Image forming apparatus

An image forming apparatus includes an image forming device that forms an image on a recording medium with a powdery material, the image being sized so as to extend beyond an edge of the recording medium; a collecting device that collects the material that has extended off the recording medium as a result of the image forming device forming the image; and a restricting unit that controls the image forming device in such a manner that the image forming device reduces an amount of use of the material in a region of the image that extends off the recording medium to a larger degree on an outer side of the image than a side of the image near the recording medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2014-152699 filed Jul. 28, 2014.

BACKGROUND

(i) Technical Field

The present invention relates to image forming apparatuses.

(ii) Related Art

Frameless images, which are images extended up to the edge of a print sheet, are known.

SUMMARY

According to an aspect of the invention, an image forming apparatus includes an image forming device that forms an image on a recording medium with a powdery material, the image being sized so as to extend beyond an edge of the recording medium; a collecting device that collects the material that has extended off the recording medium as a result of the image forming device forming the image; and a restricting unit that controls the image forming device in such a manner that the image forming device reduces an amount of use of the material in a region of the image that extends off the recording medium to a larger degree on an outer side of the image than a side of the image near the recording medium.

DETAILED DESCRIPTION

A developing device and an image forming apparatus according to exemplary embodiments of the invention are described below referring to the drawings.

FIG. 1is a schematic diagram of the configuration of a printer corresponding to an image forming apparatus according to a first exemplary embodiment.

An image forming apparatus1illustrated inFIG. 1, is a tandem color printer including image forming units10Y,10M,10C, and10K corresponding to yellow (Y), magenta (M), cyan (C), and black (K) arranged parallel with one another. The image forming apparatus1prints single-color images as well as full-color images containing four-color toner images. The image forming apparatus1also includes an optional image forming unit10P arranged parallel with the YMCK image forming units10Y,10M,10C, and10K and at the upstream most position of all the image forming units. The optional image forming unit10P is used to express a color other than YMCK colors, such as white, gold, or transparent, so that the image is capable of expressing various distinctions including granularity, fine quality, contrast enhancement, or embossing effect. In this embodiment, the optional image forming unit10P is used to express “transparency” (and colorlessness).

The image forming apparatus1includes toner cartridges18Y,18M,18C,18K, and18P that accommodate toner of YMCK colors and the color corresponding to the optional image forming unit10P.

The four image forming units10Y,10M,10C, and10K and the optional image forming unit10P have the same configuration apart from developers accommodated therein. Thus, the image forming unit10Y corresponding to yellow is described as a typical example. When image forming units or their components are collectively described below, alphabets appended to the reference numerals of the image forming units or their components are omitted regardless of color and the image forming units are simply referred to as, for example, image forming units10.

The image forming unit10Y includes a photoconductor11Y, a charging device12Y, an exposing device13Y, a developing device14Y, a first transfer device15Y, and a photoconductor cleaner16Y.

The photoconductor11Y rotates in the direction A illustrated inFIG. 1. The charging device12Y, the exposing device13Y, the developing device14Y, the first transfer device15Y, and the photoconductor cleaner16Y are arranged in this order around the photoconductor11Y.

The charging device12Y charges the surface of the photoconductor11Y. The exposing device13Y exposes the surface of the photoconductor11Y to light on the basis of an image signal supplied from an image processor100to form an electrostatic latent image. The developing device14Y develops the latent image on the surface of the photoconductor11Y using a developer containing toner into a toner image. The developing device14Y is supplied by the toner cartridge18Y with an amount of toner suitable for consumption. The first transfer device15Y electrostatically transfers the toner image on the photoconductor11Y to an intermediate transfer belt30. The photoconductor cleaner16Y includes a cleaning blade that comes into contact with and rubs against the surface of the photoconductor11Y to clean the surface of the photoconductor11Y after the transfer.

The image forming apparatus1includes an intermediate transfer belt30, a fixing device60, a sheet transporting unit80, and an image processor100. The intermediate transfer belt30is wound around belt support rollers31to35and rotationally moves in the direction of the arrow B so as to pass by the optional image forming unit10P, the image forming units10Y,10M,10C, and10K, and a second transfer device50. Toner images of the respective colors from the optional image forming unit10P and the image forming units10Y,10M,10C, and10K are transferred to the intermediate transfer belt30so as to be superposed on one another. The intermediate transfer belt30moves while carrying a color toner image formed of these superposed color toner images. The second transfer device50has a structure in which a polyimide tube covers a roller made of expanded rubber. The second transfer device50electrostatically transfers the toner image on the intermediate transfer belt30to a sheet.

