The present invention relates to a belt driving apparatus for driving a belt involved in image formation. More concretely, it is an invention related to a belt driving unit for driving an intermediary transfer belt, a direct transfer belt, a photosensitive belt, etc. It also relates to image forming apparatuses such as copying machines, printers, etc., which have a belt driving unit. It also is effectively applicable to a belt (for example, belt for conveying recording medium, and fixation belt of fixing apparatus), which is not directly involved in image formation.
In recent years, image forming apparatuses have been substantially increased in operational speed. There has been a substantial increase in the operational speed of an image forming apparatus. With the increase in operational speed, image forming apparatuses which have multiple image forming portions have become the mainstream image forming apparatuses. In the case of these apparatuses, they are provided with a belt along which multiple image forming portions are aligned in the direction parallel to the moving direction of the belt, and the image forming operations for forming multiple monochromatic images, different in color, are sequentially carried out in a partially overlapping manner. As an example of such a belt, the intermediary transfer belt employed by electrophotographic full-color image forming apparatuses can be listed as a representative one. In an image forming operation of a typical electrophotographic full-color image forming apparatus employing an intermediary transfer member, multiple monochromatic toner images, different in color, are sequentially transferred in layers onto the surface of the intermediary transfer belt, and then, the layered toner images on the intermediary transfer belt are transferred all at once onto recording medium. This type of intermediary transfer belt is suspended and kept stretched by multiple rollers, for example, a belt driving roller (driver roller), to begin with, and is circularly drivable. A belt which is supported and kept stretched by multiple rollers has been known to suffer from the problem that while it is driven, it deviates in position in its widthwise direction, because of the inaccuracy in terms of the external diameter of the rollers, and/or alignment among the belt supporting rollers.
As one of the means proposed to deal with the above described problem (belt deviation), there has been known a method for controlling a steering roller with the use of an actuator (Japanese Laid-open Patent Application H09-169449). Also known as a means to deal with the above-described problem is a structural arrangement which provides an image forming apparatus with a member for regulating the belt deviation (Japanese Laid-open Patent Application 2000-146335).
However, the means disclosed in Japanese Laid-open Patent Application H09-169449 is problematic in that it requires a complicated control algorithm, and also, its high cost attributable to electrical components, such as sensors and actuators, which it requires. The structural arrangement disclosed in Japanese Laid-open Patent Application 2000-146335 does not require sensors and actuators, but, it keeps the regulating member continuously subjected to the force which the belt deviation, generates, limiting thereby the highest speed at which the image forming apparatus can be operated. Further, this solution is problematic in that it is high in the cost for examining and controlling the accuracy with which the regulating member is attached (pasted).
There has been proposed another method for controlling the belt deviation (Japanese Laid-open Patent Application 2001-520611). This method has been known to be smaller in component count, simple, and low in cost. According to this patent application, a steering roller (steering member) automatically centers a belt based on the difference in frictional resistance.
Referring to
Next, referring to
As described already, the end members 91 are held so that they do not follow the belt movement. Therefore, they are always subjected to the friction generated between them and the inward surface of the belt.
a) is a schematic sectional view of the combination of one of the end members 91 and a belt 50 when the belt 50 is being driven in the direction indicated by an arrow mark V by being wrapped around the end member 91. The angle by which the belt 50 wraps around the end member 91 is θs. Here, it is assumed that the width of contact between the end member 91 and belt 50 is a unit width. To think of the belt length equivalent to a differential angle dθ of a given belt wrap angle θ, the belt is slack on the upstream side of the steering member, and is tense on the downstream side of the steering member. Thus, if the belt tension on the upstream side is T, the belt tension on the downstream side is T+dT. These tensions work in the direction parallel to the tangential line to the steering member. Therefore, the amount of force which the belt applies to the end member 91 toward the center of the end member 91 per differential belt length is approximately Tdθ. Thus, if the coefficient of friction between the belt 50 and end member 91 is μs, the amount of friction dF between the belt 50 and end member 91 can be obtained from the following mathematical equation:
dF=μsTdθ (1)
The tension T is governed by an unshown belt driving roller. Thus, if the coefficient of friction of the belt driving roller is νr,
dT=μrTdθ (2)
Thus,
Integrating Equation (2′) over angle of wrap θs, the amount of the tension T is obtainable from the following mathematical equation:
T=T1e−μrθ (3)
Here, T1 stands for the amount of tension at where θ=0.
