JP2004126122A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus by which cleaning is excellently performed by providing an equalizing mechanism to a cleaning blade and also installing the cleaning blade in the attitude of a specified range. <P>SOLUTION: In the image forming apparatus where the top end of the cleaning blade abutting on an intermediate transfer belt so as to be opposed to a tension roller abuts in a state that a downstream side is inclined in the running direction of the intermediate transfer belt so as to make an acute angle, the cleaning blade is pivotally supported nearly at the center part of the intermediate transfer belt in a width direction so as to be turnable, and when the acute angle out of angles formed by the cleaning blade with the tangent of the surface of the intermediate transfer belt at its abutting part is set as Φ and an angle formed by vector in a direction where the tension roller is energized by an energizing means with vector connecting the center of the tension roller and the abutting part on the downstream side of an endless belt in the running direction is set as θ, the relation of Φ-90≤θ<Φ+5 is satisfied. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for transferring an image using an endless belt, and more particularly to an image forming apparatus having a cleaning device in the form of a cleaning blade for cleaning a belt.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a laser beam printer, a toner image formed on an image carrier such as a photosensitive drum is transferred a plurality of times onto an intermediate transfer body to form a full-color image. And the like, which are configured to transfer images on a recording material at once. Above all, a plurality of image carriers for forming toner images of respective colors and an intermediate transfer belt which is an endless belt as an intermediate transfer body are brought into contact with each image carrier, and the toner images are superimposed and primary-transferred, and then recorded. 2. Description of the Related Art A configuration in which secondary transfer is collectively performed on a material is widely known.
[0003]
In a configuration using such an intermediate transfer belt, it is necessary to clean the intermediate transfer belt after secondary transfer of the toner image. The cleaning method includes a fur brush method and a cleaning blade method. A blade cleaning method using a urethane rubber plate cleaning blade is often used as a method having a simple structure and a high cleaning effect. Among them, a so-called counter abutting method in which the tip of the cleaning blade abuts in a state where the downstream side is inclined at an acute angle with respect to the running direction of the intermediate transfer belt, that is, a so-called counter abutting method, is frequently used because of good cleaning properties. .
[0004]
[Problems to be solved by the invention]
In order to drive the intermediate transfer belt, at least a driving roller for transmitting a drive from a motor to the belt and a tension roller for maintaining the tension of the intermediate transfer belt are required. Here, since the intermediate transfer belt has the largest load at the contact portion with the image carrier, it is necessary to arrange a drive roller downstream of the contact portion with the image carrier. This is because if the drive roller is disposed upstream of the contact portion with the image carrier, the belt is likely to bend, and it is necessary to apply a greater tension to the belt, so that damage to the belt increases. For this reason, the tension roller is disposed upstream of the contact portion with the image carrier, and the cleaning device for cleaning the intermediate transfer belt is disposed so that the tension roller is in contact with the opposite roller.
[0005]
The tension roller supports the belt with a constant load by a spring or the like for the purpose of applying a constant tension to the intermediate transfer belt. That is, the position of the tension roller is not fixed with respect to the apparatus main body, but is affected by the circumferential length and thickness unevenness of the belt, the eccentricity of the tension roller itself and other rollers (for example, a driving roller), and the position thereof is changed. It changes from moment to moment. When the blade cleaning system is adopted as the cleaning device, the inaccuracy of the position of the tension roller, which is the opposed roller, causes a great disadvantage.
[0006]
Although the blade cleaning method does not allow the performance of the other cleaning methods to follow the high performance at the time of the optimal setting, if the contact pressure is too high, adverse effects such as the cleaning blade being easily chattered are likely to occur. Therefore, the allowable range of the contact pressure of the cleaning blade, in other words, the allowable range of the setting tends to be narrower than other cleaning methods, for example, a cleaning method using a fur brush. Therefore, it has been difficult to employ a blade cleaning method when a roller whose position fluctuates, such as a tension roller, is used as an opposing roller.
