WO 2008/048050 PCT/KR2007/005099 1 Description WAVE ENERGY CONVERTER Technical Field [1] The present invention relates, in general, to wave energy converters and, more par ticularly, to a wave energy converter, which includes: a floating body, which is exposed above the surface of seawater due to the buoyancy thereof; an actuating unit, which has a combined rotary unit that is coupled to the floating body and the ground and is formed of at least one moving rotator or a combination of moving rotators and fixed rotators, a linear member, connected to the combined rotary unit, and a tension maintaining member for tensioning the linear member to maintain the linear member tight; and an energy converting unit, such as a generator, which is provided at a pre determined position in the actuating unit or the floating unit, thus converting wave energy into electric, potential or kinetic energy. Background Art [2] Recently, the public's interest in environment-friendly energy has increased. Solar energy, wind energy, tidal energy and wave energy are representative examples of en vironment-friendly energy. The wave power generation uses the power of waves generated at sea. A lot of research into methods of generating electricity using wave power has been conducted. [3] As representative examples of conventional techniques pertaining to wave power generation, there are a floating type generation system, a gear coupling type generation system, a generation system using a rack and pinion, etc. However, in the case of such generation systems, the construction thereof is complex, and the installation costs are thus increased. Furthermore, the conventional generation systems have not solved problems in which it is difficult to generate electricity at constant voltage due to the irregular movement of waves, and in that generation efficiency is reduced both by the low heights of waves, which are thus insufficient to generate electricity, and due to the slow movement of waves. [4] As one example, in a wave energy converter, which was proposed in PCT In ternational Publication No. WO 2006-109491, as shown in FIG. 1, a floating body is provided on the surface of seawater, and a wire is connected to the upper end of the floating body and extends upwards. The wire passes over a plurality of fixed pulleys, which are disposed on the ground above the floating body, and extends downwards. A weight is connected to the end of the wire. However, in this technique, because only the fixed pulleys, which are provided on the ground, are used, locations at which it is possible to install the wave energy converter are limited. Furthermore, in the case WO 2008/048050 PCT/KR2007/005099 2 where the heights of waves are relatively low, satisfactory electricity generation cannot be achieved. [5] Meanwhile, floating or buoyant type wave energy converters using pneumatic turbines, which are operated using the pressure of intake and discharge air, formed by the difference in the height of waves, have been developed. However, these turbines cannot be widely used either due to high installation costs and low generation efficiency. As such, wave energy, although limitless, has not been efficiently taken advantage of. Disclosure of Invention Technical Problem [6] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a wave energy converter which can efficiently convert wave energy into electric energy, potential energy or kinetic energy despite the relatively low height of waves. [7] Another object of the present invention is to provide a wave energy converter that has a simple structure and reduced installation costs and is easy to install and maintain. [8] A further object of the present invention is to provide a wave energy converter which has a wave-adaptation type structure which can appropriately adapt even to strong waves, thus being protected from damage. Technical Solution [9] In order to accomplish the above objects, the present invention provides a wave energy converter, including: a floating body exposed above a water surface due to a buoyancy thereof, the floating body being moved upwards or downwards by waves; an actuating unit, comprising: a combined rotary unit coupled to the floating body and to solid ground, the combined rotary unit including a moving rotator or being formed through a combination of a moving rotator and a fixed rotator; a linear member connected to the combined rotary unit, the linear member reciprocating depending on the movement of the floating body; and a tension maintaining member connected to one end of the linear member, the tension maintaining member tensioning the linear member to keep the linear member tight, wherein a distance that the linear member is moved is increased, by operation of the combined rotary unit, to several times as long as a distance that the floating body is moved upwards or downwards; and an energy converting unit, provided in the actuating unit or the floating unit, to convert wave energy, transmitted through reciprocation of the linear member, into other energy. [10] Preferably, the linear member may comprise a wire rope, and each of the moving rotator and the fixed rotator may comprise a pulley. [11] Alternatively, the linear member may comprise a chain, and each of the moving WO 2008/048050 PCT/KR2007/005099 3 rotator and the fixed rotator may comprise a chain wheel. [12] Preferably, the energy converting unit may comprise a generator for generating electricity using the reciprocation of the linear member. [13] Furthermore, the energy converting unit may comprise a pump for water intake. [14] In addition, the energy converting unit may comprise a compressor and a pressure container to compress and store fluid. [15] As well, a through hole may be vertically formed through the tension