Patent Application
20130195488
This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2012-016319, filed in the Japan Patent Office on Jan. 30, 2012, the entire contents of which are incorporated herein by reference.
The present disclosure relates to an image forming apparatus employing xerography, such as a copy machine and a printer.
In the image forming apparatus employing xerography, an image is formed by repeating the following cycle:
the surface of an image carrying body (photoconductor drum) is charged at a predetermined potential;
exposure is performed to form an electrostatic latent image on the surface of the image carrying body;
a toner image is formed by developing the electrostatic latent image on the surface of the image carrying body by a developing unit;
the toner image is transferred to an image transfer object such as paper; and
the surface of the image carrying body is cleaned after transfer by a cleaning unit that is in contact with the surface of the image carrying body.
In image forming apparatuses employing xerography, a charging system (charging roller system) that charges the surface of the image carrying body at a predetermined positive potential is widely applied in order to reduce ozone generation, thereby curbing the deterioration in the environment of the installation site of the apparatus in an office or the like. In the image forming apparatus adopting such a charging roller system, constant current control, in which the voltage to be applied to a transfer unit upon transfer is controlled by constant current, is generally employed for providing a superior transfer performance that allows stable transfer of the toner image formed on the surface of the image carrying body onto the image transfer object.
However, with regard to an image region that is a part of the surface of the image carrying body where a toner image is formed and a non-image region that is a part of the surface of the image carrying body where no toner image is formed, upon applying the transfer potential to the transfer unit by constant current control, a potential difference between the non-image region and the transfer unit is greater than the potential difference between the image region and the transfer unit. As a result, little of the current flows into the image region while much of the current flows into the non-image region. This may lead to inappropriate transfer of the toner image and transfer defect. In order to prevent this defect, it has been considered to improve the transfer performance by increasing the transfer current. However, if the transfer current is increased, the difference between intensities of the current flowing into the non-image region and the current flowing into the image region becomes even greater. As a result, transfer memory (charge memory) is generated due to a difference in charging characteristics on the surface of the image carrying body. This may cause an image defect in the following image formation, such as a trace of a previous image.
As a technique for reducing the occurrence of transfer defects causing image defects, an image forming apparatus (prior art) has been proposed that is provided with a pre-transfer neutralization unit that performs a neutralization process on the surface of an image carrying body by making the potential of at least a part of a non-image region in the surroundings of an image region of the image carrying body higher than that of an image region toward the same polarity as the charging characteristics of the toner, prior to transfer.
In the image forming apparatus of the prior art, a toner image can be transferred to an image transfer object, while suppressing scattering of the toner in the vicinity of an edge of the image region on the surface of the image carrying body by way of the influence of the potential of the non-image region being present in the vicinity of the edge of the image region. As a result, the transfer performance can be improved.
In the image forming apparatus of the prior art, a potential difference between the image region and the non-image region can be reduced by performing the pre-transfer neutralization. However, generation of transfer memory due to a difference in influx amount of the transfer current between the image region and the non-image region cannot be sufficiently reduced. Especially in the charging roller system, the charging ability of the image carrying body is low, and thus the occurrence of causes transfer memory is considerable, whereby image defects tend to occur.
The present disclosure has an object of providing an image forming apparatus employing the charging system that is preferable for an improvement in the environment, while being able to achieve an improvement in the transfer performance by suppressing scattering of the toner, as well as being able to form high-quality images by sufficiently suppressing the occurrence of transfer memory due to a difference in the influx amount of transfer current.
The present disclosure is an image forming apparatus including an image carrying body, a charging unit, an exposure unit, a developing unit, a transfer unit, a pre-transfer neutralization unit, a cleaning unit, a post-transfer neutralization unit, a first control unit, a second control unit, and a first setting operating unit. The image carrying body rotates about an axis of rotation and carries a toner image on a surface thereof. The charging unit is disposed to face the surface of the image carrying body and electrically charges the surface of the image carrying body at a predetermined positive potential. The exposure unit exposes the surface of the image carrying body having been electrically charged by the charging unit to thereby form an electrostatic latent image on the surface. The developing unit forms a toner image on the surface of the image carrying body by developing the electrostatic latent image. The transfer unit is disposed in contact with the surface of the image carrying body through an image transfer object and transfers the toner image onto the image transfer object by applying a predetermined transfer potential. The pre-transfer neutralization unit that is disposed between the developing unit and the transfer unit, and neutralizes electrical charge of the surface of the image carrying body prior to transfer. The cleaning unit contacts the surface of the image carrying body after transfer of the toner image onto the image transfer object to thereby clean the surface of the image carrying body. The post-transfer neutralization unit is disposed between the transfer unit and the cleaning unit, and neutralizes electrical charge of the surface of the image carrying body after transfer. The first control unit controls neutralization light intensity of the pre-transfer neutralization unit such that a dark potential (V0 potential) of a non-image region on the image carrying body after pre-transfer neutralization is higher by 50 to 150 V than a bright potential (VL potential) of a solid image region. The second control unit controls the transfer potential of the transfer unit. The first setting operating unit allows for an increase and decrease in the neutralization light intensity of the pre-transfer neutralization unit based on a status of an output image.
