Patent Grant
9874837
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-010339 filed Jan. 22, 2016.
The present invention relates to image forming apparatuses.
According to an aspect of the invention, there is provided an image forming apparatus includes multiple image carriers for carrying toner images of different colors; an intermediate transfer body for carrying the toner images transferred from the multiple image carriers; a second transfer part for transferring the toner images carried by the intermediate transfer body to a recording medium at a second transfer position; and a charge-applying part for applying a charge having a same polarity as a charging polarity of toner used to form the toner images to at least one of a leading end and a trailing end of the recording medium in a transport direction, at a position on an upstream side of the second transfer part in the transport direction of the recording medium.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Exemplary embodiments of the present invention will be described below with reference to the drawings.
First Exemplary Embodiment
Overall Configuration of Image Forming Apparatus
An image forming apparatus 1 according to the first exemplary embodiment is configured as, for example, a color printer. The image forming apparatus 1 includes image forming units 10, which form toner images developed with toner, serving as developer 4; an intermediate transfer device 20, which carries the toner images formed by the image forming units 10 and transports them to a second transfer position T2, where the toner images are second-transferred to a recording sheet 5, serving as an example of a recording medium; a paper feed device 50, which accommodates and transports recording sheets 5 to be fed to the second transfer position T2 of the intermediate transfer device 20; a fixing device 40, which fixes the toner images second-transferred to the recording sheet 5 by the intermediate transfer device 20; etc. Reference sign la in
The image forming units 10 include four image forming units 10Y, 10M, 10C, and 10K, which form a yellow (Y), magenta (M), cyan (C), and black (K) toner image, respectively. The four image forming units 10 (Y, M, C, and K) are arranged side-by-side in a line, in the horizontal direction, inside the body 1a.
The image forming units 10 (Y, M, C, and K) include rotatable photoconductor drums 11, serving as an example of an image carrier. The photoconductor drums 11 are surrounded by: charging devices 12 for charging, to predetermined electric potentials, the circumferential surfaces (image carrying surfaces) of the photoconductor drums 11 on which images can be formed; exposure devices 13 (Y, M, C, and K), which irradiate the charged circumferential surfaces of the photoconductor drums 11 with light based on image information (signal) to form electrostatic latent images corresponding to the respective colors, which have potential differences; developing devices 14 (Y, M, C, and K), serving as an example of a developing part, which develop the electrostatic latent images with the toner in the developer 4 of the corresponding color (Y, M, C, and K) into toner images; first transfer devices 15 (Y, M, C, and K), serving as an example of a first transfer part, which transfer the toner images to the intermediate transfer device 20; erase lamps 16 (Y, M, C, and K), which remove the residual charge remaining on the image carrying surfaces of the photoconductor drums 11 after the first transfer; drum cleaning devices 17 (Y, M, C, and K), which remove attached substances, such as toner, remaining on the image carrying surfaces of the photoconductor drums 11 after the first transfer to clean the photoconductor drums 11; etc.
The photoconductor drums 11 each include a grounded hollow or solid cylindrical base, and an image carrying surface, which has a photoconductive layer (photosensitive layer) formed of a photosensitive material, formed on the circumferential surface thereof. The photoconductor drum 11 is supported so as to be rotatable in the direction indicated by an arrow A by receiving a motive force supplied from a driving device (not shown).
The charging device 12 includes a contact-type charging roller, which is disposed so as to be in contact with the photoconductor drum 11. The charging device 12 includes a cleaning roller 121 for cleaning the surface thereof. The charging device 12 receives a charging voltage. If the developing device 14 performs reversal development, the charging voltage is a voltage or current having the same polarity as the charging polarity of the toner supplied by the developing device 14. Note that a non-contact charging device, such as scorotron, which is disposed so as not to be in contact with the surface of the photoconductor drum 11, may be used as the charging device 12.
