Abstract:
A display apparatus has a compressor cooler having a condenser that condenses refrigerant by radiating heat, an evaporator that evaporates the refrigerant for heat absorption and dehumidification, and a compressor that inhales vapor generated by the evaporator and compresses the vapor to be condensed; a temperature sensor that monitors temperature of the evaporator; a backlight; a first control portion that terminates the compressor when the temperature of the evaporator is a first predetermined temperature or lower; and a second control portion that increases a level of the backlight when the temperature of the evaporator is a second predetermined temperature or lower, wherein the second predetermined temperature is higher than the first predetermined temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on Japanese Patent Application No. 2010-265512 filed on Nov. 29, 2010, the contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a display apparatus and electronic equipment. 
         [0004]    2. Description of Related Art 
         [0005]    Recent years, a liquid crystal display apparatus is used for digital signage. Such display apparatus has a sealed structure, because the apparatus may be installed outdoors and thus it is necessary to prevent water or dust from entering into the apparatus. In addition, these display apparatus can display with high luminance in order to keep the visibility in the outdoors. 
         [0006]    When the display apparatus is displaying an image with high luminance, or when it is being irradiated by sunlight, heat is generated inside the housing of the apparatus. As for the display apparatus having a sealed structure as described above, it is difficult for the heat generated inside the housing to dissipate outside the housing. As a result, temperature inside the housing may rise and a malfunction of liquid crystal in the liquid crystal display apparatus may occur. 
         [0007]    One improvement is to employ a compressor-based cooling system into those LCD displays in order to solve the above-mentioned problems as described in JP 2010-164884A1 which was filed by the applicant. The disclosures of which are hereby incorporated by reference as if set forth in full herein. 
         [0008]    However, in the above-mentioned liquid crystal display apparatus, since the display apparatus is sealed structured, a dew-condensation in the housing may occur. In particular, during a cold winter season, since the outside temperature becomes lower than the temperature inside the housing, the temperature difference between the outside and the inside of the housing may cause a dew-condensation on a protection glass arranged in the front side of the liquid crystal panel. This dew-condensation decreases visibility of an image displayed on the liquid crystal panel. In order to avoid this dew-condensation, one idea is to perform dehumidification by activating a cooler when a humidity level becomes a certain level or higher. However, if the cooler is activated when the ambient temperature is low, its evaporation temperature decreases and the refrigerant pressure inside the evaporator becomes too low. This may cause a safety problem for cooler. 
       SUMMARY OF THE INVENTION 
       [0009]    A display apparatus according to the present invention includes a compressor refrigerator including a condenser that condenses refrigerant by thermal radiation, an evaporator that evaporates the refrigerant so as to perform heat absorption and dehumidification, and a compressor that inhales vapor generated by the evaporator and increases the pressure of the vapor to be condensed, a temperature sensor that monitors temperature of the evaporator, a backlight, a first control portion that stops the compressor when the temperature of the evaporator is a first predetermined temperature or lower; and a second control portion that increases a level of the backlight when the temperature of the evaporator is lower than or equal to a second predetermined temperature that is higher than the first predetermined temperature. 
         [0010]    In addition, electronic equipment according to the present invention includes a cooler including at least a compressor, a temperature sensor that measures temperature, a humidity sensor that measures humidity, and a control portion that activates the compressor when the temperature measured by the temperature sensor is higher than a first temperature and stops the compressor when the measured temperature is lower than a second temperature that is lower than the first temperature, wherein the control portion also activates the compressor when the measured temperature is between the first temperature and the second temperature, and the humidity measured by the humidity sensor is higher than a predetermined humidity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view illustrating a structure of a display apparatus  1 . 
           [0012]      FIG. 2  is a first cross sectional view illustrating the structure of the display apparatus  1 . 
           [0013]      FIG. 3  is a second cross sectional view illustrating the structure of the display apparatus  1 . 
           [0014]      FIG. 4  is a diagram illustrating a structure of cooler  30 . 
           [0015]      FIG. 5  is a block diagram of the display apparatus  1 . 
           [0016]      FIG. 6  is a flowchart illustrating a first example of temperature and humidity control performed by the display apparatus  1 . 