An embodiment of an image forming apparatus according to the present disclosure will be described hereinafter with reference to the drawings. An overall structure of the printer 1 serving as an embodiment of the image forming apparatus according to the present disclosure will be described with reference to
As shown in
As shown in
The four image forming units 15a, 15b, 15c, 15d are: the image forming unit 15a for yellow, the image forming unit 15b for cyan, the image forming unit 15c for magenta, and the image forming unit 15c for black, in this order from the upstream side.
The belt cleaning unit 20 is disposed on an outer face side of the intermediate transfer belt 7, to face the upstream side of the four image forming units 15a, 15b, 15c, 15d in the rotational direction R1 of the intermediate transfer belt 7. The belt cleaning unit 20 removes the residual toner remaining on the intermediate transfer belt 7. The belt cleaning unit 20 includes: a rotational brush 21 that rotates in contact with the intermediate transfer belt 7; a rotational roller 22 that sweeps away the residual toner scraped off by the rotational brush 21; and a residual toner container 23 that receives the residual toner thus swept.
The four image forming units 15a, 15b, 15c, 15d include: photoconductor drums 2a, 2b, 2c, and 2d as image carrying bodies (photoreceptors); charging units 10a, 10b, 10c, and 10d; laser scanner units 4a, 4b, 4c, and 4d as exposure units; developing units 16a, 16b, 16c, and 16d; toner cartridges 5a, 5b, 5c, and 5d; toner feeding units 6a, 6b, 6c, and 6d; cleaning units 11a, 11b, 11c, and 11d; and neutralization units 12-0a, 12a, 12b, 12c, and 12d.
As shown in
Configurations of the four image forming units 15a, 15b, 15c, 15d and the paper feeding/discharging unit KH of the image forming portion GK are described in detail hereinafter. First, the image forming units 15a, 15b, 15c, and 15d of the image forming portion GK are described.
In the image forming units 15a, 15b, 15c, and 15d, performed on a surface of the photoconductor drums 2a, 2b, 2c and 2d are: charging by the charging portions 10a, 10b, 10c and 10d; exposure by the laser scanner units 4a, 4b, 4c and 4d; development by the developing units 16a, 16b, 16c and 16d; primary transfer by the intermediate transfer belt 7 and the primary transfer rollers 37a, 37b, 37c and 37d; static neutralization by the neutralization units 12-0a, 12a, 12b, 12c and 12d; and cleaning by the cleaning units 11a, 11b, 11c and 11d, from an upstream side to a downstream side. In addition, secondary image transfer by the intermediate transfer belt 7, the secondary transfer roller 8 and the opposing roller 18, and fixation by the fixing unit 9 are performed in the image forming portion GK.
Each of the photoconductor drums 2a, 2b, 2c, and 2d is composed of a cylindrically shaped member and function as a photoreceptor or an image carrying body. The photoconductor drums 2a, 2b, 2c, and 2d are disposed to face primary transfer positions (described later) on the side of the outer face of the intermediate transfer belt 7 respectively. Each of the photoconductor drums 2a, 2b, 2c, and 2d is disposed so as to be rotatable in a direction of an arrow, about an axis that extends in a direction orthogonal to a direction of movement of the intermediate transfer belt 7. An electrostatic latent image can be formed on a surface of each of the photoconductor drums 2a, 2b, 2c, and 2d.
The charging portions 10a, 10b, 10c, and 10d are disposed so as to face a surface of the photoconductor drums 2a, 2b, 2c, and 2d, respectively. The charging portions 10a, 10b, 10c, and 10d are composed of charging rollers that rotate in contact with surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, respectively. The charging portions 10a, 10b, 10c, and 10d uniformly positively charge (straight polarity, positive potential) the surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, respectively.
The laser scanner units 4a, 4b, 4c, and 4d, which function as the exposure units, are disposed to be spaced apart from a surface of the photoconductor drums 2a, 2b, 2c, and 2d, respectively. The laser scanner units 4a, 4b, 4c, and 4d include, respectively, a laser light source, a polygon mirror, a polygon mirror driving motor and the like, which are not illustrated.
The laser scanner units 4a, 4b, 4c, and 4d respectively scan and expose the surface of the photoconductor drums 2a, 2b, 2c, and 2d that are charged by the charging units 10a, 10b, 10c and 10d, based on image information input from an external device such as a PC (personal computer). An electric charge of an exposed part of the surface of each of the photoconductor drums 2a, 2b, 2c, and 2d is removed, which are scanned and exposed by the laser scanner units 4a, 4b, 4c, and 4d, respectively. In this way, an electrostatic latent image is formed on a surface of each of the photoconductor drums 2a, 2b, 2c, and 2d.
