JP2005140856A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain high image quality over time and to reduce the size of an electrophotographic image forming apparatus.
A photoconductor drum 2, a charging roller 10, a laser exposure unit 12, a developing unit 3, and a transfer conveyance unit 4 are provided, on the photoconductor drum 2 upstream of the exposure position C and on the downstream side of the transfer position E. A first cleaning roller 9 and a second cleaning roller 11 are provided so that toners of predetermined polarity and reverse polarity can be adsorbed and released. Then, by using the switching control means, the toner on the photosensitive drum 2 is adsorbed when the image is formed, and the adsorbed toner is discharged onto the photosensitive drum 2 when the image is not formed, and is conveyed to the downstream side. The roller 9 and the second cleaning roller 11 are cleaned.
[Selection] Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus. In particular, the present invention relates to an image forming apparatus including a cleaning unit that can reliably remove residual toner on a photoreceptor and is suitable for downsizing.

An electrophotographic image forming apparatus, such as a laser printer, a laser fax machine, or a digital copying machine, charges a photoconductor substantially uniformly and exposes the photoconductor to form an electrostatic latent image corresponding to an image signal. Then, the toner charged by the developing device is supplied onto the photoreceptor to be visualized, and the toner image is transferred to a recording medium such as transfer paper and fixed by a fixing device to form an image. In particular, in a color image forming apparatus that forms a color image, for example, toners of four colors of yellow, magenta, cyan, and black are used, and toner images of each color are formed on a plurality of photoconductors based on color-separated image signals. The toner images are formed and sequentially transferred to a recording medium, or transferred to an intermediate transfer member and overlaid on a color, transferred to a recording medium, and then fixed.
Conventionally, in such an image forming apparatus, a visualized toner image is not completely transferred, and a slight amount of untransferred toner remains on the photoreceptor. If such residual toner and exposure position overlap, normal exposure may not be performed and image noise may occur. Therefore, generally, a cleaning means is provided for removing residual toner on the photoreceptor and collecting it in a toner recovery tank.
However, in recent years, there has been a strong demand for downsizing the apparatus, and a so-called cleaner-less system has been proposed in which a toner collection tank that occupies a large space near the photoreceptor is omitted.
For example, Patent Document 1 includes a cleaning roller that sucks residual toner on the photoconductor by a potential difference in the suction mode and sucks the toner discharged from the cleaning roller by a non-discharge mode in the discharge mode. An image forming apparatus is described which is collected by a developing unit in an operating state (when no image is formed). According to this apparatus, although the residual toner is collected by the cleaning roller, it is discharged in a non-operating state and returned to the developing unit, so that a toner collecting tank is not necessary.
Japanese Patent Laid-Open No. 9-305066 (page 4-9, FIGS. 2 and 3)

However, the conventional image forming apparatus as described above has the following problems.
In the apparatus for collecting the residual toner by the cleaning means, there is a problem that the apparatus cannot be miniaturized because the toner collection tank is provided. Although a method of arranging the toner recovery tank in an empty space of the apparatus and conveying the toner recovered by the cleaning means to the toner recovery tank by pipe conveyance is also conceivable, there is a problem that a complicated and expensive conveyance mechanism must be provided. .
The technique described in Patent Document 1 has an advantage that a toner collection tank is not required and the collected toner can be reused in a developing unit. However, in electrophotography, a transfer voltage is applied and discharged in the transfer process in order to release the charged toner from the photoreceptor, so that a reverse polarity toner is generated, which is also included in the untransferred toner. .
Since the reverse polarity toner cannot be sucked by the apparatus of Patent Document 1, the reverse polarity toner remains on the photosensitive member and is conveyed to the exposure position. Therefore, there is a problem in that latent image formation is hindered by such residual toner.
Further, since the reverse polarity toner is repelled in the developing unit due to the reverse polarity and is not collected, it accumulates on the photoconductor over time and the stain progresses, so that the image quality deteriorates.
The technique described in Patent Document 1 cannot be applied to a so-called tandem type color image forming apparatus in which a plurality of color image forming apparatuses are arranged on one transfer belt.
In the tandem system, unfixed toner remains on each color photoconductor as in the single-color image forming apparatus. However, in the transfer process for the second and subsequent colors, it contacts the other color toner transferred in the previous image forming process. However, the toner in the previous image forming process slightly adheres to the photoreceptor. Since most of the toner has a predetermined polarity, it is collected even by a developing unit of another color. As a result, there is a problem that in the developing units for the second and subsequent colors, toner color mixture occurs over time and the print quality deteriorates.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that can maintain high image quality over time and can be downsized.

