Image forming apparatus

Abstract

To prevent an image defect by eliminating wrinkles generated in a fixing member.SOLUTION: An image forming apparatus 1 comprises: a fixing unit 26 that has a first fixing member 261 having an elastic layer 62, a second fixing member 262 forming a fixing nip N1 with the first fixing member 261, and an external heating unit 263 heating the first fixing member 261 from the outside, and that applies heat and pressure to a conveyed recording material at the fixing nip N1 to fix an image on the recording material; and a control unit 21 that executes a thermal expansion mode. In the thermal expansion mode, the control unit 21 causes the external heating unit 263 to heat the first fixing member 261 to a temperature higher than the temperature during normal printing.SELECTED DRAWING: Figure 4A

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an electrophotographic image forming apparatus, an image is formed on a sheet by forming a toner image on the sheet and fixing the toner image on the sheet by a fixing device. The fixing device forms a fixing nip by pressing fixing members such as two rollers, passes the sheet through this fixing nip, and performs a fixing process of fixing the toner image on the sheet by heating and pressing the sheet (for example, Patent Document 1).

[0003] When transporting a sheet with irregularities in such a fixing nip, wrinkles (partial deformation) may occur on the surface of the fixing member, and the wrinkles on the surface of the fixing member cause image defects due to uneven fixing properties. For example, sheets with irregularities include wrinkled or bent sheets. Also, when using continuous paper as in Patent Document 1, for example, when reconnecting a sheet temporarily cut for paper jam processing, a seam is formed. At this seam portion, irregularities (steps) occur due to the tape used for adhesion or the overlapping of the front and rear sheets.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the image forming apparatus of Patent Document 1 does not regard the wrinkles of the fixing member as any problem, and there is no disclosure about eliminating the generated wrinkles.

[0006] This invention has been made in view of the above circumstances, and aims to provide an image forming apparatus that can suppress image defects by eliminating wrinkles that occur in the fixing member. [Means for solving the problem]

[0007] The above objectives of the present invention are achieved by the following means.

[0008] (1) An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, The control unit, in the thermal expansion mode, heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit, in the image forming apparatus.

[0009] (2) The image forming apparatus according to (1) above, wherein the control unit determines whether or not to perform the thermal expansion mode based on predetermined conditions set in advance.

[0010] (3) The image forming apparatus according to (2) above, wherein the control unit determines whether or not to perform the thermal expansion mode based on predetermined conditions, namely the printing conditions.

[0011] (4) Equipped with a reception unit that receives instructions from the user, The image forming apparatus according to (1) above, wherein the control unit causes the thermal expansion mode to be executed when it receives an execution instruction from the reception unit.

[0012] (5) Downstream of the fixing unit, a first detection unit is provided for detecting the image state on the recording material after fixing, or the transport state of the recording material. The image forming apparatus according to (1) above, wherein the control unit causes the thermal expansion mode to be executed according to the detection result of the first detection unit.

[0013] (6) A second detection unit for detecting the state of the first fixing member, The image forming apparatus according to (1) above, wherein the control unit causes the thermal expansion mode to be executed according to the detection result of the second detection unit.

[0014] (7) The image forming apparatus according to (6) above, wherein the control unit terminates the thermal expansion mode that is in progress according to the detection result of the second detection unit.

[0015] (8) The image forming apparatus according to (1) above, wherein the control unit determines whether or not to perform the thermal expansion mode based on the type or frequency of the transport malfunction of the recording medium.

[0016] (9) The external heating section is a rotating body in which a heating source is arranged inside and which rotates while being pressed against the outer surface of the first fixing member, The external heating section is further provided with a pressure setting mechanism for changing the pressure applied to the second fixing member, The image forming apparatus according to (1) above, wherein the control unit, when executing the thermal expansion mode, sets the contact pressure to a higher pressure than the pressure used during normal printing using the pressure setting mechanism.

[0017] (10) The device further includes a pressure release mechanism that moves at least one of the first fixing member and the second fixing member to separate the first fixing member and the second fixing member, The image forming apparatus according to (1) above, wherein the control unit separates the first fixing member and the second fixing member by the pressure release mechanism when executing the thermal expansion mode.

[0018] (11) The image forming apparatus according to (1) above, wherein the control unit sets the rotation speed of the second fixing member to a faster rotation speed than that during normal printing in the thermal expansion mode.

[0019] (12) The image forming apparatus according to any one of (1) to (11) above, wherein the recording material is continuous paper.

[0020] (13) The image forming apparatus according to any one of (1) to (11) above, wherein the thermal expansion mode is carried out during printing.

Advantages of the Invention

[0021] The image forming apparatus according to the present invention includes an image forming unit that forms an image on a recording material, a first fixing member having an elastic layer, a second fixing member that forms a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside. The apparatus further includes a fixing unit that fixes the image on the recording material by heating and pressing the conveyed recording material at the fixing nip, and a control unit that executes a thermal expansion mode. In the thermal expansion mode, the control unit causes the external heating unit to heat the temperature of the first fixing member to a temperature higher than the temperature during normal printing. This makes it possible to suppress image defects by eliminating wrinkles generated in the fixing member.

Brief Description of the Drawings

[0022] [Figure 1] It is a diagram showing a schematic configuration of an image forming apparatus according to the present embodiment. [Figure 2] It is a block diagram of an image forming apparatus. [Figure 3] It is a schematic diagram for explaining the configuration of a fixing unit. [Figure 4A] It is a flowchart showing a thermal expansion mode executed by the image forming apparatus in the first embodiment. [Figure 4B] It is a subroutine flowchart showing the process of step S11 (execution determination). [Figure 5] It is a subroutine flowchart showing the process of step S11 in Modification 1. [Figure 6] It is a subroutine flowchart showing the process of step S11 (execution determination) in Modification 2. [Figure 7] This is an example of a selection screen that accepts an instruction to execute the thermal expansion mode. [Figure 8] This is a subroutine flowchart showing the processing of step S11 in modified example 3. [Figure 9] This is a subroutine flowchart showing the processing of step S11 in modified example 4. [Figure 10] This is a subroutine flowchart showing the processing of step S11 in modified example 5. [Figure 11] This is a schematic diagram showing the configuration around the fixing part in the second embodiment. [Figure 12] This is a flowchart showing the thermal expansion modes performed in the image forming apparatus according to the second embodiment. [Figure 13] This is a schematic diagram showing the external heating elements separated. [Figure 14] This is a schematic diagram showing another example of the configuration of the external heating section. [Figure 15] This is a schematic diagram showing another example of the configuration of the external heating section. [Figure 16] This is a schematic diagram showing another example of the configuration of the external heating section. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described below with reference to the attached drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. Furthermore, although this embodiment describes an example in which continuous paper is used as the recording material, it is not limited to this, and cut paper (sheet paper) is also included as the recording material. In addition, the continuous paper may be a long label paper in which labels coated with adhesive are laminated onto a long release paper.

