Image forming device

Abstract

To increase the accuracy of predicting a temperature of a target portion while an image forming apparatus is powered on.SOLUTION: An image forming apparatus for forming an image on a recording material has: detection means that detects a temperature of a first member; and prediction means that predicts a temperature of a second member different from the first member. Based on the temperature of the second member predicted by the prediction means at a first timing before the image forming apparatus is powered off, the temperature of the first member detected by the detection means at a second timing after the image forming apparatus is powered on, and information indicating an operation history of the image forming apparatus until when the image forming apparatus is powered off, the prediction means predicts the temperature of the second member at the second timing.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a control method for improving the accuracy of predicting the temperature of an image forming apparatus. [Background technology]

[0002] In image forming apparatuses using electrophotography, the temperature at various locations within the image forming apparatus (hereinafter referred to as "internal temperature") rises due to factors such as heat generated by the fixing device during printing, the transport of heated recording materials, and heat generated by electrical elements. An excessive rise in the internal temperature can lead to image defects. However, since it is difficult to install temperature sensors in all locations susceptible to heat from the standpoint of cost and space, a method has been known in the past in which a control unit provided in the image forming apparatus predicts the internal temperature at target locations. The control unit then controls the operation of the image forming apparatus so that the predicted temperature does not exceed a preset temperature.

[0003] Patent Document 1 describes a method for accurately predicting the temperature of a developing motor that drives a developing roller using a control unit without directly detecting the temperature. In Patent Document 1, the control unit estimates the elapsed time during which power supply to an image forming apparatus has been stopped based on the temperature change of a fixing thermistor from when the power is turned off to when the power is turned on. Then, the control unit predicts the temperature of the developing motor when power is turned back on based on the estimated elapsed time and the predicted temperature of the developing motor stored in a memory unit immediately before the power is turned off. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2010-134407 Summary of the Invention [Problem to be solved by the invention]

[0005] The method of Patent Document 1 fully satisfied the prediction accuracy desired at the time for the temperature of a target location when power is turned back on, but in recent years, there has been a demand for even higher temperature prediction accuracy.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to improve the accuracy of predicting the temperature of a target location when the power of an image forming apparatus is turned on. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides an image forming apparatus that forms an image on a recording material, comprising: a detection means that detects the temperature of a first member; a prediction means that predicts the temperature of a second member different from the first member; and a storage means that stores information on a calculation formula that uses data that indicates the temperature change characteristics of the first member as an argument to derive data that indicates the temperature change characteristics of the second member, wherein the information on the calculation formula includes a plurality of different coefficients depending on information that indicates the operation history of the image forming apparatus, and the prediction means, based on the information that indicates the operation history of the image forming apparatus, A plurality of said coefficients and the prediction means predicts the temperature of the second member at the second timing based on the selected coefficient, the temperature of the second member predicted by the prediction means at a first timing before the image forming apparatus is powered off, the temperature change of the first member detected by the detection means during the period from the first timing to a second timing after the image forming apparatus is powered on, and information indicating the operation history of the image forming apparatus up until the image forming apparatus is powered off. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve the accuracy of predicting the temperature of a target location when the image forming apparatus is turned on. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic diagram of an image forming apparatus [Figure 2] System configuration diagram of image forming apparatus [Figure 3] Schematic diagram showing the temperature rise characteristics inside the machine [Figure 4] Flowchart showing the procedure for predicting the temperature inside an image forming apparatus [Figure 5] Schematic diagram showing the temperature drop characteristics of the fixing unit and cartridge of an image forming apparatus [Figure 6] Schematic diagram showing the effect of the operating history of an image forming apparatus on the temperature drop characteristics of the fixing unit [Figure 7] Flowchart showing control in the first embodiment [Figure 8] Schematic diagram showing the temperature drop characteristics of the fixing unit of an image forming apparatus [Figure 9] Flowchart showing control in the second embodiment DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail the embodiments of the present invention. However, the following embodiments are merely illustrative and do not limit the scope of the present invention to the configurations thereof.

[0011] Example 1 [Explanation of image forming device] 1 is a schematic diagram of an image forming apparatus 100 in this embodiment. In the following description, the letters a, b, c, and d at the end of a reference number indicate that the corresponding component is related to the formation of yellow (Y), magenta (M), cyan (C), and black (Bk) toner images, respectively. In the following description, when it is not necessary to distinguish between colors, reference numbers without the letters a, b, c, and d at the end may be used.

[0012] (Image forming section) First, we will explain the image forming unit (hereinafter also referred to as the image forming station) for forming a yellow (Y) toner image. The photosensitive drum 1a, which serves as a photoconductor, is a metal cylinder with multiple layers of functional organic materials, including a carrier generation layer that generates charge upon exposure to light and a charge transport layer that transports the generated charge. The outermost layer has low electrical conductivity and is essentially an insulator. The charging roller 2a, which serves as a charging means, is in contact with the photosensitive drum 1a and rotates in accordance with the rotation of the photosensitive drum 1a, uniformly charging the surface of the photosensitive drum 1a. A DC voltage or a voltage superimposed with an AC voltage is applied to the charging roller 2a, and discharge occurs in a small air gap upstream and downstream of the contact nip between the charging roller 2a and the surface of the photosensitive drum 1a, thereby charging the photosensitive drum 1a.

[0013] The scanner unit 11a, which serves as a light irradiation means, is configured to scan a laser beam using a polygonal mirror or to irradiate light using an LED array. The scanner unit 11a forms an electrostatic latent image on the photosensitive drum 1a (on the photoconductor) by irradiating a beam 12a modulated based on an image signal. The development unit 8a, which serves as a development means, is composed of a development roller 4a, a non-magnetic one-component developer 5a, and a developer application blade 7a. The development roller 4a abuts against the photosensitive drum 1a. The electrostatic latent image formed on the photosensitive drum 1a is developed into a toner image (developer image) by the development roller 4a. During development, the development roller 4a is rotated by a driving means such as a development motor (not shown). The developed toner image is primarily transferred onto the intermediate transfer belt 80 (on the image carrier) as an image carrier by applying a primary transfer bias to the primary transfer roller 81a. After the primary transfer, any residual toner remaining on the photosensitive drum 1a is cleaned by a cleaning unit 3a.

