Patent Publication Number: US-2006017657-A1

Title: Information display system

Description:
This application claims benefit of Japanese Application No. 2004-212089 filed in Japan on Jul. 20, 2004, the contents of which are incorporated by this reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an information display system including a main unit for generating display data and a head-mounted unit for displaying information.  
      2. Description of the Related Art  
      Display apparatuses for observing images by wearing on a head, such as a HMD (head-mounted display) and a HUD (head up display), have been known.  
      As an example of such a display apparatus, an image display apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 2003-248194, in-which a light emitting diode and a liquid display element are arranged at a position corresponding to a frame of a pair of spectacles, and the images generated therein are projected on a hologram optical element arranged at a position corresponding to a lens of the pair of spectacles as a combiner. The images reflected by the hologram optical element are led to and displayed on eyes of an observer so that the images can be observed as virtual images superimposed on external images.  
      In the conventional head-mounted unit mentioned above, such as the HMD and the HUD, when it is removed from a head, an observer cannot observe the displayed images. If a display is assumed being capable of displaying information on a display apparatus of a controller separated from the head-mounted unit for controlling the head-mounted unit, the information can be observed even when the head-mounted unit is removed from the head. However, even in this case, the same information may be displayed on both the head-mounted unit and the display apparatus of the controller, so that non-observed information is uselessly displayed. It is necessary to suppress the electric power consumption especially in portable systems, so that the structure consuming the electric power in vain is not preferable. If it is further assumed that a selector is provided for choosing either the head-mounted unit or the display apparatus of the controller, it is troublesome to operate the selector every time the system is used.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide an information display system capable of observing information even when a head-mounted unit is removed from a head and also suppressing the useless electric power consumption without troublesome operation.  
      In summary, an information display system according to the present invention includes a head-mounted unit having first displaying means for displaying specific information so that the information displayed by the first displaying means can be observed; a main unit having second displaying means for displaying specific information and generating display data for displaying information on the second displaying means or display data for displaying information on the first displaying means; and selecting means for alternatively selecting any one of the first displaying means and the second displaying means.  
      The above and other objects, features, and advantages of the invention will become more clearly understood from the following description referring to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view illustrating a serving condition of an information display apparatus according to a first embodiment of the present invention;  
       FIG. 2  is a front view of a head-mounted unit according to the first embodiment;  
       FIG. 3  is a plan view of the head-mounted unit according to the first embodiment;  
       FIG. 4  is a right side view of the head-mounted unit according to the first embodiment;  
       FIG. 5  is an enlarged partial plan view showing configuration of a switch according to the first embodiment for detecting open/close state of a temple provided in the vicinity of a hinge;  
       FIG. 6  is a plan view of a main unit according to the first embodiment in a state that casings are entirely closed;  
       FIG. 7  is a right side view of the main unit according to the first embodiment in a state that the casings are entirely closed;  
       FIG. 8  is a bottom view of the main unit according to the first embodiment in a state that the casings are entirely closed;  
       FIG. 9  is a rear view of the main unit according to the first embodiment in a state that the casings are entirely closed;  
       FIG. 10  is a plan view of the main unit according to the first embodiment in a state that only the upper casing is opened;  
       FIG. 11  is a plan view of the main unit according to the first embodiment in a state that the upper casing is closed and the intermediate casing is opened;  
       FIG. 12  is a block diagram mainly illustrating electronic circuits of the main unit in the information display apparatus according to the first embodiment;  
       FIG. 13  is a block diagram mainly illustrating electronic circuits of the head-mounted unit in the information display apparatus according to the first embodiment;  
       FIG. 14  is an explanatory view illustrating the principle of an optical system of a see-through information display portion according to the first embodiment;  
       FIG. 15  is a front view including a partial section showing the configuration of the optical system of the see-through information display portion according to the first embodiment;  
       FIGS. 16A and 16B  are left side views showing a configuration example of the optical system of the see-through information display portion according to the first embodiment;  
       FIG. 17  is a planar sectional view showing the configuration of the optical system of the see-through information display portion according to the first embodiment;  
       FIG. 18  is a flowchart illustrating a flow of power supply control in the information display apparatus according to the first embodiment;  
       FIG. 19  is a flowchart illustrating operation of a timer counter according to the first embodiment for controlling the time of the electric power supply to the head-mounted unit and the main unit;  
       FIG. 20  is a flowchart illustrating an adjustment process of an initial position of a display screen according to the first embodiment;  
       FIG. 21  is a drawing of a display example when adjusting the initial position of the display screen according to the first embodiment;  
       FIG. 22  is a drawing of a display example when the initial position of the display screen according to the first embodiment has been adjusted;  
       FIG. 23  is a flowchart of a process controlling the image display position when the information display apparatus according to the first embodiment is used in an information input mode;  
       FIG. 24  is a flowchart showing a scroll process executed as an interrupt handling according to the first embodiment; and  
       FIG. 25  is a flowchart illustrating the display control when the information display apparatus is operated as a playback device according to the first embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Embodiments according to the present invention will be described below with reference to the drawings.  
      FIGS.  1  to  25  show a first embodiment of the present invention.  FIG. 1  is a perspective view illustrating an operational pattern of an information display apparatus  1  in use.  
      The information display apparatus  1 , as shown in  FIG. 1 , is substantially composed of a glasses type head-mounted unit  2  and a main unit  3  configured separately from the head-mounted unit  2  for giving/receiving information by communicating with the head-mounted unit  2  by radio.  
      The head-mounted unit  2  allows a user to observe a subject (external thing) substantially directly in a see-through display mode and also to observe information superimposed thereon. The head-mounted unit  2 , as is understood from the glasses type shape, is worn on a head in substantially the same way as a general pair of spectacles for eyesight-correcting, and a feeling of wearing is improved by reducing the size and weight so as to approximate to those of a general pair of spectacles as much as possible.  
      The main unit  3  transmits display information and a remote control signal to the head-mounted unit  2  by wireless communication, and further controls the entire information display apparatus  1 . As for the main unit  3 , reduction in size and weight is performed within a possible range in the same way as in the head-mounted unit  2 .  
      Thus, a user can behave freely and smoothly without being annoyed by cables while wearing the head-mounted unit  2  thereon. The main unit  3  also has improved operability and portability because no cable is extended therefrom.  
      Then, the external shape and summary of the head-mounted unit  2  will be described with reference to FIGS.  2  to  4 .  FIG. 2  is a front view of the head-mounted unit  2 ;  FIG. 3  is a plan view thereof; and  FIG. 4  is a right side view thereof.  
      The head-mounted unit  2  comprises a front portion  11  corresponding to lenses, a rim, a bridge, and joints of general glasses, and temples  12  extending rearward (opposite to an object) from lateral both sides of the front portion  11  and being collapsible relative to the front portion  11 .  
      The front portion  11  includes a frame portion  13  and transparent optical members  14  and  15  attached to the frame portion  13  so as to correspond to both eyes, respectively, for guiding light.  
      The frame portion  13  is provided with a nose pad  16  arranged at the center for placing the head-mounted unit  2  on a nose bridge and a bridge  17  arranged on the upper portion between the transparent optical members  14  and  15 .  
      The temples  12  are connected to the front portion  11  with hinges  24  and  25  therebetween, respectively, so as to be collapsible relative to the front portion  11 . That is, when in non-use, the temples  12  can be folded toward the center so as to have a state collapsed along the front portion  11 , the storage and carrying can be conveniently performed by miniaturizing. End covers  18  and  19  for placing the head-mounted unit  2  on the ears are provided at the distal ends of the left and right temples  12 .  
      Furthermore, an electric equipment unit  20  for storing electronic circuits mainly for controlling see-through display is integrally provided at the left-eye (on the right in  FIG. 2  or  3 ) temple  12 , and a battery storage portion  21  for mainly storing a power supply circuit  92  (see  FIG. 13 ) for the head-mounted unit is integrally provided at the right-eye temple  12 . The battery storage portion  21  is configured so as to detachably store a battery, and is provided with a power supply switch  23  arranged on the upper surface for turning on/off the power supply for the head-mounted unit  2 . Accordingly, when the temples  12  are folded, the electric equipment unit  20  and the battery storage portion  21  are also collapsed according to the temples  12 . In such a manner, the electric equipment unit  20  and the battery storage portion  21  are arranged on the temples  12 , so that the information display apparatus  1  can be stored in compact.  
      In addition, the front portion  11 , the electric equipment unit  20 , and the battery storage portion  21  are configured so as to have an excellent wearing feeling by appropriately balancing shapes and weights.  
      Also, the electric equipment unit  20  is provided with a speaker  22  arranged to extend therefrom for hearing a voice on the left ear. According to the embodiment, a monaural sound can be heard by arranging the speaker  22  only on the left ear side; alternatively, speakers may be provided on both ears, respectively, so as to listen to a stereo sound.  
      A portion between the right of the front portion  11  and the hinge  24  is a box  26  to be stored with a flexible printed board connecting various circuits inside the front portion  11  to various circuits in the electric equipment unit  20 . Similarly, a portion between the left of the front portion  11  and the hinge  25  is a box to be stored with a power supply line and a signal line connecting various circuits inside the front portion  11  to various circuits in the battery storage portion  21 .  
