Patent Grant
7254348
1. Field of the Invention
The present invention relates to an image forming apparatus equipped with a developing apparatus for use in an electrophotographic copying machine, a printer, a facsimile apparatus, etc., and in particular, to an image forming apparatus equipped with a developing apparatus using a developer containing toner and carrier.
2. Related Background Art
Conventionally, in an image forming apparatus, such as an electrophotographic copying machine, a developing apparatus effecting development by a two-component developing system using a two-component developer containing a mixture of toner and carrier, is generally widely used. In particular, in the case of color image forming apparatuses, from the viewpoint of image color tint, etc., many developing apparatuses use a two-component developer.
In a developing apparatus using a two-component developer, the toner is consumed by developing operation, and new toner is supplied in an amount corresponding to the consumed amount. In contrast, the carrier is not consumed but remains in a developing container, which is a developer accommodating portion of the developing apparatus. Thus, the carrier, which is agitated together with the toner, is degenerated by being agitated. The degeneration of the carrier occurs as a result of adhesion of toner to the surface of the carrier due to the friction when agitating the developer and to the compression during passage through the gap between a developing roller serving as a developer carrier for carrying developer to the developing position by rotating and a developer regulating member (developer regulating blade) for regulating the thickness of the toner layer on the developing roller. Degeneration of the carrier results in a deterioration in the charging performance of the developer. In view of this, it is general practice to periodically replace the carrier.
To replace the carrier, the developer is discharged through a developer discharging port provided in the developing apparatus, and the developing apparatus is filled with new developer. That is, the replacement of the carrier substantially means the total replacement of the developer in the developing apparatus, and in this process, the toner is naturally also renewed. During the replacement operation, it may occur that the toner, which is in the powder form, is scattered to stain the image forming apparatus and the periphery thereof.
In view of this, there has been proposed a developing apparatus in which the degeneration of the developer is restrained, so there is no need to perform the developer replacement operation (see, for example, Japanese Patent Publication No. H02-21519. The apparatus adopts a system generally referred to as a trickle system, in which a discharge port is provided at a predetermined height on a side wall of a housing constituting the developing container of the developing apparatus, and in which a developer containing toner and carrier is supplied to the developing apparatus, whereby surplus developer in the developing apparatus is successively discharged through the discharge port, thereby keeping the characteristics of the developer fixed (see, for example, Japanese Patent Application Laid-Open No. 2003-215903).
The above-mentioned conventional apparatus, however, has a problem in that, when the toner density of the developer to be replenished (replenishment agent) and the T/D ratio, which is the ratio of toner to developer, fluctuate, the toner replenishment accuracy deteriorates, with the result that the toner supply to the developing apparatus becomes deficient or excessive.
When the toner supply becomes deficient or excessive, the toner density of the developer in the developing apparatus fluctuates, which may lead to a fluctuation in the toner image density or scattering of toner from the developing apparatus.
Alternatively, due to a fluctuation in environmental conditions such as humidity, the electric charge of the toner (triboelectricity) fluctuates, which leads to a change in bulk density and a deterioration in the accuracy with which developer is supplied to the developing apparatus, with the result that the toner supply to the developing apparatus becomes deficient or excessive, thus involving the same problem as mentioned above.
It is an object of the present invention to provide an image forming apparatus equipped with a developing apparatus using a developer containing toner and carrier, in which, taking into account a change in the toner density of a replenishment agent, the supply of replenishment agent to the developing apparatus is effected with high accuracy, thereby forming a stable image involving no scattering of toner.
The above object is attained by the image forming apparatus according to the present invention. That is, the present invention provides an image forming apparatus including: an image bearing member having a surface on which an electrostatic latent image is formed; a developing apparatus that develops the electrostatic latent image with a developer containing toner and carrier; and a replenishment agent supply device that supplies a replenishment agent containing the toner and the carrier to the developing apparatus, in which the replenishment agent is gradually supplied to the developing apparatus from the replenishment agent supply device while the developer is gradually discharged in correspondence therewith through a developer discharging port, and in which the replenishment agent supply device comprises a first toner density detecting means for detecting the toner density of the replenishment agent.