maintaining member, such that the linear member passes through the tension maintaining member. [16] Preferably, the tension maintaining member may comprise one selected from among a balance weight, a spring and an underwater buoyant body, which pulls the linear member upwards using buoyancy thereof, and the balance weight, the spring or the underwater buoyant body is connected to the end of the linear member. [17] Furthermore, the generator may have a transmission gear to increase a speed of rotation thereof. [18] As described above, it is to be appreciated that the object of the present invention provides the wave energy converter that can efficiently conduct energy conversion, for example, electricity generation, despite the relatively low height of waves. To achieve this object, the present invention includes the combined rotary unit. The combined rotary unit consists of at least one moving rotator or a combination of a moving rotator and a fixed rotator. Depending on the combination of the rotators, the distance that the free end of the linear member, connected to the combined rotary unit, is moved can be increased until it is several times as long as that of the floating body. Thereby, the speed at which the linear member is moved is increased. Therefore, even though the heights of waves are relatively low, the energy converting unit can be effectively operated. Advantageous Effects [19] The wave energy converter according to the present invention is constructed such that the distance that a linear member is moved is increased so that it is several times as long as that of a floating body, thus increasing the speed at which the free end of the linear member is moved. Therefore, there is an advantage in that satisfactory energy conversion can be achieved even though the heights of waves are relatively low. [20] Furthermore, because the structure is simple, it is easy to install and maintain the wave energy converter. In addition, there is an advantage in that the economic burden is reduced by the reduced installation costs. [21] As well, the present invention can efficiently adapt to strong waves, thus being protected from damage, thereby maintaining high durability. Brief Description of the Drawings WO 2008/048050 PCT/KR2007/005099 4 [22] FIG. 1 is a schematic view illustrating a conventional wave energy converter; [23] FIG. 2 is a schematic view illustrating a wave energy converter, according to a first embodiment of the present invention; [24] FIG. 3 is a schematic view illustrating a wave energy converter, according to a second embodiment of the present invention; [25] FIG. 4 is a schematic view illustrating a wave energy converter, according to a third embodiment of the present invention; [26] FIG. 5 is a schematic view illustrating a wave energy converter, according to a fourth embodiment of the present invention; [27] FIG. 6 is a schematic view illustrating a wave energy converter, according to a fifth embodiment of the present invention; [28] FIG. 7 is a schematic view illustrating a wave energy converter, according to a sixth embodiment of the present invention; [29] FIG. 8 is a schematic view illustrating a wave energy converter, according to a seventh embodiment of the present invention; [30] FIG. 9 is a schematic view illustrating a wave energy converter, according to another embodiment of the present invention; and [31] FIG. 10 is a schematic view illustrating a wave energy converter, according to another embodiment of the present invention. [32] <Description of the elements in the drawings> [33] 100: floating body 210: combined rotary unit [34] 212: moving rotator 214: fixed rotator [35] 220: linear member 232: underwater buoyant body [36] 234: balance weight 236: spring [37] 300: generator 310: transmission gear [38] 400: ground Best Mode for Carrying Out the Invention [39] Hereinafter, wave energy converters according to preferred embodiments of the present invention will be described in detail with reference to the attached drawings. [40] FIG. 2 is a schematic view illustrating a wave energy converter according to a first embodiment of the present invention. [41] Referring to FIG. 2, the present invention includes a floating body 100, an operating unit and an energy converting unit. The actuating unit includes a combined rotary unit 210, a linear member 220 and a tension maintaining member 232, 234, 236. [42] First, the floating body will be explained herein below. The floating body 100 is filled with solid buoyant material, such as EPS (expanded polystyrene) or polyurethane, which has a density lower than that of seawater. As shown in FIG. 2, the WO 2008/048050 PCT/KR2007/005099 5 floating body 100 always maintains constant buoyancy, and is thus moved upwards or downwards by the waves of seawater. [43] Here, the floating body 100 is not limited to a body that is filled with solid buoyant material having a density lower than seawater. For example, a sealed hollow barrel or the like may be used as the floating body. [44] Next, the actuating unit will be explained herein below. The actuating unit is connected to the floating body 100 and to solid ground 400, so that, when the floating body 100 is vertically reciprocated by waves, the linear member 220 reciprocates depending on the movement of the floating body 100, thus actuating the energy converting unit including a generator 300. [45] The combined rotary unit 210 used in the present invention serves to increase the distance that one end of the linear member 220, which is connected to the combined rotary unit 210, is moved, so that it is several times the distance that the floating body is moved. The combined rotary unit 210 consists of a moving rotator 212 or a combination of a moving rotator 212 and a fixed rotator 214. [46] In other