Fixing device, image forming apparatus including the same, and heating control method for fixing unit

Abstract

To estimate the ability of a power source to supply a stable voltage and to perform fixing control according to the ability of the power source.SOLUTION: The image forming apparatus includes a fixing member including a fixing member and a pressurizing member that pass a printing paper on which toner is applied and fix the toner to the printing paper, a temperature detection unit that detects a temperature of the fixing member, and a heating member that heats the fixing member, a heating control unit that controls power supplied from a power supply to heat the heating member, and a power supply capability estimation unit that sequentially detects a state of the power supply in a heating state in which the power is supplied and a non-heating state in which the power is not supplied and sequentially estimates self variability related to a variation caused by switching between the heating state and the non-heating state and initial variability related to a variation caused without switching. The heating control part determines control characteristics corresponding to the self-variability and initial variability of the power source and applies them to the control.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fixing device, an image forming apparatus including the fixing device, and a method for controlling heating of a fixing unit, and more particularly to a method for determining control characteristics according to the capacity of a power source to control heating of the fixing unit. [Background technology]

[0002] In recent years, belt-fixing type fixing devices, in which a fixing roller and a pressure roller are pressed together via a fixing belt, have been used to shorten the waiting time (warm-up period) required for the fixing device to warm up. Belt-fixing type fixing devices have a shorter warm-up period because the heat capacity of the fixing belt, which is the object to be heated, is smaller than that of roller-fixing types in which a heater is disposed inside the fixing roller. On the other hand, the temperature of the fixing belt changes quickly, requiring strict settings for optimal control accuracy and responsiveness to keep the temperature within the target range. Therefore, duty control of the current waveform when power (usually an AC power source) is supplied to the heating element (heater) is known. This control turns on and off the power supplied to the heating element in half-wave or full-wave units, and sets the on / off ratio (duty ratio) to a predetermined percentage (duty value) (see, for example, Patent Document 1).

[0003] Furthermore, to reduce the impact of disturbances such as fluctuations in the power supply voltage on fixing temperature control, the power supply voltage is detected and the duty cycle is corrected in accordance with the detected power supply voltage. This is because image forming devices are used in a variety of environments, each with its own power supply status. The following fixing control device is known in this regard: It detects and stores the minimum voltage value within a predetermined sampling period among the voltage values ​​input from a commercial power source. If a new minimum voltage value lower than the stored minimum voltage value is detected, the stored minimum voltage value is updated to the newly detected minimum voltage value. Then, the duty cycle for supplying power to ensure a predetermined fixing rate is calculated based on the stored minimum voltage value (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-258601 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-052045 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned fixing control device determines an appropriate duty value at the minimum possible voltage so as to ensure a fixing rate at the minimum voltage value. In other words, the control focuses only on the worst-case conditions, and does not attempt to estimate the fluctuation characteristics of the power supply, determine appropriate control characteristics according to those fluctuation characteristics, and apply them to the control. Furthermore, there are limitations to simply correcting the duty value according to the power supply voltage, and the reality is that it is not possible to fully respond to various power supply conditions. This invention has been made in consideration of the above circumstances, and for example, even if the power supply voltage is detected, the fixing control is not changed simply depending on whether the magnitude is the rated value or a reduced voltage, but rather the power supply's ability to supply a stable voltage is estimated and fixing control is performed in accordance with the power supply's capacity. [Means for solving the problem]

[0006] The present invention provides a fixing device comprising: a fixing unit including a fixing member and a pressure member that heat and fix toner on printing paper that has toner carried on it as the printing paper passes through; a temperature detection unit that detects the temperature of the fixing member; and a heating member that heats the fixing member; a heating control unit that controls the power supplied from a power source to heat the heating member; and a power supply capacity estimation unit that sequentially detects the state of the power source in a heated state in which power is supplied and a non-heated state in which power is not supplied, and sequentially estimates self-variability related to fluctuations that occur when switching between the heated state and the non-heated state, and initial variability related to fluctuations that occur unrelated to the switching, wherein the heating control unit determines control characteristics according to the self-variability and initial variability of the power source and applies them to the control.

