Abstract:
A tilt sensor includes a light emitting element and two light receiving elements accommodated in a case. The case is formed with an inner space in which a rolling member is provided in a freely movable manner by the pulling force of gravity. A cover plate is fixed to the case to close the inner space. The cover plate is provided with an irregular, inner ceiling surface that is exposed to the inner surface so as to come into sliding contact with the rolling member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a tilt sensor for detecting the tilting of a device such as a digital still camera. The invention also relates to a method for making such a tilt sensor. 
     2. Background of the Art 
       FIG. 15  illustrates an example of conventional tilt sensor (see JP-A-2007-139643). The illustrated tilt sensor X includes a mount board  91 , a case  92 , a cover plate  93 , a pair of light receiving elements  94 A and  94 B, a light emitting element  95  and a rolling member  96 . The case  92  includes a hollow which opens upward. The hollow is closed by the cover plate  93 , whereby an inner space  92   a  is defined. The rolling member  96  is arranged to move freely by the pulling of gravity in the inner space  92   a . The light receiving elements  94 A,  94 B and the light emitting element  95  are mounted on an obverse surface of the mount board  91 . The light emitted from the light emitting element  95  is directed into the inner space  92   a . Then, the light is reflected by a reflective film  93   a  provided on the cover plate  93 . The rolling member  96  rolls within the inner space  92   a  in accordance with the change in posture of the tilt sensor X. In particular, the rolling member  96  can move to a position to conceal the light receiving element  94 A, a position to conceal the light receiving element  94 B, and a position to conceal the light emitting element  95 . Depending on the position of the rolling member  96 , the light emitted from the light emitting element  95  reaches only the light receiving element  94 A, only the light receiving element  94 B or does not reach the light receiving element  94 A nor the light receiving element  94 B. Thus, by monitoring the light reception by the light receiving elements  94 A,  94 B, the tilting within a plane including the obverse surface of the mount board  1  is detected. 
     To ensure accurate tilt detection, the rolling member should be arranged to move smoothly within the inner space  92   a  by gravity. However, in the conventional structure, the rolling member  96  may often adhere to the case  92  or the cover plate  93 , thereby failing to shift position properly even when the pulling direction of gravity (relative to the sensor X) changes. This problem may occur more frequently as the size of the tilt sensor X is reduced. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed under the circumstances described above. It is therefore an object of the present invention to provide a tilt sensor in which the rolling member moves smoothly. 
     According to a first aspect of the present invention, there is provided a tilt sensor including: a light emitting element and a pair of light receiving elements spaced from each other in a surface direction of a detection target plane; and a rolling member adapted to take any one of a complete light shielding position, a partial light shielding position and a light unshielding position, where the complete light shielding position is a position at which the rolling member blocks the light emitted from the light emitting element so that the light does not reach neither of the paired light receiving elements, the partial light shielding position is a position at which the rolling member blocks the light emitted from the light emitting element so that the light reaches only one of the paired light receiving elements, and the light unshielding position is a position at which the rolling member fails to block the light emitted from the light emitting element so that the light reaches both of the paired light receiving elements. The tilt sensor also includes a case formed with an inner space for accommodating the rolling member, and an irregular ceiling surface exposed to the inner space. 
     With the above arrangement, the rolling member does not adhere to the cover plate, whereby the detection of tilting is performed accurately. 
     Preferably, the rolling member may be a cylindrical member having a central axis perpendicular to the surface direction. With this arrangement, the rolling member can move smoothly while appropriately blocking the light from the light emitting element. 
     Preferably, the irregular ceiling surface may be provided with a plurality of projections each being smaller in area, when viewed in a direction perpendicular to the surface direction, than the rolling member. 
     Preferably, the projections may be arranged at intervals smaller than a diameter of the rolling member. 
     Preferably, the projections may be circular in cross section. 
     Preferably, the projections may be elongated projections arranged in a radially extending manner. 
     Preferably, the tilt sensor of the present invention may further comprise a cover that provides the ceiling surface, and the projections may be constituted by a plating film formed on the cover. 
     Preferably, the tilt sensor may further comprise: a base plating layer in direct contact with the cover; and an intermediate plating layer formed on the base plating layer; wherein the base plating layer is greater in area than the projections, the intermediate plating layer has a shape corresponding to the projections, and the projections are formed on the intermediate plating layer. 
     Preferably, the base plating layer and the projections may be made of Cu, and the intermediate plating layer may include a Ni layer and a Cu layer, where the Ni layer is arranged close to the base plating layer, while the Cu layer is arranged close to the projections. 
