Image forming device

Abstract

To improve transfer performance while preventing toner scattering and transfer memory.SOLUTION: A printer comprises: a photoreceptor drum 11 that is provided along a conveyance path 10 for conveying a sheet; an electrifying roller 12 that electrifies the photoreceptor drum 11; a developing device 14 that develops a latent image formed on the photoreceptor drum 11 electrified by the electrifying roller 12 by using toner; a transfer roller 15 that is opposite to the photoreceptor drum 11 with the conveyance path 10 therebetween and generates a transfer bias; a first static eliminator 30 that irradiates the photoreceptor drum 11 with light on the downstream of the developing device 14 in a rotation direction Z of the photoreceptor drum 11 and on the upstream side of the transfer roller 15 in the rotation direction Z; and a control unit that controls the first static eliminator 30 to irradiate only a non-paper feed part of the photoreceptor drum 11 with light.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus that forms an image by electrophotography. [Background technology]

[0002] In the process of transferring a toner image on a photoreceptor to a sheet or intermediate transfer belt, it is common to apply a constant current to the transfer roller to stabilize the transfer electric field and obtain good transfer performance. However, when comparing the image area (exposed area) on the photoreceptor with the non-image area (unexposed area), the potential difference between the non-image area and the transfer roller is greater than the potential difference between the image area and the transfer roller, so the transfer current of the opposite polarity to the non-image area flows more in the non-image area and less in the image area. Therefore, fine pixels are difficult to transfer, which is an obstacle to high image quality. As a means to avoid this obstacle, it is possible to increase the transfer current to improve transfer performance, but if the transfer current is increased, the difference in the amount of transfer current flowing into the image area and the non-image area becomes larger, so the residual charge in the non-image area increases, and transfer memory (shading indicating the transfer history) occurs in the subsequent image. In recent years, charging devices have been shifting from the corona discharge type to the charging roller type, which generates less ozone, but in the case of the charging roller type, the transfer memory tends to appear more prominently than in the corona discharge type.

[0003] Therefore, conventionally, techniques for improving the static elimination capability of a photoconductor have been considered. For example, Patent Document 1 proposes a configuration in which a static elimination light source disposed between a primary transfer position and a cleaning unit in a tandem-type color image forming apparatus using an intermediate transfer belt also serves as a pre-transfer static elimination light source for an image forming unit adjacent in the rotation direction of the intermediate transfer belt. Patent Documents 2 to 5 propose a configuration in which a static elimination light is irradiated onto a photoconductor through a sheet at a position upstream of a transfer device in the transport direction or at the same position as the transfer device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-221405 A [Patent Document 2] Japanese Patent Application Publication No. 01-4782 [Patent Document 3] Japanese Patent Application Publication No. 11-84912 [Patent Document 4] Japanese Patent Application Publication No. 02-73666 [Patent Document 5] JP 2003-5535 A Summary of the Invention [Problem to be solved by the invention]

[0005] The potential difference between the image area and the non-image area acts as a binding force for the toner, but as the potential difference becomes smaller, the binding force also becomes weaker, making toner scattering (the scattering of toner from the image area to the non-image area) more likely to occur. In the configuration proposed in Patent Document 1, light is also irradiated to the paper passing area of ​​the photoconductor (the area where the sheet comes into contact during transfer), so the potential of the non-image area of ​​the paper passing area decreases, making toner scattering more likely to occur.

[0006] In the configurations proposed in Patent Documents 1 to 5, when a toner image is directly transferred to a sheet without an intermediate transfer body, more transfer current flows into non-paper passing areas (areas where the sheet does not contact during transfer) than into paper passing areas, making it difficult to control the transfer current and causing a potential drop due to transfer memory. The higher the potential of the non-paper passing areas, the stronger this tendency becomes. For example, when the potential at the development position is 500V, if the potential of the non-paper passing areas is 150V or more higher than the image area, the drop in transfer performance becomes noticeable. Increasing the transfer current to improve transfer performance causes the transfer memory to become darker.

