Image forming apparatus

Abstract

To reduce the occurrence of an image failure in a fixing device.SOLUTION: An image forming apparatus comprises a fixing device that fixes a toner image to a recording material, and control means that controls fixation of the toner image to the recording material performed by the fixing device according to at least one control condition. The fixing device includes a rotatable fixing member, a pressure member that sandwiches and conveys the recording material with the fixing member, a heating body that heats the fixing member, and measuring means that measures the temperature of the heating body. The control means controls supply of power to the heating body by using the measured temperature of the heating body measured by the measuring means, determines if the temperature of the fixing member is affected by an air current on the basis of the measured temperature, and changes the at least one control condition according to the determination that the temperature of the fixing member is affected by the air current.SELECTED DRAWING: Figure 9

Description

[Technical Field]

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

[0002] Conventionally, many electrophotographic image forming apparatuses fix a toner image formed on a recording material (also called a sheet) to the recording material by applying heat and pressure to the toner image. For example, Patent Document 1 discloses an image forming apparatus equipped with a film-heating fixing device. The fixing device in Patent Document 1 includes a rotatable, cylindrical heat-resistant film, a heater (e.g., a ceramic heater) that heats the heat-resistant film from within, and a pressure roller. When the recording material passes through the fixing nip between the heat-resistant film and the pressure roller, the toner image formed on the recording material is melted by the heat from the high-temperature heat-resistant film and then fixed to the recording material by pressure applied by the pressure roller. The film-heating method has the advantage of reducing power consumption and shortening standby time (quick start) by using a thin film with low thermal capacity as the fixing member.

[0003] Temperature control in a fixing device is an important function for achieving stable fixing performance. For example, if the temperature of the fixing member is lower than the required temperature, the toner does not melt properly and the toner image is not sufficiently fixed to the recording material, resulting in an image defect (hereinafter referred to as fixing defect). If the temperature of the fixing member is excessively high, the viscosity of the toner decreases, causing the toner to transfer to the fixing member, resulting in an image defect (hereinafter referred to as hot offset).

[0004] In general, in image forming apparatuses that employ a film heating method, it is difficult to directly measure the temperature of the film, which is a thin fixing member. Therefore, Patent Document 2 discloses an image forming apparatus that predicts the film temperature from the temperature of the heater instead of directly measuring the film temperature. The image forming apparatus in Patent Document 2 predicts the film temperature from the measured temperature of the heater using a prediction model that models heat transfer between members including the heater and the fixing film, and controls the heating of the fixing film during printing operations based on the predicted film temperature. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 04-44075 [Patent Document 2] Japanese Patent Publication No. 2020-16731 Summary of the Invention [Problem to be solved by the invention]

[0006] However, no matter what kind of prediction model is used to predict the temperature of the fixing member, the image forming apparatus may not always be operated under the conditions assumed by the prediction model. In particular, the temperature of a fixing member using a film heating method is easily affected by external disturbances. For example, if a strong air current exists in the environment where the image forming apparatus is installed, the temperature of the fixing member may deviate from the predicted temperature due to the influence of the air current, which may result in poor image quality.

[0007] In view of the above, the present invention aims to realize a mechanism for reducing the occurrence of image defects in a fixing device. [Means for solving the problem]

[0008] According to one aspect, there is provided an image forming apparatus comprising a fixing device that fixes a toner image to a recording material, and a control means that controls the fixing of the toner image to the recording material by the fixing device in accordance with at least one control condition, wherein the fixing device includes a rotatable fixing member, a pressure member that clamps and transports the recording material together with the fixing member, a heating element that heats the fixing member, and a measurement means that measures the temperature of the heating element, and the control means controls the supply of power to the heating element using the measured temperature of the heating element measured by the measurement means, determines whether the temperature of the fixing element is affected by air flow based on the measured temperature, and changes the at least one control condition in accordance with a determination that the temperature of the fixing element is affected by the air flow. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce the occurrence of image defects in a fixing device. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of a configuration related to the fixing device shown in FIG. [Figure 3] 10 is a graph for explaining an example of a change over time in a prediction result of a fixing temperature as a conventional example. [Figure 4] 6 is a graph for explaining some examples of changes over time in the actual temperature of the fixing film. [Figure 5] 6 is a graph for explaining the influence of airflow on the actual temperature of the fixing film. [Figure 6] 10 is a graph for explaining an example of a cause of an image defect when the actual temperature of the fixing film deviates from the predicted temperature. [Figure 7] 6 is a graph for explaining the relationship between the temperature of the fixing film and the temperature of the heater when there is no influence of airflow and when there is an influence of airflow. [Figure 8]10 is a graph for explaining a reduction in the predicted temperature of the fixing film when there is an influence of air current. [Figure 9] 6 is a flowchart showing an example of the flow of a temperature monitoring process according to the first embodiment. [Figure 10] 10 is a graph for explaining correction of the predicted temperature of the fixing film in a modified example. [Figure 11] 10 is a graph for explaining determination of the influence of airflow based on the rate of decrease in measured temperature. [Figure 12] 10 is a flowchart showing an example of the flow of a temperature monitoring process according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0012] <1. Overview of image forming device> 1 is a schematic diagram showing an example of the configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is a laser beam printer that forms an image on a recording material using an electrophotographic method. Note that the technology according to the present disclosure is not limited to this example and may be applied to other types of printers, as well as other types of image forming apparatuses such as copiers and multifunction peripherals.

[0013] 1, the image forming apparatus 1 includes a cassette 5, an image forming unit 10, a conveying unit 20, a fixing device 30, an ejection tray 45, and a control unit 100. The cassette 5 is a storage unit that stores a stack of recording materials.

[0014] The image forming unit 10 is an image forming means that forms a toner image on a recording material. The image forming unit 10 includes a photosensitive drum 11, a charging roller 12, an exposure unit 13, a developing unit 14, a transfer roller 15, and a drum cleaner 16. As an example, the photosensitive drum 11, the charging roller 12, the developing unit 14, and the drum cleaner 16 may be included in a process cartridge that is a component that can be attached to and detached from the housing of the image forming apparatus 1.

[0015] The photosensitive drum 11 is a drum-shaped image carrier. Driven by a drum drive motor (not shown), the photosensitive drum 11 rotates in the direction of arrow R1 (clockwise) in the figure at a predetermined peripheral speed (process speed). A charging voltage (charging bias) is applied to the charging roller 12, which uniformly charges the surface of the rotating photosensitive drum 11 to a predetermined potential, for example, negative polarity. The exposure device 13 may be, for example, a laser scanner. The exposure device 13 scans the charged surface of the photosensitive drum 11 with a laser beam modulated according to input image data, thereby forming an electrostatic latent image on the surface of the photosensitive drum 11. The charge on the portion of the surface of the photosensitive drum 11 exposed to the laser beam is removed. The developing device 14 includes a toner container 14a and a developing roller 14b. The toner container 14b contains toner as a developer. A developing voltage (developing bias) is applied to the developing roller 14b, and the developing roller 14b supplies toner in the toner storage portion 14b to the rotating photosensitive drum 11, thereby developing (visualizing) the electrostatic latent image on the surface of the photosensitive drum 11 and forming a toner image (developer image). At this time, the toner carried by the developing roller 14b is charged, for example, to a negative polarity due to friction with a regulating member (not shown), and adheres to the photosensitive drum 11 due to the action of the potential difference between the developing roller 14b and the photosensitive drum 11. The transfer roller 15 is disposed opposite the photosensitive drum 11 at the transfer nip Nt, and is urged toward the photosensitive drum 11. When no recording material is present, the transfer roller 15 comes into contact with the photosensitive drum 11 at the transfer nip Nt. The photosensitive drum 11 carries the toner image and transports it from the development position to the transfer nip Nt.