A combination of the four image forming units10Y,10M,10C, and10K, the optional image forming unit10P, the intermediate transfer belt30, the second transfer device50, and the fixing device60corresponds to an example of an image forming device according to an exemplary embodiment of the invention and toner corresponds to an example of a powdery material according to an exemplary embodiment of the invention.

A belt cleaner70has a blade, which is brought into contact with the intermediate transfer belt30to scrape the toner off the surface of the intermediate transfer belt30. The second transfer device50also includes a transfer-device cleaner51that has a blade, which is brought into contact with the surface of the second transfer device50to scrape the toner off the surface.

The fixing device60fixes toner onto a sheet. The fixing device60includes a heating roller61and a pressing roller62. The heating roller61includes a heating device installed therein. The heating roller61and the pressing roller62causes a sheet carrying an unfixed toner image to pass therethrough to fix a toner image onto the sheet while squeezing the sheet from both sides. The fixing device60also includes fixing-device cleaners63and64, which remove toner from the surfaces of the heating roller61and the pressing roller62, respectively.

The transfer-device cleaner51and the fixing-device cleaners63and64correspond to examples of a collecting device according to an exemplary embodiment of the present invention.

The sheet transporting unit80transports sheets along a sheet transport path TP along which the sheets pass by the second transfer device50and the fixing device60. The sheet transporting unit80picks up sheets contained in a sheet container SC using a pick-up roller81, transports the sheets using transport rollers82, and feeds the sheets to the second transfer device50using registration rollers84. The sheet transporting unit80also ejects the sheets to the outside using ejection rollers86.

The image processor100processes data of an original image captured from a device such as an external personal computer or a scanner to generate image signals for respective colors and transfers the respective image signals to the image forming units10of the corresponding colors. For generating image signals corresponding to respective colors, the image processor100executes screen processing to reproduce a halftone image with dots. Upon receipt of an instruction from a user through a user interface, not illustrated, the image processor100executes processing such as removal of a background color or frameless printing for forming an image so sized as to fully expand throughout the entire sheet.

In the frameless printing, the image forming unit10forms a toner image having a size slightly larger than the sheet size. Thus, the edge portion of the toner image extends off the sheet and the toner in the edge portion is later collected by the transfer-device cleaner51or the fixing-device cleaners63and64. The amount of toner collected in the frameless printing is larger than the amount of toner collected in normal printing other than the frameless printing. The amount of toner collectable by collecting devices such as the transfer-device cleaner51or the fixing-device cleaners63and64is limited. When the amount of the collected toner arrives at the upper limit, the life of the image forming apparatus1is exhausted and the image forming apparatus1requires recovery operations such as maintenance. In other words, frameless printing shortens the life of the image forming apparatus1compared to normal printing. Moreover, if the amount of toner that extends off a sheet is large, some amount of toner may adhere to the edge of the sheet due to melting while being fixed and cause matter protruding from the edge of the sheet, impairing the appearance of the edge. For the purposes of preventing shortening of the apparatus life caused by frameless printing or for other purposes, the image forming apparatus1according to the embodiment reduces the amount of collected toner. Now, the function of reducing the amount of collected toner is described below.

FIG. 2is a functional block diagram illustrating the functions of an image processor at the time of frameless printing.

As a functional structure at the time of frameless printing, the image processor100includes an enlarging/shrinking unit110and a toner-amount restricting unit120.

The enlarging/shrinking unit110converts an original image to an image having a size slightly larger than a sheet size by enlarging or reducing the size of the original image. Here, the “size slightly larger than a sheet size” in this embodiment is a size that allows for misalignment of the toner image and the sheet that may be caused by, for example, sheet transport errors or toner-image transfer errors occurring in the sheet transporting unit80. This size is the minimum size that allows the edge portion of the sheet to be prevented from remaining white even when the toner image and the sheet are misaligned with each other.

The toner-amount restricting unit120restricts the amount of use of toner at an outer edge portion of the toner image. The toner-amount restricting unit120corresponds to an example of a restricting unit according to an exemplary embodiment of the invention.