[0014] The charging roller 2a is connected to a charging bias power supply 20a, which supplies voltage to the charging roller 2a, and receives power. The developing roller 4a is connected to a developing bias power supply 21a, which supplies voltage to the developing roller 4a, and receives power. The primary transfer roller 81a is connected to a primary transfer bias power supply 84a, which supplies voltage to the primary transfer roller 81a, and receives power. The photosensitive drum 1a, charging roller 2a, cleaning unit 3a, developing roller 4a, non-magnetic single-component developer 5a, developer application blade 7a, and developing unit 8a described above can be integrated into a process cartridge 9a that is detachably mounted on the image forming apparatus 100. In other words, the process cartridge 9 contains developer. However, the cartridge configuration is not limited to this, and can also be divided into a drum cartridge including the photosensitive drum 1a, etc., and a developing cartridge including the developing unit 8a, etc.

[0015] The above is the configuration of the image forming station corresponding to yellow, and the image forming stations corresponding to magenta, cyan, and black have similar configurations. Each component is designated by the same reference numeral followed by the letters b, c, and d, and detailed explanations will be omitted here. Hereinafter, the station for forming a yellow (Y) toner image will also be referred to as the first station. Similarly, the station for forming a magenta (M) toner image will also be referred to as the second station, the station for forming a cyan (C) toner image will also be referred to as the third station, and the station for forming a black (K) toner image will also be referred to as the fourth station. In the direction of movement of the intermediate transfer belt 80, the first station is located at the most upstream position, followed by the second station, the third station, and the fourth station.

[0016] The intermediate transfer belt 80 is supported by three rollers: a secondary transfer opposing roller 86, a drive roller 14, and a tension roller 15, which serve as tensioning members, to maintain an appropriate tension. By driving the drive roller 14, the intermediate transfer belt 80 rotates forward relative to the photosensitive drums 1a-1d at approximately the same speed. Primary transfer rollers 81a-81d are disposed inside the intermediate transfer belt 80, facing the photosensitive drums 1a-1d and abutting against the intermediate transfer belt 80. The primary transfer rollers 81a-81d are connected to primary transfer bias power supplies 84a-84d. The primary transfer rollers 81a-81d sequentially transfer the color toner images formed on the photosensitive drums 1a-1d onto the intermediate transfer belt 80, thereby forming a color image. Discharge members 23a-23d are disposed downstream of the primary transfer rollers 81a-81d in the direction of rotation of the intermediate transfer belt 80. The drive roller 14, tension roller 15, charge removing members 23a to 23d, and secondary transfer opposing roller 86 are electrically grounded by wiring (not shown).

[0017] When recording material P, such as paper, is fed from paper feed cassette 16, pickup roller 17 is driven by a stepping motor (not shown) (hereinafter also referred to as paper feed motor). This causes bottom plate 29 to rise, pushing up the recording materials P stacked in paper feed cassette 16. The topmost sheet of the pushed-up recording material P comes into contact with pickup roller 17, and as the pickup roller 17 rotates, the recording material P is fed. The fed recording material P is transported to registration roller 18. When registration sensor 35 detects the leading edge of recording material P, the drive of the paper feed motor is stopped, temporarily halting the transport of recording material P. The recording material P, which has been temporarily stopped by registration roller 18, is re-transported at a predetermined timing in accordance with the movement of the toner image transferred onto intermediate transfer belt 80, and is transported to the secondary transfer unit.

[0018] The toner images formed on the photosensitive drums 1a to 1d are transferred, respectively, and the color images formed on the intermediate transfer belt 80 are moved to a secondary transfer position, which is a secondary transfer section consisting of a secondary transfer roller 82 and the intermediate transfer belt 80. By applying a secondary transfer bias to the secondary transfer roller 82, the color image on the intermediate transfer belt 80 is secondarily transferred onto the recording material P. A secondary transfer bias power supply 85 is connected to the secondary transfer roller 82, and a secondary transfer bias is applied to the secondary transfer roller 82 by this secondary transfer bias power supply 85.

[0019] The recording material P onto which the color image has been secondarily transferred is conveyed to a fixing unit 19 (first member) including a fixing film 31 (heating member) and a pressure roller 32 (pressure member) that applies pressure to the recording material P. The fixing unit 19 applies heat and pressure to the color image secondarily transferred onto the recording material P to fix the toner image to the recording material P. The fixing unit 19 is provided with a fixing heater 33 and a fixing thermistor 34, and the fixing thermistor 34 detects the temperature of the fixing heater 33. The temperature of the fixing heater 33 is adjusted according to the detection result of the fixing thermistor 34. The recording material P onto which the toner image has been fixed in the fixing unit 19 is detected by a paper discharge sensor 30 (discharge sensor) and then discharged to a paper discharge tray 36, completing the image forming operation. The image forming operation described above is executed by the engine control unit 200 controlling each component.

[0020] [Device temperature detection means] In this embodiment, the sensors provided in the image forming apparatus 100 for detecting temperature include a fixing thermistor 34 provided in the fixing unit 19 and an environmental temperature sensor 37 provided near the paper feed cassette 16. As described above, the fixing thermistor 34 is provided to determine the temperature of the fixing heater 33 and, ultimately, the fixing unit 19. The environmental temperature sensor 37 is provided to determine the temperature outside the image forming apparatus 100.