[0016] The conveying unit 20 is a conveying means that conveys the recording material along the conveying path. The conveying unit 20 includes a feed roller 21, a first conveying roller pair 22, a top sensor 23, a guide 24, a second conveying roller pair 25, and a discharge roller pair 26. The feed roller 21 picks up recording materials one by one from a stack of recording materials in the cassette 5 and feeds them to the conveying path. The first conveying roller pair 22 sends the recording material into the transfer nip Nt in synchronization with the timing at which the toner image on the surface of the photosensitive drum 11 reaches the transfer nip Nt. The top sensor 23 detects the leading edge of the recording material and outputs a detection signal to the control unit 100. The control unit 100 controls the conveyance of the recording material by the first conveying roller pair 22 based on the detection signal from the top sensor 23.

[0017] The toner image on the surface of the photosensitive drum 11 is transferred at the transfer nip Nt to a recording material being conveyed while being sandwiched between the photosensitive drum 11 and the transfer roller 15. At this time, a transfer voltage (transfer bias) having a polarity (e.g., positive polarity) opposite to the polarity (e.g., negative polarity) of the toner is applied to the transfer roller 15. The toner image is transferred to the recording material by the potential difference with this transfer voltage. The drum cleaner 16 includes a cleaning blade 16a and a waste toner container 16b. The cleaning blade 16a scrapes off toner (waste toner) remaining on the surface of the photosensitive drum 11 and collects the waste toner in the waste toner container 16b. The waste toner is accumulated in the waste toner container 16b.

[0018] The fixing device 30 is a fixing unit that fixes a toner image formed on a recording material to the recording material. The recording material to which the toner image has been transferred is transported along a guide 24 and sent into the fixing nip Nf of the fixing device 30. In the example shown in FIG. 1, the fixing device 30 includes a fixing film 31, a pressure roller 32, a heater 33, a heater holder 34, and a stay 35. The fixing film 31 is a flexible, endless fixing member that can rotate in the direction of arrow R2 in the figure. The pressure roller 32 is disposed opposite the fixing film 31 in the fixing nip Nf and is biased toward the fixing film 31. The pressure roller 32 is driven by a fixing drive motor (not shown) to rotate in the direction of arrow R3 in the figure, thereby sandwiching and transporting the recording material that has reached the fixing nip Nf together with the fixing film 31. The heater 33 is a heating element that heats the fixing film 31. The heater holder 34 holds the heater 33. The stay 35 fixedly supports the heater holder 34. The toner of the toner image formed on the recording material is heated through the fixing film 31 in the fixing nip Nf to melt, and is then pressed by the pressure roller 32 to be fixed to the recording material. As a result, the toner image is fixed to the recording material. An example of a more detailed configuration of the fixing device 30 will be described later.

[0019] The second conveying roller pair 25 conveys the recording material that has passed through the fixing nip Nf downstream of the conveying path. The discharge roller pair 26 discharges the recording material onto a discharge tray 45 located on the top surface of the housing of the image forming apparatus 1.

[0020] The control unit 100 is a control means that controls the overall operation of the image forming apparatus 1. The control unit 100 may include, for example, a memory for storing computer programs and various data, a processing circuit for executing the computer programs, an input / output interface for signal input / output, and a communication interface for communication with external devices. The memory may include a combination of any type of non-volatile and volatile storage medium, such as a read-only memory (ROM) and a random access memory (RAM). The processing circuit may include, for example, one or more central processing units (CPUs). For example, when a print job is received from an external host computer, the control unit 100 controls the image forming unit 10, the conveying unit 20, and the fixing unit 30 to form an image on a recording material based on image data included in the received print job. As an example, the image forming apparatus 1 may be a high-speed machine capable of forming images on A4-sized recording materials at a speed of 70 sheets per minute.

[0021] <2. Details of the fixing device> Fig. 2 is a schematic diagram showing an example of the configuration related to the fixing device 30 shown in Fig. 1. Fig. 2 schematically shows an example of the configuration when the cross section of the fixing device 30 is viewed from the rotation axis direction of the pressure roller 32, how the recording material P passes through the fixing nip Nf together with unfixed toner T, and an example of the connection relationship between the fixing device 30 and the control unit 100. Furthermore, an example of the detailed configuration of the heater 33 of the fixing device 30 is shown in an enlarged view.

[0022] <2-1. Fixing materials> The fixing film 31 is a cylindrical film that extends in the depth direction in the figure. The fixing film 31 is loosely fitted onto the heater holder 34. The heater 33 is held by the heater holder 34 by fitting into a recess formed in the lower part of the heater holder 34. In the fixing nip Nf, the inner surface of the fixing film 31 slidably contacts the lower surface of the heater 33 and the lower surface of the heater holder 34 (around the recess) over the width W. Since the heater holder 34 is fixedly supported by the stay 35, even if the fixing film 31 rotates in response to the rotation of the pressure roller 32 and the conveyance of the recording material P, the heater holder 34 does not rotate and the heater 33 does not move. The heater holder 34 acts as a guide member that guides the fixing film 31 to the fixing nip Nf.

[0023] The fixing film 31 has a structure in which, for example, a base layer, an elastic layer, and a surface layer are laminated in this order from the inside to the outside. The base layer is formed of a highly heat-resistant resin material such as polyimide (PI), polyamideimide (PAI), polyetheretherketone (PEEK), or polyethersulfone (PES). The thickness of the base layer is selected so as to achieve both sufficient mechanical strength and a small heat capacity for quick start performance. For example, the thickness of the base layer may be in the range of 18 to 150 micrometers (μm), preferably in the range of 30 to 100 μm, and more preferably in the range of 50 to 80 μm. The base layer may be made conductive by adding carbon as an electronic conductive agent (or a metal complex as an ionic conductive agent). The elastic layer may be formed of, for example, highly heat-resistant silicone rubber or fluororubber, and may be made conductive by adding carbon as an electronic conductive agent. The elastic layer may be imparted with high thermal conductivity by adding an inorganic material such as ceramic powder, metal oxide powder, or metal powder (e.g., alumina, metal silicon, silicon carbide, or zinc oxide) as a thermally conductive filler. For example, a thermal conductivity of 0.9 W / m·K or higher is suitable for high-speed machines. From the viewpoint of heating efficiency for fixing performance, the thickness of the elastic layer may be, for example, within a range of 30 to 500 μm, preferably within a range of 100 to 400 μm, and more preferably within a range of 200 to 300 μm. The surface layer acting as a release layer is required to have high toner releasability and high abrasion resistance. For example, the surface layer may be formed as a coating layer obtained by baking a fluororesin dispersion, or as a tube layer formed from a fluororesin. The surface layer may be made electrically conductive by adding carbon as an electronic conductor (or a metal complex as an ionic conductor). From the viewpoints of mold releasability, abrasion resistance, and heating efficiency, the thickness of the surface layer may be, for example, in the range of 1 to 50 μm, preferably in the range of 5 to 40 μm, and more preferably in the range of 10 to 30 μm. The heater holder 34 is formed of a highly heat-resistant resin material, such as liquid crystal polymer (LCP), phenol resin, polyphenylene sulfide (PPS), or PEEK.

