Patent Publication Number: US-2020280269-A1

Title: Vibration-powered generation device and sensor system

Description:
TECHNICAL FIELD 
     The present disclosure relates to a vibration power generation device and a sensor system. In particular, the present disclosure relates to a vibration power generation device suitable for generating electric power in response to displacement of a portion of a specimen and to a sensor system. 
     BACKGROUND ART 
     Conventionally, vibrations (vibrational energy) from machines and other equipment have been converted into electric power. 
     For instance, PTL 1 discloses a vibrational energy harvester that includes a piezoelectric transducer having a layer of a piezoelectric material. An end of the piezoelectric transducer is a free end, and the vibrational energy harvester allows the free end to vibrate in response to external vibrations. The vibrational energy harvester converts vibrational energy acquired at the free end into electric energy through the layer of the piezoelectric material. 
     Unfortunately, in a power generation mechanism as disclosed in PTL 1, the piezoelectric transducer directly receives external vibrations and elastically vibrates. Thus, an amount of displacement of the piezoelectric transducer is likely to be small. As a result, electric power acquired by the power generation mechanism tends to be small. 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2014/116794 
     SUMMARY OF THE INVENTION 
     The present disclosure has been made in view of the problem described above. It is an object of the present invention to provide a vibration power generation device capable of generating large electric power relative to an amount of displacement of a portion of a specimen, as well as a sensor system including the vibration power generation device. 
     A vibration power generation device according to an aspect of the present disclosure includes a piezoelectric part and a displacement enhancer. In response to displacement of a portion of a specimen, the displacement enhancer displaces a portion of the piezoelectric part by a displacement amount greater than an amount of the displacement of the portion of the specimen. When the portion of the piezoelectric part is displaced, the piezoelectric part generates electric power in accordance with an amount of the displacement of the portion of the piezoelectric part. 
     A sensor system according to an aspect of the present disclosure includes the vibration power generation device and a sensor. The sensor includes the piezoelectric part or is a device that is different from the piezoelectric part and that is driven by electric power generated by the piezoelectric part. 
     The vibration power generation device according to the aspect of the present disclosure is able to generate large electric power relative to an amount of displacement of the portion of the specimen. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a schematic side view illustrating a vibration power generation device according to a first exemplary embodiment. 
         FIG. 1B  is a schematic cross-sectional view illustrating a piezoelectric part in the vibration power generation device of the first exemplary embodiment. 
         FIG. 2A  is a schematic side view illustrating a vibration power generation device according to a second exemplary embodiment. 
         FIG. 2B  is a schematic side view illustrating an example mode in which the vibration power generation device of the second exemplary embodiment is attached to a suspension bridge. 
         FIG. 2C  is a schematic side view illustrating an example mode in which the vibration power generation device of the second exemplary embodiment is attached to a cable-stayed bridge. 
         FIG. 3A  is a schematic side view illustrating an example of a vibration power generation device according to a third exemplary embodiment. 
         FIG. 3B  is a schematic side view illustrating another example of the vibration power generation device according to the third exemplary embodiment. 
         FIG. 4A  is a schematic side view illustrating an example of a vibration power generation device according to a fourth exemplary embodiment. 
         FIG. 4B  is a schematic side view illustrating another example of the vibration power generation device of the fourth exemplary embodiment. 
         FIG. 5  is a schematic side view illustrating a vibration power generation device according to a fifth exemplary embodiment. 
         FIG. 6A  is a schematic side view illustrating an example of a vibration power generation device according to a sixth exemplary embodiment. 
         FIG. 6B  is a schematic side view illustrating another example of the vibration power generation device of the sixth exemplary embodiment. 
         FIG. 7  is a schematic side view illustrating a vibration power generation device according to a seventh exemplary embodiment. 
         FIG. 8  is a schematic block diagram illustrating a sensor system according to an exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments of the present disclosure will now be described. 
     1. Vibration Power Generation Device 
     Vibration power generation device  1  includes piezoelectric part  2  and displacement enhancer  3 . In response to displacement of a portion of specimen  4  (hereinafter also referred to as displacement part  41 ), displacement enhancer  3  displaces a portion of piezoelectric part  2  (hereinafter also referred to as displacement-affected part  25 ) by a displacement amount greater than an amount of the displacement of displacement part  41 . If displacement-affected part  25  is displaced, piezoelectric part  2  generates electric power in accordance with an amount of the displacement of displacement-affected part  25 . Thus, vibration power generation device  1  is able to generate large electric power relative to the displacement amount of displacement part  41 . 
     Exemplary embodiments of vibration power generation device  1  will be described in more detail below. 
     1.1. First Exemplary Embodiment 
       FIG. 1A  schematically illustrates vibration power generation device  1  according to a first exemplary embodiment.  FIG. 1B  schematically illustrates piezoelectric part  2  in vibration power generation device  1 . 
     In the first exemplary embodiment, specimen  4  is a component having a length. Specimen  4  expands and contracts in a direction of its length. Specimen  4  is, for example, a structural member of a bridge. 
     Vibration power generation device  1 , as described above, includes piezoelectric part  2  and displacement enhancer  3 . 
     Displacement enhancer  3  includes first pulley  32 , second pulley  33  having a diameter larger than a diameter of first pulley  32 , first string  38 , and second string  39 . First and second pulleys  32  and  33  are allowed to coaxially rotate in conjunction with each other. First string  38  is partly wound on first pulley  32  and is used to connect first pulley  32  and displacement part  41  of specimen  4  together. Second string  39  is partly wound on second pulley  33  and is used to connect second pulley  33  and displacement-affected part  25  of piezoelectric part  2  together. 
     More specifically, displacement enhancer  3 , as shown in  FIG. 1A , includes pulley unit  31  including first and second pulleys  32  and  33  and fixing unit  35 . Pulley unit  31  is fixed to reference part  42 , whereas fixing unit  35  is fixed to displacement part  41 . In the first exemplary embodiment, a portion of specimen  4  on which pulley unit  31  is fixed is reference part  42 , and a portion of specimen  4  on which fixing unit  35  is fixed is displacement part  41 . Reference part  42  and displacement part  41  are spaced along the length direction of specimen  4 . 
     Pulley unit  31  includes support  34  fixed to reference part  42  of specimen  4  and first and second pulleys  32  and  33  supported by support  34 . As described above, the diameter of second pulley  33  is larger than the diameter of first pulley  32 . First pulley  32  is supported by support  34  such that the first pulley is rotatable. Second pulley  33  is also supported by support  34  such that the second pulley is rotatable. First and second pulleys  32  and  33  rotate on a common rotation axis at an identical rotational speed. In other words, first and second pulleys  32  and  33  are allowed to coaxially rotate in conjunction with each other. First and second pulleys  32  and  33  are, for example, integrated together. The rotation axis is orthogonal to the length direction of specimen  4 . Support  34  and first and second pulleys  32  and  33  are each made of metal, plastic, or another appropriate material. 
