The invention relates to an image forming apparatus, and particularly to photosensitive drums in which an insert is provided for reducing noise and/or vibration.
Image forming apparatuses, such as printers or photocopiers, include a photosensitive member, typically in the form of a photosensitive drum. The performance of the photosensitive drum is of critical importance, since the image being produced (or reproduced) is formed and developed on the drum surface. The developed image is then transferred from the drum to, for example, a sheet of paper. Typically, the drum is formed of metal, such as aluminum, and the metal is anodized or coated with a thin dielectric layer. Normally, the drum is then coated with photogeneration and photoconduction layers over the dielectric layer.
In forming an image, the drum is rotated, and a given location on the outer surface of the drum is thereby rotated past a charging device, an exposure location, a developing location (at which toner is applied), a transfer location (at which the toner image is transferred from the drum to paper), and a cleaning location at which a cleaning blade removes excess toner from the drum so that the process can be repeated. During an image forming operation, as a result of the rotation of the photosensitive drum and its interaction with the various other components of the image forming apparatus, noise and vibration can occur. This is particularly true since the photosensitive drum is a thin-walled metal drum, and thus has a characteristic harmonic sound spectrum which is easily driven by any mechanical resonance.
For example, vibration (and associated noise) can occur from the rotation of the drum, and any imperfections of the drum, the gear flanges attached to the drum, and/or the drive which interacts with the gear flanges of the drum. Further, an alternating current (AC) electric field is applied to the charge roller, and the alternating current can also cause noise and/or vibration of the drum or between the drum and other components. In addition, as the drum rotates past the cleaning blade (which is in contact with the drum), noise is often generated, particularly if the drum surface is roughened by use. This interaction between the drum and cleaning blade is also known as chatter vibration or xe2x80x9cstick-slipxe2x80x9d vibration. (See, e.g., Chatter Vibration of a Cleaner Blade in Electrophotography, by Kawamoto, in the January/February 1996 issue of Journal of Imaging Science and Technology.) The noise and vibration associated with operation of a photosensitive drum not only presents an annoyance to workers using (or in the vicinity of the image forming apparatus, but also, the noise/vibration can lead to image deterioration or damage to the apparatus. In particular, the vibration can result in poor performance or interaction between the photosensitive drum and one or more of the components with which the drum interacts, including the cleaning blade, the charge roller, the developer device and the like.
Vibration may also cause image blurring especially with the current trend to higher resolution devices (evolution from 300 to greater than 1200 dots per inch). For example, if the cleaning blade does not properly remove residual toner, undesirable resolution of character images can occur in subsequent images. Further, if the drum is not charged or developed properly, the resulting image can have white spaces where the image has not been properly formed, developed or transferred, or black spots where undesired toner has been transferred to the sheet of paper. Noise problems can also occur as a result of the generation of gases (ozone) which occurs during an image forming operation, however this noise is typically relatively small.
To eliminate noise and/or vibration, the physical characteristics of the drum can be modified, for example, by increasing the thickness of the drum. Thus, the drum can be designed so that its natural frequency differs from that of other components of the apparatus and/or that of the process cartridge (the unit within which the drum is disposed). As a result, the vibrations are eliminated or reduced, or the frequency of the noise which might occur can be shifted so that it is outside of the audible range. However, increasing the thickness of the drum can make the drum more expensive to manufacture, particularly if the tooling utilized to manufacture a drum must be replaced. Moreover, when photosensitive drums are manufactured as replacement parts, they will often be inserted into process cartridges of another manufacturer. The process cartridge could be refurbished or a newly manufactured replacement process cartridge of a different manufacturer than that of the photosensitive drum, and the manufacturer/refurbisher of the process cartridge could change (or the design of a given manufacturer/refurbisher could change). Thus, it can be difficult to simply select a thickness of the drum which will be suitable for avoiding noise problems, since even if a thickness is selected for a certain process cartridge, that thickness could be unsuitable for another process cartridge. As a result, noise problems can be particularly problematic with photosensitive drums manufactured as replacement parts.
A further difficultly which can arise with photosensitive drums is that the roundness or circularity of the drum can vary over time, which can also lead to image deterioration. The roundness or circularity of the drum can more rapidly deteriorate if the drum is vibrating and contacting other components disposed about the drum. This problem can also be reduced by providing a thicker drum, however as discussed above, increasing the thickness of the drum can increase the cost, from a materials standpoint and/or the requirement for new tooling.
An alternate solution which has been utilized in the past for solving noise and/or vibration problems has been to insert plugs within the photosensitive drum. U.S. Pat. No. 5,488,459 to Tsuda et al. discloses an example of such an approach. With this solution, a disk or cylindrical object is inserted into the drum, and the insert provides additional weighting to the drum to alter the mass/frequency characteristics of the drum. However, the use of plug-type inserts is undesirable for a number of reasons. First, the plug is often required to be positioned at a precise location within the drum, which can complicate the manufacturing process. Further, the plug must be secured in place, which can require the use of an adhesive, thus further complicating the manufacture/assembly process. Further, the plug must be precisely manufactured. If it is too large, it could cause deformation of the drum, or require a high insertion force, which complicates the assembly process.