According to an aspect of the present invention, the first toner density detecting means is arranged in the vicinity of a portion where the replenishment agent is supplied to the developing apparatus.
According to another aspect of the present invention, the supply of the replenishment agent to the developing apparatus is effected based on a replenishment amount set by a replenishment table, and in which the replenishment table is switched based on the density detected by the first toner density detecting means.
According to another aspect of the present invention, the first toner density detecting means is an inductance detection sensor that detects a magnetic permeability of the replenishment agent, and a developer replenishment table taking into account a change in the bulk density of the replenishment agent is obtained from the detection value of the first toner density detecting means, and in which the supply of the replenishment agent to the developing apparatus is effected according to the replenishment table obtained.
According to another aspect of the present invention, the replenishment agent supply device carries and supplies the replenishment agent by rotating a spiral member, and includes an agitating means arranged in the vicinity of the first toner density detecting means and adapted to agitate the replenishment agent.
According to another aspect of the present invention, the replenishment agent supply device has a detachable replenishment agent container for containing the replenishment agent, the replenishment agent container being selected from at least two or more kinds of replenishment agent container differing in the toner density of the replenishment agent contained therein.
According to another aspect of the present invention, the image forming apparatus includes a second toner density detecting means for detecting the toner density of the developer contained in the developing apparatus, the replenishment table being set in terms of the amount of replenishment agent supplied to the developing apparatus from the replenishment agent supply device in correspondence with the detection result of the second toner density detecting means.
The image forming apparatus of the present invention has a replenishment agent supply device for supplying replenishment agent containing toner and carrier to the developing apparatus, in which the replenishment agent is gradually supplied to the developing apparatus from the replenishment agent supply device while the developer is gradually discharged in correspondence therewith through a developer discharge port, and in which the replenishment agent supply device has a first toner density detecting means for detecting the toner density of the replenishment agent, so that, by detecting the toner density of the replenishment agent, it is possible to supply toner with high accuracy even if the toner density of the developer to be supplied to the developing apparatus fluctuates, thus making it possible to provide an image forming apparatus capable of forming a stable image involving no scattering of toner.
Further, it is possible to provide an image forming apparatus which is capable of effecting toner supply with high accuracy even if an environmental condition, such as humidity, fluctuates and which is capable of forming a stable image involving no scattering of toner.
In the following, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.
An image forming apparatus 1 according to an embodiment of the present invention will be described with reference to
The copying machine 1 shown in
As the image forming means, a primary charger 7 uniformly charges the surface of the photosensitive drum 2, and an exposure portion 10 exposes image information on the uniformly charged surface of the photosensitive drum 2 to form a latent image. An original with a desired image recorded thereon is guided by an original treatment apparatus 11 to an optical reading system 9 constituting an image reading portion, and the above-mentioned image information is read from the original by a CCD 9a constituting the optical reading system 9.
The latent image formed on the peripheral surface of the photosensitive drum 2 by the exposure portion 10 is visualized by a developing apparatus 3 constituting the image forming means by causing toner contained in a developer to adhere thereto. That is, it is developed into a toner image.
The toner image thus visualized on the photosensitive drum 2 is transferred to a sheet P serving as the recording medium by a transfer means 5 constituting the image forming means.
After the transfer of the surface toner image, the residual developer and other adhering materials are removed from the surface of the photosensitive drum 2 by a cleaning device 6 for next image formation.
In this example, four developing apparatuses 3 are mounted on a rotary 3a, and through rotation thereof, they are successively conveyed to a position where they are opposed to the photosensitive drum 2. The developing apparatuses 3 each contain developers of different colors, e.g., developers respectively having pigments of yellow, magenta, cyan, and black. First, a toner image of a first color is formed on the photosensitive drum 2, and is transferred to the sheet P. After the residual developer after the transfer (toner) of the toner image of the first color on the photosensitive drum 2 has been removed by the cleaning device 6, the photosensitive drum 2 is charged again, and a toner image of a second color is formed to be transferred to the sheet P so as to be superimposed on the toner image of the first color transferred thereto. In this way, toner images of the four colors are successively transferred to the sheet P so as to be superimposed one upon the other, and a full color toner image is formed on the sheet P.
