Patent Application
20190041776
The present invention relates to a cleaning member for cleaning a charging member in an image forming apparatus using electrophotographic process such as a copier and a laser printer.
An electrophotographic image forming apparatus using electrophotographic image forming process uses a process cartridge system which includes, in an integral form, a photosensitive drum (hereinafter referred to as the “drum”), charging means for charging an upper surface of the drum, developing means, and cleaning means for cleaning the upper surface of the drum. Detachably providing the process cartridge to a main body of the image forming apparatus makes it easier for the user to carry out maintenance.
In recent years, a cleaner-less method has been proposed for the purpose of reducing the size of an image forming apparatus and a process cartridge (see Japanese Patent Application Publication No. H02-272589). According to the cleaner-less method, a residual developer (hereinafter referred to as “toner”) on the drum after a transfer step is cleaned simultaneously with developing process by developing means and removed from the drum to be recovered and reused. By the cleaner-less method, a waste toner storage which stores waste toner scraped from above the drum using cleaning means is not necessary, which eliminates the necessity of replacing the filled waste toner storage. In this manner, a cartridge including only a drum and charging means in an integral form and a cartridge including only developing means in an integral form may be discretely provided, so that the user needs only replace the developing means. Such cartridges available on a functional basis may be even more compact and easily handled by the user. Multiple developing means each storing an amount of toner for a printable number of sheets desired by the user may be provided, so that the developing means may be used in combination for various uses.
As the charging means for charging the drum in the process cartridge, a contact-type charging device using a charging roller has been commercially available. A drum as a member to be charged is contacted by a conductive charging roller as a charging member, charging voltage is applied to the charging roller, and a drum surface is charged to a prescribed polarity or potential. The contact charging is carried out by discharge in a gap between the charging roller and the drum surface, which is advantageous over conventional corona charging means in that application voltage is lower and less ozone is generated.
The charging roller contacts the drum upper surface and therefore the surface is stained with toner, an external additive for improving the fluidity or charging performance of the toner, etc. Resistance is different between the stained part and the unstained part of the charging roller surface, and charging non-uniformity is generated on the drum, which causes a noticeable density difference to appear especially in a half-tone image depending on the resistance values. In particular, according to the cleaner-less method, there is no cleaning means which would normally be provided upstream of the charging member in the rotation direction of the drum, and therefore mainly transfer residual toner or fogging toner directly adheres to the charging member through the drum, which is more likely to cause charging non-uniformity.
As cleaning means for removing a stain from the charging roller, an approach of having a felt-type cleaning member abut against a charging roller has been proposed (see Japanese Patent Application Publication No. H02-272589), and another approach of contacting a cleaning member of resin foam (sponge member) to the charging roller in a rotatable manner has been proposed (see Japanese Patent Application Publication No. H08-062948). Using the cleaning means, the stain is removed from the surface of the charging roller physically or electrically by voltage application. These approaches need only a simple structure, and therefore means for removing stain by having a fixed type cleaning member abut against a charging roller is mainly provided.
Toner scraped from the surface of the charging roller is stored inside the fixed type cleaning member for cleaning the surface of the charging roller. As the amount of stored toner gradually increases and then exceeds a certain storage amount, the toner partly oozes out from the cleaning member and drops to stain the cartridge or the image forming apparatus in some cases. Therefore, cleaning operation for removing the stored toner from the cleaning member should be carried out. A method for carrying out the operation of cleaning the cleaning member for the charging member has been proposed (see Japanese Patent Application Publication No. 2011-133690).
However, during continuous printing, the cleaning member cannot be cleaned sufficiently, and the printing operation must be forcibly stopped for cleaning operation after a certain number of prints. Naturally, the cleaning operation lowers the productivity for the user since extra time for the operation in addition to printing is necessary. Therefore, there has been a demand for an image forming apparatus that can prevent the inside of the main body of the image forming apparatus from being stained, if the printable number of sheets before the start of the operation of cleaning by the cleaning member is increased.
In addition, when mounting a cartridge including a drum and charging unit in an integral form into the main body of the image forming apparatus, toner from the cleaning member for cleaning the charging roller drops to stain the main body because of an impact given by the mounting. This is because, in the cleaner-less method, nothing can completely seal around the drum and the charging roller like the cleaning unit or the waste toner storage as described above. The problem does not occur in an early stage of use and is in particular encountered after a certain number of prints when the user takes out the cartridge from the image forming apparatus to solve a trouble such as paper jamming in a state where toner is stored in the cleaning member for the charging roller.
With the foregoing in view, it is an object of the present invention to provide an image forming apparatus which is less prone to toner dropping from a cleaning member for a charging roller and can prevent the inside of the main body of the image forming apparatus from being stained if the toner drops.
