Abstract:
A tilt sensor capable of detecting more diverse orientations is to be provided. The tilt sensor includes a light emitting element and a plurality of photodetectors, a rolling element, and a hollow portion that accommodates the rolling element so as to allow the rolling element to roll in all of x-, y-, and z-direction, and to locate the rolling element, according to a direction of the gravity, at one of detecting positions including a complete blocking position that inhibits light from the light emitting element from reaching any of the photodetectors, a plurality of partial blocking positions that inhibits the light from the light emitting element from reaching at least one but not all of the photodetectors, and a nonblocking position that permits the light from the light emitting element to reach all of the photodetectors, and two of the detecting positions are each located on a respective end portion of the hollow portion in the x-, y-, and z-direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a tilt sensor. 
     2. Description of the Related Art 
       FIGS. 9 and 10  depict an example of a conventional tilt sensor (see Japanese Laid-open Patent Publication No. 2007-139643). The illustrated tilt sensor X includes a substrate  91 , a housing  92 , a cover  93 , a pair of photodetectors  94 A,  94 B, a light emitting element  95 , and a rolling element  96 . (The cover  93  is omitted in  FIG. 10 .) The pair of photodetectors  94 A,  94 B and the light emitting element  95  are mounted on a surface of the substrate  91 , and enclosed in the housing  92 . The housing  92  and the cover  93  define a hollow portion or space  92   a . The hollow portion  92   a  is of such a shape that permits light from the light emitting element  95  to enter the space, and that causes the light reflected by the housing  92  to reach the photodetectors  94 A,  94 B. The hollow portion  92   a  contains the rolling element  96 . The rolling element  96  is of a circular column shape, and free to roll inside the hollow portion  92   a  along the xy-plane. The lower surface of the substrate  91  is formed with terminals for surface mounting of the tilt sensor on a circuit board, for example. 
       FIG. 10  illustrates a state where the rolling element  96  is superposed on the light emitting element  95  under the pull of gravity. In this state, the light emitted by the light emitting element  95  is blocked by the rolling element  96 , thereby inhibited from reaching neither of the photodetectors  94 A,  94 B. In the case where the tilt sensor X is inclined to the left from the state shown in  FIG. 10 , the rolling element  96  becomes superposed on the photodetector  94 A. In this state, the light from the light emitting element  95  solely reaches the photodetector  94 B. On the contrary, when the tilt sensor X is inclined to the right from the state shown in  FIG. 10 , the rolling element  96  becomes superposed on the photodetector  94 B, in which case the light from the light emitting element  95  solely reaches the photodetector  94 A. In the case where the tilt sensor X is implemented on a circuit board for example, a tilting motion of the circuit board about an axis perpendicular thereto can be detected through monitoring the photo detection signal from the pair of photodetectors  94 A,  94 B. Employing such tilt sensor X enables detecting, for example, a vertical or horizontal orientation of a mobile phone set by the user viewing the display screen thereof, and changing the orientation of the image on the display screen according to the orientation of the mobile phone. 
     The tilt sensor X thus designed is intended for detecting an orientation in the case where the tilt sensor is rotated about the axis extending in a z-direction (Ref.  FIG. 9 ), from the state shown in  FIG. 10 . Accordingly, it is difficult to detect the orientation with the tilt sensor X in the case where the tilt sensor is rotated about an axis extending in an x-direction, from the state shown in  FIG. 10 . To utilize the tilt sensor X for more various purposes, it is preferable that the tilt sensor X is capable of detecting more diverse orientations. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed under the foregoing circumstances. It is therefore an object of the present invention to provide a tilt sensor capable of detecting more diverse orientations. 
     The present invention provides a tilt sensor comprising a light emitting element and a plurality of photodetectors, a rolling element, and a hollow portion that accommodates the rolling element so as to allow the rolling element to roll in a first direction, a second direction different from the first direction, and a third direction different from the first and the second direction, and to locate the rolling element, according to a direction of the gravity, at one of detecting positions including a complete blocking position that inhibits light from the light emitting element from reaching any of the photodetectors, and a plurality of partial blocking positions that inhibits the light from the light emitting element from reaching at least one but not all of the photodetectors, or including the complete blocking position, the plurality of partial blocking positions, and a nonblocking position that permits the light from the light emitting element to reach all of the photodetectors, wherein two of the detecting positions are each located on a respective end portion of the hollow portion in the first, the second, and the third direction. 
     The tilt sensor thus configured allows detecting the orientation, irrespective of which of the forward and the backward direction in the first, the second, and the third direction is aligned with the gravity direction. Such tilt sensor can, therefore detect more diverse orientations. 