From Equations (1) and (3),
dF=μsT1e−μ
Referring to
dFs=μsT1e−μrθ sin(θ+α)dθ) (5)
Integrating Equation (5) with the angle θs of wrap,
The amount of the downward force (per unit width), indicated by the arrow mark S, which each end member 91 receives from the belt 70 when the belt 50 is being driven can be obtained from Equation (6).
b) is a plan view of the steering member and belt 50, as seen from the direction indicated by an arrow mark TV in
The direction in which the steering member 97 is tilted by the force resulting from the above described principle is equivalent to the direction in which the belt 50 is to be shifted back. Therefore, the belt 50 is automatically centered.
However, the method for automatically centering the belt, which is proposed in Japanese Laid-open Patent Application 2001-520611, is problematic in that because the steering member 97 is allowed to freely rotate about the steering shaft 95, the steering member 97 is too easily affected by (excessively sensitive to) external shocks. That is, in the case of an intermediary transfer belt, the turning-on, or turning-off, of the electrostatic load in the primary transfer portion, the entrance of a sheet of transfer medium into the second transfer portion, and the like, may be listed as the external shocks.
In the case of the belt centering automatic mechanism disclosed in Japanese Laid-open Patent Application H09-1694449, which is controlled with the use of an actuator or the like, even if the belt steering mechanism is subjected to a large amount of external shock, the inertia of the motor, etc., plays the role of preventing the steering member 97 from being excessively affected by the external shock.
On the other hand, in the case of the belt centering automatic mechanism shown in
Next, referring to
If the belt 50 is driven in the direction indicated by an arrow mark V while remaining in the attitude γ, the belt 50 will be in the position indicated by a broken line at a point (5+Δt) in time. If it is assumed that the position of one of the belt edges in terms of the widthwise direction of the belt is measured at points M1 and M2 at times t and t+Δt, respectively, the point Pt of the belt edge, which is at the point M when the belt edge position is measured, and the point Pt+Δt, which is at the point M when the belt edge position is measured, are the same point of the belt edge. Thus, if there is no belt deviation, the position of the point Pt and the position of the point Pt+Δt in terms of the belt width direction should coincide.
In a case where the belt 50 remains stable in attitude γ while being driven, the locus of the point P of the belt edge between the point Pt and Pt+Δt is parallel to the direction x. In other words, the belt 50 is in the ideal condition. That is, there is no positional deviation of the belt 50 in the direction y (primary scan direction) between the belt edge position detecting points M1 and M2.
Referring to
In the case of Japanese Laid-open Patent Application 2001-520611, the supporting plate 92 is provided with a pair of leaf springs 98, which are at the lengthwise ends of the plate 92, one for one, and the two leaf springs 98 function as a means for regulating the rotational movement of the steering member 97, which occurs when the image forming apparatus (belt steering member) is suddenly subjected to a large amount of external disturbance, such as those described above.
In the case of Japanese Laid-open Patent Application 2001-520611, however, if the image forming apparatus (belt steering member) is suddenly subjected to a large amount of load, the springs 98 are likely to excessively respond as a shock damping absorbing means during the period Tr; they are likely to cause the steering member 97 to overshoot (points OS1, OS2, OS3 . . . ). Further, the steering member 97 changes in the direction, in which it rotationally moves, at the points OS1, OS2, OS3 . . . , as shown in
Therefore, the structural arrangement which regulates the rotational movement of the belt steering member 97 by providing a resistance R, the amount of which is proportional to the steering angle β as shown in
The primary object of the present invention is to provide an image forming apparatus the belt steering member of which is superior in shock resistance to any of the conventional image forming apparatuses which employ a belt steering member.
According to an aspect of the present invention, there is provided a belt driving apparatus for rotationally driving a belt member, said belt member driving apparatus comprising a stretching member for stretching the belt member; steering means including a steering member having a rotatable portion which is rotatable with rotation of the belt member, a frictional portion slidable relative to the belt member and provided at each of longitudinally outsides of said rotatable portion, and further including supporting means supporting said steering member, and a rotation shaft rotatably supporting said supporting means, said steering means being effective to steer the belt member by inclining said steering member by a force produced by sliding between said frictional portion and the belt member; and resisting force applying means for applying a resisting force against inclination of said steering member, the resisting force increases with increase of rate of change of an inclination angle of said steering member with respect to time.