[0007] From a different perspective, the present invention provides a heating control method for a fixing unit, the method comprising the steps of: a processor controlling power supplied from a power source to a fixing unit including a fixing member and a pressure member that heat and fix toner on printing paper by passing the printing paper carrying toner thereon, a temperature detection unit that detects the temperature of the fixing member, and a heating member that heats the fixing member; sequentially detecting the state of the power source in a heating state in which power is supplied and a non-heating state in which power is not supplied, and sequentially estimating self-variability related to fluctuations that occur when the heating state and the non-heating state are switched and initial variability related to fluctuations that occur unrelated to the switching; and determining control characteristics according to the self-variability and initial variability of the power source and applying them to the control. [Effects of the Invention]

[0008] The fixing control device of this invention includes a power supply capacity estimation unit that sequentially detects the state of the power supply in a heating state in which power is supplied and in a non-heating state in which power is not supplied, and sequentially estimates the self-variability associated with fluctuations caused by switching between the heating state and the non-heating state, and the initial variability associated with fluctuations caused unrelated to the switching. The heating control unit determines control characteristics according to the self-variability and initial variability of the power supply and applies them to the control, thereby estimating the power supply's ability to supply a stable voltage, and performing fixing control according to the power supply's capacity. The heating control method for the fixing unit according to the present invention also achieves the same effects. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an explanatory diagram showing an example of the configuration of an image forming apparatus including a fixing device as one embodiment of the present invention; [Figure 2] 1 is a first flowchart showing an example in which a processor executes processing related to a power supply capability estimation unit in an embodiment of the present invention. [Figure 3] 10 is a second flowchart showing an example in which the processor executes processing related to the power supply capability estimation unit in the embodiment. [Figure 4] 10 is a third flowchart showing an example in which the processor executes processing related to the power supply capability estimation unit in the embodiment. [Figure 5] 10 is a graph showing an example in which the power supply voltage is detected multiple times before the start of warm-up in the embodiment. [Figure 6] 6 is a graph showing an example different from FIG. 5 in which the power supply voltage is detected multiple times before the start of warm-up in the embodiment. [Figure 7] 7 is a graph showing an example different from FIGS. 5 and 6 in which the power supply voltage is detected multiple times before the start of warm-up in the embodiment. [Figure 8] 5A and 5B are diagrams of voltage waveforms showing an example of how the power supply voltage fluctuates during printing in an embodiment. [Figure 9] 9 is a voltage waveform diagram showing an example of how the power supply voltage fluctuates during printing, different from that shown in FIG. 8, in the embodiment. [Figure 10] 10 is a voltage waveform diagram showing an example of how the power supply voltage fluctuates during printing, different from those in FIGS. 8 and 9, in the embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in more detail below with reference to the accompanying drawings. Note that the following description is given by way of example only in all respects and should not be construed as limiting the present invention. (Configuration example of fixing device and image forming apparatus) Fig. 1 is an explanatory diagram showing an example of the configuration of an image forming apparatus including a fixing device as one embodiment of the present invention. As shown in Fig. 1, image forming apparatus 10 includes image forming section 11 that forms a toner image and transfers it to printing paper, paper feed section 12 that supplies the printing paper, fixing section 13 that heats the toner transferred to the printing paper and fixes it to the printing paper, and output tray 14 to which the fixed printing paper is discharged.

[0011] The fixing unit 13 includes a fixing member 13F, a heating member 13H, a heat transfer member 13T, a temperature detection unit 13S, and a pressure member 13P. The fixing member 13F is an endless belt-like member heated by the heating member 13H. The base material of the fixing member 13F can be a resin material such as polyimide, polyamide, or fluororesin. Alternatively, a metal material such as stainless steel can be used. The heating member 13H is disposed inside the fixing member 13F and generates heat when electricity is applied. Examples of the heating member 13H that can be used include a resistance heating element such as carbon, graphite, or ceramic, as well as a halogen heater. The heat transfer member 13T is a highly heat-conductive member that transfers heat from the heating member 13H to the fixing member 13F. Examples of suitable materials include a metal material such as aluminum or copper. The heat transfer member 13T is disposed in contact with the fixing member 13F and transfers heat to the fixing member 13F at a contact point 13C. 1, heat transfer member 13T contacts fixing member 13F at flat contact portion 13C. Pressure member 13P is disposed opposite contact portion 13C. Pressure member 13P is a roller with a soft surface, and the surface deforms where it comes into contact with contact portion 13C to form a nip. As pressure member 13P, for example, a roller whose shaft is made of metal such as aluminum and has a silicone rubber layer around its periphery can be used.