For example, it is ideal to use expanding chucks to hold a photosensitive drum by its inner surface during certain manufacturing processes, since damage to the outer surface of the drum is prevented. However, expanding chucks have limited holding ability. Therefore, if a high insertion force is required to insert a plug into a photosensitive drum, it may not be possible to use an expanding chuck to hold the drum during insertion without distorting the shape of the drum. On the other hand, if the plug is too small, it can be difficult to position the plug within the drum and secure the plug in place. Thus, the use of a plug or weight which is inserted inside of the drum has been less than optimal.
Another problem that has arisen with respect to inserts that are bonded to the inside of a photosensitive drum, is that in recycling such equipment, dissimilar materials must be separated from each other. For example, photosensitive drums are typically made from aluminum, while inserts are typically made of rubbers, plastics or foams. Therefore, in order to recycle the drum, the drum must be separated from the insert. If, however, the insert has been bonded to the inside of the photosensitive drum with an adhesive, extreme measures must be taken to remove the insert from the drum.
Similar problems arise with respect to the mounting of end pieces to a photosensitive drum, such as gears and/or flanges. For example, if a gear is attached to the end of a photosensitive drum, to provide an interface with a toothed gear of a motor, and thereby transmit rotational forces to the drum, the gear must be anchored with sufficient strength to withstand such rotational forces over its useful life span. It has been well-known to use adhesives, or to cut an end of the drum to provide a keyway, or other mechanical interlacing techniques to attach a gear to a drum. However, the use of adhesives causes problems discussed above with respect to drum inserts. Furthermore, specialized machining of the drum ends may require special tooling.
In view of the foregoing, a device and method are needed for reducing noise and/or vibration in image forming apparatus, particularly noise and/or vibration associated with operation of a photosensitive drum. Such a device and method are preferably suitable for use in both original equipment and for replacement parts.
It is an object of the present invention to provide a device and method for reducing noise and/or vibration in an image forming apparatus.
It is another object of the invention to provide a device and method for eliminating or reducing noise or vibration which can occur during operation of a photosensitive drum in original equipment of an image forming apparatus, or during operation of replaced or refurbished parts of an image forming apparatus.
It is a further object of the invention to provide a device and method which will provide for more reliable and consistent performance of a photosensitive drum in an image forming apparatus.
It is a further object of the invention to provide an insert device for a photosensitive drum which can be easily installed inside of a photosensitive drum, without requiring the insert to be bonded within the drum.
It is yet another object of the invention to provide a drum with an insert and an end piece such as a gear and/or flange which does not require adhesive or special machining of the drum to anchor the end pieces or the insert to the drum.
Another object of the invention is to provide an insert for a photosensitive drum which can be inserted and removed without damaging the photosensitive drum.
The above and other objects and advantages are achieved in accordance with the present invention by providing a noise prevention device inserted into a photosensitive drum and which is constructed of an elastic member having, in a relaxed state, an outer diameter which is larger than an inner diameter of the inner surface of the photosensitive drum. According to the invention, the insert is configured such that when the elastic member is elongated in a longitudinal direction, the outer diameter of the elastic member may be elastically reduced to a diameter equal to or less than the inner diameter of the photosensitive drum. Therefore, the insert may be installed to the interior of a photosensitive drum by elongating the insert then releasing the insert so that it expands into contact with the inner surface of the drum such that a pressure contact between the insert and the drum increases, since the outer diameter of the insert, in a relaxed state, is larger than the inner diameter of the drum. The inner diameter, outer diameter and material used for constructing the insert are chosen such that, in a relaxed state, and after being inserted into the photosensitive drum, the insert provides sufficient force or pressure contact against the inner surface of the drum such that the insert is anchored to the inside of the drum. The insert can also be compressed (with or without elongating the insert) as it is placed in the drum, such that once the insert is inside of the drum, the elasticity of the insert urges it against the inner surface of the drum to hold the insert in place within the drum. Therefore, the complications associated with using adhesive to bond an insert to the interior of a photosensitive drum are avoided and recycling of the drum is simplified since the insert may be removed relatively easily. Furthermore, since the insert can be inserted with little or no insertion force, the drum is rendered more durable and less susceptible to deformation or deviation in roundness about the circumference of the drum.
In a presently preferred form of the invention, the insert is made from an elastomeric material and is structured such that when it is elongated in a longitudinal direction, the outer diameter can be reduced within the elastic range of deformation of the insert such that the outer diameter of the insert can be made smaller than the inner diameter of the drum. Furthermore, the outer diameter of the insert in a relaxed state, is such that a frictional force between the outer surface of the insert and the inner surface of the drum, maintains the radially outward force necessary for anchoring the insert within the photosensitive member. The present invention can therefore avoid the need for adhesive and provides an insert that is relatively simple to insert into and remove from a photosensitive member, with little or no insertion force.