According to another aspect of the present invention, there is provided an image forming apparatus for forming an image comprising said belt, and said belt driving apparatus.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.
a) and 2(b) are perspective views of the intermediary transfer belt unit of the image forming apparatus in the first embodiment of the present invention.
a) and 5(b) are detailed views of one of the end portions of the belt centering automatic mechanism in the first embodiment of the present invention.
a) and 7(b) are graphs for describing the characteristic properties of the resistance (friction) generating means.
a) and 8(b) are graphs for describing the relationship between the belt and friction ring, in terms of the width of the area of contact between the belt and friction ring.
a) and 9(b) are perspective views of the belt centering automatic mechanism in the second embodiment of the present invention.
a) and 13(b) are drawings for describing the principle on which the belt centering automatic mechanism is based.
<Image Forming Apparatus>
Next, the image forming apparatus in this embodiment of the present invention will be described.
First, referring to
<Conveyance of Transfer Medium>
Multiple sheets S of recording medium are stored in layers in a recording medium storing portion 61, being supported by a recording medium lifting apparatus 62. The sheets S of recording medium are fed into the main assembly of the image forming apparatus 60 by a sheet feeding apparatus 63, in synchronism with the progression of an image forming operation. One of the methods for separating one of the sheets of recording medium in the recording medium storing portion is the method which separates one of the sheets S of recording medium from the rest by suction (vacuum). The image forming apparatus 60, shown in
<Image Formation Process>
Next, the image formation process which is carried out in synchronism with the above described conveyance of the recording sheet S to the second transfer portion will be described.
The image forming apparatus 60 in this embodiment has: an image forming portion 613Y which forms an image with the use of yellow (Y) toner; an image forming portion 613M which forms an image with the use of magenta (M) toner; an image forming portion 613C which forms an image with the use of cyan (C) toner, and an image forming portion 613BK which forms an image with the use of black (BK) toner. The image forming portions 613Y, 613M, 613C, and 613BK are the same in structure although they are different in the color of the toner they use. Thus, the image formation process will be described with reference to the image forming portion 613Y.
The image forming portion 613Y, which is a toner image forming means, is made up of: a photosensitive member 608, which is an image bearing member; a charging device 612 for charging the photosensitive member 608; an exposing apparatus 611a; a developing apparatus 610; a first transferring apparatus 607; and a photosensitive member cleaner 609. The photosensitive member 608 is rotated in the direction indicated by an arrow mark m in the drawing. As the photosensitive member 608 is rotated, its peripheral surface is uniformly charged by the charging device 612. The charged portion of the peripheral surface of the photosensitive member 608 is exposed by the exposing apparatus 611a. More specifically, as the exposing apparatus 611a is driven, a beam of light is projected from the exposing apparatus 611a, while being modulated by the inputted signals which reflect the information of the image to be formed. This beam of light is deflected so that it scans the charged area of the peripheral surface of the photosensitive member 608. As a result, an electrostatic latent image is effected upon the peripheral surface of the photosensitive member 608. Then, the electrostatic latent image is developed by the developing apparatus 610. As a result, a visible image is formed of toner (yellow toner, in this case), on the peripheral surface of the photosensitive member 608 (this visible image will be referred to as toner image, hereafter). Then, the yellow toner image is transferred onto the intermediary transfer belt 606, which is the first transfer member, by a preset amount of pressure applied by the first transferring member 607 and a preset amount of electrostatic bias (load) applied between the photosensitive member 608 and first transferring member 607. Thereafter, the transfer residual toner, that is, the toner remaining on the peripheral surface of the photosensitive member 608 after the transfer, is recovered by the photosensitive member cleaner 609, to prepare the photosensitive member 608 for the next image formation.
There are four image forming portions 613, that is, image forming portions for forming yellow (Y), magenta (M), cyan (C), and black monochromatic toner images, one for one, in the image forming apparatus 60, shown in
Next, the intermediary transfer belt 606 will be described. The intermediary transfer belt 606 is supported and kept stretched by four rollers, more specifically, a driver roller 604 which is a belt driving member; a steering roller 1, which is a belt steering member; a tension roller 617 which is a belt tensioning member; and a second transfer roller 603 which is on the inward side of the loop which the belt forms. The intermediary transfer belt 606 is an endless belt, and is driven in the direction indicated by the arrow mark V in the drawing.
