drive motor 701 to start and stop the rear transport roller section 601 and control the rear transport speed. Furthermore, the control unit 300 controls the belt drive motor 702 to start and stop the first belt 21 and control the cooling transport speed. In this embodiment, when the image forming job is started, the control unit 300 sets the cooling transport speed of the first belt 21 and the rear transport speed of the rear transport roller section 601 to a speed (referred to as the first nominal speed) that is 1.5% faster than the fixing transport speed of the fixing roller 8a. This makes it difficult for loops to form in the recording material S between the fuser 8 and the cooler 310, even when the recording material S is transported while sandwiched between the fixing nip section N1 and the cooling nip section N2.

[0041] An ammeter 501 is connected to the belt drive motor 702 to detect the current flowing through it. The control unit 300 has a belt torque detection unit 303 as an acquisition means for acquiring 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 torque. In this embodiment, the control unit 300 has a 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 the 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 torque and controls the cooling transport speed at which the cooler 310 transports the recording material S.

[0042] Incidentally, during the execution of the image forming job, depending on the length of the transport direction of the recording material S, there are cases in which the recording material S is transported while being held in the fixing nip section N1 and also held in the cooling nip section N2. In such cases, as mentioned above, if the cooling transport speed is faster than the fixing transport speed (first nominal speed), the recording material S is transported while being pulled away from the fuser 8 by the first belt 21, so the cooling drive torque increases.

[0043] When the rear end of the recording material S passes the fixing nip section N1 while the cooling drive torque is still increased, the tension on the recording material S is released. At that time, the first belt 21 rotates temporarily faster, causing the cooling transport speed to exceed the first nominal speed, and then return to the first nominal speed. When the cooling transport speed temporarily exceeds the first nominal speed in this way, a loop is created in the recording material S between it and the rear transport roller section 601 which is rotating at the first nominal speed, and this loop may cause loop marks or image defects on the recording material S. To prevent this, the cooling drive torque must be suppressed so that the cooling transport speed temporarily exceeds the first nominal speed at the point when the rear end of the recording material S passes the fixing nip section N1, in other words, before the tension on the recording material S is released.

[0044] <Speed ​​control processing> Therefore, in view of the above points, in this embodiment, the cooling drive torque is detected and the cooling transport speed is adjusted based on the detected cooling drive torque. The speed control process to achieve this will be described below with reference to Figures 1, 3, and 4, and with reference to Figures 5 and 6. Figure 5 is a flowchart of the speed control process of the first embodiment. Figure 6 is a graph showing the change in cooling drive torque over time for one recording material S, with the upper section showing the change in cooling transport speed over time for the lower section. 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, the control unit 300 determines, based on the detection result of the fixer exit sensor 401, that the leading edge of the recording material S has passed the fixer nip section N1 (time t0), and 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. When the cooler 310 is idle (until time t1), the cooling transport speed, along with the downstream transport speed, is set to a first nominal speed (first speed: for example, 450 mm / s) which is 1.5% faster than the fixer transport speed (for example, 443 mm / s). When the leading edge of the recording material S reaches the cooling nip section N2 (time t1), the recording material S is held between the fixer nip section N1 and the cooling nip section N2, and is pulled away from the fixer 8 by the first belt 21 as it is transported. From there, the cooling drive torque increases. The cooling drive torque during idle rotation is, for example, 200 mA. In this specification, torque values ​​are expressed using the current value of the belt-driven 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 the lower limit of the torque at which the cooling transport speed temporarily becomes faster than the rear transport speed when the rear end of the recording material S, which is pulled between the fuser 8 and the cooler 310, passes through the fuser nip section N1. For example, it is "500mA". That is, when the cooling drive torque exceeds the torque threshold and the rear end of the recording material S passes through the fuser nip section N1, a loop is likely to occur in the recording material S between the cooler 310 and the rear transport roller section 601.