     Preferably, the hollow portion communicates at the complete blocking position with a light emission port through which the light from the light emitting element is emitted, at the partial blocking position with a light reception port through which the light is incident upon the photodetector. 
     Preferably, the hollow portion is of a spherical shape. Such configuration facilitates the rolling element to roll. 
     Preferably, the hollow portion is of a regular octahedral shape, in which the light emission port and the light reception port are each located on an apex. 
     Preferably, the first, the second, and the third direction are orthogonal to each other. 
     Preferably, the complete blocking position and the partial blocking position are located on the respective end portions of the hollow portion in the first direction. 
     Preferably, the complete blocking position and the nonblocking position are located on the respective end portions of the hollow portion in the first direction. 
     Preferably, the rolling element is of a spherical shape. Such configuration facilitates the rolling element to roll. 
     Other features and advantages of the present invention will become more apparent through the following detailed description given with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a tilt sensor according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along a line II-II in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along a line III-III in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view for explaining use of the tilt sensor according to the present invention; 
         FIG. 5  is another cross-sectional view for explaining use of the tilt sensor according to the present invention; 
         FIG. 6  is still another cross-sectional view for explaining use of the tilt sensor according to the present invention; 
         FIG. 7  is a cross-sectional view showing a tilt sensor according to a second embodiment of the present invention; 
         FIG. 8  is another cross-sectional view showing a tilt sensor according to the second embodiment of the present invention; 
         FIG. 9  is a cross-sectional view of a conventional tilt sensor; and 
         FIG. 10  is a front view of the conventional tilt sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below with references to the accompanying drawings. 
     Referring to  FIGS. 1 to 6 , a first embodiment of the present invention will be described. 
     As shown in  FIG. 1 , the tilt sensor A 1  of the first embodiment is surface-mounted on e.g. a circuit board S for detection of an inclination with respect to the vertical direction (i.e. the direction of gravity). The tilt sensor A 1 , generally square in plan, has a size of approximately 1.5 to 3.0 mm for each side of the square. As shown in  FIGS. 2 and 3 , the tilt sensor A 1  includes a base substrate  1 , lateral substrates  2   a ,  2   b ,  2   c ,  2   d , a cover substrate  3 , a light emitting element  5 , photodetectors  6   a - 6   d  cooperating with the light emitting element  5 , a contoured resin member  7 , and a rolling element  8 . The directions x, y and z mutually define an angle of 90 degrees (that is, the three directions are perpendicular to each other). 
     Referring to  FIG. 2 , the base substrate  1  is a rectangular insulating substrate. The base substrate  1  extends along a yz-plane. The base substrate  1  is made of, for example, a glass epoxy resin (glass fiber-reinforced epoxy), and provided with wiring patterns (not shown). The wiring patterns are made of, for example, a Cu—Ni—Au plated layer. The wiring patterns include portions formed on the upper and lower surfaces of the base substrate  1  and portions in through-holes for electrically connecting the upper and lower wiring portions. The light emitting element  5  is mounted, by die-bonding, on the wiring portion formed on the upper surface of the base substrate  1 . The wiring portion formed on the lower surface of the base substrate  1  serves as terminals for surface-mounting the tilt sensor A 1  on the circuit board S. 
     The light emitting element  5  is an infrared beam emitting diode, for example. In this embodiment, the size of the light emitting element  5  is approximately 0.25 mm for each side of the square. For the light emitting element  5 , use may be made of a diode adapted to emit light of different wavelengths (e.g. visible light) than the infrared beam. 
     Referring to  FIGS. 2 and 3 , the lateral substrates  2   a ,  2   b ,  2   c ,  2   d  are rectangular insulating substrates. The lateral substrates  2   a  to  2   d  are held upright with respect to the base substrate  1 . As shown in  FIG. 3 , the lateral substrates  2   a  and  2   c  extend in the y-direction, facing each other. The lateral substrates  2   b  and  2   d  extend in the z-direction, facing each other. The lateral substrates  2   a  to  2   d  are made of a glass epoxy resin. The lateral substrates  2   a  to  2   d  are bonded to a surface of the base substrate  1  at the respective end portions in the x-direction. As shown in  FIG. 3 , the adjacent ones of the lateral substrates  2   a  to  2   d  are bonded to each other, and thereby constitute a frame, as viewed in the yz-plane (in other words, as viewed in the x-direction). The inner surfaces of the lateral substrates  2   a  to  2   d  (the inner sides of the frame shown in  FIG. 3 ) are provided with wiring patterns (not shown) made of, for example, a Cu—Ni—Au plated layer, as those provided on the base substrate  1 . 