Here, the photosensitive drum 2, the developing apparatuses 3, the transfer means 5, the cleaning device 6, and the primary charger 7 constitute an image forming portion 8.
When it consists of an ordinary paper sheet, the sheet P constituting the recording medium is fed from a sheet feeding portion 12, and conveyed through a main body path 13. When it consists of a special kind of sheet, such as an OHP or a thick sheet, the sheet P is fed from a manual feed tray 23, and conveyed to the image forming portion 8. Then, the sheet P is sent by registration rollers 19 arranged in the vicinity of the photosensitive drum 2 to a position where the toner images formed on the photosensitive drum 2 are transferred thereto by the transfer means 5.
The toner images transferred to the sheet P in the image forming portion 8 are fixed to the sheet P by a fixing apparatus 14, whereby a desired image product is completed. Thereafter, the sheet P is conveyed by inner discharging rollers 20 and reaches a discharging portion flapper 22, where the conveying path for the sheet P is switched according to whether it is discharged as it is or printing is also effected on the rear surface of the sheet. In the case in which it is discharged as it is, the sheet P is conveyed to a sheet discharging portion 15 provided on the side surface of the image forming apparatus 1 in this case by outer discharging rollers 21 before being discharged to the exterior of the image forming apparatus 1. When printing is to be performed also on the rear surface of the sheet, the sheet P is conveyed to a re-feed path 16 for guiding the sheet to be re-fed at the time of two-side recording, and is reversed by a sheet surface reverse path 17. The reversed sheet P is conveyed to the registration rollers 19 by way of a duplex transport path 18 before being sent to the image forming portion 8 again.
The above-described construction of the image forming apparatus is only given by way of example, and it is also possible to adopt some other type of construction. For example, it is also possible to adopt an electrostatic recording type image forming apparatus, or an intermediate transfer system in which after transferring toner images of four colors to an intermediate transfer member by using the intermediate transfer member as a transfer means, the toner images are collectively transferred to the sheet P. Further, the construction of the image forming means may be other than that shown in
Here, in the image forming apparatus of this embodiment, the developing apparatuses 3 execute a two-component type development, and the developing apparatuses 3 accommodate developers containing toners and carriers. Here, a developing apparatus 3 and a replenishment agent supply device 4 for supplying replenishment agent thereto will be described with reference to
The developing apparatus 3 is of a contact magnetic brush development type using a two-component developer containing toner and carrier.
To effect replacement of developer, that is, automatic refreshment of the carrier (ACR), the developing apparatus 3 is supplied with replenishment agent containing toner and carrier, and at the same time, discharge of developer is conducted. In the developing apparatus 3 of this embodiment, the toner density in the developing apparatus 3, that is, the mass mixture ratio of toner T to developer D, i.e., the T/D ratio, is 8%, and the T/D ratio of the replenishment agent is 85%.
As shown in
The developing apparatus 3 is equipped with the developing container 24 that performs development while circulating two-component developer, and a discharging pipe 26 for discharging degenerated developer. Inside the discharging pipe 26, there is arranged a screw 26a, which discharges degenerated developer into the developer recovery tank 27. At the lower end of the discharging pipe 26, there is detachably mounted the developer recovery tank 27. The replenishment agent supply device 4 for supplying replenishment agent is connected to the developing apparatus 3.
The developing container 24 has a replenishment agent supply port 24a and a developer discharging port 24b. The discharging pipe 26 is connected to the developer discharging port 24b.