In order to achieve the object, a cartridge according to the present invention includes
an image bearing member which is rotatable and is provided in the cartridge, the cartridge being detachably provided to an apparatus main body of an image forming apparatus;
a charging roller which contacts and charges the image bearing member; and
a cleaning member which cleans the charging roller,
wherein the cleaning member has a brush portion in abutment against a surface of the charging roller, and
in a section substantially orthogonal to a rotation axis of the image bearing member in a state where the cartridge is mounted to the apparatus main body,
where a downstream end of an abutment region of the brush portion against the charging roller in a rotation direction of the charging roller is a first end, an upstream end of the abutment region in the rotation direction of the charging roller is a second end, and among tangents to the image bearing member, a tangent extending from a point of tangency in a rotation direction of the image bearing member and crossing the first end is a first tangent,
the point of tangency of the first tangent on the image bearing member is vertically above a horizontal line passing through a center of the image bearing member, and the second end is vertically above the first end.
In order to achieve the object, an image forming apparatus according to the present invention includes
the cartridge described above,
wherein the image forming apparatus forms an image on a recording medium.
According to the present invention, more toner stains on the charging roller can be stored in the cleaning member for the charging roller and can be restrained from dropping into the main body of the image forming apparatus. An image forming apparatus can provided which can be prevented from being stained inside if toner drops into the image forming apparatus main body.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, a description will be given, with reference to the drawings, of embodiments (examples) of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments.
In
A sheet tray 2 which stores a recording medium (hereinafter as the “sheet material P”) on which an image is to be formed is provided under the cartridge B. In the apparatus main body A, a pickup roller 3, a transport roller pair 4, a transfer roller 5, a fixation device 6, a discharge roller pair 8, a discharge tray 9, and other elements are sequentially arranged in the transport direction D of the sheet material P. Note that the fixation device 6 includes a heating roller 7a and a pressure roller 7b.
Image Forming Process
Now, general aspects of the image forming process will be described with reference to
Meanwhile, as the section of the cartridge in
As shown in
Untransferred toner remaining on the drum 10 after the transfer includes toner charged to have positive polarity by discharge of transfer voltage (+1 kV) applied on the transfer roller 5 and fogging toner with positive polarity and is sent to the abutment position against the charging roller 11 as the drum 10 rotates. In the vicinity of the abutment position against the charging roller 11 the toner becomes toner T with negative polarity by discharge of charging voltage (−1500 V) applied by the charging roller 11 and is sent to a developing region G in which the developing roller 25 and the drum 10 are opposed to each other as the drum 10 rotates. In the developing region G, the toner T with negative polarity is recovered for reuse from the drum 10 to the developing roller 25 by the potential difference between the drum 10 and the developing roller 25.
Structure of Cartridge B
Now, an overall structure of the cartridge B will be described with reference to
Structure of Latent Image Apparatus Unit B1
Now, a structure of the latent image apparatus unit B1 will be described with reference to
The cleaning member 12 is provided in abutment against the charging roller 11 in order to remove toner adhering to the upper surface of the charging roller 11. The cleaning member 12 is press-contacted to the charging roller 11 through a spring 14 provided at the container frame body 13 in the latent image apparatus unit B1. As shown in
Structure of Cleaning Member 12
Now, a structure of the cleaning member 12 according to the present example will be described with reference to
The cleaning member 12 and the charging roller 11 are normally kept at the same potential. This is because if the potential of the cleaning member 12 is on the negative polarity side with respect to the charging roller 11, the positive polarity toner enters the cleaning member 12, and the toner is collected excessively to the side of the cleaning member 12, which necessitates frequent cleaning operation. Conversely, if the potential of the cleaning member 12 is on the positive polarity side with respect to the charging roller 11, the effect of rubbing by the cleaning member 12 is reduced, and therefore a DC voltage of −1500 V is applied from a power supply (not shown) so that the cleaning member 12 and the charging roller 11 are normally kept at the same potential.
Abutment Position of Cleaning Member 12
Now, the abutment position of the cleaning member 12 according to the present example will be described with reference to
Behavior of Toner T
Now, the behavior of the toner T in the vicinity of the drum 10 will be described with reference to
Meanwhile, the entire toner is not charged to the negative polarity by the discharging, and part of the toner maintains its positive polarity. The positive polarity toner as is moved to the charging roller 11 by the potential difference between the charging roller 11 (−1500 V) and the surface potential (−800 V) of the drum 10 as shown in
Cleaning Operation by Cleaning Member 12
Now, cleaning operation for discharging the toner T collected by the cleaning member 12 will be described with reference to
During the cleaning operation, the cleaning member 12 is applied with a DC voltage of −1300 V so as to have positive polarity with respect to the charging roller 11. At the time, the toner T is moved from the cleaning member 12 to the charging roller 11 by the potential difference between the cleaning member 12 and the charging roller 11. The effect of rubbing as the toner passes the cleaning member 12 is reduced, but the charging voltage applied to the charging roller 11 generates discharge, which causes the toner T to have negative polarity and move onto the drum 10. The negative polarity toner moved onto the drum 10 is recovered into the developing apparatus unit B2 in the developing region G as the developing roller 25 is again made to abut against the drum 10.