       FIG. 5  is a partially enlarged plan view of a structure of a switch arranged in the vicinity of the hinge  24  for detecting opening or closing state of the temples  12 .  
      As shown in  FIG. 5 , the box  26  is provided with a contact point  27   a  having a convex plunger extending toward the electric equipment unit  20  while the temple  12  is provided with a contact point  27   b  having a planer pedestal arranged at a position opposing the contact point  27   a.  These contact points  27   a  and  27   b  constitute the switch  27  for detecting opening/closing state of the temples  12 .  
      The box  26  is also provided with a concave portion  29  for supporting the contact point  27   a  slidably in the forward/backward direction and a spring  29   a  provided inside the concave portion  29  for urging the contact point  27   a  toward the electric equipment unit  20 .  
      By such a structure, when the contact point  27   a  does not abut the contact point  27   b,  the contact point  27   a  stops at a position abutting the internal wall of the box  26  so as to partially extend the projection from the external wall of the box  26 .  
      Then, upon opening the temple  12  via the hinge  24 , the contact point  27   a  comes into contact with the contact point  27   b  so as to close the switch  27  at a position slightly before the opened position shown in  FIG. 3  (a position when the temple  12  is folded by more than a predetermined angle toward the closed position along the front portion  11  from the opened position shown in  FIG. 3 ).  
      By such a structure, corresponding to whether the switch  27  is opened or closed, it can be detected whether the temple  12  is not opened to a predetermined position (an unavailable state) or the temple  12  is opened to a predetermined position (an available state).  
      In addition, at a position corresponding to the left side of  FIG. 3 , i.e., in the vicinity of the hinge  25 , there is provided a switch  28  (see  FIG. 13 ) structured in the same way.  
      It is assumed that when at least one of the switches  27  and  28  is opened, the head-mounted unit  2  be in non-use such as a stored state. Alternatively, granted that it is mounted on a head, and at least one of the switches  27  and  28  is opened, the information displayed cannot be normally projected to user&#39;s eyes, so it is not preferable to be observable as it is. Accordingly, when at least one of the switches  27  and  28  is opened in such a manner, the electric power supply from a power supply circuit  92  (see  FIG. 13 ) for the head-mounted unit  2  is forcedly turned off by determining that the head-mounted unit  2  is unavailable. By such a control, the electric power can be suppressed from being consumed in vain when the head-mounted unit  2  is in the unavailable state.  
      Also, when the information display apparatus  1  is used in a playback mode (will be described later and see  FIG. 11 ) and the switches  27  and  28  are closed, the display in an LCD  104  of the head-mounted unit  2  is forcedly carried out. On the other hand, in an initial state of the playback mode, when at least one of the switches  27  and  28  is opened so as to be in an unavailable state (i.e., when at least one of the temples  12  is folded), information is forcedly displayed on an LCD  51  of the main unit  3 .  
      Next, the external shape and summary of the main unit  3  will be described with reference to FIGS.  6  to  11 .  FIG. 6  is a plan view of the main unit  3  in a state that the entire casings are closed;  FIG. 7  is a right side view of the main unit  3  in a state that the entire casings are closed;  FIG. 8  is a bottom view of the main unit  3  in a state that the entire casings are closed;  FIG. 9  is a back view of the main unit  3  in a state that the entire casings are closed;  FIG. 10  is a plan view of the main unit  3  in a state that only the upper casing is opened; and  FIG. 11  is a plan view of the main unit  3  in a state that the upper casing is closed while an intermediate casing is opened.  
      The main unit  3  is layered of three substantially rectangular and planar casings, an upper casing  31 , an intermediate casing  32 , and a lower casing  33 , which are deposited in the thickness direction.  
      The upper casing  31 , as shown in  FIG. 10 , is rotatably attached to the intermediate casing  32  with hinges  34  therebetween. The hinge  34  has a contact inside configured with a known structure for electrically connecting between the upper casing  31  and the intermediate casing  32 .  
      The intermediate casing  32 , as shown in  FIG. 11 , is also attached to the lower casing  33  rotatably via a hinge  35 . The hinge  35  has a contact inside configured with a known structure for electrically connecting between the intermediate casing  32  and the lower casing  33 .  
      The lower casing  33 , as shown in  FIGS. 7 and 8 , is provided with a battery storing portion  36  formed on the bottom surface, and a detachable battery built therein can be replaced by sliding a cover  37  in the left direction of  FIG. 8 . The lower casing  33 , as shown in  FIG. 7 , is also provided with a recording medium storing portion  41  formed on the right side face for storing a recording medium such as a detachable memory card. By operating an eject button  42 , the recording medium can be removed.  
      Next, when the upper casing  31  is opened through the hinges  34 , it becomes the state shown in  FIG. 10 .  
      The upper casing  31 , as shown in  FIG. 10 , is provided with a first power supply switch  43 , a pad-type pointing device  46 , a left button  47 , and a right button  48  formed on the bottom surface exposed in the opened state (it is the upper surface in the opened state of  FIG. 10 ).  
      The first power supply switch  43  is signal generating means for supplying an electric source to a circuit for making the information display apparatus  1  carry out a function of an information input device. According to the embodiment, there is provided an independent power supply switch to be operated by a finger; alternatively, it may be structured as a power supply switch operatively associated with the rotating operation of the hinge  34 . In this case, it is assumed that the power supply switch is provided inside the hinge  34 . By such a structure, by only opening the upper casing  31 , the information display apparatus  1  can be made to carry out a function of the information input device.  
      The intermediate casing  32 , as shown in  FIG. 10 , is also provided with a keyboard  45  arranged on the upper surface exposed in the opened state for inputting information such as characters.  
      Thus, in the state that only the upper casing  31  is opened as shown in  FIG. 10 , the main unit  3  functions as an operating switch capable of operating in the same way as that in a keyboard and a mouse in a general personal computer.  
      Subsequently, when the intermediate casing  32  is opened relative to the lower casing  33  via the hinge  35  after the upper casing  31  is closed, it becomes the state shown in  FIG. 11 .  
      In the state shown in  FIG. 11 , the main unit  3  serves as a playback device to display images, and also functions as an operating switch for operating the playback device. A mode, in which the information display apparatus  1  is used for the playback device as shown in  FIG. 11 , is referred to as a playback mode.  
      The intermediate casing  32 , as shown in  FIG. 11 , is provided with a speaker  52  for generating a sound and the LCD  51  for displaying playback images as a second displaying means which are arranged on the bottom surface exposed in the opened state (it is the upper surface in the opened state of  FIG. 11 ).  
      The lower casing  33 , as shown in  FIG. 11 , is provided with a second power supply switch  44 , a menu button  53 , a determination switch  55 , menu select switches  56 ,  57 ,  58 , and  59 , a playback/stop switch  61 , a fast reverse switch  62 , a fast forward switch  63 , and a display select switch  64  arranged on the upper surface exposed in the opened state.  
      The second power supply switch  44  is arranged on the surface of the lower casing  33  at the upper left, for example, and it is signal generating means for supplying an electric source to a circuit for making the information display apparatus  1  carry out a function of a playback device. According to the embodiment, there is provided an independent power supply switch to be operated by a finger; alternatively, it may be structured as a power supply switch operatively associated with the rotating operation of the hinge  35 . In this case, it is assumed that the power supply switch is provided inside the hinge  35 . By such a structure, by only opening the intermediate casing  32 , the information display apparatus  1  can be made to carry out a function of the playback device.  
      In such a manner, the first and second power supply switches  43  and  44  may also be referred to as mode select switches to make the information display apparatus  1  whether carry out a function of the information input device or a function of the playback device.  
      The display select switch  64  is included in a second operation switch  73  (will be described later and see  FIG. 12 ) as selecting means and arranged on the surface of the lower casing  33  at the lower left, for example. The display select switch  64  is of an automatic return type. When the information display apparatus  1  is functioning as the playback device, a first display mode displaying information on the LCD  51  is switched to a second display mode displaying information on the head-mounted unit  2  repeatedly every time the display select switch  64  is turned on.  
      According to the embodiment, in an initial state that the intermediate casing  32  is opened and the second power supply switch  44  is turned on, the main unit  3  transmits a signal for determining whether the head-mounted unit  2  is unavailable or not to the head-mounted unit  2 .  
      Then, when a power supply circuit  92  (see  FIG. 13 ) is turned on, the head-mounted unit  2  transmits a signal for indicating whether the head-mounted unit  2  is unavailable or not to the main unit  3 . Whereas, the head-mounted unit  2  does not return any signal of course when the power supply circuit  92  is turned off. Hence, the main unit  3  can determine whether the power supply circuit  92  is turned on or not by the presence of the reply from the head-mounted unit  2 . Even when a user thinks that the power source of the head-mounted unit  2  is turned on, the power supply circuit  92  may be forcedly turned off by a power saving function due to non-use for a predetermined time. Even in such a case, the state of the power supply circuit  92  of the head-mounted unit  2  can be determined by the presence of the reply. The main unit  3  classifies the head-mounted unit  2  as the unavailable state in the absence of the reply from the head-mounted unit  2 .  
      Also, in the presence of the reply from the head-mounted unit  2 , the main unit  3  further determines whether the reply content shows the available state or the unavailable state.  