     Fixing unit  35  includes support  335  fixed to displacement part  41  of specimen  4  and third pulley  36  and fourth pulley  37  supported by support  335 . A diameter of third pulley  36  is smaller than a diameter of fourth pulley  37 . Third pulley  36  is supported by support  335  such that the third pulley is rotatable. Fourth pulley  37  is also supported by support  335  such that the fourth pulley is rotatable. Third and fourth pulleys  36  and  37  rotate on a common rotation axis at an identical rotational speed. In other words, third and fourth pulleys  36  and  37  are allowed to coaxially rotate in conjunction with each other. Third and fourth pulleys  36  and  37  are, for example, integrated together. The rotation axis of third and fourth pulleys  36  and  37  is parallel to the rotation axis of first and second pulleys  32  and  33 . Further, first and second pulleys  32  and  33  and third and fourth pulleys  36  and  37  are aligned along the length direction of specimen  4 . Support  335  and third and fourth pulleys  36  and  37  are each made of metal, plastic, or another appropriate material. 
     Vibration power generation device  1  also includes first string  38 , second string  39 , and third string  310 . First string  38 , second string  39 , and third string  310  are each a wire, a cord, a rope, or a cable, for example. A first end of first string  38  is wound on first pulley  32  of pulley unit  31 , and a second end of first string  38  is wound on third pulley  36  of fixing unit  35 . As a result, first pulley  32  and displacement part  41  are connected together by first string  38  partly wound on first pulley  32  through fixing unit  35 . A direction in which first string  38  is wound on first pulley  32  is opposite a direction in which first string  38  is wound on third pulley  36 . A first end of second string  39  is wound on second pulley  33  of pulley unit  31 , and a second end of second string  39  is connected, as described later, to displacement-affected part  25  of piezoelectric part  2 . A direction in which second string  39  is wound on second pulley  33  is opposite the direction in which first string  38  is wound on first pulley  32 . A first end of third string  310  is wound on fourth pulley  37  of fixing unit  35 , and a second end of third string  310  is connected, as described later, to holding part  26  of piezoelectric part  2 . A direction in which third string  310  is wound on fourth pulley  37  is opposite the direction in which second string  39  is wound on third pulley  36 . 
     Piezoelectric part  2  includes at least two electrodes  21  (first electrode  21   a  and second electrode  21   b ) and piezoelectric film  22  interposed between the two electrodes  21 . In the first exemplary embodiment, piezoelectric part  2 , as shown in  FIG. 1B , includes a plurality of piezoelectric films  22 , a plurality of first electrodes  21   a , a plurality of second electrodes  21   b , and a plurality of insulating layers  23 . These elements are stacked repeatedly in an order of first electrode  21   a , piezoelectric film  22 , second electrode  21   b , and insulating layer  23 . 
     Piezoelectric film  22 , for example, contains a piezoelectric polymer and has an orientation. The piezoelectric polymer is, for example, poly-L-lactic acid, poly-D-lactic acid, or polyvinylidene fluoride. The orientation of piezoelectric film  22  is generated when piezoelectric film  22  is drawn at a time of manufacture. In other words, an orientation of the piezoelectric polymer contained in piezoelectric film  22  agrees with a direction in which piezoelectric film  22  is drawn. When piezoelectric film  22  is deformed by being drawn in a direction orthogonal to a direction of its thickness, piezoelectric film  22  is polarized in the direction of its thickness to generate a voltage. 
     Piezoelectric part  2  further includes two external electrodes  24  having conductivity. One of two external electrodes  24  is electrically connected to all first electrodes  21   a  and is not electrically connected to any second electrodes  21   b . The other of two external electrodes  24  is electrically connected to all second electrodes  21   b  and is not electrically connected to any first electrodes  21   a . Since piezoelectric part  2  includes external electrodes  24 , eclectic power can be drawn from piezoelectric part  2  through external electrodes  24  in response to the generation of a voltage in piezoelectric films  22 . 
     Piezoelectric part  2  further includes outer sheath  27 . Outer sheath  27  houses external electrodes  24 , piezoelectric films  22 , first electrodes  21   a , and second electrodes  21   b  inside. Outer sheath  27  may be made of an appropriate material. 
     Piezoelectric part  2  may have any structure other than the structure described above. In other words, piezoelectric part  2  may have a publicly known structure. 
     In the present exemplary embodiment, an end of piezoelectric part  2  facing one direction orthogonal to a direction in which electrodes  21  and piezoelectric films  22  are stacked is displacement-affected part  25 . As described above, the end of second string  39  is connected to displacement-affected part  25 . An end of piezoelectric part  2  opposite displacement-affected part  25  is holding part  26 . As described above, the end of third string  310  is connected to holding part  26 . 
     Operation of vibration power generation device  1  will now be described. When specimen  4  extends in the length direction, displacement part  41  is displaced, with respect to reference part  42 , in a direction so as to be away from reference part  42 . Since first pulley  32  and displacement part  41  are connected together by first string  38  through fixing unit  35 , first pulley  32  rotates along with displacement of displacement part  41 . Thus, second pulley  33  rotates in conjunction with first pulley  32 . In the present exemplary embodiment, first string  38  is connected to third pulley  36  of fixing unit  35 , and hence third pulley  36  of fixing unit  35  also rotates along with the displacement of displacement part  41 . Thus, fourth pulley  37  rotates in conjunction with third pulley  36 . In this way, second and fourth pulleys  33  and  37  rotate, and tensile force is thereby applied to piezoelectric part  2  through second and third strings  39  and  310 . As a result, in piezoelectric part  2 , displacement-affected part  25  is displaced, with respect to holding part  26 , in a direction so as to be away from holding part  26 , and piezoelectric part  2  is deformed. The deformation of piezoelectric part  2  causes piezoelectric films  22  inside piezoelectric part  2  to be deformed, resulting in the generation of a voltage by piezoelectric films  22 . Thus, piezoelectric part  2  generates electric power in accordance with an amount of the displacement of displacement-affected part  25 . Hence, every time specimen  4  expands and contracts, piezoelectric part  2  can generate electric power. As described above, the diameter of second pulley  33  is larger than the diameter of first pulley  32 , and the diameter of fourth pulley  37  is larger than the diameter of third pulley  36 . Accordingly, when displacement-affected part  25  is displaced along with the displacement of displacement part  41 , the displacement amount of displacement-affected part  25  is greater than the displacement amount of displacement part  41 . Thus, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3  displaces displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 . This configuration enables vibration power generation device  1  to generate large electric power relative to the displacement amount of displacement part  41 . 
     Vibration power generation device  1  may have stopper  340  to place an upper limit on the displacement amount of displacement-affected part  25 . In the first exemplary embodiment, vibration power generation device  1  includes first stopper  341  and second stopper  342  as stopper  340 . First stopper  341  regulates rotation of first and second pulleys  32  and  33 , and second stopper  342  regulates rotation of third and fourth pulleys  36  and  37 . First stopper  341  is disposed on second pulley  33 , and second stopper  342  is disposed on fourth pulley  37 . When the displacement amount of displacement-affected part  25  reaches the upper limit, first stopper  341  gets caught by support  34  and thereby restricts the rotation of first and second pulleys  32  and  33  and second stopper  342  gets caught by support  335  and thereby restricts the rotation of third and fourth pulleys  36  and  37 . In this way, first and second stoppers  341  and  342  are configured. This configuration prevents displacement-affected part  25  from being displaced to an extent that exceeds the upper limit of the displacement amount and stops piezoelectric part  2  from being damaged due to an excessive deformation. Preferably, the upper limit of the displacement amount of displacement-affected part  25  is set such that a deformation of piezoelectric part  2  does not cause piezoelectric films  22  to be deformed in excess of an elastic limit. If the piezoelectric polymer contained in piezoelectric film  22  is poly-D-lactic acid or poly-L-lactic acid, the elastic limit of piezoelectric films  22  is around 2%. If the piezoelectric polymer contained in piezoelectric film  22  is polyvinylidene fluoride, the elastic limit of piezoelectric films  22  is around 1%. 
