JP2007065413A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set proper target fixation temperature by estimating the temperature of a pressure member more accurately even when a fixing device having no cleaning mechanism is employed. <P>SOLUTION: After a heating heater is turned OFF after fixation by the fixing device 58 ends, the heating heater is turned ON for a specified time to clean the pressure member (pressure roller). Transition of the temperature of the pressure member after the heating heater is turned OFF is estimated at the end of the cleaning of the pressure member based upon prescribed conditions. According to the estimation result, target fixation temperature is set as heating heater temperature needed for fixation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which a toner image is formed on a recording material by a transfer method or a direct method by an image forming process such as an electrophotographic method or an electrostatic recording method, and the toner image is heated and fixed by a fixing device. This is related to fixing control.

  In an image forming apparatus using an image forming process such as an electrophotographic method or an electrostatic recording method, an electrostatic latent image is formed on a photosensitive member, and the latent image is developed using a developer to be visualized as a toner image. The toner image is transferred onto a recording material such as paper, and then the recording material onto which the toner image has been transferred is passed through a fixing nip formed by a fixing roller and a pressure roller provided in the fixing device. Thus, the toner image is heat-fixed as a permanent image on the recording material.

  In recent years, a fixing method that suppresses power consumption as much as possible without supplying power to the fixing device especially during standby, and more specifically, film heating that fixes a toner image on a recording material through a thin film between a heater and a pressure roller. Patent Documents 1 to 4 propose fixing methods of the type. Japanese Patent Application Laid-Open No. 2004-228688 discloses a method of starting up an engine unit of an image forming apparatus in advance so that a printing operation can be started simultaneously with the end of image development and avoiding various troubles caused by a temperature rise in the fixing device. Proposed.

  Conventionally, image forming apparatuses such as printers and copiers using a film heating type fixing device eliminate the need for preheating during standby and shorten the waiting time due to the high heating efficiency and startup speed of the fixing device. There are many advantages compared to the case of using a conventional fixing device such as a heat roller.

In an image forming apparatus that employs a film heating method, the waiting time during each stage from when the user issues an instruction to start printing to when the printing operation is completed is developed in the pixel information conversion unit (video controller). The time required for the image forming apparatus, the start-up time of the image forming apparatus, and the time of the image forming process (printing operation) after the paper feeding operation starts are added.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP 2002-91230 A JP 2002-169411 A Japanese Patent Laid-Open No. 11-344894

  As described above, when a printing operation is performed by a conventional method, after image development is performed by the pixel information conversion unit (video controller) in the image forming apparatus, a print signal is output to the image forming apparatus control unit (engine controller). Since the engine was started up and the printing operation was started, the waiting time when using the image forming apparatus was long.

  That is, there is a waiting time that can be divided into an image development time and an apparatus start-up time after the user issues an instruction to start printing at the external information device until the printing operation starts. Here, the engine controller receives a print signal instructing start-up after the image development is completed by the video controller. Therefore, the engine is not performing any operation while the image development is being performed. There will be no.

  Due to the recent spread of the Internet due to the high performance of personal computers and the development of terminal devices that record image information such as digital cameras, the manuscripts created by users on personal computers are complex including photographs and graphics. The amount of such image data has become very large. When trying to print such an image with a large amount of data, a long time is required for image development processing by the video controller, and as a result, the waiting time of the user is increasing.

  Therefore, in order to improve the above problems, even if it takes a lot of time to develop the image, the engine unit of the image forming apparatus is started during that time so that the printing operation can be performed anytime. In this case, the printing operation can be started at the same time as the image development is completed and the print signal is received. In other words, it is possible to shorten the time taken for the startup until now, and to reduce the stress that the user has ever felt for the waiting time.

  However, starting up the engine unit of the image forming apparatus in advance during image development in this way starts energizing the heater of the fixing device at a timing earlier than the normal timing. If the fixing device reaches the fixing possible temperature during the image development time, the heater stands by while maintaining the target fixing temperature until the engine controller receives a print signal. If the image development time is long, the fixing device has to wait at a high temperature for a very long time, and the heat of the heater is directly transmitted to the pressure roller at the fixing nip portion. There is a concern that the temperature will be much higher than when raising.

  Further, the fixing temperature during printing is determined so that the fixing property can be secured and thermal offset does not occur. When the fixing device is cooled, such as when the power is turned on, the heater is controlled at a high heater temperature, and when printing continues, the pressure roller, film guide, rigid pressure stay (T stay, metal stay), etc. are warmed. Generally, the fixing temperature is lowered according to the number of prints.

  However, in the case of intermittent printing, the pressure roller is heated by the residual heat in each printing process and stored, so that the temperature tends to be higher than in continuous printing.

  Furthermore, the heater on timing of the fixing operation is the printing operation when the printer receives the print signal so that the fixing device components such as the pressure roller and the fixing film are sufficiently warmed before the paper enters the fixing device at the start of printing. In general, the heater is turned on when. At this time, it is general that the heater is turned on after the paper feed sensor is turned on at the start of printing and after the top sensor or the registration sensor is turned on before the paper enters the fixing nip.

  In intermittent printing with a short stop interval, the pressure roller temperature becomes excessively high compared to continuous printing, and the temperature in the fixing nip portion becomes high. A print pattern having a high dot ratio, for example, an image pattern, such as a solid black image or a graphic pattern such as halftone, has a toner image formed on the entire print surface on paper. When the paper passes, the moisture contained in the recording material is heated and evaporated, and is discharged to the outside as water vapor. When the temperature of the pressure roller is high, water vapor is released at a very high pressure, so that a layer of water vapor is formed between the recording material and the pressure roller, and the frictional force between the recording material and the pressure roller is reduced. Considering that the recording material is driven and conveyed by the frictional force with the pressure roller, if the frictional force becomes extremely small, the recording material cannot be slid and conveyed with respect to the pressure roller. A paper jam (jam) occurs due to slip in the machine.

