Image forming apparatus and fixing control method

Abstract

To estimate a nip part with a simple configuration, and control a more appropriate fixing temperature on the basis of the estimation to ensure fixing quality.SOLUTION: An image forming apparatus comprises: a rotatable heating section that includes a heat source; a rotatable pressure section that is in contact with and applies pressure to the heating section; a temperature detector that detects the temperature of the heating section or the temperatures of the heating section and pressure section; a conveying section that leads a printing sheet to which toner is transferred to a nip part where the heating section and pressure section are in contact with each other, and causes the printing sheet to pass therethrough; and a control section that controls the heat source and conveying section. The control section controls the heat source to adjust the temperature of the heating section to be a target temperature during execution of a print job, rotates the heating section and pressure section when the print job is not executed, determines a nip width on the basis of the relationship between the transition of temperature of at least one of the heating section and pressure section and heat generation of the heat source, and changes the target temperature on the basis of a result of the determination.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus including a rotatable heating section and a pressure section that is rotatable in contact with the heating section, and a fixing control method. [Background technology]

[0002] There is known an image forming apparatus equipped with a fixing device including a heating section and a pressure section that is in pressure contact with the heating section in order to fix the toner on a print sheet to which the toner has been transferred. For example, there is an image forming apparatus that includes a fixing device equipped with a heating section consisting of a fixing belt stretched between a heating roller having a heat source such as a heater inside and a fixing roller, a pressure roller that is in pressure contact with the fixing roller, and a sensor such as a thermistor that detects the temperature of the surface of the heating roller (see, for example, Patent Document 1).

[0003] In such a fixing device, heat is transferred to the nip portion by the rotation of the heating roller, and when the heating roller is stopped, the temperature of the nip portion does not rise. The fixing device in Patent Document 1 focuses on this point, and in order to accurately detect the temperature of the nip portion, when a printing instruction or the like is received in a non-operating state such as a sleep state and the heating roller is switched to an operating state in which it rotates, the measurement of the rotation time is started and the temperature of the nip portion is estimated. That is, during the warm-up before the start of printing, the temperature of the nip portion is estimated based on the rotation time from when the rotation of the heating portion started and the stop time before the rotation. At the time when the measurement of the rotation time is started, in other words, at the start of the warm-up before printing, the nip portion may be warmed to some extent by the rotation of the heating portion immediately before. Therefore, the initial value of the rotation time at the start of the measurement of the rotation time is added according to the rotation time of the heating portion even before the stop time of the heating portion immediately before the measurement is started. If the estimated temperature of the nip portion obtained in this way is higher than the target temperature, the power supplied to the heating portion is reduced according to the difference. On the other hand, if the estimated temperature of the nip portion is lower than the target temperature, the power supplied to the heating portion is increased according to the difference.

[0004] Also, an image forming apparatus is known that includes a fixing device equipped with a heating roller provided with a heater, a pressure roller that rotates in contact with the heating roller, a thermistor that detects the temperature of the heating roller, and a switching mechanism that switches the nip width between plain paper and envelopes (see, for example, Patent Document 2). The device in Patent Document 2 receives a print instruction from a user to detect the nip width using existing components. When the temperature reaches or exceeds a predetermined rotation start temperature, the heating roller starts rotating in a state where it directly contacts the pressure roller and rotates. Then, the temperature gradient of the temperature detected by the thermistor TH after the start of the rotation is calculated. Based on the calculated temperature gradient, it is determined whether the current nip width is in a normal state corresponding to the paper type (plain paper / envelope) indicated by the print instruction, or in an abnormal state, and if it is determined to be abnormal, the user is notified of the abnormality. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-026739 A [Patent Document 2] JP 2009-228480 A Summary of the Invention [Problem to be solved by the invention]

[0006] The nip width, i.e., the width of the nip portion in the sheet conveying direction, is one of the factors that greatly affect fixation. The nip width divided by the speed of the print sheet passing through the nip portion corresponds to the time required for the print sheet to pass through the nip portion, i.e., the heating time during which heat is supplied from the heating portion. Factors that cause the size of this nip width to vary from one image forming apparatus to another include the variation in the hardness of the pressure roller and the mechanical variation of the pressure means (such as the variation in the distance between the axes of the heating roller and the pressure roller, and the variation in the pressure of the pressure spring). Furthermore, even in the same image forming apparatus, the size of the nip width may change over time due to a decrease in the hardness of the pressure roller.

[0007] Variations in the size of the nip due to variations or changes over time can have an undesirable effect on fixability. If the nip is too small, there is a risk of poor fixation. Conversely, if the nip is too large, there is a risk of overheating, resulting in a deterioration in fixation quality. Furthermore, if the nip is too large, more heat will move from the heating section to the pressure section, and more heat will escape from the heating section to other members than expected, which is undesirable from the standpoint of energy conservation.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to ensure fixing quality by estimating the nip portion with a simple configuration and performing more appropriate control of the fixing temperature based on the estimation. [Means for solving the problem]

[0009] The present disclosure provides an image forming device comprising: a rotatable heating unit including a heat source; a pressure unit which is in contact with the heating unit to apply pressure and rotate; a temperature detector which detects the temperature of the heating unit or the temperatures of the heating unit and the pressure unit; a transport unit which rotates and stops the heating unit and the pressure unit, and guides a printing sheet onto which toner has been transferred to a nip unit where the heating unit and the pressure unit contact, and a control unit which controls the heating source and the transport unit, wherein the control unit controls the heat source so that the temperature of the heating unit becomes a target temperature while a print job is being executed in which the printing sheet passes through the nip unit, and when the print job is not being executed, rotates the heating unit and the pressure unit to determine the size of the nip width based on the relationship between the temperature trend of at least one of the heating unit and the pressure unit and the heat generation of the heat source, and changes the target temperature based on the determination.