[0012] Print paper fed from paper feed unit 12 and having toner transferred thereon in image forming unit 11 passes through the nip between fixing member 13F and pressure member 13P of fixing unit 13. As the paper passes through the nip, the toner is heated and melted by the heat from fixing member 13F, and is fixed to the print paper. After passing through fixing unit 13, the print paper is discharged onto discharge tray 14. Temperature detection unit 13S is disposed opposite fixing member 13F and detects the temperature of fixing member 13F. As temperature detection unit 13S, for example, a non-contact temperature sensor using infrared rays can be applied.

[0013] The image forming apparatus 10 further includes a heating control unit 15 and a power supply capacity estimation unit 16. The image forming apparatus 10 is connected to a power source 17 and receives power from the power source 17. The heating control unit 15 acquires information on the temperature detected by the fixing member 13F from the temperature detection unit 13S and information on the state of the power source 17 estimated by the power supply capacity estimation unit 16. Based on this information, the heating control unit 15 controls the power supplied from the power source 17 to the heating member 13H. The heating control unit 15 is centered around a processor that executes control-related processing, and is also composed of a circuit that controls the power supplied to the heating member 13H and an interface circuit that acquires signals and information from the temperature detection unit 13S and the power supply capacity estimation unit 16. The circuit that controls the power to the heating member 13H may include elements such as a thyristor, a triac, or a transistor. The processor and the interface circuit may also include a microprocessor. The power supply capacity estimation unit 16 detects the state of the power source 17. It detects at least the voltage of the power source 17 and, more preferably, the current from the power source 17 to the fixing unit 13. The power supply capacity estimation unit 16 is centered around a processor that executes processing, and is composed of a detection circuit that detects at least the voltage as the state of the power supply 17, and preferably detects the current to the fixing unit 13, and an interface circuit that acquires signals and information from the detection circuit and provides the estimation results to the heating control unit 15. The processing related to the power supply capacity estimation unit 16 and the processing related to the heating control unit 15 may be executed by a single processor. However, the present invention is not limited to this configuration, and the processing may be executed by different processors.

[0014] (Example of processing related to the power supply capacity estimation unit) Next, an example of processing related to the power supply capacity estimation unit 16 and the heating control unit 15 will be described with reference to the flowchart shown in FIG. 2-4. The flowchart shown in FIG. 2-4 illustrates an example of processing related to the power supply capacity estimation unit 16 performed by a processor. When the power switch is turned on or the power saving state is canceled, the processor of the image forming apparatus 10 receives power from the power supply 17 and starts processing. The processor, acting as the power supply capacity estimation unit 16, detects the voltage of the power supply 17 multiple times before starting warm-up (step S11). Then, it determines whether the detected voltage is within a predetermined rated value and its distribution (step S13). If the detected voltage is within a standard distribution range with the rated value as its peak (Yes in step S13), it determines to adopt standard control characteristics prepared in advance for heating control (step S15).

[0015] Specific examples of control characteristics include the warm-up period, temperature trouble determination period, printing speed, and feedback amount. The warm-up period is a period during which requested printing is not initiated and is suspended until at least that period has elapsed since the start of heating of the fixing member 13F. During that period, the fixing member 13F is heated to a temperature at which the toner can be fixed. The temperature trouble determination period is a period during which a trouble is determined if the fixing member 13F has not reached a predetermined temperature after that period has elapsed since the start of heating. The printing speed is a value indicating how many sheets of paper of a given size (e.g., A4 landscape) are printed per unit time (e.g., one minute). The printing speed is determined by the paper transport speed and the spacing between the sheets. The feedback amount indicates how much the temperature of the fixing member 13F detected by the temperature detection unit 13S differs from a predetermined target temperature, i.e., the temperature deviation is calculated, and the amount of change in the power supplied to the heating member 13H is determined based on that deviation. The heating control unit 15 performs feedback control, changing the power supplied to the heating element 13H according to the deviation from the target temperature. There is a time delay (response delay) between when the heating control unit 15 changes the power to the heating element 13H and when the temperature detected by the temperature detection unit 13S changes. To perform appropriate control, including the response delay, PID control is often used instead of simple proportional control. In this case, the feedback amount refers to the feedback amount (control gain) for each of the elements P (proportional), I (integral), and D (differential).