The exposure device 13 irradiates the charged circumferential surface of the photoconductor drum 11 with light LB (indicated by a solid line with an arrowhead), which is generated corresponding to the image information input to the image forming apparatus 1, to form an electrostatic latent image. The exposure devices 13 (Y, M, C, and K) correspond to the yellow (Y), magenta (M), cyan (C), and black (K) image forming units 10. When latent images are to be formed, the exposure devices 13 receive, from the controller 100, full-color or black-and-white image information (signal) input to the image forming apparatus 1 through an arbitrary device. The exposure devices 13 may be formed of light-emitting-diode (LED) print heads, in which multiple LEDs, serving as light-emitting devices arranged in the axial direction of the photoconductor drums 11 of the image forming units 10, irradiate the photoconductor drums 11 with light corresponding to the image information, thereby forming electrostatic latent images.
The developing devices 14 (Y, M, C, and K) each include, inside a device housing 140 having an opening and a developer container chamber, a developing roller 141, serving as an example of a developer carrier, which carries and transports the developer 4 to a developing area where it faces the photoconductor drum 11; a supply-and-transport member 142, such as a screw auger, which supplies the developer 4 to the developing roller 141 while stirring; a stir-and-transport member 143, such as a screw auger, which stirs and transports the developer 4 while exchanging the developer 4 with the supply-and-transport member 142; and a layer-thickness restricting member (not shown), which restricts the amount (layer thickness) of developer 4 carried by the developing roller 141. The developers 4 of four colors (Y, M, C, and K) are two-component developers, each containing a nonmagnetic toner and a magnetic carrier.
The first transfer devices 15 (Y, M, C, and K) are contact-type transfer devices, which are rotated while being in contact with the circumferences of the corresponding photoconductor drums 11 with the intermediate transfer belt 21 therebetween, and which have first transfer rollers supplied with first transfer voltages. The first transfer voltages are direct-current voltages having the opposite polarity to the charging polarity of the toner and supplied from a power supply device (not shown).
The erase lamps 16 uniformly expose the surfaces of the photoconductor drums 11 to the light after the first transfer, thereby removing the residual charges on the surfaces of the photoconductor drums 11.
The drum cleaning devices 17 each include: a partially open container-shaped body; a cleaning plate disposed so as to be in contact with the circumferential surface of the photoconductor drum 11 after the first transfer at a predetermined pressure to remove attached substances, such as residual toner, to clean the photoconductor drum 11; and a delivery member, such as a screw auger, which recovers the attached substances, such as toner, removed by the cleaning plate and delivers the toner to a recovery system (not shown).
As shown in
The intermediate transfer belt 21 is an endless belt formed of a material composed of, for example, a synthetic resin, such as polyimide resin or polyamide resin, with a resistance adjusting agent, such as carbon black, dispersed therein. The belt-support roller 22 serves as a driving roller that is rotationally driven by a driving device (not shown), the belt-support roller 23 serves as a surface-forming roller that forms the image forming surface of the intermediate transfer belt 21, the belt-support roller 24 serves as a tension roller for applying tension to the intermediate transfer belt 21 and as a meandering correction roller for correcting meandering of the intermediate transfer belt 21, the belt-support roller 25 serves as a second-transfer back-support roller, and the belt-support roller 26 serves as an opposing roller for the belt cleaning device 27.
