JP4327577B2 - Image forming apparatus - Google Patents

Description

The present invention is an electrophotographic copying machine using a fixing equipment having a capacitor, a printer, relates to an image forming apparatus such as a facsimile, more particularly those improving the efficiency of the capacitor utilized by these devices.

  In an image forming apparatus such as a copying machine, an image is formed on a recording medium such as plain paper or OHP, and an electrophotographic method is often employed because of high-speed image formation, image quality, cost, and the like. The electrophotographic method is a method in which a toner image is formed on a recording medium, and the formed toner image is fixed on the recording medium with heat and pressure. As the fixing method, the heat roller method is currently most frequently used from the viewpoint of safety and the like. In the heat roller method, a heat roller heated by a heat generating member such as a halogen heater and a pressure roller disposed opposite to the heat roller are pressed to form a mutual pressure contact portion called a nip portion, and a toner image is formed in the nip portion. Is heated and pressurized through the recording medium to which the toner has been transferred, thereby fixing the toner to the recording medium.

  In recent years, environmental problems have become important, and energy saving is also progressing in image forming apparatuses such as copying machines and printers. In considering the energy saving of this image forming apparatus, what cannot be ignored is the power saving of the fixing device for fixing the toner to the recording medium. Therefore, to reduce the power consumption of the fixing device during standby of the image forming apparatus, the temperature of the heating roller is kept at a constant temperature slightly lower than the fixing temperature during standby, and immediately rises to a usable temperature during use. Many methods are employed to prevent a person from waiting for the temperature of the fixing roller to rise. In the case of this method, a certain amount of power must be supplied even when the fixing device is not used, thereby consuming extra energy. This standby energy consumption is said to correspond to approximately 70% to 80% of the energy consumption of the devices constituting the image forming apparatus.

  Accordingly, it has been desired to reduce energy consumption during standby and to further save power, and there is a demand for zero power supply when not in use. However, if energy consumption is reduced to zero during standby, the heating roller of the fixing device mainly uses a metal roller such as iron or aluminum and has a large heat capacity, so that the temperature rises to a usable temperature of about 180 ° C. Requires a long heating time of several minutes to several tens of minutes. Such a waiting time deteriorates the usability of the user, so that a heating method that consumes as little power as possible while rapidly rising from the standby state is desired.

  In order to shorten the heating time of the heating roller, it is clear that it is better to increase the input energy per unit time, that is, the rated power. In fact, in an image forming apparatus called a high-speed machine with a high printing speed, In many cases, the power supply voltage is 200V. However, in general offices in Japan, the commercial power supply is 100V, 15A, and it is necessary to carry out special work on the power-related equipment at the installation site in order to make it compatible with 200V. It's not an ideal solution.

  That is, as long as a commercial power supply of 100 V and 15 A is used, the maximum input energy is determined by the power supply even when the temperature of the heating roller is to be raised in a short time. When the temperature of the fixing device becomes low, a voltage lower by a certain level is supplied to the heating roller to delay the temperature of the fixing device from dropping (for example, refer to Patent Document 1), or the secondary battery as an auxiliary power source is charged during standby of the fixing device, When the fixing device is started up, power is supplied from the main power supply device and the secondary battery or the primary battery to shorten the rising time (see, for example, Patent Document 2).

  However, the technique disclosed in Japanese Patent Laid-Open No. 2004-228561 is not sufficient power saving because it supplies a low voltage to the fixing device by a certain level even during standby. Moreover, the maximum supply power at the time of start-up is not mainly intended to be higher than the power supplied from the main power supply device. On the other hand, the fixing device disclosed in Patent Document 2 supplies power from a main power supply device and a secondary battery or a primary battery at the time of start-up. As a secondary power supply, a lead storage battery, a nickel cadmium battery, or a nickel metal hydride battery is generally used. I use it. Such a secondary battery has a property that the capacity deteriorates and decreases when charging and discharging are repeated, and the life is shortened as discharging is performed with a large current. There is also a phenomenon of capacity reduction due to the memory effect. Even if it is generally considered to have a long life with a large current, the number of charge / discharge cycles is about 500 to 1000 times. If 20 cycles of charge / discharge are repeated per day, the battery life will be reached in about one month. It will end up. Therefore, the replacement frequency of the battery is increased, and it takes much labor, and the running cost such as the cost of the battery to be replaced increases. Furthermore, in lead storage batteries, liquid sulfuric acid is used as the electrolyte, which is undesirable for office equipment.