[0021] When an image forming operation is performed, the temperature inside the image forming apparatus 100 rises due to heat generation from the fixing heater 33, heat generation from the electric elements provided in the electric board, and the conveyance of the recording material P heated by the fixing unit 19. As a mechanism for suppressing the rise in the temperature inside the apparatus, the image forming apparatus 100 has one cooling fan (not shown).

[0022] The above-mentioned rise in internal temperature generally occurs in all components included in the image forming apparatus 100. Among these, components that are significantly affected by the temperature rise include the process cartridge 9 and the paper discharge sensor 30 provided near the fixing unit 19.

[0023] [Control block diagram] FIG. 2A is a block diagram showing the configuration of the engine control unit 200. The image forming apparatus 100 is provided with the engine control unit 200 as control means for comprehensively controlling the operation of each unit of the apparatus. The engine control unit 200 is configured to include a CPU 201 as calculation means, and a ROM 202, RAM 203, and NVRAM 204 as storage means. The CPU 201 performs various calculation processes required for controlling the image forming apparatus 100. The ROM 202 is storage means for storing fixed information, and is a memory that stores information such as programs, parameters, and tables required for calculations by the CPU 201. The RAM 203 is a rewritable memory that temporarily stores information required for calculations by the CPU 201. The NVRAM 204 is a non-volatile memory whose information is not initialized even when the power supply to the image forming apparatus 100 is stopped.

[0024] In this embodiment, temperature control of the process cartridge 9 will be described. The process cartridge 9 experiences a large temperature rise, particularly when performing continuous printing of a large volume in double-sided printing mode. If the temperature of the development unit 8 rises excessively at this time, the developer 5 contained therein may exceed its glass transition point and melt, possibly adhering to the sealing member inside the process cartridge 9. This may result in poor image quality or toner leakage. Therefore, the image forming apparatus 100 of this embodiment predicts the temperature of the process cartridge 9 (second component), particularly the development unit 8, and controls operation so that the predicted temperature does not exceed a preset temperature.

[0025] FIG. 2B is a block diagram showing functions realized by the CPU 201 executing a program stored in the ROM 202 in the engine control unit 200. The engine control unit 200 has a temperature prediction unit 211 as prediction means for predicting the temperature of the process cartridge 9 (particularly the development unit 8) as a prediction target, and a temperature rise suppression unit 212 as temperature rise suppression means. The temperature prediction unit 211 uses information from the fixing thermistor 34 and the ambient temperature sensor 37 when predicting the temperature of the process cartridge 9. The temperature rise suppression unit 212 controls the operation of the image forming apparatus 100 so that the cartridge temperature T does not exceed a threshold temperature Tmax, which is a predetermined threshold set in advance. The threshold temperature Tmax is stored in advance in the ROM 202 as a temperature rise suppression parameter 214.

[0026] The temperature prediction unit 211 has a normal operation prediction unit 211a and a power-on prediction unit 211b. The normal operation prediction unit (hereinafter also referred to as the "first prediction unit") 211a predicts the cartridge temperature T at time intervals Δt during normal operation of the image forming apparatus 100. Normal operation refers to a state in which power is supplied to the image forming apparatus 100, the power switch is on, and normal operation is possible, i.e., a state in which a printing operation or adjustment operation is being performed, or a state in which a printing operation or adjustment operation is being waited for. The power-on prediction unit (hereinafter also referred to as the "second prediction unit") 211b predicts the cartridge temperature T when power is supplied to the image forming apparatus 100, for example, when power is restored from a power outage or when the inlet cable is plugged into an outlet.

[0027] Furthermore, the temperature prediction unit 211 uses a temperature prediction parameter 213 as a fixed parameter when calculating the cartridge temperature T. The temperature prediction parameter 213 is experimentally obtained in advance by attaching a thermocouple (not shown) to the development unit 8 and monitoring fluctuations in the actual temperature Tt, which is an actual measurement value of the temperature, during various operations and while the image forming apparatus 100 is stopped. The obtained temperature prediction parameter 213 is stored in the ROM 202 in advance.

[0028] In this embodiment, the temperature is predicted for the process cartridge 9, but the present invention is not limited to this, and the temperature may be predicted for other components within the image forming apparatus 100. In particular, from the standpoint of space and cost, the control of this embodiment is effective when predicting the temperature of a location where no sensor is provided to directly detect the temperature.

[0029] [In-machine temperature control details] Temperature prediction of image forming apparatus 100 in this embodiment can be broadly divided into two types of control by first prediction unit 211a and second prediction unit 211b described above. By predicting the temperature inside the apparatus using each type of control, it becomes possible to monitor temperature fluctuations inside the apparatus (=cartridge temperature T) in all situations, both while the apparatus is operating and when it is stopped. Below, the methods for predicting the temperature inside the apparatus by first prediction unit 211a and second prediction unit 211b will be described in order.

[0030] (Temperature Prediction in the First Prediction Unit) When calculating the cartridge temperature T, the first prediction unit 211a uses the reaching temperature rise amount Cx and the fluctuation temperature coefficient (temperature change coefficient) k as the temperature prediction parameters 213. The cartridge temperature T can be expressed by the following formula with the environmental temperature of the image forming apparatus being Te. T = Te + Cc (1)

[0031] Cc represents the temperature rise amount of the process cartridge 9 with respect to the environmental temperature. In this embodiment, the cartridge temperature rise amount Cc is modeled using the following formula. Cc = Cx - (Cx - C0)·exp(-kt) (2) Here, in formula (2), t is the elapsed time, and C0 is the initial temperature rise amount of the process cartridge 9 (the temperature rise amount at t = 0).