At the replenishment agent supply port 24a, there is formed, as the replenishment agent supply means, a replenishment agent carrying path 28 for carrying and supplying toner and carrier stored in the toner bottle 42 of the replenishment agent supply device 4 shown in detail in
As shown in
Further, as shown in
As shown in
Due to this construction, when new replenishment agent is supplied from the replenishment agent supply device 4 to the developing apparatus 3 and the volume of the developer in the developing container 24 increases, the developer in the developing container 24 overflows from the developer discharging port 24b, thereby effecting automatic refreshment (ACR) of the carrier.
As shown in
Here, as can be seen from
Here, as stated above, the average T/D ratio of the replenishment agent accommodated in the toner bottle 42 is 85%, however, when filling the toner bottle 42 with toner and carrier or due to vibration, etc. during transportation, the distribution of the T/D ratio may cease to be uniform to become uneven. When the filling with toner was effected in the most uneven manner, the T/D ratio, which is 85% on the average, was 50 to 95% in some places.
The replenishment agent containing toner is supplied with a view to compensating for the toner consumption as a result of image formation. However, when the T/D ratio of the replenishment agent is changed with respect to the desired toner supply amount, the amount of toner to be supplied fluctuates, making it impossible to attain a desired value of T/D ratio in the developing apparatus.
In this way, when the toner density of the developer (replenishment agent) to be supplied and the T/D ratio, which is the ratio of toner to developer, fluctuates, the accuracy with which toner is supplied deteriorates in the conventional apparatus as described above, resulting in fluctuation in the toner density of the developer in the developing apparatus, a variation in image density, scattering of toner, or the like.
In view of this, as a feature of this embodiment, a toner density sensor 52 is provided on the hopper portion 41 equipped with the agitating means of the replenishment agent supply device 4, and the T/D ratio of the replenishment agent is detected, the supply of replenishment agent being effected with the replenishment table for the replenishment agent changed.
Like the toner density sensor 51 of the developing container 24, the toner density sensor 52 for detecting the T/D ratio of the replenishment agent provided on the hopper portion 41 is an inductance detection sensor that detects density by detecting the magnetic permeability of the replenishment agent. Since the T/D ratio of the replenishment agent is higher than that of the developer, the sensor is set so as to be suitable for high T/D ratio.
In this embodiment, the replenishment table for the replenishment agent is changed according to the T/D ratio detection result. The replenishment table is a table showing the relationship between the output value of the toner density sensor 51 for detecting the toner density in the developing container 24, set in the control portion of the image forming apparatus main body controlling the operation of the image forming means, and the rotating amount of the replenishment screw 28a detected by the encoder 29. The rotating amount of the replenishment screw 28a means the supply amount of the developer.
Lines A, B, C, and D respectively correspond to the T/D ratios of the replenishment agent of 95%, 85%, 70%, and 55% as detected by the toner density sensor 52 installed on the replenishment agent supply device 4. The difference in the inclinations of the lines A to D is due to the difference in the amount of toner contained in the replenishment agent discharged through one rotation of the replenishment screw 28a.
The amount (mass) of toner contained in the replenishment agent discharged through one rotation of the replenishment screw 28a used in this embodiment was 0.202 g, 0.197 g, 0.188 g, and 0.174 g for the T/D ratio of the toner bottle 42 of 95%, 85%, 70%, and 55% in order, respectively. The less the amount of toner contained in the replenishment agent discharged through one rotation of the replenishment screw 28a, the steeper the inclination of the replenishment table.
The T/D ratio of the developing apparatus 3 of this embodiment accommodating 165 g of developer is 8%, so that the amount of toner in the developer is 13.2 g. The maximum toner consumption when successively forming images with the image forming apparatus of this embodiment (the toner consumption when an image of maximum density is placed on the entire original plate) is 13.8 g/min, and the toner thus consumed must be successively replenished.
That is, when there is no toner density sensor on the hopper portion 41 of the replenishment agent supply device 4, and replenishment is effected at the T/D ratio of 85% without detecting the accurate T/D ratio of the replenishment agent, the amount of toner contained in the replenishment agent discharged through one rotation of the replenishment screw 28a is 0.197 g, so that, in order to replenish 13.8 g of toner, the requisite number of times that the replenishment screw 28a is rotated is 70.
