JP6288463B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, there is known an image forming apparatus that includes a conveyance belt that contacts a photosensitive drum to form a nip and a transfer roller that is pressed against the photosensitive drum with the conveyance belt interposed therebetween (for example, Patent Documents). 1). A transfer voltage having a polarity opposite to that of the toner is applied to the transfer roller when the sheet passes the nip position. As a result, the toner image carried on the photosensitive drum is transferred to the sheet. A stretching roller is provided downstream of the nip position in the sheet conveying direction. The tension roller stretches the conveyance belt at a separation position where the sheet is separated from the conveyance belt.

JP 2002-031960 A

  However, when the stretching roller is grounded in the image forming apparatus shown in Patent Document 1, when the trailing end of the sheet is separated from the conveyance belt, the charge (toner charge polarity and toner) held on the sheet and the conveyance belt is separated. The charge of reverse polarity) is discharged to the ground through the stretching roller. When this discharge (so-called peeling discharge) occurs, there is a problem that the toner image cannot be held on the sheet due to the charge having the opposite polarity to the charge polarity of the toner, and a part of the toner image is scattered.

  The present invention has been made in view of such a point, and an object of the present invention is to prevent peeling discharge when the trailing edge of the sheet is peeled from the conveying belt and to prevent toner scattering. There is.

An image forming apparatus according to an aspect of the present invention includes an image carrier that carries a toner image, a conveyance belt that contacts the image carrier to form a nip, and conveys a sheet via the nip position; A voltage having a polarity opposite to the charging polarity of the toner forming the toner image is applied, a transfer roller for transferring the toner image to the sheet at the nip position, and a downstream side of the sheet conveyance direction from the nip position. The conveyor belt is stretched at a peeling position where the sheet is peeled off from the conveyor belt, a tension roller to which a voltage having a polarity opposite to the charging polarity of the toner is applied, and the conveyor belt is attached to the tension roller. A conductive opposing member disposed oppositely across the housing, a housing that houses the image carrier and is provided with an opening / closing cover on a side surface, and an opening movement of the opening / closing cover As a result, the image carrier moves to a protection position that covers the opening / closing cover side of the image carrier, and the image moves to an open position that opens the opening / closing cover side of the image carrier as the opening / closing cover closes. and a bearing member protecting member, the image bearing member protecting member is that acts as the counter member in the protective position.

  According to the present invention, it is possible to prevent peeling discharge when the trailing edge of the sheet peels from the conveying belt, and to prevent toner scattering.

FIG. 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment. FIG. 2 is a view corresponding to FIG. 1 showing a state in which the opening / closing cover of the image forming apparatus is opened. FIG. 3 is a schematic diagram showing the configuration of the transfer device. FIG. 4 is a block diagram illustrating a configuration of a control system that controls the first power supply unit to the third power supply unit connected to the transfer device. FIG. 5 is a time chart showing an example of voltage application control by the controller.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

<Embodiment>
FIG. 1 shows a monochrome copying machine which is an example of an image forming apparatus 1 in the present embodiment. The image forming apparatus 1 includes a housing 2, an image reading unit 3, and an ADF (automatic document feeder) 4. The image reading unit 3 is attached to the upper end of the housing 2, and the ADF is disposed so as to cover the document placement surface of the image reading unit 3. The image reading unit 3 includes a light source, a reflection mirror, a CCD (Charge Coupled Device), and the like, and optically reads an image of a document set on a document placement surface or a document image supplied from an ADF. The image reading unit 3 converts the read document image into data and transmits it to the image forming unit 20 described later.

  In the housing 2, a paper feeding unit 10, an image forming unit 20, and a fixing unit 30 are accommodated. The paper feeding unit 10 is provided at the bottom of the housing 2. The paper feeding unit 10 includes a paper feeding cassette 11 that stores a plurality of sheets S that are stacked on each other, a pick roller 12 that takes out the sheets S in the paper feeding cassette 11 one by one, and a single sheet S that has been taken out. A feed roller 13 and a retard roller 14 that are separated and sent to the conveyance path T are provided.

  The image forming unit 20 is provided above the paper feeding unit 10 in the housing 2. The image forming unit 20 includes a photosensitive drum 21 that is an image carrier rotatably provided in the housing 2, a charger 22 disposed around the photosensitive drum 21, a developing device 23, a transfer device 24, and the like. A cleaning unit 25 and an optical scanning device 26 disposed above the photosensitive drum 21 are provided.