[0010] From a different viewpoint, the present disclosure provides a fixing control method, in which a control unit controls an image forming apparatus including a rotatable heating unit including a heat source, a pressure unit that contacts the heating unit to apply pressure and rotates, a temperature detector that detects the temperature of the heating unit or the temperatures of the heating unit and the pressure unit, and a transport unit that rotates and stops the heating unit and the pressure unit, and guides a printing sheet onto which toner has been transferred to a nip unit where the heating unit and the pressure unit contact each other, and passes the printing sheet through the nip unit, the control unit controlling the heating source so that the temperature of the heating unit becomes a target temperature while a print job is being executed, a step of rotating the heating unit and the pressure unit by the transport unit when the print job is not being executed, and determining the size of the nip width based on the relationship between the temperature transition of at least one of the heating unit and the pressure unit and the heat generation of the heating source, and a step of changing the target temperature based on the determination. Effect of the Invention

[0011] In the image forming apparatus according to the present disclosure, the control unit rotates the heating unit and the pressure unit when a print job is not being executed, judges the size of the nip width based on the relationship between the temperature trends of at least one of the heating unit and the pressure unit and the heat generation of the heating source, and changes the target temperature based on that judgment, so that the nip portion can be estimated with a simple configuration and fixing temperature can be more appropriately controlled based on that estimation, thereby ensuring fixing quality. The fixing control method according to the present disclosure also achieves the same effects. [Brief description of the drawings]

[0012] [Figure 1] 1 is an explanatory diagram illustrating an internal configuration of a multifunction peripheral that is an embodiment of an image forming apparatus according to the present disclosure. [Diagram 2] 2 is a block diagram showing a configuration of the multifunction peripheral shown in FIG. 1. [Diagram 3] FIG. 2 is a cross-sectional view showing a schematic configuration of a fixing unit according to an embodiment of the present disclosure. [Figure 4]6 is a graph showing an example of temperature transitions of a fixing belt and a pressure roller and ON / OFF states of a heater when printing one print sheet in an embodiment of the present disclosure. [Diagram 5] Unlike FIG. 4, this is a graph showing an example of temperature transitions of a fixing belt and a pressure roller and ON / OFF states of a heater when a plurality of print sheets are printed continuously. [Figure 6] 11 is an explanatory diagram showing an example of on / off of a heater and the associated transition of temperatures of a fixing belt and a pressure roller when a control unit determines whether a nip width is large or small in an embodiment of the present disclosure. FIG. [Figure 7] 7 is an explanatory diagram showing temperature transitions corresponding to those shown in FIG. 6 for a fixing unit having a nip portion larger than the reference value in the embodiment of the present disclosure. [Figure 8] 7 is an explanatory diagram showing temperature transitions corresponding to those shown in FIG. 6 for a fixing unit having a nip portion smaller than the reference in the embodiment of the present disclosure. [Figure 9] 11 is a flowchart showing an example of a process in which a control unit turns a heater on and off in a predetermined pattern, estimates a nip width, and changes a control target temperature in the first embodiment of the present disclosure. [Figure 10A] 11 is a data table showing an example of calculation of nip width estimation and target control temperature correction based on temperature transition of a pressure roller in an embodiment of the present disclosure. [Figure 10B] 11 is a data table showing an example of numerical values ​​for estimating a nip width based on a temperature transition of a pressure roller and correcting a target control temperature in an embodiment of the present disclosure. [Figure 11] 11 is a flowchart showing an example of a process in which a control unit turns on and off a heater in a predetermined pattern, estimates a nip width, and changes a control target temperature in the second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present disclosure will be described in further detail below with reference to the drawings. Note that the following description is illustrative in all respects and should not be construed as limiting the present disclosure. <Configuration example of image forming apparatus> 1 is an explanatory diagram showing the internal configuration of a digital multifunction peripheral which is an embodiment of an image forming apparatus according to the present disclosure, and FIG.

[0014] As shown in Fig. 1, the multifunction peripheral 100 has an image reading unit 111 that reads an original and a printing unit 115 that forms an image in its main body. In addition, a feed tray 18 is provided below the printing unit 115. A discharge tray 39 is provided above the printing unit 115 and below the image reading unit 111. Also, a document transport unit 103 that transports an original to the reading unit is provided above the image reading unit 111. Furthermore, an operation unit 105 (not shown in Fig. 1, see Fig. 2) that accepts user operations is provided in front of the image reading unit 111.

[0015] Here, the internal configuration of the multifunction peripheral 100 relating to image formation will be described. The multifunction device 100 forms toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (BK), by an electrophotographic process, and superimposes them on the intermediate transfer belt 21 to print a color image on a print sheet. Alternatively, a monochrome image using a single color (e.g., black) is printed on a print sheet. For this purpose, the printing section 115 is provided with four process units 30 each including a developing unit 12, a photoconductor drum 13, a charger 14, a drum cleaner 15, etc. (shown as 30y, 30m, 30c, and 30k in FIG. 1). Also, an optical scanning unit 11 is provided that exposes and scans the photoconductor drum 13 corresponding to each color with a laser beam. The multifunction device 100 also includes a sheet transport mechanism as a transport section. The sheet transport mechanism 20 includes rollers arranged along a transport path, a motor for driving the rollers, a clutch, etc. The sheet transport mechanism 20 functions as a transport section and feeds a print sheet from a feed tray 18 , and guides the sheet to an ejection tray 39 or a double-sided transport path 40 via a secondary transfer unit 23 and a fixing unit 17 .

[0016] The multifunction device 100 has process units 30y, 30m, 30c, and 30k for each color, but in FIG. 1, only the components of the yellow process unit 30k are labeled with a reference symbol, and those for the other colors are omitted. The process units may also be referred to as process unit 30 using a representative reference symbol. The explanation using the representative reference symbol should be understood to apply to each of the colors Y, M, C, and K. Toner storage units 27 corresponding to each color are disposed above the printing section 115.

