Image forming apparatus, image forming method, and computer readable medium having image density adjustment control

An image forming apparatus includes an image forming unit and a controller. The image forming unit forms an image on a continuous recording medium by transferring to the continuous recording medium a toner image obtained by developing a latent image formed on a photoreceptor. The controller controls the image forming unit such that an image based on image information is formed in a specific image area on the continuous recording medium, and at the same time, a specific image pattern is formed in a specific side area outside the image area on the continuous recording medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2013-187432 filed Sep. 10, 2013.

BACKGROUND

Technical Field

The present invention relates to an image forming apparatus, an image forming method, and a computer readable medium.

SUMMARY

According to an aspect of the invention, there is provided an image forming apparatus including an image forming unit and a controller. The image forming unit forms an image on a continuous recording medium by transferring to the continuous recording medium a toner image obtained by developing a latent image formed on a photoreceptor. The controller controls the image forming unit such that an image based on image information is formed in a specific image area on the continuous recording medium, and at the same time, a specific image pattern is formed in a specific side area outside the image area on the continuous recording medium.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present invention will be explained with reference to the drawings.FIG. 1is a diagram illustrating a schematic configuration of an image forming apparatus10according to this exemplary embodiment of the invention.

As illustrated inFIG. 1, the image forming apparatus10according to this exemplary embodiment includes a paper feeder12that feeds a continuous recording medium, which is, for example, paper, an image forming device14that forms an image on the continuous recording medium fed by the paper feeder12, a storage device16that stores the continuous recording medium on which an image is formed by the image forming device14, and a controller18that controls each of the paper feeder12, the image forming device14, and the storage device16.

The paper feeder12feeds long, continuous paper P as a continuous recording medium, and the storage device16stores the continuous paper P on which an image is formed by the image forming device14.

The continuous paper P is, for example, paper made of a synthetic resin such as PP (polypropylene), glassine, or high-quality paper. In general, as illustrated inFIGS. 2A,2B, and2C, so-called label paper5is used as the continuous paper P, in which a surface base material53which is arranged as an uppermost layer is adhered, via an adhesive layer52which is made of adhesive material such as glue and is arranged as an intermediate layer, onto release paper51which serves as a mount and is removed at the time of usage. Patterns and characters are printed on the surface base material53. Depending on the usage, the label paper5may, for example, be arranged as rolled paper with the surface base material53side of the label paper5being positioned as an image forming surface (outer peripheral surface) of the roll.

The paper feeder12includes a paper feed roll20which is made of the continuous paper P taken up into a roll. With a driving unit which is not illustrated, the paper feed roll20is rotationally driven, and the continuous paper P is fed into the image forming device14.

Furthermore, the storage device16includes a storage roll22which is made of the continuous paper P on which an image is formed, taken up into a roll.

The image forming device14forms an image on the continuous paper P using toners in four colors, yellow (Y), magenta (M), cyan (C), and black (K), based on image information. The image forming device14includes an image forming unit24which forms a toner image developed by toners which configure developer, an intermediate transfer unit26which carries each toner image formed by the image forming unit24and conveys the toner image to a secondary transfer location where secondary transfer of the image to the continuous paper P is eventually performed, a secondary transfer unit46in which secondary transfer of the toner image to the continuous paper P is performed at the secondary transfer location, a fixing unit28which fixes the toner image on the continuous paper P that has been subjected to secondary transfer by the secondary transfer unit46, and the like.

The image forming unit24includes four image forming parts,24Y,24M,24C, and24K dedicated to formation of toner images in yellow, magenta, cyan, and black, respectively.

The image forming unit24includes a corresponding photoconductor drum30, which is an example of a rotatable image carrier, as illustrated inFIG. 3. A charger32, an exposure part34, a developing part36, a first transfer part38, a cleaner40, and the like, each of which will be described later, are arranged around the photoconductor drum30.

The photoconductor drum30has an image holding surface including a photoconductive layer (photosensitive layer) made of photosensitive material on a peripheral surface of a grounded base in a cylindrical or a columnar shape. The photoconductor drum30is supported in such a manner that a motive power transmitted by a driving unit, which is not illustrated, allows the photoconductor drum30to rotate.

The charger32includes a contact-type charging roller32A which is arranged in contact with the photoconductor drum30, and charges the peripheral surface on the photoconductor drum30on which an image may be formed. Charging voltage is supplied to the charger32. In the case of the developing part36which performs reversal development, a voltage or current having the same polarity as the charging polarity of toner supplied from the developing part36, is supplied as the charging voltage.