     Preferably, the tilt sensor may further comprise an outer plating layer for covering the projections and the base plating layer, where the outer plating layer includes an obverse surface made of Au. 
     According to a second aspect of the present invention, there is provided a method for making a tilt sensor according to the first aspect of the present invention. The method comprises the steps of: forming a base plating layer on a cover plate providing the ceiling surface; forming an intermediate plating layer covering the base plating layer; forming a projection yield layer covering the intermediate plating layer; forming a plurality of projections by patterning the projection yield layer and part of the intermediate plating layer; and forming an outer plating layer covering the projections and the base plating layer. 
     Preferably, the intermediate plating layer may comprise a first layer close to the base plating layer and a second layer close to the projections, where the first layer differs in material from the second layer and the base plating layer, and the second layer is the same in material as the projection yield layer. 
     Preferably, the forming of the projections may comprise first etching and second etching subsequent to the first etching, where the first etching is performed for selectively etching away the second layer and the projection yield layer while allowing the first layer to remain, and the second etching is performed for selectively etching away the first layer while allowing the base plating layer to remain. 
     Other features and advantages of the present invention will become more apparent from detailed description given below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a tilt sensor according to a first embodiment of the present invention; 
         FIG. 2  is a plan view illustrating the tilt sensor according to the first embodiment of the present invention; 
         FIG. 3  is a sectional view taken along lines III-III in  FIG. 2 ; 
         FIG. 4  is a plan view illustrating a cover plate of the tilt sensor of  FIG. 1 ; 
         FIG. 5  is a sectional view illustrating a process of forming a base plating layer on a cover plate in making the tilt sensor of  FIG. 1 ; 
         FIG. 6  is a plan view illustrating the process of forming a base plating layer on a cover plate in making the tilt sensor of  FIG. 1 ; 
         FIG. 7  is a sectional view illustrating a process of forming an Ni plating layer and a Cu plating layer to become an intermediate plating layer in making the tilt sensor of  FIG. 1 ; 
         FIG. 8  is a sectional view illustrating a process of forming Cu plating layers to become projections in making the tilt sensor of  FIG. 1 ; 
         FIG. 9  is a sectional view illustrating a process of forming projections in making the tilt sensor of  FIG. 1 ; 
         FIG. 10  is a sectional view illustrating the etching of the Ni plating layer; 
         FIG. 11  is a sectional view illustrating a process of forming an outer plating layer in making the tilt sensor of  FIG. 1 ; 
         FIG. 12  is a plan view illustrating another example of projections formed on the cover plate of the tilt sensor of  FIG. 1 ; 
         FIG. 13  is a sectional view illustrating a tilt sensor according to a second embodiment of the present invention; 
         FIG. 14  is a sectional view taken along lines XIV-XIV in  FIG. 13 ; and 
         FIG. 15  is a sectional view illustrating a conventional tilt sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described below with reference to the accompanying drawings. 
       FIGS. 1-3  illustrate a tilt sensor A 1  according to a first embodiment of the present invention. The tilt sensor A 1  includes a mount board  1 , a case  2 , a cover plate  3 , a pair of light receiving elements  4 A and  4 B, a light emitting element  5  and a rolling member  6 . As illustrated in  FIG. 1 , the tilt sensor A 1  can be surface-mounted on an upright or substantially upright circuit board S to detect the tilting of the circuit board S within a tilt detection target plane, that is, the plane containing the obverse surface of the circuit board S. In this embodiment, the tilt sensor A 1  has a size of about 4.2 mm×4.2 mm and a thickness of about 3.0 mm. In  FIG. 2 , the illustration of the cover plate  3  is omitted. 
     The mount board  1  is a rectangular insulating substrate and made of e.g. a glass fiber-reinforced epoxy resin. In this embodiment, the mount board  1  has a size of about 4.2 mm×4.2 mm and a thickness of about 0.6 mm. The mount board  1  is formed with a wiring pattern  7 , which may be formed by etching a thin copper film. The wiring pattern  7  includes portions formed on the obverse and the reverse surfaces of the mount board  1  and through-hole portions (not shown) electrically connecting the obverse and the reverse portions. The light emitting element  5  and the light receiving elements  4 A and  4 B are bonded to the portion of the wiring pattern  7  on the obverse surface of the mount board  1 . As illustrated in  FIG. 3 , the portions of the wiring pattern  7  on the reverse surface of the mount board  1  serve as terminals  7   a ,  7   b  for surface mounting the tilt sensor A 1 . 