[0017] The multifunction device 100 further includes an image processing circuit 41 that generates an input signal to the optical scanning unit 11 (see FIG. 2). The image processing circuit 41 processes image data of a document read by the image reading unit 111 to generate exposure data related to an exposure pattern of the photoconductor drum 13. The exposure data corresponds to the pattern of an electrostatic latent image to be formed on the surface of the photoconductor drum 13. Under the control of the image formation control unit 133 shown in FIG. 2, control is performed so that a toner image of Y, M, C, or K is formed on the photosensitive drum 13 through an electrophotographic process including cleaning by the drum cleaner 15, charging by the charger 14, exposure by the optical scanning unit 11, and development by the developing unit 12.

[0018] A primary transfer roller 16 is disposed at a position where it comes into contact with the photoconductor drum 13 of the process unit 30 via the intermediate transfer belt 21. The image formation control unit 133 applies a voltage to the primary transfer roller 16 to transfer the Y, M, C, and K toner images formed on the photoconductor drum 13 onto the intermediate transfer belt 21 in a superimposed manner, and sends it to a position where it comes into contact with the secondary transfer unit 23. The image formation control unit 133 drives the secondary transfer unit and applies a voltage to it to transfer the toner images onto a print sheet fed from the feed tray 18.

[0019] Furthermore, the image formation control unit 133 controls the sheet conveying mechanism 20 to feed and convey the print sheet from the feed tray 18. The image formation control unit 133 conveys the print sheet onto which the toner image has been transferred by the secondary transfer unit 23 to the fixing unit 17. The fixing unit 17 includes a heating unit 24 in which a heater 36, which is a heat source, is disposed, a fixing belt 31, and a pressure roller 32. The fixing unit 17 further includes a temperature detector 38 for detecting the temperature of either or both of the heating unit 24 and the pressure roller 32. The image formation control unit 133 controls the sheet conveying mechanism 20 to guide the print sheet to the nip portion formed between the fixing belt 31 and the pressure roller 32 and pass it through. The fixing unit 17 pressurizes and heats the print sheet passing through the nip portion to fix the toner image transferred to the print sheet to the print sheet. The fixing control unit 131 shown in FIG. 2 controls the power supply to the heater of the heating unit 24. Note that the configuration of the fixing unit 17 shown in FIG. 1 is merely an example, and the present disclosure is not limited thereto. For example, the heating section may not have a fixing belt or a fixing roller, but may only have a heating roller with a heater disposed inside, and the pressure roller 32 may come into contact with the heating roller to form a nip portion.

[0020] The image formation control unit 133 controls the sheet transport mechanism 20 to discharge the print sheet that has passed through the fixing unit 17 onto the discharge tray 39. Alternatively, the print sheet that has been switched back is guided to the double-sided transport path 40 and returned to the secondary transfer unit 23. Then, a toner image is transferred onto the back side of the print sheet, and the print sheet is discharged onto the discharge tray 39 via the fixing unit 17.

[0021] 2, the control unit 110 includes devices such as a processor 121, a RAM 122, and a non-volatile memory 123 as hardware resources. The processor 121 executes a control program stored in advance in the non-volatile memory 123 and cooperates with the hardware resources to realize the functions of the control unit 110. The control unit 110 includes a fixing control unit 131 and an image formation control unit 133. The image formation control unit 133 processes data related to a print job when the multifunction device 100 executes the print job, and controls the operation of each unit of the printing unit 115. The fixing control unit 131 controls the fixing unit 17.

[0022] <Configuration of the fixing unit> Next, the fixing unit 17 of this embodiment will be described in detail. Fig. 3 is a cross-sectional view showing a schematic configuration of the fixing unit 17 according to this embodiment. As described above, the fixing unit 17 includes the fixing belt 31 and the pressure roller 32, which are rotary fixing members. Furthermore, the fixing unit 17 includes a support member 33, a fixing pad 34, a sliding sheet 35, a heater 36, and a reflecting plate 37 as a heating section 24 inside the fixing belt 31. The fixing unit 17 also includes a first fixing temperature sensor 38A and a second fixing temperature sensor 38B as a temperature detector 38.

[0023] The fixing belt 31 is an endless flexible belt formed in a substantially circular shape. The fixing belt 31 has a configuration in which a release layer is provided on the surface of a band-shaped base material formed of, for example, a synthetic resin such as polyimide or a metal such as nickel. The fixing belt 31 is provided so as to be rotatable about an axis line perpendicular to the paper surface in FIG. 2. The inner diameter of the fixing belt 31 is, for example, 30 mm.

[0024] The fixing pad 34 is formed in a long plate shape extending along the axial direction of the fixing belt 31, and is made of, for example, synthetic resin. A sliding sheet 35 is provided on the outer peripheral surface (the surface on the side close to the fixing belt 31) of the fixing pad 34. The length of the fixing pad 34 is approximately equal to the length of the fixing belt 31 in the axial direction.

[0025] The sliding sheet 35 is provided so as to be in sliding contact with the inner circumferential surface of the fixing belt 31. The fixing belt 31 rotates, but the fixing pad 34 and the sliding sheet 35 are fixed to it. A lubricant may be applied to the sliding surface of the sliding sheet 35 that is in sliding contact with the inner circumferential surface of the fixing belt 31 in order to reduce the frictional force with the fixing belt 31.

[0026] The support member 33 is a member that supports the fixing pad 34 and the sliding sheet 35 while pressing them against the inner circumferential surface of the fixing belt 31. The support member 33 has, for example, a substantially L-shaped cross section and has a long plate-shaped fixed portion to which the fixing pad 34 is fixed and a long plate-shaped standing portion that stands up from the fixed portion.

[0027] The heater 36 is a member for heating the fixing belt 31, and is disposed so as to extend in the width direction of the fixing belt 31 (the depth direction relative to the paper surface in FIG. 2). The heater 36 is, for example, a lamp heater such as a halogen lamp. However, the heater is not limited to this, and may be one that applies the principle of induction heating, for example. The fixing belt 31 is heated by the heater 36 to, for example, 200°C to 250°C.

[0028] The reflecting plate 37 is in the form of a thin plate, and is disposed so as to cover the surface of the supporting member 33 that faces the heater 36. The fixing belt 31 is configured so as to be efficiently heated by the reflecting plate 37.

