Abstract:
The vibration power generator includes: a plurality of permanent magnets ( 1, 2 ) integrated together to have given inter-magnet gaps under a state in which the same poles of the permanent magnets are opposed to each other; and a plurality of coils ( 3 ,  4 ) arranged on respective outer peripheries of the plurality of permanent magnets so as to have a distance from the plurality of permanent magnets, and is configured to generate an electric power through relative movement of the plurality of permanent magnets and the plurality of coils. A relationship between a length of the opposed coils and a length of the permanent magnet is set so that the length of the coils is larger than the length of the permanent magnet and equal to or smaller than a sum of the length of the permanent magnet and a length of the inter-magnet gap.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a vibration power generator configured to use a magnet and a conductive coil to utilize an electric power to be generated by relative vibration of the magnet and the conductive coil. 
       BACKGROUND ART 
       [0002]    When a magnet is vibrated so that the magnet passes through the inside of a conductive coil, an induced current flows in the coil to generate an electromotive force. The electromotive force is generally small on the order of milliwatts. A conceivable method for enhancing the electromotive force is to use a plurality of magnets and a plurality of coils. 
         [0003]    As a related art, there is given one generator including a plurality of coils arranged around magnets in which the same poles are opposed to each other, and the magnets and the coils are desired to have equal lengths and be arranged at equal intervals (see, for example, Patent Literature 1). Then, when a gap between the magnets is halved, a larger electromotive force may be obtained. 
         [0004]    As another related art, there is also given a vibration power generator configured to use a plurality of permanent magnets and a plurality of coils surrounding the permanent magnets to generate an electric power through relative movement with vibration. In the vibration power generator, the permanent magnets are arranged so that the same poles are opposed to each other, and integrated together to have a gap therebetween, and the plurality of coils are arranged on the outer peripheries of the plurality of permanent magnets so as to have a distance from the permanent magnets. The plurality of coils wound in opposite directions are alternately arranged, and the length of each coil is set to 70% to 90% of the length of the permanent magnet (see, for example, Patent Literature 2). In Patent Literature 2,  FIGS. 4 and 9  show that the electromotive force is enhanced. 
       CITATION LIST 
     Patent Literature 
       [0005]    [PTL 1] JP 4684106 B 
         [0006]    [PTL 2] JP 4704093 B 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    The related arts, however, have the following problems. 
         [0008]    In Patent Literature 1, there is no sufficient quantitative description that the magnets and the coils are desired to have equal lengths and be arranged at equal intervals. 
         [0009]    In the vibration power generator disclosed in Patent Literature 2, the length of the coil is smaller than the length of the permanent magnet. Thus, as compared to the case where a coil having the same length as the permanent magnet is used, if the coil is produced under the same conditions, there is a problem in that the electromotive force becomes smaller because the number of turns of the coil is reduced. 
         [0010]    In free vibration using a spring or the like, there is a problem in that the electromotive force becomes smaller when the amplitude is so small that the coil cannot cross the vicinity of an edge of the permanent magnet at which magnetic flux density is large. 
         [0011]    The present invention has been made in order to solve the problems described above, and it is an object thereof to provide a vibration power generator including at least one permanent magnet and a plurality of coils and capable of generating a larger electromotive force than hitherto through relative movement or free vibration. 
       Solution to Problem 
       [0012]    According to one embodiment of the present invention, there is provided a vibration power generator including: a plurality of permanent magnets integrated together to have given inter-magnet gaps under a state in which the same poles of the permanent magnets are opposed to each other; and a plurality of coils arranged on respective outer peripheries of the plurality of permanent magnets so as to have a distance from the plurality of permanent magnets, the vibration power generator being configured to generate an electric power through relative movement of the plurality of permanent magnets and the plurality of coils. A relationship between a length of the opposed coils and a length of the permanent magnet is set so that the length of the coils is larger than the length of the permanent magnet and equal to or smaller than a sum of the length of the permanent magnet and a length of the inter-magnet gap. 
       Advantageous Effects of Invention 
       [0013]    According to the vibration power generator according to one embodiment of the present invention, the relationship between the length of the opposed coils and the length of the permanent magnet is set so that the length of the coils is larger than the length of the permanent magnet and equal to or smaller than the sum of the length of the permanent magnet and the length of the inter-magnet gap. Thus, in minute vibration, the coils are allowed to cross the vicinity of the edge of the permanent magnet at which magnetic flux density is large. Consequently, it is possible to provide the vibration power generator including at least one permanent magnet and the plurality of coils and capable of generating a larger electromotive force than hitherto through relative movement or free vibration. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a schematic sectional view of portions of magnets and coils of a vibration power generator according to a first embodiment of the present invention. 