[0024] <2-2. Heating element> As shown enlarged in FIG. 2, the heater 33 includes a heater substrate 36, a resistor pattern 37, an overcoat glass 38, and an insulating layer 39. The heater substrate 36 is a highly heat-resistant substrate made of a ceramic material such as aluminum nitride or alumina. The heater substrate 36 may be made of a metal material instead of a ceramic material. The resistor pattern 37 is a pattern of a heat-generating resistor layer formed on the upper surface of the heater substrate 36. The resistor pattern 37 is connected to a power source via a switching element 105 (described later). When the switching element 105 is turned on, a current flows through the resistor pattern 37, causing the resistor pattern 37 to generate heat. The overcoat glass 38 is a flat, electrically insulating and abrasion-resistant protective member that covers the lower surface of the heater substrate 36. The insulating layer 39 protects the resistor pattern 37 on the upper surface of the heater substrate 36.

[0025] In this embodiment, a thermistor 40 is disposed near the heater 33, more specifically on the upper surface of the heater 33 (the surface opposite to the surface that contacts the fixing film 31). The thermistor 40 is a measuring unit that measures the temperature of the heater 33. The thermistor 40 outputs a signal indicating the measured temperature of the heater 33 to the control unit 100.

[0026] <2-3. Pressure Member> The pressure roller 32 comprises, for example, a core shaft, a cylindrical elastic layer surrounding the core shaft, and a surface layer covering the surface of the elastic layer. The core shaft may be a solid columnar member or a hollow cylindrical member formed from a metal material such as aluminum, an aluminum alloy, or iron. The elastic layer of the pressure roller 32 may be formed from, for example, silicone rubber with high heat resistance, and may be made conductive by adding carbon as an electronic conductor. The surface layer of the pressure roller 32 may be formed from, for example, fluororesin, and may also be made conductive by adding carbon as an electronic conductor (or a metal complex as an ionic conductor). By making the elastic layer and surface layer conductive, it is possible to suppress charging of the pressure roller 32 caused by the passage of a recording material carrying a toner image through the fixing nip Nf.

[0027] Although not shown in FIG. 2, the core shaft of the pressure roller 32 has a drive gear at its end that receives a driving force from the fixing drive motor. When the fixing drive motor rotates under the control of the control unit 100, the pressure roller 32 rotates. This rotation of the pressure roller 32 is transmitted to the fixing film 31 by the frictional force between the fixing film 31 and the pressure roller 32 at the fixing nip Nf. As a result, the fixing film 31 rotates around the heater holder 34 and the stay 35 while sliding against the lower surfaces of the heater 33 and the heater holder 34.

[0028] 3. Fixing temperature control The control unit 100 controls the fixing of the toner image onto the recording material P by the fixing device 30 in accordance with at least one control condition. The control condition for fixing control includes, for example, the heat generation amount of the heater 33 during the fixing operation. To control the heat generation amount of the heater 33, a switching element 105 is provided on a power supply line from a power source 50 (for example, a commercial power source) to the heater 33. The switching element 105 may be, for example, a triac. When the CPU 101 switches the switching element 105 on, power is supplied from the power source 50 to the heater 33, the resistor pattern 37 of the heater 33 generates heat, and the heater 33 heats the fixing film 31. When the CPU 101 switches the switching element 105 off, the power supply from the power source 50 to the heater 33 is cut off. Other examples of the control conditions for fixing control will be further described later.

[0029] As described above, appropriate control of the temperature of the fixing film 31 during the fixing operation (hereinafter referred to as the fixing temperature) is important for achieving stable fixing performance. The fixing temperature may be controlled by adjusting the duty ratio of the switching element 105 through typical feedback control based on the difference between the current temperature and the target temperature. However, in an image forming apparatus 1 that employs a film heating method, it is difficult to directly measure the fixing temperature at the fixing nip Nf. Therefore, in this embodiment, the CPU 101 predicts the current fixing temperature using the temperature of the heater 33 measured by the thermistor 40, and controls the supply of power to the heater 33 based on the predicted temperature.

[0030] <3-1. Prediction of Fixing Temperature> The CPU 101 may predict the current fixing temperature by inputting the measured temperature of the heater 33 into any known prediction model. For example, the prediction model described in Patent Document 2 consists of a set of relational equations that model heat transfer between components, including the heater and the fixing film. Applying this to the configuration example shown in FIG. 2, the temperature of the heater 33 affects the temperatures of the fixing film 31 and heater holder 34 after one control cycle has elapsed. If power is supplied to the heater 33 during that control cycle, the heater 33 generates heat according to the newly received power amount. The temperature of the fixing film 31 affects the temperatures of the recording material P or the pressure roller 32, the heater 33, and the heater holder 34. The temperature of the heater holder 34 affects the temperatures of the fixing film 31, the heater 33, and the stay 35. Therefore, by defining the influence of the temperature of each component on the temperature of other components after one control cycle has elapsed using relational equations with predetermined coefficients, the temperature of each component at a subsequent time point can be predicted based on the temperature of each component at a certain time point. At this time, the temperature of the heater 33 is determined by taking into account not only the influence of the temperatures of other components but also the temperature increase due to new heat generation. Naturally, other parameters, such as the process speed or the number of rotations of the roller, the area ratio (print rate) of the toner T, or the ambient temperature, may be further taken into account in the relational equation. The memory 103 stores a prediction model consisting of a set of such relational equations. For example, a state in which the temperatures of all components are equal to the ambient temperature is set as the initial state of prediction. Then, for each control cycle, the CPU 101 inputs the measured temperature of the heater 33 and the amount of power supplied to the heater 33 (as well as other optional parameters) into the prediction model to predict the temperature of the fixing film 31 (and the temperatures of other components). By repeating this process over multiple control cycles, the temperature of the fixing film 31, which changes over time, can be continuously predicted.

[0031] FIG. 3 is a graph for explaining an example of a change over time in the prediction result of the fixing temperature as a conventional example. The horizontal axis of the graph represents the passage of time in seconds, and the vertical axis represents the predicted temperature in degrees Celsius. FIG. 3 shows a predicted temperature profile E f1is plotted. The predicted temperature profile E f1 According to this, in response to receiving a print job, CPU 101 starts supplying power from power supply 50 to heater 33 at time T1. Then, the predicted temperature rises rapidly. At time T2, the leading edge of recording material P on which a toner image has been formed reaches fixing nip Nf, and at time T3, the trailing edge of recording material P leaves fixing nip Nf. From time T2 to time T3, the predicted temperature levels off and then drops slightly. After time T3, CPU 101 stops supplying power to heater 33, causing the predicted temperature to drop due to natural cooling.

[0032] <3-2. Fixing performance> Predicted temperature profile E f1 In the example of Fig. 3, if the predicted temperature of the fixing film 31 during the period when the recording material P passes through the fixing nip Nf (hereinafter referred to as the fixing period) is within the target range and there is no prediction error, the expected fixing performance should be achieved. In the example of Fig. 3, the fixing period is the period from time T2 to time T3.

