Image transfer device, image forming apparatus having the image transfer device, and method of measuring resistance of a printing medium or an endless track belt of the image forming apparatus

An image transfer device to accurately measure a resistance of a printing medium or a transfer belt, an image forming apparatus having the image transfer device, and a method of measuring the resistance of the printing medium. The image transfer device includes a conveyance unit, to which a reference voltage or current is applied, and which includes a first roller having variations of resistance along a circumferential direction, and a second roller to support the first roller, a transfer roller spaced apart from the first roller by a distance corresponding to at least the circumference of the first roller to transfer a developer agent of a photosensitive drum onto a printing medium, and a controller to measure resistance of the printing medium by detecting electric current or voltage difference between the first and the second rollers, and to supply the transfer roller with a transfer voltage or a current according to the detected resistance of the printing medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2006-88607 filed on Sep. 13, 2006, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to an image transfer device of an image forming apparatus. More particularly, the present general inventive concept relates to an image transfer device which accurately measures a resistance of a printing medium or an endless track belt, and an image forming apparatus having the same.

2. Description of the Related Art

A conventional laser beam printer includes an image forming means such as a paper cassette, a developing device and a fuser, and carries out a printing operation by attracting toner onto a paper sheet.

The operation of a laser beam printer can be mainly categorized into charging, writing, developing, transferring, and fusing. When charging, a charger is energized to a high voltage of approximately 7000V and forms a minus (−) charge on the surface of a photoconductor drum by a Corona discharge. When writing, a laser beam scans the surface of the photoconductor drum bearing the (−) charge so that a desired electrostatic latent image is formed according to the (−) charge pattern. When developing, a developing roller and photoconductor drum are rotated in intimate contact with each other so that toner particles of the (−) charge are attracted onto the electrostatic latent parts. When transferring, a transfer device is energized to a predetermined voltage and the other side of the paper sheet has a (+) charge so that toner particles of the (−) charge are attracted onto a paper sheet when the paper sheet is passed between the photoconductor drum and the transfer device. When fusing, the toner image is fixed into the paper sheet by appropriate heat and pressure. Accordingly, the paper sheet bearing the final image is released.

Meanwhile, each type of printing medium has a different resistance depending on the thickness, wetness, or quality, and the printing quality heavily depends on the resistance. An endless track belt also has a resistance which varies depending on manufacturing processes or use.

To prevent image quality degradation, a conventional image forming apparatus includes a roller which is connected with a resistance measuring circuit, so that a resistance of a paper sheet or an endless track belt can be measured and an associated transfer voltage can be transmitted to the transfer roller before an image transfer.

However, because there are different types of materials included in an inner side of a resistance measuring roller, resistance of the resistance measuring roller varies in the circumferential direction. A conventional image forming apparatus fails to reflect a potential varying resistance of the paper sheet or the endless track belt, because the interval between the resistance measuring roller and the transfer roller is shorter than the circumference of the resistance measuring roller, which means that the varying resistance in the circumferential direction of the resistance measuring roller is not completely considered.

SUMMARY OF THE INVENTION

The present general inventive concept provides a transfer device of an image forming apparatus, which measures a resistance of a printing medium accurately by reflecting a varying resistance in a circumferential direction of a resistance measuring roller.

The present general inventive concept also provides an image forming apparatus including a transfer device which measures the resistance of the printing medium with accuracy.

The present general inventive concept also provides a method of measuring the resistance of printing medium with accuracy.

The foregoing and/or other aspects and utilities of the present general inventive concept are achieved by providing an image transfer device of an image forming apparatus including a conveyance unit, to which a reference voltage or current is applied, and which includes a first roller and a second roller to support the first roller, a transfer roller spaced apart from the first roller by a distance corresponding to at least the circumference of the first roller to transfer a developer agent of a photosensitive drum onto a printing medium, and a controller to measure a resistance of the printing medium by detecting electric current or voltage difference between the first and the second rollers, and to supply the transfer roller with a transfer voltage or current according to the detected resistance of the printing medium.

The first roller may have variations of resistance along a circumferential direction. The first roller may be made of a conductive rubber. The second roller may be made of metal.

The controller may measure the resistance of the printing medium by incorporating at least once the variations of resistance in the circumferential direction of the first roller. The controller may obtain the resistance of the printing medium by dividing the reference voltage during at least one rotation by a current flowing through first and the second rollers.