           [0015]      FIG. 2  is an explanatory view relating to a spring according to the first embodiment of the present invention. 
           [0016]      FIG. 3  is a graph showing simulation results of an electromotive force of the vibration power generator according to the first embodiment of the present invention. 
           [0017]      FIG. 4  shows simulation results of distribution of magnetic flux density obtained by the magnets illustrated in  FIG. 1  according to the first embodiment of the present invention. 
           [0018]      FIG. 5  is a schematic sectional view of portions of magnets and coils of a vibration power generator according to a second embodiment of the present invention. 
           [0019]      FIG. 6  is an explanatory diagram for extracting an electromotive force from the configuration of  FIG. 5  according to the second embodiment of the present invention. 
           [0020]      FIG. 7  is a graph showing simulation results of the electromotive force of the vibration power generator according to the second embodiment of the present invention. 
           [0021]      FIG. 8  is a structural sectional view of a vibration power generator having the configurations of the magnets and the coils described in the first embodiment mounted thereon and an equivalent circuit thereof according to a third embodiment of the present invention. 
           [0022]      FIG. 9  is a waveform diagram showing measurement results of an electromotive force generated by the circuit of  FIG. 8  according to the third embodiment of the present invention. 
           [0023]      FIG. 10  is a structural sectional view of a vibration power generator having the configurations of the magnets and the coils described in the second embodiment mounted thereon and an equivalent circuit thereof according to the third embodiment of the present invention. 
           [0024]      FIG. 11  is a waveform diagram showing measurement results of an electromotive force generated by the circuit of  FIG. 10  according to the third embodiment of the present invention. 
           [0025]      FIG. 12  is another waveform diagram showing the measurement results of the electromotive force generated by the circuit of  FIG. 10  according to the third embodiment of the present invention. 
           [0026]      FIG. 13  is a block diagram of a wireless transmission device using the vibration power generator according to a fourth embodiment of the present invention. 
           [0027]      FIG. 14  shows simulation results of distribution of magnetic flux density when a yoke is arranged between magnets according to a fifth embodiment of the present invention. 
           [0028]      FIG. 15  is a graph showing simulation results of an electromotive force of a vibration power generator according to the fifth embodiment of the present invention. 
           [0029]      FIG. 16  shows simulation results of distribution of magnetic flux density when an inter-magnet gap is changed and yokes are arranged at three locations according to the fifth embodiment of the present invention. 
           [0030]      FIG. 17  is a graph showing simulation results of an electromotive force of the vibration power generator according to the fifth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    The technical feature of the present invention resides in that the object of enhancing an electromotive force to be generated by electromagnetic induction due to relative vibration of a magnet and a coil is achieved by utilizing a shortened inter-coil gap to set the length of a coil to be larger than the length of a permanent magnet and equal to or smaller than the sum of the length of the permanent magnet and the length of an inter-magnet gap. 
         [0032]    More specifically, the first approach is to utilize a shortened inter-magnet gap to set the length of the coil to be larger than the length of the magnet, to thereby enhance the electromotive force. The second approach is to utilize a shortened inter-magnet gap to arrange two or more divided coils for each magnet, to thereby efficiently extract a change in magnetic flux density to enhance the electromotive force. Note that, those two approaches may be used in combination. 
       First Embodiment 
       [0033]      FIG. 1  is a schematic sectional view of portions of magnets and coils of a vibration power generator according to a first embodiment of the present invention. Referring to  FIG. 1 , columnar or cylindrical permanent magnets (hereinafter referred to as “magnets”)  1  and  2  are arranged so that the same poles are opposed to each other. In addition, the magnets  1  and  2  are surrounded by a coil  3  ( 3   a  and  3   b ) and a coil  4  ( 4   a  and  4   b ). 
         [0034]    In this case, the magnets  1  and  2  each have a diameter of 10 mm, a length of 9 mm, and an inter-magnet distance (gap) of 3 mm. The coils  3  and  4  each have a length of 11 mm and an inter-coil distance (gap) of 1 mm. As the distance between the magnet  1  and the coil  3  or the distance between the magnet  2  and the coil  4  becomes smaller, a larger change occurs in magnetic flux density of the coil. This means that the electromotive force becomes larger in inverse proportion to the distance. 
         [0035]      FIG. 2  is an explanatory view relating to a spring according to the first embodiment of the present invention. Specifically,  FIG. 2  is an external view of a spring called “machined spring” as an example of housing the magnets  1  and  2  and the coils  3  and  4 , as viewed from obliquely above and obliquely below. An integrated unit of the magnets  1  and  2  of  FIG. 1  is mounted on the inside of the spring and is vibrated. The coils  3  and  4  are fixed at a downward position to surround the magnets  1  and  2 . 
