Heating device, fuser device, and image forming apparatus including power supply devices for supplying power to a heating unit

A heating device includes a heating unit, a main power supply device configured to supply an electric power to the heating unit from an external power supply, an auxiliary power supply device configured to be chargeable by use of the external power supply, and a charger configured to charge the auxiliary power supply device during formation of an image while neither the main power supply device nor the auxiliary power supply device is supplying an electric power to the heating unit, such that a maximum limit of a charge amount of the auxiliary power supply device is set to a predetermined amount smaller than a full-charge amount of the auxiliary power supply device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to heating devices, fuser devices, and image forming apparatuses, and particularly relates to a fuser device which is provided with a main power supply device for supplying power from an external power supply and an auxiliary power supply device capable of charging electricity based on the external power supply, these power supply devices serving as power supply means for supplying power to a heating unit.

2. Description of the Related Art

Image forming apparatuses such as copier machines form images on recording media such as paper sheets or overhead projector sheets. As consideration is given to the speed, image quality, and cost of an image forming process, an electrophotographic system is typically employed. The electrophotographic system forms a toner image on a recording medium, and fuses the formed toner image with the recording medium by applying heat and pressure. As a fusing system, a heat roller system is most commonly used from the safety point of view. The heat roller system includes a heating roller for providing heat by use of a heating member such as a halogen heater, and includes a mutually pressuring unit called a nip unit in which a pressuring roller is situated to oppose the heating roller and pressed against the heating roller. A recording medium on to which a toner image is transferred is passed through the nip unit, thereby experiencing heat and pressure, which fuse the toner image on the recording medium.

In recent years, out of consideration for environmental issues, there has been an ongoing effort to reduce power consumption in image forming apparatuses such as copier machines and printer apparatuses. In order to reduce power consumption in image forming apparatuses, an effective measure is to lower the temperature of the heating unit such as a fusing roller and fusing belt provided in the fuser device during the period in which no paper sheet is traveling in the image forming apparatus (e.g., during the standby period).

When the temperature of the heating unit is lowered during a no-paper-sheet-travel period, the heating unit needs to return to a certain temperature prior to the subsequent use of the fuser device. The user thus needs to wait in the meantime. Since it takes time before the apparatus becomes usable, convenience regarding the use of the apparatus is not satisfactory. In order to avoid such inconvenience, it is conceivable to shorten the time period in which the temperature of the heating unit is increased by providing an auxiliary power from an auxiliary power supply apparatus. In consideration of this, reducing the heat capacity of the fusing roller is desired.

The fusing roller comes in contact with a transfer member, and its heat is thus deprived of at the time of image formation. As a result, the temperature of the surface of the fusing roller drops rapidly despite the large heat capacity of the fusing roller, resulting in temperature below the minimum temperature necessary to achieve satisfactory fusing performance. In consideration of this, an auxiliary power supply apparatus that can be charged may be provided in an image forming apparatus, and supplies an electric power to the heater at the time of image formation, thereby preventing the temperature of the surface of the fusing roller from dropping.

Patent Document 1 discloses a fuser device provided with a main power supply device and an auxiliary power supply device, the fuser device having a heating unit comprised of a main heat generating body and an auxiliary heat generating body, the main heat generating body receiving an electric power from the main power supply device, and the auxiliary heat generating body receiving an electric power from the auxiliary power supply device having a capacitor. When heating of the heating unit starts, a large electric power is supplied from the main power supply device and from the auxiliary power supply device simultaneously, thereby raising the temperature of the heating unit to a desired temperature in a short time. During the standby period, the heating unit does not receive an electric power.

In the related-art fuser device as described above, the auxiliary power supply device is not charged by the external power supply at the time of image formation. There is thus a need to charge the auxiliary power supply device after the forming of one image before the forming of the next image. This results in an inconvenience in that a waiting period before the next image is formed is prolonged due to the time required for electric charge.

Further, during the forming of an image, the pressuring roller inside the fuser device is sufficiently heated. If the auxiliary power supply device is charged to its full capacity, and is then allowed to discharge for the purpose of heating, the heating unit ends up providing excessive heat to the transfer member and toner. This creates a risk of causing a failure such as the blocking of the toner and transfer member after the forming of the image.

Accordingly, there is a need for a heating device, a fuser device, and an image forming apparatus in which a time period between an image formation and the next image formation can be shortened, and, also, excessive heating of the heating unit can be prevented.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a heating device, a fuser device, and an image forming apparatus that substantially obviate one or more problems caused by the limitations and disadvantages of the related art.

