Abstract:
A metal detection system and method to reduce damage due to the introduction of metal into microwave dryers of fluid ejection systems. One embodiment of the invention causes paper pick-up rollers and feed rollers to stop when metal is detected. Another embodiment causes the electromagnetic field in the microwave dryer to be turned off when metal is in the drying cavity of the microwave dryer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to fluid ejection systems that use microwave dryers. 
     2. Description of Related Art 
     A fluid ejection system, such as an ink jet printer, typically has at least one printhead from which droplets of fluid are directed towards a recording medium or recording sheet. Within the printhead, the fluid is contained in a plurality of channels. Droplets of the fluid are expelled as required from orifices or nozzles located at the end of the channels. 
     A fluid ejector head may be incorporated into either a carriage type fluid ejection system, a page-width type fluid ejection system, or a combination of the two. The carriage type fluid ejection system typically has a relatively small fluid ejector head containing the fluid channels and nozzles. The fluid ejector head is often sealingly attached to a disposable fluid supply cartridge. The combined fluid ejector head and cartridge assembly is attached to a carriage, which is reciprocated to eject fluid according to one swath of information at a time on a receiving medium. After the swath is formed, the receiving medium is stepped a distance equal to the height of the swath, or a portion of the swath, so that the next swath overlaps or is contiguous with the previous swath. The procedure is repeated until all of the information has been used. In contrast, the page-width fluid ejection system includes a fluid ejector head having a length sufficiently long to eject fluid across the width or length of the receiving medium. The receiving medium is continually moved past the page-width fluid ejector head in a direction normal to the length of the fluid ejector head and at a constant or varying speed during the fluid ejection process. 
     Many fluids, particularly those used in ink jet printing, include a colorant and a liquid. Some fluids also include a low vapor pressure solvent. When fluid is ejected onto the receiving medium, the individual spots of fluid deposited on the receiving medium form a desired pattern. Once deposited, the liquid is removed from the fluid to leave a desired residue. 
     Liquid can be removed from the fluid and the receiving medium by a number of methods. One simple method is natural air drying, in which the liquid component of the fluid deposited on the receiving medium is allowed to evaporate without mechanical assistance. A significant amount of fluid is diffused and absorbed into the receiving medium when this method is used. In high-speed page-width fluid ejection systems, drying is usually achieved by transporting the receiving media through a microwave dryer to evaporate the liquid from the fluid. 
     Microwave dryers are particularly efficient for drying fluid on receiving media in high speed thermal ink jet printing. However, introducing foreign metallic materials, such as, for example, staples, paper clips, decorative metallic leaf on letterhead and the like, into a microwave dryer cavity can have damaging consequences when the dryer is generating electromagnetic waves. Any metal entering the microwave dryer cavity under these conditions will immediately couple microwave power. This causes the metal to heat up dramatically and to arc and possibly damage the microwave dryer. Receiving media and transport belts in close proximity to the metal and the arc will rapidly heat up and deform. Damage to transport belts can affect the output quality of the fluid receiving medium, affect the reliability of the entire fluid ejection system and frustrate the user. Further, electromagnetic coupling results in electromagnetic radiation from the cavity of the microwave dryer which is a safety hazard. Preventing this problematic scenario requires assuring that foreign metallic materials cannot enter the microwave dryer cavity when microwave RF power is applied. 
     SUMMARY OF THE INVENTION 
     This invention provides systems and methods that detect metallic materials during feeding recording media to the ejection area of the fluid ejection system. 
     This invention separately provides systems and methods that reduce damage to a microwave dryer by stopping feeding operations upon detecting offending materials and allowing the removal of the offending materials. 
     This invention separately provides systems and methods that detect metallic materials prior to entry of such metallic materials into a microwave dryer. 
     This invention additionally provides systems and methods that reduce damage by turning off microwave power when metallic materials are detected in this manner. 
     This invention separately provides systems and methods that detect metallic materials after the offending materials exit from a microwave dryer and to turn on microwave power after the metallic materials exit the microwave dryer cavity. 
     These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of this invention will be described in detail, with reference to the following figures, wherein: 
     FIG. 1 is a schematic view of an exemplary embodiment of a conventional ink jet printer suitable for use with the this invention. 
     FIG. 2 is a schematic view of an exemplary embodiment of the printing portion of an ink jet printer incorporating a first exemplary embodiment of the detection and control system according to the invention. 
     FIG. 3 is a schematic view of an exemplary embodiment of the printing portion of an ink jet printer incorporating a second exemplary embodiment of the detection and control system according to the invention. 
     FIG. 4 is a schematic view of an exemplary embodiment of the printing portion of an ink jet printer incorporating a third exemplary embodiment of the detection and control system according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following detailed description of various exemplary embodiments of the fluid ejection systems according to this invention are directed to one specific type of fluid ejection system, an ink jet printer, for sake of clarity and familiarity. However, it should be appreciated that the principles of this invention, as outlined and/or discussed below, can be equally applied to any known or later developed fluid ejection systems, beyond the ink jet printer specifically discussed herein. 
