Patent Publication Number: US-6911770-B2

Title: Apparatus with a cap and cover assembly, an electron gun with a cap assembly, and a method of using a tube

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to the field of electron emission and more specifically to methods and apparatuses using electron sources. 
   2. Description of the Related Art 
   Apparatuses and methods for incorporating conventional thermionic electron emission sources into devices, such as cathode ray tubes (CRTs), X-radiation tubes, or microwave tubes, are well known. Electron emission sources with better performance than common thermionic sources, such as field emission electron sources, may be less compatible with the apparatuses and methods designed for the common thermionic sources and can have their performance impaired by these apparatus and methods. 
   A common process for producing a vacuum tube  10 , shown in  FIG. 1 , such as a CRT, involves securing an electron source or sources  12  to a support cap  14  that is a part of the electron gun structure  16  located in an end of the tube  10 . A common support cap  14 , illustrated in  FIG. 2 , is generally a cup or can shaped structure with at least one aperture  20  to allow electrons generated by the electron source to pass. Referring again to  FIG. 1 , a vacuum is commonly achieved in the tube by pumping the gas out of the tube through an opening  18  at the terminal end of the neck and then sealing the opening. When the gas is pumped out of the tube, the gas as well as particles of phosphor, DAG coating, or other particles existing in the tube may flow over the electron source. These particles may interfere with the emission properties of field emission electron sources and can even result in catastrophic electrical shorts. 
   Accordingly, apparatus and methods for preventing gas or particles present in the conventional processes of common electron source applications are needed to enable the benefits of improved electron sources to be more fully realized. 
   SUMMARY OF INVENTION 
   In embodiments described below, an apparatus may overcome the problems above by providing a structure to cover an electron and thus enable the utilization of a non-thermionic electron or source in a tube manufactured by conventional processes designed for thermionic electron sources. In other embodiments, methods are disclosed for using a tube incorporating a cover structure. Tubes using the disclosed apparatuses and methods may exhibit improved performance compared to prior tubes. 
   In one set of embodiments, an apparatus can comprise a cap including an aperture and can be configured to allow an electron to pass along an electron path through the aperture. The apparatus may further comprise a cover assembly that includes a cover adjacent to the aperture. The cover can be configured to lie along the electron path during at least one point in time. The cover assembly may further comprise a means for displacing the cover. 
   In another embodiment, an electron gun may comprise a cap assembly and a focus electrode spaced apart and electrically insulated from the cap assembly. The cap assembly can comprise a cap aperture, a cover, and a spring. The cover may overlie the cap aperture during at least one point in time. The spring can comprise a first end attached to the cover and a second end attached to the cap. The focus electrode may comprise a focus aperture in alignment with the cap aperture. 
   In yet another embodiment, a method of using a tube can comprise placing at least a portion of an electron gun within a first end of the tube. The electron gun may comprise a cap including an aperture. The cap may further comprise an attenuator assembly including an attenuator adjacent to the aperture. The attenuator may lie along a path for a electron beam within the electron gun when the electron gun is activated. The method may further comprise flowing a gas at least near a portion of the electron gun while the attenuator blocks the aperture, and sealing the tube. In one embodiment, flowing the gas may evacuate the tube. 
   The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the accompanying figures. 
       FIG. 1  includes an illustration of a cross-sectional view of a portion of a prior art tube with an electron gun and a tubulation. 
       FIG. 2  includes an illustration of a prior art support cap with apertures. 
       FIG. 3  includes an illustration of a top view of a support cap with apertures and a cover with openings in an open position exposing the apertures. 
       FIG. 4  includes an illustration of a cross sectional view of a portion of the side of a support cap with a cover and a spring in a closed position, a material holding the spring in a closed position, and a focus electrode. 
       FIG. 5  includes an illustration of a cross-sectional view of a cover with an extension that may form a spring. 
       FIG. 6  includes an illustration of a cross-sectional view of the side of a support cap of  FIG. 4  after the cover and spring are moved to an open position. 
     FIG.  7  and  FIG. 8  each include an illustration of a cross-sectional view of the front of a support cap with a cover in a closed position and a cover guide and a focus electrode. 
       FIG. 9  includes an illustration of a top view of a support cap with a cover and a mechanical actuator for the cover. 
       FIG. 10  includes an illustration of a cross-sectional view of a portion of an gun with an electron source and first focus electrode incorporating a support cap with a cover and a cover guide. 
       FIGS. 11 and 12  include illustrations of a cross-sectional view of a portion of a tube during a process of using the tube. 
   

   Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. 
   DETAILED DESCRIPTION 
   Reference is now made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts (elements). 
   Described generally below are apparatuses and methods for protecting electron sources that can be used during tube production processes. A cap assembly for an electron source may comprise an aperture and an attenuator that blocks the aperture and protects the underlying electron source during processing. An electron gun may comprise a support cap assembly with an aperture and an attenuator and a focus electrode. A method of using a tube may comprise displacing an attenuator near an aperture through a cap assembly in an electron gun after the tube is sealed. 
