Abstract:
In a fluorescent display tube having an electrostatic capacitor type touch switch portion on a front plate, a shield electrode is provided between a filament cathode and the touch switch portion. Electrons emitted from the filament cathode are prevented from irradiating on the touch switch portion and the touch switch portion and a neighbor thereof are prevented from being charged up, thereby an operation of the electrostatic capacitor type touch switch becomes stable.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to Japanese Patent Application No. 2008-287307 filed on Nov. 8, 2008, the contents of which are hereby fully incorporated by reference. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a fluorescent display device having a touch switch portion. 
         [0005]    2. Description of the Related Art 
         [0006]    It is known that a fluorescent display tube in which electrons emitted from heated filament cathode are caused to impinge upon a phosphor covering a top wall of an anode, and to excite the phosphor to produce luminescence. The fluorescent display tube is used as a display in various electronic/electric devices and a vehicle. Signals to be displayed are normally inputted from a switch provided around the fluorescent display tube. 
         [0007]    Recently, it has been required that the switch is formed on a part of an envelope composing the fluorescent display tube in view of downsizing of components, and design. As an example of such a structure, it is known that a fluorescent display device in which electrodes of a touch switch are arranged adjacent to an inner wall of a front panel which is a part of the envelope, and a detection-control part detects a change of electrostatic capacity between the electrodes to switch a display of the fluorescent display tube (For example, see Japanese Published Patent Application No. S58-5989). 
         [0008]    A fluorescent display device having a conventional touch switch portion will be explained with reference to  FIGS. 6 and 7 .  FIG. 6  is an exploded perspective view showing a conventional fluorescent display tube.  FIG. 7  is a block diagram showing an electrical structure of the whole conventional fluorescent display. In  FIG. 6 , reference numeral  101  indicates a fluorescent display tube. This fluorescent display tube  101  includes an envelope  103  having a display window  102 . This envelope  103  is composed of a substrate  105  on which a pattern display part  104  is formed, a side plate  106  extending vertically on an outer periphery of the substrate  105 , and a front plate  107  overlapped with the substrate  105  to sandwich the side plate  106  with the substrate  105 . 
         [0009]    A NESA film as a transparent conductive film is coated on an inner wall of the front plate  107  to form a transparent switch electrode part  108 . This transparent switch electrode part  108  is composed of a common electrode  108   a  and a plurality of opposite electrodes  108   b  separated from the common electrode  108   a  by an insulating part  109 . A touch switch detecting part S is formed by this switch electrode part  108  and an outer wall  107   a  of the envelope  103 . 
         [0010]    Further, in an interior of the envelope  103  which is maintained in a high vacuum state, anodes  104   a  on which a phosphor is coated to compose the pattern display part  104 , a plurality of control electrodes  110  covering top walls of the anodes  104   a , and a filament cathode  111  disposed above the control electrodes  110  are encapsulated. The electrodes  104   a ,  110 ,  111  are respectively electrically connected to lead terminals  112 ,  112 ,  112  extended outward from the envelope  103 . Components of the switch electrode part  108  are respectively electrically connected to the lead terminals  112  with connecting tongue pieces  113 . 
         [0011]    The common electrode  108   a  and the opposite electrodes  108   b  of the switch electrode part  108  are connected to a switch control circuit part  114  shown in  FIG. 7 . Outputs of the switch control circuit part  114  are connected to anodes  104   a  in the fluorescent display tube  101  and a display control part  115  for controlling electric current applied to the control electrodes  110 . Because the common electrode  108   a  faces the opposite electrodes  108   b  with a gap of the insulating part  109 , electrostatic capacity exists between the electrodes  108   a ,  109  to form a kind of capacitor. 
         [0012]    The switch control circuit part  114  detects a change of the electrostatic capacity between a state that nothing touches the touch switch detecting part S and a state that a finger of an operator touches the switch detecting part S. Then, corresponding to an output of the switch control circuit part  114 , a display of the pattern display part  104  is changed via the display control part  115 . Thus, the fluorescent display tube  101 , the switch control circuit  114 , and the display control part  115  compose the fluorescent display device having a touch switch. 