  In addition, since the temperature in the fixing nip portion becomes too high, the toner is not fixed to the recording material and melts and adheres to the fixing film side to cause an offset (high temperature offset) on the image. In addition, toner contamination of the pressure roller occurs.

  With respect to the above problem, Patent Document 6 discloses a method of setting the heater ON timing in accordance with the temperature of the heating member at the time of receiving a print signal. This is a method of setting the heater ON timing by artificially estimating the pressure roller temperature. When the temperature of the heating member = pressure roller temperature = high temperature, the heater ON timing is delayed to increase the pressure roller temperature. When the temperature of the pressure roller is low, the heater ON timing is advanced, and the pressure roller is raised to a temperature at which it does not slip to ensure the fixing property.

  By the way, in a fixing device without a cleaning mechanism, in order to prevent the pressure roller from being soiled, the fixing nip portion is heated when the fixing device is stopped after the end of image formation and after the rotation of fixing driving as described in Patent Document 7. Then, of the toner adhering to the pressure roller due to offset or the like, the toner in the fixing nip portion is melted to form a larger toner mass than before melting. Thereafter, since the surface temperature of the fixing film having a small heat capacity becomes lower than the temperature of the pressure roller having a large heat capacity, the above-mentioned molten toner is transferred to the fixing film having a low temperature. The transferred toner is transferred to the recording material when the next recording material passes through the fixing nip portion, and is discharged together with the recording material. The offset toner at this time is a small amount of toner that is invisible because the recording material is passed through several to several tens of sheets, and the toner discharged to the recording material is naturally visible. Such offset toner adheres to the recording material. By this cleaning sequence operation, it is possible to prevent the pressure roller from being soiled without contacting the cleaning member with the pressure roller, and the cost can be reduced.

  However, when the fixing device is stopped after post-rotation of the fixing drive, the temperature relationship between the heating member and the pressure roller becomes different by heating the fixing nip portion for cleaning the pressure roller. The temperature of the pressure roller cannot be predicted. Therefore, in the fixing device adopting the above configuration, the pressure roller temperature is generally poorly estimated. In this case, when the fixing temperature and the heater ON timing are set from the estimated pressure roller temperature, there is a large difference between the actual pressure roller temperature and the estimated temperature. This is accompanied by the following adverse effects.

  If the estimated pressure roller temperature is higher than the actual temperature, fixing failure occurs. For example, when one sheet is printed in the cold state and the next print signal is received during the cleaning sequence operation, the estimated pressure roller temperature is set higher than the actual temperature. In such a case, since the heater ON timing is late, the pressure roller temperature rises slowly, or the fixing temperature setting is set low, which causes a fixing failure.

  Such a problem may be avoided by setting the fixing temperature after the preprocessing for a few seconds after the end of printing. However, in the case of the intermittent mode (1 sheet / 15 seconds), the pressure roller reaches about 10 sheets and reaches a high temperature, so that a paper jam (jam) may occur due to slip.

  As described above, conventionally, in order to reduce the printing time by starting up the fixing device during image development, it is not easy to optimally set the heater-on timing and the fixing temperature for the above problems. .

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of more accurately estimating the temperature of the pressure member even when a fixing device having no cleaning mechanism is employed.

  Another object of the present invention is to set an appropriate fixing temperature based on the estimated temperature of the pressure member, and to set the sheet feeding timing of the recording material. An object of the present invention is to provide an image forming apparatus capable of suppressing the temperature rise of the pressure roller so as not to occur.

  An image forming apparatus according to the present invention comprises: an image forming unit that forms a toner image on a recording material; and a heating device that heats and fixes a toner image formed on the recording material on the recording material based on input image information. A fixing device that heats and fixes the toner image on the recording material by passing the recording material on which the toner image is formed through a fixing nip portion formed by press-contacting a heating member and a pressure member including a heater; And a control means for controlling the fixing device, wherein the control means performs a function of cleaning the pressure member by turning on a heater for a predetermined time after completion of fixing, and after completion of the cleaning of the pressure member. And a function of estimating the transition of the temperature of the pressure member based on a predetermined condition.

  This image forming apparatus has a function of cleaning the pressure member by turning on the heater for a predetermined time after the heater is turned off, instead of having a pressure member cleaning mechanism. Along with this, the transition of the temperature of the pressure member after the heater is turned off at the end of cleaning of the pressure member is estimated based on a predetermined condition, and the heater temperature required for fixing is determined according to the estimation result. Set a target fixing temperature.

  The pressure member temperature is estimated by, for example, the elapsed time from a predetermined time after the end of the previous image forming operation, the paper size, the number of sheets to be passed, and the surface temperature of the heating member at a predetermined time after the end of the previous image forming operation. This can be performed based on at least one of the detection temperatures of the temperature detection unit that detects the above.

  The control unit starts up the heater before image development is completed, causes the heater to wait at a temperature (standby temperature) lower than a target fixing temperature that is a heater temperature necessary for fixing, and at least inputs And a function of controlling the heater to reheat to the target fixing temperature after the image development of the image information is completed, and switching the standby temperature according to the estimation result of the temperature of the pressure member. May be. As a result, the fixing device is started up while the image is being developed, so that the waiting time until the image forming operation is completed can be shortened, and the standby temperature is determined according to the estimated temperature of the pressure member. Therefore, it is possible to reliably reach the target fixing temperature after standby, and to minimize the amount of electric power supplied to the heater.