In order to solve the above-described problems, in the invention described in claim 1, an electrostatic latent image is formed on a photosensitive member, a charging unit that charges the photosensitive member substantially uniformly, and a photosensitive member charged by the charging unit. An exposure unit for forming, a developing unit for supplying toner charged to a predetermined polarity to visualize the electrostatic latent image, and a toner image on the photosensitive member formed by the developing unit is transferred to a recording medium. An image forming apparatus having a transfer conveying unit configured to convey the toner on the photosensitive member upstream of the exposure position and downstream of the transfer position. A cleaning unit, a second cleaning unit that enables adsorption and release of toner having a polarity opposite to the predetermined polarity, and a switching control unit that switches between adsorption and release of toner in the first and second cleaning units, respectively. With When the image is formed, the toner on the photoconductor is adsorbed, and when the image is not formed, the adsorbed toner is discharged onto the photoconductor and conveyed downstream, thereby cleaning the photoconductor and performing the first and second operations. The cleaning unit is configured to perform cleaning.
According to the present invention, during the image formation, the switching control means causes the toner remaining on the photoreceptor (hereinafter simply referred to as “residual toner”) on the downstream side of the transfer position to be charged with the first polarity. The toner charged to a polarity opposite to the predetermined polarity by the cleaning means is adsorbed by the second cleaning means, and these residual toners can be removed from the photoreceptor on the upstream side of the exposure position. As a result, the residual toner remains at least at the exposure position, so that exposure is not hindered and a good latent image can be formed.
In addition, since the residual toner adsorbed by the first and second cleaning means can be discharged to the photosensitive member by the switching control means and the downstream side can be conveyed by the photosensitive member when the image is not formed. Cleaning for removing the toner adsorbed by the cleaning means can be performed. As a result, the adsorption performance of the first and second cleaning means can be kept good over time.
In addition, since it is not necessary to provide a toner recovery tank or the like in the vicinity of the first and second cleaning means, the configuration around the photosensitive member can be made compact.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an applied voltage of the first and second cleaning units ranges from 0 V to an applied voltage of the charging unit during image formation. The configuration can be set by.
According to the present invention, it is possible to control the adsorption and release of the residual toner by changing the applied voltage of the first and second cleaning means relative to the applied voltage of the charging means. Moreover, since the variable range of the applied voltage is from 0 V to the same polarity range, the switching control means and the high voltage power supply can be manufactured at low cost.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the first and second cleaning means are conductive or semiconductive, and hold toner on the surface and inside. And a roller member in which a gap is formed.
According to the present invention, since the first and second cleaning means have conductivity or semi-conductivity, the toner can be easily adsorbed or released by changing the electric potential, and since it is a roller member, Can be manufactured at low cost. Further, since a gap for holding the toner is formed on the surface and inside, the load is small even when contacting the photoreceptor, and the toner adsorption efficiency is high. Further, for example, it can be easily mounted without requiring a high mounting accuracy like a cleaning blade.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the charging unit comprises a charging roller having conductivity or semiconductivity, and the first cleaning unit is conductive. Alternatively, the second cleaning means is a conductive member provided in parallel to a position separated from the charging roller, and is composed of a roller member having a semiconductivity and having a surface and a gap for holding toner on the inside. Belt having a heat-conducting property or semi-conducting property, and a belt that is wound around the power supply roller and the charging roller and is rotationally driven in contact with the surface of the photosensitive member to hold toner on the surface and inside thereof. It is set as the structure which consists of a member.
According to the present invention, the second cleaning means comprises the power supply roller and the belt member that is wound around the charging roller and contacts the surface of the photosensitive member. The efficiency can be improved and the photosensitive member need not be strongly contacted, so that the photosensitive member can be driven easily. As a result, the residual toner can be efficiently removed and the photosensitive member can be driven smoothly, so that the image quality can be improved.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the power supply roller is disposed on the downstream side of the photosensitive member with respect to the charging roller, and the power supply roller and the second cleaning unit The applied voltage can be set in a range from 0 V to the applied voltage of the charging unit during image formation.
According to the present invention, it is possible to control the adsorption and release of the residual toner by changing the applied voltage of the power supply roller and the second cleaning unit relative to the applied voltage of the charging unit. Moreover, since the variable range of the applied voltage is from 0 V to the same polarity range, the switching control means and the high voltage power supply can be manufactured at low cost. Further, it is possible to prevent the power supply roller and the second cleaning unit from affecting the charging potential of the photosensitive member.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the developing unit discharges from the first and second cleaning units onto the photoconductor when no image is formed. The toner is allowed to pass through, and the toner released on the photoconductor is attracted onto the transfer conveying means and collected.
According to the present invention, since the toner released from the first and second cleaning means passes through the developing means and is conveyed downstream, residual toner is not mixed into the developing means.
Further, since the toner that has passed through the developing means is attracted and collected on the transfer conveying means, it does not remain on the photoreceptor again. Further, since the residual toner on the photoconductor and the toner cleaning mechanism which is not involved in image formation on the transfer / conveyance means can be used together, the configuration can be simplified.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the developing means is of a one-component non-contact developing type.
According to the present invention, a so-called cleaner-less system can be realized because it is not necessary to provide a toner collection tank for collecting toner even if the developing unit cannot collect toner in the one-component non-contact developing system. And miniaturization can be achieved.

According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, a plurality of image forming units each including the photoconductor, the charging unit, the developing unit, and the first and second cleaning units. And the transfer conveying means is provided in common with them.
According to the present invention, a color image forming apparatus that includes a plurality of image forming units including a photosensitive member, a charging unit, a developing unit, and first and second cleaning units, and is capable of printing in a plurality of colors with a common transfer conveyance unit. In this case, since it is not necessary to provide a toner collection tank in each image forming unit, the apparatus can be miniaturized.
In addition, even when toner adheres to the photoreceptor of the other image forming unit from the toner image formed in one image forming unit and becomes residual toner, it is recovered on the transfer conveying means, It is possible to prevent toner from being mixed in the developing means.

According to the image forming apparatus of the present invention, the residual toner on the photoconductor from the transfer position to the exposure position is adsorbed by the first and second cleaning means for each polarity and is released when the image is not formed. Therefore, it is possible to clean the surface of the photoconductor during exposure and to maintain high image quality over time.
Further, the toner adsorbed by the cleaning unit can be discharged to the downstream side of the photoconductor when the image is not formed without providing a toner recovery tank or the like in the vicinity of the cleaning unit, so that the apparatus can be downsized. There is an effect.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and redundant description is omitted.
FIG. 1 is a schematic explanatory diagram for explaining a schematic configuration of a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a control block diagram for explaining a schematic configuration of the control unit.
The image forming apparatus 1 of the present embodiment scans and exposes a laser beam modulated according to an image signal, and performs printing on a printing medium 8 (recording medium) such as paper or a plastic sheet by a dry electrophotographic method. It can be used as a laser printer, a laser fax machine, a digital copying machine, or a part thereof.
As shown in FIGS. 1 and 2, the schematic configuration of the image forming apparatus 1 includes a laser exposure unit 12 (exposure unit), an image forming unit 20, a paper feeding / conveying unit (not shown), and a transfer / conveying unit 4 (transfer / conveying unit). ) And a fixing unit (not shown), a driving unit 55, a detecting unit 56, a controller 50, an operation unit 51 and an image signal input unit 52, and an apparatus main body (not shown) for holding them together.