   An embodiment illustrated in  FIG. 3  may comprise a support cap assembly  30  with a cover  32  that may cover the apertures in  34  in the support cap  30  during at least one point in time, generally during tube assembly and evacuation. The support cap assembly  30  is similar to support cap  14  in  FIG. 2  in that the assembly  30  also comprises three apertures  34  as would generally be found in an electron gun for a polychromatic tube. In other embodiments, nearly any number of apertures in the support cap assembly  30  may be used. As illustrated, the apertures  34  are exposed. Support cap  30  may comprise a generally can-shaped structure comprising stainless steel or another material of similar physical and reactive properties. The apertures  34  may have a span in the range of approximately 0.5-2 millimeters. Apertures  34  may be positioned such that electrons or other particles emitted from an electron source (e.g., x-rays or the like) (not shown) mounted to the support cap assembly  30  may pass through apertures  34 . 
   In an embodiment, the cover  32  may be stamped, molded, cut, or formed via another common manufacture process and can comprise stainless steel, polyimide, an insulator, or another material able to withstand temperatures in the range of approximately 300-600 degrees Celsius as well as evolving minimal gases when placed in a low pressure environment. The cover  32  may have a length, width, and shape sufficient to cover at least one aperture  34  and may generally have a length and width in the range of approximately 3-20 millimeters and may have a thickness within the range of approximately 25-250 microns. The cover may further comprise openings  36  arranged to expose the apertures  34  when the cover is in an open position as illustrated in FIG.  3 . 
   Another embodiment may comprise a means for displacing the cover  32 .  FIG. 4  illustrates a cover assembly comprising a spring  40  having one end attached to the cap assembly and the other end attached to the cover  32 . Alternatively, the spring may  40  contact but not be attached to the cap assembly. The spring  40  may comprise the same material as the cover  32  and may be soldered, bonded, welded, or otherwise fastened at one end to the cover  32  and at the other end to the cap  30 . In an embodiment the spring  40  may be formed as a part of the cover  32  (i.e., spring  40  and cover  32  from a single piece of material), as illustrated in FIG.  5 . Referring to  FIG. 4 , the spring  40  may be positioned such that it is compressed, or is otherwise storing potential energy, when the cover  32  covers the apertures  34 . 
   An embodiment may comprise a means for releasing the spring. Again referring to  FIG. 4 , the means for releasing the spring  40  may comprise a material  42  fastened at one end to the spring  40  and at another end to a substantially stationary object such as a focus electrode  44 . The material  42  may comprise stainless steel or another conductor and may have a thickness in the range of approximately 30-90 microns and a width in the range of approximately 2-4 mm. Material  42  can comprise a substantially thin portion  46  that may have a width of approximately 1-2 mm. 
   Illustrated in  FIG. 6 , an electrical circuit (not shown) can be activated to pass current through the material  42 , which may act as a fuse. When a sufficient amount of electrical current passes through the material  42 , the thin portion  46  may melt and release the spring  40 . An electrical current of approximately 0.2-1 amp may melt the thin portion  46 . Upon release, the spring  40  may displace the cover  32  such that the apertures  34  are exposed and may allow particles, such as electrons, photons, ions, or the like, to pass through the apertures  34  and openings  36 . Openings  36  in the cover may surround the apertures  34 . After reading the specification, skilled artisans realize that the material and cross-sectional area of the thin portion  46  can determine the current needed to blow the “fuse.” 
   Yet another embodiment may comprise a cover guide  70 , shown in  FIG. 7. A  material, such as stainless steel or any material capable of withstanding temperatures in the range of approximately 300-600 degrees Celsius without substantially deforming or evolving gas or other material may be used. The cover guide  70  may be soldered, bonded, welded, or otherwise attached to the cap  72 . The cover  74  should be able to move along the path of the cover guide  70 . The cover guide  70  may substantially prevent the cover  74  from contacting other parts such as focus electrode  44 . 
   Alternatively, a cap may comprise indentions  80  formed in the side of the cap  84  through crimping, bending, or otherwise indenting the cap  84 , as illustrated in FIG.  8 . The cover  86  may be formed by bending, molding, or otherwise shaping the cover such that portions  82  of the cover  86  fit into cap indentations  80 . 
   In yet another embodiment, the cover assembly may further comprise an actuator. The cover  90  may be displaced by an actuator, such as a gear, piston, electromagnet, or other micro- or nano-machine structure.  FIG. 9  shows a cover  90  formed with teeth  92  along one edge. A gear  94  may be driven by an electric motor (not shown) that may be mounted to the top or side of the cap  96  or to a different structure. An electronic circuit (not shown) can control of the electric motor and may allow the cover  90  to move to completely or partially expose apertures  98 . The cover  90  may be moved more than one time. 