      Even when the power supply circuit  92  is turned on, if at least one of the switches  27  and  28  is opened (turned off), the head-mounted unit  2  is to return a signal showing the unavailable state.  
      That is, the main unit  3  determines that the head-mounted unit  2  is in the available state when both the switches  27  and  28  are closed and also the power supply of the power supply circuit  92  is turned on, while determines that the head-mounted unit  2  is in the unavailable state when at least one of the switches  27  and  28  is opened or when the power supply of the power supply circuit  92  is turned off.  
      When the main unit  3  determines that the head-mounted unit  2  is in the available state, the second display mode is selected, while when the main unit  3  determines that the head-mounted unit  2  is in the unavailable state, the first display mode is selected.  
      In such a manner, it is determined which is suitable between the LCD  104  of the head-mounted unit  2  and the LCD  51  of the main unit  3  so as to alternatively select the LCD assumed to be suitable.  
      By such a structure, even when the head-mounted unit  2  is removed from a head, a user can confirm information by displaying the information on the main unit  3 .  
      Furthermore, since a user is not required to select any one of the first display mode and the second display mode and information can be displayed on a suitable display apparatus, the operation is simplified and usability is improved.  
      When the main unit  3  inquires whether the head-mounted unit  2  is in the available state, if no reply is returned, the head-mounted unit  2  is determined to be in the unavailable state so as to automatically select the LCD  51  of the main unit  3  and display information thereon. Thereby, even when the power supply to the head-mounted unit  2  is completely turned off, or when the head-mounted unit  2  is located at a position where a wireless signal from the main unit  3  does not reach (specifically, in a case where the main unit  3  is stored in a bag hardly transmitting a wireless signal or in a case where a user brings only the main unit  3  and the head-mounted unit  2  is left at a house), information can be observed by appropriately and rapidly selecting the display mode without troublesome operation.  
      Because information is not simultaneously displayed on the head-mounted unit  2  and the main unit  3 , useless electric power consumption is suppressed.  
      Moreover, since the information display apparatus  1  has power supplies in both the main unit  3  and the head-mounted unit  2 , no cable is required for supplying an electric power source to the head-mounted unit  2 , i.e., cables are not necessary to be connected to the head-mounted unit  2  for an image signal and the electric power source, so that the system is convenient to be carried due to the wireless.  
      Back to  FIG. 11 , the playback/stop switch  61  is used for playing back or temporarily stopping image information recorded on a record memory  83  (will be described later and or a hard disk  85 ) (see  FIG. 12 ).  
      The fast reverse switch  62  is used for quickly returning images recorded on the record memory  83  (or the hard disk  85 ) in a direction reverse to the playback direction to be searched.  
      The fast forward switch  63  is used for fast-forwarding images recorded on the record memory  83  (or the hard disk  85 ) in the playback direction to be searched.  
      The menu button  53  is used for displaying a menu screen for executing various settings regarding image editing on the LCD  51 .  
      The menu select switches  56 ,  57 ,  58 , and  59  are used for moving an interest item among items displayed on the menu screen in the horizontal and vertical directions or for scrolling displayed information.  
      The determination switch  55  is used for determining an interest item displayed on the menu screen.  
      In the information display apparatus  1  according to the embodiment, if a period of time in which images are vanished from a display frame, which is a region for displaying images as will be described later, becomes longer than a predetermined time Ts, the display is to be in a low power consumption mode for reducing the power consumption of the entire information display apparatus  1 . The predetermined time Ts in this case can also be established by operating the menu button  53 , the menu select switches  56 ,  57 ,  58 , and  59 , and the determination switch  55 .  
       FIG. 12  is a block diagram mainly showing the configuration of an electronic circuit of the main unit  3  in the information display apparatus  1 .  
      The main unit  3  includes a transmitter-receiver  76 , a communication controller  77 , a main unit memory  78 , a D/A converter  79 , the LCD  51 , an LCD driver  81 , a compression/expansion circuit  82 , a select circuit  84 , the record memory  83 , the hard disk  85 , the speaker  52 , a first operating switch  72 , a second operating switch  73 , a character generator  74 , a power supply circuit  75 , the first power supply switch  43 , the second power supply switch  44 , and a second CPU  71 .  
      The transmitter-receiver  76  is used for receiving a wireless signal transmitted from the head-mounted unit  2  via an antenna or for transmitting a wireless signal to the head-mounted unit  2  via the antenna so as to serve a double purpose of second transmitting means and second receiving means.  
      The communication controller  77  is communication controlling means for frame synchronizing (synchronizing in frame unit by time-division multiple systems) and data formatting a slot, which is a component of a frame and configured including a pair of an attribute and an attribute value, so as to constitute the second transmitting means and the second receiving means.  
      The main unit memory  78  is storing means configured of a frame buffer or the like for temporarily storing information such as characters and images produced by the second CPU  71  or information such as characters and images read out of the detachable record memory  83  or the hard disk  85 .  
      The D/A converter  79  is used for converting a digital signal stored in the main unit memory  78  into an analog signal.  
      The LCD  51  is displaying means for displaying images based on an analog image signal converted by the D/A converter  79 .  
      The LCD driver  81  is display-drive controlling means for controlling the LCD  51 .  
      The compression/expansion circuit  82  is compression/expansion means for compressing the digital signal stored in the main unit memory  78  and also for expanding the compressed digital signal read out of the record memory  83 .  
      The select circuit  84  is input/output selecting means for selecting an input source and an output target bidirectionally based on a control signal from the second CPU  71 . The bi-direction means that any of the main unit memory  78 , the record memory  83 , the hard disk  85 , and the compression/expansion circuit  82  can become any of the input source and the output target. For example, the select circuit  84  is to select a target for outputting the digital signal compressed by the compression/expansion circuit  82  from the record memory  83 , the hard disk  85 , and the main unit memory  78 . When information recorded in the record memory  83  or the hard disk  85  is stored in the main unit memory  78  so as to play back and display it, the select circuit  84  selects an output signal from any one of the record memory  83  and the hard disk  85  based on the control signal from the second CPU  71  so as to output it to the compression/expansion circuit  82 . Furthermore, the select circuit  84  is also to select whether transferring data from the main unit memory  78  to the record memory  83  or the hard disk  85  or from the record memory  83  or the hard disk  85  to the main unit memory  78  is performed through the compression/expansion circuit  82  or not based on the control signal from the second CPU  71 . When information is image data other than character data (hereinafter, “image data” is referred to as whole information except character data), the information is transferred after it is compressed or expanded through the compression/expansion circuit  82 . On the other hand, when information is character data, it is transferred without the compression/expansion circuit  82  therebetween.  
      The record memory  83 , comprising a detachable card memory, for example, is stored in the recording medium storing portion  41 , and is recording means for recording the digital signal compressed by the compression/expansion circuit  82  when the record memory  83  is selected by the select circuit  84 .  
      The hard disk  85  built in the main unit  3  is recording means for recording the digital signal compressed by the compression/expansion circuit  82  when the hard disk  85  is selected by the select circuit  84 .  
      The speaker  52  is sound generating means for playing back voices associated with images based on the control of the second CPU  71  when the images are played back.  
      The first operating switch  72  is inputting means, including various switches shown in  FIG. 10 , for operating various entries when the information display apparatus  1  is made to carry out a function of an information input device.  
      The second operating switch  73  is inputting means, including various switches shown in  FIG. 11 , for operating various entries when the information display apparatus  1  is made to carry out a function of a playback device.  
      The character generator  74  is character information generating means for generating character data.  
      The power supply circuit  75  is power supplying means for supplying a power source to the main unit  3  as a second power source including a detachable battery accommodated in the battery storing portion  36 .  
      The first power supply switch  43 , connected to the power supply circuit  75 , is a switch for supplying a power source to a circuit for making the information display apparatus  1  carry out a function of an information input device as mentioned above. Upon turning on the first power supply switch  43 , an electric current is allowed to flow through circuits other than the second operating switch  73 , the D/A converter  79 , the LCD  51 , and the LCD driver  81 .  
      The second power supply switch  44 , connected to the power supply circuit  75 , is a switch for supplying a power source to a circuit for making the information display apparatus  1  carry out a function of a playback device as mentioned above. Upon turning on the second power supply switch  44 , an electric current is allowed to flow through circuits other than the first operating switch  72 .  
      The second CPU  71 , controlling circuits in the main unit  3 , also controls the head-mounted unit  2  by communicating with a first CPU  91  (will be described later and see  FIG. 13 ) as integrated controlling means relating to the information display apparatus  1 . The second CPU  71  also serves a double purpose of display data generating means and selecting means.  
       FIG. 13  is a block diagram mainly showing the configuration of an electronic circuit of the head-mounted unit  2  in the information display apparatus  1 .  
      The head-mounted unit  2  includes a transmitter-receiver  111 , a communication controller  112 , a memory  113 , the switches  27  and  28 , the speaker  22 , angular velocity sensors  94  and  95 , amplifies  96  and  97 , an A/D converter  98 , an LED driver  101 , an LED  102 , a condenser lens  103 , the LCD  104 , an LCD driver  105 , a first holographic optical element (referred to as an HOE (Holographic Optical Element))  106 , a second HOE  107 , a power supply circuit  92 , a power supply switch  23 , and a first CPU  91 .  