     FIG. 1 illustrates a schematic view of an exemplary embodiment of a conventional ink jet printer  10 . The ink jet printer  10  includes an input tray  12  containing cut sheets  14  of paper stock to be printed upon by the ink jet printer  10 . Single sheets  14  of paper are removed from the input tray  12  by one or more pick-up rollers  16  and fed by one or more feed rollers  18  to a paper transport mechanism  20 . The paper transport mechanism  20  moves the sheet  14  by one or more feed belts  22  driven by rollers  24  beneath a printing member  26 . The belts  22  are made of a material transparent to microwave power having a low dielectric constant. The printing member  26  includes a page-width ink jet printhead which deposits ink on the sheet  14  as the sheet moves past the printhead. The page-width ink jet printhead is a linear array of print nozzles as wide as the sheet so that ink is deposited across the entire width of a sheet. This invention is equally applicable, however, to printers having an ink jet printhead which moves across the sheet  14  periodically, in swaths, to form the image, much like a typewriter. The print member  26  includes an ink supply and the necessary electronics to control the deposition of ink on the page. 
     In various exemplary embodiments, the ink that is used is formulated to be heatable using microwave power. Such ink may include compounds designed to couple with the microwave power for increasing the amount of heat introduced into the ink by the microwaves. One such compound is an ionic compound at least partially ionizable in the liquid vehicle. U.S. Pat. No. 5,220,346 discloses a suitable ink and is incorporated herein by reference in its entirety. 
     Once the sheet  14  has been printed, the sheet  14  is carried by the paper transport mechanism  20 , immediately after printing or within about 5 seconds or less, to a microwave dryer  28 . The sheet  14  enters an input slot  30  and exits an output slot  32 . A transport mechanism, such as one using a vacuum applied to the bottom side of the paper or one using a static mat, carries the paper through the microwave dryer  28 . As the sheet  14  passes through the microwave dryer  28 , microwave power is delivered to the sheet  14  to dry the ink deposited on the sheet  14 . Once the sheet  14  is substantially dry, the sheet is sent to an output tray  34 . 
     A controller  36  controls the printing member  26 , the microwave dryer  28 , and the paper transport mechanism  20  as outlined above. In addition, an adaptive dryer control can also be used. U.S. Pat. No. 5,214,442 discloses such an adaptive dryer control and is incorporated herein by reference in its entirety. 
     The microwave dryer  28  has such a fast drying rate that the excess liquid in the ink on the substrate is evaporated from the surface of the printed sheet before any appreciable absorption occurs. Additionally, microwave power generated in the microwave dryer  28  produces an electromagnetic field sufficiently powerful to effectively dry a thin layer of ink on the sheet  14 . 
     FIG. 2 illustrates schematic view of an exemplary embodiment of an ink jet printer incorporating a first exemplary embodiment of a metal detection and damage avoidance system according to this invention. In this first exemplary embodiment, a metal detector  100  is placed between the one or more pick-up rollers  16  and the one or more feed rollers  18 . The metal detector  100  may be designed to detect one or more articles made of iron, such as staples, paper clips or metallic letterheads. This metal detector  100  detects the magnetic properties of the iron-containing articles, and is very well known. Various exemplary embodiments of a metal detector  100  embody a coil that produces a magnetic field. Any modification of that field by the entry of an iron-containing article is detected and used to control the output of the metal detector. 
     Another metal detector  100  uses alternating current to produce a magnetic field. When a metal object enters the field, eddy currents are induced in the object. These eddy currents create a counter magnetic field, which alters the net magnetic field sensed by a magnetic field sensor. 
     These principles of metal detection are disclosed in U.S. Pat. Nos. 4,354,178 and 2,179,240. Both ferrous and non-ferrous metals may be detected, as demonstrated in the 178 patent. 
     When metal is detected, the metal detector  100  sends a signal to the controller  36 . In response, the controller  36  stops the one or more pick-up rollers  16  and the one or more feed rollers  18  and displays a message to the user indicating that the jam is due to metal detected on the stopped sheet. The sheet can then be removed to a purged output. Once the sheet is removed, the metal detector no longer detects the metal. Thus, the signal to the controller  36  is removed. As a result, the controller allows printing to resume. 
     FIG. 3 is a schematic view of an exemplary embodiment of an ink jet printer incorporating a second exemplary embodiment of the metal detection and damage avoidance system according to this invention. In this embodiment, a metal detector  100  is placed outside the microwave dryer  28  immediately prior to the input portion or slot  30 . When the metal detector  100  detects metal, the metal detector sends a signal to the controller  36 . In response, the controller  36  shuts off power to the microwave dryer  28 . In this embodiment, the controller  36  uses the speed of the belt  22  to determine when the metal detected by the metal detector  100  has exited the microwave dryer  28 . The controller  36  restores power to the microwave dryer  28  when the last metal detected by the metal detector  100  has had time to exit the microwave dryer  28 . 
     FIG. 4 is a schematic view of an exemplary embodiment of an ink jet printer incorporating a third embodiment of the metal detection and damage avoidance system according to this invention. In this third embodiment of the metal detection and damage avoidance system, a first metal detector  100  is placed outside the microwave dryer  28  immediately prior to the input portion or slot  30 . A second metal detector  102  is placed outside the microwave dryer  28  immediately after the output portion or slot  32 . When the first metal detector  100  senses metal, the first metal detector  100  sends a signal to the controller  36  for as long as the first metal detector  100  senses metal. In response, the controller  36  shuts off power to the microwave dryer  28 . When the second metal detector  102  detects metal, the second metal detector  102  sends a second signal to the controller  36 . In response, the controller  36  restores power to the microwave dryer  28 . The controller  36  restores power when the last element of the metal detected and set by the first metal detector  100  is detected by the second metal detector  102 , based on the first and second signals output by the first and second metal detectors  100  and  102 . 
     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.