The developing units 16a, 16b, 16c, and 16d are disposed to correspond to the photoconductor drums 2a, 2b, 2c, and 2d, respectively, facing corresponding surfaces of the photoconductor drums 2a, 2b, 2c, and 2d. The developing units 16a, 16b, 16c, and 16d form toner images respectively on the photoconductor drums 2a, 2b, 2c, and 2d, by developing the electrostatic latent images. More specifically, the developing units 16a, 16b, 16c, and 16d form color toner images on surfaces of respective photoconductor drums 2a, 2b, 2c, and 2d by depositing toners of various colors on the electrostatic latent images formed on the surface of the photoconductor drums 2a, 2b, 2c, and 2d. The developing units 16a, 16b, 16c, and 16d correspond to four colors: yellow, cyan, magenta, and black, respectively. The developing units 16a, 16b, 16c, and 16d include developing rollers that are disposed to face the surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, agitation rollers for agitating toners, respectively, and the like.
The toner cartridges 5a, 5b, 5c, and 5d are provided corresponding to the developing units 16a, 16b, 16c, and 16d, respectively, and store the toners of different colors that are supplied to the developing units 16a, 16b, 16c, and 16d, respectively. The toner cartridges 5a, 5b, 5c, and 5d store toners of yellow, cyan, magenta, and black respectively.
The toner feeding portions 6a, 6b, 6c, and 6d are provided correspondingly to the toner cartridges 5a, 5b, 5c, and 5d and the developing units 16a, 16b, 16c, and 16d, respectively. The toner feeding portions 6a, 6b, 6c, and 6d supply the toners of the colors stored in the toner cartridges 5a, 5b, 5c, and 5d to the developing units 16a, 16b, 16c, and 16d, respectively. The toner feeding apparatuses 6a, 6b, 6c, and 6d are connected with the developing units 16a, 16b, 16c, and 16d, respectively, via toner feeding paths (not illustrated).
Toner images of respective colors formed on the photoconductor drums 2a, 2b, 2c, and 2d are primarily transferred in sequence to the intermediate transfer belt 7. The intermediate transfer belt 7 is stretched around a driven roller 35, the opposing roller 18 consisting of a driving roller, a tension roller 36 (not illustrated in
The primary transfer rollers 37a, 37b, 37c, and 37d are arranged to face the photoconductor drums 2a, 2b, 2c, and 2d, respectively, across the intermediate transfer belt 7. The primary transfer rollers 37a, 37b, 37c, and 37d are composed of transfer rollers that rotate in contact with surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, respectively, through the intermediate transfer belt 7. The primary transfer rollers 37a, 37b, 37c, and 37d are arranged in contact with surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, respectively, through the intermediate transfer belt 7, and apply a predetermined transfer potential to transfer the toner images to the intermediate transfer belt 7.
Predetermined parts of the intermediate transfer belt 7 are sandwiched between the primary transfer rollers 37a, 37b, 37c, and 37d and the photoconductor drums 2a, 2b, 2c, and 2d. The sandwiched parts are pressed against surfaces of the photoconductor drums 2a, 2b, 2c, and 2d. Primary transfer nips N1a, N1b, N1c, and N1d are thus formed between the photoconductor drums 2a, 2b, 2c, and 2d and the primary transfer rollers 37a, 37b, 37c, and 37d, respectively. On each of the primary transfer nips N1a, N1b, N1c, and N1d, the toner images of the colors developed on the photoconductor drums 2a, 2b, 2c, and 2d are primarily transferred sequentially to the intermediate transfer belt 7. In this manner, a full-color toner image is formed on the intermediate transfer belt 7.
A primary transfer bias is applied to each of the primary transfer rollers 37a, 37b, 37c, and 37d by a primary transfer bias application portion (not shown). The primary transfer bias is a bias for transferring the toner images of the colors formed respectively on the photoconductor drums 2a, 2b, 2c, and 2d to the intermediate transfer belt 7.
The neutralization units 12-0a, 12a, 12b, 12c, and 12d are disposed so as to face the surfaces of the photoconductor drums 2a, 2b, 2c, and 2d. The neutralization units 12-0a, 12a, 12b, 12c, and 12d neutralize electricity (eliminate an electrical charge) of surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, before and after the primary transfer, by irradiating the surfaces of the photoconductor drums 2a, 2b, 2c, and 2d with light (neutralization light).
A specific configuration of the neutralization units 12-0a, 12a, 12b, 12c, and 12d is described later.
The cleaning units 11a, 11b, 11c, and 11d are disposed so as to face the surfaces of the photoconductor drums 2a, 2b, 2c, and 2d, respectively. The cleaning units 11a, 11b, 11c and 11d make contact with surfaces of the photoconductor drums 2a, 2b, 2c and 2d respectively after transfer of the toner images onto the intermediate transfer belt 7, to thereby clean the surfaces of the photoconductor drum 2a, 2b, 2c and 2d. More specifically, the cleaning units 11a, 11b, 11c, and 11d remove toner and attached matter remaining on the surface of the photoconductor drums 2a, 2b, 2c, and 2d, respectively, and make the removed toner carried to a predetermined collection mechanism for collection.