[0032] FIG. 3 is a schematic diagram showing the temperature rise characteristics of the process cartridge 9 represented by the above formula (2). The figure shows how the cartridge temperature T rises as the image forming apparatus 100 operates. In FIG. 3, C0 = 0, that is, it shows a case where there is no difference in the temperature of the process cartridge 9 with respect to the environmental temperature Te in the initial state of t = 0. The process cartridge 9 whose temperature has risen from the state of C0 = 0 asymptotically approaches the temperature of the reaching temperature rise amount Cx when it reaches the state of thermal equilibrium as time passes by. The fluctuation temperature coefficient k represents the degree of the change rate (slope) of the temperature rise, and the greater the value, the steeper the temperature rise. Although FIG. 3 shows the characteristics in the case of C0 < Cx, in the case of C0 > Cx, the temperature rise amount decreases from C0 and converges to Cx. In this case, the temperature drop characteristics of the cartridge can be modeled.

[0033] The temperature fluctuation of the process cartridge 9 differs depending on the operation mode of the image forming apparatus 100. Therefore, a specific temperature rise Cx and temperature fluctuation coefficient k are set for each operation mode of the image forming apparatus 100 during normal operation, such as double-sided print mode, single-sided print mode, and standby mode, and these parameters are stored in the ROM 202.

[0034] Cx and k are obtained by operating or stopping the image forming apparatus 100 in each operating mode and fitting the actually measured temperature of the process cartridge 9 to the approximate curve of equation (2). Each parameter is obtained both when the temperature is rising and when it is falling, and Cx and k for all states are obtained and stored in advance in ROM 202. Since the temperature fluctuation coefficient k when the temperature is rising and the temperature fluctuation coefficient k when the temperature is falling are usually different values, they are obtained for each mode as the temperature rise temperature change coefficient kup and the temperature fall temperature change coefficient kdown, respectively.

[0035] Next, the temperature prediction process by the first prediction unit 211a will be described with reference to the flowchart shown in Fig. 4. The flowchart shown in Fig. 4 is implemented by the CPU 201 included in the engine control unit 200 executing a program stored in the ROM 202. The actual temperature prediction process is performed by successively updating the predicted cartridge temperature rise Ccz of the process cartridge 9 using equation (2) every certain time Δt (described above). To achieve this, an algorithm is used in which the change in the temperature rise in equation (2) is converted into a difference equation and the predicted cartridge temperature rise Ccz is updated every Δt.

[0036] First, in S101, the first prediction unit 211a reads the predicted cartridge temperature rise Ccz that has been predicted so far from the RAM 204. In S102, the first prediction unit 211a reads the ultimate temperature rise Cx and the fluctuation temperature coefficient k that correspond to the operation mode of the image forming apparatus 100 from the ROM 202. In S103, the first prediction unit 211a acquires the detection result of the environmental temperature Te by the environmental temperature sensor 37. In S104, the first prediction unit 211a calculates the fluctuation temperature rise ΔCc of the predicted cartridge temperature rise Ccz during the time interval Δt using the following equation (3): ΔCc=k×Δt×(Cx-Ccz) (3)

[0037] In S105, the first prediction unit 211a calculates a predicted cartridge temperature rise amount Ccz using the following formula (4), and updates and stores it in the RAM 204. The first prediction unit 211a also calculates a predicted cartridge temperature Tcz using the following formula (5), and updates and stores it in the RAM 204. Ccz=Ccz+ΔCc (4) Tcz = Te + Ccz (5)

[0038] 4 at time intervals Δt, and constantly predicts the cartridge temperature while the engine is running. In this embodiment, the time interval Δt is set to 6 seconds.

[0039] (Temperature prediction in the second prediction section) As described above, the second prediction unit 211b predicts the initial cartridge temperature T when power supply is restored from a state in which power supply to the image forming apparatus 100 is stopped. First, the basic temperature prediction control in the second prediction unit 211b will be described.

[0040] FIG. 5 is a schematic diagram showing the temperature drop characteristics of the fuser unit temperature rise Cf and cartridge temperature rise Cc during a power outage. Because the image forming apparatus 100 is not operating during a power outage, both Cf and Cc generally decrease over time. Over a long power outage, both Cf and Cc typically eventually converge to zero (ambient temperature Te). This characteristic can be used to predict the temperature rise of the process cartridge 9 at that time based on the evaluation results of the temperature rise change (a negative value in the case of a temperature drop) in the fuser unit 19 from power outage to power resumption. In other words, if the fuser unit temperature rise change ΔCf during a power outage is known, the cartridge temperature rise change ΔCc can be uniquely determined. The characteristics in FIG. 5 vary depending on the device configuration of the image forming apparatus 100. Therefore, the cartridge temperature rise can be predicted by experimentally acquiring the characteristics in advance for the device.

[0041] 5, ΔCf and ΔCc at the time of power supply interruption are used as an example. However, the amount of cartridge temperature rise may be predicted from ΔCf and ΔCc after the power supply is restarted after the last print before the power supply interruption, through the power supply interruption. This method is adopted in this embodiment.

[0042] The above explanation is the basic concept of temperature prediction control in the second prediction unit. However, as a result of extensive research, the inventors have found a method for further improving prediction accuracy, which will be explained below.

[0043] FIG. 6 is a schematic diagram showing two types of temperature drop characteristics of the amount of temperature rise Cf of the fixing unit. Experiments have confirmed that the temperature drop characteristics of the amount of temperature rise Cf of the fixing unit change depending on the operation history of the image forming apparatus 100 up until the power supply is stopped. That is, in the image forming apparatus 100, when the temperature inside the apparatus has risen sufficiently, such as after printing a large number of sheets, the change in the amount of temperature rise ΔCf of the fixing unit over time is small. Graph 601 shows the temperature drop characteristics corresponding to this case. On the other hand, when the temperature inside the apparatus has not risen sufficiently, such as after printing a small number of sheets, the change in the amount of temperature rise ΔCf' of the fixing unit over time is large. Graph 602 shows the temperature drop characteristics corresponding to this case.