The second transfer device 30 is a contact-type transfer device having a second transfer roller 31, which constitutes a second transfer part, which is rotated by being in contact with the circumferential surface of the intermediate transfer belt 21 at the second transfer position T2, which is a position on the outer circumferential surface of the intermediate transfer belt 21 supported by the belt-support roller 25, in the intermediate transfer device 20, and to which a second transfer voltage is supplied. The second transfer device 30 includes the second transfer roller 31 and the belt-support roller 25, serving as a backup roller. A direct-current voltage, serving as a second transfer voltage, which has the opposite polarity to or the same polarity as the charging polarity of the toner is applied to the second transfer roller 31 or the belt-support roller 25. In this exemplary embodiment, as shown in
The belt cleaning device 27 has the same configuration as the drum cleaning devices 17 and includes a partially open container-shaped body, a cleaning plate (not shown) disposed so as to be in contact with the circumferential surface of the intermediate transfer belt 21 after the second transfer at a predetermined pressure to remove attached substances, such as residual toner, to clean the circumferential surface of the intermediate transfer belt 21, and a delivery member, such as a screw auger (not shown), which recovers the attached substances, such as toner, removed by the cleaning plate and delivers the toner to a recovery system.
The fixing device 40 includes a roller-shaped or belt-shaped heating rotary member 41, which is heated by a heating device such that the surface thereof is maintained at a predetermined temperature, and a roller-shaped or belt-shaped pressure-applying rotary member 42, which extends parallel to the axial direction of the heating rotary member 41 and is rotated by being in contact therewith at a predetermined pressure. In the fixing device 40, a contact part where the heating rotary member 41 and the pressure-applying rotary member 42 are in contact with each other serves as a fixing part at which predetermined fixing processing (heating and pressing) is performed.
The paper feed device 50 is disposed below the intermediate transfer device 20. The paper feed device 50 is primarily formed of multiple (or a single) sheet containers 51 for accommodating a stack of recording sheets 5 of a desired size and type, and delivery devices 52 for picking up recording sheets 5 one-by-one from the sheet containers 51. The sheet containers 51 are attached such that they can be pulled toward, for example, the front side (i.e., the side to which a user faces when using the image forming apparatus 1) of the body la.
Examples of the recording sheet 5 include normal paper used in copiers and printers of an electrophotographic system, thin paper, such as tracing paper, and OHP sheets. For an even smoother image surface after fixing, it is preferable that the surface of the recording sheet 5 be as smooth as possible, and hence, for example, coated paper formed by coating the surface of normal paper with resin or the like, and so-called thick paper, such as art paper for printing, which has a relatively large grammage, may also be suitably used. Herein, recording sheets 5 having a grammage of less than 80 g/m2 are classified as thin paper, recording sheets 5 having a grammage of greater than or equal to 80 g/m2 to less than 100 g/m2 are classified as normal paper, recording sheets 5 having a grammage of greater than or equal to 100 g/m2 to less than 200 g/m2 are classified as first thick paper, and recording sheets 5 having a grammage of greater than or equal to 200 g/m2 are classified as second thick paper. Note that these thresholds for distinguishing the thin paper, the normal paper, the first thick paper and the second thick paper from one another are merely examples and are not intended to be limiting.
As described above, various types of paper may be used as the recording sheet 5. The recording sheet 5 is deformed (e.g., bent or flexed) while being transported inside the image forming apparatus 1. For example, the grammage and the rigidity (flexural rigidity) show the ease of bending of the recording sheet 5. The grammage is the weight (g/m2) per unit area (1 m2) of the recording sheet 5. Because the thickness of the recording sheet 5 tends to increase with the weight thereof, the grammage is also used to mean the “paper thickness”. However, some relatively thick recording sheets 5 have a relatively low density of fibers constituting the sheets. Hence, the grammage does not always correspond to the “paper thickness”.
The rigidity (flexural rigidity) of the recording sheet 5 may be expressed by a value measured by “paper and board-determination of stiffness-taber stiffness tester method”, specified in JIS P 8125, which is in compliance with ISO 2493 or ISO 2493. The rigidity of the recording sheet 5 is expressed by the bending moment or load needed to bend, by 15 degrees at a constant speed, a specimen that has been conditioned for 24 hours under standard conditions (23° C., 50% RH), cut into a piece having a width of 38.0 mm and a length of 50.0 mm, and fixed at one end (short side) in a cantilever manner. In this exemplary embodiment, the flexural rigidity of the recording sheet 5 is expressed by a measurement value (mN) obtained by testing a specimen that is cut out, into a width of 38 mm and a length of 50 mm, of a recording sheet 5 that has been conditioned for 24 hours or more under standard conditions (23° C. and 50% RH), by using a flexural rigidity test machine (model number 2048-BF), manufactured by Kumagai riki kogyo Co., Ltd., with the bending angle being set to 15 degrees and the specimen support span to 10 mm, in compliance with ISO 2493.
