Patent Grant
8023855
This patent specification claims priority from Japanese Patent Application No. 2007-304134, filed on Nov. 26, 2007 in the Japan Patent Office, the entire contents of which are hereby incorporated by reference herein.
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile machine, a plotter, a multi-function machine including at least two of these functions, and a digital direct reproducer, and a development device and a process cartridge used in the above-mentioned image forming apparatus.
2. Discussion of the Background
In general, an electronographic image forming apparatus, for example, a copier, a printer, a facsimile machine, etc., includes an image forming mechanism for forming an electrostatic latent image on an image carrier, developing the latent image with toner, transferring the developed image onto a recording medium, and fixing the image thereon.
Generally, a development device using two-component developer consisting essentially of toner and magnetic carrier includes a developer carrier and a developer-transporting member, both provided inside a development case having an opening facing the image carrier. The developer carrier is partially exposed from the opening, and carries the developer.
The developer-transporting member mixes and agitates the toner and the magnetic carrier in the development device, and transports the developer whose toner concentration is appropriately controlled. After the amount of the developer is set as appropriate by a developer regulator, the developer that is carried onto the developer carrier by the developer-transporting member is transported to a development area facing the image carrier. In the development area, the toner in the developer carried on the developer carrier is adhered to the electrostatic latent image formed on the image carrier to form a desired toner image.
In the development device performing an image forming operation, air flows in from the opening, and the developer carrier located at the position facing the opening and the developer-transporting member are revolved to generate airflow inside the development device. This airflow causes internal pressure of the development device to vary locally.
Most of the toner in the development device is adsorbed onto the magnetic carrier electrostatically due to frictional charging with the magnetic carrier. As noted above, however, in the development area, an electrical field generated between the image carrier and the development carrier causes the toner attracted onto the magnetic carrier to adhere instead to the electrostatic latent image on the image carrier. In other words, the strength of the electrical field exerted on the toner exceeds the electrostatic force attracting the toner to the magnetic carrier, and therefore the toner leaves the magnetic carrier and flies to the side of the image carrier.
However, the toner, which is a powder, does not have a consistent and uniform shape and consequently some toner have an insufficient ability to accept charge. If as a result the toner is distributed unevenly and remains in a part of the development device, such toner may be insufficiently charged because the frictional charging with the magnetic carrier may be insufficient.
Moreover, the magnetic carrier in the developer inside the development device loses its charging capability over time with repeated usage of the developer, and then fails to charge the toner sufficiently. Since insufficiently charged toner has weak attractive power and since the toner is light, the toner can be scattered by the airflow generated inside the development and scatter.
As the internal pressure of the development device increases, it can scatter the toner from openings in the components of the development device all over the interior of the image forming apparatus, contaminating the image forming apparatus.
Several proposals have been made to prevent the toner form escaping from the development device and scattering. For example, in known techniques, a development device includes a discharging port provided on an upper surface thereof that reduces internal pressure by discharging air from the development device, and a developer-supporting member, like a filter, that is provided on the discharging port catches developer that does escape, so that scattering of toner from the development device is prevented or reduced.
In view of the foregoing, one illustrative embodiment of the present invention provides a development device including a developer carrier configured to carry developer and disposed in a development case, partly exposed from an opening of the development case facing an image carrier, a developer-transporting member configured to transport the developer to the developer carrier, and a discharging member housing a discharging space including a communicating path connecting to an area where the developer carrier faces the developer-transporting member, from which air is discharged into the discharging space, and a discharging port that opens in a longitudinal direction of the developer-transporting member, from which air is discharged from the discharging space.
Another illustrative embodiment of the present invention provides a process cartridge configured to be removably insertable into image forming apparatus and accommodate an image carrier and at least one unit selected from a group including a charging mechanism configured to charge the image carrier evenly, a cleaning mechanism configured to clean the image carrier, and a development device as described above.
Another illustrative embodiment of the present invention provides an image-forming apparatus including a charging mechanism configured to charge evenly an image carrier, a latent-image forming mechanism configured to form a latent image on the image carrier, a cleaning mechanism configured to clean the image carrier, and a development device as described above.
A more complete appreciation of the disclosure and many of the attendant advantage thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to
Referring to
It is to be noted that the subscripts Y, M, C, and K attached to the end of each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary.
A configuration of the image-forming unit 2 is described below with reference to
Referring to
The charging device 6 evenly charges a surface of the photoreceptor 1 that is rotated by a driving unit, not shown, and then the evenly charged surface of the photoreceptor 1 is exposed to the laser light L, and carries the electrostatic latent image.
The development device 7 develops the electrostatic latent image on the photoreceptor 1 into a toner image, and then, the toner image formed on the photoreceptor 1 is primarily transferred onto the intermediate transfer belt 3.