[0029] The pressure roller 32 is disposed at a position facing the fixing pad 34 with the fixing belt 31 interposed therebetween. The pressure roller 32 rotates about an axis parallel to the width direction of the fixing belt 31, and is disposed so as to extend approximately parallel to the width direction of the fixing belt 31. At a nip portion N between the pressure roller 32 and the fixing belt 31, the fixing belt 31 is pressed against the pressure roller 32 by the fixing pad 34. The pressure roller 32 can be configured such that the surface of a cylindrical core material formed of a metal such as aluminum is covered with an elastic material such as rubber.

[0030] A driving force from a driving source such as a motor (not shown) is transmitted to the pressure roller 32 via gears, etc. The pressure roller 32 is driven to rotate by receiving this driving force, and as the pressure roller 32 is driven to rotate, the fixing belt 31 is driven to rotate in a direction opposite to the rotation direction of the pressure roller 32. The print sheet passes through the nip portion N between the pressure roller 32 and the fixing belt 31 in the paper transport direction (the direction moving from left to right in FIG. 3).

[0031] The temperature detector 38 detects the fixing temperature, which is the surface temperature of the fixing belt 31. The peeling plate is disposed downstream of the nip portion N in the paper transport direction. 3 shows fixing unit 17 having fixing belt 31, the scope of the present disclosure is not limited thereto. For example, a roller-type fixing unit using a hollow heating roller as a rotary fixing member and having a fixing heater disposed therein as a heating section is also included in the scope of the present disclosure.

[0032] <<Fixing control during print job execution>> Next, the control of the fixing unit 17 executed by the control unit 110 will be described. First, the control of the fixing unit 17 when executing a print job will be described. FIG. 4 is a graph showing an example of the temperature transition of the fixing belt 31 and the pressure roller 32 and the ON / OFF of the heater 36 when printing one print sheet in this embodiment. Note that the fixing unit 17 related to the graph of FIG. 4 is equipped with a first fixing temperature sensor 38A that detects the temperature of the fixing belt 31 and a second fixing temperature sensor 38B that detects the temperature of the pressure roller 32. The graph shown in FIG. 4 shows the transition of the temperature of the fixing belt 31 detected by the first fixing temperature sensor 38A and the transition of the temperature of the pressure roller 32 detected by the second fixing temperature sensor 38B.

[0033] At time T0 shown in FIG. 4, control unit 110 receives an instruction for a print job and starts preparation for printing. At time T0, pressure roller 32 and fixing belt 31 of fixing unit 17 are stopped, power supply to heater 36 is turned off, and fixing belt 31 is in a cold state of 20° C., the same as the ambient temperature (room temperature). When an instruction for a print job is received, fixing control unit 131 of control unit 110 turns on power supply to heater 36 to generate heat. Image formation control unit 133 controls sheet conveying mechanism 20 to rotate pressure roller 32, which in turn rotates fixing belt 31. The temperature of fixing belt 31 rises, and the temperature of the nip portion also rises accordingly, and heat is transferred to pressure roller 32 via the nip portion, causing the temperature of pressure roller 32 to also rise.

[0034] When the temperature of the fixing belt 31 eventually reaches the first temperature, the image formation control unit 133 feeds the print sheet specified in the print job from the feed tray 18. This first temperature is a temperature selected so that the temperature of the fixing belt 31 reaches the target control temperature when the leading edge of the fed print sheet reaches the nip portion of the fixing unit 17. In the example shown in Fig. 4, time T1 is the time when the fixing belt 31 reaches the first temperature, and time T2 is the time when the leading edge of the print sheet reaches the nip portion. Time T3 is the time when the trailing edge of the print sheet passes through the nip portion.

[0035] Just before time T2, the temperature of the fixing belt 31 exceeds the target control temperature of 150° C., which triggers the fixing control unit 131 to turn off the heater 36. Between times T2 and T3, the print sheet passes through the nip portion and is fixed. Since heat is taken away by the print sheet passing through the nip portion, the temperatures of the fixing belt 31 and the pressure roller 32 drop during that period. The fixing control unit 131 controls the heater 36 to be turned on and off so that the temperature of the fixing belt 31 maintains the target control temperature. After the print sheet passes through the nip and is discharged to the discharge tray 39 and the post-processing of the image formation process is completed, the image formation control unit 133 controls the sheet conveying mechanism 20 at time T4 to stop the rotation of the fixing unit 17. At the same time, the fixing control unit 131 stops controlling the heater 36 to maintain the fixing belt 31 at the target control temperature. After time T4, the heater 36 is turned off, and the temperatures of both the fixing belt 31 and the pressure roller 32 drop.

[0036] FIG. 5 is a graph showing an example of the temperature transition of the fixing belt 31 and the pressure roller 32 and the ON and OFF of the heater 36 when multiple print sheets are printed continuously, unlike FIG. 4. The transition from time T0 to T3 is the same as FIG. 3. After the trailing edge of the first print sheet passes through the nip at time T3, the subsequent print sheets pass through the nip one after another. At time T5, the trailing edge of the last print sheet passes through the nip. Heat is taken away by the multiple print sheets passing through the nip, and the temperatures of the fixing belt 31 and the pressure roller 32 drop once and then rise during the period from time T3 to T5. During that time, the fixing control unit 131 turns on the heater 36. When the fixing belt 31 eventually reaches the target control temperature, the fixing control unit 131 turns off the heater 36. Thereafter, the heater 36 is controlled to be turned on and off so as to maintain the temperature of the fixing belt 31 at the target control temperature. The transition after time T5 when the trailing edge of the final print sheet passes through the nip portion is similar to the transition after time T3 in FIG.