[0016] The explanation of the flowchart continues. If the detected voltage distribution deviates from the rated value as determined in step S13 (No in step S13), the processor determines the magnitude of the deviation of the distribution from the rated value (step S17). Then, the control characteristic to be adopted is determined based on the magnitude of the deviation (step S19). Figures 5-7 are graphs showing the results of detecting the voltage of the power supply 17 multiple times before the start of warm-up in this embodiment. The horizontal axis represents the detected voltage. The rated voltage is 100 V, and the distribution is shown in units of 5 V. The vertical axis represents the proportion of each voltage detected relative to the total number of detections, expressed as a percentage. The example shown in Figure 5 is within a standard distribution range, with a peak at the rated value of 100 V and some distribution observed around that peak. For example, if the distribution shown in Figure 5 is obtained, the determination in step S13 will be Yes. In contrast, in the example shown in Figure 6, the voltage peaks at 85 V, not the rated 100 V, and some distribution observed around that peak. This indicates that the power supply 17 is in a reduced power state. If the distribution shown in FIG. 6 is obtained, the determination in step S13 will be No. In the case of a distribution such as that shown in FIG. 6, it is sufficient to adopt control characteristics that assume a reduced power state in advance. For example, the warm-up period may be set longer than standard. Also, the temperature rise trouble determination period may be set longer than standard. Furthermore, the print speed may be set smaller (slower) than standard.

[0017] In the example shown in FIG. 7, although the voltage peaks at the rated 100V, the peak is low and the voltage is widely distributed above and below that peak. This indicates that the voltage of power supply 17 is in a state where it fluctuates a lot. If the distribution shown in FIG. 7 is obtained, the determination in step S13 will be No. In the case of a distribution such as that shown in FIG. 7, control characteristics that assume an unstable voltage state may be adopted. For example, the adjustment range of the feedback control may be set to a large value. Note that the boundary condition of the distribution related to the determination in step S13 may be predetermined, for example, as the standard deviation of the distribution. Furthermore, control characteristics according to the magnitude of the deviation may be prepared in advance, for example, as a data table. Specific examples of control characteristics are as described above.

[0018] After determining the control characteristics to be adopted in step S15 or step S19 described above, the processor starts heating control of the fixing member 13F using the control characteristics (step S21). In other words, it starts warming up the fixing unit 13. The heating control unit 15 performs feedback control to control the power supplied to the heating member 13H so that the temperature of the fixing member 13F detected by the temperature detection unit 13S rises to a target temperature, and once the target temperature is reached, the temperature is maintained. The flowchart shown in FIG. 2-4 does not focus on the feedback control, but rather on the process of estimating the state of the power source 17 in the feedback control, and shows only the process related to that process.

[0019] After the warm-up starts, the processor waits for a predetermined period of time to elapse after detecting the power supply voltage in step S11 (step S23), and then detects the state of the power supply 17 (step S25). Specifically, the processor detects the voltage of the power supply 17, and more preferably, the processor also detects the current from the power supply 17 to the fixing unit 13. Then, the following determination is made based on the previous result of detecting the power supply state and the current result detected in step S25.

[0020] First, it is determined whether the state has switched from a non-heating state in which power is not supplied to the heating member 13H to a heating state in which power is supplied (step S27 shown in FIG. 3). That is, it is determined whether power was not supplied to the heating member 13H when the state of the power source 17 was detected last time, but whether power was being supplied to the heating member 13H when the state of the power source 17 was detected this time. If the determination is Yes (Yes in step S27), the processor obtains the magnitude of voltage fluctuation of the power source 17 when the state switched from the non-heating state to the heating state and stores this in memory as data related to self-variability (step S29). The process then proceeds to step S41, which will be described later. Note that in step S29, the speed of the fluctuation may also be obtained and stored in memory, and the magnitude of fluctuation in the current from the power source 17 to the fixing unit 13 may also be obtained and stored in memory. Because the heating control unit 15 performs feedback control, the magnitude of the power supplied to the heating member 13H at each point in the heating state varies somewhat depending on the situation, especially after the warm-up period ends, and the magnitude of the current from the power source 17 to the fixing unit 13 also varies somewhat accordingly. According to a preferred embodiment, the control characteristics can be determined by acquiring not only the fluctuation in the voltage of the power source 17 but also the magnitude of the current when the voltage fluctuation occurs. In one preferred embodiment, the processor may estimate the self-variability and the initial variability by setting the state when a predetermined power is supplied to the heating member as the power source state in the heating state. The power from the power source supplied to the heating member by the heating control unit in the heating state varies depending on the control. According to this embodiment, the self-variability and initial variability can be estimated under certain conditions by setting the state when a predetermined power is supplied from the power source as the power source state in the heating state.