     In the first exemplary embodiment, examples of specimen  4  that is a structural member of a bridge include main cables, suspender ropes, crossbeams, towers, and anchorages for suspension bridges and towers, crossbeams, and cables for cable-stayed bridges. Specimen  4  may be a combination of a plurality of kinds of structural members. 
     The structural member of the bridge expands and contracts slightly. If displacement part  41  is a portion of a structural member of a bridge, the displacement amount of displacement part  41  is, for example, a maximum of around 0.1 mm. Normally, it is difficult to obtain satisfactory electric power from a displacement amount of around 0.1 mm. However, in the present exemplary embodiment, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3 , as described above, displaces displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 . For instance, the displacement amount of displacement-affected part  25  can be made as much as around 100 times the displacement amount of displacement part  41 . Consequently, vibration power generation device  1  is able to obtain satisfactory electric power from the displacement of the portion of the structural member of the bridge. 
     The example of specimen  4  is not limited to structural members of bridges. Specimen  4  may be, for example, a structural member of a prime motor or a building, or a road as described later. 
     Displacement part  41  is not particularly limited, with proviso that the displacement part is a portion that is displaced with respect to reference part  42 , a portion of reference. It is particularly preferred that displacement part  41  be repeatedly displaced both in a direction so as to move away from reference part  42  and in a direction so as to move nearer to reference part  42 . In this case vibration power generation device  1  can generate electric power constantly. 
     In the first exemplary embodiment, both displacement part  41  and reference part  42  are portions of specimen  4 . However, displacement part  41  and reference part  42  may be present in respective different members. With proviso that displacement part  41  is displaced with respect to reference part  42 , reference part  42  may move without movement of displacement part  41  with respect to a ground, displacement part  41  may move without movement of reference part  42  with respect to a ground, or both reference part  42  and displacement part  41  may move with respect to a ground. 
     In the first exemplary embodiment, fixing unit  35  includes third and fourth pulleys  36  and  37 . However, fixing unit  35  may not include third and fourth pulleys  36  and  37 . In this case, first and third strings  38  and  310  may be fixed to fixing unit  35  without pulleys. Displacement enhancer  3  may not include fixing unit  35 , and first and third strings  38  and  310  may be directly fixed to displacement part  41 . In any of these cases, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3  is able to displace displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 , with proviso that displacement enhancer  3  includes first and second pulleys  32  and  33 . 
     1.2. Second Exemplary Embodiment 
       FIG. 2A  schematically illustrates vibration power generation device  1  according to a second exemplary embodiment. Components in  FIG. 2A  that overlap those in the first exemplary embodiment are hereinafter denoted by the same numerals or symbols, and detailed descriptions thereof are omitted as appropriate. 
     In the second exemplary embodiment, specimen  4  is a component having a length. Specimen  4  expands and contracts in a direction of its length. Specimen  4  is, for example, a structural member of bridge  5 . 
     Vibration power generation device  1 , as described above, includes piezoelectric part  2  and displacement enhancer  3 . 
     Displacement enhancer  3  includes first pulley  32 , second pulley  33  having a diameter larger than a diameter of first pulley  32 , first string  38 , and second string  39 . First and second pulleys  32  and  33  are allowed to coaxially rotate in conjunction with each other. First string  38  is partly wound on first pulley  32  and is used to connect first pulley  32  and displacement part  41  of specimen  4  together. Second string  39  is partly wound on second pulley  33  and is used to connect second pulley  33  and displacement-affected part  25  of piezoelectric part  2  together. 
     More specifically, displacement enhancer  3 , as shown in  FIG. 2A , includes pulley unit  31  including first and second pulleys  32  and  33  and fixing unit  35 . Pulley unit  31  is fixed to reference part  42 , whereas fixing unit  35  is fixed to displacement part  41 . In the second exemplary embodiment, a portion of specimen  4  on which fixing unit  35  is fixed is displacement part  41 , and a portion of specimen  4  on which pulley unit  31  is fixed is reference part  42 . Reference part  42  and displacement part  41  are spaced along the length direction of specimen  4 . 
     Pulley unit  31  includes support  34  fixed to reference part  42  of specimen  4  and first and second pulleys  32  and  33  supported by support  34 . A configuration of pulley unit  31  in the second exemplary embodiment may be the same as that of pulley unit  31  in the first exemplary embodiment. 
     Fixing unit  35  is fixed to displacement part  41  of specimen  4 . Fixing unit  35  is made of metal, plastic, or another appropriate material. 
     Vibration power generation device  1  also includes first string  38 , second string  39 , and third string  310 . First string  38 , second string  39 , and third string  310  are each a wire, a cord, a rope, or a cable, for example. A first end of first string  38  is wound on first pulley  32  of pulley unit  31 , and a second end of first string  38  is fixed to fixing unit  35 . As a result, first pulley  32  and displacement part  41  are connected together by first string  38  partly wound on first pulley  32  through fixing unit  35 . A first end of second string  39  is wound on second pulley  33  of pulley unit  31 , and a second end of second string  39  is connected, as described later, to displacement-affected part  25  of piezoelectric part  2 . A direction in which second string  39  is wound on second pulley  33  is opposite a direction in which first string  38  is wound on first pulley  32 . Third string  310  will be described later. 
     Piezoelectric part  2  includes at least two electrodes  21  and piezoelectric film  22  interposed between the two electrodes  21 . Piezoelectric part  2  has displacement-affected part  25  and holding part  26 . A configuration of piezoelectric part  2  in the second exemplary embodiment is the same as that of piezoelectric part  2  in the first exemplary embodiment. As described above, the end of second string  39  is connected to displacement-affected part  25 . An end of third string  310  is connected to holding part  26 . 
     Vibration power generation device  1  also includes holder  311  to hold piezoelectric part  2 . Holder  311  is fixed to specimen  4 . Holder  311  is positioned on an opposite side of pulley unit  31  from fixing unit  35 . In other words, holder  311 , pulley unit  31 , and fixing unit  35  are aligned in this order. A first end of third string  310  is fixed to holder  311 , and a second end of third string  310  is connected, as described above, to holding part  26  of piezoelectric part  2 . 
