JP6380758B2 - 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.

  The image forming apparatus may include a shutter that protects the photosensitive drum so that the user does not damage the surface of the photosensitive drum during jam processing (see, for example, Patent Document 2). The shutter is driven by a shutter driving mechanism in conjunction with the opening / closing operation of the opening / closing cover on the side surface of the image forming apparatus. The shutter drive mechanism moves the shutter to the drum protection position with the opening / closing cover opening operation, and moves the shutter to the drum opening position with the opening / closing cover closing operation. At the drum protection position, the open / close cover side of the photosensitive drum is covered with a shutter.

JP 2002-031960 A JP 2006-030418 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.

  In order to solve this problem, it is conceivable to apply a voltage having a polarity opposite to the charging polarity of the toner to the tension roller. Thereby, it is possible to suppress peeling discharge when the trailing edge of the sheet is peeled from the conveying belt, and to suppress toner scattering.

  However, when a voltage having a polarity opposite to the charging polarity of the toner is applied to the stretching roller, a reverse charging toner contained in a minute amount in the toner image (a polarity opposite to the charging polarity to be applied to the toner by the developing device) Toner) is bounced off the sheet by the voltage applied to the stretching roller and scattered.

  Although the amount of scattering of the reversely charged toner is small, the influence on the contamination inside the apparatus is small. However, when this toner adheres to the shutter (image carrier protecting member) for protecting the image carrier as shown in Patent Document 2, the user However, when performing jam processing or the like, there is a possibility that the operator's hand may be soiled by the reversely charged toner adhering to the shutter.

  The present invention has been made in view of such a point, and an object of the present invention is to prevent the reversely charged toner from adhering to the image carrier protection member while suppressing the amount of scattered toner in the image forming apparatus. It is in trying to prevent surely.

An image forming apparatus according to an aspect of the present invention includes a housing that houses therein an image carrier that carries a toner image, an opening / closing cover that covers an opening formed on a side surface of the housing so as to be openable and closable, When the opening / closing cover opens, the image carrier moves to a protection position that covers the opening / closing cover side, and when the opening / closing cover closes, the image carrier opens the opening / closing cover side. An image carrier protection member that moves to the image carrier, forms a nip in contact with the image carrier, and conveys a sheet via the nip position; and reverses the charging polarity of the toner that forms the toner image. A transfer roller to which a polar transfer voltage is applied and the toner image is transferred to the sheet at the nip position, and the sheet is peeled from the transport belt at a downstream side of the nip position in the sheet transport direction. A tension roller that stretches the conveying belt at a separation position; and a tension roller power supply unit that applies a toner scattering suppression voltage having a polarity opposite to the charging polarity of the toner to the tension roller. The body protection member is disposed opposite to the tension roller with the conveyance belt in between in the open position, and the image carrier protection member is in the state where the image carrier protection member is in the open position. further comprising a protective member supply unit for applying a charging polarity opposite protective member voltage of the toner, and a control unit for controlling the tension roller power unit and the protection member supply unit, the relative, the control unit In the state where the image carrier protection member is in the open position, at least from the time when the front end of the sheet reaches the peeling position to the time when the rear end of the sheet passes through the peeling position. The toner-scattering suppression voltage having a polarity opposite to the charging polarity of the toner is applied to the tension roller by the tension roller power source, and the image carrier protection member by the protection member power source The voltage application period is set to coincide with the voltage application period to the tension roller by the tension roller power supply unit .

  According to the present invention, it is possible to reliably prevent the reversely charged toner from adhering to the image carrier protection member while suppressing the amount of scattered toner in the image forming apparatus.

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. FIG. 6 is a table showing the results of the continuous printing test when the applied voltage to the shutter is variously changed. FIG. 7 is a view corresponding to FIG. 3 showing another embodiment.