[0033] 4 is a graph for explaining some examples of changes over time in the actual temperature of the fixing film 31. In FIG. 4, three actual temperature profiles R f1 , R f2 and R f3 is plotted, and the desired fixing temperature range (target temperature range) Z TGT In the example of FIG. 4, the target temperature range Z TGT The actual temperature profile R is in the range of approximately 133°C to 138°C. f1 According to the above, the actual temperature of the fixing film 31 is within the target temperature range Z throughout the fixing period. TGT On the other hand, the actual temperature profile R f2 According to the above, the actual temperature of the fixing film 31 is within the target temperature range Z throughout the fixing period. TGT In this case, the toner T does not melt properly, and the toner image is not fixed sufficiently to the recording material P. In other words, fixing failure occurs. f3According to the above, the actual temperature of the fixing film 31 is within the target temperature range Z throughout the fixing period. TGT In this case, the viscosity of the molten toner T decreases, and the toner transfers to the fixing film 31, that is, hot offset occurs.

[0034] The deviation of the fixing temperature from the target temperature is caused by an error in the prediction of the fixing temperature. For example, if the predicted temperature at the start of the image forming operation is significantly higher than the actual temperature, the difference between the target temperature and the predicted temperature becomes too small, and sufficient power is not supplied to the heater 33 to raise the temperature of the fixing film 31 to the target temperature by time T2. As a result, the actual temperature profile R f2 As shown, the fixing temperature during the fixing period is within the target temperature range Z TGT Conversely, if the predicted temperature at the start of the image forming operation is significantly lower than the actual temperature, the difference between the target temperature and the predicted temperature will be excessive. As a result, excessive power will be supplied to the heater 33 by time T2, causing the actual temperature profile R f3 As shown, the fixing temperature during the fixing period is within the target temperature range Z TGT will exceed the upper limit of

[0035] <3-3. Effects of air currents> No matter what kind of prediction model is used to predict the temperature of the fixing member, there is no guarantee that the image forming apparatus will actually be operated under the conditions assumed by the prediction model. In particular, the temperature of a fixing member using a film heating method is easily affected by external disturbances. For example, if the environment in which the image forming apparatus is installed is subject to strong air currents that are different from the assumed conditions, the temperature of the fixing member is more likely to deviate from the predicted temperature due to the influence of the air currents. Deviation of the actual temperature of the fixing member from the predicted temperature can cause image defects such as poor fixing or hot offset, as described in relation to Figure 4.

[0036] For example, one prediction model assumes that the temperature of the fixing member will decrease due to natural cooling after the completion of an image formation operation. In the prediction model described in Patent Document 2, this assumption is reflected in the coefficients of a relational equation that represents the temperature transition of the member. However, in the actual installation environment of an image forming apparatus, there are often external devices that generate airflow, such as air conditioners or ceiling fans. When airflow from such external devices enters the image forming apparatus through an opening in the housing, the temperature of the fixing member decreases faster than natural cooling. In other words, the airflow from external devices affects the temperature of the fixing member as a disturbance to the assumptions of a given prediction model (e.g., determined during the manufacturing stage of the apparatus).

[0037] 5 is a graph for explaining the influence of the airflow on the actual temperature of the fixing film 31. In FIG. 5, the same predicted temperature profile E f1 together with the actual temperature profile R f3 and R f4 The change in the actual temperature of the fixing film 31 over time can be obtained experimentally by measuring the surface temperature of the fixing film 31 at regular time intervals using a non-contact thermometer (e.g., a radiation thermometer) installed immediately after the fixing nip Nf.

[0038] Actual temperature profile R f3 The actual temperature profile R represents the change over time in the actual temperature of the fixing film 31 when there is no influence of airflow and the temperature of the fixing film 31 is naturally cooled after the image forming operation is completed at time T3. f3 is the predicted temperature profile E f1 This means that there is almost no prediction error.

[0039] On the other hand, the actual temperature profile R f4 represents the change over time in the actual temperature of the fixing film 31 when the temperature of the fixing film 31 is affected by the air flow and the temperature of the fixing film 31 drops more quickly after the image forming operation is completed. f4is the predicted temperature profile E after time T3. f1 The difference gradually deviates from the actual temperature, and for example, at time T4, 30 seconds after time T3, the difference reaches approximately 20° C. In other words, at time T4, the predicted temperature of the fixing film 31 is estimated to be approximately 20° C. higher than the actual temperature. This can cause poor fixing in the print job that is executed thereafter.

[0040] 6 is a graph for explaining an example of the cause of an image defect when the actual temperature of the fixing film 31 deviates from the predicted temperature. f1 together with the actual temperature profile R f5 The actual temperature profile R f5 represents the change over time in the actual temperature of the fixing film 31 when the predicted temperature of the fixing film 31 is estimated to be 10° C. higher than the actual temperature at time T1 when the image forming operation is started. f5 Under this condition, at the start of the image forming operation, the difference between the actual temperature of the fixing film 31 and the target temperature is 10°C larger than the difference between the predicted temperature and the target temperature. Nevertheless, since the difference is estimated to be small, the heater 33 is not supplied with enough electric power (or sufficient heating time) to raise the actual temperature of the fixing film 31 to the target temperature. As a result, the actual temperature of the fixing film 31 during the fixing period falls outside the target temperature range Z. TGT will fall below the lower limit of

[0041] Because it is impossible to know at the time of manufacturing an image forming apparatus whether or not an external device that generates air currents is present in the actual installation environment of the image forming apparatus, it is not practical to incorporate the influence of such air currents into the prediction model in advance. Therefore, in this embodiment, CPU 101 determines whether the temperature of fixing film 31 is affected by air currents based on the temperature of heater 33 measured by thermistor 40. Then, in response to the determination that the temperature of fixing film 31 is affected by air currents, CPU 101 changes at least one control condition for controlling the fixing of a toner image on a recording material by fixing device 30 from the condition when there is no influence of air currents. This compensates for the influence of air currents and reduces the occurrence of image defects. In the following sections, several examples of such control will be described in detail.

[0042] <4. First Example> <4-1. Determining the influence of air currents> In the first embodiment, the CPU 101 derives the predicted temperature of the fixing film 31 by inputting the measured temperature of the heater 33 into the above-described prediction model stored in the memory 103. The temperature of the heater 33 is measured by the thermistor 40. The fixing device 30 does not include any temperature measurement means (e.g., a temperature sensor that directly measures the temperature of the fixing film 31) other than the thermistor 40 to predict the temperature of the fixing film 31. This facilitates miniaturization and cost reduction of the fixing device 30. The CPU 101 uses the predicted temperature of the fixing film 31 as a control variable for feedback control and controls the supply of power from the power source 50 to the heater 33 so that the temperature of the fixing film 31 falls within a target temperature range during the fixing period.

[0043] Furthermore, the CPU 101 monitors the measured temperature of the heater 33 to determine whether or not the temperature of the fixing film 31 is affected by the airflow. Specifically, in the first embodiment, the CPU 101 determines that the temperature of the fixing film 31 is affected by the airflow when the measured temperature of the heater 33 is lower than a first threshold value based on the predicted temperature of the fixing film 31. The first threshold value is equal to the sum of the predicted temperature of the fixing film 31 and a predetermined offset. Note that the offset may be zero, in which case the first threshold value is equal to the predicted temperature of the fixing film 31.