The laser exposure unit 12 scans a laser beam 12a focused on a minute spot on a straight line parallel to the rotation axis in a fixed direction at an exposure position C of a photosensitive drum 2 (photosensitive member) described later. When the input signal D _i input to the image signal input unit 52 is input to the controller 50 that performs various controls such as image processing and apparatus sequence control, an output image signal D _o is generated and the laser exposure unit. 12, a laser beam 12a modulated in accordance therewith is emitted to an exposure position C.

The image forming unit 20 is a development unit along the outer periphery of the photosensitive drum 2 in which a semiconductor layer having photoconductivity is formed on the surface of a cylindrical metal drum rotated at a predetermined linear velocity in the direction of the arrow in FIG. 3 (developing means), a first cleaning roller 9 (first cleaning means), a charging roller 10 (charging means), and a second cleaning roller 11 (second cleaning means) are arranged.
Hereinafter, when expressing the relative position on the photosensitive drum 2, the rotation direction side is referred to as a downstream side, and the counter rotation direction side is referred to as an upstream side.
In the present embodiment, the metal drum that is the base of the photosensitive drum 2 is grounded, and the photosensitive member potential V _D that is the surface potential is set to V _D = −1350 (V). Then, when the laser beam 12a is exposed to the image area based on the output image signal D _o , the charge in the exposed portion is discharged, and the exposure potential V _I (where | V _D | ≧ | V _I |) is obtained. It is said. For example, in the case of binary image recording, the exposure potential V _I is configured to be a dark potential of about 0 to −100V.

Developing unit 3, the toner T of a powder having a predetermined color by frictional charging, is a negative charge, is a relatively positive potential with respect to the non-exposed portion by being dropped to the exposure potential V _I by exposure The toner T is supplied to the exposed portion and adhered thereto.
In the developing unit 3, the toner T, a stirring blade 3d that stirs and charges the toner T, a supply roller 3b that conveys the charged toner T to the developing roller 3a side, and a toner T that is supplied by the supply roller 3b And a developing blade 3c for regulating the layer thickness of the toner T on the developing roller 3a to a constant thickness on the developing roller 3a. Is provided. The stirring blade 3d, the supply roller 3b, and the developing roller 3a are each rotated in the direction of the arrow in FIG.
The developing roller 3a is disposed such that the roller surface is separated from the photosensitive drum 2 by a distance d and is opposed to a developing position D that is separated from the exposure position C on the photosensitive drum 2 by a predetermined distance upstream. The Then, connected to the developing high-voltage power supply 60 (see FIG. 2), at a predetermined timing during image formation, in order to distance d moved toward the toner T of the surface on the photosensitive drum 2, a high frequency to a DC bias potential V _B In this embodiment, V _B = −250 (V), and V _AC = 1.8 (kVp-p), in which the AC voltage V _AC is superimposed and a voltage that becomes the development potential V _d is applied. The The frequency of _{V AC} is a 2 (kHz).

A transfer conveyance unit 4 to be described later is in contact with a transfer position E downstream of the development position D. The printing medium 8 is fed to the transfer position E at a predetermined timing by a paper feeding / conveying unit (not shown).
The transfer / conveying unit 4 is held so that the transfer belt 7 can be rotationally driven in one direction by a plurality of rollers disposed on the inner peripheral portion, and the transfer belt 7 is brought into contact with the photosensitive drum 2 at the transfer position E. A transfer roller 6 and a transfer belt cleaning unit 5 having a space for abutting a cleaning blade 5a against the transfer belt 7 to scrape off deposits on the surface of the transfer belt 7 and recover the scraped deposits.
The material of the transfer belt 7 is that the toner T on the photosensitive drum 2 is sucked by the transfer voltage V _T applied to the transfer roller 6 in contact with the back surface when facing the photosensitive drum 2 across the printing medium 8. The dielectric sheet is made possible.
The transfer roller 6 has a configuration in which a roller portion is formed of, for example, a metal rotation shaft made of conductive or semiconductive synthetic rubber, and the transfer shaft 6 has a high voltage power supply 61 for transfer (see FIG. 2). It is connected so that the surface potential of the roller portion can be controlled.
The transfer voltage _VT has an optimum value depending on the material and thickness of the print medium 8, but is generally +1000 V or more.
In this specification, semi-conductive means that the resistance value is about 10 ⁴ Ω to ^{10 10} Ω. Conductivity means a material having a resistance value in a smaller range.