The secondary transfer roller 8 secondarily transfers the full-color toner image, which has been primarily transferred to the intermediate transfer belt 7, to the paper T. A secondary transfer bias is applied to the secondary transfer roller 8, by a secondary transfer bias application unit (not illustrated). The secondary transfer bias is a bias for transferring the full-color toner image formed on the intermediate transfer belt 7 to the paper T.
The secondary transfer roller 8 is brought into contact with, and spaced apart from, the intermediate transfer belt 7. More specifically, the secondary transfer roller 8 is configured to be movable between a contact position at which it is in contact with the intermediate transfer belt 7 and a spaced position at which it is spaced apart from the intermediate transfer belt 7. In particular, the secondary transfer roller 8 is disposed at the contact position for transferring the toner image primarily transferred to a surface of the intermediate transfer belt 7 to the paper T, and at the spaced position in all other circumstances.
The opposing roller 18 is disposed opposite to the secondary transfer roller 8 across the intermediate transfer belt 7. A predetermined part of the intermediate transfer belt 7 is sandwiched between the secondary transfer roller 8 and the opposing roller 18. The sheet of paper T is pressed against an outer surface (a surface to which the toner image is primarily transferred) of the intermediate transfer belt 7. A secondary transfer nip N2 is formed between the intermediate transfer belt 7 and the secondary transfer roller 8. On the secondary transfer nip N2, the full-color toner image primarily transferred to the intermediate transfer belt 7 is secondarily transferred to the paper T.
The fixing unit 9 fuses and pressurizes color toners composing the toner image secondarily transferred to the paper T, in order to fix the color toners on the paper T. The fixing unit 9 includes a heating rotator 9a that is heated by a heater, and a pressurizing rotator 9b that is brought into pressure-contact with the heating rotator 9a. The heating rotator 9a and the pressurizing rotator 9b sandwich and pressurize, and convey the paper T to which the toner image is secondarily transferred. The sheet of paper T is fed while sandwiched between the heating rotator 9a and the pressurizing rotator 9b, so that the toner transferred to the sheet of paper is fused and pressurized to be fixed to the sheet of paper T.
Next, the paper feeding/discharging portion KH is described.
As shown in
The manual feeding unit 64 is provided on a left lateral face (the left side in
The paper feed path L includes: a first paper feed path L1 from the cassette feeding unit 51 to the secondary transfer nip N2; a second paper feed path L2 from the secondary transfer nip N2 to the fixing unit 9; a third paper feed path L3 from the fixing unit 9 to the discharging portion 50; the manual paper feed path La that guides paper fed from the feeding unit 64 to the first paper feed path L1; and a reverse paper feed path Lb that reverses and returns the paper that is fed from a downstream side to an upstream side in the third paper feed path L3 to the first paper feed path L1.
The first paper feed path L1 feeds the paper T stored in the paper feeding cassette 52 toward the image forming portion GK. The manual paper feed path La feeds the paper T stored in the manual feeding portion 64 toward the registration roller pair 80 (described later).
In addition, a first junction P1 and a second junction P2 are provided in the middle of the first paper feed path L1. A first branch portion Q1 is provided in the middle of the third paper feed path L3. The first junction P1 is a junction where the manual paper feed path La joins the first paper feed path L1. The second junction P2 is a junction where the reverse paper feed path Lb joins the first paper feed path L1. The first branch portion Q1 is a branch portion where the reverse paper feed path Lb branches off from the third paper feed path L3.
A paper detection sensor (not illustrated) for detecting the paper T and a registration roller pair 80 are disposed in the middle of the first paper feed path L1 (more specifically, between the second junction P2 and the secondary transfer roller 8). The registration roller pair 80 is designed for skew compensation of the paper T and timing adjustment with respect to formation of the toner image in the image forming portion GK. The paper detection sensor is disposed immediately before the registration roller pair 80 in a conveying direction of the paper T (on an upstream side thereof in the conveying direction). The registration roller pair 80 conveys the paper T while performing the abovementioned compensation and the timing adjustment based on detection information from the paper detection sensor.
A first feeding roller pair 82 as a first roller is disposed between the first junction P1 and the second junction P2 in the first paper feed path L1. The first feeding roller pair 82 is disposed on a downstream side of the paper feeding roller pair 81, and sandwiches and feeds the paper T, which is fed from the paper feeding roller pair 81, to the registration roller pair 80.
