Fixing apparatus and image forming apparatus

Abstract

It prevents wrinkles from forming on the recording medium. [Solution] The fixing device 100 is a fixing device for fixing a toner image to a recording medium, and includes a heating roller 20 for heating a fixing belt 10 which is an endless belt, a fixing roller 30 on which the fixing belt 10 is stretched, with an elastic layer 32 formed on the outer circumference of a core metal 31, a pressure roller 40 positioned opposite the outer surface 30a of the fixing roller 30 and forming a nip portion 110 through which the recording medium passes between it and the outer surface of the fixing roller 30, a moving mechanism 50 for moving the pressure roller 40 toward or away from the fixing roller 30, a sensor 61 capable of detecting the linear velocity of the fixing belt 10 when the pressure roller 40 is away from the fixing roller 30, a thermal expansion amount calculation unit that calculates the amount of thermal expansion in the radial direction of the fixing roller based on the linear velocity of the fixing belt 10, and a control unit that controls the amount of pressure applied by the pressure roller according to the amount of thermal expansion.

Description

Technical Field

[0001] The present disclosure relates to a fixing device and an image forming apparatus.

Background Art

[0002] For example, a fixing device includes a heating roller, a fixing roller, an endless belt stretched between these heating roller and fixing roller, and a pressure roller. The fixing device forms a fixing nip between the fixing roller and the pressure roller. The fixing device fixes a toner image on a recording material (see, for example, Patent Document 1).

[0003] The fixing device includes rotation detection means for detecting the rotation speed of a heating roller that rotates as the endless belt moves. The fixing device controls the speed of a driving rotating body that rotationally drives the endless belt based on the rotation speed of a driven rotating body. The driving rotating body is a fixing roller or a pressure roller. The fixing device corrects for the thermal expansion of the heating member and controls the speed of the driving rotating body.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a fixing device according to the prior art, wrinkles may occur on the recording medium after passing through the fixing nip.

[0005] An object of the present disclosure is to provide a fixing device capable of suppressing the occurrence of wrinkles on a recording medium.

Means for Solving the Problems

[0006] The fixing device according to this disclosure is a fixing device for fixing a toner image onto a recording medium. The fixing device comprises a heating roller over which an endless fixing belt is stretched and which heats the fixing belt; a fixing roller over which an elastic layer is formed on the outer circumference of a core metal and over which the fixing belt is stretched; a pressure roller positioned opposite the outer surface of the fixing roller and forming a nip portion between itself and the outer surface of the fixing roller through which the recording medium passes; a moving mechanism for moving the pressure roller toward or away from the fixing roller; a sensor capable of detecting the linear velocity of the fixing belt when the pressure roller is separated from the fixing roller; a thermal expansion amount calculation unit that calculates the amount of thermal expansion in the radial direction of the fixing roller based on the linear velocity of the fixing belt; and a control unit that controls the operation of the moving mechanism according to the amount of thermal expansion and controls the amount of pressure applied by the pressure roller. [Effects of the Invention]

[0007] This disclosure provides a fixing device capable of suppressing the formation of wrinkles on a recording medium. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing a fixing device according to an embodiment. [Figure 2] This is a block diagram showing an example of the hardware configuration of a fixing device according to this embodiment. [Figure 3] This is a functional block diagram of the control device according to the embodiment. [Figure 4] This graph shows the relationship between the linear velocity of the fixing belt and the nip width. [Figure 5] This is a process diagram showing the paper feeding procedure in the fixing device. [Figure 6] This flowchart shows the procedure from receiving a print job to starting paper feeding. [Figure 7] This is a schematic diagram showing an image forming apparatus according to an embodiment. [Modes for carrying out the invention]

[0009] The fixing apparatus and image forming apparatus according to the embodiment will be described below with reference to the drawings.

[0010] [Fusing device 100] Figure 1 is a schematic diagram showing a fixing device 100 according to an embodiment. As shown in Figure 1, the fixing device 100 comprises a fixing belt 10, a heating roller 20, a fixing roller 30, a pressure roller 40, a pressure mechanism 50, a linear velocity sensor 61, and a control device 200.

[0011] [Fixing belt 10] The fixing belt 10 is an endless belt and is stretched between the heating roller 20 and the fixing roller 30. The fixing belt 10 moves as the fixing roller 30 rotates.

[0012] [Heating roller 20] The heating roller 20 rotates as the fixing belt 10 moves. The heating roller 20 heats the fixing belt 10 while rotating. The fixing device 100 is equipped with a heater 25 that heats the heating roller 20. The heat from the heating roller 20 is transferred to the fixing belt 10.

[0013] [Fusing roller 30] The fixing roller 30 has a core metal 31 positioned at the center of the fixing roller 30 and a rubber layer 32 positioned outside the core metal 31 in the radial direction of the fixing roller 30. The rubber layer 32 is formed around the entire circumference of the core metal 31. The outer circumferential surface 30a of the fixing roller 30 is the outer circumferential surface of the rubber layer 32. The outer diameter of the fixing roller 30 may be larger than the outer diameter of the heating roller 20. The rubber layer 32 of the fixing roller 30 expands due to heat. This increases the outer diameter of the fixing roller 30. The fixing device 100 may be equipped with a temperature sensor 63 for detecting the temperature of the fixing roller 30.