           [0017]      FIG. 7  is a flowchart illustrating a second example of temperature and humidity control performed by the display apparatus  1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    Hereinafter, an embodiment of a display apparatus according to the present invention will be described with reference to the attached drawings. First, a structure of the display apparatus will be described with reference to  FIGS. 1 to 3 . 
         [0019]    &lt;Structure of Display Apparatus&gt; 
         [0020]      FIG. 1  is a perspective view illustrating a structure of a display apparatus  1 . The display apparatus  1  has an upper housing  10  which is the housing on the upper part side and a lower housing  20  which is the housing on the lower part side. The upper housing  10  has a window part  11  so that an image displayed on a liquid crystal panel  12  (described later) arranged inside the upper housing  10  is viewable. The window part  11  is made of material which is transparent against a visible light such as glass. 
         [0021]      FIG. 2  is a diagram illustrating an A-A cross sectional view of the display apparatus  1  illustrated in  FIG. 1 . 
         [0022]    As illustrated in  FIG. 2 , inside the upper housing  10 , the liquid crystal panel  12  displaying an image, a backlight  13  irradiating light to the panel  12 , fans  14   a  and  14   b  circulating air inside the upper housing  10 , temperature sensors  15   a  and  15   b  detecting temperature inside the upper housing  10  (see  FIG. 3  for detail), humidity sensors  17   a  and  17   b  detecting humidity inside the upper housing  10 , and an evaporator  31  cooling the inside of the upper housing  10  so as to perform dehumidification are arranged. 
         [0023]    Further, as illustrated in  FIG. 2 , inside the lower housing  20 , a compressor  32  compressing refrigerant, a condenser  33  condensing the refrigerant compressed by the compressor  32  by heat radiation, and an expansion valve  34  that expands the refrigerant condensed by the condenser  33  are arranged. The evaporator  31  absorbs heat by evaporating the refrigerant expanded by the expansion valve  34 . The compressor  32  compresses the refrigerant evaporated by the evaporator  31 . Hereafter, group that consist of the evaporator  31 , the compressor  32 , the condenser  33 , and the expansion valve  34  is referred to as a cooler  30 . Details of this cooler  30  will be described later. 
         [0024]    The liquid crystal panel  12  controls orientation of liquid crystal so as to selectively transmit light from the backlight  13 , and hence an image is displayed. The image displayed on the liquid crystal panel  12  is viewable from the outside of the upper housing  10  through the window part  11 . The backlight  13  is constituted of, for example, a fluorescent tube or light emitting diodes. The backlight  13  may comprise a diffuser panel that diffuses light emitted from the light source so as to irradiate a plane (or uniform) light to the liquid crystal panel  12 , and a reflector plate that reflects light emitted from the light source. 
         [0025]    The fan  14   b  is arranged at a lower portion of the upper housing  10  and blows cooled air cooled by the evaporator  31  towards a front surface of the liquid crystal panel  12 . The fan  14   a  is arranged at an upper portion of the upper housing  10  and blows air which has passed the front surface side of the liquid crystal panel  12  to the rear side of the panel  12 . Then, this air further passes the rear side of the liquid crystal panel  12  and reaches the evaporator  31 . By circulating the air inside the upper housing  10  using the fans  14   b  and  14   a , the liquid crystal panel  12  is cooled effectively. The number or arrangement of the fans  14   b  and  14   a  are not limited to the above example. Hereafter, the fans  14   b  and  14   a  are generically referred to as a fan  14 . 
         [0026]      FIG. 3  is a diagram illustrating a B-B cross sectional view of the display apparatus  1 . 
         [0027]    As illustrated in  FIG. 3 , four temperature sensors  15   a ,  15   b ,  15   c , and  15   d  are arranged inside the upper housing  10 . Further, four humidity sensors  17   a ,  17   b ,  17   c , and  17   d  are also arranged inside the upper housing  10 . Each of the temperature sensors  15   a ,  15   b ,  15   c , and  15   d  is constituted of a temperature detecting element such as a thermistor for example. Each of the humidity sensors  17   a ,  17   b ,  17   c , and  17   d  is constituted of a humidity detecting element such as a high polymer humidity sensing element, which is an element that detects humidity based on a variation of an electrical characteristic (such as resistance or capacitance) of high polymer according to moisture). As illustrated in  FIG. 2 , each of the above-mentioned temperature sensors  15   a  to  15   d  and the humidity sensors  17   a  to  17   d  are disposed between the window part  11  and the liquid crystal panel  12 . 