The flexural rigidity of the recording sheet 5 may vary according to the paper feed direction (LEF: long edge feed or SEF: short edge feed) due to the orientation of fibers or the like. LEF means that paper is fed with the long edge as the leading edge, while SEF means that paper is fed with the short edge as the leading edge. Herein, the LEF direction is employed as the standard paper feed direction, and the flexural rigidity in the LEF direction is used as the flexural rigidity of the recording sheet 5. When the flexural rigidity significantly varies according to the paper feed direction (LEF or SEF) of the recording sheet 5, the flexural rigidity in the LEF direction or the flexural rigidity in the SEF direction may be independently used according to the paper feed direction.
A feed-and-transport path 56, which includes multiple (or single) sheet-transport roller pairs 53 and 54, a transport guide 55 for transporting the recording sheet 5 fed out of the paper feed device 50 to the second transfer position T2, and the like are provided between the paper feed device 50 and the second transfer device 30. As shown in
A short transport belt 61 and a switching gate (not shown) for switching the sheet transport paths are provided between the fixing device 40 and the sheet output roller pair 60. When images are to be formed on both sides of a recording sheet 5, the recording sheet 5 having an image formed on one side thereof is directed downward by the switching gate, temporarily transporting the recording sheet 5 to a reversing path 64, which has sheet-transport roller pairs 62 and 63. While the recording sheet 5 is held by the sheet-transport roller pair 63, the transport direction is reversed such that the recording sheet 5 is transported from the reversing path 64, whereby the recording sheet 5 is reversed. The recording sheet 5 is then transported to the general feed-and-transport path 56 via a duplex-printing transport path 66, which includes multiple sheet-transport roller pairs 65, a transport guide (not shown), etc.
In
Furthermore, reference sign 100 in
Reference sign 101 denotes a power supply for supplying power to the controller 100 and the like, and reference sign 102 denotes an operating and display part via which a user operates the image forming apparatus 1. The operating and display part 102 includes a designating part (not shown) via which the user designates the recording sheet 5 to be used for image formation. The controller 100 identifies the grammage, flexural rigidity, and the like of the recording sheet 5, on the basis of the type (e.g., first thick paper, second thick paper, or normal paper), the paper feed direction, and the like of the recording sheet 5, designated via the operating and display part 102.
Operation of Image Forming Apparatus
A basic image forming operation performed by the image forming apparatus 1 will be described below.
Herein, an operation for forming a full-color image that is composed of toner images of four colors (Y, M, C, and K) by using the four image forming units 10 (Y, M, C, and K) will be described.
In the image forming apparatus 1, when the controller 100 receives, from the operating and display part 102, an image-forming-operation (printing) request instruction information with the designation of a recording sheet 5, the four image forming units 10 (Y, M, C, and K), the intermediate transfer device 20, the second transfer device 30, the fixing device 40, etc. are actuated.
In the image forming units 10 (Y, M, C, and K), first, the photoconductor drums 11 are rotated in the direction indicated by the arrow A, and the charging devices 12 charge the surfaces of the photoconductor drums 11 to a predetermined polarity (in the first exemplary embodiment, negative polarity) and predetermined electric potentials. Then, the exposure devices 13 (Y, M, C, and K) irradiate the charged surfaces of the photoconductor drums 11 with light LB, which is emitted on the basis of the image signals obtained by converting the image signal Cin, input to the image forming apparatus 1, to the respective color components (Y, M, C, and K), thereby forming, on the surfaces thereof, electrostatic latent images corresponding to the respective color components and having predetermined potential differences.