[0014] A drive motor 91 is connected to the fixing roller 30. The rotational driving force from the drive motor 91 is transmitted to the fixing roller 30. The fixing roller 30 rotates due to the rotational driving force transmitted from the drive motor 91.

[0015] [Pressure Roller 40] The pressure roller 40 is disposed to face the outer peripheral surface 30a of the fixing roller 30. A nip portion 110 through which the recording medium passes is formed between the outer peripheral surface 40a of the pressure roller 40 and the outer peripheral surface 30a of the fixing roller 30.

[0016] [Pressurizing Mechanism 50] The pressurizing mechanism 50 moves the pressure roller 40 in a direction of approaching or separating from the fixing roller 30. The pressurizing mechanism 50 has, for example, a cam 52 and an arm 51. When the cam 52 rotates, the arm 51 in contact with the cam 52 approaches or separates the pressure roller 40 from the fixing roller 30. It may also have a drive source for moving the pressure roller 40, a driving force transmission mechanism for transmitting the driving force from the drive source, and a support mechanism for supporting the pressure roller 40 movably.

[0017] When the pressurizing mechanism 50 approaches the pressure roller 40 to the fixing roller 30, the nip width between the fixing roller 30 and the pressure roller 40 can be narrowed. When the pressurizing mechanism 50 separates the pressure roller 40 from the fixing roller 30, the nip width between the pressure roller 40 and the fixing roller can be widened.

[0018] [Linear Velocity Sensor 61] The linear velocity sensor 61 detects the linear velocity of the fixing belt 10. The linear velocity of the fixing belt 10 may be the moving speed of the fixing belt 10. The linear velocity sensor 61 may calculate the moving speed of the fixing belt 10 by detecting, for example, the rotation angle of the rotation shaft of the heating roller 20. The linear velocity sensor 61 may also be a sensor that detects data related to the linear velocity of the fixing belt 10.

[0019] [Hardware Configuration of Fixing Device 100] FIG. 2 is a block diagram showing the hardware configuration of the fixing device 100 according to the present embodiment. As shown in FIG. 2, the fixing device 100 includes a control device 200. A drive motor 91, a line speed sensor 61, a pressure mechanism 50, and a second sensor 62 are connected to the control device 200. The control device 200 may be the control device of an image forming apparatus 120 described later, and may execute control of the entire image forming apparatus 120.

[0020] The second sensor 62 is a sensor that detects the rotation angle of the rotation shaft 52a of the cam 52 of the pressure mechanism 50. The second sensor 62 outputs the detection result to the control device 200. The control device 200 can detect the rotation angle of the cam 52 and calculate the nip width based on the data detected by the second sensor 62. The second sensor 62 may be other sensors, for example, a sensor that detects the position of the arm 51, the position of the pressure roller 40, or the nip width. The fixing device 100 may include a temperature sensor 63 that detects the temperature of the heating element 31.

[0021] The control device 200 includes a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, and a RAM (Random Access Memory) 203. The CPU 201 controls the entire fixing device 100. The ROM 202 stores fixed data such as programs executed by the CPU 201. The RAM 203 temporarily stores image data and the like.

[0022] The control device 200 includes a NVRAM (Non Volatile RAM) 204 and an ASIC (Application Specific Integrated Circuit) 205. The NVRAM 204 is a non-volatile memory that retains data even while the power of the fixing device 100 is turned off. The ASIC 205 performs various signal processes on the image data, image processing such as rearrangement, and other input / output signals for controlling the entire fixing device 100.

[0023] [Functional Configuration] Next, the functional configuration of the control device 200 will be described with reference to Figure 3. Figure 3 is a functional block diagram of the control device 200 according to this embodiment. The CPU 201 shown in Figure 2 executes programs stored in a storage unit such as ROM 202 to realize the functions of the control unit 210 and the thermal expansion amount calculation unit 220 shown in Figure 3. External devices and sensors connected to the control device 200 may also perform some of these functions.

[0024] [Thermal expansion amount calculation unit 220] The thermal expansion calculation unit 220 calculates the amount of thermal expansion of the fixing roller 30 in the radial direction based on the linear velocity of the fixing belt 10. The storage unit of the control device 200 may store a map showing the relationship between the linear velocity of the fixing belt 10 and the amount of thermal expansion of the fixing roller 30 in the radial direction.

[0025] [Control Unit 210] The control unit 210 controls the operation of the pressurizing mechanism 50 according to the amount of thermal expansion of the fixing roller 30 in the radial direction. The control unit 210 controls the amount of pressure applied by the pressurizing roller 40 by controlling the operation of the pressurizing mechanism 50. The amount of pressure applied by the pressurizing roller 40 may be the nip width. The control unit 210 can control the nip width by controlling the relative positions of the fixing roller 30 and the pressurizing roller 40.