[0047] If the cooling drive torque does not reach the torque threshold (NO in S2), the control unit 300 jumps to the process in step S11. On the other hand, if the cooling drive torque reaches the torque threshold (YES in S2), the control unit 300 controls the belt drive motor 702 to change the cooling transport speed to the second nominal speed (S3). The second nominal speed (second speed) is slower than the fixing transport speed (for example, 430 mm / s). 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 reduced, and the cooling drive torque becomes smaller. Therefore, when the rear end of the recording material S passes through the fixing nip section N1, it becomes less likely for a loop to form in the recording material S between the cooler 310 and the rear transport roller section 601.

[0048] However, if the second nominal speed is maintained as is, there is a risk that a loop may form in the recording material S between the fuser 8 and the cooler 310, so the cooling and transport speed must be increased again. Therefore, in order to prevent a loop from forming in the recording material S between the fuser 8 and the cooler 310, and to avoid increasing the cooling drive torque, it is necessary to ensure that the recording material S is properly pulled between the fuser 8 and the cooler 310.

[0049] After changing the cooling transport speed to the second nominal speed, the control unit 300 monitors whether the cooling drive torque exceeds the above torque threshold at predetermined intervals (e.g., 8 ms) (S4). If the cooling drive torque, which fluctuates with the change in cooling transport speed, exceeds the torque threshold (YES in S4), the control unit 300 controls the belt drive motor 702 to slow down the cooling transport speed by a predetermined speed, as long as the cooling transport speed does not fall below a predetermined lower limit speed (NO in S5) (S7). If the cooling transport speed falls below a predetermined lower limit speed (YES in S5), the control unit 300 sets the cooling transport 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 Figure 6, after changing the cooling transport speed to the second nominal speed (time t2), the cooling drive torque exceeds the torque threshold at times t3 and t4, which occur every 8ms. Therefore, at time t3, the cooling transport speed is reduced by a predetermined speed from the second nominal speed. Also, at time t4, when the cooling transport speed is reduced by a predetermined speed from the second nominal speed, the cooling transport speed falls below the lower limit speed, so the cooling transport speed is reduced to the lower limit speed. As the cooling transport speed is reduced in this way, the tension on the recording material S by the first belt 21 weakens, and the cooling drive torque decreases in accordance with the reduction in the cooling transport speed (times t3 to t5).

[0051] On the other hand, if the cooling drive torque is below the torque threshold (NO in S4), the control unit 300 controls the belt drive motor 702 to increase the cooling transport speed by a predetermined speed (S8). The predetermined speed for increasing the speed may be the same as the predetermined speed for decreasing the speed (4 mm / s). When the cooling drive torque decreases (times t3 to t5), the cooling drive torque falls below the torque threshold (time t5). Therefore, at time t5, the cooling transport speed is increased. When the cooling transport speed is increased in this way, the tension on the recording material S by the first belt 21 becomes stronger, so the cooling drive torque increases with the increase in the cooling transport speed (from time t5). As a result, it becomes less likely for loops to form in the recording material S between the fuser 8 and the cooler 310.

[0052] The control unit 300 determines whether the rear end of the recording material S has passed the fixing nip section N1 based on the detection result of the fixing exit sensor 401 (S9). If the rear end of the recording material S has not passed the fixing nip section N1 (NO in S9), the control unit 300 returns to step S4 and repeats the processing of steps S4 to S8 described above. In this way, the cooling transport speed is increased and decreased as described above, and the cooling drive torque is maintained at a torque that makes it difficult for loops to occur in the recording material S (times t2 to t8).

[0053] When the trailing end of the recording material S passes the fixing nip section N1 (YES in S9), the control unit 300 returns the cooling transport speed to the first nominal speed (S10). By returning the cooling transport speed to the first nominal speed (time t9), the next recording material S being transported is pulled away from the fuser 8 by the first belt 21, making it less likely for loops to form in the recording material S between the fuser 8 and the cooler 310.

[0054] The control unit 300 then determines whether or not image formation on the last recording material S in the currently running image formation job 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 terminates this speed control process.