[0007]
As means for solving this problem, the cleaning blade can be relatively easily used by using a configuration in which the cleaning blade is brought into contact with the intermediate transfer belt at a constant pressure by using the force of a spring. However, for example, when there is a difference between the peripheral length on the back side and the peripheral length on the front side of the intermediate transfer belt, the axis of the tension roller is tilted, and a bus line deviation occurs with the cleaning blade. In particular, when an intermediate transfer belt having a circumference of about 2 m is used, a difference in circumference between the left and right ends of the belt occurs up to about 2 mm. When such a belt is used, the left and right positions of the tension roller are displaced by a maximum of about 1 mm, causing a non-negligible generatrix deviation between the tension roller and the cleaning blade. As a result, it has been found that the cleaning blade causes a one-sided contact, and a difference occurs between the pressure on the back side and the pressure on the front side of the cleaning blade, resulting in poor cleaning.
[0008]
Therefore, the present invention provides an image that can perform good cleaning by minimizing a bus line deviation from the tension roller by providing the cleaning blade with an equalizing mechanism and installing the cleaning blade in a posture in a specific range. It is intended to provide a forming apparatus.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a typical configuration of the image forming apparatus according to the present invention includes an image carrier, an endless belt that contacts the image carrier, a tension roller that stretches the endless belt, A biasing means for applying a tension force to the tension roller; and a cleaning blade facing the tension roller and abutting on the endless belt, and having a tip of the cleaning blade downstream with respect to a running direction of the endless belt. In the image forming apparatus, the cleaning blade is rotatably supported at a substantially central portion in the width direction of the endless belt, and the cleaning blade and the endless belt are rotated. The acute angle of the angle between the tangent of the surface and the contact portion is Φ, and the tension roller is urged by the urging means. From the vector in the direction of travel of the endless belt toward the downstream side in the running direction of the endless belt, assuming that the angle formed by the vector connecting the center of the tension roller and the contact portion is θ, the relationship of Φ−90 ≦ θ <Φ + 5 is satisfied. It is characterized by the following.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
[First embodiment]
A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a view showing the relationship between a tension roller and a cleaning blade, FIG. 2 is a view showing the vicinity of a contact portion of the cleaning blade, FIG. 3 is a view for explaining the amount of penetration of the cleaning blade, and FIG. FIG. 5 is a diagram illustrating the ratio of the amount of intrusion at each position, and FIG. 5 is an overall configuration diagram of the image forming apparatus.
[0011]
First, the entire image forming apparatus will be described with reference to FIG. The image forming apparatus shown in FIG. 1 is an electrophotographic four-color full-color image forming apparatus that forms a full-color image on a transfer material using a plurality of photosensitive drums as image carriers.
[0012]
In the figure, an intermediate transfer belt 2 running in the direction of arrow A is disposed inside an image forming apparatus 1. The intermediate transfer belt 2 is formed in an endless belt shape by a dielectric resin such as a polycarbonate, a polyethylene terephthalate resin film, a polyvinylidene fluoride resin film and the like, and is stretched by a driving roller 2a, a secondary transfer inner roller 2b and a tension roller 2c. Have been.
[0013]
Here, since the load on the intermediate transfer belt 2 at the contact portion with the photosensitive drum 5 is the largest, the drive roller 2a needs to be disposed downstream of the contact portion with the photosensitive drum 5. If the drive roller 2a is arranged on the upstream side of the contact portion with the photosensitive drum 5, the intermediate transfer belt 2 is likely to bend, and it is necessary to apply a larger tension to the intermediate transfer belt 2. This is because the damage of is increased. For this reason, the tension roller 2c is disposed upstream of the contact portion with the photosensitive drum 5, and the cleaning device 16 for cleaning the intermediate transfer belt 2 is disposed so as to contact the tension roller 2c as an opposing roller. .
[0014]
The tension roller 2c has a cylindrical shape with a diameter of about Φ30 to 60 mm, and is applied with a tension to the intermediate transfer belt 2 by pressing both ends in the direction of arrow B by a spring 2d as a biasing means. The applied pressure is about 2 kg on one side, thereby generating an appropriate tension on the intermediate transfer belt 2.