[0026] The control unit 210 may control the operation of the motor that drives the cam 52 of the pressurizing mechanism 50. The control unit 210 can receive data from the second sensor 62 regarding the rotation angle of the rotation axis 52a of the cam 52. Based on the rotation axis 52a of the cam 52, the control unit 210 can recognize the position of the pressurizing roller 40. Based on the position of the pressurizing roller 40, the control unit 210 can determine whether or not the fixing roller 30 and the pressurizing roller 40 are in contact. Contact between the fixing roller 30 and the pressurizing roller 40 includes the state in which the recording medium is nipped in the nip portion 110.

[0027] The control unit 210 can control the movement and stopping of the fixing belt 10 by controlling the operation of the drive motor 91. The control unit 210 can recognize the linear speed of the fixing belt 10 based on the data output from the linear speed sensor 61.

[0028] [Relationship between linear velocity and nip width of fixing belt 10] Next, with reference to Figure 4, the relationship between the linear velocity and nip width of the fixing belt 10 will be explained. Figure 4 is a graph showing the relationship between the linear velocity and nip width of the fixing belt 10. In Figure 4, the horizontal axis shows the linear velocity (belt speed) of the fixing belt 10, and the vertical axis shows the nip width.

[0029] Figure 4 shows the change in nip width due to the change in linear velocity of the fixing belt 10 during depressurization. The memory unit of the fixing device 100 stores data on the nip width when a nip is formed at a predetermined pressure level. The predetermined pressure level is the pressure level applied by the fixing roller 30. The data regarding the pressure level applied by the fixing roller 30 and the nip width may be expressed as a mathematical formula or as a matrix table.

[0030] [Procedure for feeding paper] Next, with reference to Figure 5, the procedure for feeding paper in the fuser 100 will be described. Figure 5 is a process diagram showing the procedure for feeding paper in the fuser 100. The storage unit of the fuser 100 stores data regarding the nip width during paper feeding, corresponding to multiple brands of envelopes which are the recording medium. The storage unit may also be the storage unit of the image forming apparatus 120. "Paper feeding" may also mean that the recording medium passes through the nip section 110.

[0031] Figure 5 shows the passage of time on the horizontal axis. Figure 5 shows the state for each item. The "State of the fixing device 100" includes "Standby state," "Pre-paper feeding state," "Paper feeding state," and "Post-paper feeding state." The "Machine state" changes in the following order, for example: "Standby state," "Pre-paper feeding state (1st time)," "Paper feeding state (1st time)," "Pre-paper feeding state (2nd time)," "Paper feeding state (2nd time)," "Post-paper feeding state," and "Standby state."

[0032] The control device 200 accepts a print job during the time T12 between the "standby state" and the "pre-paper feeding state (first time)". The fuser device 100 starts feeding paper during the time T14 after the "pre-paper feeding state (first time)". The fuser device 100 can alternate between the "pre-paper feeding state" and the "paper feeding state" multiple times.

[0033] The state of the fuser roller 30 includes "stopped state" and "rotating state". The fuser roller 30 is stopped from time T11 to time T12. At this time, the fuser device 100 is in standby state. The fuser roller 30 rotates from time T12 to time T19. The fuser roller 30 rotates when the fuser device 100 is in the "pre-feed state" and "feeding state". The fuser roller 30 stops at time T19. When the fuser device 100 is in standby state, the rotation of the fuser roller 30 is stopped. The control device 200 can control the operation of the drive motor 91 to make the fuser roller 30 rotate or stop.

[0034] The state of the pressure roller 40 includes both a "depressurized state" and a "pressurized state." The "pressurized state" is the state in which the recording medium is being fed through, and the recording medium is sandwiched between the fuser roller 30 and the pressure roller 40. In the "pressurized state," the pressure roller 40 is pressed against the fuser roller 30, and the pressure from the pressure roller 40 acts on the fuser roller 30.

[0035] The "depressurized state" is a state in which no pressure is acting on the fixing roller 30 from the pressure roller 40. In the "depressurized state," the pressure roller 40 is not in contact with the fixing roller 30.

[0036] The pressure roller 40 is in a depressurized state from time T11 to time T14. The pressure roller 40 is in a pressurized state from time T14 to time T15. The pressure roller 40 is in a depressurized state from time T15 to time T17. The pressure roller 40 is in a pressurized state from time T17 to time T18. The pressure roller 40 is in a depressurized state from time T18 to time T20.

[0037] During fixing control, from time T12 to time T13, the linear velocity sensor 61 detects the linear velocity of the fixing belt 10. During fixing control, from time T13 to time T14, the control device 200 calculates the amount of pressure applied by the pressure roller 40. The thermal expansion amount calculation unit 220 calculates the amount of radial thermal expansion of the fixing roller 30 based on the linear velocity of the fixing belt 10. The control device 200 calculates the amount of pressure applied by the pressure roller 40 based on the amount of thermal expansion and the set value of the nip width that is set in advance for the envelopes to be fed. The control device 200 calculates the amount of pressure before starting paper feeding. The control device 200 controls the pressure mechanism 50 to achieve the calculated amount of pressure.