The photoreceptor-cleaning device 8 removes toner that remains on the photoreceptor 1 after a toner image is transferred therefrom.
Referring to
The four-color superimposed toner image formed on the intermediate transfer belt 3 is transferred by a paper-transfer belt 11 onto the transfer sheet that is passed though a pair of registration rollers 10 and is transported to a transfer position. The transfer sheet on which the toner image is transferred is transported to the fixing unit 5 by the paper-transfer belt 11, where the toner image is fixed with heat, and then discharged from the printer.
Further, the printer according to the present embodiment is equipped with toner bottles 12Y, 12M, 12C, and 12K that respectively contain unused yellow, magenta, cyan, and black toner. The unused toner filling the toner bottles 12Y, 12M, 12C, and 12K is supplied as appropriate to the development devices 7Y, 7M, 7C, and 7K by toner-supplying devices 13Y, 13M, 13C, and 13K, respectively.
Moreover, the printer according to the present embodiment is equipped with a pattern detector 17 that detects a pattern image formed on the intermediate transfer belt 3 for process control, and a waste-toner container 15 that contains used toner collected from the image-forming units 2 and the intermediate transfer unit 4. The untransferred, residual toner that is removed from the image-forming units 2 by the photoreceptor-cleaning device 8 is passed through collected-toner transport routes 14 (Y, M, C, K) to be collected in the waste-toner container 15. In the intermediate transfer unit 4, the untransferred toner and the pattern image removed from the intermediate transfer belt 3 by a belt-cleaning blade 16 are passed through the collected-toner transport route 14 to be collected in the waste-toner collected container 15.
The development device 7 is described below in further detail.
Referring to
On the right of the development doctor blade 28 in
Beneath the development roller 27, a first developer-transporting screw 31a and a second developer-transporting screw 31b are disposed in parallel. The development device 7 further includes a toner concentration sensor 33, and a toner hopper 18 that contains the powder toner is disposed above the second developer-transporting screw 31b. The toner hopper 18 includes a toner-supplying screw 19 to supply the toner and a toner-supplying port 32 through which the toner is supplied from the toner bottle 12 by the toner-supplying device 13.
Referring to
The development roller container 22 contains the development roller 27 as the developer carrier, exposes a part of the development roller 27 from an opening portion of the upper case 21, and forms the development area between the development roller container 22 and the photoreceptor 1.
The developer container 24 contains two-component developer including the toner and carrier. The developer container 24 is separated by a partition wall 30 into two spaces, a first developer container 24a including the first developer-transporting screw 31a, and a second developer container 24b including the second developer-transporting screw 31b.
Further as shown in
The pressure release space 26 is equipped with a communicating path 34 that connects to an area in which the development roller 27 faces the first developer-transporting screw 31a, and a discharging port 35 that opens in a longitudinal direction of the second developer-transporting screw 31b and releases inner air to the outside. An inner surface of a wall of the pressure release case 25 is provided with an adhesive layer 36 serving as a toner catcher that catches the scattering toner. As shown in
In the development device 7 having the configuration described above, referring to
In the developer agitated and transported by the first developer-transporting screw 31a in the first developer container 24a, the carrier is attracted by a magnetic roller built into the development roller 27, and thus carried on the development roller 27.
Further, while the toner in the developer is agitated with the carrier, the toner is charged to a polarity opposite that of the carrier, and accordingly an electrostatic force is created between the carrier and the toner. Therefore, the toner is carried on the development roller 27 with the carrier.
The thickness of the layer of the developer carried on the development roller 27 is adjusted as the developer passes through a doctor gap formed between the development doctor 28 and the surface of the development roller 27. Subsequently, the developer whose layer thickness is adjusted is transferred to the development area facing the photoreceptor 1 (shown in
Then, the erect carrier on the development roller 27 supplies the toner on a surface thereof to the surface of the photoreceptor 1, while slidingly contacts the surface of the photoreceptor 1. At this time, the development roller 27 receives the image bias by a power supply, not shown, which generates a development electric field in the development area.
Therefore, between the electrostatic latent image on the photoreceptor 1 and the development roller 27, the electrostatic force toward the side of the electrostatic latent image acts on the toner on the development roller 27, and thus the toner on the development roller 27 adheres to the electrostatic latent image. That is, the electrostatic latent image on the photoreceptor 1 is developed with the toner thus adhered thereto into the toner image whose color corresponds to that of the toner.