words, the combined rotary unit 210 includes at least one moving pulley or a combined pulley set, which consists of a moving pulley and a fixed pulley which are combined with each other. Here, in the case where a chain is used as the linear member, a chain wheel may be used as each rotator, in place of a pulley. [47] The moving rotator 212 is rotated around a shaft, which is provided so as to be movable in a vertical direction. [48] The fixed rotator 214 is rotated around a shaft, which is fixed at a predetermined position. [49] In the embodiment of the present invention, a pulley or a chain wheel is used as each of the moving rotator and the fixed rotator. [50] The linear member 220 is connected to the combined rotary unit 210. In detail, the linear member 220, which comprises a linear wire or a chain, is wrapped around the combined rotary unit 210 and is moved upwards or downwards in response to the vertical movement of the floating body 100. [51] The tension maintaining member is connected to the free end of the linear member 220 and serves to pull the linear member 220 such that the linear member 220 is always tight. [52] For this, an underwater buoyant body 232, a balance weight 234 or a spring 236 may be used as the tension maintaining member. In the first embodiment, as shown in FIG. 2, the underwater buoyant body 232 is used. [53] The underwater buoyant body 232 is made of EPS, polyurethane or a hollow barrel, which has a specific gravity lower than that of seawater. In the case where the free end of the linear member 220 is oriented upwards, the underwater buoyant body 232 is WO 2008/048050 PCT/KR2007/005099 6 coupled to the free end of the linear member 220 and pulls the linear member 220 using the buoyancy thereof such that the linear member 220 maintains the tightened state. Here, the buoyancy of the underwater buoyant body 232 is less than that of the floating body 100 such that the underwater buoyant body 232 is always disposed under the water, that is, below the floating body 100, which is disposed on the surface of the seawater. [54] Meanwhile, as shown in FIG. 3, the balance weight 234 may be used as the tension maintaining member. [55] The balance weight 234 is a weight body and is used to pull the free end of a linear member 220 in the case where the free end of the linear member 220 is oriented downwards. Here, the weight of the balance weight 234 is less than the buoyancy of the floating body 100, thus allowing the floating body 100 to float on the seawater. [56] Furthermore, as shown in FIG. 7, the spring 236 may be used as the tension maintaining member. [57] As for the spring 236, it is coupled at the first end thereof to a free end of a linear member 220 regardless of orientation of the free end of the linear member 220. In the case where the free end of the linear member 220 is oriented upwards, the second end of the spring 236 is coupled to the floating body 100, and, in the case where the free end of the linear member 220 is oriented downwards, the second end of the spring 236 is fastened to the ground 400, thus tightening the linear member 220. Here, the elastic force of the spring 236 is less than the buoyancy of the floating body 100, thus allowing the floating body 100 to float on the seawater. [58] In the first embodiment of the present invention, as shown in FIG. 2, although the moving rotator has been illustrated as being provided below the floating body and the fixed rotator has been illustrated as being fixed to the ground, as shown in FIG. 3, the present invention may be constructed such that only a moving rotator, which is coupled to the floating body, is used, or, alternatively, as shown in FIG. 4, the present invention may be constructed such that a first moving rotator is coupled to the floating body and a second moving rotator is coupled to the free end of a linear member, which is coupled to the first moving rotator, which is coupled to the floating body. [59] As illustrated in the first embodiment of FIG. 2 or a second embodiment of FIG. 3, in the case where the combined rotary unit includes only one moving rotator, the distance that the free end of the linear member is moved is twice as long as that of the floating body. [60] The energy converting unit will be explained herein below. The energy converting unit serves to convert the reciprocation of the linear member 220 of the actuating unit into electric energy, kinetic energy or potential energy. Here, instead of the con struction in which energy is created from reciprocation of the linear member 220, the WO 2008/048050 PCT/KR2007/005099 7 present invention may be constructed such that rotational energy of the combined rotary unit 210, which is rotated by the linear member 220, is converted into another type of energy. [61] For example, to generate electric energy, a generator 300 is installed. The generator 300 generates electricity using the rotation of a shaft thereof in response to vertical movement of the linear member 220. In the embodiment of FIG. 2, the generator is disposed in the underwater buoyant body 232, which is the tension maintaining member. However, the present invention is not limited to a construction in which the generator is installed in the tension maintaining member, as described above. That is, the generator may be disposed in the floating body 100 or may be coupled to the moving rotator or the fixed rotator of the combined rotary unit 210 in a construction such that it can rotate along with the rotator, which is rotated by the vertical movement of the linear member, and thus generate electricity. [62] Furthermore, a transmission gear 310 may be coupled to the shaft of the generator 300 to increase the speed at which the generator 300 is rotated. [63] In the present invention, the