JP3597273B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for developing an electrostatic latent image formed by an electrophotographic method, and more particularly, to an image forming apparatus having an endless transport belt in a transfer unit.
[0002]
[Prior art]
Conventionally, electrophotographic image forming apparatuses such as copiers, facsimile machines, printers, and the like generally use a photoreceptor such as a photoreceptor drum or a photoreceptor belt to rotate the photoreceptor at the time of image formation, uniformly charge the photoreceptor, and then perform exposure. Forming an electrostatic latent image by performing image exposure by means, developing the electrostatic latent image with a developing device to form a toner image, transferring the toner image to a sheet of transfer paper or the like by a transfer device, and forming a toner image by a fixing device. After fixing, the photoconductor is cleaned by a cleaning device after the transfer of the toner image to remove residual toner on the photoconductor.
[0003]
As the transfer device, a corona charger, an endless transfer means, or the like is used, and the endless transfer means is constituted by a transfer conveyance belt. The transfer conveyance belt is rotated and driven by driving means including gears and the like, and a transfer bias is applied from a power supply to electrostatically hold and convey the sheet. The toner image on the photoreceptor is transferred to the sheet when the sheet passes through the gap.
[0004]
Since the base layer of the transfer / transport belt is made of a rubber material, if the transfer / transport belt is constantly in contact with the photoreceptor, the compounding material such as oil and wax contained in the rubber layer may vary depending on environmental conditions. A phenomenon of transferring to the photoreceptor was observed, and a problem that an abnormal image was generated sometimes occurred. Therefore, the transfer / conveying belt is brought into contact with the photosensitive member only during the image forming operation, and otherwise, the transfer / conveying belt is separated from the photosensitive member.
[0005]
In an image forming apparatus using an endless transfer unit, extra toner hardly adheres to the transfer / conveying belt, but the size of the toner image on the photoconductor and the size of the sheet are reduced due to the irregular size of the sheet. If the toner does not match, or if a sheet jam occurs, the toner may be transferred from the photoconductor to the transfer conveyance belt, and the transfer conveyance belt may directly contact the photoconductor between sheets. When a very small amount of toner is adhered to the photoreceptor (dirty toner), this toner may be transferred to the transfer conveyance belt. Therefore, when toner adheres to the transfer conveyance belt, it is necessary to dispose a cleaning device on the transfer conveyance belt to remove the toner on the transfer conveyance belt, as if a cleaning device was arranged on the photoconductor. is there.
[0006]
As this cleaning device, one that removes toner on a transfer conveyance belt by a cleaning blade has been proposed. Japanese Patent Application Laid-Open No. 2-34882 discloses an image forming apparatus using an endless transfer means. On the other hand, there is described a cleaning device that removes toner on a transfer conveyance belt by a cleaning blade that is brought into contact with the counter direction.
[0007]
[Problems to be solved by the invention]
In an image forming apparatus using a conventional transfer conveyance belt, the toner on the transfer conveyance belt is removed by a cleaning blade that is brought into contact with the transfer conveyance belt in a counter direction. On the other hand, in a high-temperature and high-humidity environment, the friction coefficient itself increases due to the increase in temperature and humidity of the cleaning blade and the belt coating layer, and the amount of background toner as a lubricant supplied from the photoconductor between the papers is extremely small. As a result, the friction coefficient between the transfer conveyance belt and the cleaning blade is increased, and the cleaning angle is narrowed due to a decrease in the Young's modulus of the cleaning blade due to an increase in temperature.
[0008]
As described above, it is necessary to provide a cleaning device in order to remove excess toner adhering to the transfer / transport belt. However, if a counter-type cleaning device is provided, the transfer / belt between the transfer / transport belt and the cleaning blade is required. A small amount of toner that plays a role of a lubricant to reduce the frictional force must always be supplied. A simple example of this frictional force phenomenon is similar to the wiper chatter that occurs when the wiper is operated without water droplets on the windshield of an automobile.