  In this case, preferably, at least one of the target fixing temperature, the standby temperature, and the paper feed timing is changed according to the elapsed time after reaching the standby temperature. Accordingly, it is possible to appropriately cope with the temperature rise of the pressure member by prolonging the standby time at the standby temperature.

  The temperature of the pressure member can be estimated based on an arithmetic expression described later.

  The present invention is preferably applied to the heating member that uses a movable film that is in pressure contact with the pressure member at the fixing nip portion. This is because the heat capacity of the film is smaller than the heat capacity of the pressure member, and the influence of the temperature of the pressure member is relatively increased with respect to fixing.

  According to the present invention, even when a fixing device having no cleaning mechanism is employed, the temperature of the pressure member can be estimated more accurately, and the appropriate temperature can be estimated based on the estimated temperature of the pressure member. By setting the fixing temperature and setting the recording material feed timing, it prevents the fixing failure and suppresses the temperature rise of the pressure roller to prevent the recording material from slipping or high-temperature offset in the fixing device. Can do.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in more detail with reference to the drawings.

  FIG. 1 is a schematic view showing an embodiment of an image forming apparatus of the present invention. As shown in this figure, the image forming apparatus includes a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is configured by forming a layer of photosensitive material such as OPC, amorphous Se, or amorphous Si on a cylindrical substrate such as aluminum or nickel, and is driven to rotate at a predetermined peripheral speed in the direction of an arrow. The The surface of the photosensitive drum 1 is uniformly charged by a charging roller 2 as a contact charging means during the rotation process, and then is turned ON / OFF based on a video signal developed by a pixel information conversion unit (video controller) (not shown). Scanning exposure with the laser beam 3 controlled to be OFF is performed, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. This scanning exposure apparatus comprises a scanner unit that scans a laser beam reflected on a polygon mirror by the rotation of the polygon mirror.

  The electrostatic latent image on the photosensitive drum 1 is developed by the developing device 4 using a developer (toner or toner + carrier) and visualized as a toner image. The toner image obtained on the photosensitive drum 1 is transferred by the transfer roller 5 onto the recording material P supplied from the paper feed cassette 9 or a paper feed tray (not shown) and conveyed to the photosensitive drum 1 by the registration roller 30 at a predetermined timing. Is done. At this time, the front end sensor 8 in front of the transfer roller 5 detects the passage of the front end of the recording material P supplied from the paper feed cassette 9, and the image formation position of the toner image on the photosensitive drum 1 and the front end of the recording material are detected. The conveyance timing of the recording material to the photosensitive drum 1 is adjusted so that the writing position (transfer start position) matches. The recording material conveyed at a predetermined timing is transferred with a toner image while being nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure.

  The recording material onto which the toner image has been transferred is conveyed to the fixing device 6 and the toner image is fixed on the recording material as a permanent image. After the fixing, the recording material is guided by a heat-resistant fixing and discharging guide, nipped and conveyed by the discharging roller and the discharging roller, and discharged onto the discharge tray 33. On the other hand, the untransferred toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

  FIG. 2 shows a schematic configuration of the fixing device 6 in the present embodiment. As shown in this figure, the fixing device 6 includes a heating member 10 and a pressure roller 20, and the heating member 10 is used as a film heating method to suppress the heat capacity of the heating member 10 as small as possible, thereby improving the quick start property. Satisfied.

  The heating member 10 is a cylindrical thin film (fixing film) 13 formed of a heat-resistant resin, and a heat-resistant stay holder (support) 12 is disposed by a support member (not shown). The heater 11 is held in a portion on the pressure roller 20 side. On the back surface of the heater 11 opposite to the fixing nip portion, for example, a thermistor 14 as a temperature detection portion of the heater 11 is provided. The pressure roller 20 is made of an elastic roller and presses against the heater 11 through the fixing film 13 to form a fixing nip portion with a predetermined width between the fixing film 13 and the pressure roller 20.

  With respect to the conveyance direction of the recording material P, an entrance guide 15 and an exit guide 16 are installed in front and rear of the fixing nip portion, respectively, and a roller 17 and a roller 18 constituting a fixing paper discharge unit are disposed behind the exit guide 16. Has been placed.

  The fixing film 13 is rotated and moved in the direction of the arrow by the rotational force of the pressure roller 20 while sliding in close contact with the surface of the heater 11 in the fixing nip portion. The fixing film 13 may be provided with a driving means to actively rotate the fixing film 13. The fixing film 13 has a cylindrical shape, but may be an endless belt-shaped member or a roll-wound end-web member.

  The temperature of the heater 11 is adjusted to the fixing temperature, the fixing film 13 is rotated in the direction of the arrow, and the recording material P carrying the toner image in that state passes through the entrance guide 15 and then the fixing nip between the fixing film 13 and the pressure roller 20. When the recording material P is introduced into the area, the recording material P is brought into close contact with the surface of the fixing film 13, is nipped and conveyed together with the fixing film 13, and passes through the fixing nip, while the recording material and the toner image thereon are passed. Is heated by the heater 11 through the fixing film 13 to fix the toner image on the recording material. The recording material that has passed through the fixing nip is peeled off from the surface of the fixing film 13 and is conveyed through an exit guide 16, a paper discharge roller 17, and a paper discharge roller 18.

A ceramic heater is generally used as the heater 11 as a heating means. For example, on the surface of the ceramic substrate having electrical insulation, good thermal conductivity, and low heat capacity such as alumina facing the one fixing film 13, silver palladium (in the direction perpendicular to the paper surface of the drawing) An energization heat generating resistance layer such as Ag / Pb) or Ta ₂ N is formed by screen printing or the like, and the resistance layer forming surface is covered with a thin glass protective layer.