FIG. 3is a schematic diagram illustrating restriction of the amount of use of toner imposed by the toner-amount restricting unit.

InFIG. 3, for convenience of illustration, probable misalignment of a toner image T and a sheet P is exaggeratingly drawn.

As described above, the size of the toner image T is larger than the size of the sheet P so that the entire surface of the sheet T is covered by the toner image T even in the case where the toner image T is misaligned with respect to the sheet P. In other words, the size of the toner image T is restricted to such a degree that the edge of the toner image T is positioned just within the edge of the sheet P when the toner image T and the sheet P have maximum misalignment.

An outer edge portion of the toner image T includes a toner-amount restricted region R, in which a toner image is formed at a density calculated by multiplying the image density of the original image by a toner use rate. The toner use rate in a region inward of the toner-amount restricted region R is 100%, which means that the amount of use of toner is not restricted at all in this region. In other words, the toner image is formed at the image density corresponding to the data of the original image.

The toner use rate in the toner-amount restricted region R linearly changes from 100% at the innermost edge of the toner-amount restricted region R to 0% at the outermost edge of the toner-amount restricted region R. In other words, the restriction on the amount of use of toner is increasingly tightened toward the outer edge of the toner-amount restricted region R. Thus, the amount of toner that has failed to be transferred to the sheet P among the toner forming the entire toner image T and that is then collected is reduced, and the reduction of the amount of toner enables minimization of shortening of the apparatus life. The toner that has failed to be transferred to the sheet P is reworded as toner left off the sheet P or toner falling out of the sheet P and includes toner that has been transferred to a portion out of the sheet at the transfer operation and toner that has flowed out of the sheet as a result of melting at the fixing operation.

In the exemplary embodiment, the restriction on the amount of use of toner is linearly tightened in view of the image density. Thus, the color or other characteristics of the image inside the toner-amount restricted region R is natural and the appearance of the image is not impaired.

On the bottom and the right ofFIG. 3, cross-sectional diagrams schematically expressing the restriction on the amount of use using the thickness of the toner image T are shown. The cross-sectional diagram taken along the direction of the arrow inFIG. 3in which the sheet is transported is shown on the right and the cross-sectional diagram taken along the direction perpendicular to the direction in which the sheet is transported is shown on the bottom. The thickness of the toner image T illustrated in the cross-sectional diagrams is zero at both ends of the toner image T and largest at the position corresponding to the innermost edge of the toner-amount restricted region R. The thickness of an actual toner image is also dependent on the image density. The thickness of the toner image T illustrated inFIG. 3corresponds to the thickness in the case of a solid image.

In this embodiment, the toner-amount restricted region R includes an outer region ROUT extending off the sheet P and an inner region RIN extending within the sheet P. Since the restriction on the amount of use of toner is imposed also on the inner region RIN, the amount of toner collected after having failed to be transferred to the sheet P is reduced compared to the case where restriction on the amount of use of toner is only imposed on the outer region ROUT. Thus, shortening of the apparatus life is minimized.

The restriction on the amount of use in the inner region RIN, which is located on the leading side of the sheet P in the direction in which the sheet P is transported, facilitates separation of the sheet P when the sheet P passes through the fixing device60illustrated inFIG. 1.

In this embodiment, restriction on the amount of use of toner is tighter in first regions R1, extending on both sides of the edges of the sheet P in the transportation direction, than in second regions R2, extending on both sides of the edges of the sheet P in the width direction perpendicular to the transportation direction. Specifically, the distance between the innermost edge of each first region R1and the edge of the sheet P in the first region R1is longer than the distance between the innermost edge of each second region R2and the edge of the sheet P in the second region R2. Thus, each first region R1is larger than each second region R2and restriction on the amount of use of toner is tighter in the first regions R1than in the second regions R2. This is because, since the degree of misalignment of the sheet P and the toner image T in the transportation direction is larger than that in the width direction, the toner image T is sized so as to extend off the sheet P to a larger degree in the transportation direction that in the width direction, so that the amount of toner that fails to be transferred to the sheet P is larger in a portion extending in the transportation direction than in a portion extending in the width direction. For convenience of illustration,FIG. 3only shows one of the first regions R1and one of the second regions R2of the sheet P, but actually, the first regions R1are located on opposing sides of the sheet P and the second regions R2are located on opposing sides of the sheet P.