         [0013]    In  FIG. 6 , electrons emitted from the filament cathode  111  are irradiated on not only the pattern display part  104 , but also the switch electrode part  108  and a neighbor on the inner wall of the front plate  107 . When the electrons are charged in the switch electrode part  108  and the neighbor on the inner wall of the front plate  107 , the electrostatic capacity of these areas are affected, and the switch control circuit  114  may wrongly detect the signal. Thus, there is a problem that a wrong display is displayed on the pattern display part  104  via the display control part  115 . 
         [0014]    Accordingly, in view of the problem in the fluorescent display device having a touch switch, an object of the present invention is to provide a fluorescent display tube having a touch switch to prevent the touch switch from detecting wrongly, and a fluorescent display device using the fluorescent display tube. 
       SUMMARY OF THE INVENTION  
       [0015]    In order to attain the object, according to the present invention, there is provided a fluorescent display device including: a fluorescent display tube having an envelope having a front plate with at least partially a display window, a filament cathode for emitting electrons, anodes on which a phosphor, which is excited and exhibits luminescence by an electron, is coated, said anodes being selectable corresponding to display data, a touch switch portion formed on an inner wall of the display window of the front plate, and a shielding electrode interposed between the filament cathode and the touch switch portion; a switch control part electrically connected to the touch switch portion for outputting the display data corresponding to an input from the touch switch portion; and a display control part. 
         [0016]    According to another aspect of the present invention, there is provided a fluorescent display tube including: an envelope having a front plate with at least partially a display window; a filament cathode for emitting electrons; anodes on which a phosphor, which is excited and exhibits luminescence by an electron, is coated, said anodes being selectable corresponding to display data; a touch switch portion formed on an inner wall of the display window of the front plate for outputting a signal to a switch control circuit; and a shielding electrode interposed between the filament cathode and the touch switch portion. 
         [0017]    In yet another aspect of the present invention, there is provided a fluorescent display tube including: an envelope having a front plate with at least partially a display window; a filament cathode for emitting electrons; anodes on which a phosphor, which is excited and exhibits luminescence by an electron, is coated, said anodes being selectable corresponding to display data; a touch switch portion formed on an inner wall of the display window of the front plate; a shielding electrode interposed between the filament cathode and the touch switch portion; and a switch control part electrically connected to the touch switch portion for outputting the display data corresponding to an input from the touch switch portion and a display control part disposed in the envelope. 
         [0018]    Preferably, the shielding electrode is a mesh-shaped metallic electrode. 
         [0019]    Preferably, the shielding electrode is fixed to the front plate at around the display window. 
         [0020]    Preferably, the same electric potential as applied to the filament cathode or the lower electric potential than that applied to the filament cathode is applied to the shielding electrode. 
         [0021]    Preferably, the touch switch portion is made of a stripe-shaped or mesh-shaped metallic thin film electrode. 
         [0022]    Preferably, a dummy electrode electrically independent from the touch switch portion and covering the display window is formed around the touch switch portion. 
         [0023]    Preferably, the electric potential of the dummy electrode is fixed to the predetermined electric potential. 
         [0024]    Preferably, the touch switch portion includes four electrodes indented each other, and detects electrostatic capacity in a manner that the electrodes at both ends are in the same phase, and the other electrodes are in phases respectively shifted 120 degree. 
         [0025]    These and other objects, features, and advantages of the present invention will become more apparent upon reading of the following detailed description along with the accompanied drawings. 
       EFFECT OF THE INVENTION  
       [0026]    In the fluorescent display device or the fluorescent display tube of the present invention, because the shielding electrode is interposed between the filament cathode and the touch switch portion, the electron emitted from the cathode is shielded by the shielding electrode, and the touch switch portion receives no charge. Therefore, the switch control circuit part  114  may not detect wrongly, and the pattern display part  104  may not display wrongly via the display control part  115 . 
