Patent Publication Number: US-6219497-B1

Title: Apparatus and method for reducing condensation in an image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to apparatus and methods of reducing condensation in an image forming apparatus. 
     2. Description of Related Art 
     Various systems designed for transporting a copy sheet in a predetermined transfer path have a number of devices to advance and control movement of the sheet while it is advanced along the predetermined path within an image forming apparatus. Examples of such sheet control devices includes sheet grippers, baffles and sheet guides. Some of the sheet devices are fixed at various stationary locations adjacent a predetermined path. Consequently, the stationary sheet control devices act on the sheet as the sheet is transported past each stationary sheet control device. Some systems have multiple sheet control devices that move in and out of operative positions. 
     SUMMARY OF THE INVENTION 
     Copy sheet jamming often occurs near the upper turn of a post fuser portion of a transfer path due to moisture forming on the baffles and other sheet control devices of this portion of the transfer path. The moisture evaporates from the hot copy sheet as it passes through the fuser and along the post fuser transfer path. The hot moisture in the air then condenses on the surrounding cooler surfaces. Coated copy sheets, which are less able to absorb moisture and have smoother surfaces, have better contact with the condensed moisture on the baffles and can stall or generate contaminates in the transfer path. Ribs on the baffles have been added to reduce the contact area between the copy sheet and the baffles, which essentially minimizes the contact area and the chance of jamming of the copy sheet in the transfer path. Venting hot moist air near the fuser and along the transfer path will reduce the moisture condensation. Both venting holes for natural convection and ribs have been added to the baffles and tested. These two methods reduce the moisture condensation, but do not eliminate the jamming problems caused by moisture condensation. 
     One problem within the image forming apparatus is that the various temperatures of the individual components throughout the various regions of the image forming apparatus cause condensation to form within the image forming apparatus and on its various components. Condensation causes many problems within the image forming apparatus and to the copy sheets. First, condensing water on the individual components of the image forming apparatus can damage the parts. Second, the water that condenses on the members and copy sheets causes jams within the image forming apparatus. The condensation causes the copy sheets to stick to surfaces of the image forming apparatus and to other copy sheets within the printing apparatus. Additionally, when condensation forms on transfer guides and the transfer guides come in contact with a copy sheet, the drag coefficient rises dramatically, and can be up to five times higher than without condensation. The combination of condensation and the high drag causes sheet skew and/or sheet stall in the transfer path. 
     Conventionally, as described above, this condensation problem has been attacked by creating slots within the paper guide. However, this has not completely disposed of the condensation which has formed and has also caused the corners of the leading edge of the copy sheet to jam within the slots. 
     This invention provides systems and methods that reduce condensation and paper jamming that occurs within an image forming apparatus. 
     In various exemplary embodiments of the systems and methods of this invention, the critical baffle areas, such as the gate and others where the moist air can not be easily vented, are heated to reduce the moisture condensation at those particular areas 
     The temperatures of the copy sheets and baffles, the moisture evaporating from the copy sheets, and the moisture condensating from moist air to cold baffles along the post fuser transfer path have been considered by the inventors. At high copy sheet temperatures, for example, at the temperature of the copy sheets right after they leave the fuser, the copy sheets have a high rate of moisture evaporation. The rate of moisture evaporation decreases with time as the copy sheets move through the image forming apparatus. Different types of copy sheets, such as different types of paper, possess different moisture diffusion coefficients. The moisture diffusion coefficients and the temperature of the paper together control the amount and rate of moisture evaporation. The moisture condensation from moist air onto cooler surfaces depends on the moisture content in the air and the temperature of the surrounding cooler surfaces. The inventors have determined that the location and conditions of moisture condensation can be predicted. The moisture condensation is likely to occur shortly downstream of a high temperature region, such as after the fuser area, because of high moisture evaporation from the copy sheet. 
     In one exemplary embodiment of an image forming apparatus that can beneficially incorporate this invention, after an electrostatic latent image is recorded on a photoconductive member, the latent image is developed by bringing a developer material into contact with the photoconductive member. The toner particles are attracted to the latent image to form a developed image on the photoconductive member. 
     This developed image is subsequently transferred to a copy sheet. The copy sheet is then heated to permanently affix the toner particles of the developed image to the sheet. After exiting the fuser portion of the image forming apparatus, the copy sheet is relatively warm. The developed copy sheet is then received by a baffle that is much colder. This change in temperature between the warm copy sheet and the cold baffle causes high relative humidity and promotes the formation of water droplets formed from condensation. The condensation that is created occurs when the fuser heats the copy sheet and the moisture that develops from the copy sheet evaporates over time in the transfer guides and other components of the transfer path that follow the fuser portion. Thus, the relative humidity of the air between the transfer guides increases. Eventually, the dew point is reached in this area and condensation forms on the surface of the transfer guides and other various components of the transfer path. 