[0009]
The conventional technical idea is that the transfer / conveyance belt is brought into contact with the photoconductor only during the image forming operation, and otherwise, the transfer / conveyance belt is separated from the photoconductor. However, in the case of such control, for example, in the following cases (1) to (3), since the mechanical operation conventionally does not involve image formation, the operation is performed with the transfer belt separated from the photoconductor. Had been
(1) In the developing device of the two-component developing system, the toner concentration in the developer (carrier + toner) decreases with the consumption of the toner. When toner is forcibly supplied until toner is supplied.
(2) At the time of the initial setting of the developer, this is so that the output voltage of the T sensor of the initial agent (the toner concentration at the time of shipment from the factory is adjusted to 2.5%) becomes a predetermined reference voltage value. In this operation, the developer in the developing device is agitated to eliminate the bias of the developer in the developing device. The T sensor is a sensor that measures the transmittance of the developer, and measures the toner density by utilizing the fact that the observed value of the magnetic permeability changes depending on the toner density. The toner concentration in the developing device is controlled by the output of the T sensor.
(3) Immediately after the power is turned on, when the fixing heater is turned on and an image is output while the temperature distribution of the pressure roller is still non-uniform, part of the thermal energy that should contribute to the fusion of the toner on the transfer paper is reduced. At the time of pre-rotation of the fixing roller, the fixing roller and the pressing roller are rotated in advance so that the temperature distribution is saturated, in order to prevent a cold offset from being caused by the temperature rise of the pressing roller.
[0010]
However, when the above operation is performed in a high-temperature and high-humidity environment, there has been a problem that the cleaning blade is turned up. When a mechanical operation is performed with the cleaning blade turned up, there has been a problem that the back surface of the transfer paper is stained because the cleaning is not performed, and the transfer conveyance belt is broken.
[0011]
In order to prevent such a problem, the drive unit of the transfer conveyance unit and the drive unit of the photoconductor are separately provided, or the drive shaft of the transfer conveyance belt is connected to the main motor via a clutch, so that the transfer conveyance belt is connected. It is conceivable that the transfer / conveying belt is not rotated at the timing when the transfer belt is separated from the photoconductor. However, in this method, since a mechanism such as a drive unit or a clutch must be added, there is a problem that the number of parts of the apparatus is increased, the cost is increased, and the apparatus is complicated.
[0012]
Therefore, the object of the present invention is to keep the transfer conveyor belt in contact with the photosensitive member whenever the main motor rotates, regardless of whether the image is being formed or not, thereby turning up the cleaning blade and transferring the transfer paper. An object of the present invention is to provide an image forming apparatus which can prevent the occurrence of back stains and can obtain a good image at low cost.
[0013]
[Means for Solving the Problems]
An image forming apparatus according to the present invention includes an image carrier that carries an electrostatic latent image, a developing unit that attaches toner to the electrostatic latent image carried by the image carrier to form a toner image, and an endless conveyance. A transfer unit configured to transfer a toner image developed by the developing unit to a transfer material, a contact / separation unit configured to contact or separate the transport belt of the transfer unit and the image carrier, and the image A signal for starting the main motor of the forming apparatus is synchronized with a signal for bringing the transfer belt of the transfer unit into contact with the image carrier, a signal for stopping the main motor, and the transfer of the transfer unit. in the image forming apparatus having a control means for synchronizing the signal to separate the belt the image carrier, the conveyor belt of endless of the transfer means has a cleaning means counter blade type, the The control means starts or stops the main motor of the apparatus even at the time of non-transfer such as initial setting of the developer for operating the main motor of the apparatus, forcible toner replenishment, and pre-rotation of the fixing roller. A signal and a signal for abutting or separating the transfer belt of the transfer unit and the image carrier are controlled in synchronization with each other.
[0017]
According to the present invention, when the transfer conveyance belt rotates, the transfer conveyance belt always comes into contact with the photoconductor, and the transfer conveyance belt is always supplied with the residual toner (ground toner) on the photoconductor. And lower the coefficient of friction.
[0018]
【Example】
Hereinafter, examples of the present invention will be described.
FIG. 1 shows an embodiment showing the structure of the image forming apparatus of the present invention. This image forming apparatus is a simultaneous two-color image forming apparatus and includes two charging units each including a charging charger, two exposing units each including a writing unit, and two developing units.