[0021] In the aforementioned step S11, the power supply voltage is detected before the warm-up starts. In other words, the state of the power supply 17 is detected in a non-heating state. After the warm-up starts, the heating state in which power is supplied to the heating member 13H and the temperature of the fixing member 13F continues until the warm-up ends. Therefore, the first determination after step S11 to step S27 is Yes. The fluctuation in power supply that occurs when switching from a non-heating state to a heating state is thought to be largely influenced by the switching between the heating state and non-heating state by the heating control unit 15, even if it includes external factors. Therefore, the data is stored in memory as data related to the self-variability associated with switching between the heating state and non-heating state.

[0022] On the other hand, if the determination in step S27 is No, the processor then determines whether the heating state has been switched to the non-heating state (step S31). That is, the processor determines whether power was supplied to the heating member 13H when the state of the power source 17 was detected last time, but whether power was being supplied to the heating member 13H when the state of the power source 17 was detected this time. If the determination is Yes (Yes in step S31), the processor obtains the magnitude of voltage fluctuation of the power source 17 when the heating state was switched to the non-heating state and stores this data in memory as data related to self-variability (step S33). The process then proceeds to step S41, which will be described later. Note that in step S33, the processor may also obtain and store in memory the speed of the fluctuation, or the magnitude of fluctuation in the current from the power source 17 to the fixing unit 13. The fluctuation in power supply that occurs when the heating state is switched to the non-heating state is considered to be largely influenced by the switching between the heating state and the non-heating state by the heating control unit 15, even if it includes external factors. Therefore, the data is stored in memory as data relating to the self-variability associated with switching between the heated state and the non-heated state.

[0023] If the determination in step S31 is No, the processor then determines whether the heating state is continuing (step S35). That is, it determines whether power was being supplied to the heating member 13H both the previous time the state of the power source 17 was detected and the current time the state of the power source 17 was detected. If the determination is Yes (Yes in step S35), the processor obtains the magnitude of voltage fluctuation of the power source 17 while the heating state is continuing and stores it in memory as data related to initial variability (step S37). The process then proceeds to step S41, which will be described later. Note that in step S37, the speed of the fluctuation may also be obtained and stored in memory. Fluctuations in the power supply that occur while the heating state is continuing are thought to be mainly due to factors external to the image forming apparatus 10, even if there is some influence from feedback control by the heating control unit 15. Therefore, this is stored in memory as data related to initial variability related to the environment in which the image forming apparatus 10 is installed.

[0024] If the determination in step S35 is No, this corresponds to a case where the non-heating state continues. In other words, this corresponds to a state where power was not supplied to the heating member 13H at either the previous time the state of the power source 17 was detected or the current time the state of the power source 17 was detected. The processor acquires the magnitude of voltage fluctuation of the power source 17 when the non-heating state continues and stores it in memory as data related to initial variability (step S39). The process then proceeds to step S41, which will be described later. Note that in step S39, the speed of the fluctuation may also be acquired and stored in memory. Fluctuations in the power supply that occur when the non-heating state continues are thought to be mainly due to factors external to the image forming apparatus 10, even if there is some influence from feedback control by the heating control unit 15. Therefore, this is stored in memory as data related to initial variability related to the environment in which the image forming apparatus 10 is installed. In this manner, in steps S29, S33, S37, and S39, the processor stores a finite number of data items related to the most recent internal variability and initial variability in the memory in a buffer-like manner. In this specification, the memory area where the data related to the internal variability and initial variability are stored is referred to as the estimate value memory unit.

[0025] 8-10 are waveform diagrams showing an example of how the voltage of the power supply 17 fluctuates during printing. The vertical axis represents voltage, and the rated voltage of the power supply 17 is 100V. The horizontal axis represents time, with the origin (zero point) representing the start of printing and the standby state before printing begins representing negative time to the left of the origin. The dashed arrows at multiple points indicate the time points (estimation points) at which the power supply capacity estimation unit 16 detects and estimates the power supply state. The power supply capacity estimation unit 16 sequentially detects the power supply state before warming up the fixing unit 13, during warming up after warming up begins, during standby after warming up is completed and before printing begins, and during printing. According to this embodiment, the power supply capacity estimation unit 16 estimates the power supply state during each of the periods before warming up begins, during warming up, standby, and printing, rather than only depending on the power supply state only before warming up begins or only on the power supply state only after warming up begins and before printing begins, and determines control characteristics based on the estimations and applies them to the control of the power used for heating. In the example shown in Figures 8-10, a period in which the heated state continues at two or more estimated points is defined as a heated state duration, and a period in which the unheated state continues at two or more estimated points is defined as a non-heated state duration. The boundary between the non-heated state duration and the heated state duration corresponds to a transition from the unheated state to the heated state, or a transition from the heated state to the unheated state. This is referred to as embodiment 1.

