Abstract:
A constant displacement oil web system for an imaging apparatus fuser is disclosed, together with its associated method of operation. In one embodiment, the actual linear advancement of the web during an indexing cycle is detected. In another embodiment, sheet count data, look-up tables and algorithms are used to determine angular rotation necessary to achieve a specified linear advancement of the web. A drive system operating cycle is adjusted to achieve a constant linear advancement of the web.

Description:
This application relates to contemporaneously filed applications Ser. No. 09/548,924, entitled “Multi-Level Oiling Device and Process for a Fuser System”, and Ser. No. 09/548,928, entitled “Multi-Level Oiling Device Drive Mechanism”, both of which are expressly incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrophotographic imaging apparatus, and more particularly to a fuser oiling apparatus and the associated method involved with its use and operation. 
     2. Description of the Related Art 
     In the electrophotographic process commonly used in imaging apparatus such as laser printers, an electrostatic image is created upon a photosensitive member such as a roll or belt. Visible electroscopic marking particles, commonly referred to as toner, are applied to the electrostatic image on the photosensitive material. Thereafter, the toner is transferred to the desired media, which may include paper, transparency sheets or the like. 
     The toner image applied to the media is not permanent, however, until the toner is fixed by the application of heat. The toner is elevated in temperature sufficiently to cause constituents of the toner to become tacky, and flow into the pores or interstices between fibers of the media. Upon cooling, the toner again solidifies, causing the toner to adhere to the media. Pressure may be applied to enhance the flow of the toner, and thereby improve the subsequent bonding of the toner to the media. 
     One approach commonly used for thermally fixing the electroscopic toner images is to pass the media, with the toner image thereon, through a nip formed by thereafter elsewhere in the apparatus. The presence of wayward toner particles in the imaging apparatus can degrade the quality of the printed sheets. 
     To overcome these problems, fusers of the type described above commonly employ an apparatus for applying a release fluid to the surface of the fuser roll. The release fluid creates a weak boundary between the heated roll and the toner, thereby substantially minimizing the offset of toner to the fuser roll, which occurs when the cohesive forces in the toner mass are less than the adhesive forces between the toner and the fuser roll. Silicone oils having inherent temperature resistance and release properties suitable for the application are commonly used as release fluids. Polydimethylsiloxane is a silicone oil that has been used for this purpose advantageously in the past. 
     Various methods and apparatuses have been used to supply oil to the fuser hot roll, including oil wicking systems, oil delivery rolls and oil webs. Oil wicking systems include reservoir tanks of the desired release agent or oil, and a piece of fabric wick material having one end mounted in the reservoir and the other end spring biased against the hot roll. Oil from the reservoir is drawn through the fabric wick by capillary action, and is deposited against the roll surface. While a wicking system can be effective in supplying oil to the fuser roll, surface deposit of the oil on the roll can be inconsistent, and the replenishment or replacement of the oil and/or system can be difficult and messy. 
     A variety of oil delivery roll systems have been used in the past, and include a roll nipped against the hot fuser roll. The oil delivery roll may be either freely rotating against the fuser roll or driven against the roll through a gear train. Oil delivered to the surface of the oil delivery roll is deposited on the hot fuser roll as the rolls rotate against each other. Various structures have been used for providing oil to the surface of the oil delivery roll, including reservoirs at the center of the roll providing oil to the surface through small dispersal holes or via capillary action through the outer material. Felts or metering membranes may be used in the oil delivery roll to control the oil flow through the roll. Another style of such roll is referred to as a web wrapped roll, and includes high temperature paper or non-woven material saturated with oil, and wrapped around a metal core. 
     Oil web systems include a supply spool of web material, generally being a fabric of one or more layers saturated with the desired oil. A take-up spool is provided for receiving the used web. A web path, commonly including one or more guide rolls, extends from the supply spool to the take-up spool. A portion of the web path brings the web material into contact with the hot fuser roll, either by wrapping a portion of the web around the hot roll, or by utilizing a spring-biased idler roll to nip the web material against the fuser roll. As the fuser roll rotates against the web in contact therewith, oil is transferred from the web to the fuser roll. Periodically, a drive mechanism for the take-up spool activates, rotating the take-up spool and advancing web material from the supply spool to the take-up spool, thereby bringing a fresh section of web material into contact with the fuser roll. 