     The light receiving elements  4 A and  4 B may be PIN photodiodes. Upon receiving infrared light, the light receiving elements  4 A and  4 B generate a photoelectromotive force corresponding to the amount of light received and cause current to flow. The light receiving elements  4 A and  4 B are arranged on a surface of the mount board  1  so as to be spaced from each other along the surface (in other words, “spaced in the surface direction”). In this embodiment, the light receiving elements  4 A and  4 B have a size of about 0.6 mm×0.6 mm. 
     The light emitting element  5  is e.g. a light emitting diode adapted to emit infrared light. As seen from  FIG. 2 , the light emitting element  5  is spaced equidistantly from the light receiving elements  4 A and  4 B along the surface of the mount board  1 , so that these three elements constitute the vertexes of an isosceles or regular triangle. In this embodiment, the light emitting element  5  has a size of about 0.25 mm×0.25 mm. 
     The case  2  may be in the form of a rectangular parallelepiped and made of an electrically conductive material such as a conductive resin. The case  2  includes a hollow  2   a . The hollow  2   a  is closed by the cover plate  3 , whereby an inner space  20   a  is defined. The case  2  further includes three windows  20   b  and three element-accommodation spaces  20   c . In this embodiment, the case  2  has a size of about 4.2 mm×4.2 mm and a thickness of about 2.0 mm. 
     The case  2  is held in contact with a portion of the wiring pattern  7  which is electrically connected to a ground terminal. Thus, the case  2  is electrically connected to the ground terminal. 
     The inner space  20   a  accommodates the rolling member  6  to allow the rolling member  6  to move to predetermined positions in accordance with the posture of the tilt sensor A 1 . The inner space  20   a  has a cross sectional shape obtained by rounding the vertices of a rhombus. In this embodiment, the cross section of the inner space  20   a  has a size of about 3.0 mm×3.0 mm. The inner space  20   a  is connected to the three windows  20   b.    
     The three windows  20   b  are provided for allowing light to travel from the inner space  20   a  toward the light receiving elements  4 A,  4 B or from the light emitting element  5  toward the inner space  20   a . The three windows  20   b  are connected to the three element-accommodation spaces  20   c , respectively. The element-accommodation spaces  20   c  accommodate the light receiving elements  4 A,  4 B and the light emitting element  5 , respectively. The two windows  20   b  connected to the element-accommodation spaces  20   c  accommodating the light receiving elements  4 A and  4 B are an example of light incident port of the present invention. The window  20   b  connected to the element-accommodation space  20   c  accommodating the light emitting element  5  is an example of light emitting port of the present invention. 
     The cover plate  3  is made of e.g. a glass fiber-reinforced epoxy resin and bonded to the case  2  with an adhesive  9  to define the inner space  20   a . As illustrated in  FIG. 3 , the cover plate  3  is formed with a base plating layer  30 , an intermediate plating layer  31 , a plurality of projections  32  and an outer plating layer  33 . 
     The base plating layer  30  is a Cu plating layer having a thickness of e.g. about 18 μm and formed directly on the cover plate  3 . The intermediate plating layer  31  consists of a plurality of circular portions each having a diameter of about 0.2 mm. Each of the circular portions is made up of an Ni plating layer  31   a  and a Cu plating layer  31   b . The Ni plating layer  31   a  is formed on the base plating layer  30  and has a thickness of about 3 μm. The Cu plating layer  31   b  is formed on the Ni plating layer  31   a  and has a thickness of about 5 μm. The projections  32  are formed on the intermediate plating layer  31 . Each of the projections  32  has a laminated structure made up of two Cu-plating layers  32   a  and  32   b . Each of the Cu plating layers  32   a  and  32   b  has a relatively large thickness, which is about 25 μm in this embodiment. As illustrated in  FIG. 4 , the projections  32  are arranged in a matrix at about 0.45 mm intervals. The outer plating layer  33  covers the projections  32  and portions of the base plating layer  30  which are not covered by the projections  32 . The outer plating layer  33  is made up of an Ni plating layer  33   a , and an Au plating layer  33   b  formed on the Ni plating layer  33   a . The Ni plating layer  33   a  has a thickness of about 3 μm, whereas the Au plating layer  33   b  has a thickness of about 0.03 μm. The Au plating layer  33   b  serves to reflect the light emitted from the light emitting element  5 . In this embodiment, the surface  3   a  of the Au plating layer  33   b  corresponds to the irregular ceiling surface of the present invention. 
     The rolling member  6  rolls within the inner space  20   a  in accordance with the posture of the inclination sensor A 1  to appropriately prevent the light emitted from the light emitting element  5  from reaching the light receiving element  4 A,  4 B. The rolling member  6  is cylindrical and made of e.g. stainless steel. 