[0044] By taking the above temperature drop characteristics into consideration, the accuracy of the cartridge temperature rise prediction in this embodiment can be improved. That is, the characteristics of the fixing unit temperature rise Cf and the cartridge temperature rise Cc after printing a small to large number of sheets are measured in advance, and the temperature drop characteristics to be used in the calculation are selected depending on characteristic values ​​indicating the operation history of the image forming apparatus 100, such as the number of sheets printed. In FIG. 6, when the fixing unit temperature rise Cf exhibits the temperature drop characteristics of graph 601, the cartridge temperature rise Cc exhibits the temperature drop characteristics of graph 603. On the other hand, when the fixing unit temperature rise Cf exhibits the temperature drop characteristics of graph 602, the cartridge temperature rise Cc exhibits the temperature drop characteristics of graph 604. These data can be obtained by experimentally measuring the respective temperatures in advance.

[0045] An example of a characteristic value indicating the operation history of the image forming apparatus 100 is the number of consecutive prints of a job executed immediately before the power supply to the image forming apparatus 100 was stopped. In addition to the number of prints, any value that changes depending on the operation history of the image forming apparatus 100 can be used, such as the cartridge temperature T predicted by the first prediction unit 211a before the power supply was stopped, or the environmental temperature Te detected by the environmental temperature sensor 37. In addition to the above, for example, the temperature detected by a temperature sensor other than the environmental temperature sensor 37 (a sensor for detecting the temperature of a component other than the cartridge) may also be used. In this embodiment, the cartridge temperature T (=cartridge temperature rise Cc) is used, and the property that the greater the number of prints, the higher the cartridge temperature T becomes is utilized.

[0046] Table 1 is a table showing the relationship between the change in the amount of temperature rise Cf of the fixing unit after the power supply is resumed and the change in the amount of temperature rise Cc of the cartridge, as determined by measurement in this embodiment. In other words, it is table information showing the correspondence between data showing the temperature change characteristics of the fixing unit 19 and data showing the temperature change characteristics of the process cartridge 9. The rate of change in the temperature of the fixing unit 19 after the power supply is resumed (second timing) relative to the temperature of the fixing unit 19 before the power supply is stopped (first timing) (hereinafter referred to as the rate of change in the amount of temperature rise of the fixing unit). The rate of change in the temperature of the process cartridge 9 after the power supply is resumed relative to the temperature of the process cartridge 9 before the power supply is stopped (hereinafter referred to as the rate of change in the amount of temperature rise of the cartridge) is listed in the second and subsequent columns.

[0047] As described above, the characteristics of the rate of change in cartridge temperature rise change depending on the value of the cartridge temperature rise Cc before the power supply is stopped (first line). In this embodiment, the operation history of the image forming apparatus 100 is classified into five patterns according to the value of the cartridge temperature rise Cc. The value of the cartridge temperature rise Cc in the first line is obtained after the final print before the power supply is stopped and saved in the NVRAM 204. Then, after the power supply is resumed, the table to be used is selected based on that value.

[0048] [Table 1]

[0049] The control in the second prediction unit 211b in this embodiment will be described below with reference to the flowchart in Fig. 7. The flowchart in Fig. 7 is implemented by causing the CPU 201 included in the engine control unit 200 to execute a program stored in the ROM 202.

[0050] In S701, after printing is completed (=after power supply to the fixing heater 33 is stopped), the second prediction unit 211b detects the fixing unit temperature Tfb and the environmental temperature Teb using the fixing thermistor 34 and the environmental temperature sensor 37, respectively. In S702, the second prediction unit 211b calculates the amount of temperature rise Cfb of the fixing unit at this timing from Tfb and Teb detected in S701 using the following equation (6). Cfb = Tfb - Teb (6)

[0051] Furthermore, the second prediction unit 211b reads the cartridge temperature rise amount Ccb from the RAM 203, and stores the values ​​of Cfb and Ccb in the NVRAM 204. In S703, it is assumed that the power supply to the image forming apparatus 100 is stopped due to an event such as a power outage or an operation by the user such as unplugging the inlet cable from the outlet. In S704, after the power supply to the image forming apparatus 100 is resumed due to an event such as a power outage being restored or an operation by the user plugging the inlet cable into the outlet, the second prediction unit 211b detects the fixing unit temperature Tfa and the environmental temperature Tea in the same manner as in S701.

[0052] In S705, the second prediction unit 211b reads the cartridge temperature rise amount Ccb stored in the NVRAM 204, and based on the value of Ccb, selects the corresponding cartridge temperature rise prediction table from Table 1. The fixing unit temperature rise change rate in Table 1 is expressed as the ratio Rf of Cf (Cfa) at the time power supply is resumed to Cf (=Cfb) at the time printing ends, and is calculated by the following formula. Rf = Cfa / Cfb (7)

[0053] The rate of change in the amount of cartridge temperature rise is expressed as the ratio Rc of Cc (Cca) when power supply is resumed to Cc (=Ccb) when printing is completed, and is calculated by the following formula. Rc = Cca / Ccb (8)

[0054] The second prediction unit 211b selects a table that represents the appropriate relationship between Rf and Rc based on Table 1 and the Ccb value read out in S704. In S706, the second prediction unit 211b calculates the amount of temperature rise Cfa of the fixing unit using equation (6) based on the fixing unit temperature Tfa and the ambient temperature Tea detected in S704. Furthermore, the second prediction unit 211b can obtain the amount of temperature rise Cca of the cartridge when power supply is resumed by applying the relationships of equations (7) and (8) to Cfb and Ccb read out in S705 and the selected table. In other words, this value corresponds to the predicted amount of temperature rise Ccz of the cartridge. Finally, the second prediction unit 211b can calculate the predicted cartridge temperature Tcz using the relationship of equation (1) based on the calculated Ccz.

[0055] In this embodiment, the relationship between the rate of change in the fixing unit temperature rise and the rate of change in the cartridge temperature rise is used as the change in the fixing unit temperature rise in Table 1, but it is also possible to use the value of the change in the temperature rise itself.