The first cleaning roller 9 is a roller member that includes a roller portion having a predetermined diameter that extends at least beyond the effective image width in the main scanning direction on the outer periphery of a rotating shaft that has conductivity and has appropriate rigidity. The roller portion is made of a material having conductivity or semi-conductivity and forming a gap for holding the toner T on the surface and inside.
The arrangement position of the first cleaning roller 9 is a first cleaning position F on the downstream side of the transfer position E, and is a position where the roller surface comes into contact with the photosensitive drum 2.
Then, it is rotated at the same linear speed as the photosensitive drum 2 by the driving means 55 (see FIG. 2), the cleaning high voltage power source 58 (see FIG. 2) is connected to the rotating shaft, and a predetermined signal is _supplied by the control signal _SCL1 of the controller 50. At the timing, a voltage is applied so as to be the cleaning potential _VCL1 .
As a material of the rotating shaft, for example, a metal shaft, conductive synthetic resin, or the like can be adopted. The material of the roller part is a brush roller shape in which conductive or semiconductive nylon fibers are electrostatically implanted on the rotating shaft, a similar woven fabric made of nylon fibers wrapped in a band shape, or conductive For example, a sponge roller-like product obtained by forming a porous foam made of a conductive or semiconductive synthetic resin into a roller shape can be suitably used. It is preferable that the sponge roller-like material has appropriate elasticity in order to flexibly contact the appropriate photosensitive drum 2 and maintain a predetermined contact width. As described above, the first cleaning roller 9 flexibly contacts the photosensitive drum 2 so that excellent cleaning characteristics can be obtained without positioning with high accuracy such as a cleaning blade. There are advantages.
Although not shown, a static eliminator for lowering the potential of the photoconductor in the previous process, which is conventionally arranged upstream of the charging means, is arranged upstream of the first cleaning roller 9.

The charging roller 10 is for setting the surface potential of the photosensitive drum 2 to the photosensitive member potential V _D at the time of image formation. The charging roller 10 is configured by forming a roller portion with a metal shaft and an elastic body imparted with conductivity. The photosensitive drum 2 is brought into contact with the charging position A on the downstream side of the first cleaning position F. Then, it is rotatably supported by a bearing (not shown), and can be rotated at the same linear speed as the photosensitive drum 2 by a driving means 55 (see FIG. 2). Further, the charging roller 10 is pressed against the photosensitive drum 2 with a predetermined load by pressing the bearing with a biasing means such as a spring. Although the predetermined load varies depending on the material of the roller, for example, a value of about 2N to 50N can be suitably used.
As a result, the roller portion is deformed to form an NIP portion that contacts the photosensitive drum 2 with a predetermined width in the circumferential direction, and the charging roller potential V _ch is charged at a predetermined timing by the control signal _Sch of the controller 50. When the DC voltage is applied, the photosensitive drum 2 can be charged to the photosensitive member potential V _D (= V _c ). The resistance value of the roller part is preferably about 1 MΩ, for example.
Here, the length of the arc FA is set so that the first cleaning roller 9 and the charging roller 10 do not contact each other. Since there is no toner collection tank or the like for collecting the toner adhering to the first cleaning roller 9 in the vicinity of the first cleaning roller 9, the arc FA can be made relatively close according to the size of the roller diameter. There are advantages.

The second cleaning roller 11 has the same configuration as that of the first cleaning roller 9, and the roller surface is a photosensitive drum at a second cleaning position B downstream of the charging position A and upstream of the exposure position C. 2 is disposed so as to abut on the surface. Then, it is rotated at the same linear speed as the photosensitive drum 2 by the driving means 55, a high-voltage power supply 59 for cleaning (see FIG. 2) is connected to the rotating shaft, and the cleaning potential at a predetermined timing by the control signal _SCL2 of the controller 50. A voltage is applied so as to be _VCL2 .
Here, the length of the arc AB is set in a range where the charging roller 10 and the second cleaning roller 11 do not contact each other. Since there is no toner collection tank or the like for collecting the toner adhering to the second cleaning roller 11 in the vicinity of the second cleaning roller 11, the arc AB can be made relatively close according to the size of the roller diameter. There are advantages.

The fixing unit includes a roller pair for thermally fixing the print medium 8 onto which the toner image is transferred and conveyed by the transfer conveyance unit 4.
The driving means 55 is for driving the movable part excluding the laser exposure unit 12, and includes at least one motor, its control circuit, a drive transmission mechanism, and the like.
The detection unit 56 includes various sensors arranged at predetermined positions in order to perform drive control of the drive unit 55.
The controller 50 is composed of at least one microcomputer loaded with a predetermined program, and can input and output data, input a detection signal S _det , and input and output various control signals. The controller 50 controls the control signals S _ch , S _CL1 , and S _CL2 for the charging high voltage power source 57, the cleaning high voltage power source 58, the cleaning high voltage power source 59, the development high voltage power source 60, and the transfer high voltage power source 61, respectively. , S _d , S _T are output, and each high voltage power source is switched to output a desired high voltage. For this reason, the controller 50 also serves as a switching control means for these high voltage voltages.
The operation unit 51 is used to input control information that can be operated by the user and to display device setting information and operation information. The operation unit 51 transmits and receives an operation control signal S _op and a display signal S _dsp to the controller 50. To do. For example, in the case of a printer, the input / output device includes a button that enables online and offline control, a liquid crystal display that displays a print status, and the like.
The image signal input unit 52 constitutes an interface for passing the input signal _Di to the controller 50. For example, in the case of a printer, the image signal input unit 52 includes a parallel port or a LAN board. In addition, in a digital copying machine or the like, an appropriate internal interface that transmits and receives data by connecting to a scanner unit may be used.

An operation of the image forming apparatus 1 of the present embodiment will be described.
Since the general operation of the image forming apparatus 1 is the same as that of a known printer or the like, the description thereof will be omitted as appropriate, and the description will focus on operations such as charging and cleaning.
The operation of the image forming apparatus 1 has a print mode (when an image is formed) and a cleaning mode (when an image is not formed).
FIG. 3 is a timing chart for explaining the potential relationship of the image forming unit and the like in the print mode of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a timing chart for explaining the potential relationship of the image forming unit and the like in the cleaning mode.

