Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field of the Invention
The present invention relates to heating apparatuses for heating various targets, such as paper and a film; fixing apparatuses; image forming apparatuses, such as a copying apparatus, a printer, and a facsimile apparatus.
2. Description of the Related Art
Image forming apparatuses, such as a copying apparatus, a printer, and a facsimile apparatus, include a process for forming an image on a heating target, such as a sheet of regular paper and OHP paper. In such image forming apparatuses, although various image formation methods are employed, an electro-photographic method is widely adopted from viewpoints of speed, image quality, cost, and so on.
In the electro-photographic method, a toner image that is to be fixed is formed on the heating target, such as a sheet of regular paper and OHP paper, and a fixing process fixes the toner image on the heating target by heat and pressure applied by a fixing apparatus. As the fixing apparatus, a heat roller is widely adopted for rapidity and safety.
The fixing apparatus adopting the heat roller includes a nip part that is constituted by a heating roller heated by a heating unit, such as a halogen heater, and a pressurization roller that counters the heating roller. The heating target is passed between the heating roller and the pressurization roller such that the toner image on the heating target is fixed by heat and pressure. The nip part carries out pressure welding.
When fluoride system resin as a release agent layer covers the metal core of the heating roller of the fixing apparatus of the heat roller method, since the fluoride system resin is hard, a problem of image quality arises as follows. The toner image on the heating target has microscopic unevenness. If the surface of the heating roller is hard, the surface cannot follow the unevenness, and microscopic compliance with the uneven surface of the heating roller becomes low. For this reason, the toner image after being fixed to the heating target contains uneven gloss between a portion where the heating roller makes contact, and a portion where the heating roller does not make contact.
In conventional monochrome copying apparatuses, since required quality of an image is not so high as compared with full color copying apparatuses, the heating roller including the core metal covered with fluoride system resin is acceptable. However, as the speed of the apparatuses is raised, and a monochrome copying apparatus is used for printing, requirements for high-definition production are becoming high.
On the other hand, requirements for producing high-definition images are higher for full color copying apparatuses than for the monochrome copying apparatuses. A high quality fixed image without uneven gloss is obtained by providing close contact between the surface of the heating roller and a toner layer on the heating target, which is realized by covering the core metal of the heating roller with an elastic layer (heat-resistant rubber), the elasticity of the rubber of a heating roller providing the close contact. This technology has been applied to monochrome copying apparatuses.
However, the metal core of the heating roller is made of a metal, such as iron and aluminum, having a high heat capacity. For this reason, the heat roller method has a shortcoming in that it takes a long starting time of several minutes, sometimes longer than ten minutes, for the temperature of the heating roller to rise to about 180 degrees C.
To cope with this problem of the image forming apparatus, power is continuously supplied to the heating roller, even if a user does not use the image forming apparatus, i.e., during standby, such that the temperature of the heating roller is maintained at a preheating temperature, which is set at a little lower than the operational temperature, so that the temperature can be quickly raised to the operational temperature when the heating roller is used. While this solution shortens the waiting time of the user, excessive energy is wasted during the standby period. In addition, an investigation report says that the consumption of energy during the standby period often ranges about 70 to 80 percent of the consumption energy of the image forming apparatus in operation.
Recently and continuing, energy-saving regulations are enacted from the rise of environmental protection consciousness in countries worldwide. In Japan, the Law concerning the Rational Use of Energy is being revised and strengthened, and in the U.S., energy-saving programs, such as energy star and ZESM (Zero Energy Star Mode), are being enacted. In order to meet these regulations and programs, it is desirable to suspend the power supply to the heating roller while the image forming apparatus is in the standby mode. Given that the power consumption during the standby mode is considerably high, such suspension will greatly contribute to power-saving.
However, if the power is not supplied to the heating roller during the standby mode in the case of the conventional fixing apparatus, it takes the long time for the temperature of the heating roller to rise at the time of reuse, and the long waiting time reduces user-friendliness. For this reason, an energy-saving type image forming apparatus wherein the temperature of the heating roller quickly rises is desired. For example, ZESM requires a re-starting time of 10 seconds or less.