[0019]
The image forming apparatus of the present embodiment is a simultaneous two-color image forming apparatus, and mainly includes a photosensitive drum 11 as an image carrier, a static eliminator 12, a first charging device 13, a first exposure device 14, and a first developing device 15. , A second charging device 16, a second exposure device 17, a second developing device 18, and a transfer device 20 as transfer means.
[0020]
The photosensitive drum 11 is a carrier for carrying an electrostatic latent image, and has an insulating layer or a photosensitive layer on its surface. The static eliminator 12 exposes the entire surface of the photosensitive drum 11 to erase residual charges on the photosensitive drum 11. Each of the first charging device 13 and the second charging device 16 has a charging charger, applies a charge to the photosensitive drum 11, and charges the photosensitive drum 11 uniformly. At this time, the surface potential becomes about -850v.
[0021]
The first exposure device 14 and the second exposure device 17 have a first writing unit and a second writing unit, and form an electrostatic latent image on the photosensitive drum 11 by laser light emitted from a laser diode. The first developing device 15 and the second developing device 18 form a visible image by attaching toner to the electrostatic latent image on the photosensitive drum 11. The transfer device 20 has a control device as control means (not shown), and transfers the visible image toner on the photosensitive drum 11 to a transfer paper P as a transfer material.
[0022]
The operation of the above main configuration will be described below. At the time of image formation, the photosensitive drum 11 is driven to rotate by a main motor. First, light is irradiated by a charge removing lamp of the charge removing device 12 to remove residual charges. At this time, the surface potential of the photosensitive drum 11 becomes a reference potential of 0V to -30V.
[0023]
Next, the photosensitive drum 11 is charged uniformly by the charge from the charging charger of the first charging device 13, and its surface potential becomes about -850V.
[0024]
The digitally recorded image information (black image information) transmitted from a device (not shown) is received by a line driver circuit (not shown) of the first exposure device 14 and is amplified by a laser driver circuit (not shown). This digitally recorded image information is a multi-valued signal of 8 bits per pixel, and the laser driver circuit activates the laser diode in accordance with the digitally recorded image information from the line driver circuit.
[0025]
The laser light emitted from the laser diode is polarized by an optical polarizer comprising a polygon mirror, passes through an f-θ lens, is reflected by a first mirror, a second mirror, and a third mirror 141, and is 11, the black document image component is exposed. Here, the surface potential of the portion (image portion) of the photosensitive drum 11 irradiated with the laser beam 142 is around -100 V, and an electrostatic latent image corresponding to a black original image is formed.
[0026]
Next, the electrostatic latent image corresponding to the black image on the photosensitive drum 11 is developed by the first developing device 15 so that black toner is adhered to an image portion to form a black toner image. During the developing operation, the first developing device 15 rotates the developing sleeves 151 and 152, the stirring roller 153, and the stirring blade 154 by a driving mechanism (not shown) to stir the developer including the black toner and the carrier in the developing device 155. It is stirred and transported by the roller 153 and the stirring blade 154.
[0027]
The developing sleeve 151 attracts and holds the developer conveyed from the stirring blade 154 by an internal magnet, and conveys the developer along with the rotation of the sleeve 151. A part of the developer on the developing sleeve 151 is scraped off by the doctor member 156, and is adjusted to a predetermined amount. Then, the developer passes between the photosensitive drum 11 and the developing sleeve 151 and the developing sleeve 152, and flows into the developing device 155. Then, the toner is again stirred by the stirring roller 153 and the stirring blade 154 and transported. Further, the developer scraped off from the developing sleeve 151 by the doctor member 156 falls through the separate 157 into the developing device 155, and is again stirred and conveyed by the stirring roller 153 and the stirring blade 154.
[0028]
As described above, the developer passes between the photosensitive drum 11 and the developing sleeve 151 and the developing sleeve 152 while circulating, thereby developing the electrostatic latent image on the photosensitive drum 11. Further, the toner in the developing device 155 is supplied with toner from a toner supply unit 158. A developing bias voltage of about -550 V is applied to the developing sleeves 151 and 152 from a power source, and toner is attached to an image portion on the photosensitive drum 11 by development by the developing device 15, but a non-image portion on the photosensitive drum 11 is-. At 850 V, the toner does not adhere even in the development by the developing device 15.
