Patent Application
20080145088
1. Field of the Invention
The present invention relates to a fixing device and a fixing method in which an image is fixed onto a recording material while supplying power to a heating part of a fixing roller from a storage unit, and to an image forming apparatus including the fixing device.
2. Description of the Related Art
A fixing device that fixes a toner image formed on a recording material, such as a recording sheet, via a heating part having a main heating element and an auxiliary heating element has been widely used. In this fixing device, the main heating element is powered by a main power supply unit, and the auxiliary heating element is powered by an auxiliary power supply unit including a capacitor. The auxiliary power supply unit is charged by an external power source through the main power supply unit when the main power supply unit does not supply power to the main heating element, and the auxiliary power supply unit is not charged by the external power source through the main power supply unit when the main power supply unit supplies power to the main heating element.
Published Japanese patent application No. 2003-257590 describes the above fixing device. The fixing device enhances the power-saving effect with a simple configuration. Further, an installation space is reduced by reducing the size of the auxiliary power supply unit.
In a fixing device using a main power supply unit and an auxiliary power supply unit including a capacitor that supply power to a heating part, it is desirable to charge the auxiliary power supply unit acting as a storage unit by effective use of electric power of an external power source; and to enhance the quality of an image fixed on a recording material even if the fixing device is in a low temperature condition.
According to an aspect of the present invention, a fixing device for fixing an image formed on a recording material includes a fixing member disposed on a recording material conveyance path, a heating part configured to heat the fixing member to fix an image formed on the recording material by heat, and a storage unit configured to be charged by an external power source to supply power to the heating part. The fixing device further includes a control unit configured to control the external power source to supply power to the heating part and to determine whether to start to supply power to the heating part from the storage unit. The control unit is configured to control the external power source to charge the storage unit during a period from when power supply from the storage unit to the heating part is completed at the time of warming-up the fixing member by the heating part to when the power supply from the storage unit to the heating part is started.
According to another aspect of the present invention, an image forming apparatus includes an image forming device configured to form an image on a recording material, and the above-described fixing device.
According to yet another aspect of the present invention, the method of fixing an image formed on a recording material includes charging a storage unit by an external power source; supplying power to a heating part from the storage unit; heating a fixing member by the heating part; and controlling the external power source to charge the storage unit during a period from when power supply from the storage unit to the heating part is completed at the time of warming-up the fixing member by the heating part to when the power supply from the storage unit to the heating part is started.
A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description of non-limiting embodiments when considered in connection with the accompanying drawings, wherein:
Non-limiting embodiments of the present invention are now described with reference to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.
The transfer device 48 is disposed opposite the lower circumferential surface of the photoreceptor 41. Reference numeral 47 in
The image forming operation of the image forming apparatus is performed as follows. First, the charging device 42 uniformly charges the rotating photoreceptor 41. Then, the exposure device 40 emits the laser light beam Lb corresponding to image data to the exposure portion 150 of the circumferential surface of the photoreceptor 41, thereby writing a latent image on the surface of the photoreceptor 41. The latent image moves to the developing device 44 by the rotation of the photoreceptor 41, and is developed with toner by the developing device 44. As a result, a toner image is formed on the surface of the photoreceptor 41.
The recording material P, which has been fed out from the sheet feeding cassette 70 by the sheet feeding roller 110, is conveyed through a sheet conveyance path 80 (indicated by dotted lines in
The residual toner which has not been transferred from the photoreceptor 41 to the recording material P is moved to the cleaning device 46 by rotation of the photoreceptor 41, and is removed from the surface of the photoreceptor 41 by the blade 46a. Subsequently, the charging device 42 uniformly charges the surface of the photoreceptor 41 to prepare for the next image forming operation. Reference numeral 120 in
The pressing roller 15 includes a core metal and an elastic layer made of rubber or the like overlying the core metal. The pressing roller 15 is press-contacted against the fixing roller 14 with a predetermined pressing force by a pressing device (not shown). While the recording material P passes through a nip part between the fixing roller 14 and the pressing roller 15, a toner image is fixed onto the recording material P under the influence of heat and pressure. The pressing roller 15 may include a foamed layer overlying the core metal. In this case, because the heat of the fixing roller 14 does not tend to be transferred to the pressing roller 15 due to the insulation effectiveness of the foamed layer of the pressing roller 15, the fixing roller 14 can be quickly heated up. The fixing device 10 of the present embodiment uses the fixing roller 14 as the fixing member and the pressing roller 15 as the pressing member. Alternatively, the fixing device 10 may use an endless belt or a film for at least one of the fixing member and the pressing member.