energy converting unit is not limited to the generator. For example, the energy converting unit may be constructed such that a pump, which is rotated using the movement of the linear member, is provided so that seawater is taken and stored at a relatively high location by the pump to obtain potential energy for generating electricity or operating other devices, or, alternatively, it may be constructed such that a compressor and a pressure container are provided and compress and store fluid such as air or seawater to use the stored energy in a desired manner. As a further alternative, the energy converting unit may be used as a power source, which directly operates a desired device, rather than converting energy into another type of energy and storing the converted energy. [64] Hereinafter, the operation and effects of the preferred embodiments of the present invention will be described with reference to the drawings. [65] <First embodiment> [66] FIG. 2 is a sectional view illustrating a wave energy converter according to a first embodiment of the present invention. [67] Referring to FIG. 2, in the first embodiment of the present invention, a moving rotator 212 is disposed below a floating body 100, and a fixed rotator 214 is fastened to the ground. A linear member 220 is fixed at the fixed end thereof to the ground and is wrapped around the moving rotator 212 and the fixed rotator 214. An underwater buoyant body 232 is coupled to the free end of the linear member 220, so that the linear member 220 maintains the state in which it is tightened by the buoyancy of the underwater buoyant body 232. [68] In the wave energy converter having the above-mentioned construction, when the WO 2008/048050 PCT/KR2007/005099 8 floating body is moved upwards by waves, the moving rotator, which is disposed below the floating body, is also moved upwards, and the underwater buoyant body, which is coupled to the free end of the linear member, is thus moved downwards. At this time, the distance that the underwater buoyant body is moved is twice as far as that of the floating body. [69] Here, a generator is provided in the underwater buoyant body and is coupled to the linear member. Therefore, the generator is rotated by the movement of the linear member, thus generating electricity. [70] <Second embodiment> [71] FIG. 3 is a view showing the construction of a wave energy converter according to a second embodiment of the present invention. [72] In the second embodiment of the present invention, only a single moving rotator 212 is provided below a floating body 100, and a linear member 220 is fastened at the fixed end thereof to the ground and is coupled at the free end thereof to a balance weight 234 to keep the linear member tight. [73] Furthermore, a generator 300 is coupled to one end of the moving rotator to generate electricity using the rotation of the moving rotator. [74] Therefore, when the floating body is moved upwards by waves, the moving rotator and the balance weight are also moved upwards. As a result, the generator generates electricity using the rotation of the moving rotator. In this case, the distance that the balance weight is moved is also twice as far as that of the floating body. [75] <Third embodiment> [76] FIG. 4 is a view showing the construction of a wave energy converter according to a third embodiment of the present invention. [77] Based on the construction of the wave energy converter of FIG. 3, the third embodiment of FIG. 4 further includes another generator 300, which is additionally provided in the balance weight 234. [78] <Fourth embodiment> [79] FIG. 5 is a view showing the construction of a wave energy converter according to a fourth embodiment of the present invention. In the fourth embodiment, two moving rotators 212 are provided at upper positions, and a fixed rotator 214, which is fastened to the ground, is provided at a lower position, so that the distance that the free end of a linear member 220 is moved is increased further by the combination of the two moving rotators and the fixed rotators. [80] <Fifth embodiment> [81] FIG. 6 is a view showing the construction of a wave energy converter according to a fifth embodiment of the present invention. In the fifth embodiment, one moving rotator 212 is provided at an upper position, and two fixed rotators 214 are provided at WO 2008/048050 PCT/KR2007/005099 9 lower positions. Furthermore, an underwater buoyant body 232 is used as a tension maintaining member. [82] <Sixth embodiment> [83] FIG. 7 is a view showing the construction of a wave energy converter according to a sixth embodiment of the present invention. The sixth embodiment has almost the same construction as the fifth embodiment, except that it has a structure in which a spring 236 is used as a tension maintaining member. The spring 236 is coupled to the floating body 100 and the linear member 220, thus keeping the linear member 220 tight. [84] <Seventh embodiment> [85] FIG. 8 is a view showing the construction of a wave energy converter according to a seventh embodiment of the present invention. The seventh embodiment is constructed such that a spring 236 is connected to a linear member 220 and the ground to maintain tensioning force. [86] As well as the embodiments described above, various types of combined rotary units can be used, as shown in FIGS. 9 and 10. [87] Here, the combined rotary unit can be realized by any combination of the moving rotator and the fixed rotator, regardless of the number of moving rotators and the number of fixed rotators, for example, through only the moving rotators or through a combination of a single moving rotator and a single fixed rotator, as long as the distance that the linear member is moved is increased to several times that of the floating body.