      Hereinafter, a unit constituted of the LED  102 , the condenser lens  103 , the LCD  104 , the first HOE  106 , and the second HOE  107  is referred to as a see-through information display portion  108 . The see-through information display portion  108  constitutes first displaying means.  
      The transmitter-receiver  111  receives various signals, such as display data and sound data, transmitted from the main unit  3  by radio or transmits various signals to the main unit  3  by radio so as to serve a double purpose of first transmitting means and first receiving means.  
      The communication controller  112  is communication controlling means composed of a receiver unit receiving data from the main unit  3  via the transmitter-receiver  111  for controlling and a transmitting unit transmitting data to the main unit  3  via the transmitter-receiver  111  for controlling so as to constitute the first transmitting means and the first receiving means.  
      First, the receiver unit of the communication controller  112  fetches data for one slot at a predetermined timing from received data supplied from a modem built in the transmitter-receiver  111 . The receiver unit extracts a synchronizing signal from the data so as to generate a frame synchronizing signal for descrambling. Then, the receiver unit transmits display data transmitted from the main unit  3  and display control data of the head-mounted unit (a display start signal and a display off signal, for example) to the first CPU  91 .  
      Next, the transmitting unit of the communication controller  112  adds a synchronizing signal to angular velocity information (or angular information calculated based on the angular velocity information) outputted via the first CPU  91  after applying scramble thereto. Then, the transmitting unit generates transmitting data for one slot so as to insert it into a predetermined slot within a frame for sending to a modem in the transmitter-receiver  111 .  
      The memory  113  is storing means for temporarily storing display data and sound data received from the main unit  3 , or capable of temporarily storing data also for transmitting to the main unit  3 . The memory  113  is connected to the first CPU  91 .  
      The switches  27  and  28  are used for detecting an open/close state of the temples  12  as mentioned above.  
      The speaker  22 , as mentioned above, is sound generating means for generating sounds so as to be heard by a user mounting the head-mounted unit  2  at the left ear, for example.  
      The angular velocity sensor  94  is angular velocity detecting means for detecting an angular velocity in a yaw direction (lateral direction) of an observer head mounting the head-mounted unit  2 .  
      The angular velocity sensor  95  is angular velocity detecting means for detecting an angular velocity in a pitch direction (front/back direction) of an observer head mounting the head-mounted unit  2 .  
      The amplifier  96  is amplifying means for amplifying the output of the angular velocity sensor  94 .  
      The amplifier  97  is amplifying means for amplifying the output of the angular velocity sensor  95 .  
      The A/D converter  98  is used for converting an analog output from the angular velocity sensor  94  amplified by the amplifier  96  and an analog output from the angular velocity sensor  95  amplified by the amplifier  97  into digital signals, respectively, so as to send them to the first CPU  91 .  
      The LED driver  101  is emission controlling means for controlling the LED  102  to emit light based on the control of the first CPU  91 .  
      The LED  102  is an emitting source for emitting light driven by the LED driver  101 , and constitutes displaying means.  
      The condenser lens  103  is used for condensing light emitted from the LED  102 , and constitutes displaying means.  
      The LCD  104  is a display element made of transmission liquid crystal for displaying information such as images, and is configured by two-dimensionally arranging a plurality of display pixels at equal intervals. The LCD  104  constitutes the displaying means, and is illuminated with light of the LED  102  via the condenser lens  103  from the back face.  
      The LCD driver  105  is display controlling means for displaying various kinds of information, such as characters and images, transmitted from the main unit  3  by transmitting a drive signal to the LCD  104  based on the control of the first CPU  91 .  
      The first HOE  106  is a reflection optical member for reflecting light emitted via the LCD  104  vertically downward (see  FIG. 16A ) while correcting aberration as will be described later, and constitutes the displaying means.  
      The second HOE  107  is a combiner configured so that information, such as characters and images, displayed on the LCD  104  is observably projected by reflecting and diffracting light from the first HOE  106  toward eyes of an observer while outside light is allowed to permeate toward eyes of the observer, and constitutes the displaying means.  
      The power supply circuit  92  is a first electric power source including a control circuit for supplying electric power to the entire head-mounted unit  2  and a battery. Upon receiving a power supply instruction signal from the main unit  3  via the first CPU  91 , electric power from the battery is automatically supplied to the entire head-mounted unit  2 .  
      The power supply switch  23  is used for turning on/off the power source of the head-mounted unit  2  as described with reference to  FIG. 3 .  
      The first CPU  91  is controlling means for mainly controlling the head-mounted unit  2  while communicating with the second CPU  71  of the main unit  3 . The first CPU  91  also serves as angular detecting means for detecting an angle of inclination of an observer head based on angular velocity information outputted from the angular velocity sensors  94  and  95 .  
      As described above, operations of the head-mounted unit  2  and the main unit  3  are roughly as follows.  
      First, when the first power supply switch  43  is pushed by opening the upper casing  31 , the information display apparatus  1  serves as an information input device. Hence, electricity is not passed through the second operating switch  73 , the D/A converter  79 , the LCD  51 , and the LCD driver  81  which are circuits operating only when the information display apparatus  1  is used for a below-mentioned playback device. Thereby, the electric power for circuits not used for the information input device is suppressed from being consumed in vain.  
      When a signal of the turning-on of the first power supply switch  43  (supply initiation signal) is detected, the second CPU  71  transmits this signal (power feed instruction signal) to the head-mounted unit  2  via the communication controller  77  and the transmitter-receiver  76 .  
      Then, the head-mounted unit  2  receives the power feed instruction signal from the main unit  3  via the transmitter-receiver  111  and the communication controller  112  so as to transmit it to the first CPU  91 .  
      Upon receiving the power feed instruction signal, the first CPU  91  transmits a predetermined signal to the power supply circuit  92 , so that the power supply circuit  92  starts supplying the electric power to the entire head-mounted unit  2 . Also, the first CPU  91  transmits a receive confirmation signal to the main unit  3  via the transmitter-receiver  111  for confirming that the power feed instruction signal is received.  
      In addition, in order to allow the power for the head-mounted unit  2  to be turned on operatively in association with the turning on of the power for the main unit  3 , it is necessary that at least the first CPU  91 , the communication controller  112 , and the transmitter-receiver  111  must be in a state capable of receiving a signal from the second CPU  71 . Accordingly, while the power supply switch  23  is turned on, the minimum required power amount is to be supplied to these circuits. Whereas, while the power supply switch  23  is turned off, the power supply to the first CPU  91 , the communication controller  112 , and the transmitter-receiver  111  is also shut off. That is, when the power supply switch  23  is opened (turned off), the power supply for the head-mounted unit  2  is entirely turned off, so that the power supply control in operatively association with the first power supply switch  43  is obviously not performed.  
      In such a manner, when the power supply is turned on for the head-mounted unit  2  in operatively association with the turning on of the power for the main unit  3 , it is necessary to turn on the power supply switch  23  in advance. In this case, although some amount of electric power is steadily consumed, the operation is advantageously simplified because of no need for operation of the power supply switch  23 .  
      Also, the second CPU  71  of the main unit  3  monitors whether a predetermined time is lapsed after the power supply for the head-mounted unit  2  is turned on. If it is determined that the predetermined time is lapsed, a predetermined power supply-off signal is transmitted to the head-mounted unit  2  from the main unit  3 . Thereby, when the predetermined time is lapsed, the power supply for the head-mounted unit  2  is automatically turned off.  
      Then, in a state that the upper casing  31  is opened (see  FIG. 10 ), the information display apparatus  1  has the same function as that of word processing software (or character input software) in a general personal computer.  
      That is, upon operating the first operating switch  72 , character information is read out of the character generator  74  corresponding to the operation, so that document data is edited by the second CPU  71 .  
      The edited data is transmitted to the head-mounted unit  2  via the communication controller  77  and the transmitter-receiver  76  with a display frame added thereto as will be described later so as to be displayed at a predetermined position of the LCD  104  of the head-mounted unit  2  by controlling the display position. In addition, the predetermined position of the LCD  104  of the head-mounted unit  2  is defined corresponding to the inclination in yow and pitch directions calculated based on the head angular velocity information transmitted from the head-mounted unit  2 .  
      The head-mounted unit  2  receives the document data which is defined at the display position and has the display frame added thereto transmitted from the main unit  3  via the transmitter-receiver  111  and the communication controller  112 . Then, the data is temporarily stored in the memory  113 .  
      The document data stored in the memory  113  is transmitted to the LCD driver  105  via the first CPU  91  so as to be displayed by the LCD  104 .  
      Simultaneously, the first CPU  91  allows the LED  102  to emit light by driving the LED driver  101 . Light emitted from the LED  102  is collimated through the condenser lens  103  so as to irradiate the LCD  104  from the back face.  
      In such a manner, the light passing through the LCD  104  is reflected by the first HOE  106  so as to be incident on eyes of an observer via the second HOE  107  as a combiner. The observer can thereby observe the document data as virtual images superimposed on ambient images.  