  In addition, the load on the heating circuit built in the heating roller increases due to a sudden current change or inrush power when starting or stopping the supply of large power, and input current is also applied to the peripheral circuits. There is also a problem that noise flows and flows. For this reason, it is not preferable to frequently turn on and off the power supply from the large-capacity auxiliary power supply. In addition, if a large amount of power is supplied at once, there is a possibility that the supply will be excessive and the temperature of the heating circuit will rise too much.

These points are improved to improve the power saving effect, reduce noise due to inrush current and sudden current change when supplying large power, shorten the rise time, and prevent the temperature from rising too much. As the fixing device that can be used, a chargeable / dischargeable capacitor is used for the auxiliary power supply, the charger charges the capacitor of the auxiliary power supply with power supplied from the main power supply, and the switching device charges the auxiliary power supply. There has been proposed a device that switches power supply from an auxiliary power supply to an auxiliary heating element and adjusts the amount of power supplied from the auxiliary power supply to the auxiliary heating element (see, for example, Patent Document 3). As a basic function of the capacitor, the auxiliary heater generates heat by using DC power supplied from the capacitor, and this heat is used to shorten the time for the heating roller to rise to a predetermined temperature and to prevent the fixing temperature from being lowered when the paper is passed. That is.
Japanese Patent Laid-Open No. 10-10913 Japanese Patent Laid-Open No. 10-282821 JP 2002-184554 A

  By the way, as described above, in order to prevent a decrease in temperature, a heating element that is energized from an auxiliary power supply has a problem, and when large power is supplied from a low-voltage auxiliary power supply, the response delay of the heating element supplied from the auxiliary power supply is a problem. It becomes. That is, since the auxiliary power supply is a voltage lower than the voltage of the commercial power supply, it is necessary to increase the filament diameter in order to reduce the resistance when taking out a large amount of power. If the filament system is thickened, the heat capacity increases, so that a light emission delay of several seconds or less occurs until the temperature reaches a temperature at which light can be emitted and the roller can be heated.

  An object of the present invention is to provide a heating device that can solve the above-described conventional problems, a fixing device using the heating device, and an image forming apparatus using the fixing device.

An image forming apparatus according to claim 1 includes: a main power supply device; an auxiliary power supply device including a chargeable / dischargeable capacitor; a first heating element that generates heat by power supplied from the main power supply device; and the auxiliary power supply device. An image forming apparatus comprising: a fixing device including a heating unit including a second heat generating element having a resistance smaller than that of the first heat generating element that generates heat by the supplied power.
A charger that enables power supply from the main power supply to the capacitor; and a power supply control unit that controls power supply from the capacitor to the second heating element,
An image forming apparatus for preheating by intermittently supplying power to the second heating element by discharging from the capacitor under the control of the power supply control unit during standby in a non-operating state where fixing operation is not performed. And
The power supply control means performs power supply for preheating during the standby according to the remaining capacity of the capacitor, and when the remaining capacity of the capacitor exceeds a predetermined value, the power supply control means performs intermittent discharge from the capacitor. Power to the heating element
When the remaining capacity of the capacitor is less than or equal to a predetermined value, charging and discharging of the capacitor are alternately repeated by the charger and the power supply control unit .

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, in addition to the charger, a switch member for alternately charging and discharging the capacitor by dividing the charging and discharging of the capacitor in a short time is provided. The charging / discharging can be performed simultaneously.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, control of power feeding to the first heat generating element and the second heat generating element is variable in accordance with a charging voltage of the capacitor during the standby time. It is characterized by making it.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the power supply control unit performs control to shift a power supply timing to the first heat generating element and the second heat generating element during the standby time. It is characterized by.