[0024] Figure 1 is a diagram showing the schematic configuration of the image forming apparatus 1 according to this embodiment. Figure 2 is a block diagram showing the hardware configuration of the image forming apparatus 1. As shown in Figure 1, the image forming apparatus 1 includes a supply device 10, an image forming apparatus body 20, an inspection device 30, and a winding device 40 that are mechanically and electrically connected to each other.

[0025] (Supplying device 10, winding device 40) The supply device 10 includes a folder 11 to which the main reel 90 of continuous paper 91 (also called roll paper) is detachably attached. The winding device 40 includes a folder 41 for winding up the continuous paper 91 fed from the main reel 90. The supply device 10 and the winding device 40 also include a control unit, a storage unit, a paper transport unit, and a communication unit (some components are not shown). These components have the same functions as the components of the image forming apparatus main body 20 with corresponding names, which will be described later. The supply device 10 feeds the continuous paper 91 from the main reel 90 attached to the folder 11 to the downstream side of the transport path. The image forming apparatus main body 20 performs image formation on the fed-out continuous paper 91. The continuous paper 91 with the image formed in the image forming apparatus main body 20 is transported to the winding device 40 via the downstream inspection device 30, where it is wound up and held in the folder 41. The supply device 10 and the winding device 40 work together to adjust the roll paper tension according to the thickness and type of continuous paper 91. For example, with thin paper, the roll paper tension is set lower compared to regular paper or thick paper.

[0026] (Image forming apparatus main body 20) As shown in Figures 1 and 2, the image forming apparatus body 20 comprises a control unit 21, a storage unit 22, an operation display unit 23, a paper transport unit 24, an image forming unit 25, a fixing unit 26, a surface state detection unit 27, and a communication unit 29, which are interconnected via signal lines.

[0027] (Control Unit 21) The control unit 21 is a CPU that controls each part of the device and performs various calculations according to the program.

[0028] (Storage unit 22) The memory unit 22 consists of a ROM for pre-storing various programs and data, a RAM for temporarily storing programs and data as a working area, and a hard disk for storing various programs and data.

[0029] (Operation display section 23) The operation display unit 23 is equipped with a touch panel, numeric keypad, start button, stop button, etc., and is used for displaying various information such as warnings, and for inputting various settings and instructions. In addition, the user can issue an instruction to execute the thermal expansion mode from an external PC via the operation display unit 23 or the communication unit 29. In this case, the operation display unit 23 or the communication unit 29 functions as a reception unit that receives the instruction to execute the thermal expansion mode.

[0030] The thermal expansion mode can be performed not only when not printing but also when printing. By heating the fixing member (first fixing member) having an elastic layer to a higher temperature than during (normal) printing, it is subjected to a state of thermal expansion that is more advanced than during normal printing. This refreshes the fixing member and eliminates wrinkles that have formed on its surface. The term "wrinkles" here refers to a concept that includes partial deformation of the fixing member. The same applies below. Hereafter, this will also be referred to as "fixing member wrinkles." Details of this thermal expansion mode will be described later.

[0031] (Paper transport section 24) The paper transport unit 24 is equipped with a transport path with multiple transport rollers and, in cooperation with the paper transport units of the supply device 10 and the winding device 40, transports the continuous paper 91 at a predetermined paper transport speed. Multiple sensors for detecting the state of the paper are placed on the transport path. In Figure 1, two sensors s1 and s2 are shown as representative examples. Each sensor (sensors s1, s2, etc.) detects the presence or absence of paper (cut paper) and the position of the paper. The control unit 21 detects transport defects such as jams related to the paper, including cut paper and continuous paper 91, based on the detection signals.

[0032] (Image forming unit 25) The image forming unit 25 forms an image, for example, by an electrophotographic method, and includes a writing unit, a developing unit, and a primary transfer unit corresponding to each of the basic colors (yellow, magenta, cyan, and black), as well as an intermediate transfer belt, a secondary transfer unit, etc. The toner images formed by developing each color in the developing unit are transferred onto the intermediate transfer belt (primary transfer) and sequentially layered to form a full-color toner image. The full-color (pre-fixing) toner image is transferred onto the continuous paper 91 by the secondary transfer unit. In this embodiment, an image forming unit using an intermediate transfer belt is illustrated, but an image forming unit using a direct transfer method that transfers directly from the photoreceptor drum to the paper without an intermediate transfer belt may also be used.

[0033] (Fixing section 26) Figure 3 is a schematic diagram illustrating the configuration of the fixing unit 26.

[0034] The fixing unit 26 fixes the toner image formed on the surface of the continuous paper 91 by heating and pressing the toner image with a fixing nip N1. As shown in Figure 3, the fixing unit 26 includes a pressurizing unit 261, a heating unit 262, an external heating unit 263, temperature sensors s5, s6, and s7, and a drive unit (not shown). The temperature sensors s5, s6, and s7 detect the surface temperature of the heating unit 262, the pressurizing unit 261, and the external heating unit 263, respectively. Multiple temperature sensors S5, S6, and S7 may be arranged in the axial direction (width direction). The pressurizing unit 261 and the heating unit 262 press against each other at a predetermined pressure to form the fixing nip N1. The drive unit consists of a motor as a drive source and a gear mechanism that transmits the driving force of the motor, and rotates at least one of the heating unit 262 or the pressurizing unit 261. For example, two motors drive the heating unit 262 and the pressurizing unit 261, respectively. In the example shown in Figure 3, the lower pressurizing section 261 functions as a first fixing member having an elastic layer, as will be described later, and the upper heating section 262 (particularly the upper pressurizing roller 53 and fixing belt 52, which will be described later) functions as a second fixing member.

[0035] (Heating section 262) The heating section 262 consists of a heating roller 51, a fixing belt 52, an upper pressure roller 53, an auxiliary roller 54, and a heater 55.