As the toner is consumed by the development, fresh toner is supplied by the toner-supplying device 13. The toner-supplying device 13 temporarily stores the new toner supplied from the toner bottle 12 in the toner hopper 18 (shown in
Then, when the toner concentration sensor detects that the toner concentration in the second developer container 24b is insufficient, the toner-supplying device 13 causes the toner-supplying screw 19 in the toner hopper 18 to rotate for a time determined according to a prescribed formula. As a result, the toner-supplying device 13 supplies the appropriate amount of the developer from the toner hopper 18 to the second developer container 24b via the toner-supplying port 32. The toner supplied in the second developer container 24b is agitated with the carrier by the second developer-transporting screw 31b, and used to develop the latent image, being circulated within the developer container 24, as described above.
Additionally, sensing of the amount of the toner remaining in the toner bottle 12 is done by a toner sensor, not shown, provided on the toner hopper 18. The toner hopper 18 is equipped with a toner sensor, not shown, that senses the amount of the toner remaining in the toner bottle 12. When the toner sensor fails to detect the presence of any toner, the toner sensor requests the toner-supplying device 13 to supply the toner. When the toner sensor continues to fail to detect the presence of the toner after the toner sensor maintains its request for a certain time period, the toner sensor determines that there is no toner in the toner bottle 12 shown in
In a series of operations performed by the development device 7 as the development roller 27 rotates, the air from the opening in the upper case 21 passes through the area between the upper case 21 and development roller 27 and reaches the communicating path 34 leading to the pressure release space 26. Then, the air that reaches the pressure release space 26 from the communicating path 34 is discharged from the discharging port 35 in a longitudinal direction of the first and second developer-transporting screws 31a and 31b.
The scattering toner in the development device 7 rides the airflow formed in the development device 7 mentioned above, and enters the pressure release space 26. Since the space 26 is not provided with a rotation member such as the development roller 27 and the developer-transporting screw 31, and is larger than the development roller container 22, it is less likely that the pressure release space 26 generates airflow faster than that in the foregoing space.
Consequently, when air and the scattering toner are introduced into the pressure release space 26 and then discharged from the discharging port 35, the amount of the toner that scatters from the discharging port 35 is smaller than when the scattering toner is directly discharged from the communicating path 34. That is, the pressure release space 26 can keep and isolate the scattering toner from spaces a user touches.
Further, because the discharging port 35 opens in the longitudinal direction of the first and second developer-transporting screws 31a and 31b, if the toner does manage to scatter from the discharging port 35, the scattering route of the scattering toner can be limited to not a vertical direction of the development device 7 but only a longitudinal direction of the development device 7.
It is to be noted that it is not necessarily advantageous that the communicating path 34 that is connected to the pressure release space 26 be relatively wide. For example, maintaining a uniform airflow distribution is difficult if the communicating path 34 extends throughout in the first developer-transporting screw 31a the longitudinal direction because partial turbulence and backflow can be generated. Therefore, in the present embodiment, the communicating path 34 connected to the pressure release space 26 does not extend the entire length in the longitudinal direction of the first developer-transporting screw 31a but is instead limited to an area sufficient to effectively control scattering of the toner.
As shown in
On the downstream side of the developer transport direction of the first developer-transporting screw 31a, the developer is sufficiently agitated until the developer reaches the downstream side, and thus the amount of electrical charge on the toner is comparatively high, and the toner is less likely to scatter.
By contrast, on the upstream side in the developer transport direction of the first developer-transporting screw 31a, the toner scatters easily. Consequently, in the present embodiment, an opening area of the communicating path 34 is located on the upstream side of the first developer-transporting screw 31a; therefore it is possible to generate relatively strong and stable discharging airflow on the upstream where the toner scatters easily.
An upstream side end portion of the communicating path 34 is close to a starting point of the area in which the development roller 27 faces the first developer-transporting screw 31a in the direction in which the developer is transported, and as a result, the distance from the communicating path 34 is longer on the downstream side in the developer transport direction of the first developer-transporting screw 31a. Therefore, although the airflow is weaker on the downstream side than on the upstream side, the toner scatters less for the foregoing reason.
By contrast, though the toner easily scatters on the upstream side, by forming the relatively strong airflow, the toner scattering can be effectively controlled.
Further, in the present embodiment, the adhesive layer 36, as a toner-containing member, is disposed on the interior of the pressure release case 25. The adhesive layer 36 catches the scattering toner that enters the pressure release case 25 passing through the communicating path 34, and prevents the scattering toner from being discharged from the pressure release space 26. By this means, the scattering toner is securely isolated from places the user touches.
The filter 37 filters the toner from the air and prevents it from discharging. In this way, the scattering toner that enters in the pressure release space 26A is securely blocked by the filter 37, and the toner cannot be discharged from the pressure release space 26A. That is, the filter 37 works as a toner-blocking member, and can reliably isolate the scattering toner from the place where the user touches.