The image forming apparatus according to the present invention controls the temperature of the heating element that generates heat when energized from the auxiliary power source, and eliminates a delay in the heat generation response, so that the startup time can be shortened when used for startup startup applications. , when used in fixing roller temperature drop preventing use during sheet passing is to improve the control response of oN / OFF, it performed better heating, it is possible to obtain a good good image quality.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view conceptually showing an image forming apparatus such as an electrophotographic copying machine or printer according to the present invention. The image forming apparatus according to the present embodiment mainly includes a reading unit 11 that reads a document, an image forming unit 12 that forms an image, an automatic document feeder (ADF) 13, a document discharge tray 14 that stacks documents sent from the ADF 13, The sheet feeding unit 19 includes sheet feeding cassettes 15 to 18 and a sheet discharge unit (sheet discharge tray 20) for stacking recording sheets.

  Then, when the document D is set on the document table 21 of the ADF 13 and an operation on an operation unit (not shown), for example, a press operation of a print key is performed, the uppermost document D is sent out in the direction of the arrow B1 by the rotation of the pickup roller 22. Then, by the rotation of the document conveying belt 23, the paper is fed onto the contact glass 24 fixed to the image reading unit 11, and stops there. The image of the document D placed on the contact glass 24 is read by a reading device 25 located between the image forming unit 12 and the contact glass 24. The reading device 25 includes a light source 26 that illuminates the document D on the contact glass 24, an optical system 27 that forms an image of the document, a photoelectric conversion element 28 that includes a CCD that forms an image of the document, and the like. After the image reading is completed, the document D is transported in the direction of arrow B2 by the rotation of the transport belt 23 and discharged onto the paper discharge tray 14. In this way, the document D is fed one by one onto the contact glass 14 and the document image is read by the image reading unit 1.

  On the other hand, a photoreceptor 30 as an image carrier is disposed inside the image forming unit 2. The photosensitive member 30 is driven to rotate clockwise in the drawing, and the surface is charged to a predetermined potential by the charging device 31. Further, the writing unit 32 emits a laser beam L that is light-modulated in accordance with image information read by the reading device 25, and the surface of the charged photoreceptor 30 is exposed with the laser beam L, whereby the photoreceptor is exposed. An electrostatic latent image is formed on the surface 30. When the electrostatic latent image passes through the developing device 33, the electrostatic latent image is transferred to the recording medium P fed between the photosensitive member 30 and the transfer device 34 by the opposing transfer device 34. The surface of the photoconductor 30 after the toner image is transferred is cleaned by a cleaning device 35.

  A plurality of paper feed cassettes 15 to 18 arranged in the lower part of the image forming unit 2 contain recording media P such as paper, and the recording media P is fed from any of the paper feed cassettes 15 to 18 in the direction of arrow B3. The toner image formed on the surface of the photoreceptor 30 as described above is transferred onto the surface of the recording medium P. Next, the recording medium P is passed through the fixing device 36 in the image forming unit 2 as indicated by an arrow B4, and the toner image transferred onto the surface of the recording medium P by the action of heat and pressure is fixed. The recording medium P that has passed through the fixing device 36 is conveyed by the discharge roller pair 37, discharged to the discharge tray 20 as indicated by an arrow B5, and stacked.

  FIG. 2 is a cross-sectional view showing an example of a fixing device 36 that heats and pressurizes the toner image transferred to the recording medium P and fixes the toner image to the recording medium. FIG. 3 shows one example of the heating device according to the present invention provided in the fixing device 36. It is a circuit diagram which shows the structure of embodiment.