As shown in FIG. 3, when a print start signal (not shown) is input to the controller 50 through the operation unit 51 or the image signal input unit 52 at time t ₀ , the cleaning high-voltage power supply 58 is turned on by the control signal S _CL1 . The voltage is applied, the first cleaning potential V _CL1 is set to V _CL1 = V ₁ = −700 (V), the voltage of the charging high-voltage power supply 57 is applied by the control signal _Sch , and the charging means potential V _ch is It is assumed that V _c = V ₂ = −1350 (V). At the same time, the driving means 55 is actuated to rotate the movable part such as the photosensitive drum 2. The paper feeding / conveying section performs a paper feeding operation at a predetermined timing, and conveys the print medium 8 toward the photosensitive drum 2.
The predetermined timing is a timing at which the leading edge of the printing medium 8 and the leading edge of the image including white spots are synchronized at the transfer position E by a registration roller (not shown).

A static eliminator (not shown) is turned on, and the potential of the previous process is dropped to a dark potential on the upstream side of the first cleaning roller 9 so that the charging roller 10 can perform substantially uniform charging.
Since V _CL1 = V ₁ <0, the first cleaning roller 9 sucks positively charged toner (reverse polarity toner) out of the toner T remaining on the photosensitive drum 2 and holds it in the gap of the roller portion. On the other hand, of the remaining toner T, negatively charged toner (predetermined polarity toner) is repelled, passed under the first cleaning roller 9 and conveyed downstream.

The charging roller 10 negatively charges the surface of the photosensitive drum 2 so as to be V _D (= V ₂ ). Since V ₂ > V ₁ , the negatively charged toner is not attracted to the charging roller 10, passes below the charging roller 10, and is conveyed downstream. Further, since the positively charged toner is removed by the first cleaning roller 9, the residual toner is sucked and attached to the charging roller 10 and the roller surface is not soiled.

On the other hand, the voltage of the second cleaning roller 11 is 0 V because no voltage is applied, but at the second cleaning position B, the photosensitive member potential V _D = V ₂ > 0, so that the second cleaning roller 11 is The potential becomes relatively high with respect to the photosensitive drum 2, and the negatively charged toner is attracted to the second cleaning roller 11. Therefore, on the downstream side of the second cleaning position B, the toner of either positive or negative polarity is removed from the photosensitive drum 2.

At the time t _{1 when the} surface of the photosensitive drum 2 positioned at the charging position A at the time of the stop passes at least the exposure position C, the gate signal _Sg is changed from the H level to the L level, and the exposure is started. That laser beam 12a which is modulated by the image signal D _o is repeated scans on exposure position C in the main scanning direction, that at the same time the photosensitive drum 2 rotates, the photosensitive drum 2 is raster scanned planar, exposure An electrostatic latent image in which only the portion is dropped to the dark potential is formed.

Then, the photosensitive drum 2 is slightly earlier time t ₂ from time to move to the development position D from the exposure position C, the control signal S _d is output from the controller 50, the developing voltage to the developing roller 3a by a development high voltage power source 60 V _d is applied. The development voltage V _d is varied between V ₄ = + 250 (V) and V ₅ = −750 (V) by superimposing the AC voltage V _AC on the DC bias voltage V _B.
As a result, the electric field negatively charged toner to move toward the photosensitive drum 2 between the photoreceptor potential V _D is fallen exposed portions of the photosensitive drum 2 by the exposure and the development roller 3a is formed. Then, the negatively charged toner T moves toward the photosensitive drum 2 from the surface of the developing roller 3a facing the exposed portion that is lowered to the dark potential, and the electrostatic latent image is visualized.

Then, in a slightly earlier time t ₃ from the time the photosensitive drum 2 is moved to the transfer position E from the developing position D, the control signal S _T is outputted from the controller 50, transferred to the transfer roller 6 by a transfer high voltage power source 61 A voltage V _T = V ₃ > 0 is applied. At the transfer position E, the print medium 8 that has arrived in synchronization with the front end position of the image is conveyed while being sandwiched between the transfer roller 6 and the photosensitive drum 2, and the toner image on the photosensitive drum 2 is transferred to the print medium 8. Sucked to the side. The transfer voltage V _T is applied until at least the exposed portion passes the development position D (time t ₅ ), and the transfer voltage V _T is applied until time t ₆ when the trailing edge of the print medium 8 passes the transfer position E. . Thereafter, if not continuous printing at time _{t 7,} the first cleaning potential _{V CL1,} a charging unit potential _{V ch} is turned off.
In this way, the visualized toner image is transferred to the print medium 8. The printing medium 8 is conveyed to the fixing unit, the toner image is fixed, and the image printing is finished.
After transfer, a certain amount of untransferred toner remains on the surface of the photosensitive drum 2, but is attracted to the respective rollers without reaching the exposure position C by the action of the first cleaning roller 9 and the second cleaning roller 11. The

  As described above, in the printing mode of the present embodiment, the residual toner on the photosensitive drum 2 is removed before exposure regardless of the polarity. Accordingly, the surface of the photosensitive drum 2 is kept clean at the exposure position C, and the residual toner does not hinder the exposure, so that a high-quality latent image can be formed.

Next, the cleaning mode of this embodiment will be described.
The cleaning mode is a mode for collecting the toner T adsorbed by the first cleaning roller 9 and the second cleaning roller 11 during the printing mode. Then, the movable parts such as the photosensitive drum 2 and the transfer belt 7 are synchronized with the print medium 8 not being conveyed.
The cleaning mode is executed at an appropriate timing before and after the printing mode or between a plurality of printing modes. The appropriate timing can be determined according to the amount of toner that can be adsorbed by the first cleaning roller 9 and the second cleaning roller 11, operation results, and the like. For example, if a sufficient amount can be adsorbed, it may be set only when the power is turned on, or may be set every predetermined time or every predetermined number of sheets passed by a timer or a sheet passing counter.
Incidentally developing unit 3 is turned off the developing voltage V _d, is not performed toner development T, the movable portion such as the developing roller 3a can may not be be operated.