In order to shorten the temperature rising (heating) time of the heating roller, it is effective to lower the heat capacity of the whole fixing apparatus including the pressurization roller. Japanese Provisional Patent No. H11-133776 discloses a fixing apparatus that realizes high-definition image production, improvement in speed, energy saving, and long service life by preparing a fixing roller containing an elastic layer, a pressurization belt constituting a nip part, and a pressurization unit arranged inside the pressurization belt, wherein a heating target is passed between the fixing roller and the pressurization belt.
Further, Japanese Patent No. 2001-92281 discloses a fixing apparatus that fixes a toner image on a transfer medium by heating and pressurization, providing high definition, energy saving, and a long service life, which includes:                a film-like rotational unit that is prepared enclosing a fixed heating element, and        a rotational unit having a roll-like structure for heat ray fixing, which further includes a heat ray irradiation unit for emitting heat rays installed countering the film-like rotational unit, a transparent cylindrical unit that transmits the heat rays, a transparent elastic layer prepared outside of the transparent cylindrical unit, and a heat ray absorption layer for absorbing the heat rays prepared outside of the transparent elastic layer.        
The temperature rising time of the heating roller can be shortened by increasing injection energy per unit time, i.e., rated power, provided to the heating element that heats the heating roller. In fact, high-speed image forming apparatuses using a power supply voltage of 200 V are available, wherein the temperature rising time of the heating roller is shortened. However, in Japan, generally available commercial power supply is at 100 V 15 A, and a 200 V power supply is available only after a special installation. Thus, expecting a voltage higher than 100 V is not realistic.
Further, image forming apparatuses that raise the total power injected to the heating element of the fixing apparatus, using two systems of the commercial power supply of 100 V 15 A are also available. However, availability of two separate power line systems is not common.
Furthermore, when the supply power to the heating element of the fixing apparatus is simply increased, safety precautions become more important. The temperature of the heating roller rises quickly as a result of supplying high power to the heating element. When a system hangs up, and control of the supply power to the heating element becomes impossible, the probability of ignition becomes considerably high. If the temperature rise of the heating roller is too quick, the temperature of the heating roller may exceed the ignition temperature of paper before safeguards, such as a temperature fuse and a thermostat, operate.
As mentioned above, conventionally, there is a limit to the amount of the injection energy for raising the temperature of the heating roller in a short time.
In order to realize energy savings when increasing the maximum power supplied to the heating element, using an auxiliary power supply for supplying power to the heating element is proposed, wherein a rechargeable battery is used as the auxiliary power supply. As the rechargeable battery, a lead storage battery, a NiCd battery, etc., are typical ones.
However, since it takes several hours to fully charge the rechargeable battery, the problem is that it cannot be used repeatedly in a day. Further, the rechargeable battery is deteriorated through repeated recharging, the capacity being decreased, and has the nature that the greater is the discharge current, the shorter the service life becomes. In the case of a NiCd battery, which is generally considered to have a long service life and being capable of providing a large current, the number of times of recharging is about 500–1000. If recharging is performed 20 times a day, the service life is about a month. Accordingly, time and effort for battery replacement are required, and operating costs, such as battery costs, become high. Further, since it takes a long time to charge the rechargeable battery, recharging is often performed at night, with the rechargeable battery being taken out of the apparatus. Further, the rechargeable battery is capable of discharging little by little, but it has difficulty providing high power for a short duration. Further, if charging is continued without discharging, gas is generated, causing a failure and being unsafe. Furthermore, the lead storage battery uses liquid sulfuric acid, which is not desirable for use in an office apparatus. Due to the shortcomings as described above, it is practically difficult to employ a rechargeable battery for supplying power to the heating element.
In order to solve the shortcomings of the rechargeable battery, proposals have been made that a mass capacitor, such as an electric double layer capacitor, be used by the fixing apparatus, as an auxiliary power supply. In the case of the mass capacitor, the number of times of recharging is almost unlimited, with almost