Next, in the image forming units 10 (Y, M, C, and K), the developing rollers 141 supply, to the electrostatic latent images of the respective color components, formed on the photoconductor drums 11, toners of corresponding colors (Y, M, C, and K) charged to a predetermined polarity (negative polarity) and make the toners electrostatically adhere thereto. As a result, the electrostatic latent images of the respective color components, formed on the photoconductor drums 11, become visible in the form of toner images of four colors (Y, M, C, and K) that have been developed with the toners of corresponding colors.
Then, when the respective color toner images formed on the photoconductor drums 11 of the image forming units 10 (Y, M, C, and K) are transported to the first transfer positions T1, the first transfer devices 15 sequentially first-transfer, in a superimposed manner, the respective color toner images to the intermediate transfer belt 21 of the intermediate transfer device 20, which is running in the direction indicated by the arrow B.
Once the first transfer has been completed, in the respective image forming units 10, the erase lamps 16 remove the residual charges on the surfaces of the photoconductor drums 11, and the drum cleaning devices 17 scrape off the attached substances, thereby cleaning the surfaces of the photoconductor drums 11. By doing this, the image forming units 10 can be used for the subsequent image forming operation.
Next, in the intermediate transfer device 20, the first-transferred toner images are transported to the second transfer position T2 by the revolving intermediate transfer belt 21. Meanwhile, in the paper feed device 50, a recording sheet 5 designated via the operating and display part 102 is fed into the feed-and-transport path 56, in accordance with the image forming operation. In the feed-and-transport path 56, the sheet-transport roller pair 54, serving as the registration rollers, feeds the recording sheet 5 to the second transfer position T2, via the transport guide 55, in accordance with the transfer timing.
At the second transfer position T2, the second transfer roller 31 of the second transfer device 30 second-transfers the superimposed toner images on the intermediate transfer belt 21 to the recording sheet 5. After the second transfer, in the intermediate transfer device 20, the belt cleaning device 27 removes attached substances, such as residual toner, on the surface of the intermediate transfer belt 21.
The recording sheet 5 to which the toner image has been second-transferred is separated from the intermediate transfer belt 21 and the second transfer roller 31 and is then transported to the fixing device 40 by the transport belts 57 and 58. The fixing device 40, by guiding the recording sheet 5 after the second transfer to the contact part between the rotating heating rotary member 41 and pressure-applying rotary member 42 and making it pass therebetween, performs necessary fixing processing (heating and pressing), thereby fixing the unfixed toner image to the recording sheet 5. Finally, when image formation is performed only on one side, the recording sheet 5 after fixing is output onto the sheet output part 59, which is provided at a side of the body 1a, by the sheet output roller pair 60.
When images are to be formed on both sides of a recording sheet 5, the recording sheet 5 provided with an image on one side is not output onto the sheet output part 59 by the sheet output roller pair 60, but is transported downward by the switching gate (not shown). The recording sheet 5 transported downward is reversed by the reversing path 64 having the sheet-transport roller pairs 62 and 63, and is then transported to the feed-and-transport path 56 via the duplex-printing transport path 66. Then, the sheet-transport roller pair 54 feeds the recording sheet 5 to the second transfer position T2 in accordance with the transfer timing. After an image is transferred and fixed to the back surface of the recording sheet 5, the recording sheet 5 is output onto the sheet output part 59, which is provided at a side of the body la, by the sheet output roller pair 60.
Through the operation described above, the recording sheet 5 on which a full-color image that is composed of toner images of four colors is formed is output.