[0007] In the configurations proposed in Patent Documents 2 to 5, it is necessary to increase the amount of light to obtain a static elimination effect in the paper passing portion of the photoconductor, but in that case, there is a problem that deterioration of the photoconductor is accelerated in the non-paper passing portion. Also, in the case of the charging roller method (especially DC charging), potential unevenness is likely to occur.

[0008] SUMMARY OF THE PRESENT DISCLOSURE In consideration of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of improving transfer performance while suppressing toner scattering and transfer memory. [Means for solving the problem]

[0009] In order to solve the above problem, the image forming apparatus of the present invention is characterized in that it comprises a photosensitive drum arranged along a transport path for transporting a sheet, a charging roller for charging the photosensitive drum, a developing device for developing a latent image formed on the photosensitive drum charged by the charging roller using toner, a transfer roller facing the photosensitive drum across the transport path and generating a transfer bias, a first static elimination device for irradiating light onto the photosensitive drum downstream of the developing device in the rotation direction of the photosensitive drum and upstream of the transfer roller in the rotation direction, and a control unit for controlling the first static elimination device so as to irradiate light only onto non-paper passing portions of the photosensitive drum.

[0010] The first static elimination device may include a plurality of light sources arranged in a width direction intersecting the conveying direction of the conveying path, and the control unit may turn on only one of the plurality of light sources that faces the non-paper passing portion according to the size of the sheet being conveyed.

[0011] The image forming apparatus may include a second static elimination device that irradiates light onto the photosensitive drum downstream in the rotation direction of the photosensitive drum from the transport path downstream in the transport direction from the transfer position of the transfer roller and upstream in the rotation direction from the charging roller, and the amount of light emitted by the first static elimination device may be less than that of the second static elimination device.

[0012] The control unit may control the amount of light of the first static eliminator so that the potential of the non-paper passing portion of the photosensitive drum is lower than that of a non-image portion of the paper passing portion before a transfer step by the transfer roller.

[0013] The image forming apparatus may further include a light blocking member that blocks light from reaching the paper passing portion when only the light source facing the non-paper passing portion is turned on.

[0014] A length of the transfer roller in a width direction intersecting with a transport direction of the transport path may be equal to or greater than a maximum length of the sheet in the width direction. Effect of the Invention

[0015] According to the present invention, it is possible to improve transfer performance while suppressing toner scattering and transfer memory. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is an oblique view illustrating the appearance of a printer according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a right side view illustrating a schematic internal configuration of a printer according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a right side view illustrating a schematic configuration of an image forming device according to an embodiment of the present invention. [Figure 4] FIG. 2 is a plan view illustrating a first static eliminator, a second static eliminator, a photosensitive drum, and a transfer roller according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a right side view illustrating a schematic configuration of an image forming device according to an embodiment of the present invention. [Figure 6] 11A and 11B are plan views showing an operation when a sheet having a width direction length longer than a transfer roller is transported according to an embodiment of the present invention. [Figure 7] 11A and 11B are plan views showing an operation when conveying a sheet whose length in the width direction is shorter than that of a transfer roller according to an embodiment of the present invention. [Figure 8] 11A and 11B are plan views showing an operation when conveying a sheet whose length in the width direction is shorter than that of a transfer roller according to an embodiment of the present invention. [Figure 9] FIG. 11 is a plan view showing a schematic diagram of a first static eliminator, a second static eliminator, a photosensitive drum, and a transfer roller according to a modified example of an embodiment of the present invention. [Figure 10]FIG. 11 is a perspective view of a first static eliminator according to a modified example of an embodiment of the present invention. [Figure 11] FIG. 11 is a plan view showing a first static eliminator according to a modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A printer 1 (an example of an image forming apparatus) according to an embodiment of the present invention will be described below with reference to the drawings.