[0015]
Above the intermediate transfer belt 2, four image forming units Pa, Pb, Pc, and Pd having the same configuration are arranged in series. The configuration will be described using the image forming unit Pa as an example. The image forming unit Pa includes a photosensitive drum 5a that is a drum-shaped image carrier that is rotatably arranged. Process devices such as a primary charger 6a, a developing device 7a, and a cleaner 8a are arranged around the photosensitive drum 5a. The other image forming units Pb, Pc, and Pd also have the same configuration as the image forming unit Pa, and only the photosensitive drums 5b, 5c, and 5d are shown in the figure. The developing devices 7a to 7d arranged in the respective image forming units store toner images of magenta, cyan, yellow, and black, respectively, and the respective image forming units form toner images of the respective colors.
[0016]
First, in the image forming unit Pa, an image signal of a magenta component color is projected from the optical unit 9a onto the photosensitive drum 5a to form an electrostatic latent image, and a magenta toner is supplied thereto from a developing device to form a magenta toner image. Is done. When the toner image reaches a transfer site where the photosensitive drum 5a and the intermediate transfer belt 2 come into contact with the rotation of the photosensitive drum 5a, the toner image is transferred onto the intermediate transfer belt 2 by the primary transfer roller 10a. Similarly, the toner images of the respective colors formed in the image forming units Pb to Pd are superimposedly transferred onto the intermediate transfer belt 2.
[0017]
On the other hand, the recording material S taken out from the feeding cassette 3 is conveyed to the intermediate transfer belt 2 via the registration roller pair 4. The recording material S is conveyed from the registration roller pair 4 to a nip between the secondary transfer inner roller 2b of the intermediate transfer belt 2 and the secondary transfer roller 11 that is separated from and brought into contact with the secondary transfer inner roller 2b. Is transferred onto the recording material S. The recording material S is transported to the fixing unit 13 by the transport belt 12, and the toner is fixed on the recording material S by heat and pressure. The fixing unit 13 has a mechanism for coating the surface of the fixing roller 13a with a releasable oil (for example, silicone oil) in order to enhance the releasability between the recording material S and the fixing roller 13a. This oil also adheres. The recording material on which the toner image has been fixed is discharged to a discharge tray 14. When a double-sided image is formed automatically, the recording material passes through a recording material reversing path (not shown) and is fed again to the image forming unit.
[0018]
Thereafter, the toner remaining on the photosensitive drums 5a to 5d is removed by the cleaners 8a to 8d, and the remaining charges are removed by pre-exposure means (not shown). Then, the photosensitive drums 5a to 5d are subjected to the next image formation. You. Further, on the downstream side of the secondary transfer portion of the intermediate transfer belt 2, a static eliminator 15 and a cleaning device 16 are disposed to remove toner and the like attached to the intermediate transfer belt 2.
[0019]
As shown in FIG. 1, the cleaning blade 16 a of the cleaning device 16 has its tip inclined at an acute angle on the downstream side with respect to the traveling direction of the intermediate transfer belt 2 (direction of arrow A), and And presses against the tension roller 2c via an urging means (not shown). The cleaning blade 16a is rotatably supported at a substantially central portion in the width direction of the intermediate transfer belt 2, and has an equalizing mechanism.
[0020]
In the above configuration, the acute angle of the angle between the tangent line of the intermediate transfer belt 2 and the cleaning blade 16a at the contact portion is defined as the angle Φ. The angle formed by the vector connecting the center of the tension roller and the contact portion from the vector in the direction in which the tension roller 2c is biased by the spring 2d toward the downstream side in the running direction of the intermediate transfer belt 2 is θ. . Then, since the contact position of the cleaning blade 16a on the surface of the intermediate transfer belt 2 was in the range of Φ−90 ≦ θ <Φ + 5, good cleaning could be achieved. Here, the contact angle Φ of the blade is generally in the range of 10 ° to 30 ° in order to ensure the function of the cleaning blade 16a, and the above inequality holds when Φ <47.5 °.