[0036] The heating roller 51 is a cylindrical metal roller with multiple heaters 55, such as halogen lamps, arranged inside. The multiple heaters 55 have different heat distributions (light distributions) in the axial direction. The heating roller 51, heated by the internal heaters 55, heats the fixing belt 52. The heated fixing belt 52 heats the paper (continuous paper 91) by passing through the fixing nip N1 together with the paper that has been transported to the fixing unit 26. The temperature sensor s5 is positioned opposite the fixing belt 52 in a non-contact manner. The temperature sensor s5 detects the surface temperature of the fixing belt 52 heated by the heaters 55. In the fixing unit 26, the power supply to the heaters 55, i.e., the ignition rate of the heaters 55, is controlled by the control unit 21 so that the temperature detected by the temperature sensor s5 reaches a predetermined control temperature (fixing temperature). The control temperature is set to 160 to 200°C under standard conditions (during image formation) (it may be set to a different temperature depending on the basis weight and thickness of the paper).

[0037] The endless fixing belt 52 is stretched by a heating roller 51, an upper pressure roller 53, and an auxiliary roller 54. The fixing belt 52 is, for example, roughly the size of an inner diameter of 168 mm. The fixing belt 52 is composed of, for example, an endless base body with a thickness of 70 μm made of conductive PI (polyimide), an elastic layer of heat-resistant silicone rubber with a thickness in the range of 100 to 400 μm provided on its outer surface, and a PFA (perfluoroalkoxy) tube, which is a heat-resistant resin, formed by covering the upper layer with a PFA tube with a thickness in the range of 10 to 40 μm (hereinafter also referred to as the PFA tube layer).

[0038] The upper pressure roller 53 has, for example, an outer diameter of 90 mm. The upper pressure roller 53 is composed of, for example, a cylindrical core made of a metal such as iron, and a 20 mm thick elastic layer made of heat-resistant solid rubber, such as silicone rubber, on its outer surface.

[0039] The auxiliary roller 54 is made of small-diameter metal or metal covered with heat-resistant rubber. The auxiliary roller 54 also functions as a tension roller, applying a predetermined pressure outward and moving within a predetermined range of motion. The auxiliary roller 54 may be omitted in the configuration.

[0040] (Pressurized section 261) The pressurizing section 261 is also called the lower pressurizing roller or lower roller. The pressurizing section 261, which functions as the first fixing member, has, for example, an outer diameter of 80 mm. The pressurizing section 261 is composed of, for example, a cylindrical core metal 61 made of a metal such as iron, an elastic layer 62 made of heat-resistant solid rubber such as silicone rubber with a thickness of several mm (for example, 6 mm) on its outer surface, and a 30 μm thick PFA layer 63 formed by covering it with an upper layer of PFA tube.

[0041] (External heating section 263) The external heating section 263 consists of a cylindrical metal roller 71 and a heater 72 placed inside it as a heat source such as a halogen lamp. The external heating section 263 is a rotating body and is pressed against the outer surface of the pressurizing section 261 at a predetermined pressure, and rotates in accordance with the rotation of the pressurizing section 261. The temperature sensor s6 is positioned opposite the external heating section 263 in a non-contact manner and detects the surface temperature of the external heating section 263 heated by the heater 72. The temperature sensor s7 is positioned opposite the pressurizing section 261 in a non-contact manner and detects the surface temperature of the pressurizing section 261. If the temperature sensor s7 detects a temperature exceeding the upper limit temperature T9, the power supply to the heater 72 may be stopped regardless of the temperature detected by the temperature sensor s6. The heater 72 may also consist of multiple heaters 72 having different heat distributions in the axial direction. For example, the system is composed of two heaters 72 with heat distribution biased towards the front and back sides in the axial direction, and the heater 72 to be used is selected according to the location where wrinkles occur in the fixing member. For example, in the modified examples 3 and 4 described later, which use the first and second detection units, the location where wrinkles occur in the fixing member in the axial direction can be estimated.

[0042] In the fixing unit 26, the power supply to the heater 72, that is, the lighting rate of the heater 72, is controlled by the control unit 21 so that the detected temperature of the sensor s6 becomes the control temperature T0 during normal printing (a concept including the standby time of preheating; the same applies hereinafter), and becomes the control temperature T1 (where the control temperature T0 < T1) in the thermal expansion mode. The control temperatures T0 and T1 may have a predetermined temperature range. Also, in the thermal expansion mode, by setting the control temperature T1 higher than the control temperature T0 during normal printing, the pressurizing unit 261 is heated to a higher temperature than during normal printing. The elastic layer 62 or the PFA layer 63 of the pressurizing unit 261 (lower pressurizing roller) is refreshed and the wrinkles of the fixing member are eliminated by being in a state where thermal expansion has progressed more than during normal printing. Note that the control temperature T0 during normal printing may be the room temperature. In this case, during normal printing, the heater 72 is always OFF. The control temperature T1 is preferably set to a temperature higher than the average temperature or saturation temperature that the surface of the pressurizing unit 261 reaches by heat conduction from the fixing nip N1 (due to the heat caused by the heater 55) during normal printing (long-time continuous printing). For example, the control temperature T1 is set to a temperature sufficiently higher than the average temperature of 90 to 100°C that the surface of the pressurizing unit 261 reaches. For example, by setting the control temperature T1 to 200°C, the surface temperature of the pressurizing unit 261 is controlled to a higher temperature of 140 to 160°C than normal.

[0043] (Surface state detection unit 27) The surface state detection unit 27 functions as a second detection unit and detects the surface state of the pressurizing unit 261. For example, the surface state detection unit 27 includes a laser displacement meter, and measures the state of the surface of the pressurizing unit 261 with this. When the presence of a step or unevenness greater than a predetermined level is detected, it is determined that wrinkles have occurred on the surface of the fixing member. For example, when there are local irregularities or steps of several to several tens of μm or more (for example, 15 μm or more) with respect to the average position (height distance) of the surface, it is determined that wrinkles have occurred on the surface of the fixing member. As another example, the surface state detection unit 27 may be composed of a camera having a light source and an imaging element such as a CCD. In this case, the surface state detection unit 27 photographs the surface state of the pressurizing unit 261 and analyzes the photographed image to detect the occurrence of wrinkles on the surface of the pressurizing unit 261.

[0044] (Communications Section 29) The communication unit 29 is an interface for communicating with other devices such as the supply device 10 and the winding device 40. The communication unit 29 also serves as an interface for network connection with external devices such as a PC.

