Patent Application
20080107459
This application claims from the benefit of Korean Patent Application No. 2006-109410, filed Nov. 7, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus using a fusing unit to fuse an image transferred onto a printable medium and, more particularly, to a fusing unit and an image forming apparatus using the same that is of an endless belt type.
2. Related Art
An electrophotographic image forming apparatus, such as a laser printer, a photocopier, a facsimile machine, or a multi-functional product, forms an electrostatic latent image by scanning light onto a photosensitive medium that is charged to a predetermined electric potential, develops the electrostatic latent image by a toner of a predetermined color, and prints an image by transferring and fusing the developed image onto a printable medium. A fusing unit is provided in a printing path of the image forming apparatus to fuse the transferred toner image onto the printable medium.
Fusing units are generally classified into two types: a roller type and a belt type. In the roller type, the toner image transferred onto the printable medium is fused by a heating roller and a pressing roller placed opposite each other with the printable medium in between. In the belt type, a contact surface between the printable medium and the heating roller is expanded using an endless belt wound on two pressing rollers.
The belt type fusing unit has the contact surface between the printable medium and the pressing roller. The contact surface is larger than a fusing nip of the roller type fusing unit. Therefore, there is no need to increase the external diameter of the pressing roller in order to expand the width of the fusing nip, which is formed by the pressure exerted between the heating roller and the pressing roller. The overall constitution can thus be made compact. Since the contact surface of the belt type fusing unit is comparably larger than that of the roller type fusing unit, the superior fusing performance of the belt type reduces warming-up time and fusing when printing at high speed.
Heat generated by the heating lamp 1 is conducted to the heating roller 3, heating a surface of the heating roller 3. The surface temperature of the heating roller 3 is maintained at a predetermined temperature. The first and the second pressing rollers 5 and 7 rotatably support the fusing pressing belt 9 and cause the fusing pressing belt 9 to come into partial contact with the heating roller 3 or the supplied printable medium 10. The first pressing roller 5 rotates and is elastically biased toward the heating roller 3 by an elastic member (not shown) to press the heating roller 3.
A width of the fusing pressing belt 9 is larger than a length of each of the first and the second pressing rollers 5 and 7 so that the heating roller 3 cannot come into direct contact with the first and the second pressing rollers 5 and 7. As shown in
The hardness of the heating roller 3 is higher than that of the first pressing roller 5 so that a fusing nip N1 can form between the heating roller 3 and the first pressing roller 5. Accordingly, if the first pressing roller 5 having a comparatively lower hardness contacts the heating roller 3 at a part 5a, the part 5a is deformed toward the center of the first pressing roller 5 by the pressure between the heating roller 3 and the first pressing roller 5. The shape of the fusing pressing belt 9 is deformed at the part 5a where the fusing nip N1 of the first heating roller 5 is formed. As shown by a dotted line in
If the fusing pressing belt 9 is employed as described in connection with
Aspects of the present invention provide a fusing unit and an image forming apparatus using the same that prevents a fusing pressing belt from wrinkling or damage.
Another aspect of the present invention provides a fusing unit and an image forming apparatus using the same that can guide a belt bias of the fusing pressing belt in one direction and can provide a friction preventing structure in a direction of the belt bias of the fusing pressing belt so as to prevent damage to the fusing pressing belt.
According to an aspect of the present invention, there is provided a fusing unit disposed in a printing path of an image forming apparatus to fuse an image transferred onto a printable medium, the fusing unit comprising a heating roller; a plurality of pressing rollers provided opposite the heating roller to press a printable medium in cooperation with the heating roller; and a fusing pressing belt wound on the plurality of pressing rollers to form a fusing nip when in contact with the heating roller, the fusing nip fusing the image onto the printable medium; wherein a surface hardness hP of at least one of the plurality of pressing rollers is greater than or equal to a surface hardness hH of the heating roller.
According to another aspect of the invention, the plurality of pressing rollers comprise a first pressing roller and a second pressing roller; the first pressing roller is placed at an upstream position along a direction in which the printable medium advances; the second pressing roller is placed at a downstream position relative to the first pressing roller, and the surface hardness of the first pressing roller is greater than or equal to the surface hardness of the heating roller.
According to another aspect of the invention, the printable medium is supplied in a direction in which a surface of the printable medium, on which a toner image transferred but not yet fused is formed, faces the heating roller.
According to another aspect of the invention, a width of the fusing pressing belt is relatively larger than a length of the plurality of pressing rollers.
