Patent Grant
8078079
Cross-reference is made to copending U.S. patent application Ser. No. 11/959,016, entitled “Upper Seal for Inhibiting Doctor Blade Toner Leakage,” filed Dec. 18, 2007 and U.S. patent application Ser. No. 11/959,058, entitled “Developer Roll Lip Seal”, filed Dec. 18, 2007 both assigned to the assignee of the present invention.
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1. Field of the Invention
The present invention relates generally to image-forming devices, and more particularly, to the cooling of a toner cartridge in an image-forming device.
2. Description of the Related Art
Image forming devices such as laser printers utilize a light beam that is focused to expose a discrete portion of a photoreceptive or image transfer drum in order to attract printing toner to these discrete portions. One component of a laser printer is the photoreceptive drum assembly. The photoreceptive drum assembly is made out of photoconductive material that is discharged by light photons, typically emitted by a laser. The drum is initially given a charge by a charge roller. As the photoreceptive drum revolves, the printer directs a laser beam across the surface to discharge certain points. In this way, the laser “draws” the letters and images to be printed as a pattern of electrical charges—an electrostatic latent image. The system can also work with either a more positively charged electrostatic latent image on a more negatively charged background, or on a more negatively charged electrostatic latent image on a more positively charged background.
The printer's laser or laser scanning assembly draws the image to be printed on the photoreceptive drum. A known laser scanning assembly may include a laser, a movable mirror, and a lens. The laser receives the image data defined by pixels that make up the text and images one horizontal line at a time. As the beam moves across the drum, the laser emits a pulse of light for every pixel to be printed. Typically, the laser does not actually move the beam. Instead, the laser reflects the light beam off a movable mirror. As the mirror moves, the light beam passes through a series of lenses. This system compensates for the image distortion caused by the varying distance between the mirror and points along the drum. The laser assembly moves in one plane horizontally as the photoreceptor drum continuously rotates, so the laser assembly can draw the next line. A print controller synchronizes this activity. In the process of forming the latent image on the photoreceptive drum, the laser discharges those areas where the latent image is formed.
When the toner becomes electrostatically charged, the toner is attracted to exposed portions of the image transfer drum. After the data image pattern is set, charged toner is supplied to the photoconductive drum. Because of the charge differential, the toner is attracted to and clings to the discharged areas of the drum, but not to the similarly charged “background” portions. Toner is an electrostatically charged powder with two main ingredients, pigment, and plastic. The pigment provides the coloring, such as black in a monochrome printer, or cyan, magenta, yellow, and black in a color printer, and forms the text and images. The pigment is blended with plastic particles so the toner will melt when passing through the heat of a fuser assembly. The toner is stored in a toner cartridge housing, a small container built into a removable casing. The printer gathers the toner from a sump within the housing and supplies it to a developer unit using paddles and transfer rollers. The developer roll is a charged rotating roller, typically with a conductive metal shaft and a polymeric conductive coating, which receives toner from a toner adder roll positioned adjacent the developer roll. Due to electrical charge and mechanical scrubbing, the developer roll collects toner particles from the toner adder roll. A doctor blade assembly engages the developer roll to provide a consistent coating of toner along the length and surface of developer roll by scraping or “doctoring” excess toner from the developer roll. The doctor blade may also induce a charge on the toner. This, in turn, provides a consistent supply of toner to the photoconductive drum. When the coating of toner on the developer roll is inconsistent, too thick, too thin, or bare, the coating of the photoconductive drum is inconsistent, and the level of darkness of the printed image may vary due to these inconsistencies. This condition is considered a print defect.
The electrostatic image on the photoconductive drum is charged such that the toner particles move from the developer roll onto the latent image on the photoconductive drum to create a toned image on the photoconductive drum. The toned image is transferred from the photoconductive drum to a printable medium such as paper or onto a intermediate transfer belt which then transfers the toned image onto the printable medium. The paper or transfer belt is oppositely charged to the toner, causing it to transfer to the paper or transfer belt. This charge is stronger than the charge of the electrostatic image, so the paper or belt pulls the toner particles away from the surface of the photoconductive drum. Since it is moving at the same speed as the drum, the paper or transfer belt picks up the image pattern exactly.
One problem that often occurs in a laser printer or other image-forming device is toner leakage. Toner from the sump can leak into the toner cartridge and interfere with the proper operation of the unit. One significant area of toner leakage is a path along portions of the developer roll where a J-seal, positioned proximate both ends of the developer roll, slidably engages the developer roll, particularly where the developer roll, doctor blade, and J-seal all meet. These locations are difficult to seal due to the tolerances, stiffness, and deflections of the aforementioned components. Observations of operational toner pressure as well as vibration and drop testing have demonstrated that the areas around the surface of the developer roll and the J-seal are a frequent toner leak path, especially in higher volume housings.