[0037] <Fixing control when determining the size of the nip width> (Embodiment 1) Next, a process performed by the control unit 110 to determine the size of the nip width will be described. FIG. 6 is an explanatory diagram showing an example of the on / off of the heater 36 and the associated temperature transition of the fixing belt 31 and the pressure roller 32 when the control unit 110 determines the size of the nip width in the embodiment of the present disclosure. In FIG. 6, the image formation control unit 133 controls the sheet conveying mechanism 20 to rotate the pressure roller 32, and the fixing control unit 131 turns the heater 36 on and off in a predetermined pattern. That is, instead of turning the heater 36 on and off to maintain the fixing belt 31 at a target control temperature as shown in FIG. 4 and FIG. 5, the heater 36 is turned on and off according to a predetermined pattern.

[0038] 4 when the fixing unit 17 has a standard nip size as designed. Furthermore, the pattern thus determined is used when the heater 36 has standard heat generation characteristics and the fixing belt 31, support member 33, fixing pad 34, sliding sheet 35, and pressure roller 32 have standard heat transfer characteristics. Here, the size of the nip is a major factor of variation compared to the heat generation characteristics of the heater 36 and the heat transfer characteristics of the fixing belt 31, support member 33, fixing pad 34, sliding sheet 35, and pressure roller 32.

[0039] The control unit 110 may determine the size of the nip width between the time when the power-off state or the power-saving state is released and the time when the print job can be executed. It is not impossible to determine the size of the nip width every time the power-off state or the power-saving state is released. However, the determination of the size of the nip width requires time because it involves measuring the temperature transition. Therefore, it is preferable to perform the determination only when a predetermined condition is satisfied, such as when the multifunction device 100 is newly installed or every time a predetermined period (for example, six months) has passed thereafter. According to this aspect, the fixing control unit can autonomously determine the size of the nip width every time or at a predetermined number of times when warming up is started from the power-off state or the power-saving state in which the heating source does not generate heat. Then, the target temperature can be changed based on the determination. Thus, a change according to the change in the nip portion due to use is realized.

[0040] Furthermore, when a print job to be executed is received at the time when the power-off state or power-saving state is released, or while the determination regarding the nip width is being made, it is preferable to give priority to the execution of the print job. That is, when a print job is received before or during the determination regarding the nip width, the determination regarding the nip width is canceled. Then, it is preferable to postpone the determination until there is an opportunity to release the power-off state or power-saving state. According to this aspect, when a print job to be executed is received, the determination regarding the nip width, which takes time, is postponed, so that the start of the print job is not delayed. Alternatively, the control unit 110 may determine the size of the nip width in response to receiving an instruction to execute a specific program for maintenance and inspection via, for example, the operation unit 105. According to this aspect, the control unit determines the size of the nip width in response to receiving a specific instruction for maintenance and inspection, so that a determination of the size of the nip width that takes time to execute can be made only when a service engineer or the like determines it is necessary.

[0041] 6, the on / off of the heater 36 is set so that a long on period indicated by T01 is followed by an off period indicated by T02, and then the on period indicated by T03 and the off period indicated by T04 are repeated a predetermined number of times. When the on / off pattern of the heater 36 set in this way is used, if the fixing unit 17 has a standard nip size, the temperature of the fixing belt 31 is maintained close to the target control temperature during the repetition of T03 and T04. The temperature of the pressure roller 32 gradually approaches the temperature of the fixing belt 31 due to the heat transferred from the fixing belt 31 via the nip.

[0042] FIG. 7 is an explanatory diagram showing an example of temperature transitions of the fixing belt 31 and the pressure roller 32 when the fixing unit 17 has a nip portion larger than the reference and the heater 36 is turned on and off in the same pattern as in FIG. 6. In the fixing unit 17 having a nip portion larger than the reference, the amount of heat transferred from the fixing belt 31 to the pressure roller 32 per unit time is larger than the reference, so that the amount of heat taken from the fixing belt 31 is larger. As a result, at the end of the on period of T01, the temperature of the fixing belt 31 is lower than that in FIG. 6, and the temperature of the pressure roller 32 is higher than that in FIG. 6. The temperature transition of the fixing belt 31 thereafter is also lower than that in FIG. 6, and drops slightly as time passes. On the other hand, the temperature transition of the pressure roller 32 is higher than that in FIG. 6.

[0043] FIG. 8 is an explanatory diagram showing an example of temperature transitions of the fixing belt 31 and the pressure roller 32 when the fixing unit 17 has a nip portion smaller than the reference and the heater 36 is turned on and off in the same pattern as in FIG. 6. In the fixing unit 17 having a nip portion smaller than the reference, the amount of heat transferred from the fixing belt 31 to the pressure roller 32 per unit time is smaller than the reference, so the amount of heat taken from the fixing belt 31 is smaller. As a result, at the end of the on period of T01, the temperature of the fixing belt 31 is higher than that in FIG. 6, and the temperature of the pressure roller 32 is lower than that in FIG. 6. The temperature transition of the fixing belt 31 thereafter is also higher than that in FIG. 6, and increases slightly as time passes. On the other hand, the temperature transition of the pressure roller 32 is lower than that in FIG. 6.

[0044] The fixing control unit 131 compares the temperature transition of the pressure roller 32 while the heater 36 is turned on and off in a predetermined pattern with pre-stored reference data, and judges the amount of heat transferred from the fixing belt 31 to the pressure roller 32 through the nip portion. For example, the amount of heat transferred can be judged using the temperature transition of the pressure roller 32 from the start of the repetition of T03 and T04 to the end of the repetition. Specifically, the amount of heat transferred can be judged using the temperature difference, such as how much the temperature rose from the start of the repetition of T03 and T04 to the end of the repetition. Alternatively, the amount of heat transferred can be judged using the average temperature from the start of the repetition of T03 and T04 to the end of the repetition. In any case, the amount of heat transferred can be judged using the temperature transition of the pressure roller 32 during the period when the heater 36 is steadily turned on and off by the repetition of T03 and T04. The amount of heat transferred thus obtained is used to judge the amount of heat transferred relative to the reference size of the nip portion.