[0021]
The above setting range will be described in detail with reference to FIG. 1. A circle A is an ideal position of the tension roller 2c, and the circumferential length and thickness unevenness of the transport belt 12, the tension roller 2c itself and other rollers (for example, a driving roller, etc.) 3) shows the position when there is no eccentricity or the like, and ideally, both the back side and the near side are at the position of the circle A. However, it is assumed that a deviation actually occurs, and one end of the tension roller 2c, for example, the front end, is shifted to the position of the circle B due to the above-described eccentricity of the roller and a difference in the belt circumference. In this case, the front cleaning blade 16a moves in the direction perpendicular to the blade surface by the rotation of the equalizing shaft. As a result, the axis of the tension roller 2c is C0-C1 ', while the line in contact with the cleaning blade 16a is A0-B. Since these two lines are not parallel, the generatrix of the line contacting the cleaning blade and the surface to be cleaned are shifted.
[0022]
A description will be given, with reference to FIG. 1 and FIG. 2, of what adverse effects are caused by such a displacement of the bus. Referring to FIG. 2, the amount of penetration of the cleaning blade 16a will be described. Since the cleaning blade 16a is an elastic body, its tip is actually bent as shown in the figure. However, assuming that the cleaning blade 16a is virtually rigid, the cleaning blade 16a cuts into the surface to be cleaned as shown by a broken line in FIG. The distance between the tip of the virtual blade 16b and the surface to be cleaned at this time is defined as the penetration amount δ. As shown in FIG. 3, the amount of penetration δ and the contact pressure of the blade are in a proportional relationship, and the larger the contact angle Φ of the blade, the higher the contact pressure.
[0023]
Here, returning to FIG. 1, considering the case where the tension roller 2 c is not displaced, the cleaning blade 16 a and the surface to be cleaned abut at a point on the circle A. The point on the far side is A0, and the point on the near side is A1. Considering this as a reference, it is assumed that the front side of the tension roller 2c has moved by m in a direction away from the cleaning blade 16a as compared with the back side. In this case, since the equalizing function works, the cleaning blade 16a moves in a direction perpendicular to the blade surface. As a result, point A1 moves to point B. The coordinates of the points A0 and B at this time are as follows.
A0 = (rcos (π−θ), rsin (π−θ), 0)
B = (rcos (π-t), rsin (π-t), m)
r indicates the distance from the tip of the cleaning blade 16a to the center of the tension roller 2c when the cleaning blade 16a is considered to be a rigid body, that is, (radius of the tension roller 2c minus the amount of penetration). At this time, the amount of penetration δ of the front side and the rear side end has the same value by the equalizing function. Further, both θ and t are angles formed by a vector connecting the center of the tension roller and the contact portion, and the pressure direction of the tension roller is 0 ° and the downstream side in the traveling direction is positive.
[0024]
Here, the following calculation is established.
Cos (t−α) = (sin θ + ((m / r) + cos θ) × tan (Φ−θ))) / (√ (tan2 (Φ−θ) +1))
Sinα = 1 / √ (tan2 (Φ−θ) +1)
At this time, considering the distance from an arbitrary point X (x, 0, wx / m) (w: length of the tension roller) on the line segment C0-C2 to the line segment A0-B, the maximum value is the line It is the midpoint of the minute C0-C1, and the minimum value is the near side or the far side end. When θ = Φ, it is possible to obtain a system with a substantially uniform penetration amount over the entire area of the cleaning blade 16a. As θ deviates from this value, the penetration amount at both ends tends to be smaller than the penetration amount at the central portion. is there.
[0025]
Experiments have shown that if the penetration amount at both ends is less than 80% of the penetration amount at the center, it is difficult to obtain an allowable cleaning range. As described above, the penetration amount and the pressure are in a substantially proportional relationship (see FIG. 3), and when the pressure at both ends becomes 80% or less of the central portion, chattering of the cleaning blade 16a from the central portion and insufficient pressure at the end portions. This is because it is difficult to prevent poor cleaning due to the cleaning. In addition, an unstable factor that the displacement of the generatrix with respect to the surface to be cleaned is increased is also added.
[0026]
Then, as shown in FIG. 4, in order for the penetration amount at both ends to be 80% or more of the center portion, it is sufficient that Φ−90 ≦ θ <Φ + 5. Conversely, within this range, good cleaning can be maintained with almost no influence of the displacement of the bus.