The exposure part34applies light based on image information to the peripheral surface of the charged photoconductor drum30, and forms an electrostatic latent image on the peripheral surface of the photoconductor drum30.

The developing part36generates a toner image by developing an electrostatic latent image formed on the peripheral surface of the photoconductor drum30by the exposure part34, with toner of the developer of a corresponding color. Although not illustrated, the developing part36includes a development roller which conveys the developer to a developing area facing the photoconductor drum30, a stirring and conveying member, such as a screw auger, which conveys the developer to the development roller while stirring the developer, a layer-thickness regulating member which controls the amount of developer held by the development roller, and the like. In the developing part36, bias voltage for developing is applied in between the development roller and the photoconductor drum30. Furthermore, the development roller and the stirring and conveying member rotate in a specific direction by transmission of motive power from a rotation and driving unit, which is not illustrated. As a developer, for example, a two-component developer may be used, which contains a non-magnetic toner and a magnetic carrier. As illustrated inFIG. 1, the toner to be supplied to the developing part36is supplied from a toner cartridge42which stores the developer which contains toner of a corresponding color. Toner used here includes a lubricating external additive. As the lubricating external additive, spherical silica is applied here. However, other substances, such as zinc stearate, polytetrafluoroethylene (PTFE), boron nitride, or the like, may also be applied.

The first transfer part38rotates while being in contact with the peripheral surface of the photoconductor drum30. The first transfer part38functions as a contact-type transfer part including a first transfer roller38A to which first transfer voltage is supplied. By the first transfer voltage being supplied to the first transfer roller38A, a toner image of each color formed on the photoconductor drum30is transferred to the intermediate transfer unit26. As the first transfer voltage, direct current (DC) voltage having a polarity that is opposite the charging polarity of the toner is applied.

The cleaner40cleans the image holding surface of the photoconductor drum30by removing deposits such as toner remaining and adhered to the image holding surface after first transfer. In this exemplary embodiment, a blade41which is in contact with the photoconductor drum30is arranged within the cleaner40. The blade41removes deposits adhered to the peripheral surface of the photoconductor drum30.

As illustrated inFIG. 1, the intermediate transfer unit26is arranged below the image forming unit24(the image forming parts24Y,24M,24C, and24K). In this exemplary embodiment, the intermediate transfer unit26mainly includes an intermediate transfer belt44which rotates in a direction represented by an arrow A illustrated inFIG. 1while passing through a first transfer location which is between the photoconductor drum30and the first transfer part38, multiple supporting rollers26A to26C which rotatably support the intermediate transfer belt44, and the secondary transfer unit46which performs secondary transfer of a toner image on the intermediate transfer belt44to the continuous paper P. Furthermore, although not illustrated, the intermediate transfer unit26includes a belt cleaner for cleaning and removing deposits, such as toner or paper dust, adhered to and remaining on the outer peripheral surface of the intermediate transfer belt44after passing through the secondary transfer unit46.

As the intermediate transfer belt44, an endless belt made of materials in which a resistance adjusting agent, such as carbon black, is dispersed within a synthetic resin, such as a polyimide resin or a polyamide resin, is used. Furthermore, a density sensor48to detect the density of a toner image transferred to the intermediate transfer belt44is provided on the intermediate transfer belt44. The supply quantity of the toner is controlled on the basis of the density detection result of the density sensor48.

The secondary transfer unit46, as illustrated inFIG. 1, functions as a contact-type transfer unit that includes a secondary transfer roller46A, which rotates while being in contact with the peripheral surface of the intermediate transfer belt44at the secondary transfer location, that is, the outer peripheral surface portion of the intermediate transfer belt44which is supported by the supporting roller26C of the intermediate transfer unit26, and to which secondary transfer voltage is supplied. Furthermore, to the secondary transfer roller46A or the supporting roller26C of the intermediate transfer unit26, a DC voltage having the polarity the same as or opposite the charging polarity of toner is applied as the secondary transfer voltage. Forward and reverse bias is applied to the secondary transfer roller46A at a specific timing. The secondary transfer roller46A is also cleaned by a brush which is not illustrated.

The fixing unit28includes a roll-type or belt-type rotatable body28A for heating which is heated by a heating part so as to maintain the surface temperature at a specific temperature, a roll-type or belt-type rotatable body28B for pressurizing which rotates by being in contact with the rotatable body28A with a specific pressure, and the like. In the fixing unit28, fixing processing is performed by heating and pressurizing a toner image that has been transferred to the continuous paper P by the secondary transfer unit46.