     The tilt sensor A 1  works as follows. In the state illustrated in  FIG. 1 , the rolling member  6  is held at a complete light shielding position P 1 . In this state, the rolling member  6  completely blocks the light emitted from the light emitting element  5  so that no light reception signal is outputted from the light receiving element  4 A or from the light receiving element  4 B. When the tilt sensor A 1  is turned counterclockwise through 90 degrees from the state shown in  FIG. 1 , the rolling member  6  is held at a partial light shielding position P 2 A. In this state, the rolling member  6  blocks the light traveling toward the light receiving element  4 A so that a light reception signal is outputted only from the light receiving element  4 B. When the tilt sensor A 1  is turned clockwise through 90 degrees from the state shown in  FIG. 1 , the rolling member  6  is held at a partial light shielding position P 2 B. In this state, the rolling member  6  blocks the light traveling toward the light receiving element  4 B so that a light reception signal is outputted only from the light receiving element  4 A. When the tilt sensor A 1  is turned through 180 degrees from the state shown in  FIG. 1 , the rolling member  6  is held at a light unshielding position P 3 . In this case, light reception signals are outputted from both of the light receiving elements  4 A and  4 B. The tilting is detected by monitoring the output of a light reception signal from the light receiving elements  4 A,  4 B. 
     A method for making the tilt sensor A 1  are described below with reference to  FIGS. 5-11 . 
     First, as illustrated in  FIG. 5 , a base plating layer  30  is formed on a cover plate  3 . Specifically, the obverse surface of the cover plate  3  is plated with Cu to have a thickness of about 18 μm, and then, the Cu plating layer is patterned by etching into the shape as shown in  FIG. 6 . Thus, the base plating layer  30  is obtained. 
     Then, as illustrated in  FIG. 7 , an Ni plating layer  31   a ′ having a thickness of about 3 μm is formed to cover the base plating layer  30  and exposed portions of the cover plate  3 . Preferably, before forming the Ni plating layer  31   a ′, a relatively thin plating layer may be formed on the base plating layer  30  and exposed portions of the cover plate  3  by electroless plating. After the formation of the Ni plating layer  31   a ′, a Cu plating layer  31   b ′ having a thickness of about 5 μm is formed on the Ni plating layer  31   a′.    
     Then, as illustrated in  FIG. 8 , Cu plating layers  32   a ′ and  32   b ′ are formed on the Cu plating layer  31   b ′. Each of the Cu plating layers  32   a ′ and  32   b ′ is formed to have a thickness of about 25 μm. 
     Then, the Cu plating layers  32   a ′,  32   b ′ and the Cu plating layer  31   b ′ are patterned. Specifically, the Cu plating layers  32   a ′,  32   b ′ and  31   b ′ are selectively etched away by using a mask formed with openings correspondingly to projections  32  shown in  FIG. 4 . As a result, as illustrated in  FIG. 9 , the Cu plating layer  31   b  made up a plurality of circular portions, and a plurality projections  32  made up of the Cu plating layers  32   a  and  32   b  are obtained. 
     Then, the Ni plating layer  31   a ′ is patterned by etching. As a result, as illustrated in  FIG. 10 , an intermediate plating layer  31  made up of an Ni plating layer  31   a  and a Cu plating layer  31   b  is obtained. 
     Then, as illustrated in  FIG. 11 , an Ni plating layer  33   a  having a thickness of about 3 μm and an Au plating layer  33   b  having a thickness of about 0.03 μm are successively formed, whereby an outer plating layer  33  is obtained. Other necessary process steps such as the mounting of the light receiving elements  4 A,  4 B and the light emitting element  5  on the mount board  1  and the formation of the case  2  are also performed. Thereafter, the mount board  1 , the case  2  and the cover plate  3  are bonded together, whereby a tilt sensor A 1  is obtained. A plurality of tilt sensors A 1  may be made collectively. In this case, a board material capable of producing a plurality of mount boards  1 , a resin material capable of producing a plurality of cases  2  and a resin material capable of producing a plurality of cover plates  3  may be bonded together and then cut. 
     The tilt sensor A 1  and the making method described above have the following advantages. 
     As noted before, in the above-described conventional structure, the rolling member may adhere to the cover plate due to the adhesive applied for bonding the cover plate and the case. Specifically, when a large amount of adhesive is applied, the adhesive projects from between the cover plate and the case, which causes the rolling member to adhere to the cover plate. Further, moisture entering the sensor in the manufacturing process may also cause the adhesion of the rolling member. Specifically, in cutting the board material and the resin material in the making process, watering is performed for lubricating and cooling. The water may accidentally enter the inner space through a small clearance between the cover plate and the case. Although the tilt sensor may be heated after the cutting process, the moisture may not be evaporated completely. 