  By energizing the energization heat generation resistance layer of the heater 11 through a power supply unit from a power supply device (not shown), the energization heat generation resistance layer generates heat, and the entire heater including the ceramic substrate and the glass protective layer rapidly rises in temperature. The temperature rise of the heater 11 is detected by a temperature detection unit (thermistor 14) on the back of the heater and fed back to an energization control unit (not shown). The temperature detection of the heater by the thermistor 14 covers the width direction region of the heater through which all the transportable recording material passes.

  The energization control unit controls power supply to the energization heating resistor layer so that the heater temperature detected by the thermistor 14 is substantially maintained at a predetermined fixing temperature. As a control method, there are a wave number control method for controlling increase / decrease in the wave number of an applied voltage, a phase control method for applying a voltage from each phase angle of voltage, and the like. By these control methods, the heater 11 is heated and adjusted to a predetermined fixing temperature.

  The fixing film 13 of the present embodiment has a thickness as thin as 20 to 70 μm so that the heat of the heater 11 can be efficiently applied to the recording material P at the fixing nip portion. This fixing film 13 has a three-layer structure of a film base layer, a primer layer, and a release layer, and is used with the film base layer on the heater side and the release layer on the pressure roller side.

  The film base layer is a layer for maintaining the mechanical strength such as the tear strength of the entire fixing film, and has a high insulating property like the glass protective layer of the heater 11, and has a high insulating property such as polyimide, polyamideimide, PEEK. Etc., and also has heat resistance and high elasticity. The primer layer is an adhesive layer between the film base layer and the release layer, and is formed in a thin layer having a thickness of about 2 to 6 μm. The releasable layer is a toner offset prevention layer for the fixing film, and is formed by coating a fluorine resin such as PFA, PTFE, FEP or the like to a thickness of about 10 μm.

  The stay holder 12 is made of, for example, heat resistant plastic, and holds the heater 11 and also serves as a conveyance guide for the fixing film 13. The stay holder 12 is supported by a support member (not shown) and is immovably disposed in the cylinder of the fixing film 13.

  The pressure roller 20 is an elastic roller, and an elastic layer 22 such as silicone rubber or silicone sponge is provided around a metal core 21 made of aluminum or the like, and a fluorine resin layer such as PFA, PTFE, or FEP is provided thereon. Is formed as a releasable layer 23. Necessary to heat and fix the toner image on the recording material between the fixing film 13 and the pressure roller 20 by pressing the pressure roller 20 to the heater 11 through the fixing film 13 with a predetermined pressure. A fixing nip portion is formed.

  When the pressure roller 20 having elasticity is pressed, the heater 11 has high rigidity. Therefore, the pressure roller 20 becomes flat at the pressure contact portion following the flat bottom surface of the heater 11, and a fixing nip having a predetermined width is obtained. By forming only the portion and heating only the fixing nip portion, quick start heat fixing is realized.

  In the image forming apparatus adopting the film heating method, as shown in FIG. 3, each part is electrically controlled. First, in the external information device 50 such as a personal computer, the user creates a document (electronic manuscript) to be printed such as a document, a figure, or an image, and issues an instruction to print the created electronic manuscript to the external information device. When issued from 50, the image data of the electronic document is sent to a pixel information conversion unit (video controller) 51 of the image forming apparatus 52. The video controller 51 develops the sent image data and converts it into a video signal. When the image development is completed, the video controller 51 transmits a signal (print signal) for starting a printing operation to the engine controller 53 and also transmits a video signal of the image.

  When the engine controller 53 receives the print signal, the engine controller 53 starts a scanning exposure device 54 for writing on the photosensitive drum 1 and starts supplying power to the fixing device 58 (the fixing device 6 in FIG. 1) so that the heater can be fixed. Command to start up to reach The fixing device 58 includes a heater temperature detection unit configured by a thermistor or the like which will be described later. When the scanning exposure device 54 and the fixing device 58 rise to a predetermined rotation speed and temperature, the paper feed unit 56 (the paper feed cassette 9 in FIG. 1 and a paper feed tray (not shown)) and the transport unit 57 are operated. The conveyance of the recording material is started, and the toner image transferred to the recording material by the fixing device 58 is heated and fixed through an image forming process in the developing / transfer section 55 (the developing device 4 and the transfer roller 5 in FIG. 1). A series of printing operations is completed.

  An example of the temperature control method of the heater 11 in the present embodiment is shown below. In the film heating type fixing device, the temperature adjustment temperature of the heater 11 as the heating means is changed according to the surface temperature of the pressure roller 20 as the pressure member. When the energization and heating resistance layer of the heater 11 is not energized (standby state) for a long time, the pressure roller 20 is sufficiently cooled, and thus the toner image is heated and fixed. In this case, the amount of heat given from the heating member 10 is mainly used. On the other hand, after the heat fixing operation has continued for a while, the surface of the pressure roller is in a sufficiently heated state. Therefore, not only the amount of heat from the heating member 10 but also the amount of heat from the pressure roller 20 is not reduced. It can be used as the amount of heat necessary for fixing an image.

  That is, the amount of heat applied from the heating member 10 to the recording material can be reduced compared to the heat fixing from the state where the pressure roller 20 is cooled. On the other hand, if it is not kept small, an excessive amount of heat is applied to the toner image on the recording material, which causes problems such as high temperature offset. Therefore, the temperature adjustment temperature of the heater 11 of the heating member 10 needs to be sequentially changed according to the temperature rising state of the pressure roller 20.