Next, a configuration of a control system of the image forming apparatus according to this exemplary embodiment will be explained.FIG. 4is a block diagram illustrating the configuration of the control system of the image forming apparatus10according to this exemplary embodiment.FIG. 4mainly illustrates the configuration of the control system of the portion that controls the image forming device14.

As described above, the image forming device14is controlled by the controller18. That is, each component of the image forming unit24is connected to the controller18. More specifically, the charger32, the exposure part34, the developing part36, the first transfer part38, and the cleaner40are connected to the controller18. Image forming operation is performed by the controller18controlling the operation of each component.

Furthermore, the image forming unit24includes a toner density sensor60that detects the toner density of the developing part36, and a toner supply motor62that supplies toner to the developing part36from the toner cartridge42to control the toner density. The toner density sensor60and the toner supply motor62are also connected to the controller18.

Furthermore, a pixel counter64is connected to the controller18. The pixel counter64counts the number of pixels, the image density (area coverage), or the like corresponding to the toner discharge amount, based on image information and the lighting time of the exposure part34or the like. The counting result is then input to the controller18.

As well as controlling the image forming operation, the controller18also controls the toner density by controlling the toner supply motor62on the basis of the detection result of the toner density sensor60, the counting result of the pixel counter64, the detection result of the density sensor48, and the like.

In the image forming apparatus10of such a configuration described above, the charging characteristics may change when the toner degrades, which may affect the image quality.

With the image forming apparatus which forms an image on each piece of cut paper, degradation of toner may be prevented by discharging the toner by forming a specific belt-shaped pattern or the like on the intermediate transfer belt at a timing when the image formation is not performed on paper. However, there is not space enough to form a belt-shaped pattern or the like between images on the continuous paper P. Therefore, it is not possible to discharge the toner in this case.

In this exemplary embodiment, as illustrated inFIG. 5A, by discharging toner outside the image area of the continuous paper P by forming specific image patterns50in specific side areas outside the image area of the continuous paper P while forming multiple images x based on image information in the image area of the continuous paper P, the circulation of the toner is urged and the degradation of the toner may be suppressed.

FIG. 5Bis a chart illustrating the toner discharge amount (area coverage) and the charge amount change when forming image patterns50in a band shape on the continuous paper P of a specific length (page) under specific conditions. Symbols in the chart represents different colors, for example, the black circle represents yellow, the black triangle represents cyan, the black square represents magenta, and the black diamond represents black. The vertical axis ofFIG. 5Brepresents a change in the charge amount when forming the image patterns50on the continuous paper P of a specific length (page) with respect to the charge amount at the time when the image formation starts.

As illustrated inFIG. 5B, when the area coverage corresponding to the toner discharge amount is small, the change in the charge amount between before and after formation of an image of the specific length is large, and when the area coverage is large, the change in the charge amount is small. Therefore, it is understood that when the area coverage (toner discharge amount) is small, the toner degrades and the charge amount change is large.

In this exemplary embodiment, the area coverage is detected by the pixel counter64or the like, and for example, by the controller18controlling the image forming device14to form the image patterns50that provide an area coverage equal to or greater than a specific threshold (for example, 3 percent) in side areas, the degradation of the toner is suppressed. In this exemplary embodiment, by adjusting the size of the image patterns50, the area coverage is increased to be equal to or greater than the threshold.

As described above, by forming the image patterns50and discharging the toner, as illustrated inFIG. 5B, the change in the charge amount decreases. When the change in the charge amount decreases, the change in the density also decreases as illustrated inFIG. 5C, and therefore the image quality becomes stable.FIG. 5Cis a diagram illustrating a change in the density with respect to a change in the charge amount. InFIG. 5C, the black diamond represents an area coverage of 2.5 percent, and the black square represents an area coverage of 25 percent.

The amount of toner to be discharged may be changed by changing the width, length, image density, or the like of the image patterns50, according to the area coverage detected by the pixel counter64or the like.

As for the shapes of the image patterns50to be formed in the side areas, they may be in band shapes as illustrated inFIG. 5A, or they may also be in block shapes as illustrated inFIG. 6A. Furthermore, as illustrated inFIGS. 6B and 6C, it is desirable that each of the four colors of the image patterns50do not overlap, in order to ensure fixing ability.