[0018] First, the overall configuration of the printer 1 will be described. Fig. 1 is a perspective view showing the exterior of the printer 1. Fig. 2 is a right side view showing a schematic internal configuration of the printer 1. In the following description, the left side of the paper in Fig. 2 is the front side (front side) of the printer 1, and the left and right directions are described based on the direction when the multifunction device 100 is viewed from the front. In each figure, U, Lo, L, R, Fr, and Rr respectively indicate up, down, left, right, front, and rear.

[0019] The printer 1 includes a rectangular parallelepiped housing 3. A paper feed cassette 4 that stores sheets S and a paper feed roller 5 that feeds sheets S from the paper feed cassette 4 are provided at the bottom inside the housing 3. An image creating device 6 that forms a toner image by electrophotography is provided above the paper feed cassette 4, and a fixing device 7 that fixes the toner image to the sheet S is provided behind the image creating device 6. A paper discharge roller 8 that discharges the sheet S on which the toner image has been fixed, and a paper discharge tray 9 on which the discharged sheets S are stacked are provided above the fixing device 7.

[0020] A transport path 10 is provided inside the housing 3, which runs from the paper feed roller 5 through the image forming device 6 and the fixing device 7 to the paper discharge roller 8. The transport path 10 is formed by plate-like members facing each other with a gap therebetween to allow the sheet S to pass through, and transport rollers 17 that hold and transport the sheet S are provided at multiple locations in the transport direction Y. A registration roller 18 is provided upstream of the image forming device 6 in the transport direction.

[0021] The image forming device 6 includes a photoconductor drum 11 whose potential changes when irradiated with light, a charging roller 12 that charges the photoconductor drum 11, an exposure device 13 that emits laser light according to image data, a developing device 14 that supplies toner to the photoconductor drum 11, a transfer roller 15 that generates a transfer bias, and a cleaning device 16 that removes toner remaining on the photoconductor drum 11. A toner container 20 that supplies toner to the developing device 14 is connected to the developing device 14.

[0022] As an example, the photoconductor drum 11 includes a positively charged photoconductor. The charging roller 12 is a positive DC (Direct Current) charging roller, and charges the photoconductor drum 11 positively. The developing device 14 charges the toner positively. The transfer roller 15 generates a negative transfer bias. The toner is magnetic toner. The positively charged image forming device 6 has the advantage of generating less ozone compared to the negatively charged type. Note that the present invention may be applied to a printer 1 in which the polarities of the charging and transfer biases are opposite to those described above. The present invention may also be applied to a printer 1 including an AC (Alternating Current) charging roller, and a printer 1 using non-magnetic toner.

[0023] The control unit 2 includes a calculation unit and a storage unit. The calculation unit is, for example, a CPU (Central Processing Unit). The storage unit includes storage media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and an EEPROM (Electrically Erasable Programmable Read Only Memory). The calculation unit performs various processes by reading and executing a control program stored in the storage unit. The control unit 2 may be realized by an integrated circuit that does not use software.

[0024] An operation panel 19 is provided on the right side of the top surface of the housing 3. The operation panel 19 includes a display panel and a keypad adjacent to the display panel. The control unit 2 displays a screen showing the operation menu and status of the printer 1 on the display panel, and controls each part of the printer 1 in response to operations detected on the keypad.

[0025] The basic image forming operation of the printer 1 is as follows. When a print job for single-sided printing is input to the printer 1 from an external computer or the like, the paper feed roller 5 feeds the sheet S from the paper feed cassette 4 to the transport path 10, the registration roller 18, whose rotation has been stopped, corrects any skew of the sheet S, and the registration roller 18 feeds the sheet S to the image forming device 6 at a predetermined timing. In the image forming device 6, the charging roller 12 charges the photosensitive drum 11 to a predetermined potential, the exposure device 13 writes a latent image on the photosensitive drum 11, the developing device 14 develops the latent image using toner supplied from the toner container 20 to form a toner image, and the transfer roller 15 transfers the toner image to the sheet S. Next, the fixing device 7 melts the toner image while clamping and transporting the sheet S to fix the toner image to the sheet S, and the paper discharge roller 8 discharges the sheet S to the paper discharge tray 9.