[0029]
Here, a method of controlling the toner density will be described.
Initially, the toner concentration of the developer is adjusted to 2.5%, and the T sensor 24 is adjusted so that the output value of the toner concentration sensor 24 (hereinafter simply referred to as T sensor 24) in this state becomes 2.5V. Output adjustment (developer initial setting). Since the output voltage of the T sensor 24 changes as shown in FIG. 2 according to the toner density in the developing device 155, the T sensor 24 controls the toner density Vt by detecting the voltage value. Further, the control reference value Vref of the toner density is changed by a value obtained from the image density read by the P sensor 26. The Vref change in this embodiment is performed once for every 200 copies.
[0030]
The P sensor 26 is a reflection-type photodiode, and irradiates a fixed amount of light to a non-image portion on the photosensitive drum 11 and an image pattern formed on the photosensitive drum 11, and the amount of reflected light returning to the light receiving element. Is detected, the image density on the photosensitive drum 11 is detected. Here, when the image density on the photosensitive drum 11 is low, the toner density control value of the T sensor 24 is set higher (Vref is lower). As described above, by combining the T sensor 24 and the P sensor 26, the toner density control is performed so that the image density is always constant.
[0031]
Next, the photosensitive drum 11 is subjected to a second charging process by a second charging device 16 composed of a charging charger, a second exposure process by a second exposure device 17 composed of a second writing unit, and a second developing process by a second developing device 18. However, the second charging step to the second developing step are performed only when the two-color mode and the mono-color (red / blue) mode are selected by an operation unit (not shown). The second exposure device and the second developing device 18 do not operate, and the black toner image on the photosensitive drum 11 proceeds to the transfer position as it is.
[0032]
In the two-color mode and the mono-color (red / blue) mode, in the second charging step in which the photosensitive drum 11 passes through the second charging device 16, a charge is applied by the second charging device 16 and the surface potential is again about -850v. It becomes. In the second exposure step in which the photosensitive drum 11 passes through the second exposure device 17, digital recording information of a color other than black, for example, red / blue, of a document input from an unillustrated device is output from the second exposure device composed of an LED array. Light emission is activated by the digitized signal.
[0033]
Here, the surface potential of the portion (image portion) of the photosensitive drum 11 irradiated with the LED light from the second exposure device 17 becomes about -100 V, and an electrostatic latent image corresponding to a red / blue original image component is formed. Is done. That is, the second charging device 16 and the second exposure device 17 constitute an electrostatic latent image forming unit.
[0034]
In the second developing step in which the photosensitive drum 11 passes through the second developing device 18, the color toner (red / red) is applied to the image portion of the electrostatic latent image corresponding to the red / blue original image component by the development by the second developing device 18. (Blue) adheres, and the electrostatic latent image becomes a red / blue color toner image. During the developing operation, the second developing device 18 rotates the agitating rollers 181 and 182, the pumping roller 183, and the developing roller 184 by the driving unit, and agitates and circulates the red / blue color toner in the developing container 185. A roller 184 develops the color toner into an electrostatic latent image corresponding to a red / blue original image component on the photosensitive drum 11 into a red / blue toner image.
[0035]
A developing bias voltage of about −750 V is applied to the developing roller 184 from a power supply. The color toner adheres to the image portion of the electrostatic latent image corresponding to the red / blue original image component on the photosensitive drum 11 by development by the developing device 18, while the non-image portion on the photosensitive drum 11 is The color toner does not adhere even in the development by.
[0036]
After passing through the developing device 18, the toner image is transferred from the photosensitive drum 11 to a transfer material formed of transfer paper P from a paper feeding device by a transfer device 20 formed of a transfer conveyance belt. In this case, the transfer paper P is fed from the paper feeding device to the registration roller 21, and the registration roller 21 applies the transfer paper P so that the leading end of the toner image on the photosensitive drum 11 and the leading end of the transfer paper P coincide with each other. It is sent to the transfer device 20 at the timing.