         [0027]    Further, because the shielding electrode is a mesh-shaped metallic electrode, the shielding electrode can shield the electron without disturbing the display of the pattern display part  104 . 
         [0028]    Further, because the shielding electrode is fixed to the front plate at around the display window, a fixed part is not visible, and does not disturb the display of the pattern display part  104 . 
         [0029]    Further, because the electric potential of the shielding electrode is at the same or lower than that of the filament cathode, the electron is reflected by the electric field, and a shielding effect of the electron is improved. 
         [0030]    Further, the touch switch portion is made of a stripe-shaped or mesh-shaped metallic thin film electrode. Because the metallic thin film electrode is widely used in an anode producing process of the fluorescent display tube, the touch switch portion is similarly produced in the anode producing process. 
         [0031]    Further, because the dummy electrode covering the display window is provided around the touch switch portion, an outlook of the display window is even, and a light emitting state of the pattern display part  104  is even in the touch switch portion and the neighbor thereof. 
         [0032]    Further, because the electric potential of the dummy electrode is fixed to a predetermined electric potential, the charge of the electron emitted from the filament cathode is surely prevented. 
         [0033]    Further, the four electrodes indented each other can allow the switch to work properly under a condition that the effect of the charge is shielded by the shielding electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a front view showing a fluorescent display tube according to an embodiment of the present invention; 
           [0035]      FIG. 2  is a sectional view taken on line X-X of  FIG. 1 ; 
           [0036]      FIG. 3  is a view showing a physical relationship between a switch electrode and a phosphor pattern according to the embodiment of the present invention; 
           [0037]      FIG. 4  is an explanatory view showing an operating principle of a electrostatic capacity type touch switch according to the embodiment of the present invention; 
           [0038]      FIG. 5  is a front view showing the fluorescent display tube according to the embodiment of the present invention; 
           [0039]      FIG. 6  is an exploded perspective view showing a conventional fluorescent display tube; and 
           [0040]      FIG. 7  is a block diagram showing an electrical structure of the whole conventional fluorescent display. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    A fluorescent display device according to an embodiment of the present invention will be explained with reference to  FIGS. 1 to 4 .  FIG. 1  is a front view showing a main part of a fluorescent display tube  1 .  FIG. 2  is a sectional view taken on line X-X of  FIG. 1 . In  FIG. 2 , a supporting structure of the filament cathode  111  is omitted. 
         [0042]    In  FIG. 2 , a terminal part  11  on which a tip part  112   a  of the lead terminal  112  is touched and a wiring  12  electrically connected to the terminal part  11  are made of a metallic thin film and formed on the substrate  105 . An insulating layer  13  is formed on the wiring  12 , and a conductor  15  contacts the wiring  12  via a through-hole  14  of the insulating layer  13 . A phosphor layer  16  covers a top wall of the conductor  15 . The insulating layer  13 , the conductor  15 , and the phosphor layer  16  correspond to the pattern display part  104  in the prior art. A control electrode  110  is fixed to the substrate  105  with an electrically conductive adhesive  17  so as to cover the insulating layer  13 , the conductor  15 , and the phosphor layer  16 . The control electrode  110  is connected to the terminal  112  with wiring (not shown). 
         [0043]    A terminal part  18  on which a tip part  112   b  of the lead terminal  112  is touched and a switch electrode  19  electrically connected to the terminal part  18  are made of a metallic thin film and formed on the front plate  107 . The metallic thin film is made by sputtering material such as aluminum, or niobium, and by etching to form a specific pattern. The switch electrode  19  is composed of a rectangular frame having a line width of about twenty to thirty micron, and stripe-shaped or mesh-shaped narrow lines having a line width of about twenty to thirty micron arranged in the frame with fifty to sixty micron intervals. 
         [0044]    A specific range from an end of an inner wall of the front plate  107  is covered with a light-blocking and insulating crossover layer  20  except the terminal  18 . An inside of the crossover layer is the display window  102 . Preferably, the display window  102  has enough space to see the pattern display part  104 . The switch electrode  19  is provided on a part of the display window  102 . A shield electrode  21  is fixed to the crossover layer  20  with an electrically conductive adhesive  22  so as to cover the display window  102 . The shield electrode  21  is connected to the lead terminal  112  with wiring (not shown) via the terminal part  18  and the tip part  112   b . The filament cathode  111  is interposed between the shield electrode  21  and the control electrode  110 . 