[0044] 7 is a graph for explaining the relationship between the temperature of the fixing film and the temperature of the heater when there is no influence of airflow and when there is an influence of airflow. In FIG. 7, the same predicted temperature profile E shown in FIG. f1 and the measured temperature profile R of the heater 33. t1 , R t2 , and the actual temperature profile R of the fixing film 31 f4 The measured temperature profile R t1 represents the change in the measured temperature of the heater 33 over time, measured directly by the thermistor 40, when there is no influence of airflow. f1 is the measured temperature profile R t1 The heater 33 generates heat by itself when energized and applies heat to the fixing film 31. Therefore, the measured temperature profile R t1 is the predicted temperature profile E over the entire period shown. f1 It shows higher values.

[0045] Measurement temperature profile R t2 represents the change over time in the measured temperature of the heater 33, which is measured directly by the thermistor 40, when there is an influence of air current. When there is an influence of air current, the temperature of the fixing film 31 should also decrease in the same manner as the decrease in the temperature of the heater 33. f4 represents the change in the actual temperature of the fixing film 31 over time.

[0046] Measurement temperature profile R t2 According to the measurement temperature profile R, the measured temperature of the heater 33 is the temperature of the heater 33 that cools naturally after time T3 when there is no influence of airflow. t1 ) and catches up with the predicted temperature of the fixing film 31 at time T4. After time T4, the measured temperature profile R t2 The measured temperature of the heater 33 indicated by is the predicted temperature profile E f1 Therefore, the CPU 101 sets the predicted temperature or the sum of the predicted temperature and a predetermined offset as a first threshold value, and compares the measured temperature of the heater 33 with this first threshold value, thereby easily determining whether the temperature of the fixing film 31 is affected by the airflow. For example, if the offset is zero and the measured temperature of the heater 33 is lower than the predicted temperature of the fixing film 31 indicated by the measured temperature profile R t2 When the temperature of the fixing film 31 decreases as shown in FIG.

[0047] <4-2. Changing control conditions> When the CPU 101 determines that the temperature of the fixing film 31 is affected by the airflow, it changes at least one control condition for controlling fixing by the fixing device 30. In this embodiment, changing at least one control condition includes increasing the amount of heat generated per unit time by the heater 33. The CPU 101 can increase the amount of heat generated per unit time by the heater 33, for example, by one or more of lowering the control variable (predicted temperature of the fixing film 31) of the feedback control, raising the target value, and increasing the gain. As a simple example, the predicted temperature as the control variable of the feedback control may be lowered to a value equal to the measured temperature of the heater 33. FIG. 8 is an explanatory diagram for explaining such a reduction in the predicted temperature. FIG. 8 shows the same predicted temperature profile E as that shown in FIG. 7. f1 Along with the modified predicted temperature profile E f1 ´ is shown. Predicted temperature profile E f1´ is the predicted temperature profile E f1 After time T4, the measured temperature profile R shown in Fig. 7 t1 That is, after time T4, the predicted temperature is lowered to the measured temperature of the heater 33 when the airflow is present. By adjusting the parameters of the feedback control in this way, power is supplied to the heater 33 at a higher duty ratio when the next image forming operation starts, and the amount of heat generated per unit time increases. This causes the temperature of the fixing film 31 to rise more quickly, reducing the possibility that the temperature of the fixing film 31 will deviate from the target temperature range during the fixing period.

[0048] <4-3. Processing flow> Fig. 9 is a flowchart showing an example of the flow of the temperature monitoring process according to Example 1. The temperature monitoring process shown in Fig. 9 can be repeatedly executed by the control unit 100 in a fixed monitoring cycle, for example, while the image forming apparatus 1 is not performing an image forming operation.

[0049] First, in S101, the control unit 100 causes the thermistor 40 disposed near the heater 33 to measure the temperature of the heater 33 and acquires the measured temperature. Next, in S103, the control unit 100 predicts the current temperature of the fixing film 31 by inputting the measured temperature of the heater 33 into a predefined prediction model. Next, in S105, the control unit 100 determines a first threshold value for determining the influence of airflow based on the predicted temperature of the fixing film 31. As described above, the first threshold value may be equal to the predicted temperature or may be the sum of the predicted temperature and a predetermined offset.

[0050] Next, in S107, the control unit 100 determines whether the measured temperature of the heater 33 acquired in S101 is lower than the first threshold value determined in S105. If it is determined that the measured temperature of the heater 33 is lower than the first threshold value, the control unit 100 changes at least one control condition for the next fixing operation in S109. If it is determined that the measured temperature of the heater 33 is not lower than the first threshold value, S109 is skipped.

[0051] Once the control conditions for the next fixing operation have been changed in S109, the temperature monitoring process in the subsequent monitoring cycle may be omitted, and the changed control conditions may be maintained until the next fixing operation.

[0052] <4-4. Comparative Test> In order to confirm the effects of the first embodiment, a comparative test was conducted to compare the fixing performance between the first embodiment and two comparative examples. In the first embodiment and the comparative examples, the components of the fixing device 30 are the same. The main features of the fixing film 31 and the pressure roller 32 are as follows: Fixing film -Outer diameter: approx. 24[mm] -Base material: PI with conductive agent added -Base layer thickness: approx. 70 μm - Elastic layer material: Silicon rubber with alumina and metal silicon added as thermally conductive fillers -Thermal conductivity of the elastic layer: 1.5 [W / m K] -Elastic layer thickness: approx. 270 μm -Surface material: Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) -Surface thickness: approx. 25 μm Fixing nip width (W in Figure 2): 9 mm Pressure roller -Outer diameter: approx. 25[mm] - Core material: Aluminum - Elastic layer material: Silicone rubber with conductive agent added -Surface material: PFA with conductive agent added -Surface thickness: approx. 30 μm -Surface electrical resistance: approx. 10 5 [Ω / cm 2 ] -Pressure: 186.2 [N] (= 19 [kgf])

[0053] Other main test conditions are as follows: Test environment: -Environmental temperature: 15[℃] - Environmental humidity (relative humidity): 10% Recording material used -Product: Canon Marketing Japan CS-068 -Size: A4 -Basic weight: 68[g / cm 2 ]

[0054] In the first embodiment, a first threshold value equal to the predicted temperature of the fixing film 31 is used, and after it is determined that the temperature of the fixing film 31 is affected by the airflow, the predicted temperature profile E after the change shown in FIG. f1 On the other hand, in the two comparative examples, the influence of the airflow is not judged, and therefore the predicted temperature of the fixing film 31 is changed according to the predicted temperature profile E f1 The transition is as follows:

[0055] In addition, in the first embodiment and the first comparative example, when the predicted temperatures at the start of the image forming operation are 15°C and 25°C, the target values ​​for temperature control are set to 165°C and 155°C, respectively. On the other hand, in the second comparative example, the target value for temperature control is set to 165°C regardless of the predicted temperature at the start of the image forming operation. The predicted temperature profiles and target values ​​for temperature control corresponding to the first embodiment, the first comparative example, and the second comparative example are summarized in Table 1 below.

[0056] [Table 1]

[0057] For each of the first example, the first comparative example, and the second comparative example, the temperature of the fixing film 31 was changed in the following two scenarios, and then the fixing performance of each was subjectively evaluated. A) After printing images on 10 sheets of recording material, let them cool naturally for 30 minutes. B) After printing images on 10 sheets of recording material, the fixing film 31 is cooled by applying airflow from an external fan to the fixing film 31.