[0026] Next, a description will be given of the configuration regarding the static elimination of the photosensitive drum 11. Fig. 3 is a right side view showing a schematic configuration of the imaging device 6. Fig. 4 is a plan view showing a schematic configuration of the first static elimination device 30, the second static elimination device 40, the photosensitive drum 11, and the transfer roller 15.

[0027] The printer 1 includes a photosensitive drum 11 arranged along a transport path 10 along which a sheet S is transported, a charging roller 12 which charges the photosensitive drum 11, a developing device 14 which uses toner to develop a latent image formed on the photosensitive drum 11 charged by the charging roller 12, a transfer roller 15 which faces the photosensitive drum 11 across the transport path 10 and generates a transfer bias, a first static elimination device 30 which irradiates light onto the photosensitive drum 11 downstream in the rotation direction Z of the photosensitive drum 11 from the developing device 14 and upstream in the rotation direction Z from the transfer roller 15, and a control unit 2 which controls the first static elimination device 30 so as to irradiate light only onto non-paper passing portions of the photosensitive drum 11.

[0028] [First static eliminator] The first static eliminator 30 includes a plurality of light sources 31 arranged in a width direction X intersecting with the transport direction Y, and a housing 32 having the width direction X as a longitudinal direction. The light sources 31 are, for example, LEDs (Light Emitting Diodes), and are housed in the housing 32 and exposed from one side of the housing 32. In the example of FIG. 4, 72 light sources 31 are arranged in a row in the width direction X, but the number of light sources 31 may be any number, and the number of rows of light sources 31 may be multiple. The first static eliminator 30 is disposed downstream of the developing device 14 in the rotation direction Z of the photoconductor drum 11 and above the transport path 10 upstream of the transfer position of the transfer roller 15 in the transport direction Y, and is fixed to the housing 3 with the light sources 31 facing the photoconductor drum 11.

[0029] The first static eliminator 30 may be disposed below the transport path 10 on the upstream side in the transport direction Y of the transfer position of the transfer roller 15. FIG. 5 is a right side view showing a schematic configuration of the imaging device 6. In this case, the members forming the transport path 10 are disposed to avoid the irradiation range of the light source 31 so that the light emitted by the light source 31 reaches the photoconductor drum 11. In other words, the first static eliminator 30 according to this embodiment irradiates the photoconductor drum 11 with light downstream of the developing device 14 in the rotation direction Z of the photoconductor drum 11 and upstream of the transfer roller 15 in the rotation direction Z.

[0030] [Second static eliminator] The second static eliminator 40 includes a plurality of light sources 41 arranged in a width direction X intersecting with the transport direction Y, and a housing 42 having the width direction X as a longitudinal direction. The light sources 41 are, for example, LEDs, and are exposed from one surface of the housing 42. In the example of FIG. 4, 72 light sources 41 are arranged in a row in the width direction X, but the number of light sources 41 may be any number, and the number of rows of the light sources 41 may be multiple. The second static eliminator 40 is disposed downstream in the rotation direction Z of the photoconductor drum 11 from the transport path 10 downstream in the transport direction Y from the transfer position of the transfer roller 15, and upstream in the rotation direction Z from the cleaning device 16, and is fixed to the housing 3 with the light sources 41 facing the photoconductor drum 11.

[0031] The second static eliminator 40 may be disposed downstream in the rotation direction Z of the cleaning device 16 and upstream in the rotation direction Z of the charging roller 12. In other words, the second static eliminator 40 according to the present embodiment irradiates the photoconductor drum 11 with light downstream in the rotation direction Z of the photoconductor drum 11 of the transport path 10 that is downstream in the transport direction Y of the transfer position of the transfer roller 15 and upstream in the rotation direction Z of the charging roller 12.