  The fixing device 36 shown in the figure has a fixing roller 40 and a pressure roller 41. For example, in a 75 cpm machine used for preventing the temperature of the fixing roller from being lowered during paper passing, the fixing roller 40 has an outer diameter Φ40 and a wall thickness t0.7 mm. Aluminum rollers are used. This is because the thickness is such that the temperature can be raised to a state where fixing can be performed within 30 seconds, and even the load necessary to form the nip width N necessary for fixing is not destroyed. The 75 cpm machine used a thick roller of about t5.0 to 10 mm when the auxiliary power supply was not used. However, by combining the thin roller and the auxiliary power supply, the start-up time can be greatly shortened. Yes. Further, it is desirable that a release layer such as PFA or PTFE is formed on the outermost layer of the fixing roller. The fixing roller 40 includes a heating unit 2 including a main heating element 2a made of, for example, a halogen heater and an auxiliary heating element 2b. The fixing roller 40 and the pressure roller 41 pass through the recording medium P on which the toner T is placed. Thus, a nip portion N to be pressurized and heated is formed.

  The heating device 1 of this embodiment includes a heating unit 2, a main power supply device 3, an auxiliary power supply device 4, a main switch 5, a charger 6, a switching device 7, and a control unit 8. In FIG. 3, the heating unit 2 composed of the main heating element 2a and the auxiliary heating element 2b is drawn outside the fixing roller 40. However, this is for convenience of illustration, and both the heating elements 2a, 2b Provided in the fixing roller 40.

  The heating unit 2 includes a main heating element 2a that generates heat by the electric power supplied from the main power supply device 3, and an auxiliary heating element 2b that generates heat by the electric power supplied from the auxiliary power supply device 4, and is a fixing roller that is a heated object. 40 is heated. Although not shown in detail, the main power supply device 3 is supplied with power from a commercial power supply in the image forming apparatus in which the heating device 1 is installed. The main power supply device 3 has a function of adjusting, for example, power supplied from an outlet or the like to a voltage corresponding to the heating unit 2.

  The auxiliary power supply 4 has a chargeable / dischargeable capacitor C. As the capacitor C, for example, a module configuration in which 15 to 40 cells having a rated voltage of 2.5 V and a capacitance of about 400 to 1000 F are connected in series to obtain a predetermined rated voltage and capacity is desirable. Further, for use in preventing a decrease in the fixing temperature during continuous paper feeding, for example, a heater having a rating of about 300 to 600 w, in which 18 to 22 cells of 500 to 700 F are connected in series, is suitable. This has sufficient capacity for power supply for about 1 to 2 minutes, and when all the stored power is supplied from a high temperature state due to a runaway control system, the power decreases as the voltage decreases, reducing the risk of ignition. This is because the capacity can be reduced. Another reason is that the voltage is about 50V and there is no danger of electric shock. In addition, for the purpose of supplying power at the time of start-up, for example, a heater having a rating of 800 to 1000 w is connected in parallel to the auxiliary power supply device to supply a total power of about 1600 to 2000 w. 44 connected in series is suitable. This is equipped with a capacity and voltage for supplying sufficient power for power supply for about 10 seconds, and a capacity capable of preventing a decrease in fixing temperature by using only one heater even when shifting during continuous paper feeding. It is for having. In actual operation, a voltage lower than the rated voltage is set as the charge target voltage because the reliability can be improved in consideration of variations in the voltage circuit and the durability of the capacitor cell. Also, a module configuration in which cells with lower capacitances of about 100 F are connected in parallel may be used. However, the number of electronic circuits required per cell can be reduced, and it is easy to detect when a failure occurs in the cell. It is desirable to connect the cells in series. The reason why the above configuration is adopted is that, unlike a secondary battery, a capacitor such as an electric double layer capacitor has excellent characteristics because it does not involve a chemical reaction.

  As described above, in the auxiliary power supply using a general nickel-cadmium battery as a secondary battery, it takes a long time of several tens of minutes to several hours even if rapid charging is performed. The device 4 can be charged quickly for several minutes, and when the standby state and the heating state are repeated within the same time, the auxiliary power supply device 4 using a capacitor is used to reliably assist when starting up the heating. Electric power can be supplied from the power supply device 4, and the heating unit 2 can be raised to a predetermined temperature in a short time. In addition, since the nickel-cadmium battery has an allowable number of repetitions of charge / discharge of about 500 to 1000 times, it has a short life as an auxiliary power source for heating, and the trouble and cost of replacement are problematic. Auxiliary power supply device 4 using a battery has an allowable number of repetitions of charge and discharge of several million times or more, and is less susceptible to deterioration due to repeated charge and discharge, and does not require liquid replacement or replenishment unlike lead-acid batteries. It requires little maintenance and can be used stably for a long time.