     Oil web systems can be used to deliver oil with good uniformity across the fuser roll surface. However, the oil flow is dependent upon the amount of web material brought into contact with the fuser roll over a given period of time. Both, the frequency of indexing and the length of web advancement during indexing influence the amount of oil that is applied to the fuser roll over a given time period. In oil web systems utilized heretofore, the simplified drive systems for the take-up spool have been operated for a consistent duration of time, or for established revolutions or partial revolutions of the take-up spool, at constant intervals throughout the life of the web system. Therefore, as spent material passes onto the take-up spool, and the diameter of the take-up spool increases, the linear length of material brought into contact with the fuser roll increases during each web advancement, thereby increasing the amount of oil deposited on the fuser roll. 
     Excess oil on the fuser roll has undesirable effects. Since the paper passing through the fuser system generally carries away a portion of the oil deposited on the fuser roll, an excess amount of oil on the fuser roll, when picked up by the paper or other media, can cause an undesirable glossy appearance to the media. In duplexing systems, oil carried on the first printed side can be transferred to other areas of the imaging apparatus, when the media passes again through the apparatus for printing on the second side. Excessive amounts of oil deposited in other sections of the imaging apparatus can decrease print quality, and otherwise produce undesirable operating effects. Additionally, increased linear advancement of the web as the take-up spool diameter increases is wasteful, and shortens the useful life of the oiling system, necessitating replacement and expense. 
     A further problem can occur in the event of a failure of the drive mechanism for the take-up spool, a web break or other failure of the oil web system to operate properly when web advancement is required. Malfunctions such as these may go unnoticed until operating problems result from the lack of oil application to the fuser roll. The same may occur if the oil web is completely advanced off from the supply spool. If unnoticed, these conditions can result in more severe problems after time. 
     What is needed is a constant displacement oil web system for an imaging apparatus fuser drum in which a more consistent deposit of oil occurs on the fusing drum than occurs from previously known systems. More specifically, what is needed is an oil web system for an imaging apparatus in which a consistent amount of web material is brought into contact with the fuser drum during a given period of operation, throughout the life of the supply spool. 
     SUMMARY OF THE INVENTION 
     The present invention provides an imaging apparatus having a constant displacement oil web system for the fuser roll, and an operating method for an oil web system, whereby the deposit of oil from the web on the fuser roll is consistent throughout the life of the web supply spool. 
     The present invention comprises a supply spool having a web wound thereon, the web having oil therein. A take-up spool is provided for receiving the spent web from which the oil has been transferred to the fuser roll. A drive mechanism is activated periodically, for rotating the take-up spool and advancing the web. A web path extends from the supply spool to the take-up spool, and includes one or more guide rolls defining the path such that, along at least a portion of the path, the web material is brought into contact with the fuser roll. A drive mechanism control receives input such that the operation of the drive mechanism indexes consistent lengths of web material along the path throughout the life of the supply spool. 
     In one form of the invention, consistent linear advancement of the web material is accomplished through the use of an encoder wheel attached to a shaft located for constant contact with the web material. A sensor is placed to determine rotation of the encoder wheel, and thereby the actual linear advancement of the web material. Operation of the oil web system drive mechanism is adjusted in response to the detected advancement of the web. 
     In a second form of the invention, sheet counter data and a stored look-up table and algorithm are used to calculate take-up roll diameter, and the angular displacement on the take-up spool necessary to achieve consistent linear advancement of the web material 
     An advantage of the present invention is the consistent application of oil to the fuser roll through the consistent linear advancement of the web material. 
     Another advantage of the present invention is increased life for a web supply spool resulting from consistent use of the material and the minimization of waste. 
     Yet another advantage of the present invention is the minimization of oil dumps and, therefore, the reduction of oil carry over by printed media and resulting contamination of other portions in the imaging apparatus or production of undesirable glossy images. 
     A further advantage of the present invention is the detection of a spent or malfunctioning oil web system, prompting replacement or repair of the system. 