         [0045]    The crossover layer  20  is formed by printing and burning a paste composed of a black-pigment-mixed low-softening-temperature glass frit. A mesh made of stainless steel or nickel-chromium alloy having a thickness of about fifty micron similar to the control electrodes  110  of the fluorescent display tube  1  is used as the shield electrode  21 . The electrically conductive adhesive  22  is made of a mixture composed mostly of a powdered metal, such as aluminum, and a low-softening-temperature glass frit. 
         [0046]    In the front view of  FIG. 1 , the crossover layer  20  is extended all around the front plate  107  in a specific width from an edge of the front plate  107 , and the display window  102  is formed in an inside of the crossover layer  20 . Because the electrically conductive adhesive  22  fixing the shield electrode  21  is disposed at a rear of the crossover layer  20 , the electrically conductive adhesive  22  cannot be seen from a front side of the fluorescent display tube  1 . The shield electrode  21  is provided on the display window  102  except both ends of the display window  102 . This corresponds to a whole area in which the shield electrode  21  can be extended and the pattern display part  104  can be formed. Areas  102   a ,  102   b  which are not covered with the shield electrode  21  are the areas on which supporters supporting the filament cathode  111  are provided, thereby no display can be displayed on the areas  102   a ,  102   b.    
         [0047]    In  FIG. 1 , a linear switch  23  composed of four linear switch electrodes  23   a  to  23   d  which outputs, for example, with a 128-position resolution and three switch electrodes  19  are provided on an area of the shield electrode  21 . A behavior of the linear switch  23  is described later. A switch electrode  19  is provided in each of the display windows  102   a ,  102   b.    
         [0048]      FIG. 3  shows a physical relationship between these switch electrodes  19  and patterns of the phosphor layer  16  provided on the pattern display part  104 . In  FIG. 3 , a phosphor pattern  16   a  indicating a word “HDD”, a phosphor pattern  16   b  indicating a word “USB”, a phosphor pattern  16   c  indicating a symbol of “mail”, and a phosphor pattern  16   d  indicating a bar graph are provided over the substrate  105 . Boxes composed of a dashed line  19 ′ indicate positions of the switch electrodes  19 , and a box composed of a dashed line  23 ′ indicates a position of the linear switch  23 . 
         [0049]    Each time when an operator&#39;s finger touches the outer wall  107   a  upon the switch electrode  19  on the phosphor layer  16 , the electrostatic capacitor of the switch electrode  19  is changed. The change is judged and outputted by the switch control circuit part  114 , and the display control part  115  receives the output and turns on/off the light of the phosphor layer  16 . 
         [0050]    Further, when an operator&#39;s finger touches the outer wall  107   a  upon the linear switch  23 , an output from the linear switch  23  is continuously changed corresponding to the touching position to vary a lighting area of the bar graph. The output can be also used to adjust a volume of a speaker which is simultaneously used with the fluorescent display tube  1 . 
         [0051]    An operating principle of a touch switch according to the present invention will be explained with reference to  FIG. 4 . A switch control circuit  2  includes a pulse generator  24 , a comparator  25 , and a capacitor C interposed between one of inputs of the comparator  25  and the pulse generator  24 . The switch electrode  19  is connected to the pulse generator  24  and to another input of the comparator  25 . 
         [0052]    When the operator&#39;s finger touches the outer wall  107   a  (touching point S) on the switch electrode  19 , an electrostatic capacitor is generated between the finger and the switch electrode  19  as a kind of a capacitor. The capacitor C corresponds to the electrostatic capacitor of the switch electrode  19  on which the finger is not touched. 