     Operation of vibration power generation device  1  will now be described. When specimen  4  extends in the length direction, displacement part  41  is displaced, with respect to reference part  42 , in a direction so as to be away from reference part  42 . Since first pulley  32  and displacement part  41  are connected together by first string  38  through fixing unit  35 , first pulley  32  rotates along with displacement of displacement part  41 . Thus, second pulley  33  rotates in conjunction with first pulley  32 . In this way, second pulley  33  rotates, and tensile force is thereby applied to piezoelectric part  2  through second and third strings  39  and  310 . As a result, in piezoelectric part  2 , displacement-affected part  25  is displaced, with respect to holding part  26 , in a direction so as to be away from holding part  26 , and piezoelectric part  2  is deformed. The deformation of piezoelectric part  2  causes piezoelectric films  22  inside piezoelectric part  2  to be deformed, resulting in the generation of a voltage by piezoelectric films  22 . Thus, piezoelectric part  2  generates electric power in accordance with an amount of the displacement of displacement-affected part  25 . Hence, every time specimen  4  expands and contracts, piezoelectric part  2  can generate electric power. As described above, the diameter of second pulley  33  is larger than the diameter of first pulley  32 . Accordingly, when displacement-affected part  25  is displaced along with the displacement of displacement part  41 , the displacement amount of displacement-affected part  25  is greater than the displacement amount of displacement part  41 . Thus, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3  displaces displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 . This configuration enables vibration power generation device  1  to generate large electric power relative to the displacement amount of displacement part  41 . 
     This vibration power generation device  1  may have, in a similar way to the first exemplary embodiment, stopper  340  to place an upper limit on the displacement amount of displacement-affected part  25 . In the second exemplary embodiment, stopper  340  is disposed on second pulley  33 . When the displacement amount of displacement-affected part  25  reaches the upper limit, stopper  340  gets caught by support  34  and thereby restricts the rotation of first and second pulleys  32  and  33 . In this way, stopper  340  is configured. This configuration prevents displacement-affected part  25  from being displaced to an extent that exceeds the upper limit of the displacement amount and stops piezoelectric part  2  from being damaged due to an excessive deformation. 
     In the second exemplary embodiment, examples of specimen  4  that is a structural member of bridge  5  include main cable  53 , suspender rope  54 , crossbeam  57 , tower  56 , and anchorage  55  for suspension bridge  51  and tower  59 , crossbeam  510 , and cable  58  for cable-stayed bridge  52 . Specimen  4  may be a combination of a plurality of kinds of structural members. The example of specimen  4  is not limited to structural members of bridge  5 . Specimen  4  may be, for example, a prime motor or a road as described later. 
       FIG. 2B  illustrates an example of places at which holder  311 , pulley unit  31 , and fixing unit  35  are fixed when specimen  4  is a structural member of suspension bridge  51 . In  FIG. 2B , specimen  4  is suspender rope  54 , and holder  311 , pulley unit  31 , and fixing unit  35  are fixed to suspender rope  54 . One of pulley unit  31  and fixing unit  35  may be fixed to suspender rope  54 , whereas the other of the two units may be fixed to main cable  53 . One of pulley unit  31  and fixing unit  35  may be fixed to suspender rope  54 , whereas the other of the two units may be fixed to crossbeam  57 . Apart from these places, pulley unit  31  and fixing unit  35  may be fixed to various places on suspension bridge  51 . In the first exemplary embodiment as well, pulley unit  31  and fixing unit  35  may be fixed to various places on suspension bridge  51 . 
       FIG. 2C  illustrates an example of places at which holder  311 , pulley unit  31 , and fixing unit  35  are fixed when specimen  4  is a structural member of a cable-stayed bridge. In  FIG. 2C , specimen  4  is cable  58 , and holder  311 , pulley unit  31 , and fixing unit  35  are fixed to cable  58 . One of pulley unit  31  and fixing unit  35  may be fixed to cable  58 , whereas the other of the two units may be fixed to tower  59 . One of pulley unit  31  and fixing unit  35  may be fixed to cable  58 , whereas the other of the two units may be fixed to crossbeam  510 . Apart from these places, pulley unit  31  and fixing unit  35  may be fixed to various places on cable-stayed bridge  52 . In the first exemplary embodiment as well, pulley unit  31  and fixing unit  35  may be fixed to various places on cable-stayed bridge  52 . 
     In a similar way to the first exemplary embodiment, displacement part  41  is not particularly limited, with proviso that the displacement part is a portion that is displaced with respect to reference part  42 , a portion of reference. In a similar way to the first exemplary embodiment, displacement part  41  and reference part  42  may be present in respective different members. The two parts may be configured in any way, with proviso that displacement part  41  is displaced with respect to reference part  42 . 
     1.3. Third Exemplary Embodiment 
       FIGS. 3A and 3B  schematically illustrate vibration power generation device  1  according to a third exemplary embodiment. Components in  FIGS. 3A and 3B  that overlap those in the first and second exemplary embodiments are hereinafter denoted by the same numerals or symbols, and detailed descriptions thereof are omitted as appropriate. 
     Specimen  4  is prime motor  6 . Prime motor  6  includes foundation  61  and main body  62  put on foundation  61 . Main body  62  is, for example, an electric motor, an internal-combustion engine, or fluid machinery. This vibration power generation device  1  has a configuration similar to that in the second exemplary embodiment except that holder  311 , pulley unit  31 , and fixing unit  35  are fixed to places that differ from those in the second exemplary embodiment. 
     In  FIG. 3A , pulley unit  31  is fixed to main body  62 , and holder  311  is fixed to a part of main body  62  that is located above pulley unit  31 . Fixing unit  35  is fixed to foundation  61 . A portion of main body  62  on which pulley unit  31  is fixed is reference part  42 , and a portion of foundation  61  on which fixing unit  35  is fixed is displacement part  41 . 
     In the vibration power generation device shown in  FIG. 3A , when main body  62  is driven and thereby vibrates, displacement part  41  of foundation  61  is displaced with respect of reference part  42  of main body  62 . Accordingly, in a similar way to the second exemplary embodiment, piezoelectric part  2  is able to generate electric power. 
     In  FIG. 3B , pulley unit  31  is fixed to foundation  61 , and holder  311  is fixed to a part of foundation  61  that is located on an opposite side of pulley unit  31  from main body  62 . Fixing unit  35  is fixed to a part of main body  62  that is located above pulley unit  31 . A portion of foundation  61  on which pulley unit  31  is fixed is reference part  42 , and the part of main body  62  on which fixing unit  35  is fixed is displacement part  41 . 
     In the vibration power generation device shown in  FIG. 3B , when main body  62  is driven and thereby vibrates, displacement part  41  of foundation  61  is displaced with respect of reference part  42  of foundation  61 . Accordingly, in a similar way to the second exemplary embodiment, piezoelectric part  2  is able to generate electric power. 
     1.4. Fourth Exemplary Embodiment 
       FIGS. 4A and 4B  schematically illustrate vibration power generation device  1  according to a fourth exemplary embodiment. Components in  FIGS. 4A and 4B  that overlap those in the first to third exemplary embodiments are hereinafter denoted by the same numerals or symbols, and detailed descriptions thereof are omitted as appropriate. 
     Specimen  4  is a structural member of building  7 . Examples of the structural member of building  7  include bases, foundations, pillar  71 , beams, walls, and floor  72 . This vibration power generation device  1  has a configuration similar to that in the second exemplary embodiment except that holder  311 , pulley unit  31 , and fixing unit  35  are fixed to places that differ from those in the second exemplary embodiment. 
     In  FIG. 4A , pulley unit  31  is fixed to pillar  71 , and holder  311  is fixed to a part of pillar  71  that is located above pulley unit  31 . Fixing unit  35  is fixed to floor  72 . A portion of pillar  71  on which pulley unit  31  is fixed is reference part  42 , and a portion of floor  72  on which fixing unit  35  is fixed is displacement part  41 . 