  An electric double layer capacitor does not have a dielectric, and uses the absorption and desorption reactions (charging and discharging) of the ion adsorbing layer of the electric double layer in which the charge of ions or solvent molecules formed at the solid electrode and solution interface is concentrated. Resistant to repeated charging / discharging, long life, no maintenance required, environmentally friendly, shorter charging time compared to other types of batteries, high charging / discharging efficiency, and easy detection of remaining power through voltage detection Recently, a large-capacity capacitor having an electrostatic capacity of tens of thousands of F and an energy density of several tens of wh / kg has been developed, and the capacity is being further increased.

  The main switch 5 turns on / off the power supplied from the main power supply device 3 to the main heating element 2a, and the charger 6 is a voltage corresponding to the auxiliary power supply device 4 using the power supplied from the main power supply device 3. And the capacitor C is charged. The switching device 7 switches charging of the auxiliary power supply 4 and power supply from the auxiliary power supply 4 to the auxiliary heating element 2b.

  The control means 8 has a switch 9 and a CPU 10 and performs control to turn on / off the power supplied from the auxiliary power supply device 4 to the auxiliary heating element 2b under preset conditions described later. However, the configuration of the control means 8 shown in the drawing is merely an example showing only a portion that controls the heating unit 2, and various configurations such as a device that controls the entire image forming apparatus can be employed. Further, the connection form for controlling the auxiliary power supply 4 is not limited to the illustrated example. For example, various forms such as a configuration in which the switching device 7 is switched to perform on / off control or the like can be employed.

  The basic operation of such a heating device 1 will be described. First, at the time of standby, the switching device 7 is switched and the charger 6 is connected to the auxiliary power supply device 4 to charge the capacitor C of the auxiliary power supply device 4. When heating the heating unit 2 with the heating device 1 in this state, the main switch 5 is turned on to supply power from the main power supply device 3 to the main heating element 2a, and at the same time, the switching device 7 is switched and the auxiliary power supply device 4 is switched. Electric power is supplied to the auxiliary heating element 2b, and a large amount of electric power is supplied to the heating unit 2. Thus, when heating of the heating unit 2 is started, a large amount of power is supplied from both the main power supply device 3 and the auxiliary power supply device 4 to the heating unit 2, so that the heating unit 2 is brought to a predetermined temperature in a short time. Can be launched.

  Further, when a predetermined time elapses after the auxiliary power supply 4 supplies electric power to the auxiliary heating element 2b of the heating unit 2 and starts heating, the control means 8 receives auxiliary heating from the auxiliary power supply 4. The electric power supplied to the body 2b is cut off to prevent overheating of the heating unit 2 and maintained at a predetermined temperature. The power supplied from the auxiliary power supply 4 to the auxiliary heating element 2b decreases as time elapses after the supply is started. A time for cutting off the power supplied from the auxiliary power supply 4 to the auxiliary heating element 2b is determined according to the reduction amount of the supplied power, and when the supply power is reduced to some extent, the auxiliary power supply 4 changes to the auxiliary heating element 2b. When the supplied power is cut off, it is possible to prevent deterioration of each component of the surrounding circuit and electromagnetic noise that occur when cutting off in the state of supplying a large amount of power.