[0056] In this embodiment, the relationship in Table 1 can also be expressed using an approximate formula. As an example, the relationship expressed in the case of [1] Cc>20 in Table 1 can be approximated by a second-order polynomial and expressed as in formula (9). Rc = -1.36(Rf) 2 + 2.36(Rf) (9)

[0057] Equation (9) is a calculation formula that uses data (ratio Rf) indicating the temperature change characteristics of the fixing unit 19 as an argument to derive data (ratio Rc) indicating the temperature change characteristics of the process cartridge 9. Then, if the ratio Rc can be determined, the amount of cartridge temperature rise Cca when power supply is resumed can be determined using equation (8).

[0058] Similarly, cases [2] to [5] in Table 1 can also be expressed using an appropriate approximation formula. According to this method, it is not necessary to store the numerical data shown in Table 1 in ROM 202, and it is only necessary to store multiple pieces of data such as coefficients used in the approximation formula according to the operation history of image forming apparatus 100, thereby reducing the storage capacity of ROM 202. The second prediction unit 211b selects a coefficient to be used according to a characteristic value that represents the operation history of image forming apparatus 100, and calculates the amount of cartridge temperature rise Cca when power supply is resumed using an appropriate approximation formula.

[0059] Furthermore, in this embodiment, the process of storing the characteristic value (=cartridge temperature rise amount Cc) representing the operation history of the image forming apparatus 100 was performed immediately after printing was completed, but it may be performed at any time between the end of printing and the stop of power supply. In this case, it is conceivable to control the process so that the characteristic value is stored in the NVRAM 204 at regular intervals and the most recent value at the time of power supply stop is used. It is also conceivable to control the process so that the characteristic value is stored in the NVRAM 204 at the same time as the power supply stop is used as a trigger.

[0060] Furthermore, in this embodiment, the cartridge temperature rise amount Ccb before the power supply was stopped was also used as a characteristic value representing the operation history of the image forming apparatus 100, but it is also possible to use the cartridge temperature rise amount Ccb obtained at a different timing. That is, the cartridge temperature rise amount Cc1 obtained immediately after printing is completed is used as a parameter only for selecting a table from Table 1. It is also possible to subsequently obtain the cartridge temperature rise amount Cc2 at a timing closer to the power supply being stopped, and use this value as the cartridge temperature rise amount Ccb before the power supply was stopped.

[0061] In this embodiment, the fixing unit temperature rise amount Cf is obtained twice, before (Cfb) and after (Cfa) the power supply is stopped, based on the detection result of the fixing thermistor 34, but it is also possible to obtain it only after the power supply is stopped. In other words, a preset constant value is used for the fixing unit temperature rise amount Cfb before the power supply is stopped, and only Cfa is obtained based on the detection result of the fixing thermistor 34, and the predicted cartridge temperature rise amount Ccz is calculated.

[0062] Also, in this embodiment, the calculation of the cartridge temperature Tcz after the resumption of power supply is performed immediately after the resumption of power supply, but it may be performed at any time as long as it is before the power is supplied to the fixing heater 33 again.

[0063] Also, in this embodiment, the cartridge temperature T (cartridge temperature rise amount Cc) is predicted. However, without being limited thereto, temperature prediction is possible for members and elements in the image forming apparatus 100 such as the above-described paper discharge sensor 30. In that sense, the prediction control in this embodiment can also be collectively referred to as in-machine temperature prediction.

[0064] (Control in the temperature rise suppression unit) As described above, the temperature rise suppression unit 212 described in FIG. 2(b) performs control so that the cartridge temperature T does not exceed the threshold value Tmax. When T≧Tmax, the temperature rise suppression unit 212 shifts to the temperature rise suppression mode so that the temperature of the process cartridge 9 does not rise any further. In the temperature rise suppression mode, even if the user tries to perform further printing, the image forming apparatus 100 does not execute printing. Also, when shifting to the temperature rise suppression mode during continuous printing, subsequent printing is stopped and the continuous printing is interrupted. After that, when the cartridge temperature T decreases without printing and T<Tmax, the temperature rise suppression unit 212 returns from the temperature rise suppression mode to the normal operation mode and printing can be performed again. When continuous printing has been interrupted, printing is resumed. <​​​​​As described above, according to this embodiment, it is possible to improve the accuracy of predicting the temperature of the target location when power is turned on again.

[0067] Example 2 The temperature prediction control of the second embodiment will be described. The basic device configuration is the same as that of the first embodiment, so the description will be omitted. Here, the control different from that of the first embodiment will be described.

[0068] [Control of Example 2] In Example 1, as described above, the temperature of the process cartridge 9 after the power supply is resumed is predicted using the relationship between the rate of change in the amount of temperature rise of the fixing unit and the rate of change in the amount of temperature rise of the cartridge after the power supply is resumed. In this example, the formulas (3) to (5) used for predicting the amount of temperature rise of the cartridge Cc are also applied to the amount of temperature rise of the fixing unit Cf to predict the temperature inside the apparatus.

[0069] In this embodiment, the temperature Ts of the paper discharge sensor 30 is predicted, rather than the temperature Tc of the process cartridge 9. As shown in FIG. 1, the paper discharge sensor 30 is often installed near the fixing unit 19 and is therefore susceptible to the heat of the fixing unit 19. Furthermore, a photointerrupter is often used as the paper discharge sensor 30, and the optical elements contained in the photointerrupter may be affected by heat and their characteristics may change. As a result, the detection accuracy of the paper discharge sensor 30 may decrease, or the paper discharge sensor 30 may even malfunction. Therefore, it is necessary to accurately predict the temperature of the paper discharge sensor 30 and activate the temperature rise suppression mode as necessary.