  The fixing unit 30 is disposed above the image forming unit 20. The fixing unit 30 includes a fixing roller 31 that is heated by a heating unit such as a heater, and a pressure roller 32 that is pressed against the fixing roller 31.

  In the image forming unit 20, when image data is received from the image reading unit 3, the photosensitive drum 21 is rotationally driven by a motor (not shown), and the surface of the photosensitive drum 21 is charged to a predetermined potential by the charger 22. . In the present embodiment, the charger 22 charges the surface of the photosensitive drum 21 to a positive polarity. Thus, after the surface of the photosensitive drum 21 is charged, laser light is emitted from the optical scanning device 26 to the photosensitive drum 21 based on the image data from the image reading unit 3. An electrostatic latent image is formed on the surface of the photosensitive drum 21 by irradiation with laser light. The electrostatic latent image formed on the photosensitive drum 21 is developed with toner charged by the developing device 23 and visualized as a toner image. In this embodiment, a toner image is formed by so-called reversal development, and the charging polarity of the toner charged by the developing device 23 is positive (the same polarity as the charging polarity of the surface of the photosensitive drum 21). . The toner image may be formed not only by reversal development but also by regular development. In this case, the toner charge polarity is negative.

  After the toner image is formed on the surface of the photosensitive drum 21, the sheet S sent from the registration roller pair 16 is pressed against the surface of the photosensitive drum 21 by the transfer device 24. Then, the toner image on the photosensitive drum 16 is transferred to the sheet S by applying a transfer voltage having a toner charging polarity and a reverse charging polarity (negative polarity in this embodiment) to the sheet S from the transfer device 24. Is done. The sheet S on which the toner image is transferred is heated and pressed by the fixing roller 31 and the pressure roller 32 in the fixing unit 30. As a result, the toner image is fixed on the sheet S.

  An opening 2 a is formed in a portion of the housing 2 located on the right side of the transfer device 24. The opening 2a is closed by an opening / closing cover 6 so as to be opened and closed. The opening / closing cover 6 and the transfer device 24 are unitized. The open / close cover 6 is rotatable about a shaft portion 7 extending in the front-rear direction along the lower edge of the opening 2a. FIG. 1 shows a state in which the opening 2 a is closed by the opening / closing cover 6. When the opening / closing cover 6 is rotated to the right from the shaft 7 as a fulcrum from this state, the opening 2a is opened as shown in FIG. The operator can perform jam processing of the sheet S through the opening 2a.

  A shutter 28 is provided on the upper right side of the photosensitive drum 21 (see FIG. 1). The shutter 28 has a function of protecting the photosensitive drum 21 so that the user does not damage the surface of the photosensitive drum 21 when the opening / closing cover 6 is opened. The shutter 28 is made of a conductive member. Examples of the conductive member include stainless steel (SUS), conductive polyethylene (PE), and conductive polyacetal (POM).

  The shutter 28 is driven by a shutter drive mechanism 27 (see FIG. 3) in conjunction with the opening / closing operation of the opening / closing cover 6. The shutter drive mechanism 27 moves the shutter 28 to the drum protection position with the opening operation of the opening / closing cover 6, and moves the shutter 28 to the drum opening position with the closing operation of the opening / closing cover 6. At the drum protection position, the shutter 28 covers the open / close cover 6 side of the photosensitive drum 21 (see FIG. 2). At the drum open position, the shutter 28 is retracted above the drum protection position, and the opening / closing cover 6 side of the photosensitive drum 21 is opened (see FIG. 1). The shutter 28 functions as a conductive facing member that faces the downstream roller 244 with the conveyance belt 241 interposed therebetween at the drum open position. The separation distance between the shutter 28 and the downstream roller 244 is 8 mm in this embodiment, and is preferably in the range of 5 mm to 10 mm, for example. The shutter 28 is grounded via the ground line G1.

  The shutter drive mechanism 27 may be, for example, a mechanical drive mechanism using a cam or the like. The shutter drive mechanism 27 detects the opening / closing operation of the opening / closing cover 6 with a sensor and drives the shutter 28 with a motor based on the detection result. A drive mechanism may be used.

  As shown in FIG. 3, the transfer device 24 includes an endless conveyance belt 241, a transfer roller 242, an upstream roller 243, a downstream roller 244, a first power supply unit 246, and a second power supply unit 247. .