[0055] As described above, in this embodiment, when the cooling drive torque reaches a torque threshold while the recording material S is held between the fixing nip section N1 and the cooling nip section N2, the cooling transport speed is changed to a second nominal speed that is slower than the fixing transport speed. This makes it less likely for a loop to form in the recording material S between the cooler 310 and the rear transport roller section 601 when the rear end of the recording material S passes through the fixing nip section N1.

[0056] Furthermore, when the recording material S is held between the fuser 8 and the cooler 310, the cooling transport speed is increased or decreased so that the cooling drive torque, which fluctuates with changes in the cooling transport speed, does not exceed the torque threshold. If the cooling drive torque does not exceed the torque threshold, the cooling transport speed will not temporarily become faster than the rear transport speed when the rear end of the recording material S passes through the fuser nip section N1. Therefore, when the rear end of the recording material S passes through the fuser nip section N1, no loop is formed in the recording material S between the cooler 310 and the rear transport roller section 601, thus preventing image defects caused by loops. In addition, even when the recording material S is held between the fuser 8 and the cooler 310, the cooling transport speed is increased or decreased based on the torque fluctuations of the cooling drive torque, preventing the formation of loops in the recording material S between the fuser 8 and the cooler 310.

[0057] In this embodiment, the control unit 300 is configured to determine that the leading or trailing end of the recording material S has passed the fixing nip section N1 based on the detection result of the fixing exit sensor 401, but it is not limited to this. For example, a fixing inlet sensor may be placed upstream of the fixing nip section N1, and it may be possible to detect that the leading or trailing end of the recording material S has passed the fixing inlet sensor based on the timing of the recording material S passing the fixing inlet sensor and the fixing transport speed. In addition, the cooling drive torque is detected based on the current value flowing through the belt drive motor 702 detected by the ammeter 501, but it 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] By the way, if the length of the recording material S in the transport direction is longer than the distance from the fuser 8 to the rear transport roller section 601, the recording material S will reach the rear transport roller section 601 while still being held by the fuser 8. In other words, the recording material S will be held by the fuser nip section N1, the cooling nip section N2, and the transport nip section N3. The gripping force of the rear transport roller section 601 is set to be weaker than that of the fuser 8 and stronger than that of the cooler 310. In this case, as mentioned above, if the rear transport speed is 1.5% faster than the fuser transport speed, the same as the cooling transport speed, the rear transport roller section 601 will be more prone to slipping over the held recording material S, thereby increasing the driving torque of the rear transport roller section 601.

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

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

[0061] Therefore, below, a speed control process that takes into account the control of the cooling transport speed when the transport length of the recording material S is longer than the distance from the fuser 8 to the rear transport roller section 601 will be explained with reference to Figures 1, 3, and 4, and using Figures 7 and 8. However, in the speed control process shown in Figure 7, steps S1 to S11 are the same as the speed control process of the first embodiment (see Figure 5), so the explanation will be omitted.

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

[0063] If the length of the recording material S in the transport direction is shorter than a predetermined length (NO in S21), the control unit 300 returns the cooling transport speed to the first nominal speed (S10). This process is the same as in the first embodiment described above, and since the cooling transport speed is returned to the first nominal speed (see time t9 in Figure 6), the next recording material S to be transported is pulled away from the fuser 8 by the first belt 21, making it less likely for loops to form in the recording material S between the fuser 8 and the cooler 310.