Preferably, the elastic member is in the form of a corrugated sleeve, where the outer diameter of the sleeve is larger than the inner diameter of the photosensitive drum. By constructing the insert as such, upon elongation, the folds forming the corrugated sleeve are easily flattened, thereby allowing the outer diameter of the sleeve to be easily reduced, which simplifies insertion and reduces forces necessary for insertion. Additionally, the corrugated sleeve may include at least one closed end. By providing the sleeve with at least one closed end, the insert can be elongated by inserting a tool into an end of the insert opposite the closed end, then pressing the tool against the closed end, so as to elongate the insert. Since the insert is configured such that the outer diameter of the insert can be elastically reduced to be smaller than the inner diameter of the drum, at least a portion of the elastic member can be elongated such that the inner diameter of the elastic member is constricted, thereby allowing the elastic member to be inserted into the drum with little or no insertion force. Once the pressure from the tool is released, the outer surface of the elastic member is pushed against the inner surface of the drum, thereby anchoring the insert within the drum. Similarly, in order to remove the insert, the tool can be inserted into the same position as during insertion, and pushed until the insert is completely removed from the drum. Therefore, insertion and removal can be performed by inserting a tool into the same end of the drum, thereby simplifying insertion and removal procedures.
According to a further aspect of the present invention, a method for inserting an elastic insert into a photosensitive drum includes the steps of elastically elongating an insert which has an outer diameter that is greater than an inner diameter of a photosensitive drum, such that an outer diameter of the insert is contracted to a diameter that is less than an inner diameter of the photosensitive drum. The insert is then inserted into the drum and released so as to allow the insert to return to a relaxed state, and thereby increase a contact pressure between the insert and the inner surface of the drum.
According to another aspect of the present invention, a tool includes first and second engaging devices which are commonly connected to a controlling device. The controlling device is configured to move the first and second engaging devices relative to each other. In a presently preferred embodiment, the engaging devices are configured to engage first and second ends of an inner surface of an elastic insert for a photosensitive drum, and the controlling device is configured to move the first and second engaging devices relative to each other along a first direction, so that the elastic insert can be stretched. With such a tool, an elastic insert, such as the inserts described with respect to the above aspects and embodiments of the present invention, can be inserted into a photosensitive drum. Preferably, the controlling device is configured to move the first and second engaging devices with sufficient force so as to elongate an elastic insert such that an outer diameter of the insert is reduced to a diameter less than the inner diameter of the drum.
The arrangement of the present invention is advantageous in a number of respects. First, since the outer surface of the insert is in contact with the inner surface of the photosensitive drum, the insert can vary the mass/frequency characteristics of the drum, to thereby ensure that the resonance frequency of the drum is outside of the audible range, or does not match the resonance frequency of other components of the apparatus. Further, since the elastic member of the noise prevention device can be elongated so as to have a diameter less than that of the inner surface of the drum, the noise prevention device can be inserted with little or no insertion force, thereby preventing damage during the assembly of the drum with the noise prevention device. A further advantage is that the drum and insert material can be easily recycled, since it is not necessary to use an adhesive to bond the insert with the interior of the drum.
Additionally, during transportation of photosensitive drums from a manufacturer to a downstream user, assembled photosensitive drums may be exposed to temperatures between xe2x88x9220xc2x0 C. and 40xc2x0 C., or even temperatures as extreme as xe2x80x9440xc2x0 C. to 80xc2x0 C. The exposure of drums to such thermal cycling has caused photosensitive drum inserts to become dislodged from the inner surface of the drum, thereby changing the characteristics of noise suppression in the image forming apparatus during use. For example, such thermal cycling has caused an insert to drop completely out of a photosensitive drum if the end of the drum is not closed with a gear for example. If the drum includes a gear or flange attached to the end thereof, the insert may move within the drum thereby changing the noise dampening effect of the insert. Additionally, the movement of the insert may damage the gear and/or flanges provided at the ends of the drum. Although adhesives have been used in the past to ensure the positioning of an insert within a drum, differences in the coefficients of thermal expansion between the adhesives, the insert, and the drum have caused adhesives to rupture during cyclic thermal encountered during transportation of drums. Therefore, by removing the need for adhesives to maintain the position of the insert within a photosensitive drum, the present invention is not affected by problems caused by adhesive that has been ruptured by thermal cycling.
According to alternate embodiments of the invention, the insert includes a plurality of projections which are compressed to allow the insert to be placed inside of the drum. These projections can include a plurality of annular projections or a plurality of smaller projections positioned about the circumference and along the length of the elastic member or insert.