  FIG. 4 shows an example of transition of the fixing temperature adjustment temperature in this temperature adjustment control. In this figure, the horizontal axis indicates the number of sheets to be passed, that is, the number of fixed sheets when continuous fixing is started from the state where the pressure roller 20 is cooled, and the vertical axis indicates the control temperature of the heater, that is, the fixing temperature adjustment temperature. When image formation is performed by the image forming apparatus when the pressure roller 20 is in a cold state, in this example, a predetermined temperature corresponding to the first sheet in FIG. The thermistor 14 is controlled so as to keep the temperature of the heater 11 constant at the temperature control temperature. In the case where images are continuously heat-fixed, the surface temperature of the pressure roller gradually increases in accordance with the number of fixed sheets. Therefore, in the figure, the temperature adjustment temperature of the heater 11 is decreased by 5 ° C. every 20 sheets to 185 ° C. It is lowered.

  Conventionally, when heat fixing is started after the pressure roller 20 has been warmed to some extent, the control temperature of the heater 11 is determined according to the temperature detected by the thermistor 14 when a print signal is input to the image forming apparatus. To decide. For example, when the detection temperature of the thermistor 14 is 50 to 70 ° C. at the start of printing (at the start of energization to the energization heating resistor layer), the detection temperature is 70 to 70 ° C. from 205 ° C. corresponding to the 21st sheet in FIG. In the case of 90 ° C., temperature control is started from 200 ° C. corresponding to the 41st sheet in FIG. Thereby, heater temperature control is set according to the heating condition of the pressure roller 20.

  However, as shown in FIG. 8, when a cleaning sequence for heating the fixing nip portion is performed when the fixing device is stopped after the post-rotation of the fixing drive as described above, the temperature of the heater 11 and the temperature of the pressure roller 20 are changed. The difference becomes large, and fixing failure may occur. Therefore, in the present embodiment, the following sequence is adopted in order to set an appropriate fixing temperature that does not slip while ensuring the fixing property.

First, as shown in FIG. 5, a method for setting a fixing temperature when starting the next job after one sheet is completed after the heater 11 and the pressure roller 20 are cooled (Cold state from a low temperature environment) will be described. . This condition is a fixing temperature setting method when the actual pressure roller temperature is relatively low and the heater 11 temperature is high.
(1) First, when one sheet is passed, the pressure roller temperature after printing is estimated. Since there is a temperature difference between the heater and the pressure roller at this time (due to the relationship between the heating member and the non-heating member), the post-rotation (idling) is performed for a predetermined time (here, 12 seconds) with the heater energized OFF. As a result, the temperatures of the pressure roller 20 and the heater 11 are in an equilibrium state, so that the pressure roller temperature PT0 after the printing can be accurately estimated. Further, the relationship between the estimated temperature of the pressure roller 20 of the present embodiment and the actually measured temperature and the post-rotation time (idling time) is as the post-rotation time elapses as shown in the graph of FIG. It can be seen that it decreases almost linearly. In order to increase durability and production performance, the post-rotation time may be shortened and correction may be applied.
(2) Next, the above cleaning sequence for preventing pressure roller contamination is started. That is, first, when the fixing device is stopped after the post-rotation of the fixing drive, the fixing nip portion is heated for 5 seconds to melt the toner in the fixing nip portion of the toner attached to the pressure roller by offset or the like, Make the toner mass larger than before melting. Thereafter, when the heater 11 is turned off, the surface temperature of the fixing film having a small heat capacity becomes lower than the temperature of the pressure roller having a large heat capacity, so that the above-described molten toner is transferred to the fixing film having a low temperature. The transferred toner is transferred to the recording material when the next recording material passes through the fixing nip portion, and is discharged together with the recording material. The offset toner at this time is a small amount of toner that is invisible because the recording material is passed through several to several tens of sheets, and the toner discharged to the recording material is naturally visible. The offset toner is adhered to the recording material at a level that is not present.
(3) The pressure roller temperature estimation starts simultaneously with (2).
The image forming apparatus used in the present embodiment does not include means for directly detecting the temperature of the pressure roller. Therefore, the temperature of the pressure roller is estimated. The method for this is that the heat capacity of the heater 11, the film 13, etc. is very small, and the energization of the energization heating resistance layer of the heater 11 is shut down during standby, so that the detected temperature of the thermistor 14 is greater than that of the heater. This is possible because the temperature of the pressure roller converges to a large value. However, since the cleaning sequence is performed after the printing is completed, the temperature and pressure detected by the thermistor 14 serving as the temperature detection unit depend on the elapsed time from the predetermined time after the last image forming operation, the paper size, and the number of sheets passed. Since an unacceptable deviation occurs between the roller temperature and the roller temperature, a method for accurately estimating the pressure roller temperature according to these various cases was derived by experiments.

  In this embodiment, the pressure roller temperature decay curve according to the elapsed time from the predetermined time after the end of the image forming operation is formulated into a numerical formula, and the pressure roller temperature is estimated using this.

  An example is shown below. Here, the pressure roller temperature transition after passing one sheet of A4 size paper and the pressure roller temperature transition after passing 30 sheets are measured and plotted in FIG. 10, and the average value is plotted as the pressure roller temperature. Formulated as an attenuation curve. As can be seen from the graph of FIG. 10, the slope of the pressure roller temperature transition after passing one A4 size sheet is almost equal to the slope of the pressure roller temperature transition after passing 30 sheets, and is a y-intercept. It can be seen that by operating a constant (107.7 in the average graph in the figure), it is possible to estimate the pressure roller temperature for each sheet passing number. Since the change in the y-intercept corresponds to the difference in temperature at the start (pressure roller temperature at 0 sec on the horizontal axis in the graph), the pressure roller is estimated after the heater is turned off and idling after printing is completed. It can be seen that the temperature may be calculated from the temperature PT0.