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

[0065] As described above, from the time the rear end of the recording material S passes through the fixing nip section N1 until it passes through the cooling nip section N2, in short, while the recording material S is not held by the fixing unit 8 and is held by the cooler 310 and the rear transport roller section 601, the cooling transport speed is made slower than the rear transport speed. That is, at the time the rear end of the recording material S passes through the fixing nip section N1, the cooling transport speed does not become faster than the rear transport speed, and at the time the rear end of the recording material S passes through the cooling nip section N2, the cooling transport speed becomes faster than the rear transport speed. This makes it less likely for a loop to form in the recording material S between the cooler 310 and the rear transport roller section 601 when the transport length of the recording material S is longer than the distance from the fixing unit 8 to the rear transport roller section 601. [Explanation of Symbols]

[0066] 8... Fixing means (fixer), 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... Rear transport means (rear transport roller section), 702... Drive means (belt drive motor), N1... Fixing nip section, N2... Cooling nip section, N3... Transport nip section, S... Recording material

Claims

1. Image forming means for forming a toner image on a recording material, A fixing means having a fixing nip section that holds and transports the recording material on which a toner image has been formed by the image forming means, and applies heat and pressure to fix the toner image to the recording material, A cooling means having a cooling nip section that is positioned to hold the recording material while it is held in place by the fixing means, and that cools the recording material while holding and transporting the recording material on which the toner image has been fixed by the fixing means, A rear transport means is provided which a recording material is positioned to be held between the cooling means and which has a transport nip portion for holding and transporting the recording material cooled by the cooling means, A driving means for driving the cooling means, An acquisition means for acquiring information regarding the torque of the drive means, The system includes a control means that controls the drive means based on information regarding the torque and controls the cooling transport speed for transporting the recording material by the cooling means, The control means, when the recording material is held between the fixing nip and the cooling nip, controls the torque information, If the torque is below a threshold, the cooling transport speed is set to a first speed that is faster than the fixing transport speed at which the fixing means transports the recording material. If the torque exceeds the threshold, the cooling and transport speed is set to a second speed that is slower than the first speed. An image forming apparatus characterized by the following features.

2. The control means, after setting the cooling transport speed to the second speed, detects the torque at predetermined intervals while the recording material is held between the fixing nip and the cooling nip, and if the torque is below a threshold, increases the cooling transport speed by a predetermined speed, and if the torque exceeds the threshold, decreases the cooling transport speed by a predetermined speed. The image forming apparatus according to feature 1.

3. The control means controls the cooling and transport speed so that it does not fall below a predetermined lower limit speed when the cooling and transport speed is reduced to a predetermined speed. The image forming apparatus according to feature 2.

4. The cooling and transport speed before the recording material reaches the fixing nip section is the first speed. The image forming apparatus according to feature 1.

5. The rear transport speed at which the recording material is transported by the rear transport means is the first speed. The control means controls the cooling and transport speed to the first speed after the rear end of the recording material has passed the fixing nip portion. The image forming apparatus according to any one of claims 1 to 4.

6. The control means, when the length of the recording material in the transport direction is greater than or equal to a predetermined length such that it is held between the fixing nip, the cooling nip, and the transport nip, sets the rear transport speed of the rear transport means to be approximately the same as the fixing transport speed before the recording material reaches the fixing nip, and controls the cooling transport speed to a third speed slower than the rear transport speed after the rear end of the recording material has passed the fixing nip. The image forming apparatus according to any one of claims 1 to 4.

7. The control means, when the length of the recording material in the transport direction is shorter than the predetermined length, sets the rear transport speed of the rear transport means to the first speed before the recording material reaches the fixing nip section, and controls the cooling transport speed to the first speed after the rear end of the recording material has passed the fixing nip section. The image forming apparatus according to feature 6.

8. The control means controls the cooling transport speed to the first speed after the rear end of the recording material has passed the cooling nip section. The image forming apparatus according to claim 6 or 7.

9. The aforementioned driving means is a motor, The information relating to the torque is the current value flowing through the motor. The image forming apparatus according to any one of claims 1 to 8.

10. The cooling means has a pair of belts, The image forming apparatus according to any one of claims 1 to 9.

11. The cooling means further comprises a heatsink and a fan. The image forming apparatus according to feature 10.

12. The cooling means further comprises a plurality of rollers that contact the inner circumferential surface of the pair of belts. The image forming apparatus according to claim 10 or 11.

Images