    
    
     BRIEF DESCRIPTON OF THE DRAWINGS 
     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 the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a simplified schematic representation of a laser printer in which the present invention may be utilized advantageously; 
     FIG. 2 is a schematic representation of an oil web system according to a preferred form of the present invention; 
     FIG. 3 is a cross-sectional view of the oil web system shown in FIG. 2, taken along line  3 — 3  of FIG. 2; 
     FIG. 4; is a flow diagram of the control procedure, according to the present invention, for the oil web system shown in FIG.  2  and FIG. 3; 
     FIG. 5 is a schematic representation similar to that of FIG. 2, but showing a modified embodiment of the present invention; and 
     FIG. 6 is a flow diagram of an alternative control procedure, according to the present invention, for the oil web system shown in FIG.  5 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more specifically to the drawings, and to FIG. 1 in particular, numeral  10  designates an imaging apparatus in the form of a laser printer, in which a constant displacement oil web system  12  of the present invention, shown in FIG. 2, may be used advantageously when operated in accordance with an encoder wheel drive mechanism control method  14  shown in FIG.  4 . 
     It should be understood that the laser printer  10  shown in FIG. 1 is merely one type of imaging apparatus in which the present invention may be used advantageously. Other types of imaging apparatuses, including other types and configurations of laser or other printers, may readily employ use of the present invention to achieve the advantages incumbent therein. The particular embodiment of the laser printer shown in FIG. 1 should not be construed as a limitation on the use and application of the present invention, nor on the scope of the claims to follow. 
     The general structure of a laser printer, and the operation of the electrophotostatic process used therein, will be readily understood by individuals skilled in the art, and will not be described in detail herein. For reference purposes in describing the present invention, in FIG. 1 a laser printhead  20  is shown, which creates an electrostatic image in known fashion on a photosensitive member. Toner is applied to the electrostatic image. It should be understood that in a non-color printer only one printhead may be used; however, in a color printer separate printheads for black, magenta, cyan and yellow toners may be used. The toner image is created on a photoconductive drum and/or image transfer belt  22 , and thereafter transferred to the selected media. The media, such as paper or the like, on which the image is to be printed, is provided from a media supply tray  24  or  30 . The media follows a media path, indicated by the arrows  26 , from tray  24  or  30  through an image transfer nip  28 , at which the image is transferred from image transfer belt  22  to the media. Media path  26  includes a series of guide surfaces or belts  32 , and guide rolls  34  to direct the media through printer  10 . A printed media receiving zone  36  is provided at the end of media path  26 , to accumulated the completed pieces of media. 
     To fix the toner image on the media, a fuser  40  is provided, to apply heat and pressure to the image on the media, thereby causing the toner to melt and flow into the pores or interstices of the media. Fuser  40  includes a hot roll  42  and a backing roll  44  creating a fuser nip  46  through which the media passes. To prevent paper from sticking to hot roll  42 , and to minimize toner offset to hot roll  42 , oil web system  12  is provided, to apply a release agent, such as silicone oil, to the surface of hot roll  42 . 
     Referring now to FIG. 2, oil web system  12  includes an elongated web  52 , which has been saturated or coated with the selected release agent to be applied to fuser hot roll  42 . The web material, preferably, is a non-woven fabric of polyester and aramid fibers, such as Nomex 200   manufactured by and available from DuPont. The release agent may be a silicone oil such as polydimethylsiloxane, which has been used advantageously in the past. Web  52  is provided on a supply spool  54 , from which it is dispensed periodically to apply release agent on hot roll  42 . The used or spent portion of web  52 , from which the release agent has been transferred to fuser hot roll  42 , is accumulated on a take-up spool  56 . Between supply spool  54  and take-up spool  56 , web  52  follows a web path, indicated by arrows  58 , the web path being defined by positions of web guiding members, which includes the relative positions of supply spool  54 , take-up spool  56  and other guide rolls and/or guide surfaces, as necessary. Along a portion of the web path, web  52  comes in contact with hot roll  42 . In the structure shown in FIG. 2, a spring loaded biasing roll  60  is shown, to urge web  52  against hot roll  42  at an oiling nip  62 . As hot roll  42  rotates against web  52  in oiling nip  62 , the release agent from web  52  is transferred to the surface of hot roll  42 . 