[0070] (Control in the second prediction unit) FIG. 8 is a schematic diagram showing the temperature drop characteristics of the fixing unit temperature rise Cf in this embodiment. Similar to the process cartridge 9, the change in the temperature rise of the fixing unit 19 can be expressed using equations (3) to (5). Therefore, if the change in Cf between two points is known, the elapsed time (ΔT) between them can be estimated by calculation based on equations (3) to (5). In this way, the temperature drop characteristics of the fixing unit 19 are measured in advance, and the values ​​of the fluctuation temperature coefficient k and the ultimate temperature rise Cx are experimentally obtained, thereby making the above estimation. The acquired fluctuation temperature coefficient k (Cx is normally 0) is stored in ROM 202.

[0071] In this case, too, for the same reasons as in the first embodiment, the temperature drop characteristics of the fixing unit 19 differ depending on the operation history of the image forming apparatus 100. Therefore, the fluctuation temperature coefficient k also differs depending on the operation history. Table 2 shows an example of the fluctuation temperature coefficient k representing the temperature drop characteristics of the fixing unit temperature rise Cf in this embodiment. In this embodiment, the operation history is classified into four patterns, and the k value (which becomes the kdown value) is determined for each operation history. Note that in Table 2, the discharge sensor temperature rise Cs is used as the characteristic value representing the operation history of the image forming apparatus 100. In this embodiment, the discharge sensor temperature rise Cs is constantly predicted by the first prediction unit 211a during normal operation in the same manner as the cartridge temperature rise Cc described in the first embodiment.

[0072] [Table 2]

[0073] In this embodiment, an appropriate k (= kf) is selected based on the value of the paper discharge sensor temperature rise Cs at the end of printing. Then, the elapsed time ΔT from when the power supply is stopped to when it is resumed is estimated by a fuser unit temperature prediction calculation using the kf selected when the power supply is resumed. Then, based on the estimated elapsed time ΔT, the paper discharge sensor temperature rise Cs is predicted by the normal temperature prediction method using equations (3) to (5).

[0074] Control in the second prediction unit 211b in this embodiment will be described using the flowchart of Fig. 9. The flowchart shown in Fig. 9 is implemented by causing the CPU 201 included in the engine control unit 200 to execute a program stored in the ROM 202.

[0075] In S901, after printing is completed, the second prediction unit 211b detects the temperature Tfb of the fixing unit 19 and the environmental temperature Teb using the fixing thermistor 34 and the environmental temperature sensor 37, respectively. In S902, immediately after S901, the second prediction unit 211b calculates the fixing unit temperature rise Cfb using the relationship in equation (6) and reads out the paper discharge sensor temperature rise Csb. The second prediction unit 211b stores Cfb and Csb in the NVRAM 204.

[0076] In S903, the second prediction unit 211b detects the temperature Tfb of the fixing unit 19 and the environmental temperature Teb before the power supply was stopped using the fixing thermistor 34 and the environmental temperature sensor 37, respectively. In S904, immediately after S903, the second prediction unit 211b calculates the amount of temperature rise Cfb of the fixing unit before the power supply was stopped using the relationship in equation (6) and reads the amount of temperature rise Csb of the paper discharge sensor. The second prediction unit 211b stores Cfb and Csb in the NVRAM 204. This is an update process of Cfb and Csb stored in the NVRAM 204 in S902.

[0077] Note that steps S903 and S904 are repeated at predetermined time intervals after S902 is completed. This is because it is impossible to predict when the power supply will be stopped. In this embodiment, the repetition time is one minute. If the power supply is stopped within one minute after S902 is completed, steps S903 and S904 are skipped, and the values ​​stored in NVRAM 204 in S902 are used.

[0078] In S905, it is assumed that the power supply to the image forming apparatus 100 is stopped due to an event such as a user unplugging the inlet cable from the outlet or a power outage. In S906, after the power supply to the image forming apparatus 100 is resumed due to an event such as a user plugging the inlet cable into the outlet or recovery from the power outage, the second prediction unit 211b detects the fixing unit temperature Tfa and the environmental temperature Tea in the same manner as in S901.

[0079] In S907, the second prediction unit 211b reads the discharge sensor temperature rise Csb stored in the NVRAM, and based on the value of Csb, selects the corresponding kf for predicting the temperature rise of the fixing unit from Table 2. In S908, the second prediction unit 211b calculates the temperature rise Cfa of the fixing unit after the power supply is resumed using equation (6) from the fixing unit temperature Tfa detected in S906 and the environmental temperature Tea.

[0080] In S909, the second prediction unit 211b calculates the predicted amount of temperature rise Cfz of the fixing unit after a certain time Δt seconds (6 seconds in this embodiment) using Cfb read out in S907, the selected kf, and equations (3) to (5). In S910, if Cfz calculated in S909 is equal to or less than Cfa calculated in S908, the second prediction unit 211b performs S911. In other cases, the second prediction unit 211b again calculates the predicted amount of temperature rise Cfz of the fixing unit after Δt seconds in S909, and proceeds to step S910 to repeat the calculation.

[0081] In S911, the second prediction unit 211b calculates the time ΔT required for the fixing unit temperature to change from Tfb to Tfa using the following equation (10). If n is the number of repeated calculations, ΔT is expressed by the following equation (10).

[0082] ΔT = n Δt (10) In S912, the second prediction unit 211b calculates the predicted discharge sensor temperature rise amount Csz using ΔT calculated in S911 and the same relationship as in equations (3) to (5), and then calculates the predicted discharge sensor temperature Tsz using equation (1).

[0083] In this embodiment, only the fluctuation temperature coefficient kfb, which indicates the temperature drop characteristic of the fixing unit temperature rise amount Cf, is stored for each operating history of the image forming apparatus 100, so the amount of data stored in ROM 202 can be reduced compared to embodiment 1.