For a case of performing duplex printing of the paper T, a reverse paper feed path Lb is provided for making an opposite surface (an unprinted surface), to a surface that has already been printed, face toward the intermediate transfer belt 7. A plurality of second feeding roller pairs 83 that feed the paper T to the second junction P2 is disposed at predetermined intervals in the reverse paper feed path Lb. The reverse paper feed path Lb can reverse and return the paper T, fed from the first branch portion Q1 toward the discharging portion 50, to the first paper feed path L1, in order to feed the paper T to an upstream side of the registration roller pair 80 disposed on an upstream side of the secondary transfer roller 8. At the secondary transfer nip N2, a predetermined toner image is transferred to the unprinted surface of the sheet of paper T that has been reversed by the reverse paper feed path Lb.
A regulating member 58 is provided in the first branch portion Q1. The regulating member 58 regulates a feed direction of the paper T, which is discharged from the fixing unit 9 and fed from the upstream side to the downstream side of the third paper feed path L3, to a direction toward the discharging portion 50. The regulating member 58 regulates a feed direction of the paper T, which is fed from the discharging portion 50 from the downstream side to the upstream side of the third paper feed path L3, to a direction toward the reverse paper feed path Lb.
The discharging portion 50 is formed in an end portion of the third paper feed path L3. The discharging portion 50 is disposed in an upper portion of the apparatus main body M. The discharging portion 50 has an opening toward a left lateral face of the apparatus main body M (left side in
A discharged paper accumulating portion M1 is formed in the vicinity of the opening of the discharging portion 50. The discharged paper accumulating portion M1 is formed on an upper face (outer face) of the apparatus main body M. The discharged paper accumulating portion M1 is a portion of the upper face of the apparatus main body M formed to be dented downward. The bottom face of the discharged paper accumulating portion M1 is composed of a top cover member M2 constituting a part of the upper face of the apparatus main body M. The paper T, on which a predetermined toner image is formed and which is discharged from the discharging portion 50, is stacked and accumulated on the upper face of the top cover member M2 constituting the discharged paper accumulating portion M1. A sensor for detecting a sheet of paper is disposed at a predetermined position of each paper feed path.
Next, operation of the printer 1 according to the embodiment is briefly described with reference to
The paper T stored in the paper cassette 52 is fed to the first paper feed path L1 by way of the forward feed roller 61 and the paper feeding roller pair 81. And then, the paper T is fed to the registration roller pair 80 by way of the first feeding roller pair 82 via the first junction P1 and the first paper feed path L1. The registration roller pair 80 performs skew compensation of the paper T and timing adjustment with respect to the toner image in the image forming portion GK.
The paper T discharged from the registration roller pair 80 is introduced into between the intermediate transfer belt 7 and the secondary transfer roller 8 (the secondary transfer nip N2) via the first paper feed path L1. A toner image is transferred to the paper T between the intermediate transfer belt 7 and the secondary transfer roller 8. Thereafter, the paper T is discharged from between the intermediate transfer belt 7 and the secondary transfer roller 8, and introduced into the fixing nip between the heating rotator 9a and the pressurizing rotator 9b in the fixing unit 9 via the second paper feed path L2. Toner is then fused in the fixing nip and fixed onto the paper T.
Subsequently, the paper T is conveyed to the discharging portion 50 via the third paper feed path L3 and discharged from the discharging portion 50 to the discharged paper accumulating portion M1 by the discharging roller pair 53. Single-side printing on the paper T housed in the paper feeding cassette 52 is thus completed.
In a case of single-side printing on the paper T placed on the manual feeding tray 65, the paper T placed on the manual feeding tray 65 is dispatched to the manual paper feed path La by the paper feeding roller 66, and then conveyed to the registration roller pair 80 via the first junction P1 and the first paper feed path L1. Other operations are the same as in the case of single-side printing on the paper T housed in the paper feeding cassette 52, and therefore descriptions thereof are omitted.
Next, operation of the printer 1 performing duplex printing is described.
In a case of single-side printing, as described above, printing is completed by discharging the paper T printed on one side from the paper discharging portion 50 to the discharged paper accumulating portion M1. On the other hand, in a case of duplex printing, the paper T, one side of which has been printed, is reversed via the reverse paper feed path Lb. The paper T is then re-fed to the registration roller pair 80 to thereby complete duplex printing on the paper T.
In more detail, the operation is the same as in the abovementioned single-side printing until before discharging of the paper T printed on one side from the paper discharging portion 50 by the discharging roller pair 53. In a case of duplex printing, the discharging roller pair 53 stops rotating and rotates again in an opposite direction, in a state of holding the paper T printed on one side. By thus rotating the discharging roller pair 53 in an opposite direction, the paper T held by the discharging roller pair 53 is conveyed in an opposite direction in the third paper feed path L3 (a direction from the paper discharging portion 50 to the first branch portion Q1).
As described above, when the paper T is fed in the opposite direction in the third paper feed path L3, the regulating member 58 directs the paper T to the reverse paper feed path Lb, and then the paper T enters into the first paper feed path L1 via the second junction P2. Here, the paper T is reversed from the orientation thereof in printing on the one side.
