Abstract:
A display device has the first and second flexible printed circuits (FPCs). An end of the first FPC is connected to a terminal on the second FPC. The first and second FPCs transmit electrical signals to a heater and an LCD panel, respectively. Only the first FPC is connected to an external part. With above configuration, electrical signals are inputted to both LCD and heater. A process of electrically connecting the display device to the external part is simplified, because only the first FPC is connected to the external part which controls both LCD and heater.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-212556 filed on Jul. 12, 2001.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to a display device utilizing an LCD panel and an assembling method for the device.  
         BACKGROUND OF THE INVENTION  
         [0003]    A display device utilizing an LCD panel is generally mounted in a meter panel to display information that a driver needs. The response characteristic of the LCD is exacerbated under low temperature. To maintain the LCD at a proper temperature, a transparent plane heater is mounted on the LCD surface.  
           [0004]    The LCD and heater generally have conductive members, such as flexible printed circuit (FPC) boards. Those conductive members are used for transmitting electrical signals to the LCD and heater from other parts. The LCD and heater are separately assembled and glued together. However, the LCD and heater are not electrically connected. Therefore, when mounting the display device in the meter panel, each conductive member of the LCD or the heater is electrically connected to external parts. This requires a large amount of man-hours.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention therefore has an objective to provide a display device and its assembly method that reduces man-hours required for making electrical connections of the device.  
           [0006]    According to the present invention, a conductive member for an LCD and a conductive member for a heater are electrically connected. With this configuration, electrical signals from external parts are transmitted to the LCD and heater via either of the conductive members that is electrically connected to the external parts. Since connecting points with the external parts are reduced, the amount of man-hours required for making electrical connections can be reduced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The above and other objectives, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:  
         [0008]    [0008]FIG. 1A is a front view of a display device according to the first embodiment of the present invention;  
         [0009]    [0009]FIG. 1B is a side view of the display device shown in FIG. 1A;  
         [0010]    [0010]FIG. 2A is a front view of a heater included in the device shown in FIG. 1A;  
         [0011]    [0011]FIG. 2B is a side view of the heater shown in FIG. 2A;  
         [0012]    [0012]FIG. 3 is a block diagram showing an electrical circuit of the display device according to the first and second embodiments of the present invention;  
         [0013]    [0013]FIG. 4 is a front view of a display device according to the second embodiment of the present invention;  
         [0014]    [0014]FIG. 5 is a side view of the display device shown in FIG. 5;  
         [0015]    [0015]FIG. 6 is a front view of a modified display device shown in FIG. 1A;  
         [0016]    [0016]FIG. 7A is a front view of another modified display device shown in FIG. 1A; and  
         [0017]    [0017]FIG. 7B is a side view of the modified display device shown in FIG. 1B. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Preferred embodiments of the present invention will be explained with reference to the accompanying drawings. In the drawings, the same numerals are used for the same components and devices.  
         [0019]    [First Embodiment] 
         [0020]    Referring to FIGS. 1A and 1B, a display device  1  has an LCD panel  10  and a heater  20 . The device  1  is connected to an external drive unit  100  that controls displaying operation of the device  1  as shown in FIG. 3. The device  1  performs the displaying operation based on drive signals from the drive unit  100 . The drive unit  100  also controls a power supply to the heater  20  to maintain the LCD  10  at a proper temperature.  
         [0021]    Referring to FIG. 3, the LCD  10  has a display  11 , a driver  14 , a flexible printed circuit (FPC) board  12 . The display  11  has a pair of glass substrates (not shown). On the inner surface of the glass substrates, transparent electrodes are provided. A liquid crystal material is sealed between the glass substrates.  
         [0022]    The driver  14  is an integrated circuit (IC). It controls a voltage application to the transparent electrodes so that the displaying operations are properly performed based on the electrical signals from the unit  100 . When the device  1  is installed in an instrument panel, an end  12   a  of the FPC  12  is connected to a printed circuit board (PCB) on which the unit  100  is mounted. When an electrical signal is supplied to the driver  14  via the FPC  12 , the displaying operation starts.  
         [0023]    A terminal  12   b  is extended from the FPC  12  and located between the end  12   a  and display  11 . The terminal  12   b  is provided to electrically connect the LCD  10  with the heater  20 . A thermistor  13  is a temperature sensor mounted on the FPC  12  at an appropriate position for a display temperature measurement. Power is supplied to the heater  20  based on the measured temperature so that the display is maintained at the predetermined temperature.  
         [0024]    Referring to FIGS. 2A and 2B, the heater  20  has a heating element  21  and an FPC  22 . The heating element  21  has a transparent heating material affixed to the surface of a transparent glass plate. The plate is approximately in the same size and shape as the display  11 . An example of the heating material is an indium tin oxide (ITO).  
         [0025]    The FPC  22  has two arms  22   b  and  22   c  fixed to the heating element  21  along its vertical edges. The FPC  22  refers to as the second conductive member and transmits electrical signals. The end  22   a  of the FPC  22  is soldered to the terminal  12   a . Therefore, power is supplied to the heater  20  via the FPCs  12  and  22 . This requires only one connecting point to make an electrical connection between the device  1  and external parts. Therefore, man-hours required for soldering can be reduced.  