     This invention provides systems and methods for reducing condensation by drawing ambient heated air into the vacuum transport. 
     This invention separately provides an image forming apparatus that is less susceptible to humidity-related faults. 
     This invention separately provides an image forming apparatus in which condensation is less likely to form. 
     This invention separately provides an image forming apparatus that has improved air flow and/or humidity control in baffled and vacuum transport areas. In the systems and methods according to this invention, the blower motor of an image forming apparatus is turned on when an image forming apparatus is turned on. 
     These and other features and advantages of the systems and methods of this invention are described in or are apparent from the following detailed description of the various exemplary embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will be described in relation to the following drawings in which reference numerals refer to like elements, and wherein: 
     FIG. 1 is a block diagram side view of one exemplary embodiment of the fuser and vacuum transport in an image forming apparatus according to this invention. 
     FIG. 2 is a graph showing the moisture condensation along the post fuser transfer path for a Color Expressions 24# paper. 
     FIG. 3 is a graph showing the moisture condensation along the post fuser transfer path for a Lustrogloss B80 paper. 
     FIG. 4 is a side view of post fuser transfer path. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a block diagram side view of one exemplary embodiment of the fuser and vacuum transport region  100  in an image forming apparatus according to this invention. As shown in FIG. 1, the fuser and vacuum transfer region  100  includes a fuser roll  110 , a pressure roll  112 , a baffle  114  and a vacuum transport  130 . The vacuum transport  130  includes a vacuum transfer belt  132  and a vacuum blower  134 . 
     In operation, a copy sheet, or more generally, an image recording medium, passes between the fuser roll  110  and the pressure roll  112  and is received by the finger baffle  114 . The finger baffle  114  transfers the image recording medium, such as, for example, a sheet of paper, to the vacuum belt  132  of the vacuum transport  130 . The image recording medium is drawn to the vacuum belt  132  by the vacuum blower  134  so that the image recording medium does not skew as it is transferred by the vacuum transport  130 . Thus, it should be appreciated that the fuser and vacuum transport region  100  shown in FIG. 1 includes a post fuser portion of the transfer path of the image forming apparatus. 
     Referring to FIG. 1, the vacuum transport  130  is generally used to transfer the recording medium from one location in the image forming apparatus to another location. In order to reduce the build up of condensation on the post fuser vacuum transport  130 , various exemplary embodiments of the systems and methods according to this invention include an air circulation device that is activated during machine warm-up. The air circulation device may be a fan, a vacuum, a blower or any other known or later developed device able to create a flow of air. In one exemplary embodiment, the transport vacuum  130  is used as the air circulation device. In this exemplary embodiment, the transport vacuum  130  is run during machine warm-up so that the warm air surrounding the fuser roll  110  circulates and warms the surfaces of the fuser and vacuum transport region  100  and reduces the likelihood of condensation within the fuser and vacuum transport region  100 . Conventionally, the vacuum transport  130  is generally not operated until the image forming apparatus begins to perform an image forming operation. However, the inventors have discovered that, when the image forming apparatus is initially turned on, a significant amount of condensation forms in the fuser and vacuum transport region  100  during this period. This condensation is due to the fuser roll  110  being heated to a high temperature while all the surrounding components are kept at or near ambient temperature. The significant change in temperature between the fuser and vacuum transport region  100  and the fuser roll  110  creates a high dew point. By running the vacuum transport  130  during start-up, the dew point is lowered. The resulting lower dew point greatly reduces any condensation potential within the fuser and vacuum transport region  100 . 
     Various exemplary embodiments of the systems and methods according to this invention are able to reduce condensation by performing a plurality of procedures which may be performed in any order. Initially, a user turns on the image forming apparatus or causes the image forming apparatus to switch from a suspend mode to an active mode. When the image forming apparatus is turned on or is initially warming up after being switched from the suspend mode to the active mode, the fuser  110  is activated and the fluser roll  110  begins to heat up. Usually, it takes the image forming apparatus up to about 10 minutes to heat the fuser roll  110  to a temperature where the image forming apparatus is capable of performing image forming operations. In various exemplary embodiments, at about the same time that the time the image forming apparatus and the fuser roll  110  are turned on, the vacuum transport  130  is activated so that vacuum blower  134  within the vacuum transport  130  circulates the air within at least the fuser and vacuum transport region  100  of the image forming apparatus. 
     Because the fuser roll  110  is heated to a high temperature while the surrounding components within at least the fuser and vacuum transport region  100  of the image forming apparatus remain at or near ambient temperature, a significant difference in temperature within the image forming apparatus occurs. However, by turning on the vacuum blower  134 , the warmer temperature air surrounding the fuser roll  110  is drawn toward and circulated by the vacuum transport  130 . This causes the warmer air to circulate in at least the fuser and vacuum transport region  100 , thus warming the surfaces of the vacuum transport  130  and surrounding areas of at least the fuser and vacuum transport region  100 . Once the fuser roll  110  has been heated to the desired temperature and the image forming apparatus is in a condition to perform image forming operations, the vacuum blower  134  may be turned off until the image forming apparatus is required to perform an image forming operation. 