[0037]
The transfer device 20 includes a control device (not shown), a transfer conveyance belt 201, a driving roller 202 that stretches the transfer conveyance belt 201, a driven roller 203, a bias roller 204, and a cleaning device 205. Through a main motor (not shown) as a main motor. The transfer / transport belt 201 rotates with the rotation of the main motor, and is brought into contact with the photosensitive drum 11 by the belt contact / separation device 60 as a contact / separation unit. In addition, the transfer / conveyance belt 201 is separated from the photosensitive drum 11 by the operation of the belt contact / separation device 60 immediately before the rotation of the main motor stops after the end of the job.
[0038]
3 and 4 are enlarged sectional views of the contact / separation device 60. FIG.
The contact / separation device 60 for the transfer / transport belt 201 includes a contact plate 61 on the lower surface of the frame on which the transfer / transport belt 201 is stretched, a pressure arm 62 having the contact plate 61 as a free end thereof, One end is supported on a shaft 62a provided at the base end of the arm 62, a contact / separation lever 63, a cam 64 disposed in contact with the other end of the contact / separation lever 63, and attached to the shaft 62a. It comprises a half-turn clutch (not shown).
[0039]
The contact / separation lever 63 is configured to press the pressing arm 62 from above by a stay (not shown) attached to the rotating shaft 62a, and the force from the lower surface of the pressing arm 62 by the compression spring 66. Since the force of a certain spring is regulated, the pressing arm 62 also moves up and down about its axis in conjunction with the up and down movement of the contact / separation lever 63 by the cam 64. Therefore, the transfer / conveyance belt 201 can perform an operation of coming and going with respect to the photosensitive drum 11.
[0040]
FIGS. 5 and 6 show a flowchart showing the control of the contact / separation operation and timing diagrams of the main motor and the half-turn clutch. At the time of image formation, with the rotation of the main motor (step 501), the half-rotation clutch attached to the shaft 64a is turned on (step 502), and drive from the main motor is given to the shaft 64a via a gear. When the cam 64 rotates to release the extension force of the pressure spring 66 at the free end of the pressure arm 62, the transfer conveyance belt 201 comes into contact with the photosensitive drum 11. At this time, the transfer nip width formed by the photosensitive drum 11 and the transfer conveyance belt 201 is set to be 12 mm. In this state, the image forming operation is performed (Step 503).
[0041]
Immediately before the rotation of the main motor stops, the half-rotation clutch is turned off (step 505), the transfer conveyance belt 201 is separated from the photosensitive drum 11, and the main motor is stopped (step 506).
[0042]
In the image forming apparatus shown in the present embodiment, the main motor rotates other than the time of image formation, for example, at the time of initial setting of the developer, in the forced toner supply mode, and at the time of pre-rotation of the fixing roller (step 504). In (2), the transfer / conveyance belt 201 is controlled so as to rotate in contact with the photosensitive drum 11.
[0043]
When the transfer paper P is sent from the registration roller 21 to the transfer device 20, a transfer bias having a polarity opposite to the charging polarity of the black toner / color toner is applied to the bias roller 204 from the high voltage power source 206, and the toner on the photosensitive drum 11 is transferred. The image is transferred to the transfer paper P at a transfer nip formed by the photosensitive drum 11 and the transfer conveyance belt 201.
[0044]
The transfer / transport belt 201 is applied with a bias from a high-voltage power supply 206 via a bias roller 204 to generate an induced charge in a coating layer on the surface of the transfer / transport belt 201 so that the transfer paper P is electrostatically attracted and conveyed. I do. As described above, the transfer paper P is electrostatically separated from the photosensitive drum 11 after the toner image on the photosensitive drum 11 is transferred. If the transfer paper P is not separated from the photosensitive drum 11 at this time, the transfer paper P is separated from the photosensitive drum 11 by the separation claw 22 and is conveyed by the transfer conveyance belt 201.
[0045]
The transfer paper P is conveyed by the transfer conveyance belt 201, separated from the transfer conveyance belt 201 by the drive roller 202 by curvature separation using the stiffness of the transfer paper P, passes through the delivery guide plate 27, and is fixed by the fixing roller 280. It is sent to the fixing device 28 constituted by the pressure roller 281. The transfer paper P is heated and pressed by the fixing device 28, and the toner image on the transfer paper P is fused and fixed, and is discharged as a copy outside the apparatus.