         [0053]    When the operator&#39;s finger touches the touching point S, the finger works as a dielectric body, and the electrostatic capacitor of the switch electrode  19  is changed. Then, a balance between the electrostatic capacitors of the switch electrode  19  and the capacitor C breaks down, and pulse voltages applied to both inputs of the comparator  25  become different from each other, and an output is outputted from the comparator  25 . 
         [0054]    In the linear touch switch  23 , electrodes at the both ends  23   a ,  23   d  are connected to a common line, and the electrodes  23   b ,  23   c  are connected to independent lines, and the electrodes are used as three sets of electrodes. These sets are respectively driven by wave signals each having substantially the same amplitude and shifted by 120 degree. 
         [0055]    The additional electrostatic capacitor formed by touching the outer wall  107   a  with the operator&#39;s finger is changed corresponding to the position of the finger, and the phase of the signal generated from the electrode under the outer wall  107   a  is changed corresponding to the position of the finger touching the outer wall  107   a.    
         [0056]    This signal is inputted to the switch control circuit part  114 , and predetermined display data is outputted to the display control part  115  based on this signal, and a display on the fluorescent display tube  1  is changed. A drive circuit and the like of this linear touch switch is already known by Japanese Published Patent Application No. S56-1438 and the like, and an explanation of these is omitted here. 
         [0057]    Incidentally, the electrostatic capacitor type touch switch used in the present invention is not limited to the switch described in this embodiment, and various touch switches in the prior art can be used. Further, a well-known display control circuit using a microprocessor and a driver can be used as the display control circuit in the present invention. 
         [0058]    An operating condition of the touch switch when an electric potential applied to the shield electrode  21  is changed will be explained. A structure of an assessed sample is that a height from an inner wall of the substrate  105  to the control electrodes  110  is about 0.5 mm, a height to the filament cathode  111  is about 1.5 mm, a height from an inner wall of the front plate  107  to the shield electrode  21  is about 0.5 mm, and a height to the filament cathode  111  is about 1.5 mm. 
         [0059]    While 5 volts is applied to the filament cathode  111 , 45 volts is applied to the control electrodes  110  and the wiring  12 , and the voltage potential of the shield electrode  21  is changed from 0 to 20 volts, when the electric potential of the shield electrode  21  is over 10 volts, an operation of the touch switch using the switch electrode  19  becomes unstable. 
         [0060]    This is believed that when the electric potential of the shield electrode  21  is higher than the electric potential of the filament cathode  111 , an electron beam irradiates the switch electrode  19 . Accordingly, preferably, the electric potential of the shield electrode  21  is the same as or lower than that of the filament cathode  111 . This unstable operation is more notable in the linear switch which detects more strictly the position of the operator&#39;s finger. 
       Embodiment 1 
       [0061]    An embodiment of the present invention will be explained with reference to  FIG. 5 . In  FIG. 5 , the display window  102  is covered by a dummy pattern  26  except the switch electrode  19 , a wiring connecting the switch electrode  19  and the terminal part  18 , the linear switch electrodes  23   a  to  23   d , and wirings connecting the linear switch electrodes  23   a  to  23   d  and the terminal parts  18 . 
         [0062]    Similar to the switch electrode  19 , the dummy pattern  19  is formed by arranging the stripe-shaped or mesh-shaped narrow lines having a line width of about twenty to thirty micron with fifty to sixty micron intervals. Preferably, the dummy pattern is produced in the same process as the switch electrode  19 , and a pattern design of the dummy pattern is the same as the switch electrode  19 . 
       Embodiment 2 
       [0063]    As another embodiment of the present invention, a fluorescent display tube having the switch control circuit part  114  and the display control part  115  will be explained. Recently, so-called chip-in-glass fluorescent display tube in which a plurality of driver ICs are assembled on the substrate  105  has been known. 
         [0064]    According to the present invention, not only a driver IC but also ICs of the switch control circuit part  114  and the display control part  115  can be assembled on the substrate  105  of the fluorescent display tube  1 . Thus, a smaller fluorescent display tube module can be realized than a module in which the switch control circuit part  114  and the display control part  115  are assembled on a print circuit board. 
         [0065]    Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.