[0058] In scenario A, even after 30 minutes of natural cooling, the actual temperature of the fixing film 31 was 25° C., which was 10° C. higher than the ambient temperature of 15° C. In scenario B, on the other hand, after 30 minutes of cooling, the actual temperature of the fixing film 31 dropped to 15° C., the same as the ambient temperature.

[0059] Table 2 below shows the results of each evaluation. A circle in the table indicates that no image defects (poor fixing or hot offset) that would be a problem in practical use occurred. A cross indicates that an image defect that would be a problem in practical use occurred.

[0060] [Table 2]

[0061] In the first comparative example, no image defects occurred in scenario A, which was not affected by the outside air, but poor fixing occurred in scenario B, which was affected by the outside air. The reason why poor fixing occurred in scenario B is that the predicted temperature of the fixing film 31 at the start of the image forming operation was 25°C, so the target value for temperature control was set to 155°C, but the actual temperature at the start was 15°C, which was 10°C lower than the predicted temperature. In this case, the heater 33 was unable to generate a sufficient amount of heat by the time the fixing period began, and the temperature of the fixing film 31 did not reach the lower limit of the target temperature range.

[0062] In the second comparative example, no image defects occurred in scenario B, which was affected by the outside air, but hot offset occurred in scenario A, which was not affected by the outside air. The reason why hot offset occurred in scenario A is that the predicted temperature of the fixing film 31 at the start of the image formation operation was 25°C, so the target value for temperature control was set to 165°C, but this target value was too high. In this case, the heater 33 generates an excessive amount of heat before the fixing period, and as a result, the temperature of the fixing film 31 exceeds the upper limit of the target temperature range.

[0063] In contrast, in the first embodiment, no image defects occurred in either Scenario A or Scenario B. The reason why hot offset did not occur in Scenario A is that the predicted temperature of the fixing film 31 at the start of the image forming operation was 25°C, which had no error with respect to the actual temperature, and the target temperature control value of 155°C was appropriate. The reason why fixing defects did not occur in Scenario B is that although the predicted temperature at the start of the image forming operation was 10°C higher than the actual temperature, the heat generation amount of the heater 33 was increased in response to a determination that there was an influence of the outside air.

[0064] <4-5. Change of control conditions (variation example)> Up to this point, an example of changing at least one control condition has been described, mainly in which the amount of heat generated by the heater 33 during the fixing operation is increased, but the present embodiment is not limited to this example.

[0065] In the first modified example, the CPU 101 may extend the time (hereinafter referred to as preheating time) from the start of power supply to the heater 33 until the recording material reaches the fixing nip Nf in response to the determination that the temperature of the fixing film 31 is affected by the airflow. For example, the CPU 101 can extend the preheating time by delaying the timing of feeding the recording material by the feeding roller 21.

[0066] In the second modified example, when toner images are formed successively on a plurality of recording materials, the CPU 101 may extend the time interval between fixing operations for successive recording materials in response to a determination that the temperature of the fixing film 31 is being affected by an air current. For example, the CPU 101 can extend the time interval between fixing operations by delaying the timing at which the feed roller 21 feeds the second and subsequent sheets of recording material.

[0067] In either modification, the heater 33 heats the fixing film 31 for a longer time before the fixing period, thereby reducing the possibility that the temperature of the fixing film 31 will deviate from the target temperature range during the fixing period. These modifications may be combined with the first embodiment in any way. For example, the CPU 101 may increase the amount of heat generated per unit time by the heater 33 and extend the preheating time in response to a determination that the temperature of the fixing film 31 is being affected by the airflow.

[0068] <4-6. Other variations> As a further modification, the CPU 101 may correct the predicted temperature of the fixing film 31 so that the difference obtained by subtracting the predicted temperature of the fixing film 31 from the measured temperature of the heater 33 is maintained constant. Fig. 10 is a graph for explaining the correction of the predicted temperature of the fixing film 31 in such a modification. Fig. 10 shows a graph for explaining the correction of the predicted temperature of the fixing film 31 in the same manner as in Fig. 7, where the measured temperature profile R t1 and the corrected predicted temperature profile E f1 ' is shown. Here, the CPU 101 sets the sum of the predicted temperature and the offset Δt as the first threshold value, and determines whether the temperature of the fixing film 31 is affected by the airflow by comparing the measured temperature of the heater 33 with this first threshold value. In the example of FIG. 10, the measured temperature of the heater 33 gradually drops after the fixing period and catches up with the first threshold value at time T5. Thereafter, the CPU 101 uses the value obtained by subtracting the offset Δt from the measured temperature of the heater 33 as the predicted temperature of the fixing film 31. Therefore, the predicted temperature profile E f1 ´´ indicates the measured temperature profile R after time T5. t1 By using the predicted temperature corrected in this way, it is possible to increase the amount of heat generated per unit time by the heater 33 at the start of the next image forming operation.

[0069] As another modification, the CPU 101 may correct the predicted temperature of the fixing film 31 based on the environmental temperature measured by a temperature sensor (e.g., a thermistor) additionally provided in the image forming apparatus 1. For example, when the predicted temperature of the fixing film 31 is lower than the environmental temperature, the CPU 101 may correct the predicted temperature to a value equal to the environmental temperature. Normally, the temperature of the fixing film 31 should not fall below the environmental temperature, regardless of the influence of airflow. Therefore, when the predicted temperature of the fixing film 31 is lower than the environmental temperature, it is likely to be an abnormal value. Therefore, by correcting the predicted temperature of the fixing film 31 to a value at least equal to or higher than the environmental temperature, it is possible to reduce image defects caused by prediction errors.

[0070] <4-7. Summary of the first embodiment> According to the first embodiment described above, a control unit (e.g., control unit 100) of the image forming apparatus controls the supply of power to the heater using the measured temperature of the heater measured by a measuring unit (thermistor 40). The control of the supply of power to the heater may typically be performed based on the predicted temperature of the fixing member (fixing film 31) predicted using the measured temperature of the heater. When the control unit determines that the temperature of the fixing member is affected by airflow based on the measured temperature of the heater, it changes at least one control condition for controlling the fixing of the toner image to the recording material by the fixing device. Specifically, when the measured temperature of the heater is lower than a first threshold value based on the predicted temperature of the fixing member, the control unit determines that the temperature of the fixing member is affected by airflow, and changes at least one control condition so that the temperature of the fixing member during the fixing period falls within a target temperature range. This flexible change of the control condition reduces the occurrence of image defects in the fixing device due to disturbances. For example, even if the temperature of the fixing member drops due to the influence of airflow beyond the extent predicted by the predictive model, the influence can be counteracted by changing the control conditions, and the fixing member can be heated to the appropriate temperature to perform the fixing operation.

[0071] <5. Second Example> <5-1. Determining the influence of air currents> In the second embodiment, similarly to the first embodiment, the CPU 101 derives the predicted temperature of the fixing film 31 by inputting the measured temperature of the heater 33 into the above-described prediction model. The temperature of the heater 33 is measured by the thermistor 40. The CPU 101 uses the predicted temperature of the fixing film 31 as a control variable for feedback control, and controls the supply of power from the power source 50 to the heater 33 so that the temperature of the fixing film 31 falls within the target temperature range during the fixing period.