The controller may obtain the resistance of the printing medium by dividing the reference voltage during at least one rotation of the first roller by a voltage between the first and the second rollers.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image transfer device of an image forming apparatus, including a printing medium conveyance belt to run in an endless track with an exterior surface in a contact with as plurality of photosensitive drums and to convey a printing medium, a first and a second roller which supports the first roller, wherein a reference voltage or a current is received between the first and the second rollers, a plurality of transfer rollers which include a first transfer roller formed next to the first roller in the direction of conveyance by a distance which corresponds to at least a circumference of the first roller, the transfer rollers disposed in tandem with the photosensitive drums wherein the printing medium conveyance belt is interposed between the transfer rollers and the photosensitive drums, and a controller to detect a current or a voltage difference between the first and second rollers to measure resistance of the printing medium, and to supply the transfer roller with a transfer voltage or a current according to the measured resistance of the printing medium.

The first roller may have variations of resistance along a circumferential direction.

The first roller may include a printing medium moving roller to move the printing medium onto the printing medium conveyance belt. The printing medium moving roller may be made of a conductive rubber.

The second roller may be made of metal.

The controller may measure the resistance of the printing medium by incorporating at least once the variations of resistance in the circumferential direction of the first roller.

The controller may obtain the resistance of the printing medium by dividing a reference voltage during at least one rotation by an average current of the currents flowing through the first and the second rollers.

The controller may obtain the resistance of the printing medium by dividing a reference current during at least one rotation by a voltage between the first and the second rollers.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image transfer device of an image forming apparatus, including an endless track belt which includes a first roller and a second roller to support the first roller, wherein a reference voltage, or current is received between the first and the second rollers, a transfer roller spaced apart from the first roller by a distance corresponding to at least the circumference of the first roller to transfer a developer agent of a photosensitive drum onto the endless track belt, and a controller to measure a resistance between the first and the second rollers by detecting an electric current or a voltage difference between the first and the second rollers, and to supply the transfer roller with a transfer voltage or a current according to the detected resistance.

The first roller may have variations of resistance along a circumferential direction.

The first roller or the second roller may be made of conductive rubber or metal.

The controller may measure the resistance between the first and the second rollers, by at least once incorporating variations of resistance in the circumferential direction of the first roller.

The controller may obtain the resistance between the first and the second rollers by dividing a reference voltage by a current flowing through the first and the second rollers during at least one rotation.

The controller may obtain the resistance between the first and the second rollers by dividing a reference voltage during at least one rotation by a voltage between the first and the second rollers.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image forming apparatus, including a printing medium feeding device which picks up a printing medium and feeds the picked up printing medium to a conveyance path, a developing unit which develops an electrostatic latent image by attaching a developer agent onto the electrostatic latent image, one of the aforementioned image transfer devices, and a fusing device which fixes a developed image in the printing medium.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of measuring a resistance of a printing medium of an image forming apparatus, including supplying a reference voltage, or current to a first roller, detecting an average resistance of the first roller and a second roller which supports the first roller during at least one rotation of the first roller, detecting an average resistance between the first and the second rollers when the printing medium is passed between the first and the second rollers, during at least one rotation of the first roller, and obtaining a resistance of the printing medium by subtracting the average resistance of the first and the second rollers from the average resistance between the first and the second rollers.

The first roller may have variations of resistance along a circumferential direction.

The obtaining the average resistance between the first and the second rollers may include measuring electric currents between the first and the second rollers during at least one rotation of the first roller, and obtaining the resistance of the printing medium by applying Ohm's law to the average of the currents and the reference voltage.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of measuring a resistance of an endless track belt of an image forming apparatus, including supplying a reference voltage, or current to a first roller, detecting a resistance of the first roller and a second roller which supports the first roller during at least one rotation of the first roller, positioning the endless track belt between the first and the second rollers and detecting a resistance between the first and the second rollers during at least one rotation of the first roller, and obtaining a resistance of the endless track belt by subtracting the average resistance of the first and the second rollers from the average resistance between the first and the second rollers.

The first roller may have variations of resistance along a circumferential direction.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image transfer device of an image forming apparatus, including a photosensitive drum on which an electrostatic latent image is formed, a transfer roller arranged in tandem with the photosensitive drum to convey a printing medium therebetween and to transfer developer onto the printing medium, a moving roller to move the printing medium to a position to be simultaneously conveyed by the photosensitive drum and the transfer roller after the moving roller completes at least one full rotation while maintaining contact with the printing medium, and a resistance measuring circuit to measure a total resistance of the printing medium after the at least one full rotation of the moving roller and to supply the transfer roller with a transfer voltage or current according to the measured resistance of the printing medium.

The total resistance of the printing medium may be measured by subtracting an average resistance of the moving roller during a first full rotation of the moving roller from an average resistance of the moving roller during a second full rotation of the moving roller.