[0032] The control unit 2 controls the light amount of the first charge removing device 30 and the second charge removing device 40. Specifically, in order to stabilize the potential of the photosensitive drum 11 at the time of recharging after the toner image transfer, it is necessary to set the light amount at least to the extent that no charge remains on the photosensitive drum 11. However, when an LED is used as the light source 31, the light of the LED does not have directivity, so that the light of the light source 31 facing the non-paper passing portion is also irradiated to the paper passing portion. Therefore, when the first charge removing device 30 is provided above the conveying path 10 (see FIG. 3), the potential of the non-image portion of the paper passing portion may decrease, and toner scattering may occur. Also, when the first charge removing device 30 is provided below the conveying path 10 (see FIG. 5), depending on the light amount of the first charge removing device 30, the light may pass through the sheet S, and in that case, toner scattering may also occur. Therefore, the control unit 2 controls the light amount of the first charge removing device 30 to be less than that of the second charge removing device 40.

[0033] More specifically, when the first static eliminator 30 is provided below the transport path 10 (see FIG. 5), the control unit 2 controls the light amount of the first static eliminator 30 to an amount that does not transmit through the thinnest printing paper among printing papers that can be used for image formation using the printer 1, or, even if it does transmit, to an amount of light that is less than the half-life exposure amount (exposure amount required to halve the potential) of the photoconductor drum 11. Furthermore, regardless of whether the first static eliminator 30 is located above or below the transport path 10, the control unit 2 controls the light amount of the first static eliminator 30 for the non-paper passing portion to at least ⅓ of the half-life exposure amount of the photoconductor drum 11.

[0034] For example, when the potential of the photosensitive drum 11 at the development position of the development device 14 is set to 500 V, the control unit 2 controls the light amount of the first charge removal device 30 so that the potential of the non-paper passing portion of the photosensitive drum 11 is 50 to 300 V lower than the non-image portion of the paper passing portion before the transfer process by the transfer roller 15.

[0035] In this embodiment, the length of the transfer roller 15 in the width direction X is less than the maximum length of the sheet S in the width direction X. The maximum length of the sheet S in the width direction X is, for example, the length of the long side of an A4 size sheet. The reason for this configuration is that when a sheet S having the maximum length in the width direction X is used, the sheet S is interposed between the transfer roller 15 and the photoconductor drum 11 over the entire area in the width direction X, so that no transfer current flows into the non-paper passing portion, and no charge removal is required for the non-paper passing portion.

[0036] Next, there will be described the operation of the printer 1. In any of the following cases, the control unit 2 at least turns on the second static eliminator 40.

[0037] 6 is a plan view showing the operation when conveying a sheet S whose length in the width direction X is longer than that of the transfer roller 15. Here, an example is shown in which an A4-sized sheet S is conveyed with its long side oriented perpendicular to the conveying direction Y. In this case, as described above, it is not necessary to remove static electricity from the non-paper passing portion. Therefore, the control unit 2 does not turn on the first static eliminator 30. On the other hand, the control unit 2 turns on the second static eliminator 40.

[0038] 7 and 8 are plan views showing the operation when transporting a sheet S whose length in the width direction X is shorter than that of the transfer roller 15. Of these, Fig. 7 shows an example in which a JIS (Japanese Industrial Standards) B5 size sheet S is transported with its long side oriented perpendicular to the transport direction Y. Fig. 8 shows an example in which an A4 size sheet S is transported with its short side oriented perpendicular to the transport direction Y.

[0039] The control unit 2 controls the first static eliminator 30 so that light is irradiated only to the non-paper passing portion of the photosensitive drum 11. Specifically, the control unit 2 identifies the paper passing portion and the non-paper passing portion from the size of the sheet S indicated by the print job input to the printer 1, and turns on only the light source 31 facing the non-paper passing portion. In the example of FIG. 7, of the 72 light sources 31 provided in the first static eliminator 30, the first 5 light sources 31 from both ends are turned on, and the remaining 62 light sources 31 are not turned on. In the example of FIG. 8, the first 10 light sources 31 from both ends are turned on, and the remaining 52 light sources 31 are not turned on. In either case, the paper passing portion is not neutralized, so that the drop in the potential of the non-image portion of the paper passing portion is suppressed, and toner scattering is suppressed. On the other hand, the non-paper passing portion is neutralized and the potential is reduced, so that even if the transfer current is increased, the inflow of the transfer current to the non-image portion via the non-paper passing portion is suppressed, and transfer memory is suppressed.