[0045] In this embodiment, the amount of heat transferred is not determined based on how much the temperature of the pressure roller 32 has risen during the ON period of T01. The ON period of T01 corresponds to the period from the start to the end of warm-up, but the warm-up period until the print job can be started can be said to be a period during which the user is kept waiting, so the warm-up is designed to be as short as possible. On the other hand, judging the size of the nip width requires accurate judgment due to the setting of an appropriate target temperature. According to this aspect, the temperature transition can be made to be gentle by suppressing the amount of heat generated per unit time when the heating unit is heated to the target temperature before printing. By doing so, it is possible to transfer heat from the heating unit to the pressure unit over a longer period of time. As a result, the size of the nip width can be determined more accurately. Also, according to this aspect, when judging the size of the nip width, the amount of heat transferred from the heating unit through the nip unit while the print sheet is rotating without being conveyed is detected as the temperature transition of the pressure unit, so that the size of the nip width can be determined.

[0046] Then, the target control temperature of the fixing belt 31 is changed according to the result of the judgment of whether the nip is larger than the reference size. In the fixing unit 17 having a nip larger than the reference size, the amount of heat transferred from the fixing belt 31 to the pressure roller 32 per unit time is larger than the reference size as described above, so the drop in the target control temperature of the fixing belt 31 becomes larger quickly. The fixing control unit 131 sets the target control temperature to a higher temperature accordingly, or increases the amount of power supplied to the heater 36. However, if it is judged that the size of the nip is larger than the allowable range, the control unit 110 may display a message on the operation unit 105 to prompt the user to replace the pressure roller 32. Conversely, in the fixing unit 17 having a nip smaller than the reference size, the amount of heat transferred from the fixing belt 31 to the pressure roller 32 per unit time is smaller than the reference size, so the drop in the target control temperature of the fixing belt 31 becomes smaller. The fixing control unit 131 sets the target control temperature to a lower temperature accordingly, or decreases the amount of power supplied to the heater 36. However, when it is determined that the size of the nip portion is smaller than the allowable range, the control unit 110 may cause the operation unit 105 to display a message prompting the user to inspect the fixing unit 17 .

[0047] <Flowchart> Next, the process in which the control unit turns on and off the heater 36 in a predetermined pattern and judges the size of the nip width will be described with reference to a flowchart. Fig. 9 is a flowchart showing an example of the process in which the control unit 110 as the fixing control unit 131 in this embodiment turns on and off the heater 36 in a predetermined pattern, estimates the nip width, and changes the control target temperature. Fig. 10A is a data table showing an example of the estimation of the nip width based on the temperature transition of the pressure roller 32 and the calculation of the target control temperature correction, and Fig. 10B is a data table showing an example of numerical values.

[0048] As shown in FIG. 9, when the control unit 110 executes the judgment regarding the size of the nip width (Yes in step S11), it turns on and off the heater 36 in a predetermined pattern, for example, as shown in FIG. 6, while rotating the pressure roller 32. Then, the fixing control unit 131 records the temperature transition of the pressure roller 32 detected by the second fixing temperature sensor 38B during that period. That is, it stores it in the RAM 122 (a loop that returns to step S13 via step S13 and step S15 No). When the predetermined pattern of turning on and off the heater 36 is completed (Yes in step S15), the fixing control unit 131 compares the temperature transition of the pressure roller 32 stored in the RAM 122 with the reference data (step S17). Then, it judges the size of the nip width based on the result of the comparison. In this embodiment, as one aspect of the judgment regarding the size of the nip width, the fixing control unit 131 estimates the size of the nip width (step S19).

[0049] FIG. 10A shows an example of a data table used by the fixing control unit 131 to estimate the nip width. In the example shown in FIG. 10A, the reference size (design value) of the nip width is 10 mm. The fixing control unit 131 of the control unit 110 starts recording the temperature transition of the pressure roller 32 at the time when T03 and T04 shown in FIG. 6 start to be repeated (T=11 sec). The recording of the temperature transition ends at the time when T03 and T04 are repeated five times (T=31 sec) (not shown in FIG. 6). The predetermined pattern for turning the heater 36 on and off is determined with reference to the on and off of the heater 36 when the warm-up of the fixing unit 17 having the reference characteristics such as the nip width is performed and the temperature of the fixing belt 31 is maintained at the target control temperature without passing a print sheet. Therefore, in the case of the fixing unit 17 having the reference nip width, when T03 and T04 are repeated in a predetermined pattern, it is predicted that the temperature of the fixing belt 31 will transition at approximately the same target control temperature as in FIG. 6. The temperature of the pressure roller 32 is predicted to change in a manner similar to that shown in FIG. 6. In FIG. 10A, the same temperature value as that of the waveform in FIG. 6 is set as the "reference value." FIG. 10B shows specific numerical examples of the predicted temperatures. When the nip width is the reference value, the temperature of the pressure roller 32 (set as the reference value of the pressure roller temperature) is 105° C. at the start of recording, and 137° C. at the end of recording. The temperature of the fixing belt 31 (set as the reference value of the fixing belt temperature) is 145° C. at the start of recording, and 145° C. at the end of recording. The numerical examples are the average values ​​for one cycle in which the heater 36 is turned on and off (see the middle row in FIG. 10B).

[0050] When the nip width of the fixing unit 17 is 1 mm larger than the reference value, the amount of heat taken from the fixing belt 31 is greater as shown in FIG. 7. As a result, the temperature of the pressure roller 32 is predicted to be 4° C. higher than the reference value of the pressure roller temperature at the start of recording, and 34° C. higher than the reference value of the pressure roller temperature at the end of recording. In contrast, the temperature of the fixing belt 31 is predicted to be 6° C. lower than the reference value of the fixing belt temperature at the start of recording, and 11° C. lower than the reference value at the end of recording (see the bottom line of FIG. 10A). In the specific numerical example shown in FIG. 10B, the temperature of the pressure roller 32 is predicted to be 109° C. at the start of recording, and 139° C. at the end of recording. The temperature of the fixing belt 31 is predicted to be 139° C. at the start of recording, and 134° C. at the end of recording (see the bottom line of FIG. 10B). Conversely, when the nip width is 1 mm smaller than the reference value, the amount of heat taken from the fixing belt 31 is less as shown in FIG. 8. As a result, the temperature of the pressure roller 32 is predicted to be 4°C lower than the reference value at the start of recording and 25°C higher than the reference value at the end of recording. In contrast, the temperature of the fixing belt 31 is predicted to be 4°C higher than the reference value at the start of recording and 15°C higher than the reference value at the end of recording (see the top row in FIG. 10A). In the specific numerical example shown in FIG. 10B, the temperature of the pressure roller 32 is predicted to be 101°C at the start of recording and 130°C at the end of recording (see the top row in FIG. 10B).