To achieve these and other advantages in accordance with the purpose of the invention, the invention provides a heating device that includes a heating unit, a main power supply device configured to supply an electric power to said heating unit from an external power supply, an auxiliary power supply device configured to be chargeable by use of the external power supply, and a charger configured to charge said auxiliary power supply device during formation of an image while neither said main power supply device nor said auxiliary power supply device is supplying an electric power to said heating unit, such that a maximum limit of a charge amount of said auxiliary power supply device is set to a predetermined amount smaller than a full-charge amount of said auxiliary power supply device.

According to another aspect of the present invention, a fuser device for use in an image forming apparatus includes a fusing roller, a heating unit embedded in said fusing roller, a main power supply device configured to supply an electric power to said heating unit from an external power supply, an auxiliary power supply device configured to be chargeable by use of the external power supply, and a charger configured to charge said auxiliary power supply device during formation of an image while neither said main power supply device nor said auxiliary power supply device is supplying an electric power to said heating unit, such that a maximum limit of a charge amount of said auxiliary power supply device is set to a predetermined amount smaller than a full-charge amount of said auxiliary power supply device.

According to another aspect of the present invention, an image forming apparatus includes a unit configured to form a toner image by use of an electrophotographic system, and a fuser device configured to heat and fuse the toner image with a recording medium, wherein said fuser device include a fusing roller, a heating unit embedded in said fusing roller, a main power supply device configured to supply an electric power to said heating unit from an external power supply, an auxiliary power supply device configured to be chargeable by use of the external power supply, and a charger configured to charge said auxiliary power supply device during formation of an image while neither said main power supply device nor said auxiliary power supply device is supplying an electric power to said heating unit, such that a maximum limit of a charge amount of said auxiliary power supply device is set to a predetermined amount smaller than a full-charge amount of said auxiliary power supply device.

According to at least one embodiment of the heating device, the fuser device, and the image forming apparatus of the present invention, the time required to charge the auxiliary power supply device before the forming of a next image is shortened, and the heating unit can avoid applying excessive heat to a transfer member and toner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a cross-sectional schematic view of an image forming apparatus such as a copier machine or a printer apparatus based on the electrophotography system according to the present invention. The image forming apparatus according to this embodiment is capable of processing 100 sheets continuously (75 CPM (CPM: copy speed)), for example, and mainly includes a scan unit11for scanning a document, an image forming unit12for forming an image, an auto-document feeder13, a document ejection tray14for keeping a stack of documents ejected from the auto-document feeder13, a sheet supply unit19having sheet supply cassettes15through18, and a sheet ejection tray20for keeping a stack of the recorded sheets. The auto-document feeder13may be capable of loading 100 sheets at the maximum, and the scan unit11may require 60 seconds to scan 100 sheets of documents.

A document D is set on a document platform21of the auto-document feeder13, and an operation on an operation unit (not shown) such as the pressing of a print key is performed. In response, the sheet at the top of the document D is slid out in a direction B1through the rotation of a pickup roller22, and is carried and placed on a contact glass24fixed in the scan unit11through the rotation of a document conveyor belt23. An image of the document D placed on the contact glass24is scanned by a scan device25that is situated between the image forming unit12and the contact glass24. The scan device25includes a light source26for illuminating the document D on the contact glass24, an optical system27for focusing the document image, and a photoelectric conversion device28such as a CCD on which the document image is focused. After the scanning of the image, the document D is carried in a direction B2through the rotation of the document conveyor belt23so as to be ejected on to the document ejection tray14. In this manner, the document D is carried and placed one sheet after another on the contact glass24, and the scan unit11scans the document images.

Inside the image forming unit12, a photoconductor30serving as an image carrier is provided. The photoconductor30rotates clockwise inFIG. 1. A charger31charges the surface of the photoconductor30to a predetermined potential. A write unit32shines a laser beam L modulated in response to image information indicative of the image scanned by the scan device25. The laser light L illuminates the charged surface of the photoconductor30, thereby forming a latent electrostatic image on the surface of the photoconductor30. This latent electrostatic image passes through a developing device33, and is transferred by a transfer device34on to a transfer member (recording medium) P that is supplied to a space between the photoconductor30and the transfer device34. The surface of the photoconductor30is cleaned by a cleaner35after the transfer of the toner image.

The sheet supply cassettes15through18provided at the bottom of the image forming unit12accommodate a recording medium P such as paper sheets. The recording medium P is slid out in a direction B3from one of the sheet supply cassettes15through18. The toner image formed on the surface of the photoconductor30as described above is transferred on to the surface of the recording medium P. The recording medium P then passes through a fuser device36provided inside the image forming unit12as indicated by an arrow B4. Heat and pressure is applied to fuse the transferred toner image with the surface of the recording medium P. The recording medium P having passed through the fuser device36is carried by a pair of ejection rollers37and ejected as indicated by an arrow B5, thereby being placed on the sheet ejection tray20.