      Then, as shown in  FIG. 11 , when the second power supply switch  44  is closed (turned on) in a state that the upper casing  31  is closed and the intermediate casing  32  is opened, the information display apparatus  1  serves as the playback device. As described above, while the second power supply switch  44  is closed, electricity is allowed to pass through circuits other than predetermined part of the circuits including at least the first operating switch  72 .  
      The relationship between the operation of the second power supply switch  44  and the power supply control of the head-mounted unit  2  operated in association with the switch operation is the same as that between the operation of the first power supply switch  43  and the power supply control of the head-mounted unit  2  operated in association with the switch operation.  
      By operating the menu button  53 , the menu select switches  56 ,  57 ,  58 , and  59 , and the determination switch  55  included in the second operating switch  73 , information already stored in the record memory  83  or the hard disk  85  is selected. Furthermore, when the playback/stop switch  61  is operated so as to instruct the playback, the following procedure will be executed.  
      First, if the information stored in selected one of the record memory  83  and the hard disk  85  is image data, the data is expanded by the expansion circuit unit within the compression/expansion circuit  82  so as to be temporarily stored in the main unit memory  78 .  
      On the other hand, when the information stored in selected one of the record memory  83  and the hard disk  85  is character data, this data is temporarily stored in the main unit memory  78  without the compression/expansion circuit  82  therebetween.  
      The information stored in the main unit memory  78  is converted into an analog image signal by the D/A converter  79 , and then is displayed on the LCD  51  or transmitted to the head-mounted unit  2  and displayed on the LCD  104  of the see-through information display portion  108 . At this time, the operation of the LCD  51  is controlled by a drive signal generated from the LCD driver  81  based on the instruction of the second CPU  71 .  
      At present, if the information display apparatus  1  is set in the first display mode (i.e., the mode displayed on the LCD  51  of the main unit  3 ) by the display select switch  64  shown in  FIG. 11 , the information display apparatus  1  is operated as follows.  
      First, when the second operating switch  73  is operated in a predetermined manner, various kinds of information, such as characters, sounds, and images, stored in the record memory  83  or the hard disk  85  are selected by the select circuit  84  so as to be temporarily stored in the main unit memory  78 .  
      Among these various kinds of information, display data, such as images and characters, are converted into analog data by the D/A converter  79 , and then displayed on the LCD  51  based on the control of the LCD driver  81 .  
      Among them, sound data is played back through the speaker  52  based on the control of the second CPU  71 .  
      On the other hand, if the information display apparatus  1  is set in the second display mode (i.e., the mode displayed on the LCD  104  of the head-mounted unit  2 ) by the display select switch  64 , the information display apparatus  1  is operated as follows.  
      First, when the second operating switch  73  is operated in a predetermined manner, various kinds of information, such as characters, sounds, and images, stored in the record memory  83  or the hard disk  85  are selected by the select circuit  84  so as to be temporarily stored in the main unit memory  78 .  
      Among these various kinds of information, display data, such as images and characters, are transmitted to the head-mounted unit  2  via the communication controller  77  and the transmitter-receiver  76  with a display frame added thereto as will be described later so as to be displayed at a predetermined position of the LCD  104  of the head-mounted unit  2  by controlling the display position. As described above, the predetermined position of the LCD  104  is defined corresponding to the head inclination in yaw and pitch directions calculated based on head angular velocity information (or angular information) transmitted from the head-mounted unit  2 . Then, the head-mounted unit  2  receives these various kinds of information via the transmitter-receiver  111  and the communication controller  112  so as to temporarily store it in the memory  113 . Then, the information such as an image and a character is displayed by the see-through information display portion  108 .  
      Among these various kinds of information, sound data is transmitted to the head-mounted unit  2  via the communication controller  77  and the transmitter-receiver  76 . The head-mounted unit  2  receives the various kinds of information via the transmitter-receiver  111  and the communication controller  112  in the same way as in the display data, and temporarily stores it in the memory  113 . Then, the sound data is played back through the speaker  22  based on the control of the first CPU  91 .  
      Subsequently, with reference to FIGS.  14  to  17 , the optical configuration of the see-through information display portion will be mainly described.  FIG. 14  is a drawing illustrating the principle of the optical system of the see-through information display portion;  FIG. 15  is a front view including a partial section showing the configuration of the optical system of the see-through information display portion;  FIGS. 16A and 16B  are left side views showing a configuration example of the optical system of the see-through information display portion; and  FIG. 17  is a planar sectional view showing the configuration of the optical system of the see-through information display portion.  
      The see-through information display portion  108  can display information, such as characters and images, and a display frame showing a display range by superimposing them as virtual images on an object to be substantially directly observed by a photographer. Such a display is referred to as a see-through display below. In addition, “substantially directly observing” includes not only observing with naked eyes but also observing through a planar transparent member made of glass or plastics and lenses for eyesight-correcting.  
      First, with reference to  FIG. 14 , the display principle of see-through images by an optical system of the see-through information display portion  108  according to the first embodiment (referred to as a see-through information display optical system below) will be described.  
      The light emitted from the LED  102  is condensed by the condenser lens  103  so as to illuminate the LCD  104  from the back face. The LED  102  is composed of three-color light-emitting diodes of R (red), G (green), and B (blue). When color images are displayed, all three colors are used; only one color, such as G (green), may be radiated when characters or the display frame are displayed.  
      The first CPU  91  generates a signal corresponding to the display frame showing a display range so as to output to the LCD driver  105 . The LCD driver  105  displays characters and images on the LCD  104  by driving the LCD  104  based on the signal.  
      The characters and images emitted from the LCD  104  by receiving light of the LED  102  are led to eyes of an observer after being reflected by the second HOE  107 . In such a manner the observer can observe the characters and images as virtual images VI. In addition, as  FIG. 15  is illustrating the principle, the first HOE  106  is not shown.  
      The second HOE  107  is a volume phase holographic optical element using a sensitive material, such as a photo-polymer and bichromic acid gelatin, and is designed to have characteristics that reflect light at the maximum reflectance in each of wavelengths of R, G, and B emitted from the LED  102 . Accordingly, if G light is emitted when characters and images are displayed, green characters and images are clearly displayed as virtual images. The HOE has excellent wavelength selectivity, so that while exhibiting high reflection characteristics for very narrow wavelength intervals of each of the wavelengths of R, G, and B, the HOE has high permeation characteristics for beams with wavelengths other than those. Therefore, while external light with the same wavelength range as that of display light is diffracted and reflected so as not to reach pupils of an observer, external light with wavelength ranges other than that reaches the pupils of the observer. In general, visible light has a wide band width of the wavelength, so that although light with very narrow wavelength intervals including each of the wavelengths of R, G, and B does not reach the observer, the external images can be observed without hindrance.  
      The first HOE  106  not only reflects light from  104  so as to lead it to the second HOE  107  but also has a function for correcting a curvature of field. According to the embodiment, the first HOE  106  is used; instead, an optical element with a free-form surface may be used. Since the optical element with a free-form surface can correct complicated aberrations with small size and weight, clear images with small aberration can be displayed without too much increasing its weight.  
      Subsequently, with reference to FIGS.  15  to  17 , a specific arrangement example of the see-through information display optical system will be described.  
      At positions within the frame portion  13  in the object side and on the transparent optical member  14  (or the transparent optical member  15 ), the LED  102 , the condenser lens  103 , the LCD  104 , and the first HOE  106  are arranged in the order of  FIG. 15 . These members, as shown in  FIG. 17 , are attached and sandwiched between holding frames  124  and  125 . At this time, the LED  102  is fixed to the holding frames  124  and  125  in a state mounted on an electric circuit board  121 . Among them, the first HOE  106  is inclined so as to reflect the light from the LED  102  vertically downward, as described above.  
      The transparent optical member  14  (or the transparent optical member  15 ), as shown in  FIGS. 16A and 16B , includes light guide members  122  and  123  made of transparent glass or plastics so as to have a predetermined thickness and the second HOE  107  sandwiched between the light guide members  122  and  123  and inclined so as to reflect light rearward. In such a structure, the light reflected from the first HOE  106  passes through the light guide member  122  arranged on the second HOE  107  so as to reach the second HOE  107 . The light propagation within the light guide member  122  may be only permeation as shown in  FIG. 16A  or it may be a combination of the permeation and the total reflection on the internal surface as shown in  FIG. 16B . The optical design shown in  FIG. 16B  enables the transparent optical member  14  (or the transparent optical member  15 ) to be reduced in thickness, so that the head-mounted unit  2  can be further reduced in weight.  
      At a position within the frame portion  13  in the head side of a photographer (opposite to the object to be observed), as shown in  FIG. 17 , an electric circuit board  126  mounting the LED driver  101  and the LCD driver  105  thereon is arranged opposite to the see-through information display optical system with the holding frame  124  therebetween.  
      In addition, the see-through information display optical system includes the LED  102 , the condenser lens  103 , the LCD  104 , the first HOE  106 , the second HOE  107 , and the light guide members  122  and  123  among those members described above.  
      Since an observer generally observes an object with both eyes, as to the arrangement of the see-through information display portion  108 , two examples may be assumed as follows.  