   In an embodiment illustrated in  FIG. 10 , a substantially complete electron gun  100  may comprise a support cap assembly  102  and a cover  104 , both similar to those described above. An electron source  105 , such as a field emission cathode, may be mounted to the support cap  102  using conventional methods such as mounting the electron source  105  to a support  106  and welding, soldering, bonding, or otherwise mounting the support  106  to the cap  102 . 
   The electron gun  100  may further comprise a focus electrode  107  spaced apart and electrically insulated from the cap assembly  102  and comprising a focus aperture  108 . The first focus electrode  107  may be aligned with the support cap  102  such that electrons emanating from the electron source may pass through the support cap  102  and focus electrode  107 . The aligned cap  102  and focus electrode  107  may be assembled using conventional beading processes that result in the insulating support structure  109 . Additional focus electrodes may be used, wherein each focus electrode may have aperture(s) corresponding to aperture(s) in the support cap. 
   An exemplary method of using a tube is illustrated in  FIGS. 11 and 12 . The method can comprise placing at least a portion of an electron gun  110  within a first end of the tube  111 . The electron gun may comprise a support cap  112  comprising, as described above, an aperture  113 , a cover  114 , and a means for displacing the cover, such as a spring  115 . The cover may cover the aperture and thus lie along the path of the electron beam (not shown in  FIG. 11 ) generated when the electron gun is activated. 
   The method may further comprise flowing a gas  117  at least near a portion of the electron gun  110  while the cover  114  covers the aperture  113 . Flowing the gas  117  may comprise evacuating the tube  111 . The tube  111  may generally be pumped down to a pressure of approximately 1E5 torr or lower. The gas may comprise air or common processing gases, such as methane or natural gas, as well as particles existing in the tube, such as DAG or phosphor coatings. The cover  114  may substantially prevent these gases  117  and particles from contaminating the electron source  118 . After the tube  111  is evacuated, the tube  111  may be sealed by conventional tube sealing methods such as a melt  120  shown in FIG.  12 . In addition, gettering agents may be activated to further reduce the pressure in the tube. The cover can prevent these gettering materials from contaminating the particle source. 
   The method may still further comprise moving the cover  114  for a first time to an open (first) position, so that the electron beam  116  can pass through the aperture  113  to a location near a second end of the tube that is opposite the first end. In one embodiment, moving the cover  114  for the first time may permanently move the cover so that it no longer blocks the path of the electron beam  116  that passes through the apertures  113 . The means for displacing the cover may comprise a spring  115  as described above. The spring  115  may be released when a material (not shown), acting as a fuse, is blown by passing an electrical current through it. In an alternative embodiment, the cover may be moved by activating a circuit that moves the cover to expose at least a portion of the aperture. 
   Alternatively, a cover (not shown) may be solid (no apertures) but may be sufficiently thin that the electron beam  116  may erode or break through that cover. In this instance, the cover could be static (i.e., is not moved to align apertures in the cover and cap). 
   In yet another embodiment, the method can further comprise moving the cover at least a second time to a closed (second) position. While the cover  114  lies at the closed position, so the cover  114  substantially prevents the electron beam  116  from reaching a location near an opposite end of the tube. In this particular embodiment, the cover  114  is moved to the open position when the gun is activated to generate the electron beam  116  that passes through the apertures  113 , and the cover  114  is moved to the closed position when the gun is not activated. This method allows electron source  118  to be protected when not in use. The method may comprise activating an actuator (not shown) that moves the cover between the open and closed positions. 
   Accordingly, support caps and electron guns can be produced that may substantially prevent or significantly reduce fouling or contamination of electron sources mounted or used therein. Electron sources used in conjunction with such devices may exhibit longer lifetimes as well as better performance than sources used in prior support caps or electron guns. Tubes used accordingly may be manufactured using conventional methods, but can be manufactured without contaminating the electron source during evacuation and sealing processes. 
   Many other embodiments are possible. In addition to the covers previously described, other attenuators may be used. For example, a miniature electrical precipitator may be used to remove particles (originating from the DAG coating, phosphor, etc.) from the gas during the gas flowing act. Regardless whether the attenuator is a cover or precipitator, the attenuator can block particles from entering aperture(s) in the support cap or support cap assembly. In still another embodiment not illustrated, an attenuator may be activated by a magnetic field used to active the electron gun. The attenuator may rotate as an alternative to linear motion. 
   As used in this specification, “assembly” refers to an item by itself or in conjunction with other parts. For example, the support cap assembly may only include a support cap, a support cap and another member that holds the electron source, or other potential assemblies. Similarly, an attenuator assembly may include a cover, a cover in combination with other parts, an electrical precipitator and its corresponding operating circuit, or other potential assemblies. 
   In the foregoing specification, the invention has been described with reference to specific embodiments. However, after reading this specification, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. 
   Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required or essential feature or element of any or all the claims. 
   As used herein, the terms comprises, comprising, “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. In one example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).