However, as stated above, there are cases in which the T/D ratio of the replenishment agent is reduced to approximately 55%. When the T/D ratio is 55%, the amount of toner contained in the replenishment agent is 12.18 g even if the replenishment screw 28a is rotated 70 times. That is, only 12.18 g of toner is replenished when 13.8 g of toner has been consumed, so that the amount of developer in the developing apparatus 3 is deficient by 1.62 g, and the T/D ratio of the developer in the developing apparatus 3 is reduced to 7% in one minute.
As in the case of this embodiment, when the T/D ratio of the replenishment agent is detected by the toner density sensor 52 of the hopper portion 41 of the replenishment agent supply device 4, and the rotating amount of the replenishment screw 28a, that is, the replenishment table, is selected according to the T/D ratio of the replenishment agent, it is possible to supply an accurate amount of toner to the developing apparatus 3.
Here, in this embodiment, it is possible to select a toner bottle 42 from a plurality of kinds of toner bottles containing replenishment agents of different toner densities and mount it to the replenishment agent supply device 4. Also in this case, the toner density of the replenishment agent is detected by the toner density sensor 52.
As stated above, when the distribution of the T/D ratio of the replenishment agent, which is 85% on the average, becomes uneven, there is a variation in T/D ratio within the range of 50 to 95%. For example, when, in order to expedite the replacement of the carrier of the developer of the developing apparatus 3, the toner bottle 42 is replaced by one in which the average T/D ratio is 20%, it may occur that the T/D ratio partially becomes approximately 10%.
In such cases, when detection of the T/D ratio of the replenishment agent is not effected by the toner density sensor 52, the T/D ratio of the developer in the developing apparatus 3 after one minute is reduced to 5.4%. In contrast, when the T/D ratio of the replenishment agent is detected by the toner density sensor 52 of the hopper portion 41, it is possible to supply an accurate amount of toner to the developing apparatus 3, making it possible to maintain the developer density at a fixed level.
It is desirable for the toner density sensor 52 to be provided in the vicinity of the agitating member (not shown) of the hopper portion 41 as in this embodiment. Further, since the toner density sensor 52 detects the T/D ratio of the replenishment agent supplied to the developing apparatus 3, it is desirable for the sensor to be on the side nearer to the developing apparatus 3. Thus, as shown in
The constructions of the image forming apparatus, the developing apparatus 3, and the replenishment agent supply device 4 of this embodiment are the same as those described with reference to Embodiment 1, so that a description thereof will be omitted. Also in this embodiment, the toner density sensor 52 for detecting the T/D ratio of the replenishment agent is arranged on the hopper portion 41 of the replenishment agent supply device 4 as shown in
When the T/D ratio of the replenishment agent sufficiently agitated is fixed, the output value of the inductance detection sensor is generally determined. However, strictly speaking, it fluctuates depending on the bulk density of the replenishment agent.
That is, when containers containing the same developer are left to stand for 12 hours in different environments, their inductance detection sensor output values are different. For example, when the room temperature was 23° C. and the humidity was 50% rh, the inductance detection sensor output of a replenishment agent whose T/D ratio was 70% was 2.5 V, whereas, when this replenishment agent was left to stand in an environment in which the room temperature was 30° C. and the humidity was 90% rh for 2 hours, the inductance detection sensor output was 3.0 V.
This phenomenon is due to the fact that the inductance detection sensor performs detection on carrier, which is a magnetic substance. That is, due to the high humidity environment, the triboelectricity of the developer (the electric charge per unit mass) was reduced, and the bulk of the developer was reduced, that is, it was increased in density, with the result that the carrier amount per unit volume increased, thereby increasing the carrier amount in replenishment agent per unit volume. The increase in carrier amount is detected as an increase in carrier ratio, and an increase in carrier ratio means a reduction in toner ratio, that is, T/D ratio. Actually, however, only the bulk density of the replenishment agent is increased as a whole, and there is no change in T/D ratio, which is a mass ratio.