The interface between the developer roll and the J-seal, identified on the developer roll as the “clean band,” creates heat inside the toner cartridge when the developer roll turns. Friction is unavoidable with current designs because the J-seal must contact the developer roll around its periphery at all times. The J-seal interface is a source of high friction because the J-seal must be made from a pliable material in order to securely contain the toner in the cartridge. The J-seal interface contacts the developer roll, which is frequently covered by a polymeric or rubberized material with a high coefficient of friction. It will be appreciated that the temperature of the developer roll along its length is significantly higher at the clean bands than it is at intermediate positions due to friction with the J-seal.
One solution to excessive heat from the J-seal interface has been to apply a lubricant to the clean band area in an attempt to decrease the coefficient of friction. However, such an approach has significant drawbacks. Any lubricant applied to the J-seal or to the ends of the developer roll can potentially contaminate the toner and ruin any printed image. Additionally, the lubricant can seep into other areas of the cartridge or printer, causing unwanted damage and interfere with the proper operation of the unit.
Another solution to excessive heat from the J-seal has been to utilize directed airflow, such as from a fan, to blow air across the entire length of the developer roll. However, this had been found to be ineffective in lowering the temperature of the developer roll by any significant amount.
In addition, the heat created by the friction at the J-seal interface causes further problems with the proper operation of a laser printer or other image-forming device as print speed increases. Since it is essential to maintain pressure between the J-seal and the developer roll, more heat is created as the print speed increases. In known printers, a print speed of 35 pages per minute (ppm) is slow enough that, even with continuous printing, the heat created at the J-seal can be dissipated into the surrounding cartridge parts and into the atmospheric air to prevent heat related failure. In such an instance, the toner cartridge can reach a thermal equilibrium and still operate properly with undirected machine airflow as a cooling method. However, printing at higher speeds such as at or above 50 ppm causes extreme overheating, which is localized at the ends of the developer roll around the J-seal interface. Low thermal conductivity of the developer roll worsens the heating condition, and a large temperature gradient can be created around the clean bands in the axial direction of the developer roll.
It will be appreciated that high temperatures negatively affect the ability of the J-seal to seal toner inside the cartridge. As heat from the clean band areas increases, the temperature of the surface of the developer roll increases, and the temperature of the toner in the immediate region also increases. Temperatures of up to 70° C. around the J-seal interface have been measured when a printer was operated at 50 ppm. For some toners, fusing can occur at approximately 46° C. Thus, it will be appreciated that toner fusing may occur in the area of contact between the J-seal and the developer roll when the image forming device is operated at speeds of 50 ppm or higher. In such an instance, the J-seal contacts an irregular layer of fused toner on the developer roll, and not an extremely smooth surface, which is the most desirable condition in order to achieve a consistent and reliable seal. This condition allows toner to escape past the J-seal and out of the toner cartridge.
Once toner leakage at the J-seal begins, toner loss almost always continues at a rapid rate, permitting several grams of toner per minute to escape into the printer. Such large amounts of toner losses are substantial enough to severely affect cartridge yield, and may result in yields of several thousand pages fewer than expected. In addition, major print defects occur, as the escaped toner from the toner cartridge can spill directly onto the transfer belt near the location of the first transfer or onto the print media.
In accord with the present invention, a cartridge for containing toner material used in an image forming device comprises a developer roll, a seal providing an interface with the developer roll and the toner, and an air duct for conducting air flow across the interface to cool the developer roll.
Further in accord with the present invention, an air duct in a cartridge for containing toner material, a developer roll, and a seal providing an interface with the developer roll, the developer roll having a distal end and a proximal end, with one seal located at each of the distal and proximal ends, comprises an elongated hollow body, a pair of nozzles in fluid communication with the hollow body, one of the nozzles being disposed at the distal end of the developer roll and the other of the nozzles being disposed at the proximal end of the developer roll.
Still further in accord with the present invention, in an image forming device having a cartridge for containing toner material, a developer roll, and a J-seal providing an interface therebetween, the improvement comprises an air duct disposed adjacent the developer roll for conducting air flow across the J-seal interface to cool the developer roll and J-seal.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings.
Referring now to
Referring now to
The developer assembly 40 includes J-seals 70 at the ends of the developer roll D. The developer roll D is exploded in
Referring now to
The blade 54 extends from the bracket 52 toward a peripheral surface of the developer roll D in order to scrape excess toner from the outer surface of the developer roll D. The blade 54 is generally rectangular in shape, having a long or width-wise dimension substantially parallel to the direction of the axial dimension of the developer roll D. The blade 54 includes a front surface 55 and a rear surface 57. The blade 54 is straight in its natural state, but, in order to provide a “doctoring” force on the developer roll D, has a slight curvature due to interference with the developer roll D upon installation. In addition, the blade 54 has notches N near ends of the blade for removing all toner from the ends of the developer roll D where printing does not occur. The blade 54 may also receive an electrical potential in order to charge the developer roll D with a desired polarity during operation. The lower surface of the bracket 52 engages an upper surface 62 of the doctor blade seal 60, so as to capture the seal 60 between the doctor blade assembly 50 and the J-seal 70. The blade 54 may be formed of phosphor bronze to provide the desired elasticity and electrical conductivity, or alternatively, may be formed of a hardened stainless steel to provide a desired elasticity and also withstand corrosion that might damage the developer roll D. Other materials may also be utilized.