[0038] In fuser control, the control device 200 executes paper feeding from time T14 to time T15. In fuser control, the control device 200 starts the timer at time T14. From time T14 to time T15, the control device 200 determines whether to interrupt the print job.

[0039] During fixing control, from time T15 to time T16, the linear velocity sensor 61 detects the linear velocity of the fixing belt 10. During fixing control, from time T16 to time T17, the control device 200 calculates the amount of pressure applied by the pressure roller 40.

[0040] During fuser control, the control device 200 executes paper feeding from time T17 to time T18. During fuser control, the control device 200 starts the timer at time T14. From time T14 to time T15, the control device 200 determines whether to interrupt the print job.

[0041] The nip width may change due to the expansion of the fuser roller 30 during paper feeding. In fuser control, paper feeding can be interrupted if the nip width changes. In fuser control, there are the following triggers for interrupting paper feeding: (1) to (3).

[0042] In fixing control, paper feeding may be interrupted after a certain period of time has elapsed since the start of paper feeding (Method (1)).

[0043] In fixing control, when the linear speed of the fixing belt 10 before paper feeding is low, the amount of expansion of the fixing roller 30 is small, and in this case, a large rate of change in the amount of expansion is expected. Thus, when the expansion rate of the fixing roller 30 is small, the time until paper feeding is interrupted may be shortened (method (2)).

[0044] In fixing control, the control device 200 may make a decision on whether or not to interrupt paper feeding based on the temperature change of the core metal 31 (method (3)). When the temperature of the core metal 31 is high, the amount of expansion of the fixing roller 30 is greater compared to when the temperature of the core metal 31 is low. The control device 200 may decide to interrupt paper feeding if the temperature change of the core metal 31 exceeds a determination threshold.

[0045] [Processing steps until paper feeding begins] Next, the processing procedure up to the start of paper feeding will be described. Figure 6 is a flowchart showing the processing procedure from the acceptance of a print job to the start of paper feeding. The control device 200 accepts a print job output from the printer driver (step S11). The print job includes information about the recording medium that will pass through the nip section 110. The information about the recording medium includes information about the type (brand) of the recording medium and information about the size of the recording medium.

[0046] Next, the CPU 201 of the control device 200 determines whether the recording medium included in the received print job is an envelope (step S12). If the recording medium is an envelope (step S12; YES), the control device 200 executes the process in step S13; if the recording medium is not an envelope (step S12; NO), the control device 200 terminates the process at this point.

[0047] Next, the control device 200 determines the nip width to set based on the brand of envelopes included in the print job (step S13). The storage unit of the control device 200 stores information regarding the nip width set for each type of envelope. Information showing the relationship between the envelope type and the nip width is stored in the storage unit in advance. Information regarding the envelope type includes, for example, information regarding the paper quality, size, and thickness of the envelope.

[0048] Next, the control device 200 acquires information regarding the current linear velocity of the fixing belt 10 (step S14). The control device 200 acquires information regarding the linear velocity of the fixing belt 10 from the linear velocity sensor 61. The linear velocity sensor 61 measures the linear velocity of the fixing belt 10 when the pressure roller 40 is separated from the fixing roller 30.

[0049] Next, the control device 200 calculates the amount of pressure applied by the pressure roller 40 (step S15). The control device 200 calculates the amount of pressure applied by the pressure roller 40 based on the nip width set for each envelope brand and the current linear speed of the fixing belt 10. The thermal expansion amount calculation unit 220 calculates the amount of thermal expansion of the fixing belt 10 in the radial direction based on the linear speed of the fixing belt 10.

[0050] Next, the control device 200 controls the pressure mechanism 50 to control the amount of pressure applied by the pressure roller 40 (step S16). The control device 200 controls the position of the pressure roller 40 so that the calculated amount of pressure is achieved. The control device 200 moves the pressure roller 40 so that the set nip width is achieved.

[0051] Next, the control device 200 starts feeding the envelope (step S17).

[0052] [Example of calculating pressurization amount] Next, an example of calculating the pressurization amount will be explained with reference to Figure 4. Figure 4 shows the relationship between the current linear velocity of the anchoring belt 10 and the preset nip width. Figure 4 illustrates several graphs (pressurization amounts P11, P12, P13). Pressurization amount P11 is the case when pressurization amount P11 = 100, pressurization amount P12 is the case when pressurization amount P12 = 2000, and pressurization amount P13 is the case when pressurization amount P13 = 3000. The unit of pressurization amount is, for example, msec. The pressurization amount may also be, for example, the rotation time of the cam 52.

[0053] The control device 200 can calculate the amount of pressure corresponding to the preset nip width based on the relationship between "the intersection point of the current linear velocity of the fixing belt 10 and the preset nip width" and the acquired data.