4, time _{t 10} is a cleaning start timing.
At time _{t 10,} the first cleaning potential _{V CL1 = V 11 = -700 (} V), and the charging roller voltage _{V ch = V 12 = -1350 (} V). Then, the photosensitive drum 2 is the photosensitive drum 2 in this state until time t ₁₁ which rotates over one turn, rotates the transfer belt 7. At this time, the transfer voltage V _T is turned off (V _T = 0 (V)), and the static eliminator is turned on.
During this period, all residual toner is again attracted to the first cleaning roller 9 and the second cleaning roller 11.
At time t ₁₁ , the control signals S _CL1 , S _ch , and S _CL2 are switched by the controller 50 to turn off the first cleaning potential V _CL1 and the charging unit potential V _ch (V _CL1 = V _ch = 0 (V). ), And the second cleaning potential V _CL2 = V ₁₃ = −1350 (V).
Then, the positively charged toner adsorbed by the first cleaning roller 9 is sucked toward the negatively charged photosensitive drum 2 and is thus discharged onto the photosensitive drum 2. Then, it passes under the charging roller 10.
On the other hand, since the second cleaning roller 11 is negatively charged, it adsorbs the positively charged toner to pass therethrough and releases the negatively charged toner to the photosensitive drum 2. Then, the photoreceptor potential on the downstream side of the second cleaning position B is charged to V _D = V ₁₃ . At this time, since the negative potential charged by the charging roller 10 remains in the region where the photosensitive drum 2 advances from the charging position A to the second cleaning position B, the second cleaning roller 11 and the photosensitive drum are left behind. 2, negatively charged toner is released. However, after that, charging by the charging roller 10 is finished, and a potential difference is generated between the second cleaning roller 11 and the photosensitive drum 2, and the negatively charged toner is reliably discharged.

At time _{t 12} the second cleaning position B at time _{t 11} reaches the transfer position E moves, the transfer voltage _{V T = V 14 = + 500} (V) is applied to the transfer roller 6. Thereby, the negatively charged toner released from the second cleaning roller 11 is adsorbed to the transfer belt 7.
In this way, all the positively charged toner is discharged from the first cleaning roller 9 and adsorbed by the second cleaning roller 11, and all the negatively charged toner adsorbed and held by the second cleaning roller 11 is adsorbed by the transfer belt 7. It continues to drive up to time _{t 13} that. Although this time depends on the toner adsorption capacity and the like, it is preferable that the first cleaning roller 9 and the second cleaning roller 11 be several times or more.

Then, at time _{t 13,} the first cleaning roller 9, the charging roller 10 is switched to the same state as the potential of the second cleaning roller 11 to the time _t 10 _{~t 11.} Further, at time _{t 14} that the elapsed time _(t 12 _{-t 11),} applies a transfer voltage _{V T = V 15 = -500 (} V) to the transfer roller 6. As a result, the second cleaning roller 11 is in a state of adsorbing negatively charged toner and releasing positively charged toner in the same manner as in the printing mode, and the positively charged toner adsorbed from time t _{11 to} t ₁₃ is applied to the photosensitive drum 2. To be released.
Since the developing voltage _Vd is 0 V, the positively and negatively charged toner does not move to the developing unit 3 and passes through the developing unit 3 while remaining on the photosensitive drum 2 as it is.
They toner reaches the transfer position E at time t _14, by the action of the transfer roller 6 whose polarity is switched, is attracted to the transfer belt 7. Then, at time _{t 15} which over time _(t 13 _{-t 11),} turns off the transfer voltage _{V T.}
In this way, all residual toner adsorbed by the first cleaning roller 9 and the second cleaning roller 11 is conveyed by the photosensitive drum 2 and adsorbed by the transfer belt 7.
The residual toner adsorbed on the transfer belt 7 is conveyed to the transfer belt 7, scraped off from the surface by the cleaning blade 5 a, and collected in the transfer belt cleaning unit 5.
This completes the cleaning mode.

As described above, according to the image forming apparatus 1 of the present embodiment, in the printing mode, the residual toner on the photosensitive drum 2 is attracted to the exposure position C regardless of the charging polarity, High image quality can be maintained. Further, in the cleaning mode, all of the adsorbed residual toner can be adsorbed on the transfer belt 7 of the transfer conveyance unit 4 and collected together by the transfer belt cleaning unit 5 that is a cleaning mechanism of the transfer belt 7. Therefore, the photosensitive drum 2 can be cleaned without arranging a toner recovery tank in the vicinity of the first cleaning roller 9 and the second cleaning roller 11.
As a result, there is room in the component arrangement space around the photosensitive drum 2, and the image forming unit 20 can be downsized.

Next, a first modification of the embodiment of the present invention will be described.
FIG. 5 is a schematic explanatory diagram of an image forming unit for explaining a schematic configuration of a first modification of the present embodiment.
In the above embodiment, the positively charged toner is adsorbed upstream of the charging roller 10 and the negatively charged toner is adsorbed downstream of the charging roller 10, but the first modification example is as shown in FIG. 1, the positional relationship between the charging roller 10 and the second cleaning roller 11 is reversed so that positive and negative charged toner is adsorbed on the upstream side of the charging roller 10. Except for the roller arrangement, the operation is the same as that in the above embodiment, and detailed operations are omitted. For example, each time in the timing charts of FIGS. 3 and 4 is slightly shifted with the change of the arrangement position, but the relative relationship is the same, and the change is very easy.
In this case, since the charging position A is adjacent to the exposure position C, it is possible to suppress the attenuation of the photosensitive member potential V _D of until exposure, there is an advantage that higher quality can be obtained.