Furthermore, the registration roller pair 80 performs the abovementioned compensation or the abovementioned adjustment on the paper T, which is then introduced into the secondary transfer nip N2 via the first paper feed path L1. Since an unprinted surface of the paper T faces the intermediate transfer belt 7 as a result of passing through the reverse paper feed path Lb, a toner image is transferred to the unprinted surface and duplex printing is thus realized.
Next, the configuration of the neutralization units 12-0a, 12a, 12b, 12c, and 12d in the four image forming units 15a, 15b, 15c, and 15d of the printer 1 according to the embodiment will be described with reference to
As shown in
The neutralization units 12a, 12b, 12c, and 12d irradiate regions on the photoconductor drums 2a, 2b, 2c and 2d constituting the four image forming units 15a, 15b, 15c, and 15d with first neutralization light 131, the regions spanning from positions facing the primary transfer positions to positions facing the cleaning units 11a, 11b, 11c, and 11d, respectively. In addition, the neutralization units 12-0a, 12a, 12b and 12c irradiate regions on the photoconductor drums 2a, 2b, 2c and 2d constituting the four image forming units 15a, 15b, 15c and 15d with the second neutralization light 132, the regions spanning from positions facing the developing units 16a, 16b, 16c and 16d and to positions facing the primary transfer positions.
Here, the first neutralization light 131 irradiates regions on the photoconductor drums 2a, 2b, 2c and 2d constituting the four image forming units 15a, 15b, 15c, and 15d, the regions spanning from positions facing the primary transfer positions to positions facing the cleaning units 11a, 11b, 11c, and 11d, respectively. The first neutralization light 131 thereby neutralizes residual charge on the surface of the photoconductor drums 2a, 2b, 2c and 2d after the primary transfer of a toner image to the intermediate transfer belt 7 (post-transfer neutralization).
As a result, it is possible to suppress the generation of an exposure memory image due to a difference in surface potential lower than the peripheral potential upon follow-up charging of the exposed part. In addition, it is possible to prevent a part in which the memory image is generated from being printed to be darker than a periphery in a background part.
The second neutralization light 132 irradiates regions on the photoconductor drums 2a, 2b, 2c and 2d constituting the four image forming units 15a, 15b, 15c, and 15d, the regions spanning from positions facing the developing units 16a, 16b, 16c and 16d to positions facing the primary transfer positions, respectively. The second neutralization light 132 performs neutralization such that a dark potential (V0 potential) of a non-image region on the photoconductor drums 2a, 2b, 2c and 2d on which toner images have been formed is higher by approximately 100 V than a bright potential (VL potential) of a solid image region (pre-transfer neutralization).
As a result, with regard to an image region that is a part of the surface of the photoconductor drum where a toner image is formed and a non-image region that is a part of the surface of the photoconductor drum where no toner image is formed, a potential difference between the non-image region and the transfer unit and the potential difference between the image region and the transfer unit are reduced in comparison to a case without the pre-transfer neutralization. As a result, more current flows into the image region, thereby improving the transfer performance. The improvement in the transfer performance allows lowering of the transfer voltage. In addition, this reduces a difference of values of influx current and a difference of charging characteristics between the image region and the non-image region, thereby preventing the generation of transfer memory.
In other words, in the present embodiment, the neutralization unit 12a functions as a post-transfer neutralization unit that is disposed between the primary transfer roller 37a and the cleaning unit 11a and emits the first neutralization light 131 to neutralize the surface of the photoconductor drum 2a after transfer, while functioning as a pre-transfer neutralization unit that is disposed between the developing unit 16b and the primary transfer roller 37b and emits the second neutralization light 132 to neutralize the surface of the photoconductor drum 2b before transfer. The same applies to the neutralization units 12b and 12c.
It should be noted that the post-transfer neutralization unit that emits the first neutralization light 131 and the pre-transfer neutralization unit that emits the second neutralization light 132 can be configured as separate neutralization units.
Next, a configuration of a characterizing part of the printer 1 according to the present embodiment is described with reference to
For the pre-transfer neutralization of the photoconductor drum 2b by the neutralization unit 12a, the image forming portion GK includes: a neutralization driver 140 that controls a light emitting behavior of the neutralization unit 12a; a first control unit 141 that controls the neutralization light intensity of the neutralization unit 12a; and a first setting operating unit 142. The first setting operating unit 142 allows for an increase and decrease of light intensity for the pre-transfer neutralization as appropriate, according to a status of an output image.
More specifically, the neutralization driver 140 controls the neutralization light intensity of the neutralization unit 12a based on a light intensity for the pre-transfer neutralization that has been set by the first control unit 141 and the first setting operating unit 142. The neutralization unit 12a thus emits the first neutralization light 131. Here, the bright potential (VL potential) of a solid image region is approximately +100 V, while the dark potential (V0 potential) of a non-image region is +200 V, which is higher than the bright potential (VL potential) by approximately 100 V.