The supply of the replenishment agent is effected through rotation of the replenishment screw 28a. The accuracy with which the replenishment agent is supplied is influenced by the bulk density of the replenishment agent supplied by rotating the replenishment screw 28a.
That is, in the above environment in which the room temperature was 23° C. and the humidity was 50% rh, the amount of toner contained in the replenishment agent discharged through one rotation of the replenishment screw 28a was 0.188 g, whereas, in the case in which the room temperature was 30° C. and the humidity was 90% rh, the amount of toner contained was 0.193 g, and in the case in which the room temperature was 15° C. and the humidity was 5% rh, the amount of toner contained was 0.182 g. Thus, a change in environment causes a fluctuation in the replenishment agent discharging amount by as much as 5 to 6% at maximum.
When the replenishment operation is conducted by taking into account solely the toner density of the developer in the developing container 24, with the replenishment table unchanged, without taking into account the toner density of the replenishment agent, the amount of developer fluctuates, and the amount of toner contained therein fluctuates, which leads to a fluctuation in the density of the developer of the developing apparatus 3.
Thus, as in this embodiment, when an inductance detection sensor is used also in the hopper portion 41 as the toner density sensor 52, it is possible to ascertain the bulk density of the replenishment agent from the density detection result of the toner density sensor 52. That is, it is possible to ascertain the discharging amount when the replenishment screw 28a makes one rotation at the bulk density, so that it is possible to change the replenishment table accordingly, making it possible to accurately control the amount of replenishment agent to be supplied to the developing apparatus 3 and facilitate the stabilization of the T/D ratio of the developer in the developing apparatus 3.
To convert the output value of the toner density sensor 52, which is the inductance detection sensor, to the bulk density of the developer, it is necessary to grasp the relation between them beforehand. In the developer of this embodiment, when the bulk density is 0.536 g/cm3, the output of the toner density sensor 52 is 2.5 V; when the bulk density is 0.519 g/cm3, the output of the toner density sensor 52 is 2.1 V; and when the bulk density is 0.550 g/cm3, the output of the toner density sensor 52 is 3.0 V. The discharging amount resulting from one rotation of the replenishment screw 28a when the output of the toner density sensor 52 is 2.5 V, 2.1 V, and 3.0, is 0.269 g, 0.260 g, and 0.276 g, respectively. At this time, the amount of toner in the developer is a value obtained by multiplying the discharging amount resulting from one rotation of the screw by the T/D ratio (which, in this case, is 70%, that is, 0.7).
As described above, the density of the replenishment agent is detected by the inductance detection sensor, and the replenishment table is selected taking into account the change in the bulk density of the replenishment agent, whereby it is possible to supply toner to the developing apparatus 3 in a satisfactory manner in any environment.
The dimensions, materials, configurations, relative positions, etc. of the components of the image forming apparatus described above should not be construed restrictively unless otherwise specified. That is, it is possible for the density of the replenishment agent and the method of supplying the same to be other than those described above.
As stated with reference to Embodiment 1, there are no particular limitations regarding the constructions of the image forming apparatus, the developing apparatus, and the replenishment agent supply device. However, the present invention is particularly effective when applied to the developing apparatus of an image forming apparatus, such as a color copying machine or a color printer, which often outputs image of high density.
This application claims priority from Japanese Patent Application No. 2004-105758 filed on Mar. 31, 2004, which is hereby incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-105758 | Mar 2004 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5754916 | Kitayama et al. | May 1998 | A |
| 5848326 | Komuro et al. | Dec 1998 | A |
| 6240264 | Yajima et al. | May 2001 | B1 |
| Number | Date | Country |
|---|---|---|
| 62293267 | Dec 1987 | JP |
| 2-21519 | May 1990 | JP |
| 2000056639 | Feb 2000 | JP |
| 2003-215903 | Jul 2003 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20050220463 A1 | Oct 2005 | US |