[0045] (Inspection device 30) The inspection device 30 comprises a control unit 31, a storage unit 32, a reading unit 33, a paper transport unit 34, and a communication unit 39, which are interconnected via signal lines. The control unit 31, storage unit 32, paper transport unit 34, and communication unit 39 have functions similar to the corresponding named components of the control unit 21, storage unit 22, paper transport unit 24, and communication unit 39.

[0046] The inspection device 30, or the control unit 31 and reading unit 33 of the inspection device 30, functions as a first detection unit. The first detection unit determines the paper transport status and sends the determination result to the control unit 21. The control unit 21 of the image forming apparatus main body 20 determines whether or not to execute the thermal expansion mode, as described later, according to the determination result.

[0047] The reading unit 33 is a so-called scanner and consists of a first reading unit 33a located above the transport path and a second reading unit 33b located below it. The first reading unit 33a located above reads the image on the image-forming surface in single-sided mode, or the back side (second side) in double-sided mode. The reading unit 33b located below reads the image on the front side (first side) in double-sided mode. In double-sided mode, when cut paper is used as the paper, the image forming unit 25 and the fixing unit 26 of the image forming apparatus body 20 form the image on the first side, and then the second side is formed via a double-sided transport path (not shown), thereby forming an image on both sides of the paper.

[0048] The first reading unit 33a (and the second reading unit 33b similarly) reads the image formed on the paper (continuous paper 91, etc.) by the image forming apparatus body 20 and generates a read image (also called read image data). The first reading unit 33a includes a sensor array, an optical system, and an LED light source. The sensor array is a color line sensor in which multiple optical elements such as CCDs are arranged in a line along the width direction (main scanning direction), and is capable of reading the entire width range of the continuous paper 91 (or cut paper) in the width direction. The optical system consists of multiple mirrors and lenses. Light from the LED light source illuminates the surface of the continuous paper 91 as it passes the reading position on the main transport path. The image of the reading position is guided by the optical system and formed on the sensor array.

[0049] (State determination unit) The control unit 31 functions as a state determination unit and determines the image state and / or transport state. The control unit 31 (state determination unit) analyzes the read image obtained by reading the continuous paper 91 with the reading unit 33 (mainly the first reading unit 33a) and determines the image state. For example, the control unit 31 compares the image density of the read image with the density expected from the image signal of the source data (normal density) in a certain area on the paper, and determines the image state as image defect or normal depending on the level of insufficient density or periodic unevenness of density. Image defects to be determined include periodic image unevenness corresponding to the rotation period of the fixing member caused by wrinkles that occur in the fixing member (especially the first fixing member) of the fixing unit 26, and image defects caused by wrinkles in the paper itself. In addition, as a transport state, the control unit 31 detects the widthwise edge of the continuous paper 91 from the read image and determines whether transport is being performed normally. If paper wrinkles occur near the edge, the presence of paper wrinkles can be detected by detecting the edge. The control unit 31 of the inspection device 30 sends the detection result of the image state on the continuous paper 91 after fixing, or the transport state of the continuous paper 91, based on the read image, to the control unit 21 of the image forming apparatus main unit 20. The control unit 21 determines whether or not to execute the thermal expansion mode according to the detection result.

[0050] The inspection device 30 may be equipped with, or in place of, the scanner described above, a CCD camera, a density meter, or a laser displacement meter, and may be configured to detect the image state of the paper or the paper transport state based on the detection data.

[0051] (Thermal expansion mode in the first embodiment) Next, with reference to Figures 4A to 10, the thermal expansion modes performed in the image forming apparatus 1 in the first embodiment will be described.

[0052] Here, we will explain the wrinkles in the fixing member of the fixing section 26 that are improved by the thermal expansion mode. The pressurized section 261 (first fixing member) is covered with a PFA tube (PFA layer 63) as the uppermost layer (surface layer). When paper with a step, such as wrinkled paper or continuous paper 91 with seams, is passed through the fixing nip N1, wrinkles occur on the surface of the pressurized section 261 due to the step. That is, wrinkles occur in the PFA layer 63. These wrinkles are more likely to occur the thinner the PFA layer 63 is, and also the thicker the elastic layer 62 (silicone rubber layer) of the pressurized section 261 (first fixing member). Furthermore, the lower the temperature of the pressurized section 261 when the step passes, the more likely wrinkles are to occur (and the more likely they are to remain as wrinkles). Normally, during printing, the heating unit 262 is controlled to reach a predetermined control temperature (fixing temperature) by heating with the heater 55 in order to fix the toner image, but the pressurizing unit 261 is not actively heated. During printing, it is only warmed to some extent by heat conduction through the fixing nip N1. Therefore, normally, the pressurizing unit 261 is at a lower temperature than the heating unit 262. Due to these configuration and temperature conditions, wrinkles are more likely to occur in the fixing member of the pressurizing unit 261 (lower pressurizing roller) than in the fixing belt 52, and when wrinkles occur in the fixing member, they tend not to return to their original state immediately and easily, but remain as wrinkles (recognized as a wrinkle phenomenon). These fixing member wrinkles cause uneven fixing, resulting in image defects. In this embodiment, the image forming apparatus 1 executes the following thermal expansion mode for eliminating fixing member wrinkles in order to suppress the occurrence of image defects due to fixing member wrinkles. Figure 4A is a flowchart of the thermal expansion mode.

[0053] (Step S11) The control unit 21 of the image forming apparatus main body 20 (image forming apparatus 1) determines whether or not to execute the thermal expansion mode. Figure 4B is a subroutine flowchart showing the process of step S11.

[0054] (Step S101) In step S101, the control unit 21 determines whether the image forming apparatus 1 satisfies predetermined conditions based on the conditions stored in the memory unit 22. For example, (1) when the power to the image forming apparatus 1 is turned ON, or (2) each time the drive distance of the fixing unit 26 reaches a certain distance, for example, each time the paper transport distance (also called the nip travel distance) reaches a determination threshold (e.g., 100m), or each time the number of printed sheets in cut paper reaches a determination threshold (e.g., 2000 sheets). Note that the determination thresholds related to the drive distance (transport distance, number of printed sheets) may be changed by the user via the operation display unit 23.

[0055] If the control unit 21 determines that the predetermined conditions are met (YES), it proceeds to step S102. On the other hand, if the predetermined conditions are not met (NO), it terminates the subroutine processing in Figure 4B and the main processing in Figure 4A (circled number 20).

[0056] (Step S102) When the control unit 21 receives instructions from the user and satisfies predetermined conditions, it terminates (returns) the subroutine flowchart in Figure 4B and starts executing the thermal expansion mode shown in steps S12 to S16 of the main flowchart in Figure 4A.