The steering roller 1 functions also as a belt tensioning roller, which provide the intermediary transfer belt 606 with a preset amount of tension, in coordination with the tension roller 617. The above described image formation process is carried out in the image forming portions 613Y, 613M, 613C, and 613BK, with such timings that the image formed in the downstream image forming portion of the adjacent two image forming portions will be transferred onto the intermediary transfer belt 606 in such a manner that it will be layered upon the image having formed in the upstream image forming portion and having transferred upon the intermediary transfer belt 606. Consequently, a full-color toner image is effected upon the intermediary transfer belt 606. This full-color toner image is conveyed to the second transfer portion. Incidentally, the number of the rollers by which the intermediary transfer belt 606 is supported and kept stretched, does not need to be limited to that in
<Process after Second Transfer>
As the recording sheet S is conveyed to the second transfer portion in synchronism with the formation of the full-color toner image on the intermediary transfer belt 606, the full-color toner image formed through the above described image forming process and transferred onto the intermediary transfer belt 606 is transferred onto the recording sheet S in the second transfer portion. Then, the recording sheet S is conveyed to the fixing apparatus 68 by a recording medium conveying portion 67, which is between the second transfer portion and fixing apparatus 68. Although there are many structural arrangements and fixing methods for a fixing apparatus, the fixing apparatus 68, which is shown in
<Structural Arrangement for Steering Intermediary Transfer Belt>
a) and 2(b) are perspective views of the intermediary transfer belt unit 50 of the image forming apparatus 60 shown in
<Details of Structure of Belt Centering Automatic Mechanism>
Next, referring to
a) and 5(b) are detailed drawings of one of the lengthwise end portions of the belt centering automatic mechanism.
Each of the pair of friction rings 3 is shaped like a friction rings 3a, shown in
Also in this embodiment, the width of the intermediary transfer belt 606 is more than that of the roller 2, and is less than that of the steering member 1 (roller 2+two friction rings 3 located at lengthwise ends, respectively, of roller 2). Thus, when the intermediary transfer belt 606 is remaining ideally positioned (centered), the relationship between the intermediary transfer belt 606 and friction rings 3 in terms of area of contact is as shown in
Next, the coefficient μs of static friction of the friction rings 3a will be described.
Concretely describing, in a case where the friction rings 3 in this embodiment are tapered as shown in
Further, it is assumed that the coefficient of friction of the peripheral surface of each friction ring 3 is greater than that of the peripheral surface of the roller 2. The material of the friction ring 3a is resinous substance, such as polyacetal (POM), which is relatively slippery. Further, in consideration of the electrostatic problem attributable to the electricity generated by the friction between the friction rings 3a and intermediary transfer belt 606, the material for the friction ring 3a is made electrically conductive. Incidentally, in a case where the friction rings 3 are shaped as shown in
Next, the coefficient μSTR of static friction of the roller 2 will be described. The roller 2 is formed of aluminum. Its peripheral surface is made to be roughly 0.1 in coefficient μSTR of static friction; μSTR≈0.1. That is, it is made lower than the coefficient μs of friction of the friction rings 3.
The substrate layer of the intermediary transfer belt 606 is made of polyimide, and is roughly 18,000 N/cm2 in coefficient of tensional elasticity (E): E≈18,000 N/cm2. A large amount of tensional stress, which occurs in a substance which is large in coefficient of tensional elasticity E, can be efficiently converted into the belt centering force, by reducing the roller 2 in coefficient μs of friction.
At the same time, because the distortion which occurs to the intermediary transfer belt 606 is continuously released, it does not occur that the intermediary transfer belt 606 is driven while remaining subjected to the excessive amount of load.
Therefore, not only is the intermediary transfer belt 606 automatically centered, but also, it is prevented from breaking or suffering from the like problems. Incidentally, it is not mandatory that the material for the substrate layer of the intermediary transfer belt 606 is polyimide. It may be a resinous substance other than polyimide, or a metallic substance, as long as the substance is similar in coefficient of tensional elasticity to polyimide, and is unlikely to easily stretch. Further, the material for the roller 2 may be a substance other than aluminum, as long as the substance can meet the following requirement: it prevents the problem that μSTR≦μ.
At this time, the method for measuring the coefficient of friction of the friction ring 3, roller 2, driving roller, etc., described above, will be described. The coefficients of friction of the components of the belt steering automatic mechanism in this embodiment were measured with the use of the method for testing coefficient of plastic film and sheet (JIS K7125). More concretely, a piece of the inward layer of the intermediary transfer belt 606, which in this embodiment is made of polyimide, is used as a test piece.