[0027]
[Other embodiments]
In the first embodiment, the cleaning blade 16a is configured to have an equalizing function with the central portion as an axis and press the tension roller 2c. However, since the cleaning blade 16a is made of an elastic material such as rubber, pressure is not necessarily required. If the pressure is not applied, the fluctuation of the total pressure cannot be completely corrected when the bus displacement of the cleaning blade 16a with respect to the surface to be cleaned occurs. However, the equalizing function and the abutting position regulation according to the present invention prevent the cleaning blade 16a from moving. This is because the contact pressure distribution in the thrust direction can be made sufficiently uniform.
[0028]
Further, in the first embodiment, the case where the cleaning blade 16a is an elastic body has been described. However, even when the cleaning blade 16a is a rigid body, if the opposing tension roller 2c and the intermediate transfer belt 2 are elastic bodies, The invention is fully established. Further, when the tension roller and the intermediate transfer belt 2 are rigid, the concept of the amount of intrusion becomes meaningless. However, if the cleaning blade 16a is configured to be urged by spring pressure, a rigid cleaning blade is used. It is possible to do. Even in this case, substantially the same theory can be constructed by replacing r in the first embodiment with the distance from the center of the tension roller 2c to the surface to be cleaned (the intermediate transfer belt in this case). . This can also be understood from the fact that the equation of Φ−90 ≦ θ <Φ + 5 consists only of the relationship between the contact angle and the contact position of the cleaning blade.
[0029]
In the first embodiment, the description is made using the intermediate transfer belt as the endless belt.However, in a cleaning device having a configuration in which a cleaning blade is disposed opposite to a roller that applies tension to the belt, the present invention Always holds. That is, the present invention can be applied to all cleaning devices such as a photosensitive belt, a transfer belt, and a fixing unit belt.
[0030]
【The invention's effect】
As described above, in an image forming apparatus that performs cleaning by rotatably supporting a cleaning blade at a substantially central portion in the width direction of the endless belt and abutting the cleaning blade against the tension roller and against the endless belt. By setting the contact angle .PHI. Of the cleaning blade and the contact position .theta. Of the cleaning blade so as to satisfy the relationship of .PHI.-90.ltoreq..theta. <. PHI. + 5, the displacement of the bus between the cleaning blade and the surface to be cleaned is minimized. And good cleaning can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a relationship between a tension roller and a cleaning blade.
FIG. 2 is a view showing the vicinity of a contact portion of a cleaning blade.
FIG. 3 is a diagram illustrating the amount of penetration of a cleaning blade.
FIG. 4 is a diagram illustrating the ratio of the amount of intrusion at each position with respect to the center of the cleaning blade.
FIG. 5 is an overall configuration diagram of the image forming apparatus.
[Explanation of symbols]
P: Image forming unit S: Recording material 1: Image forming device 2: Intermediate transfer belt 2a: Driving roller 2b ... Secondary transfer inner roller 2c: Tension roller 2d: Spring 3: Feeding cassette 4: Registration roller pair 5: Photosensitive Body drum 6 Primary charger 7 Developing device 8 Cleaner 9 Optical means 10 Primary transfer roller 11 Secondary transfer roller 12 Conveyor belt 13 Fixing unit 13a Fixing roller 14 Discharge tray 15 Charge removing charger 16 cleaning device 16a cleaning blade 16b virtual blade

Claims (2)

An image carrier;
An endless belt that contacts the image carrier;
A tension roller for stretching the endless belt,
Urging means for applying tension to the tension roller,
A cleaning blade that faces the endless belt in opposition to the tension roller,
In an image forming apparatus, the tip of the cleaning blade is in contact with the endless belt in a state where the downstream side is inclined at an acute angle with respect to the traveling direction of the endless belt.
The cleaning blade is rotatably supported at a substantially central portion in the width direction of the endless belt, and
Of the angles formed by the cleaning blade and the tangent to the surface of the endless belt at the contact portion, the acute angle is Φ,
From the vector in the direction in which the tension roller is biased by the biasing means, toward the downstream in the running direction of the endless belt, the angle formed by the vector connecting the center of the tension roller and the contact portion is θ. ,
Φ-90 ≦ θ <Φ + 5
An image forming apparatus characterized by satisfying the following relationship: The image forming apparatus according to claim 1, wherein the cleaning blade is in contact with the endless belt at a predetermined pressure by blade urging means.

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