[0057] (Step S12) If the fixing unit 26, including the control unit 21 and the pressurizing unit 261 (lower pressurizing roller), is not rotating, the drive is started. If it is already rotating, such as during printing, the drive is continued. In the first embodiment, the thermal expansion mode is executed whether printing is in progress or not.

[0058] (Step S13) The control unit 21 changes the control temperature T0 of the external heating unit 263 to a higher control temperature T1. Power supply to the heater 72 is controlled to achieve this control temperature T1.

[0059] (Step S14) The control unit 21 determines whether or not the termination condition has been met. For example, the control unit 21 determines that the termination condition has been met when the elapsed time since the start of the thermal expansion mode has reached a predetermined time (e.g., 1 to several minutes). The elapsed time may also be determined by the time elapsed since the control temperature T1 was first reached after the start of the thermal expansion mode (or since power supply to the heater 72 was started). If the termination condition has not been met (NO), the thermal expansion mode continues. On the other hand, if the termination condition is met (YES), the control unit 21 proceeds to step S15.

[0060] (Step S15) Here, the control temperature T1 is returned to the lower control temperature T0. This stops the power supply to the heater 72.

[0061] (Step S16) If printing is not currently in progress, the drive of the fixing unit 26, including the pressure unit 261 (lower pressure roller), is stopped and the process ends (end).

[0062] Thus, in the thermal expansion mode, the image forming apparatus according to the first embodiment raises the temperature of the first fixing member to a higher temperature than the temperature during normal printing, using an external heating unit. This increases the thermal expansion of the first fixing member (especially the thermal expansion of the elastic layer) compared to printing, thereby eliminating fixing member wrinkles that occur on the first fixing member and suppressing image defects.

[0063] In particular, in the first embodiment, the thermal expansion mode is performed by heating the external heating unit 263, so it can be performed regardless of whether printing is in progress. Therefore, productivity does not decrease even when the thermal expansion mode is performed. Especially when continuous paper is used, the thermal expansion mode can be performed without removing the continuous paper from the fixing unit 26, so it does not lead to a deterioration in workability. In particular, in this embodiment, the first fixing member (pressure unit 261) that is heated and thermally expanded by the external heating unit 263 is a lower pressure roller located on the back side opposite to the side of the recording material on which the toner image to be fixed is formed. Therefore, even if the temperature is raised during normal printing, there is almost no effect on the image (image after fixing) or transportability. Also, in the first embodiment, the image forming apparatus 1 makes a decision based on whether or not predetermined conditions are met (Figure 4B), so it can be performed without providing any special input device or detection unit.

[0064] (Variations 1 to 5) In the first embodiment shown in Figures 4A and 4B, the image forming apparatus 1 determined whether or not the thermal expansion mode could be executed by determining whether or not the operating state of the image forming apparatus 1 met predetermined conditions. However, the image forming apparatus 1 is not limited to this, and may determine whether or not the mode can be executed by the methods shown in the following modified examples.

[0065] (Example 1 (Print Conditions)) Figure 5 is a subroutine flowchart showing the processing of step S11 in Modification Example 1. Modification Example 1 is performed at the start of printing or during printing. A print job that is accepted for execution includes print data (image data) and print setting data called a job ticket. The print settings include information on the type of paper to be used (paper thickness (basis weight), paper type, paper brand), and information on the number of sheets to print (in the case of cut sheets) or the number of pages to print (in the case of continuous paper). In addition, the temperature and humidity of the surrounding environment may be obtained by a temperature and humidity sensor (not shown) placed inside the housing of the image forming apparatus 1.

[0066] (Steps S151, S152) The control unit 21 obtains the print settings for the print job to be executed. At the same time, it obtains the temperature and humidity inside the machine using the temperature and humidity sensor (not shown) of the image forming apparatus 1.

[0067] The control unit 21 determines whether or not to execute the thermal expansion mode based on one of the following print conditions 1 to 3. (Condition 1) Cardboard with a specified basis weight or greater (e.g., 300 g / m²) 2 When performing a print job using cut sheets of uncoated paper, there is a high possibility that unevenness or wrinkles will occur in the pressure section 261 due to the step at the leading edge of the cardboard. (Condition 2) Thin paper with a basis weight of less than or equal to the specified amount (e.g., 100 g / m²) 2 When performing a print job using the continuous paper described below, the roll paper tension is set to 15N or less. In this case, paper wrinkles are more likely to occur, and the resulting step in the paper wrinkles is likely to pass through the fuser nip N1, causing wrinkles in the fuser member. (Condition 3) The temperature and humidity sensor detects high humidity (e.g., 80% RH or higher), and the paper is thin (e.g., 100 g / m² basis weight). 2 When performing a continuous paper print job using the following method: In this case, if the paper is left unattended in a high-humidity environment, the paper may warp, causing wrinkles in the paper and, consequently, wrinkles in the fixing material.

[0068] The control unit 21 uses at least one of conditions 1 to 3 and determines that the conditions for executing the thermal expansion mode are met for every predetermined number of printed sheets / or every predetermined transport distance if conditions 1 to 3 are met.

[0069] For example, if condition 1 is used, the control unit 21 determines that the conditions for executing the thermal expansion mode are met each time the number of printed sheets of cut paper reaches a predetermined number (for example, 2000 sheets) when condition 1 is satisfied.

[0070] If conditions 2 and 3 are used, the control unit 21 determines that the conditions for executing the thermal expansion mode are met each time the continuous paper transport distance reaches a predetermined distance (e.g., 100 m) when either condition 2 or condition 3 is met.

[0071] The control unit 21 determines, based on one of the above judgments, whether the conditions for executing the thermal expansion mode are met according to the print conditions. If the conditions are met (YES), the process proceeds to step S153. On the other hand, if the conditions are not met (NO), the subroutine processing in Figure 5 and the main processing in Figure 4A are terminated.

[0072] (Step S153) The control unit 21 terminates (returns to) the subroutine flowchart in Figure 5 and starts executing the thermal expansion mode shown in steps S12 to S16 of the main flowchart in Figure 4A.

[0073] In this modified example 1, the feasibility of executing the thermal expansion mode is determined according to the printing conditions, so that wrinkles in the fixing material can be eliminated at a more appropriate timing, and image defects can be suppressed.

[0074] (Example 2 (User Instructions)) Figure 6 is a subroutine flowchart showing the processing of step S11 in Modification Example 2. Modification Example 2 is performed not only during printing but also outside of printing.