  The recording medium P to which the toner image T sent to the fixing device 36 having such a configuration is transferred is conveyed between the fixing roller 40 and the pressure roller 41, and the toner T is heated by the fixing roller 40 heated to a constant temperature. Is heated and melted and fixed on the recording medium P as a toner image. Therefore, power is supplied from the main power supply device 3 and the auxiliary power supply device 4 to the main heating element 2a and the auxiliary heating element 2b included in the heating unit 2 of the fixing roller 40, thereby increasing the temperature of the fixing roller 40 and the auxiliary power supply. By controlling on / off of the power supplied from the device 4, the temperature of the fixing roller 40 is prevented from becoming too high, and the fixing temperature is kept at a constant temperature or a desired temperature, or a required temperature change is shown. Thus, the toner T is stably heated and melted, and a good quality toner image T is fixed on the recording medium P. Further, since the power is supplied from the main power supply device 3 and the auxiliary power supply device 4 to the main heating element 2a and the auxiliary heating element 2b of the heating unit 2 built in the fixing roller 40, the temperature of the fixing roller 40 is raised. The surface temperature of the toner can be quickly raised to a predetermined fixing temperature.

  FIG. 4A is a diagram illustrating a change in power consumption of the image forming apparatus configured as described above, and FIG. 4B is a diagram illustrating a voltage change of the capacitor C. From the state in which less power is consumed during standby, the power consumption increases to the upper limit with the start of image formation, decreases slightly from the upper limit during image formation, and then returns to the standby state. In general, the capacitor C of the auxiliary power supply device 4 is charged by utilizing the fact that there is a power margin during image formation (indicated by X in FIG. 4). The output voltage of the capacitor C shows the maximum value during standby, decreases when supplying power for heating the fixing roller 40 during startup, and returns to the standby state when charged during image formation.

  In FIG. 4B, the solid line indicates charging when image formation is performed, and the alternate long and short dash line indicates charging immediately after image formation. Generally, charging is performed immediately after image formation. This is because, when image formation is performed immediately after the previous image formation is completed, if charging of the capacitor C is not completed, cpm (copy speed) decreases or charging waits. This is because time is generated and the function of the entire image forming apparatus is deteriorated. That is, when the power supplied from the auxiliary power supply 4 to the auxiliary heating element 2b is cut off, the auxiliary power supply 4 is not sufficiently charged. Therefore, when the temperature of the heating unit 2 is stable and relatively no power is consumed, the switching device 7 is switched to the charger 6 side, and the charger 6 is connected to the auxiliary power supply 4 to be supplied from the main power supply 3. The auxiliary power supply 4 is charged with electric power. When it is necessary to supply a large amount of power again to the heating unit 2, a large amount of energy is supplied to the heating unit 2 by supplying power from the auxiliary power supply device 4 together with the main power supply device 3. Further, FIG. 4C shows a case where the capacitor C is used for the purpose of preventing the fixing roller temperature from being lowered due to insufficient power supply during continuous paper feeding. In general, immediately after start-up, the entire apparatus is cold, so that power is likely to be insufficient. Therefore, power is supplied from the capacitor C during continuous paper feeding. As a result, it is possible to prevent a decrease in productivity such as cpm down or stop until the fixing roller temperature recovers during continuous paper feeding.

  FIG. 5 is a diagram illustrating a temperature change of the fixing roller 40. At the time of standby, the temperature is low, and at the time of start-up, the heat generated by both of the heat generating elements 2a and 2b rises to a predetermined fixing temperature (180 ° C. in the drawing). Take the process of gradually decreasing with the end. At this time, the temperature of the fixing roller 40 decreases to room temperature (the temperature at the place where the image forming apparatus is installed) or the temperature inside the image forming apparatus depending on environmental conditions.

  By the way, in the case of the above configuration, the auxiliary heating element 2b, which is a DC heater, has a large filament diameter and a large heat capacity, so that a light emission response delay of several seconds or less occurs until the temperature reaches a temperature at which light can be emitted and the roller can be heated. This is as described above. Therefore, the present invention performs power supply control that enables power supply to at least the auxiliary heating element 2b regardless of the operating and non-operating conditions.

<Example of always warming the auxiliary heating element during standby>
During standby, that is, when the image forming apparatus is not performing image forming or the like, the auxiliary heating element 2b is intermittently turned on by discharge from the capacitor C under appropriate control, and the auxiliary heating element 2b is turned on. Always warm and preheat filaments and heater tubes.