     In the vibration power generation device shown in  FIG. 4A , when building  7  is shaken by an earthquake or other causes, displacement part  41  of floor  72  is displaced with respect of reference part  42  of pillar  71 . Accordingly, in a similar way to the second exemplary embodiment, piezoelectric part  2  is able to generate electric power. 
     In  FIG. 4B , pulley unit  31  is fixed to floor  72 , and holder  311  is fixed to a part of floor  72  that is located on an opposite side of pulley unit  31  from pillar  71 . Fixing unit  35  is fixed to a part of pillar  71  that is located above pulley unit  31 . A portion of floor  72  on which pulley unit  31  is fixed is reference part  42 , and the part of pillar  71  on which fixing unit  35  is fixed is displacement part  41 . 
     In the vibration power generation device shown in  FIG. 4B , when building  7  is shaken by an earthquake or other causes, displacement part  41  of pillar  71  is displaced with respect of reference part  42  of floor  72 . Accordingly, in a similar way to the second exemplary embodiment, piezoelectric part  2  is able to generate electric power. 
     1.5. Fifth Exemplary Embodiment 
       FIG. 5  schematically illustrates vibration power generation device  1  according to a fifth exemplary embodiment. Components in  FIG. 5  that overlap those in the first to fourth exemplary embodiments are hereinafter denoted by the same numerals or symbols, and detailed descriptions thereof are omitted as appropriate. 
     In the present exemplary embodiment, displacement enhancer  3  includes toothed wheel  312  and rack  314 . Rack  314  is fixed to displacement part  41  of specimen  4  and engages with toothed wheel  312 . 
     In the present exemplary embodiment, displacement enhancer  3  further includes circular component  313 . Circular component  313  has a diameter larger than a diameter of toothed wheel  312 . Toothed wheel  312  and circular component  313  are allowed to coaxially rotate in conjunction with each other. A portion of piezoelectric part  2  is connected to an outer circumference of circular component  313 . 
     A configuration of vibration power generation device  1  will be described more specifically. 
     In the present exemplary embodiment, specimen  4  is road  8 . Plate  81  that constitutes a portion of road  8  is displacement part  41 . 
     In the present exemplary embodiment, storage space  83  exists below ground  82 . Storage space  83  has opening  84  through which to communicate with an atmosphere above the ground. Plate  81  is disposed so as to close opening  84 . Displacement enhancer  3  and piezoelectric part  2  are housed in storage space  83 . 
     Disposition area  85  is formed near an edge of opening  84  inside storage space  83 . Disposition area  85  is a surface facing upward and being located at a level higher than a bottom surface of storage space  83 . Coil spring  86  is disposed on disposition area  85 . Plate  81  is supported by coil spring  86 . Hence, if a load is downwardly applied to plate  81 , coil spring  86  is elastically deformed and plate  81  is thereby displaced downward, and subsequently, when the load disappears, coil spring  86  returns to its original shape and plate  81  is thereby put back into position. In this way, plate  81  is configured. 
     Displacement enhancer  3  has first gear unit  315  including toothed wheel  312  and circular component  313  and second gear unit  319  including second toothed wheel  317  and second circular component  318 . Circular component  313  and second circular component  318  are circular members. In the present exemplary embodiment, both circular component  313  and second circular component  318  are pulleys. First and second gear units  315  and  319  are disposed so as to be spaced along a direction parallel to a horizontal plane. 
     In first gear unit  315 , a diameter of circular component  313  is larger than a diameter of toothed wheel  312 . Circular component  313  and toothed wheel  312  rotate on a common rotation axis at an identical rotational speed. In other words, circular component  313  and toothed wheel  312  are allowed to coaxially rotate in conjunction with each other. Circular component  313  and toothed wheel  312  are, for example, integrated together. The rotation axis is parallel to the horizontal plane and is orthogonal to a direction along which first and second gear units  315  and  319  are aligned. Circular component  313  and toothed wheel  312  are each made of metal, plastic, or another appropriate material. 
     In second gear unit  319 , a diameter of second circular component  318  is larger than a diameter of second toothed wheel  317 . Second circular component  318  and second toothed wheel  317  rotate on a common rotation axis at an identical rotational speed. In other words, second circular component  318  and second toothed wheel  317  are allowed to coaxially rotate in conjunction with each other. Second circular component  318  and second toothed wheel  317  are, for example, integrated together. The rotation axis is parallel to the horizontal plane and is orthogonal to a direction along which first and second gear units  315  and  319  are aligned. Second circular component  318  and second toothed wheel  317  are each made of metal, plastic, or another appropriate material. 
     Displacement enhancer  3  also includes rack  314  and second rack  320 . Rack  314  has a length. A direction of the length of rack  314  runs parallel with a vertical direction. Rack  314  has gear face  316  that faces in a direction orthogonal to the length direction of rack  314 . Gear face  316  has gear teeth. Second rack  320  also has a length. A direction of the length of second rack  320  runs parallel with the vertical direction. Second rack  320  has gear face  321  that faces in a direction orthogonal to the length direction of second rack  320 . Gear face  321  has gear teeth. Rack  314  is disposed on an opposite side of toothed wheel  312  from second gear unit  319 . Gear face  316  of rack  314  faces toothed wheel  312 , and the gear teeth on gear face  316  engage with toothed wheel  312 . An upper end of rack  314  is fixed to plate  81 . Second rack  320  is disposed on an opposite side of second toothed wheel  317  from first gear unit  315 . Gear face  321  of second rack  320  faces second toothed wheel  317 , and the gear teeth on gear face  321  engage with second toothed wheel  317 . An upper end of second rack  320  is also fixed to plate  81 . 
     In the present exemplary embodiment, vibration power generation device  1  also includes first string  322  and second string  323 . First string  322  and second string  323  are each a wire, a cord, a rope, or a cable, for example. A first end of first string  322  is wound on circular component  313  of first gear unit  315 , and a second end of first string  322  is connected, as described later, to displacement-affected part  25  of piezoelectric part  2 . As a result, the outer circumference of circular component  313  and displacement-affected part  25  of piezoelectric part  2  are connected together through first string  322 . A first end of second string  323  is wound on second circular component  318  of second gear unit  319 , and a second end of second string  323  is connected, as described later, to holding part  26  of piezoelectric part  2 . As a result, an outer circumference of second circular component  318  and holding part  26  of piezoelectric part  2  are connected together through second string  323 . A direction in which second string  323  is wound on second circular component  318  is opposite a direction in which first string  322  is wound on circular component  313 . 
     Piezoelectric part  2  includes at least two electrodes  21  and piezoelectric film  22  interposed between the two electrodes  21 . Piezoelectric part  2  has displacement-affected part  25  and holding part  26 . A configuration of piezoelectric part  2  in the fifth exemplary embodiment is the same as that of piezoelectric part  2  in the first exemplary embodiment. As described above, the end of first string  322  is connected to displacement-affected part  25 . The end of second string  323  is connected to holding part  26 . 
     In the present exemplary embodiment, reference part  42  may be any portion that is not displaced in response to the displacement of displacement part  41 . For instance, the reference part is at a place where toothed wheel  312  is disposed. 