         [0026]    Moreover, a temperature switch is mounted on the FPC  22  to halt a power supply to the heating element  21  when a temperature of the element  21  exceeds a predetermined value. An example of the temperature switch is a positive temperature coefficient (PTC) switch. When the temperature of the PTC switch exceeds the predetermined value, a resistance of the PTC switch is increased. This automatically reduces a current supply to the element  21  to prevent an excessive temperature increase of the heating element  21 .  
         [0027]    The method for producing the display device  1  includes the following steps.  
         [0028]    (1) Mounting the driver  14  on the glass plate of the LCD  10 .  
         [0029]    (2) Affixing one end of the FPC  12  to the transparent plate that is extended to the glass plate with solder or adhesive.  
         [0030]    (3) Mounting the thermistor  13  on the FPC  12 .  
         [0031]    (4) Fusion bonding or soldering arms  22   b  and  22   c  of the FPC  22  onto the heating element  21  along its vertical edges.  
         [0032]    (5) Mounting the temperature switch  23  on the FPC  22 .  
         [0033]    (6) Affixing the heating element  21  to the back of the LCD  10  with a double-faced tape or an adhesive.  
         [0034]    (7) Soldering the end  22   a  of the FPC  22  to the terminal  12   b  that is located at the middle point of the FPC  12  so that they are electrically connected.  
         [0035]    [Second Embodiment] 
         [0036]    Referring to FIGS. 4 and 5, a display device  30  includes the display device  1  shown in FIGS. 1A and 1B, a speedometer  31 , a printed circuit board (PCB)  32 , a backlight  33 , the drive unit  100  shown in FIG. 3 and a meter case. The display device  1  is installed in a lower part of a display board  34  so that it faces toward a driver. The display board  34  is a part of a speedometer. The end  12   a  of the FPC  12  is soldered to the printed circuit board (PCB)  32 . The FPC  12  transmits electrical signals to the device  1 . The PCB  32  has the drive unit  100  that controls display operation of the device  1 . The device  1  is connected to the drive unit  100  via the PCB  32 .  
         [0037]    Referring to FIG. 3, when an ignition (IG) switch  102  is closed, power is supplied to the drive unit  100 . Then, the drive unit  100  starts display operation control to the device  1  and power supply control to the heater  20 . Various sensors are connected to the drive unit  100 . Those sensors include room temperature sensor  103 , outside air temperature  104 , mileage sensor  105  and door switch sensor  106 . The drive unit  100  processes output signals from those sensors and the processed signals are inputted to the device  1  via the FPC  12 . Then, the device  1  starts predetermined display operations.  
         [0038]    Even when the IG switch  102  is open, power can be supplied to the drive unit  100  by a battery  101 . The drive unit  100  starts power supply control to the heater  20  when open and close of a door is detected by the door switch sensor  106 . As a result, the LCD  10  is warmed up to the appropriate temperature so that the device  1  can provide stable display operation from the point that the IG switch is closed.  
         [0039]    The backlight  33  is mounted on the PCB  32 . The device  1  performs display operations in the condition that the display  11  is irradiated with a light from the backlight  33  via the heater  20 . This provides good visibility to a driver. Moreover, heat produced by the backlight  33  also warms up the display  11 . Since a transparent heating material (e.g., ITO) is used for the heater  20 , light from the backlight  33  hardly fades. Therefore, sufficient brightness can be provided. The temperature sensor  13  detects a condition in which sufficient temperature is not provided by the backlight  33  for maintaining the display operation. When that condition is detected, heat is produced until the temperature reaches a predetermined value.  
         [0040]    In the device  1 , the end  22   a  of the FPC  22  is soldered to the terminal  12   b  and the end  12   a  is electrically connected to the external parts. The other end of FPC  12  is soldered to the transparent electrode on the LCD  10 . The terminal  12   b  is located at the vertical edge of the FPC  12 . The arms  22   b  and  22   c  of the FPC  22  are soldered to the heater  20 .  
         [0041]    In the assembly process for the display device  30 , the display device  1  and PCB  32  are electrically connected in one step. This reduces man-hours for electrical connecting process of the device  30  in comparison with methods used previously.  
         [0042]    The above embodiments can be modified as shown in FIG. 6. One more terminal  12   b  is added to the FPC  12 . Even with this configuration, only one point of the FPC  12  is soldered for electrically connecting the device  1  with the PCB  32 . Therefore, man-hours for electrical connecting process can be reduced.  
         [0043]    The above embodiments can be modified as shown in FIGS. 7A and 7B. In this configuration, the terminal  12   b  is located at the extended part of the FPC  12  on the LCD  10 . The end  22   a  of the FPC  22  is bent so that it wraps under the heater  20  and LCD  10  to be soldered to the terminal  12   b . This eliminates unwanted extended part provided at the edge of the FPC  12 .  
         [0044]    In the above embodiments, the heating element  21  may be mounted on the front of the LCD  10 .