From the above, the following relational expression was obtained.
(A) Elapsed time from a predetermined time after the end of the immediately preceding image forming operation t: less than 60 sec and PT0: less than 125 ° C. Paper size of the immediately preceding image forming operation: width 279 mm or more
Or
Elapsed time from a predetermined time after the end of the immediately preceding image forming operation t: less than 60 sec, PT0: less than 125 ° C., and paper size of the immediately preceding image forming operation: less than 279 mm in width and continuously 4 sheets or less PT1 = A × t ² -B * t + PT0 ----- (1)
(B) Elapsed time from a predetermined time after the end of the immediately preceding image forming operation: less than 60 sec, PT0: 125 ° C. or more, paper size of the immediately preceding image forming operation: less than 279 mm in width, and the number of sheets passed: 5 or more continuously PT1 = C × t ² −t + PT0 −−−−− (2)
(C) Elapsed time t from the predetermined time after the end of the immediately preceding image forming operation: When 60 sec to 90 sec, PT1 = detected temperature of the temperature detecting section-D ----- (3)
(D) Elapsed time t from the predetermined time after the end of the immediately preceding image forming operation: 90 sec or more and the paper size of the immediately preceding image forming operation: width 279 mm or more PT1 = detection temperature of the temperature detecting unit −E −−−− -(4)
(E) Elapsed time t from the predetermined time after the end of the immediately preceding image forming operation: 90 sec or more, and the paper size of the immediately preceding image forming operation: less than 279 mm in width and the number of sheets to be passed: 5 consecutive sheets or more PT1 = temperature detection unit Detection temperature -F-----(5)
here,
PT0 is a predicted pressure member temperature value calculated from the temperature detected by the temperature detector at a predetermined time after the end of the previous image forming operation,
PT1 is the pressure member predicted temperature value after the acquisition time of PT0,
t = elapsed time from a predetermined time after the end of the previous image forming operation,

In the formula, A to F are predetermined constants obtained from experiments, and in the present embodiment, the following numerical values are obtained.
A = 0.177, B = 1.800, C = 0.007,
D = 40 ° C., E = 30 ° C., F = 40 ° C.

  FIG. 5 is a graph showing the temperature drop after the cleaning sequence when starting in the cold state in a low temperature environment. This graph shows the thermistor temperature, the measured temperature of the pressure roller 20, and the estimated temperature. Comparing the measured temperature of the pressure roller 20 and the estimated temperature, it can be seen that the pressure roller temperature can be estimated with an error of Δ16 ° C. at the maximum. A steep change is observed in the estimated pressure roller temperature in the vicinity of the time from 55 seconds to 60 seconds, which is due to an error at the boundary of the section of time t in the above equations (2) and (3).

  In a specific operation, when a print signal is received, first, a predicted pressure member temperature PT1 after the PT0 acquisition time is set by the above equations, and a target fixing temperature corresponding to this PT1 is set. FIG. 6 described above is a graph showing the relationship between the post-rotation time after passing one sheet and the correction temperature (detection temperature−measurement temperature of the pressure roller) for correcting the detection temperature for predicting the pressure roller temperature. . From this figure, it can be seen that the difference between the detected temperature and the actually measured pressure roller temperature gradually decreases with the passage of the post-rotation time, and the difference becomes zero in about 12 seconds. This means that the temperature difference between the two is reduced by post-rotation. From this relationship, the temperature of the pressure roller can be predicted and corrected even if the post-rotation is stopped before the temperature difference becomes zero.

  For example, the target fixing temperature is determined as follows. When a print signal is received 5 seconds after the pressure roller estimated temperature PT0 at the end of the previous printing, as shown in the graph of FIG. 5 (in FIG. 5, the heater is turned off after the cleaning sequence is completed, so the time of 0 second in FIG. Since PT1 = 65 ° C. (5 seconds have passed since the setting of PT0 at the time), the target fixing temperature = 200 ° C. is set from the relationship of Table 2 described later. If 120 seconds have elapsed from the setting of PT0, PT1 = 30 ° C. is set from the graph of FIG. 5, and the target fixing temperature is set to 210 ° C. from the relationship shown in Table 2.

  As described above, since the pressure roller temperature at the start of printing is estimated without completely depending on the thermistor detection temperature, an appropriate target fixing temperature can be set based on the estimated pressure roller temperature. it can.

In order to increase productivity, the first print out time (First_Print_Out_Time = FPOT) is shortened. For example, the following two methods (1) and (2) were compared for the time from when the user issued a print start signal from the personal computer of the external information device to when the printing operation was completed.
(1) When the conventional print operation control is followed: When the start-up operation of the fixing device is started after the print signal is sent to the engine controller after the image is developed by the video controller.
(2) When the fixing device is started up in advance: The fixing device is started up before starting image development in the video controller, and the print signal is started immediately after receiving the print signal after the end of image development.

  The control (2) was performed as follows. First, when the personal computer 50 in FIG. 3 sends image data to the video controller 51 of the image forming apparatus, the video controller 51 signals the engine controller 53 to start up the fixing device 58 of the engine unit before starting image development. (Preheat signal) is sent. When the engine controller 53 receives the preheat signal, it immediately starts to start up the fixing device 58. Thereafter, after the image development is completed, a print signal and a video signal are received, and a print operation is started. The rise time of the fixing device is the time when the pressure roller is raised from the sufficiently cooled state (cold state) as described above. The rise time described below is the cold state unless otherwise specified. The time taken from is shown.

  FIG. 4 is a diagram illustrating the relationship between the time required from the print start instruction to the completion of the operation and the controls (1) and (2) when an instruction to print an electronic manuscript that requires 10 seconds for image development is given from the personal computer. 7 and schematically shown in FIG. In the figure, the section where “printing in progress” is displayed is the time during which the engine unit of the image forming apparatus is performing the printing operation.