     According to this embodiment, however, the adhesive  8  projecting from between the case  2  and the cover plate  3  as well as the moisture which has accidentally entered the inner space  20   a  are retained in the recesses of the ceiling surface  3   a  which are defined between the projections  32 . Thus, the projecting portions of the ceiling surface  3   a , which are to come into contact with the rolling member  6 , are kept dry. Thus, the rolling member  6  is prevented from adhering to the ceiling surface  3   a , so that the tilting is detected accurately. Particularly, the rolling member  6 , which is cylindrical, is suitable for proper light shielding and smooth rolling. Although the cylindrical rolling member  6  comes into contact with the ceiling surface  3   a  at a relatively large contact area, the cylindrical rolling member  6  is also prevented from adhering to the cover plate owing to the irregular ceiling surface  3   a.    
     The area of the end surface of each projection  32  is smaller than that of the rolling member  6 . Thus, the rolling member  6  is prevented from tightly fitted to one of the projections  32 . Since the interval between the projections  32  is smaller than the diameter of the rolling member  6 , the rolling member  6  is prevented from inclining. 
     The projections  32  are formed by a plating process that is similar to the process for forming the base plating layer  30  and the outer plating layer  33 . Thus, the manufacturing process is simplified. 
     In the process of etching away the Ni plating layer  31   a ′, the surface of the base plating layer  30  is washed to become a smooth surface. As a result, the outer plating layer  33  is uniformly formed on the base plating layer  30 . The uniform outer plating layer  33  properly reflects the light emitted from the light emitting element  5 . Since the outer plating layer  33  has a uniform thickness also at portions which are to be held in contact with the case  2 , the cover plate  3  does not incline relative to the case  2 . 
     The intermediate plating layer  31  is made by forming the Ni plating layer  31   a ′ and the Cu plating layer  31   b ′. The material of the Cu plating layer  31   b ′ is the same as that of the Cu plating layers  32   a ′,  32   b ′, which form the projections  32 . This makes it possible to perform etching collectively with respect to the Cu plating layer  31   b ′ and the Cu plating layers  32   a ′,  32   b ′, while using the Ni plating layer  31   a ′ as the etching stop layer. Further, the Ni plating layer  31   a ′ and the base plating layer  30  are made of different materials. Thus, only the Ni plating layer  31   a ′ can be selectively etched away, while washing the base plating layer  30 . 
       FIGS. 12-14  illustrate other embodiments of the present invention. In these figures, the elements which are identical or similar to those of the tilt sensor according to the first embodiment are designated by the same reference signs as those used for the first embodiment. 
       FIG. 12  illustrates another example of projections  32 . In this example, the cover plate  3  is formed with four projections  32  each of which is in the form of an elongated strip having a width of about 0.2 mm and a length of about 0.9 mm. The projections  32  are arranged in a radially extending manner, with their axial lines intersecting at the center of the cover plate  3  and forming the right angle (90 degrees) between adjacent lines. Each of the projections  32  is spaced from the center of the cover plate  3  by about 0.3 mm, so that the distance between two mutually facing projections  32  (i.e., the pair of upper and lower projections or the pair of right and left projections) is about 0.6 mm. This arrangement also ensures the smooth rolling of the rolling member  6  and hence precise tilting detection. 
       FIGS. 13 and 14  illustrate a tilt sensor A 2  according to a second embodiment of the present invention. The tilt sensor A 2  of this embodiment differs from the first embodiment in arrangement of the inner space  20   a , the light emitting element  5  and the light receiving elements  4 A,  4 B. 
     In the second embodiment, the three element-accommodation spaces  20   c  are arranged around the inner space  20   a . The light receiving elements  4 A and  4 B are arranged on two sides of the inner space  20   a . As illustrated in  FIG. 14 , a plurality of projecting parts are formed on the cover plate  3  so that the height of the windows  20   b  is smaller than that of the element-accommodation spaces  20   c . In this embodiment again, the ceiling surface  3   a  is irregular due to the provision of the projections  32  on the cover plate  3 . The complete light shielding position P 1 , the partial light shielding position P 2 A, P 2 B and the light unshielding position P 3  in this embodiment are as illustrated in  FIG. 13 . 
     The arrangement of the second embodiment also ensures the smooth rolling of the rolling member  6  and hence precise tilting detection. The tilt sensor A 2  is suitable for reducing the thickness. 
     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 design in many ways.