Next, the rotary damper 20 will be described. Referring to
Further, even in terms of the evaluation of the belt centering automatic mechanism from the standpoint of control, the belt edge movement in the direction y quickly returns to the normal range, without overshooting, as shown in
The present invention is related to the improvement of a belt centering automatic mechanism in terms of responsiveness. Therefore, it is reasonable to think that the present invention is applicable to a wide range of belt driving apparatuses, regardless of the presence of an image forming apparatus. For example, in the case of the fixing apparatus 68 shown in
<Characteristic Features of Belt Centering Automatic Mechanism, and Tuning of Mechanism in Torque>
In this embodiment, the belt centering automatic mechanism has to be adjusted (tuned) in belt centering property, and in the torque of the rotary damper 20. The material of the intermediary transfer belt 606 is polyimide, or the like, which is relatively high in elasticity. Therefore, it is limited in the steering range in which the belt can be automatically centered by the resistance attributable to the tensional stress of the belt itself. In this embodiment, the range is roughly ±2°. However, the overall length of the steering member 1 is roughly 370 mm, which is relatively long. Therefore, the range of the positional deviation of the intermediary transfer belt 606, in terms of the movement of its lengthwise ends, is roughly 13 mm, which is sufficient. That is, in the case of a structural arrangement for a belt centering automatic mechanism which directly uses the steering speed dβ/dt of the steering shaft 21 as shown in
Therefore, even if the steering speed dβ/dt is low, the amount by which the resistance R is generated by the rotary damper 20 can be increased by adjusting the gear ratio between the gears 40 and 41 in accordance with the belt centering property of the belt centering automatic mechanism. Further, this method uses the pair of gears to adjust the amount by which the damper 20 can provide resistance. Therefore, the employment of the structural arrangement shown in
As described above, the employment of this embodiment can provide a belt centering automatic mechanism with such a resistance that is effective to only a sudden and large amount of external disturbance, and yet, does not interfere with the normal belt centering function. In other words, it can minimize the weakness of a conventional belt centering automatic mechanism. Therefore, it can provide a belt driving apparatus, the steering shaft of which is significantly more shock resistant, and which is significantly less likely to suffer from sudden change in attitude of its belt, and consequential misalignment of monochromatic images in terms of the primary scan direction, than any of the conventional belt driving apparatuses. In particular, the application of this embodiment to an intermediary transfer belt unit, and an image forming apparatus having an intermediary transfer belt can solve the two problems, that is, poor image quality and belt deviation, while reducing the apparatus in cost.
a) and 9(b) are perspective views of the belt centering automatic mechanism in the second embodiment of the present invention. More specifically, they are perspective views of the essential portions of the belt centering automatic mechanism of the intermediary transfer belt unit 50 (
The direct damper 170 also is a resistance generating means which uses the viscous resistance of oil or the like, as does the rotary damper 20 in the first embodiment. Therefore, the amount of resistance R it generates is proportional (theoretically) to the steering speed dβ/dt, as shown in
As described above, the usage of this embodiment can also provide a belt centering automatic mechanism which resists only a large amount of sudden external disturbance, that is, which does not interferes with the normal belt centering operation. In other words, it can minimize the weakness of a conventional belt centering automatic mechanism, that is, excessive sensitivity of the steering shaft to a large amount of sudden external disturbance. Thus, it can provide a belt driving apparatus which is significantly less likely to suddenly change the belt in attitude, and therefore, is significantly less in the amount of the misalignment of monochromatic images, different in color, in the primary scan direction, which is attributable to the sudden change of the belt attitude, than any of the conventional belt driving apparatus.