[0084] In this embodiment, the fluctuation temperature coefficient ks (fluctuation temperature coefficient of the paper discharge sensor 30) used in calculating Csz in S912 is a fixed value independent of the value of Cs. This is a value experimentally obtained in advance, as described in the prediction of the cartridge temperature T in the first embodiment. In this embodiment, like kf for estimating the amount of temperature rise Cf in the fixing unit, the value of ks can also be determined depending on Cs, which represents the operation history of the image forming apparatus 100. This is because, like the fixing unit 19, the temperature drop characteristics of the internal temperature of a portion close to the fixing unit 19 may change depending on the operation history of the image forming apparatus 100. This can also be achieved by experimentally obtaining the value of ks for each Cs in advance and storing it in ROM 202. Then, as in S907, the second prediction unit 211b may select an appropriate value of ks depending on the value of Cs.

[0085] As described above, according to this embodiment, it is possible to improve the accuracy of predicting the temperature of the target location when power is turned on again.

[0086] Note that one key point of the second embodiment described above is that the length of the period from the first timing before the power supply is stopped to the second timing after the power supply is resumed is calculated. To calculate the length of the period during which the power supply is stopped, an alternative method would be to have the CPU 201 mounted in the engine control unit 200 measure the time. However, as described above, the state in which the power supply is stopped in this embodiment refers to a state in which a power outage has occurred, a state in which the inlet cable is unplugged, or the like, and therefore it is not possible to use a method in which the CPU 201 functions to measure the time. Therefore, it becomes necessary to use the method of the second embodiment described above.

[0087] On the other hand, when the power switch of the image forming apparatus 100 is simply turned off without a power outage and the inlet cable is connected to an outlet, the CPU 201 can continue to function and measure time, depending on the configuration. For example, if the power switch is a soft switch type, power is supplied to the engine control unit 200 even when the power is turned off, and the CPU 201 can continue measuring time. Therefore, in the above-described first and second embodiments, when the power switch is simply turned off, the CPU 201 counts the length of the period until the power switch is next turned on and predicts the cartridge temperature T based on the length of that period. Note that this also applies when the image forming apparatus 100 enters sleep mode.

[0088] However, this does not prevent the present invention from being applied when the power switch is simply turned off or when image forming apparatus 100 enters sleep mode. In other words, the present invention may be applied not only when the power supply to image forming apparatus 100 is stopped, but also when the power supply to image forming apparatus 100 is turned off. This eliminates the need for CPU 201 to measure time, leading to energy savings in image forming apparatus 100.

Claims

1. In an image forming apparatus for forming an image on a recording material, a detection means for detecting the temperature of the first member; a prediction means for predicting a temperature of a second member different from the first member; a storage means for storing information on a calculation formula for deriving data indicating the temperature change characteristic of the second member using data indicating the temperature change characteristic of the first member as an argument; and the information on the calculation formula includes a plurality of different coefficients depending on information indicating an operation history of the image forming apparatus; the prediction unit selects a coefficient to be used from the plurality of coefficients based on information indicating an operation history of the image forming apparatus; An image forming apparatus characterized in that the prediction means predicts the temperature of the second member at the second timing based on the selected coefficient, the temperature of the second member predicted by the prediction means at a first timing before the image forming apparatus is turned off, the temperature change of the first member detected by the detection means during the period from the first timing to a second timing after the image forming apparatus is turned on, and information indicating the operating history of the image forming apparatus up until the image forming apparatus is turned off.

2. 2. The image forming apparatus according to claim 1, wherein the predicting means calculates a change in temperature of the first member during the period based on the temperature of the first member detected by the detecting means at the first timing.

3. a storage means for storing table information indicating a correspondence relationship between data indicating the temperature change characteristics of the first member and data indicating the temperature change characteristics of the second member; the table information includes a plurality of data representing temperature change characteristics of the second member according to information representing an operation history of the image forming apparatus, The image forming apparatus according to claim 1 or 2, characterized in that the prediction means selects data to be used from a plurality of data indicating the temperature change characteristics of the second member based on information indicating the operating history of the image forming apparatus, and predicts the temperature of the second member at the second timing based on the selected data, the temperature change of the first member, and the temperature of the second member at the first timing.

4. a storage unit that stores a plurality of data items that indicate temperature change characteristics of the first member, the data items being set in accordance with the operation history of the image forming apparatus; The image forming apparatus according to claim 1 or 2, characterized in that the prediction means selects data to use from a plurality of data indicating the temperature change characteristics of the first member based on information indicating the operating history of the image forming apparatus, calculates the length of the period from the first timing to the second timing based on the selected data, and predicts the temperature of the second member at the second timing based on the length of the period and the temperature of the second member at the first timing.

5. The image forming apparatus according to claim 1, characterized in that the memory means further stores a plurality of data indicating the temperature change characteristics of the second member, and the prediction means, when predicting the temperature of the second member, selects data to use from the plurality of data indicating the temperature change characteristics of the second member based on information indicating the operating history of the image forming apparatus.

6. An image forming apparatus according to any one of claims 1 to 5, characterized in that the first timing is a timing before the power supply to the image forming apparatus is stopped and after the printing operation performed immediately before the power supply is stopped is completed, and the second timing is a timing after the power supply to the image forming apparatus is resumed and before the power supply to the first member is resumed.

7. 7. The image forming apparatus according to claim 1, wherein the information indicating the operation history of the image forming apparatus is the temperature of the second member at the first timing predicted by the prediction unit.

8. 7. The image forming apparatus according to claim 1, wherein the information indicating the operation history of the image forming apparatus is the number of consecutive prints of a job executed immediately before the power of the image forming apparatus was turned off.

9. 9. The image forming apparatus according to claim 1, wherein the first member is a fixing unit for fixing an image onto a recording material, and the detecting means is a thermistor for detecting the temperature of a heater provided in the fixing unit.

10. 10. The image forming apparatus according to claim 1, wherein the second member is a cartridge that stores a developer, or a discharge sensor that detects a recording material on which an image has been formed.

Images