The image forming apparatus according to an exemplary embodiment of the invention may be structured so as to, for example, restrict only the amount of use of “transparent” (and colorless) toner, corresponding to the optional image forming unit10P, but not to restrict the amount of use of YMCK color toners. However, the image forming apparatus1according to the exemplary embodiment restricts both amounts of use of colorless and color toner. Nevertheless, the degree of restriction imposed on colorless toner and that on color toner are different from each other.

FIG. 4is a schematic diagram illustrating the restriction on the amount of use of “transparent” toner andFIG. 5is a schematic diagram illustrating the restriction on the amount of use of color toner.

FIG. 4schematically illustrates the state of a toner layer TP of “transparent” toner formed on the sheet P viewed from one side of the sheet P.FIG. 5schematically illustrates the state where a toner layer TKCMY of color toner formed on the sheet P viewed from one side of the sheet P. Actually, the toner layer TKCMY of color toner and the toner layer TP of “transparent” toner are superposed. However, for convenience of illustration, the toner layers TP and TKCMY are separately illustrated inFIGS. 4 and 5.

Both of the toner layer TP of “transparent” toner and the toner layer TKCMY of color toner are so sized as to extend beyond the edge of the sheet P. The outer edges of these toner layers TP and TKCMY are positioned at the outer edge of the range covering the maximum misalignment of the sheet P and the toner layers TP and TKCMY.

The degree of restriction on the amount of “transparent” toner in the toner layer TP is continuously tightened from a portion inward of the edge of the sheet P to the outer edge of the toner layer TP. Since the “transparent” toner is used for the purpose of exerting a glossy effect on the image, the “transparent” toner is formed in a solid form so as to cover the entire image. Thus, reduction of the amount of collected “transparent” toner contributes to minimization of shortening of the apparatus life to a large degree. In addition, the restriction on the amount of “transparent” toner from the portion inward of the edge of the sheet P negligibly affects the appearance of the image.

On the other hand, the degree of restriction on the amount of color toner in the toner layer TKCMY in the exemplary embodiment is continuously tightened from the edge of the sheet P to the outer edge of the toner layer TKCMY. Since the toner layer TKCMY of color toner naturally carries a visible toner image itself, excessively restricting the amount of color toner may affect the appearance of the image. Thus, in the exemplary embodiment, the degree of restriction on the amount of color toner in the toner layer TKCMY is made smaller than the degree of restriction on the amount of “transparent” toner in the toner layer TP. Such restriction contributes to minimization of shortening of the apparatus life and minimizes an adverse effect on the appearance of the image.

The exemplary embodiment has described, as a preferable example, an example in which the degree of restriction on the amount of use of color toner is different from the degree of restriction on the amount of use of “transparent” toner. However, an image forming apparatus according an exemplary embodiment of the invention may restrict the amount of use of color toner and the amount of use of “transparent” toner to the same degree.

This exemplary embodiment has described, as a preferable example, an example in which the degree of restriction on the amount of use of toner in the first region R1illustrated inFIG. 3is different from the degree of restriction on the amount of use of toner in the second region R2illustrated inFIG. 3. However, an image forming apparatus according to an exemplary embodiment of the invention may restrict the amount of use of toner in the first region R1and the amount of use of toner in the second region R2to the same degree.

The exemplary embodiment has described, as a preferable example, an example in which the amount of use of toner is restricted in both of the inner region RIN and the outer region ROUT illustrated inFIG. 3. However, an image forming apparatus according to an exemplary embodiment of the invention may restrict the amount of use of toner only in the outer region ROUT.

The description has provided a printer as an example of the image forming apparatus according to the exemplary embodiment. However, an image forming apparatus according to an exemplary embodiment of the invention may be, for example, a copying machine or a multifunctional machine.

The description has provided a tandem color printer as an example of the image forming apparatus according to the exemplary embodiment. However, an image forming apparatus of the invention may be a revolver color printer or a black-and-white printer.

The description has provided an indirect transfer apparatus including an intermediate transfer belt as an example of the image forming apparatus according to the exemplary embodiment. However, an image forming apparatus according to an exemplary embodiment of the invention may be a direct transfer apparatus that directly transfers a toner image from image forming units of different colors onto a sheet.