Configuration of Characteristic Part of Image Forming Apparatus
In the image forming apparatus 1 configured as above, as shown in
As shown in
If a discharge occurs between the toner image T on the intermediate transfer belt 21 and the trailing end 5a of the recording sheet 5, the charge moves across the gap G, and, as a result, the toner image T carried by the intermediate transfer belt 21 tends to be charged to the opposite (positive) polarity to the initial charging polarity (negative polarity). At this time, as shown in
The white patches 73 in the image due to a discharge occur not only at the trailing end 5a of the recording sheet 5 on the downstream side in the transport direction, but also at the leading end 5b of the recording sheet 5 on the upstream side in the transport direction. The vibration caused by the trailing end 5a of the recording sheet 5 on the downstream side in the transport direction colliding with the surface of the intermediate transfer belt 21 when being separated from the transport guide 55 is more apparent with thick paper, which exerts a relatively large restring force when returning from the deformed state, and sheets having high flexural rigidity values.
To suppress the vibration caused by the downstream end of the recording sheet 5 in the transport direction colliding with the surface of the intermediate transfer belt 21 when being separated from the transport guide 55, a configuration as shown in
However, if the transport guide 55 for guiding the recording sheet 5 is disposed at a position away from the second transfer position, as shown in
To counter this problem, in this exemplary embodiment, as shown in
The charging mechanism 80 includes a pair of charging rollers 81 and 82, which are in contact with each other from above and below so as to be rotatable. One charging roller, 81, is formed of, for example, a metal core and a conductive elastic layer formed on the outer circumference thereof, similarly to the charging devices 12. The other charging roller, 82, is formed of a cylindrical metal roller. The charging roller 82 is disposed at a fixed position so as to be rotatable, whereas the charging roller 81 is urged against the charging roller 82 by a pressing device (not shown) at a predetermined pressure, so as to be rotatable. The charging roller 81 is provided with a high voltage having the same (negative) polarity as the charging polarity of the toner by a high-voltage power supply 83. The charging roller 82 is grounded. The application timing and voltage value of the high voltage applied to the charging roller 81 by the high-voltage power supply 83 are controlled by the controller 100.
In this exemplary embodiment, the charging mechanism 80 applies a charge having the same (negative) polarity as the charging polarity of the toner only to the leading end 5b and the trailing end 5a of the recording sheet 5. Herein, the leading end 5b and the trailing end 5a of the recording sheet 5 include areas extending from the leading end and the trailing end of the recording sheet 5 to positions at a predetermined length L from the leading end and the trailing end of the recording sheet 5. Although the predetermined length L is set to, for example, about 20 to 50 mm, it is not limited thereto. The charging mechanism 80 applies a charge having the same (negative) polarity as the charging polarity of the toner only to the leading end 5b and the trailing end 5a of the recording sheet 5, not to the area other than the leading end 5b and the trailing end 5a of the recording sheet 5, that is, the overall surface of the recording sheet 5. If a charge having the same (negative) polarity as the charging polarity of the toner is applied to the overall surface of the recording sheet 5, the negative charge applied to the overall surface of the recording sheet 5 and the toner image on the intermediate transfer belt 21, which has a negative charge, repel each other, causing an image defect in the area other than the leading end 5b and the trailing end 5a of the recording sheet 5. Thus, it is inappropriate.
Operation of Characteristic Part of Image Forming Apparatus
The operation of the characteristic part of the image forming apparatus 1 will be described below.
As shown in
At this time, if the controller 100 determines that the recording sheet 5 is second thick paper, which has a grammage of 200 g/m2 or more, on the basis of the signal from the operating and display part 102, as shown in
When the recording sheet 5 has a relatively high grammage or flexural rigidity, as in the case of thick paper, as shown in
At this time, as shown in
However, with this configuration, as shown in
To counter these problems, in this exemplary embodiment, a charge having the same (negative) polarity as the charging polarity of the toner is applied to both the leading end 5b and the trailing end 5a of the recording sheet 5, over a predetermined length L, using the charging mechanism 80. As shown in
Similarly, as shown in
In this exemplary embodiment, a charge having the same (negative) polarity as the charging polarity of the toner is applied to both the leading end 5b and the trailing end 5a of the recording sheet 5, over the predetermined length L, using the charging mechanism 80. Hence, even when the gap G is formed between the intermediate transfer belt 21 and the trailing end 5a of the recording sheet 5 as a result of the trailing end 5a of the recording sheet 5 striking (colliding with) the surface of the intermediate transfer belt 21, because the trailing end 5a of the recording sheet 5 is charged to the same (negative) polarity as the charging polarity of the toner, the occurrence of a discharge at the gap G can be prevented or suppressed.