Next, a second modification will be described.
Although this modification is not particularly illustrated, the arrangement of the first cleaning roller 9 and the second cleaning roller 11 in FIG. 5 is exchanged. This effect is the same as that of the first modification except that the negatively charged toner is first adsorbed by the second cleaning roller 11 and then the positively charged toner is adsorbed by the first cleaning roller 9. Therefore, the operation order of FIGS. 3 and 4 needs to be replaced, but the replacement is self-explanatory and will not be described.

Next, a third modification will be described.
FIG. 6 is a schematic explanatory diagram of an image forming unit for explaining a schematic configuration of a third modification of the present embodiment.
In this modification, instead of the charging roller 10 and the second cleaning roller 11 of the above-described embodiment, a charging roller 13 and a power supply roller 14 are provided, and the charging position A and the power supply roller position I on the downstream side of the first cleaning position F, respectively. The cleaning belt 15 (second cleaning means) is wound around the charging roller 13 (charging means) and the power supply roller 14.
The charging roller 13 has the same configuration as that of the charging roller 10, but is pressed against the photosensitive drum 2 via the cleaning belt 15, and therefore the elasticity and surface properties of the charging roller 13 drive the cleaning belt 15. There is an advantage that a wide range of values can be obtained rather than the formation of the discharge NIP portion.
The power supply roller 14 is a roller part formed of an elastic body or foamed elastic body having conductivity or semiconductivity on a rotating shaft having rigidity and conductivity such as metal, and a voltage is applied by a high-voltage power supply 59 for cleaning. Thus, the second cleaning potential V _CL2 can be set.

The cleaning belt 15 can employ a configuration in which a woven fabric obtained by forming synthetic fibers such as nylon fibers imparted with conductivity or semiconductivity into a belt shape and a gap for adsorbing toner between the fibers is provided. . Then, when wound around the charging roller 13 and the power supply roller 14, at least from the charging position A to the power supply roller position I, while being in close contact with the surface of the photosensitive drum 2, the same line as the photosensitive drum 2. It is moved at high speed.
In order to efficiently perform charging and cleaning, the resistance value of the cleaning belt 15 has a ratio of the resistance value in the circumferential direction between the charging roller 13 and the power supply roller 14 to the resistance value in the belt thickness direction is 10 or more. It is desirable that Further, the absolute value of the resistance value between the charging roller 13 and the power supply roller 14 is desirably 10 ⁸ Ω or more.
When the volume resistivity is substantially uniform, the ratio of the resistance value between the thickness direction and the length direction (circumferential direction) is substantially proportional to the length (thickness). And such a configuration is easy. For example, in the case where the synthetic fiber is formed as described above, the volume resistivity is relatively uniform.
On the other hand, the cleaning belt 15 may have a brush-like belt surface by flocking or woolen fabric, but in this case, since the thickness direction is the fiber direction, the resistance value is low, and the fibers are independent in the belt circumferential direction. Therefore, the resistance value becomes high. Therefore, also in this case, the above resistance value condition can be easily satisfied.

According to such a configuration, by applying a voltage to the charging roller 13 and the power supply roller 14 so that the charging means potential V _ch and the second cleaning potential V _CL2 in FIGS. It can be demonstrated.
At that time, since the residual toner is adsorbed to the cleaning belt 15, even if the charging roller 13 has a relatively small diameter, the toner adsorbing capacity can be increased. Therefore, there is an advantage that the interval for performing the cleaning mode can be reduced. In addition, since the charging roller 13 can have a small diameter, there is an advantage that the image forming unit 20 can be reduced in size.
Further, since the cleaning belt 15 can be flexibly brought into contact with the photosensitive drum 2, there is an advantage that the driving load can be reduced.
Further, since the charging roller 13 does not directly contact the residual toner, there is an advantage that the charging performance is not deteriorated and the life can be extended.

Next, a fourth modification will be described.
FIG. 7 is a schematic explanatory diagram of an image forming unit for explaining a schematic configuration of a fourth modification of the present embodiment.
In this modified example, the first cleaning roller 9 in the third modified example is moved to the first cleaning position H on the downstream side of the charging unit including the charging roller 13, the feeding roller 14, and the cleaning belt 15, and the second cleaning unit. Is.
According to this configuration, after the negatively charged toner is attracted to the cleaning belt 15, the positively charged toner is attracted to the first cleaning roller 9. Therefore, the operation order of FIGS. 3 and 4 needs to be replaced, but the replacement is self-explanatory and will not be described.
The effects of the power supply roller 14 and the cleaning belt 15 and the point that all the residual toner can be collected in the transfer belt cleaning unit 5 are the same as those of the third modification.

In the above description, specific numerical values of the first cleaning potential V _CL1 and the second cleaning potential V _CL2 have been described. However, the residual toner is conveyed downstream without adhering to the charging unit. As long as the relative relationship is satisfied, an appropriate value can be taken between the surface potential of the non-exposed portion of the photoreceptor and 0 V, and the setting conditions are not limited to these values.

  In the above description, the toner is negatively charged and attached to the exposed portion of the photoconductor for development. However, in the case of the electrophotographic method, the non-exposed portion is developed with the positively charged toner. Needless to say. Even in this case, it is easy for those skilled in the art to change the above-described embodiment in accordance with polarity inversion.