As described above, periodic cleaning operation for example after printing operation or printing a prescribed number of sheets allows the collected toner in the cleaning member 12 to be reduced, so that good printing can be continued during normal operation.
Structure of Abutment Part of Cleaning Member 12 at Upstream End H1 according to Present Example
Now, how the toner T drops from the cleaning member 12 will be described with reference to
Therefore, the charging roller 11, the cleaning member 12, and the drum 10 are arranged as follows. As shown in
Structure of Abutment Part of Cleaning Member 12 at Downstream End H2 according to Present Example
The upstream end H1 of the cleaning member 12 is set vertically above the downstream end H2, so that the toner retention amount until the toner T drops from the cleaning member 12 increases, while the toner T may drop from the downstream end H2 as shown in
The toner T drops on the drum 10 from the downstream end H2 under the following condition. As shown in
As described above, the toner may be prevented from dropping from the upstream end H1 of the cleaning member 12, while the inside of the apparatus main body A can be prevented from being stained by the toner from the downstream end H2.
Verification Experiments
The degree of collection of toner T depending on the arrangement of the cleaning member 12 with respect to the charging roller 11 was examined.
As a toner dropped state, whether the toner dropped in the apparatus main body A after the same number of prints was also evaluated. The number of prints at the time was 100. In the table, O represents the case in which no toner dropped in the apparatus main body A, Δ represents the case in which a small amount of toner dropped in the apparatus main body A, and X represents the case in which a large amount of toner dropped in the apparatus main body A. Table 1 gives the result of verification experiments.
In the first and second comparative examples, the upstream end H1 where toner collected by the cleaning member 12 aggregated as described above was vertically below the downstream end H2, and the toner T was not retained by the cleaning member 12 and more easily dropped. Also in the first comparative example, the angle α was outside the angle range of 0°<α<90°. In the second comparative example, the angles α and β were both greatly outside the ranges according to the first example expressed by 0°<α<90° and 0°<β<90°. Therefore, the number of prints allowed until cleaning operation by the cleaning member 12 in the first and second comparative examples was small. In a third comparative example, since the upstream end H1 was vertically above the downstream end H2, the angle α was within the same range as the first example unlike the first and second comparative examples. However, although the amount of dropped toner was small, toner dropped from the downstream end H2. This is because the point of tangency P of the tangent M1 on the drum through the downstream end H2 was below the horizontal line h of the drum 10, and the toner more easily dropped from the downstream end H2. Therefore, the number of prints allowed until cleaning operation by the cleaning member 12 was smaller than that in the first example.
From the result, the configuration according to the first example allows the amount of toner dropped from the cleaning member 12 to be reduced, so that the number of prints allowed until cleaning operation by the cleaning member 12 is carried out can be increased.
The description of the first example concerns toner dropped from the cleaning member 12 during normal printing. In the following description of a second example, another case in which toner drops from the cleaning member 12 will be described with reference to the case in which an impact is generated by mounting the cartridge B.
As described in connection with the first example, printing is forcibly stopped to carry out cleaning operation by the cleaning member 12 during continuous printing. However, in a particular case such as paper jamming, the user may take the cartridge out in order to recover the situation. In particular, when the cartridge is taken out before cleaning operation by the cleaning member 12 is forcibly carried out during continuous printing, toner may be accumulated in the cleaning member 12. When the cartridge is once again mounted after the recovery, an impact generated by mounting the cartridge may cause toner to drop from the cleaning member 12 and stain the inside of the apparatus main body A. In the second example, an image forming apparatus that can prevent the inside of the apparatus main body A from being stained in such a situation can be provided. The apparatus main body A and the cartridge B in the present example are basically the same as those in the first example, and only features unique to the second example will be described.
Impact Generation Mechanism
Here, the reason for the impact generation during mounting will be described.
Projections 41 for guiding the cartridge to move along the guide rails 32 are provided at side surfaces of the latent image apparatus unit B1 as shown in
Here, a cartridge insertion direction W in the present example will be defined. In
Relation between Cartridge Insertion Direction W and Toner Flying Direction
The cartridge B butts against the positioning portion 51 during insertion, so that toner is spattered in two directions from the cleaning member 12. One of the directions coincides with the cartridge insertion direction W on the principle of inertia. As for the other direction, the toner is pressed by the cleaning member 12 in the direction in which the cleaning member 12 receives force as the cartridge butts against the positioning portion 51 and the toner is more likely to fly in the opposite direction to the cartridge insertion direction W. More specifically, the toner flies in the direction along the cartridge insertion direction W and the opposite direction thereto. Therefore, the positional relation between the cartridge insertion direction W and the cleaning member 12 will be described.