Because the occurrence of a discharge between the intermediate transfer belt 21 and the trailing end 5a of the recording sheet 5 is prevented or suppressed, even when the toner image T to be transferred to the trailing end 5a of the recording sheet 5 includes, in the direction intersecting the transport direction of the recording sheet 5, the high-density image 71, which is relatively dense as a solid image, and the low-density image 72, which is relatively less dense as a monochrome halftone image, as shown in
Similarly, because the occurrence of a discharge between the intermediate transfer belt 21 and the leading end 5b of the recording sheet 5 is prevented or suppressed, even when the toner image T to be transferred to the leading end 5b of the recording sheet 5 includes, in the direction intersecting the transport direction of the recording sheet 5, the high-density image 71, which is relatively dense as a solid image, and the low-density image 72, which is relatively less dense as a monochrome halftone image, as shown in
The inventors produce a benchmark model of the image forming apparatus 1, as shown in
As is clear from
In contrast, when a charge having the same (negative) polarity as the charging polarity of the toner is not applied to the leading end 5b of the recording sheet 5, using the charging mechanism 80, noticeable white patches are generated in the 50% black halftone image at the leading end 5b of the recording sheet 5, and the image-quality grade is 5, “very poor”.
As is clear from
To confirm the difference in level of the white patches generated in 50% black halftone images due to the difference in type of the recording sheet 5, the inventors perform the following evaluation (Comparative Example 1). In Comparative Example 1, unlike the configuration in Example 1, the charging mechanism 80 is not provided, and New DV (trade name) having a grammage of 400 g/m2, which is an A3-size specialty white paperboard manufactured by Hokuetsu Kishu Sales Co., Ltd., and OS coated paper W having a grammage of 127 g/m2, which is an A3-size gloss two-sided coated paper manufactured by Fuji Xerox Co., Ltd., which is processed by a high-precision paper cutter and is subjected to a paper dust removal treatment, are used as the recording sheets 5.
As is clear from
In contrast, when the recording sheet 5 is first thick paper having a relatively small grammage of 127 g/m2, no white patch is generated in the 50% black halftone image at the trailing end 5a of the recording sheet 5, and the image-quality grade is 1, “excellent”.
Second Exemplary Embodiment
As a result, as is clear from
Third Exemplary Embodiment
In the third exemplary embodiment, as shown in
In the third exemplary embodiment, as shown in
The inventors produce a benchmark model of the image forming apparatus 1, as shown in
In Condition 1, only the voltage to be applied to the charging mechanism 80 with respect to the area 1 is set to 0 V, and the voltages to be applied to the charging mechanism 80 with respect to the areas 2 to 5 are set uniformly to −800 V.
In Condition 2, the voltage to be applied to the charging mechanism 80 with respect to the area 1 is set to 0 V, the voltage to be applied to the charging mechanism 80 with respect to the area 2 is set to −350 V, the voltage to be applied to the charging mechanism 80 with respect to the area 3 is set to −650 V, the voltage to be applied to the charging mechanism 80 with respect to the area 4 is set to −1100 V, and the voltage to be applied to the charging mechanism 80 with respect to the area 5 is set to −1500 V.