      First, in a first example, a portion corresponding to one eye of both the eyes is configured of the see-through information display optical system shown in  FIG. 15  while a portion corresponding to the other eye is configured by a simple transparent optical member without a see-through information display function. In this case, the transparent optical member corresponding to the other eye may preferably have the same luminous transmittance characteristics as those of the transparent optical member  14  (or the transparent optical member  15 ). Thereby, tiredness of the eyes can be reduced even in a long time use.  
      Then, in a second example, for each of both eyes, the see-through information display optical system shown in  FIG. 15  is configured. When such a pair of see-through information display optical systems are used, tiredness of the eyes can be further reduced as well as stereo images can be displayed on demand.  
      Then,  FIG. 18  is a flowchart illustrating a flow of power supply control in the information display apparatus  1 .  
      Upon operating the first power supply switch  43  or the second power supply switch  44 , the interrupt handling of the power supply switch is carried out.  
      Upon initiating the handling, the second CPU  71  determines whether the switch turned on is the first power supply switch  43  or not (Step S 1 ).  
      When the switch turned on is the first power supply switch  43 , a flag (playback mode flag) is established showing the playback mode is selected so as to allow the information display apparatus  1  to function as the playback device (Step S 2 ).  
      Also, when the switch turned on is the second power supply switch  44 , a flag (information input mode flag) is established showing the information input mode is selected so as to allow the information display apparatus  1  to function as the information input device (Step S 3 ).  
      When the flag in Step S 2  or Step S 3  is established, a timer counter for counting a time elapsed from the turning-on of the first power supply switch  43  or the second power supply switch  44  (the counter is built in the second CPU  71 ) is set (Step S 4 ).  
      Subsequently, the head-mounted unit  2  is determined whether it is available or not (Step S 5 ). As described above, it is determined that the head-mounted unit  2  is unavailable if no signal is replied when a predetermined confirming signal is transmitted to the head-mounted unit  2 . If a signal is replied from the head-mounted unit  2 , it is determined whether the head-mounted unit  2  is unavailable or available corresponding to the replied content. When a signal is replied, the signal in what state shows the head-mounted unit  2  is available or unavailable is as described above.  
      In Step S 5 , when the head-mounted unit  2  is determined available, a power supply turning-on signal (power&#39;supply instruction signal) is then transmitted to the head-mounted unit  2  so as to return to a predetermined parent routine (Step S 6 ). The electric power is thereby supplied for the entire head-mounted unit  2 . As described above, because while the power-supply switch  23  of the head-mounted unit  2  is opened, the power supply of the head-mounted unit  2  is in a forcedly turned-off state, in order to make the power supply from the power supply circuit  92  of the head-mounted unit  2  operate in operatively association with the first power supply switch  43  or the second power supply switch  44  of the main unit  3 , it is necessary to close (turn-on) the power supply switch  23  in advance.  
      On the other hand, at Step S 5 , when the second CPU  71  determines that the head-mounted unit  2  is in an unavailable state, the second CPU  71  then determines whether the head-mounted unit  2  is in the information input mode or not (Step S 7 ). This determination is carried out based on the flag established at Step S 2  or Step S 3 .  
      When the information input mode is determined, since there is no means for visually confirming the information inputted from the main unit  3  in the state shown in  FIG. 10  (i.e., since the LCD  51  of the main unit  3  in the state of  FIG. 10  cannot be used because the head-mounted unit  2  is turned off), the power supply of the main unit  3  is turned off (Step S 8 ). In addition, according to the embodiment, the power supply of the main unit  3  is turned off; it is not limited to this, and the main unit  3  may be set in the low power consumption mode (stand-by state).  
      At Step S 7 , if the information input mode is not determined, that is, the playback mode is determined, the processing is finished and it returns to the predetermined parent routine.  
      As described above, the information input mode is effected only when the main unit  3  and the head-mounted unit  2  integrally function, so that when the head-mounted unit  2  is unavailable, the power supply of the main unit  3  is instantly turned off (Step S 7  and Step S 8 ). By such control, the useless power consumption is suppressed. Also even when the power supply of the main unit  3  is turned on by carelessly operating the first power supply switch  43  or the second power supply switch  44 , the electric power supply is automatically suppressed, so that the waste of the electric power can be suppressed.  
      While the information display apparatus  1  is in the playback mode, the main unit  3  can also be used individually, so that even if the head-mounted unit  2  is unavailable, the power supply of the main unit  3  is remained in the turned-on state. At this time, it is just not to transmit the power supply turning-on signal to the head-mounted unit  2  from the main unit  3 .  
      In such a manner, according to the information display apparatus  1  described above, the power source can be appropriately supplied to the head-mounted unit  2  and the main unit  3  only by simple operation.  
       FIG. 19  is a flowchart illustrating operation of the timer counter for controlling the time of the electric power supply to the head-mounted unit  2  and the main unit  3 .  
      Upon starting this processing, the timer counter set at Step S 4  is down-counted at a predetermined time intervals (Step S 11 ).  
      Then, the counter value is determined if it becomes zero (Step S 12 ).  
      Until the counter value becomes zero, the timer counter is down-counted with predetermined time intervals by returning the process to Step S 11 .  
      At Step S 12 , when the counter value becomes zero, the second CPU  71  transmits the power supply turning-off signal to the power supply circuit  75  of the main unit  3  and the head-mounted unit  2  (Step S 13 ).  
      When the head-mounted unit  2  receives the power supply turned-off signal from the main unit  3 , the first CPU  91  transmits the power supply turning-off signal to the power supply circuit  92 . Thereby, the power supply from the power supply circuit  92  to the circuits within the head-mounted unit  2  is reduced or turned off, so that the first CPU  91  itself becomes the stand-by state.  
      Similarly, in also the main unit  3 , the second CPU  71  transmits the power supply turning-off signal to the power supply circuit  75 , so that the power supply from the power supply circuit  75  to the circuits within the main unit  3  is reduced or turned off, and the second CPU  71  itself becomes the stand-by state.  
      Subsequently,  FIG. 20  is a flowchart illustrating an adjustment process of an initial position of a display screen. The process of  FIG. 20  will be described with reference to  FIGS. 21 and 22 .  FIG. 21  is a drawing of a display example when adjusting the initial position of the display screen; and  FIG. 22  is a drawing of a display example when the initial position of the display screen has been adjusted.  
      The information display apparatus  1  according to the embodiment can display information on the head-mounted unit  2  as if the display image were fixed to the external world (just like an observer watches a stationary monitor or TV set, for example) regardless of the movement of the head of an observer. Hence, if the observer tilts the head, the image is shifted corresponding to the movement in real time by the displacement amount corresponding to the head inclination in the opposite direction. The process shown in  FIG. 20  is of the adjustment in which an inclination angle of the head is determined as a reference to shift the image. Thereby, the display screen can be watched as if a virtual stationary monitor were installed at the optimum observing position.  
      At a time when the observer just faces the front, the screen like in  FIG. 21  is displayed. In  FIG. 21 , a displayable range  131  is indicated by a dotted line, and a display frame  132  is displayed at a lower right position within the displayable range  131 . Inside the display frame  132 , a display screen  133  is provided.  
      In such a state, when the observer sets the information display apparatus  1  in an adjustment mode by predetermined key operation using the first operating switch  72  and the second operating switch  73  of the main unit  3 , an “ADJ” character  134  is displayed at a position on the left within the displayable range  131  for showing the adjustment mode, as shown in  FIG. 21  (Step S 21 ).  
      Then, when predetermined horizontal and vertical keys of the main unit  3  (the menu select switches  56 ,  57 ,  58 , and  59  shown in  FIG. 11  or the pad-type pointing device  46  shown in  FIG. 10 , for example) are operated, the second CPU  71  detects this key entry (Step S 22 ). While the key entry continues, display information is generated showing the shifting of the display frame  132  and the display screen  133  by key operation at a predetermined movement speed in an instructed direction so as to be written in the main unit memory  78 .  
      That is, when the upward key operation is detected, display data is produced so as to move the display frame  132  and the display screen  133  at a predetermined moving speed in the upward direction within the displayable range  131  while the key is operated, and the display data is written in the main unit memory  78 . Thereby, the data in the main unit memory  78  is transmitted to the head-mounted unit  2  by radio, so that images moved upward within the displayable range  131  are displayed by the head-mounted unit  2  (Step S 23 ).  
      Also, when the downward key operation is detected, display data is produced so as to move the display frame  132  and the display screen  133  at a predetermined moving speed in the downward direction within the displayable range  131  while the key is operated, and the display data is written in the main unit memory  78 . Thereby, the data in the main unit memory  78  is transmitted to the head-mounted unit  2  by radio, so that images moved downward within the displayable range  131  are displayed by the head-mounted unit  2  (Step S 24 ).  
      Furthermore, when the leftward key operation is detected, display data is produced so as to move the display frame  132  and the display screen  133  at a predetermined moving speed in the leftward direction within the displayable range  131  while the key is operated, and the display data is written in the main unit memory  78 . Thereby, the data in the main unit memory  78  is transmitted to the head-mounted unit  2  by radio, so that images moved leftward within the displayable range  131  are displayed by the head- mounted unit  2  (Step S 25 ).  