         [0036]      FIG. 3  is a graph showing simulation results of the electromotive force of the vibration power generator according to the first embodiment of the present invention. Specifically, the simulation results show a half-cycle electromotive force generated when the spring is vibrated to move upward and downward by 12 mm. The graph shows a DC component of the electromotive force generated in the coil  3  when the length of the coil is 11 mm and 8 mm. In this case, the coil is wound to have the same number of turns per unit length. 
         [0037]    Note that,  FIG. 1  illustrates a stationary state, and hence the spring moves upward and downward around the illustrated position. The value of the electromotive force on the vertical axis of  FIG. 3  is not an absolute value but a relative comparison value. The horizontal axis is the time axis in which the time period required for the movement of 12 mm is divided into 24 equal segments. 
         [0038]    The graph of  FIG. 3  shows that the electromotive force of the 11-mm coil is larger than that of the 8-mm coil by 15%. In this case, 12 mm is the sum of the length of 9 mm of each of the magnets  1  and  2  and the inter-magnet gap of 3 mm. Thus, for a larger vibration than 12 mm, the electromotive force periodically changes to maintain the tendency shown in  FIG. 3 , and hence the 11-mm coil generates a larger electromotive force. 
         [0039]      FIG. 4  shows simulation results of distribution of magnetic flux density obtained by the magnets  1  and  2  illustrated in  FIG. 1  according to the first embodiment of the present invention. When a neodymium magnet is used, magnetic flux density for each magnet is approximately 0.5 tesla. Provided that the surroundings are filled with the air, the magnetic flux density on the line apart from the magnet by 1 mm is measured as shown in the upper graph of FIG.  4 . 
         [0040]    The contour lines in the lower graph of  FIG. 4  show the areas of equal magnetic flux density. In the upper graph, the magnet edges at the middle at which the same poles are opposed to each other have high magnetic flux density, and the outer edges of the magnets have lower magnetic flux density than that at the middle (compared in absolute values). 
         [0041]    The electromotive force is proportional to the change in magnetic flux density, and hence the electromotive force becomes larger when the coil crosses the middle edges of the magnets at which the magnetic flux density changes with an abrupt inclination. The change in magnetic flux density becomes more abrupt as the absolute value of the magnetic flux density becomes larger, and hence a larger electromotive force is generated. 
         [0042]    For small vibration, although depending on the position of the 8-mm coil, the electromotive force becomes smaller if the 8-mm coil does not cross the vicinity of the edges of the magnets  1  and  2  based on the distribution of the magnetic flux density of  FIG. 4 . 
         [0043]    As described above, according to the first embodiment, the inter-magnet gap of the plurality of magnets is reduced, and the length of the coil is set to be larger than the length of the magnet so as to reduce the inter-coil gap as much as possible. Consequently, in minute vibration, the coil crosses the vicinity of the edge of the permanent magnet at which the magnetic flux density is large, and hence there is an effect that a larger electromotive force than hitherto is generated and the electromotive force becomes larger than hitherto even in minute vibration. 
       Second Embodiment 
       [0044]      FIG. 5  is a schematic sectional view of portions of magnets and coils of a vibration power generator according to a second embodiment of the present invention. Referring to  FIG. 5 , the number of coils for each magnet is two, and the inter-coil gap is reduced so that an edge of the coil on one side is arranged in the vicinity of the magnet edge in the stationary state. 
         [0045]    In the coil longer than the magnet, the change in magnetic flux density, that is, the differential coefficient has the same polarity depending on the position, which affects the electromotive force. The electromotive force is proportional to the change in magnetic flux density in the entire coil, and hence as shown in  FIG. 4 , the electromotive force may be more efficiently extracted as the length of the coil becomes smaller. 
         [0046]      FIG. 6  is an explanatory diagram for extracting the electromotive force from the configuration of  FIG. 5  according to the second embodiment of the present invention. Specifically,  FIG. 6  is a block diagram for generating a DC voltage at a terminal of a capacitor  13  via rectifier circuits  11  and  12  from both terminals of divided coils  5  ( 5   a,    5   b ) and  6  ( 6   a,    6   b ). 
         [0047]      FIG. 7  is a graph showing simulation results of the electromotive force of the vibration power generator according to the second embodiment of the present invention. Specifically, similarly to  FIG. 3 , the simulation results show the electromotive force generated when the number of coils for each magnet is one and two in the case where the spring is subjected to free vibration by the half cycle of 12 mm. 