     The photodetectors  6   a ,  6   b ,  6   c ,  6   d  are mounted, by die-bonding, on the wiring patterns formed on the lateral substrates  2   a ,  2   b ,  2   c ,  2   d , respectively. The photodetectors  6   a ,  6   c  are disposed so as to face each other. The photodetectors  6   b ,  6   d  are disposed so as to face each other. The photodetectors  6   a  to  6   d  are, for example, phototransistors adapted to generate photovoltaic power upon receiving infrared beam, thereby causing a current flow. The size of each photodetector  6   a  to  6   d  is approximately 0.6 mm×0.4 mm. 
     The contoured resin member  7  is provided on the base substrate  1  and surrounded by the lateral substrates  2   a  to  2   d . The resin member  7  is made of, for example, an epoxy resin. The resin member  7  is formed with an internal hollow portion  74 . An accommodation space  71  is defined by the resin member  7  and the base substrate  1 . Likewise, accommodation spaces  72   a  to  72   d  are defined by the resin member  7  and the lateral substrates  2   a  to  2   d , respectively. 
     As shown in  FIG. 2 , the accommodation space  71  accommodates the light emitting element  5 . A light emission port  76  is provided between the accommodation space  71  and the hollow portion  74 . The light emission port  76  serves as a path through which the light from the light emitting element  5  is emitted into the hollow portion  74 . 
     As shown in  FIG. 3 , the accommodation spaces  72   a  to  72   d  each accommodate the photodetectors  6   a  to  6   d , respectively. Between each of the accommodation spaces  72   a - 72   d  and the hollow portion  74 , a light reception port  77   a - 77   d  is provided, respectively. The light reception ports  77   a  to  77   d  serve as a path through which the light travels from the hollow portion  74  to the photodetectors  6   a  to  6   d.    
     The hollow portion  74  accommodates the rolling element  8  in a manner such that the rolling element  8  can move freely (by gravity) to take one of predetermined detecting positions, depending on the posture of the tilt sensor A 1 . The hollow portion  74  in this embodiment is generally spherical, though the present invention is not limited to this. The hollow portion  74  communicates with the light emission port  76  and also with the respective light reception ports  77   a  to  77   d.    
     The rolling element  8  moves within the hollow portion  74  as the posture of the tilt sensor A 1  changes. At a given detecting position, the rolling element  8  can block the light from the light emitting element  5 , so that the light does not reach a selected one or ones of the photodetectors  6   a  to  6   d . The rolling element  8  is of a spherical shape, having a diameter of 0.7 to 0.8 mm, for example. The rolling element  8  is made of a metal having relatively high density, such as stainless steel or tungsten. 
     Tilt detection by the tilt sensor A 1  is performed in the following manner. 
       FIGS. 2 and 3  illustrate an initial state (or default state) of the tilt sensor A 1 . In  FIG. 2  (and  FIGS. 4 to 6 ), the downward direction is a direction in which the rolling element  8  is pulled by the gravity. In the initial state, the rolling element  8  in the hollow portion  74  is located in front of the light emission port  76  or at a complete blocking position p 1  (one of the detecting positions), thereby closing the port  76  as a whole. The hollow portion  74  is regarded as being connected to the light emission port  76  at the complete blocking position p 1 . 
     When the rolling element  8  is at the complete blocking position p 1 , the light from the light emitting element  5  is completely blocked by the rolling element  8 . Accordingly, the light does not reach any photodetectors  6   a  to  6   d . Consequently, when none of the photodetectors  6   a  to  6   d  provide any photo detection signal, it can be determined that the tilt sensor A 1  is held in the default orientation shown in  FIG. 2 . 
       FIG. 4  depicts a state where the tilt sensor A 1  has been rotated counterclockwise by approximately 90 degrees from the orientation shown in  FIG. 2  about an axis extending perpendicularly to the drawing sheet (in the y-direction). Such rotation causes the rolling element  8  to move, under the gravity, toward an end of the hollow portion  74  in the z-direction. Then the rolling element  8  comes to a position in front of the light reception port  77   a  (partial blocking position p 2   a ; one of the detecting positions), thereby blocking the port  77   a . The hollow portion  74  is regarded as being connected to the light reception port  77   a  at the partial blocking position p 2   a    
     When the rolling element  8  is at the partial blocking position p 2   a , the light from the light emitting element  5  does not reach the photodetector  6   a . On the other hand, the light from the light emitting element  5  can reach the other photodetectors  6   b ,  6   c  and  6   d . Accordingly, when only the photodetectors  6   b ,  6   c  and  6   d  output photo detection signal, it can be determined that the rolling element  8  is at the partial blocking position p 2   a  and hence the tilt sensor A 1  is oriented as shown in  FIG. 4 . 