[0054] [Example 1 of calculating pressurization amount] In the calculation example 1 of the pressure amount, the control device 200 searches for the pressure amount closest to the current point PN11 among the acquired data. In the graph shown in Figure 4, the intersection of the current linear velocity of the fixing belt 10 and the preset nip width is called the "current point PN11". The current linear velocity of the fixing belt 10 is data detected by the linear velocity sensor 61. The preset nip width is a value that is preset for each brand of envelope.

[0055] The control device 200 selects the graph (curve) of acquired pressurization levels that is closest to the current point PN11. The "graph (curve) of acquired pressurization levels" is the "graph (curve) of pressurization levels that has been set in advance."

[0056] In the case shown in Figure 4, the control device 200 can determine that the graph with pressurization amount P12 = 2000 is the closest to the current point PN11. The control device 200 selects the graph with pressurization amount P12 = 2000.

[0057] [Example 2 of calculating pressurization amount] In the calculation example 2 for the amount of pressure, interpolation (linear interpolation) may be performed. The control device 200 may perform a linear calculation based on the relationship between the current point PN11, the distance between this point PN11 and the graphs (curves) above and below it, and the amount of pressure, to calculate the amount of pressure. In the case of Figure 4, the control device 200 can calculate the amount of pressure P = 1667.

[0058] Calculation example 2 for pressurization amount has higher accuracy in nip width compared to calculation example 1. Calculation example 1 for pressurization amount has a lower computational load compared to calculation example 2.

[0059] [Effects of the fixing device 100 according to the embodiment] The fixing device 100 according to this embodiment is a fixing device 100 for fixing a toner image to a recording medium, and comprises: a fixing belt 10 which is an endless belt, stretched over a heating roller 20 that heats the fixing belt 10; a fixing roller 30 which has a rubber layer (elastic layer) 32 formed on the outer circumference of a core metal 31 over which the fixing belt 10 is stretched; a pressure roller 40 which is positioned opposite the outer circumferential surface 30a of the fixing roller 30 and forms a nip portion between itself and the outer circumferential surface 30a through which the recording medium passes; a pressure mechanism (movement mechanism) 50 which moves the pressure roller 40 in a direction toward or toward the fixing roller 30; a linear velocity sensor (sensor) 61 which can detect the linear velocity of the fixing belt 10 when the pressure roller 40 is separated from the fixing roller 30; a thermal expansion amount calculation unit 220 which calculates the amount of thermal expansion of the fixing roller 30 in the radial direction based on the linear velocity of the fixing belt 10; and a control unit 210 which controls the operation of the pressure mechanism 50 according to the amount of thermal expansion and controls the amount of pressure applied by the pressure roller 40.

[0060] With this type of fixing device 100, the nip width can be changed in response to changes in the amount of thermal expansion of the fixing roller 30. Therefore, it is possible to suppress the formation of wrinkles in the envelope, which is the recording medium.

[0061] Furthermore, the multiple recording media include a first recording media and a second recording media that is fed through the nip section 110 after the first recording media. The linear velocity sensor 61 detects the first linear velocity of the fixing belt 10 before the first recording media is fed through the nip section 110. The thermal expansion amount calculation unit 220 calculates the first thermal expansion amount based on the first linear velocity. The control unit 210 adjusts the amount of pressure, setting the nip width, which is the width of the nip section 110, as the first nip width according to the first thermal expansion amount, to feed the first recording media, and interrupts the feeding of the recording media after the first recording media has passed through the nip section 110. The linear velocity sensor 61 detects the second linear velocity of the fixing belt 10 during the interruption period after the feeding of the first recording media and before the start of feeding of the second recording media. The thermal expansion amount calculation unit 220 calculates the second thermal expansion amount based on the second linear velocity. The control unit 210 adjusts the amount of pressure by setting the nip width to the second nip width according to the second amount of thermal expansion, and then passes the second recording medium through the paper.

[0062] With this configuration of the fixing device 100, the linear velocity of the fixing belt 10 can be measured during the interruption period between feeding the first recording medium and before feeding the second recording medium, and the nip width can be changed according to the measurement result. Even if the thermal expansion coefficient of the fixing roller 30 changes due to a temperature change of the fixing roller 30 before feeding the second recording medium, the nip width can be readjusted. As a result, the fixing device 100 can suppress the formation of wrinkles in the envelope, which is the recording medium.

[0063] In addition, in the fixing device 100, the linear velocity sensor 61 may detect the linear velocity by detecting the rotational speed of the fixing roller 30. Alternatively, the linear velocity sensor 61 may detect the rotational speed of the rotation axis of the fixing roller 30 and calculate the linear velocity of the fixing belt 10 based on this detection result.