The fixing device 10 further includes a heating part 1 having an AC heating element 1a (hereafter referred to as a main heating member 1a) and DC heating elements 1b (hereafter referred to as auxiliary heating members 1b). As a non-limiting example, the heating part 1 includes one main heating member 1a and two auxiliary heating members 1b. The main heating member 1a and auxiliary heating members 1b may be disposed at any desired position where the main heating member 1a and the auxiliary heating members 1b heat the fixing roller 14. In this embodiment, the main heating member 1a and auxiliary heating members 1b are disposed in the fixing roller 14 to heat the fixing roller 14 from inside. The fixing device 10 of
With reference to
The main power supply unit 2 is powered by an external power source such as a commercial power source to feed electric power to each unit of the image forming apparatus when the power switch 120 of the image forming apparatus is turned on. The main power supply unit 2 is configured to feed electric power to each unit of the image forming apparatus by being connected to an outlet 50 of the commercial power source via a plug 51 (shown in
The storage unit 3 acting as an auxiliary power supply unit is formed from an electric double layer capacitor, and is powered by the main power supply unit 2 to supply power to the auxiliary heating members 1b. That is, each of the auxiliary heating members 1b is heated via power derived from the storage unit 3. Instead of the electric double layer capacitor, the storage unit 3 may be formed from a lithium-ion secondary battery, a nickel metal hydride secondary battery, or a pseudocapacitor using redox. As illustrated in
As a non-limiting example, the storage unit 3 is formed by a capacitor module made up of a plurality (for example, forty) of electric double-layer capacitor cells connected in series. Each capacitor cell may have a capacitance of approximately 800 F at a rated voltage of 2.5 V, so as to realize a high output voltage of approximately 100V from the capacitor module. Each capacitor cell may have an internal resistance of about 5 m.OMEGA. or less, a diameter of about 35 mm, and a length of about 120 mm. Stable operation of the storage unit 3 can be achieved for a long period of time by providing a voltage balance circuit (not shown) to keep a voltage balance among capacitor cells connected in series. If the internal resistance of each capacitor cell is set to about 5 m.OMEGA. or less, the decrease of the voltage between terminals of the storage unit 3 can be less than that of the secondary battery, such as a lithium-ion battery, and a nickel metal hydride battery, even if a large electric current over 20 A flows to the auxiliary heating members 1b at the time of warming-up the fixing roller 14. Further, as a large amount of electric power can be obtained from a relatively small number of capacitor cells, the cost and size of the storage unit 3 can be decreased.
The storage unit 3 is chargeable and dischargeable. Because the storage unit 3 uses an electric double-layer capacitor which has a large capacity and is not accompanied by chemical reactions, the storage unit 3 can be rapidly charged and its useful lifetime is longer than a secondary battery. In the case of using a nickel-cadmium battery as an auxiliary power supply, which is generally used as a secondary battery, several tens of minutes to several hours may be necessary for charging the nickel-cadmium battery, even if a boosting charge is provided. For this reason, a large power can be supplied to units of an apparatus only several times a day, so that the use of the nickel-cadmium battery as an auxiliary power supply is not practical. In contrast, the storage unit 3 using an ultra capacitor can be charged in about several tens of seconds to several minutes. Thus, the time for charging the storage unit 3 can be lessened. For example, the storage unit 3 using an ultra capacitor can be charged when the main power supply unit 2 can afford to charge the storage unit 3, for example, during a non-image forming state of the image forming apparatus. Thus, the number of heating operations, by using the storage unit 3 as the auxiliary power supply unit, can be increased to a practical number.
The useful lifetime of the nickel-cadmium battery is short because the number of allowable charge-discharge iteration times of the nickel-cadmium battery is about 500 to 1000 times. Accordingly, it may be necessary to replace the nickel-cadmium battery very frequently, thereby resulting in a corresponding replacement task and increasing costs for battery replacement. In contrast, the number of allowable charge-discharge iteration times of the capacitor is about 10,000 times or more. Further, the capacitor is not easily deteriorated even if the capacitor is charged and discharged repeatedly. Maintenance of the capacitor is rarely required because the capacitor does not need any liquid exchange or supplement otherwise used in a lead-acid battery.