  The conveyance belt 241 conveys the sheet S while electrostatically attracting the sheet S to the outer peripheral surface. The outer peripheral surface of the conveyance belt 241 is in contact with the photosensitive drum 21 to form a nip with the photosensitive drum 21. The conveyor belt 241 is stretched around the upstream roller 243 and the downstream roller 244 with a predetermined tension. The transport belt 241 is driven in the direction of arrow B in FIG. 3 when the upstream roller 243 or the downstream roller 244 is rotationally driven by a motor (not shown). The conveyor belt 241 is formed by coating a fluororesin on the outer peripheral surface of a rubber belt-shaped member, for example.

  The transfer roller 242 is disposed to face the photosensitive drum 21. The outer peripheral surface of the transfer roller 242 is in contact with the inner peripheral surface of the transport belt 241. The transfer roller 242 is pressed against the photosensitive drum 21 with a predetermined load with the conveyance belt 241 interposed therebetween. As a result, the sheet S is nipped between the conveyance belt 241 and the photosensitive drum 21 at the nip position A1. The transfer roller 242 applies a transfer voltage C1 having a polarity opposite to the toner charging polarity to the sheet S passing through the nip position A1, thereby transferring the toner image to the sheet S.

  The upstream roller 243 stretches the conveyance belt 241 at a conveyance start position A2 that is upstream of the nip position A1 in the sheet conveyance direction and the front end of the sheet S reaches the conveyance belt 241. The upstream roller 243 is formed of a conductive member such as a metal and is grounded via the ground wiring G2. In the present embodiment, the front and rear ends of the sheet S mean the front and rear ends of the sheet in the sheet conveyance direction.

  The downstream roller (stretching roller) 244 stretches the conveyance belt 241 at a separation position A3 where the trailing edge of the sheet S is separated from the conveyance belt 241 on the downstream side of the nip position A1 in the sheet conveyance direction. The downstream roller 244 is formed of a conductive member such as metal.

  A guide member 245 is provided on the downstream side of the downstream roller 244 in the sheet conveyance direction. The guide member 245 guides the sheet S separated from the conveyance belt 241 to the fixing unit 30 at the peeling position A3. The guide member 245 is made of a conductive member such as metal. The guide member 245 is grounded via the ground wiring G3.

  The first power supply unit 246 selectively switches between the transfer voltage C <b> 1 and the standby voltage C <b> 2 and applies it to the transfer roller 242. The negative terminal of the first power supply unit 246 is connected to the transfer roller 242 via the wiring L1, and the positive terminal of the first power supply unit 246 is grounded via the ground wiring G4.

  Here, the transfer voltage C1 is a voltage having a polarity opposite to the charging polarity of the toner, and is a voltage for transferring the toner image on the photosensitive drum 21 to the sheet S. The standby voltage C2 is a voltage having the same polarity as the charging polarity of the toner, and is a voltage for preventing the toner from adhering to the transfer roller 242 during non-image formation.

  Here, the transfer voltage C1 is a voltage having a polarity opposite to the charging polarity of the toner, and is a voltage for transferring the toner image on the photosensitive drum 21 to the sheet S. The standby voltage C2 is a voltage having the same polarity as the charging polarity of the toner, and is a voltage for preventing the toner from adhering to the transfer roller 242 during non-image formation. The controller 100 controls the magnitude and application timing of the transfer voltage C1 and the standby voltage C2.

  The second power supply unit 247 applies the toner scattering suppression voltage C <b> 3 to the downstream roller 244. The negative electrode side terminal of the second power supply unit 247 is connected to the downstream roller 244 via the wiring L2. The positive terminal of the second power supply unit 247 is grounded via the ground wiring G5.

  The toner scattering suppression voltage C3 is a voltage having a polarity opposite to the charging polarity of the toner, and prevents the sheet S from flowing out from the sheet S at the peeling position A3. The peeling discharge at the time of peeling is suppressed, and thus the scattering of toner is suppressed.