[0064] Furthermore, the fixing device 100 may include a driven roller (rotating member) 12 that contacts the inner circumferential surface of the fixing belt 10 and rotates in conjunction with the movement of the fixing belt 10. The linear velocity sensor 61 may detect the linear velocity by detecting the rotational speed of the driven roller 12. The inner circumferential surface of the fixing belt 10 includes a surface that can contact the outer circumferential surface 30a of the fixing roller 30. The driven roller 12 that contacts the inner circumferential surface of the fixing belt 10 may be a tension roller that provides tension to the fixing belt 10, a guide roller that guides the fixing belt 10, or a heating roller 20. The linear velocity sensor 61 may detect the speed of the outer circumferential surface of the driven roller 12 that rotates in conjunction with the rotation of the fixing belt 10, or it may detect the rotation angle of the rotation axis of the driven roller 12, or it may detect the rotational speed of other rotating members that rotate in conjunction with the rotation of the driven roller 12.

[0065] Furthermore, the recording medium includes a plurality of first recording media and a plurality of second recording media, and the control unit may interrupt the feeding of the first recording media after a certain period of time has elapsed since the start of feeding the first recording media. In the fixing device 100 with this configuration, the linear speed of the fixing belt 10 can be detected during the interruption period after the certain period of time has elapsed, and the nip width can be readjusted. The certain period of time can be set based on experimental results or past performance. When multiple recording media are fed through, wrinkles tend to form in the envelopes that are the recording media after a certain period of time has elapsed. In the fixing device 100, a certain period of time can be set to interrupt the feeding of paper before wrinkles form, and the feeding of paper can be interrupted after the certain period of time has elapsed and the nip width can be readjusted.

[0066] Furthermore, the recording medium includes a third recording medium that is fed through the nip section 110 after the second recording medium. The control unit 210 can execute control to feed multiple first recording media during the first period, multiple second recording media during the second period following the first period, and multiple third recording media during the third period following the second period. The linear velocity sensor 61 can detect the second linear velocity of the fixing belt 10 during the first interruption period between the first and second periods, and detect the third linear velocity of the fixing belt 10 during the second interruption period between the second and third periods. The second period may be longer than the first period, and the third period may be longer than the second period.

[0067] Generally, when the expansion amount of the fuser roller 30 is small, it can be expected that the change in expansion amount during paper feeding will be larger compared to when the expansion amount is large. The fuser device 100 can change the time from when paper feeding starts until it is interrupted. By making the second period, which is after the first period, longer than the first period, and the third period, which is after the second period, longer than the second period, the number of interruptions can be reduced, and productivity can be improved when printing multiple envelopes.

[0068] Furthermore, the fuser device 100 may be equipped with a temperature sensor 63 for detecting the temperature of the fuser roller 30. The control unit 210 may determine the length of the period from when the feeding of the recording medium is started until the feeding of the recording medium is interrupted, based on the temperature of the fuser roller 30. In this configuration of the fuser device 100, the period from when the feeding of paper is started until the feeding of paper is interrupted can be determined in accordance with the temperature change of the fuser roller 30. When the amount of expansion changes due to the temperature change of the fuser roller 30, the nip width changes. In the fuser device 100, the feeding of paper can be interrupted in accordance with the temperature change of the fuser roller 30, the fuser belt 10 can be detected again, and the nip width can be readjusted. This can suppress the formation of wrinkles in the envelope.

[0069] [Image forming apparatus 300 according to the embodiment] Next, an image forming apparatus 300 according to the embodiment will be described. Figure 7 is a schematic diagram showing the image forming apparatus 300 according to the embodiment. The image forming apparatus 300 includes the fixing device 100 according to the above embodiment.

[0070] The image forming apparatus 300 is an electrophotographic tandem color printer. It may also be a high-speed machine equipped with an image forming unit 310 and a paper feeding unit 320. The image forming unit 310 is located at the top of the apparatus body, and the paper feeding unit 320 is located below the image forming unit 310. The image forming unit 310 has a fuser 100.

[0071] [Image forming unit 310] The image forming unit 310 includes an intermediate transfer belt 311 and photoreceptors 312Y, 312M, 312C, and 312K. Photoreceptor 312Y is an image carrier capable of carrying a yellow (Y) toner image. Photoreceptor 312M is an image carrier capable of carrying a magenta (M) toner image. Photoreceptor 312C is an image carrier capable of carrying a cyan (C) toner image. Photoreceptor 312K is an image carrier capable of carrying a black (K) toner image. The image carriers may also be latent image carriers. The photoreceptors 312Y, 312M, 312C, and 312K are arranged along the upper transfer surface of the intermediate transfer belt 311. When the photoreceptors 312Y, 312M, 312C, and 312K are not distinguished, they are referred to as photoreceptor 312.

[0072] Each photoreceptor 312 has a drum shape that allows it to rotate in the same direction. Around each photoreceptor 312 are a charging device 313Y, 313M, 313C, 313K, a developing device 314Y, 314M, 314C, 314K, and a primary transfer device 315Y, 315M, 315C, 315K.

[0073] Each developing unit 314Y, 314M, 314C, and 314K houses its respective color toner. Additionally, optical writing units 316Y, 317M, and 316C, 316K are located at the top of the image forming unit 310.