A capacitor which can store a large amount of electric energy has been developed, so that the use of the capacitor in an electric car is under review. For example, the electric double-layer capacitor developed by Nippon Chemicon Co. has an electrostatic capacitance of about 2000 F at a rated voltage of 2.5 V, which is sufficient for power supply for several seconds to several ten seconds. Further, a capacitor named HYPER CAPACITOR (trade name) manufactured by NEC Corp. has an electrostatic capacitance of about 80 F. Moreover, JEOL Ltd. discloses a NANOGATE CAPACITOR (trade name) which has a voltage proof of about 3.2 to 3.5V and an electric energy density of about 50 to 75 wh/kg.
The main heating member 1a and the auxiliary heating members 1b may be formed from halogen heaters. The halogen heater heats by flowing electric current through a filament formed in a glass tube. Instead of the halogen heater or halogen lamp, the main heating member 1a and the auxiliary heating members 1b may be formed from induction heaters or ceramic heaters. For example, the main heating member 1a, which is powered by the main power supply unit 2, may be formed from a halogen heater, which can provide a 1200 W output at the voltage of 100V. For example, the auxiliary heating members 1b, which are powered by the storage unit 3, may be formed from two halogen heaters connected in parallel. One of the halogen heaters can provide a 1000 W output at the voltage of 100V, and the other halogen heater can provide a 700 W output at the voltage of 100V, for example.
As described above, the heating part 1 of the fixing roller 14 receives power such that the main heating member 1a is supplied with power from the main power supply unit 2 and the auxiliary heating members 1b are supplied with power from the storage unit 3. The power from the main power supply unit 2 is supplied to the storage unit 3 through the charger 4, and the storage unit 3 supplies stored power to the auxiliary heating members 1b at an arbitrary timing.
Before warming-up the fixing roller 14 at a startup of the fixing device 10 (i.e., an initial state), the storage unit 3 including the electric double-layer capacitor having a large capacity is charged by the main power supply unit 2 through the charger 4. At the time of warming-up the fixing roller 14, the temperature of the fixing roller 14 is rapidly raised from a room temperature to a target temperature by supplying power to the main heating member 1a from the main power supply unit 2, and by supplying power to the auxiliary heating members 1b from the storage unit 3. The present inventors carried out experiments under the following conditions:
(1) The fixing roller 14 made of aluminum has a diameter of about 40 mm and a thickness of about 0.7 mm;
(2) The power of about 1200 W is supplied to the main heating member 1a from the main power supply unit 2 and the power of about 1700 W is supplied to the auxiliary heating members 1b from the storage unit 3. So, a total of about 2900 W power is supplied to the heating part 1 of the fixing roller 14.
According to the experimental results, when the fixing roller 14 was heated by supplying power only to the main heating member 1a from the main power supply unit 2, the temperature of the fixing roller 14 was raised from room temperature to a target temperature in about 30 seconds (i.e., a warm-up time). In contrast, when the fixing roller 14 was heated by supplying power to the heating part 1 from both the main power supply unit 2 and the storage unit 3, the warm-up time was reduced to about 10 seconds.
Because the storage unit 3 is constructed from a capacitor, the power supplied from the storage unit 3 to the auxiliary heating members 1b is gradually decreased from about 1700 W due to the decrease of voltage during supplying power to the auxiliary heating members 1b. With this characteristic of the capacitor, the power supplied from the storage unit 3 becomes small after a predetermined time has elapsed. Therefore, even if the temperature of the fixing roller 14 is raised to about 500 degrees centigrade at which the recording material P may ignite, the temperature of the fixing roller 14 gradually decreases due to the above-described characteristic of the capacitor. By using the capacitor as the storage unit 3, the temperature of the fixing roller 14 can be safely raised in a short period of time.
To ensure safety, a safety device is provided in case that the system goes out of control. For example, the safety device may terminate the power supply by cutting off a power supply circuit with a safety circuit, such as a temperature fuse or a thermostat.