         [0028]    The temperature sensor  15   a  and the humidity sensor  17   a  are arranged on the upper right side of the window part  11 . The temperature sensor  15   b  and the humidity sensor  17   b  are arranged on the lower right of the window part  11 . The temperature sensor  15   c  and the humidity sensor  17   c  are arranged on the upper left side of the window part  11 . The temperature sensor  15   d  and the humidity sensor  17   d  are arranged on the lower left side of the window part  11 . However, the arrangement of the temperature sensors or the humidity sensor is not limited to the above. For instance, only a single humidity sensor may be arranged near the evaporator  31 . 
         [0029]    &lt;Schematic Structure of Cooler&gt; 
         [0030]    With reference to  FIG. 4 , a structure of the cooler  30  will be described. 
         [0031]    The cooler  30  includes an evaporator  31 , the compressor  32 , the condenser  33 , and the expansion valve  34 . In this cooler  30 , the refrigerant circulates in a closed loop, and there is no need to exchange the refrigerant. 
         [0032]    The compressor  32  compresses the refrigerant evaporated by the evaporator  31  so that the refrigerant becomes a high temperature and high pressure state. The condenser  33  condenses the refrigerant compressed by the compressor  32 , by heat exchange (heat radiation). The cooler  30  may include a fan for expediting the heat exchange in the condenser  33 . 
         [0033]    The expansion valve  34  expands the refrigerant condensed by the condenser  33  so that the refrigerant becomes a low temperature and low pressure state. Then, the evaporator  31  evaporates the refrigerant expanded by the expansion valve  34  by heat exchange (heat absorption). Here, moisture contained in the air inside the upper housing  10  is dew-condensed on the evaporator  31 . Then, moisture dew-condensed on the evaporator  31  is drained outside the upper housing  10 . The cooler  30  may include a fan for expediting heat exchange or dehumidification in the evaporator  31 . 
         [0034]    As described above, the cooler  30  cools and dehumidify the inside of the upper housing  10 , by changing the state of the refrigerant between liquid and gas repeatedly and by the exchanging heat (heat absorption and radiation). 
         [0035]    At inlet of the evaporator  31  in a flow path of the refrigerant, evaporator temperature sensor  311  detecting temperature of the evaporator  31  or evaporator pressure sensor  312  detecting pressure of the evaporator  31  is arranged. Further, at outlet of the condenser  33 , a condenser temperature sensor  332  detecting temperature of the condenser  33  and a condenser pressure sensor  331  detecting pressure of the condenser  33  are arranged. 
         [0036]    Each of the evaporator temperature sensor  311  and the condenser temperature sensor  332  has a temperature detecting element (e.g., a thermistor). The evaporator temperature sensor  311  indirectly detects temperature of the refrigerant flowing into the evaporator  31 . In detail, the sensor  311  detects temperature of the refrigerant between outgoing from expansion valve  34  and ingoing to evaporator  31 . The condenser temperature sensor  332  detects temperature of the refrigerant flowing out from the condenser  33 . In detail, the sensor  332  indirectly detects temperature of the refrigerant condensed by the condenser  33  before it is expanded by the expansion valve  34 . 
         [0037]    In the cooler  30 , if the flow path of the refrigerant is in a “closed loop”, a relationship between the pressure and the temperature of the refrigerant is uniquely determined. Therefore, by referring to the temperature detected by the evaporator temperature sensor  311 , the pressure of the refrigerant can be estimated. 
         [0038]    Instead, the pressure of the refrigerant may be measured directly using pressure sensors  312  and  331  may be adopted. These pressure sensors have a pressure detecting element such as a strain gage (which detects deformation of diaphragm caused by pressure of the refrigerant). 
         [0039]    &lt;Control of Temperature and Humidity&gt; 
         [0040]    The control of temperature and humidity of the display apparatus  1  is described with reference from  FIGS. 5 to 7 .  FIG. 5  is a block diagram illustrating a schematic structure of the apparatus  1 . 