[0026] The heating state duration corresponds to a case where the determination in step S35 shown in FIG. 3 is Yes, and the non-heating state duration corresponds to a case where the determination in step S35 is No. A switch from a non-heating state to a heating state corresponds to a case where the determination in step S27 shown in FIG. 3 is Yes, and the magnitude of the fluctuation at that time is indicated by arrows D51, D52, and D53 in FIG. 8, for example. Similar arrows are also used in FIG. 9 and FIG. 10. On the other hand, a switch from a heating state to a non-heating state corresponds to a case where the determination in step S31 is Yes, and the magnitude of the fluctuation at that time is indicated by arrows U51, U52, and U53 in FIG. 8, for example. Similar arrows are also used in FIG. 9 and FIG. 10.

[0027] For example, the fluctuation caused by switching from a non-heating state to a heating state, which corresponds to D51 in Fig. 8, passes through multiple estimated points before the voltage of power supply 17 stabilizes. Therefore, in a different embodiment, the estimated points until the voltage after the fluctuation stabilizes may be included in the switching from the non-heating state to the heating state or the switching from the heating state to the non-heating state.

[0028] This embodiment is referred to as embodiment 2 in comparison with the first embodiment described above. In embodiment 2, the rate of fluctuation can be determined based on the time required for the voltage to stabilize after the fluctuation. If one or more estimated points until the voltage stabilizes after the fluctuation are included in the switching from the non-heating state to the heating state or the switching from the heating state to the non-heating state, those estimated points are excluded from the heating state duration or the non-heating state duration. According to embodiment 2, the self-variability can be estimated based on the fluctuation in the power supply voltage when switching between the non-heating state and the heating state, and the initial variability can be estimated based on the fluctuation in the power supply voltage in at least one of the non-heating state and the heating state. Furthermore, a preferred embodiment in which the current from the power supply 17 to the fixing unit 13 is also detected in addition to detecting the voltage of the power supply 17 has already been described above. A preferred embodiment of embodiment 3 is referred to as embodiment 1 and 2 in comparison. According to embodiment 3, the self-variability can be estimated by taking into account the change in current in addition to the fluctuation in the power supply voltage when switching between the non-heating state and the heating state.

[0029] Returning to the description of the flowchart, in step S41, the processor references data related to the initial variability stored in the estimated value storage unit. Then, based on the data related to the initial variability, it determines whether or not to update the control characteristics (step S43). For example, in the voltage waveform shown in FIG. 8, the magnitudes of fluctuation D51, D52, and D53 differ when switching from the non-heating state to the heating state. Furthermore, the magnitudes of fluctuation U51, U52, and U53 when switching from the heating state to the non-heating state also differ. Therefore, it is preferable to update the control characteristics not based only on the current estimated point and the previous estimated point, but also on data from previous switchings to the heating state and / or from the heating state to the non-heating state. In other words, it is preferable that the processor determine the control characteristics of heating control unit 15 based on the data stored in the estimated value storage unit. According to this preferred embodiment, even at the start of warm-up, for example, it is possible to determine the control characteristics according to the estimation by referring to data previously estimated and stored in the estimated value storage unit, and apply the control characteristics to the control of the power used for heating. Furthermore, since the control characteristics are determined based on not only the most recent estimate but also estimates from a period going back to the most recent period, a stable transition in the control characteristics can be obtained.

[0030] For example, both Figures 9 and 10 show the same voltage waveform of power supply 17. However, the voltage fluctuation when switching from a non-heating state to a heating state or from a heating state to a non-heating state is larger in the voltage waveform of Figure 9 than in the voltage waveform of Figure 10. If it is determined that there has been a change in the magnitude of the voltage fluctuation in this way, it is determined in step S43 that the control characteristics should be updated (Yes in step S43).