The supply of power to the heating part 1 can be increased by using two series of commercial power sources or by using a secondary battery or a fuel battery. However, in this case, a large amount of power is continuously supplied to the heating part 1, so that the warm-up time for raising the temperature of the fixing roller 14 to a target fixing temperature is reduced and the temperature elevation is sharper. In this condition, a safety circuit cannot follow the temperature elevation. When the safety circuit starts to operate, the temperature of the heating part 1 may get too high and cause a recording sheet to ignite. In contrast, in a configuration using a capacitor, even if the system goes out of control and the power supply is not stopped, heating of the heating member is stopped after a predetermined amount of power stored in the capacitor is used up, and the temperature rise of the heating member is automatically stopped. Thus, the warm-up time for raising the temperature of the fixing roller 14 to a target fixing temperature can be safely reduced by using a capacitor as a power supply.
As the fixing roller 14 is a thin-layered roller, if the number of recording materials passing through the nip part between the fixing roller 14 and the pressing roller 15 per unit time increases, the surface temperature of the fixing roller 14 typically decreases. However, in the fixing device 10 of the present embodiment, the surface temperature of the fixing roller 14 is prevented from dropping by supplying power to the auxiliary heating members 1b from the storage unit 3 in addition to the supply of power from the main power supply unit 2 to the main heating member 1a during a sheet passing operation as shown in the time chart of
If only one of the auxiliary heating members 1b capable of providing a 700 W output is heated during the sheet passing operation, the heating part 1 of the fixing roller 14 may be supplied with a power output of about 500 W from the storage unit 3, in addition to the power from the main power supply unit 2 during the sheet passing operation. In this configuration, because the drop of the temperature of the fixing roller 14 after the sheet passage through the fixing device 10 can be prevented, the image forming apparatus according to the embodiment of the present invention can achieve a high-speed image formation, for example, 75 copies per a minute (CPM). In a background image forming apparatus using a thin-layered fixing roller without performing the power supply from a capacitor during a sheet passing operation, the image formation speed is about 60 CPM at most.
Both of the two auxiliary heating members 1b may be used during the sheet passing operation, or the heating part 1 of the fixing roller 14 may include only one auxiliary heating member 1b. Employing a plurality of (e.g., two) auxiliary heating members 1b and one of the auxiliary heating members 1b increases the supply of power and enhances temperature control performance.
As shown in the time chart of
As described above, by using a capacitor as the storage unit 3 for heating the heating part 1 of the fixing device 10, an advantage which cannot be obtained from a secondary battery can be obtained.
As shown by a line “a” (both the main power supply unit and the auxiliary power supply unit) of
In a low temperature condition in which the local ambient temperature Ta detected by the local ambient temperature detecting unit 90 is less than a low threshold temperature “T1”, for example, about 15 degrees centigrade, the temperature T of the fixing roller 14 may be lower than the low threshold temperature “T1”. This low temperature condition occurs when the fixing roller 14 is heated in a colder environment. In this low temperature condition, as shown by a line “b” of
If the local ambient temperature Ta detected by the local ambient temperature detecting unit 90 is lower than the low threshold temperature T1 before warming-up the fixing roller 14, the fixing roller 14 may be warmed-up by using only the main power supply unit 2 without using the storage unit 3 or by using the main power supply unit 2 and using the storage unit 3 with its power supply reduced. By lowering power consumption at the time of warming-up the fixing roller 14 and by using the saved power of the storage unit 3 during the sheet passing operation, a fixing failure can be prevented even in a low temperature condition.
For example, in the case of using the auxiliary heating member 1b rated at 700 W at 100V, the voltage between terminals of the auxiliary heating member 1b decreases from 100V to 85V due to the power supply of the storage unit 3 at the time of warming-up the fixing roller 14, and the auxiliary heating member 1b provides about a 500 W output during the sheet passing operation. If the storage unit 3 does not supply power to the auxiliary heating member 1b at the time of warming-up, the auxiliary heating member 1b can provide a 700 W output at the voltage of 100V during the sheet passing operation. In this condition, the fixing roller 14 can apply a sufficient amount of heat to the recording material P having a low temperature, and the power supplying time of the storage unit 3 can be extended during the sheet passing operation.