Upstream End H1 of Cleaning Member 12 in Present Example
Since the upstream end H1 of the cleaning member 12 is vertically above the downstream end H2 similarly to the first example, the toner does not drop in the apparatus main body A if an impact is generated in any direction during insertion. With reference to
In
In
Downstream End H2 of Cleaning Member 12 in Present Example
Now, different cartridge insertion directions W in connection with the downstream end H2 of the cleaning member 12 will be described. In consideration of various cartridge insertion directions W, toner may spatter from the downstream end H2 and stain the inside of the apparatus main body A when the cartridge is inserted in a certain cartridge insertion direction W. This may happen when the cartridge is inserted in the following insertion direction. As shown in
This is because when the cartridge insertion direction W is in any of the directions, the toner dropped from the downstream end H2 directly falls into the apparatus main body A instead of falling onto the drum 10. Meanwhile, when the cartridge insertion direction W is in a direction not between the two tangents, the toner does not fall into and stain the apparatus main body A.
More specifically, as the tangents M1 and M2 cross each other, the region including the charging roller 11, the drum 10, etc. is divided into four. Among the four regions, the region including the charging roller 11 is a first region, and the regions other than the first region are referred to as second, third, and fourth regions in the rotation direction of the charging roller 11 or in the anticlockwise direction in
Verification Experiments
Experiments were carried out to examine whether the structure according to the second example does not allow toner to stain the inside of the apparatus main body A. As an examination method, while changing the cartridge insertion direction W and the abutment arrangement of the cleaning member 12, it was examined whether the toner stained the inside of the apparatus main body A. More specifically, as shown in
In the first comparative example, the cartridge insertion direction W was in the direction toward the region γ1 between M1 and M2 as described above, the abutment angle α of the cleaning member 12 was 45°, the angle β between the point of tangency P and the horizontal line h through the center of the drum 10 was 30°. The first comparative example is identical to the second example except for the cartridge insertion direction W. In the second comparative example, the cartridge insertion direction W was leftward, the abutment angle α of the cleaning member 12 was 135°, and the angle β between the point of tangency P and the horizontal line h through the center of the drum 10 was 70°. In the second comparative example, the cartridge insertion direction W was the same direction as that in the second example while the position of the cleaning member 12 was different for comparison.
In the verification experiments, the amount of toner collected by the cleaning member 12 was kept constant, and the velocity during cartridge insertion was constant. More specifically, before the start of cleaning operation by the cleaning member 12, the driving was forcibly stopped once, the number of prints for which the amount of toner collected by the cleaning member 12 reached a fixed amount was checked, and the driving was forcibly stopped. Then, the cartridge B was taken out from the main body and inserted back into the apparatus main body A. At the time, the cartridge B was taken out again and it was visually checked whether the toner T had dropped in the apparatus main body A. The total amount of toner collected by the cleaning member 12 was 10 mg and the insertion velocity in insertion was 0.5 m/sec.
The result of verification is given in Table 2. The evaluation was carried out in an environment in which the temperature was 20° C. and the humidity was 50%, O represents the case in which no toner dropped in the apparatus main body A, Δ represents the case in which a small amount of toner dropped in the apparatus main body A, and X represents the case in which a large amount of toner dropped in the apparatus main body A.
According to the second example, the toner did not drop either from the upstream end H1 and the downstream end H2. In the first comparative example, the angles α and β are the same as those in the second example, the cartridge insertion direction is between the tangent M1 to the drum 10 passing through the downstream end H2 and the tangent M2 through the contact point between the charging roller 11 and the central part H3 in the abutment region between the charging roller 11 and the cleaning member 12. Therefore, the toner dropped from the downstream end H2 and stained the inside of the apparatus main body A. In the second comparative example, the angle α was greater than the range in the second example, the upstream end H1 of the cleaning member 12 is directed downward in the vertical direction, and therefore a large amount of toner dropped from the upstream end H1 and stained the inside of the apparatus main body A more than in the first comparative example.
As in the foregoing, the tangent M2 to the charging roller 11 passes through the contact point between the central part H3 of the abutment region between the charging roller 11 and the cleaning member 12, and the tangent M1 to the drum 10 passes through the downstream end H2 of the cleaning member 12. In this case, when the cartridge insertion direction W is present in a direction not between M1 and M2, the toner does not stain the inside of the apparatus main body A, and high quality images can be provided.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2017-152667, filed on Aug. 7, 2017, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-152667 | Aug 2017 | JP | national |