[0051] The fixing control unit 131 compares the recorded temperature transition of the pressure roller 32 with the predicted temperature shown in FIG. 10B to estimate the nip width. For the comparison with the predicted temperature, for example, the average value of the difference between the recording temperature at the start of recording and the predicted temperature (first difference) and the difference between the recording temperature at the end of recording and the predicted temperature (second difference) may be used as the deviation from the reference value. Alternatively, more precisely, the predicted temperature at the end of each repetition of T03 and T04 may be prepared, and the deviation from the reference value may be calculated using the average value of the difference between the recording temperature at the end of each repetition and the predicted temperature. FIG. 10B shows examples of the predicted temperature values ​​corresponding to the reference value of the nip width at the start of recording and the end of recording, and three cases of the reference value ±1 mm. If the recorded temperature transition of the pressure roller 32 is within that range, it is preferable that the fixing control unit 131 estimates the nip width in units of 1 mm or more precisely using a method of complementation. The complementation may be linear complementation or higher-dimensional complementation. According to the estimated nip width, the fixing control unit 131 corrects the target control temperature (step S21 shown in FIG. 9). For example, if the estimated nip width is 1 mm larger than the reference value, the target control temperature is set to the reference value×0.95 (see the bottom row of the rightmost column in FIG. 10A). In the numerical example shown in FIG. 10B, the target control temperature is changed to 143° C. (see the bottom row of the rightmost column in FIG. 10B). Conversely, if the estimated nip width is 1 mm smaller than the reference value, the target control temperature is set to the reference value×1.05 (see the top row of the rightmost column in FIG. 10A). In the numerical example shown in FIG. 10B, the target control temperature is changed to 158° C. (see the top row of the rightmost column in FIG. 10B).

[0052] As with the estimation of the nip width, it is preferable to apply a complementation technique to the correction of the target control temperature. If the temperature transition exceeds the range shown in FIG. 10A or FIG. 10B, the fixing control unit 131 determines that the nip width exceeds the allowable range. In this case, the control unit 110 causes the operation unit 105 to display a message urging the user to replace the pressure roller 32 or inspect the fixing unit. The nip width range shown in FIG. 10A or FIG. 10B, i.e., the reference value ±1 mm, is merely an example. The allowable range may be wider than that, for example, the reference value ±3 mm. In this case, predicted temperatures of the reference value ±2 mm and the reference value ±3 mm may be prepared.

[0053] (Embodiment 2) In the first embodiment, the fixing control unit 131 compares the temperature transition of the pressure roller 32 with the reference data to determine whether the nip is large or small relative to the reference size. In contrast, in this embodiment, the temperature transition of the fixing belt 31 is used in addition to the temperature transition of the pressure roller 32, and the ratio of the two is compared with the reference data to determine whether the nip is large or small relative to the reference size. The amount of heat generated per unit time when the heater 36 is turned on may vary due to voltage fluctuations of the AC power supply. Even if the amount of heat supplied per unit time from the heater 36 to the fixing belt 31 varies due to fluctuations in the voltage of the AC power supply, it can be said that the proportion of the amount of heat transferred to the pressure roller 32 out of the total amount of heat supplied is approximately the same if the size of the nip is the same. Therefore, the size of the nip can be more accurately determined relative to the reference size by using the temperature transition of the fixing belt 31 related to the amount of heat supplied per unit time to the fixing belt 31 via the fixing belt 31 and the temperature transition of the pressure roller 32 related to the amount of heat transferred to the pressure roller 32. According to this aspect, when determining the size of the nip width, the amount of heat transferred from the heating unit through the nip portion while the print sheet is rotating without being transported can be detected from both the temperature transition of the heating unit and the temperature transition of the pressure unit. This makes it possible to estimate the total amount of heat supplied to both the heating unit and the pressure unit, and the amount of heat supplied to the pressure unit through the nip portion, thereby making it possible to more accurately determine the size of the nip width.

[0054] FIG. 11 is a flowchart showing an example of a process in which the control unit 110 turns on and off the heater in a predetermined pattern, estimates the nip width, and changes the control target temperature in the second embodiment. That is, it corresponds to the flowchart in FIG. 9 according to the first embodiment. In FIG. 11, the same processes as those in FIG. 9 are given the same reference numerals. The process is almost the same as FIG. 9 up to the process of estimating the nip width in step S19. The difference from FIG. 9 is that the fixing control unit 131 records the temperature transition of the fixing belt in addition to the temperature transition of the pressure roller 32 (step S31 shown in FIG. 11). As in FIG. 9, the fixing control unit 131 estimates the nip width based on the temperature transition of the pressure roller 32 (step S19 in FIG. 11).

[0055] Next, the fixing control unit 131 determines the average value of the difference between the recording temperature and the predicted temperature as the deviation from the reference value (step S33). That is, in addition to the first and second differences, the deviation from the reference value is obtained by using the average value of the difference between the recording temperature of the fixing belt 31 at the start of recording and the predicted temperature (third difference) and the difference between the recording temperature of the fixing belt 31 at the end of recording and the predicted temperature (fourth difference). As described above, the first difference is the difference between the recording temperature of the pressure roller 32 at the start of recording and the predicted temperature. The second difference is the difference between the recording temperature of the pressure roller 32 at the end of recording and the predicted temperature. The fixing control unit 131 corrects the target control temperature according to the obtained deviation from the reference value. That is, the temperature transition of the pressure roller 32 and the temperature transition of the fixing belt 31 are added to the calculation of the deviation from the reference value, and it is determined whether or not the correction of the target control temperature is necessary based on the calculation result (step S35).