     Operation of vibration power generation device  1  will now be described. When automobile  89  passes on plate  81 , which is displacement part  41 , plate  81  is displaced downward with respect to reference part  42  owing to a load downwardly applied to plate  81  by automobile  89 . Along with the displacement of plate  81 , rack  314  and second rack  320  move downward and in response to the movement, toothed wheel  312  engaging with rack  314  and second toothed wheel  317  engaging with second rack  320  rotate. The rotating directions of toothed wheel  312  and second toothed wheel  317  are opposite to each other. Circular component  313  rotates along with the rotation of toothed wheel  312 , and second circular component  318  rotates along with the rotation of second toothed wheel  317 . Hence, tensile force is applied to piezoelectric part  2  from the outer circumferences of circular component  313  and second circular component  318  through first and second strings  322  and  323 . As a result, in piezoelectric part  2 , displacement-affected part  25  is displaced, with respect to holding part  26 , in a direction so as to be away from holding part  26 , and piezoelectric part  2  is deformed. Because of the deformation of piezoelectric part  2 , piezoelectric part  2  generates electric power in accordance with an amount of the displacement of displacement-affected part  25 . Thus, every time automobile  89  passes on plate  81 , which is a portion of specimen  4 , and plate  81  thereby descends, piezoelectric part  2  can generate electric power. As described above, the diameter of circular component  313  is larger than the diameter of toothed wheel  312 , and the diameter of second circular component  318  is larger than the diameter of second toothed wheel  317 . Accordingly, when displacement-affected part  25  is displaced along with the displacement of displacement part  41 , the displacement amount of displacement-affected part  25  is greater than the displacement amount of displacement part  41 . Thus, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3  displaces displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 . This configuration enables vibration power generation device  1  to generate large electric power relative to the displacement amount of displacement part  41 . 
     In the fifth exemplary embodiment, vibration power generation device  1  includes second gear unit  319  and second string  323 . Vibration power generation device  1  may, however, not include second gear unit  319  and second string  323 . In this case, holding part  26  of piezoelectric part  2  may be fixed inside storage space  83  by an appropriate method. Even in this case, in response to the displacement of plate  81 , displacement enhancer  3  is able to displace displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of plate  81 , with proviso that displacement enhancer  3  includes toothed wheel  312 , circular component  313 , and rack  314 . 
     In the fifth exemplary embodiment, as described above, circular component  313  is a pulley, and the outer circumference of circular component  313  and displacement-affected part  25  of piezoelectric part  2  are connected together through first string  322 . However, the outer circumference of circular component  313  and displacement-affected part  25  may be connected together by another method. For instance, circular component  313  may be equivalent to toothed wheel  312 , and an outer circumference of circular component  313  and displacement-affected part  25  may be connected together through a rack. In other words, displacement enhancer  3  may include another rack different from rack  314  and second rack  320  described above, and the other rack may engage with circular component  313  and be fixed to displacement part  41 . In the present exemplary embodiment, as described above, second circular component  318  is a pulley, and the outer circumference of second circular component  318  and holding part  26  of piezoelectric part  2  are connected together through second string  323 . However, the outer circumference of second circular component  318  and holding part  26  may be connected together by another method. For instance, second circular component  318  may be equivalent to toothed wheel  312 , and an outer circumference of second circular component  318  and holding part  26  may be connected together through a rack. In other words, displacement enhancer  3  may include another rack different from rack  314  and second rack  320  described above, and the other rack may engage with second circular component  318  and be fixed to holding part  26 . 
     The example of specimen  4  is not limited to road  8 . Specimen  4  may be, for example, a structural member of a bridge, or a structural member of a prime motor or a building. 
     1.6. Sixth Exemplary Embodiment 
       FIGS. 6A and 6B  schematically illustrate vibration power generation device  1  according to a sixth exemplary embodiment. Components in  FIGS. 6A and 6B  that overlap those in the first to fifth exemplary embodiments are hereinafter denoted by the same numerals or symbols, and detailed descriptions thereof are omitted as appropriate. 
     In the present exemplary embodiment in a similar way to the fifth exemplary embodiment, displacement enhancer  3  includes toothed wheel  312  and rack  314 . Rack  314  is fixed to displacement part  41  of specimen  4  and engages with toothed wheel  312 . 
     In the present exemplary embodiment, displacement enhancer  3  further includes second toothed wheel  325  and circular component  326 . Second toothed wheel  325  is configured so as to receive turning force transferred from toothed wheel  312 . Circular component  326  has a diameter larger than a diameter of second toothed wheel  325 . Second toothed wheel  325  and circular component  326  are allowed to coaxially rotate in conjunction with each other. Displacement-affected part  25  of piezoelectric part  2  is connected to an outer circumference of circular component  326 . 
     A configuration of vibration power generation device  1  will be described more specifically. 
     In the present exemplary embodiment, specimen  4  is road  8 . Plate  81  that constitutes a portion of road  8  is displacement part  41 . 
     In the present exemplary embodiment in a similar way to the fifth exemplary embodiment, storage space  83  exists below a ground. Storage space  83  has opening  84  through which to communicate with an atmosphere above the ground. Plate  81  is disposed so as to close opening  84 . Displacement enhancer  3  and piezoelectric part  2  are housed in storage space  83 . 
     In a similar way to the fifth exemplary embodiment, disposition area  85  is formed near an edge of opening  84  inside storage space  83 . Coil spring  86  is disposed on disposition area  85 . Plate  81  is supported by coil spring  86 . 
     Displacement enhancer  3  has a gear mechanism that includes toothed wheel  312 , second toothed wheel  325 , and circular component  326 . Circular component  326  is a circular member. In the present exemplary embodiment, circular component  326  is a pulley. 
     The diameter of circular component  326  is larger than the diameter of second toothed wheel  325 . Circular component  326  and second toothed wheel  325  rotate on a common rotation axis at an identical rotational speed. In other words, circular component  326  and second toothed wheel  325  are allowed to coaxially rotate in conjunction with each other. Circular component  326  and second toothed wheel  325  are, for example, integrated together. Toothed wheel  312 , circular component  326 , and second toothed wheel  325  are each made of metal, plastic, or another appropriate material. Preferably, the diameter of circular component  326  is larger than a diameter of toothed wheel  312 . 
     The gear mechanism includes at least one intermediate toothed wheel  328  to transfer turning force between toothed wheel  312  and second toothed wheel  325 . In the gear mechanism, toothed wheel  312  and intermediate toothed wheel  328  rotate while engaging with each other (see  FIG. 6A ), or toothed wheel  312  and intermediate toothed wheel  328  coaxially rotate (see  FIG. 6B ), for example, and turning force is thereby transferred from toothed wheel  312  to intermediate toothed wheel  328 . In the gear mechanism, two intermediate toothed wheels  328  rotate while engaging with each other (see  FIG. 6A ), or two intermediate toothed wheels  328  coaxially rotate (see  FIG. 6A ), for example, and turning force is thereby transferred between intermediate toothed wheels  328 . In the gear mechanism, intermediate toothed wheel  328  and second toothed wheel  325  rotate while engaging with each other (see  FIGS. 6A and 6B ), or intermediate toothed wheel  328  and second toothed wheel  325  coaxially rotate, for example, and turning force is thereby transferred from intermediate toothed wheel  328  to second toothed wheel  325 . In the gear mechanism, one revolution of toothed wheel  312  preferably causes second toothed wheel  325  to rotate at a number of revolutions greater than one. Preferably, in such a way, toothed wheel  312 , intermediate toothed wheel  328 , and second toothed wheel  325  included in the gear mechanism are configured. 