The printing medium may be moved by the moving roller after the first full rotation.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of an image forming apparatus, the method including moving a printing medium from a moving roller to a position to be simultaneously conveyed by a photosensitive drum and a transfer roller after the moving roller completes at least one full rotation while maintaining contact with the printing medium, measuring a total resistance of the printing medium after the at least one full rotation of the moving roller, and supplying the transfer roller with a transfer voltage or current according to the measured resistance of the printing medium.

The total resistance of the printing medium may be measured by subtracting an average resistance of the moving roller during a first full rotation of the moving roller from an average resistance of the moving roller during a second full rotation of the moving roller.

The printing medium may be moved by the moving roller after the first full rotation.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image transfer device of an image forming apparatus, including a feeding unit to feed a printing medium to be positioned between a photosensitive drum and a transfer roller, and a circuit to measure a resistance of the printing medium during an entire feeding of the printing medium, and to supply the transfer roller with a transfer voltage or current according to the measured resistance of the printing medium.

The entire feeding of the printing medium may include a time period during which a leading end of the printing medium enters the feeding unit and a trailing end exits the feeding unit.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of an image forming apparatus, including feeding a printing medium through a feeding device to position the printing medium between a photosensitive drum and a transfer roller, measuring a resistance of the printing medium during an entire feeding of the printing medium, and supplying the transfer roller with a transfer voltage or current according to the measured resistance of the printing medium.

The entire feeding of the printing medium may include a time period during which a leading end of the printing medium enters the feeding unit and a trailing end exits the feeding unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a schematic view illustrating a tandem type image forming apparatus according to an exemplary embodiment of the present general inventive concept.

Referring toFIG. 1, an image forming apparatus1may include a printing medium feeding unit2, to feed a printing medium such as, for example, paper, four toner image forming units3M,3C,3Y,3B, four transfer rollers4a,4b,4c,4d, a conveyance belt16to circulate a printing medium P along the transfer rollers4a,4b,4c,4d, and a fusing unit14.

The toner image forming units3M,3C,3Y,3B may form magenta (M), cyan (C), yellow (Y) and black (B) toner images, respectively, and each of the toner image forming units3M,3C,3Y,3B may include a laser scanning unit (not illustrated) to emit a laser beam, a photoconductor drum6which is charged by a charging roller5and on which an electrostatic latent image is written by the laser beam, a developing roller7to apply a developing agent onto the photoconductor drum6, and a photoconductor drum cleaner8.

The transfer rollers4a,4b,4c,4dare arranged in tandem with the photoconductor drums6, respectively, and transfer the toner images of the photoconductor drums6onto a printing medium P. The conveyance belt16circulates along the transfer rollers4a,4b,4c,4d, and is supported by a second roller9, a driven roller10, a first tension roller11, and a second tension roller12. A first roller15is supported by the second roller9, and positioned at the front side of the conveyance belt16. A cleaner13is installed on one side of the endless track belt16to remove and collect waste remaining on the conveyance belt16. The first roller15may be implemented as a printing medium moving roller to move the printing medium P onto the conveyance belt16, and the second roller9may be implemented as a supporting roller to support the first roller15.

The fusing unit14may include a plurality of rollers to thermally fuse the toner image in the printing medium P which is conveyed along the conveyance belt16.

The first roller15may be made of conductive rubber material, and thus may include variations of resistance in a circumferential direction. The second roller9is formed on the inner portion of the conveyance belt16in a location corresponding to the first roller15, to move the printing medium P between the first roller15and the conveyance belt16.

The second roller9may be made of metal material, and thus may include negligible variations of resistance. A resistance between the first roller15and the second roller may be calculated by sending a reference voltage or a reference current to the first roller15, measuring a current at the second roller9which supports the first roller15, or measuring a voltage between the first roller15and the second roller9, and applying Ohm's law.

A distance d1between the first roller15and the first transfer roller4a, which is located next to the first roller15in the direction of printing medium conveyance, is longer than a length (2πr1, where r1is a radius of the first roller15) of an outer circumference of the first roller15(i.e., d1≧2πr1).

Accordingly, a resistance of the printing medium P is calculated by applying all the variations in resistance along the outer circumference of the first roller15during one rotation of the first roller15to the printing medium P. As a result, an appropriate transfer voltage or current can be applied to the transfer rollers4a,4b,4c,4d.

FIG. 2illustrates a constant-voltage type resistance measuring circuit of the transfer device ofFIG. 1, according to an exemplary embodiment of the present general inventive concept.

Referring toFIG. 2, a resistance measuring circuit30may include a Vp generating unit31to supply a reference voltage Vp between the first roller15and the second roller9, a current/voltage detecting unit32to measure an electric current flowing through the second roller9, or to measure a voltage or a resistance of the second roller9, a controller33to measure a resistance of the printing medium P, and a Vo generating unit34to supply a transfer voltage Vo to the transfer rollers4a,4b,4c,4d.