         [0041]    As illustrated in  FIG. 5 , the display apparatus  1  has a control portion  16  that controls operations of the cooler  30 , the liquid crystal panel  12 , the backlight  13 , and the fan  14 . The control portion  16  obtains information detected by the temperature sensor  15 , the humidity sensor  17 , the evaporator temperature sensor  311 , and the condenser temperature sensor  332 . 
         [0042]    The cooler  30  is designed to terminate its operation when the pressure of the evaporator  31  becomes lower than a predetermined pressure. The cooler  30  is designed to terminate because when the refrigerant pressure inside the evaporator is too low, it may make cooler  31  harmful. A decrease of the refrigerant pressure is equivalent to a decrease of the refrigerant temperature inside the evaporator. In addition, the cooler  30  is specified to stop at the safety point of view when the pressure of the condenser  33  detected by the condenser pressure sensor  331  becomes Pc  1  or higher. 
         [0043]    [First Example of Temperature and Humidity Control] 
         [0044]      FIG. 6  is a flowchart showing an example of temperature and humidity control performed by the display apparatus  1 . This flowchart shows the control performed recursively by the control portion  16 . This flowchart can be roughly divided into a process of Steps S 1  to S 6  and a process of Steps S 7  to S 11 . The former one is for preventing a malfunction due to an increase of temperature in the housing, and the latter is a process for preventing a malfunction due to a decrease of temperature in the housing. 
         [0045]    First, the former process is discussed. As shown in  FIG. 6 , first, in Step S 1 , the control portion  16  detects the temperature inside the upper housing  10 , referring to outputs of the temperature sensors  15 . 
         [0046]    In Step S 2 , the control portion  16  determines whether the temperature detected in Step S 1  is temperature Th-or-higher or not. For instance, it determines whether at least one of the sensors  15   a  to  15   d  measures the temperature Th or higher. Here, Th is a temperature that is lower than an upper limit temperature that normal display on the liquid crystal panel  12  is guaranteed. For example, the temperature is 43 degrees centigrade. 
         [0047]    If the temperature inside the housing  10  is Th or higher (Yes in Step S 2 ), the control portion  16  proceeds to Step S 3  and drives the cooler  30 . Here, if the cooler  30  is already being driven, this driving state is maintained. In this case, the control portion  16  may drive the fan  14  together with the driving of the cooler  30 . 
         [0048]    On the other hand, if the temperature inside the housing  10  is lower than Th (No in Step S 2 ), the control portion  16  proceeds to Step S 4  and detects humidity inside the housing  10 . 
         [0049]    In Step S 5 , the control portion  16  determines whether the humidity inside the housing  10  is Hh-or-higher or not. For instance, it determines whether at least in one of the sensors  17   a  to  17   d  measures a humidity Hh-or-higher or not(Hh is for example, 80%). 
         [0050]    If the humidity inside the housing  10  is Hh or higher (Yes in S 5 ), assuming that the dew-condensation may occur, the control portion  16  proceeds to Step S 3  and drive the cooler  30 . Thus, the dew-condensation can be prevented. If the humidity inside the housing  10  is lower than Hh (No in S 5 ), the driving of the cooler  30  is stopped in Step S 6 . Because the temperature inside the upper housing  10  is in a normal range and there is no risk of the condensation, the control portion  16  stops the driving of the fan  14  in synchronization with the cooler  30 . 
         [0051]    Next, the latter process is discussed. First, in Step S 7 , the control portion  16  detects temperature of the evaporator  31  referring to an output of the evaporator temperature sensor  311 . 
         [0052]    In Step S 8 , the control portion  16  determines whether the temperature detected in Step S 7  is Te 2 -or-lower or not. Here, Te 2  is a temperature a little higher than a lower limit temperature that normal operation of the evaporator  31  is guaranteed. This temperature is referred to as temperature Te 1 . 
         [0053]    When the temperature of the evaporator  31  is Te 2  or lower (Yes in Step S 8 ), the control portion  16  controls an output level of the backlight  13  to be a level higher than a normal level so as to prevent the temperature from decreasing down to the temperature Te 1 . 