In the case where positioning marks or the like to be used in post-processing or the like are formed on the continuous paper P, it is desirable that the image patterns50are formed with characteristics different from the positioning marks, so as to avoid detection error such as confusion between the image patterns50and the positioning marks. The positioning marks may be formed by the image forming apparatus, and image formation may be performed according to image information on the continuous paper P on which the positioning marks are formed. For example, the image patterns50may be formed so as to have specific fixed positional relationships with the positioning marks, so that the image patterns50are not erroneously detected as the positioning marks. More specifically, as illustrated inFIG. 6D, it is desirable to form positioning marks54and the image patterns50so that they are distinguishable, by forming the image patterns50at positions shifted in the direction perpendicular to the conveying direction of the continuous paper P, with respect to the positioning marks54. Furthermore, it is effective to form the positioning marks54and the image patterns50so that they do not overlap in the direction along the conveying direction of the continuous paper P. Alternatively, instead of arranging the positions to be formed, the positioning marks54and the image patterns50may be formed so that the sizes or the shapes differ from one another.

Because of the use of the continuous paper P, it is unable, when controlling the toner density, to form between images a patch or the like for controlling the toner density. In this exemplary embodiment, at the time when image formation starts, the toner density is adjusted by forming a patch for controlling the toner density on the intermediate transfer belt44and controlling the toner supply motor62on the basis of the detection result of the density sensor48, and during image formation, due to an inability to form a patch, the toner density is adjusted based on the charged state and a change in the toner density estimated using a table prepared in advance or the like. For example, the density adjustment is made by controlling the toner supply motor62on the basis of the detection results of the pixel counter64and the toner density sensor60.

Next, a basic image forming operation by the image forming apparatus10will be described.

When the image forming apparatus10receives a request of an image forming operation (printing), the image forming unit24including the four image forming parts24Y,24M,24C, and24K, the intermediate transfer unit26, the secondary transfer unit46, the fixing unit28, and the like start.

Then, in the image forming unit24, the photoconductor drum30is rotated first, with the surface of the photoconductor drum30being charged to a specific polarity and a specific potential by the charger32. Next, the exposure part34applies light based on image information to the surface of the charged photoconductor drum30, thereby an electrostatic latent image of the corresponding color component being formed on the surface of the photoconductor drum30.

Then, the developing part36supplies to the electrostatic latent image with the corresponding color component formed on the surface of the photoconductor drum30toner of the corresponding color (Y, M, C, or K) charged to the specific polarity, which is then electrostatically adhered, and the electrostatic latent image is developed. The electrostatic latent image with the corresponding color component formed on the surface of the photoconductor drum30is thus manifested as a toner image in the corresponding color (Y, M, C, or K) developed by toner of the corresponding color.

When the toner image of the corresponding color formed on the photoconductor drum30of the image forming unit24is conveyed to the first transfer location, the first transfer part38performs first transfer of the toner image of the corresponding color in such a manner that the toner images of the individual colors overlap in order on the intermediate transfer belt44.

Furthermore, after the first transfer finishes, in the image forming unit24, the cleaner40removes the deposits, such as toner or the like, remaining on the surface of the photoconductor drum30, and cleans the surface of the photoconductor drum30. This enables the image forming unit24to proceed to the next image forming operation.

In the intermediate transfer unit26, the toner images that have been subjected to first transfer by rotation of the intermediate transfer belt44are retained and conveyed to the secondary transfer location. In contrast, the paper feeder12, prior to an image forming operation, supplies the continuous paper P from the paper feed roll20to the secondary transfer location along a specific conveyance path.

At the secondary transfer location, the secondary transfer unit46collectively performs secondary transfer of the toner images on the intermediate transfer belt44onto the continuous paper P. After the secondary transfer finishes, in the intermediate transfer unit26, a cleaner which is not illustrated removes deposits, such as toner or the like, remaining on surface of the intermediate transfer belt44after the secondary transfer.

Then, the continuous paper P to which secondary transfer of the toner images have been performed is conveyed to the fixing unit28. By a fixing process performed by the fixing unit28, the toner images are fixed on the continuous paper P. In the end, the continuous paper P for which the fixing process is completed is ejected from the image forming device14and taken up into the storage roll22of the storage device16.

Through the above operation, the continuous paper P on which a full color image of a combination of the four-color toner images is formed is output.

Next, a specific flow of a process performed by the controller18of the image forming apparatus10will be described.FIG. 7is a flowchart illustrating an example of the flow of the process performed by the controller18of the image forming apparatus10according to this exemplary embodiment.

When an image forming instruction is issued, it is determined in step100whether or not the continuous paper P is set. For example, the determination is made based on a detection result of a paper detection sensor or the like. When a negative determination result is obtained, the process proceeds to step102. When an affirmative determination result is obtained, the process proceeds to step104.