[0040] The printer 1 according to the present embodiment described above includes a photosensitive drum 11 arranged along a transport path 10 along which a sheet S is transported, a charging roller 12 which charges the photosensitive drum 11, a developing device 14 which uses toner to develop a latent image formed on the photosensitive drum 11 charged by the charging roller 12, a transfer roller 15 which faces the photosensitive drum 11 across the transport path 10 and generates a transfer bias, a first static elimination device 30 which irradiates light onto the photosensitive drum 11 downstream in the rotation direction Z of the photosensitive drum 11 from the developing device 14 and upstream in the rotation direction Z from the transfer roller 15, and a control unit 2 which controls the first static elimination device 30 so as to irradiate light only onto non-paper passing portions of the photosensitive drum 11.

[0041] According to this configuration, the paper passing portion is not discharged, so that the potential drop of the non-image portion of the paper passing portion is suppressed, and toner scattering is suppressed. On the other hand, the non-paper passing portion is discharged and the potential is reduced, so that even if the transfer current is increased, the transfer current is suppressed from flowing into the non-image portion through the non-paper passing portion, and transfer memory is suppressed. When a sheet S having a length in the width direction X that is equal to or longer than the transfer roller 15 is conveyed, the sheet S is interposed between the transfer roller 15 and the photosensitive drum 11 over the entire area in the width direction X, so that the transfer current does not flow into the non-paper passing portion, and therefore it is not necessary to discharge the non-paper passing portion. Therefore, according to this embodiment, it is possible to improve the transfer performance while suppressing toner scattering and transfer memory.

[0042] Furthermore, according to the printer 1 of this embodiment, the first static elimination device 30 is provided with a plurality of light sources 31 arranged in a width direction X intersecting the transport direction Y, and the control unit 2 turns on only the light source 31 among the plurality of light sources 31 that faces the non-paper passing portion according to the size of the sheet S being transported, so that light can be irradiated onto the non-paper passing portion according to the size of the sheet S being transported.

[0043] Furthermore, the printer 1 according to this embodiment is provided with a second static elimination device 40 that irradiates light onto the photosensitive drum 11 downstream in the rotation direction Z of the photosensitive drum 11 from the transport path 10 downstream in the transport direction Y of the transfer position of the transfer roller 15, and upstream in the rotation direction Z from the charging roller 12. Since the amount of light of the first static elimination device 30 is less than that of the second static elimination device 40, the static elimination effect on the paper passing section by the first static elimination device 30 is suppressed, and toner scattering can be suppressed.

[0044] Furthermore, in the printer 1 according to this embodiment, the control unit 2 controls the light amount of the first static elimination device 30 so that the potential of the non-paper passing areas of the photosensitive drum 11 is lower than the non-image areas of the paper passing areas before the transfer process by the transfer roller 15, thereby making it possible to suppress the flow of transfer current into the non-image areas via the non-paper passing areas.

[0045] The above embodiment may be modified as follows.