According to another aspect of the invention, the fusing unit further comprises a supporting unit rotatably supporting the plurality of pressing rollers to guide the fusing pressing belt. The supporting unit comprises a first supporting member comprising a first restriction unit to restrict a movement of the fusing pressing belt in an axial direction of the first or second pressing roller and a first contacting unit protruding from the first restriction unit toward the fusing pressing belt to contact with an inner plate surface of the fusing pressing belt; and a second supporting member comprising a second restriction unit to restrict the movement of the fusing pressing belt in the axial direction of the first or second pressing roller, and a second contacting unit protruding from the second restriction unit toward the fusing pressing belt to contact with the inner plate surface of the fusing pressing belt.
According to another aspect of the invention, the first contacting unit is formed to be inclined so that the shape of the first contacting unit becomes smaller gradually from the first restriction unit as far as the protruded end, and the second contacting unit is formed so that a surface of the second contacting unit contacting the fusing pressing belt is perpendicular to a restriction surface of the first restriction unit.
According to another aspect of the invention, an inclination angle of the first contacting unit is more than 0° and equal to or less than 10°.
According to another aspect of the invention, the fusing nip formed between the heating roller and the fusing pressing belt has a shape of the pressing roller or a straight line.
According to another aspect of the invention, a major diameter D1 of the first contacting unit is greater than a major diameter D2 of the second contacting unit, so that the fusing pressing belt biases toward the first supporting member while the fusing pressing belt is rotating.
According to another aspect of the invention, the fusing unit further comprises a wearing prevention plate, inserted in the first contacting unit and provided between the first restriction unit and the fusing pressing belt, to guide the rotation of the fusing pressing belt and to prevent wearing.
According to another aspect of the invention, the wearing prevention plate comprises a conductive material.
According to another aspect of the present invention an image forming apparatus is provided comprising: a developing unit to develop a supplied toner to form an image; a light scanning apparatus to scan a light onto the developing unit to form an electrostatic latent image; a transfer unit provided opposite the developing unit to transfer the image formed by the developing unit onto a printable medium; and a fusing unit to fuse a toner image transferred onto the printable medium.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
As shown in
The heat source 21 may comprise a halogen lamp, resistance heating coil or other type of heat source. Especially, if the heat source 21 comprises the halogen lamp, the heat source 21 is provided at a hollow part 26a of the heating roller 25. The heating roller 25 comprises a core 26 functioning as a rotation supporting shaft and a heating unit 27 provided at a circumference of the core 26 having a predetermined thickness. The core 26 is heated by the heat source 23 and an outer surface of the heating unit 27 is heated by conduction to maintain a predetermined fusing temperature.
The plurality of pressing rollers 31 and 35 are placed opposite the heating roller 25 and press the supplied printable medium 10 in cooperation with the heating roller 25. The plurality of pressing rollers 31 and 35 are elastically biased toward the heating roller 25 by an elastic member (not shown), forming a predetermined fusing nip N2 in a contacting part between the fusing pressing belt 40 and the heating roller 25.
If a surface hardness of the heating roller 25, that is, a surface hardness of the heating unit 27, is hH and a surface hardness of at least one of the plurality of the pressing rollers 31 and 35 is hP, the hardness hH and the hardness hP should satisfy the condition of Equation 1.
hP≧hH (Equation 1)
The nip N2 formed between the heating roller 25 and the fusing pressing belt 40 has a shape of the pressing roller 31 or a shape of a straight line. According to an example embodiment of the present invention, the surface hardness hP of the pressing rollers 31 and 35 is higher than the surface hardness hH of the heating unit 27.
The plurality of the pressing rollers may comprise first and second pressing rollers 31 and 35. The first pressing roller 31 is placed at an upstream position along a direction in which the supplied printable medium 10 advances and the second pressing roller 35 is placed at a downstream position relative to the first pressing roller 31. The first pressing roller 31 comprises a shaft 32 rotatably supported by the supporting unit 50 and a pressing unit 33 formed on the shaft 32 with a predetermined thickness.
The surface hardness of the first pressing roller 31, that is, the hardness of the pressing unit 33, satisfies Equation 1. If hP is higher than hH, the shape of the fusing nip N3 which is formed by the pressure between the heating roller 25 and the first pressing roller 31 can be described as follows. The shape of the pressing unit 33 is maintained by the difference in the hardness between the heating unit 27 and the pressing unit 33. The shape of the heating unit 27, which has a comparably low hardness, is deformed.