[0072] Furthermore, the CPU 101 monitors the measured temperature of the heater 33 to determine whether or not the temperature of the fixing film 31 is affected by the airflow. Specifically, in the second embodiment, the CPU 101 determines that the temperature of the fixing film 31 is affected by the airflow when the rate at which the measured temperature of the heater 33 drops after the fixing device 30 has finished operating is lower than a second threshold. The memory 103 stores the second threshold. The second threshold may be a fixed value that is independent of time, or may be a value that changes depending on the time elapsed since the end of the fixing operation or image forming operation.

[0073] 11 is a graph for explaining the determination of the influence of the airflow based on the rate of decrease in the measured temperature. In FIG. 11, the measured temperature profile R of the heater 33, which is the same as that shown in FIG. t1 and R t2 together with the threshold profile E t0 As mentioned above, the measured temperature profile R t1 represents the change over time in the measured temperature of the heater 33 when there is no influence of airflow (for example, assuming natural cooling). t2 represents the change in the measured temperature of the heater 33 over time when there is an influence of airflow. t1 and R t2 A comparison of the threshold profile E shows that the temperature of the heater 33, which peaks during the fixing period, drops at a faster rate after the fixing operation is completed when there is an airflow effect than when there is no airflow effect. t0 are the two measured temperature profiles R at each time. t1and R t2 The second threshold value described above indicates a value (for example, an average value) between the values ​​indicated by the threshold profile E t0 The slope of the curve can be determined in advance by calculating the slope of the curve, and can be stored in the memory 103 in association with the elapsed time from the end of the operation.

[0074] <5-2. Changing control conditions> In this embodiment, if the CPU 101 determines that the temperature of the fixing film 31 is affected by the airflow, it changes at least one control condition for controlling the fixing by the fixing device 30. The change in the control condition here may be one or a combination of two or more of the methods described in relation to the first embodiment. For example, the CPU 101 may increase the heat generation amount per unit time of the heater 33 by lowering the control variable (predicted temperature of the fixing film 31) of the feedback control, raising the target value, or increasing the gain. The CPU 101 may also extend the preheating time from the start of power supply to the heater 33 until the recording material reaches the fixing nip Nf. The CPU 101 may also extend the time interval between fixing operations for consecutive recording materials when toner images are formed consecutively on multiple recording materials. This increases the temperature of the fixing film 31 more quickly or over a longer period of time, thereby reducing the possibility that the temperature of the fixing film 31 will deviate from the target temperature range in the next fixing period.

[0075] <5-3. Processing flow> Fig. 12 is a flowchart showing an example of the flow of the temperature monitoring process according to Example 2. The temperature monitoring process shown in Fig. 12 can be repeatedly executed by the control unit 100 in a fixed monitoring cycle, for example, while the image forming apparatus 1 is not performing an image forming operation.

[0076] First, in S201, the control unit 100 causes the thermistor 40 disposed near the heater 33 to measure the temperature of the heater 33 and acquires the measured temperature. Next, in S203, the control unit 100 calculates the rate of decrease in the measured temperature of the heater 33. Next, in S205, the control unit 100 acquires from the memory 103 a second threshold value (fixed or time-dependent) for determining the influence of airflow.

[0077] Next, in S207, the control unit 100 determines whether the rate of decrease in the measured temperature of the heater 33 calculated in S203 is faster than the second threshold value acquired in S205. If it is determined that the rate of decrease in the measured temperature is faster than the second threshold value, the control unit 100 changes at least one control condition for the next fixing operation in S209. If it is determined that the rate of decrease in the measured temperature is not faster than the second threshold value, S209 is skipped.

[0078] Once the control conditions for the next fixing operation have been changed in S209, the temperature monitoring process in the subsequent monitoring cycle may be omitted, and the changed control conditions may be maintained until the next fixing operation.

[0079] <5-4. Comparative Test> In order to confirm the effect of the second embodiment, a comparative test was conducted to compare the fixing performance of the second embodiment and two comparative examples. In the second embodiment and the comparative examples, the configuration of the members of the fixing device 30 is the same as the configuration described in relation to the comparative test of the first embodiment.

[0080] In the second embodiment, if it is determined that there is no influence of air currents, the target temperature is set to 155°C if the next operation starts 20 minutes after the previous operation has ended, and the target temperature is set to 165°C if the next operation starts 30 minutes after the previous operation has ended. Also, if it is determined that there is an influence of air currents, the target temperature is set to 165°C if the next operation starts 20 minutes after the previous operation has ended, and the target temperature is set to 170°C if the next operation starts 30 minutes after the previous operation has ended.

[0081] On the other hand, in two comparative examples (third and fourth comparative examples), the influence of airflow is not evaluated. In the third comparative example, the target temperature is set to 155°C when the next operation starts 20 minutes after the end of the previous operation, and the target temperature is set to 165°C when the next operation starts 30 minutes after the end of the previous operation. In the fourth comparative example, the target temperature is set to 165°C when the next operation starts 20 minutes after the end of the previous operation, and the target temperature is set to 175°C when the next operation starts 30 minutes after the end of the previous operation. The target values ​​of temperature control under the test conditions for each of the second example, third comparative example, and fourth comparative example are summarized in Table 3 below.

[0082] [Table 3]

[0083] For each of the second example, the third comparative example, and the fourth comparative example, the temperature of the fixing film 31 was changed in the following four scenarios, and then the fixing performance of each was subjectively evaluated. C) After printing images on 10 sheets of recording material, let them cool naturally for 20 minutes. D) After printing images on 10 sheets of recording material, let them cool naturally for 30 minutes. E) After printing images on 10 sheets of recording material, the fixing film 31 is cooled for 20 minutes by applying airflow from an external fan to the fixing film 31. F) After printing images on 10 sheets of recording material, the fixing film 31 is cooled for 30 minutes by applying airflow from an external fan to the fixing film 31.

[0084] The following Table 4 shows a list of the evaluation results. The meanings of the circles and crosses in the table are the same as those in Table 2.

[0085] [Table 4]

[0086] In the third comparative example, no image defects occurred in scenarios C and D, which were not affected by the outside air, but fixing defects occurred in scenarios E and F, which were affected by the outside air. In the fourth comparative example, no image defects occurred in scenarios E and F, which were affected by the outside air, but hot offset occurred in scenarios C and D, which were not affected by the outside air.

[0087] In contrast, in the second embodiment, no image defects occurred in any of scenarios C to F. The reason why hot offset did not occur in scenarios C and D is thought to be because there was no error between the predicted temperature of the fixing film 31 at the start of the image forming operation and the actual temperature (the target temperature was too high in the fourth comparative example). The reason why fixing defects did not occur in scenarios E and F is thought to be because although the predicted temperature at the start of operation was higher than the actual temperature, the heat generation amount of the heater 33 was increased in response to a determination that there was an influence of outside air (the heat generation amount was insufficient in the third comparative example).

[0088] <5-5. Summary of the second example> According to the second embodiment described above, a control unit (e.g., control unit 100) of the image forming apparatus controls the supply of power to the heater using the measured temperature of the heater measured by the measuring unit (thermistor 40). When the control unit determines that the temperature of the fixing member is affected by airflow based on the measured temperature of the heater, the control unit changes at least one control condition for controlling the fixing of the toner image on the recording material by the fixing device. Specifically, when the rate of decrease in the measured temperature of the heater after the fixing device finishes operation is lower than a second threshold, the control unit determines that the temperature of the fixing member is affected by airflow and changes the control condition so that the temperature of the fixing member during the fixing period falls within the target temperature range. This flexible change in control condition reduces the occurrence of image defects in the fixing device due to disturbances. For example, even if the temperature of the fixing member drops due to the influence of airflow beyond the level predicted by the prediction model, the control condition can be changed to counteract this effect, allowing the fixing member to be heated to an appropriate temperature and perform the fixing operation.