When the printing medium P is passed between the first roller15and second roller9, a current value or a voltage difference is generated in a proportion or an inverse proportion to the resistance of the printing medium P. The generated value may be variable according to the variations of resistance in the circumferential direction of the rotating first roller15.

Referring to the transfer device ofFIGS. 1 and 2,FIG. 3is a graphical representation of the electric current value flowing through the first roller15and the second roller9ofFIGS. 1 and 2when the voltage Vp is supplied between the first roller15and the second roller9via the Vp generating unit31, according to an exemplary embodiment of the present general inventive concept.

Referring toFIG. 3, the detected current periodically varies according to the rotation of the first roller15, due to the variations of resistance in the circumferential direction of the first roller15. According to the Ohm's law, the resistance of the first roller15can be obtained by dividing the reference voltage Vp by an average current Im of a period T1.

A process of obtaining the resistance of the printing medium P is explained below.

A first average resistance R1of the first roller15and the second roller9may be detected during at least one rotation of the first roller15. A second average resistance R2of the first roller15and the second roller9may be obtained during at least one rotation of the first roller15, when the printing medium P is passed between the first roller15and the second roller9. A third average resistance Rp of the printing medium P may be obtained by subtracting R1from R2.

The average resistance during at least one rotation of the first roller15can be obtained by applying Ohm's law, using the average current Im of the first roller15and the second roller9and the voltage Vp.

FIG. 4illustrates an intermediate transfer type image forming apparatus according to another exemplary embodiment of the present general inventive concept.

Referring toFIG. 4, the image forming apparatus uses an endless track belt such as a transfer belt42to substitute the printing medium conveyance belt16ofFIG. 1, and additionally includes a printing medium transfer roller41on an outer side of the transfer belt42. A printing medium P is passed between the transfer belt42and the transfer roller41. Accordingly, the transfer belt42circulates in a paper feeding direction, and developer agents of respective colors are transferred onto the transfer belt42according to color electrostatic latent images as the transfer belt42runs along first to fourth transfer rollers4a,4b,4c,4d, respectively. Developed images are subsequently transferred onto the printing medium P as it passes through the printing medium transfer roller41.

Transfer voltages of the first to fourth transfer rollers4a,4b,4c,4dmay be controlled according to a resistance of the transfer belt41. A distance d1between the first roller15and the first transfer roller4amay be longer than at least the length (2π1where r1is a radius of the first roller15) of an outer circumference of the first roller15(i.e., d1≧2πr1). The resistance of the transfer belt41may be obtained by a similar process as explained above, to reflect variations of resistance of the first roller15. Accordingly, the resistance of the transfer belt41may be obtained by supplying a reference voltage between the first roller15which has resistance variations in a circumferential direction and the second roller9which supports the first roller15, detecting an average resistance R3of the first roller15and the second roller9during one rotation of the first roller15, positioning the transfer belt42between the first roller15and the second roller9, and detecting an average resistance R4between the first roller15and the second roller9during at least one rotation of the first roller15and subtracting the average resistance R3from the average resistance R4to obtain a resistance Rb of the transfer belt42.

The average resistances R3and R4can be obtained with the resistances that are measured during the at least one rotation of the first roller15. The average resistances R3and R4—may be obtained by applying Ohm's law, using an average current Im and the reference voltage Vp between the first roller15and the second roller9.

Alternatively, a constant-current type resistance measurement may be employed. A constant-current type transfer device may be configured in the same manner as the above constant-voltage type transfer device ofFIG. 4, in which the distance d1between the first roller15and the first transfer roller4anext to the first roller15in the direction of paper conveyance, is longer than at least the length of the outer circumference21πr1of the first roller15. In the constant-current type transfer device, a resistance value reflecting all the resistance variations along the outer circumference of the first roller15is obtained by sending a reference current to the first roller15in at least one rotation of the first roller15, measuring a voltage between the first roller15and the second roller9and applying Ohm's law. A resistance of a paper sheet is then calculated in the same manner as in the constant-voltage type resistant measurement, and thus an appropriate transfer voltage or transfer current is applied to the transfer rollers4a,4b,4c,4d, respectively.

The present general inventive concept will not be construed as limited to the above exemplary embodiments, and one in the art may apply the present general inventive concept to various tandem type image forming apparatus, or an image forming apparatus using a single developing cartridge.

According to the exemplary embodiments of the present general inventive concept, a resistance of a printing medium or a transfer belt can be measured with accuracy, by completely incorporating variations of resistances along a circumferential direction of a resistance measuring roller. As a result, an appropriate transfer voltage can be supplied to the transfer roller, which will subsequently improve image quality.