     Displacement enhancer  3  also includes rack  314 . Rack  314  has a length. A direction of the length of rack  314  runs parallel with a vertical direction. Rack  314  has gear face  316  that faces in a direction orthogonal to the length direction of rack  314 . Gear face  316  has gear teeth. Rack  314  is disposed on an opposite side of toothed wheel  312  from second toothed wheel  325 . Gear face  316  of rack  314  faces toothed wheel  312 , and the gear teeth on gear face  316  engage with toothed wheel  312 . An upper end of rack  314  is fixed to plate  81 . 
     In the present exemplary embodiment, vibration power generation device  1  further includes first string  322 . First string  322  is a wire, a cord, a rope, or a cable, for example. A first end of first string  322  is wound on circular component  326 , and a second end of first string  322  is connected, as described later, to displacement-affected part  25  of piezoelectric part  2 . As a result, the outer circumference of circular component  326  and displacement-affected part  25  of piezoelectric part  2  are connected together through first string  322 . 
     In the present exemplary embodiment, vibration power generation device  1  further includes holder  311  and second string  323 . Holder  311  is fixed to an interior of storage space  83 . A first end of second string  323  is fixed to holder  311 , and a second end of second string  323  is connected, as described later, to holding part  26  of piezoelectric part  2 . 
     Piezoelectric part  2  includes at least two electrodes  21  and piezoelectric film  22  interposed between the two electrodes  21 . Piezoelectric part  2  has displacement-affected part  25  and holding part  26 . A configuration of piezoelectric part  2  in the fifth exemplary embodiment is the same as that of piezoelectric part  2  in the first exemplary embodiment. As described above, the end of first string  322  is connected to displacement-affected part  25 . The end of second string  323  is connected, as described above, to holding part  26 . 
     In the present exemplary embodiment, reference part  42  is at a place where toothed wheel  312  is disposed. 
     Operation of vibration power generation device  1  will now be described. When an automobile passes on plate  81 , which is displacement part  41 , plate  81  is displaced downward with respect to reference part  42  owing to a load downwardly applied to plate  81  by the automobile. Along with the displacement of plate  81 , rack  314  moves downward and in response to the movement, toothed wheel  312  engaging with rack  314  rotates. In the gear mechanism, turning force is transferred from toothed wheel  312  to second toothed wheel  325 . Along with the rotation of second toothed wheel  325 , circular component  326  rotates. Hence, tensile force is applied to piezoelectric part  2  from the outer circumferences of circular component  326  through first string  322 . As a result, in piezoelectric part  2 , displacement-affected part  25  is displaced, with respect to holding part  26 , in a direction so as to be away from holding part  26 , and piezoelectric part  2  is deformed. Because of the deformation of piezoelectric part  2 , piezoelectric part  2  generates electric power in accordance with an amount of the displacement of displacement-affected part  25 . Thus, every time an automobile passes on plate  81 , which is a portion of specimen  4 , and plate  81  thereby descends, piezoelectric part  2  can generate electric power. 
     In the present exemplary embodiment, displacement enhancer  3  is able to make the displacement amount of displacement-affected part  25  larger than an amount of the displacement of displacement part  41  if the diameter of toothed wheel  312 , the diameter of second toothed wheel  325 , the diameter of circular component  326 , and the number of revolutions of second toothed wheel  325  in response to one revolution of toothed wheel  312  are appropriately designed. Hence, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3  is able to displace displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 . This configuration enables vibration power generation device  1  to generate large electric power relative to the displacement amount of displacement part  41 . 
     In the sixth exemplary embodiment, as described above, circular component  326  is a pulley, and the outer circumference of circular component  326  and displacement-affected part  25  of piezoelectric part  2  are connected together through first string  322 . However, the outer circumference of circular component  326  and displacement-affected part  25  may be connected together by another method. For instance, circular component  326  may be a toothed wheel, and an outer circumference of circular component  326  and displacement-affected part  25  may be connected together through a rack. In other words, displacement enhancer  3  may include another rack different from rack  314  described above, and the other rack may engage with circular component  326  and be fixed to displacement part  41 . 
     In the sixth exemplary embodiment, displacement enhancer  3  may not include intermediate toothed wheel  328 , and toothed wheel  312  may engage with second toothed wheel  325 . In this case as well, displacement enhancer  3  is able to make the displacement amount of displacement-affected part  25  larger than an amount of the displacement of displacement part  41  if the diameter of toothed wheel  312 , the diameter of second toothed wheel  325 , the diameter of circular component  326 , and the number of revolutions of second toothed wheel  325  in response to one revolution of toothed wheel  312  are appropriately designed. 
     In the sixth exemplary embodiment, displacement enhancer  3  may include an element used to transfer turning force from toothed wheel  312  to second toothed wheel  325 , other than intermediate toothed wheel  328 . Examples of the element include timing belts, timing chains, and other endless belts. 
     The example of specimen  4  is not limited to road  8 . Specimen  4  may be, for example, a structural member of a bridge, or a structural member of a prime motor or a building. 
     1.7. Seventh Exemplary Embodiment 
       FIG. 7  schematically illustrates vibration power generation device  1  according to a seventh exemplary embodiment. Components in  FIG. 7  that overlap those in the first to sixth exemplary embodiments are hereinafter denoted by the same numerals or symbols, and detailed descriptions thereof are omitted as appropriate. 
     In the present exemplary embodiment, displacement enhancer  3  includes lever  329 . A point of effort  330  of lever  329  is connected to displacement part  41  of specimen  4  whereas a point of load  331  of lever  329  is connected to displacement-affected part  25  of piezoelectric part  2 . A distance from the point of load  331  to fulcrum  332  of lever  329  is larger than a distance from the point of effort  330  to fulcrum  332 . 
     A configuration of vibration power generation device  1  will be described more specifically. 
     In the present exemplary embodiment, specimen  4  is road  8 . Plate  81  that constitutes a portion of road  8  is displacement part  41 . 
     In the present exemplary embodiment, storage space  83  exists below a ground. Storage space  83  has opening  84  through which to communicate with an atmosphere above the ground. Plate  81  is disposed so as to close opening  84 . Displacement enhancer  3  and piezoelectric part  2  are housed in storage space  83 . 
     Displacement enhancer  3  includes lever  329 . Lever  329  has the point of effort  330 , fulcrum  332 , and the point of load  331 . Lever  329  is a member having a length. Lever  329  has a first end and a second end on both ends along a longitudinal axis. The point of effort  330  is located at the first end of lever  329 , and the point of load  331  is located near the second end of lever  329 . Fulcrum  332  is at a place between the point of effort  330  and the point of load  331  of lever  329 . As described above, the distance from the point of load  331  to fulcrum  332  is larger than the distance from the point of effort  330  to fulcrum  332 . Weight  333  is disposed at the second end of lever  329 . 