[0046]
In this embodiment, after the fixing roller 280 is heated to a predetermined temperature at the same time when the power of the image forming apparatus is turned on, the fixing roller 280 and the heating roller 280 are heated for the purpose of preventing defective fixing caused by the surface temperature of the pressure roller 281 being unsaturated. The pressure roller 281 is pre-rotated.
[0047]
The transfer conveying belt 201 has a residual toner scraped off by a cleaning device 205 including a cleaning brush 205a, a cleaning blade 205b, and the like. The cleaning blade 205b is disposed in contact with the rotation direction of the transfer conveyance belt 201 in a counter direction.
[0048]
After the transfer, the toner image on the photosensitive drum 11 is completely removed by the cleaning device 23 including the cleaning brush 231 and the cleaning blade 232, and the process proceeds to the next image forming process.
[0049]
In the present embodiment, the transfer clutch is always in the ON state when the main motor is rotating, not only during image formation, and the transfer conveyance belt 201 is brought into contact with the photosensitive drum 11 so that a small amount of toner ( The background transfer toner 201 is supplied to the transfer / transport belt 201 to reduce the friction coefficient between the transfer / transport belt 201 and the cleaning blade 205b. Can also be realized.
[0050]
In this embodiment, the transfer / conveyance belt 201 is made of semiconductive rubber, and the contact / separation device 60 for bringing the transfer / conveyance belt 201 into contact with / separating from the photosensitive drum 11 is provided. Instead, a resin material such as PET may be used. In this case, the photosensitive drum 11 and the transfer / conveyance belt 201 may be kept in contact with each other without being separated from or separated from each other.
[0051]
【The invention's effect】
As is apparent from the above description, according to the image forming apparatus of the present invention, the transfer conveyance belt is always in contact with the photosensitive drum when the transfer conveyance belt rotates, and the transfer conveyance belt remains on the surface of the transfer conveyance belt. Since the background toner, which is toner, is always supplied, the coefficient of friction between the cleaning blade and the transfer conveyance belt can be reduced. Therefore, the turning of the cleaning blade can be prevented, and further, the back stain of the transfer paper can be prevented. Moreover, since a complicated mechanism is not required, an image forming apparatus which can obtain a good image at low cost can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view illustrating a configuration of an embodiment of an image forming apparatus of the present invention.
FIG. 2 is a diagram illustrating a relationship between a toner density and an output of a toner density sensor.
FIG. 3 is an enlarged sectional view showing a configuration of an embodiment of a contact / separation device in the image forming apparatus of the present invention.
FIG. 4 is an enlarged sectional view showing a configuration of an embodiment of a contact / separation device in the image forming apparatus of the present invention.
FIG. 5 is a flowchart illustrating an operation example of the contact / separation device in the image forming apparatus of the present invention.
FIG. 6 is a timing chart of a main motor and a half-turn clutch.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Static eliminator 13 First charging device 14 First exposure device 15 First developing device 16 Second charging device 17 Second exposure device 18 Second developing device 20 Transfer device 60 Contact / separation device

Claims (1)

An image carrier that carries an electrostatic latent image, a developing unit that forms a toner image by attaching toner to the electrostatic latent image carried on the image carrier, and an endless transport belt, the developing unit comprising: Transfer means for transferring the toner image developed in the step (c) to a transfer material, contact / separation means for contacting or separating the transfer belt of the transfer means and the image carrier, and starting a main motor of the image forming apparatus. A signal and a signal for bringing the transfer belt of the transfer unit into contact with the image carrier are synchronized, and a signal for stopping the main motor, and the transfer belt and the image carrier of the transfer unit are in the image forming apparatus having a control means for synchronizing the signal to separate, the conveyor belt of endless of the transfer means has a cleaning means counter blade type, the control means, the main of the apparatus A signal for starting or stopping the main motor of the apparatus even at the time of non-transfer such as initial setting of the developer for operating the motive, forcible toner replenishment, and pre-rotation of the fixing roller, and An image forming apparatus, wherein a signal for bringing a conveyor belt and an image carrier into contact with or separated from each other is controlled in synchronization with each other.

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