In Condition 3, the voltage to be applied to the charging mechanism 80 with respect to the area 1 is set to 0 V, the voltage to be applied to the charging mechanism 80 with respect to the area 2 is set to −350 V, the voltage to be applied to the charging mechanism 80 with respect to the area 3 is set to −500 V, the voltage to be applied to the charging mechanism 80 with respect to the area 4 is set to −1350 V, and the voltage to be applied to the charging mechanism 80 with respect to the area 5 is set to −2100 V.
As is clear from
In Condition 2, although the image quality is better than that is Condition 1, the image-quality grades in the evaluation areas 2 and 3 are about the same as those in the current situation, and the image-quality grade in the evaluation area 5 exceed the allowable image-quality grade 2. Thus, the result is also unsatisfactory.
In contrast, in Condition 3, the image-quality grades in the evaluation areas 1 to 5 are all 1, “excellent”, showing that a satisfactory image-quality improving effect can be obtained.
Next, the inventors produce a benchmark model of the image forming apparatus 1, as shown in
In Condition 1, the voltages to be applied to the charging mechanism 80 with respect to the areas 1 to 5 are set uniformly to −800 V. In Condition 2, the voltages to be applied to the charging mechanism 80 with respect to the areas 1 to 5 are set uniformly to −1500 V. In Condition 3, the voltages to be applied to the charging mechanism 80 with respect to the areas 1 to 5 are set uniformly to −2100 V.
As is clear from
In Condition 2, the image-quality grades in the evaluation areas 1 to 5 are about 2, “good (allowable)”, or 2.5. Thus, the result is satisfactory.
In Condition 3, although the image-quality grades in the evaluation areas 1 and 2 are worse than those in the current situation, the image-quality grade is 3, “slightly poor”, which is still usable, and the image-quality grades in the evaluation areas 3 to 5 are 2, “good (allowable)”. Thus, the result is satisfactory.
Fourth Exemplary Embodiment
An image forming apparatus 1 according to a fourth exemplary embodiment is configured such that the amount of charge applied to a recording medium is varied between when an image is to be formed on one side of the recording medium and when images are to be formed on both sides of the recording medium.
More specifically, in the fourth exemplary embodiment, when images are to be formed on both sides of a recording sheet 5, the controller 100 sets a larger absolute value of voltage to be applied to the charging mechanism 80 than that when an image is to be formed on one side. By doing so, when images are to be formed on both sides, it is possible to charge the recording sheet 5, which has already been subjected to fixing processing by the fixing device 40 and thus has been increased in resistance value, to the same polarity as the charging polarity of the toner.
Thus, when images are to be formed on both sides, it is possible to suppress the generation of white patches at the ends of the recording sheet in the transport direction.
Although, in the above-described exemplary embodiments, the configuration in which the controller 100 controls the voltage to be applied to the charging mechanism 80 has been described, it is also possible to configure such that a user switches or sets, via the operating and display part 102, whether or not a charge is applied to the recording sheet 5, according to the type of the recording sheet 5.
Furthermore, although, in the above-described exemplary embodiments, the case where the charging mechanism 80 formed of the charging rollers is used as the charge-applying part has been described, the charge-applying part may be formed of, besides the charging rollers, a charging blush, a charging blade, sheet metal, corotron, or the like.
Furthermore, although, in the above-described exemplary embodiments, the case where a direct-current high voltage is applied to the charging mechanism 80, serving as the charge-applying part, has been described, the voltage applied to the charging mechanism 80 is not limited thereto, and an alternating-current voltage superposed on the direct-current voltage may also be used. In such a case, it is possible to stably improve the charge applying efficiency, regardless of the resistance and the moisture content of the recording sheet 5.
The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-010339 | Jan 2016 | JP | national |
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| 20020064405 | Tomiki | May 2002 | A1 |
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| 20150160589 | Hayami | Jun 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 8-202177 | Aug 1996 | JP |
| 2001-194916 | Jul 2001 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20170212453 A1 | Jul 2017 | US |