[0031] If it is determined that the control characteristics should be updated, the processor determines the control characteristics to be adopted and updates the control characteristics to the determined control characteristics (step S45). The process then proceeds to step S47 shown in FIG. 4. On the other hand, if it is determined that the control characteristics do not need to be updated (No in step S43), the process proceeds to step S47 shown in FIG. 4. Specific examples of control characteristics are, as described above, the warm-up period, the temperature rise trouble determination period, the printing speed, and the feedback amount. For example, the voltage of power supply 17 during the non-heating state is the rated value of approximately 100 V in the voltage waveform shown in FIG. 8, but is approximately 80 V, which is lower than the rated value, in the voltage waveform shown in FIG. 9. The change in voltage during the non-heating state is attributed to external factors, i.e., the environment in which image forming apparatus 10 is installed, rather than to heating control unit 15. The voltage during the heating state is also 80 to 90 V in FIG. 8, but is lower, at 60 to 70 V, in FIG. 9. For the same duty value, the power supplied to the heating member 13H is smaller in the state shown in FIG. 9 than in the state shown in FIG.

[0032] Therefore, the processor may control the printer to compensate for the lower power supply voltage by increasing the amount of feedback in the voltage waveform state of Figure 9 compared to the voltage waveform state of Figure 8. Also, in the state of Figure 9 where the power supply voltage is low, at least one of the warm-up period and the temperature rise trouble determination period may be set longer than in the state of Figure 8 where the power supply voltage is high, and the printing speed may also be set slower.

[0033] Returning to the explanation of the flowchart, the processor then references the data relating to the self-variability stored in the estimated value storage unit (step S47 shown in FIG. 4). Then, it determines whether or not the control characteristics should be updated based on the data relating to the self-variability (step S49). Specific examples of the control characteristics are, as described above, the warm-up period, the temperature rise trouble determination period, the printing speed, and the feedback amount. For example, consider a case where the voltage fluctuations during switching from a non-heating state to a heating state, or from a heating state to a non-heating state, change from large fluctuations as shown in FIG. 9 to small fluctuations as shown in FIG. 10. For the same duty value, the power supplied to the heating element 13H during the heating period is greater in the state shown in FIG. 10 than in the state shown in FIG. 9.

[0034] Therefore, the processor may reduce the amount of feedback in the voltage waveform state of FIG. 10 compared to the voltage waveform state of FIG. 9. Furthermore, in the state shown in FIG. 9, the upper limit of the power that can be supplied to the heating element 13H during the heating state duration is lower than in the state shown in FIG. 10. Therefore, at least one of the warm-up period and the temperature rise trouble determination period may be set longer than in the state shown in FIG. 10, and the printing speed may be set slower than in the state shown in FIG. 10. If it is determined that the control characteristics should be updated (Yes in step S49), the processor determines the control characteristics to be adopted and updates them to the determined control characteristics (step S51). Then, the processor returns to step S23 shown in FIG. 2 to wait for the next time when the power supply status should be detected. On the other hand, if it is determined that the control characteristics do not need to be updated (No in step S49), the processor returns to step S23 shown in FIG. 2 to wait for the next time when the power supply status should be detected.

[0035] As described above, according to a preferred embodiment, if it is estimated that at least one of the self-variability and the initial variability is greater than the assumed standard state, the warm-up period may be set longer than the standard. The temperature rise trouble determination period may also be set longer than the standard. Furthermore, the print speed may be set smaller (slower) than the standard. Furthermore, the feedback gain may be adjusted in consideration of stability against fluctuations, and the feedback responsiveness may be adjusted according to the speed of fluctuations. Furthermore, power supply capability estimation unit 16 may acquire average voltage levels of power supply 17 in the non-heating state and the heating state, and determine control characteristics according to those voltage levels. According to this embodiment, the processor can determine appropriate control characteristics in consideration of the average voltage levels of power supply 17 in each of the non-heating state and the heating state, and apply them to heating control.

[0036] The heating control unit 15 determines control characteristics according to the settings of the print to be performed, in addition to the magnitude of the self-variability and initial variability, and the average voltage level of the power source 17 in the non-heating and heating states, and applies these to the heating control. For example, the feedback amount may be changed depending on the size of the print paper. For paper larger than the standard size, the amount of heat lost when a single sheet of paper passes through the fixing unit 13 is large, so the feedback amount may be increased. Conversely, for paper smaller than the standard size, the amount of heat lost when a single sheet of paper passes through the fixing unit 13 is small, so the feedback amount may be decreased. Furthermore, for cardboard, which is thicker than regular paper, the amount of heat lost when a single sheet of paper passes through the fixing unit 13 is large, so the feedback amount may be increased. Furthermore, the transport speed, i.e., the printing speed, may be slowed down to supply sufficient heat to the print paper. According to this aspect, the control heating unit can determine control characteristics according to the settings of the printing to be performed, such as the size and type of paper to be printed, in addition to the control characteristics according to the estimation, and apply these to the control of the power used for heating.