  In the present embodiment, since the printing operation is started when the leading end of the recording material P is positioned at the exit position A of the paper feeding cassette 9 in FIG. 1, the recording material is fixed to the fixing device 6 from the start of feeding of the recording material P. It took about 3.0 seconds for the printing operation to finish. As is apparent from FIGS. 7 and 8, when the normal startup of (1) is performed, it takes 20 seconds to complete the printing, and when the preheating of (2) is performed, it takes 13 seconds to complete the printing. Take it. Therefore, in (2), it can be seen that the printing operation is completed earlier by 7 seconds as the startup time of the fixing device. Thus, if the fixing device is preheated simultaneously with the image development, the waiting time can be shortened by the time required for starting up the fixing device.

  However, as is apparent from a comparison of the fixing device set temperature graphs of FIGS. 7 and 8, in the case of performing the preheating of (2), there is a waiting time for holding at the target fixing temperature after the fixing device starts up. In the case of FIG. 8, the apparatus waits for 3 seconds at a high target fixing temperature. During this time, the heater continues to heat the pressure roller at a high temperature.

  The actual temperature of the pressure roller at the moment when the recording material enters the fixing device was compared in the cases (1) and (2). When the target fixing temperature was set to 210 ° C., the temperature was 70 ° C. when the normal start-up of (1) was followed, whereas the temperature was raised to 95 ° C. when pre-heating of (2) was performed. That is, the pressure roller is heated by 25 ° C. in the waiting time of 4 seconds in FIG. This temperature is a temperature when the pressure roller is raised from a room temperature state (cold state).

  Table 1 shows the relationship between the temperature of the pressure roller 20 and the temperature at which the paper enters the fixing nip and the results of the occurrence of slip and high temperature offset when preheating (2) is performed. In Table 1, “paper NIP rush temperature” is the temperature of the pressure roller when the leading edge of the paper rushes into the fixing nip.

  From the above results, when the pressure roller 20 was raised by the method (2) in a state where the temperature of the pressure roller 20 was high, the pressure roller was heated to 170 ° C. This temperature is a pressure roller temperature that is so high that it cannot be reached by the normal startup method of (1). Moreover, a high temperature offset occurs at this temperature, which is unacceptable as the image quality of the image forming apparatus. In addition, if the image development time is longer than this, the pressure roller may further rise in temperature, and not only high temperature offset but also the water vapor released from the recording material may be caused by the paper type and water content of the recording material. Thus, a paper jam due to slip occurs.

  Therefore, in this embodiment, in order to prevent such excessive temperature rise of the pressure roller, the startup method has been improved as follows. In FIG. 8, the section indicated as “printing operation” is a section in which the engine unit performs a printing operation after receiving a print signal. When this printing operation is divided, (a) a recording material is fed. The paper is fed from a cassette or paper feed tray, the toner image is fixed at the transfer unit, and then reaches the fixing device, and (b) the recording material enters the fixing device and is heated and fixed. be able to. In the case of the image forming apparatus of the present embodiment, the time required for the section (a) is about 2.0 seconds, although it varies depending on the paper feed location and the recording material size, and the time required for the section (b) is about 1 second. It is weak.

  Since it is considered that the fixing device should reach the target fixing temperature at least when the recording material arrives at the fixing device, the target fixing temperature may be reached in the required time of 2 seconds in the section (a). As shown in Table 2, the preheat temperature control setting and the paper feed timing were set from the temperature transition of the heater 11 reaching the temperature of 210 ° C. from the 9 Cold state. In this embodiment, the paper feed timing is determined based on the thermistor detection temperature reaching the paper feed start temperature.

  In Table 2, the target fixing temperature and the preheat temperature control temperature are changed (reduced) in accordance with the time elapsed after the thermistor detection temperature has reached the preheat temperature control temperature. This is because when the preheat temperature control temperature is set high, the temperature of the pressure roller 20 is raised faster. By suppressing the temperature rise of the pressure roller 20 and setting an appropriate target fixing temperature according to the temperature of the pressure roller 20, the power input amount at the time of start-up can be minimized. As a result, it is possible to ensure fixing properties and prevent slipping and high temperature offset.

  As described above, in this embodiment, since the pressure roller temperature at the start of printing is estimated without completely depending on the temperature detected by the thermistor 14, an appropriate target fixing temperature can be set. Also, before image data from an external information device such as a video controller or personal computer is developed into a video signal, a preheat signal for starting up the engine unit of the image forming apparatus is output to the engine controller, and the fixing device is installed during image development. Since it has been started up, the waiting time can be shortened.

  Also, as shown in FIG. 7, before the image development is completed, the heater is started up until the image development is completed, or until preparations for conditions other than fixing, such as scanner, high-voltage output, and paper conveyance conditions, are completed. Wait for the heater at a temperature lower than the target fixing temperature, and reheat it to the target fixing temperature after completion of image development, or after preparations for conditions other than fixing, such as scanner, high-voltage output, and paper transport conditions. May be. As described above, it is possible to prevent excessive temperature increase of the pressure roller due to preheating by waiting at a preheat temperature control temperature (standby temperature) lower than the target fixing temperature as much as possible during image development. The preheat temperature control temperature can be changed according to the pressure member temperature estimated immediately before starting up the heater. For example, when the estimated temperature is low, the preheat temperature adjustment temperature is increased, and when the estimated temperature is high, the preheat temperature adjustment temperature is decreased, so that the target fixing temperature after standby can be reliably reached.