  This preheating lighting during standby is preferably performed according to the remaining capacity (voltage) of the capacitor C. For example, if the capacitor C is excessively discharged for preheating during standby and the remaining capacity (voltage) drops below a predetermined value, the capacitor C is charged as described above so that it can be sufficiently charged during the image forming operation. To control. In the case of the configuration shown in FIG. 3, charging power from the main power supply device 3 that receives power supply from a commercial power source is used for heating the auxiliary heating element 2b via the charger 6 that performs AC / DC conversion. In other words, the capacitor C can be charged and discharged during standby. However, if charging and discharging are repeated alternately with a switch member such as an FET or IGBT, the charging can be performed simultaneously. Will not decrease, and the amount of charge will not be insufficient during the image forming operation. Therefore, there is no response delay of heat generation, and good fixed image quality can be obtained.

<Example in which the auxiliary heating element is warmed before the recording medium reaches the fixing nip>
Simultaneously with the start of passing of the recording medium P, for example, the capacitor C is discharged by a print signal indicating the start of the image forming operation, and the auxiliary heating element 4b is turned on in a so-called start-off manner before the recording medium P reaches the fixing nip. It can also be done. In this case, it is preferable to control by setting the control temperature during standby and paper passing so that the standby temperature is lower than the paper passing temperature, for example. A delay in the heat generation response of the auxiliary heating element 4b is eliminated when the paper is passed, and a good fixed image quality can be obtained.

<Example of heating the auxiliary heating element with the main power supply device>
FIG. 6 shows an example in which power can be supplied from the main power supply device 3 to the auxiliary heating element 2b. In this example, the main switch 5 is switched to supply power from the main power supply device 3 to the auxiliary heating element 2b to generate heat, so that the amount of power stored in the capacitor C does not need to be reduced. If the amount of power stored in the capacitor C is not reduced, the amount of charge will not be insufficient during the image forming operation.

  In any of the embodiments described above, the lighting ratio of the main heating element 2a and the auxiliary heating element 2b can be varied according to the charging voltage of the capacitor C. When the charging voltage of the capacitor C is low, the lighting ratio of the auxiliary heating element 2b may be lowered. That is, if the ratio of the lighting of the heating element by the power supply from the commercial power supply and the lighting of the heating element by the power supply from the capacitor C is varied by the charging voltage of the capacitor C, the filament and the heater tube of the auxiliary heating element 2b can be connected during standby. Capacitor C can be charged while warming, and a sufficient charging voltage of capacitor C can be ensured when a sheet is passed to obtain a good fixed image quality.

  Further, the lighting timing of the main heating element 2a and the auxiliary heating element 2b may be shifted. By shifting the timing of lighting of the heating element by power supply from the commercial power supply and lighting of the heating element by power supply from the capacitor C, the ripple of the fixing temperature during standby can be minimized. Then, since the fixing temperature at the start of paper feeding can be made constant, the operation of the auxiliary heating element 2b can be controlled efficiently.

<Example in which the heat generation start timing of the auxiliary heating element is varied during paper feeding>
During continuous paper feeding, the fixing image quality is always good without falling below the lower limit of fixing temperature that satisfies the fixing property of the fixing roller 40 and the pressure roller 41 and without causing the main heating element 2a and the auxiliary heating element 2b to generate excessive heat. In order to make it possible to obtain the above, it is preferable to change the heater heat generation start timing of the auxiliary heat generating element 4b during paper feeding. The heater heat generation start timing in this case may be calculated from the fixing temperature profile at the time of the previous continuous sheet passing. The fixing temperature profile at the time of paper feeding is obtained by preparing a microcomputer or the like in the image forming apparatus, the fixing apparatus 36 or the heating apparatus 1, processing and storing data obtained by various sensors and the like, and performing timely arithmetic processing. What should I do?