The fusing pressing belt 40, which is rotated by the first and the second pressing rollers 31 and 35, forms the fusing nip N2 by contacting with the heating roller 25 or the supplied printable medium 10 at a part 40a. As shown in
Since the shape of the pressing unit 33 is maintained, the shape of the fusing pressing belt 40 wound on an outer surface of the pressing unit 33 remains as it is at the parts corresponding to the protruded widths W1 and W2, in an area where the fusing nip N3 is formed. The shape of the fusing pressing belt 40 is therefore not deformed in the area where the fusing nip N3 is formed and the fusing pressing belt 40 wound on the first and the second pressing rollers 31 and 35 is not loosened. As both end parts 41 of the fusing pressing belt 40, which protrude in the lengthwise direction of the first and the second pressing rollers 31 and 35, are not wrinkled or folded even at the area where the fusing nip N3 is located, damage due to wrinkling or folding thereof can be avoided.
With regard to the direction in which the printable medium 10 is supplied, the printable medium 10 may be supplied so that a surface of the printable medium, on which the transferred but not fused toner image 15 is formed, faces the heating roller 25. As the heated outer surface of the heating roller 25 contacts the toner image 15 directly, fusing efficiency may be increased. In addition, contamination of the fusing pressing belt 40 by removal of the image due to an incomplete fusion may be prevented.
As shown in
The first and the second restriction parts 61 and 71 restrict the movement of the fusing pressing belt 40 in an axial direction of the first and the second pressing rollers 31 and 35. The first and the second contacting parts 65 and 75 extend from the first and the second restriction unit 61 and 71, respectively, toward the fusing pressing belt 40, and contact an inner plate surface of the fusing pressing belt 40.
The first contacting unit 65 is formed to be inclined so that the shape of the first contacting unit 65 may become gradually smaller from the first restriction unit 61 to the protruded end part of the first contacting unit 65. The first contacting unit 65 may have the appearance of a truncated cone. An inclination angle θ of the first contacting unit 65 may satisfy the condition of Equation 2.
0°<θ≦10° (Equation 2)
The lower limit value of Equation 2 is the minimum condition for the first contacting unit 65 to be formed to be inclined. If the upper limit value is exceeded, bending is increased at an inclination start position of the fusing pressing belt 40 that is wound on the first contacting unit 65, and the fusing pressing belt 40 may be damaged. As a bias force F2 according to the inclination increases as described below, the fusing pressing belt 40 may be biasing against a desired bias toward the first contacting unit 65. The inclination angle θ may be equal to or less than 3° considering that the inclination angle θ exceeds the upper limit value.
The second contacting unit 75 is formed so that a surface of the second contacting unit 75 in contact with the fusing pressing belt 40 can be perpendicular to a restriction surface of the first restriction unit 71.
A major diameter D, of the first contacting unit 65 and a major diameter D2 of the second contacting unit 75 may satisfy Equation 3 as follows.
D1>D2 (Equation 3)
If the major diameter D1 of the first contacting unit 65 is larger than the major diameter D2 of the second contacting unit 75, the fusing pressing belt 40, while rotating, receives a force in a direction of an arrow F1 in
A wearing prevention plate 80 may be further provided between the first restriction unit 61 and the fusing pressing belt 40. The wearing prevention plate 80 may be inserted in the first contacting unit 65 and contacts a lateral surface of the fusing pressing belt 40, which biases toward the first supporting member 60, to guide the rotation of the fusing pressing belt 40. The wearing prevention plate 80 may be made of a material having a low coefficient of friction, so that damage to the fusing pressing belt 40, which contacts with the wearing prevention plate 80, may be prevented.
The wearing prevention plate 80 may be made of a conductive material having a high electric conductivity. The fusing pressing belt 40 may be continuously in contact with the wearing prevention plate 80 by the biasing force corresponding to the difference between F1 and F2 in order to be grounded. This may improve the electrical safety of the fusing pressing belt 40.
The plurality of the pressing rollers may comprise a first pressing roller 31 and a second pressing roller 35. The first pressing roller 31 is placed at an upstream position along a direction in which the supplied printable medium 10 advances. The second pressing roller 35 is placed at a downstream position relative to the first pressing roller 31. The first pressing roller 31 comprises a shaft 32 rotatably supported by the supporting unit 50 and a pressing unit 33′ formed at a circumference of the shaft 32 with a predetermined thickness.