[0075] (Step S201) In step S201, the control unit 21 displays a button to accept the thermal expansion mode on the operation display unit 23 or on the PC display in response to user input. Figure 7 shows an example of the selection screen d1 displayed on the operation display unit 23. The user can instruct the system to execute the thermal expansion mode (refresh mode) by operating the "Yes" button. Alternatively, instead of the operation display unit 23, a dedicated hard switch may be provided, and the system may accept instructions to execute the thermal expansion mode by the user operating this switch. If the control unit 21 receives an instruction from the user to execute the thermal expansion mode (YES), it proceeds to step S202. For example, a user familiar with the equipment, such as one working in a print shop, may visually inspect the printed material (continuous paper 91) and determine that an image defect caused by wrinkles in the fixing member has occurred, instructing the system to start the thermal expansion mode. On the other hand, if the system does not accept an execution instruction from the user (NO), the system terminates the subroutine processing in Figure 6 and the main processing in Figure 4A.

[0076] (Step S202) The control unit 21, upon receiving instructions from the user or fulfilling other predetermined conditions, terminates (returns to) the subroutine flowchart in Figure 6 and starts executing the thermal expansion mode shown in steps S12 to S16 of the main flowchart in Figure 4A.

[0077] Thus, in Modification 2, the same effects as in the first embodiment can be obtained, and by performing the modification only when instructed by the user, the thermal expansion mode can be performed only when necessary.

[0078] (Modified example 3 (first detection unit)) Figure 8 is a subroutine flowchart showing the processing of step S11 in Modification 3. Modification 3 is performed during printing, and the processing of step S11 is executed at predetermined intervals, for example, each time the image of each page image is formed.

[0079] (Step S301) The control unit 21 acquires detection results from the first detection unit (inspection device 30). Specifically, as described above, the first detection unit generates detection results for the image state or transport state by analyzing the read image obtained by optically reading the continuous paper 91. The inspection device 30 then transmits these detection results to the image forming apparatus main unit 20.

[0080] (Step S302) The control unit 21 determines whether the conditions for executing the thermal expansion mode are met based on the detected image state or transport state. If the conditions are met (YES), the process proceeds to step S303. For example, if the control unit 21 determines, based on the detection results, that image irregularities caused by the fixing member have occurred or are highly likely to occur as an image state, or that paper wrinkles have occurred as a transport state, it determines that the conditions for executing the thermal expansion mode are met. On the other hand, if the conditions are not met (NO), the subroutine processing in Figure 8 and the main processing in Figure 4A are terminated.

[0081] (Step S303) The control unit 21 terminates (returns to) the subroutine flowchart in Figure 8 and starts executing the thermal expansion mode shown in steps S12 to S16 of the main flowchart in Figure 4A.

[0082] Thus, in Modification 3, the same effects as in the first embodiment can be obtained, and the thermal expansion mode is executed at a more appropriate timing depending on the image state or transport state, thereby suppressing the occurrence of image defects.

[0083] (Modified example 4 (second detection unit)) Figure 9 is a subroutine flowchart showing the process of step S11 in Modification 4. Modification 4 can be performed not only during printing but also outside of printing. Note that fixing member wrinkles are more likely to occur when the pressurizing section 261 is at a low temperature. For example, if the image forming apparatus 1 has not been used for a long time and the entire fixing section 26 is at a temperature close to room temperature when use begins (a so-called cold start), the pressurizing section 261 will not be sufficiently warmed up for a predetermined time, for example, less than 30 minutes after the heating of the fixing section 26 begins, and fixing member wrinkles are more likely to occur. Therefore, it is preferable to perform the process of Modification 4 within a predetermined time from the cold start.

[0084] (Step S401) The control unit 21 acquires the detection result from the second detection unit. Specifically, as described above, the surface state detection unit 27, which functions as the second detection unit, detects the surface state of the pressurizing unit 261, and the control unit 21 acquires this detection result.

[0085] (Step S402) The control unit 21 determines whether the conditions for executing the thermal expansion mode are met based on the surface condition detected. If the conditions are met (YES), the process proceeds to step S403. For example, if the control unit 21 determines that wrinkles have occurred in the fixing member based on the detection results, it determines that the conditions for executing the thermal expansion mode are met. On the other hand, if the conditions are not met (NO), the subroutine processing in Figure 9 and the main processing in Figure 4A are terminated.

[0086] (Step S403) The control unit 21 terminates (returns) the subroutine flowchart in Figure 9 and starts executing the thermal expansion mode shown in steps S12 to S16 of the main flowchart in Figure 4A. In this modified example 4, the termination condition may be the elimination (healing) of wrinkles in the fixing member. Specifically, in modified example 4, even while the thermal expansion mode is being executed, the second detection unit performs detection and determines that the termination condition in step S14 of Figure 4A is met when the wrinkles in the fixing member disappear.

[0087] In this modified example 4, the feasibility of executing the thermal expansion mode is determined according to the state of the fixing member, so that wrinkles in the fixing member can be eliminated at a more appropriate timing, thereby suppressing image defects.

[0088] (Variation 5 (Transportation malfunction)) Figure 10 is a subroutine flowchart showing the processing of step S11 in Modification Example 5. Modification Example 5 is performed during printing.

[0089] (Step S501) If the control unit 21 detects a predetermined type of transport malfunction within the image forming apparatus body 20 using sensors s1, s2, etc. during printing (YES), it determines that the thermal expansion mode should be executed and proceeds to step S502.

[0090] The specified types of transport malfunctions include transport jams in the fuser unit 26, double feeding when using cut paper, feeding the wrong media, or transporting continuous paper in a twisted state. Double feeding refers to the feeding of multiple cut sheets stacked on top of each other from the paper tray. Feeding the wrong media refers to the case where the paper type specified in the print settings differs from the paper type actually used. The paper type actually used is determined from the detection data of the media detection sensor placed in the paper transport path. Furthermore, the thermal expansion mode may be executed if the same type of transport malfunction occurs more than a predetermined number of times (for example, two or more times) within a predetermined period (within a predetermined transport distance or within a predetermined number of prints).

[0091] (Step S502) The control unit 21 terminates (returns to) the subroutine flowchart in Figure 10 and starts executing the thermal expansion mode shown in steps S12 to S16 of the main flowchart in Figure 4A.