[0037] It should be understood that the present invention also includes any combination of the above-described aspects. In addition to the above-described embodiment, various modifications of the present invention are possible. These modifications should not be interpreted as not falling within the scope of the present invention. The present invention should include all modifications that have the meaning equivalent to the scope of the claims and that fall within the scope of the present invention. [Explanation of symbols]

[0038] 10: Image forming device, 11: Image forming unit, 12: Paper feeding unit, 13: Fixing unit, 13C: Contact unit, 13F: Fixing member, 13H: Heating member, 13P: Pressure member, 13S: Temperature detection unit, 13T: Heat transfer member, 14: Discharge tray, 15: Heating control unit, 16: Power supply capacity estimation unit, 17: Power supply

Claims

1. a fixing unit including a fixing member and a pressure member through which printing paper carrying toner passes to heat the toner and fix it to the printing paper, a temperature detection unit that detects the temperature of the fixing member, and a heating member that heats the fixing member; a heating control unit that controls power supplied from a power source to heat the heating member; a power supply capacity estimation unit that sequentially detects the state of the power supply in a heating state in which power is supplied and a non-heating state in which power is not supplied, and sequentially estimates an internal variability related to a variation caused by switching between the heating state and the non-heating state and an initial variability related to a variation caused not by the switching, The heating control section determines control characteristics according to the self-variability and initial variability of the power source and applies the control characteristics to the fixing device.

2. 2. The fixing device according to claim 1, wherein the power supply capacity estimation unit successively detects the voltage of the power supply and estimates the self-variability and the initial variability based on the magnitude and speed of the fluctuation.

3. The fixing device according to claim 2 , wherein the power supply capacity estimating section further sequentially detects a current flowing through the heating member in the heating state, and estimates the self-variability including the current.

4. The fixing device according to claim 2 , wherein the power supply capacity estimation unit obtains average voltage levels of the power supply in the non-heating state and the heating state, and determines control characteristics according to the average voltage levels.

5. 2. The fixing device according to claim 1, wherein the power supply capacity estimation unit sequentially detects the state of the power supply in the non-heated state before starting warm-up of the fixing unit, the state of the power supply in the heated state after starting warm-up and before starting printing, and the state of the power supply in the heated state after starting printing.

6. The fixing device according to claim 1 , wherein the heating control unit determines control characteristics according to the magnitude of the self-variability and the initial variability as well as the settings of the print to be executed and applies the control characteristics to the control of the power used for heating.

7. The fixing device according to claim 1 , wherein the power supply capacity estimating section estimates the self-variability and the initial variability based on a state when a predetermined amount of power is supplied to the heating member as a power supply state in the heating state.

8. 2. The fixing device according to claim 1, wherein the heating control unit determines at least one of the feedback characteristics for adjusting the power supplied to the heating member based on the warm-up period, the temperature rise trouble determination period, the printing speed, and the deviation of the temperature detected by the temperature detection unit from a target temperature, in accordance with the estimated self-variability and the initial variability.

9. an estimated value storage unit that stores a finite number of data items related to the internal variability and the initial variability, the data items being sequentially estimated by the power supply capability estimator; 2. The fixing device according to claim 1, wherein the heating control section determines the control characteristics of the heating control section by taking the data stored in the estimated value storage section into consideration.

10. An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

11. a fixing unit including a fixing member and a pressure member that heats and fixes the toner on the printing paper by passing the printing paper carrying the toner thereon, a temperature detection unit that detects the temperature of the fixing member, and a heating member that heats the fixing member; and a processor that controls power supplied from a power source to the fixing unit to heat the heating member; a step of sequentially detecting the state of the power source in a heating state in which power is supplied and a non-heating state in which power is not supplied, and sequentially estimating an internal variability related to a variation caused by switching between the heating state and the non-heating state and an initial variability related to a variation caused without the switching; determining a control characteristic according to the self-variability and initial variability of the power supply and applying the control characteristic to the control;

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