The first and second embodiments described above were related to the intermediary transfer intermediary transfer belt unit 50, and the image forming apparatus 60 which has the intermediary transfer intermediary transfer belt unit 50. This embodiment is related to a belt involved in image formation other than the belts in the first and second embodiments. More specifically, this embodiment is related to the direct transfer belt 71, with which the image forming apparatus 70 shown in
The image forming portion 613 is made up of primarily: a photosensitive member 608; a charging device 612; an exposing apparatus 611a; a developing apparatus 610; a transferring apparatus 73; and a photosensitive member cleaner 609. The photosensitive member 608 is rotated in the direction indicated by an arrow mark m in the drawing. As the photosensitive member 608 is rotated, its peripheral surface is uniformly charged by the charging device 612. The charged portion of the peripheral surface of the photosensitive member 608 is exposed by the exposing apparatus 611a. More specifically, as the exposing apparatus 611a is driven, a beam of light is projected from the exposing apparatus 611a while being modulated with the inputted signals which reflect the information of the image to be formed. This beam of light is deflected by the beam deflecting means 611b, etc., so that it scans the charged area of the peripheral surface of the photosensitive member 608. As a result, an electrostatic latent image is effected upon the peripheral surface of the photosensitive member 608. Then, the electrostatic latent image is developed by the developing apparatus 610 which uses toner. As a result, a visible image is formed of toner (yellow toner, in this case), on the peripheral surface of the photosensitive member 608 (visible image will be referred to as toner image, hereafter). Meanwhile, the recording sheet S is released by a pair of registration roller 32 in synchronism with the formation of the yellow toner image in the most upstream image forming portion 613 (613Y). Then, the recording sheet S is held to the recording sheet holding surface of the direct transfer belt 71 by the static electricity or the like, and is conveyed further by the direct transfer belt 71. As the recording sheet S is conveyed by the direct transfer belt 71, the toner image on the photosensitive member 608 is transferred onto the recording sheet S by the pressure and electrostatic bias (load) applied by the transferring apparatus 73. The image forming and transferring operations similar to the one described above are carried out, sequentially and partially overlapping manner, in the downstream image forming portions, that is, the magenta (M), cyan (C), and black (BK) image forming portions. Then, the images are sequentially transferred onto the recording sheet S on the direct transfer belt 71 which is being driven, with such timings that the images formed in the downstream image forming portions are layered upon the images formed and transferred in the upstream image forming portions. Consequentially, a full-color toner image is effected on the recording sheet S. Then, the recording sheet S is separated from the direct transfer belt 71, and is conveyed to the fixing apparatus 68 by the recording sheet conveying portion 67, which is between the recording sheet separating portion and the fixing apparatus 68. The transfer residual toner, that is, a small amount of toner remaining on the peripheral surface of the photosensitive member 608 after the direct transfer, is recovered by the photosensitive member cleaner 613 to prepare the photosensitive member 608 for the next image formation. In the case of the image forming apparatus shown in
Next, the direct transfer belt unit, which is a belt driving unit for driving the direct transfer belt 71, will be described about its structure. The direct transfer belt 71 is suspended and kept stretched by a driver roller 604, steering member 1, and a pair of follower rollers 72 and 617, and is driven in the direction indicated by an arrow mark V in the drawing. The follower rollers 72 and 617 are allowed to freely rotate, and rotate following the rotation of the direct transfer belt 71. The steering member 1 doubles as a tension roller for providing the direct transfer belt 71 with a preset amount of tension.
The structural arrangement for supporting the steering member 1 in this embodiment is the same as that of the belt centering automatic mechanism described above with reference to
Incidentally, the image forming portion 613 in this embodiment, which is shown in
The belt involved in image formation in this embodiment is a photosensitive belt 81 with which the image forming apparatus 80 is provided. Basically, the image forming apparatus 80 shown in