[0092] In this modified example 5, the feasibility of executing the thermal expansion mode is determined in response to transport malfunctions, allowing for the elimination of wrinkles in the fixing member at a more appropriate timing and suppression of image defects.

[0093] (Second embodiment) In the first embodiment, the thermal expansion mode could be executed regardless of whether printing was in progress or not. In the second embodiment shown below, the thermal expansion mode is executed with the fixing nip N1 released by separating the fixing members when not printing.

[0094] Figure 11 is a schematic diagram showing the configuration around the fixing unit in the second embodiment, and Figure 12 is a flowchart showing the thermal expansion modes performed by the image forming apparatus in the second embodiment. Configurations other than those shown in Figures 11 and 12 are the same as in the first embodiment and will not be described. Note that Figure 11 corresponds to Figure 3, but in Figure 11, some reference numerals and the surface state detection unit 27 are omitted.

[0095] In the second embodiment, the image forming apparatus 1 (image forming apparatus body 20) includes a moving mechanism 28a and a crimping release mechanism 28b.

[0096] The moving mechanism 28a includes a biasing part such as a spring, a drive source such as a drive motor, a cam, an arm, etc. The moving mechanism 28a holds both ends of the rotation axis of the external heating unit 263 and changes the pressure applied to the pressurizing unit 261. For example, it is set to pressure p0 during normal printing and to pressure p1 during thermal expansion mode. Here, pressure p0 < pressure p1. For example, pressure p0 is 20N and pressure p11 is 100N. These pressures are sufficiently lower than the pressure px at the fuser nip N1. Furthermore, the moving mechanism 28a may also be set to a non-contact separated state by moving the external heating unit 263 away from the pressurizing unit 261 (Figure 13, described later).

[0097] The crimp release mechanism 28b similarly includes a biasing part such as a spring, a drive source such as a drive motor, a cam, an arm, etc. The crimp release mechanism 28b applies pressure between the pressurizing part 261 and the heating part 262, and sets the pressing force at that time to a predetermined pressure px. For example, the pressure px is 1000N. The crimp release mechanism 28b also switches the state of the fixing nip N1 between a pressed state and a separated state by moving at least one of the pressurizing part 261 and the heating part 262 (at least one of the first and second fixing members) away from the other. Figure 11(a) shows the pressed state, and Figure 11(b) shows the separated state. Figure 11(b) shows an example in which both the pressurizing part 261 and the heating part 262 are separated by moving them up and down (in the direction of the arrow).

[0098] (Thermal expansion mode in the second embodiment) (Step S81) Here, the control unit 21 of the image forming apparatus main body 20 (image forming apparatus 1) determines whether or not to execute the thermal expansion mode. The process of step S81 in Figure 12 is equivalent to the process of step S11 shown in Figure 4A, and is executed by any of the subroutine flowcharts in Figures 4B, 6, and 8 to 10.

[0099] (Step S82) The control unit 21 separates the pressurizing section 261 (lower pressurizing roller) using the pressure release mechanism 28b. If printing is currently in progress, the ongoing print is interrupted and the drives of the paper transport section 24, image forming section 25, fixing section 26, etc. are stopped before the separation process in step S82. In addition, the moving mechanism 28a changes the pressure of the external heating section 263 on the pressurizing section 261 to a higher pressure. For example, it changes from the normal pressure p0 to a higher pressure p1.

[0100] (Step S83) The control unit 21 sets the rotation speed of the motor that drives the pressurizing unit 261 to a higher speed than the normal speed, and drives the pressurizing unit 261 to rotate. For example, if the normal speed during normal printing is 300 mm / sec (converted to paper transport speed), then in thermal expansion mode, it is set to a high speed of 600 mm / sec.

[0101] (Steps S84, S85) The process here is the same as S13 and S14 in Figure 4A. The control unit 21 sets the control temperature of the external heating unit 263 to control temperature T1 and rotates the external heating unit 263 while keeping it in contact with the pressurizing unit 261 until the termination condition is met. This causes the pressurizing unit 261 (especially the elastic layer 62) to undergo more thermal expansion than during normal printing, thereby eliminating wrinkles in the fixing member.

[0102] (Step S86) The control unit 21 performs a recovery process here. The control unit 21 returns the control temperature of the external heating unit 263 to the control temperature T0 and the pressure applied to the pressurizing unit 261 to the pressure p0. It also stops the driving of the pressurizing unit 261 (and the external heating unit 263) and returns to the pressed state (Figure 11(a)) by the pressure release mechanism 28b. If printing was in progress, it also resumes the interrupted printing.

[0103] Thus, in the second embodiment, in the thermal expansion mode, the temperature of the first fixing member is raised from the external heating unit to a higher temperature than the temperature during normal printing. In addition, the thermal expansion mode is performed after setting the fixing unit to a separated state. As a result, similar to the first embodiment, thermal expansion is promoted, which eliminates fixing member wrinkles that have occurred on the first fixing member and suppresses image defects. In particular, in the second embodiment, the pressurizing unit 261 and the external heating unit 263 are rotated at high speed while in a separated state, so heat can be supplied to the pressurizing unit 261 efficiently. Furthermore, by performing the operation in a separated state, the transfer of heat supplied to the pressurizing unit 261 by the external heating unit 263 through the fixing nip N1 can be suppressed, and heating of the pressurizing unit 261 can be performed efficiently.

[0104] Furthermore, in the second embodiment, in the thermal expansion mode, the pressure p1 applied by the external heating section 263 to the pressurizing section 261 is set to a high pressure. This allows the deformation of the elastic layer 62 of the pressurizing section 261 to be resolved more quickly and made uniform.

[0105] (Other configuration examples) Refer to Figures 13 to 16 to illustrate other examples and configurations. These examples are applicable to the first and second embodiments and their respective modifications described above.

[0106] Figure 13 is a schematic diagram showing the external heating section 263 in a separated state. Switching to the separated state is performed by the moving mechanism 28a. The external heating section 263 may be brought into contact with the pressurizing section 261 only when performing the thermal expansion mode, and otherwise set to the separated state as shown in Figure 13.

[0107] Figures 14 to 16 are schematic diagrams showing other configuration examples of the external heating section. In Figure 14, two external heating sections 263a and 263b are arranged. Each external heating section 263a and 263b has the same configuration as the external heating section 263 shown in the first embodiment, etc. By arranging multiple external heating sections 263a and 263b as in Figure 14, heat can be supplied to the pressurizing section 261 quickly, thereby enabling the thermal expansion mode to be performed in a short time. This is particularly suitable when the pressurizing section 261 and the heating section 262 are separated and the thermal expansion mode is performed, as in the second embodiment.