         [0054]    For instance, if the guaranteed temperature Te 1  is −15 degrees centigrade, the control portion  16  controls the level of the backlight  13  to be 65% of the maximum value when the temperature of the evaporator  31  lowers −10 degrees. If the temperature lowers −12 degrees, the level of the backlight  13  is controlled to be 80%. By making the output level of the backlight high, inside the display apparatus  1  is heated and the temperature of the refrigerant rises. As a result, a decrease of the evaporation temperature (evaporate pressure) is prevented, and hence it can prevent the cooler from terminating unintentionally. Further, since the cooler is prevented from termination, dew-condensation at a low temperature can be avoided. 
         [0055]    When the temperature of the evaporator  31  is Te 1  or lower (Yes in Step S 10 ), the cooler  30  is terminated in Step S 11 . 
         [0056]    In this case, the control portion  16  may also terminate the operation of the liquid crystal panel  12  and the backlight  13 . 
         [0057]    According to this example, it is possible to prevent dew-condensation, while safety of the cooler  30  is maintained. 
         [0058]    [Second Example of Temperature and Humidity Control] 
         [0059]      FIG. 7  is a flowchart showing another example of the temperature and humidity control performed by the display apparatus  1 . In the first example described above, the level of the backlight is controlled based on the detection result of the temperature of the evaporator. However, this example differs that the level of the backlight is controlled based on the humidity inside the upper housing  10  rather than based on the detection result of the temperature of the evaporator. 
         [0060]    As shown in  FIG. 7 , first, in Step S 21 , the control portion  16  detects the temperature inside the upper housing  10 . In Step S 22 , the control portion  16  determines whether the temperature detected in S 21  is Th-or-higher or not. If the temperature is lower than Th (NO in S 22 ), the humidity inside the upper housing  10  is detected (S 23 ). If the humidity is lower than Hh (NO in S 24 ), the cooler  30  is terminated (S 25 ). 
         [0061]    On the other hand, if the temperature inside the upper housing  10  is Th or higher (YES in S 22 ), the control portion  16  drives the cooler  30  (S 26 ). 
         [0062]    If the temperature inside the upper housing  10  is lower than Th (NO in S 22 ) and the humidity is Hh or higher (YES in S 24 ), the cooler  30  is driven (S 27 ). Further, the backlight  13  is controlled so as to increase its output level (S 28 ). As described above, the level of the backlight is increased when the cooler  30  (compressor) is driven based on the humidity in the housing. Thereby, it can increase the heat load even when the temperature inside the housing is low. 
         [0063]    In this case, the control portion  16  adjusts the level of the backlight  13  to a predetermined level (80%, for example) regardless of the temperature of the evaporator  31 . If the level of the backlight  13  is already larger than predetermined value, the control portion  16  may maintain the level of the backlight  13 . 
         [0064]    &lt;Variations&gt; 
         [0065]    In order to prevent the cooler  30  from frequent activation and termination, the control portion  16  may additionally perform following control in the flowchart shown in  FIG. 6  or  7 . For example, in Step S 2  of  FIG. 6  and Step S 22  of  FIG. 7 , the threshold value temperature Th may be set different value depending on whether the cooler  30  is to be activated or to be terminated. For example, 43 degrees centigrade may be adopted when driving, and 38 degrees centigrade when terminating. In other words, the threshold value temperature Th may have a hysteresis. The control portion  16  may perform a control so as not to terminate the cooler  30  while a predetermined time period (for example, ten minutes) has not elapsed since the activation of the cooler  30 . The vice-versa control may be performed (i.e. do not activate while a predetermined time has not elapsed since the termination) 
         [0066]    Instead of steps S 7  to S 10  shown in  FIG. 6 , in which the backlight or the cooler  30  are controlled according to the temperature of the evaporator  31 , these controls may be performed according to temperature of the condenser  33 . However, it is preferable, to perform control based on temperature of the condenser  33  after a predetermined time period (for example, 10 minutes) has elapsed from the activation of the cooler  30  so that the temperature of the condenser  33  is raised and stabilized. 
         [0067]    The embodiment of the present invention is described above, however, the scope of the present invention is not limited to this. It can be modified variously within the scope of the present invention without deviating from the spirit thereof.