In the following, a description will be given of the fuser device36according to an embodiment of the present invention.FIG. 2is a front view of the fuser device36according to the present invention.FIG. 3is a block diagram showing the configuration of a heat generating device according to the present invention.

In this example, the fuser device36includes a fusing roller1, a pressuring roller2pressed against the fusing roller1, and a fuse separating nail5pressed against the fusing roller1with a predetermined pressure. Further, the fuser device36includes a heating unit4, a main power supply device6for supplying an electric power from an external power supply (commercial power supply), and an auxiliary power supply device7that is chargeable by use of the external power supply. The heating unit4is embedded inside the fusing roller1. The heating unit4includes a main heating unit4areceiving an electric power from the main power supply device6and an auxiliary heating unit4breceiving an electric power from the auxiliary power supply device7. These heating units4a,4bare implemented by use of halogen heaters or the like.

The fusing roller1is provided with a temperature detecting unit3such as a thermistor. A control unit10of the image forming apparatus controls the switch-on/off of the main heating unit4aand the auxiliary heating unit4bso as to control the temperature of the surface of the pressuring roller2. With the fuser device36having the configuration as described above, a yet-to-be-fused image of toner T formed on the transfer member P is heated and melted, so that the toner T is fused with the transfer member P.

The main power supply device6is connected to a commercial power supply via a plug or the like. As shown inFIG. 3, the auxiliary power supply device7is configured to be chargeable through a charger8. In the heating unit4of this example, the main heating unit4areceives an electric power from the main power supply device6, and the auxiliary heating unit4breceives an electric power from the auxiliary power supply device7. Switching is performed under the control of the charger8by operating the switches provided in a charge switching unit9and a control unit10.

With this configuration, the main power supply device6supplies an electric power to the main heating unit4a, and the auxiliary power supply device7supplies an electric power to the auxiliary heating unit4b. This provides for an electric power exceeding the maximum power supply capacity of the main power supply device6to be supplied to the fuser device36for a predetermined time period.

In this example, the charger8charges the auxiliary power supply device7during the forming of an image while the main power supply device6is not supplying an electric power to the heating unit4, and neither is the auxiliary power supply device7supplying an electric power to the auxiliary heating unit4b. Namely, the charger8charges the auxiliary power supply device7while the heating units4aand4bare switched-off without the temperature of the surface of the fusing roller1dropping.

The full-charge amount (in terms of voltage) of the auxiliary power supply device7is denoted as V0, the power of the heater immediately following a discharge from the fully-charged state denoted as W0, the maximum limit of a charge amount during the forming of an image denoted as V1, and the power of the heating unit4immediately following a discharge from the maximum charge limit denoted as W1. In this example, provision is made such that the charger8performs charging to satisfy the following relationship.
V0>V1, W0>W1

In this example, thus, the maximum limit of a charge amount of the auxiliary power supply device7is set smaller than the full-charge amount of the auxiliary power supply device7, thereby shortening the time required for electric charge. As a result, the time required to charge the auxiliary power supply device7before the forming of the next image can be shortened. Further, the amount of an electric discharge is also suppressed, thereby preventing excessive heat from being applied to a transfer member and toner. This can avoid a failure such as the blocking of the toner and transfer member following the forming of an image.

In this example, further, the charger8is configured such that the maximum limit of a charge amount of the auxiliary power supply device7is set to V0during the times other than the time of image formation. This ensures that the amount of power supply from the auxiliary power supply device7to the heating unit4is sufficient, thereby making it possible to avoid a fusing failure.

In this example, the auxiliary power supply device7is implemented as electric double-layer capacitors (condensers). This provides for a sufficient electric power to be supplied even if the charging time is as short as a few minutes. If a secondary battery such as a typical nickel-cadmium battery is used as the auxiliary power supply device7, at least a few hours of rapid charging is necessary.

An electric double-layer capacitor has an almost infinite life, which is advantageous in comparison with a nickel-cadmium battery, which can only be charged and discharged 500 times to 1000 times. Another merit is that there is little degradation even after repeated charging and discharging.

In the embodiment described above, an electric double-layer capacitor is used as the auxiliary power supply device7. The auxiliary power supply device7of the present invention is not limited to this example, and a battery that can be charged and discharged repeatedly may as well be used. As a heat generating member, a halogen heater is not a limiting example. A plate-shape heat generating member or a heat generating member utilizing the IH system may as well be used.

The present application is based on Japanese priority application No. 2004-341445 filed on Nov. 26, 2004, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.