  By performing the control as shown in Table 2, it is possible to reliably reach the target fixing temperature when restarting after standby, regardless of the use environment of the image forming apparatus. Furthermore, since the amount of power input at the time of start-up with the pressure roller warmed can be minimized, there is no problem of slip or high temperature offset.

  Also, by changing the target fixing temperature or preheat temperature or paper feed timing according to the preheat temperature adjustment elapsed time, excessive temperature rise of the pressure member surface temperature can be prevented, and problems such as high temperature offset and slip can be prevented. be able to.

  In the embodiment described above, the case where the present invention is applied to a film heating type fixing device using a thin fixing film having a small heat capacity has been described. The present invention is not limited to this, and a heat roller system in which the heat capacity of the fixing member is made smaller than before by shortening the thickness of the elastic rubber layer of the fixing member such as the fixing roller so that the rise to the fixing temperature is accelerated. The present invention can also be applied to a fixing device of the same type and has a similar effect. Moreover, the specific formula and numerical value mentioned above are the illustrations for description, and the present invention is not limited to them.

1 is a schematic view showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is a cross-sectional view showing a fixing device installed in the image forming apparatus of FIG. 1. FIG. 2 is a schematic diagram illustrating a configuration example of control hardware of the image forming apparatus in FIG. 1. It is explanatory drawing which shows the temperature control system performed with the fixing device of FIG. It is a graph which shows pressure roller estimated temperature with the thermistor and pressure roller temperature when one sheet passes from a cold state in a low temperature environment. It is a graph which shows transition of the thermistor detection temperature when a heater energization is turned off after the end of printing, and a pressure roller measured value temperature difference. FIG. 10 is an explanatory diagram showing a relationship between a time required for printing by conventional fixing device start-up control and temperature control. FIG. 6 is an explanatory diagram showing a relationship between a time required for printing by a fixing device start-up control before image development and temperature control. It is a graph which shows the temperature transition of the heater according to the elapsed time from the Cold state in embodiment of this invention. A graph showing the pressure roller temperature transition after passing one A4 size sheet and the pressure roller temperature transition after passing 30 sheets, and showing the average value as an attenuation curve of the pressure roller temperature. is there. FIG. 10 is an explanatory diagram of another embodiment of the present invention in which a heater is made to stand by at a standby temperature lower than a target fixing temperature, and after completion of image development, preparation for conditions other than fixing is completed and then reheating to the target fixing temperature is performed. FIG. 10 is an explanatory diagram of a cleaning sequence for heating a fixing nip portion when the fixing device is stopped after post-rotation of fixing driving.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 6 Fixing device 9 Paper feed cassette 10 Heating member 11 Heating heater (fixing heater)
12 Stay Holder 13 Fixing Film 14 Temperature Detection Unit (Thermistor)
20 Pressure roller 50 External information device (personal computer)
51 Pixel information converter (video controller)
53 Image forming apparatus control unit (engine controller)
56 Paper Feeding Unit 58 Fixing Device

Claims (9)

In an image forming apparatus that heats and fixes a toner image formed on a recording material based on input image information to the recording material,
An image forming means for forming a toner image on the recording material;
A fixing device that heats and fixes the toner image on the recording material by passing the recording material on which the toner image is formed through a fixing nip portion formed by pressing a heating member having a built-in heater and a pressure member against each other. When,
Control means for controlling the fixing device,
The control means includes
A function of cleaning the pressure member by turning on the heater for a predetermined time after the fixing;
An image forming apparatus comprising: a function of estimating a change in temperature of the pressure member after completion of cleaning of the pressure member based on a predetermined condition.   The pressure member temperature is estimated based on the elapsed time from the predetermined time after the end of the previous image forming operation, the paper size, the number of sheets passed, and the temperature of the heating member at the predetermined time after the end of the previous image forming operation. The image forming apparatus according to claim 1, wherein the image forming apparatus performs the detection based on at least one of detected temperatures of a temperature detecting unit to detect. The image forming apparatus according to claim 1, further comprising: a temperature detection unit configured to detect a surface temperature of the heating member, wherein the temperature of the pressure member is estimated based on an arithmetic expression described below. .
(A) PT0: Low (less than a predetermined threshold)
When ^{PT1 = A × t 2 -B ×} t + PT0 ----- (1)
(B) PT0: High (above a predetermined threshold)
When ^{PT1 = C × t 2 -t +} PT0 ----- (2)
here,
t is an elapsed time from a predetermined time after the end of the immediately preceding image forming operation,
PT0 is a predicted pressure member temperature value calculated from the temperature detected by the temperature detector at a predetermined time after the end of the previous image forming operation,
PT1 is the pressure member predicted temperature value after the acquisition time of PT0,
In the formula, A to C are predetermined constants.   At the end of the image forming operation, the heater is turned off to perform idling for a predetermined time, and the temperature detected by the temperature detection unit at the end of idling is set as the PT0, and from the end of idling 4. The image forming apparatus according to claim 3, wherein the elapsed time is t.   The control unit starts up the heater before image development is completed, causes the heater to wait at a temperature (standby temperature) lower than a target fixing temperature that is a heater temperature necessary for fixing, and at least inputs A function of controlling the heater to reheat to the target fixing temperature and switching the standby temperature according to the estimated result of the temperature of the pressure member after the image development of the image information is completed. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 5, wherein at least one of the target fixing temperature and the standby temperature is changed according to an elapsed time after reaching the standby temperature.   The heating member includes a movable film that is in pressure contact with the pressure member at the fixing nip portion, and a heater that contacts the film disposed inside the film at the fixing nip portion. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 7, wherein the film is formed in a cylindrical shape and is rotated by rotation of the pressure member.   The image forming apparatus according to claim 1, wherein the pressure member includes an elastic roller.