[0108] The external heating section 264 in Figure 15 consists of two metal rollers 71, a heater 72, and a belt 73 around which the metal rollers are wound. The belt 73 is made of the same material as the fixing belt 52 and is in contact with the pressurizing section 261. By having the external heating section 264 with the belt 73 as shown in Figure 15, the contact time (contact distance) with the pressurizing section 261 is increased. This allows for rapid heat supply to the pressurizing section 261, enabling the thermal expansion mode to be performed in a short time. This is particularly suitable when the pressurizing section 261 and the heating section 262 are separated and the thermal expansion mode is performed, as in the second embodiment.

[0109] Figure 16 shows that the external heating section 265 consists of a halogen lamp heater 72 and a reflective member 74. Using this type of external heating section 265 provides the same effect as other external heating sections 263, etc.

[0110] The configuration of the image forming apparatus described above is intended to illustrate the main components in order to explain the features of the above embodiment, and is not limited to the above configuration; various modifications can be made within the scope of the claims. Furthermore, it does not preclude configurations that are generally found in image forming apparatuses.

[0111] For example, in the image forming apparatus 1 according to the first embodiment shown in Figure 1, an example is shown that includes a first detection unit (inspection device 30) and a second detection unit (surface state detection unit 27), but these may be omitted. Furthermore, each modified example and configuration example may be applied to each of the first and second embodiments, or to a combination thereof. For example, a configuration in which the moving mechanism 28a sets the pressure p1 of the external heating unit 263 to the pressurizing unit 261 to a higher pressure than usual when performing thermal expansion mode (Figure 12), or separates them when not in thermal expansion mode (Figure 13), can be applied to the first embodiment and each modified example.

[0112] Furthermore, regarding the configuration of the fixing unit 26, in the example shown in Figure 3, the pressure unit 261, which serves as the lower first fixing member, is positioned on the lower side, and the heating unit 262 on the upper side (the side facing the toner image surface before fixing) functions as the second fixing member. However, the configuration is not limited to this. Alternatively, the first fixing member having an elastic layer may be positioned on the upper side (the side facing the toner image surface before fixing), and the second fixing member may be positioned on the lower side (the side facing the non-toner image surface). That is, the upper pressure roller 53 having an elastic layer may be provided with an external heating unit, and this upper pressure roller 53 may function as the first fixing member, and the pressure unit 261 (lower pressure roller) may function as the second fixing member. Also, the second fixing member may be a fixing roller system that forms a fixing nip N1 with a pair of fixing rollers, rather than a fixing belt system using a fixing belt. Furthermore, in the thermal expansion mode, an example was shown in which the temperature detected by the temperature sensor s6, which measures the surface temperature of the external heating unit 263, was controlled to become the control temperature T1. However, the sensor s7 may also be used to control the system so that the temperature detected by the sensor s7, which measures the surface temperature of the pressurizing unit 261, becomes a control temperature that is higher than the average temperature during normal printing.

[0113] Furthermore, the means and methods for performing various processing in the image forming apparatus according to the above embodiment can be implemented by either a dedicated hardware circuit or a programmed computer. The program may be provided, for example, on a computer-readable recording medium such as a USB memory stick or a DVD (Digital Versatile Disc)-ROM, or it may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is usually transferred to and stored in a storage unit such as a hard disk. The program may also be provided as a standalone application software, or it may be incorporated into the software of the apparatus as a function of the apparatus. [Explanation of symbols]

[0114] 1. Image forming apparatus 10 Feeding device 20 Image forming apparatus main unit 21 Control Unit 22 Memory section 23 Operation display section 24 Paper transport section 25 Image forming unit 26 Fixing section 261 Pressurized section (first fixing member) 61 Mandrel 62 Elastic layer 63 PFA layer 262 Heating section (second fixing member) 51 Heating roller 52 Fixing belt 53 Upper pressure roller 54 Auxiliary rollers 55 Heater 27 Surface condition detection unit (second detection unit) 30 Inspection device (first detection unit) 31 Control Unit 32 Storage section 33 Reading Unit 40 Winding device

Claims

1. An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, In the thermal expansion mode, the control unit heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit. The control unit determines whether or not to perform the thermal expansion mode based on the print conditions, which are predetermined conditions set in advance, in an image forming apparatus.

2. An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, In the thermal expansion mode, the control unit heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit. Downstream of the fixing unit, a first detection unit is provided for detecting the image state on the recording material after fixing, or the transport state of the recording material. The control unit causes the thermal expansion mode to be executed according to the detection result of the first detection unit, in an image forming apparatus.

3. An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, In the thermal expansion mode, the control unit heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit. The control unit determines whether or not to perform the thermal expansion mode based on the type or frequency of the storage medium transport malfunction, in an image forming apparatus.

4. The external heating section is a rotating body in which a heating source is arranged inside and which rotates while being pressed against the outer circumferential surface of the first fixing member. The external heating section is further provided with a pressure setting mechanism for changing the pressure applied to the first fixing member, The image forming apparatus according to any one of claims 1 to 3, wherein the control unit, when executing the thermal expansion mode, sets the contact pressure to a higher pressure than the pressure used during normal printing using the pressure setting mechanism.

5. An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, In the thermal expansion mode, the control unit heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit. The system further includes a pressure release mechanism that moves at least one of the first fixing member and the second fixing member to separate the first fixing member and the second fixing member, The control unit, when executing the thermal expansion mode, separates the first fixing member and the second fixing member using the pressure release mechanism, in an image forming apparatus.

6. The image forming apparatus according to any one of claims 1 to 3, wherein the control unit sets the rotation speed of the first fixing member to a faster rotation speed than that during normal printing in the thermal expansion mode.

7. An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, In the thermal expansion mode, the control unit heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit. The aforementioned recording material is continuous paper, in an image forming apparatus.

8. An image forming unit that forms an image on a recording material, A fixing unit comprising a first fixing member having an elastic layer, a second fixing member forming a fixing nip with the first fixing member, and an external heating unit that heats the first fixing member from the outside, wherein the image on the conveyed recording material is fixed by heating and pressurizing the recording material with the fixing nip, It comprises a control unit that executes a thermal expansion mode, In the thermal expansion mode, the control unit heats the first fixing member to a temperature higher than the temperature during normal printing using the external heating unit. The aforementioned thermal expansion mode is performed during printing in an image forming apparatus.

Images