  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 as an image carrier protecting member is provided on the photosensitive drum 21 on the upper right side in FIG. 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 such as SUS. The shutter 28 is driven by the shutter drive mechanism 27 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 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 conveying belt 241, a transfer roller 242, an upstream roller 243, a downstream roller 244, a first power supply unit 246, a second power supply unit 247, and a third power supply. Part 248.

  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 the arrow in FIG. 3 by rotating the upstream roller 243 or the downstream roller 244 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 through a bearing or the like. In the present embodiment, the front end and the rear end of the sheet mean the front end and the rear end of the sheet in the sheet conveying 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 is made of a conductive member such as metal. The guide member 245 is grounded in this embodiment.

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 through the line L1, the positive terminal of the first power source unit 246 is grounded via the ground wiring G.

  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 G.

  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.

  The third power supply unit 248 applies the shutter voltage C <b> 4 to the shutter 28. A negative terminal of the third power supply unit 248 is connected to the shutter 28. The positive terminal of the third power supply unit 248 is grounded via the ground wiring G.

  The shutter voltage C4 is a voltage having a polarity opposite to the charging polarity of the toner, and the reversely charged toner (a negative polarity toner in the present embodiment) contained in a small amount in the toner image carried on the sheet S is scattered and the shutter 28 is discharged. Suppresses adhesion to the surface.

  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. A toner scattering suppression voltage C3 having a polarity opposite to the toner charging polarity (negative polarity in this embodiment) is applied to the roller 244, and a shutter voltage C4 having a polarity opposite to the toner charging polarity is applied to the shutter 28. Is done. At time t2 ″, the front end of the sheet S reaches the peeling position A3. At this time, the toner scattering suppression voltage C3 and the shutter voltage C4 are already applied to the downstream roller 244. At time t3, the sheet S The voltage applied to the transfer roller 242 is switched from the transfer voltage C1 to the standby voltage C2 at the same time as the trailing edge passes through the nip position A1.At time t4, when the trailing edge of the sheet S passes the peeling position A3, the downstream roller The application of the toner scatter suppression voltage C3 to 244 is stopped and the application of the shutter voltage C4 to the shutter 28 is stopped, and at time t5 to t7, the same processing as time t2 to t4 is executed when printing the subsequent sheet S. At time t8, the application of voltage to the transfer roller 242 is stopped and 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.

  However, as described above, when a voltage (toner scatter suppression voltage C3) having a polarity opposite to the charging polarity of the toner is applied to the downstream roller 244, the reversely charged toner contained in a minute amount in the toner image (to the developing device 23). The toner having a polarity opposite to the charging polarity to be applied to the toner is bounced and scattered from the sheet S by the voltage applied to the downstream roller 244.

  Although the reversely charged toner has a small amount of scattering and thus has little influence on the contamination inside the apparatus, when the reversely charged toner adheres to the surface of the shutter 28 that protects the photosensitive drum 21, when the operator performs jam processing or the like, There is a possibility that the operator's hand is soiled with toner adhering to the surface of the shutter 28.

  On the other hand, in the present embodiment, the shutter 28 is applied with the shutter voltage C4 having the opposite polarity to the toner charging polarity (the same polarity as the reverse charging toner) from the third power supply unit 248. It is possible to prevent the reversely charged toner from adhering to the surface.

  In the present embodiment, the period during which the toner scattering suppression voltage C3 is applied to the downstream roller 244 and the period during which the shutter voltage C4 is applied to the shutter 28 are made to coincide. According to this, the shutter voltage C4 is applied to the shutter 28 only in a situation where the reversely charged toner is particularly likely to scatter. Therefore, energy saving can be improved compared to the case where the shutter voltage C4 is continuously applied over the entire period from the start to the end of the printing operation.

  Note that the time chart shown in FIG. 5 is merely an example. For example, the application timing of the toner scattering suppression voltage C3 and the shutter voltage C4 may be set to a time t2 ″ that is later than the time t2.