The “output image” indicates an image that is actually output (toner image), with the influence of transfer memory, scattered toner and the like.
The “solid image region” indicates a region where a solid image is formed as a result of being exposed on the photoconductor drum after charging. The “non-image region” indicates a region where no image is formed (blank) as a result of not being exposed on the photoconductor drum after charging.
The “bright potential (VL potential)” indicates a potential of the solid image region after charging. The “dark potential (V0 potential)” indicates a potential of the non-image region after charging.
On the other hand, with regard to the primary transfer roller 37b, the image forming portion GK includes: a primary transfer potential application unit 370 that applies an intermediate transfer potential to the primary transfer roller 37b upon primary transfer to the intermediate transfer belt 7 (image transfer object); a second control unit 371 that controls an applied amount of the intermediate transfer potential; and a second setting operating unit 372 (see
The second setting operating unit 372 inputs a setting of the intermediate transfer potential. The second control unit 371 controls the transfer potential to be applied to the primary transfer roller 37b by the primary transfer potential application unit 370 so as to be a predetermined potential, based on the intermediate transfer potential thus set by the second setting operating unit 372.
More specifically, the second control unit 371 adjusts (controls) the applied amount such that, in a case in which a resistance value of the surface of the primary transfer roller 37b to which −1000 V is applied as the intermediate transfer potential is 1×107-8.50Ω, a transfer current is in a range of −2.5 to −5.0 μA, based on the intermediate transfer potential being set. The value of the (primary) transfer current (−2.5 to −5.0 μA) corresponds to, for example, 25 to 50% of the value of the (primary) transfer current in a case without the pre-transfer neutralization.
In the printer 1 of the embodiment thus configured, the potential of the non-image region on the photoconductor drum 2b is maintained to be higher than the potential of the solid image region by approximately +100 V by the first control unit 141 controlling the neutralization light intensity before transfer, thereby allowing for a reduction in potential difference of the solid image region and the non-image region relative to the primary transfer roller 37b. As a result, on the surface of the photoconductor drum 2b, scattering of the toner in an edge area of the solid image region toward the periphery of the solid image region is suppressed, whereby transfer performance for fine pixels can be improved.
In addition, the intermediate transfer current is adjusted to be in a range of −2.5 to −5.0 μA, by the second control unit 371 controlling the intermediate transfer potential. As a result, generation of transfer memory due to a difference in the influx amount of the transfer current between the solid image region and the non-image region, due to the potential difference of the solid image region and the non-image region relative to the primary transfer roller 37b, is reduced. Especially, even if a charging system of low charging performance that charges the surface of the photoconductor drum 2b at a predetermined positive potential, is employed in order to reduce ozone generation and to curb the deterioration in the environment of the installation site of the apparatus such as an office, the generation of the transfer memory can be sufficiently reduced and a clean image without a trace of a previous image can be obtained.
The following test was conducted. The bright potential (VL potential) of the solid image region on the photoconductor drum 2b was set to be +100 V, while the potential of the non-image region on the photoconductor drum 2b after the pre-transfer neutralization was set to 4 levels: +600 V; +400 V; +200 V; and +100 V. In addition, the primary transfer current by the primary transfer roller 37b was set to 5 levels: −10 μA; −5.0 μA; −3.5 μA; −2.5 μA; and −1.5 μA. Toner scattering, generation of transfer memory, and transfer performance were assessed for cases with and without the pre-transfer neutralization. The results obtained are shown in Table 1.
In the column for toner scattering in Table 1, a circle indicates an absence of toner scattering and an X indicates presence of toner scattering. In the column for transfer memory, XX indicates the generation of extremely large transfer memory; X indicates generation of large transfer memory; a triangle indicates the generation of a little transfer memory; and a combination of a circle and triangle indicates the generation of slight transfer memory. In the column for transfer performance, a circle indicates superior transfer performance; a triangle indicates slightly inferior transfer performance; and X indicates impaired transfer performance.
As is evident from the results shown in Table 1, it was confirmed that the toner scattering can be suppressed to improve the transfer performance, and the generation of transfer memory due to a difference in influx amount of transfer current can be sufficiently reduced to allow formation of a high-quality image, by: the first control unit 141 adjusting the bright potential (VL potential) of the solid image region to be +100 V and the potential of the non-image region after the pre-transfer neutralization to be +200 V, which is higher than the bright potential (VL potential) of the solid image region by 100 V, as well as the second control unit 371 adjusting the intermediate transfer current to be in a range of −2.5 μA to −5.0 μA.
The printer 1 of the present embodiment provides, for example, the following effects.