       FIG. 5  depicts a state where the tilt sensor A 1  has been rotated clockwise by approximately 90 degrees from the orientation shown in  FIG. 2  about an axis extending perpendicularly to the drawing sheet (y-direction). Such rotation causes the rolling element  8  to move, under the gravity, toward another end of the hollow portion  74  in the z-direction. Then the rolling element  8  comes to a position in front of the light reception port  77   c  (partial blocking position p 2   c ; one of the detecting positions), thereby blocking the light reception port  77   c . As seen from  FIG. 5 , the partial blocking position p 2   c  and the above-noted partial blocking position p 2   a  are aligned along a line extending in the z-direction (that is, the centers of the respective positions p 2   c  and p 2   a  are on the single line extending in the z-direction), partially overlapping with each other. The hollow portion  74  is connected to the light reception port  77   c  at the partial blocking position p 2   c.    
     When the rolling element  8  is at the partial blocking position p 2   c , the light from the light emitting element  5  does not reach the photodetector  6   c . On the other hand, the light from the light emitting element  5  can reach the other photodetectors  6   a ,  6   b  and  6   d . Accordingly, when only the photodetectors  6   a ,  6   b ,  6   d  output photo detection signals, it can be determined that the rolling element  8  is at the partial blocking position p 2   c  and hence the tilt sensor A 1  is oriented as shown in  FIG. 5 . 
       FIG. 6  depicts a state where the tilt sensor A 1  has been rotated by approximately 180 degrees from the state shown in  FIG. 2  about an axis extending perpendicularly to the drawing sheet (y-direction). Such rotation causes the rolling element  8  to move, under the gravity, toward another end of the hollow portion  74  in the x-direction. Then the rolling element  8  reaches a position (nonblocking position p 3 ; one of the detecting positions) which is opposite to the light emission port  76 . At this position, the rolling element  8  does not block the light emission port  76  nor any one of the light reception ports  77   a - 77   d . As seen from  FIG. 6 , the nonblocking position p 3  and the above-noted complete blocking position p 1  are aligned along a line extending in the x-direction, partially overlapping with each other. 
     When the rolling element  8  is at the nonblocking position p 3 , the light from the light emitting element  5  is emitted into the hollow portion  74  through the light emission port  76 . Then, the light reaches all the photodetectors  6   a - 6   d  through the light reception ports  77   a - 77   d  respectively, without being blocked by the rolling element  8 . Accordingly, when all of the photodetectors  6   a - 6   d  output photo detection signals, it can be determined that the rolling element  8  is at the nonblocking position p 3  and hence the tilt sensor A 1  is oriented as shown in  FIG. 6 . 
     Though not illustrated, a rotation of the tilt sensor A 1  from the orientation shown in  FIGS. 2 and 3  about an axis extending in the z-direction causes the rolling element  8  to move so as to block the light reception ports  77   b ,  77   d . In  FIG. 3 , such positions of the rolling element  8  are indicated as partial blocking positions (detecting positions) p 2   b  and p 2   d , respectively. The partial blocking position p 2   b  is located at an end of the hollow portion  74  in the y-direction, and the partial blocking position p 2   d  at the other end. In other words, the partial blocking position p 2   b  and the partial blocking position p 2   d  are aligned along a line extending in the y-direction, partially overlapping with each other. The hollow portion  74  is connected to the light reception port  77   b  at the partial blocking position p 2   b , while being also connected to the light reception port  77   d  at the partial blocking position p 2   d . When the rolling element  8  is located at the partial blocking position p 2   b  or p 2   d , the orientation of the tilt sensor A 1  can also be determined in the same manner described above. 
     With the above-described arrangements, the tilt sensor A 1  is advantageous in the following respects. 
     When the tilt sensor A 1  is tilted or rotated, starting from the orientation shown in  FIG. 2 , about an axis extending in the y-direction, the rolling element  8  moves to take one of the complete blocking position p 1 , the partial blocking positions p 2   a , p 2   c , and the nonblocking position p 3 . Likewise, when the tilt sensor A 1  is tilted or rotated about an axis extending in the z-direction, the rolling element  8  moves to take one of the complete blocking position p 1 , the partial blocking positions p 2   b , p 2   d , and the nonblocking position p 3 . Accordingly, the tilt sensor A 1  can detect six orientations (two for each of the x, y and z-directions), depending on which one of the six detecting positions is located the lowest. 