The image forming portion 6130 is made up of primarily: a photosensitive belt 81; a charging apparatus 84; an exposing apparatus 611a; a developing apparatus 610; etc. The photosensitive belt 81 has a photosensitive layer as its surface layer. It is suspended and kept stretched by a driver roller 604, a steering member 1, a follower roller 617, and an inward transfer roller 82, and is driven in the direction indicated by an arrow mark V in the drawing. The follower roller 617 is allowed to freely rotate, and rotates following the movement of the photosensitive belt 81. The inward transfer roller 82 a roller disposed on the inward side of the photosensitive belt loop back up the photosensitive belt 81 against a transfer roller 83. As the photosensitive belt 81 is driven in the arrow V direction, its peripheral surface is uniformly charged by the charging apparatus 84. The charged portion of the peripheral surface of the photosensitive belt 81 is scanned by the exposing apparatus 611a, whereby an electrostatic latent image is formed on the photosensitive belt 81. More specifically, as the exposing apparatus 611a is driven, a beam of light is projected from the exposing apparatus 611a while being modulated with the inputted signals which reflect the information of the image to be formed. This beam of light is deflected by the beam deflecting means 611b, etc., so that it scans the charged area of the peripheral surface of the photosensitive belt 81. As a result, an electrostatic latent image is effected upon the peripheral surface of the photosensitive belt 81. Then, the electrostatic latent image is developed by the developing apparatus 610 which uses toner. As a result, a visible image is formed of toner, on the peripheral surface of the photosensitive belt 81 (visible image will be referred to as toner image, hereafter). The image forming and transferring operations similar to the one described above are carried out in yellow (Y), magenta (M), cyan (C), and black (BK) image forming portions, starting from the yellow (Y) image forming portion, that is, the most upstream one, sequentially and in a partially overlapping manner, with such timings that the images formed in the downstream image forming portions are layered upon the images form in the upstream image forming portions. Consequentially, a full-color toner image is effected on the photosensitive belt 81. Then, as the photosensitive belt 81 is circularly driven further, the full-color toner image is conveyed to the transfer nip, which is formed by the inward transfer roller 82 and outward transfer roller 83. The transfer of the full-color toner image onto the recording sheet S in the transfer nip, and the transfer timing, are basically the same as those of the image forming apparatus of the intermediary transfer type described with reference to
The structural arrangement for supporting the steering member 1 in this embodiment is the same as that of the belt centering automatic mechanism described above with reference to
As described above, the present invention which is related to a belt centering automatic mechanism based on the difference in friction is characterized in that it is provided with a means for increasing the amount of resistance R in proportion (theoretically) to the change in the steering angle β of the steering member 97 per unit length of time t (dβ/dt), instead of the steering angle β alone. The characteristic of the steering action of a belt centering automatic mechanism based on friction is that its cycle of response is very long, that is, the peripheral surface of the steering shaft is in the range in which the rate of shear is very low. On the other hand, a large amount of sudden external disturbance, to which a belt centering automatic mechanism is desired to be virtually immune, makes the steering shaft substantial in shear speed. Therefore, as long as the belt centering automatic mechanism is operating in the normal range, the effects of the resistance R is very small; only as the image forming apparatus is suddenly subjected to a substantial amount of external disturbance, the resistance R becomes large enough to prevent the steering shaft from excessively react to the disturbance.
As described above, according to the present invention, as long as the shear speed of the peripheral the steering shaft remains low, the effect of the friction between the belt and friction rings is very small, and only as the belt centering automatic mechanism is subjected to a large amount of sudden external disturbance, the friction provide the steering member with a large amount of resistance to the external disturbance. In other words, the present invention can eliminate the flaw of conventional belt centering automatic mechanisms, that is, the excessive sensitivity to a large amount of sudden external disturbance. Therefore, it can provide a belt centering automatic mechanism which prevents a belt from being suddenly changed in attitude, and therefore, can minimize the misalignment among monochromatic color images, different in color, in the primary scan direction, which is attributable to the sudden change in the belt attitude.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 134185/2009 filed Jun. 3, 2009, which is hereby incorporated by reference.
Number | Date | Country | Kind |
---|---|---|---|
2009-134185 | Jun 2009 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
5659851 | Moe et al. | Aug 1997 | A |
5737003 | Moe et al. | Apr 1998 | A |
6134406 | Moe et al. | Oct 2000 | A |
6181900 | Lee et al. | Jan 2001 | B1 |
6804486 | Lee et al. | Oct 2004 | B2 |
6816691 | Kabata et al. | Nov 2004 | B2 |
RE41934 | Maruta et al. | Nov 2010 | E |
7873311 | Hara | Jan 2011 | B2 |
8045905 | Hara | Oct 2011 | B2 |
8112021 | Mochizuki | Feb 2012 | B2 |
20030035661 | Kabata et al. | Feb 2003 | A1 |
20030129000 | Lee et al. | Jul 2003 | A1 |
20060100046 | Fuse | May 2006 | A1 |
20070283624 | Yasumoto | Dec 2007 | A1 |
20080260424 | Hara et al. | Oct 2008 | A1 |
20100247174 | Hori et al. | Sep 2010 | A1 |
Number | Date | Country |
---|---|---|
1773392 | May 2006 | CN |
101324769 | Dec 2008 | CN |
2003512 | Dec 2008 | EP |
09-169449 | Jun 1997 | JP |
2000-089588 | Mar 2000 | JP |
2000-146335 | May 2000 | JP |
2001-520611 | Oct 2001 | JP |
Number | Date | Country | |
---|---|---|---|
20100310286 A1 | Dec 2010 | US |