         [0048]    The electromotive force of the configuration of  FIG. 5  is generated by combining the coil  5  and the coil  6 , and hence has three peaks. Consequently, the obtained electromotive force was 1.4 times as large as the case where a single coil longer than the length of the magnet was used as in the first embodiment. 
         [0049]    As described above, according to the second embodiment, the shortened inter-magnet gap is utilized to arrange two or more coils for each magnet. Consequently, as compared to the configuration of the first embodiment, the total number of turns of the coils can be increased, and the change in magnetic flux density can be efficiently extracted owing to the shortened coil length, to thereby enhance the electromotive force. 
       Third Embodiment 
       [0050]    In a third embodiment of the present invention, a detailed description is given of measurement results of the electromotive force generated by the vibration power generator having the configurations of the magnets and the coils described in the first and second embodiments mounted thereon. 
         [0051]      FIG. 8  is a structural sectional view of the vibration power generator having the configurations of the magnets and the coils described in the first embodiment mounted thereon and an equivalent circuit thereof according to the third embodiment of the present invention.  FIG. 8  is a sectional view in which an integrated magnet unit is mounted on the inside of the spring illustrated in  FIG. 2 , and two coils are mounted on the bottom. The coils were each wound with 1,000 turns (T) in opposite directions, and the electromotive force was measured at end portions of the coils and at end portions of 2,000 turns (T) of the coils. 
         [0052]      FIG. 9  is a waveform diagram showing measurement results of the electromotive force generated by the circuit of  FIG. 8  according to the third embodiment of the present invention. Each coil has the peaks of approximately ±3 V and approximately ±1.2 V, and the waveform thereof is repeated. Then, a combined voltage of the coils was approximately ±4.2 V. 
         [0053]      FIG. 10  is a structural sectional view of the vibration power generator having the configurations of the magnets and the coils described in the second embodiment mounted thereon and an equivalent circuit thereof according to the third embodiment of the present invention. Referring to  FIG. 10 , four coils were mounted with 500 turns (T) each. The coils are wound in the same direction within the magnet and in the opposite directions between the magnets. 
         [0054]      FIGS. 11 and 12  are waveform diagrams showing measurement results of the electromotive force generated by the circuit of  FIG. 10  according to the third embodiment of the present invention. Specifically,  FIG. 11  shows measurement results for [ 1 ], [ 3 ], and [ 1 ]+[ 3 ] of  FIG. 10 . Each coil has the peaks of approximately ±2.4 V and approximately ±0.8 V. For [ 1 ]+[ 3 ], the coils have the peaks of approximately ±3.4 V and approximately ±2.2 V. 
         [0055]      FIG. 12  shows measurements results for [ 2 ], [ 4 ], and [ 2 ]+[ 4 ] of  FIG. 10 , and substantially the same results as those of  FIG. 11  are obtained. The combined result of the electromotive forces of each of  FIGS. 11 and 12  is apparently larger than the combined result of the electromotive forces of  FIG. 9 , and matches with the simulation results shown in  FIG. 7 . 
         [0056]    As described above, according to the third embodiment, the validity of the simulation results in the first and second embodiments was able to be verified based on the actual measured values. 
       Fourth Embodiment 
       [0057]    In a fourth embodiment of the present invention, a description is given of a wireless transmission device to which the vibration power generator of the present invention is applied. 
         [0058]      FIG. 13  is a block diagram of the wireless transmission device using the vibration power generator according to the fourth embodiment of the present invention. The wireless transmission device illustrated in  FIG. 13  includes a vibration power generator  100 , a wireless sensor device  200 , and a data reception unit  300 . 
         [0059]    Then, the wireless sensor device  200  includes a rectifier circuit  210 , a constant voltage circuit  220 , an electric storage element  230 , a microcontroller  250 , a sensor  260 , a wireless transmission circuit  270 , and an antenna  280 . The data reception unit  300  includes an antenna  310 , a wireless reception circuit  320 , and a processing unit  330 . 
         [0060]    Next, an operation of the wireless transmission device is described. The vibration power generator  100  outputs an electromotive force generated by electromagnetic induction based on vibration applied from the outside, and inputs the generated electromotive force to the wireless sensor device  200 . The rectifier circuit  210  included in the wireless sensor device  200  converts and rectifies the electromotive force input from the vibration power generator  100  from an AC electric power as shown in  FIGS. 11 and 12  into a DC electric power. 
         [0061]    The constant voltage circuit  220  stores the DC electric power input from the rectifier circuit  210  into the electric storage element  230  such as a capacitor, and steps up or down the DC electric power so as to be a constant voltage, to thereby generate a supply voltage  240 . 