An end portion 61 of the doctor blade seal 60 is shown above one of the J-seals 70. The doctor blade seal 60 has first and second ends 61 (
The doctor blade seal 60 has the upper surface 62, a lower surface 63 and a plurality of sides extending between the upper and lower surfaces 62, 63. Along the front of the doctor blade seal 60, toward the doctor blade 54, a tongue 64 is integrally formed with and extends from the doctor blade seal end 61. On an outer end of the tongue 64 is a tongue end surface 65 of the doctor blade seal 60. Perpendicular to tongue end surface 65 of the tongue 64 near the blade 54 is a tongue-extending surface 66. Angled from the tongue-extending surface 66 is an angled or tapered surface 68. The angled surface 68 joins the tongue-extending surface 66 and a front seal surface 69, which extends the distance of the doctor blade seal 60 to the opposite end 61 (not shown) of the doctor blade seal 60. Therefore, the tongue 64 generally extends from the angled surface 68 in a direction substantially perpendicular to the front seal surface 69. In combination, the surfaces 69, 68, 66 define a recess wherein an upper seat inner seal wall 78 of the J-seal 70 is received. An end wall 67 is indented and is received against upper seat outer seal wall 82. As previously indicated, the doctor blade seal 60 extends in a width-wise direction, which corresponds to the width of a media sheet, and perpendicular to the media feed path direction to an opposite end of seal 60.
Beneath the doctor blade seal 60, the J-seal 70 comprises an upper seat portion 72, and a developer roll leg 74, which is substantially j-shaped and depends from the upper seat portion 72. The J-seal 70 may be formed in a molding process, such as injection molding, compression molding, or other known processes for forming a plastic, such as a thermoplastic rubber having the trade name SANTOPRENE. The leg 74 has a front surface 75 comprising a plurality of grooves 76, which provide several functions. The grooves 76 “snowplow” the toner on the developer roll D and capture toner between the grooves to inhibit leakage. The grooves 76 also direct the toner toward a storage area via rotation of the developer roll D (
The upper seat portion 72 comprises a seating surface 73, the upper seat inner seal or seal wall 78, and an upper seat outer seal or seal wall 80. A gap 86 is disposed between the upper seat inner seal 78 and the upper seat outer seal 80, wherein the tongue 64 may be closely received within the upper seat portion 72 to interlock the J-seal 70 and the doctor blade seal 60. The seating surface 73 also comprises an aperture 73a made for receiving an alignment pin for proper positioning of the J-seal 70 to the housing 42.
The upper seat inner seal wall 78 extends upwardly from the upper seat surface 73. The upper seat inner seal 78 is disposed at an acute angle with respect to the outer seal 80, which corresponds to that of the angled surface 68, so that the upper seat inner seal 78 and angled surface 68 engage one another in sealing fashion. Further, the upper seat inner seal 78 is received within the recess defined by the surfaces 66, 68, 69.
As is known, the laws of heat transfer provide three basic ways to move heat from one location to another: convection, conduction, and radiation. In the case of a laser printer 10 such as the one depicted in
Turning now to
q=hAΔT (Equation 1)
where
q=heat transfer rate
h=heat transfer coefficient
A=surface area
ΔT=temperature difference between surface and ambient air
As is evident from Equation 1, greater heat transfer occurs with increasing temperature difference. In the case of the developer roll D, the temperature difference between ambient air and the surface of the developer roll D is much greater at the clean bands 130, 132 than across the other portions of the developer roll D. Also, the heat transfer coefficient, h, increases with air velocity. It will thus be appreciated that the most effective cooling of developer roll D occurs when the air blown onto the clean bands 130, 132 occurs at the highest possible velocity.
The air duct 128 carries ambient air through the toner cartridge 112 and directs it onto the proximal and distal ends 146, 144 of the developer roll D, without obstructing the laser path through the printer 10, in order to maximize the air velocity at the clean bands 130, 132. The equation determining the flow through the air duct 128 is known as the Bernoulli equation, and describes the operating conditions at any point in a straight duct where the flow is steady and friction is neglected.
where
Since the Bernouilli Equation (Equation 2) describes any point in the air duct 128, the density of the air inside the air duct 128 is approximately constant, and the height at every point inside the air duct 128 is approximately zero. The Bernoulli Equation (Equation 2) can thus be simplified to relate the air velocity at the inlet and exit of the air duct 128 for a given pressure difference, and the resulting equation is
where
v1=pressure at duct inlet
v2=pressure at duct exit
ρ=density of air
Δp=pressure difference between inlet and exit (operating pressure difference provided by the fan)
From Equation 3, one of skill in the art will recognize that increasing the pressure difference across the air duct 128 increases the exit velocity. However, increasing the pressure difference across the air duct 128 provides a lower flow rate.
Referring now to
With reference to
Referring now to
The foregoing description of embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.
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| Number | Date | Country |
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| 2006208673 | Aug 2006 | JP |
| 2006259118 | Sep 2006 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20090202270 A1 | Aug 2009 | US |