      Then, when the rightward key operation is detected, display data is produced so as to move the display frame  132  and the display screen  133  at a predetermined moving speed in the rightward direction within the displayable range  131  while the key is operated, and the display data is written in the main unit memory  78 . Thereby, the data in the main unit memory  78  is transmitted to the head-mounted unit  2  by radio, so that images moved rightward within the displayable range  131  are displayed by the head-mounted unit  2  (Step S 26 ).  
      Upon completing any one of Steps S 23  to S 26 , a predetermined confirmation operation (the operation of the determination switch  55  shown in  FIG. 11  or the clicking of the left button  47  shown in  FIG. 10 , for example) is waited (Step S 27 ). Until the confirmation is operated, the key entry is continuously performed back to Step S 22 .  
      On the other hand, when the confirmation is operated, the position of the display frame  132  is settled. Simultaneously, the “ADJ” character  134  for showing the adjustment mode vanishes. Thereby, the display frame  132  and the display screen  133  in the state shown in  FIG. 22  are displayed as virtual images.  
      Then, head angular data in yaw and pitch directions θy and θp calculated based on the outputs from the angular velocity sensors  94  and  95  is reset (Step S 28 ) so as to complete the positional adjustment of the display screen.  
      By such adjustment, while positions of the display frame  132  and the display screen  133  in the initial state are settled, the head angular data θy and θp are measured thereafter using the initial state as a reference point.  
      In the examples of  FIGS. 21 and 22 , the display frame  132  is expressed clearly with a boundary line; however, it is not necessarily expressed clearly.  
      According to the embodiment, the adjustment of the initial position is performed by the process shown in  FIG. 20 ; it is not limited to this. For example, when the head is inclined at a predetermined inclination (specifically, when an observer allows the head to be inclined at an angle desired at the initial position), the display screen may be settled at a predetermined position by a predetermined key entry (the operation of the determination switch  55  or the clicking of the left button  47 , for example) while the angular data θy and θp may also be reset. By adopting such an operation system, the initial positions of the display frame  132  and the display screen  133  can be more simply adjusted.  
      Subsequently,  FIG. 23  is a flowchart of a process controlling the image display position when the information display apparatus  1  is used in the information input mode. This information input mode, as mentioned above, is used for using the information display apparatus  1  as the information input device (see  FIG. 10 ).  
      The process shown in  FIG. 23  offers a feeling that as if an observer were observing a monitor fixed to the external world by shifting the image display region in a direction opposite to the head inclination angle.  
      When the monitor display region is shifted corresponding to the head inclination angle, there is no problem if the change in the display region follows the change in the head inclination angle smoothly at high speed; however, because the changing speed of the display region has a limit in practice, the changing smoothness of the display region may be impaired. So, according to the embodiment, the display region is to be changed only when the angular change is more than a predetermined value so as not to impair the smoothness extremely.  
      However, despite such a process, every time the head inclination angle is minutely changed, the display region is changed with a delay to some extent. In particular, when the changes are frequent, an observer may feel a sense of discomfort. And so, according to the embodiment, the threshold value of the change in the head inclination angle is varied to have a difference between when the head inclination is changing in a normal direction and directly after the head inclination is changed in the opposite direction. That is, by adding so-called hysteresis characteristics that the angular change directly after the detection of the angular change in the opposite direction is increased relative to the angular change in a normal direction for changing the display region, the sense of discomfort is alleviated (see below-mentioned Steps S 35  to S 40  and S 44 ).  
      Furthermore, in order to reduce the head-mounted unit  2  in size and weight as much as possible, the calculation process in the head-mounted unit  2  is reduced.  
      That is, the head-mounted unit  2  mainly has the functions to receive predetermined display information from the main unit  3  so as to display the information on the see-through information display portion  108 , to receive a sound signal from the main unit  3  so as to play back, and to detect an angular velocity of a head and a variation in the head inclination for a predetermined time so as to transmit the results to the main unit  3 .  
      On the other hand, the main unit  3  mainly has the functions to read out information from a recording medium (the record memory  83  and the hard disk  85 ) having the information, such as sound signals, images, and characters, recorded thereon; to produce display data giving a sense just like watching a monitor fixed to the external world by processing display information among various kinds of information read out of the recording medium based on a head inclination angle so as to transmit the display data to the head-mounted unit  2 ; and to play back the sound signals and images recorded on the recording medium by the main unit  3  itself.  
      Such processing will be described in detail with reference to  FIG. 23 . In  FIG. 23 , the operation of the main unit  3  is shown on the right and the operation of the head-mounted unit  2  is shown on the left.  
      Upon initiating the processing, first, the angular velocity information in a yaw direction of an observer head detected by the angular velocity sensor  94  is inputted (Step S 31 ) while the angular velocity information in a pitch direction of the observer head detected by the angular velocity sensor  95  is inputted (Step S 32 ).  
      Then, the angular velocity in the yaw direction obtained at Step S 31  is time-integrated so as to calculate an angular change in the yaw direction Δθy [rad] (Step S 33 ) while the angular velocity in the pitch direction obtained at Step S 32  is time-integrated so as to calculate an angular change in the pitch direction Δθp [rad] (Step S 34 ).  
      In the example shown in  FIG. 23 , the angular changes Δθy and Δθp are calculated by the head-mounted unit  2 , and then, the calculated angular changes Δθy and Δθp are transmitted to the main unit  3  (see below-mentioned Step S 36 ); however it is not limited to this, so that the angular velocity information obtained from the angular velocity sensors  94  and  95  may be transmitted to the main unit  3  as it is so as to calculate the angular changes Δθy and Δθp in the main unit  3  based on the received angular velocity information. In this case, the processing load on the head-mounted unit  2  can be reduced.  
      Then, it is determined whether at least one of the absolute value of the angular change in the yaw direction |Δθy| [rad] and the absolute value of the angular change in the pitch direction |Δθp| [rad] within a predetermined time (duration) is larger than a predetermined value (a predetermined first threshold value) α1 or not. That is, it is determined whether at least one of |Δθy|&gt;α1 and |Δθp|&gt;α1 is established or not (Step S 35 ).  
      When it is determined that at least one of |Δθy| and |Δθp| is larger than the predetermined value α1, the head-mounted unit  2  transmits data of Δθy and Δθp to the main unit  3  (Step S 36 ).  
      After the processing of Step S 36 , the head-mounted unit  2  returns to Step S 31  so as to repeat the operation described above.  
      On the other hand, the main unit  3  receives the data of Δθy and Δθp transmitted from the head-mounted unit  2  at Step S 36  (Step S 37 ).  
      Then, it is determined whether the received angular change Δθy or Δθp is in a direction opposite to that of the previously detected value (i.e., whether it differs in sign from the previously detected value) (Step S 38 ). This processing determines whether the angular change in the head inclination remains in the normal direction or changes in the opposite direction.  
      When it is determined that the angular change is in the opposite direction at Step S 38 , it is further determined whether at least one of the absolute value of the angular change in the yaw direction |Δθy| and the absolute value of the angular change in the pitch direction |Δθp| is larger than a second predetermined value (a predetermined second threshold value) α2 or not (the second predetermined value α2 satisfies α2&gt;α1). That is, it is further determined whether at least one of |Δθy|&gt;α2 and |Δθp|&gt;α2 is established or not (Step S 39 ).  
      When it is determined that both |Δθy| and |Δθp| are smaller than the second predetermined value α2 at Step S 39 , the main unit  3  returns to Step S 37  so as to repeat the operation described above.  
      When it is determined that at least one of |Δθy| and |Δθp| is larger than the second predetermined value α2 at Step S 39 , or when it is determined that the angular change is not in the opposite direction at Step S 38  (i.e., the head inclination angle is changing in the normal direction), the displacement amount of the display frame  132  (and the display screen  133 ) corresponding to Δθy or Δθp is calculated (Step S 40 ). The calculation of the displacement amount is performed by deriving from L×Δθy or L×Δθp, where L is the distance between observer eyes and the screen.  
      Then, based on the calculated displacement amount, it is determined whether at least part of the displaced display frame  132  (and the display screen  133 ) is located within the displayable range  131  or the entire is out of the displayable range  131  (Step S 41 ).  
      When it is determined that the entire display frame  132  is out of the displayable range  131 , it is determined whether the time measured by the timer provided in the second CPU  71 , which is continued after the entire display frame  132  is first out of the displayable range  131 , is larger than the predetermined time Ts stored in the main unit memory  78  in advance (Step S 42 ).  
      The predetermined time Ts, as mentioned above, can be set at a desired period of time by operating the menu button  53 , the menu select switches  56 ,  57 ,  58 , and  59 , and the determination switch  55  which are shown in  FIG. 11 .  
      When it is determined at Step S 42  that the predetermined time Ts has elapsed, the power supply circuit  75  of the main unit  3  is set in the low power consumption mode so as to reduce the electric power supplied from the power supply circuit  75  while a signal indicating the low power consumption mode is transmitted to the head-mounted unit  2  (Step S 43 ).  
      Then, the first CPU  91  of the head-mounted unit  2  interprets the received signal indicating the low power consumption mode so as to set the power supply circuit  92  in the low power consumption mode.  
      In the low power consumption mode, specifically, operations other than part of functions of the first CPU  91  and the second CPU  71  or operations of blocks other than CPUs are stopped, and it is the same as known means.  
