Electrophotography – Image formation – Development
Reexamination Certificate
2002-04-29
2004-08-10
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S043000, C399S088000
Reexamination Certificate
active
06775503
ABSTRACT:
BACKGROUND
1. Field of the Invention
This patent specification relates generally to an image forming method and apparatus, and more specifically to such apparatus for use in digital copying, printing machine and facsimile apparatus, provided with improved toner transport capabilities.
2. Discussion of the Background
The electrophotographic image forming process is well known. In image forming apparatuses such as a copying machine, printer and facsimile apparatus, in general, the formation of the images is carried out through the electrophotographic process steps of forming electrostatic latent images on an image bearing member or photoreceptor, developing as visible toner images using toner particles, and transferring the toner images onto a copy sheet which subsequently passes through a fixing unit to form fixed images on the sheet.
When the amount of toner in the fixing unit decreases during the developing steps, the toner is supplied to the fixing unit from a toner container in a copying apparatus, which may be housed separately from one another.
In regard to the toner, some portion thereof remains on the photoreceptor as residual toner following the transfer of toner images during the developing steps. As is well known, this residual portion of the toner is then removed from the photoreceptor by scraping off with a cleaning blade housed in a cleaning unit.
With increasing concern for resources and operation costs in recent years, recycling of the used toner material has been attracting considerable attention. For example, Japanese Laid-Open Patent Application No. 6-175488 discloses that the used toner is collected and returned by a toner transport unit to a developing unit to be admixed with fresh toner material, and is subsequently reused for forming toner images on the image bearing member.
As to the above noted toner transport unit, a powder screw pump (or powder pump) is generally included for its design flexibility and capability of transporting powder materials. In addition, the process of the toner transport is also known, which is pneumatically carried out for an admixed system of the recovered toner and gaseous flow generated by an air pump (Japanese Laid-Open Patent Application No. 11-73079).
The powder pump is formed, as previously known, to be a suction type uniaxial-eccentric screw pump (i.e., uniaxial pump having eccentric screw structure), including at least a stator which is provided with a through hole, and a rotor. The rotor has a screw-shaped surface structure, and is rotatably interfit to the stator along the axis of the cylindrical holder in contact with inner face of a wall of the stator. This uniaxial-eccentric powder pump is also known to be capable of transporting a relatively constant amount of material continuously at high mixing ratio with air, to thereby be able to attain precise amount of the toner transport.
An image forming apparatus has been previously disclosed in Japanese Laid-Open Patent Application No. 2000-47465 by the present inventors, in which the toner is transported by such uniaxial-eccentric powder pump incorporated into the apparatus.
In that disclosure, the powder pump in the image forming apparatus was designed, as shown in
FIG. 7
, to be driven directly by a motor
100
which also serves to drive major parts of the apparatus such as sheet supply unit, and developer and fixing stations. In addition, the developer station herein utilized a two-component developer containing toner and carrier components, and the station was controlled to maintain the toner concentration approximately constant by means of a toner supply unit. With this construction, the toner supply unit was able to support any mode of printing operation including solid monochrome printing.
The amount of toner transported in unit time by the powder pump was measured as a function of the number of rotor revolution of 125 rpm, 250 rpm and 400 rpm, with a pump having similar characteristics for identical distance and elevation to transport path. The results obtained from the measurements are shown in FIG.
8
.
The results indicate, although the amount of toner transported in unit time reach approximately the same level of 50 mg/sec with the transport time of 500 msec or larger for each of rotor revolution of 125 rpm, 250 rpm and 400 rpm, the transient change during leading periods is considerably different (FIG.
8
).
It should be noted herein that the number of revolutions for the main driving motor
100
may arbitrarily be adjusted, for example, to be smaller for relatively thick transfer sheets, or to be larger in a faster printing mode. When the number of revolutions decreases for the main motor, therefore, the number for the rotor also decreases accordingly.
As a result, for the previous construction of the toner transport system, difficulties may be encountered such that responsive toner supply can not be carried out for the slower mode of printing, to thereby not be able to produce a maximum sized printing in solid color.
Also, the distance and elevation of the transport path may be different. For example, for a full color image forming apparatus equipped with a toner supply unit incorporating plural powder pumps, the distances for the toner transport L
1
, L
2
, L
3
and L
4
, and the elevations (differences in height) H
1
, H
2
, H
3
and H
4
, for the stations
4
M,
4
C,
4
Y and
4
Bk, respectively, differ from each other as illustrated in FIG.
9
.
As a result, the toner transport capability also differs for respective toner transport paths, thereby causing further complications for the toner transport including its control system, among others.
SUMMARY OF THE INVENTION
It is therefore an object of the present disclosure to provide a toner supply unit and image forming apparatus incorporating such supply unit, which are capable of implementing responsive supply of the toner unaffected by the operation mode change with preferably simpler construction of the supply unit.
In another aspect, with the decrease in the overall size of a development unit in recent years, there exists increasing needs of more precise control of the powder pump, which will be detailed herein below.
Utilizing the powder pump, the toner transporting unit is devised to be capable of securely transporting the toner, which is recovered from the cleaning unit, admixed with gaseous flow through a transport tube made of elastic materials.
From the consideration of durability, sealing performance, temperature increase, and powder scattering, the secure transportation can be achieved by operating the pump not continuously but intermittently over specified periods of time, when the amount of toner in a toner reservoir is measured, by a toner level detecting means, and then found to have reached a predetermined value.
In addition, also disclosed is the toner transporting unit incorporating the powder pump, which is alternatively configured to be capable of initiating the intermittent pump operation when an accumulated count of copied sheets reaches a predetermined number, in place of the above-mentioned method for determining the timing for initiating the pump operation based on the detected amount of toner in the toner reservoir.
The toner transporting unit utilizing the powder pump is thus operated, as noted above, not continuously but intermittently. This operation mode consists of, for example, driving with a unit driving time of 0.1 sec, 0.2 sec, etc. and halting with a unit halting time of 3 sec, 4 sec, etc. That is, the intermittent operation may be iterative cycles repeated a certain times, each cycle consisting of 0.1 sec of driving followed by 3 sec of halting, for example, thereby attaining a desired amount of the toner supplied to the developing unit.
With the decrease in the overall size of a developing unit in recent years, the amount of developer stored therein has also decreased.
Since the concentration of the toner in the developer tends to considerably fluctuate with more ease in the developing unit in such reduced size, the amount of toner supplied by the powder pump has
Hattori Yoshio
Sudo Kazuhisa
Yanagisawa Takaaki
Chen Sophia S.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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