  FIG. 5 is a time chart showing an example of voltage application control executed by the controller 100. This time chart shows an example in which continuous printing is performed on two sheets S. When the image forming apparatus 1 accepts a print start request, a printing operation is started and a charging voltage is applied to the photosensitive drum 21, and then a developing voltage is applied in the developing unit 23. At the time t1, the printing operation of the image forming apparatus 1 starts, and at the same time, the standby voltage C2 having the same polarity as the toner charging polarity (positive polarity in this embodiment) is applied to the transfer roller 242. At time t2, as soon as the front end of the sheet S reaches the nip position A1, a transfer voltage C1 having a polarity opposite to the toner charging polarity (negative polarity in this embodiment) is applied to the transfer roller 242 and further downstream. To the roller 244, a toner scattering suppression voltage C3 having a polarity opposite to the toner charging polarity (negative polarity in this embodiment) is applied. At time t2 ″, the front end of the sheet S reaches the peeling position A3. At this time, the toner scattering suppression voltage C3 is already applied to the downstream roller 244. At time t3, the rear end of the sheet S is nipped. Simultaneously with passing the position A1, the applied voltage to the transfer roller 242 is switched from the transfer voltage C1 to the standby voltage C2. At time t4, when the trailing edge of the sheet S passes the peeling position A3, the toner scatters to the downstream roller 244. The application of the suppression voltage C3 is stopped, and at time t5 to t7, the same processing as that at time t2 to t4 is performed when printing the subsequent sheet S. At time t8, the application of voltage to the transfer roller 242 is stopped. The printing operation ends.

  In the image forming apparatus 1, at least from the time when the front end of the sheet S reaches the peeling position A3 (time t2 ″) to the time when the rear end of the sheet S passes the peeling position A3 (time t4), the downstream side A toner scattering suppression voltage C4 having a polarity opposite to the charging polarity of the toner is applied to the roller 244. As a result, when the trailing edge of the sheet S is peeled from the conveying belt 241 at the peeling position A3, It is possible to prevent the charge having the opposite polarity to the toner from flowing out to the downstream roller 244 from the end and discharging it, so that the charge having the opposite polarity to the toner polarity is held on the sheet S and the toner image is transferred to the sheet. S can be reliably adsorbed to S.

  In the present embodiment, the opposing member (shutter 28) made of a conductive member is disposed at the position facing the conveying belt 241 with respect to the downstream roller 244, so that the downstream S 244 is applied to the sheet S. It is possible to more reliably supply the charge having the opposite polarity to the charging polarity of the toner. That is, when the shutter 28 which is the opposing member is formed of an insulating member, the flow path of the charge supplied to the sheet S from the downstream roller 244 is route R1 (conveying belt 241 → upstream roller 243 → ground line G2 → There are only two paths: ground) and path R2 (guide member 245 → ground line G3 → ground). However, by configuring the shutter 28 with a conductive member, the electric charge on the sheet S tends to flow through the path R3 (the shutter 28 → the ground wiring G1 → the ground). Therefore, as compared with the case where the charge flow path is only of two systems of the path R1 and the path R2, the charge (charge having a polarity opposite to the toner charge polarity) is smoothly supplied from the downstream roller 244 to the sheet S. Is called. Therefore, the peeling discharge of the sheet S can be prevented more reliably.

  Moreover, in this embodiment, the product cost can be reduced by using the shutter 28 which is an existing component as an opposing member that faces the downstream roller 244.

<< Other embodiments >>
In the above embodiment, a copying machine has been described as an example of the image forming apparatus 1. However, the present invention is not limited to this, and the image forming apparatus 1 may be a printer, a multifunction peripheral (MFP), or the like.

  In the above-described embodiment, the example in which the charging polarity of the toner as the developer is positive is described. However, the present invention is not limited to this, and the present invention is also applicable to the case where the charging polarity of the toner is negative. Can do.

  As described above, the present invention is useful for an image forming apparatus.

S Sheet A1 Nip position A3 Separation position 1 Image forming apparatus 6 Open / close cover 21 Photosensitive drum (image carrier)
26 Shutter (opposing member, image carrier protecting member)
241 Conveyor belt 242 Transfer roller
244 Downstream roller (stretching roller)

Claims (1)

An image carrier for carrying a toner image;
A conveying belt that contacts the image carrier to form a nip and conveys the sheet via the nip position;
A transfer roller to which a voltage having a polarity opposite to the charging polarity of the toner forming the toner image is applied and transferring the toner image to the sheet at the nip position;
The conveying belt is stretched at a peeling position downstream of the nip position in the sheet conveying direction and the sheet is peeled from the conveying belt, and a voltage having a polarity opposite to the charging polarity of the toner is applied. A rack roller,
A conductive counter member disposed opposite the tension roller across the conveyor belt ;
A housing that houses the image carrier and is provided with an open / close cover on a side surface;
As the opening / closing cover is opened, the image carrier moves to a protection position that covers the opening / closing cover side, and as the opening / closing cover is closed, the image carrier is opened to open the opening / closing cover side. An image carrier protection member that moves to a position;
Said image-bearing member protecting member is that acts as the counter member in the protective position, the image forming apparatus.

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