In the time chart of
For example, in the case of using the auxiliary heating member 1b rated at 700 W at 100V, the voltage between terminals of the auxiliary heating member 1b decreases from 100V to 85V due to the power supply of the storage unit 3 at the time of warming-up the fixing roller 14, and the auxiliary heating member 1b provides about a 500 W output during the sheet passing operation. If the storage unit 3 is charged by the main power supply unit 2 immediately before the sheet passing operation, the auxiliary heating member 1b can provide a 700 W output at the voltage of 100V during the sheet passing operation. In a low temperature condition such as occurs on a winter morning, the amount of heat absorbed by the recording material P from the fixing roller 14 is relatively large during the sheet passing operation. However, the decrease of temperature of the fixing roller 14 can be prevented during the sheet passing operation by charging the storage unit 3 by the main power supply unit 2 before performing the sheet passing operation. The level of the charging of the storage unit 3, that is, the value of the voltage of the charged storage unit 3 may be set depending on environmental conditions.
If the answer is YES in step S12, the control unit 60 switches OFF the power supply from the storage unit 3 to the auxiliary heating members 1b in step S14. In this condition, as the initial temperature of the fixing roller 14 is high, the fixing roller 14 can be rapidly warmed-up without using the storage unit 3. Then, in step S15, the storage unit 3 starts to be charged from the main power supply unit 2 (from the commercial power source) through the charger 4 during a period between the time “t1” and “t2” in
Subsequently, in step S17, the fixing temperature detecting unit 8 detects the temperature T of the fixing roller 14 at the time of sheet passage. Then, the control unit 60 determines whether the temperature T of the fixing roller 14 is greater than or equal to the target temperature “T0” (T.gtoreq.T0) in step S118. If the answer is NO in step S18, the control unit 60 switches ON the power supply from the storage unit 3 to the auxiliary heating members 1b in step S19. Then, the control operation returns to reexecute step S17. If the answer is YES in step S18, the control unit 60 switches OFF the power supply from the storage unit 3 to the auxiliary heating members 1b in step S20.
As a non-limiting example, the control unit 60 may control the main power supply unit 2 (the commercial power source) so as not to charge the storage unit 3 based on operation information of the image forming apparatus during the period between the time “t1” and “t2” in
Instead of using the size of the recording material P to control operation, the operation information of the image forming apparatus may be the local ambient temperature detected by the local ambient temperature detecting unit 90 or the number of sheets to be printed. Specifically, if the local ambient temperature detected by the local ambient temperature detecting unit 90 is relatively high or the number of sheets to be printed is relatively small, the control unit 60 controls the main power supply unit 2 so as not to charge the storage unit 3 after the power supply from the storage unit 3 to the auxiliary heating members 1b is completed at the time of warming-up the fixing roller 14. By doing so, unnecessary power consumption can be prevented.
When performing the second sheet passing operation immediately after performing the first sheet passing operation in which a large number of sheets are consecutively passed through the nip part between the fixing roller 14 and the pressing roller 15, the remaining power of the storage unit 3 is small but the main power supply unit 2 can afford to supply power to the storage unit 3 because the main power supply unit 2 need not supply a large power to the main heating member 1a which has been sufficiently heated during the first sheet passing operation period. In this case, the storage unit 3 may be charged by the main power supply unit 2 during the second sheet passing operation period in which a plurality of recording materials P pass through the nip part between the fixing roller 14 and the pressing roller 15.
In the above-described embodiments, the storage unit 3 acting as an auxiliary power supply unit can be charged by effective use of electric power of the external power source during a period from when the power supply from the storage unit 3 to the auxiliary heating members 1b is completed at the time of warming-up the fixing roller 14 to when the power supply from the storage unit 3 to the auxiliary heating members 1b is started at the time of the sheet passing operation.
The present invention has been described with respect to the exemplary embodiments illustrated in the figures. However, the present invention is not limited to these embodiments and may be practiced otherwise.
Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore understood that within the scope of the appended claims, the present invention may be practiced other than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-260985 | Sep 2004 | JP | national |
This application is a continuation of U.S. patent application Ser. No. 11/220,686 filed Sep. 8, 2005, which claims priority to Japanese Patent Application No. 2004-260985 filed in the Japanese Patent Office on Sep. 8, 2004, the entire contents of each of which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11220686 | Sep 2005 | US |
| Child | 12029890 | US |