      On the other hand, when it is determined at Step S 41  that at least part of the display frame  132  is located within the displayable range  131  so that images can be displayed, or when the non-displayed time of the display frame  132  is shorter than the predetermined time Ts at Step S 42 , information of the display frame  132  and information of the display screen  133  are mapped and stored in the main unit memory  78  so that the display screen is moved by a distance corresponding to the displacement amount calculated at Step S 40  in a direction opposite to the angular change of the observer head in the yaw direction or the pitch direction (Step S 44 ).  
      The data stored in each address of the main unit memory  78  one-to-one corresponds to the display position in the LCD  104  of the head-mounted unit  2  (each pixel position)  
      Then, the display data mapped on each address of the main unit memory  78  is transmitted to the head-mounted unit  2  (Step S 45 ).  
      After the processing of Step S 45 , the main unit  3  returns to Step S 37  so as to repeat the operation described above.  
      On the other hand, the head-mounted unit  2  receives the display data transmitted from the main unit  3  (Step S 46 ) so as to be stored in the memory  113  (Step S 47 ).  
      The data stored in each address of the memory  113  one-to-one corresponds to the data stored in each address of the main unit memory  78 . Hence, the data stored in each address of the memory  113  one-to-one corresponds to each pixel constituting the LCD  104 . In such a manner, by mapping (storing two-dimensional display data) the display data on each address of the main unit memory  78  of the main unit  3  or the memory  113  of the head-mounted unit  2 , arbitrary information can be displayed on the LCD  104 .  
      Then, the head-mounted unit  2  displays the display data stored in the memory  113  by the LCD  104  (Step S 48 ).  
      After the processing of Step S 48 , the head-mounted unit  2  returns to Step S 31  so as to repeat the operation described above.  
      Subsequently,  FIG. 24  is a flowchart showing a scroll process executed as an interrupt handling.  
      In the information display apparatus  1 , the images displayed within the display frame  132  can be scrolled. Upon scrolling, the interrupt is generated so as to execute the scrolling processing.  
      That is, upon initiating the interrupt processing, the data in the main unit memory  78  is mapped so that data, such as characters and images, within the display frame  132  are shifted in a predetermined direction corresponding to the operated scrolling direction and the scroll amount (Step S 51 ). Then, the interrupt processing is returned to the original processing.  
      The scrolling operation is performed by operating a predetermined key arranged in the keyboard  45  of the main unit  3  (see  FIG. 10 ). While the key is pushed, the scrolling operation is performed in a predetermined direction. Upon scrolling, the display region is updated so that images within the display region are scrolled.  
      Next,  FIG. 25  is a flowchart illustrating the display control when the information display apparatus  1  is operated as the playback device. The main unit  3  of the information display apparatus  1  in the playback mode is in the state shown in  FIG. 11 .  
      Upon starting the processing in the playback mode, the state of the display select switch  64  shown in  FIG. 11  is detected at first (Step S 61 ).  
      When “BDY” is selected by the display select switch  64  (the main unit  3  is referred to as “BDY”), i.e., the playback information by the LCD  51  of the main unit  3  is selected, the processing in the first display mode is executed (Step S 62 ). The first display mode is the same as the display control in a general playback device, in which information stored in the record memory  83  or the hard disk  85  is read out so as to be temporarily stored in the main unit memory  78 ; the information stored in the main unit memory  78  is converted into analog data by the D/A converter  79  so as to be displayed on the LCD  51 .  
      On the other hand, when “HD” is selected by the display select switch  64  (the head-mounted unit  2  is referred to as “HD”), i.e., the playback information by the LCD  104  of the head-mounted unit  2  is selected, the processing in the second display mode is executed (Step S 63 ). In the second display mode, data read out of the record memory  83  or the hard disk  85  is temporarily stored in the main unit memory  78 ; the data is transmitted to the head-mounted unit  2  so as to be displayed on the LCD  104  of the head-mounted unit  2 .  
      In the playback mode shown in  FIG. 25 , the difference between the second display mode (the first display mode here is used for displaying information on the LCD  51  of the main unit  3 , and because the LCD  51  is not used in the information input mode shown in  FIG. 10 , it is omitted from the comparative object here) and the information input mode shown in  FIG. 23  is as follows. First, in the information input mode, information is input by operating the first operating switch  72  so as to display the input information. Whereas, in the second display mode, information stored in the record memory  83  or the hard disk  85  is displayed. In such a manner, the input end of information is the only difference between the second display mode and the information input mode, and the other operations, such as operation that the position of the display frame  132  is controlled corresponding to the head inclination so as to play back and display information as if an observer were watching a monitor installed in the external world, are the same.  
      In the above description, the record memory  83  or the hard disk  85  is used for the information source when the information display apparatus  1  is used for the playback device; it is not limited to this, so that the external information source via communicating means may also be used as the information source to input information for playing back. Specifically, information may be input from the Internet via a network interface. In this case, the information display apparatus  1  can be used as an Internet terminal.  
      According to the first embodiment, regardless of the head inclination of an observer, images are shifted in a direction opposite to the inclination direction of the observer head so that the position of virtual images observed from the observer substantially remains constant, so that the observer can observe images as if he or she were watching a display screen (large sized, for example) fixed to the external world.  
      Furthermore, since the initial position of images to be displayed is adjustable, the optimum initial position corresponding to differences among individuals and purposes of the usage for an observer can be selected. Thus, when using this display in a tram as a monitor of a personal computer, for example, by setting the display screen to downward slant, characters can be inputted from the keyboard of the main unit. Because the head inclination angle is detected using the initial position as a reference, images can be observed about the head position in natural posture, for example. Such initial position adjustment of the display screen gives an observer a sense just like setting a display screen installed on the external world at an optimum position, improving convenience.  
      Even when the head inclination is changed, if the angular variation within a predetermined time is less than the first threshold value, the display screen is not shifted in a direction opposite to the head angular change, so that it is not necessary to perform calculation every time the head is minutely changed, reducing the load on CPUs.  
      Moreover, when the head inclination is changed in the opposite direction, a threshold value for determining whether the display screen is shifted in the direction opposite to the head angular change is set (second threshold value) larger than that in the same direction, so that the screen flickering due to the head minute vibration about the predetermined position can be efficiently prevented.  
      Since the display information within the display region can be scrolled in the horizontal and vertical directions, desired information can be displayed at the most easily viewable position. Thereby, information can be observed in a comfortable watching state even in the compact light weight device.  
      Furthermore, the head-mounted unit mainly displays information and detects angular information while other complicated computation and information recording are performed in the main unit, so that the processing load on the head-mounted unit can be reduced. Thereby, the electric power consumption of the head-mounted unit can be reduced so that the power supply battery can be miniaturized, resulting in a compact head-mounted unit with airy availability.  
      In particular, since the head-mounted unit communicates with the main unit by radio, the head-mounted unit is not restrained by wirings, and an observer can observe specific information while behaving freely as usual.  
      Since when the display frame deviates from the displayable range and images are not displayed for more than a predetermined time, the information display apparatus is automatically switched to the low power consumption mode, the electric power consumption can be reduced so as to extend a battery life without intentionally shutting off the power supply. For example, as mentioned above, even if using this display in a tram as a monitor of a personal computer and the display screen is set to downward slant, when an observer gets off the tram and raises the head, the screen vanishes from the visual range, so that external world can be freely observed without hindrance, and the observer can normally behave with safety without removing the display apparatus. Also, the electric power consumption can be reduced without shutting off the power supply.  
      Because the main unit is provided with an LCD, even when the head-mounted unit is removed from the head, information can be observed. At this time, the information display end is to be alternatively selected between the head-mounted unit and the main unit, so that information cannot be displayed on the non-observed side, suppressing consumption of the electric power in vain.  
      Furthermore, it is natural that when the head-mounted unit is available, an observer intends to observe information through the head-mounted unit. In accordance with this, the system is designed so that information is displayed with priority to the head-mounted unit when it is available, resulting in improved operability due to automated operation.  
      Because only by turning on/of the power source of the main unit, the power source of the head-mounted unit is simultaneously turned on/off, operation is simple and convenient especially in this information display system in which both the main unit and the head-mounted unit may be simultaneously used.  
      When there is no reply from the head-mounted unit, the main unit is set to be in a power off state or a stand by state, so that even when the power supply is turned on by mistake, useless power consumption is prevented or suppressed. For example, when the system is carried in a bag, there is little chance that both the main unit and the head-mounted unit, which are separated from each other, are simultaneously turned on by mistake, so that useless power consumption is securely suppressed.  
      The suppression of the power supply described above is effective especially for portable information display systems demanding reduction in size and weight, and battery life elongation.  
      In such a manner, even though it can be used casually, the system has enough value as a wearable and portable information display apparatus by providing advanced capabilities.  
      In the above description, in the head-mounted unit, by projecting information displayed by the first displaying means to eyes of an observer, the information is displayed so that the observer can observe it as virtual images; however, a head-mounted unit applicable to the present invention is not limited to this, so that any unit may be incorporated as long as information displayed by the first displaying means can be displayed to be observed.  
      Having described the preferred embodiments of the invention referring to the accompanying drawings, it should be understood that the present invention is not limited to those precise embodiments and various changes and modifications thereof could be made by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.