[0074] The intermediate transfer belt 311 is stretched over the drive roller and the driven roller. A secondary transfer roller 318 is provided at a position opposite to one of the driven rollers, the secondary transfer opposing roller 317. The transport path of the recording medium from the secondary transfer roller 318 to the fixing device 100 may be a substantially horizontal lateral path. The recording medium may be, for example, an envelope. The recording medium may also be a sheet of paper.

[0075] [Paper feed section 320] The paper feeding unit 320 includes a paper feeding tray 321 for stacking and storing paper, and a transport mechanism that separates the paper in the paper feeding tray 321 one sheet at a time, starting from the bottom, and transports it to the position of the secondary transfer roller 318.

[0076] [Image formation in the image forming apparatus 300] The surface of the photoreceptor 312Y is uniformly charged by the charging device 313Y, and an electrostatic latent image is formed on the photoreceptor 312Y based on image information from the image reading unit. The formed electrostatic latent image is made visible as a toner image by the developing device 314Y which contains yellow (Y) toner. This toner image is then primary transferred onto the intermediate transfer belt 311 by the primary transfer device 315Y to which a predetermined bias is applied.

[0077] With the other photoreceptors 312M, 312C, and 312K, the same image formation occurs, differing only in the toner color. The toner images of each color are then sequentially transferred onto the intermediate transfer belt 311 by electrostatic force and superimposed.

[0078] The toner image, which has been primarily transferred onto the intermediate transfer belt 311, is then transferred to the recording medium that has been transported by the secondary transfer opposing roller 317 and the secondary transfer roller 318. The recording medium on which the toner image has been transferred is then transported to the fuser unit 100.

[0079] When the pressure roller 40 is pressed towards the fuser roller 30, the toner image on the recording medium is fixed to the recording medium. A structure capable of performing such fixing is sometimes referred to as a "nip section." The recording medium discharged from the nip section is sent to the stacker 331 along the discharge path.

[0080] Transfer residue toner that remains on the photoreceptor 312 without being transferred to the intermediate transfer belt 311 is removed by the photoreceptor cleaning devices 319Y, 319M, 319C, and 319K, respectively. Transfer residue toner that remains on the intermediate transfer belt 311 without being transferred to the paper is removed by the belt cleaning device 332 to prepare for the next image formation.

[0081] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0082] Each function performed by the control device 200 of the embodiment described above can be realized by one or more processing circuits. Hereinafter, "processing circuit" as used herein includes processors programmed to execute each function by software, such as CPUs implemented by electronic circuits, and devices such as ASICs (Application Specific Integrated Circuits), DSPs (digital signal processors), FPGAs (field programmable gate arrays), and conventional circuit modules designed to execute each function described above.

[0083] One aspect of the present invention may be as follows: <1> A fixing device for fixing toner images onto a recording medium, An endless belt, which is a fixing belt, is stretched across, and a heating roller is used to heat the fixing belt, An elastic layer is formed on the outer circumference of the core metal, and the fixing roller over which the fixing belt is stretched, A pressure roller is positioned opposite the outer circumferential surface of the fixing roller, and between it and the outer circumferential surface of the fixing roller, forming a nip portion through which the recording medium passes. A moving mechanism for moving the pressure roller in a direction toward or toward the fixing roller, When the pressure roller is separated from the fixing roller, a sensor capable of detecting the linear velocity of the fixing belt is provided, A thermal expansion amount calculation unit calculates the amount of thermal expansion of the fixing roller in the radial direction based on the linear velocity of the fixing belt, A fixing device comprising: a control unit that controls the operation of the moving mechanism according to the amount of thermal expansion, thereby controlling the amount of pressure applied by the pressure roller. <2> The recording medium includes a first recording medium and a second recording medium that is passed through the nip portion after the first recording medium. The sensor detects the first linear speed of the fixing belt before the first recording medium is fed through the nip section. The thermal expansion amount calculation unit calculates a first thermal expansion amount based on the first linear velocity, The control unit, The amount of pressure is adjusted so that the nip width, which is the width of the nip portion, is set to the first nip width according to the first amount of thermal expansion, and the first recording medium is passed through the paper. After the first recording medium has passed through the nip section, the feeding of the recording medium is interrupted. The sensor detects the second linear speed of the fixing belt during the interruption period after the first recording medium has been fed and before the second recording medium has been fed. The thermal expansion amount calculation unit calculates the second thermal expansion amount based on the second linear velocity, The control unit, The above method adjusts the amount of pressure by setting the nip width to the second nip width according to the amount of thermal expansion, thereby passing the second recording medium through the paper. <1> The fixing device described above. <3> The sensor detects the rotational speed of the fixing roller, thereby detecting the linear velocity. <1> or <2> The fixing device described above. <4> The fixing belt is equipped with a rotating member that contacts the inner circumferential surface of the fixing belt and rotates as the fixing belt moves, The sensor detects the rotational speed of the rotating member, thereby detecting the linear velocity. <1> ~ <3> A fixing device as described in any one of the following. <5> The recording medium includes a plurality of first recording media and a plurality of second recording media. The control unit, The above procedure interrupts the feeding of paper from the first recording medium after a certain period of time has elapsed since the start of feeding paper from the first recording medium. <2> The fixing device described above. <6> The recording medium includes a third recording medium that is fed through the nip portion after the second recording medium, The control unit, During the first period, multiple of the aforementioned first recording media are fed through paper, During the second period, multiple of the aforementioned second recording media are fed through paper. During the third period, control can be performed to feed multiple of the third recording media through the paper. The aforementioned sensor is During the first interruption period between the first period and the second period, the second linear velocity of the fixing belt is detected. During the second interruption period between the second and third periods, the third linear speed of the fixing belt is detected. The second period is longer than the first period. The above third period is longer than the above second period. <2> The fixing device described above. <7> The system includes a temperature sensor that detects the temperature of the fixing roller, The control unit determines the length of the period from when the feeding of the recording medium is started until the feeding of the recording medium is stopped, based on the temperature of the fixing roller. <1> ~ <6> A fixing device as described in any one of the following. <8> The above <1> ~ <7> An image forming apparatus comprising a fixing device as described in any one of the following. [Explanation of symbols]