[0056] If it is determined that the target control temperature needs to be corrected (Yes in step S35), the target control temperature is changed based on FIG. 10A or FIG. 10B (step S37). On the other hand, if it is determined that the target control temperature does not need to be corrected (No in step S35), the current target control temperature is maintained (step S39). Then, the process ends. As described with reference to FIG. 9, a warning message may be displayed if the deviation of the temperature transition from the reference value exceeds an allowable range.

[0057] (Embodiment 3) In the first and second embodiments, the nip width is determined at least using the temperature transition of the pressure roller 32, on the assumption that the fixing unit 17 is equipped with the second fixing temperature sensor 38B that detects the temperature of the pressure roller 32. Even if the fixing unit 17 does not have the second fixing temperature sensor 38B that detects the temperature of the pressure roller 32, it has the first fixing temperature sensor 38A that detects the temperature of the fixing belt 31. It is also possible to determine the size of the nip portion relative to a reference size using only the temperature transition of the fixing belt 31. If the voltage fluctuation of the AC power supply is negligible, the size of the nip portion relative to a reference size can be determined based on whether the temperature transition of the fixing belt 31 is high or low relative to the reference data.

[0058] It should be understood that the present disclosure also includes any combination of the above-described aspects. In addition to the above-described embodiment, various modifications of the present disclosure are possible. These modifications should not be interpreted as not belonging to the scope of the present disclosure. The invention according to the present disclosure should include all modifications that are equivalent to the scope of the claims and that belong to the scope of the present disclosure. [Explanation of symbols]

[0059] 11: Optical scanning unit, 12: Development unit, 13: Photoconductor drum, 14: Charger, 15: Drum cleaner, 16: Primary transfer roller, 17: Fixing unit, 18: Feeding tray, 20: Sheet transport mechanism, 21: Intermediate transfer belt, 23: Secondary transfer unit, 24: Heating section, 27: Toner storage unit, 30, 30y, 30m, 30c, 30k: Process unit, 31: Fixing belt, 32: Pressure roller, 33: Support member, 34: Fixing pad, 35: Sliding sheet, 36: Heater, 37: Reflection plate, 38: Temperature detector, 38A: First fixing temperature sensor, 38B: Second fixing temperature sensor, 39: Discharge tray, 40: Double-sided transport path, 41: Image processing circuit 100: multifunction device, 103: document transport unit, 105: operation unit, 110: control unit, 111: image reading unit, 115: printing unit, 121: processor, 122: RAM, 123: non-volatile memory, 131: fixing control unit, 133: image formation control unit

Claims

1. A rotatable heating unit including a heat source; A pressurizing unit capable of rotating by contacting and applying pressure to the heating unit; a temperature detector for detecting a temperature of the heating unit or for detecting the temperatures of the heating unit and the pressure unit; a conveying section that rotates and stops the heating section and the pressure section, and guides the print sheet onto which the toner has been transferred to a nip section where the heating section and the pressure section come into contact with each other, and causes the print sheet to pass through the nip section; A control unit that controls the heating source and the transport unit, The control unit controls the heating source so that the temperature of the heating unit becomes a target temperature while a print job is being executed, and when the print job is not being executed, the control unit rotates the heating unit and the pressure unit using the conveying unit to determine the size of the nip width based on the relationship between the temperature trends of at least one of the heating unit and the pressure unit and the heat generation of the heating source, and changes the target temperature based on that determination.

2. The image forming apparatus of claim 1, wherein the control unit reduces the amount of heat generated per unit time by the heating source when determining whether the nip width is large or small to less than the amount of heat generated per unit time when raising the heating unit to a target temperature to execute or make the print job executable.

3. 2. The image forming apparatus according to claim 1, wherein the temperature detector obtains the temperature transition of the pressure applying section using a pressure applying side temperature detector which detects the temperature of the pressure applying section, and determines the size of the nip width based on the relationship between the temperature transition and the heat generation of the heat source.

4. The image forming apparatus according to claim 1, wherein the temperature detector obtains temperature trends of the heating section and the pressure applying section using a pressure applying side temperature detector which detects the temperature of the pressure applying section and a heating side temperature detector which detects the temperature of the heating section, and determines the size of the nip width based on the relationship between these temperature trends and the heat generation of the heat source.

5. The image forming apparatus according to any one of claims 1 to 4, wherein the control unit rotates the heating unit and the pressure unit each time or when predetermined conditions are satisfied after warming up after starting processing from a power-off state or a power-saving state in which processing is stopped, and determines the size of the nip width based on the relationship between the heat generation and the temperature change.

6. 3. The image forming apparatus according to claim 2, wherein the control unit rotates the heating unit and the pressure unit and determines the size of the nip width based on the relationship between the heat generation and the temperature change every time or when predetermined conditions are satisfied after warming up after starting processing from a power-off or power-saving state in which processing is stopped, but when there is a print job to be executed, the execution of the print job is prioritized and no judgment is made on the nip width.

7. The image forming apparatus according to any one of claims 1 to 4, wherein the control unit, when receiving an instruction prepared in advance for maintenance and inspection, executes a process of determining whether the nip width is large or small in response to the instruction.

8. A rotatable heating unit including a heat source; A pressurizing unit capable of rotating by contacting and applying pressure to the heating unit; a temperature detector for detecting a temperature of the heating unit or for detecting the temperatures of the heating unit and the pressure unit; a control unit for controlling an image forming apparatus including a conveying unit that rotates and stops the heating unit and the pressure unit, and guides the print sheet onto which the toner has been transferred to a nip portion where the heating unit and the pressure unit are in contact with each other, controlling the heating source so that the temperature of the heating unit becomes a target temperature during execution of a print job; a step of rotating the heating unit and the pressure unit by the conveying unit when the print job is not being executed, and determining a size of a nip width based on a relationship between a temperature transition of at least one of the heating unit and the pressure unit and heat generation of the heat source; and changing the target temperature based on the determination.

Images