     As shown in FIG. 2, hot roll  42  and take-up spool  56  rotate in the same direction, counterclockwise as shown, so that at oiling nip  62  hot roll  42  and web  52  move in opposite directions past each other. In this manner, as web  52  drags against hot roll  42 , hot roll  42  creates tension on that portion of web  52  between biasing roll  60  to take-up spool  56 , and tension in the wind-up of used portions of web  52  on take-up spool. Tension in the wind-up creates a smoother, cleaner wind-up on take-up spool  56 . Additionally, the directional relationship between web  52  and hot roll  42  causes a slackening of that portion of web  52  between supply spool  54  and biasing roll  60 , thereby inhibiting free-wheeling or accidental unwind of supply spool  54 . 
     While biasing roll  60  has been shown and described for bringing web  52  into contact with hot roll  42 , it should be understood that other arrangements for a web path can be used as well. For example, two spaced idler rolls may be used, positioned closely to hot roll  42 , such that web  52  partially wraps hot roll  42  along the portion of the web path between the idler rolls. Alternatively, a single idler roll could be used, with the idler roll and take-up spool  54  positioned in a manner to provide the same relationship, that is a segment of web  52  wrapping a portion of hot roll  42  between the idler roll and take-up spool  54 . Web guiding surfaces other than idler rolls also may be used to define a web path. 
     To effect transfer of web  52  from supply spool  54  to take-up spool  56 , a drive mechanism  64  is provided, connected to take-up spool  56  for rotation thereof to draw web from supply spool  54 . Drive mechanism  64  may include an independent, dedicated prime mover and gear train, a gear train from a common drive for other apparatus in printer  10 , a direct drive prime mover, or the like. The prime mover may be a stepper motor, a solenoid, or other positional activator. Such drive mechanisms are known in the industry, and will not be described in further detail herein. Operation of drive mechanism  64  is controlled by drive controller  66 , which transmits signals to drive mechanism  64 , including start and stop signals. Drive controller  66  may include a microprocessor, and other digital or analog control components, and a suitable signal transmission pathway  68  to drive mechanism  64 . 
     In accordance with the present invention, a web advancement sensor system  70  is provided. The sensor system  70  includes an idler shaft  72 , properly journaled in bearings, low friction bushings or the like (not shown). A web engagement portion  74  of shaft  72 , such as a sleeve, boss, shoulder portion of shaft  72 , or the like, is positioned to be in contact with, and partially wrapped by web  52 . Advantageously, web advancement sensor system  70  will be disposed along that segment of web  52  between take-up spool  56  and biasing roll  60 , that segment along which there is tension in web  52 . Since web  52  partially wraps engagement portion  74 , as web  52  advances along the path, idler shaft  72  of web advancement sensor system  70  is rotated in direct proportion to the linear movement of web  52 . 
     An encoder wheel  76  is disposed on idler shaft  72  or engagement portion  74 , for rotation therewith. Encoder wheel  76  includes surface indicia, holes or the like, movement of which may be detected by an appropriate sensor. In the embodiment shown, a band or region  78  is provided near the periphery of the encoder wheel  76 . Within band or region  78 , a hole or opening  80  (FIG.  3 ), or a plurality thereof are provided, and may be in specific patterns or orientations. Although band or region  78  is shown as only a segment on wheel  76 , it may extend along a greater portion or entirely around encoder wheel  76 , near the periphery thereof. A transmissive sensor, including an emitter  82  and a receiver  84 , is used to detect movement of encoder wheel  76 , as evidenced by the passage of hole or holes  80  through a region  86  between emitter  82  and receiver  84 . The structures and operations of appropriate sensors that may be used in the present invention, to ascertain the pattern or frequency of hole passings, are known for other uses, will not be described in further detail herein and will be referred to as an encoder wheel sensor  88 . Data signals from encoder wheel sensor  88  are transmitted along a suitable signal pathway  90  to drive controller  66 . 
     Other types of web movement sensors may be used advantageously in the present invention. The encoder wheel  76  and encoder wheel sensor  88  shown and described are not the only suitable sensors, but are a preferred, low cost and accurate alternative. 