     The point of effort  330  of lever  329  is attached to a lower surface of plate  81 . Thus, the point of effort  330  of lever  329  is connected to plate  81 . While no load is downwardly applied to plate  81 , the first end of lever  329  is disposed at a level higher than the second end because of a load applied downwardly to the second end by weight  333 . As a result, lever  329  supports plate  81  at a place so as to close opening  84 . 
     A bottom of storage space  83  includes first bottom  87  and second bottom  88  disposed at a level lower than first bottom  87 . The first end, the point of effort  330 , and fulcrum  332  of lever  329  are located above first bottom  87 , whereas the point of load  331  and the second end of lever  329  are located above second bottom  88 . 
     Displacement enhancer  3  further includes support member  334  to support fulcrum  332  of lever  329 . Support member  334  is placed on first bottom  87 . 
     Displacement enhancer  3  further includes holder  311 , first string  322 , and second string  323 . Holder  311  is fixed to a part of second bottom  88  directly below the point of load  331  of lever  329 . A first end of first string  322  is fixed to the point of load  331  of lever  329 , and a second end of first string  322  is connected, as described later, to displacement-affected part  25  of piezoelectric part  2 . A first end of second string  323  is fixed to holder  311 , and a second end of second string  323  is fixed, as described later, to holding part  26  of piezoelectric part  2 . 
     Piezoelectric part  2  includes at least two electrodes  21  and piezoelectric film  22  interposed between the two electrodes  21 . Piezoelectric part  2  has displacement-affected part  25  and holding part  26 . A configuration of piezoelectric part  2  in the seventh exemplary embodiment is the same as that of piezoelectric part  2  in the first exemplary embodiment. As described above, the end of first string  322  is connected to displacement-affected part  25 . The end of second string  323  is connected, as described above, to holding part  26 . 
     In the present exemplary embodiment, reference part  42  may be any portion that is not displaced in response to the displacement of displacement part  41 . For instance, the reference part is at a place where fulcrum  332  of lever  329  is disposed. 
     Operation of vibration power generation device  1  will now be described. When automobile  89  passes on plate  81 , which is displacement part  41 , a load is downwardly applied to the point of effort  330  of lever  329  via plate  81  owing to a load downwardly applied to plate  81  by automobile  89 . As a result, plate  81  is displaced downward with respect to reference part  42 . Along with the displacement, lever  329  operates such that the point of effort  330  goes down against the load of weight  333  and the point of load  331  rises. To ensure that lever  329  operates in this way, mass of weight  333  is appropriately set. Along with the rise of the point of load  331 , tensile force is applied to displacement-affected part  25  of piezoelectric part  2  from the point of load  331  of lever  329  through first string  322 . As a result, in piezoelectric part  2 , displacement-affected part  25  is displaced, with respect to holding part  26 , in a direction so as to be away from holding part  26 , and piezoelectric part  2  is deformed. Because of the deformation of piezoelectric part  2 , piezoelectric part  2  generates electric power in accordance with an amount of the displacement of displacement-affected part  25 . Thus, every time an automobile passes on plate  81 , which is a portion of specimen  4 , and plate  81  thereby descends, piezoelectric part  2  can generate electric power. 
     In the present exemplary embodiment, the distance from the point of load  331  to fulcrum  332  of lever  329  is, as described above, larger than the distance from the point of effort  330  to fulcrum  332 . Accordingly, an amount of the upward movement of the point of load  331  is larger than an amount of the downward movement of the point of effort  330  along with the displacement of plate  81 . Hence, in response to the displacement of displacement part  41  of specimen  4 , displacement enhancer  3  is able to displace displacement-affected part  25  of piezoelectric part  2  by a displacement amount greater than the displacement amount of displacement part  41 . This configuration enables vibration power generation device  1  to generate large electric power relative to the displacement amount of displacement part  41 . 
     The example of specimen  4  is not limited to road  8 . Specimen  4  may be, for example, a structural member of a bridge, or a structural member of a prime motor or a building. 
     2. Sensor System 
     Sensor system  9  that includes vibration power generation device  1  will now be described. 
       FIG. 8  is a block diagram of an example of sensor system  9 . Sensor system  9  includes vibration power generation device  1  and sensor  91 . Sensor  91  is made up of piezoelectric part  2  included in vibration power generation device  1  or is a device that is different from piezoelectric part  2  and that is driven by electric power generated by piezoelectric part  2 . Sensor system  9  may further include, as shown in  FIG. 8 , communication device  92  that transmits a result detected with sensor  91 . 
     If sensor  91  is piezoelectric part  2 , sensor  91  outputs a signal in response to displacement of displacement part  41  of specimen  4 . If specimen  4  is, for example, a structural member of a bridge as in the first and second exemplary embodiments, sensor  91  is able to detect a vibration created in the structural member of the bridge and output a signal in response to the vibration. In this case, sensor system  9  can be used, for example, to check whether an excessive vibration is created in the structural member of the bridge. If specimen  4  is a prime motor as in the third exemplary embodiment, sensor  91  is able to detect a vibration created in the prime motor and output a signal in response to the vibration. In this case, sensor system  9  can be used, for example, to check whether an abnormal vibration is created in the prime motor. If specimen  4  is a structural member of a building as in the fourth exemplary embodiment, sensor  91  is able to detect a vibration created in the structural member of the building and output a signal in response to the vibration. In this case, sensor system  9  can be used, for example, as a seismograph. If specimen  4  is a road as in the fifth to seventh exemplary embodiments, sensor  91  is able to detect a displacement of a portion of the road when an automobile passes on the road portion and output a signal in response to the displacement. In this case, sensor system  9  can be used, for example, to investigate automobile traffic on the road. 
     If sensor  91  is different from piezoelectric part  2  and is driven by electric power generated by piezoelectric part  2 , information detected with sensor  91  may contain any facts. Sensor  91  may be, for example, a temperature sensor, a humidity sensor, a gas sensor, or an image sensor. In this case, sensor system  9  is able to detect information about temperature, humidity, gas composition, image, or others at a location where sensor system  9  is placed or in an area around the location. 
     Sensor system  9  according to the present exemplary embodiment is not required to receive the supply of electric power from an outside in order to drive sensor  91 . Thus, sensor system  9  is able to detect information in accordance with a type of sensor  91  through sensor  91  even at a place where it is difficult to receive the supply of electric power. 
     If sensor system  9  includes communication device  92 , sensor system  9  is able to transmit a result detected with sensor  91  to receiver  10  installed outside as appropriate via communication device  92 . Communication device  92  may transmit the detection result by wire or wireless. Communication device  92  may be driven by electric power generated by vibration power generation device  1  or by electric power supplied from a power source different from vibration power generation device  1 . 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
         
           
               1  vibration power generation device 
               2  piezoelectric part 
               21  electrode 
               22  piezoelectric film 
               25  displacement-affected part 
               3  displacement enhancer 
               32  first pulley 
               33  second pulley 
               38  first string 
               39  second string 
               312  toothed wheel 
               313  circular component 
               314  rack 
               322  first string 
               323  second string 
               326  circular component 
               329  lever 
               330  point of effort 
               331  point of load 
               332  fulcrum 
               4  specimen 
               41  displacement part 
               5  bridge 
               6  prime motor 
               7  building 
               8  road 
               9  sensor system 
               91  sensor 
               92  communication device