     The rolling element  8  has a spherical shape. Thus, the rolling element  8  can move smoothly in the hollow portion  74  and can block the light emission port  76  and the light reception ports  77   a - 77   d  without leaving a gap. 
       FIGS. 7 and 8  illustrate a second embodiment of the present invention. In these drawings, elements identical or similar to those of the foregoing embodiment are indicated by the same signs.  FIGS. 7 and 8  correspond to  FIGS. 2 and 3  (the first embodiment), respectively, except for the following differences. 
       FIG. 7  is a cross-sectional view of a tilt sensor A 2  as viewed in the xz-plane.  FIG. 8  is a cross-sectional view of a tilt sensor A 2  as viewed in the yz-plane. The illustrated tilt sensor A 2  is different from the tilt sensor A 1  of the first embodiment in that the hollow portion  74  is octahedral, with the light emission port  76  and the light reception ports  77   a - 77   d  are each located on one of the apexes, and also in that the light emitting element  5  and the photodetector  6   a  are exchanged in position. Accordingly, the accommodation space  71  and the accommodation space  72   a  are exchanged, the light emission port  76  and the light reception port  77   a  are exchanged, and the complete blocking position p 1  and the partial blocking position p 2   a  are exchanged. 
     As shown in  FIGS. 7 and 8 , in the hollow portion  74 , the complete blocking position p 1  and the partial blocking position p 1   c  are aligned along a lien extending in the z-direction, partially overlapping with each other. Likewise, the nonblocking position p 3  and the partial blocking position p 2   a  are aligned along a line extending in the x-direction, partially overlapping with each other. 
     According to the second embodiment, since the hollow portion  74  is octahedral, the inner surfaces defining the hollow portions  74  (in other words, the inner surfaces which are located between the port  76 , the port  77   a , the port  77   b , the port  77   c  and the port  77   d ) are substantially flat. Such configuration enables stable positioning of the rolling element  8  at each of the detecting positions (i.e. the complete blocking position p 1 , the partial blocking positions p 2   a -p 2   d , and the nonblocking position p 3 ), thereby contributing to accurate tilt detection. 
     The scope of the present invention is not limited to the foregoing embodiments. The specific structure of each part of the tilt sensor according to the present invention may be varied in various ways. In the above-described tilt sensors A 1  and A 2 , a nonblocking position p 3  is provided. Alternatively, the nonblocking position p 3  may be replaced by a partial blocking position, with an additional photodetector disposed near the partial blocking position. In the tilt sensor A 1  with the spherical hollow portion  74 , the light emitting element  5  and the photodetectors  6   a - 6   d  may be arranged in the same way as those of the second embodiment. Likewise, in the tilt sensor A 2  with the octahedral hollow portion  74 , the light emitting element  5  and the photodetector  6   a - 6   d  may be arranged in the same way as those of the first embodiment. 
     In the foregoing embodiments, six detecting positions (the complete blocking position p 1 , the partial blocking positions p 2   a -p 2   d , the nonblocking position p 3 ) are distributed in equal number for each of the three directions (x, y and z) and are arranged in a manner such that two detecting positions for the same direction are aligned to each other in this direction. Alternatively, the nonblocking position p 3  and the complete blocking position p 1 , for example, may not be completely aligned in the x-direction, but may be shifted apart from each other as viewed in the x-direction. The light emitting element  5  and the photodetectors  6   a  to  6   d  may all be mounted on the base substrate  1 . Further, three directions (corresponding to the above-mentioned x, y and z-directions) may not be perpendicular to each other, but may be slanted at a predetermined angle. In this manner, it is possible to modify the tilt sensor so as to detect a different set of tilt angles. 
     The above mentioned tilt sensor can be utilized in several manners, equipped in various products. When the tilt sensor is equipped in a cell phone, a camera, a digital photo frame, a PDA (personal digital assistant), the tilt sensor is utilized to rotate a picture of a display according to the direction of the display equipped in the products. Further more, when the cell phone is put on a desk with its display oppose to the desk, the tilt sensor is also utilized to turn off the display (i.e., the tilt sensor is utilized as upside-down detecting sensor). 
     When the tilt sensor is equipped in a controller of a game machine, a cell phone or a PDA, the tilt sensor is utilized to play game or to control the brightness of a display equipped in the products according to the direction of the products. 
     When the tilt sensor is equipped in a television, the tilt sensor is utilized to turn off the power when the television is tumbled. Likewise, when the tilt sensor is equipped in a household electrical equipment like a compact heater or a stove, the tilt sensor is utilized to turn off the power in case of the tumble of them.