[0084] 100 Fixing device 10 Fixing belt 20 heating rollers 30 Fixing roller 30a Outer surface 31 Mandrel 32. Rubber layer (elastic layer) 40 Pressure rollers 40a Outer surface 50 Pressurization mechanism (movement mechanism) 61 Linear velocity sensor (sensor) 110 Nip section 210 Control Unit 220 Thermal expansion calculation unit 300 Image forming apparatus [Prior art documents] [Patent Documents]

[0085] [Patent Document 1] Japanese Patent Publication No. 2019-3167

Claims

1. A fixing device for fixing toner images onto a recording medium, An endless belt, which is a fixing belt, is stretched across, and a heating roller is used to heat the fixing belt, An elastic layer is formed on the outer circumference of the core metal, and the fixing roller over which the fixing belt is stretched, A pressure roller is positioned opposite the outer circumferential surface of the fixing roller, and between it and the outer circumferential surface of the fixing roller, forming a nip portion through which the recording medium passes. A moving mechanism for moving the pressure roller in a direction toward or toward the fixing roller, When the pressure roller is separated from the fixing roller, a sensor capable of detecting the linear velocity of the fixing belt is provided, A thermal expansion amount calculation unit calculates the amount of thermal expansion of the fixing roller in the radial direction based on the linear velocity of the fixing belt, A fixing device comprising: a control unit that controls the operation of the moving mechanism according to the amount of thermal expansion, thereby controlling the amount of pressure applied by the pressure roller.

2. The recording medium includes a first recording medium and a second recording medium that is passed through the nip portion after the first recording medium. The sensor detects the first linear speed of the fixing belt before the first recording medium is fed through the nip portion. The thermal expansion amount calculation unit calculates a first thermal expansion amount based on the first linear velocity, The control unit, The amount of pressure is adjusted so that the nip width, which is the width of the nip portion, is set to the first nip width according to the first amount of thermal expansion, and the first recording medium is passed through the paper. After the first recording medium has passed through the nip section, the feeding of the recording medium is interrupted. The sensor detects the second linear speed of the fixing belt during the interruption period after the first recording medium has been fed and before the second recording medium has been fed. The thermal expansion amount calculation unit calculates the second thermal expansion amount based on the second linear velocity, The control unit, The fixing device according to claim 1, wherein the amount of pressure is adjusted by setting the nip width to the second nip width according to the amount of the second thermal expansion, and the second recording medium is passed through the paper.

3. The fixing device according to claim 1 or 2, wherein the sensor detects the linear velocity by detecting the rotational speed of the fixing roller.

4. The fixing belt is equipped with a rotating member that contacts the inner circumferential surface of the fixing belt and rotates as the fixing belt moves, The fixing device according to claim 1 or 2, wherein the sensor detects the linear velocity by detecting the rotational speed of the rotating member.

5. The recording medium includes a plurality of first recording media and a plurality of second recording media. The control unit, The fixing device according to claim 2, wherein after the start of feeding the first recording medium, the feeding of the first recording medium is interrupted after a certain period of time has elapsed.

6. The recording medium includes a third recording medium that is passed through the nip portion after the second recording medium, The control unit, During the first period, multiple first recording media are fed through paper, During the second period, multiple of the aforementioned second recording media are fed through paper. During the third period, control can be performed to feed multiple of the aforementioned third recording media through the paper. The aforementioned sensor is During the first interruption period between the first period and the second period, the second linear velocity of the fixing belt is detected. During the second interruption period between the second and third periods, the third linear speed of the fixing belt is detected. The second period is longer than the first period. The fixing apparatus according to claim 2, wherein the third period is longer than the second period.

7. The system includes a temperature sensor that detects the temperature of the fixing roller, The fixing apparatus according to claim 1 or 2, wherein the control unit determines the length of the period from when the feeding of the recording medium is started until the feeding of the recording medium is interrupted, based on the temperature of the fixing roller.

8. An image forming apparatus comprising the fixing device described in claim 1.

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