     However, it should be appreciated that the vacuum blower  134  may be left on continuously while the image forming apparatus is turned on. In various exemplary embodiments of the systems and methods described herein, the vacuum transport  130  has two primary functions. The first function of the vacuum blower  134  is to circulate air when the image forming apparatus is turned on or placed into the activated mode to decrease the dew point within the image forming apparatus and to reduce condensation. The second function is to hold the image recording medium down along the vacuum transport  130  during transfer of the image recording medium from the fuser roll  110  along the post fuser transfer path. 
     FIG. 2 graphically illustrates the moisture condensation rates for moisture evaporation from CX24 paper on the baffles  114  along the post fuser transfer path shown in FIG. 1 with an active ambient volume of 1,500 cm 3 . The graph shown in FIG. 2 illustrates the moisture condensation of CX24 paper exiting the fuser roll  110  at temperatures of 105°, 115° and 125° Celsius. The room ambient conditions include an ambient air temperature of 72° F. and a relative humidity of 37%. Immediately downstream of the fuser roll  110 , the condensation rate is high because of more moisture evaporation in that region. Downstream of this high condensation area, the condensation rate starts to decrease because less moisture is available from evaporation of moisture from the CX24 paper. The temperatures of the baffle  114 , the ambient room temperature, and the active ambient volume are the important parameters for the moisture condensation. 
     FIG. 3 graphically illustrates moisture condensation rates for moisture evaporation from LS80 coated paper along the post fuser transfer path shown in FIG.  1 . The active ambient volume and ambient conditions are the same as for the case of CX24 plain paper. The moisture condensation rate for the LS80 coated paper is lower than the moisture condensation rate for the CX24 paper. If the copy sheet exits the fuser roll  110  at a lower temperature of 105°C., the moisture condensation on the baffle will not occur in most of the paper path. And, if the active ambient volume is increased to 6,200 cm 3 , the moisture doesn&#39;t condense on the baffle for all three temperatures, i.e., for a copy sheet exiting the fuser at temperatures of 125°, 115°, and 105° C. For the 6 cases shown in FIGS. 2 and 3, the peak condensation occurs at locations not too far away from the fuser. These peak condensation locations will change if the conditions are different. 
     Venting the moist air can be improved by using forced convention instead of just natural convection. As shown in FIG. 4, a small suction fan  140  near the post fuser transfer path should be sufficient to direct the air flow opposite to the transfer direction so that hot moist air does not flow into the cooler downstream section. The amount of air flow should be selected so that the fuser roll  110  is not overcooled and to avoid disturbing the flow or motion of the copy sheet. 
     That is, there are some areas along the transfer path where the air should not be forced to flow. For these difficult areas, moisture condensation is avoided by raising the surface temperatures of elements in those areas. For example, one such area includes a transfer path gate area  150  where there is more than one possible path for the copy sheet to take. Adding an additional air flow in this gate area  150  may cause the copy sheet to take the wrong path. 
     The gate area  150  includes a baffle  152  that defines a space  154 . A heating element  156  is placed in the space  154 . The heating element  156  heats the baffle  152  so that the temperature of the baffle  152  is generally above the saturation temperature. With this approach, the moisture will not condense at these critical locations. This local heating can be accomplished by many different ways. The easiest way is by attaching the heating elements  156  to the baffles  152  or to components at the critical areas or mounting heating lamps at a close proximity. 
     FIG. 4 shows the arrangement of this suction fan  140  and the critical heated gate area  150  along the post fuser paper path. The gate area  150  can be heated with a flexible heater, cartridge heater, or a rope heater. The other such critical areas of image forming apparatus can easily be heated with flexible heaters. 
     The heating element  156  is connected to a temperature controller  164  so that the power can be turned off when the heating element  156  reaches a certain temperature. A simple on-off thermostat can act as the controller  164 . The set temperature of the controller  164  is determined by the saturation temperature, which itself is a function of the ambient temperature and the relative humidity. In one exemplary embodiment, a first sensor  160  is used to measure the ambient temperature and a second sensor  162  is used to measure the relative humidity. Once the ambient temperature and relative humidity are known, a look-up table can be used to determine the saturation temperature. The set temperature should be slightly higher than the saturation temperature. In an exemplary embodiment, pairs of the sensors  160  and  162  are located near the critical areas throughout the image forming apparatus. 
     It should also be appreciated that, in addition to, or instead of, controlling the heating element  156 , the controller  164  can be used to control either or both of the fan  140  and/or the vacuum transport  130 . Thus, the controller  164  can be used, for example, to control when the vacuum transport  130  is turned on, in addition to, or in place of, the times/events described above during which the vacuum transport  130  is turned on. 
     While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.