"Example"
FIG. 6 is a table showing the results of a continuous printing test by the image forming apparatus 1 adopting the configuration of the above embodiment. The charging polarity imparted to the toner by the developing device 23 is positive, and the magnitude thereof is +30 to +40 μC / g. In the first to third embodiments, the shutter 28 is made of SUS, which is a conductive metal, and a negative shutter voltage C4 is applied to the shutter 28. In Comparative Example 1 and Comparative Example 2, the shutter 28 is made of polycarbonate and ABS resin, which are insulating members, and no voltage is applied to the shutter 28. In Comparative Example 3 and Comparative Example 4, the shutter 28 is made of SUS, which is a conductive metal, as in Example 1 and Example 2, and a positive voltage is applied to the shutter 28. Then, continuous printing was performed by setting the printing rate of the sheet S to 30%, and it was confirmed whether or not the shutter 28 was soiled at the end of printing of 10K (K = 1000) sheets and at the end of printing of 100K sheets. “◯” in the table means that there is no dirt, and “X” means that there is dirt.

  When a shutter voltage C4 having a negative polarity (polarity opposite to the toner charging polarity) is applied to the shutter 28 (in the case of the first to third embodiments), the toner is applied to the shutter 28 at the end of printing 100K sheets. In contrast, when a positive voltage is applied to the shutter 28 and when no voltage is applied to the shutter 28, toner is attached to the shutter 28 at the end of printing 100K sheets. Recognize.

<< 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 polarity of the toner as the developer is positive has been described. However, the present invention is not limited to this, and the present invention can be applied to the case where the charging polarity of the toner is negative. it can.

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

S sheet A2 nip position A3 peeling position S sheet 1 image forming apparatus 6 opening / closing cover 21 photosensitive drum (image carrier)
26 Shutter (image carrier protection member)
27 Shutter drive mechanism 100 Controller (control unit)
241 Conveyor belt 242 Transfer roller
244 Downstream roller (stretching roller)
247 Second power supply (stretching roller power supply)
248 Third power supply (protective member power supply)

Claims (4)

A housing that houses therein an image carrier that carries a toner image;
An open / close cover that covers the opening formed on the side surface of the housing so as to be openable and closable;
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 protecting member that moves to a position;
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 transfer voltage having a polarity opposite to the charging polarity of the toner forming the toner image is applied, and the toner image is transferred to the sheet at the nip position;
A stretching roller that stretches the conveying belt at a peeling position where the sheet is peeled from the conveying belt on the downstream side of the nip position in the sheet conveying direction;
A tension roller power supply unit that applies a toner scattering suppression voltage having a polarity opposite to the charging polarity of the toner to the tension roller;
The image carrier protection member is disposed to face the tension roller with the conveyance belt in between in the open position,
A protective member power supply that applies a protective member voltage having a polarity opposite to the charging polarity of the toner to the image carrier protective member in a state where the image carrier protective member is in the open position ;
Further comprising a control unit for controlling the tension roller power unit and the protection member supply unit,
In the state where the image carrier protecting member is in the open position, the control unit is configured to perform at least a time from when the front end of the sheet reaches the peeling position to a time when the rear end of the sheet passes through the peeling position. The toner-scattering suppression voltage having a polarity opposite to the charging polarity of the toner is applied to the tension roller by the tension roller power source, and the image carrier protection member by the protection member power source An image forming apparatus configured to match a voltage application period to the voltage application period to the tension roller by the tension roller power supply unit . The image forming apparatus according to claim 1.
The image carrier protection member is an image forming apparatus made of a conductive member. The image forming apparatus according to claim 1 or 2 ,
The image forming apparatus, wherein an absolute value of the protection member voltage is smaller than an absolute value of the transfer voltage. The image forming apparatus according to any one of claims 1 to 3 ,
The image forming apparatus, wherein an absolute value of the protection member voltage is larger than an absolute value of the toner scattering suppression voltage.

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