In step102, a specific continuous paper setting process for setting the continuous paper P is performed, and the process proceeds to step104. In the continuous paper setting process, for example, each of the paper feeder12, the image forming device14, and the storage device16is controlled to convey the continuous paper P so that the continuous paper P is pulled out from the paper feed roll20of the paper feeder12and is stored into the storage device16through the image forming device14.

In step104, the image forming device14is controlled so that a specific density adjustment pattern is formed on the intermediate transfer belt44. Then, the process proceeds to step106.

In step106, the density adjustment pattern is detected by the density sensor48, and the process proceeds to step108.

In step108, the toner supply motor62is controlled and density adjustment is made based on the detection result of the density sensor48. Then, the process proceeds to step110. In this exemplary embodiment, density control is performed by causing the density sensor48to detect the density of the density adjustment pattern formed on the intermediate transfer belt44. However, density control may be performed by forming a density adjustment pattern on the continuous paper P and then detecting the density of the density adjustment pattern formed on the continuous paper P. Furthermore, density control based on the detection result of the density sensor48may be performed during the continuous paper setting process in step102.

Next, in step110, image information is acquired, and the pixel counter64counts the number of pixels. Then, the process proceeds to step112. The pixel counter64is described here as a device to count the number of pixels of the image information. However, the pixel counter64is not limited to this. The pixel counter64may count the lighting time of the exposure part34.

In step112, the image patterns50to be formed in side areas are determined based on the count result of the pixel counter64, and the process proceeds to step114. For example, when the area coverage is smaller than or equal to a threshold, the image patterns50having a size equal to or greater than a threshold are determined. In this case, for example, the image patterns50may be determined in such a manner that the amounts of toner discharged are the same among individual colors by determining the image patterns50such that a large amount of toner is discharged for the color with a small area coverage and that a small amount of toner or no toner is discharged for the color with a large area coverage. In the case where a toner discharge amount for a certain color exceeds a specific amount (for example, an area coverage of 8 percent), the toner discharge amount of the other colors may be fixed to the above-mentioned specific amount. Furthermore, when determining the image patterns50, the positions at which the image patterns50are formed may also be determined according to the paper width of the continuous paper P. For example, the positions where the image patterns50are formed may be corrected for every paper width, on the basis of the detection result of a detecting unit, such as a paper-width detection sensor, or the result of paper-width specification by a user using a specifying unit, such as an operation unit of the controller18, which specifies the paper width. Accordingly, the image patterns50may be formed in side areas even when the continuous paper P of different paper widths is used. Alternatively, the image patterns50may be formed by determining the positions at which the image patterns50are formed not according to the width of the continuous paper P but according to the size of images formed on the continuous paper P.

In step114, each part of the image forming unit24is controlled such that images are formed in the image area and the image patterns50are formed in side areas, and the process proceeds to step116.

In step116, the toner density is controlled based on the count result of the pixel counter64including the image patterns50, and the process proceeds to step118. In other words, by controlling the toner supply motor62on the basis of the count result of the pixel counter64, control of the toner density during image formation is performed.

In step118, it is determined whether or not image formation is completed. When a negative determination result is obtained, the process returns to step110and the above-mentioned processing steps are repeated. When an affirmative determination result is obtained, the series of processing steps is terminated.

As described above, in the image forming apparatus10according to this exemplary embodiment, by forming the image patterns50in side areas of the continuous paper P, the circulation of the toner is urged and the degradation of the toner is suppressed.

Furthermore, as described above, the toner includes an external additive, which is sandwiched between the blade41and the photoconductor drum30and functions as a lubricant for suppressing friction of the blade41. When the toner degrades, the external additive will be buried in the toner and the performance of the external additive to suppress friction of the blade41may be undermined. However, in this exemplary embodiment, due to the formation of the image patterns50in side areas of the continuous paper P, the degradation of the toner will be suppressed, thus preventing the external additive being buried in the toner. Accordingly, the friction suppression performance of the blade41is maintained.

In the above exemplary embodiment, the described example assumes label paper as the continuous paper P in which side areas in which the image patterns50are formed are to be removed. However, the continuous paper P is not necessarily label paper. The continuous paper P of another type may be used. For example, continuous form paper or the like may be employed and side areas in which the image patterns50are formed may be cut off by post-processing or the like.

Furthermore, the process performed by the controller18of the image forming apparatus10in the above exemplary embodiment may be stored as a program in a storage medium and distributed.