         [0062]    The microcontroller  250  uses the supply voltage  240  supplied from the constant voltage circuit  220  to process measurement data obtained periodically from the sensor  260 , and outputs the processed measurement data to the wireless transmission circuit  270 . The wireless transmission circuit  270  uses the supply voltage  240  supplied from the constant voltage circuit  220  to transmit measurement information input from the microcontroller  250  as wireless information from the antenna  280 . 
         [0063]    On the other hand, the data reception unit  300  performs reception processing on a wireless signal transmitted from the wireless sensor device  200 . Specifically, the wireless reception circuit  320  included in the data reception unit  300  receives via the antenna  310  the wireless signal that is periodically transmitted from the wireless sensor device  200 , and outputs the wireless signal to the processing unit  330 . 
         [0064]    The processing unit  330  extracts measurement data from the received data input from the wireless reception circuit  320 , and accumulates and displays the measurement data. Note that, the processing unit  330  may be constructed by an apparatus including a processing device such as a microcontroller and a display unit such as an LCD, or a personal computer. 
         [0065]    As described above, according to the fourth embodiment, the vibration power generator of the present invention can be applied to the wireless transmission device. Besides, by fixedly mounting springs on both sides of the magnet, the vibration power generator of the present invention can be applied to the applications for any vibration direction. In addition, by mounting a secondary cell, the vibration power generator of the present invention can be used as a charger. 
       Fifth Embodiment 
       [0066]    In a fifth embodiment of the present invention, a description is given of the case where a yoke is inserted between the magnets instead of an air layer to improve the magnetic flux density, to thereby enhance the electromotive force. 
         [0067]      FIG. 14  shows simulation results of distribution of the magnetic flux density when the yoke is arranged between the magnets according to the fifth embodiment of the present invention. More specifically, the simulation results show the distribution of the magnetic flux density when a columnar yoke (corresponding to material having relative permeability of more than 1) is inserted between the magnets instead of the air layer. 
         [0068]    With the yoke inserted, the magnetic flux concentrates on the yoke surface, with the result that the magnetic flux density between the magnets becomes larger. The peak value of  FIG. 14  is approximately 0.36 tesla, which is 1.44 times as large as 0.25 tesla of  FIG. 4  measured with no yoke inserted. 
         [0069]      FIG. 15  is a graph showing simulation results of the electromotive force of the vibration power generator according to the fifth embodiment of the present invention. Specifically, the simulation results show the electromotive force generated when the number of coils for each magnet is one and two with respect to the magnetic flux density of  FIG. 14 . The divided 5.5-mm coils were able to obtain a total electromotive force that was 1.51 times as large as the electromotive force of the not-divided 11-mm coil. 
         [0070]    Further, the 11-mm coil and the 5.5-mm coils were able to obtain electromotive forces that were 1.14 times and 1.22 times as large as those of  FIG. 7  using no yoke. 
         [0071]      FIG. 16  shows simulation results of distribution of the magnetic flux density when the inter-magnet gap is changed and the yokes are arranged at three locations according to the fifth embodiment of the present invention. The configuration of  FIG. 16  aims at further enhancing the electromotive force by setting the magnet length to 11 mm and the inter-magnet gap to 1 mm and arranging the yokes between the magnets and at both ends of the magnets. The peak magnetic flux density in this case is approximately 0.54 tesla, which reaches 1.44 times as large as the case of  FIG. 14  in which the yoke is arranged only at one location between the magnets. 
         [0072]      FIG. 17  is a graph showing simulation results of the electromotive force of the vibration power generator according to the fifth embodiment of the present invention. Specifically, the simulation results show the electromotive force generated when the number of coils for each magnet is one and two with respect to the magnetic flux density of  FIG. 16 . The divided 5.5-mm coils were able to obtain a total electromotive force that was 1.41 times as large as the electromotive force of the not-divided 11-mm coil. 
         [0073]    Further, the 11-mm coil and the 5.5-mm coils were able to obtain electromotive forces that were 1.16 times and 1.09 times as large as those of  FIG. 15  in which the yoke was arranged only at one location between the magnets. 
         [0074]    As described above, according to the fifth embodiment, the yoke is inserted between the magnets instead of the air layer. Consequently, in addition to the effects of the first and second embodiments, the electromotive force can be enhanced due to the improvement of magnetic flux density. 
         [0075]    Note that, the case where the number of magnets is two has been described above in the embodiments, but it should be understood that the same effects can be expected even when the number of magnets is three or more. The case where the coil is divided into two pieces has been described above, but the coil may be divided into three or more pieces. The inter-coil gap may be eliminated.