[0089] <6. Other embodiments> The above-described embodiment can also be realized in the form of a process in which a program for realizing one or more functions is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program, or by a circuit (e.g., ASIC) that realizes one or more functions.

[0090] The disclosure of the present specification includes at least the following image forming apparatus. (Item 1) a fixing device that fixes the toner image on the recording material; a control unit that controls the fixing of the toner image onto the recording material by the fixing device in accordance with at least one control condition; An image forming apparatus comprising: the fixing device, a rotatable fuser member; a pressure member that, together with the fixing member, pinches and conveys the recording material; a heating element for heating the fixing member; a measuring means for measuring the temperature of the heater; Including, The control means controlling the supply of power to the heating element using the measured temperature of the heating element measured by the measuring means; determining whether the temperature of the fixing member is affected by an air flow based on the measured temperature; changing the at least one control condition in response to a determination that the temperature of the fixing member is affected by the airflow; Image forming device. (Item 2) The control means predicting a temperature of the fuser member using the measured temperature of the heater; controlling the supply of power to the heater based on the predicted temperature of the fixing member; Item 1. The image forming apparatus according to item 1. (Item 3) 3. The image forming apparatus according to claim 2, wherein the control unit determines that the temperature of the fixing member is affected by the airflow when the measured temperature is lower than a first threshold value based on the predicted temperature. (Item 4) 4. The image forming apparatus according to item 3, wherein the first threshold value is equal to the predicted temperature. (Item 5) 4. The image forming apparatus according to item 3, wherein the first threshold value is equal to the sum of the predicted temperature and a predetermined offset. (Item 6) the control means derives the predicted temperature by inputting the measured temperature into a predetermined prediction model; the airflow affects the temperature of the fixing member as a disturbance to the assumptions of the prediction model; Item 6. The image forming apparatus according to any one of items 2 to 5. (Item 7) 7. The image forming apparatus according to claim 6, wherein the preconditions of the prediction model include that the temperature of the fixing member decreases due to natural cooling. (Item 8) the measuring means is a thermistor disposed in the vicinity of the heating element, the fixing device does not include a temperature measuring means other than the thermistor for predicting the temperature of the fixing member; 8. The image forming apparatus according to any one of items 2 to 7. (Item 9) 2. The image forming apparatus according to claim 1, wherein the control unit determines that the temperature of the fixing member is affected by the air flow when the rate of decrease in the measured temperature after the operation of the fixing device is completed is lower than a second threshold value. (Item 10) 10. The image forming apparatus according to any one of items 1 to 9, wherein changing the at least one control condition in response to a determination that the temperature of the fixing member is affected by the airflow includes increasing the amount of heat generated per unit time of the heating element. (Item 11) 11. The image forming apparatus according to any one of items 1 to 10, wherein changing the at least one control condition in response to a determination that the temperature of the fixing member is affected by the air flow includes extending a time period from when power supply to the heating element starts until the recording material reaches a nip between the fixing member and the pressure member. (Item 12) 12. The image forming apparatus according to any one of items 1 to 11, wherein changing the at least one control condition in response to a determination that the temperature of the fixing member is affected by the air flow includes extending the time interval between fixing operations for successive recording materials when toner images are formed continuously on multiple recording materials. (Item 13) 13. The image forming apparatus according to any one of items 1 to 12, wherein the fixing member is a flexible endless film. (Item 14) 14. The image forming apparatus according to any one of items 1 to 13, wherein the airflow is caused by an external device present in an installation environment of the image forming apparatus.

[0091] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0092] 1: image processing device, 5: cassette, 10: image forming unit, 20: conveying unit, 30: fixing device, 31: fixing film (fixing member), 32: pressure roller (pressure member), 33: heater (heating body), 34: heater holder, 35: stay, 40: thermistor (measuring means), 45: discharge tray, 50: power supply, 100: control unit (control means), 101: CPU (control means), 103: memory, 105: switching element, Nt: transfer nip, Nf: fixing nip, P: sheet, T: toner

Claims

1. a fixing device that fixes the toner image on the recording material; a control unit that controls the fixing of the toner image onto the recording material by the fixing device in accordance with at least one control condition; An image forming apparatus comprising: the fixing device, a rotatable fuser member; a pressure member that, together with the fixing member, pinches and conveys the recording material; a heating element for heating the fixing member; a measuring means for measuring the temperature of the heater; Including, The control means controlling the supply of power to the heating element using the measured temperature of the heating element measured by the measuring means; determining whether the temperature of the fixing member is affected by an air flow based on the measured temperature; changing the at least one control condition in response to a determination that the temperature of the fixing member is affected by the airflow; Image forming device.

2. The control means predicting a temperature of the fuser member using the measured temperature of the heater; controlling the supply of power to the heater based on the predicted temperature of the fixing member; The image forming apparatus according to claim 1 .

3. 3. The image forming apparatus according to claim 2, wherein the control unit determines that the temperature of the fixing member is affected by the airflow when the measured temperature is lower than a first threshold value based on the predicted temperature.

4. The image forming apparatus according to claim 3 , wherein the first threshold value is equal to the predicted temperature.

5. The image forming apparatus according to claim 3 , wherein the first threshold value is equal to the sum of the predicted temperature and a predetermined offset.

6. the control means derives the predicted temperature by inputting the measured temperature into a predetermined prediction model; the airflow affects the temperature of the fixing member as a disturbance to the assumptions of the prediction model; The image forming apparatus according to claim 2 .

7. The image forming apparatus according to claim 6 , wherein the preconditions of the prediction model include that the temperature of the fixing member decreases due to natural cooling.

8. the measuring means is a thermistor disposed in the vicinity of the heating element, the fixing device does not include a temperature measuring means other than the thermistor for predicting the temperature of the fixing member; The image forming apparatus according to claim 2 .

9. 2. The image forming apparatus according to claim 1, wherein the control unit determines that the temperature of the fixing member is affected by the air flow when the rate of decrease in the measured temperature after the operation of the fixing device has ended is lower than a second threshold value.

10. 2. The image forming apparatus according to claim 1, wherein changing the at least one control condition in response to a determination that the temperature of the fixing member is affected by the air flow includes increasing the amount of heat generated per unit time of the heating element.

11. 2. The image forming apparatus according to claim 1, wherein changing at least one control condition in response to a determination that the temperature of the fixing member is affected by the air flow includes extending the time from when power supply to the heating element begins until the recording material reaches the nip between the fixing member and the pressure member.

12. 2. The image forming apparatus according to claim 1, wherein changing at least one control condition in response to a determination that the temperature of the fixing member is affected by the air flow includes extending the time interval between fixing operations for successive recording materials when toner images are formed continuously on multiple recording materials.

13. 2. The image forming apparatus according to claim 1, wherein the fixing member is a flexible endless film.

14. The image forming apparatus according to claim 1 , wherein the airflow is caused by an external device present in an installation environment of the image forming apparatus.

Images