In the above description, an example of a single-color printer having only one image forming unit 20 has been described. However, a plurality of image forming units 20 are arranged on the transfer conveyance unit 4, and toners are sequentially formed on the transfer conveyance unit 4. A color image forming apparatus that superimposes images can also be used. In this case, although the operations of the image forming unit 20 described above are executed with a predetermined timing shifted according to their arrangement positions, the individual operations are essentially the same. The same configuration can be used individually as a modification.
In such a configuration of the color image forming apparatus, a particularly remarkable effect is that toner color mixing in the developing unit can be prevented.
In the case of a color image forming apparatus, a transfer process is performed on the recording medium on which the toner image of the developing unit on the upstream side is already transferred to the photoreceptors for the second and subsequent colors. For this reason, at the transfer position, the photosensitive member easily comes into contact with the toner of another color contained in other developing means and adheres to the photosensitive member. Therefore, the toner of another color that has been transferred together with the untransferred toner becomes the residual toner on the photoreceptor.
Although reverse polarity toners exist in such toners, most are toners of a predetermined polarity. If a conventional so-called cleaningless system in which residual toner is collected in the developing unit is used, color mixing occurs in the developing unit. , Image quality is significantly degraded.
According to the configuration of the present embodiment, even when such different color toner is included in the residual toner, it is collected in the transfer conveyance unit without being collected in the developing unit, so that color mixing can be reliably prevented. There is an advantage that high image quality can be maintained over time.

  In the above description, the example in which the one-component non-contact developing method is adopted as the developing unit has been described. However, any developing method can be used as long as the residual toner on the photoreceptor is not collected by the developing unit in the cleaning mode. It may be used. For example, in the case of the two-component development method, the developing brush may be cut off so as not to contact the photosensitive member or separated from the photosensitive member in the cleaning mode. Even in the one-component contact development method, the developing unit may be configured to be in non-contact with the photosensitive member in the cleaning mode.

1 is a schematic explanatory diagram for explaining a schematic configuration of a main part of an image forming apparatus according to an embodiment of the present invention. It is a control block diagram for demonstrating schematic structure of the control part similarly. 6 is a timing chart for explaining a potential relationship of an image forming unit or the like in a print mode of the image forming apparatus according to the embodiment of the present invention. 12 is a timing chart for explaining the potential relationship of the image forming unit and the like in the cleaning mode. It is a schematic explanatory drawing of the image creation part for demonstrating schematic structure of the 1st modification of this embodiment. It is a model explanatory drawing of the image creation part for demonstrating schematic structure of the 3rd modification of this embodiment. It is a model explanatory drawing of the image creation part for demonstrating schematic structure of the 4th modification of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photosensitive drum (photosensitive body)
3 Development unit (development means)
3a Development roller 4 Transfer conveyance unit (transfer conveyance means)
5 Transfer belt cleaning unit 6 Transfer roller 7 Transfer belt 8 Printing medium (recording medium)
9 First cleaning roller (first cleaning means)
10, 13 Charging roller (charging means)
11 Second cleaning roller (second cleaning means)
12 Laser exposure unit (exposure means)
14 Power supply roller (second cleaning means)
15 Cleaning belt (second cleaning means)
20 image forming unit 50 controller (switching control means)
57 High-voltage power supply for charging (charging means)
58 High-voltage power supply for cleaning (first cleaning means)
59 High-voltage power supply for cleaning (second cleaning means)
C Exposure position E Transfer position

Claims (8)

A photosensitive member; a charging unit that charges the photosensitive member substantially uniformly; an exposure unit that forms an electrostatic latent image on the photosensitive member charged by the charging unit; and a toner charged to a predetermined polarity. An image forming apparatus comprising: a developing unit that visualizes an electrostatic latent image; and a transfer conveying unit that transfers and conveys a toner image on a photoreceptor formed by the developing unit to a recording medium,
On the upstream side of the exposure position on the photoreceptor and the downstream side of the transfer position,
First cleaning means for allowing adsorption and release of the toner of the predetermined polarity;
A second cleaning means that enables adsorption and release of toner having a polarity opposite to the predetermined polarity;
Switching control means for switching between adsorption and release of toner in the first and second cleaning means,
When the image is formed, the toner on the photoconductor is adsorbed, and when the image is not formed, the adsorbed toner is discharged onto the photoconductor and conveyed downstream, thereby cleaning the photoconductor and performing the first and second operations. An image forming apparatus that performs cleaning of a cleaning unit.   2. The image forming apparatus according to claim 1, wherein an applied voltage of the first and second cleaning units can be set in a range from 0 V to an applied voltage of the charging unit during image formation. .   3. The first and second cleaning means are composed of a roller member having conductivity or semi-conductivity and having a surface and a gap for holding toner on the inside. The image forming apparatus described in 1. The charging means comprises a charging roller having conductivity or semi-conductivity;
The first cleaning means is composed of a roller member having conductivity or semi-conductivity and having a surface and a gap for holding toner on the inside.
The second cleaning means is a conductive or semiconductive power supply roller provided in parallel to a position separated from the charging roller, and is wound around the power supply roller and the charging roller so as to be wound on the surface of the photoreceptor. The image forming apparatus according to claim 1, further comprising: a belt member that is driven to rotate in contact with the belt and is formed with a gap for holding toner on the surface and inside thereof. The power supply roller is disposed on the downstream side of the photoreceptor from the charging roller,
5. The image formation according to claim 4, wherein an applied voltage of the power supply roller and the first cleaning unit can be set in a range from 0 V to an applied voltage of the charging unit at the time of image formation. apparatus. The developing unit is configured to allow the toner discharged from the first and second cleaning units to pass through the photoreceptor when no image is formed;
6. The image forming apparatus according to claim 1, wherein the toner discharged onto the photosensitive member is collected by being attracted onto the transfer conveying unit.   The image forming apparatus according to claim 6, wherein the developing unit is of a one-component non-contact developing type.   A plurality of image forming sections each including the photosensitive member, the charging unit, the developing unit, and the first and second cleaning units are provided, and one transfer conveying unit is provided in common to them. The image forming apparatus according to claim 6, wherein the image forming apparatus is an image forming apparatus.

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