The fusing pressing belt 40, which is provided to be rotated by the first and the second pressing rollers 31 and 35, forms a fusing nip N2′ by contacting the heating roller 25 or the supplied printable medium 10 at a part 40b. As the hardness of the heating unit 27′ is the same as that of the pressing unit 33′, a fusing nip N3′, formed between the heating roller 25 and the first pressing roller 31, has a shape of a straight line. Since the fusing pressing belt 40 has the shape of a straight line in an area where the fusing nip N3′ is formed, the fusing pressing belt 40 is prevented from loosening. Therefore, the problem that a conventional fusing pressing belt is damage due to wrinkling or folding can be avoided.
Components other than the components described in connection with
The cabinet 110 forms an outer appearance of the image forming apparatus and has a discharging unit 111 at the outer surface to stack the discharged printable medium 10. A supplying unit 120 to load the printable medium 10 to be supplied is detachably provided in the cabinet 110. The printable medium 10, which is supplied by the supplying unit 120, is supplied through a conveying path toward the developing unit 150. The supplying unit 120 is provided in the cabinet 110. The supplying unit 120 picks up a sheet of the loaded printable medium 10 by rotation of a feeding roller 125, and supplies the picked-up printable medium 10 through a conveying roller 127.
The photosensitive medium 130 is provided in the developing unit 150. The photosensitive medium 130 responds to a beam scanned by the light scanning unit 140 to form an electrostatic latent image on the outer surface of the photosensitive medium 130. The developing unit 150 comprises a toner container 151 accommodating a toner T, a developing roller 155 placed opposite to the photosensitive medium 130 to develop the toner for an area of the photosensitive medium 130 where the electrostatic latent image is formed, a supplying roller 156 to supply the developing roller 155 with the toner T, and a charger 157 to charge the photosensitive medium 130 to a predetermined electric potential. A cleaning blade 159 may be further provided to remove a waste toner remaining on the photosensitive medium 130.
The developing unit 150 and the photosensitive medium 130 are provided for each color to form a full color image by a single path type.
The light scanning unit 140 scans a beam onto each of the plurality of photosensitive media 130 to form electrostatic latent images. The light scanning unit 140 has a multi-beam light scanning structure to scan beams onto a plurality of photosensitive media 130 simultaneously. The light scanning unit 140 comprises a light source (not shown), a beam deflector 141 to deflect and scan a beam applied by the light source, and an f-θ lens 145 to image the light deflected and scanned by the beam deflector 141 onto a scanning surface. The light source may have a structure where a plurality of emitting points is provided, or a structure where a plurality of semiconductors device having a single emitting point respectively is provided for each color. As shown in
The transfer unit 160 is positioned opposite the photosensitive medium 130 to have the printable medium 10 conveyed through the conveying path between the transfer unit 160 and the photosensitive medium 130. The transfer unit 160 transfers the toner image 15 formed on the photosensitive medium 130 onto the supplied printable medium 10. The transfer unit 160 comprises a transfer belt 161 and a transfer backup roller 163 that are positioned opposite the plurality of photosensitive media 130. The image that has been transferred onto the printable medium 10 by the transfer unit 160 is fused by the fusing unit 170.
The fusing unit 170 comprises a heat source 171, a heating roller 173, a plurality of pressing rollers 175, and a fusing pressing belt 177. The surface of the heating roller 173 is heated by the heat source 171. The toner image 15 transferred onto the printable medium 10 is fused by pressure between the pressing roller 175 and the fusing pressing belt 177.
The structure and an operation of the fusing unit 170 are substantially the same as those of the fusing unit according to the first or the second embodiment of the present invention.
As described above, according to aspects of the present invention, deformation of the shape of the fusing pressing belt in the area where the fusing nip N3 is formed can be reduced by making the pressing roller have a surface hardness equal to or greater than the surface hardness of the heating roller, so that wrinkling or folding of the fusing pressing belt may be reduced. Damage due to wrinkling or folding can therefore be avoided.
The belt bias of the fusing pressing belt is guided in one direction and the friction preventing structure is provided in the direction of the belt bias of the fusing pressing belt, so that damage to the fusing pressing belt can be prevented.
According to aspects of the present invention, a uniform fusibility can be obtained using the fusing unit described above, so that printing quality can be enhanced. Especially, if the fusing unit according to aspects of the present invention is used in the electrophotographic image forming apparatus of the tandem type where a wide fusing nip is required compared to a monochromatic electrophotographic image forming apparatus, fusion stability may be highly enhanced.
Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-109410 | Nov 2006 | KR | national |