In order to take full advantage of the effect of the filter 37, it is preferable to provide a space 39 between a communicating path 34 and the filter 37 and a space 40 between the filter 37 and a discharging port 35. Providing a sufficiently large filter surface for the filter 37 prevents the toner from clogging the filter 37.
Additionally, in the image-forming unit 2, the photoreceptor 1, the charging device 6, the development device 7 shown in
Referring to
Thus, because the image-forming unit 2Y is configured to be removable from the main body of the printer, when maintenance is needed, the user only needs to exchange the image-forming unit 2; therefore, the convenience is enhanced. It is to be noted that, for ease of illustration, in
Referring to
The airflow fan 43 can control an increase in temperature of the printer parts, and cause the airflow discharged from the discharging port 35 via the pressure release space 26 to flow toward the back side of the image-forming unit 2. If the air discharged from the discharging port 35 includes the scattering toner, the route of the scattering toner can be limited to that toward the back side of the image-forming unit 2.
As a result, the airflow fan 43 can prevent the scattering toner from adhering to the lever 41 disposed on the front side of the image-forming unit 2, and the unit-holding portion 42 disposed on the upper surface of the image-forming unit 2.
The toner is described below with reference to
In the printer according to the present embodiment, to attain high quality images, the toner used in development desirably has a first shape factor SF1 and a second shape factor SF2 both within a range of 100 to 180. The first shape factor SF1 is explained with reference to
Referring to
SF1={(MXLNG)2/AREA}×(100π/4) (1)
wherein MXLNG is a maximum length of a toner particle projected on a two-dimensional surface and AREA is an area of the toner particle.
The toner particle is a sphere when the first shape factor SF1 is 100. The larger the SF1 becomes, the more the toner particle becomes amorphous.
Referring to
SF2={(PERI)2/AREA}×(100π/4) (2)
wherein PERI is a peripheral length of a toner particle projected on a two-dimensional surface and AREA is the area of the toner particle.
The toner particle is flat when the first shape factor SF1 is 100. The larger the first shape factor SF1 becomes, the more the toner particle has irregularities.
The first shape factor SF1 and second shape factor SF2 can be measured by taking a photograph using a scanning electron microscope, S-800 (Hitachi, Ltd.) and analyzing the photograph using an image analyzer, LUSEX3 (NIRECO CORPORATION).
It is to be noted that although in the present embodiment the color printer equipped with the four image-forming unit, 2Y, 2M, 2C, and 2K as shown in
As described above, the development device 7 according to the embodiments of the present invention can keep away the scattering toner from the portions that the user touches by containing the scattering toner in the pressure release space 26 as a discharging place. As a result, the user can change the development device 7 without touching the scattering toner, thereby facilitating maintenance of the development device 7.
Further, in the development device 7 according to the embodiments of the present invention, the communicating path 34 connecting to the pressure release space 26 is formed in the specific area W that extends from the upstream side end portion of the first developer-transferring screw 31a in the direction in which the developer is transported.
Because an upstream side in the direction in which the first developer-transferring screw 31a transports developer is where the supplied toner tends to be insufficiently dispersed and insufficiently charged, the communicating path 34 as an entrance to the pressure release space is disposed in that area to efficiently control scattering of the toner.
Further, because the development device 7 according to the embodiment described above is equipped with the adhesive layer 36 as the toner catcher in the pressure release space 26, the pressure release space 26 can reliably retain the scattering toner.
Additionally, because the development device 7 according to the present embodiment is equipped with the filter 37 in the pressure release space 26 as the toner catcher, the pressure release space 26 can reliably retain the scattering toner.
Because the development device 7 according to the present embodiment is equipped with the spaces both side of the filter 37 in the pressure release place 26, the discharging of the air and the holding of the scattering toner can be efficiently operated.
The image-forming unit 2 according to the present embodiment is configured as a process cartridge including the development device described above. Therefore, when the user changes the image forming unit, the user's skin and clothes are not contaminated by the scattering toner, and maintenance is easy.
In the printer according to the present embodiment, the discharging port 35 in the pressure release space 26 is located on the back side in the direction of insertion of the image-forming unit 2, which can limit a direction of the scattering toner from the discharging port 35 to a direction far from the portions that the user can touch.
In the printer according to the present embodiment, because the airflow fan 43 as an airflow-generating unit is disposed on back side in the direction of insertion of image-forming unit 2, a direction in which the toner scatters from the discharging port 35 can be comparatively easy to control.
According to the present embodiment, scattering of the toner can be reduced also when images of a relatively high image area ratio are output and when the printer is a color printer equipped with the multiple development devices 7 and the multiple image-forming units 2 as described above.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
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