Patent Grant
7551869
This application claims priority to Japanese Patent Application No. 2004-242055 filed in the Japanese Patent Office on Aug. 23, 2004, the entire contents of each of which is hereby incorporated by reference herein.
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 by heat and that includes 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. When the heating part starts to generate heat, the amount of power supplied from the capacitor to the auxiliary heating element is adjusted based on the temperature of the heating part.
For example, Published Japanese patent application No. 2002-184554 describes the above-described fixing device. In the fixing device, the heating part is rapidly warmed-up to a predetermined temperature by being supplied with a large amount of power from both the main power supply unit and the auxiliary power supply unit. During a stand-by state of the fixing device, the main power supply unit and the auxiliary power supply unit do not supply power to the heating part. Thus, the power-saving effect is enhanced, and the noise caused by a sudden current change or an in-rush current at the time of starting or stopping the supply of high power is reduced. Further, a warm-up time of the heating part is reduced, and the heating part is prevented from overheating. The fixing device further includes a charger, a switching unit, a temperature detecting unit, and a control unit. The charger charges the capacitor of the auxiliary power supply unit with power supplied from the main power supply unit. The switching unit performs switching between the charge of the auxiliary power supply unit and the supply of power from the auxiliary power supply unit to the auxiliary heating element. The temperature detecting unit detects the temperature of the heating part. The control unit controls the amount of power supplied from the auxiliary power supply unit to the auxiliary heating element based on the temperature of the heating part detected by the temperature detecting 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 efficiently save the power supplied to the heating part from the auxiliary power supply unit 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 the 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 fixing temperature detecting unit configured to detect a temperature of the fixing member, and 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 based on the temperature of the fixing member, at the time of warming-up the fixing member by the heating part.
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; detecting a temperature of a fixing member; supplying power to a heating part from the storage unit; heating the fixing member by the heating part; controlling the external power source to supply power to the heating part at the time of warming-up the fixing member by the heating part; and determining whether to start to supply power to the heating part from the storage unit based on the temperature of the fixing member at the time of warming-up the fixing member by the heating part.
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 when considered in connection with the accompanying drawings, wherein:
Preferred embodiments of the present invention are described in detail referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.
The transfer device 48 is disposed opposite to 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 the 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 a next image forming operation.
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 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 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. Similarly to generally-used electric devices, 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 heats by being supplied with power 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 mΩ 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 mΩ 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 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 long as compared to 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 are necessary for charging the nickel-cadmium battery even if boosting charge is performed. For this reason, a large power can be supplied to units of an apparatus only several times in 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 rapidly 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 is necessary to replace the nickel-cadmium battery very frequently, thereby resulting in the corresponding replacement task and increasing in running 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 which otherwise is needed in a lead-acid battery.
In recent years, 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, is 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, are 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 in 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 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 secure safety, a safety device is preferably 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 extremely sharp. 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 may cause a recording sheet to ignite in the worst case scenario. In contrast, in a configuration using a capacitor, even if the system goes out of control and the power supply is not stopped, the 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 P 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 is 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, an image formation speed is about 60 CPM at most.
As alternative examples, 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. However, it is preferable that the heating part 1 include a plurality of (e.g., two) auxiliary heating members 1b and one of the auxiliary heating members 1b be heated in the sheet passing operation to achieve the supply of great power and to enhance 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, the advantage which cannot be obtained from a secondary battery can be obtained.
As shown by a line “a1” (both the main power supply unit and the auxiliary power supply unit) of
As shown by a line “b” (the main power supply unit only) and a line “a2” (both the main power supply unit and the auxiliary power supply unit) of
In contrast, when the fixing roller 14 is heated on a winter morning, for example, the temperature T of the fixing roller 14 may be lower than a predetermined low threshold temperature “T2”, for example, about 15 degrees centigrade. In this low temperature condition, as shown by a line “c” 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 an about 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.
If the answer is YES in step S32, the control unit 60 switches OFF the power supply from the storage unit 3 to the auxiliary heating members 1b in step S34. 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. The line “b” of
Subsequently, in step S37, 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 if the temperature T of the fixing roller 14 is greater than or equal to the target temperature “T0” (T≧T0) in step S38. If the answer is NO in step S38, the control unit 60 switches ON the power supply from the storage unit 3 to the auxiliary heating members 1b in step S39. Then, the control operation returns to reexecute step S37. If the answer is YES in step S38, the control unit 60 switches OFF the power supply from the storage unit 3 to the auxiliary heating members 1b in step S40.
Each of the storage units 3a and 3b acting as auxiliary power supply units is formed from an electric double layer capacitor. By using the two storage units 3a and 3b, the power stored in each of the storage units 3a and 3b can be supplied to the heating part 1 of the fixing roller 14 when the supply of a large amount of power is required, for example, at the time of warming-up the fixing roller 14 and at the time of consecutively passing a plurality of the recording materials P through the fixing device 10. With this configuration, a large amount of power greater than the amount of power supplied by the main power supply unit 2 can be supplied to the heating part 1 of the fixing roller 14.
In this embodiment, the control circuit of the fixing device 10 includes the two chargers 4a and 4b. Alternatively, the control circuit of the fixing device 10 may include one charger, and the charger may switchably charge a plurality of storage units at predetermined time intervals.
As a non-limiting example, the storage unit 3a is formed by a capacitor module made up of a plurality (for example, twenty) of electric double-layer capacitor cells connected in series. Each capacitor cell may have a capacitance of approximately 500 F at a rated voltage of 2.5 V, so as to realize an output voltage of approximately 50V from the capacitor module. Each capacitor cell may have an internal resistance of about 5 mΩ or less, a diameter of about 35 mm, and a length of about 120 mm.
The storage unit 3b 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 200 F at a rated voltage of 2.5 V, so as to realize an output voltage of approximately 100V from the capacitor module. Each capacitor cell may have an internal resistance of about 5 mΩ or less, a diameter of about 35 mm, and a length of about 120 mm.
For example, the storage unit 3a may supply power to the auxiliary heating member 1b1 during a period of consecutively passing a plurality of the recording materials P through the fixing device 10, and the storage unit 3b may supply power to the auxiliary heating member 1b2 during warming-up the fixing roller 14. The auxiliary heating member 1b1 may be formed from a halogen heater which can provide about 500 W output, and the auxiliary heating member 1b2 may be formed from a halogen heater which can provide about 1200 W output.
As described above, one pair of the storage unit and the heating member may be used during warming-up the fixing roller 14, and another pair of the storage unit and the heating member may be used during a period of consecutively passing a plurality of the recording materials P through the fixing device 10. Alternatively, both of the storage units may discharge at the same time.
According to the above-described embodiments, 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 an about 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 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.
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.
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