[0046] In the above embodiment, an LED is used as the light source 31, but since the light of the LED has no directivity, even if only the light source 31 facing the non-paper passing portion is turned on, the light is also irradiated to the paper passing portion. Therefore, in addition to the configuration of the above embodiment, the following configuration may be provided. FIG. 9 is a plan view showing a first static eliminator 30, a second static eliminator 40, a photoconductor drum 11, and a transfer roller 15 according to a modified example. FIG. 10 is a perspective view of the first static eliminator 30 according to a modified example. In this example, a light shielding member 33 is provided on the surface of the housing 32 of the first static eliminator 30 on which the light source 31 is provided. The light shielding member 33 is a plate-shaped member and is provided at a position corresponding to the boundary between the paper passing portion and the non-paper passing portion in the example of FIG. 7 and the boundary between the paper passing portion and the non-paper passing portion in the example of FIG. 8. According to this configuration, the light-shielding member 33 blocks light reaching the paper-passing portion when only the light source 31 facing the non-paper-passing portion is turned on, thereby suppressing toner scattering caused by a decrease in the potential of the non-image portion of the paper-passing portion.

[0047] In the above embodiment, an example has been shown in which the length of the transfer roller 15 in the width direction X is less than the maximum length of the sheet S in the width direction X, but the length of the transfer roller 15 in the width direction X may be equal to or greater than the maximum length of the sheet S in the width direction X. With this configuration, it is not necessary to expand the margin in the width direction X, so that restrictions on the size of the image can be avoided. Also, it is possible to prevent foreign matter from adhering to the edge of the sheet S.

[0048] In the above embodiment, the light sources 31 and 41 are LEDs, but the light sources 31 and 41 may be halogen lamps or the like.

[0049] 11 is a plan view showing a first static eliminator 30 according to a modified example. In this example, the first static eliminator 30 includes a light source 31 that faces only the non-paper passing portion when a sheet S having a minimum length in the width direction X is transported. The sheet S having a minimum length in the width direction X is, for example, an A6 size sheet S with a long side disposed perpendicular to the transport direction Y. In this configuration, as in the above embodiment, the control unit 2 controls the first static eliminator 30 to irradiate light only when a sheet S having a length in the width direction X intersecting with the transport direction Y that is shorter than that of the transfer roller 15 is transported. This configuration can reduce manufacturing costs. [Explanation of symbols]

[0050] 1. Printer (image forming device) 2. Control section 10 Transport path 11 Photoconductor drum 12 Charging roller 14 Developing device 15 Transfer roller 30 1st static eliminator 31 Light source 33 Light-shielding material 40 Second static eliminator

Claims

1. A photosensitive drum provided along a conveying path for conveying a sheet; a charging roller for charging the photosensitive drum; a developing device that develops, with toner, the latent image formed on the photosensitive drum that has been charged by the charging roller; a transfer roller that faces the photosensitive drum across the transport path and generates a transfer bias; 、 a first static elimination device that irradiates the photosensitive drum with light downstream of the developing device in a rotation direction of the photosensitive drum and upstream of the transfer roller in the rotation direction; a control unit that controls the first static eliminator so as to irradiate light only onto a non-sheet passing portion of the photosensitive drum; a second static elimination device that irradiates light onto the photosensitive drum downstream in the rotation direction of the photosensitive drum from the transport path downstream in the transport direction from the transfer position of the transfer roller and upstream in the rotation direction from the charging roller, 2. An image forming apparatus comprising: a first charge removing device and a second charge removing device, the first charge removing device being arranged to remove a light beam from the first charge removing device;

2. The first static eliminator includes a plurality of light sources arranged in a width direction intersecting a conveying direction of the conveying path, The image forming apparatus according to claim 1 , wherein the control unit turns on only one of the plurality of light sources that faces the non-sheet passing portion according to a size of the sheet being conveyed.

3. The image forming apparatus according to claim 1 or 2, characterized in that the control unit controls the amount of light of the first discharge device so that the potential of the non-paper passing portion of the photosensitive drum is lower than the non-image portion of the paper passing portion before the transfer process by the transfer roller.

4. 3. The image forming apparatus according to claim 2, further comprising a light blocking member for blocking light entering the paper passing portion when only the light source facing the non-paper passing portion is turned on.

5. 5. The image forming apparatus according to claim 1, wherein a length of the transfer roller in a width direction intersecting a conveying direction of the conveying path is equal to or greater than a maximum length of the sheet in the width direction.

Images