The printer 1 of the present embodiment includes: the charging unit 10b; the developing unit 16b; the primary transfer roller 37b; the neutralization unit 12a; the cleaning unit 11b; the neutralization unit 12b; the first control unit 141; the second control unit 371; and the first setting operating unit 142. The charging unit 10b charges the surface of the photoconductor drum 2b at a predetermined positive potential. The developing unit 16b forms a toner image on the surface of the photoconductor drum 2b by developing the electrostatic latent image. The primary transfer roller 37b is arranged in contact with the surface of the photoconductor drum 2b through the intermediate transfer belt 7, and applies a predetermined transfer potential to transfer the toner image to the intermediate transfer belt 7. The neutralization unit 12a as the pre-transfer neutralization unit is arranged between the developing unit 16b and the primary transfer roller 37b, and neutralizes the surface of the photoconductor drum 2b before transfer. The cleaning unit 11b makes contact with the surface of the photoconductor drum 2b after transfer of the toner images onto the intermediate transfer belt 7 to clean the surface of the photoconductor drum 2b. The neutralization 12b as the post-transfer neutralization unit is arranged between the primary transfer roller 37b and the cleaning unit 11b, and neutralizes the surface of the photoconductor drum 2b after transfer. The first control unit 141 controls the neutralization light intensity of the neutralization unit 12a as the pre-transfer neutralization unit such that the dark potential (V0 potential) of the non-image region on the photoconductor drum 2b after the pre-transfer neutralization is higher by +50 to +150 V than the bright potential (VL potential) of the solid image region. The second control unit 371 controls the transfer potential of the primary transfer roller 37b. The first setting operating unit 142 allows for an increase and decrease of the neutralization light intensity of the neutralization unit 12a as the pre-transfer neutralization unit, based on a status of the output image.
As a result, scattering of the toner in an edge area of the image toward the non-image region can be suppressed; and the transfer memory, which is a trace of a previous image visible on an image currently formed, generated due to a difference in the charging characteristics of the photoconductor drum under the influence of a primary transfer can be prevented.
In addition, by the second control unit 371 controlling the applied amount of the intermediate transfer potential, the intermediate transfer current can be adjusted to reduce a potential difference of the solid image region and the non-image region relative to the primary transfer roller 37b. As a result, generation of transfer memory due to a difference in influx amount of the transfer current between the solid image region and the non-image region on the photoconductor drum 2b can be reduced.
As described above, adjustment can be made by appropriately combining: adjustment of the potential difference between the solid image region and the non-image region by the first control unit 141; and adjustment of the transfer potential by the second control unit 371. This can suppress scattering of the toner and achieve an improvement of transfer performance, while being a charging system that is preferable for an improvement in the environment. In addition, generation of transfer memory due to a difference in influx amount of the transfer current can be sufficiently reduced, thereby allowing formation of a high-quality clean image without unevenness and inconsistent density.
Furthermore, in the present embodiment, the transfer unit comprises the primary transfer roller 37b that rotates in contact with the surface of the photoconductor drum 2b through the intermediate transfer belt 7, which is the transfer object, and the charging unit 10a comprises a charging roller that rotates in contact with the surface of the photoconductor drum 2b. Since the transfer unit and the charging unit are rollers in line contact with the surface of the photoconductor drum 2b, degradation of a film on the surface of the photoconductor drum 2b, leading to abrasion of the drum, can be suppressed. As a result, durability of the photoconductor drum 2b can be improved. Furthermore, this can simplify configurations of, and reduce costs for, the transfer unit and the charging unit.
In the present embodiment, the first control unit 141 controls the neutralization light intensity of the neutralization unit 12a as the pre-transfer neutralization unit such that the dark potential (V0 potential) of the non-image region on the photoconductor drum 2b after the pre-transfer neutralization is higher by +50 to +150 V than the bright potential (VL potential) of the solid image region. In addition, the second control unit 371 controls the transfer unit such that, in a case in which a resistance value of the surface of the primary transfer roller 37b to which −1000 V is applied as the transfer potential is 1×107-8.5Ω, a transfer current corresponding to the transfer potential −600 V is in a range of −2.5 to −5.0 μA.
This can, in the pre-transfer neutralization by the neutralization unit 12a, consistently maintain the potential of the non-image region to be higher than that of the solid image region by about +100 V, and adjust the applied amount of the intermediate transfer potential such that the transfer current corresponding to the intermediate transfer potential is maintained in a range of −2.5 to −5.0 μA. As is evident from the test results in Table 1, this can improve the transfer performance by suppressing scattering of the toner, while sufficiently suppressing generation of transfer memory due to a difference in influx amount of transfer current.
A preferred embodiment of the present disclosure has been described above; however, the present disclosure is not limited thereto and can be carried out in various modes.
For example, the image transfer object described in the above embodiment is the intermediate transfer belt 7; however, the present disclosure is not limited thereto. In an image forming apparatus employing a direct transfer system in which an image is directly transferred from the photoconductor drum to an image transfer object without primary transfer, the image transfer object is paper, a film-like sheet, or the like.
The printer 1 is exemplified in the present embodiment as an image forming apparatus; however, the present disclosure is not limited thereto and can be a copy machine, a facsimile machine, or a multi-functional peripheral having functions thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-016319 | Jan 2012 | JP | national |