The various corresponding embodiments described above can be implemented either alone or in combination with others. In each embodiment, the control unit 8 provided in the heating device 1 performs control for varying the amount of power supplied to the capacitor C. However, the present invention is not limited to this, and the fixing device 36 or the same is provided. A control unit may be provided on the image forming apparatus side to control the amount of supplied power. In any case, a dedicated control unit for controlling the amount of supplied power may be provided, or other control may be performed. Any means may be used, and the means is not limited to the illustrated example. The course not limited to the example of using a capacitor such as an electric double layer capacitor as an auxiliary power source device can be carried out in the same manner for other types of auxiliary power.

  In the embodiment described above, the nip portion N is formed by two rollers, that is, the fixing roller 40 and the pressure roller 41. However, the fixing device of the present invention and the image forming apparatus using the same are as follows. The present invention is not limited to such a configuration, and there are various configurations such as a type in which the recording medium P is slidably in contact with or close to the heated body, such as a roller and belt, a belt and a belt forming a nip portion N, and the like. It can be adopted. The present invention is not limited to the illustrated type of image forming apparatus. For example, the photosensitive member is not a drum but a belt type, and a color image forming apparatus using an intermediate transfer belt. Applicable.

1 is a conceptual cross-sectional view showing an embodiment of an image forming apparatus according to the present invention. Conceptual cross-sectional view showing a configuration of a constant deposition apparatus Ru use in an image forming apparatus of FIG. 1 2 is a circuit diagram showing a configuration of a heating device provided in the fixing device of FIG. FIG. 1A shows a change in power consumption of the image forming apparatus in FIG. 1 and FIG. 1B shows a voltage change in a capacitor C. Diagram showing temperature change of fixing roller Circuit diagram showing an example in which power can be supplied from the main power supply to the auxiliary heating element

Explanation of symbols

1: heating device 2: heating unit 2a: main heating element 2b: auxiliary heating element 3: main power supply device 4: auxiliary power supply device 5: main switch 6: charger 7: switching device 8: control means 9: switch 10: CPU
11: Reading unit 12: Image forming unit 13: Automatic document feeder (ADF)
14: Document discharge trays 15, 16, 17, 18: Paper feed cassette 19: Paper feed unit 20: Paper discharge tray 21: Document tray 25: Reading device 30: Photoconductor 31: Charging device 32: Writing unit 33: Development Device 34: Transfer device 35: Cleaning device 36: Fixing device 37: Discharge roller pair 40: Fixing roller 41: Pressure roller C: Capacitor D: Document P: Recording medium T: Toner N: Nip portion

Claims (4)

A main power supply device; an auxiliary power supply device including a chargeable / dischargeable capacitor; a first heating element that generates heat by the power supplied from the main power supply device; and the first power source that generates heat from the power supplied from the auxiliary power supply device. An image forming apparatus comprising: a fixing device including a heating unit including a second heating element having a resistance smaller than that of the heating element.
A charger that enables power supply from the main power supply to the capacitor; and a power supply control unit that controls power supply from the capacitor to the second heating element,
An image forming apparatus for preheating by intermittently supplying power to the second heating element by discharging from the capacitor under the control of the power supply control unit during standby in a non-operating state where fixing operation is not performed. And
The power supply control means performs power supply for preheating during the standby according to the remaining capacity of the capacitor, and when the remaining capacity of the capacitor exceeds a predetermined value, the power supply control means performs intermittent discharge from the capacitor. Power to the heating element
When the remaining capacity of the capacitor is equal to or less than a predetermined value, charging and discharging of the capacitor are alternately repeated by the charger and the power supply control unit . 2. The image forming apparatus according to claim 1, further comprising a switch member that, in addition to the charger, separates charging and discharging of the capacitor in terms of time and alternately repeating charging and discharging, so that the capacitor can be charged and discharged simultaneously. An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the control of power supply to the first heating element and the second heating element is varied in accordance with a charging voltage of the capacitor during the standby. apparatus. The image forming apparatus according to claim 1, wherein the power supply control unit performs control to shift a power supply timing to the first heating element and the second heating element during the standby time.

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