     In the conventional operation of an oil web system, the drive mechanism is operated at pre-established intervals for a pre-established duration of time. Therefore, when the oil web system is new, with most of the length of the web being on the supply spool and only a small portion thereof on the take-up spool, a certain length of web material will pass through the oiling nip during each activation of the drive mechanism. However, as the diameter of the supply spool decreases, and the diameter of the take-up spool increases, during the same duration of web advancement, a longer segment of web will pass through the oiling nip. Therefore, more release agent or oil will be applied to the hot roll when the take-up spool is large in diameter than when the take-up spool is of a smaller diameter. This is wasteful of the web system and oil, and can provide an excessive amount of oil on the hot roll, that is more oil than is required for release of the media. 
     In the use and operation of oil web system  12  according to encoder wheel drive mechanism control method  14 , the frequency of advancement or indexing of web  52  is also determined by pre-established parameters in drive controller  66 . When the pre-established time interval has passed, drive controller  66  activates drive mechanism  64 , to rotate take-up spool  56 . Web  52  is drawn from supply spool  54 , through oiling nip  62 , and spent portions of web  52  are wrapped onto take-up spool  56 . As web  52  is advanced along that segment of the web path between biasing roll  60  and take-up spool  56 , web  52  passes over and rotates idler shaft  72 , and thereby encoder wheel  76 . As encoder wheel  76  rotates, and holes  80  pass through region  86  between emitter  82  and receiver  84 , data related to the passing of holes  80  is transmitted along signal pathway  90  to drive controller  66 , in known manner. Using data from encoder wheel sensor  88 , drive controller  66  terminates the drive signal to drive mechanism  64 , stopping advancement of web  52  when the desired length of web  52  has moved along the web path. This determination is made independent of the angular movement of take-up spool  56 . In this manner, regardless of the diameter of take-up spool  56 , a consistent, specified, predetermined length of web  52  is advanced during each indexing step. The linear advancement of web  52  will remain constant, for any diameter of take-up spool  56  throughout, the duration of the life of oil web system  12 . 
     In addition to the consistent application of oil through out the life of oil web system  12 , oil web system  12  can provide a fail-safe response to system malfunctions. If drive mechanism  64  fails, web  52  breaks or web  52  reaches its end, no movement of encoder wheel  76  will occur if web  52  is not advanced. If, in spite of activation signals having been sent to drive mechanism  64 , drive controller  66  determines that no advancement of web  52  has occurred, an error signal can be sent, the machine shut down or other steps taken to prevent more serious ramifications from the failure of the oil web system  12 . 
     An alternative embodiment of the present invention is shown in FIG.  5  and FIG.  6 . Oil web system  112 , shown in FIG. 5, is similar to the oil web system  12  shown in FIG. 2, but without the use of encoder wheel  76 , emitter  82  and receiver  84 . However, web oil system  112  may also be operated to provide consistent incremental advancement of web  52 , independent of the diameter of take-up spool  56 . FIG. 6 shows a sheet count operating method  114  for the oil web system  112  shown in FIG.  5 . Drive controller  116 , which may be a microprocessor, uses a stored look-up table, or other algorithm, to relate the angular displacement necessary for a given diameter of take-up spool  56  to achieve the desired linear displacement of web  52 . A sheet counter  118  provides sheet count data to drive controller  116  along a signal pathway  120 . Drive controller  116  relates the sheet count data to the calculated take-up spool diameter, and to the required angular rotation of the take-up spool necessary to provide the specified linear advancement of the web. Sheet count data may be provided from common sheet count sensors provided for other purposes elsewhere in the imaging apparatus. However, to eliminate the need for resetting the sheet count information when an oil web system  112  is replaced, advantageously sheet counter  118  is a part of any unitary structure of oil web system  112 . In this way, the sheet count data will be unique to the specific oil web system  112 , independent from the sheet count for fuser  40  or the total sheet count history of printer  10 . Suitable sheet count devices are known to those knowledgeable in the art, and will not be described in further detail herein. Utilizing the sheet count data, drive controller  116  generates start and stop data signals, which are transmitted to drive mechanism  64  along signal transmission pathway  68 . 
     While this invention has been described as having a preferred design, and a modification thereof, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.